Properties, thermal

Thermal expansion-contraction of inorganic fillers is much lower compared with that of plastics. Therefore, the higher the filler content, the lower the coefficient of expansion-contraction of the composite material (see Chapter 10). Many inorganic nonmetallic fillers decrease thermal conductivity of the composite material. For example, compared with thermal conductivity of aluminum (204 W/deg Km) to that of talc is of 0.02, titanium dioxide of 0.065, glass fiber of 1, and calcium carbonate of 2-3. Therefore, nonmetallic mineral fillers are rather thermal insulators than thermal conductors. This property of the fillers effects flowability of filled plastics and plastic-based composite materials in the extruder. 

Thermal conductivity of materials can only be dehned for homogeneous materials, where the thickness is greater than that for which the apparent thermal resistivity of the material does not change by more than 2% with further increase in thickness. The thermal resistance must be sufficiently independent of the area of the specimen and for a flat slab specimen the thermal resistance must be proportional to the thickness. When all these conditions are met  

The reciprocal of the thermal conductivity is called thermal resistivity (r). 

The most common units for thermal conductivity are cal/cm.s.°C and Btu.in/ft. h.°F. The SI unit for conductivity is W/mK. Since a variety of units has been in practice for thermal properties, the conversion factors are given in Table 12.27. 

The heating unit has a separation (or gap) not greater than 4 mm between the surface plates of the metering area and the guard. Two specimens should be selected from each sample with their surfaces made plane. The temperature difference between the hot and cold surfaces of the specimens should be not less than 5 K [De Ponte and Di Filippo, 1974]. 

The central heat source and the guard should have independent power supplies. The cold sur- 

Thermal Conductivity The thermal conductivity of the ideal greiphite crystal was reviewed in Ch. 3, Sec. 4.3. The mechanism of heat transfer is by lattice vibration and the thermal conductivity is approximately 200times greater in the basal plane (ab directions) than across the planes (c direction), thus reflecting the anisotropy of the graphite crystal. 

This anisotropy is less pronounced in molded graphites and carbon materials and the thermal conductivity is more isotropic. Typical values for graphite and other high-conductivity materials are given in Table 5.7.f l 

Electrographite (from petroleum coke) 159 Electrographite (from lampblacl 31.4 

The relationship between the thermal conductivity of molded graphite and temperature is similar to that of single-crystal graphite. After an initial 

Thermal Expansion. The thermal expansion of the graphite ciystal was reviewed in Ch. 3, Sec. 4.4. This expansion has a marked anisotropy. It is low in the ab directions (lower than most materials) but an order of magnitude higher in the c direction. 

Thermal decomposition of PBO in air is about 650°C and under nitrogen or argon more than 700°C which is 100°C higher than Kevlar [49].TG-mass spectra analysis and TG-Fourier transformed 

Thermal analysis techniques, in particular differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), are valuable tools to study the thermal behavior of PEs. DSC allows us to calculate the proportion of crystallinity, to detect the formation of new crystalhne phases, free guest salt or uncomplexed polymer chains, to monitor the loss of solvent(s) (e.g. occluded water, alcohol), to determine the Tg value and to distinguish between endo- and exothermic events. TGA provides rich information 

5 DSC curves of (a) d-U(2000) LiTFSI (adapted from Barbosa et a ) and (b) d-U(900) LiTFSI (adapted from Barbosa ef a/3 ) di-ureasil systems. 

For the DSC measurements of di-ureasil ormolyte samples, sections have been usuaUy removed from dry films and subjected to thermal analysis under a flowing inert atmosphere between 25 and 300 °C and at a heating rate of 5°C min. Samples are then transferred to aluminium cans. 

1 Thermal Degradation Behavior of Rubber-Based Nanocomposites 

The formation of polymer-filler nanocomposite affects the thermal behavior of the matrix because the well-dispersed nanofillers lead to modification of the degradation pathways [165-168]. This concept was first introduced by researchers from Toyota [169] who discovered the possibility to build nanocomposites from nylon-6 

In the case of 34NBR, the polymer chains have H-bonding interactions with the clay along with van der Waals interactions. These in turn improve the thermal stability of the nanocomposite. 

Compatibility of NA with organic polymer is much inferior to the compatibility of , 15A, and SP. Thus, Sl-NA-4 has inferior thermal stability as compared to the other three clays. Moreover, the intergallery spacing of NA is very small (only 1.22 nm, obtained from XRD results, Fig. 26a). Only a few chains of HNBR (with 34% acrylonitrile content), being bulky in nature, can find their way into such a small gallery space, which results in poor polymer-filler interaction. This is confirmed by both XRD and (Fig. 26a, b). 

Two mechanisms have been suggested to account for the reduction in the heat release rate a barrier mechanism, in which the clay functions as a barrier to mass transfer of the polymer, and a radical trapping mechanism, which occurs due to the presence of iron or other paramagnetic impurities as a structural component in the 

The thermal stability of PLAs depends on the molecular modifications, additives, residual initiators, catalysts, monomers, and water content. The thermal stabiUty of PLLA synthesized using aluminum tri(isopropoxide) as an initiator is higher than that synthesized using tin(II) bis(2-ethyUiexanoate) [156]. In addition, Jamshidi et al. found that the thermal stability of PLLA synthesized using tin(II) bis(2-ethylhexanoate) increases when the terminal carboxyl group is acetylated and that residual monomers enhance the thermal degradation of PLLA [157]. 

The thermal expansion of wood is less than that of the commodity plastics commonly used as matrices. Thermal expansion coefficients for wood are directional and are roughly [17] 

The specific heat of dry wood does not have a strong dependence on specific gravity and is roughly 0.324 cal/(g K) or 1360 J/(kg K) [17]. This is about half the specific heat of common polyolefins such as polypropylene and polyethylene, for which values are approjdmately 2-3000 J/(kg K.) 

Thermal conductivity, k, of dry wood has been reported to increase linearly with density, q, according to [17] 

Thermal diflusivity is a measure of the rate at which a material changes temperature when the temperature of its surroundings changes. The thermal diflusivity, h, is the ratio of thermal conductivity, k, and the product of specific heat, c, and density, 

There is a wide range of wood flour suppliers, and they cater to a number of different industries. These are both large companies that have broad distribution networks as well as small, single source suppliers catering to single customers. Because of the varied and disperse nature of these suppliers, there are currently few good resources that list wood flour manufacturers. 

The thermal behaviour of the starburst molecules has been investigated by differential scanning calorimetry and thermogravimetric measurements. 

The thermal behavior of compound 33 is somewhat different. No reproducible DSC scans are obtained in subsequent heating-cooling cycles. We attribute this to thermal cross-linking of the triple bonds [24]. 

The thermal stability has been monitored by thermogravimetric measurements. In most cases the onset of decomposition is in the range from 330-370 °C. The oxadiazole compound 32 with a triphenyl benzene core shows a somewhat higher thermal stability up to 410 °C. 

The starburst oxadiazole compoimds are now being tested as electron injection and transport layer in organic LEDs and as photoconductors. First tests of two layer LEDs with PPV show that the novel materials possess properties comparable to 2 but have the great advantage to show no recrystallization if thin films were made by spin-coating. We will report on these measurements in the near future. 

Borsenbeiger, D.S. Weiss in Organic Photoreceptors Bor Imaging Systems, M. Dekker, New York, (1993) 

Flow properties of polyethylene have been widely studied. Because of the wide range of average molecular weights amongst commercial polymers the viscosities vary widely. The most commonly used materials, however, have viscosities lower than for unplasticised PVC and polyfmethyl methacrylate) and higher than for the nylons. 

Typical of thermoplastics (see Chapter 8) the melts are pseudoplastic and also in common with most thermoplastics the zero shear rate apparent viscosity of linear polyethylene is related to the weight average molecular weight by the relationship 

Polymers with long branches do not fit these equations and different relations exist with polymers of different degrees of long branching. In many cases the equation 

It is interesting to note that so-called linear low-density polyethylenes are said to be less pseudoplastic than conventional low-density polyethylenes. Thus on 

Effect of increase of On viscosity On flow behaviour index On critical shear rate On sharkskin 

Thermal Properties. Themud Conductivity. As stated above, the thermal conductivities of phenolic foams vary remarkable depending on whether they are closed cell or open cell. Generally, the thermal conductivities of foams with 90% or more closed cells are within the range of 0.015 kcal/mh°C but if they have open cells, the thermal conductivities increase to 0.030 to 0.035 kcal/mh C. If the foams have 50 to 80% closed cells their thermal conductivities will be an intermediate value between the above two figures. Meantime, the thermal conductivities of foams with 50% or less closed cells will be almost the same as that of open-cell foams. 

Thermal Coefficients. The thermal coefficients of phenolic foams are almost the same as those of resol- and novolac-type foams. Examples are as follows specific heat, 0.38 to 0.42 cal/g°Q flash point, 520 to 540 Q ignition point, 570° to 580°C softening point, do not soften. 

Flame Retardance. The most important reason for phenolic foam being an excellent flame retarder is that the phenolic polymer is easily carbonized and the char part formed as a result is highly stabilized. This mechanism of char-formation is considered that of a multi-aromatic ring with chemically stabilized strong bond formed through a dehydrogenation reaction by heating and oxidation. 

Examples of phenolic-foam flammabUity are shown in Table 69 (7). The smoke developed from burning phenolic foam is very small. The result, of course, varies depending solely on the test conditions but an example shows that when phenolic foam is binned the coefficient of light reduction is about 1/10 of that of polyisocyanurate being burned and 1/10 to 1/20 of that of polyurethane foam. 

ASTM EI62, Radiant-panel Test, No ignition  

Thermal Properties Pitzer s equations for ln7 and p [equations (18.18) to (18.26)] can be used to obtain relative partial molar enthalpies L and Li, and relative partial molar heat capacities8 J and Ji, by taking derivatives. For 

The relative partial molar enthalpy and relative partial molar heat capacity are obtained from8 

Volumetric Properties Equations for 4 V, the apparent molar volume, can also be obtained. They are as follows 

In equations (18.29) to (18.43), the terms are the same as defined in equations (18.18) to (18.26) with Ah, Aj, and Av as the Debye-Hiickel parameters. In addition, T is the temperature and Mw is the molecular weight of the solvent (water) in kg-mol-1. Values for these coefficients for a number of electrolytes are given in Appendix 7, and can be used to calculate the appropriate quantity J 

Thermal properties of PET are greatly influenced by the presence of the aromatic benzyl group substituted in 1,4 (para) positions which provides an overall stiffness of the polymer repeating unit. It explains the relatively high thermal stability (for a polymer) of PET. The value of the experimental melting temperature of commercial PET (fibers) is in the range 250 - 265 °C. It is possible to calculate a theoretical value of 292 °C which can be experimentally approached if a correct annealing process is applied (8). 

The glass transition temperature (T ) depends on the polymer chain arrangement T is equal to 67 in an amorphous state, 81 °C in a semi-crystalline state and 125 °C in a crystalline and oriented state. 

PET is a semi-crystalline polymer but amorphous PET can be obtained by rapid cooling. In fact PET crystallization is slow and 30 % of crystalline phase (triclinic crystal structure) can be obtained to the best. In this amorphous state, PET is transparent and can be 

The heat deflection temperature (or heat distortion temperature (HOT)), temperature at which a polymer or plastic sample deforms under a specified load is given below for amorphous and loaded PET samples  

Specific Heat Thermal Conductivity Thermal Expansion  

Of note are the higher specific heats and thermal conductivities of the borides. 

The thermal properties of polymers include their behavior during heating from the solid amorphous (glassy) or crystalline to the liquid (molten) state, but also their chemical and mechanical stability in the entire range of application. 

In industrial practice temperature stability of a polymer means that it is able to maintain its mechanical properties up to a certain temperature and over a certain time period. Depending on the environmental conditions under which the thermal stability is measured one ftuther differentiates between two cases physical thermostability if the thermal treatment occurs in inert atmosphere and chemical thermostability if the thermal treatment is done, e.g., in the presence of air (thermooxidative stability). 

The prediction of the chemical thermostability is based on the rules on the thermal stability and the reactivity of chemical bonds known for low-molecular-weight compounds. Instead, the physical thermostability depends on the transition points of the macromolecules, i.e., the glass transition temperature Tg in case of amorphous polymers, and additionally the crystalline melting point in case of crystalline polymers. 

In designing polymers with high physical stability valuable information is obtained from the Gibbs equation  

This equation shows that a high melting temperature is obtained by raising the melt enthalpy AH and/or a lowering of the melt entropy AS. Since and 

The thermal properties of ice cream, such as the heat capacity and the thermal conductivity, are important for several reasons. Parameters of the production process, such as the length of time required to harden the ice cream, depend on the thermal properties, as does the rate at which ice cream warms up and melts. This is important in storage and distribution and also when the ice cream is consumed. It should not melt so rapidly that it falls off the stick before it can be eaten. The thermal properties also affect the sensory properties such as the perception of coldness in the mouth. Furthermore, the freezing point and glass transition lines on the phase diagram, and the ice curve, are obtained from measurements of the thermal properties. The main techniques for measuring the thermal properties are calorimetry, conductivity measurements, thermal mechanical analysis and meltdown. 

The heat capacity, freezing point curve and the ice curve of ice cream can be determined by calorimetry. In adiabatic calorimetry, the sample is held in an insulated chamber. A controlled amount of heat is input 

The thermal properties of fibre-reinforced composites are anisotropic. Expansion in the direction of the fibre is usually very small or negative, but the thermal conductivity of some carbon fibre composites in the fibre direction can be high. Most polymers and several types of fibre are good electrical insulators. Carbon and some ceramic fibres have a much lower resistivity. It is thus possible to use composites for manufacturing radomes as well as for electromagnetic screening materials and systems which absorb radar signals. 

Some general thermal properties of typical polymer matrices are given in Table 7.1. 

The resins used were isophthalic polyester phenolic epoxy bis-maleimide and several thermoplastics - PES, PEEK (ICI) and PPS (Phillips Petroleum). 

The figures quoted are for measurements at room temperature or slightly above but below the Tg of the system. The specific heat and particularly the CTE increase with increasing temperature. 

Some quoted data on the thermal expansion and thermal conductivity of fibres are given below in Table 7.2. 

The thermal properties of plastics are generally those expected for organic substances, modified in some cases by the polymer structure. Thus, partially 

The thermal properties of most interest at low temperatures to the process engineer are specific heat, thermal conductivity, and thermal expansivity. Each of these important properties is discussed in this section. It will be shown that each of these properties depends upon the intermolecular potential of the lattice, and thus these properties are interrelated. 

The specific heat of any material is defined from thermodynamics as 

Cy is a property that is actually more useful to theory, since it directly relates internal energy, and hence the microscopic structure of the solid, to temperature. However, it must be remembered that most solids expand when they are heated at constant pressure. As a result, the solid does work against both internal and external forces. The specific heat measured at constant pressure Cp then includes some additional energy to provide this work. Under ordinary circumstances, Cp is the specific heat observed. Therefore, must 

The theory of lattice specific heat was basically solved by Einstein, who introduced the idea of quantized oscillation of the atoms. He pointed out that, because of the quantization of energy, the law of equipartition must break down at low temperatures. Improvements have since been made on this model, but all still include the quantization of energy. Einstein treated the solid as a system of simple harmonic oscillators of the same frequency. He assumed each oscillator to be independent. This is not really the case, but the results, even with this assumption, were remarkably good. All the atoms are assumed to vibrate, owing to their thermal motions, with a frequency v, and according to the quantum theory each of the three degrees of freedom has an associated energy of which replaces the kT as postulated by 

The important thing to notice about the Debye function is that for a given substance, the lattice heat capacity is dependent only on a mathematical function of the ratio of the absolute temperature to the characteristic Debye temperature. This mathematical function applies for all materials, with 0 varying from material to material. Selected values of 9 are given in Table 3.3. 

The thermal properties of hydrazinium salts are evaluated in terms of their TG-DTA graphs (TG, thermogravimetry DTA, differential thermal 

On heating solid N2H5SCN at 100 °C for 9 h at atmospheric pressure, the peaks due to N—N stretching disappear and peaks between 1000 and 800 cm due to the CS group of thiosemicarbazide are observed (2.6). It is known that hydrazinium thiocyanate rearranges to thiosemicarbazide similar to the classical rearrangement of ammonium cyanate to urea [8]  

it decomposes exothermically and vigorously, forming a white solid with the evolution of NH3, H2O, SO2, and S and so on, which have been detected by qualitative analysis. 

Hydrazinium acetate is one of the few hydrazinium salts to decompose endothermically. The results of TG and DTA are complementary. 

2 Hydrazinium Salts with Oxidizing Anions—N2H5A (A- = N3, NO2, NO3, CIO4, etc.) 

Exceptionally high thermal conductivity of CNTs is expected to impart high thermal conductivity to the polymer composites (13,15). 

Consolidated data on the mechanical, electrical and thermal performance of these composites reported by different authors is compiled in Table 7.1. 

Group CNT Type CNT As- Composite Composite Mechanical Electrical Thermal Remarks 

Haggenmueller SWCNT Laser As-grown soot Combination of Film Fibers Film  

Du ct al. 2003 SWCNT HiPco Purified SWCNT Coagulation Unaligned Elastic Percolation Increased ther- Increased 

Common thermal properties include glass transition temperature, melting temperature, decomposition temperature, heat capacity, thermal conductivity, dimensional stability, and flammabihty. 

Heat capacity is the amount of energy required to raise the temperature of a fiber by one degree, while the thermal conductivity is the property of a fiber s ability to conduct heat. Dimensional stability is the ability of a fiber to keep its dimensions while raising the temperature. Flammability is about how easily a fiber will bum or ignite, causing fire or combustion 

All these properties are important, and different applications have different requirements for them. 

Although polymer fibers generally are insulators, their corrductivity could increase significarrtly when they absorb moisture. Therefore, in some production processes, the relative hurrridity is corrtrolled to reduce the buildup of static charges. However, not all polymer fibers absorb moisture. Fibers that do not absorb moisture can be surface-treated to reduce the static charge accumulation by increasing their ability to absorb arrd hold moisture. Corrductive additives also can be added to syrrlhetic polymerfibers to directly increase the electrical conductivity. 

Fillers usually have a thermal conductivity about 20 times higher than plastics, and the specific heat is about 50%. By improving the heat transfer in the melt, the use of a filler may therefore give a faster set-up when moulding, and so improve the cycle time. In applications, the same effect may be useful in engineering components, improving heat dissipation and/or producing a thermal expansion closer to that of metal. 

TABLE 14.10 Examples of Thermally Stable Polymers [6] Continued) 

The glass transition temperature of amorphous polymers is a function of the chemical structure of the polymer chain. It varies widely with the types of skeletal atoms present, with the t T)es of side groups, and with the tacticity of side groups along the polymer backbone. Table 14.11 demonstrates the effects of structural variations on the crystalline melting temperature and glass transition temperature for several polymers. 

TABLE 14.11 Approximate Temperatures of Thermal lyansRIona for Selected Semicrystalline Polymers [7,8] 

TABLE 14.12 Glass lyensition Temperature (T,) of Diene Polymers 

Many polymers have a coefficient of linear thermal expansion in the range of 2-20 X 10 K , compared to that for steel which is about 1 x 10 . This complicates the design of molds for precision parts and the design of metal inserts in polymer parts. Of course, varies with the state of the polymer, as indicated earlier in comments on the variations of specific volume at 7 and T (Section 3.4). Replacement of polymer by less expansile fillers lowers the overall expansion. 

Thermal conductivity of polymers is uniformly low. Values of = 0.05-0.20 Btu/fth°F are common. 

Conductivity is not easily increased. A high concentration of a metal in powder or fiber form can raise it perhaps tenfold. The thermal conductivity of the base resins in Table 11.3 can be increased by aluminum or copper metal. These also increase the electrical conductivity. If low electrical conductivity, of the order of 10 (ohm cm) , must be combined with high thermal conductivity, the mixture of aluminas (Table 11.3) will increase the former by a factor of only 1.5 over that of the base epoxy resin, whereas the latter is increased by a factor of 12. Foaming with air or some other gas is used to decrease the thermal conductivity. A foamed polystyrene with a density of 15 kg/m and = 0.040 W/m °C is useful as insulation for a variety of applications, from picnic baskets to boxcars. 

Thermal Conductivity of Various Filled Epoxy Resins 

Filler Compound Filler Base Resin Compound 

The most important thermal properties of wood to consider in design are its thermal conductivity, specific heat capacity, and coefficient of thermal expansion. 

The effect of temperature dependence of thermal conductivity is relatively small actually, thermal conductivity increases about 2-3% per 10°C. 

Specific heat capacity. The specific heat capacity of wood depends on the temperature and its moisture content but is practically independent of the density or species. The specific heat capacity of dry wood expressed in J.kg -K is approximately related to thermodynamic temperature T (K) by the simple equation  

The specific heat capacity of wood that contains water is obviously greater than that of dry wood due to the important contribution of the elevate specific heat capacity of pure water (4186 J.kg K ). Below fiber saturation, the specific heat capacity of the wood is the sum of the heat capacity of the dry wood and that of water (c J and an additional adjustment factor that accounts for the additional energy contained in the wood-water bond  

There are a variety of thermal properties of materials such as heat capacity, thermal conductivity, thermal expansion coefficient, and many more. For purposes of this text we will focus on the thermal conductivity as it is critical to many electronic devices. The reader is referred to the suggested readings for details of the full spectrum of thermal properties and for details not described here. The thermal conductivity, k, of a material results from transport of energy via electrons or via lattice vibrations (phonons). The total thermal conductivity can thus be written simply as  

Typical thermal conductivities for a range of materials are given in Table 2.2. Let us consider the two contributions to thermal conductivity separately. 

Source citation numbers for values are given parentheses. 

The phonon (lattice vibration) contribution to thermal conductivity is well approximated by  

It can be shown that the phonon mean free path in a typical solid can be written approximately as  

The only effects on the thermal properties seen from the incorporation of a fire retardant additive occurs in the case of high-impact polystyrene (HIPS) where, as shown in Table 8.4, the incorporation of a fire retardant leads to a decease in expansion coefficient and, in the case of the polyesters, where the incorporation of a fire retardant produces a small improvement in heat distortion temperature. 

Early in the year 2000, based on molecular dynamics (MD) simulation, the thermal conductivity of suspended single-layer graphene had been predicted to be as high as 6000 W/mK. This value is higher than for any other material. The experimental measurement of thermal conductivity of graphene 

FIGURE 1.20 Schematic illustration of experimental apparatus for measurement of thermal conductivity of suspended graphene. (With permission from Balandin, A. A. et al, Nano Lett., 8, 902, Copyright 2008. American Chemical Society.) 

PEN is considered to be a high-performance polyester material. The advantageous properties of PEN are derived from its chemical structure which contains both 

Technol. Polym. Adv. Mater., 4, 141-151 (1998), and reproduced with permission of Kluwer Academic/Plenum Publishers 

According to Rebouillat et al. [55], cellulose nanoparticles mostly have two major thermal characteristics. The onset of thermal chemical degradation usually occurs at 300°C and 260°C for freeze-dried MCC and NCC (produced via sulfuric acid hydrolysis of the same MCC) respectively. In work by different authors it has been observed that the coefficient of thermal expansion of nanocellulose reinforced composite materials was improved in which coefficient of thermal expansion of the nanoparticle in the axial direction was at 0.1 ppm/K. The value is similar to that of quartz glass. Yano et al. [74] showed that the flexible plastic composites reinforced with this renewable resource have thermal expansion coefficients of 6 x 10 °C.  

PLA can be amorphous or semicrystalline depending on its stereochemical structure and thermal history. Amorphous PLLDA 

Like other semi-crystalline polymers, the glass transition of PLA is influenced by physical aging [150], crystallinity, morphology, and impurities [151, 152]. Other properties of PLA such as the mechanical strength also depend on the morphology, crystallinity, and orientation. It was found by Wong et al. [153] that the orientation of the crystalline phase was always higher than that of the amorphous phase. 

Reproduced from ref. 169 with permission from Elsevier. 

All the products display a high crystallinity between 50% and 73%. Melting temperature is proportional to the molecular weight according to the classical Flory equation  

As reported by Migliaresi et al. [167], thermal history has a significant influence on the thermal properties of similar molecular weight PLAs. As shown in Fig. 11.6, the crystallinity increases with annealing time and with decreasing molecular weight. 

This section describes some of the other thermal properties that affect polymer behaviour besides the temperature effects detailed above. 

In common with most polymers that are completely or partly amorphous, ferroelectric polymers experience a phase change at the glass transition temperature Tg. Below Tg, the polymers are hard, rigid glasses. At Tgand above, the polymers become flexible and elastomeric. Brittle, rigid polymers have a Tg above room temperature for example, polystyrene has Tg = 100 °C. Rubbery or elastomeric materials have a Tg below room temperature. This is the case for PVDF and the copolymers, which have a Tg in the region of — 40 °C. 

The mechanical properties of polymers show significant changes at temperatures close to the glass transition. In some cases this amounts to a decrease in elastic modulus by a factor of over 1000 times. This effect on the mechanical properties will be passed onto the piezoelectric properties of PVDF and VDF TrFE through the relationships described in section 5.3.3. 

The glass transition temperature can be determined by measurement of the elastic constant as a function of temperature using modern dynamic mechanical thermal analysis (DMTA). 

The heat capacity of a material is defined as the amount of heat required to raise its temperature by 1 K. In pyroelectric applications it is more 

In addition to offering resistance to degradation at high temperatures, polysulfones maintain their mechanical properties at high temperatures without reinforcement. The effect of temperature on PSF tensile stress-strain behavior is shown in Fig. 13.2. It can be seen that the retention of useful properties extends to approximately 150°C for PSF. This useful temperature range approaches 180°C for PES and PPSF 

The thermal behaviour of agro-polymers is complicated relative to conventional polymers. As with mechanical properties, the thermal properties of 

Thermal analysis refers to a range of techniques were one or more properties of a material is measured as a function of temperature. Common techniques, their abbreviations and their application are listed in Table 7.2. Of these, DSC, DMA and TGA are widely used for characterizing thermal transitions and 

DSC measures the difference in heat flow between a specimen and a reference as a function of temperature. Specimens are placed in a special pan, which can either be sealed or not. The reference is usually an identical, but 

Thermogravimetry or thermal gravimetric analysis TG or TGA Mass change Decomposition temperature Oxidation temperature Volatilisation of moisture and plasticiser Moisture content 

Differential thermal analysis DTA Temperature difference Exothermic and endothermic thermal events 

Thermal transport in the bulk medium is one of most important factors that affect the phase transformation of gas hydrates. Thermal properties are needed to estimate the heat transfer in hydrates sediments. Thermal properties of gas hydrates vary a 

864 No data available Most probably it will be less than liquid water and possibly similar to ice. 

The thermal conductivity of gas hydrates is dependent on temperature, but has no pressure dependence. Table 10.4 shows the thermal conductivities of ice, water, CO2 hydrates, and methane hydrates. 

It is clear that the thermal conductivity of gas hydrates is much less than that of ice, but similar to hquid water. Furthermore, when it comes to hydrate/gas/water or hydrate/gas/water/sediment systems, the thermal properties are usually determined as the average values of the properties of the components by considering their saturation (volumetric fraction) in the sample. Because of the paucity of data of CO2 hydrates, the heat capacities of ice, methane and ethane hydrates are shown in Table 10.5. Considering the similarity between CO2 hydrates and other gas hydrates, the heat capacity of CO2 hydrates is certainly less than that of liquid water and may be similar to that of ice. 

Another thermal property is thermal expansion, which is important when estimating the density of CO2 hydrates. Udachin et al. [26] combined his results with others work and obtained the lattice parameter for CO2 hydrates as a polynomial function of temperature as follows  

An evaluation of the effect of high pressure carbon dioxide with three polymers (two amorphous and one semicrystalline) is presented. The properties studied include the glass transition temperature, the melting temperature, and the melting enthalpy. 

Block copolymers consisting of PPV and poly(methyl methacrylate) (PMMA) blocks, can be obtained by atom transfer radical polymerization. The thermal stability is slightly improved in comparison to neat PPV derivates by the introduction of PMMA blocks. The onset of thermal degradation starts around 200°C. 

BAMH-PPV Poly(2,5-bis-(A-methyl-A-hexylamino)phen-ylene vinylene) 26 

BuEH-PPV Poly(2-butyl-5-(2 -ethyl-hexyl)l,4-phenylene vinylene) 36 b 

CzEH-PPV Poly[2-(carbazol-9-yl)-5-(2-ethylhexyloxy)-1,4-phenylene vinylene] b 

The aim of adding clay into polymer matrix is to improve various properties (mechanical, thermal, barrier, etc.) of the composites. The thermal stabiUty of neat polymer is rather poor and improvement is required for a wide range of applications. As well known, nanoclays are thought to play important roles in the 

Therefore, the activation energy can be determined by plotting InP against 1/T according to Eq. (5.1), as the slope of the line is proportional to the activation 

The DSC thermogram of a representative star block showed two TgS corresponding to the PIB (at -67 °C) and PpClSt (at 127 C) segments. The star block showed high thermal stability. The 5% decomposition temperature, Tj, was 

The behavior of the material can divide in two categories thermal and mechanical. Very important thermal properties (except for thermal expansion) are needed to assess the ultimate service state (e.g., temperature reached in the unexposed side) and mechanical properties needed to evaluate the structural integrity at ultimate limit state. While most studies on the variation of the thermal and mechanical properties as a function of temperature have been made on materials such as concrete, steel or wood in the case of the masonry are considered properties of interest are essentially physical, mechanical, and thermal [27]. Often, there are differences between the values reflected in several references for the same material. These differences can be attributed to small differences in the composition of the material, the geometry of the element, differences in methodology of the trial (device used, levels of load, etc.). 

In order to proceed to the exposition of the factors involved in the behavior of masonry structures subjected to high temperatures the following thermal and mechanical properties will be discussed  

Below the principal characteristics of these properties as a function of temperature to then specify these characteristics depending on the piece and the mortar. 

In order to calculate the heat transfer to the unexposed side of the element. 

To provide data for analyzing the structural response, explaining the thermal stresses, thermal deformation, and the dependence of the material properties with respect to temperatme. 

Solid compounds react to heat by expanding or with phase transitions such as melting. The thermal properties that are most interesting for the designer are the melting point (or glass point), the solid-phase transition temperature, the thermal expansion coefficient, and the heat conductivity. These last two properties determine the thermal shock resistance.  

The melting points of covalent inorganic compounds are generally high (Table 4.9 gives a few values). Glass points and sinter temperatures are a fraction of the melting points and refractory solids can be sintered only at comparatively 

Phase transitions in solid compounds are intrinsic and there are tables that give transition temperatures (Table 4.9) of materials. However, the transition temperature can often be changed by alloying the compound with another one while leaving the other properties more or less intact. As was shown in Section 4.5 the cubic modification of Zr02 at high temperatures can be stabilized 

The specific heat of solids is only indirectly related to structure. Its temperature-dependence is described by a universal curve of the specific heat with respect to the reduced temperature T/6j), where (the Debye temperature) is specific for the compound. It can be shown that the specific heat increases at low temperatures with in which d is the dimension of the lattice. 

For linear chains d = 1, for planar nets 2, and for three-dimensional stackings d = 3. The parameter d can also be a noninteger in solids that have a special microstructure. 

There are many excellent differential scanning calorimeter systems available which can be used to measure the specific heat which, when combined with the sample density can be used to give c . The thermal diffusivity (which can be important for thermal imaging systems if the target is not reticulated) can be measured directly on a pyroelectric substrate using the laser intensity modulation method described by Lang [23], 

It was observed that the phosphorous- and siloxane-modified tetra epoxy matrices exhibited better thermal properties, char yield and enhanced LOI values than the sulphone and neat epoxies. The higher values of LOI exhibited by phosphorous- and siloxane-based tetrafunctional epoxies (Table 3.7) maybe attributed to the synergistic effect offered by phosphorous and siloxane. 

Though the phosphorous-hased tetra epoxies showed an earlier degradation at lower temperatures, their char enrichment nature exhibited enhanced char yield values compared to that of the sulphone-hased tetra epoxies. 

Resin System Storage modulus (MPa) Glass transition temperature T ( C) Heat distortion temperature ( C) 

Resin System Initial decomposition temperature O C) Char yield (%) LOI 

When a solid is exposed to a thermal environment, it will either absorb or release heat. This thermal energy is delivered via heat transfer mechanisms of conduction, convection, and radiation. Typical thermal properties of a solid include specific heat, thermal conductivity, thermal expansion, and thermal radiation properties. 

The specific heat at constant pressure, cp, is defined as the amount of heat needed to increase the temperature of 1 kg of material by 1 K. Thus, cp can be expressed as 

When an object is heated or cooled, the characteristic length of the body is expanded or contracted by thermal expansion. Thermal expansion also changes stresses in the material and, in some cases, makes stresses large enough to cause fracture. The simplest form for a linear thermal expansion is given by 

When a temperature gradient exists in a material, energy in the form of heat is conducted from a high-temperature region to a low-temperature region through intermolecular and atomic impacts, lattice vibrations, and transport of electrons. This type of thermal energy transfer is called conductive heat transfer. The relation between heat flux induced by thermal conduction and temperature can be described by Fourier s law as 

Radiative heat transfer of a solid involves both receiving and emitting radiant energy. Most solids in gas-solid flows can be regarded as thermally opaque. When a radiant heat flux strikes a solid surface, the incident energy is both reflected and absorbed with little heat transmitted. The fraction of absorbed radiant energy defines the thermal absorptivity of the 

An impressive amount of data published in the literature indicates, based on TGA, that many heterocyclic polymers can be used at temperatures more than 350—4(X) °C. All experiments conducted later with these polymers, in actual long-term thermal operations, showed that heat-resistant polymers exhibit only a very short-term thermal stability at the onset of degradation revealed by TGA. In actual use, the thermal stability of a given polymer is approximately 150 to 2(X) °C less than the value provided by dynamic TGA. However, it is worth noting that significant differences exist between materials such as films and adhesives. In the former case, the surface area subjected to pyrolysis or oxidation is far greater than the periphery of an adhesive joint. 

To support this assumption, the variation of the mechanical properties of polyphenylquinoxaline 

As adhesive compositions are most often obtained by mixing an organic binder with inorganic fillers and various additives, thermomechanical analysis is generally conducted with an expansion probe. The 

thermomechanical analysis provides both the Tg value and the coefficients of linear thermal expansion (CTE) before and after Tg. 

There are three important aspects on which the addition of LDHs to the polyethylene matrix has a larger effect on the thermal properties of PE/ LDH nanocomposites, namely  

Increase in the thermal degradation temperature, which means a higher stability of the composite material. 

Decomposition rate, which provides information on the decomposition process. 

Flame retardant effect, important for using these highly flamable materials. 

Nanocomposites show higher decomposition temperatures than micro-compsites. They also produce larger amoimts of solid residues, thus providing better barrier properties. 

The thermal conductivity (in W m 1 K-1) of PDMS (0.15) appears to be sufficient, although it is lower than PC (0.16), PET (0.2), glass (0.7-1.0), fused silica (1.38), and silicon (124) [159,246]. Since the channels in the plastic chip are usually narrow (i.e., with high surface-to-volume ratio), the heat dissipation properties of the plastic (e.g., acrylic) channel compared favorably with that of a fused silica capillary (75 pm i.d.) [186]. 

The more common techniques used to analyze thermosets and composites are thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), which can determine the thermal properties and also the best conditions for application of the materials. These techniques can be apphed to polymers to determine their specific heat, degree of polymerization, flanunability, degradation, cure, glass transition temperature (Tg), and other characteristics. Analysis of composites should consider the behavior of each component, including the matrix, reinforcement, plasticizers and fire retardants. 

Thermal analyses arc frequently combined to interpret the results. TGA and DSC are generally comparative and complementary. The thermal transitions do not involve mass loss and are therefore not detected by TGA but are detected by DSC or DMTA (Hatakeyama and Quinn, 1994). 

TGA and DSC indicate that the residual cure stage of the phenolic thermoset hes between 100 and 200°C and releases water and other volatile by-products. The cure stage is observed as an exothermic peak in the DSC curves (Siegmann and Narkis, 1977). The condensation stage involving two phenolic hydroxyls may occur around 300°C and form diphenyl-ether type bonds with consequent mass loss (Pilato, 2010a Vazquez et al., 2002 El Mansouri et al., 2011). This event corresponds to an endothermic peak in DSC curves (Siegmann and Narkis, 1977). 

Phenolic thermosets are known to be resistant to high temperatures and generate high amounts of char during pyrolysis (Knop and Pilato, 1985). The thermal decomposition of phenolic thermosets can be divided into three 

To prepare thermal insulating materials, Carvalho et al. (2003) prepared phenolic and lignophenolic (lignin-phenol-formaldehyde) foams and determined their thermal conductivities 0.057 W m K (density of 0.12 g cm ) for phenolic foam and 0.072 W m K (density of 0.45 g cm ) for lignophenolic foam. Tondi et al. (2009) prepared tannin-based rigid foams with thermal conductivity values between 0.024 and 0.030 W m K for densities between 0.08 and 0.12 g cm , respectively. 

Unlike metals and other inorganics, plastics are extremely sensitive to changes in temperature. The mechanical, electrical, or chemical properties of plastics cannot be considered without knowing the temperature at which the values are obtained. The thermal properties of a polymer typically determine its low- and high-temperature applications, impact properties, and processing characteristics. Generally, temperature limitations of PE range between -180 and +90 C. HDPE has superior heat resistant characteristics (up to 900 °C). 

XPE-AL-XPE capitalises on the corrosion and chemical resistance of the plastic and the pressure capacity of the metal by laminating the aluminium layer between layers of plastic. XPE-AL-XPE does not corrode, and resists most acids, salt solutions, alkalis, fats, and oils. It is widely used throughout North America in residential and commercial plumbing, municipal water service lines, residential and industrial heating, and compressed air and compressed gas systems. 

At the glass transition temperature (Tg), a thermoplastic material changes from a glassy state to a rubbery state. The properties of the material also change significantly. Tg values most often listed for polymers correspond to stiffening temperatures [3], The coefficient of thermal expansion usually doubles below Tg for these materials. Materials above the 7 , may be functional, but the performance may become unpredictable because most thermoplastic components are designed based on properties tested below 7 ,. 

The melting point, Tm, is the transition temperature at which a thermoplastic material changes from a rubbery state to a fluid state. Above Tm, a thermoplastic material completely loses its function. For a thermoplastic component, the optimum application temperature is the usage range below its Tg. 

Thermoset materials such as polyimides behave quite differently from thermoplastic materials. They usually do not exhibit noticeable temperature transitions. The term thermoset is applied to materials that, once heated, react irreversibly so that subsequent applications of heat and pressure do not cause them to soften and flow [3], This property leads to good thermostability. 

One factor which is somewhat adversely affected by the presence of polymer is the coefficient of expansion, which has been shown to be increased about 25 % by the presence of 6 wt % poly(methyl methacrylate) or polystyrene in concrete (Steinberg et a/., 1968). This phenomenon is a consequence of the polymer exhibiting a larger coefficient of expansion than the cement. Slight 5 %) increases in thermal diffusivity and slight decreases in thermal conductivity were also noted (Steinberg et ai, 1968). 

The viscosity of a material suddenly changes and loses fluidity at the gel point. Techniques to follow this phenomenon as a function of temperature are called thermal analysis techniques. According to the definition of the International Confederation of Thermal Analysis and Calorimetry, thermal analysis is a series of collective techniques to measure the physical properties of a material (or a reaction product) by changing the temperature according to a certain program [212, 213]. There are various thermal analyses depending on the physical properties to be measured. In this section, differential scanning calorimetry (DSC), which is the technique to measure heat capacity of the sample, and thermomechanical analysis (TMA), which measures the viscosity or modulus, will be discussed. 

As in aH solids, the atoms in a semiconductor at nonzero temperature are in ceaseless motion, oscillating about their equilibrium states. These oscillation modes are defined by phonons as discussed in Section 1.5. The amplitude of the vibrations increases with temperature, and the thermal properties of the semiconductor determine the response of the material to temperature changes. Thermal expansion, specific heat, and pyroelectricity are among the standard material properties that define the linear relationships between mechanical, electrical, and thermal variables. These thermal properties and thermal conductivity depend on the ambient temperature, and the ultimate temperature limit to study these effects is the melting temperature, which is 1975 KforZnO. It should also be noted that because ZnO is widely used in thin-film form deposited on foreign substrates, meaning templates other than ZnO, the properties of the ZnO films also intricately depend on the inherent properties of the substrates, such as lattice constants and thermal expansion coefficients. 

On the basis of the DSC data summarized in Table 8.3, the crystallization temperature (T ) of PLA fibers becomes lower than that of as-received PLA pellets. It is convincing that the crystallization process can be accelerated by the well-structured PLA molecular chains when tailored into the fiber-like form. By decreasing HMW PCL concentration from 15 to 9wt%/v, the glass transition temperature (T ) of PCL within PLA/PCL blends is reduced whereas the of PLA is hardly identified in that its point has overlapped the melting peak of PCL. The different thermal properties in terms of and melting temperature (T ) may be influenced by the variation of fiber diameters as well as electrospinning process for the orientation of polymer chains [32]. In comparison to HMW PCL with PLA in blends, LMW PCL gives rise to an evident increase in the of PLA, but a considerable decline in the of PCL. The solvent effect on thermal 

Transition temperatures that characterize the stmcture and behavior of polymers have already been dealt with some length. From a practical point of view, limiting temperatures for use is also of interest. One should differentiate between a statistical value derived from use data without material damage and a standard test under prescribed conditions, namely, heat distortion or deflection. In the latter, the temperature is measured wherein the samples undergo a definite deformation under a defined load (usually 264 psi). This temperature is taken to be an upper limit for use of the material without the danger of warping. This value obviously depends on the load (inversely affected). Thermal endurance can also be expressed by time and temperature data that affect mechanical and electrical properties. Data verify that for most polymers, the upper limiting useful temperature is rather low (60 -85 C), 

In polymers, heat transfer coefficients in conduction are rather low (K = 

In this discussion we deal with the resistance of polymers to various chemicals, (mainly water, acids, bases or organic solvents) as well as with their endurance after being exposed to climatic conditions or to fire. Most polymers show very low water absorbency, except for Nylon and cellulose derivatives that are sensitive to humidity. Most polymers also withstand mild inorganic chemicals at ambient temperatures. Excelling at this are the fluoro compoimds, Noryl, polyimide and polysulfone while polypropylene, PVC and epoxy are considered fair. Polyester and polycarbonate are sensitive to bases, while Nylon is affected by acids. Detailed tables of data exist, describing the resistance of plastics to many chemicals at specific temperatures. Most thermoplastics have a tendency to dissolve in specific organic solvents. 

Permeability (P) is another important property, and measures the rate of transfer of gases and vapors through a layer of polymer (mainly a film). It is expressed as P = SD, where S = solubility and D = diffusivity. The character of the gas, its chemical affinity to the polymer, the structure of the polymer and its degree of crystallinity — all strongly affect the permeability (which drops with an increase of crystallinity). This property plays a major role in the packaging of food. 

Another crucial factor consists of flame resistance. Except for outstanding polymers like fluoro compoimds, Noryl, or aromatic polyamides, it is well known that most polymers based on organic compoimds bum well. (There have been many attempts to synthesize non-flammable inorganic polymers, but with minor commercial success.) However, there are polymers that are considered to be self extinguishing (more or less) such as PVC and others. 

For older measured values, see [4, 6]. Theoretical densities as a function of the M ionic radius are also shown in Fig. 3 from [9]. 

Some of the first questions that arise when looking at a new group of polymers such as hyperbranched polymers concern the glass transition temperature -what determines it, what molecular motions determine it, is there a difference in Tg for different parts of the molecule Since hyperbranched polymers are almost exclusively amorphous materials, the glass transition temperature will be one of the most important features. 

The thermal stability of hyperbranched polymers is related to the chemical structure in the same manner as for linear polymers for example, aromatic esters are more stable than aliphatic ones. In one case, the addition of a small amount of a hyperbranched polyphenylene to polystyrene was found to improve the thermal stability of the blend as compared to the pure polystyrene [31]. 

A study of the PVT properties of hyperbranched aliphatic polyesters by Hult et al. [ 117] showed that these polyesters were dense structures with smaller thermal expansion coefficients and lower compressibility compared to some linear polymers. 

TPX exhibits heat resistance, resistance against microwaves. For these reasons it is suitable in food packaging applications. 

It has a high melting point of 240°C (15, p. 219). Due to the high melting point and good temperature stability, TPX is used for au-toclavable medical equipment, components in microwave devices, and as cookware. 

The heat flow through a material can be defined by Fourier s law of heat conduction. Fourier s law can be expressed as 

Polymer Specific gravity Specific heat kJ/kg/K Thermal conduc. W/m/K Coeff. therm. expan. /tm/m/K Thermal diffusivity (m2/s)10 7 Max temp. °C 

Typical values of thermal properties for selected polymers are shown in Table 6.1 [7, 17]. For comparison, the properties for stainless steel are also shown at the end of the list. It should be pointed out that the material properties of polymers are not constant and may vary with temperature, pressure or phase changes. This section will discuss each of these properties individually and present examples of some of the most widely used polymers and measurement techniques. For a more in-depth study of thermal properties of polymers the reader is encouraged to consult the literature [24,46, 66], 

Hydroxides and hydrated oxides lose water under heating and turn into anhydrous ordinary oxides (except strongly basic hydroxides of alkaline metals that melt without decomposition). 

The data on decomposition temperatures of hydroxides and hydrated oxides, as well as the data on enthalpy and entropy of their formation, are listed in Table 2.7 according to [30-32]. 

Compound Temperature range of water removal, C °fonn kJ/mol S°I9S. J/molK 

One can see that decomposition temperatures of these compounds are within temperature range 40-600°C. Some compounds, such as monohydrate of lithium hydroxide (40°C), hydrated titanium dioxide (60°C), iron hydroxide (100°C), manganese (145°C) and cobalt (150°C) hydroxides, tungsten acid (180°C), etc., start to release water at relatively low temperatures. Other compounds decompose at a temperature above 200°C. No correlation between formation enthalpy and thermal stability of hydroxides and hydrated oxides is observed. 

The heat distortion resistance of finished HIPS parts is dependent on their shape, the production conditions, the type of heat source and the duration of heating, and also on the HIPS grade in question. Parts produced without application of an external load and having low internal stresses can be heated for a short time to about 15 °C below the Vicat softening temperature without undergoing distortion. 

The high melting point (highest of all metals) is the most prominent and important property in regard to all applications as refractory metal. It is a consequence of the electron density of states. Small amounts of impurities, such as carbon, lower the melting point. 

The molar volume increases by 8% on melting. This is the largest expansion observed for bcc metals [1.70]. 

Vapor Pressure. Timgsten has the lowest vapor pressure of all metals. Within the temperature range from 2600 to 3100 K, it obeys the following equation [1.76]  

Boiling Point, calculated from rates of evaporation of solid tungsten. 

Thermal expansion. At room temperature, values between 4.32 and 4.68 X 10 K were obtained for the linear coefficient of expansion a, depending on the material (P/M sheet, arc-cast sheet, etc.) and the type of measurement Values for low and high temperatures are listed in Table 1.12. The linear coefficient of expansion can also be calculated according to the following equations [1.76]  

What happens in these Lattices when Heat Transports Vibrations through a solid mass  

Tic Waves called phonons that obey Max Planck s 

Umklapp Switchbacks, and Isotopes play pranks Upon his Formulae, Debye deserves warm Thanks. 

As a consequence of their brittleness and their low thermal conductivities, ceramics are prone to thermal shock i.e., they will crack when subjected to large thermal gradients. This is why it is usually not advisable to pour a very hot liquid into a cold glass container, or cold water on a hot ceramic furnace tube — the rapidly cooled surface will want to contract, but will be restrained from doing so by the bulk of the body, so stresses will develop. If these stresses are large enough, the ceramic will crack. 

Another important thermal property dealt with in Sec. 13.6 is thermal conductivity. It is the low thermal conductivity of ceramics, together with their chemical inertness and oxidation resistance, that renders them as a class of materials uniquely qualified to play an extremely demanding and critical role during metal smelting and refining. Many ceramics such as diaspore, alumina, fosterite, and periclase are used for the fabrication of high-temperature insulative firebrick without which the refining of some metals would be impossible. 

TABLE 1.15 Cluster Size Evolution from Experimental Data for Glycine-Water 

Concentration (g/IOOg solvent) Solution Age (h) Viscosity (cP) Cluster Size (svitc= Diffusivity (x10 cm /s) Cluster Size (ffdm = Cluster Size Calculated (Lo and Myerson 1990) 

Hartley-Crank (Hartley and Crank 1949) equation that appears below 

T) 2 = infinite dilution diffusivity T) = self-diffusion coefficient of the solvent Ps = viscosity of the solution pi = viscosity of the solvent 

If no diffusivity data is available at any concentration, estimation can still be used. First, the infinite dilution diffusivity is estimated using one of several methods available (Reid et al. 1987) such as the Wilke-Chang (Wilke and Chang 1955) method 

The calorific value is reported as GCV, with a correction made if NCV is of interest (ASTM, 2011b,i,o,p ISO, 2011c). For solid fuels such as coal, the gross heat of combustion is the heat produced by the combustion of a unit quantity of the coal in a bomb calorimeter with oxygen and under a specified set of conditions. The unit is calories per gram, which may be converted to the alternate units (1.0 kcal/kg = 1.8 Btu/lb = 4.187 kJ/kg). 

The experimental conditions require an initial oxygen pressure of 300-600 psi and a final temperature in the range of 20°C-35°C (68°F-95°F) with the products in the form of ash, water, carbon dioxide, sulfur dioxide, and nitrogen. Thus, once the GCV has been determined, the NCV (i.e., the net heat of combustion) is calculated from the GCV (at 20°C 68°F) by deducting 1030 Btu/lb (2.4 X 10 kJ/kg) to allow for the heat of vaporization of the water. The deduction is not actually equal to the heat of vaporization of water (1055 Btu/lb 2.45 x 10 kJ/kg) because the calculation is to reduce the data from a gross value at constant volume to a net value at constant pressure. Thus, the differences between the GCV and the NCV are given by 

The enthalpy, or heat content, of various coals has also been reported (Table 9.11) but has actually received somewhat less attention than the calorific value. 

There are also reports of the use of DTA for the determination of the calorific value of coal (Munoz-Guillena et al., 1992). 

FIGURE 9.10 Variation of calorific value with rank. (From Baughman, G.L., Synthetic Fuels Data Handbook, 2nd edn., Cameron Engineers, Inc., Denver, CO, 1978.) 

Solid solutions also result in reduced mobUities, but not equally. Substitutions on the A sites appear to have little effect on q [86], whereas substitutions on the X-sites have an effect that is only observed if the concentration of defects - presumably vacancies and displaced atoms - in the end-members are low. Consistent with the fact that the Fermi level is dominated by d-d orbitals of the M-sites, substitution on these, however, can have a more dramatic effect on increasing resistivities above those of the end members [93]. 

One of the unique properties the Si- and Ge-containing MAX phases is their small and temperature independent Seebeck coefficients [86, 87]. Using ah initio calculations, Chaput et al. [94] calculated the thermopower to be negative alongthe c axis and positive in the basal planes. The small value experimentally observed was thus ascribed to a compensation between the thermopowers of the two nonequivalent crystallographic axes. Yet, while certainly reasonable, this prediction awaits experimental verification on epitaxial thin films or large single crystals. 

Interestingly, solids with essentially zero thermopower can, in principle, be used as leads to measure the absolute thermopower of other solids. In other words, th could be used as reference materials in thermoelectric measurements. 

Typically the total thermal conductivity of a solid, k, can be considered to be the sum of the electronic, kg and phonon, kph, contributions that is  

The room-temperature results are listed in Table 7.4, together with the corresponding parameters for near-stoichiometric TiC, TiC and NbC for comparison. From these results it is reasonable to conclude that  

Early work [119-124] showed that the thermo-oxidative instability of carbon fibers affected the stability of high temperature laminates at 300° C. 

The thermal oxidative behavior in air at 250 and 300°C of several grades of PAN based carbon fibers was studied by Gourdin [125] and the weight losses at 250 and 300°C as a 

1700 T800/+3620 OT800/5245 TIMA-5/4a620 Celion st/5245 T400/+3620 

Schola, of United Technology Research Center, believes that it is not necessary to use the most thermo-oxidatively stable fiber to achieve a good high temperature system. Although T-40 has a greater thermo-oxidative stability than AS4 or Celion G30-500, the retention of properties is better with these low modulus fibers. The thermo-oxidative stability is not directly related to the presence of impurities such as Na or K. Rather, it is a function of the 

Weight loss of carbon fibers after ageing at 250°C. Source Reprinted from Gourdin C, SAMPE, Bourdeaux, 49-61, Oct 17-20 1983. 

Fibre type Glass content (%) Tensile strength (MPa) Tensile modulus (GPa) Flexural strength (MPa) Flexural modulus (GPa) 

The attractiveness of dynamic analysis is that an accurate determination of the viscoelastic behavior can be made. A common geometry for dynamic measurements is the cone and plate rheometer. In dynamic analysis, the viscosity components can be measured up to an angular frequency of about 500 radians/s. Cox and Merz [72] found empirically that the steady shear viscosity corresponds to the complex viscosity if the shear rate in s is plotted on the same scale as the angular frequency in radians/s. This can be stated as  

This empirical rule seems to hold up quite well for most polymers. Using this rule, it is possible to determine viscosity data up to 500 s with a cone and plate rheometer by applying an oscillatory motion to the cone. This would be impossible if a steady rotational motion was applied to the cone. In steady shear measurements on a cone and plate rheometer, the maximum shear rate that can be measured is around 1 s, which is much too low for applications to extrusion problems. The same is true for measurements in the parallel plate test geometry. Thus, the dynamic measurement extends the shear rate measurement range considerably, while still being able to take advantage of the cone and plate geometry. 

Dynamic mechanical analysis is not limited to just shear deformation it is also used with elongational deformation. Further, dynamic mechanical analysis is employed in the characterization of solids as well as liquids. In 1982, a new standard was established, ASTM D4065, to standardize procedures for testing all types of materials. 

By the nature of the plasticating extrusion process, thermal properties are very important. In the early portion of the extruder, solid polymer particles are heated to the melting point. In the midportion of the extruder, the molten polymer is raised in temperature to a level considerably above the melting point while the remaining solid particles continue to heat up and melt. In the last portion of the extruder, the molten polymer has to reach a thermally homogeneous state. When the extrudate leaves the extruder die, it has to be cooled down, usually to room temperature. Through this whole process, the polymer experiences a complicated thermal history. The thermal properties of the polymer are crucial to being able to describe and analyze the entire extrusion process. 

The melting point was reported as 119 K [2]. A lower melting point 109.7 K (which is cited e.g. in [3]) is thought to be caused by contamination of O2F2 by other oxygen fluorides [2]. 

A particular advanu e in the production of glass-ceramics is that products demonstrating almost zero shrinkage can be produced. These specific materials are produced on a large scale for industrial, technological, and domestic applications (e.g., kitchenware). 

Usually, substances can exist in three possible physical states solid, liquid and gas. In polymeric materials, things are not so straightforward. For example, most polymers will decompose before they boil, and cross-linked pol5miers decompose before they melt. 

According to their basic thermal properties, four different types of polymers are distinguished. 

Thermoplastics are polymeric materials, which are more or less rigid at room temperature and can be melted by heat. 

Thermosets are also rigid at room temperature, but due to the cross-links in their molecular structure, they cannot be melted. 

Rubbers are flexible at room temperature. Most of them are amorphous materials and do not show a melting point. They have a glass transition point instead which is well below room temperature. Below lliis glass transition temperature they are rigid. 

For convenience in derivations to follow, expressions from Chap. 5 are repeated here that apply to processes in a closed system in the absence of nonexpansion work (i.e., dw =0). For a process at constant volume we have  

A closed system of one eomponentin a single phase has only two independent variables. In such a system, the partial derivatives above are complete and unambiguous defiiutions of Cy and Cp because they are expressed with two independent variables—T and V for Cy, and T and p for Cp. As mentioned on page 142, additional conditions would have to be specified to define Cy for a more eomplieated system the same is true for Cp. 

The value of for a substance is greater than Cy m- The derivation is simple in the case of a fixed amount of an ideal gas. Using substitutions from Eq. 7.3.3, we write 

Division by n to obtain molar quantities and rearrangement then gives 

For any phase in general, we proceed as follows. First we write 

Trajectories of center-of-mass for the surface and inner chains were calculated at every picosecond interval to analyze the diffusion coefficient at a temperature. Diffusion coefficients in the surface and inner chains were computed from mean-square displacement (MSD) [194,209,210]. The average mean-square displacement of center-of-mass for the chains can be determined. 

The plot for the surface chains gives two steps of the melting transition. The first step (mechanical melting) is at a temperature of 200 K and the second (thermodynamic melting) is 230 K. The first step is an early melting stage at which all 

DMTA has been used to measure various melting temperatures [61, 62] including melting point [63], crystallisation temperature [63], heat distortion temperature [64], heat deflection temperature [65] and melt flow index [63]. See also references [14, 46, 59, 66-82], 

HNT—ASP, which becomes more noticeable relative to that with unmodified 1 wt%/v HNTs. The nucleating-agent role of HNTs is proven to promote the heterogeneous nucleation of polymeric molecules, which is confirmed by the decrease of T, particularly in PLATS wt%/v HMW PCL composites embedded with 2wt%/v HNT—ASP, as opposed to PLA PCL counterpart. 

An important consideration of the crystallization process for a crystalline component of a polymer blend is the spherulitic growth rate. The theory for the kinetics of spherulitic growth has been well-established for unblended crystalline polymers with seminal contributions of Hoffman et al. [116-119] The growth rate of the spherulite is controlled by the nucleus formation determined by the undercooling (T — Tg) and the ability of the polymer chains to diffuse to the crystalline surface determined by the difference in T (crystallization temperature) and the Tg. The maximum crystallization rate is in the range of (Tg + Tm)l2. 

For miscible blends, the spherulitic growth rate equation can be employed to predict the crystallization kinetics. This equation, commonly employed for unblended crystalline polymers, is  

PVF2 Various polymers Bi2 values reported on PVF2 blends with PEA, PVMK, PEMA, PMAc, PMMA and PVAc all blends were miscible 105 

PEG SAA Increasing AA content in SAA yielded larger negative values for Bi2 (3 12) 95 

PTT PETG PTT = poly(trimethylene terephthalate) PETG = amorphous polyester. yi2 = —0.38 110 

Designers and material selectors of plastic products constantly face the challenge of selecting a suitable plastic for elevated temperature performance. The difficulty arises because of the varying natures and capabilities of various types and grades 

Handbook of Plastics Testing and Failure Analysis, Third Edition, by Vishu Shah Copyright 2007 by John Wiley Sons, Inc. 

When studying the performance of plastics at elevated temperatures, one of the most important considerations is the dependence of key properties such as modulus, strength, chemical resistance, and environmental resistance on time. Therefore, the short-term heat resistance data alone is not adequate for designing and selecting materials that require long-term heat resistance. For the sake of convenience and simplicity, we divide the elevated temperature effects into two categories  

Apparatus and Test Specimens. The apparatus for measuring heat deflection temperature consists of an enclosed oil bath fitted with a heating chamber and automatic heating controls that raise the temperature of the heat transfer fluid at a 

More recently, automatic heat deflection temperature testers have been developed. These testers typically replace conventional temperature and deflection measuring devices with more sophisticated electronic measuring devices containing a digital read-out system and a chart recorder that prints out the results. Such an automatic apparatus eliminates the need for the continuous presence of an operator and thereby minimizes operator-related errors. 

Here we will look at the organotin polyamines to iUustrafe general behavior. The organotin polyamines begin degrading in both air and nitrogen between 100°C 

This is followed by a large loss of weight, generally 20-80% over the next 100 range. Most then continue to about 900 C with little additional weight loss. The relative stabilities in air and nitrogen are somewhat similar. 

The very high melting point of alumina makes it useful as a refractory. Even though alumina is soluble in glass, it is useful as a glass tank refractory because the rate of dissolution is small. 

Porosity increases the creep rate. The stress dependence of creep in porous alumina was foimd to be between that of diffusion and dislocation creep mechanisms [17]. Strain rates were foimd to vary between the second and third power of the stress. With respect to the diffusion of ions, the diffusion of AF+ ions was foimd to be the rate-determining step [18]. 

It was found that the diffusion coefficient decreased by a factor of 20 with the addition of 2000 parts per million of MgO to high-density sintered alumina [19]. Mg2+ ions can substitute Al ions in the alumina lattice or a part of the ions can occupy interstices— the other part going to the lattice sites. When alumina was doped with MgTiOj, it was found that the diffusion coefficient of AF+ did not change. This is because there is charge compensation between the host cations and doped cations resulting in no point defects being produced. 

If impurities do not dissolve in an oxide, at elevated temperatures the liquid phase may form by way of an eutectic reaction. Such liquids decrease the refractoriness drastically. Dense alumina finds use at high temperatures because of its low permeability toward gases. High purity is required to make it impervious. 

The usual shapes in alumina are tubes and crucibles. Fused alumina is mixed with clay to produce alundum cement. This cement is tempered with water and can be hand-molded. It is useful in laboratories. On firing, it shrinks a little and gives rise to a porous refractory. It also spalls easily and is inexpensive. Depending on the grade, it is useful in the range of 1500°C-1700°C. 

Polymers exhibit a temperature-dependent elastic-viscoplastic behavior. Temperature effects can influence the stability of geotextUes. Both tensile strength and elongation 

The test can be conducted to determine the effects of in situ temperature applications and strength changes owing to abnormal temperatures during material storage, and to evaluate cyclic freeze—thaw effects. 

The melting point of the aramid elastomer varied from 173 to 225°C with decreasing molecular weight of the soft segments. The melting point depression was successfully explained by the solvent effect [62] defined by 

Figiire 8. Crystal structures of the aramid compounds naphthalene-2,6-dicarboxylic acid bis[4-(ethoxycarbonyl)phenylamide (top) and benzene-1,4-dicarboxylic acid bis(4-ethoxy-carbonyl)phenylamide (bottom) [58] 

The elongation at break reduces with increasing temperature, but the modulus is temperature independent. This indicates that aramid domains retain a crystal state and act as stable physical crosslinks even at elevated temperatures. 

The former is the glass transition of PTMO segments, and the latter is the melting transition of aramid segments. The modulus of each sample shows a sharp drop at the melting point [39]. 

AE volume change AW weight change Shore A hardness after immersion for 200 h at RT 

As shown in Fig. 6.30, a DSC curve of dried PpPTA polymer shows a small endothermic baseline shift, in conjunction with an endothermic peak near 290°C, probably representing the glass transition temperature of the polymer. This Tg value agrees with the one found by Brown and Ennis.It is also in line with the observation found for a wide variety of polymers that Tg/Tm = 0-66. However, it differs from the values found 

Prolonged exposure of PpPTA fibers at temperatures up to 250°C for more than 100 hours results in a relatively small decrease (about 17%) of the strength. Short-time exposures up to 450°C can be applied without large strength losses. The temperature dependence of the strength in the range from about — 40°C and higher is much smaller than that of conventional synthetic fibers such as PETP and the nylons.  

PBT fibers show a very small strength loss of only 2% after an exposure of 65 hours in air at 300°C. This indicates a thermal stability of the mechanical properties which is even better than that of the aromatic polyamide fibers.  

Heat treatment at 600°C of as-spun PBO fibers increases the modulus by almost a factor of 2, but the strength is also slightly improved (see Table 6.4). Higher temperatures cause a reduction of strength due to degradation. 

We thank F.A.M. Schenkels, H.G. Weijland, J.J. van Aartsen, S. Picken, S. van der Zwaag, H. Jansen, A. Weeda and H.M. Heuvel for critical reading of the manuscript and many helpful discussions. In particular, the technical assistance of Mrs B. Schaffers-Korff is gratefully acknowledged. 

Sound Velocity. A sound velocity of 1300 m/s in liquid HN3 is cited in [5]. The sound velocity at 294 K in pure, gaseous HN3 and HN3-N2 mixtures was given in [6] as follows  

Viscosity. The viscosity of gaseous HN3 of 295 = 109 was calculated from kinetic theory and agrees with the experimental value. The Lennard-Jones parameters a = 3.98 A and 8/k = 355 K were calculated from empirical relations [7]. 

Triple Point. Boiling Point. The triple point temperature of HN3 is 193 K, where the vapor pressure is 1 Torr. The normal boiling point of 308.9 K was extrapolated from the vapor pressure curve [3]. 

Heats of Transition. An enthalpy of melting of 6.0 kJ/mol was estimated for HN3 by comparison with the data of other inorganic substances [4]. The experimental heat of evaporation is 30.5 kJ/mol at 286.6 K and yields a Trouton constant of 92 J mol K indicative of an unassociated liquid [3]. 

Vapor Pressure. The vapor pressure of HN3 between 273 and 195 K is described by log(p/Torr) = 6.8426-1302.1/T +0.0567 log T. The temperature range between 273 K and the boiling point requires slightly different constants log(pZTorr) = 7.8533- 1578.3/T +0.0567 logT[3]. 

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The thermal properties of an ideal gas, enthalpy, entropy and specific heat, can be estimated using the method published by Rihani and Doraiswamy in 1965 ... 

We will use the method established by Lee and Kesler in 1975 because it is related to the calculation of thermal properties method we have selected and will discuss later. 

Thermal Properties and Temperature related Behavior of Rock/fluid Systems... 

Jesson B J, Foley M and Madden P A 1997 Thermal properties of the self-interstitlal In aluminum an ab initio molecular-dynamics study Pbys. Rev. B 55 4941-6... 

Frenkel D, Mooij GAM and Smit B 1992 Novel scheme to study structural and thermal properties of continuously deformable molecules J. Phys. Oondens. Matter4 3053-76... 

The thermodynamic properties that we have considered so far, such as the internal energy, the pressure and the heat capacity are collectively known as the mechanical properties and can be routinely obtained from a Monte Carlo or molecular dynamics simulation. Other thermodynamic properties are difficult to determine accurately without resorting to special techniques. These are the so-called entropic or thermal properties the free energy, the chemical potential and the entropy itself. The difference between the mechanical emd thermal properties is that the mechanical properties are related to the derivative of the partition function whereas the thermal properties are directly related to the partition function itself. To illustrate the difference between these two classes of properties, let us consider the internal energy, U, and the Fielmholtz free energy, A. These are related to the partition function by ... 

An extensive new Section 10 is devoted to polymers, rubbers, fats, oils, and waxes. A discussion of polymers and rubbers is followed by the formulas and key properties of plastic materials. Eor each member and type of the plastic families there is a tabulation of their physical, electrical, mechanical, and thermal properties and characteristics. A similar treatment is accorded the various types of rubber materials. Chemical resistance and gas permeability constants are also given for rubbers and plastics. The section concludes with various constants of fats, oils, and waxes. 

The industrial value of furfuryl alcohol is a consequence of its low viscosity, high reactivity, and the outstanding chemical, mechanical, and thermal properties of its polymers, corrosion resistance, nonburning, low smoke emission, and exceUent char formation. The reactivity profile of furfuryl alcohol and resins is such that final curing can take place at ambient temperature with strong acids or at elevated temperature with latent acids. Major markets for furfuryl alcohol resins include the production of cores and molds for casting metals, corrosion-resistant fiber-reinforced plastics (FRPs), binders for refractories and corrosion-resistant cements and mortars. 

Material Properties. The properties of materials are ultimately deterrnined by the physics of their microstmcture. For engineering appHcations, however, materials are characterized by various macroscopic physical and mechanical properties. Among the former, the thermal properties of materials, including melting temperature, thermal conductivity, specific heat, and coefficient of thermal expansion, are particularly important in welding. 

Thermal Properties and Enduranee. The heat capacity or specific heat, is a quantity of theoretical thermodynamic significance as well as of practical importance. It has been determined for Parylene N over the temperature range of 220 to 620 K (—53 to +347° C) (24,29). 

The many commercially attractive properties of acetal resins are due in large part to the inherent high crystallinity of the base polymers. Values reported for percentage crystallinity (x ray, density) range from 60 to 77%. The lower values are typical of copolymer. Poly oxymethylene most commonly crystallizes in a hexagonal unit cell (9) with the polymer chains in a 9/5 helix (10,11). An orthorhombic unit cell has also been reported (9). The oxyethylene units in copolymers of trioxane and ethylene oxide can be incorporated in the crystal lattice (12). The nominal value of the melting point of homopolymer is 175°C, that of the copolymer is 165°C. Other thermal properties, which depend substantially on the crystallization or melting of the polymer, are Hsted in Table 1. See also reference 13. 

Mechanical and Thermal Properties. The first member of the acrylate series, poly(methyl acrylate), has fltde or no tack at room temperature it is a tough, mbbery, and moderately hard polymer. Poly(ethyl acrylate) is more mbberflke, considerably softer, and more extensible. Poly(butyl acrylate) is softer stiU, and much tackier. This information is quantitatively summarized in Table 2 (41). In the alkyl acrylate series, the softness increases through n-octy acrylate. As the chain length is increased beyond n-octy side-chain crystallization occurs and the materials become brittle (42) poly( -hexadecyl acrylate) is hard and waxlike at room temperature but is soft and tacky above its softening point. 

Thermal Properties. ABS is also used as a base polymer in high performance alloys. Most common are ABS—polycarbonate alloys which extend the property balance achievable with ABS to offer even higher impact strength and heat resistance (2). 

J. M. Pakulak and C. M. Anderson, Naval Weapons Center Standard Methods for Determining Thermal Properties of Propellants andExplosives, NWC TP 6118, Naval Weapons Center, China Lake, Calif., Mar. 1980. 

Smoke, Flash, and Fire Points. These thermal properties may be determined under standard test conditions (57). The smoke poiat is defined as the temperature at which smoke begias to evolve continuously from the sample. Flash poiat is the temperature at which a flash is observed whea a test flame is appHed. The fire poiat is defiaed as the temperature at which the fire coatiaues to bum. These values are profouadly affected by minor coastitueats ia the oil, such as fatty acids, moao- and diglycerides, and residual solvents. These factors are of commercial importance where fats or oils are used at high temperatures such as ia lubricants or edible frying fats. 

Solubility Properties. Fats and oils are characterized by virtually complete lack of miscibility with water. However, they are miscible in all proportions with many nonpolar organic solvents. Tme solubiHty depends on the thermal properties of the solute and solvent and the relative attractive forces between like and unlike molecules. Ideal solubiHties can be calculated from thermal properties. Most real solutions of fats and oils in organic solvents show positive deviation from ideaHty, particularly at higher concentrations. Determination of solubiHties of components of fat and oil mixtures is critical when designing separations of mixtures by fractional crystallization. 

Table 2. Thermal Properties of Olefins and Other Fiber-Forming Polymers...

Density, mechanical, and thermal properties are significantly affected by the degree of crystallinity. These properties can be used to experimentally estimate the percent crystallinity, although no measure is completely adequate (48). The crystalline density of PET can be calculated theoretically from the crystalline stmcture to be 1.455 g/cm. The density of amorphous PET is estimated to be 1.33 g/cm as determined experimentally using rapidly quenched polymer. Assuming the fiber is composed of only perfect crystals or amorphous material, the percent crystallinity can be estimated and correlated to other properties. 

The glass-transition temperature, T, of dry polyester is approximately 70°C and is slightly reduced ia water. The glass-transitioa temperatures of copolyesters are affected by both the amouat and chemical nature of the comonomer (32,47). Other thermal properties, including heat capacity and thermal conductivity, depend on the state of the polymer and are summarized ia Table 2. 

Thermal Properties. Fibers are not thermoplastic and stable to temperatures below 150°C, with the possible exception of slight yellowing. They begin to lose strength gradually above 170°C, and decompose more rapidly above 300°C. They ignite at 420°C and have a heat of combustion of 14,732 J/g (3.5 kcal/g). 

Table 2. General and Thermal Properties of Film and Sheet...

Thermal Properties. Modified ETFE copolymer has a broad operating temperature range up to 150°C for continuous exposure (24). Cross-linking by radiation improves the high temperature capabiUty further. However, prolonged exposure to higher temperatures gradually impairs the mechanical properties and results in discoloration. 

Cell si has been characterized by measurements of the cell diameter in one or more of the three mutually perpendicular directions (143) and as a measurement of average cell volume (144,145). Mechanical, optical, and thermal properties of a foam are all dependent upon the cell size. 

Two classes of fat replacers exist mimetics, which are compounds that help replace the mouthfeel of fats but caimot substitute for fat on a weight for weight basis and substitutes, compounds having physical and thermal properties similar to those of fat, that can theoretically replace fat in all appHcations (46). Because fats play a complex role in so many food appHcations, one fat replacer is often not a satisfactory substitute. Thus a systems approach to fat replacement, which reHes on a combination of emulsifiers, gums, and thickeners, is often used. 

Specific gravity is the most critical of the characteristics in Table 3. It is governed by ash content of the material, is the primary deterrninant of bulk density, along with particle size and shape, and is related to specific heat and other thermal properties. Specific gravity governs the porosity or fractional void volume of the waste material, ie. 

Thermal Properties. Many commercial glass-ceramics have capitalized on thek superior thermal properties, particularly low or zero thermal expansion coupled with high thermal stabiUty and thermal shock resistance properties that are not readily achievable in glasses or ceramics. Linear thermal expansion coefficients ranging from —60 to 200 x 10 j° C can be obtained. Near-zero expansion materials are used in apphcations such as telescope mirror blanks, cookware, and stove cooktops, while high expansion frits are used for sealing metals. 

A knowledge of the viscous and thermal properties of non-Newtonian fluids is essential before the results of the analyses can be used for practical design purposes. Because of the nonlinear nature, the prediction of these properties from kinetic theories is as of this writing in its infancy. Eor the purpose of design and performance calculations, physical properties of non-Newtonian fluids must be measured. 

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