Thermal properties determination

ISO 10351 (1992). Method of testing plastics. Part I. Thermal properties, determination of the combustibility of specimens using a 125 mm flame source. 

Thermal Properties Determined by Differential Scanning Calorimetry. 77... 

The use of representative thermal properties is an important aspect of performing the analysis. The thermal properties determine how fast thermal energy travels from one component to another. As a result, the thermal properties used have a significant impact on the overall outcome of the heat transfer analysis. 

A.7 Effect of Carbon Fiber on the Cooling Time of a Composite. A 0.4064 cm thick laminate (layers of polymer sheet reinforced with long continuous fibers) consisting of 60 volume % carbon fiber and 40 volume % PEEK is cooled from 350 °C to 100 °C in a mold with the wall temperatures set at 75 °C. Neglecting crystallization and assuming constant thermal properties, determine how much faster the composite cools down to the final temperature relative to the pure matrix of the same thickness. The properties of the fiber and matrix are given in Table 5.11. 

Boerio-Goates J and Callanan J E 1992 Differential thermal methods Determination of Thermodynamic Properties, Physical Methods of Chemistry 2nd edn vol VI ed B W Rossiter and R C Baetzold (New York Wiley)... 

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 ... 

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). 

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. 

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. 

Alloy selection depends on several factors, including electrical properties, alloy melting range, wetting characteristics, resistance to oxidation, mechanical and thermomechanical properties, formation of intermetaUics, and ionic migration characteristics (26). These properties determine whether a particular solder joint can meet the mechanical, thermal, chemical, and electrical demands placed on it. 

Thermal Properties. The thermal stabiUty of cellulose esters is deterrnined by heating a known amount of ester in a test tube at a specific temperature a specified length of time, after which the sample is dissolved in a given amount of solvent and its intrinsic viscosity and solution color are deterrnined. Solution color is deterrnined spectroscopically and is compared to platinum—cobalt standards. Differential thermal analysis (dta) has also been reported as a method for determining the relative heat stabiUty of cellulose esters (127). 

Critical Temperature The critical temperature of a compound is the temperature above which a hquid phase cannot be formed, no matter what the pressure on the system. The critical temperature is important in determining the phase boundaries of any compound and is a required input parameter for most phase equilibrium thermal property or volumetric property calculations using analytic equations of state or the theorem of corresponding states. Critical temperatures are predicted by various empirical methods according to the type of compound or mixture being considered. 

The pressure is to be identified as the component of stress in the direction of wave propagation if the stress tensor is anisotropic (nonhydrostatic). Through application of Eqs. (2.1) for various experiments, high pressure stress-volume states are directly determined, and, with assumptions on thermal properties and temperature, equations of state can be determined from data analysis. As shown in Fig. 2.3, determination of individual stress-volume states for shock-compressed solids results in a set of single end state points characterized by a line connecting the shock state to the unshocked state. Thus, the observed stress-volume points, the Hugoniot, determined do not represent a stress-volume path for a continuous loading. 

All these thermal properties relate to how to determine the best useful processing conditions to meet product performance requirements. There is a maximum temperature or, to be more precise, a maximum time-to-temperature relationship for all materials preceding loss of performance or decomposition. Figure 7-13 provides a temperature guide for continuous heating of plastics. 

Dimensional stability is an important thermal property for the majority of plastics. It is the temperature above which plastics lose their dimensional stability. For most plastics the main determinant of dimensional stability is their Tg. Only with highly crystalline plastics is Tg not a limitation. 

We observe that all constants in (4) or (5) can be determined by measurements of the thermal properties of the system, with the exception of a or A, which are indeterminate from the point of view of classical thermodynamics. 

If a particulate composite is considered, consisting of a polymeric matrix and an elastic filler, by the previous procedure, the mechanical and thermal properties, as well as the volume fraction of the mesophase can be determined. The mesophase is also expected to exhibit a viscoelastic behaviour. The composite consists, therefore, of three phases, the third phase (the mesophase) being also viscoelastic. The presence... 

Network properties and microscopic structures of various epoxy resins cross-linked by phenolic novolacs were investigated by Suzuki et al.97 Positron annihilation spectroscopy (PAS) was utilized to characterize intermolecular spacing of networks and the results were compared to bulk polymer properties. The lifetimes (t3) and intensities (/3) of the active species (positronium ions) correspond to volume and number of holes which constitute the free volume in the network. Networks cured with flexible epoxies had more holes throughout the temperature range, and the space increased with temperature increases. Glass transition temperatures and thermal expansion coefficients (a) were calculated from plots of t3 versus temperature. The Tgs and thermal expansion coefficients obtained from PAS were lower titan those obtained from thermomechanical analysis. These differences were attributed to micro-Brownian motions determined by PAS versus macroscopic polymer properties determined by thermomechanical analysis. 

W-3 CHF correlation. The insight into CHF mechanism obtained from visual observations and from macroscopic analyses of the individual effect of p, G, and X revealed that the local p-G-X effects are coupled in affecting the flow pattern and thence the CHF. The system pressure determines the saturation temperature and its associated thermal properties. Coupled with local enthalpy, it provides the local subcooling for bubble condensation or the latent heat (Hfg) for bubble formation. The saturation properties (viscosity and surface tension) affect the bubble size, bubble buoyancy, and the local void fraction distribution in a flow pattern. The local enthalpy couples with mass flux at a certain pressure determines the void slip ratio and coolant mixing. They, in turn, affect the bubble-layer thickness in a low-enthalpy bubbly flow or the liquid droplet entrainment in a high-enthalpy annular flow. 

Heat evolution calculations and laboratory testing are usually needed to define the reactivity hazards. This book outlines methods for identifying hazardous reactions and determining safe conditions. Data are needed on various rate phenomena, enthalpies, and other thermal properties. 

The reason for the lower liquid crystalline (LC) temperature of the BB model compound seems to be that the biphenyl unit of this compound was adopting a twisted structure in the LC state [26], Therefore, we prepared various polyarylates containing the BB unit and determined their thermal properties and the moduli of the as-spun fibers, as shown in Table 19.3. 

---