Method thermal

Two thermal methods have been extensively studied in recent years, pyrolysis-gas chromatography (Py-GC) - mass spectrometry (MS) and evolved gas analysis involving infrared spectroscopy (IR) - MS, thermogravimetry and differential scanning calorimetry (DSC). 

For powders, electrothermal evaporation may be used as most substances volatilize far below the volatilization temperature of graphite ( 3600 °C). This approach is often hampered by the sample inhomogeneity, as it is generally a micromethod, as well as by anion effects causing chemical interferences [187]. Furthermore, transport losses can occur. 

In order to solve the problems related to microsamples, suitable solutions may lie in the use of larger furnaces with higher power dissipation so that much larger samples than the usually 2-5 mg admitted to a conventional graphite furnace for 

Transport phenomena occur particularly when transporting the vapors themselves. They disappear completely when the sample is inserted directly into the signal generation source, where it is evaporated thermally. This approach is known from work with graphite or metal probes in atomic absorption, where for example W wire cups and loops are used. The technique is also used in plasma spectrometry with the inductively coupled plasma (ICP), both in atomic emission [189-191] and in mass spectrometry [192]. Its absolute power of detection is extremely high and the technique can be used both for the analysis of dry solution residues as well as for the volatilization of microamounts of solids. 

Solid substances such as AgCl and also PTFE powder can be used as thermochemical reagents (see e.g. Ref. [191] for an ICP application). In the case of Ti in the presence of C and PTFE the following reactions have to be considered  

At high temperature the last reaction is favored thermodynamically as well as kinetically, the latter because TiF4 is volatile. 

gradual temperature increase from 350 to 2400 °C (600 °C per min). (Reprinted with permission from Ref. [219].) 

Increase in signals with sampled amounts in direct mpling ETV-ICP-OES with the addition of AgCI [34]. 

Several closed-cycle thermal processes have been developed whereby hydrogen can be produced from water using, e.g., coal as the source of heat. Three common schemes are presented in Table 6.7. 

The corrosive nature of some of the products implies rather elaborate precautions in construction and design. The total energy required for the reaction 

The major use of hydrogen today is in the production of ammonia via the Haber reaction  

The nitrogen is prepared by the fractional distillation of liquid air (b.p. N2 = — 196°C, b.p. O2 = — 183°C), whereas the hydrogen is usually prepared by the thermal cracking of natural gas  

Hydrogen, as a component of synthesis gas, is also following reactions made from carbon and methane by the  

Another group employing surfactant-based methods was that of Pileni and colleagues [124]. In this case, truncated silver nanoplates were produced by the sonication of two reverse micellar solutions consisting of silver di(2-ethyl-hexyl)sulfosuccinate (Ag(AOT)) and sodium di(2-ethyl-hexyl)sulfosuccinate (Na(AOT)) isooctane with Na(AOT) and hydrazine. The nanoplate size could be tuned by the amount of reducing agent added during the synthesis. 

Figu re 3.24 (a, b) TEM images and illustrations showing the truncation procedure with time (c) UV-visible absorption spectra of sol with time, showing the blue-shift of the in-plane dipole, consistent with truncation of the sharp nanoprisms. Reprinted with permission from Ref [126] 2007 Wiley-VCH Verlag GmbH, Co. KGaA. 

In a recent report, the Xia group also suggested another mechanism for the formation of these triangular plates [129]. Trimeric silver clusters, which are a common species in silver nitrate solutions, act as nucleation sites for the addition of the newly reduced silver atoms. Mass spectrometry was used to identify the presence of silver clusters. It is worthy of mention at this point that the authors emphasized that the end morphology of a nanocrystal is determined by the interplay of many parameters, all of which must be considered before an appropriate growth mechanism can be proposed. 

Other aqueous procedures that produce nanoprisms with reasonable control over the size are discussed below. Zou and Dong s procedure involves the reduction of silver nitrate by hydrazine in the presence of seed particles and trisodium citrate [6]. The size of the nanoplates is simply controlled by adjusting the concentration of seed particles used-that is, larger nanoplates can be produced when a 

The Kelly group have developed a number of seed-mediated procedures for the growth of silver nanoplates. The first method involved the reduction of silver nitrate by ascorbic add in the presence of seeds, followed by a seed-mediated reduction of silver nitrate by ascorbic acid in the presence of PVA [3]. The group s second method involved the reduction of silver nitrate by ascorbic acid in the presence of trisodium citrate and PVP [132]. In this case, the position of the in-plane dipole SPR could be tuned by varying the concentration of citrate present. The reaction was carried out at room temperature but interestingly, as the temperature was increased, the monodispersity and uniformity of the particles was also increased. Another procedure has also been developed within the group which involved the silver seed-catalyzed reduction of Ag by ascorbic acid. Unlike the previous method, no additional citrate was required and the concentration of 

Whereas hot stage microscopy can be used to obtain qualitative information on polymorphic behaviour, thermal analysis provides quantitative information about the relative stability of polymorphic modifications, the energies involved in phase changes between them and the monotropic or enantiotropic nature of those transitions. The two techniques are best used in conjunction. 

In the classical differential thermal analysis (DTA) system both sample and reference are heated by a single heat source. The two temperatures are measured by sensors embedded in the sample and reference. In the so-called Boersma system, the temperature sensors are attached to the sample pans. The data are recorded as the temperature difference between sample and reference as a function of time (or temperature). The object of these measurements is generally the determination of enthalpies of changes, and these in principle can be obtained from the area under a peak together with a knowledge of the heat capacity of the material, the total thermal resistance to heat flow of the sample and a number of other experimental factors. Many of these parameters are often difficult to determine hence, DTA methods have some inherent limitations regarding the determination of precise calorimetric values. 

On the other hand, in a genuine DSC instrument, sample and reference are each heated individually. A null balance principle is employed, whereby any change in the heat flow in the sample, (e.g. due to a phase change) is compensated for in the reference. The result is that the temperature of the sample is maintained at that of the reference by changing the heat flow. The signal which is recorded (dH/dt) (the heat flow as a function of time (temperature)), is actually proportional to the difference between the heat input into the two channels as a function of time (temperature). 

SO that the integration under the area of the peak directly yields the enthalpy of the transition. 

Thermogravimetric analysis (TGA) measures the change in mass of a sample as a function of temperature. It therefore provides information on the presence of volatile components, in the present context particularly solvents or water, which form the basis of solvates or hydrates respectively, as well as processes such as decomposition and sublimation. 

DSC-OIT appears thus a reliable for detecting stabilizers in virgin polyolefins stabilized with phenolic antioxidants. However, in the case of polymers having previously undergone whether an irradiation or any thermal treatment likely to provoke some thermal oxidation, OIT value expresses 

The elaboration of UHMWPE hips is particularly challenging. As nicely illustrated by Atwood [1]  

Vitamin E offers the possibility to trap residual radicals and avoid some post irradiation effects. However, it directly competes with crosslinking. It could be an interesting strategy for add vitamin E by an impregnation method in the crosslinked UHMWPE. 

However, it seems difficult, at this state of our knowledge, to completely compare the wide variety of methods for designing UHMWPE hips, differing by dose rate, total dose, temperature and time for the thermal treatment, method for incorporation of vitamin E. 

We have then chosen to gather all the physicochemical parameters describing the vitamin E action. We discussed their physical sense by comparing their values with those published for common antioxidants. We dispose now of a numerical tool permitting to describe the stabilization by Vitamin E. We presented in this chapter some simulations in thin films, but they can be adapted in a diffusion- reaction coupling model, which will be finally helpful for discussing the method for designing UHMWPE materials by a non-empirical way. 

The heat flow into (endothermic) or out (exothermic) of a sample as a function of temperature and time is measured using the technique of DSC. In particular, it is used to study and determine the temperature of thermal transitions. For polymers, these include Tg, the glass transition temperature, Tc, the (exothermic) temperature of crystallisation for polymers that can crystallise, and Tm, the (endothermic) melting temperature. A DSC measurement requires only a small amount of sample 2-20 mg of a film, powder, fibre or liquid samples can be analysed in a DSC pan. 

DSC can yield both qualitative and quantitative information, and is a relatively fast technique, with typical heating rates being about 10°Cmin 1. It is routinely used to determine oxidation-induction time, see Section 2.1, which can be a useful parameter in assessing the thermal stability of a series of materials [103]. 

Differential photocalorimetry (DPC) is included here since the instrument used is essentially an adaptation of DSC instrumentation. The photocalorimeter comprises a DSC instrument with a UV/visible source mounted on top, such that light of appropriate wavelength or wavelength region from the source is focused onto the measuring head (both reference and sample pans). The most frequent use of DPC is in the study of polymer cure reactions, but it may also be used to follow such as UV degradation. 

The derivative DTG curves shown in the inset represent the degradation rates. Reprinted from Archodoulaki et al. [107]. Copyright 2004, with permission from Elsevier. 

Recently, these researchers, again using a combination of TGA and TGA-MS, published further studies on the thermo-oxidative ageing of POM, including determining various activation energies [108]. 

An attempt to compare the sensitivity, reproducibility, and accuracy of some methods has been made by Zieniuk and Chivers [ 17], In our own survey above, the dosimetry techniques quoted will have advantages and limitations a summary of which appears below. Only a few methods allow the direct and absolute measurement of transmitted power and these include thermal methods, radiation pressure measurements, and electrical or mechanical measurements at the transducer. 

From a practical point of view, the most generally applicable and the easiest dosimeters to use are those based on thermal methods, especially those using thermal probes. These probes have almost no limitations since they can be used (a) in any reaction vessel below or beyond the cavitation threshold, (b) in free or 

Some care should be exercised when using coated thermocouples since the response of the probe strongly depends on the coating. Although a calorimeter is important for the basic calibration of transducers, the calorimeter itself of little interest for sonochemical studies, unless it is used as the reactor. 

The techniques described here depend on heat transfer to form particulates into larger entities. Agglomeration occurs through one or more of the following mechanisms  

Heat may be transferred directly as in the burning of solid fuel mixed with the particulates in the sintering of ores or indirectly as in the combustion of fuel to produce hot gases in pellet hardening. External heat transfer may also take place across a metallic surface as in drum and belt driers and flakers. 

FIGURE 12.4 Specific heat capacity plotted against temperature for atactic polypropylene, showing the glass transition in the region of 260 K. (From O Reilly, J.M. and Karasz, F.E., 

Perhaps the most useful techniques now in use to locate the are differential thermal analysis (DTA) and differential scanning calorimetry (DSC) (see Chapter 10). Both methods provide a means of characterizing thermal transitions as either exothermic or endothermic peaks (melting and crystalhzation), or as changes in heat capacity (glass transition). 

Among other methods, dielectric loss measurements (see Chapter 13) offer additional information on polymer dynamics across the glass transition and have been used extensively. 

We have seen that the magnitude of varies over a wide temperature range for different 

In semi-crystalline polymers, some of the macromolecules are arranged in crystalline regions, known as crystallites, while the matrix is amorphous. The greater the concentration of crystallites, i.e., the greater the crystallinity, the more rigid is the polymer, i.e., the higher the value. 

The true melting points of crystalline polymers can be determined by plotting the DSC melting peak temperatures as a function of the square root of heating rate and linear extrapolations to zero heating rate. 

Differential thermal analysis has been used to study the effect of side-chain length in polymers on melting point, and the effect of heating rate of polymers on their melting point. DSC has been used to evaluate multiple peaks in polystyrene (PS) [23-25]. 

DSC measurements of the energy during melting of aqueous polymer solutions and gels yield heats of mixing and sorption [26]. The technique has also been used to study the heat changes occurring in a polymer as it is cooled (plots of temperature versus heat flow (mW)). 

Thermomechanical analysis (TMA) has been used for softening measurements of polymers and the measurement of the amount of probe penetration into a polymer at particular applied forces as a function of temperature. This technique allows evaluations of and the evaluation of dimensional properties over the temperature range of use or under actual accelerated conditioning cycles (plots of temperature versus compression (mm)). 

Temperature sensors, such as the thermistors and thermopiles described in 4.4.4, can be used to monitor the variation in enthalpy arising from a reaction catalysed by an enzymatic label on either an andgen or an andbody. This technique is called TELISA (thermometric enzyme linked immunosorbent assay), and involves the use of reactor columns lined with antibodies, which detect antigens such as albumin [261]. These reactors, however, are not real biosensors. 

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Boerio-Goates J and Callanan J E 1992 Differential thermal methods Physical Methods of Chemistry... 

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)... 

Thoen J 1998 Thermal methods Handbook of Liquid Crystais Voi 1. Fundamentais ed D Demus, J Goodby, G W Gray, H-W Spiess and V Vill (New York Wiley-VCH)... 

Potassium is never found free in nature, but is obtained by electrolysis of the hydroxide, much in the same manner as prepared by Davy. Thermal methods also are commonly used to produce potassium (such as by reduction of potassium compounds with CaC2, C, Si, or Na). 

These thermal methods for preparing amides are limited m their generality Most often amides are prepared m the laboratory from acyl chlorides acid anhydrides or esters and these are the methods that you should apply to solving synthetic problems... 

Key properties are its flexibility, translucency, and resistance to all known chemicals except molten alkali metals, elemental fluorine and fluorine precursors at elevated temperatures, and concentrated perchloric acid. It withstands temperatures from —270° to 250°C and may be sterilized repeatedly by all known chemical and thermal methods. 

Wendlandt, W. W. Thermal Methods of Analysis, 2nd ed. Wiley New York, 1986. 

The thermal method is based on the much higher solubiUty of KCl in hot water as compared to the solubiUty of NaCl. The KCl is recovered in vacuum crystallizers, filtered or centrifuged, dried, and sometimes granulated by compaction. Product from the thermal beneficiation method usually is of relatively high purity and is particularly suitable for use in formulating solution-type fertilizers. Guaranteed K2O content of this product is usually 62%... 

A review pubHshed ia 1984 (79) discusses some of the methods employed for the determination of phenytoia ia biological fluids, including thermal methods, spectrophotometry, luminescence techniques, polarography, immunoassay, and chromatographic methods. More recent and sophisticated approaches iaclude positive and negative ion mass spectrometry (80), combiaed gas chromatography—mass spectrometry (81), and ftir immunoassay (82). 

Thermoanalytical methods (tga, dta) often enable definite identification of the type of asbestos fibers (Fig. 7). For example, the strong exotherm observed with chrysotile at 830°C can be used as a routine indicator for determining the chrysotile content of talc (4,10). Thermal methods are also usefiil for determining certain mineral contaminants of asbestos fibers, for example bmcite and calcite in chrysotile. 

Chlorine free radicals used for the substitutioa reactioa are obtaiaed by either thermal, photochemical, or chemical means. The thermal method requites temperatures of at least 250°C to iaitiate decomposition of the diatomic chlorine molecules iato chlorine radicals. The large reaction exotherm demands close temperature control by cooling or dilution, although adiabatic reactors with an appropriate diluent are commonly used ia iadustrial processes. Thermal chlorination is iaexpeasive and less sensitive to inhibition than the photochemical process. Mercury arc lamps are the usual source of ultraviolet light for photochemical processes furnishing wavelengths from 300—500 nm. 

Methane, chlorine, and recycled chloromethanes are fed to a tubular reactor at a reactor temperature of 490—530°C to yield all four chlorinated methane derivatives (14). Similarly, chlorination of ethane produces ethyl chloride and higher chlorinated ethanes. The process is employed commercially to produce l,l,l-trichloroethane. l,l,l-Trichloroethane is also produced via chlorination of 1,1-dichloroethane with l,l,2-trichloroethane as a coproduct (15). Hexachlorocyclopentadiene is formed by a complex series of chlorination, cyclization, and dechlorination reactions. First, substitutive chlorination of pentanes is carried out by either photochemical or thermal methods to give a product with 6—7 atoms of chlorine per mole of pentane. The polychloropentane product mixed with excess chlorine is then passed through a porous bed of Fuller s earth or silica at 350—500°C to give hexachlorocyclopentadiene. Cyclopentadiene is another possible feedstock for the production of hexachlorocyclopentadiene. 

In addition to conventional thermal cracking in tubular furnaces, other thermal methods and catalytic methods to produce ethylene have been developed. None of these are as yet commercialized. 

Thermal Methods Level-measuring systems may be based on the difference in thermal characteristics oetween the fluids, such as temperature or thermal conductivity. A fixed-point level sensor based on the difference in thermal conductivity between two fluids consists of an electrically heated thermistor inserted into the vessel. The temperature of the thermistor and consequently its electrical resistance increase as the thermal conductivity of the fluid in which it is immersed decreases. Since the thermal conductivity of liquids is markedly higher than that of vapors, such a device can be used as a point level detector for liquid-vapor interface. 

The preparation of semiconductors by thermal decomposition would appear to be impossible because of the high amount of energy required to break all of the metal-carbon bonds before the atomic species could be formed. However, the thermal method is successful because the reaction to form free methyl radicals, which combine to form ethane, lowers the energetic requirements for the formahon of gallium, for example, according to the equation... 

A large number of CVD diamond deposition technologies have emerged these can be broadly classified as thermal methods (e.g., hot filament methods) and plasma methods (direct current, radio frequency, and microwave) [79]. Film deposition rates range from less than 0.1 pm-h to 1 mm-h depending upon the method used. The following are essential features of all methods. 

In catalytic incineration, organic contaminants are oxidized to carbon dioxide and water. A catalyst is used to initiate the combustion reaction, which occurs at a lower temperature than in thermal incineration. Catalytic incineration uses less fuel than the thermal method. Many commercial systems have removal efficiencies eater than 98%. 

Ethers can be obtained by the thermal method in 25-50% yield" " even from alcohols, which contain the A -3-ketal function an 80% yield of 18,20a-ether has been reported from a 20a-alcohol.""... 

It is possible to distinguish between SBR and butyl rubber (BR), NR and isoprene rubber (IR) in a vulcan-izate by enthalpy determination. In plastic-elastomer blends, the existence of high Tg and low Tg components eases the problems of experimental differentiation by different types of thermal methods. For a compatible blend, even though the component polymers have different Tg values, sometimes a single Tg is observed, which may be verified with the help of the following equation ... 

In addition to the main general methods of analysis outlined above there are also certain specialised techniques which are applied in special circumstances. Among these are X-ray methods, methods based upon the measurement of radioactivity, mass spectrometry, the so-called kinetic methods, and thermal methods. 

Delmas and his co-workers have done extensive work on pyroaurite-type materials which has recently been reviewed [73], In addition to precipitation methods, they have prepared the materials by mild oxidative hydrolysis of nickelates that were prepared by thermal methods similar to those used for the preparation of LiNiOz [74]. A cobalt-substituted material NaCoA ( Ni( A02) was prepared by the reaction of Na20, Co304 and NiO at 800 °C under a stream of oxygen. The material was then treated with a 10 molL-1 NaCIO +4 molL 1 KOH solution for 15h to form the oxidized y -oxyhydroxide. The pyroau-... 

Black OsBr3 and OSI3 (/j = 1.8 /uB) are also prepared by thermal methods... 

Rapid loading of cross-linked PS Wang resin (4-(benzyloxy)benzyl alcohol PS) with a selection of /3-ketoesters was shown to reach completion within 1-10 min if microwave irradiation at 170 °C was employed. The conventional thermal method for acetoacetylation of hydroxymethyl-functionalized polystyrene resins takes several hours therefore, microwave heating allowed for... 

There are two important ways of adding alkanes to alkenes—the thermal method and the acid-catalysis method." Both give chiefly mixtures, and neither is useful for the preparation of relatively pure compounds in reasonable yields. However, both are useful industrially. In the thermal method, the reactants are heated to high temperatures ( 500°C) at high pressures (150-300 atm) without a catalyst. As an example, propane and ethylene gave 55.5% isopentane, 7.3% hexanes, 10.1% heptanes, and 7.4% alkenes. The mechanism is undoubtedly of a free-radical type and can be illustrated by one possible sequence in the reaction between propane and ethylene ... 

FIGURE 6.4 Steam flooding is one of two principal thermal methods for oil recovery and has been commercially applied since the early 1960s. A mixture of steam and hot water is continuously injected into the oil-bearing formation to displace mobilized oil to adjacent production wells. Reprinted with permission from Enhanced Oil Recovery. Copyright 1984 by the National Petroleum Council. 

THERMAL METHODS OF RAW MATERIALS RECYCLING OF PLASTICS WASTES... 

The present state of technology is reviewed (mainly from German literature of 1993 -4) in the Add of three principal thermal methods used for plastics wastes, namely pyrolysis (high-temperature carbonisation, coking), hydrocracking and gasification. 36 refs. Articles from this journal can be requested for translation by subscribers to the Rapra produced International Polymer Science and Technology. 

Details are given of the thermal methods of recycling plastics. Emphasis is given to pyrolysis, hydrocracking, and gasification. 36 refs. 

Stearic acid (5 wt%) was compounded with a linear polymer prepared from 3,9-bis(ethylidene-2,4,8,10-tetraoxaspiro[5,5]undecane) and a 30 70 mole ratio of 1,6-hexanediol and trans-cyclohexanedi-methanol by thermal, solvent, or powder methods (Table 4). The thermal method (flux mixer and roller mill) resulted in good stearic... 

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