Thermal Decompositions

Thermal decomposition of PVC is believed to be linked to the loss of plasticizers. Activation energy of thermal degradation is given by equation  

Ejy activation energy of plasticizer evaporation E activation energy of PVC degradation. 

Plasticizer evaporation during thermogravimetric analysis is given by the equation  

Ep[ energy needed to evaporate plasticizer mpj plasticizer mass 

The amount of plasticizer in the sample did not affect the temperature of plasticizer removal but the maximum temperature of plasticizer removal increased when the rate of temperature increase during thermogravimetric studies was smaller.  

The rates of decomposition of peroxyesters (38) arc very dependent on the nature of the substituents R and R. The variation in the decomposition rale with R follows the same trends as have been discussed for the corresponding diaeyl peroxides (see 3.3.2.1.1). 

For /-butyl peresters there is also a variation in efficiency in the series where R is primary secondary tertiary. The efficiency of /-butyl peroxypentanoate in initiating high pressure ethylene polymerization is 90%, that of /-butyl peroxy-2-ethylhexanoate ca 60% and that of/-butyl peroxypivalate ca 40%.196 Inefficiency is due to cage reaction and the main cage process in the case where R is secondary or tertiary is disproportionation with /-butoxy radicals to form /-butanol and an olefin.196 

The low conversion initiator efficiency of di-r-butyl pcroxyoxalatc (0.93-0.97)1-1 is substantially higher than for other peroxyeslers [/-butyl peroxypivalale, 0.63 /-butyl peroxyacetate, 0.53 (60 °C, isopropylbenzene)195]. The dependence of cage recombination on the nature of the reaction medium has been the subject of a number of studies. 12I,1 0 20CI The yield of DTBP (the main cage product) depends not only on viscosity but also on the precise nature of the solvent. The effect of solvent is to reduce the yield in the order aliphatic aromatie protic. It has been proposed199 that this is a consequence of the solvent dependence of p-scission of the f-butoxy radical which increases in the same series (Section 3.4.2.1.1). 

The reaction is facilitated when R is electron withdrawing, when R has a high migratory aptitude (ability to stabilize a carbonium ion), and by polar reaction media. 

The thermal decomposition reaction of PH3 can be used to produce ultrapure phosphorus. Thus this reaction attracted much interest in recent years, for example, in experiments directed at growing layers or crystals of III-V semiconductors such as InP, GaP, GaASi xPx, etc., by vapor-phase epitaxy (cf. 1.3.1.6, pp. 293/308). An effort has not been made to systematically scan the prolific literature in that area. 

Based on JANAF or equivalent thermochemical data, equilibrium constants were calculated for the gas-phase equilibria  

Rate constants for unimolecular homogeneous PH3 decomposition were calculated by the Rice-Ramsperger-Kassel-Marcus (RRKM) theory and by the use of estimated values for the activation energies. Rate constants at the high-pressure limit for reaction (5), log(k/s)= 14.18-11 610/T [5] or 14.00-12610/T [4], include activation energies of 222 or 241 kJ/mol, respectively. Calculated rate constants for reaction (6) are log(k/s)=15.74-18 040/T with an activation energy of 345 kJ/mol. At 900 K PH formation is thus predicted to exceed PH2 formation by a factor -10. Calculated fall-off pressures for both reactions which indicate the onset of second-order decomposition, are quite high, about 10 Torr in an H2 bath gas [5]. 

On the experimental side, thermal decomposition of gaseous PH3 appears to be a complex reaction see Phosphor C, 1965, pp. 31/3, and [6 to 8]. The reaction is kinetically inhibited and, apart from two more recent studies [9 to 11], noticeable decomposition was reported to occur above 400 C. There is agreement that PH3 decomposition shows all the characteristic features of a heterogeneous, i.e., surface-catalyzed, reaction (for possible homogeneous contributions at high temperatures, see below). Moreover it was shown recently that techniques used for sampling and analysis of the reaction mixture still have a profound influence on the results. Several conclusions drawn from the results of standard ex-situ techniques (the decomposing PH3 gas is probed, for instance, at some distance from the hot surface by a mass spectrometer) were thus rendered obsolete [9 to 11], see Fig. 10, p. 202. 

Gaseous P4 nucleated, and solid deposits of phosphorus were occasionally observed in colder parts of the reactor [11, 12]. 

The thermal decomposition behavior of Pb(C2H5)4 depends greatly on its purity and its physical state. Thus, the decomposition of Pb(C2H5)4 proceeds far more readily in the liquid than in the gas phase [69, 92]. 

Subsequently the usual recombination and disproportionation reactions of ethyl radicals occur [52]. The thermal decomposition of a mixture of Pb(C2H5)4 and Pb2(C2H5)e was studied [58] in this case also, the concentration of Pb2(C2H5)6 initially increased [59]. 

Finely divided lead has an autocatalytic effect on the thermal decomposition of Pb(C2H5)4 [58, 59] see also [63]. The walls of the vessel have no substantial effect on the decomposition of Pb(C2H5)4 [59]. Repeated fractionation does not free Pb(C2H5)4 of traces of Pb2(C2H5)e, since the former changes into the latter at higher temperatures [52]. 

The products of the vapor phase dissociation are distinctly different from those obtained in the liquid phase H2 is produced in quantity, and the amount of butane is much greater [12, 14, 20]. 

Controlled thermal decomposition of Pb(C2H5)4 in a stream of hydrogen or of a mixture of He and Ne in a glass or quartz tube under reduced pressure is a method for producing free ethyl radicals [13 to 16, 19, 22], e.g., at a temperature of 550 [78] see also [11, 

The chemical energy H generated by the decomposition of the explosive can be calculated from the heat lost to the surroundings F and the accumulation of heat in the explosive Q as shown in Equation 4.3. 

The amount of chemical energy H generated by the decomposition of an explosive will give information on the sensitivity of the explosive, since the mechanism for the initiation of explosives is thermal. Concomitantly, a high value for H will result in a more sensitive explosive. 

Experimental studies on the thermal decomposition and combushon processes of AP have been carried out and their detailed mechanisms have been reported.P-iil Fig. 5.1 shows the thermal decomposition of AP as measured by differential thermal analysis (DTA) and thermal gravimetry (TG) at a heating rate of 0.33 K s f An endothermic peak is seen at 520 K, corresponding to an orthorhombic to cubic lattice crystal structure phase transition, the heat of reaction for which amounts to 

The burning rate of a pressed strand of AP as a function of pressure has been dealt with by Ardenlil and by Levy and Friedman.PI The lower pressure limit of AP burning is about 2.7 MPa and the burning rate increases as the pressure is increased above this lower limit. The thickness of the gas-phase reaction of NH3/ HCIO4 is less than 100 pm at 10 MPa and decreases as the pressure is increased, and the reaction time is inversely proportional to the pressure (MPa) represented by 6.5 X 10 /p seconds.[ 1 

All explosive substances undergo thermal decomposition at temperatures far below those at which explosions occur. During thermal decomposition, strong exothermic reactions take place which generate a lot of heat. Some of this heat is lost to the surroundings, but the remainder will raise the temperature of the explosives even further. When the rate of heat generated is greater than the rate of heat lost, spontaneous decomposition will occur, 

CapyrightO2011 ftoyal Societ r of Chemistry Retrieved lromwww.knoveLcom 

Under nonoxidative conditions, the thermal decomposition of the RF-aerogel binder used leads to BTX-free decomposition products such as CO2, CO, and methane as expected. 

For casting processes it is necessary to reduce toxic emissions and to develop products in a more environmental acceptable direction. Up to now the development of AeroSand improves on this aspect. 

At temperatures below the ignition point, the thermal decomposition of black powder provides an interesting insight into the processes which are thought to control the reaction rate during subsequent burning. In decomposition experiments it has been shown that the overall reaction proceeds in several steps. As the temperature is increased the steps become shorter and the reaction faster. Since these reactions involve gases, the effect of pressure is also important. 

The first reaction has been shown to be the formation of hydrogen sulfide (H2S) from sulfur and volatile organic material originating from the charcoal as shown in reaction (2.1), 

The NO2 can also be produced by reactions between sulfur and potassium nitrate (KNO3) with the formation of nitric oxide (NO) and nitrogen dioxide (NO2) as shown in reactions (2.3) and (2.4)  

There is then a gas-phase reaction between the main products of these reactions, as in reaction (2.5)  

It has been suggested that reaction (2.5), with the regeneration of sulfur, proceeds until all of the H2S has been used up. The NO2 then reacts with the free sulfur as in reaction (2.6)  

The first reaction has been shown to be the formation of hydrogen 

While some details of the kinetics of radical production from dialkyidiazenes remain to be unraveled, their decomposition mechanism and behavior as polymerization initiators are largely understood. Kinetic parameters for some common azo-initiators are presented in Table 3.2. 

Thcnnolysis rates ( j) of dialkyidiazenes (15) show a marked dependence on the nature of R (and R ). fhe values of increase in the series where R (=R ) is aryl primary secondary tertiary allyl. In general, is dramatically accelerated by a-substituents capable of delocalizing the free spin of the incipient radical. For example, Timberlake has found that for the case of dialkyidiazenes, 

X-C(CH3)3-N=N- (CH3)2-X that increases in the series where X is CH3 -OCH3 -SCH3 -C02R—CN -Ph -CH=CH2 (see also Table 3.2). These results can be rationalized in terms of the relative stability of the radicals generated (R, R ). 

However, steric factors are also important.Riichardt and coworkers showed, for a series of acyclic alkyl derivatives, that a good correlation exists between and ground state strain. Additional factors are important for bicyclic and other conformalionally constrained azo-compounds. Wolf has described a scheme for calculating based on radical stability (HOMO Ji-delocalization energies) and ground state strain (stcric parameters). 

There have been numerous studies on the kinetics of decomposition of AIBN, AlBMe and other dialkyldiazenes. Solvent effects on are small by conventional standards but, nonetheless, significant. Data for AIBMc is presented in Table 3.3. The data come from a variety of sources and can be seen to increase in the series where the solvent is aliphatic ester (including MMA) aromatic (including styrene) alcohol. There is a factor of two difference between in methanol and in ethyl acetate. The value of for AIBN is also reported to be higher in aromatic than in hydrocarbon solvents and to increase with the dielectric constant of the medium. The of AIBMc and AIBN show no direct correlation with solvent viscosity (see also 3.3.1.1.3), which is consistent with the reaction being irreversible ie. no cage return). 

Ashmore and Levitt and later Ashmore and Burnett found an anomalously fast rate early in the reaction with the rate falling to a value in agreement with the earlier workers after about 10 % decomposition. The fast initial rate was eliminated on adding NO. These effects were explained by concurrent molecular and free radical paths to the decomposition, viz. 

The overall rate coefficient for the dissociation is given by References pp. 195-200 

Later the second term becomes small and k = Arrhenius parameters for (19) found by various workers are shown in Table 3. The work of Bodenstein and Ramstetter shows the anomalous initial rate found by Ashmore and Burnett and the data have been recalculated by the latter authors to obtain the values shown in Table 3. The technique used by Rosser and Wise ensured that the values of the 

Ashmore and Burnett were also able to measure ks and found 

Values of kz and k were also obtained and these have been discussed earlier. 

When compounds decompose, they don t necessarily split up into their constituent elements but sometimes into smaller compounds. In the Yorkshire and Derbyshire Dales a lot of limestone is quarried. Much of this is used as a construction and building material, but a lot is thermally decomposed in lime kilns. 

Limestone is, chemically, calcium carbonate it is made up of calcium, carbon and oxygen. When it is heated, it doesn t split up into these three elements, but into two simpler compounds - calcium oxide and carbon dioxide. 

Calcium oxide has the ancient name of quicklime. Most carbonates, when heated, undergo thermal decomposition to form the metal oxide and carbon dioxide. Sodium and potassium carbonate, on the other hand, don t decompose at all when heated, because sodium and potassium are very reactive metals, so their compounds are very stable. 

Nitrates are made up of a metal, nitrogen and oxygen. Most nitrates undergo thermal decomposition to the metal oxide, oxygen and nitrogen dioxide  

Sodium and potassium nitrates, however, give off oxygen as the only gas on heating, and leave the corresponding nitrite. 

The heat resistance of a polymer may be characterised by its temperatures of initial and of half decomposition. The latter quantity is determined by the chemical structure of the polymer and can be estimated by means of an additive quantity the molar thermal decomposition function. The amount of char formed on pyrolysis can be estimated by means of another additive quantity the molar char-forming tendency. 

The way in which a polymer degrades under the influence of thermal energy in an inert atmosphere is determined, on the one hand, by the chemical structure of the polymer itself, on the other hand by the presence of traces of unstable structures (impurities or additions). 

The decomposition temperature of PLA is normally 230—260°C. Therefore, it is considered to be safe for room temperature applications. PLA is seldom used at elevated temperatures, such as the boiling point of water, because PLA tends to lose its structural properties at temperatures 60°C. Although PLA is unlikely to release toxic substances extensively, residues of plasticizer or oligomers still need further attention. PLA undergoes initial thermal decomposition at temperatures above 200°C by hydrolysis reaction followed by lactide reformation, oxidative main-chain scission, and inter-or intramolecular transesterification reaction (Jamshidi et al., 1988). Thermal decomposition can occur at 200°C without catalysts, but it requires higher temperatures to induce a faster and more prevalent reaction (Achmad et al., 2009). 

The depolymerization of PLLA at a high temperature induces the chain-transfer intra- and inter-transesterification and depolymeiization reactions by the evident change of the specific optical rotation number. In other words, the high capacity of a transition metal is able to coordinate ester groups and accelerate reactions. 

Conversion, a Ozawa-Flynn-Wall Method Friedman s Method  

As mentioned in Chapter 2, the blending of starch with PLA is an important approach in order to make cost savings while 

Palladium complexes containing allyls with substituents evolve HCl and the corresponding diene [equation (7.85)]. 

The knowledge of end groups, especially in condensation polymers, is of crucial importance to understand the mechanism of 

Cyclovinylidene unsaturated end groups were detected in PCT untreated samples, and after the thermal treatment at 300 °C, both, cyclovinylidene and methylcyclohexene end groups were present, the formers in minor amounts. In PE7(,C3qT most of unsaturated end groups came from 1,4-CHDM units since the elimination process is enhanced for the /S-tertiary carbon near to the ester group. 

Thermogravimetry/DSC/mass spectrometry analysis of PE Cj T samples heated from room temperature up to 650 °C showed that the thermal decomposition was almost completed in a single step at 

425 °C with releasing of the main following products acetaldehyde, carbon dioxide, benzene, benzoic acid, l,4-bis(methylene)-cyclo-hexane, 4-methyl-benzaldehyde, and 4-methylene-cyclohexane-methanol (103). Yu et al. (104,105) studied the pyrolysis of this copolyester and of PCX by pyrolysis-gas chromatography-mass spectrometry in the 300-700 °C heating range. They concluded that the aliphatic moiety of the copolyester played a dominant role in controlling the pyrolytic behavior. 

Allen et al. (106) studied the thermal and UV degradation of PECT samples and the degradation products where characterized by fluorescence and observed the presence of mono and dihydroxytere-phthalate cromophores in the degraded samples. They also studied (107) the thermal and photochemical oxidation of PECT by chemiluminescence and evaluated the influence of stabilizers. They concluded that the hydroperoxide sites formed during oxidation were responsible for the chemiluminescence response. 

Gaseous Pb(CH3)4 displays a half-life of 320 h in purified dry air in the dark at 295 3 K. The decay in the dark is first-order in Pb(CH3)4. It is enhanced by NO2, but inhibited by the presence of water vapor [40]. Pb(CH3)4 is assumed to decompose on adsorption on activated coal [27]. 

Metallic lead is deposited during decomposition of Pb(CH3)4 as a sputtered film [7] or as a mirror [3, 5, 7, 8, 9]. Mirrors produced at low temperature contain carbon [7] see also [5, 30]. At first, lead exists as a vapor, which then condenses at a temperature of about 900 K on a millisecond time scale into particles, provided that the lead vapor exceeds a critical 

The relationship of rate constants of decomposition of Pb(CH3)4, other lead tetraalkyls, and various other antiknock compounds as determined In engines and temperature is depicted graphically. The decomposition rate Is unaffected by pressure, and is also independent of fuel type and the presence of other compounds in the fuel when Pb(CH3)4 is employed as the antiknock agent [23]. 

Thermal decomposition of Pb(CH3)4 was employed to measure the ionization potential of methyl radicals by the molecular beam method [11, 12]. 

Single pulse shock tube experiments at temperatures between 731 and 931 K show Pb(CH3)4 to be thermally more stable than (CH3)4 nPb(C2H5)n (n = 1 to 4) [24]. After 5.6 ms at 744 K, about 90% of the original Pb(CH3)4, but only 37% of Pb(C2H5)4, remained [26]. However, Pb(CH3)4 was reported to be more explosive and sensitive to shock than Pb(C2H5)4 and the explosive characteristics of Pb(CH3)4 to be comparable to those of picric acid. The sensitivity of Pb(CH3)4 is reduced by addition of toluene [25]. 

Equation 5.4 is easily used by substituting different values of conversion (jc), which ranged from 0.1 to 0.8. The values of dxidt and T were determined for each conversion at different heating rates (8°C/min, 12°C/min, 16°C/min) by using the first derivative obtained from TGA. By linear regression of Equation 5.4, a series of activation energies (pj) and frequency factors k are obtained as function of asphaltene conversion. The application of this method has been reported with detail elsewhere (Trejo et al., 2010). 

Modeling of Processes and Reactors for Upgrading of Heavy Petroleum 

FIGURE 5.2 Thermogram and derivative weight of atmospheric residue and its fractions at 8°C/min of heating rate under nitrogen atmosphere. 

Aromatics. They did not undergo any significant weight loss up to 100°C. From 100°C to 320°C the most prominent changes occur likely by volatilization of mono-, di-, and tri-aromatics and higher aromatic compounds. Resins undergo cracking reactions from 320°C to 480°C and the coke yield is 3.8 wt%, which is very close to that produced by resins. 

Coke Yield for Atmospheric Residue and Its SARA Fractions at Heating Rate of 8°C/min 

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Reboiler temperature increases with a limit often set by thermal decomposition of the material being vaporized, causing excessive fouling. 

B.p. — 29X. Monomer used to form polymers (only under rather drastic conditions) or copolymers with C2F4 and vinylidene fluoride, CH2 = CF2. Hexafluoropropene may be prepared by thermal decomposition of CF3CF2CF2C02Na or is prepared commercially by low pressure pyrolysis of C2F4. 

Tellurium monoxide, TeO. Black solid resulting from thermal decomposition of TeSOj (Te plus SO,). 

H2S is found with the reservoir gas and dissolved in the crude (< 50 ppm by weight), but it is formed during refining operations such as catalytic cracking, hydrodesulfurization, and thermal cracking or by thermal decomposition of sulfur[Pg.322]

Johnston H S 1951 Interpretation of the data on the thermal decomposition of nitrous oxide J. Chem. Phys. 19 663-7... 

Votsmeier M, Song S, Davidson D F and Hanson R K 1999 Shock tube study of monomethylamine thermal decomposition and NH2 high temperature absorption coefficients int. J. Chem. Kinetics 31 323-30... 

Oxygen can also be prepared by the thermal decomposition of certain solid compounds containing it. These include oxides of the more noble metals, for example of mercury or silver ... 

Pure oxygen is conveniently prepared by the thermal decomposition of potassium manganate(VII) ... 

Ozone is formed in certain chemical reactions, including the action of fluorine on water (p. 323) and the thermal decomposition ofiodic(VII) (periodic) acid. It is also formed when dilute (about 1 M) sulphuric acid is electrolysed at high current density at low temperatures the oxygen evolved at the anode can contain as much as 30% ozone. 

Tellurium trioxide, TeOa, is an orange yellow powder made by thermal decomposition of telluric(VI) acid Te(OH)g. It is a strong oxidising agent which will, like H2Se04, oxidise hydrogen chloride to chlorine. It dissolves in hot water to give telluric(VI) acid. This is a weak acid and quite different from sulphuric and selenic acids. Two series of salts are known. 

The substance is pure, but on warming undergoes slight thermal decomposition before the melting-point is reached, and the decomposition products then act as impurities and depress the melting-point. 

Distillation under Reduced Pressure. Occasionally a liquid, when distillation is attempted under atmospheric pressure, will undergo partial or complete decomposition before its boiling-point is reached. To overcome this difficulty, the liquid is distilled under reduced pressure, so that its boiling-point shall be definitely below its thermal decomposition point. 

Action of nitrous acid. To a few ml. of 20% NaNO, solution add a few drops of cold dil. acetic acid. Pour the mixture into a cold aqueous solution of glycine, and note the brisk evolution of nitrogen. NH CH COOH -h HNO2 = HO CH2COOH + N + H O. Owing to the insolubility of cystine in acetic acid use a suspension in dU. acetic acid for this test. In each case care must be taken not to confuse the evolution of nitrogen with any possible thermal decomposition of the nitrous acid cf. footnote, p, 360). 

The controlled thermal decomposition of dry aromatic diazonium fluoborates to yield an aromatic fluoride, boron trifluoride and nitrogen is known as the Schiemann reaction. Most diazonium fluoborates have definite decomposition temperatures and the rates of decomposition, with few exceptions, are easily controlled. Another procedure for preparing the diazonium fluoborate is to diazotise in the presence of the fluoborate ion. Fluoboric acid may be the only acid present, thus acting as acid and source of fluoborate ion. The insoluble fluoborate separates as it is formed side reactions, such as phenol formation and coupling, are held at a minimum temperature control is not usually critical and the temperature may rise to about 20° without ill effect efficient stirring is, however, necessary since a continuously thickening precipitate is formed as the reaction proceeds. The modified procedure is illustrated by the preparation of -fluoroanisole ... 

The thermal decomposition of ammonium succinate gives a good yield of succlnimlde ... 

Silicon is prepared commercially by heating silica and carbon in an electric furnace, using carbon electrodes. Several other methods can be used for preparing the element. Amorphous silicon can be prepared as a brown powder, which can be easily melted or vaporized. The Gzochralski process is commonly used to produce single crystals of silicon used for solid-state or semiconductor devices. Hyperpure silicon can be prepared by the thermal decomposition of ultra-pure trichlorosilane in a hydrogen atmosphere, and by a vacuum float zone process. 

It can be isolated by elecytrolysis of the fused cyanide and by a number of other methods. Very pure, gas-free cesium can be prepared by thermal decomposition of cesium azide. 

Ruthenium is a hard, white metal and has four crystal modifications. It does not tarnish at room temperatures, but oxidizes explosively. It is attacked by halogens, hydroxides, etc. Ruthenium can be plated by electrodeposition or by thermal decomposition methods. The metal is one of the most effective hardeners for platinum and palladium, and is alloyed with these metals to make electrical contacts for severe wear resistance. A ruthenium-molybdenum alloy is said to be... 

Uranium can be prepared by reducing uranium halides with alkali or alkaline earth metals or by reducing uranium oxides by calcium, aluminum, or carbon at high temperatures. The metal can also be produced by electrolysis of KUF5 or UF4, dissolved in a molten mixture of CaCl2 and NaCl. High-purity uranium can be prepared by the thermal decomposition of uranium halides on a hot filament. 

The (thermal) decomposition of thiazol-2-yldiazonium salts in a variety of solvents at 0 C in presence of alkali generates thiazol-2-yl radicals (413). The same radicals result from the photolysis in the same solvents of 2-iodothiazole (414). Their electrophilic character is shown by their ability to attack preferentially positions of high rr-electron density of aromatic substrates in which they are generated (Fig. 1-21). The major... 

The thermal decomposition of thia2ol-2-yl-carbonyl peroxide in benzene, bromobenzene, or cumene affords thiazole together with good yields of 2-arylthiazoles but negligible amounts of esters. Thiazol-4-ylcarbonyl peroxide gives fair yields of 4-arylthiazoles, but the phenyl ester is also a major product in benzene, indicating reactions of both thiazol-4-yl radicals and thiazol-4-carbonyloxy radicals. Thiazole-5-carbonyl peroxide gives... 

In agreement with the theory of polarized radicals, the presence of substituents on heteroaromatic free radicals can slightly affect their polarity. Both 4- and 5-substituted thiazol-2-yl radicals have been generated in aromatic solvents by thermal decomposition of the diazoamino derivative resulting from the reaction of isoamyl nitrite on the corresponding 2-aminothiazole (250,416-418). Introduction in 5-position of electron-withdrawing substituents slightly enhances the electrophilic character of thiazol-2-yl radicals (Table 1-57). 

The evidence obtained in compaction experiments is of particular interest in the present context. Figure 3.22 shows the results obtained by Avery and Ramsay for the isotherms of nitrogen on compacts of silica powder. The hysteresis loop moved progressively to the left as the compacting pressure increased, but the lower closure point did not fall below a relative pressure of 0-40. Similar results were obtained in the compaction of zirconia powder both by Avery and Ramsay (cf. Fig. 4.5), and by Gregg and Langford, where the lower closure point moved down to 0-42-0-45p° but not below. With a mesoporous magnesia (prepared by thermal decomposition of the hydrated carbonate) the position of the closure point... 

Many materials need to be dried prior to their analysis to remove residual moisture. Depending on the material, heating to a temperature of 110-140 °C is usually sufficient. Other materials need to be heated to much higher temperatures to initiate thermal decomposition. Both processes can be accomplished using a laboratory oven capable of providing the required temperature. 

Thermogravimetry The products of a thermal decomposition can be deduced by monitoring the sample s mass as a function of applied temperature. (Figure 8.9). The loss of a volatile gas on thermal decomposition is indicated by a step in the thermogram. As shown in Example 8.4, the change in mass at each step in a thermogram can be used to identify both the volatilized species and the solid residue. 

Determine the identities of the volatilization products and the solid residue at each step of the thermal decomposition. 

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