Thermal-decomposition temperature

Anhydrite also has several common classifications. Anhydrite I designates the natural rock form. Anhydrite 11 identifies a relatively insoluble form of CaSO prepared by high temperature thermal decomposition of the dihydrate. It has an orthorhombic lattice. Anhydrite 111, a relatively soluble form made by lower temperature decomposition of dihydrate, is quite unstable converting to hemihydrate easily upon exposure to water or free moisture, and has the same crystal lattice as the hemihydrate phase. Soluble anhydrite is readily made from gypsum by dehydration at temperatures of 140—200°C. Insoluble anhydrite can be made by beating the dihydrate, hemihydrate, or soluble anhydrite for about 1 h at 900°C. Conversion can also be achieved at lower temperatures however, longer times are necessary. 

It is not possible, however, to calculate accurately actual gas composition by using the relationships of reactions (27-14) to (27-19) in Table 27-12. Since the gasification of coal always takes place at elevated temperatures, thermal decomposition (pyrolysis) takes place as coal enters the gasification reactor. Reaction (27-15) treats coal as a compound of carbon and hydrogen and postulates its thermal disintegration to produce carbon (coke) ana methane. Reaction (27-21) assumes the stoichiometiy of hydrogasifying part of the carbon to produce methane and carbon. 

A comparison of the electron impact (El) and chemical ionization (Cl-methane) mass spectra of 1//-azepine-1-carboxylates and l-(arylsulfonyl)-l//-azepines reveals that in the El spectra at low temperature the azepines retain their 8 -electron ring structure prior to fragmentation, whereas the Cl spectra are complicated by high temperature thermal decompositions.90 It has been concluded that Cl mass spectrometry is not an efficient technique for studying azepines, and that there is no apparent correlation between the thermal and photo-induced rearrangements of 1//-azepines and their mass spectral behavior. 

Figure 2. Co-nanocrystals synthesized using high-temperature thermal decomposition technique using thermal OA and TOPO as ligands.

Thermal properties such as thermal capacity, thermal expansion, melting temperature, thermal decomposition and sublimation are all important in considering processes to which minerals may be directly subjected in a pyro way. As for example, roasting or calcination or any pyro pre-treatment of a mineral concentrate is greatly influenced by its thermal properties. The chapter on pyrometallurgy deals with these aspects. 

According to the above model developed for the interpretation of the Mossbauer spectra, iron is "mono-dispersed" on the Ti02 surface following low temperature thermal decomposition of Fe(C0)5, either as an oxidized species (Fe +) or as a subcarbonyl species. 

Potassium nitrite also may be obtained by high temperature thermal decomposition of nitrate ... 

In their original paper, Ayscough and Steacie42 claimed that the photolysis was very simple and that only carbon monoxide and hexa-fluoroethane were formed as a result of a reaction of type B. Subsequent work has thrown some doubt on this simple interpretation, nevertheless, the ratio of the quantum yields of carbon monoxide and hexafluoro-ethane was close to unity for a temperature range of 25-300°C. (above which temperature, thermal decompositions become important) and at wavelengths of 3130 A. and 2537 A. No trace of perfluorobiacetyl was found, nor any other product which could arise from the reactions of the trifluoroacetyl radical. 

They suggest that the rate determining step for the high temperature thermal decomposition is a proton-transfer on the surface of the solid followed by oxidation of the ammonia gas by radicals resulting from the decomposition of perchloric acid. It seems probable that perchloric acid should undergo fast decomposition at these temperatures, generating oxygen atoms which oxidize the ammonia ... 

Both are white solids, unstable at room temperature. Thermal decomposition of the two solids follows a different route ... 

The first nematic guest-host prototype nematic GH-LCD reported by Heilme-ier and Zanoni " contained methyl red (157) as the dichroic dye dissolved in 4-butoxybenzoic acid as the nematic liquid crystal host. Other hosts investigated later included 4-methoxycinnamic acid and 4-ethoxy-4-aminoben-zonitrile (28), see Table 3.4. The melting point of these three single components is very high. Therefore, prototype GH-LCDs had to be operated and evaluated at very high temperatures. Thermal decomposition of the mixtures led sequentially to lower contrast, homeotropic orientation due to decomposition products and finally device breakdown. However, these initial experiments were sufficient to demonstrate the feasibility of this display type. 

Thermal decomposition of cis- and fraw-l-propenylcopper and their mono(tri-M-butylphosphine) complexes yields the hexadienes, with retention of configuration at the double bonds, and copper metal (293, 294). The cis isomer is configurationally unstable under the conditions of room-temperature thermal decomposition. However, the isomerization could be almost completely suppressed by performing the thermal... 

Chlorine nitrate and HCl are considered to be the most important chlorine reservoir species in the stratosphere. Iodine nitrate has also been considered as a reservoir species for iodine radicals that could destroy tropospheric ozone, but photodissociation of IONO2 to form iodine radicals is only effective at temperatures below 290 K, at higher temperatures thermal decomposition takes place which does not yield iodine radicals. ... 

To explain their results, they proposed a modification of the mechanism suggested by Avery and Bradley for the high-temperature thermal decomposition of NH3, viz. 

At higher temperatures thermal decomposition of the C4H9 radicals occurs, leading to chain processes. The mercury-photosensitized decomposition of isobutane has also been investigated by several workers ". ... 

The decomposition of ozone at ordinary temperatures complicates the preparation of mixtures of known composition. At liquid air temperatures, thermal decomposition is negligible and, with precautions to avoid sensitized decomposition, stable liquid mixtures may be prepared. The density of liquid ozone has been reported (3) with a margin of error of 0.25%, permitting volumetric preparation of mixtures with comparable accuracy. 

Scheme 2. Presumed mechanism of electron shifts at the beginning of low-temperature thermal decomposition of 3,3 -dimethyl-2,2, 4,4, 6,6 -hexanitrodiphenylsulfide with participation of nitro group at 2-position in the reaction center (typical trinitrotoluene mechanism - left formula) and with participation of nitro group at 6-position in the reaction center (right formula - real pathway of the fission).

Fig. 11. Relationship between the activation energies, of low-temperature thermal decomposition and NMR chemical shifts, Sn, of nitrogen atoms in the most reactive nitro group of nitramines taken from Ref [77].

The chemical micro-mechanisms of primary fission processes in molecules of polynitro compounds during initiation by mechanical stimuli (inclusive of the detonation course) and electric spark should be the same as in the case of their low-temperature thermal decomposition. In the case of initiation of nitramines by impact and shock, an excellent agreement in this respect was also found with the results of molecular-dynamic simulation by Kohno et al. [27]. The more complex molecular structure of polynitro arenes makes the problem of their primary fission somewhat complicated, too. If a molecule of these compounds contains several types of substituents, it can contain several potential reaction centres (e.g. the TMPM and PYX molecules). The initiation proper can then be realised by the molecule simultaneously participating by... 

The homol3d ic fragmentations or reactions of the C-NO2, N-NO2, N-NO, and O-NO2 groupings, or other bearers of explosibility (i.e. explosophores), are common primary fission processes of energetic materials under thermal [1-18], impact [1,3,4,6,16,19-27], shock [1,6,18,19,20,24,26-32] and electric spark stimuli [5, 32-36]. Therefore, it is natural that relationships exist between characteristics of low-temperature thermal decomposition and impact [6,37,38] or electric spark [35,39,47] sensitivities and also detonation characteristics [26,40-48,50] of pol3mitro compounds. 

---