Volatile species formation

Typical characterization of the thermal conversion process for a given molecular precursor involves the use of thermogravimetric analysis (TGA) to obtain ceramic yields, and solution NMR spectroscopy to identify soluble decomposition products. Analyses of the volatile species given off during solid phase decompositions have also been employed. The thermal conversions of complexes containing M - 0Si(0 Bu)3 and M - 02P(0 Bu)2 moieties invariably proceed via ehmination of isobutylene and the formation of M - O - Si - OH and M - O - P - OH linkages that immediately imdergo condensation processes (via ehmination of H2O), with subsequent formation of insoluble multi-component oxide materials. For example, thermolysis of Zr[OSi(O Bu)3]4 in toluene at 413 K results in ehmination of 12 equiv of isobutylene and formation of a transparent gel [67,68]. 

The reaction of ammonia and hydrogen chloride in the gas phase has been the subject of several studies in the last 30 years [56-65], The interest in this system is mainly that it represents a simple model for proton transfer reactions, which are important for many chemical and biological processes. Moreover, in the field of atmospheric sciences, this reaction has been considered as a prototype system for investigation of particle formation from volatile species [66,67], Finally, it is the reaction chosen as a benchmark on the ability, of quantum chemical computer simulations, to realistically simulate a chemical process, its reaction path and, eventually, its kinetics. 

The absence of EC in the discussions of all these reports " is interesting, since one would suspect that, based on the knowledge about EC reactivity, alkoxide could also attack its cyclic structure and cause irreversible reactions.One possibility would be that, using gas chromatography, the identification of a high-volatility species such as linear carbonate is easy and reliable, while the formation of the polymeric species, which EC would most likely decompose into, is more difficult to detect. 

Comparison of the silicone-epoxy ion profiles indicates that the presence of the flame retardant in sample E has little effect on the composition or formation rates of the major volatile species. The specific ion profiles characteristic of HBr and from the flame retardant in sample E... 

The original parfait method rested on the use of vacuum distillation—lyophilization to concentrate the poorly volatile species in water. It might be expected that the removal of water under vacuum should be simple and straightforward. Vacuum distillation and lyophilization do indeed recover the poorly volatile contaminants from unfractionated surface waters. However, the compounds are often obtained in an intractable, insoluble form. These intractable precipitates are believed to form when bicarbonate dissociates under vacuum to form metal carbonate precipitates that trap organic polymers and lipids (4, 5). The parfait method prevents the formation of these precipitates by removing metal ions on an acidic cation-exchange bed. 

As in the case of the land surface burst, complete characterization of the particle population requires only that particle mass, a volatile species, and a refractory species distribution with particle size be determined. All other isotopic distributions may be deduced from the istotope partition calculations described above. In the subsurface detonation, the earliest aerial cloud sample was obtained in the cloud 15 minutes after detonation. The early sample was, therefore, completely representative of the aerial cloud particle population. In Figure 5 the results of the size analysis on a weight basis are shown. Included for comparison is a size distribution for the early, local fallout material. The local fallout population and the aerial cloud population are separated completely from the time of their formation. 

A second example of metal transport by single-component gas involves the formation of metal carbonyls that are unstable in carbon monoxide. Shen et al. (72) discovered that supported nickel particles are not stable in carbon monoxide. Under certain conditions, CO combines with the metal in the particles to form volatile metal carbonyls, such as nickel carbonyl. These volatile species carry the metal out of the reactor, resulting in a rapid net loss of metal. In some cases, metal is not carried out of the reactor, but new metal particles form at pore mouths, blocking them and effectively deactivating the catalyst. 

The state of the alkoxides in the gas phase appears important in connection with their purification. The mass-spectra of the volatile species indicate the existence of aggregates, whose size is usually corresponds to that established for the solid phase by the X-ray single crystal studies [952, 1655]. It is, however, important to take into consideration the fact that the distillation is in some cases accompanied by ether elimination reaction and formation of oxoalkox-ides ... 

We report on a number of on-line chemical procedures which were developed for the study of short-lived fission products and products from heavy-ion interactions. These techniques combine gas-jet recoil-transport systems with I) multistage solvent extraction methods using high-speed centrifuges for rapid phase separation and II) thermochromatographic columns. The formation of volatile species between recoil atoms and reactive gases is another alternative. We have also coupled a gas-jet transport system to a mass separator equipped with a hollow cathode- or a high temperature ion source. Typical applications of these methods for studies of short-lived nuclides are described. 

The foregoing two sections revealed that lanthanide centers like to expand their coordination sphere by additional adduct formation despite the presence of very bulky ligands such as tritox or OC6H2tBu3-2,4,6. With regard to headwords such as sublimation and homogeneity , these neutral co-ligands are a nuisance and undesired. For example, upon thermal treatment, they often separate off and dimerization occurs along with the formation of a less volatile species [29,78],... 

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