Mass change analysis, high-temperature

Faber et al. ( ) have studied the weight change of graphite in CP at high temperatures. Our reanalysls of their data use the equilibrium constants for CF, CFg and CP from the JANAF Tables (2) the only other C-F species considered is assumed to be CP. This treatment yields negative values for the CP pressure except at the highest temperature, where 3rd law analysis of the equilibrium constant yields AjH"(CP, g, 298.15 K) 59.4 kcal mol". Parber et al. ( ) also investigated mass-spectrometrically the vapor species present at equilibrium and followed the intensities of CP and P. Prom a 2nd law treatment of the intensities they report AjH"(CF, g, 2300 K) 62.0 kcal mol", or A H (CP, g, 298.15 K) - 64 kcal mol". ... 

Simple crucibles of nickel, iron, silver, and gold are used as containers for the high-temperature fusion of samples that are not soluble in aqueous reagents. Attack by both the atmosphere and the contents may cause these crucibles to suffer mass changes. Moreover, such attack will contaminate the sample with species derived from the crucible. The crucible whose products will offer the least interference in subsequent steps of the analysis should be used. 

Partial pressures of different species present in the vapour phase over Th02, UO2, UC, were studied at very high temperature (>3000 K), by transient heating of the sample with a 532 nm laser pulse of ca. 8 ns duration with time-resolved mass-spectrometric detection. The surface temperature was varied by changing the laser incident power on the sample. For Th02, the authors give partial pressures of Th(g), ThO(g), Th02(g) and 0(g) at 5146 and 6253 K. Since in this type of experiment, it is difficult to establish reliably the relevant temperatures, these data have not been used in the analysis. Never-... 

The experiments used to determine resistance to corrosion at high temperatures will differ depending on the aggressive gas that acts on the metal. There are general behavior patterns which make it possible to evaluate the character of the attack. Thus, the study of the change in the mass with the exposiue time, or the analysis of the transversal cut in the samples studied will reveal the rate of the corrosion process at high temperatiues and determine the profundity of the attack. 

Along with temperature increases, the solid-state reactions of starch start with the combination of phase transitions such as melting, evaporation and sublimation as well as chemical condensation, decomposition and finally carbonisation at very high temperatures [a.444]. Thermal analysis techniques - TG and DSC - are normally applied to monitor the mass loss and the endothermic or exothermic nature of any physicochemical changes involved in thermal processes. These provide valuable insights when assessing the chemistry... 

Figure 9 Anion photoelectron spectroscopy. Its unique features are (I) Intrinsic mass selectivity and (ii) neutrals as final states. Here, as an example the results for compounds of iron, carbon and hydrogen are shown which exist in catalytic processes, high-temperature terrestrial or low-temperature astrophysical chemistry. Bottom spectrum a primary anion mass spectrum containing anions of the complexes of interest. Top spectra anion photoelectron spectra obtained by electron kinetic energy analysis after laser-induced photodetachment. They reveal the change of molecular structure and electronic energies for increasing numbers of hydrogen atoms in the complex.

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