Vaporization incongruent

Ti 0, (cr) vaporizes incongruently such that the residue approaches the congruently vaporizing composition of TigOg(B). References... 

Wallace and Butt (chapter 3) present an extensive review of experimental results in both areas as well as methods for modeling the incongruent vaporization process. Lengauer et al. (chapter 4), present diffusivity data for Group 5 carbides and nitrides and the latest phase diagrams in these systems. 

The mass vaporization rate at XeC c is at a minimum relative to the incongruent mass vaporization rates that occur at compositions greater and less than XeCwC- When VmC is calculated for XeC diT), we call it the mass congruent vaporization rate. 

The incongruent vaporization of the compounds of the Ta-Al system and of WSCj (see Table 7) was studied by an apparatus combining Knudsen effusion mass spectrometry and mass-loss measurements. Schiffman et al. [240] obtained an enthalpy change of AH298 = 311 3 kJmoP for the reaction of evaporation 1/2 WSe Cs) 1/2 W(s) -h Se(g). 

Odoj and Hilpert [58] showed the incongruent vaporization of BaZr03(s) to BaO(g). They determined the enthalpy of formation of BaZr03(s) from the component oxides as AfH° = — 106 21 kJmol by evaluating the enthalpies of vaporization according to the second- and third-law methods. 

In nonstoichiometric compounds, the partial vapor pressures of various chemical species in the gaseous phase depend on the composition in the solid phase, and the composition in the gaseous phase is not necessarily the same as that in the solid phase. Hence, in such a case, the vaporization process proceeds, the composition in the solid phase gradually varies, and this is called incongruent vaporization. If the composition in the gaseous phase happens to be equal to that in the solid phase, the latter remains unchanged with time, which is called congruent vaporization. 

Incongruent evaporation of solid disulfides has been shown by numerous studies the vaporization began at temperatures of 600-700"C and the vapor was found to consist only of sulfur species (Biltz 1911, Picon and Patrie 1956, Flahaut and Guittard 1956b,... 

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