Sublimation of Cr₂O₃ at High Temperatures

Abstract

One assumes the validity of the modified Clausius-Clapeyroii equation in which A x is the mean heat of vaporization between the teniperatures TI and Tz. At the high temperatures concerned, this equation should be fairly accurate.At the normal boiling point of PbO, the heat of vaporization is 51 kcal. per sole.il(no If the value 70 mm. at llOO°C., as re-ported by Preston and Turner, is substituted into the equation, the impossible value of 29 kcal. is obtained for A H . However, if a value of 10 mm. is assumed as the vapor pressure of PbO a t 1100"C., one arrives a t a reasonable value of 55 kcal. per mole for A H between 1472'' and llOO°C. Utilizing this value, it is possible to calculate the approximate vapor pressure of liquid PbO at other temperatures assuming a linear dependence of with the temperature. The calculated pressure of 0.2 mm. a t 900°C. has been shown to cr~rrcspond quite well with observations. The sublimation of chromic oxide, Crz03, has been observed in vacuum by the Langmuir technique using induction and solar heating. Extensive sublimation did not yield any new phases on the basis of X-ray powder studies, and condensates of CrZ03 were always obtained. Flash vaporization and flow experiments in CO or O2 atmospheres and in vacuum indicated no appreciable differences in rates of sublimation. Weight-loss experiments showed that the rate of sublimation was slightly higher than predicted for decomposition to the elements and suggested that small amounts of complex molecules, e.g. CrO and CrO,, were also present in the equilibrium vapor.

Melting temperature measurement of refractory oxide ceramics as a function of oxygen fugacity using containerless methods

“…Similar Cr evaporation has been encountered previously for samples with high Cr content. 12,58,[85][86][87][88] The liquidus temperature ranges for samples 5-9 agree with previous reports. 58 These results suggest that the method presented here is a reliable way to construct phase diagrams by measuring the liquidus temperatures with temperature, composition and oxygen fugacity as independently controllable parameters.…”

XPS study of the thermal stability of passivated NiCrFeCoMo multi‐principal element alloy surfaces

“…Alteration mechanisms of the passivated MPEA-15Cr10Mo surface upon vacuum heating the low bulk Cr concentration, the fact that the Cr oxide in the passive oxide film is not well crystallized, 39,67 and the redeposition of CrO 3(g) in the form of Cr 2 O 3 35,36 in the colder parts of the chamber may reduce the threshold of the reactions. The possibility of having Cr oxide reduction by residual reductive gas, for example, H 2(g) or CO (g) , cannot be excluded.…”

“…Regarding thermal stability, many works addressed the behavior of the surface oxide film formed on conventional alloys upon heating under reducing, oxidizing, or humid conditions for practical applications. [30][31][32][33][34] Some works also focused on the heating-induced alteration of the surface oxide film under inert gas atmosphere 35 or vacuum (technically low pressures) [36][37][38] in order to provide basic insight into the thermal stability of the oxide components, which is crucial for further understanding the behavior of oxide films upon heating in a specific environment. 39,40 As for surface oxide films formed on MPEAs, such investigations are still lacking.…”

In Situ High-Temperature Synchrotron Diffraction Studies of (Fe,Cr,Al)3O4 Spinels

“…The gas emissions on the samples with lower Cr concentrations (J1, J3, and J7) were low enough to carry out the diffraction and cooling trace experiments. Sublimation of Cr-containing materials was studied previously; − according to the FactSage database, Cr and its oxides volatilize as CrO 3 and CrO 2 vapor species in air …”