Vaporization of Inorganic Substances: B₂O₃, TeO₂ and Mg₃N₂

Abstract

The necessity for auxiliary experiments in the study of vaporization of substances at high temperatures is discussed. Earlier work pertaining to the vaporization of B203 and Te02 is reviewed and new vapor pressure determinations are presented which extend the temperature ranges of the measurements. In the temperature ranges studied B203 and Te02 are found to vaporize as B202(g) and Te02(g) molecules, and vapor pressure equations are given. AH% of sublimation has been calculated from vapor pressure data for B203 with the aid of free energy functions, and the heats of sublimation, vaporization and fusion are given for Te02. Vapor pressure measurements have been supplemented by spectroscopic observations and bands attributable to the B203(g) molecule have been found. The vaporization of Mg3N2 has also been studied and found to be more complex. It is found that the Mg2(g) molecule is involved in the process of vaporization of Mg3N2. From the Mg2(g) band spectrum the dissociation energy of the molecule has been estimated. Final products of Mg3N2 vaporization are Mg(g) and N2(g).In most cases where vaporization or evaporation processes at high temperatures have been studied carefully by modern techniques, the reactions have been found to be more complex than formerly believed. The idea that stable species at high temperatures are necessarily simple is found not to be true, and many indications of large and/or new molecules are found through careful interpretation of vapor pressure, spectroscopic and mass spectrographic data.

Oxidation kinetics of LaB 6 in oxygen rich conditions

“…LaB 6 samples are 99.5% in purity and have a sintered density of 3.61g/cm 3 , which is correspondent to 13 vol.% open porosity. Sample surfaces were ground by No.…”

“…450 C. B 2 O 3 -species may evaporate in the oxidation process when the temperature is higher than 1000 C. 12 When the temperature is close to 1000 C, the evaporation of B 2 O 3 could be obvious. 13 Therefore, the oxidation mass change might be a result of the evaporation of B 2 O 3 at the temperatures 5995 C. Then, part of the curves in Fig. 3(b) does not obey the parabolic law.…”

Oxidation behavior of SiC–SiBCN ceramics

“…In our experiments, the influences on oxidation resistance discussed at 1200 1C and 1300 1C still existed. However, the effect of boron on the oxidation reduced further because of its higher volatile rate [30]. That was beneficial to the oxidation resistance.…”

Corrosion of Ceramic Materials

“…First, consider the formation of liquid boria. It is well known that boria is very volatile, forming both B203(g) (Soulen et al, 1955) and volatile hydroxide species (Margrave, 1956;Meschi et al, 1960). At temperatures where the volatility of boria is readily observed, oxidation kinetics will therefore follow a paralinear rate law in which oxidation weight gains occur simultaneously with boria volatilization.…”