Volatilization of Aluminum Oxycarbides and of Alumina with Carbon in Reduction of Alumina

Abstract

The volatilization in the A1-O-C(-Si-Fe) system have been investigated mainly by thermal gravimetry in vacuum for four cases; (1) aluminum oxycarbides, (2) mixtures of alumina and carbon with and without additives (iron oxide, silicon nitride and silicon carbide), (3) mixtures of alumina and aluminum carbide or silicon carbide and (4) mixtures of alumina, silica (mullite), iron oxide and carbon. A12OC evaporated essentially congruently, whereas A14O4C evaporated incongruently; a -A12O3 was formed in addition to vapors. The volatilization reaction between alumina and carbon was found to be enhanced remarkably when iron was added, unchanged by SiC addition and prevented slightly in the presence of Si3N4. The mixtures of alumina and carbide volatilized at lower temperatures than did those of alumina and carbon. These features are discussed in terms of the equilibrium pressure in the light of previous results of reaction experiments focussed upon the oxycarbide formation.

Investigation into the vaporization of Al2O3 in the presence of carbon at high temperatures

“…In [8], the authors studied aluminum oxycarbides, mixtures of aluminum oxide with carbon, mixtures of aluminum oxide and aluminum carbide with silicon carbide, and mixtures of aluminum oxide with silicon dioxide and carbon. It was shown that Al 2 OC vaporizes congruently and Al 4 O 4 C vaporizes incongruently with the accumulation of aluminum oxide in the condensed phase.…”

“…Yokokawa et al [8] investigated the volatility of the components in the Al-O-C system (under vacuum) by thermogravimetric analysis. In [8], the authors studied aluminum oxycarbides, mixtures of aluminum oxide with carbon, mixtures of aluminum oxide and aluminum carbide with silicon carbide, and mixtures of aluminum oxide with silicon dioxide and carbon.…”

“…Interaction of Al 2 O 3 with carbon has been studied repeatedly [2][3][4][5][6][7][8][9][10][11][12][13][14]. Vert et al [2] investigated the reaction of aluminum oxide with carbon in the temperature range 1773-2173 K. It was revealed that the reduction of Al 2 O 3 begins at a temperature of 1873 K. Moreover, it was noted that aluminum losses (in the gaseous state) and the amount of formed AlC are insignificant as compared to the amount of released oxygen.…”

“…The relative content of a more reduced form, i.e., atomic aluminum, in the vapor in the case of direct contact between the sample and graphite is somewhat higher than that in the absence of direct contact. It is known[2,3,[8][9][10] that the reaction of aluminum oxide with carbon gives the spinel phase of the Al 2 OC · nAl 2 O 3 composition. This phase during the vaporization behaves as a binary system formed by components with different volatilities.…”

Comment Using Chemical Equilibria Calculation on Discussion about “Synthesis of Titanium Nitride Whiskers from Potassium Fluorotitanate (IV)”

“…Journal of the Ceramic Society of Japan 100 [7] 1992 981 graphite did not proceed when two materials were placed separately in vacuum, while the reaction proceeded in Ar flows without their direct contact. According to Motzfeldt and Steinmo8), the reaction between separated Al2O3 and C proceeds through the following reactions; Al2O3(s)+4Al(g)=3Al2O(g), (2) 3Al2O(g)+3C(s)=6Al(g)+3CO(g).…”