Thermochemistry of gaseous SiO(OH), SiO(OH)2, and SiO2

摘要

The gaseous species SiO(OH) and SiO(OH)2were detected as products of the reaction of SiO2(l) and H2O(g) near 2000 K, using effusionhyphen;beam mass spectrometry. No other siliconhyphen;containing hydroxides or oxyhydroxides were observed. From third law analysis of equilibrium data, values ofDgr;fHdeg;298of SiO(OH) and SiO(OH)2were evaluated as minus;118 and minus;213 kcalthinsp;molminus;1, respectively, both plusmn;4 kcalthinsp;molminus;1. Several equilibrium measurements on gaseous SiO2yielded aDgr;fHdeg;298value of minus;67 kcalthinsp;molminus;1, which is 6ndash;10 kcalthinsp;molminus;1less stable than values given in most compilations. It appears that the new thermochemical data for SiO(OH) and SiO(OH)2, plus a literature estimate for Si2O(OH)6, can be used to model the equilibrium behavior of the silicandash;steam system over a wide range of temperatures and pressures.