AN ANALYSIS OF SOME OF THE PHYSICAL AND CHEMICAL PROPERTIES OF SILICA (SIO2) OF IMPORTANCE IN ABLATION BEHAVIOR

The physical properties and thermochemistry of decomposition of SiO2 at high temperatures was thoroughly reviewed and detailed calculations were made of thermodynamic properties of interest for re-entry vehicle applications. Available thermodynamic data indicate that the primary reaction involved in the vaporization of SiO2 under neutral conditions is SiO2Liquid yields SiO2Gas 12 O2Gas. The vapor pressure relation corresponding to this equilibrium is given. A normal boiling point of 3085K is predicted from the relation. If other equilibria are considered, including formation of SiO2gas, dimer formation, and dissociation of oxygen, a more refined boiling point of 3070 70K is obtained. This value was compared with data in the literature and is consistent with the most reliable data available. When SiO2 is heated from room temperature to its boiling point and decomposed at that temperature, the total heat absorption is calculated to be 6650 Btulb. Many other physical properties of SiO2 which are of interest for re-entry vehicle design purposes, were reviewed and are summarized in an appendix at the end of the report.