Halogenated glass systems for the protection of structural carbon-carbon composites

Abstract

Oxidation protection systems or carbon-carbon composites have met limited success, particularly between 900 and 1500 °C where internal glass inhibitors are relied upon to protect the composite. Thi study investigated potential halogenated glass protection systems for the protection of structural carbon-carbon composites. A series of fluoride and fluoroborate glass compositions were selected based on thermodynamic predictions; specifically, to reduce volatility of current B 2O 3 based protection systems at elevated temperatures. The halogenated glass candidates examined in this study included a series of fluoroborate glasses containing 5 and 10 mol% CaF 2, MgF 2 and NaF. Since B 2O 3 is currently used as the matrix inhibitor, the effectiveness of these glasses was compared to B 2O 3 based upon their high temperature durability and ability to inhibit oxidation of SP-1 and HLM-85 graphite. The high temperature durability of the glasses were compared during two hour isothermal holds in oxygen at 900, 1100, 1300 and 1500 °C. The ability of the halogenated glasses to inhibit the oxidation of SP-1 and HLM-85 graphite was analyzed by examining the oxidation kinetics of compacts containing 33 wt% of the glass inhibitor and graphite. This study is unique in that the oxidation kinetics of inhibited carbon materials were studied in the temperature range of 900 to 1500 °C. This temperature range is of critical importance in the application of these materials.