HALOGENATED GLASS SYSTEMS FOR THE PROTECTION OF STRUCTURAL CARBON-CARBON COMPOSITES

Oxidation protection systems or carbon-carbon composites have met limi ted success, particularly between 900 and 1500 degrees C where interna l glass inhibitors are relied upon to protect the composite. This stud y investigated potential halogenated glass protection systems for the protection of structural carbon-carbon composites. A series of fluorid e and fluoroborate glass compositions were selected based on thermodyn amic predictions; specifically, to reduce volatility of current B2O3 b ased protection systems at elevated temperatures. The halogenated glas s candidates examined in this study included a series of fluoroborate glasses containing 5 and 10 mol% CaF2, MgF2 and NaF. Since B2O3 is cur rently used as the matrix inhibitor, the effectiveness of these glasse s was compared to B2O3 based upon their high temperature durability an d ability to inhibit oxidation of SP-1 and HLM-85 graphite. The high t emperature durability of the glasses were compared during two hour iso thermal holds in oxygen at 900, 1100, 1300 and 1500 degrees C. The abi lity of the halogenated glasses to inhibit the oxidation of SP-1 and H LM-85 graphite was analyzed by examining the oxidation kinetics of com pacts containing 33 wt% of the glass inhibitor and graphite. This stud y is unique in that the oxidation kinetics of inhibited carbon materia ls were studied in the temperature range of 900 to 1500 degrees C. Thi s temperature range is of critical importance in the application of th ese materials.