At temperatures between 300-1450C isothermal oxidation kinetics were characterized in terms of weight change measurements using continuously recording Cahn RH-100 and 2000 microbalances. At lower temperatures the experiments were performed in similar equipment, but used furnaces other than the molydisilicide. Two sample sizes were standardized for uncoated CC composite tests. These were designated large and reduced. The large size was 25-10-4mm with a bulk surface area of 7.8 cm2. The small or reduced size was 13-5-3mm with a bulk surface area of 2.4 cm2. All coated samples were 26-20-4 mm in size with a bulk area of about 14 cm2. The coated samples were large, but the size limited potentially significant “edge” effects.
The gas flow rates used in the testing uncoated CC composite varied between 14 and 550 cc/min. These volume flow rates correspond to linear velocities between 0.03 and 1.16 cm/sec. The flow rates used in coated sample work were between 50 and 70 cc/min. The gas used in most isothermal oxidation tests was ultra high purity O2.
To examine the effects of water vapor on the oxidation of uninhibited and inhibited CC composite, experiments were performed in which oxygen was passed through two consecutive water baths at a fixed temperature prior to passing over the specimen. The weight changes of specimens were measured using a Cahn microbalance.