High-temperature oxidation of boron nitride: I, monolithic boron nitride

High-temperature oxidation of monolithic boron nitride (BN) is examined at 900-1200 degrees C. Hot-pressed BN and both low- and high-density chemicall y vapor-deposited BN are studied. The oxidation product is B2O3(I) and the oxidation kinetics are sensitive to crystallographic orientation, porosity, and impurity levels. The B2O3 product also reacts readily with ambient wat er vapor in the test furnace (ppm levels) to form the volatile species HBO2 (g), leading to overall paralinear kinetics. The linear rate constant extra cted from these experiments agreed with that predicted from diffusion of HB O2(g) across a static boundary layer.