Determination of Retained B 2 O 3 Content in ZrB 2 ‐30 vol% SiC Oxide Scales

The composition of the borosilicate glass layer formed during oxidation of ZrB 2 ‐30 vol% SiC was determined to elucidate the extent of B 2 O 3 retention in the oxide during high‐temperature oxidation. Oxidation was conducted in stagnant air at 1300°C, 1400°C, and 1500°C for times between 100 and 221 min. Specimens were characterized using mass change and scanning electron microscopy. After oxidation, the borosilicate glass layer was dissolved from the specimens sequentially with deionized H 2 O and HF acid, to analyze the glass composition using inductively coupled plasma optical emission spectrometry. It was found that the average B 2 O 3 content in the glass scale ranged from 23 to 47 mol%. Retained B 2 O 3 content in the bulk of the glass decreased with increasing temperature, confirming increased volatility with temperature. Boron depth profiles were also obtained in the near surface region using X‐ray photoelectron spectroscopy and energy dispersive spectroscopy. The measured B concentrations were used to estimate the B 2 O 3 concentration profile and B diffusion coefficients in the borosilicate glass. Implications for the ZrB 2 ‐SiC oxidation process are discussed.