Determination of Retained B2O3 Content in ZrB2‐30 vol% SiC Oxide Scales

The composition of the borosilicate glass layer formed during oxidation of ZrB₂‐30 vol% SiC was determined to elucidate the extent of B₂O₃ 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 H₂O and HF acid, to analyze the glass composition using inductively coupled plasma optical emission spectrometry. It was found that the average B₂O₃ content in the glass scale ranged from 23 to 47 mol%. Retained B₂O₃ 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 B₂O₃ concentration profile and B diffusion coefficients in the borosilicate glass. Implications for the ZrB₂‐SiC oxidation process are discussed.