Evaporation behavior of SiO₂ glass doped with various transition metal oxides

Abstract

To investigate the effect of transition metal oxides on the evaporation characteristic of SiO 2 glass at 1700°C, nine transition metal oxides were added to SiO 2 glass. The results show that V 2 O 5 , MoO 3 , and WO 3 have little effect on the high-temperature stability of SiO 2 glass due to their evaporation at 1500-1700°C. Besides, Nb 2 O 5 and Ta 2 O 5 reduce the evaporation of SiO 2 by covering the surface of the sample. Moreover, by improving the content of cristobalite, the evaporation of the SiO 2 -Cr 2 O 3 sample decreases. Meanwhile, TiO 2 , ZrO 2 , and HfO 2 are beneficial to decreasing the evaporation of SiO 2 glass because Ti, Zr, and Hf diffuse into c-SiO 2 . Meanwhile, the SiO 2 -HfO 2 sample possesses the least evaporation.

Long-term oxidation of MoSi2-modified HfB2–SiC–Si/SiC–Si coating at 1700°C

“…Contrary to the SEM images, a certain amount of Mo can be seen. A possible explanation could be that only a small amount of Mo (in the form of MoB) was dissolved in the Hf-doped Si-based glass to produce the Hf, Mo co-doped Si-based glass, which was difficult to identify by reasons of its low content as well as the low resolution of SEM elemental analysis [30].

Figure 9 Thermal dynamic analysis of the HMSS/SS coating oxidation reactions at 1700°C: (a) Gibbs free energy variation curves; (b) partially enlarged view of (a).

Figure 10 TEM results of the coated sample after being oxidized for 120 h: (a) TEM image; (b,c) high-resolution TEM image of (a); (d–h) HAADF image and related elemental mapping images.

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“…Contrary to the SEM images, a certain amount of Mo can be seen. A possible explanation could be that only a small amount of Mo (in the form of MoB) was dissolved in the Hf-doped Si-based glass to produce the Hf, Mo co-doped Sibased glass, which was difficult to identify by reasons of its low content as well as the low resolution of SEM elemental analysis [30].…”

Ablation behavior of (Hf–Ta–Zr–Nb–Ti)C high‐entropy carbide and (Hf–Ta–Zr–Nb–Ti)C–xSiC composites

“…However, the highest surface temperature was much higher than the melting point of SiO 2 (1600°C) and was very close to the boiling point of SiO 2 (2250°C). The SiO 2 was thus melted during ablation and the evaporation of SiO 2 may happen at temperatures below its boiling point 37,38 . The liquid SiO 2 may change to vapor during ablation so that less melted SiO 2 was detected on the surface of HEC–20SiC‐90 than HEC–10SiC‐90 and the ablated surface became porous.…”

“…The SiO 2 was thus melted during ablation and the evaporation of SiO 2 may happen at temperatures below its boiling point. 37,38 The liquid SiO 2 change to vapor during ablation so that less melted SiO 2 was detected on the surface of HEC-20SiC-90 than HEC-10SiC-90 and the ablated surface became porous. However, the linear ablation rate of HEC-20SiC-90 was still lower than that of the ablated HEC-0 samples, which have large pores on their ablated surface.…”