High-Temperature Chemistry and Oxidation of ZrB<sub>2</sub>Ceramics Containing SiC, Si<sub>3</sub>N<sub>4</sub>, Ta<sub>5</sub>Si<sub>3</sub>, and TaSi<sub>2</sub>
作者:Inna G. Talmy、James A. Zaykoski、Mark M. Opeka
DOI:10.1111/j.1551-2916.2008.02420.x
日期:2008.7
The effect of Si3N4, Ta5Si3, and TaSi2 additions on the oxidation behavior of ZrB2 was characterized at 1200°–1500°C and compared with both ZrB2 and ZrB2/SiC. Significantly improved oxidation resistance of all Si‐containing compositions relative to ZrB2 was a result of the formation of a protective layer of borosilicate glass during exposure to the oxidizing environment. Oxidation resistance of the Si3N4‐modified ceramics increased with increasing Si3N4 content and was further improved by the addition of Cr and Ta diborides. Chromium and tantalum oxides induced phase separation in the borosilicate glass, which lead to an increase in liquidus temperature and viscosity and to a decrease in oxygen diffusivity and of boria evaporation from the glass. All tantalum silicide‐containing compositions demonstrated phase separation in the borosilicate glass and higher oxidation resistance than pure ZrB2, with the effect increasing with temperature. The most oxidation‐resistant ceramics contained 15 vol% Ta5Si3, 30 vol% TaSi2, 35 vol% Si3N4, or 20 vol% Si3N4 with 10 mol% CrB2. These materials exceeded the oxidation resistance of the ZrB2/SiC ceramics below 1300°–1400°C. However, the ZrB2/SiC ceramics showed slightly superior oxidation resistance at 1500°C.
Si3N4、Ta5Si3和TaSi2添加物对ZrB2氧化行为的影响已在1200°C至1500°C范围内进行了表征,并与纯ZrB2及ZrB2/SiC进行了比较。所有含硅的复合材料相较于纯ZrB2显示出显著增强的氧化抗性,这是由于在氧化环境中形成了具有保护作用的硼硅酸盐玻璃层。Si3N4改性陶瓷的氧化抗性随Si3N4含量的增加而提高,并可通过添加Cr和Ta的二硼化物(CrB2和TaB2)进一步增强。Cr和Ta氧化物诱发了硼硅酸盐玻璃中的相分离,导致玻璃液相温度和粘度的增加,同时降低了氧扩散率和玻璃中硼的蒸发速率。所有含钽硅化物的复合材料均在硼硅酸盐玻璃中表现出相分离,并且相较于纯ZrB2具有更高的氧化抗性,且该效应随温度升高而增强。最具有氧化抗性的陶瓷材料含有15体积百分比的Ta5Si3、30体积百分比的TaSi2、35体积百分比的Si3N4或20体积百分比的Si3N4并伴有10摩尔百分比的CrB2。这些材料在低于1300°C至1400°C的温度下超越了ZrB2/SiC陶瓷的氧化抗性。然而,在1500°C时,ZrB2/SiC陶瓷显示出略优于上述材料的氧化抗性。