Abstract
Oxide impurities such as boria (B2O3) and zirconia (ZrO2) on the surfaces of zirconium diboride (ZrB2) particles are known to limit their sinterability. Among the impurities, B2O3 on the surface of ZrB2 particles could be easily removed by methanol or hydrofluoric acid. However, the remaining ZrO2 still gave negative influences on the sinterability. In this study, ZrB2 particles were treated with various acids to remove oxide impurities on their surfaces. The acid treatments were found to vary in efficacy, according to acid type, and affect the crystallinity and morphology of ZrB2 particles to varying degrees, in some cases forming additional impurities. In particular, the change in the oxygen content of the ZrB2 particles induced by acid treatment was found to depend on the type of acid. The results of the acid treatments were compared which revealed that HNO3 treatment optimizes the purity of ZrB2 particles. In addition, the effects of acid treatment on the surface properties of ZrB2 particles were considered. In particular, the correlation between the surface properties of the acid-treated ZrB2 particles and their dispersibility in aqueous solution was investigated.
Highlights
A critical factor affecting the development of aerospace technologies such as hypersonic flight vehicles is the requirement for materials with high-temperature tolerance, excellent mechanical strength, and oxidation resistance [1,2,3]
This study investigated the efficacy of acid treatment in enhancing the purity of commercial ZrB2 powder, i.e., removing Zr–O impurities which are one of the main factors limiting the sinterability of ZrB2
To eliminate oxides like B2 O3, the ZrB2 powder was subjected to repeated washing processes, and each time it was ultrasonicated during centrifugation in 40 mL methanol (99.9%, Daejung Chemicals and Metals Co., Siheung, Korea) for 10 min [14]
Summary
A critical factor affecting the development of aerospace technologies such as hypersonic flight vehicles is the requirement for materials with high-temperature tolerance, excellent mechanical strength, and oxidation resistance [1,2,3]. Among UHTCs, zirconium diboride (ZrB2 ) is especially suitable for application in extreme environments owing to properties such as a high melting point (3246 ◦ C); hightemperature stability and strength; high electrical and thermal conductivities; excellent corrosion resistance and hardness; a high elastic modulus; and a chemically stable crystal structure [5,6,7,8,9,10,11] These physicochemical properties result from its strong covalent bonds and low self-diffusion coefficient [5,6,7,12]. Oxide impurities such as boron trioxide (B2 O3 ) and zirconium dioxide (ZrO2 ) were formed on ZrB2 particles during milling processes or storage due to moisture in the atmosphere [17,18,19,20]
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