3.2. ZrB2 powder synthesis in argon atmosphere
Fig. 5 shows the XRD patterns of the synthesized powders at different temperatures under argon atmosphere. When using carbon black as carbon source, ZrO2 peaks were observed at 1300 °C and 1400 °C (Fig. 5(a)), but the ZrO2 peaks did not present at 1300 °C or above in the vacuum (Fig. 1(a)). The result indicates that the synthesis temperature of ZrB2 powder derived from carbon black in the argon atmosphere is higher than that in vacuum. From Fig. 5, for graphite batch, the ZrO2 phase did not disappear until 1500 °C. It should be noted that the synthesis temperature of the pure ZrB2 powder derived from the carbon black mixture (ZC) is the same with the graphite mixture (ZG) in argon atmosphere.