Synthesis and formation mechanism of ZrB2–Al2O3 composite powder starting from ZrO2, Al, and BN

• ZrB2–Al2O3 in situ composite powders were successfully synthesized at 1550 °C.
• ZrO2, Al, and BN were firstly used as precursors for ZrB2–Al2O3.
• A novel formation mechanism was put forward for the ZrB2–Al2O3 powders.
• Zr–Al alloy compounds acted as an intermediary phase leading to boride formation.
• These boride–alumina products formed an interwoven network and were intimately mixed.

ZrB2–Al2O3 in situ composite powders were synthesized at 1550 °C via a novel solid-state precursor route using ZrO2, Al, and BN as raw materials. The final ZrB2–Al2O3 composite powders, consisting of large crystal Al2O3 particles (several micrometers) and fine ZrB2 particles (100–400 nm), form an interwoven network and are intimately mixed on a microscopic scale. The formation mechanism for ZrB2–Al2O3 composite powders comprises two steps: aluminothermic reduction of ZrO2, which generates Zr–Al alloy compounds and the coproducts Al2O3, then followed by a series of solid reactions between Zr and BN to give the ZrB, ZrN, and ZrB2 products. The aluminothermic reduction is a fast reaction, while the reaction between Zr and BN to obtain the final ZrB2 product is the limiting step in the conversion process of the precursor powders.

Figure optionsDownload as PowerPoint slide