Microstructural Evaluation of ZrB₂/ZrO₂ Ceramic Powders Prepared by Milling-Assisted Magnesiothermic Reduction of Oxide Raw Materials

Abstract

This study reports on the synthesis and microstructural evaluation of ZrB 2 /ZrO 2 ceramic powders prepared by milling-assisted magnesiothermic reduction of oxide raw materials. Powder blends containing ZrO 2 , B 2 O 3 and Mg reactants were milled in different type of mills at different durations and were subsequently annealed in a tube furnace under Ar atmosphere. An additional purification step (HCl leaching) was conducted on the milled and annealed samples to obtain only Zr-based products. FactSage TM thermochemical software was used in order toshow a preliminary route for the experiments. The effects of milling duration (up to 100 h), milling type (a SPEX TM 8000D Mixer/Mill and a planetary ball mill), excess Mg amount (5-20 wt.%) and annealing duration (6 and 12 h) on the formation and microstructure of the products were examined. The milled, annealed and leached products were characterized using an X-ray diffractometer (XRD), stereomicroscope (SM), scanning electron microscope (SEM) and differential scanning calorimeter (DSC). Pure ZrB 2 /ZrO 2 ceramic powders having particles in size range of 200 nm-1 μm and containing two different crystal structures of ZrO 2 phase (monoclinic and tetragonal) were obtained after milling in the SPEX TM 8000D Mixer/Mill for 30 h, annealing at 1200 °C for 12 h and leaching with 5 M HCl.

Mechanochemical synthesis of nanostructured and composite oxide ceramics: From mechanisms to tailored properties

“…In one study, submicron ZrO 2 –ZrB 2 ceramic powders 147 were synthesized with Mg powder as reducing agent. High chemical stability of ZrO 2 makes it impossible to completely reduce to ZrB 2 .…”