Low temperature synthesis and pressureless sintering of nanocrystalline zirconium diboride powders

In the present study, we report on the synthesis and pressureless sintering of nanocrystalline zirconium diboride (ZrB2) prepared by a solution based chemical method in which zirconium oxychloride, boric acid and citric acid (as both gelling agent and carbon source) were used. The zirconium diboride precursors gelled from solutions were prepared and calcined from 1100 to 1500 °C under argon atmosphere. ZrB2 powder with mechanical activation as well as Fe and Ni addition was compacted and then sintered at 1750 °C for 5 h. The powders and sintered samples were characterized by XRD, TG-DTA, SEM and TEM. ZrB2 powders prepared at 1500 °C had a surface area of 1.6 m2/g and hexagonal rod-like morphology with 60 nm of crystallite size. ZrB2 ceramics fabricated from activated powders in wet environment were sintered to a relative density of 86% and Vickers׳ hardness of 3.9 GPa without sintering aid, while hardness and density values were found to be 15.8 GPa and 94.8% for Ni addition and 14.9 GPa and 99.9% for Fe addition.