Reaction Synthesis Process Of ZrB₂Powder

ZrO2, SiC and B2O3are using as raw material to explore a novel route ofsynthesizing ZrB2.B2O3content, process parameters and additives on the reactantphases have been discussed on morphology of reaction product and its impact onthe growth behavior of ZrB2crystal.New synthesis pathways were first elucidatedthrough theoretical thermodynamic calculations and synthesize thermal analys is(TG-MS-IR), phases and morphology of ZrB2were studied by XRD, SEM, TEM andEDS systematically.ZrB2synthesis pathway has been proved by calculating the thermodynamictheory of Gibbs free energy change. ZrB2is formed at1200oC associating with COand CO2gas. With increasing temperature, CO2has been transformed into CO.ZrB2particle converts nearly equiaxed-shaped into the nearly cube-shaped at1500oC with B2O3content increasing. However, B2O3content has little effect onmorphology of ZrB2crystal when temperature is1600oC. Otherwise, with theincrease of the content of B2O3, the reaction carries forward to generating moreZrB2, and then carried in the reverse direction.The reaction temperature increasing makes the reactio n driving force magnify,gradually increasing the relative content of ZrB2, and gradually increases thereaction degree. However, the degree of reaction resulting in a decl ine withincreasing temperature continues. The reaction time may be extended to promotethe synthesis of ZrB2, and after7h the reaction is substantially reached steady.Reducing the reaction of CO generated more ZrB2, and CO2play a very significantinhibition during the reaction, resulting in no ZrB2generated. However, CO andCO2both can significantly inhibit the growth of grains.ZrB2is nearly equiaxed particle from the nearly cube-shaped at1500oC withexcessive100%B2O3content. The preferential growing crystal faces ofcube-shaped ZrB2are (0001),(1010) and (1210) respective ly.The growth rate ofperpendicular to ZrB2plane is, under hot pressing conditions (1010)>(1011)>(0001),while under pressureless sintering (0001)>(1011)>(1010). Such the pressure alongthe c-axis direction ZrB2crystal planes of the slowest growth that most easilyretained in the crystals.