In-situ Catalytic Synthesis Of MgO Whiskers And Preparation Of ZrB₂-SiC/MgO-C Low Carbon Refractory

The catalytic preparation of M gO whiskers and the physical properties,the high temperature mechanical performance,thermal shock resistance,oxidation resistance and corrosion resistance of ZrB₂-SiC/MgO-C low carbon refractory were investigated detailedly in this thesis.（1）MgO whiskers with diameters of about 40–200 nm were catalytic synthesised after fired at 1400℃ for 2 h by using ferric nitrate,cobalt nitrate and nickel nitrate as catalyst precursors,and the magnesia,graphite and aluminum powders as raw materials.The optimized process conditions of the preparation of MgO whiskers were as following: 1wt% Fe₂O₃、CoO and N iO,3wt% Al powders and 1400℃.The addition of graphite was 4wt% using Fe₂O₃ and NiO as catalyst,and 6wt% for the case of using CoO as catalyst.（2）ZrB₂-SiC/MgO-C low carbon refractories with different addition of ZrB₂-SiC composition powders with various ZrB₂ :SiC ratio were prepared.The physical properties,hot modulus of rupture and relationships between stress and strain of the ZrB₂-SiC/MgO-C low carbon refractories were studied,the results showed that the ZrB₂-SiC/MgO-C low carbon refracto ries with 80wt% of ZrB₂-SiC（ZrB₂ :SiC=80:20）composite powders possessed excellent physical properties and hot modulus of rupture.The temperature of elastic deformation of the ZrB₂-SiC/MgO-C low carbon refractories was 25–600 ℃,and temperature of plastic deformation was about 600–800℃.（3）The results of thermal shock resistance of ZrB₂-SiC/MgO-C low carbon refractories showed that its thermal shock resistance decreased with the testing temperature increase,the ZrB₂ :SiC ratio in ZrB₂-SiC composite powders had slight influence on the thermal shock resistance.The thermal shock resistance of refractories decreased with the substitution content of ZrB₂-SiC composite powders increasing in a reducing atmosphere,however,the thermal shock resistance increased with the substitution content increasing in a oxidizing atmosphere.（4）Effect of addition of ZrB₂-SiC composite powders on the oxidation resistance of ZrB₂-SiC/MgO-C low carbon refractories was investigated.The area of decarbonized layer of the refractories without ZrB₂-SiC powders was about 3.08% after oxidation in air at 1250℃ for 120 min.The area of decarbonized layer of refractories with 50wt% of ZrB₂-SiC powders was only 0.15%.Therefore,the addition of ZrB₂-SiC powders could significantly improve the oxidation resistance of the low carbon refractories.（5）Studies on corrosion resistance by static crucible method of ZrB₂-SiC /MgO-C low carbon refractories showed that the slag resistance of the refractories decreased with testing temperature increased,and the effect of the addition of ZrB₂-SiC powders was neligible.