免烧成低密度Si_3N_4/SiC复相耐火材料的制备及性能研究

Preparation and Properties of Sintering-Free Low Density Si_3N_4/SiC Composite Refractory

针对氮化烧成Si3N4/SiC复相耐火材料的成本高、能耗大及传热损失大的突出问题,研究制备了免烧成低密度Si3N4/SiC复相耐火材料。研究以硅藻土作为硅源,蔗糖作为碳源,通过碳热还原氮化法制备了Si3N4/SiC复相粉体。再以该复相粉体为原料,以添加不同量Si粉（0%,5%,10%）的蔗糖作为结合剂,分别在60、90、120℃3个温度点热处理2 h,150℃热处理8 h后,制备成免烧成低密度Si3N4/SiC复相耐火材料。采用XRD和SEM对粉体的物相及微观形貌进行表征。结果表明:粉体的物相为α-Si3N4,β-Si3N4,β-Si C和Fe3Si,通过计算得到α-Si3N4,β-Si3N4和β-Si C的相对含量分别为4.28%,29.74%和59.40%;硅藻土中含有较高含量的Fe杂质元素导致少量Fe3Si生成;粉体中β-Si3N4呈短柱状,β-Si C以细小颗粒的形式存在。在N2（99.999%）保护条件下,1000°C模拟使用这种Si3N4/SiC复相耐火材料1h后发现,Si粉的添加量对其体积密度和显气孔率的影响不大,体积密度变化范围是1.481.51g·cm-3,显气孔率变化范围是33.36%34.62%;Si粉添加量为5%时,材料的抗折强度和抗压强度达到最大,分别为3.78和31.95 MPa。

In order to cope with the critical problems(e.g., high cost, high energy consumption and high heat loss), which were raisedduring the high temperature sintering process in the traditional preparation technique of the Si_3N_4/SiC composite refractories, this studyprepared sintering-free low density Si_3N_4/SiC composite refractory. This research synthesized Si_3N_4/SiC composite powder bycarbothermal reduction nitridation using diatomite and sucrose as silicon and carbon source, respectively The results show that phasecomposition of the powder are α-Si_3N_4, β-Si_3N_4, β-Si C and Fe_3Si; Fe_2O_3 is the cause of Fe_3Si formation; the relative content of α-Si_3N_4,β-Si_3N_4 and β-Si C are 4.28%, 29.74% and 59.40%, respectively. The β-Si_3N_4 presents short columnar and β-Si C presents fine particles.The following procedure was adding sucrose(binder) which contained different contents of Si powder(0%, 5%, 10%) in the powder toprepare low density porous Si_3N_4/SiC composite refractory. After tested at 1000 °C, the results show that the addition of Si powder haslittle effect on the bulk density and porosity; the variation range of the bulk density and porosity is 1.48~1.51 g·cm-3 and 33.36%~34.62%,respectively. As Si powder dosage is 5%, the bending strength and compressive strength reach the maximum of 3.78 MPa and 31.95 MPa,respectively.