碳热还原氮化菱镁石和铝矾土合成MgAl_2O_4-SiAlON的物相演变

Phase transformation of MgAl_2O_4-SiAlON composites synthesized by carbonthermal reduction and nitridation method from magnesite and bauxite

以菱镁石和煅烧铝矾土为主要原料,焦炭为还原剂,在氮气中采用碳热还原氮化法合成MgAl2O4-SiAlON材料,并利用XRD研究了试样在1350、1400、1500和1600℃下分别保温3h处理后产物的物相变化及配碳量(分别为理论配碳量、过量50%和过量100%)对反应产物的影响。结果表明:(1)不同温度处理后的反应产物均存在MgAl2O4相和SiAlON相,增加配碳量有利于SiAlON相的生成。本试验确定合成MgAl2O4-SiAlON的适宜工艺条件为:氮化温度1500℃,配碳过量50%。(2)配碳过量50%时,在1350和1400℃处理后产物中含有MgAl2O4、α-Al2O3和MgAl2Si4O6N4相,1500℃处理后为MgAl2O4和β-SiAlON,1600℃处理后为MgAl2O4和Mg1.25Si1.25Al2.5O3N3。

MgAl2O4 （spinel） - SiAlON composites were synthesized by carbothermal reduction and nitridation （CRN） method in nitrogen atmosphere using magnesite and calcined bauxite as starting materials,coke as reducing agent. The phase transformation of the specimens heated at 1350, 1400, 1500 and 1600℃ for 3 h were investigated by XRD, and effect of coke additions （theoretical amount,50 wt% excessive and 100 Wt% excessive, respectively） was also studied. The results showed that： （1） MgAl2O4 -SiAlQN composites were synthesized at different temperatures and increase of coke additions can benefit SiAION formation. The appropriate synthesizing condition of MgAl2O4 -SiAIQN composites was： at 1500 ℃ nitridation temperature with 50 wt% excessive of coke. （2）When 50 wt% excessive of coke was added,the initial phases of the raw materials transformed into phases of MgAl2O4, α-Al2O3 and MgAl2Si4O6N4 at 1 350 and 1400℃, into MgAI204 and β-SiAION at 1 500℃,and into MgAl2O4 and Mg1.25Si1.25 Al2.5O3N3 at 1600℃.