Abstract:

Magnesia-carbon refractories were prepared using fused magnesia,flake graphite and metal aluminum powder as starting materials,phenolic resin as the binder,heat-treating at 1 300-1 600 ℃ in a nitrogen atmosphere.The phase reconstruction and the microstructure evolution of the obtained magnesia-carbon refractories were analyzed.The formation mechanisms of magnesia crystals with different morphologies by chemical vapor deposition were revealed.The results show that at 1 300-1 500 ℃,the non-oxides within the samples are aluminum carbide (Al₄C₃),aluminum nitride (AlN) and magnesium aluminum nitride (Mg₃Al_nN_n+2,n=2 or 3);at 1 600 ℃,the diffraction characteristic peak intensity of Al₄C₃ and AlN decreases sharply,and sharp diffraction characteristic peaks of nitrogen aluminum carbide (Al₇C₃N₃) appear.Mg(g) is produced by the aluminothermic reduction and carbothermal reduction of magnesia.On the surface of the samples,Mg(g) reacts with oxygen to form MgO whiskers.Inside the samples,Mg(g) and O₂(g) undergo a CVD chemical deposition reaction to form cubic MgO crystals.There is a phase relationship between flake AlN and flake Mg₃Al_nN_n+2,and they are so associated with each other that the morphology is difficult to distinguish.

Key words: magnesia-carbon refractories, phase reconstruction, non-oxide, magnesia

摘要：

以电熔镁砂、鳞片石墨和金属铝粉为原料,酚醛树脂为结合剂,在氮气气氛中,经1 300~1 600 ℃热处理后制备了镁碳耐火材料。分析了镁碳耐火材料的物相重构和微结构演变,揭示了化学气相沉积反应形成两种不同形貌氧化镁的机制。结果表明:在1 300~1 500 ℃时,试样的非氧化物组成为碳化铝(Al₄C₃)、氮化铝(AlN)和镁铝氮化物(Mg₃Al_nN_n+2, n=2或3);在1 600 ℃时,热处理后试样中碳化铝和氮化铝的衍射特征峰值强度急剧降低,出现氮碳化铝(Al₇C₃N₃)的尖锐衍射特征峰。铝热还原MgO和碳热还原MgO产生了Mg(g)。在试样表面,Mg(g)与氧气反应形成MgO晶须;在试样内部,Mg(g)与氧气发生CVD化学沉积反应形成立方MgO晶体。在热处理后试样的微区组织结构中,片状AlN与片状Mg₃Al_nN_n+2存在一定的位相关系,二者伴生存在,形貌难以区分。

关键词: 镁碳耐火材料, 物相重构, 非氧化物, 氧化镁