Abstract:

The specimens were prepared using low grade magnesite as the raw material,added with 0-3 mass% La₂O₃,calcined at 1 600 ℃ for 3 h.The bulk density,the apparent porosity and the cold modulus of rupture of the specimens were measured.The composition and microstructure of the calcined specimens were analyzed.The results show that adding La₂O₃ into magnesite can form lanthanum calcium silicate,which is dendritic and interlaces at MgO grain boundaries,and the dendrite toughens the specimen and increases the modulus of rupture.When 2 mass% La₂O₃ is added,the mechanical properties of the specimen are the best,and the modulus of rupture of the specimen reaches 103.1 MPa.La₂O₃ can promote the growth of periclase grains.When the La₂O₃ addition exceeds 2 mass%,the growth of periclase grains slows down,which may be due to the large number of second phases presenting at grain boundaries,inhibiting the growth of periclase grains,thus partly offsetting,the promotion of grain growth by La₂O₃.

Key words: magnesite, lanthanide, mechanical properties, microstructure

摘要：

以低品位菱镁矿为原料,向其添加0~3%(w)的La₂O₃,于1 600 ℃下保温3 h煅烧,测定了烧后试样的体积密度、显气孔率、常温抗折强度等,并分析了烧后试样的物相组成和显微结构。结果表明:在菱镁矿中添加La₂O₃,生成的硅酸钙镧矿物相呈树枝状交错分布在MgO晶界处,枝晶增韧,增大了抗折强度。加入2%(w)La₂O₃时试样的力学性能最佳,烧结试样的抗折强度达到103.1 MPa。La₂O₃可以促进方镁石晶粒的生长,当La₂O₃加入量超过2%(w)时,方镁石晶粒尺寸的增长有减缓的趋势,这可能是由于大量的第二相存在于晶界处,抑制了方镁石晶粒的生长,从而抵消了部分La₂O₃对晶粒生长的促进作用。

关键词: 菱镁矿, La₂O₃, 力学性能, 显微结构