六铝酸钙材料的合成及其显微结构研究

Synthesis and its microstructure of calcium hexaluminate material by reaction sintering

分别采用轻质碳酸钙和活性氧化铝 ,或纯铝酸钙水泥和活性氧化铝为初始原料 ,反应烧结合成了六铝酸钙 (CA6)材料 ,研究了原料和成型压力对合成材料的烧结性能和显微结构的影响 ,同时借助于XRD、TG -DSC、SEM和EDAX等测试手段对其反应过程、物相变化和显微结构进行了分析和观察。研究结果表明 :(1) 130 0℃时 ,合成材料的主晶相为刚玉相和CA2 ,并开始有CA6形成 ;温度升至14 0 0℃ ,CA6大量生成 ;15 0 0℃时反应完成 ,产物全部为CA6相。 130 0～ 15 0 0℃时 ,上述反应表现为体积膨胀过程 ,试样的体积密度和径向线收缩率随温度的变化不大 ;而高于 15 0 0℃时 ,试样明显趋向烧结 ,体积密度升高 ,线收缩率加大。采用纯铝酸钙水泥和活性氧化铝合成的试样的体积密度均高于采用轻质CaCO3 和活性氧化铝的 ,尤其在烧成温度高于 15 0 0℃时。坯体的成型压力对这两种合成试样的烧结性能均没有显著影响。 (2 )合成六铝酸钙材料的晶粒形貌与合成工艺有关 ,制备片状晶粒的六铝酸钙材料需满足两个条件 :一是晶核有足够的发育空间 ,二是从晶核生长形成片状结构需足够的物质扩散。采用纯铝酸钙水泥和活性氧化铝为原料的试样 ,其CA6晶核很容易发育成片状晶形 ,且随着坯体成型压力的增加 ,片状CA6有向等轴状发展的趋势 ;采用?

Calcium hexaluminate (CA 6) was synthesized by reaction sintering of two kinds of mixtures of CaCO 3/α-Al 2O 3 and pure calcium aluminate cement/α-Al 2O 3,respectively.The effect of raw materials and compact pressure on the sintering properties of the product was studied.The reaction evolution,phase change and microstructure of the products were determined and observed by means of XRD,TG-DSC,SEM and EDAX.The results show that:(1) CA 6 forms at 1300 ℃ along with corundum and CA 2 as the main phases,a plenty of CA 6 is produced with intermediate phases CA 2 disappearing at 1400℃ and the reaction completely finishes at 1500 ℃.Correspondingly,the bulk density and the radial linear change of specimens against temperatures keep basically constant due to the reaction accompanying volume expansion.Up to 1600 ℃,the bulk density increases and the radial linear shrinkage emerge apparently.Compared with the specimens with CaCO 3/α-Al 2O 3 as starting materials,specimens using cement/α-Al 2O 3 become denser at the range of 1300～1650 ℃,especially at temperature higher than 1500 ℃,however,the compact pressure gives hardly no obvious effects on the sintering properties in these two experiments.(2) Morphology of CA 6 grains is closely related to the synthesizing process.In the process of pure calcium aluminate/α-Al 2O 3 mixture,a platelet morphology of CA 6 grains is easily produced.With the increase of compact pressure of specimens,the growth tendency of the platelet CA 6 grains into equi-axed grains is observed.In the case of the mixture CaCO 3/ α-Al 2O 3 used,the platelet CA 6 grains are obvious when specimens pressed at 50 MPa,however,granular CA 6 grains are predominant when compact pressure is up to 200 MPa.