Synthesis Of Calcium-spinel Composites And Their Effect On Adherence Performance

Magnesia-spinel bricks have excellent thermal shock resistance and alkali, chlorine, sulfur,resistance, etc, which are the development trend of chrome-free basic refractories in cementrotary kiln burning zone. But magnesia-spinel bricks’ adherence performance of cement clinkerare poor in service process, which limits its application. This paper reviews erosion and damagemechanism of magnesia-spinel in service process, in addition, reaction characteristics ofrefractories with cement clinker are analyzed. In this paper, calcium-spinel composites wereprepared by modifing synthetic spinel, which hoped to improve the adherence performance ofspinel. The properties and microstructure of calcium-spinel composites were analyzed, inaddition, reaction characteristics of composites with cement clinker were studied. Following,calcium-spinel composites were introduced into the magnesia-spinel bricks, and the effect onadherence performance of the addition of composites in bricks were researched. The promotingmechanism of adherence performance was studied from the perspective of microstructure byscanning electron microscopy. The conclusions are as follows:（1）Dolomite, magnesite and industrial alumina as raw material, CA₂-MA MA-CA₂andMA-CA₆composites can be prepared by control of the raw material composition and the firingtemperature. The bulk density of CA₂-MA MA-CA₂and MA-CA₆composites were2.75g/cm³，3.08g/cm³and3.16g/cm³after firing at1700℃.（2）MA and CA₂subregionally distributed in MA-CA₂composites，MA crystals showedoctahedral morphology，but CA₂crystals showed fine long strips and clusters distributionmorphology. In MA-CA₆composites，MA crystals showed hypautomorphic and euhedraloctahedral morphology，CA₆crystals showed a peculiar crystal habit，which flaky crystalsgrowed along the base level and stacked thickening. CA₆grains evenly interspersed among MAgrains，showed interlaced mesh distribution，which achieved complex phase-toughening effect.（3）In the composites, CA₂and CA₆reacted prior to MA with C₂S and C₃S of cementclinker, generated CA and C₂AS with high melting point. A dense reaction sintered layerformed between the clinker and composites, which inhibited chemical erosion and liquidpenetration of cement clinker. Compared with MA-CA₂and MA-CA₆composites，CA₂-MAcomposites had better resistance to erosion and penetration of cement clinker，however,adherence performance of cement clinker was worst.（4）Cement clinker reacted with CA₂and CA₆and generated gehlenite and calciumaluminum（CA CA₂）, which inhibitied the process of cement clinker reacted with M2S andgenerated CMS in magnesia-spinel bricks. Moreover, the reaction reduced the react degreebetween MA and cement clinker. These factors prevented formation of the calcium aluminatelow-melting phase and dissolution of spinel in bricks, maintained the stability of kiln coating on the surface of magnesia-spinel brick, and gave magnesia-spinel bricks better adherenceperformance of cement clinker.