Research On Using Gypsum Waste To Produce Anorthite/Mullite Phase Ceramics

Nowadays, there are many challenges faced with ceramic industry. The higher sinteringtemperature with immense energy consumption, lower toughness strength and theincreasingly decreasing of high quality raw material were considered as the three mainchallenged issue. Including daily-use ceramic and building ceramic, the traditional silicateceramic is composed of cristobalite (SiO2) and mullite((Al6Si2O13) crystal phase andfeldspathic glass as the binding phase. The each thermal expansion of the three phases is11×10-6/℃for cristobalite,5.7×10-6/℃for mullite and5.3~5.8×10-6/℃for feldspathic glass.It is obviously that the thermal expansion of cristobalite phase is quite lower than mullitephase and feldspathic glass. The critical micro cracks are apt to shaping in the ceramic duringthe sintering process for the mismatch of phase shrinkage. The toughness strength of ceramicis reduced by the cracks.In order to improving the thermal expansion coefficient of the ceramic chip, the method ofanorthite phase generated and cristobalite phase decreased in the ceramic is adopted in thiswork. Anorthite phase with thermal expansion of4.82×10-6/℃is correspond with the mullitephase and feldspathic glass. The anorthite phase generates from the reaction of calcium sourceand ceramic body. The affections of the different calcium source, quantities and sinteredtemperature on the phase component and microstructure of ceramic are studied in this paper.In addition, the high calcium industrial wastes-desulfurization gypsum is used to synthesizethe micro acicular anorthite and mullite ceramic with lower cristobalite phase. The measuringtechnique of XRF, XRD, TG-DSC and SEM is used for characteristic the chemicalcomposition and thermal properties of raw material and microstructure of ceramic, and alsofor optimizing the preparation.According to calculation based on thermodynamic data, CaO-Al2O-SiO2ternary system, thegeneration of anothite is easier the mullite. And the anorthite can be converted into mullite inhigher temperature according to the result of the relative content of crystalline phasecalculated by Maud and the thermodynamic data. The result of different calcium source,quantity and sintered temperature effect on the phase component and microstructure ofceramic is that only when the calcium sulfates as the calcium source the anorthie and mullite phase coexistence and lower cristobalite in the ceramic at1240℃. And the ceramic has thehighest flexural strength.The main ingredients of desulfurization gypsum is CaSO4·2H2O. In this work thedesulfurization gypsum and ceramic body are used to preparation micro-needlelike anorthiteand mullite ceramic. The viscosity test shows that the fairy water is the effective dispersingagent for the slurry. Compared with the different molding manner, the dry press molding with10to20MPa pressure is the optimum manner. The sintered sample test result shows that,calcined at1200~1240℃, the body with5%desulfurization gypsum addition format amicrostructure which large scare of needlelike anorthite and mullite overlapping each other.And the sample has a well apparent morphology and lower pore rate0.08~0.1%. The blendingstrength of the sample reachs118~125.2MPa, while the raw body sintered at1200℃is49.5MP and at1320℃is89.3MPa。...