无水石膏AⅢ对β半水石膏性能的影响及作用机理

Effects and mechanism of anhydrite AⅢ on the performance ofβ-hemihydrate gypsum

以磷石膏为原料生产β半水石膏粉,研究了可溶性无水AⅢ对半水石膏粉的影响,采用常规分析方法、TG-DSC、XRD和扫描电镜等方法对磷石膏原料,β半水石膏粉和石膏产品进行分析和表征。差热分析结果表明：磷石膏低温脱水出现两个DSC吸热峰,峰值仅相差6℃并存在重叠现象,说明脱水反应分两步进行,发生了不同反应,熟石膏粉中存在不同相混合物。半水石膏粉煅烧最佳工艺：焙烧温度在170±5℃内,焙烧时间2h,熟石膏新粉结晶水含量约3.0%,通过陈化,控制结晶水含量4.8%~5.2%,有利于提高熟石膏粉质量。半水石膏水化热效应结果表明：AⅢ活性高,水化速度快,导致添加减水剂时几乎未见减水增强效果,说明AⅢ影响熟石膏粉质量。陈化粉添加减水剂能提高石膏制品强度,聚羧酸系HC掺量0.7%时,绝干强度达到15.0 MPa,强度提高近64.84%;奈系FDN掺量0.7%时,绝干强度达到14.8 MPa,强度提高近62.64%;木质素减水剂掺量0.7%时,绝干强度达到13.9 MPa,强度提高近52.75%。

Theβ-hemihydrate gypsum was prepared from phosphogypsum and the effects of the soluble anhydrous AⅢ were investigated.The Conventional analytical methods,TG-DSC,XRD and SEM were used to analyze and characterize theβ-hemihydrate gypsum and their products.The thermal analysis results showed that two endothermic peaks in the phosphogypsum dehydration reaction,and those two peaks overlapped partly.The difference between the two peaks was only 6℃,which indicated that the dehydration reaction included two steps of different reactions and theβ-hemihydrate gypsum existed as mixed phase structure.The optimal conditions forβ-hemihydrate gypsum calcinations were 170±5℃ for 2hours.The content of the crystal water inβ-hemihydrate gypsum was about 3.0%.The properties of the gypsum powder could be improved if the content of the crystal water content changed in range of 4.8~5.2%through aging process.The highly activity and fast hydration rate of AⅢoffset the effect of the water reducing agents during the hydration ofβ-hemihydrate gypsum indication that AⅢaffects the performance ofβ-hemihydrate gypsum.The addition of water reducing agents could improve the strength of gypsum products.When 0.7% HC polycarboxylate was added,the strength ofβ-hemihydrate gypsumcan reached to 15.0 MPa,nearly an increase of 64.84%.When 0.7% superplasticizer-FDN was added,the strength reached to 14.8 MPa,nearly an increase of 62.64%,and when 0.7% lignin was added,the strength increased nearly by 52.75%to 13.9 MPa.