三聚磷酸钠对建筑石膏水化进程的影响及缓凝机理研究

系统研究了三聚磷酸钠对建筑石膏水化进程、液相离子浓度与过饱和度及二水石膏晶体形貌的影响,结合X光电子能谱分析技术对其缓凝机理进行了分析.结果表明:三聚磷酸钠使建筑石膏水化放热变缓,早期水化率降低,诱导期延长;三聚磷酸钠使液相离子浓度和过饱和度降低,二水石膏晶体粗化,晶型由针状转化为短柱状;三聚磷酸钠使二水石膏晶核表面钙元素2p电子结合能发生1.267eV化学位移,它与二水石膏表面的钙元素作用,在其表面形成化学吸附层,阻碍二水石膏晶核生长;三聚磷酸钠形成磷酸钙难溶盐覆盖在建筑石膏表面抑制其溶解和三聚磷酸钠在二水石膏晶核表面形成化学吸附层阻碍其生长是三聚磷酸钠缓凝的内在原因.

Effect of Sodium Tripolyphosphate on Hydration Process of Building Gypsum and Its Retarding Mechanism

Effect of sodium tripolyphosphate on the hydration process,ion concentration and supersaturation degree in liquid phase,and crystal morphology of building gypsum was systemically investigated.Furthermore,by using XPS technique,its retarding mechanism was also analyzed.The results indicate that the addition of sodium tripolyphosphate slows down the hydration heat evolution,decreases hydrationrate at early stage and prolongs the induction period of building gypsum.After addition of sodium tripolyphosphate,ion concentration and supersaturation degree of gypsum in liquid phase is decreased,the crystal of dihydrate is coarsened,and the crystal morphology is altered from needle-like to short prismatic.XPS measurement shows the 2p electric bonding energy of Ca element on the surface of gypsum particles takes place 1.267eV of chemical shift before and after adsorption of sodium tripolyphosphate,which suggests a chemisorption layer of sodium tripolyphosphate is formed on gypsum surface,and therefore the growth of crystal nuclei is inhibited.The intrinsic retarding mechanism of sodium tripolyphosphate could be ascribed to two aspects:(1) the surface of gypsum particles is covered with the insoluble calcium phosphate precipitation formed by reaction of sodium tripolyphosphate and Ca2 ,and its dissolution is inhibited;(2) sodium tripolyphosphate is chemically adsorbed on the surface of crystal nuclei and hinders its growth strongly.