Study On Structure Of Anhydrous Calcium Sulphoaluminate And Hydration Products

Anhydrous calcium sulphoaluminate is the main mineral of sulfuraluminate cementclinker. Its rapid hardening, high early strength and microdilatancy hydration characteristics isclosely related to the crystal structure. Study on crystal structure of anhydrous calciumsulphoaluminate has important significant for understanding and improving its performance.The main hydration products of anhydrous calcium sulphoaluminate have ettringite andaluminum gel. Structural of ettringite is instability. Its crystalline structure contains a lot ofcrystal water. And it can be transformed into monosulfoaliminate hydrate under certainconditions. The study on crystal structure of ettringite has important significance forunderstanding and controlling formation and decomposition of ettringite, as well as improvingthe performance of cement concrete products.This paper explores the preparation of anhydrous sulfur powder and single crystal ofcalcium aluminate and solution synthesis and anhydrous sulphoaluminate single mineralhydration prepared ettringite. Be prepared for a single mineral XRD tests with TOPAS,DIAMOND software for structural analysis of test results and calculations. Compare thestructural differences between the laboratory synthesis of ettringite and natural ettringite,combined ettringite crystal structure analyzes its thermal stability, the results showed that:(1) Anhydrous calcium sulphoaluminate have two kind of crystal structure. They belongto the orthorhombic and cubic, respectively. Space group of orthorhombic C4A3S is makedas Pcc2. The crystal unit cell volume V=1552.6943. Cell parameters a0=13.0318,b0=12.9638, c0=9.1907, α=β=γ=90°, Z=4. Space group of cubic C4A3S is maked as I—43m.Its unit cell volume V=777.9103. Cell parameters a0=b0=c0=9.2048, α=β=γ=90°, Z=2.It`s for the growth environment of anhydrous calcium sulphoaluminate, resulting indifferent structures. Orthorhombic C4A3S is prepared in solid. Best ratio of raw material forpreparation of anhydrous calcium sulphoaluminate single mineral is, gypsum37.0597g,calcium carbonate44.0568g and aluminum hydroxide76.6713g. Best mix mode is rawmaterial stirred in water. The firing temperature1320℃and holding time of1hour. CubicC4A3S is prepared in melt. Temperature for crystal growth is750℃~850℃. Mass ratio of PbCl2and C4A3Sis150:1to200:1.(2)Structure of ettringite prepared by solution synthesis and hydration of anhydrouscalcium sulphoaluminate mineral both are trigonal, space group is maked as P31c. Unit cellvolume of ettringite preparaed by the solution synthesis is V=2335.8143, cell parametersa0=b0=11.2112, c0=21.4589. α=β=90°, γ=120°, Z=2. And unit cell volume of ettringitepreparaed by hydration is V=2336.3723. Cell parameters a0=b0=11.2123, c0=21.4596,α=β=90°, γ=120°, Z=2. These two kinds structure of AFt are smaller than that of the crystalstructure of single crystal of natural ettringite in unit cell volume and parameters a, b, c.Intensity ratio of main diffraction peak of ettringite preparaed by solution synthesis ishigher than that of ettringite preparaed by hydration. This is due to the different synthesismethods. Formation of ettringite preparaed by solution synthesis is relyed on reassortment ofions in solution. Aluminum elements make up the skeleton structure of ettringite comes fromC4A3Sin the formación of ettringite preparaed by hydration. Ettringite is formed after thecrystal structure of C4A3Sbroken. Its atoms can not be like ettringite preparaed by solutionsynthesis as orderly arranged.In the [Ca3(OH)6Al] skeleton structure of ettringite, difference of bonds length of AFtprepared by solution synthesis and nature is less than that of AFt preparaed by hydration.Length of AFt prepared by solution synthesis is less than that of nature AFt in this skeletonstructure. For the length of the Ca-O bond connect with coordinated water in AFt preparaedby hydration. It is longer than that of AFt prepared by solution synthesis. And structure of AFtpreparaed by hydration is more unstable.