硅灰石制备二氧化硅材料过程中晶体结构的变化

EVOLUTION PROCESS OF CRYSTAL STRUCTURE DURING SYNTHESIZING SILICA MATERIALS FROM WOLLASTONITE

利用XRD技术研究了三斜晶系普通硅灰石在酸解形成二氧化硅材料过程中晶体结构的变化。结果表明 :三斜晶系普通硅灰石在浓度为 2mol/LHCl溶液中的酸解浸蚀方向严格受晶体结构控制 ,酸解初期晶粒首先并主要沿垂直于 [10 0 ]带轴方向浸蚀 ,结果导致衍射面 ( 10 0 ) ,( 2 0 0 )和 ( 3 0 0 )的衍射强度增大 ;随着酸解时间的延长 ,[SiO4 ]单四面体与 [CaO6 ]八面体共棱连接方向成为主要浸蚀方向 ,在XRD图谱中表现为d =0 .2 98nm衍射峰一直保持较大的衍射强度。酸解反应过程中 ,三斜晶系普通硅灰石除被转变成mSiO2 ·nH2 O外 ,其晶体结构存在向单斜晶系副硅灰石、针钠钙石型结构、硬硅钙石和傅硅钙石的晶型转变现象 ,60min前以形成单斜晶系副硅灰石的多型转变为主 ,60min后则以形成针钠钙石型结构。

Evolution process of crystal structure in acid hydrolysis to synthesizing silica materials with triclinic wollastonite was investigated by means of XRD method. Results indicate that when the concentration of HC1 solution is 2 mol/L, the etching orientation of wollastonite crystal acid hydrolysis is strictly controlled by the crystal structure. Grains are mainly etched in the zone perpendicular to [l00] direction at the beginning of acid hydrolysis, resulted in the increase of the diffraction intensities of reflection planes (100),(200) and (300); while the co-edge orientation between [CaO6] octahedron and [SiO4] single tetrahedron becomes main etching orientation along with the extension of time for acid hydrolysis. This can be confirmed by the stronger diffraction peak on d=0.298 nm in XRD pattern. During the acid hydrolysis process, besides the transformation of the triclinic wollastonite into mSiO2&middotnH2O, there exists the transformation of the triclinic wollastonite into monoclinic wollastonite, pectolite type structure, xenotlite and foshagite. The polytype transformation of wollastonite from triclinic to monoclinic mainly took place during the first 60 min, and after 60 min of hydrolysis, the major structure transformation is to form pectolite type structure, xenotlite and foshagite.