共沉淀法合成三硅酸镁及其微观分析

由Na_2O·nSiO_2和Mg(NO_3)_2经沉淀法合成了三硅酸镁,用450℃煅烧或酸化方法对合成的样品进行改性. 采用XRD、IR、TG/DTA和BET等表征手段,考察了原料加入顺序、酸化和煅烧过程对样品的结晶度和表面织构的影响规律,并对其影响机理进行了探讨. 结果表明,不同滴定顺序和不同活化方法制得的样品均为非晶态物质. TG/DTA分析显示不同滴定顺序样品的组成相同. pH对样品的表面织构有明显的影响. BET分析表明,Mg(NO_3)_2滴加入泡花碱溶液合成的样品为微孔材料,以1～3nm和0.7～0.9nm的微孔为主,比表面积达568.93m~2·g~(-1),水合硅酸镁含量较高. 泡花碱滴加入Mg(NO_3)_2合成的样品为大孔材料,比表面积为179.40m~2·g~(-1),水合硅酸镁含量降低. 煅烧和酸处理增加样品的结晶度,减少样品比表面积,并改变样品的孔径分布. 煅烧使中孔含量增加,形成中孔材料. 酸处理使Mg~(2+)被H~+取代,表面形成硅羟基基团,材料以中孔为主.

Synthesis of magnesium trisilicate by a reverse strike method and its microscopic analysis

Magnesium trisilicate was synthesized by precipitation using Na_2O·nSiO_2 and Mg (NO_3)_2 as raw materials. The precipitate was subject at 450℃ or activated by 15% H_2SO_4, following which the samples were characterized by XRD, IR, TG/DTA and BET to investigate the effects of strike methods, acidic activation and calcination on the crystal phase and surface texture. It is shown that the samples activated by different methods are amorphous. TG/DTA analysis indicates that the samples have the same composition as magnesium silicate hydrate with different contents. pH in the reaction has significant effect on the surface texture of the samples. BET analysis reveals that the sample synthesized by adding Mg(NO_3)_2 to the sodium silicate solution is microporous with the specific surface area of 568.93m~2·g~(-1) and exhibits a multimodal pore width distribution at the micropore regions of 1 to 3nm and 0.7 to 0.9nm. The sample with the specific surface area of 179.4m~2·g~(-1) synthesized by adding Mg(NO_3)_2 to the sodium silicate solution is mesoporous. Calcination and acidic activation increase the crystalline degree, reduce the specific surface area and change the distribution of pore width. The reactive mechanism was discussed primarily. Calcination increases the quantity of mesopores. Acidic activation makes H~+ replaced by Mg~(2+) to form the Si-OH, and most of the acidic activation samples are mesoporous.