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

Magnesium trisilicate was synthesized by precipitation using Na₂O·nSiO₂ and Mg (NO₃)₂ as raw materials. The precipitate was subjeet at 450℃ or activated by 15% H₂SO₄, following whieh 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(NO₃)₂ to the sodium silicate solution is microporous with the specific surface area of 568.93 m² · g^-1 and exhibits a multimodal pore width distribution at the micropore regions of 1 to 3 nm and 0.7 to 0.9 nm. The sample with the specific surface area of 179.4 m²·g^-1 synthesized by adding Mg(NO₃)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 Mg²⁺ to form the Si-OH, and most of the acidic activation samples are mesoporous.