Effect of sodium silicate on the nature of crystallization products in calcium phosphate systems

Abstract

Solid phases have been prepared in Ca(NO₃)₂–(NH₄)₂HPO₄–Na₂SiO₃–NH₄ОН–H₂O (c_Са/c_P = 1.70) systems with widely varying amounts of the sodium silicate dopant (у = c_Si/c_P = 0–5). The product formed under the test conditions is highly disperse and poorly crystallized apatite, in which up to 1.4 mol of phosphates (per mole of the salt) is substituted by carbonate and silicate ions. The excessive SiO₄⁴⁻ anions in the system are hydrolyzed to yield amorphous SiO₂. When the silicon agent is in a considerable excess over the phosphate agent (у ≥ 2), minor calcium hydrosilicate is identified in the solid phase. The coprecipitation of the aforementioned compounds results in microcomposites with developed surface areas exceeding 100 m²/g.