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

Solid phases have been prepared in Ca(NO3)2–(NH4)2HPO4–Na2SiO3–NH4ОН–H2O (cСа/cP = 1.70) systems with widely varying amounts of the sodium silicate dopant (у = cSi/cP = 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.