Mechanochemical Synthesis of SiO₄^4–‐Substituted Hydroxyapatite, Part III – Thermal Stability

Abstract

Thermal stability of mechanochemically synthesized silicon‐substituted hydroxyapatite containing 0.6, 0.8, 1.0, and 1.2 mol of silicon per mol of apatite unit cell has been studied for the first time. The powders of the silicon‐substituted hydroxyapatite were annealed within the temperature range 700–1300 °C. It was found that the substituted hydroxyapatites remain single‐phase after annealing at temperatures of up to 900 °C for all concentrations of added silicon. The second phase – silicocarnotite Ca5(PO4)2SiO4 – appears in the materials containing 1.0 and 1.2 mol of added silicon that have been annealed at 1000 °C. In the powder containing 0.8 mol of added silicon, silicocarnotite was detected after annealing at 1100 °C. The formation of silicocarnotite is likely to occur in the nanoparticles of the silicon‐substituted hydroxyapatite with silicon concentrations much higher than the average value. It was found that the silicon‐substituted hydroxyapatite containing 0.6 mol of silicon per mol of apatite unit cell has the highest thermal stability and remains single‐phase up to a temperature of 1200 °C, similarly to pure hydroxyapatite obtained by the same synthesis method.

Soft mechanochemical synthesis and thermal stability of hydroxyapatites with different types of substitution

“…Thermal stability of synthetic HA is crucial for the manufacture of ceramics and HA coatings. It is necessary to correctly select the conditions of thermal treatment when a technological process is designed because when substituted HAs are heated, structural transformations can take place, accompanied by the formation of impurity phases [14,15], which affect not only physical but also biological properties of the resultant product.…”

Effects of both Sr and Mg substitution on compositions of biphasic calcium phosphate derived from hydrothermal method

“…The sample of 100% Ca and the samples with 10% Sr and 30% Sr addition showed no obvious endo-or exothermic peaks because their main phases were HA and b-TCP, which gain their thermal stability until 1300°C and 1200°C. 43,44 The samples with 30% Mg and 50% Mg addition presented same trend as the samples with 30% Mg and 50% Mg addition in Figure 6 due to their similar phase compositions. Slight exothermic peaks appeared at 785°C for samples with 30% Mg addition and 50% Mg addition, which might correspond to the formation of trace MgO.…”

“…Figure shows the DSC curves of the samples synthesized at pH 10.5 without heat treatment. The sample of 100% Ca and the samples with 10% Sr and 30% Sr addition showed no obvious endo‐ or exothermic peaks because their main phases were HA and β‐TCP, which gain their thermal stability until 1300°C and 1200°C . The samples with 30% Mg and 50% Mg addition presented same trend as the samples with 30% Mg and 50% Mg addition in Figure due to their similar phase compositions.…”