Effect of ZrO2 addition on crystallization behaviour, porosity and chemical-mechanical properties of a CaO-TiO2-P2O5 microporous glass ceramic

2-6 mol% ZrO₂ was added to a base glass composition of P₂O₅ 31.25, CaO 43.75, TiO₂ 25 (mol%) at the expense of TiO₂. The prepared glasses were crystallized to bulk glass ceramics containing the major phases of β-Ca₃(PO₄)₂ and CaTi₄(PO₄)₆. DTA was utilized to determine the appropriate phase separation-nucleation and crystallization temperatures. The crystalline products and resulting microstructures were examined by XRD and SEM. The β-Ca₃(PO₄)₂ phase was dissolved out by leaching the resulting glass ceramics in HCl, leaving a porous skeleton of CaTi₄(PO₄)₆. It was shown that ZrO₂ addition resulted in reduction of volume porosity and mean pore diameter while the specific surface area was increased. The smallest median pore diameter and largest surface area were 8.6 nm and 32 m² g⁻¹ respectively obtained for the specimen containing 6 mol% ZrO₂. The ZrO₂ addition also improved the chemical durability and bending strength of porous glass ceramics.