The effect of zirconia addition on crystallization behaviour and machinability of potassium mica and fluorapatite glass-ceramics

Machinable bioactive glass-ceramics containing microcrystalline phases of mica and apatite can be considered as new materials for bone implants and substitutes in human body. Such a glass-ceramic has a better machinability than others due to the large amount of layered mica phase which is oriented randomly and distributed uniformly in glass matrix. Consequently, it is easier to process mica-based glass-ceramics into surgical parts with different complex shapes by using normal clinical machining methods. The purpose of this study is to investigate the crystallization behavior and mechanical properties of machinable glass ceramics having 3:7 weight ratio of fluorapatite (Ca₅(PO ₄)₃F) to potassium mica (K₂Mg ₃AlSi₃O₁₀F₂) as a function of zirconia addition, as nucleating agent. Glass compositions were prepared and casted at proper temperatures. Differential thermal analysis (DTA) and XRD methods were applied to characterize phase precipitation sequence and identification of phases. Disc and cylindrical shaped samples were prepared to determine microstructural and mechanical properties in terms of microhardness and machinability. FE-SEM was used to characterize variation of microstructural constituents depending on the amount of nucleating agent.