Preparation of Machinable Bioactive Glass-ceramics by Sol-gel Method

The purpose of this research was to prepare machinable bioactive glass-ceramics by sol-gel method. A multi-component composite sol with great uniformity and stability was first prepared by a 2-step method. The composite sol was then transformed into gel by aging under different temperatures. The gel was dried finally by super critically drying method and sintered to obtain the machinable bioactive glass-ceramics. Effect of thermal treatment on crystallization of the glass-ceramics was investigated by X-ray diffraction (XRD) analysis. Microstructure of the glass-ceramics was observed by Scanning Electron Microscopy (SEM) and the mechanism of machinability was discussed. Phlogopite and hydroxylapatite were identified as main crystal phases by XRD analysis under thermal treatment at 750 ℃ and 950 ℃ for 1.5 h separately. The relative bulk density could achieve 99% under 1050 ℃ for 4 h. Microstructure of the glass-ceramics showed that the randomly distributed phlogopite and hydroxylapatite phases were favorable to the machinability of the glass-ceramics. A mean bending strength of about 160-180 MPa and a fracture toughness parameter K_ IC of about 2.1-2.3 were determined for the glass-ceramics.