Peter Wange

Microstructure-property relationship in high-strength MgO–Al2O3–SiO2–TiO2 glass-ceramics

Abstract An MgO–Al 2 O 3 –TiO 2 –SiO 2 glass was exposed to various two-step heat treatments in order to produce high-strength glass-ceramics. The maximum fracture toughness of 4.3 MPa m 1/2 (accompanied by an elastic modulus of 139 GPa and a hardness of 9.5 GPa) was obtained after a two-hour pre-treatment at 800 °C followed by annealing at 1080 °C. Based on TEM imaging, energy-dispersive X-ray spectrometry, X-ray diffraction and dilatometry, an understanding of the microstructure-property relationship is developed. The high-quartz low-quartz phase transition is shown to play the key role for achieving high-strength glass-ceramics.

Control of phase formation processes in glass-ceramics for medicine and technology

Abstract The control of phase separation processes in silicate glasses makes possible the control of nucleation and crystallization of base glasses. Ti(III,IV)-species influence the phase formation in SiO 2 –Al 2 O 3 –MgO glasses to form glass-ceramics based on s- and α-quartz solid solutions. Additions of Na 2 O, K 2 O and F in a specific composition range and heat treatment of the glass result in an new glass-ceramic with curved micas. The structure of these crystals shows a high tetrahedral rotation. Glasses of the SiO 2 –Al 2 O 3 –MgO–Na 2 O–K 2 O–P 2 O 5 –F system show a double phase separation. Apatites and micas grow as a result of controlled in situ crystallization. The material can be machined and has bioactive properties. Phosphate glasses show no glass-in-glass phase separation. However, the high supersaturation is cancelled by a thermal treatment of the glass and a primary crystal is formed. Apatite crystals grow in the primary phase.