Crystallisation characteristics and properties of glasses based on fluorapatite–anorthite eutectic system

Abstract

The effect of partial replacement of CaO by MgO or ZnO on the crystallisation behaviour of glasses based on 30 fluorapatite–70 anorthite eutectic composition has been investigated using the differential thermal analysis, X-ray diffraction and scanning electron microscopy. Minor additive of TiO₂ oxide was added on the glass batches as nucleating agents. The main crystalline phases formed after controlled heat treatment of the glasses were fluorapatite, anorthite, wagnerite and gahnite. The resultant glass–ceramic samples were characterised by the thermal expansion coefficient and Knoop microhardness. The α values of the crystallised glasses in the range of 25–500°C varied from 67×10⁻⁷ to 79×10⁻⁷ °C⁻¹. In this case, the microhardness values of glass–ceramic samples decreased in the range of 6117–6884 MPa with increasing thermal expansion coefficient value. Precipitation of the wagnerite or gahnite phases in the crystallised glasses causes an improvement in wear resistance of the glass ceramic samples.

Keywords:

• Glass
• Crystallisation
• Glass–ceramic
• Apatite
• Anorthite