Development of gehlenite-based glaze recipes in vitrified applications

Gehlenite is a melilite group mineral. Melilite is a sorosilicate composed of aluminium and magnesium calcium silicates. Gehlenite is the aluminium (Ca₂Al[AlSiO₇]) end member and akermanite (Ca₂Mg[Si₂O₇]) is the magnesium end member. Within the scope of this study, which was carried out in order to improve the properties of ceramic glazes used in vitrified bodies, the use of gehlenite phase, which is among calcium alumina silicate glasses, in glassy crystalline form, was realised for the first time in the literature. Gehlenite was added to vitrified glaze in certain percentages to improve the mechanical strength and abrasion resistance of the glaze composition. Gehlenite crystal has the chemical composition of 2CaO. Al₂O₃.SiO₂ (CAS). Calcium oxide (CaO) required for the production of gehlenite was obtained from the recycling of egg shells within the scope of waste utilisation and environmentally friendly product development. Afterwards, the calcium oxide (CaO) obtained was subjected to chemical analysis and calcination, fire loss was checked and carbon dioxide was removed. The calcium oxide obtained in the second part was combined with aluminium oxide and silicon oxide to form the recipe required for the gehlenite phase. The recipe formed with calcium oxide, aluminium oxide and silicon oxide was ground again in the planetary ball mill for 4 hours and a mixture was obtained. According to the X-ray diffraction analysis (XRD) of the glass composition produced at 1550℃ for 12 hours, 100% pure gehlenite phase with a sharp crystalline peak was obtained. The obtained gehlenite was added to the vitrified glaze composition at the rates of 1%, 3%, %4, %5 and %7 was compared with the existing vitrified glaze after firing. Grain sizes, chemical analyses, hardness, flexural strength, abrasion resistance and colour measurement (L,a,b) tests of vitrified glazes with and without gehlenite (Ca₂Al[AlSiO₇]) additives were performed.