The Effect of Firing Temperature on Colour and Structural Properties of Malayaites With Cr

Abstract

Malayaites are calcium tin silicate compounds derived from natural occurring mineral the malayaite which has the chemical formula CaSnSiO5. Malayaites are characterized by monoclinic crystal structure consisting of chains of distorted SnO6 octahedra connected with tops of SiO4 tetrahedra, forming a framework containing chains of CaO7 polyhedra. This incurred structure is then stable for bond of metal ion and takes part in the final pigment colouring. In this contribution the compounds with the chemical formula of Ca(SnCr)SiO5±δ (molar ratio of Cr/Sn = 0.015) were prepared. For the synthesis the classical ceramic method was used, i.e. procedures of calcination in an elec¬tric furnace at the temperatures 1200-1500 °C for 4 h (one-step calcination) and multiple calcination (two-step calcination) for obtaining products with higher quality. Therefore, the objective of this work was to compare samples which were prepared by the one-step and also two-step calcination procedures. The two-step calcination procedure was carried out at two temperatures, during which the first calcina¬tion was always held at 1100 °C for 4 hours. The second calcination was performed for 4 h at an appropriate temperature from the range 1200-1500 °C. The colour properties were studied by a spectrophotometer ColorQuest XE (HunterLab, USA). The colour moved from pink to burgundy in dependence on temperature of calcination. The phase composition of tested compounds was verified by using X-ray dif¬fraction analysis with using a diffractometer D8 Advance (Bruker, GB). A particle size distribution of heat treatment samples was measured by Mastersizer 2000/MU (Malvern Instruments, Ltd., GB). The signal was evaluated on the basis of Fraunhofer bending. Thermal stability was investigated by heating microscope EM201-12 (Hesse-Instruments, Germany).