Thermal Decomposition of Zircon Refractories

Zircon can be used to make refractory brick for the glass industry. At elevated temperatures it is known to dissociate into silica and zirconia. This study was undertaken because one of the factors that can adversely affect the quality of the glass melted in zircon-lined tanks is the degree of dissociation. The thermal dissociation of purified and unpurified zircon refractory was studied by ambient- and high-temperature X-ray diffraction (HTXRD) to understand the high-temperature performance of brick made from this material. Most of the data were collected on powders at or below 1650°C; however, data were collected between 1400° and 2000°C. In addition, small pieces of the refractory were heated to 1650°C, cooled to room temperature, and then examined under ambient conditions. The degree of dissociation was shown to be dependent on purity, particle size, peak temperature, and time at temperature. The HTXRD dissociation was monitored using the intensity of the tetragonal zirconia peaks. The monoclinic polymorph was measured in the ambient runs. High-temperature mass spectrometry (HTMS) showed that the silica is vaporized at elevated temperatures.