Effect of Quebracho Bark on the Properties of Opaque Glazes
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Date
2018
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Abstract
In this work, the effect ofquebracho bark (QB) on the physical and chemical properties of opaqueglaze/glazes (OG) was investigated. Various ratios (0.25-10 weight percent) of quebracho bark wereincorporated into the glazes to obtain experimental glaze recipes and meltingtemperatures of the glaze compositions were calculated through the fluxingfactors of the oxides present in the glazes. Thereafter, the glaze compositionswere fired at the calculated temperature value of 1100°C. Viscosity, thixotropyand pH tests were conducted on OG and OG+QB glaze suspensions. Standard coloringanalyses, crazing resistance, impact resistance, resistance to acid andalkalis, water absorption, firing strength, and surface hardness tests wereconducted. After establishing the Seger formulas, surface tensions of theglazes were calculated by making use of the molar surface tension factors ofthe oxides already present in the glaze compositions at the same sinteringtemperature of 1100°C. QB additions decreased the viscosity and standardthixotropy values of the OG and had no significant effect on the pH of the OGslurry. On the other hand, QB additions caused an increase in the whiteness (opacity)of the OG. No crazing and impact fractures were observed on the glaze surfaces.Furthermore, the glaze surfaces showed good resistance to acid and alkalis. OnQB incorporation, water absorption decreased in all the experimental glazes.Firing strength and surface hardness increased with increasing QB content.According to the experimental results, 5 weight percent (wt. %) QB addition wasfound to be the optimum amount.