The effect of temper on the thermal conductivity of traditional ceramics: Nature, percentage and granulometry

Traditional ceramics were commonly produced using a mixture of clay and temper materials, which were added in different percentage according to the craftsman purposes. The present study aims to examine up to which extent some technological parameters (nature, granulometry and percentage of the temper and firing temperature) affect the thermal conductivity of traditional ceramics. With this purpose a kaolinitic clay was tempered either with quartz or limestone belonging to two different granulometric distributions in percentage of 5%, 15% and 25%, and fired at 500, 750 and 1000 °C. Moreover the dependence on firing temperature was studied. Thermal conductivity was measured with a modified Lee's disks apparatus in a temperature range from 120 to 370 °C. It was found that quartz-tempered ceramics are more conductive than the fired non-tempered clay, while limestone-tempered sample are less conductive. Mineralogical and microstructural data are also provided and the influence of the α–β quartz-phase transition on the thermal conductivity of ceramics is discussed