Thermal conductivity of fired clay of varied mineral composition made from selected Uganda clay types

Abstract

The use of thermal insulators is one of the most important applications in thermal energy conservation systems. This study determined the effect of varying mineral compositions on thermal conductivity. Dry powders of kaolin, ball clay, quartz and feldspar were prepared by ball milling, sieved to particle size of 45μm and then mixed in different proportions to make 100g. For each formulation, three of the four minerals were kept in fixed proportions by mass while varying one. Eighty clay rectangular shapes of dimensions 100mm x 50mm x 20mm were compressed at a pressure of 75MPa and then fired to a maximum temperature of 1200°C. The first formulation had the proportion of Quartz varied while that of other minerals fixed. The second formulation had the proportion of Ball clay varied while that other three fixed. The third formulation had the proportion of feldspar varied while that other three fixed. The forth formulation had the proportion of kaolin varied while that other three fixed. And the fifth formulation had the proportion of all the minerals varied. The Quick thermal conductivity meter was used in the measurement of thermal conductivity at room temperature of approximately 25°C. The study showed that thermal conductivity value increased with increasing proportion of Quartz from 3.305x10-1 to 3.32x10-1 Wm-1K-1. Thermal conductivity values also increased with decreasing proportion of ball clay from 3.225x10-1 to 3.267x10-1Wm-1K- 1. The thermal conductivity value increased with increasing proportion of Feldspar from 3.313x10-1 to 3.274x10-1 Wm-lK-1. The thermal conductivity value increased with decreasing proportion of kaolin from 3.179x10-1 to 3.28x10-1 Wm-lK-1. And when all the mineral proportions was varied, The thermal conductivity value increased with decrease in proportion of kaolin and ball clay in each mixture, and ranged from 3.239x10-1 to 3.288x10-1 Wm-lK-1. From the samples studied, formulation consisting of (Quartz-15%, Ball clay-15%, Feldspar- 15%, and Kaolin-55%) was the best insulating material with thermal conductivity value of 0.3179 Wm-lK-1. The highest thermal conductivity values was due to high proportions of quarts, while the lowest thermal conductivity values was due to high proportions of kaolin. The study recommended further work to be done on thermal conductivity of clays by varying pressure, particle size, firing temperature and the impact of combustible organic wastes on the thermal conductivity.