Influence of Rate of Temperature Rise during Firing process on Compressive Strength of Mukono Ntawo Ball Clay

Abstract

This study was focused on the effect of varying the rate of temperature rise during firing process on the compressive strength of ball clay slab from Ntawo clay deposit from Mukono District, in central Uganda. The rectangular clay slabs of dimensions of 16cm by 4cm by 1cm were produced of clay particles of 45μm size. They were dried under open shade and fired at varied rate of temperature rise of 2 0 C min -1 ,3 0 C min -1 ,4 0 C min -1 ,5 0 C min -1 and 6 0 C min -1 to firing temperatures of 500 0 C, 600 0 C, 700 0 C. 800 0 C, 900 0 C and 100 0 C and held at the temperatures for one hour. The fired slabs were then cooled to room temperature in the electric furnace. The chemical composition by percentage weight of the unfired clay sample was determined by x-ray diffraction using RIX 3000 spectrometer. The compressive force of the samples were measured using 500SN-1299417 compressive machine. It was observed that Ntawo ball clay to contained 67.20% of silica, 18.20% of alumina,2.83% of iron oxide,1.38% of titanium, 0.06% of phosphorous penta-oxide, 0.31% of calcium oxide, 0.98% of potassium oxide and 0.19% of sodium oxide. The compressive strength of the samples decreased with increase in the rate of temperature rise. The null hypothesis that the compressive strength of the fired samples did not depend on the rate of temperature rise during the firing process was rejected at α=0.05 and α=0.01 levels of significance. The decrease of compressive strength with increase of the rate of temperature rise between 2 0 C min -1 to 3 0 C min -1 was negligible for all the firing temperatures. The percentage decrease f compressive strength with the rate f temperature rise was appreciable for firing temperatures 0f 500 0 C and 1000 0 C of 11%.