Ultrasonic characterization of Kenyan clay Refractories

Abstract

Characterization of cerami.c materials is important in order to improve their quality. In this study uLtrason io nondestructive technique has been used to characterize some Kenyan clay refractories. Ultrasonic: parameters used for characterization were velocity and frequency dependent attenuation measurements. It was found that the ultrasonic parameters are influenced by the material fabrication conditions. The measured ultrasonic velocity in the clay refractories was found to mcrease as the firing temperature and/or the compaction (loading) pressure were increased. Meanwhile the ultrasonic attenuation decreased with increase in the firing temperature and/or the compaction pressure. Further, clay refractories fabricated from different types of clay, (red firing' clay -RFC and red hill clay -RHC) gave different velocity and attenuation values. Ultrasonic velocity in refractories fabricated from the clays with a 'finer' particle Slze distribution (WC) was higher' than that in refractories fabricated from clays with a coarser particle size distribution (RHC). The nateri.e.Iproperties such as linear drying shrinkage -%LDSf and were also found to increase with bulk density and shrinkage (both linear firing shr-inkage -%LFSd) increasing firing temperature or loading pressure. Further, high shrinkage values were noted in samples with a 'finer' particle size distribution (RFC). X-ray diffraction (XRD) and chemical (rational) analysis showed that the proportions of most of the major clay minerals (such as quartz, mica and feldspar) increased as firing temperature was increased. The proportion of kaolinite however dropped with temperature.