Electrical Porcelain Production From Selected Kaolin Deposit in South Western Nigeria Using Slip Casting

Abstract

The production of Electrical porcelain by slip casting using Ikere-Ekiti Kaolin and clay fro m South Western Nigeria was the focus of this work. Atomic Absorbtion Spectrometric(AAS) analyses of samples of Ikere -Ekit i Kaolin and clay, Ile-Ife clay and Iwo Kaolin was done. AAS analyses showed Iwo Kao lin and Ile -ife clay having lo w alu mina and high impurity contents making them low refractory. Init ial tests confirmed its low refractoriness as Iwo Kao lin could not withstand the bisque firing at 900℃ cracking extensively. Thus Ile-ife clay and Iwo Kaolin were disqualified as candidate materials for electrical porcelain production. Ikere-Ekiti kao lin and clay found to be high in alu mina content and having low impurity contents were used in the experimental production. Results showed Ikere -Ekiti kaolin and clay suitable for porcelain pro- duction. Values of standard refractory tests fell with in standard values for porcelain production. Kaolin is commercial clay co mposed principally of the hydrated aluminosilicate clay mineral kaolinite. The co m- mercial value of kaolin is based on the mineral"s whiteness and fineness, but controllable part icle size wh ich may be optimized during processing. Particle size affects fluid ity, strength, plasticity, colour, abrasiveness and ease of disper- sion. Other important properties include the flat particle shape, which increases opacity and hiding power, its soft and non abrasive texture, due to the absence of coarser impurities, an its chemical inertness. These key properties distinguish kaolin fro m other kaolin itic clays like ball clay and fireclay. The kaolinite content of processed grades of kaolin varies, but is generally in the range of 75% to 94%. Associated minerals may have considerable influence on the suitability of the clay for a particular application. Kao lin fro m different parts of the world have markedly different properties. Kaolin has a chemical formu la of Al2Si2O5(OH)4. It is non - plastic with a Mohr scale hardness of 2 to 2.5. It has a dull and earthy luster and a refractive index o f α 1.553 - 1.565, β 1.559 - 1.569, γ 1.569 - 1.570, with a specific gravity of 2.16 - 2.68. The melting temperature is as h igh as over 1700℃ and it is triclin ic in its crystal system(1). On the other hand, ball clay is an earth material of very fine part icle size which forms as an end result of the the res idu e due to weat hering o r by hyd ro thermal act ion