DEVELOPMENT OF SLIP CAST ELECTRICAL PORCELAIN BODIES

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Date
1987-01
Authors
Henry, Ehibhanre Okojie
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Abstract
Electrical porcelains are glazed or unglazed vitreous ceramic whitewares used for electrical insulation. These materials which are widely used in the country as insulators in electrical power transmission and as insulator components in a number of electrical and electronic devices are currently being imported. The main raw materials for the manufacture of electrical porcelains are clays, feldspar and quartz and despite the availability of fuel and large deposits of these materials in the country, the porcelains are not being produced locally. The aim of this work was to investigate the optimal processing conditions and suitable body compositions for the production of electrical porcelains from local raw materials. Kankara clay, Bukuru clay, Okene feldspar and Amper quartz were selected as the major raw materials. The mineralogical compositions of the materials were investigated by X-ray diffraction technique to ascertain their suitability for body formulation. The rheological properties of the clays and porcelain body slips were studied as a .function of deflocculants content to determine the appropriate amounts required in casting slip. Various bodies were formulated, wet ball milled, slip cast, dried and fired. The important green and fired properties of the casts were studied to determine their suitability for various applications. The apparent viscosity of Kankara clay slip increased from 21.30 to 36.50 poises as the sodium carbonate concentration was increased from 0.001 to 0.005 percent. The unusual increase in apparent viscosity was attributed to a reduction of the electrical potential at the clay surfaces due to the presence of excess sodium ions in the medium resulting from the hydrolysis of sodium carbonate. This reduction enhanced the aggregation of clay particles by the universal van der Waals forces and the development of inter-aggregate links between the floes. Only silicate ions of the two deflocculants, sodium carbonate and sodium silicate, appeared to have the greatest effect in deflocculating Kankara clay, Bukuru clay and Kankara clay-based porcelain body slips. The porcelain body slip exhibited considerable thixotropy as the sodium silicate concentration was increased from 0.017 to 0.052 percent. However, it was destroyed when the deflocculant concentration exceeded 0.061 percent. The green and fired modulus of rupture increased with the clay content, and for a given clay content, the strength increased as the quartz content was increased from 20 to 25 percent and then decreased as the percentage of quartz was further increased to 30 percent. The dry-to-fired shrinkage for all the bodies studied was about 12.5 percent while the differential shrinkage between diameter and length was about 1.25. The latter value indicated that the clay particles were preferentially aligned during the casting process. The porosity and water absorption values for the high feldspar body C, and high clay bodies E and F were less than 1 percent which is well within the range of industrial vitrification. However, the values of these properties for the high quartz bodies, B and G were higher than 2 percent. Microscopic'studies of thin sections of fired specimens showed that a significant proportion of quartz remained undissolved in the glass matrix. Some of the residual quartz showed extensive fracturing. Comparisons of the properties of the porcelains developed with standard specifications for low and high voltage porcelain insulators clearly indicated that Bodies A, C, D and E are suitable for low voltage applications while Body F is suitable for both low and high voltage insulation
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A THESIS Presented to The Postgraduate School Ahmadu Bello University, Zaria In Partial Fulfilment of the Requirements for the Award of the Degree Master of Science (Physics) with Specialization in Solid State Physics. Department of Physics Faculty of Science Ahmadu Bello University Zaria - NIGERIA JANUARY - 1987
Keywords
DEVELOPMENT OF SLIP,, CAST ELECTRICAL,, PORCELAIN BODIES
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