DEVELOPMENT OF SLIP CAST ELECTRICAL PORCELAIN BODIES
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
Description
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