T. Asokan et Ts. Sudarshan, DEPENDENCE OF THE SURFACE FLASHOVER PROPERTIES OF ALUMINA ON POLISHING ABRASIVE PARAMETERS, IEEE transactions on electrical insulation, 28(4), 1993, pp. 535-544
Systematic investigations have been made to understand the relationshi
p between the surface finish, the polishing medium, and surface flasho
ver properties of high purity polycrystalline alumina ceramics. The su
rface of as-machined specimens were subjected to mechanical polishing
by using 60 grit (268 mum) to 600 grit (16 mum) SiC abrasive discs and
diamond abrasives of 15 to 0.25 mum. The samples polished with the Si
C abrasives displayed a linear behavior, with the breakdown strength i
ncreasing, with decreasing surface roughness. The breakdown properties
of the diamond polished samples were found to be influenced significa
ntly by the polishing sequence adopted. The samples subjected to conve
ntional forward sequence polishing (i.e., polishing from coarser to fi
ner finish) were found to exhibit erratic surface breakdown properties
. Contrarily, the breakdown properties of the samples subjected to a n
ew reverse sequence polishing (i.e., polishing from finer to coarser f
inish) were found to vary linearly with respect to the particle size o
f the abrasive used in the final polishing. The breakdown strength of
these samples were found to increase linearly with decreasing particle
size to approximately 9 mum finish and decrease linearly below 9 mum
finish. The observed results are discussed in terms of surface and sub
surface defects that are formed during diamond polishing. The breakdow
n properties of the samples in relation to the abrasive type are also
analyzed. The magnitude of the luminosity in the case of SiC polished
samples was found to be higher than the diamond polished samples. Cont
rarily, the samples displayed an opposite trend in relation to the bre
akdown current magnitude.