100 research outputs found
alpha-Cristobalite formation in ceramic tile and sewage pipe bodies derived from Westerwald ball clay and its effect on elastic-properties
The formation of α-cristobalite and its effect on the elastic modulus (E modulus) was investigated in sewage pipe
(SP) and tile bodies derived from Westerwald ball clay (WBC), employing the results of previous research on
WBC as a baseline. In this study, the SP and tile bodies derived from WBC are compared with the bodies derived
from two residual Turkish kaolin and one Turkish ball clay, resulting in four sources of α-cristobalite formation:
tile, SP, residual kaolin and ball clay. The crystallization of α-cristobalite in the fired WBC results from two
primary pathways. The first pathway occurs as a devitrification product from the glass phase saturated with
excess silica, which is typically present in ball clay after â„1100 °C; the second pathway results from a minor
amount of transformation of peripheries of quartz crystals, firing at over â„1200°. In addition to these two
sources, other α-cristobalite sources for sewage-pipe bodies include smectitic clay and chamotte (prefired clay)
addition. Conversely, no α-cristobalite occurred in tile mixture bodies containing â2 wt% potassium oxide
(K 2O). The α-cristobalite phase only forms in kaolinite-rich ball clay when K 2O content is less than â2 wt%
because devitrification of excess silica phase of tile bodies is primarily governed by K 2O content. The â2 wt%
K 2 O ratio inhibited α-cristobalite formation in tile bodies, while the same percentage or greater of K 2O content in
SP bodies did not inhibit the α-cristobalite formation due to the presence of chamotte and smectitic clay in the SP
mixture. The measured minimum E moduli were attributed to cristobalite formations because of chamotte and
smectitic clay additions to SP bodies. In the bodies derived from Turkish residual kaolin at over 1000 °C, the
opaline and chalcedonic silica phase are transformed to α-cristobalite at a lower temperature than those ob-
served for rock crystal quartz and Si-rich glassy phase in WBC bodies. Thus, determining the different α-cris-
tobalite sources in clay-based ceramic bodies derived from either the ball clay, the residual kaolin or the bodies
containing smectitic clay together with chamotte provides the essential pre-condition for the optimum admixing
ratio in industrial SP and tile bodies
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