the densi cation rate by a factor of 3 (Ref. 8) by increasing the diVusion rate. 9 ,1 0 Brook 1 1 proposed that magnesia T he eVects of varying the alumina/clay ratio and of decreases the rate of grain growth during sintering by additions of 5 wt-% dolomite and/or BaO on the physilowering the surface diVusion coeYcient. On the other hand cal, mechanical, and electrical properties of alumina Moreno et al. 1 2 have shown that MgO additions have no porcelain bodies have been studied. T he results show eVect on Al 2 O 3 grain growth. The introduction of complex that increasing the alumina content at the expense of mineralisers in the form BaCO 3 +ZnO reduces the sintering clay increases the bulk density and improves mechanical temperature without aVecting the main body properties. 1 3 properties. Doping of the bodies decreased the sintering Complex dopants such as TiO 2 +MnO 2 +SiO 2 +MgO temperature and improved electrical properties. (Ref. 14) and BaO+MgO+SrO (Ref. 15) have also been BCT /495 studied. It was found that the bivalent alkaline earth ions render changes in the ux combination and the ring T he authors are in the Department of Ceramics, conditions in each case. Talc has been used as a source of

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compositions of the samples investigated are given in Table 1. ZnO was added as a dopant, in concentrations of 2, 3, Discs of 25 mm dia. and 3 mm thick, 50 mm dia. and and 4 wt-%, to alumina based porcelain batches, in 2 mm thick, as well as bars of 7•0×1•0×1•0 cm were order to study its eVect on the fired materials charfabricated by the semi-dry press method under a load of acteristics. An additional composition containing 30 kN to measure the physical, electrical and mechanical 4 wt-%ZnO and 1 wt-%L iF was also investigated.properties respectively. The samples were dried at 110°C T he results showed that the addition of 4 wt-%ZnO overnight then fired between 1275 and 1450°C at 25°C decreased the maturing temperature and improved the temperature intervals. The physical properties of fired electrical properties. It also promoted the development samples were measured by the classical immersion technique of a mullite phase from the glassy phase. On the other and the results plotted against the corresponding temperhand, the combination of ZnO and L iF had a negative atures (Fig. 1). The semi-quantitative estimation of crystal-eVect on the electrical properties and on the mullite line phases was made by XRD using an internal standard content. T he L i+ ions caused the dissolution of mullite method. Modulus of rupture measurements on sintered crystals and the crystallisation of new phases.samples was carried out according to ASTM C-689-71. The BCT /432 volume resistivity was measured by a wide range megohmmeter apparatus according to ASTM D-257, and dielectric T he authors are in the Department of Ceramics, strength was measured using a portable oil tester, model

Influence of TiO 2 and Ta 2 O 5 on crystallisation for ceramic based on Li-Ca-Al-Si was studied. Sintering of glass-ceramics leads to the formation of β-eucryptite, anorthite and Ca-olivine. These phases are developed only on samples containing TiO 2 and Ta 2 O 5 . Incorporation of either TiO 2 or Ta 2 O 5 gives clear crystals of low pores than in the base sample. Addition of Ta 2 O 5 or TiO 2 improves densification properties and reduces sintering temperature. Electrical measurements were done in audio frequency range and lower (90 Hz-100 kHz). Composition changes on electrical properties were examined. Experimental electrical data show that the response of specimens was not simple (not a linear relation). The increase of TiO 2 and Ta 2 O 5 generally decreases the electrical properties of the ceramic specimens used in this case. Electrical properties were able to follow and interpret the change in composition. This information was correlated to the internal structure of the samples.

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compositions, granite can be used in the range 15-40% for both conventional and fast ring regimes, whilst substituting M ica schist, a rock composed mainly of ne grained feldspars by rhyolite or felsite favours early maturing of the muscovite mica and quartz with orthoclase and microproduct. Also, the latter substitution leads to crystallisation cline feldspars as accessory minerals, was used to of mullite with much ner grains (<1-2 mm) than the use substitute feldspars from pegmatite in tile recipes. T he of granite, where grain size can reach 10 mm. When the rock is easily crushed and ground and contains a high accessory minerals separated from kaolin after bene ciation proportion of silica and potash ( 71 and 6•9% respect-(mainly mica) were used, no proper melt was recorded in ively) . Compositions containing 40% ne powder the mixes, and the presence of feldspar was found to be (<50 mm) were used. T he presence of feldspar and essential for the development of the ceramic bond in the quartz caused dissolution of the mica in the melt and red bodies. 9 Fiori and Fabbri 1 0 showed that additions of inhibited a tendency towards pinholing resulting from the same proportion of granite could be used for the separate melting of the mica grains. T he crystallisation production of red stoneware tiles in rapid ring cycles. of mullite doubled the modulus of rupture. Addition of Rhyolite has also been used to prepare glaze recipes by borate, however, reduced the content of mullite, which Bansagli and Szilagyi. 1 1 in turn decreased the modulus of rupture and caused In an attempt to recycle sludge byproduct in ceramic separate melting of the mica. BCT /547 plants, Ibrahim et al.1 2 studied the addition of 3-10% borate frit, equivalent to 1-2%B 2 O 3 , as a co uxing material Professor Ibrahim