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glass ceramic

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 ماجد محي شكر المقدادي
10/25/2011 9:08:39 AM
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Abstract Lead silicate glasses with three composition ratio B1, B2, and B3 of ( SiO2, Al2O3, Na2O, K2O, and PbO ) were prepared in this study by conventional melt quenching technique. K2O percentage increases in compositions B2 and B3 to improve physical and electrical properties. Also glass – ceramic of lead silicate with three composition ratio C1, C2, and C3 of ( SiO2, Al2O3, Na2O, K2O, PbO, and TiO2 ) were prepared by conventional melt quenching technique as a first stage, and then converted to glass – ceramic by heat treatments of the parent glass as a first step and render nucleation plus crystallization as a second step. 5 wt.% of TiO2 is used as a nucleation agent in preparing of glass – ceramic. Physical and electrical properties for all prepared specimens were investigated, we have noted increasing of dielectric strength with increasing of sintering temperatures for glass samples, where they have maximum value at 600 °C. Whereas the glass – ceramics samples have a maximum value at C3 composition. Dissipation factor for glass and glass-ceramic samples have been decreased with increasing of K2O content at all sintering temperatures. Dielectric constant ( ??r ) for glass samples at low frequencies has a maximum value at B1 composition and for sintering temperatures of 525 and 550 °C. At high frequencies, it has maximum value at B3 composition and for sintering temperature of 550 °C. Dielectric constant (??r) for glass-ceramic samples at low frequencies has a maximum value at C1 composition, and at high frequencies it has maximum value at C3 composition. 1. Introduction Glass-ceramics are polycrystalline materials formed by the controlled nucleation and crystallization of special formulated glasses[1]. The amorphous glass article is initially formed and then thermally converted via heat treatment to a crystalline material, called a “glass-ceramic.” These glass-ceramic materials go back to their discovery by S.D. Stookey in the 1950 s [2]. Glass-ceramics are an important class of materials that have been commercially quite successful , which is characterized by the lack of porosity and ease of forming [3]. Alkali-lead silicate glasses are an important source of glass ceramics. Such glasses typically contain over 10% lead oxide PbO. Lead glasses containing 20-30% PbO, 54- 58% SiO2 and about 14% alkalis are highly insulating and therefore of great importance in electrical engineering [4]. The glass-ceramic of lead glasses possesses increased impact

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  • Lead glass