Use of scrap glass as raw material for porcelain stoneware tiles

Abstract

The possibility of recycling scrap glass (soda lime, lead and barium based glasses) by incorporation into a porcelain stoneware tile mix has been examined. Starting from a standard porcelain stoneware body mix, several modified mixes were prepared by replacing different amounts of the fluxing component, a sodium feldspathic sand, with three types of scrap glass: a soda lime glass from urban wastes, a lead based glass from the neck part of cathode ray tubes (CRTs), and a barium based glass from CRT panels. The replacement of feldspar sand with a soda lime scrap glass, in the range 5-10 wt-%, allows porcelain stoneware materials to be obtained with good characteristics. A slight decrease in the water absorption of the fired material is observed after sintering at the same temperature as the reference mix. Furthermore, flexural strength remains high and the microstructural homogeneity enhances reliability. The presence of 2 and 5 wt-%, of lead and barium based scrap glass respectively, both characterised by lower liquid viscosity at higher temperature, makes possible a significant decrease in the sintering temperature of the modified porcelain stoneware products while maintaining good mechanical properties.

Evolution with Temperature of Crystalline and Amorphous Phases in Porcelain Stoneware

“…On the other hand, the Rietveld method 10 is currently the most useful tool to obtain direct quantitative phase analysis (QPA) of complex materials. Inherent advantages of this methodology have increased its application to mineralogical characterization of porcelains, 11–15 porcelain stoneware materials, 16–20 or other industrial materials such as cements 21–22 . This methodology involves no standards, but the crystal structures of every crystalline phase in the sample must be known, as the process consists of the comparison between the measured and calculated powder diffraction patterns.…”

Recycle of Waste Glass into “Glass–Ceramic Stoneware”

“…The most interesting products of this type are ceramic tiles. Many experiences, reported in the literature, refer to the use of glass, derived from waste materials or recycled, as a sintering aid 7–10 . In practice, the glass acts as a fluxing agent, providing a viscous liquid mass upon sintering, in addition to that provided by traditional feldspar fluxes.…”

Tailored waste based glasses as secondary raw materials for porcelain stoneware

“…[4][5][6] Glass cullet is one of the most widely recycled forms of waste, employed, in porcelain stoneware tile formulations, as a partial substitution for feldspar flux. 7,8 Some waste glasses are scarcely employed as recycled raw materials in the glass industry, due to risks of contamination and overall decay of qualitative standards. Typical examples are the glasses from dismantled cathode ray tubes (CRTs), constituted by Ba based glasses (two-thirds of the total glass mass, corresponding to the screen or 'panel' part) and Pb based glasses (one-third of the total glass mass, corresponding to the internal part of TV sets).…”

“…7,16 In the specific field of traditional ceramics, to preserve the mechanical and technical performances of porcelain stoneware tiles, the percentages of recycled CRT glass can not exceed 5 wt-%. 8 This percentage can increase, when soda lime scrap glass (SLS) is employed (up to 10 wt-%). 8,17 A second type of glass, which can be used as additive for traditional ceramics, is the 'waste glass', developed by melting several inorganic waste materials.…”

“…8 This percentage can increase, when soda lime scrap glass (SLS) is employed (up to 10 wt-%). 8,17 A second type of glass, which can be used as additive for traditional ceramics, is the 'waste glass', developed by melting several inorganic waste materials. The main scope of this kind of preparation is the sealing of several pollutants in glassy materials, with a high chemical stability.…”