Glass-ceramics are polycrystalline materials of fine microstructure that are produced by the controlled crystallisation (devitrification) of a glass. Numerous silicate based wastes, such as coal combustion ash, slag from steel production, fly ash and filter dusts from waste incinerators, mud from metal hydrometallurgy, different types of sludge as well as glass cullet or mixtures of them have been considered for the production of glass-ceramics. Developments of glass-ceramics from waste using different processing methods are described comprehensively in this review, covering R&D work carried out worldwide in the last 40 years. Properties and applications of the different glass-ceramics produced are discussed. The review reveals that considerable knowledge and expertise has been accumulated on the process of transformation of silicate waste into useful glass-ceramic products. These glass-ceramics are attractive as building materials for usage as construction and architectural components or for other specialised technical applications requiring a combination of suitable thermo-mechanical properties. Previous attempts to commercialise glass-ceramics from waste and to scale-up production for industrial exploitation are also discussed.

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Glass-ceramics: Their production from wastes—A Review

This paper is an overview on the utilisation of solid wastes with focus on blast furnace slag, red mud and fly ash generated in large quantities from iron and steel industry; primary aluminium production and coal fired power plants, respectively. Innovative methodologies, based on the recent research by the authors, are highlighted and these include: (a) smelting reduction of red mud to produce pig iron and titania rich slag, (b) mechanical activation of the slag and fly ash to prepare improved blended cements in terms of higher usage of waste and enhanced cement properties, (c) synergistic usage of fly ash, blast furnace slag and iron ore tailings in the preparation of floor and wall tiles and (d) preparation of synthetic granite from fly ash as a value added product.

http://thaiceramicsociety.com/download/Innovation_methodologiesfor_the_utilisation_waste_from_metallugical_industries.pdf

Innovative methodologies for the utilisation of wastes from metallurgical and allied industries

This paper is a critical overview on fly ash utilisation with emphasis on mechanical activation of fly ash in developing processes for medium to high volume utilisation of fly ash. Applications of mechanical activation that are particularly highlighted include blended cement containing high volume (50–60%) of fly ash, and geopolymer materials, such as high compressive strength (up to 120 MPa) geopolymer cements and self glazed tiles. The schemes for the utilisation of fly ash involving mechanical activation are worked out that have potential to evolve as sustainable solutions.

Towards sustainable solutions for fly ash through mechanical activation

Quartz was progressively replaced by 5, 10 and 15 wt.% fly ash (a byproduct of Indian thermal power plant) in a traditional triaxial porcelain composition consisting of kaolinitic clay, quartz and feldspar. The effects of this substitution upon firing at different temperatures (1150–1300 °C) were investigated by measuring the linear shrinkage, bulk density, porosity and flexural strength. Quantitative estimation of mullite and residual quartz content was done by XRD and microstructures of some selected samples were studied using SEM. The results show that fly ash containing samples achieved higher densities (max. 2.46 g cm −3 ) in the entire temperature range (1150–1300 °C) of firing and matured early than a traditional porcelain composition. The maximum flexural strength (70.5 MPa) was obtained at 1300 °C in the 15 wt.% fly ash containing sample compared with (61.1 MPa) obtained in the traditional porcelain sample. XRD studies reveal higher mullitization in fly ash containing samples. SEM photomicrographs of the polished and etched specimens of 1300 °C heated samples show the presence of quartz grains and secondary mullite needles embedded in feldspathic glassy matrix. Quartz grains (25–50 μm) are associated with circumferential cracks around them.

Effect of substitution of fly ash for quartz in triaxial kaolin–quartz–feldspar system

http://www.thaiceramicsociety.com/download/Synthesis_cordierite.pdf

Synthesis of cordierite powder from talc, diatomite and alumina

The effect of fly ash additions on the mechanical properties of porcelainised stoneware tile composition has been investigated. Fly ash additions in the range of 0–40 wt% have been added in to the tile body composition, wet milled, spray dried, shaped and fired at 1250°C. The MOR strength improved with increasing fly ash content and reached maximum when 25–30 wt% fly ash used, and with greater additions it decreased. A linear correlation between strength development and mullite formation was found. The tiles with 25 wt% fly ash had improved bending strength, abrasion resistance and hardness compared to the conventional tiles and conform to all other properties at an EN standard specification.

Effects of fly ash additions on the mechanical and other properties of porcelainised stoneware tiles

Synthesis of cordierite from fly ash and its refractory properties

In-plane displacement measurement using a photorefractive speckle correlator

We investigate the dynamics of beam fanning in a photorefractive barium titanate crystal at different wavelengths and with a mixed-polarization state of the input beam. The investigations reveal a remarkable difference in the behaviours at different wavelengths. This is further used to advantage for edge enhancement and image intensity inversion processes. Incoherent erasure to control the beam fanning has been exploited to perform some of the logic operations. The simplified geometry, ease of alignment and low input intensities involved are some features of the present work.

K. Singh

Papers

Effects of fly ash additions on the mechanical and other properties of porcelainised stoneware tiles

Synthesis of cordierite from fly ash and its refractory properties

In-plane displacement measurement using a photorefractive speckle correlator

Edge enhancement, contrast reversal and logic operations using beam fanning in a photorefractive iron-doped barium titanate crystal

Performance of a wavelet matched filter with optimized dilation designed using simulated annealing algorithm