Porcelain stoneware tile is a non-equilibrium porcelain material produced by a fast firing process of kaolinitic clay, quartz and feldspar mixtures. This building material, generally used in pavements and also as wall covering and ventilated façades, is endowed with high technological properties such as low water absorption, high bending strength and abrasion resistance and excellent chemical and frost resistance. These properties cause that porcelain stoneware tile was actually the material with the highest increase in production and sales over all other ceramic building material. Nevertheless, there is a scarcity of high quality research focused on the effect of mullite growth on technological properties of porcelain stoneware tile and on the effect of different fluxing agents on both mullite growth and evolution of physical and technological properties during firing. In this paper, the behaviour of a potassic porcelain stoneware body during the firing process is investigated. A porcelain stoneware composition was prepared by mixing 50% kaolinitic clay, 40% feldspar and 10% quartz. The samples were sintered following a fast firing process. The sintering behaviour of the fired samples was evaluated by linear shrinkage, water absorption and porosity measurements. Both green powder and fired samples were characterized by means of differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), dilatometry and bending strength measurements.

Glass-ceramics are ceramic materials produced through controlled crystallisation (nucleation and crystal growth) of a parent glass. The great variety of compositions and the possibility of developing special microstructures with specific technological properties have allowed glassceramic materials to be used in a wide range of applications. One field for which glass-ceramics have been developed over the past two decades is that of glazes for ceramic tiles. Ceramic tiles are the most common building material for floor and wall coverings in Mediterranean countries. Glazed tiles are produced from frits (glasses quenched in water) applied on the surface of green tiles and subjected to a firing process. In the 1990s, there was growing interest in the development of frits that are able to crystallise on firing because of the need for improvement in the mechanical and chemical properties of glazed tiles. This review offers an extensive evaluation of the research carried out on glass-ceramic glazes used for covering and pavement ceramic tile is accomplished. The main crystalline phases (silicates and oxides) developed in glass-ceramic glazes have been considered. In addition, a section focused on glazes with specific functionality (photocatalytic, antibacterial and antifungal activity, or aesthetic superficial effects) is also included.

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Microstructural evolution on heating was investigated in a reference industrial composition (50% kaolinitic clay, 40% feldspar and 10% quartz) of porcelain stoneware, fast fired at different temperatures (500-1400 °C). The evolution of mullite crystals, regarding shape and size progress, was examined by scanning electron microscopy (SEM). The proportion of Type I mullite crystals decreases with firing temperature and simultaneously, the size of crystals increases, reaching the maximum value of aspect ratio (3:1) at 1400 °C. Type II and Type III secondary mullite needles increase with temperature in both number and length, which leads to an increase in the aspect ratio from 5:1 to ∼20:1 in Type II crystals and from ∼33:1 to 50:1 in Type III mullite needles. Finally, clusters of Type III mullite fibres are observed in porcelain stoneware samples fast fired in the 1250-1280 °C interval.

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of fibreglass polyester composite and reutilisation of the glass fibre residue to obtain a glass-ceramic material.

This paper reports the results of a study of the feasibility of recycling the solid residues from domiciliary waste incineration by producing a glass-ceramic. The major components of the raw material (TIRME F+L), which was from a Spanish domiciliary incinerator, were CaO, SiO 2 and Al 2 O 3 but nucleating agents, such as TiO 2 , P 2 O 5 , and Fe 2 O 3 were also present in reasonable amounts. It was found that a relatively stable glass with suitable viscosity could be obtained by mixing 65 wt% TIRME F+L with 35 wt% glass cullet. The heat treatment required to crystallise the glass produced from this mixture, designated TIR65, was nucleation at 560°C for 35 min followed by crystal growth at 100°C for 120 min. The resulting glass-ceramic contained a number of crystalline phases, the most stable being clinoenstatite (MgSiO 3), or perhaps a pyroxenic phase which incorporates Ca, Mg and Al in its composition, and åkermanite (Ca 2 MgSi 2 O 7). The microstructure contained both fibre-like and dendritic crystals. The mechanical properties were acceptable for applications such as tiles for the building industry.