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 glass–ceramic 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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Glass–ceramic glazes for ceramic tiles: a review

State of the art on the development of cool coatings for buildings and cities

Porcelain tile: Almost 30 years of steady scientific-technological evolution

Thermal conductivity of traditional ceramics. Part I: Influence of bulk density and firing temperature

In water treatment applications, the use of ceramic membranes is associated with numerous advantages relative to polymer-based filtration systems. High-temperature stability, fouling resistance, and low maintenance requirements contribute to lower lifecycle costs in such systems. However, the high production costs of most commercially available ceramic membranes, stemming from raw materials and processing, are uneconomical for such systems in most water treatment applications. For this reason, there is a growing demand for new ceramic membranes based on low-cost raw materials and processes. The use of unrefined mineral feedstocks, clays, cement, sands, and ash as the basis for the fabrication of ceramic membranes offers a promising pathway towards the obtainment of effective filtration systems that can be economically implemented in large volumes. The design of effective ceramic filtration membranes based on low-cost raw materials and energy-efficient processes requires a balance of pore structure, mass flow, and robustness, all of which are highly dependent on the composition of materials used, the inclusion of various pore-forming and binding additives, and the thermal treatments to which membranes are subjected. In this review, we present recent developments in materials and processes for the fabrication of low-cost membranes from unrefined raw materials, including clays, zeolites, apatite, waste products, including fly ash and rice husk ash, and cement. We examine multiple aspects of materials design and address the challenges relating to their further development.

Materials and Applications for Low-Cost Ceramic Membranes.

Obtaining low-cost ceramic membranes has attracted great interest in the scientific community in last years, as it allows to preserve the advantages of ceramic materials while significantly reduce their manufacturing costs. This type of membranes is mainly based on the use of raw materials and manufacturing processes typical of traditional ceramic materials, i.e silicate-based ceramics. This work exhaustively reviews the raw materials, ceramic compositions and variables of the manufacturing processes used in the development of these membranes, with special emphasis on their numerous potential industrial applications.

Low-cost ceramic membranes: A research opportunity for industrial application

Porcelain tile is a product characterised by low water absorption (usually less than 0.1%) and excellent mechanical properties. To enhance tile aesthetic qualities, much of the porcelain tile production is polished to provide a high-gloss surface finish, in which certain closed pores in the tile body become visible. This apparent porosity of the polished tile, which had been closed porosity before polishing, sometimes lowers the product's stain resistance. Test pieces were formed from a porcelain tile composition prepared under different milling conditions, pressing variables being kept constant, and the pore size distribution of these pieces was determined. The effect of the porous texture of the green pieces on the evolution of porosity during sintering and on the residual porosity of the densified body was analysed. It was verified that the porous texture of the fired piece was conditioned by the porosity and size of the largest pores in the green piece. The effect of residual porosity on stain resistance was determined by two cleaning methods. The presence of large pores in the green body, stemming from insufficient milling of the raw materials mixture, led to tiles with greater residual porosity and worse stain resistance.

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

Effect of the green porous texture on porcelain tile properties

A significant contribution to the reduction of the Urban Heat Island effect and cooling energy demand is given today by the so called cool materials for the building envelope with enhanced reflecting and emitting properties. The present study shows some preliminary results of the EU project COOL-Coverings aiming at developing innovative nanobased coatings with improved Near InfraRed reflecting capabilities. The key idea is to work on a nanoscale by tuning the crystal size and distribution of selected nanostructured oxides. Cool prototypes of brown colored ceramic tiles and green acrylic paints have been developed and compared to conventional ones showing an improvement in solar reflectance without any perceptual difference in color. The material characterization has been based on the measurement of spectral reflectance on a wide wavelength range (300–2200 nm) using a UV/Vis/NIR spectrophotometer. In parallel with the development of nanostructured cool materials, natural aging tests on ceramic and painted concrete tiles have been performed with the goal of identifying and measuring the effects of the main aging factors affecting reflective properties. A significant drop of solar reflectance for paints has been noticed from the very beginning of the testing period while ceramic tiles have confirmed excellent resistance to weathering. However, both for paints and tiles the effect of soiling cannot be neglected and, if combined to weathering, it can lead to a solar reflectance reduction as high as 10%. This preliminary study will pave the way to a future development of dedicated accelerated aging testing procedures for cool materials.

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Nanobased coatings with improved NIR reflecting properties for building envelope materials: Development and natural aging effect measurement

Opaque ceramic tile glazes can be obtained by using a type of frit based on the system SiO 2 -Al 2 O 3 -B 2 O 3 -CaO-K 2 O-TiO 2 . In these glazes, opacification and whiteness are due to the presence of titanite (sphene) crystals, formed by devitrification during firing from the frit applied in the form of a glaze composition onto the ceramic body. Though not widely used in tile manufacture, this type of frit is considered an alternative to the zirconium-containing frits currently used for fabricating opaque ceramic glazes. The present study shows that the addition of small quantities (around 1%, w/w) of P 2 O 5 to a frit composition of the above oxide system considerably modifies resulting glaze gloss, converting a matt glaze into a glossy glaze. In order to determine how the P 2 O 5 addition contributes to increasing gloss in opaque white wall tile glazes, we determined the arising changes in glaze melt viscosity and glaze microstructure, establishing the latter by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the presence of P 2 O 5 inhibits wollastonite devitrification in the glaze melt and gives rise to changes in sphene crystal morphology, modifying glaze microstructure.

A. Gozalbo

Papers

Low-cost ceramic membranes: A research opportunity for industrial application

Effect of the green porous texture on porcelain tile properties

Nanobased coatings with improved NIR reflecting properties for building envelope materials: Development and natural aging effect measurement

Microstructural study of opaque glazes obtained from frits of the system: SiO2-Al2O3-B2O3-(P2O5)-CaO-K2O-TiO2

Kinetic model for the isothermal sintering of low porosity floor tiles