M. Romero

Glass-ceramic glazes for ceramic tiles - a review

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.

Use of vitrified urban incinerator waste as raw material for production of sintered glass-ceramics

Abstract The crystallization behavior of vitrified industrial waste (fly ash from domiciliary solid waste incineration) was examined by differential thermal analysis, X-ray diffractometry and scanning electron microscopy. It was demonstrated that powder processing route was required to transform the vitrified industrial waste into glass-ceramics products. Time-Temperature-Transformation (TTT) diagrams were drawn for the two main crystalline phases, diopside and wollastonite. The wollastonite existed in both monoclinic and triclinic forms and an iron-rich phase was also observed at the boundaries between glass particles. The morphology of the crystalline phases and the development of microstructure were observed as a function of heat treatment time and temperature. The optimum heat treatment was 900°C for 40–50 minutes.

Effect of iron oxide content on the crystallisation of a diopside glass–ceramic glaze

Abstract The effect of iron oxide content on the crystallisation of a diopside glass–ceramic glaze was investigated using a glass–ceramic frit in the K 2 O–ZnO–MgO–CaO–Al 2 O 3 –SiO 2 system and a granite waste glass. Measurements by X-ray diffraction (XRD) combined with scanning electron microscopy (SEM) and EDX microanalysis showed that the distribution of Fe 3+ ions among different crystalline phases such as franklinite (ZnFe 2 O 4 ) and hematite Fe 2 O 3 depends on the iron content in the original diopside mixture. Thus, the original glaze crystallises to franklinite or hematatite when iron content is greater than 2 and 15%, respectively.

Preparation and properties of high iron oxide content glasses obtained from industrial wastes

The formulation and preparation of new glasses has been carried out by the recycling of goethite (FeOOH) industrial wastes originating from zinc hydrometallurgy with glass cullet and dolomite as complementary raw materials. The mineralogic (XRD) and microstructural (SEM, TEM) characterization of the product has been determined and the thermal, mechanical and chemical properties of original glasses have been measured. The results indicate that glass production is an effective recycling method for this kind of waste, yielding black stable glasses with good mechanical and chemical properties.

Utilisation of IGCC slag and clay steriles in soft mud bricks (by pressing) for use in building bricks manufacturing.

The subject of this study is the application to the construction of soft mud bricks (also known as pressed bricks), both green and heat-treated bodies, built from raw materials from Santa Cruz de Mudela, Ciudad Real, and IGCC slag from the power central of Puertollano (Ciudad Real, Spain). For this purpose, industrial level tests have been performed: the production of these kind of bricks from mixes of waste from ores of construction clays and to significant fraction of different ratios and clay granulometries mixed with IGCC slag. The results of this experimentation suggests that not only can IGCC slag be applied to a ceramic process, but also its use gives several advantages, as water and energy savings, as well as improvements on the final properties of products.

Some aspects of crystallization microstructure on new glass-ceramic glazes

The nucleation and crystallization of thin layers of glasses (glazes) over ceramic substrates during the fast firing of tiles for pavements and wall tiles has been a topic of great interest for tile and ceramic paving industries in recent years. Here a wide range of glass-ceramic compositions having different types of crystallization microstructure has been investigated. Based on observations by scanning electron microscopy and energy-dispersive X-ray microanalysis, several aspects of nucleation and crystallization of these new types of glass-ceramic glazes are presented and discussed.

Crystallisation of a zirconium-based glaze for ceramic tile coatings

Abstract The effect of iron oxide content on the crystallisation of a zirconium-based glass-ceramic glaze was investigated using a glass-ceramic “white of zirconium” frit and a granite waste glass. Measurements by X-ray diffraction (XRD) combined with scanning electron microscopy (SEM) and EDX microanalysis showed that Fe 2 O 3 gives rise to the crystallisation of an iron-zinc ferrite, which is acting as nucleating agent of feather-like crystals of pyroxene while granite frit enhances the partial dissolution of zircon into the glassy phase, which is sharply increased for granite frit additions greater than 50%.

Physico-chemical characterization of slag waste coming from GICC thermal power plant

The new gas installations of combined cycle (GICC) thermal power plants for production of electricity are more efficient than conventional thermal power plants, but they produce a high quantity of wastes in the form of slags and fly ashes. Nowadays, these by-products are stored within the production plants with, until now, no applications of recycling in other industrial processes. In order to evaluate the capability of these products for recycling in glass and ceramics inductory, an investigation for the full characterization has been made by usual physico-chemical methods such as: chemical analysis, mineralogical analysis by XRD, granulometry, BET, DTA/TG, heating microscopy and SEM/EDX.

Effect of particle size on kinetics crystallization of an iron-rich glass

The effect of glass particle size on the crystallization kinetics of an iron-rich glass from a nickel leaching waste has been investigated by means of differential thermal analysis (DTA). The results show that the crystallization of a pyroxene phase occurs by bulk nucleation from a constant number of nuclei. The crystallization mode and the dimensionality of crystals are strongly dependent on the glass particle size, 100 μm being the critical size. Glass fractions with particle size >100 μm show three-dimensional crystal growth controlled by diffusion, whereas a particle size <100 μm leads to an interface reaction mechanism with two-dimensional growth of crystals.

Microstructural characterization of a goethite waste from zinc hydrometallurgical process

Abstract The different hydrometallurgical processes for the metallic zinc recovery produce a high quantity of wastes in the form of muds that at the moment are stored within the production plants in large clamps without until now may have been found an effective way for their recycling. A possible solution for these wastes would be the utilization of the vitrification and glass ceramic materials technology. Because of this, the characterization of a goethite waste has been accomplished. The results of the granulometric analysis, chemical, mineralogie, microstructural characterization and thermal analysis demonstrate that the goethite waste, mixed with other raw materials can be used in the formulation and production of glasses and glass ceramics.