4

In Brazil, the second largest tile producer of the world, at present, 70% of the tiles are produced by the dry route. One of the main reasons that lead to this development is the fact that the dry route uses approximately 30% less thermal energy them the traditional wet route. The increasing world concern with the environment and the recognition of the central role played by the water also has pointed towards privileging dry processes. In this context the objective of the present work is to study the feasibility of producing high quality porcelain tiles by the dry route. A brief comparison of the dry and wet route, in standard conditions industrially used today to produce tiles that are not porcelain tiles, shows that there are two major differences: the particle sizes obtained by the wet route are usually considerably finer and the capability of mixing the different minerals, the intimacy of the mixture, is also usually better in the wet route. The present work studied the relative importance of these differences and looked for raw materials and operational conditions that would result in better performance and glazed porcelain tiles of good quality.

This paper considers recent and current potential developments in the international standardisation of slip resistance. It identifies some limitations of the wet barefoot ramp test, such that changes should be made if it is to be more widely used. It also identifies some limitations of the new European SlipSTD Publicly Available Specification, such as insufficient allowance for the deterioration of slip resistance as tiles inevitably wear.

The low porosity of porcelain tile is the result of strict control of the material’s processing conditions (milling of raw materials, compaction and sintering) and the characteristics of the raw materials used in its formulation (formation of liquid phases). Sealed pores remaining after the manufacturing process are revealed at the surface after polishing and are the main factor responsible for staining the product. The porous microstructure of the sintered material depends on the characteristics of the porous microstructure of the green compact and on how the densification process evolves during sintering. The present work evaluated how the size distribution of spray-dried granules acts upon the porous microstructure of green compacts and of polished porcelain tile. The results revealed that minor adjustments in the granulometric distribution curve can reduce the visibility of stains on the polished surface, thus improving this property.

The present work investigates the possibility of adopting a new kinematics at the industrial polishing lines of porcelain stoneware tile. An alternative motion of the transverse oscillation of the polishing heads is proposed, in which no radical changes in the industries facilities are required. The basic idea is to replace the purely sinus motion of the polishing heads by a rather trapezoid wavelike motion. In theory this could be achieved simply by adopting regular delays at the transverse oscillation motion. Consequences of this alternative kinematics were quantitatively analyzed considering the spatial homogeneity of polishing expected for tiles. Such homogeneity was represented by the coefficient of variation of the distribution of polishing time over the surface, which was in turn determined by means of computational simulations, taking into account the effect of multiple polishing heads.

The aim of the present work is to realise ceramic tiles with superior surface mechanical characteristics and chemical resistance, by the addition of nano-oxides, such as zirconia and alumina, since such advanced ceramics oxides are well known for their excellent mechanical properties and good resistance to chemical etching. In order to avoid any dangerousness, the nanoparticles were used in form of aqueous suspension and they were sprayed, by airbrush, directly onto the dried ceramic support, before firing.
To observe the distribution of the nanoparticles and to optimise the surface treatment, SEM-EDS analyses were carried out on the fired samples. XRD analysis was conducted to assess the phases evolution of the different materials during the firing step.
The surface mechanical characteristics of the samples have been evaluated by Vickers’ hardness and scratch test. In addition, also chemical resistance tests were performed.
Microstructural observations allowed to understand how alumina and zirconia nanoparticles acted to improve the surface performances of the modified ceramic tiles.

Hydrothermal oxidation (OVH: “Oxydation par Voie Humide”) is an innovative technology used for waste water treatment, which is presented as an alternative to sewage sludge spreading and incineration. This process generates a fine-grain (D50 = 2 µm) mineral by-product, which is very useful for the ceramics industry due to its high content in argillaceous elements, quartz, phosphate and calcium carbonate.
Therefore, this work describes the recycling of this OVH residue in the ceramics industry, and more particularly in the manufacture of calcareous earthenware wall tiles.
The residue can be combined with a white calcareous earthenware body up to a level of 7% without significant colorimetric deterioration, and if this is raised to 15%, it is possible to completely replace the crushed chalk, some of the quartz and reduce costly imported tight-burning clays by 6%. The developed body exceeds standardised requirements (modulus of rupture: + 40%; moisture swelling and glaze quality), which means that a 20°C reduction in firing temperature might be envisaged.
An industrial pilot test of 1500 kg conducted by the DESVRES site managers with 100 m2 of tiles (format: 15 x 20 cm) confirmed these laboratory results, in particular validating the absence of rheological disturbance of the slip and the harmlessness of the addition on the maturing glaze quality. Furthermore, the nature of the fumes emitted in the test complied with current regulations, and the finished product did not exceed the thresholds defined by European regulations for inert waste classification.

A sodium salt of a modified lignosulfonate at different percentages was added to a porcelain stoneware suspension and the effects on the rheological properties of slips and on the mechanical properties of prepared samples were investigated. As the presence of sulfonates groups can change the stability of dispersion, a rheological characterisation was necessary to find the critical concentration to obtain well dispersed suspensions and high MOR values. The suspensions stability was tested by oscillatory measurements and the increase of elastic modulus in the suspension corresponded to a MOR and to Young’s modulus increase as well. Finally, to explain the results obtained by the mechanical characterisation of the prepared samples, a model drawing on the composite materials experience, is suggested.

Aluminium oxide is a synthetic raw material manufactured from bauxite by the Bayer process, whose Al2O3 content typically exceeds 99%. Four main types of alumina can be defined, depending on the processing used: hydrargillite Al(OH)3, boehmite AlOOH, transition aluminas (calcined at low temperatures, 1000 °C, with an intermediary crystallographic structure between hydrates and alpha alumina), and a-Al2O3 (calcined at high temperatures, >1100 °C). In glaze manufacturing, a-Al2O3 is the main type of alumina used. This raw material acts as a matting agent: the matt effect depends on alumina particle size and content in the glaze. This study examines the effect of the degree of alumina calcination on glaze technical and aesthetic properties. For this purpose, aluminas with different degrees of calcination were added to a glaze formulated with a transparent frit and kaolin, in order to simplify the system to be studied. The results show that, depending on the degree of calcination, alumina particles can react with the glaze components (SiO2, CaO, and ZnO) to form new crystalline phases (anorthite and gahnite). Both crystallisations extract CaO and ZnO from the glassy phase, increasing glassy phase viscosity. The variation in crystalline phases and glassy phase viscosity yields glazes with different technical and aesthetic properties.

An apparatus for X-Ray non destructive inspection of bulk density distribution in large ceramic tiles has been designed, built and patented. This technique has many advantages compared with other methods: it allows tile bulk density distribution to be mapped and is neither destructive nor toxic, provided the X-ray tube and detector area are shielded to prevent leakage.
In the present study, this technique, whose technical feasibility and accuracy had been verified in previous studies, has been used to scan ceramic tiles formed under different industrial conditions, modifying press working parameters. The use of high-precision laser telemeters allows tile thicknesses to be mapped, facilitating the interpretation of manufacturing defects produced in pressing, which cannot be interpreted by just measuring bulk density. The bulk density distributions obtained in the same unfired and fired tiles are also compared, a possibility afforded only by this measurement method, since it is non-destructive. The comparison of both unfired and fired tile bulk density distributions allows the influence of the pressing and firing stages on tile end porosity to be individually identified.

Large-sized ceramic slabs – with dimensions up to 360x120 cm2 and thickness down to 2 mm – are manufactured through an innovative ceramic process, starting from porcelain stoneware formulations and involving wet ball milling, spray drying, die-less slow-rate pressing, a single stage of fast drying-firing, and finishing (trimming, assembling of ceramic-fiberglass composites). Fired and unfired industrial slabs were selected and characterized from the technological, compositional (XRF, XRD) and microstructural (SEM) viewpoints. Semi-finished products exhibit a remarkable microstructural uniformity and stability in a rather wide window of firing schedules. The phase composition and compact microstructure of fired slabs are very similar to those of porcelain stoneware tiles. The values of water absorption, bulk density, closed porosity, functional performances as well as mechanical and tribological properties conform to the top quality range of porcelain stoneware tiles. However, the large size coupled with low thickness bestow on the slab a certain degree of flexibility, which is emphasized in ceramic-fiberglass composites. These outstanding performances make the large-sized slabs suitable to be used in novel applications: building and construction (new floorings without dismantling the previous paving, ventilated façades, tunnel coverings, insulating panelling), indoor furnitures (table tops, doors), support for photovoltaic ceramic panels.

The present research was conducted to assess the feasibility of using two kinds of industrial wastes as opacifiers in porcelain tile bodies, as well as to define what pre-treatment would be required to prepare the wastes for such use.
The characteristics of the wastes were analysed, first, to determine their chemical and mineralogical composition, as well as their behaviour when subjected to heat, in order to identify any undesirable substances and to establish suitable conditions for removing these with simple methods. This allowed suitable materials to be obtained for use in porcelain tile compositions.
The effects were then studied of the incorporation of these pre-treated waste materials on porcelain tile characteristics. The results obtained indicate that the two waste materials used in this research have a significant opacifying capability, which makes them of great interest as possible raw materials for products that are not required to have maximum whiteness values. The only drawback detected in one of these wastes was that the porcelain tile composition needed to be slightly adjusted in order to ensure that its behaviour during firing did not change.

The ceramic tile manufacturing process is energy intensive since it contains several stages in which the product is subject to thermal treatment. The thermal energy used in the process is usually obtained by combustion of natural gas, which is a fossil fuel whose oxidation produces emissions of carbon dioxide, a greenhouse gas.
Energy costs account for 15% of the average direct manufacturing costs, and are strongly influenced by the price of natural gas, which has increased significantly in the last few years.
Carbon dioxide emissions are internationally monitored and controlled in the frame of the Kyoto Protocol. Applicable Spanish law is based on the European Directive on emissions trading, and the assignment of emissions rights is based on historical values in the sectors involved. Legislation is scheduled to change in 2013, and the resulting changes will directly affect the Spanish ceramic tile manufacturing industry, since many facilities will become part of the emissions trading system.
The purpose of this study is to determine current thermal energy consumption and carbon dioxide emissions in the ceramic tile manufacturing process.
A comprehensive sectoral study has been carried out for this purpose on several levels: the first analyses energy consumption and carbon dioxide emissions in the entire industry; the second determines energy consumption and carbon dioxide emissions in industrial facilities over a long period of time (several months); while the third level breaks down these values, determining energy consumption and emissions in terms of the product made and the manufacturing stage.

The evaluation of the colour of so-called ‘metallised’ glazes is an important problem, especially since there is no clear definition for this type of material. The study shows that a spectrophotometer is not sufficient for evaluating the colour of these glazes, whereas a goniospectrophotometer with four angles of viewing enables a set of data to be obtained that more closely describe glaze appearance. However, the description of the colour component of glaze appearance using twelve chromatic coordinates is difficult to handle. For that reason, an index is proposed, similar to the whiteness or yellowness indices, for the evaluation of ‘metallised’ appearance. This index is calculated from the goniospectrophotometer data, and has allowed ‘metallised’ glazes to be differentiated from ‘non-metallised’ glazes, in the set of samples used in this study.

The Rio Tinto Minerals company has developed a new borate (E-4972), which can be used in glaze formulation (patent WO 2007/148101).
This new borate, synthesised by low-temperature calcination, fundamentally contributes five oxides: silicon oxide (SiO2), aluminium oxide (Al2O3), boron oxide (B2O3), calcium oxide (CaO), and sodium oxide (Na2O), its content in B2O3 being between 10 and 11% by weight. It is largely amorphous, and quartz is the major crystalline phase present.
The characteristics of this new borate, such as its low solubility and ability readily to form glassy phase, enable it to be used as a raw material in glaze compositions. Its suitability for glaze formulation has been the result of several years’ research in collaboration with the Instituto de Tecnología Cerámica.
In this paper, the feasibility has been studied of fabricating ceramic glazes by using a new synthetic borate raw material that contributes boron to the glaze composition without this needing to be done in fritted form. It has been possible to obtain fired glazes with similar technical and aesthetics characteristics to those obtained from industrial glaze compositions that contain typical frits in their compositions, thus enabling glazes to be formulated by using the new synthetic boron raw material. The results obtained show that this new raw material (E-4972) is particularly appropriate for use in producing glazes with low gloss at high temperature.

This study analyses, first, the influence of sodium carbonate content on the behaviour of the ceramic tile body composition during the different manufacturing process stages (preparation of the suspension, pressing, and firing), as well as on unfired tile mechanical strength. It has been verified that sodium carbonate can be used as a binder in ceramic tile compositions, since small percentages considerably enhance dry tile mechanical strength. It has furthermore been determined that for each composition there is an optimum addition content, with high increased mechanical strength (up to 70%), without this noticeably affecting the rheological behaviour of the suspension to be spray dried. These results are currently being patented (patent applicationº P200930148).
Once the binding effect of sodium carbonate had been verified, it was sought to establish its action mechanism. For this purpose, drops of mixtures of a standard ceramic composition and increasing quantities of sodium carbonate were prepared. The drops were rapidly dried and the granules were characterised by scanning electron microscopy. It was thus verified that the most likely sodium carbonate action mechanism was formation of solid bridges by crystallisation.

Environmental concerns, growing public pressure and regulatory measures are changing the way people do business around the world. Consumers and shareholders are increasingly demanding environmentally-friendly ceramic products, as well as transparency in the environmental performance of the companies. Since its creation in 1995, The Eco-Management and Audit Scheme (EMAS) is a voluntary tool recognized as the most reliable environmental management system available in EU for organizations to evaluate, improve and report companies’ environmental performance. Regulation (EC) No 1221/2009 of the European Parliament and of the Council, known as EMAS III or Global EMAS, allows organizations outside EU to participate, making EMAS more attractive for ceramic companies that usually export.
Ceramic companies that implement EMAS, achieve marketplace advantages and improve company image, as well as adding credibility and confidence with customers, stakeholders and public authorities. They also benefit of environmental legislation relief and other advantages as exception of financial insurance obligation included in new Environmental Responsibility legislation.