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Current trends in the ceramic industry see an increasing interest on porcelain stoneware, by which is possible to produce large tiles and slabs. These products are manufactured by spray-dried powders, which have excellent technological properties but require high energy and water consumption. Dry-processed granulates allow to reduce such a consumption, but suffer from a different technological behavior. A solution to improve the environmental sustainability of ceramic tile-making is mixing powders prepared by the wet and the dry routes. The technological features of industrially manufactured mixed powders was investigated (rheological properties, compaction response and firing behavior) in order to point out advantages and possible pitfalls. Dry-processed and spray-dried granulates exhibit different distributions of size, shape and moisture that reflect on distinct rheological and compaction behaviors. Mixed powders show a more or less accentuated deviation from linearity between the end terms. This fact makes possible to add up to ∼50% dry granulates by keeping the technological properties close to current industrial bodies. Sparings of water, energy and CO2 emission for the milling and granulation stages are estimated for a mix 50% spray-dried and 50% dry-processed powders.

The growing demand for fluxes, dictated by the shift toward porcelain stoneware, is urging the ceramic tile industry to find a viable alternative to feldspathic materials. Sericite, a microcrystalline form of muscovite, is present in many ceramic raw materials. It melts during firing and can be a suitable substitute for potassic feldspar. The aim of this study is to understand in depth the effects of replacing feldspar with sericite in porcelain stoneware batches with nearly the same chemical composition. Characterization includes phase composition (X-ray powder diffraction, XRPD Rietveld), melt chemical composition (calculated), sintering behavior (optical thermo-dilatometry), and microstructure (scanning electron microscope (SEM). The results indicate a different vitrification path, mostly in the early stage of sintering, related to the different mineralogical composition and particle size distribution of sericite for K-feldspar. Nevertheless, at temperatures higher than 1150 degrees C, the bodies have similar phase composition, microstructure, melt chemical composition, and physical properties. Densification kinetics is faster in the batch with sericite, while the body with feldspar is able to reach a higher bulk density.

The addition of wastes to silicate ceramics can considerably expand the compositional spectrum of raw materials with a possible inclusion of hazardous components. The present work quantitatively examines relevant literature to determine whether the benefits of incorporating hazardous elements (HEs) into silicate ceramics outweigh the pitfalls. The mobility of various HEs (Ba, Zn, Cu, Cr, Mo, As, Pb, Ni, and Cd) has been parameterised by three descriptors (immobilisation efficiency, mobilised fraction, and hazard quotient) using leaching data. HEs can be incorporated into both crystalline and glassy phases, depending on the ceramic body type. Moreover, silicate ceramics exhibit a remarkably high immobilisation efficiency (often exceeding 99.9%), as accomplished for Ba, Cd, Ni, and Zn elements. The pitfalls of the inertization process include an insufficient stabilisation of incorporated HEs, as indicated by the high hazard quotients (beyond the permissible limits established for inert materials) obtained in some cases for Mo, As, Cr, Pb, and Cu elements. Such behaviour is related to oxy-anionic complexes (Mo, As, Cr) that can form their own phases or are not linked to the tetrahedral framework of aluminosilicate glass. Pb and Cu elements are preferentially partitioned to glass with a low coordination number, while As and especially Mo are not always stabilised in silicate ceramics. These drawbacks necessitate conducting additional studies to develop appropriate inertisation strategies for these elements.

Waste recycling has become an important issue in the environmental sustainability of mining operations. Beneficiation of borate ores produces a boron-bearing sludge, which utilization in ceramic manufacturing may lower the process energy demand. A case-study was carried out on a sludge coming from the processed ore of an evaporite located at the Tincalayu mine in the Salta province, Argentina. The use in vitrified tiles of this sludge was appraised addressing key-points in processing and product performances. The sludge was added to stoneware batches (up to 10% wt.) and tested at the laboratory scale. It consists of feldspars, quartz, illite and chlorite, plus ulexite (6.4% B2O3) that turns this sludge into a powerful flux. The waste had a minor effect during milling but allowed an improved compaction. The reactivity during firing was increased: the maximum temperature can be reduced from 1200 °C down to 1140 °C, according to the amount of sludge added. Stoneware tiles have a suitable technical performance, but the sludge tends to lower bulk density and increase closed porosity. Although the influence on phase composition is apparently limited, the sludge can significantly change the melt composition (enriched in boron and alkaline-earth oxides) which governs the sintering behavior. The actual amount of boron sludge recyclable in vitrified tiles is up to 5% by weight. Resumen: El reciclaje de desechos se ha convertido en un tema importante en la sostenibilidad ambiental de las operaciones mineras. El beneficio de los minerales de borato produce un lodo que contiene boro, cuya utilización en la fabricación de cerámica puede reducir la demanda de energía del proceso. El lodo estudiado proviene del mineral procesado de una evaporita ubicada en la mina Tincalayu en la provincia de Salta, Argentina. El uso en azulejos vitrificados de ese lodo se evaluó abordando los puntos clave en el procesamiento y el rendimiento del producto. El lodo se agregó a los lotes de gres (hasta el 10% en peso) y se probó a escala de laboratorio. Se compone de feldespatos, cuarzo, illita y clorita, más ulexita (6,4% B2O3) que convierte este lodo en un poderoso fundente. El desecho tuvo un efecto menor durante la molienda, pero permitió una compactación mejorada. La reactividad durante la cocción aumentó: la temperatura máxima se puede reducir de 1200 °C a 1140 °C, según la cantidad de lodo añadida. Las baldosas de gres tienen un rendimiento técnico adecuado, pero el lodo tiende a reducir la densidad aparente y aumentar la porosidad cerrada. Aunque la influencia en la composición de la fase es aparentemente limitada, el lodo puede cambiar significativamente la composición de la masa fundida (enriquecida en óxidos de boro y alcalino-térreos) que rige el comportamiento de sinterización. La cantidad real de lodo reciclable en baldosas vitrificadas es hasta el 5% en peso. Keywords: Boron sludge, Ceramic flux, Stoneware tiles, Waste recycling, Palabras clave: Lodo de boro, Fundente cerámico, Azulejos de gres, Reciclaje de residuos

The advent of digital decoration has changed the technological requirements of colorants and the way they are applied onto ceramic substrates. This technological revolution has introduced additional steps in colorant production (ink micronization) and new constraints in application (ink-jet printing) that cannot be reproduced in a standard ceramic laboratory, so stretching the distance between academic and industrial research. The goal of this work is to provide an up-to-date picture of ceramic pigments, dyes and effects, with emphasis on their behavior in the current decoration technologies, which are shortly reviewed. Technological performance expected for ceramic colorants and new requirements imposed by digital decoration are discussed in detail. An extensive overview of both industrially used and candidate pigments, dyes and effects is focused on the suitability to different ceramic applications and firing conditions. Finally, lines of future research are outlined and commented.

Using spray-dried powders is widely consolidated in ceramic production, especially for porcelain stoneware tiles and slabs. However, a novel micro-granulation process can reduce the consumption of water and energy. It is based on wetting-agglomeration-drying operations that can be managed either as dry (dry-milled powders, micro-granulation) or hybrid route (wet-milled slurry and dry-milled powders, micro-granulation). The goal is to compare these new dry and hybrid micro-granulates with conventional spray-dried and dry-granulated powders by determining: grain size, shape and moisture distribution; static and dynamic angles of repose; poured and tap density, Hausner ratio; mass flow rate; compaction response; microstructure, pore size distribution and yield strength. The new micro-granulates exhibit improved rheological performances, approaching under some manufacturing conditions those of spray-dried powders, particularly in case of the hybrid route. Differences persist in compaction behavior: this is the consequence of distinct microstructure, porosity and stiffness of spray-dried agglomerates and dry/hybrid micro-granules.

In view of the transition to circular economy, the ceramic industry is searching for suitable flux substitutes. Glassy wastes are promising candidates, even though they may significantly affect the firing behaviour and particularly high temperature permanent deformations. The goal of this study is to assess the sintering behaviour of porcelain stoneware bodies containing glassy wastes. Five different sources (bottle, PC-TV screen, lamp, frit manufacturing and porcelain stoneware grinding) provided glassy wastes that were separately added to a reference batch (20-40-60%) in substitution of feldspars. Each batch was characterized from the chemical point of view and its sintering kinetics were determined in isothermal conditions by optical thermo-dilatometric analysis. The quantitative phase composition after firing was determined by XRD-Rietveld in order to calculate chemical and physical properties of the vitreous phase at high temperature. The substitution of feldspathic fluxes determines a clear change in the firing behaviour: waste glasses lower the temperature at which the densification starts, and extend the early stage occurring before a constant rate sintering takes place. In some cases, the deviation is important and entails a lower sintering efficiency. The reasons behind this different firing behaviour are discussed in terms of composition, structure, and properties of the melt.

The technological behavior of porcelain stoneware bodies during deposition and pressing of large slabs depends on the rheological properties of spray-dried powders and the way they affect compaction. Although the literature offers some insights into the characteristics of spray-dried powders for ceramic tiles, no data are available on bodies utilized by novel technologies for large slabs (>4 m2). In order to fill this gap, a systematic approach to properties and behavior of spray-dried powders for porcelain stoneware slabs was carried out. For this purpose, twenty industrially-manufactured spray-dried powders were characterized for intrinsic features (particle size and agglomerate size distribution; shape and moisture distribution in function of agglomerate size) and rheological properties (mass flow, static and dynamic angles of repose, poured and tap density, Hausner ratio). The effect of intrinsic characteristics on the flowability of powders was appraised, as the mutual relationships between the rheological parameters, in order to unveil the best parameters to be used in ceramic tile production. Two broad classes of spray-dried powders occur with a finer and a coarser agglomerate size distribution. Results reveal that ceramic powders are free-flowing, with rheological properties fluctuating in a rather narrow range of values, which makes hard to see significant relationships among the various methods (the only strict correlation is between mass flow rate and tap density). Flowability mainly depends on the occurrence of coarser aggregates, particularly those irregular in shape, stemming from coalescence of three or more individual agglomerates. A phenomenological description of how the spray-dried powders behave in the deposition on tape and the early stage of compaction is outlined.

Cobalt-based pigments were synthesized using clinopyroxene as crystalline host. The pigments are a Ca(Co x Mg 1- x )Si 2 O 6 solid solution, with x = 0.05, 0.2, 0.4, 0.5, 0.6, 0.8 Co apfu , and were synthesized from melt. The pigments were characterized by single-crystal X-ray diffraction, SEM-EDS, optical microscopy, colorimetry and optical spectroscopy. The pigments were then tested in glazes and glassy coatings for ceramic tiles to determine their colouring performance. The synthesized pigments showed a pink colour with different shades, due to the absorption of Co 2+ in octahedral coordination. The colour disappeared in the Ca(Co 0.05 Mg 0.95 )Si 2 O 6 pigment after grinding. The Ca(Co x Mg 1- x )Si 2 O 6 pigments partially dissolved in glazes, acting like dyes, and bestowed a blue shade on coatings, with a colour efficiency similar to industrially used blue colorants (cobalt aluminate spinel and cobalt olivine). In the glassy coatings, pigment dissolution occurred at a lower extent, and a colour intermediate between the pyroxenes and the pigment-bearing glazes was obtained. The Co content in pyroxene dyes is lower than conventional pigments, being down to 5%wt.

In the last years, the ceramic sector started to focus on the exploitation of local georesources with circular economy solutions based on waste recycling. The present work aims to assess both the technological feasibly of waste recycling in the clay bricks manufacturing and the effect of different degreasers on the same clay body in order to disclose which factors control technological behavior. Non-plastic waste materials (e.i. mining and construction wastes) were added to a plastic clay and the brickmaking process was performed at the laboratory scale. The main technological properties of the semi-finished and finished products does not suffer any significant variations, indeed with the addition of mining and construction wastes were improved the plasticity reaching optimal values for the clay bricks extrusion. A clear disadvantage is found related to the decrease of mechanical strength, both in dry and fired products, ascribable to the convergence of microstructural factors. In conclusion, the different effects on the technological properties of clay bricks are correlated to the type of waste added as degreaser and the complex interplay of particle size distribution and mineralogical composition in ceramic matrix.

Several batches of porcelain stoneware were formulated by partial replacement of coarse Na and Na-K feldspars (standard batch) with quartz in two different grain sizes, micronized K-feldspar or a mixture of these components. Everyone was processed (laboratory scale) by wet and dry routes to compare: sintering curve, microstructure, phase composition and viscosity of the liquid phase at high temperature. Pyroplasticity index was determined by 3-point bending test. Results indicate that finer the quartz particles, more they dissolved in liquid phase, increasing viscosity and reducing deformation. Micronized K-feldspar increased the sintering kinetics (causing deformation). However, when K-feldspar was combined with quartz, densification rate was improved without compromising integrity of tile. About dry route, microstructural heterogeneity turned as fundamental to prevent Pyroplastic deformation. As conclusion, pyroplastic deformation occurs by different mechanisms in samples prepared by the two processing routes and bodies prepared via dry route are less likely to undergo pyroplastic deformation. (C) 2016 Elsevier Ltd. All rights reserved.

The present chapter is focused on the main different applications of the natural zeolites and modified clays in the building materials, considering the environmental, economic and technical advantages/disadvantages of their incorporation into in cementitious, ceramic and composite products. Natural zeolites and modified clays can be introduced either as raw materials, which play well-defined technological actions, or as components to define the performance of the finished products. The main effects of zeolites and modified clays on the technological behavior of building materials is outlined

The ceramic industry is going to be deeply involved in the transition to a circular economy. However, the main obstacle to a widespread recourse to waste recycling is the lack of knowledge about its effect in ceramic tile manufacturing. The rationale behind this work is to look at recycling from the industrialist's point of view. The goal is overviewing the effects of different kinds of waste on technological behavior, technical performance, and environmental impact of ceramic tiles in the prospect of an industrial transfer. Technical constraints that waste recycling must comply to be transferable to ceramic tile manufacturing were examined in detail. Available information on the behavior of ceramic tile bodies containing wastes from various sources was critically reviewed for every manufacturing stage. The main outcome is an outlook about feasibility (expressed in terms of Technology Readiness Level) and recommended recyclable amount. In addition, hindrances to scale up and matters of concern (e.g., hazardous components and gaseous emissions) are pointed out and discussed. Examples and reasons of success/unsuccess are briefly illustrated, and prospect of waste recycling in ceramic tiles production from a circular economy perspective was appraised.

The pyroxene structure was successfully used as a crystalline host for a new Co-based pink pigment. Different compositions of Ca1-xCo1+xSi2O6 (0 2O6 end-member. For increasing cobalt content, an assemblage of Co-olivine, Co-åkermanite and Ca,Co-pyroxene was found. Samples containing Co-åkermanite have a deep blue color stemming from Co2+ in tetrahedral coordination, while those with Co-olivine are violet due to Co2+ in octahedral coordination. The best conditions for the synthesis of a CaCoSi2O6 single phase were then investigated, finding that a proper annealing cycle at 1150 °C prevents the formation of metastable Co-åkermanite. The CaCoSi2O6 pyroxene was tested as a ceramic pigment into glazes and glassy coatings. In most cases, it behaves like a dye, completely dissolving in the melted glaze, analogously to Co-olivine.

WOS: 000353176300049, Inkjet printing is increasingly used to decorate ceramic tiles, with pigmented inks in most cases. These inks are manufactured by micronizing conventional ceramic pigments down to median diameters of 0.2-0.6 mu m. Although such a size reduction theoretically offers significant advantages in terms of the optical and fluid mechanical properties of the pigment particles, still unanswered questions concern color strength and the efficiency of the milling process. The present study aimed to elucidate how micronizing influences the pigments' particle size and shape, and the specific surface area. For this purpose, industrial pigments were selected to represent crystal structures of different density, hardness, cleavage and fracture toughness, i.e. rutile, spinel and zircon. The pigments were micronized in a pilot plant, controlling carrier, solid load, dispersant type and concentration, rotation speed, amount and size of grinding media, temperature and milling time. The pigments were characterized by particle size distribution (laser diffraction and dynamic light scattering) and morphology (SEM). The results revealed a different behavior of the pigments during micronization, with changes in particle size and shape partially consistent with the literature. The pigments' grindability differed: zircon > ruffle >= spinel, Scientific and Technological Research Council of Turkey (TUBITAK) [111M773]; Ceramic Research Centre (SAM), We would like to thank the Consiglio Nazionale delle Ricerche (CNR) and the Scientific and Technological Research Council of Turkey (TUBITAK) on behalf of the joint cooperation program under the contract number 111M773 and the title "Water based inks for ceramic tile decoration by inkjet printing", between the Department of Materials Science and Engineering of Anadolu University and the Institute of Science and Technology for Ceramics (CNR-ISTEC). Authors are also grateful to Ceramic Research Centre (SAM) for their financial and technical support.

In the last decade, the drop-on-demand (DOD) ink-jet printing has become the leading technology for the decoration of ceramic tiles. The inks employed for such application are colloidal suspensions of oxide particles (0.3 mu m) whose stability (against agglomeration and over time) is fundamental to get successfully the tile decoration. Jettability from the DOD print heads is a key requirement along with proper colour after sintering. This means that a careful set up of inks properties (viscosity, density, surface tension) is required. The phenomena involved in the different stages of the ink-jet printing process (drop ejection from the nozzles, impact and spreading on the substrates) are described through dimensionless numbers as Reynolds, Weber, and Bond numbers, or their combinations. In literature physical constraints, obtained with a semi-theoretical approach on the basis of experimental evidences on other systems, allow to define a reference region in the space of the dimensionless numbers (here called "printable fluid region," PER) where the inks should be suitable for the application. In this paper, 26 inks currently used for ceramic tile decoration were characterized and mapped in the space of dimensionless numbers for several printing conditions. For typical nozzle diameters (20-50 mu m) and drop velocities (6-8 m/s), it has been found that they fall in the region identified by 3 < Re < 30, 27 < We < 160, and 0.6 < 1/Oh

The Co 2+ ion in fourfold coordination provides d-d electronic transitions with the strongest optical density among oxides and silicates. For this reason, it is widely used in pigments and dyes to get blue shades detectable down to a very low cobalt concentration. Such a low-detection limit turns the Co 2+ ion into a suitable probe to disclose the local ligand environment in a wide range of materials by means of optical spectroscopy. Even if extensively studied in organometallic complexes, an in-depth investigation of optical properties of Co 2+ in tetrahedral coordination into oxidic structures is limited to some case-study in minerals and synthetic analogs (spinel, zincite, gahnite, willemite, calcium cobalt selenite). The present study represents an attempt to outline crystal structural (long-range metal–oxygen distances, O–T–O bond angles, and distortion parameters by XRD) and optical parameters (10 Dq , Racah B and C , band splitting by EAS) in 13 samples of oxides and silicates providing a wide set of different local fourfold coordination around Co 2+ added as a dopant. Subtle variations of crystal field strength and interelectronic repulsion can be appreciated in gahnite, Ca-Sr-hardystonite, Ca-Sr-Ba-akermanite, willemite, Ba 2 MgSi 2 O 7 melilite-related (where Co 2+ substitutes Mg 2+ or Zn 2+ by 0.25–0.3 apfu) as well as in gehlenite and fresnoite (where Co 2+ substitutes Al 3+ and Ti 4+ , respectively, by 0.2 apfu due to charge mismatch). Results are compared with literature data about hibonite, spinel s.s. , staurolite, yttrium garnets, and zincite. Spectral interpretation is not straightforward owing to the occurrence of different Co 2+ bands: spin-allowed and spin-forbidden electronic transitions, two- or threefold split due to both lowering of point symmetry at the tetrahedron and spin-orbit coupling plus presumably vibronic transitions. Optical spectra vary significantly even for apparently small changes in the long-range CoO 4 arrangement as measured by XRD. The expected relationship between 10 Dq and the mean Co–O distance is fulfilled, but the accommodation into small AlO 4 sites in gehlenite (YAG and hibonite) implies a significant structural relaxation around the Co 2+ ion. The threefold splitting of the spin-allowed 4 T 1 (F) and 4 T 1 (P) bands can be related to the angular distortion of the CoO 4 tetrahedra. Overall, changes of spectral features of tetrahedrally coordinated Co 2+ can be attributed to different local arrangement of ligands with an effect correlated to the second nearest neighbors by the bond valence theory. This was disclosed contrasting 10 Dq with the ratio of the observed and ideal bond valence sum for the polyhedra sharing oxygen with the Co-centered tetrahedron.

The shear viscosity and the glass-vapor surface tension at high temperature are crucial to understand the viscous flow sintering kinetics of porcelain stoneware. Moreover, the pyroplastic deformation depends on the viscosity of the whole body, which is made up of a suspension of crystals dispersed in the melt. The existing fundamental theoretical background, along with semi-empirical constitutive laws for viscous flow sintering and glass densification, can be exploited through different approaches to estimate the physical properties at high temperatures starting from amount and chemical composition of the melt. In this work, a comprehensive attempt to predict the properties of the liquid phase is proposed by means of a detailed overview of existing models for viscosity and surface tension of glasses and melts at high temperature. The chemical composition of the vitreous phase and its physical properties at high temperature are estimated through an experimental approach based on the qualitative and quantitative chemical and phase analyses (by Rietveld refinement of X-ray powder diffraction patterns) of different porcelain-like materials. Repercussions on the firing behavior of ceramic bodies, are discussed. Comparative examples are provided for porcelain stoneware tiles, vitreous china and porcelain bodies, disclosing differences in composition and properties but a common sintering mechanism.

The present study shows the results of direct ceramization of textile substrates with commercial derived TiO2 nanosols. A deep investigation on relationship between TiO2 based nanosols and nanocoatings properties and their performances in term of hydrophilicity and photocatalytic efficiency was performed. Five nanosols, differing for starting pH and relative agglomerates size were analyzed. The hydrophilic behavior and the catalytic performance of TiO2 coatings supported on different substrates (fabric, glass and ceramic) were assessed and related to physicochemical characterization results. The described correlations between TiO2 nanoscale properties (nanostructure or surface chemistry), macroscale properties (hydrophilicity), as well as functional properties (photocatalytic activity), represents a first attempt to provide sound criteria for the control of material performance by design experiments. The pH dependent aggregation state, is correlated to an increase of surface acidity as the shift of i.e.p. towards acid pH reveals. Such increase of acidity justifies an increase of hydrophilicity, consequent to stronger interaction with water molecules, that occurs when a higher amount of Ti−O− sites are available. As well, the photocatalytic performances and the hydrophilic behavior, resulted in a good agreement: the higher the hydrophilicity, the better the self-cleaning activity, so providing useful indications for the scale-up exploitation of such application.

This paper reports a new black pigment based on strontium M-type hexaferrite (SrM) obtained from pure reagents or by the inclusion of Fe-rich wiredrawing sludge. The fired powders show a clear predominance of SrFe12O19. Also, haematite (alpha-Fe2O3) and iron spinel were detected in variable amounts. These two phases are present in higher amounts (57 wt.%) in the sludge-based pigment, due to the interference of contaminants. The optical measurements illustrated that the prepared pigments displayed good colorimetric properties, close to those shown by a black commercial pigment. However, the addition of Fe-rich sludge slightly reduced this black colour by increasing the L* and b* colour coordinates. Since the variance is slight, further trials were carried out by minor addition of chromophores (Co, Mn and Ni). The chromatic measurements showed that the best pigment was obtained by adding cobalt. Nevertheless, in ceramic porcelainized bodies, the combination of Co and Mn assured the nearest hue to the commercial pigment. Nickel was not effective in the colouration because it was mostly assimilated by the spinel (trevorite) phase and was not inserted in the hexaferrite phase. Other trials with non-stoichiometric formulations showed a bleaching of the black colouration in stoneware supports, especially on sludge-containing formulations, along with an apparent increasing of the green hue. (C) 2012 Elsevier Ltd. All rights reserved.

There is a growing concern on lightweight aggregates (LWA) for recycling of waste materials: this manufacturing technology is considered a flexible tool to make it possible the conversion of large amounts of residues into building products. The main challenge for this purpose is the control on the technological behavior during firing of waste-bearing batches. The target is engineering the sintering and expansion of LWA in order to tailor bulk density, mechanical strength and water absorption on various possible applications (e.g., structural and non-structural lightweight concretes, lightweight mortars, filtration substrates, floriculture). The prediction of the aggregate expansion - and hence the batch design - is usually carried out utilizing the Riley's and/or Cougny's schemes, which are based on the bulk chemical composition of clay bodies. However, collecting the literature data on waste-based LWA and plotting them in the Riley's and Cougny's diagrams, no reliable discrimination turns out between expanding and non-expanding batches. In the same way, the attempt to modify the Riley's and Cougny's parameters, including elements present in wastes but not in natural raw materials, was unsuccessful. From this standpoint, a new approach to assess the batch expandability was developed through a deeper comprehension of mechanisms acting on sintering and expansion of LWA. A specific characterization protocol was set up, entailing hot-stage microscopy and determination of phase composition and microstructure. This implies a paradigm shift from batch (chemical composition) to vitreous phase (amount, chemical composition, and viscosity at high temperature). The vitreous phase plays a key-role for bloating, microstructure and physical properties of LWA. A working example is presented about new LWA based on waste glasses, ceramic tile polishing sludge and clay raw materials. (C) 2016 Elsevier Ltd. All rights reserved.

WOS: 000370882600019, Digital decoration of ceramic tiles has turned to be a prevalent and dynamic technology in the last decade. Current printers use drop-on-demand (DOD) ink-jet print heads (UP) fed with solvent-based inks containing ceramic pigments as coloring agents. However, due to environmental constraints, water based systems are envisaged as a green alternative for ceramic tiles decoration. Nevertheless, aqueous suspensions are difficult to be managed because physical properties of water are far away from the DOD UP operating window. Thus, the control on the stability, homogeneity and rheology of such water-based systems is an important factor to achieve better product performances. This study was aimed at exploring both the rheological behavior and stability of three inks based on micronized pigments dispersed in water and water-MEG solutions: (V,Zr)SiO4 (turquoise zircon, TZ), (Cr,Sb)TiO2 (orange rutile, OR) and (Co,Mn) (Fe,Cr)(2)O-4 (black spinel, BS). The pigments were ground to submicronic size in water using a circulation type agitator mill and by changing the main parameters affecting the particle-size distribution (rotation speed, type and amount of dispersants). The stability of aqueous pigment suspensions was studied by measuring the zeta potential as function of pH and by sedimentation tests. The zeta potential was sufficiently strong (lower than -30 mV) to render the inks stable in the 7-10 pH range. Rheological measurements of the suspensions showed a Newtonian flow behavior for zircon and rutile inks and slightly pseudoplastic for the spinel one. An attempt was also made to evaluate the inks printability with the help of dimensionless numbers based on the relevant physical and rheological properties affecting the jetting, i.e. viscosity, surface tension and density. It was observed that the ground aqueous systems fall in the printable fluid region obtained with semi-empirical models, National Research Council of Italy (CNR); Scientific and Technological Research Council of Turkey (TUBITAK) [111M773]; Ceramic Research Centre (SAM), We would like to thank the National Research Council of Italy (CNR) and the Scientific and Technological Research Council of Turkey (TUBITAK), on behalf of the joint cooperation program, under the contract number 111M773 and title "Water based inks for ceramic tile decoration by inkjet printing", between the Department of Materials Science and Engineering of Anadolu University and the Institute of Science and Technology for Ceramics (CNR-ISTEC). Authors are also grateful to Ceramic Research Centre (SAM) for the financial and technical support.

The impact resistance of ceramic tiles is an important technical requirement, especially for large size and/or low thickness slabs. The standard test for ceramic tiles (ISO 10545-5) is non-destructive: it determines the coefficient of restitution of a small sample (75 x 75 mm(2)) assembled on a concrete substrate under a weak impact energy (0.27 J). This method does not provide neither an impact strength nor information on the way a ceramic tile is broken by impact. In order to fill this gap, an investigation was undertaken to describe, by a phenomenological approach, how ceramic tiles break under different conditions of impact. For this purpose, unglazed porcelain stoneware tiles with different size (12 x 12, 25 x 25 and 60 x 60 cm(2)) and thickness (3.5, 5 and 8 mm) were assembled on a concrete basement and tested for the coefficient of restitution (ISO 10545-5) and Roesler index. Their physical and mechanical properties were determined by measuring: water absorption, porosity, bulk density (ISO 10545-3), flexural strength (EN 843-1), elastic moduli (EN 843-2), fracture toughness (SENB). The impact strength was measured by falling steel balls (50, 80, 200 and 500 g) with increasing energy (from 0.2 to 6 J) and with different speed at the moment of impact (from 1.9 to 5.5 m/s). The effects caused by impact were visually inspected, revealing for increasing energy the formation of an impact ring, radial cracks, one or two concentric Hertzian cone fractures, a highly fractured inner zone. Such damages were quantified by measuring the impact ring diameter as well as number, length and estimated surface of radial and conical cracks. A nearly linear dependence on the impact energy was found for crack length and surface, while the ring diameter and crack number seem to follow a quadratic law. The impact strength depends on the tile thickness, but also the sample size may somehow affect the mechanical behavior under impact. A map of seven levels of damage was drawn by contrasting increasing impact energy with tile thickness: it can help to predict the tile behavior in operation and to address the correct tile type in different applications. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

The industrial feasibility of large-sized, photocatalytic building materials was assessed by the adoption of suitable, fast and environmental friendly technological solutions. Nanostructured TiO 2 coatings can be realized by ink-jet or roller printing of nano-anatase suspensions by modifying, in one single step, the chemistry and microstructural features of products. Functional coatings must be consolidated through additional thermal steps, which necessarily entail modifications of the current production cycles of ceramic tiles. This is due to the fact that the direct functionalization of unfired ceramics is detrimental to the photocatalytic performance. The microstructure of coatings depends on deposition technologies and processing conditions. However, photoactive materials that also display superhydrophilic behaviour can be obtained by employing much lower amounts of TiO 2 than 1.0 g m −2 , and by annealing at temperature as low as 400–500 °C. A limited increase of the cost of products is involved, especially in the case of large-sized elements.

Raising cost, limited reserves, and toxicity make a pressing need to reduce the consumption of cobalt in the ceramic industry, trying to improve efficiency and sustainability of pigments. A novel blue colorant, based on the melilite structure, has been developed by searching for a ceramic pigment stable in very aggressive media, like the calcium- and zinc-rich glazes used in porous tiles (stoneware and monoporosa). Hardystonite was selected as a typical crystalline compound found in these coatings, which has just one fourfold crystallographic site where Co2+ ions can be accommodated, thus ensuring its unrivalled blue color. Five samples (Ca2Zn1−xCoxSi2O7 with x=0.05, 0.1, 0.2, 0.3, and 0.4) were prepared by a solid-state synthesis in industrial-like conditions (∼95% yield) and characterized by XRD, DRS, SEM–EDS, and technological testing. Increasing cobalt doping gives rise to a gradual expansion of the hardystonite unit cell, unexpected on the basis of Zn2+ and Co2+ ionic radii, attributed to a change of the covalent character of M–O bonding. Optical spectra are dominated by the strong absorption bands of Co2+ in tetrahedral coordination (crystal field strength Dq=421 cm−1, Racah B parameter=793 cm−1). The best compromise between cobalt concentration and optical response was found to be around x=0.3. The hardystonite pigment bestows a deep blue color on glazes and glassy coatings, withstanding aggressive media rich in CaO and ZnO better than industrial blue pigments (cobalt aluminate, spinel) with similar color efficiency than industrial blue dyes (cobalt silicate, olivine) but with the advantage to avoid specking defects of highly staining colorants.

This work reports the development of inorganic pigments based on chromium doped titanite (CaTiSiO5). For economical and environmental reasons, wastes were used as raw materials but similar formulations from pure reagents were also prepared to assess the effect of impurities contained in wastes. Pigments were characterised by XRD, SEM + EDS microprobe analysis, and UV–vis–NIR spectroscopy. The colouring mechanism (the pigment is reddish brown) seems to result from the combined contribution of octahedral Cr(III) and tetrahedral Cr(IV) species replacing Ti4+ and Si4+, respectively. In both pure reagents and waste-based pigments, colorimetric parameters were evaluated and their colouring performance was tested in transparent and opaque ceramic glazes. Intense and stable brown hues were developed with optimized formulations, i.e. containing 0.044Cr at 1300 °C.

Cr-doped CaTiSiO5 was synthesized by spray drying and conventional ceramic method in order to assess its potential as ceramic pigment. The evolution of the phase composition with thermal treatment was investigated by X-ray powder diffraction (XRPD) and thermal analyses (DTA-TGA-EGA). Powder morphology and particle size distribution were analyzed by scanning electron microscopy (SEM) and laser diffraction, respectively. The color efficiency of pigments was evaluated by optical spectroscopy (UV–vis–NIR) and colorimetric analysis (CIE Lab). Results proved that spray drying is an efficient procedure to prepare highly reactive pigment precursors. The spray-dried powders consist of hollow spherical particles with aggregate size in the 1–10 μm range, developing a brown coloration. Optical spectra reveal the occurrence of Cr(III) and Cr(IV), both responsible for the brown color of this pigment. The former occupies the octahedral site of titanite, in substitution of Ti(IV), while the latter is located at the tetrahedral site, where replaces Si(IV).

This work describes the high temperature reaction sequence of commercial Man Made Vitreous Fibers (MMVF) Cerafiber, Superwool, Rock wool and Glass wool which may be used as substitute for asbestos in some industrial applications. Knowledge of the reaction path and transformation sequence is very important to assess whether carcinogenic crystalline phases are formed during devitrification, which may occur when used as insulators. In addition, knowledge about the nature of the phases formed at high temperature is mandatory to assess if thermally transformed MMVF can be safely recycled as secondary raw material (SRM). In this scenario, this study provides useful information for the optimization of the industrial annealing process aimed to attain a safe, recyclable product. The results of this work show that one of the high-temperature products of Cerafiber and Superwool is cristobalite which is classified as a carcinogenic. It was possible to define the temperature interval at which Cerafiber and Superwool fibers can be safely used as thermal insulators (e.g. insulators in tunnel and/or roller kilns, etc.). As cristobalite is formed in both synthetic fiber products at temperatures higher than 1200 degrees C, their use should be limited to devices operating at lower temperatures. Rock and Glass wool melt upon thermal treatment. As far as the industrial process of inertization is concerned, a maximum firing temperature of 1100 and 600 degrees C is required to melt Rock wool and Glass wool, respectively, with the high-temperature products that can be safely recycled as SRM. Recycling of these products in stoneware tile mixtures were subsequently attempted. The addition of 1-2 wt.% of the melts of Rock and Glass wool gave promising results in terms of viscous sintering reactions and resistance to staining with the only weak characteristic being the color properties of the fired bodies which tend to worsen.

Compounds based on the YCrO3 perovskite structure, doped with Al, Ti and Ca, were studied by XRD and DRS, aiming at assessing their potential as green ceramic pigments. Nine samples were synthesized by the ceramic route according to the Y1−yCayCr1−x−yAlxTiyO3 stoichiometry, where 0

A water-based sol-gel combustion synthesis was optimized in order to achieve pure yttrium aluminium perovskite (YAlO3, YAP). The method involved three main steps: xerogel formation, combustion treatment and calcination of the combusted precursors. TG DTA, FTIR and XRPD, used to investigate the precursor phase evolution, confirmed the strong influence of gel synthesis conditions, combustion temperature and calcination rate on YAP purity. Both stoichiometry and kinetics control during all the preparation steps are crucial in order to avoid the formation of undesired Y3Al5O12 (YAG) and Y4Al2O9 (YAM) stable phases. This method allowed to synthesize, for the first time from an aqueous sol-gel process, single phase samples of YAP. A series of samples with composition: YAl(1-x)Cr(x)O3 where x is 0, 0.035, 0.135, 0.250, 0.500, 0.750 was obtained. A consistent decrease of calcination temperature, with respect to conventional solid state synthesis, was achieved by sol-gel combustion, avoiding polyphase materials even without the use of mineralizers. This is an important result in several applications like the synthesis of ceramic pigments.

Ceramic nano-pigments have been recently developed for ink-jet printing decoration of ceramic tiles by the quadrichromy technology (cyan, magenta, yellow, and black colours). The colouring mechanisms and performance of these nano-pigments (CoAl2O4, Au, (Ti,Cr,Sb)O2, CoFe2O4) were investigated by DRS, XRD and colourimetry. Nano-pigments were dispersed in several ceramic glazes and glassy coatings and their colour performance compared with that of conventional micro-pigments. Each nano-pigment is characterized by its own colour mechanism and chemico-physical stability in ceramic applications. Intense colours are achievable, besides the very small particle size of pigments ( 50 nm) even though the colour of high quality micro-pigments appears to be more saturated. Limitations to the use of nano-pigments arose for very high firing temperatures (1200ºC) due to particle growth (e.g. Au) or dissolution in the glassy phase (e.g. titania).

The synthesis and characterisation of chrome­-tin red malayaite Ca(Cr,Sn)SiO5 pigments are reported. The novel approach of using a galvanizing sludge from the Cr/Ni plating process as colouring agent is investigated. The ceramic pigments were prepared using common solid state reaction process, with optimisation of milling and firing conditions. Characterisation was done by x-­ray powder diffraction, diffuse reflectance spectroscopy, and application in standard ceramic glazes. The ceramic pigments were of high purity (= 96% malayaite) and developed a burgundy colour due to the occurrence of Cr4+ and Cr3+, and also Ni2+ in the sludge-­bearing samples. The hue of the pigments complied with standard expectations, and optimal formulations showed better performance than some commercial pigments also tested for comparison, perhaps due to the contribution of nickel.

The Patagonian kaolins offer a wide set of origin of deposits, composition, mineral processing and ceramic properties, giving a rare opportunity for investigating the interdependence of mineralogy, chemical composition, particle size distribution, texture, and surface activity with their technological behaviour in sanitaryware and porcelain stoneware production. Plasticity is strictly dependent on surface activity, < 2 μm fraction and expandable clay minerals; slip rheology is affected by soluble salts and expandable clay minerals, but also by high specific surface or tubular halloysite. Kaolinite/halloysite play an opposite role versus smectite/interstratified I/S in slip casting and tile pressing: the former allow faster casting rates, while the latter improve powder flowability and mechanical strength. Kaolinite and quartz are beneficial for drying behaviour while high surface activity or expandable clay minerals increase significantly drying sensitivity. Firing behaviour is mainly affected by minor components supplying "fluxing" (i.e. iron, alkali and alkaline-earth) oxides. A great deal of technological parameters seem to be reasonably predicted by the surface activity of clays and especially the Methylene Blue index, which is the most reliable, simple and economic method to predict and control the ceramic response of kaolins and ball clays. Fil: Dondi, Michelle. Istituto di Scienza e Tecnologia dei Materiali Ceramici; Italia Fil: Iglesias, Claudio. Piedra Grande Sa; Argentina Fil: Dominguez, Eduardo Alejandro. Universidad Nacional del Sur; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; Argentina

The improvement of the physico-chemical resistance of hematite pigment in ceramic bodies has been pursued through its inclusion into a transparent and refractory matrix of silica or zirconia. The inclusion process was accomplished by heterocoagulation followed by spray-drying. The heterocoagulation process was optimised through an electrokinetic technique, that measured the ζ potential of both matrix and pigment as a function of pH and of different amounts of dispersing agents. Suspensions of pigment and matrix were designed in order to achieve the maximum surface charges. The heterocoagulated mix was then spray-dried in order to avoid any separated coagulation of pigment and matrix and to obtain a well granulated powder suitable for application in ceramic bodies. A stable red-coloured ceramic pigment for low firing applications was obtained starting from amorphous silica as matrix and hematite as colorant.

Low-cost, naturally-occurring mixtures of feldspar and zeolite occurring in epiclastic rocks are promising substitutes for conventional quartz-feldspathic fluxes in ceramic bodies, since their fusibility and low hardness are expected to improve both grinding and sintering. Three epiclastic outcrops, with a different zeolite-to-feldspar ratio, were characterized (XRPD, fusibility) and tested in porcelain stoneware bodies; their behaviour during processing was appraised and compared with that of a reference. The addition of an epiclastic rock (20 wt.%), replacing rhyolite and aplite fluxes, brought about some significant advantages, mainly represented by better grindability, lower firing temperature with improved mechanical strength and lower porosity. Disadvantages concern increased slip viscosity, worse powder compressibility, resulting in larger firing shrinkage, and a darker colour of the tiles due to relatively high amounts of iron oxide.

Aim of this research is an evaluation of the zeolitized facies of Campanian Ignimbrite as raw material for the production of lightweight expanded aggregates (LEA). A commercial product (Cab70) was used as reference for this rock. Tests were carried out on “pure” samples or mixed with an industrial waste mud (DPM — Dried Polishing Mud) deriving from a porcelain stoneware tile polishing process. This mud contains SiC, a phase known to act as bloating enhancer. Raw materials were subjected to mineralogical (XRPD–RIR method) and chemical (XRF) analyses. Bloating upon heating was measured (Leitz heating microscope) on Cab70, DPM and on three mixtures having the following Cab70/DPM ratios: 85/15 (Mix1); 70/30 (Mix2); 50/50 (Mix3). LEA production was assessed both in static (muffle kiln) and in dynamic (rotating kiln) conditions by firing pellets, 3–8 mm in size, between 1220–1380 °C. The unit weight of the single particle was determined on fired and unfired products. All materials evidenced a decreasing density with temperature whereas the same parameter decreases with DPM increasing content. Cab70 LEAs never dropped below 0.90 g/cm3, even at the highest temperature, whereas DPM LEAs range between 0.86 g/cm3 (at 1260 °C) and 0.46 g/cm3 (at 1380 °C). A direct but not linear relationship between DPM content and density was evidenced. Among the three mixtures, Mix2 showed the lowest DPM content able to produce the strongest density reduction. To get LEAs with the same density the rotating kiln required temperatures generally 60–80 °C higher than those of the muffle kiln. This difference should be related to the different thermal insulation of the two systems during firing. Two sets of LEAs were massively produced in dynamic conditions from Cab70 (at 1380 °C) and Mix2 (at 1300 °C). These latter showed better technical performances in terms of unit weight of the single particle (0.81 vs. 0.98 g/cm3), bulk unit weight (460 vs. 565 kg/m3), water absorption coefficients (1.4 vs. 5.5% after 24 h) and compressive strength of the particles (2.9 vs. 0.6 MPa). Differences in pore shape, dimension, abundance and spatial distribution were observed by SEM between the two sets. The technical features of these LEAs were comparable to some expanded clays, with similar grain size, commercialised in Italy. These results are worth interesting as they reveal new perspectives of application both for a rock characterized by a low exploitation cost and widely available in central-southern Italy, as well as for an industrial waste produced in high amount but not recycled at all.

Pseudobrookite pigments were synthesised by the conventional ceramic route, calcining at 1300 C four mixtures, with a Fe2O3:TiO2 ratio ranging from 47:53 to 40:60, and were characterised by XRPD, DRS and colouring performance in several ceramic matrices. Titania in moderate excess of the Fe2TiO5 stoichiometry, necessary to minimise the occurrence of unreacted precursors, induced lattice parameters smaller than ideal 4þ 3þ pseudobrookite, in agreement with the different radii of Ti and Fe ions. These pigments exhibit a peculiar, intensely brown coloration 5 originated by several light absorptions in the visible spectrum due to both d electronic transitions and a magnetically-coupled paired transition 6 4 4 3þ between iron ions in adjacent lattice sites. A doubling of the A1/ T1 and T2 bands is related to the occurrence of Fe in both octahedral sites of pseudobrookite. Besides, distinct metaleoxygen distances imply different energy absorptions in good accordance with the crystal ?eld theory, despite the strongly covalent character of the FeeO bonding. Although an entropy-stabilised phase, pseudobrookite persists dispersed in glazes and glassy coatings even after fast ?ring at 1200 C, so being suitable as ceramic pigment. However, its colouring performance depends on the chemico-physical properties of ceramic matrices: saturated brown shades achieved in low temperature glasses shift to a lighter brown in opaci?ed glazes and fade to a light gray in wall tile glazes, where the high CaO and ZnO content contributes to rapidly dissolve pseudobrookite. 2007 Elsevier Masson SAS. All rights reserved.

WOS: 000353176300050, Drop on demand ink-jet printing is turning to be the leading technique in the decoration of ceramic tiles. This technology makes use in most cases of pigmented inks which are manufactured by micronizing conventional ceramic pigments in the 0.2-0.6 mu m range (median diameter). Although significant improvements to optical properties are in theory put forth by reducing the pigment particle size, not all the expected advantages occur and still unanswered questions concern the color strength of micronized pigments. This is the second part of a study aimed at disclosing what happens during pigment micronizing; it is focused on phase composition and color in the submicrometric field. For this purpose, representative industrial pigments were selected: Cr-Sb-doped rutile (orange yellow), Co-Cr-Fe-Mn-Ni spinel (black), and V-doped zircon (turquoise blue). Such pigments were micronized in a pilot plant and characterized for particle size and morphology (SEM and HR-TEM), phase composition, crystallite size and unit cell parameters (XRD-Rietveld), optical properties (DRS) and color after application in glazes for porcelain stoneware tiles fast fired at 1200 degrees C (CIE L*a*b*). Results highlight a different behavior during micronization: crystal structural and optical features are substantially changed once pigment particles turn into submicronic size. A gradually lower particle dimension is accompanied by reduction of crystallite size and increasing frequency of lattice defects (inferred from variation of unit cell parameters and optical properties) up to amorphization that may attain 75 wt%. The formation of amorphous phase takes place below a critical crystallite size (30-40 nm) which discriminates two regimes with fast and slow comminution rates. These structural changes are associated to decreasing color strength and increasing brightness through the submicrometric field, Scientific and Technological Research Council of Turkey (TUBITAK) [111M773]; Ceramic Research Centre (SAM), We would like to thank the Consiglio Nazionale delle Ricerche (CNR) and the Scientific and Technological Research Council of Turkey (TUBITAK) on behalf of the joint cooperation program under the contract number 111M773 and the title "Water based inks for ceramic tile decoration by inkjet printing", between the Department of Materials Science and Engineering of Anadolu University and the Institute of Science and Technology for Ceramics (CNR-ISTEC). Authors are also grateful to Ceramic Research Centre (SAM) for their financial and technical support.

Rutile is widely used as ceramic pigment for its excellent optical properties, high melting point and intense coloration when doped with transition elements. Industrial ceramic pigments are manufactured from anatase plus chromophore elements (Cr, Mn, Ni or V) and counterions (Nb, Sb or W). Several solid state reactions occur during the synthesis, involving both the anatase-to-rutile transformation (A → R) and the formation of accessory phases. The A → R transition is heavily affected by chromophores with a lowering of the onset temperature: V O bond length, with longer basal Ti O distances and a shorter apical Ti O distance. The pigment co-doped with V and W is different for its minimum Ti O bond length distortion (BLD), an almost regular TiO6 octahedron, and the occurrence of Ti3+ within the accessory compound Ti5O9.

Industrial rutile pigments are manufactured using several chromophores: Cr (giving an orange hue), Mn (tan), Ni (yellow) and V (gray); a second element, the so-called counterion (i.e. Mo, Sb, Nb or W) is always added in order to achieve the desired coloration and/or improve the technological properties (e.g. chemico-physical resistance in ceramic bodies and glazes). The colour of these pigments is determined by both metal–ligand charge transfer (Ti 4+ ↔ O 2− ) and crystal field effects (transition metals substituting Ti 4+ in octahedral coordination). Though the absorbance bands are broad and frequently overlapped, the UV–vis–NIR spectra suggest the occurrence of Cr 3+ , Mn 2+ , Mn 3+ , Ni 2+ , V 3+ , and V 4+ as chromophores. Rutile pigments are suitable for through-body (up to 1250 °C) and glaze applications (up to 1100 °C). The best coloration of porcelain stoneware bodies is achieved with Sb or W as counterions, though the higher stability is ensured by Sb, but in the Ti–Ni–W system. The best glaze colours are accomplished by W-bearing pigments, which however are less stable than Nb- or Sb-containing ones, except than for the V + W coupling. This latter represents a new and very interesting Co-free and Cr-free black pigment for low temperature applications.

Porcelain stoneware tiles frequently undergo a polishing process, aimed at improving their aesthetical appearence, that brings about a consistent material removal, with formation of superficial defects and opening of closed pores. The consequent degradation of surface characteristics—and especially the increased sensitivity to stains—represent the main limit to the use of polished tiles in many indoor and outdoor applications. In order to better understand the role of microstructure on the resistance to stains, a phenomenological study of staining/cleaning operations (ISO 10545 parts 14 and 16) and a thoroughful physico-microstructural characterisation of tile working surfaces (SEM, open and closed porosity, rugosimetry, MIP) were carried out on twelve industrially manufactured and polished products. Diverse staining behaviours proved to be connected with different tile microstructures, being the surface roughness as well as the amount and shape of coarser pores the most influent variables. Through a statistical approach, an empirical predictional model of the amount of stain retained by the tile surface after mild washing with warm water was set up. It is based on roughness measurements (both R a and R t ), estimation of macropores (i.e. 1–50 μm by MIP) and pore roundness (by image analysis of SEM photomicrographs).

This work, unlike previous others, deals with ceramic products obtained exclusively from gravel pit by-products. The residues are originated from the sand and gravel washing process of middle-course Jarama river Quaternary sediments, located in Madrid region, central Spain. These natural aggregates allow an intense exploitation, because of quality (well-rounded quartzite) and reserves (up to 700×10 6 m 3 ), generating considerable waste volumes. Thirty silty–clay by-products, collected from seven gravel pits, have been tested at a laboratory scale. The mineralogical composition of these materials is mainly represented by phyllosilicates (muscovite-illite, smectite, kaolinite and chlorite), quartz and feldspars. For the technological characterization, six representative mixtures (M1 to M6) were designed combining suitable mineralogy and grain-size distribution of the 30 raw samples. A wide range of values was measured on mixture powders, determining specific surface (13–76 m 2 g −1 , BET method), methylene blue index (5–20) and Atterberg limits (W l : 43–90; W p : 25–38). Ceramic characterization was performed on extruded bodies, testing drying sensitivity (Bigot curves and Ratzemberger test). Smectitic content influences directly the parameters measured on dried bodies. This influence can be controlled by increasing the silty component, and the ceramic properties measured on these mixtures (M3, M4 and M5) get better: hygroscopicity (less than 2%), drying shrinkage (4–7 cm m −1 ), keeping the bending strength above 5 MPa. Three maximum firing temperatures were studied: 850, 950 and 1050 °C. On mixtures fired at 950 °C, firing shrinkage is less than 4 cm m −1 , bending strength may reach 69 MPa and water absorption range from 23% to 0.5%. Efflorescence susceptibility is faint, and colour is red for all the samples, getting darker for increasing temperature. The positive results obtained in this set of preliminary tests drive to envisage new research programs, focused on testing these by-products on a semi-industrial scale, assessing the effective possibilities of using them as ceramic raw materials.

Two very different illitic–chloritic clays (calcareous and non-calcareous), both currently used in the Italian brickmaking industry, were used. Technological testing consisted in a simulation of the industrial processing performed at a laboratory scale. The pieces were obtained by three shaping techniques, pressing, extrusion and moulding, and fired at 1000 and 1100 °C, in fast and slow heating cycles. In each case their technological properties were studied. The microstructure and technological parameters of the ceramic pieces vary greatly, depending on the clay composition and the processing techniques. Pressing always produces pieces made from non-calcareous clay with the lowest drying and firing shrinkage, open porosity and water absorption. As it regards the calcareous clay, the lowest values of drying and firing shrinkage and water absorption are obtained by extrusion and moulding, respectively. The mechanical resistance, pore size distribution and critical pore diameter do not reflect clearly the influence of shaping techniques. Independently from the shaping technique adopted, all non-calcareous bodies show higher Maage's indexes than the calcareous ones. In any case, the Maage's durability factor is higher in extruded samples.

This contribution reports the use of industrial wastes, red mud and tionite, obtained upon refining and extraction of bauxite and titania ores, respectively. For red mud, two applications were explored: geopolymers and clinker/cement. According to this study, only after 14 days the effects of addition of red mud are translated into technological properties of geopolymers. Moreover, in small proportions the mechanical strength was improved at 28 days curing, certainly due to the high alkaline nature of the waste. Belitic clinkers with balanced amounts of cementitious phases were produced at 1,350 degrees C. Mortars cured for 10 days produced from those clinkers/cements show mechanical strength that tends to increase when high amounts of C3S are formed. The relative content of C2S is also important in the hardening process. With the addition of red mud, the technological properties of the mortars were enhanced due to the pozzolanic reactivity of this sludge. The tionite was selected to be recycled as ceramic pigment. The colorimetric parameters of tionite pigment calcined at 1,200 degrees C and its application in transparent glaze show a light brownish colour, due to the strong brightness (L*). This colour should be exalted by the intercalation of metal ions present in the sludge that could form a metal bearing rutile phase. In the glaze, the yellow component (+b*) doubled and responds for the final beige coloration.

The influence of magnesium silicates, as sintering promoters, on the technological behaviour of porcelain stoneware tiles has been investigated. Three different raw materials formulations were studied: a typical industrial body, containing sodium feldspar as flux, and two alternative mixtures containing talc or chlorite as magnesium source, in partial replacement of feldspar. The comparison of the technological properties of fired products highlighted a higher reactivity during sintering of bodies containing magnesium silicates, that seems to be connected with both a larger amount and a lower viscosity of the liquid phase formed at high temperature. (orig.)

Kaolinitic materials crop out in the Tresnuraghes mining district (Western Sardinia, Italy). Three main kaolinitic deposits, located in the Patalza, Salamura and Su Fongarazzu areas, respectively, were investigated in order to assess their potential in the ceramic industry. The parent rock-types of this raw material are the Oligocene–Miocene rhyolitic–rhyodacitic ignimbrites. Chemical and mineralogical analyses were performed on representative samples of each deposit, by XRD and XRF methodologies. The chemical analyses generally show high silica and low alumina contents in all samples, typical of weakly kaolinized materials. The main mineralogical association consists of kaolinite and cristobalite with quartz and smectite as the minor components. Alunite may be present as a main mineral in the Salamura and Su Fongarazzu deposits, making these clay materials unsuitable for ceramic applications. The Patalza deposit exhibits low iron and sulphur contents, but low plasticity and excessive refractoriness. The Patalza materials can be used as unconventional raw materials to replace both kaolin and silica in white-firing bodies. Results show that the introduction of the Patalza “kaolins” was well tolerated in bodies for tableware, wall and floor tiles, without significant changes in porosity, bulk density, pore size distribution and coefficient of thermal expansion. The main drawback of using the Patalza material is the slight increase of firing shrinkage, while the main advantage is a systematic increase in mechanical resistance.

The use of a zirconium compound (ZrOCl 2 ) to neutralize HF in the microwave-assisted acid dissolution of ceramic glazes for their chemical analysis was tested. Zr is a strong complexing agent for the fluorine ion and permits the determination of those elements which would form insoluble fluorides. The use of Zr implies strong spectral interferences and a high salt content; however, we found that at least 27 elements can be measured with low detection limits, and satisfactory precision and accuracy. In addition, the use of ZrOCl 2 would permit the complete analysis of a ceramic glaze with a single attack when acid-resistant mineral phases are not present. For potassium determinations in acid matrix, the addition of an ionization buffer was studied in order to increase sensitivity, avoiding ionization interferences and non-linear calibration curves.

Growing environmental concern is promoting the necessity of additional ceramic tests. The use of unknown materials with potential contamination conditions requires further studies to demonstrate that the piece encapsulates the pollutant and that during its firing it does not produce the emission of harmful volatile elements. The objective of this work was to perform both tests in a ceramic paste made with slip-casting wastes and electro-plating residues. The leaching methods for determining the encapsulation of potential harmful elements were performed following the TCLP, EP-Tox norm. Having precise chemical analysis of both crude and fired brick, the problem of emissions losses during the firing can be solved by the gain/loss techniques used in geological studies. In particular, the Isocon method that permits a quick visualization of the lost elements is useful. Once the volatile elements were determined, their amount was calculated considering a constant element and the chemical concentrations normalized by the loss of ignition, or using the crude/fired brick ratio densities. The leaching tests indicate that the ceramic brick does not produce harmful leachates according to Argentinean specifications. The leachates of B and Ca are high. Ca does not seem to be a problem while the B content is beyond the permitted limits. During the firing, volatilized elements are Ag, Br, Cl, F, Hg, S, Se, and H 2O. The loss of Ag, Br, and Se are negligible. For F and Cl the potential emission rate is very low (100 mg/kg) while in the case of S, the 2,600 mg/kg rate is high. However, extrapolated emission rates at the chimney assuming an air-to-brick ratio of 2.5 N m 3/kg, are approximately 1,040 mg/N m 3 for S and 40 mg/N m 3 for F and Cl, falling inside environmentally acceptable values. The geochemical procedures proved to be useful tools to assess the element mobilization during firing of ceramic wares and in the analyzed case, the results indicate that the paste is environmentally acceptable. Fil: Dominguez, Eduardo Alejandro. Universidad Nacional del Sur. Departamento de Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; Argentina Fil: Dondi, Michele. Instituto di Scienza e Tecnologia dei Materiali Ceramici; Italia Fil: Iglesias, Claudio. Piedra Grande S.A.; Argentina