Search

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.

Clays are irreplaceable raw materials for ceramic processing. The availability of clay deposits of suitable quality and quantity is an important competitive factor and a key issue for the economic sustainability of ceramic production. The identification of adequate sources of clay materials is an important issue that requires an appropriate methodological approach. In the form of simple guidelines, this articles reports on how to conduct clay prospecting and evaluate the technological properties of raw materials. This first part describes the deposits of different types of ceramic clays, illustrating their origin, composition and geological criteria in the prospection. The second part will introduce the technological evaluation of clay materials, and describe in detail the four steps of clay prospecting.

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.

The purpose of this study is to evaluate different lightweight concretes for the first time formulated with lightweight expanded aggregates produced only with industrial waste. The motive is that a lack of knowledge still exists in the literature about how to integrate these waste-based aggregates in lightweight concrete. To achieve the desired bloating and aggregates physical properties, PC-TV screen glass and ceramic tile polishing sludge were selected as suitable raw materials. Both were characterized by mineralogical and chemical analyses and the effect of different combinations was pointed out. Hot-stage microscopy was used to determine the bloating rates and firing behavior. Lightweight expanded aggregates were obtained using both static laboratory kiln and rotating pilot kiln, by firing at maximum temperatures between 1150 and 1200 ◦C, to simulate the industrial production process and favor scaling up. The so obtained aggregates were characterized from the physical-mechanical point of view, highlighting an important bloating attitude and bulk density lower than 700 kg/m3 for all the test conditions. Bulk density, water absorption and mechanical properties are fully comparable to commercial counterparts. The best material was used as coarse aggregate in lightweight structural concrete and cellular concrete prepared at pilot scale (for structural application and thermal/acoustic insulation, respectively). The technical properties are consistent with standard requirements of compressive strength (>25 MPa for lightweight structural concrete) and thermal conductivity (18–24 W/m*K for cellular concrete). These results demonstrate the technological feasibility of using waste-based aggregates into lightweight concrete design, according to a circular economy vision.

In recent years, the management of construction and demolition residues (CDRs) has become a major challenge for the construction industry due to the increasing volume of waste produced and its associated environmental impact. The aim of this article is to assess the effect of fine-grained fractions (&lt, 0.125 mm–0.6–0.125 mm) of construction and demolition residues, obtained by industrial sorting in a CDR processing plant in Rovigo (Italy), on the technological behavior and technical performance of clay bricks. Simulating the brickmaking process on a laboratory scale, it was appraised whether the CDR additions determined any change in the main properties of both fired and unfired bricks, taking a CDR-free brick body as a reference. The results indicated that the use of CDR is technologically feasible. It is possible to obtain, through proper crushing and sorting operations, grain-sized fractions with quite homogenous chemical and mineralogical composition. The residues did affect the compositional properties, porosity and water absorption of the clay bricks. Nevertheless, the characterization of the residual-added semi-finished and fired products highlighted their good technological and mechanical properties, which allowed them to provide performances similar to those of standard bricks manufactured with raw natural materials.

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.

The production of ceramic tiles is continuously increasing worldwide, implying a growing demand for raw materials. On the other hand, the progressive depletion of the main feldspathic flux deposits is forcing the ceramic industry to search for suitable substitutes. Although the tile-making industry proved to be able to recycle its own processing residues, the use of wastes from further sources is at present quite limited. The use of glassy wastes, for instance, is usually hindered by technological reasons: a low-melting glass can significantly affect the firing behavior and particularly high temperature permanent deformations. The main goal of this study is therefore to assess the firing behavior of porcelain stoneware bodies containing glassy wastes, and particularly to verify if the sintering kinetics can be satisfactorily predicted applying the well-known models inherited by the glass densification theory, as the Frenkel's model. Five different sources (bottle, PC-TV screen, lamp, glaze manufacturing and porcelain stoneware grinding sludge) provided glassy wastes that were separately added to a reference body in amount of 20%. Each batch was characterized from the chemical point of view and its sintering kinetics were determined in isothermal conditions by optical thermo-dilatometric analysis (TA ODP868). The isothermal tests were carried out at Tgr (gresification temperature) with a heating rate of 80°C/min up to Tgr and 30 min of dwell time. The quantitative phase composition after firing at Tgr was determined by XRD-Rietveld in order to calculate the chemical and physical properties of the vitreous phase. Shear viscosity and liquid-air surface tension were used as input of the Frenkel's model to calculate the initial sintering rate of the bodies. Such calculated sintering rates were then compared with the experimental rates derived from sintering curves. The introduction of a certain amount of glass into a porcelain stoneware body determines a clear change in the sintering mechanism. The waste-free batch behaves substantially in agreement with the Frenkel's model, confirming that the initial sintering rate is fundamentally governed by the physical properties of the liquid phase. However, the addition of 20% glass reflects into a significant deviation from the behavior of the benchmark, that sees the Frenkel's model failing to predict accurately the sintering rate on the basis of melt viscosity and surface tension just in two cases.

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.

Porcelain stoneware is sintered by partial vitrification through viscous flow of a liquid phase formed at high temperature. This sintering process involves a complex evolution of both phase composition and chemistry of the liquid phase, according to the dynamic equilibrium established with the residual minerals and the new crystalline phases formed during firing. The present contribution overviews the evolution of phase composition and microstructure of seven body formulations during firing at different temperatures and dwell times. Each mixture was characterized from the chemical point of view and, once fired, by XRPD (quantitative phase composition), SEM and optical microscopy (microstructure). Moreover, the sintering behavior of the batches was investigated in isothermal conditions by optical thermo-dilatometric analysis. The results indicate that the continuous variation of the phase composition during the heating treatment affects the chemical composition of the liquid phase reflected on the densification kinetics and pyroplastic deformation of tiles.

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.

Ceramic foams represent an interesting class of materials for applications as insulator, thanks to their low flammability, which makes them a safer alternative to polymeric insulation products. Ceramic foams are characterized by peculiar microstructures with a porous texture, which formation can be induced by the introduction of foaming agent. Its activation within the ceramic batch is achieved during the firing process. The integration of Phase Change Materials (PCM) into the pores of the ceramic matrix represents a challenging goal to significantly improve the thermal insulating performances and comfort of buildings. The possibility to embody PCM into porous fired tiles is strictly related to the size and number of pores formed during the process. For this purpose, the capability to control and predict the bloating phenomena as a function of the tile size is a key point to define the thermal performances of final device. Starting from a typical porcelain stoneware tile formulation, silicon carbide (SiC) powder was added as foaming agent. Furthermore, the bulk composition was optimized by addition of glass scraps aiming to reduce the carbide stability in order to observe bloating phenomena in a temperature range typical of the industrial ceramic tiles production. To evaluate how the tile size can influence microstructure, in terms of amount, shape and size of pores, a laboratory scale up process was carried out. It was done passing from small specimen (30 mm of diameter) to a demonstrator device (150x150 mm). The samples were characterized by bulk density, linear expansion, water absorption and pores distribution. The effects of the firing process parameters on physical properties were studied. The increase of temperature led to an initial decrease of the bulk density, given by gas formation due to SiC oxidation, followed by a progressive densification regardless the increased expansion potential. The amount, size and shape of pores are dependent on both the efficiency of SiC decomposition and glass viscosity. The changes in terms of density are consistent with the porosity, affecting the potential amount of PCM that could be incorporated. Linear bloating and pores size showed an evident relationship to the specimens size, emphasized by the reduction of the heating rate.

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.

The technological behaviour 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 used by novel technologies for large slabs (>4 m2). In order to fill this gap, a systematic approach to properties and behaviour of spray-dried powders for porcelain stoneware slabs was carried out. For this purpose, 11 industrially-manufactured spraydried powders were characterised for their intrinsic features (particle size and agglomerate size distribution; shape and moisture distribution in function of agglomerate size); rheological properties (mass flow, static and dynamic angles of repose, poured and tapped density); compaction behaviour (curves of bulk density, intergranular and intragranular porosity in function of applied load); and firing behaviour, in order to reveal any effect of dry bulk density on shrinkage and bulk density of fired samples. The effect of these intrinsic characteristics on the flowability and compressibility of powders was appraised, as was the mutual relationships between the rheological parameters. 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 strict correlations between the various methods. Flowability mainly depends on the occurrence of coarser aggregates, particularly those irregular in shape, stemming from coalescence of three or more individual agglomerates. The features of green compacts are somehow inherited by the fired bodies, especially in terms of shrinkage and densification kinetics, even though the starting differences are damped during firing. The performance of spray-dried bodies during compaction is crucial to control uniformity, in terms of porosity and bulk density, which has important repercussions on the properties of final slabs, especially considering that residual stresses may be related to differential shrinkages during firing due to density gradients.

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.

In the latest years, the interest about Phase Change Materials (PCM) in building applications grew in force of their capability to adsorb heat and limit in-out building heat exchanges. The main problem is how to introduce PCM into the building envelope, also in case of ventilated facades. For this purpose, a ceramic foam was studied. Two different batches based on porcelain stoneware and soda-lime glass scraps were prepared to understand the involved bloating phenomena. Suitable bulk density and porous microstructure were achieved by adding a foaming agent and batch optimization. Specimen size was scaled up (from ∅ 3 cm to 15 × 15 cm) and its effect on bloating, PCM incorporation, and thermal properties was studied. Furthermore, different firing temperatures and heating rates were evaluated. The whole study was focused to disclose possible drawbacks in the industrial transfer of the PCM-bearing composite production.

This work aimed to characterize bentonites with different features and origins (Brazil, Argentina, Italy and United States) that were impregnated with Ag, TiO 2 , Pd and Au nanoparticles. Either commercial (TiO 2 ) or synthesized (Ag, Pd and Au) nanoparticles (NP) were used and characterized by DLS and XRD. Subsequently, the dispersed NP was impregnated on bentonite by two alternative methods, imbibition or dipping. The efficiency of impregnation of bentonite by metallic nanoparticles was finally tested by ICP-OES, which was over 90% in all cases. Particularly, Ag nanoparticles showed an impregnation efficiency above 99%, as confirmed by SEM-FEG. To improve impregnation, a thermal pretreatment for the bentonites was necessary at 700 °C. Both impregnation methods resulted in a suitable distribution and stability of Ag nanoparticles.

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 tile industry is a big consumer of feldspathic rocks and further raw materials able to act as flux during firing. This demand is currently fed with the recourse to a wide range of sources of igneous, sedimentary, metamorphic and metasomatic origin. The main geological features of flux deposits actually exploited by the ceramic industry are reviewed. The chemical and mineralogical composition is described to have a general picture of raw fluxes as well as average data and compositional perimeter for deposits of different origin. Overall beneficiation routes are drawn to trace the compositional path from deposit to commercial flux. The technological behavior in tile-making is shortly overviewed and new experimental data are provided on flux fusibility (by hot-stage microscopy). A chart is proposed to discriminate fluxes according to different fusibility.

The progressive depletion of the main feldspathic flux deposits in the World is forcing the ceramic industry to search for suitable substitutes. The aim of this study is to assess the potential of some feldspar sources in the Egyptian Eastern Desert, particularly syenites from Abu Khruq, in the manufacture of ceramic tiles. Beneficiated samples obtained by lab-scale mineral processing were tested into porcelain stoneware batches (from 10% to 30% wt in replacement of feldspars) and compared with a reference body through a laboratory reproduction of the industrial processing. The technological behavior of unfired tiles does not suffer any significant alteration due to the use of syenites. On the other hand, syenite-bearing bodies exhibit some changes in the phase composition and the chemistry of the melt, which turns richer in alkali, especially K2O. The consequently increased sintering rate depends mainly on the viscosity of the liquid phase formed during firing. In conclusion, syenites can be used without technological hindrances to manufacture porcelain stoneware tiles. The firing behavior of syenite-bearing batches can be reasonably adjusted by setting key parameters (e.g., the feldspar amount and the Na/K ratio), but the color of fired bodies requires to furtherly lower the iron oxide.

Recent trends in the raw materials market unveil a growing dependence of the European ceramic tile industry on imports from sources outside the European Union. This tendency reflects significant changes in the typologies of ceramic products, which in turn result in a modified batch design and different raw materials. Such an evolution implies an increasing stress on the supply chain, which role is strategic in terms of resource efficiency and competitiveness of the ceramic industry. Despite the importance of a secure and affordable supply, a global knowledge of raw materials flows over the last years is still lacking. In this paper, the supply chain was examined by quantifying the apparent consumption of raw materials and current trends, and detecting possible criticalities. While the supply chain in Italy kept stable, the raw material flows in the Spanish industry changed noticeably due to the increase in white-firing bodies production, that implies a growing dependence on imports. Beyond the specific features of each country, the resulting supply patterns are turning similar over time, with an increasing competition for the same sources. Efforts to strengthen the supply chain reside on the diversification of raw materials sources, which entails the use of secondary raw materials, the search for new deposits and purification processes, and improvement of logistics. The choice of raw materials (and consequently the supply chain) is driven in a complex way by various factors, which are identified and discussed for the different product typologies..

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 firing behaviour of five waste glasses was studied to define key parameters able to predict bloating performances in industrial lightweight aggregates production. Bloating was investigated by hot-stage microscopy and laboratory kiln experiments, also with SiC as expanding agent. In-situ and ex-situ results were contrasted to shed light on the scale up process. Both macro- and microstructure of aggregates are related to the melt properties and crystallization phenomena. A phenomenological model for SiC-induced expansion was proposed. The glass chemical composition controls melt viscosity and kinetics of expansion, while the increase of aggregate size fosters the extent of bloating.