Waste recycling in ceramic tiles: a technological outlook

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

Recycling PC-TV waste glass in clay bricks and roof tiles

Disposal of PC and TV sets is a growing problem, involving for over 40 wt. % waste glasses with high Pb (funnel) or Ba-Sr concentration (panel) which cannot be recycled in the glass manufacture. A possible way to re-use these glasses is in the manufacturing of clay bricks and roof tiles, that was appraised by laboratory simulation of the brickmaking processing and technological characterization of unfired and fired products. The recycling of both funnel and panel glasses into clay bodies is technologically feasible, resulting in a behaviour substantially plasticity-reducing during shaping-drying (implying a reduction of mechanical strength) and promoting sintering during firing. No significant release of Pb, Ba and Sr was found during firing and leaching test for the carbonate-poor body; in contrast, some Pb volatilization during firing and Sr leaching were observed for the carbonate-rich body. Additions of 2 wt. % appear to be practicable, while 5 wt. % glass induces unacceptable modifications of technological properties. The recommended amount is within 2 and 4 wt. %, depending on the characteristics of clay bodies. The main constraint is that glass must have a particle size below the limit of pan mills used in brickmaking (<1 mm)

Titania slag as a ceramic pigment

The phase transformations and colouring mechanisms that occur during the ceramic processing of titania slag were investigated using XRF-EDS, XRD, DRS and laboratory-scale application in glazed and unglazed tiles. The slag transforms to pseudobrookite, undergoing a drastic colour change during firing as a consequence of thermal oxidation with Fe2+ to Fe3+ and Ti3+ to Ti4+ reactions. The intense brown colour imparted by titania slag is stable at both low (up to 1050 degrees C) and high (around 1200?C) temperatures and is suitable for porcelain stoneware tiles. In through-body application, titania slag enables \u27spotting\u27 effects to be achieved

Expression of Tight Junction and Drug Efflux Transporter Proteins in an in vitro Model of Human Blood–Brain Barrier

Interendothelial cell tight junctions (TJs) proteins contribute to maintain the structural and functional integrity of the blood–brain barrier (BBB) and several efflux transporters regulate transport of compounds across BBB. A unique double compartment-model of the BBB, consisting of cerebral endothelial cells isolated from cryopreserved human glial tumors, alone and in the presence of human astroglial cells derived from the same tissue preparation was established. Endothelial cell viability and transendothelial electrical resistance (TEER) were measured in this model and three representative TJ proteins – occludin (OCLN), zonula occludens-1 (ZO-1) and claudin-5 (CLN-5) – as well as several drug efflux transporters – P-glycoprotein (P-gp), multidrug resistance protein-1 and 2 (MRP-1 and MRP-2), organic anion-transporting polypeptide-1 and 3 (oatp1 and oatp3) were analyzed at both the protein and gene transcript level. Functional activity of P-gp and MRP-1 was also assessed. Endothelial cell viability as well as TEER significantly increased in the presence of glial cells. A significant increase of expression of OCLN, ZO-1, and CLN-5 proteins as well as of several drug transporter proteins except oatp3 and MRP-1, was also found in the presence of glial cells. All the gene transcripts protein analyzed were found to be significantly increased in the presence of glial cells. A suitable functional activity of P-gp and MRP-1 was also found. These results demonstrate that this brain endothelium culture system mimics a physiologically relevant situation and may therefore provide a new tool for studying the effects of biological fluids such as serum and cerebrospinal fluid from patients with neurological disorders underlying a BBB alteration in disease pathogenesis

Alternative route for the synthesis of Lanthanum Strontium Titanate as SOFC Ni-free anode material

Among the perovskite structures, lanthanum-doped strontium titanates have attracted a lot of attention as possible candidates for SOFC Ni-free anodes. In particular the composition LaxSr1-(3x/2)TiO3 with x = 0.4 (LST) was recently considered for its tolerance to redox cycles and sufficiently high conductivities values. In this work an extensive study on the synthesis of LST powders with low-cost and easy-scalable methods is reported. The solid state and chemical synthesis as well as a combination of solution-solid state synthesis were considered. The influence of either the nature of the precursors (oxides, carbonates or nitrates) and the calcination temperature (from 500 to 1350?C) onto the perovskite formation was evaluated. The as-synthesized powders were morphologically, structurally and chemically characterized. The Pechini method leads to pure perovskite phase at 700?C for 1h, but it allows the production of only few grams of powder for each batch. On the other hand the solid state synthesis is a more up-scalable method but the phase can be obtained only at 1100?C for 1h. In addition the high reactivity of the lanthanum towards the humidity leads to a difficult control of the system stoichiometry and therefore of the final phase composition. An alternative solution-solid state synthesis was considered to produce batch of 100g of LST powders with good phase purity and in relatively mild conditions. The pure perovskite phase with the correct stoichiometry was obtained starting from the La and Sr nitrate aqueous solutions, highly reactive TiO2 followed by freeze-drying and calcination at 900?C for 1

Process of pyroplastic shaping for special-purpose porcelain stoneware tiles

A novel technique to manufacture special-purpose tiles (i.e. trim pieces, steps, skirting boards, etc.) has been recently developed on the basis of a pyroplastic shaping of porcelain stoneware tiles. This innovative process involves a second firing, peaking at temperatures close to those of sintering, whose effect was investigated by comparing industrially-manufactured tiles before and after pyroplastic shaping. Characterization by XRF, XRPD, SEM and standard testing (ISO 10545) put in evidence that pyroplastic bending induced little changes in the water absorption and bulk density values, as in phase composition. Limited variations occurring to closed porosity, mechanical strength and microstructure do not significantly affect the overall technological performance of the special-purpose tiles, which is substantially the same of the original porcelain stoneware tiles. A detailed microstructural characterization was performed for the first time on porcelain stoneware tiles: coarse grains (>10 ?m) represent 10-15% of total volume, while fine-grained crystals, dispersed in the glassy phase, amount from 30% to 65% of the viscous matrix. The pyroplastic behaviour was found to depend in a complex way on such microstructural and compositional features, which deeply affect the effective viscosity of the matrix

Recycling the insoluble residue from titania slag dissolution (tionite) in clay bricks

Tionite is the insoluble residue from the titania slag dissolution process for TiO2 manufacturing. It is a fine grained sludge consisting of rutile, anatase, amorphous phase and bassanite. Chemical composition is TiO2 (ca. 50%), SiO2 (ca. 30%) and minor Al, Ca, Mg, and Fe, plus residual sulfur, implying an acidic pH of waste. Moisture is about 35% of dry weight. The potential of tionite as colouring agent in clay bricks was appraised by admixing (up to 9%) either as-produced or neutralized tionite to four industrial clay bodies. The effect on technological behaviour was assessed by laboratory simulation of the industrial brickmaking process and determining working moisture, drying sensitivity, shrinkage and bending strength, water absorption, bulk density, efflorescence, and colour. The use of tionite is technologically feasible, with little adjustment of industrial cycle, and resulting brick performances depend remarkably on the composition and properties of clay bodies. Carbonate-rich bodies seem to be affected by tionite more during drying than during firing; carbonate-poor bodies range from little changes to consistent worsening of brick performances. No relevant changes of process and product parameters were found up to 3% tionite. Additions over 5% induce significant variations, such as increase of working moisture and water absorption, decrease of bulk density and bending strength. A definite and consistent improvement of this technological behaviour is achieved by using neutralized tionite. The yearly output of tionite could be entirely recycled by approximately four average size brickworks adding about 3% of residue (dry weight

Glass-ceramic frits for porcelain stoneware bodies: effects on sintering, phase composition and technological properties

In the present work, the effects of glass-ceramic frits (10wt%) added to a porcelain stoneware body in replacement of non-plastic raw materials, were evaluated simulating the tile-making process. Each glass-ceramic frit plays its own peculiar effect on the compositional properties and only some precursors behave as real glass ceramic materials. The positive influence of glass-ceramic precursors in promoting the sintering stands out when temperature onset densification and sintering rate are considered: both of them are improved with respect to the reference body. The presence of glass-ceramic frits allows the preserve good technological properties, complying with the latest requirements of the industrials practice

Processing and properties of large-sized ceramic slabs

Large-sized ceramic slabs - with dimensions up to 360x120 cm2 and thickness down to 2 mm - are manufactured through an innovative ceramic process, starting from porcelain stoneware formulations and involving wet ball milling, spray drying, die-less slow-rate pressing, a single stage of fast drying-firing, and finishing (trimming, assembling of ceramic-fiberglass composites). Fired and unfired industrial slabs were selected and characterized from the technological, compositional (XRF, XRD) and microstructural (SEM) viewpoints. Semi-finished products exhibit a remarkable microstructural uniformity and stability in a rather wide window of firing schedules. The phase composition and compact microstructure of fired slabs are very similar to those of porcelain stoneware tiles. The values of water absorption, bulk density, closed porosity, functional performances as well as mechanical and tribological properties conform to the top quality range of porcelain stoneware tiles. However, the large size coupled with low thickness bestow on the slab a certain degree of flexibility, which is emphasized in ceramic-fiberglass composites. These outstanding performances make the large-sized slabs suitable to be used in novel applications: building and construction (new floorings without dismantling the previous paving, ventilated fa?ades, tunnel coverings, insulating panelling), indoor furnitures (table tops, doors), support for photovoltaic ceramic panelsSe han fabricado piezas de gran formato, con dimensiones de hasta 360x120 cm, y menos de 2 mm, de espesor, empleando m?todos innovadores de fabricaci?n, partiendo de composiciones de gres porcel?nico y utilizando, molienda con bolas por v?a h?meda, atomizaci?n, prensado a baja velocidad sin boquilla de extrusi?n, secado y cocci?n r?pido en una sola etapa, y un acabado que incluye la adhesi?n de fibra de vidrio al soporte cer?mico y el rectificado de la pieza final. Se han seleccionado piezas en verde y cocidas, caracteriz?ndolas desde el punto de vista tecnol?gico, composicional (FRZ, DRX) y microestructural (MEB). Los productos semiacabados muestran una destacada uniformidad microestructural y estabilidad dimensional, dentro de un amplio margen de temperaturas de cocci?n. La composici?n de las fases y la compacidad de la microestructura, son muy semejantes a las que presentan las baldosas de gres porcel?nico convencionales. Los valores de la capacidad de absorci?n de agua, densidad aparente, porosidad cerrada, propiedades funcionales as? como las propiedades tribol?gicas y mec?nicas se sit?an en los mejores valores de las piezas de gres porcel?nico. No obstante las grandes dimensiones, unidas al reducido espesor dotan a las piezas de una cierta flexibilidad, que refuerza el empleo de la capa de fibra de vidrio. Estas destacadas propiedades hacen utilizables, a los grandes formatos, en nueva s aplicaciones, construcci?n y edificaci?n (sin desmontar los pavimentos preexistentes, fachadas ventiladas, revestimiento de t?neles, paneles aislantes etc.) muebles ( encimeras y puertas), soporte de paneles fotovoltaico