Recycling of polishing porcelain stoneware residues in ceramic tiles

The possibility of recycling residues, coming from the industrial polishing process of porcelain stoneware tiles, by their incorporation in a porcelain stoneware body mix, was studied. Starting from a standard body mix, several modified body mixes were prepared by replacing different amounts of the fluxing component, a sodium feldspar sand, with these wastes. The densification behaviour of the different body mixes was investigated by determining water absorption, linear shrinkage and bulk density of the as fired specimens. Phase and microstructural examination, by quantitative X-ray diffractometry and scanning electron microscopy-energy dispersive spectroscopy, made it possible to explain the mechanical behaviour, i.e. flexural strength, Young's modulus and Weibull's modulus. The presence of polishing porcelain stoneware residues, PPR, in particular in a 10 wt% of replacement, made possible a consistent decrease in the maximum temperature of the thermal cycle. That did not cause significant variations in the mechanical strength of the materials, while a slight decrease of the elastic modulus and a remarkable increase of the reliability were registered.     

Influence of mineralogical composition of applied ball clays on properties of porcelain tiles

Relations between quality of ball clays applied in raw materials batches for manufacture of porcelain tiles, and physical properties and microstructure of obtained tiles, were investigated. Studied clays constituted 35% of the batch, while the other components were unchangeable. Stoch index, new IR 3620/3700 index and XRIR index (Stoch index multiplied by IR 3620/3700 index), were proposed to take into account crystallinity of kaolinite and contents of illite and smectites in studied clays. Relationship between XRIR index value of clay, and water absorption and abrasion resistance of the obtained ceramic material, was found. Water absorption of the tile is also correlated with grain size distribution and bending strength of used clay. Optimal ball clay for porcelain tile production should exhibit: Stoch index - min. 4.3; IR 3620/3700 index - min. 1.2; XRIR index - min. 4.8; grain size median - max. 0.27 μm; bending strength after drying - min. 8.0 MPa.     

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 μm) 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.     

Effect of soda-lime glass on sintering and technological properties of porcelain stoneware tiles

The feasibility of waste glass recycling in ceramic tile production was assessed with special reference to fully vitrified products (porcelain stoneware). Soda-lime float or container glass was introduced, in replacement of sodic feldspar, in typical porcelain stoneware bodies (up to 10 wt.%) that underwent a laboratory simulation of tilemaking process, with a technological and compositional characterization of both fired and unfired tiles. Soda-lime glass had no significant effect on semi-finished products, but it influenced remarkably the firing behaviour, increasing shrinkage and closed porosity, decreasing open porosity and bulk density, and lowering mechanical and tribological performances. Waste glass promotes a more effective melting of quartz and a partial dissolution of mullite, leading to a more abundant and less viscous liquid phase, which accelerates the sintering kinetics. In conclusion, soda-lime glass can be used in small amounts (5% or less) with tolerable modifications of technological behaviour and performances of porcelain stoneware tiles.     

Utilization of granodiorite in the production of porcelain stoneware tiles

In the present study, the use of granodiorite, as fluxing agent in a body mix for stoneware ceramic tiles production, was assessed. Four batches were formulated using clay from Khaboba, and natural granodiorite from Saint Katherine, Sinai, Egypt. The batches were tailored to completely replace both feldspatic and inert components of stoneware ceramic tiles. Densification was studied according to ISO rules, while sinterability was estimated by optical dilatometry. The dependence of microstructure and mechanical properties of stoneware ceramic tiles on granodiorite content was discussed. Strength measurements showed that increasing granodiorite content the bending strength of the bodies increased. In particular the studied batches can be used for the production of industrial fast firing tiles. The obtained ceramic tiles possess properties similar to commercial ceramic floor and/or wall tiles.     

Development of lightweight porcelain stoneware tiles using foaming agents

Recent market trends for porcelain stoneware tiles indicate that there is a growing interest for lightweight products, to be used vertically, in internal walls or ventilated facades. The decorative and structural functions have now been coupled with additional features, such as thermal insulation. The optimization of all functionalities depends on a careful control of porosity, in terms of overall amount, size and morphology. In this paper, we propose fundamental correlations between mechanical properties, water absorption, porosity and technological aspects, and particle size and the amount of foaming agent (SiC). The data indicate that the addition of SiC powder with a size < 10 μm enables the fabrication of tiles possessing a suitable strength, negligible water absorption and a weight reduced by 26%. The loss of mechanical strength of the tiles and their pyroplastic deformation controls the maximum attainable decrease in weight.     

Effect of strong mineral fluxes on sintering of porcelain stoneware tiles

Strong fluxes are needed to fire vitrified ceramics at temperatures significantly lower than those usually reached in industrial firing cycles. This work is aimed at understanding the role of strong fluxes in the microstructural evolution during sintering. Six fluxes (colemanite, ulexite, wollastonite, diopside, spodumene and phonolite) were individually added to a porcelain stoneware batch and processed in standard conditions. Compacts and fired bodies were characterized by optical dilatometry, XRD-Rietveld, SEM and measuring technological properties. Strong fluxes change the firing behaviour with a complex interplay of sintering kinetics, microstructural features, and phase composition. Every flux has its own repercussion on the properties of the liquid phase (chemical composition, degree of polymerization, viscosity and surface tension) which are key points to explain the observed microstructure, densification rates, and stability at high temperature. Batches with phonolite, wollastonite or diopside exhibit characteristics closer to standard porcelain stoneware, while spodumene and borates suffer from unsatisfactory microstructures and lower densification efficiency.     

Dependence of surface porosity on the polishing depth of porcelain stoneware tiles

Porcelain stoneware tile polishing is a process that adds value to ceramic tiles due to the high gloss achieved upon reducing surface roughness. However, surface polishing removes a fine layer of the product, revealing numerous “closed” pores initially located inside the material, which may compromise some of its properties such as stain resistance. The literature indicates a possible orientation of pores on surfaces parallel to that of the use of the product. Based on this hypothesis, the present work aimed to evaluate how the thickness of the layer removed by polishing acts upon the profile of exposed surface pores, and hence, on the stain resistance of the product. The results of this study are novel and reveal that the staining tendency of porcelain stoneware tile can be altered significantly by varying the conditions of the surface wear produced by polishing.     

The role of viscosity on microstructure development and stain resistance in porcelain stoneware tiles

Effect of composition on viscosity of porcelain stoneware tiles and role of the viscosity on microstructure development and stain resistance in porcelain stoneware tiles were investigated. The viscosity of the tiles was successfully measured by a thermomechanical analyzer. Na₂O/K₂O ratio was used as a parameter to change the viscosity. As the Na₂O/K₂O ratio increases, the viscosity decreases. This reduction in the viscosity results in improvement of microstructure (i.e., spherical pore morphology and reduced closed porosity) and usually increases the stain resistance significantly. However, too low viscosity may also cause deformation of the tile during production. Therefore, the viscosity of the tiles should be carefully controlled and it should lie between a lower limit (in this study this value is between 10^7.93 and ～10^8.35 P) and an upper limit (in this study this value is 10^8.67 P) to achieve high stain resistant porcelain tiles with no deformation.     

Evaluation of texture distribution during the industrial polishing process of porcelain stoneware tiles

The present work addresses the distribution of texture over the surface of porcelain stoneware tiles due to kinematics imposed by industrial polishing process. The scratching process was simulated using a computational algorithm, which was based on the kinematic equations for the whole myriad of abrasive particles. Different scratching patterns were identified over the polished surface and their corresponding positions were mapped. The experimental results showed that regions in the tile centre present smaller tendencies for exhibiting preferential textures than those of the lateral ones. The final texture was slightly asymmetric and different from those simply left by the last scratches. The definition of three polishing domains was then suggested according to different phenomenological criteria. Results from both experiments and simulations made evident the influence of the kinematic parameters adopted by the industries on the polishing quality of porcelain stoneware tiles.     

Effect of waste glass and zircon on ceramic properties and microstructure of porcelain tiles

Abstract

The possibility of using waste glass as a flux in porcelain tiles without deterioration in mechanical properties has been assessed. Waste glass was added to a typical porcelain tile body, replacing feldspar by up to 15%. Zircon was also added at 5% in partial replacement of quartz. The prepared batches were fired at temperatures of 1160 to 1240°C with 20 min soaking time. Addition of 5% zircon in the presence of 5% waste glass resulted in unusual mechanical and physical characteristics. Further additions of waste glass enhanced vitrification and consequently some surface and mechanical properties, but worsened modulus of rupture (MOR) and toughness. Generally specimens containing zircon had better physicomechanical properties.     

The role of surface microstructure on the resistance to stains of porcelain stoneware tiles

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).     

Effect of microstructure on mechanical properties of porcelain stoneware

This work examines the effect of microstructure (aspect ratio of mullite crystals and proportion of crystalline and amorphous phases) as well as different physical features (bulk density, closed and open porosity and absolute density) on the mechanical properties of a standard porcelain stoneware composition (50% kaolinitic clay, 40% feldspar and 10% quartz) fired in the 1200–1300 °C temperature interval using a fast firing schedule. The mechanical behaviour was evaluated in terms of bending strength, Vickers microhardness, fracture toughness and Young's modulus. After viewing the results, it can be concluded that increased σ_f, H_v and E values were mainly due to open porosity, percentage of mullite phase and morphology of secondary mullite needles, whereas closed porosity and quartz particles have no influence on these properties.     

Kinematics of a single abrasive particle during the industrial polishing process of porcelain stoneware tiles

In order to achieve glossiness the porcelain stoneware tiles must undergo an industrial polishing process, which can be optimized by either the scratching phenomena or the polishing kinematics. This paper is focused on the latter. Thus, the most important kinematic equations involved in polishing process were described. The lateral oscillation used in modern polishing machines, as well as the other available motions were taken into account. The trajectory of abrasives, the scratching speed and the curvature radius could be obtained for each instant. The importance of adopting good kinematics parameters for the accomplishment of the polishing process was highlighted, and the equations furnished hereby serve as useful tools for further attempts in optimizing the polishing process.     

Utilization of muscovite granite waste in the manufacture of ceramic tiles

Granite waste is by-product from a decorative rock industry. The present study aims to investigate the effect of muscovite granite waste on the physico-mechanical properties of ceramic tiles to demonstrate its suitability for industrial production. A series of flooring- and facing ceramic tiles were prepared by adding 20, 25, and 30 wt% muscovite granite waste into the batch compositions. The sintering behavior and degrees of densification of two kinds of ceramic tiles were evaluated by determining their physico-mechanical properties and characterizing them by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. As expected, the facing ceramic tile (FacCT1) sample, containing wollastonite, hematite, anorthite, quartz, and cristobalite, with 20 wt% muscovite granite waste showed lower physico-mechanical properties than those of the flooring ceramic tile (FloCT3) sample, containing mullite, calcium aluminosilicate, quartz, and cristobalite, with 30 wt% muscovite granite waste. The reason is that lower firing temperatures cannot accelerate a complete fusion of the granite waste which behaves like an inert non-plastic material similar to quartz. These results illustrate the prospects of utilizing muscovite granite waste in ceramic tile production.     

Firing transformations of Chilean clays for the manufacture of ceramic tile bodies

This contribution is focused on the study of the mineralogical changes occurring in the ceramic body after heating ceramic clays. Chile has an important local ceramic industry. Five deposits of clays with industrial applications were studied. The clays came from San Vicente de Tagua-Tagua (SVTT), Litueche (L), Las Compañías-Río Elqui (LC), La Herradura-Coquimbo (LH) and Monte Patria-Coquimbo (MP). The samples were heated to 830, 975, 1080 and 1160 °C keeping at the maximum temperature for 35 min. The bending strength of each ceramic body was determined at 1100 °C. Mineralogical analysis of the fired samples was carried out by X-ray diffraction. The SVTT contained quartz, spinel, cristobalite, microcline, albite, anorthite, hematite and enstatite; the LC clays quartz, mullite, spinel, microcline, albite, anorthite, hematite, diopside, enstatite, illite/muscovite and talc; the LH clays quartz, cristobalite, microcline, albite, anorthite, hematite, diopside, illite and augite; the MP clays quartz, cristobalite, microcline, albite, anorthite, hematite, diopside, gehlenite, enstatite and wollastonite and the L clays quartz, microcline and mullite. The persistence of illite at at least 900 °C was observed for LC and LH. SVTT and LH showed the required specifications for earthenware. The L clays were refractory clays with very low bending strength.     

Effect of moulding pressure on microstructure and technological properties of porcelain stoneware

The properties of green and fired porcelain stoneware bodies have been studied in samples moulded at different pressures (10, 20, 30 and 40 MPa). In green tiles, higher differences in properties have been found at lower moulding pressure. After the fast-firing process, the tiles have been tested to obtain the technological properties such us lineal shrinkage, water absorption, porosity and bending strength. Results show that higher moulding pressures (30 and 40 MPa) give rise to tiles with similar technological properties. The amount of mullite and quartz remains constant in all pieces after firing process. SEM observations show that mullite crystals are longer as moulding pressure increases, that means that initial moulding pressure has a marked effect on mullite development, which is the main responsible of final properties.     

Effect of fugitive phase addition on porosity evolution and properties of stoneware tiles

Abstract

Abstract

Different percentages of fugitive phase with three different average particles were added to the green porcelain compositions. The fugitive phase was burnt out during the sintering, and the shrinkage of the samples was proportional to the added volume. The lower the particle size of the fugitive phase was, the higher the shrinkage became. The properties of stoneware tiles as apparent density, linear shrinkage, modulus of rupture, porosity, roughness and water absorption were studied as function of the added fugitive phase. A reduction of the porosity was obtained when the added fugitive phase was <5?vol.-%. The modulus of rupture improvement was found in samples with higher density. The surface roughness increased by both the volume and the particle size of fugitive phase. Large added porosity volume was effectively eliminated, and the porosity was equilibrated to a fixed value related to the initial particle size of the fugitive phase. The main mechanism that contributed to the elimination of porosity during liquid assisted sintering was the gas diffusion. Large pores were hindered by the crystalline phases, and thus pore, coalescence was avoided in the porcelain stoneware.