Porous single-fired wall tile bodies: Influence of quartz particle size on tile properties

This study examines the effect of quartz particle size in raw material composition customarily used for the manufacture of porous single-fired wall tile bodies on the characteristics of the green tiles and on the thermal and mechanical properties of the fired tiles. Quartz particle size was varied, while the quantity and particle size of the other raw materials were kept constant. Tile compacts were formed by uniaxial pressing and fired at different peak temperatures. The resulting fired microstructure was then characterised and tile thermal and mechanical properties were determined. Microcrack formation around quartz particles leads to hysteresis of the coefficient of thermal expansion during heating and cooling. The studied mechanical and thermal properties are shown to be a function of the magnitude of the hysteresis and porosity. This relationship is independent of the operating variables (pressing pressure, operating temperature, and quartz particle size) used. The results obtained confirm that the green and fired properties of porous single-fired wall tiles may be considerably enhanced, while holding low shrinkage and high porosity, compatible with low moisture expansion, by reducing quartz particle size and appropriately adjusting the pressing pressure and peak firing temperature. This should enable thin and/or large-sized porous wall tiles to be manufactured, without (immediate or delayed) curvatures, and with a higher breaking load than that required by the standards.     

Porcelain tile microstructure: implications for polishability

The present study examines the influence of porcelain tile microstructure on tile polishability and polishing efficiency. A range of different fired porcelain tile microstructures was obtained by varying the quartz particle size and content in the starting composition, and the peak firing temperature.The polishability of these porcelain tile specimens was evaluated with a tribometer designed to simulate the industrial polishing operation, using cement-matrix silicon carbide abrasive tools. The wear rates of both the tile samples and the abrasive tools were measured. A new parameter, termed ‘polishing efficiency’, was defined as the ratio of tile specific wear rate to pin specific wear rate.Quartz particle size and content in the starting composition, as well as peak firing temperature, strongly affected the fired tile microstructure, and hence the polishability. When the firing temperature lies below the optimum value (at which porosity is minimised) the polishing efficiency increases, while the polished surface quality decreases (i.e. porosity rises). Quartz particle size and content should be minimised in the starting composition to achieve maximum polished surface quality and polishing efficiency.     

Effect of quartz particle size on the mechanical behaviour of porcelain tile subjected to different cooling rates

Porcelain tile is a high-performance ceramic tile, in which quartz is a major compositional component. After the firing cycle, macroscopic residual stresses develop in the product as a result of rapid cooling. Further, during cooling, the presence of quartz particles also increases natural flaw size. Both phenomena significantly affect the product's mechanical behaviour. This study examines the effect of quartz particle size on the mechanical behaviour of porcelain tile subjected to two very different cooling rates: a rapid or a slow cooling rate. A series of porcelain tile compositions were designed for this purpose, in which quartz particle size was varied. The mechanical behaviour of the sintered pieces was evaluated on the basis of linear elastic fracture mechanics. It was verified that, in the slowly cooled material, the modulus of elasticity and fracture energy increased, and natural flaw size decreased as quartz particle size decreased. However, fracture energy also diminished in pieces that contained excessively small particles, with an advanced state of dissolution. For the rapidly cooled material, though the larger sized quartz particles debonded at higher temperatures owing to thermal stress, their presence, even in small quantities, contributed to natural flaw growth. The lower fracture energy associated with this last type of piece also favours this phenomenon.     

Effect of the green porous texture on porcelain tile properties

Porcelain tile is a product characterised by low water absorption (usually less than 0.1%) and excellent mechanical properties. To enhance tile aesthetic qualities, much of the porcelain tile production is polished to provide a high-gloss surface finish, in which certain closed pores in the tile body become visible. This apparent porosity of the polished tile, which had been closed porosity before polishing, sometimes lowers the product's stain resistance.Test pieces were formed from a porcelain tile composition prepared under different milling conditions, pressing variables being kept constant, and the pore size distribution of these pieces was determined. The effect of the porous texture of the green pieces on the evolution of porosity during sintering and on the residual porosity of the densified body was analysed. It was verified that the porous texture of the fired piece was conditioned by the porosity and size of the largest pores in the green piece. The effect of residual porosity on stain resistance was determined by two cleaning methods. The presence of large pores in the green body, stemming from insufficient milling of the raw materials mixture, led to tiles with greater residual porosity and worse stain resistance.     

Cleaner production of porcelain tile powders. Fired compact properties

A new ceramic powder preparation process, the droplet-powder granulation process (DPGP), was recently proposed for the cleaner production of ceramic tiles. The DPGP granules and resulting pressed compacts were characterized and compared with the granules and compacts obtained by spray-drying (SD) and dry granulation (G) processes in a previous paper. The results showed the feasibility of using the DPGP in the pre-firing stage of porcelain tile manufacture.This study compares the firing behaviour and fired properties of compacts pressed from three different types of granulated powders: DPGP, SD, and G and from a non-granulated powder (NG) obtained by dry milling. The evolution of compact microstructure (porosity and pore size distribution) with firing temperature was monitored and the fired compact properties (bulk density, water absorption, and stain resistance) were determined.The study shows that the DPGP improved the sintering behaviour and final properties of the resulting porcelain tiles with respect to those obtained by the G process. However, the fired compacts prepared from the DPGP powder exhibited a higher porosity and pore size compared with those of the compacts obtained from the SD granules at the same pressing pressure. The results obtained open up the possibility of manufacturing glazed porcelain tiles with a more eco-friendly process. However, the results also indicate that polished porcelain tile manufacture by the DPGP requires further research in order to improve granule characteristics, in particular green granule deformability, which is the critical factor in porcelain tile densification and vitrification during firing.     

Development of a multipurpose tile body: Phase and microstructural development

In this study, an attempt was made in order to develop a multipurpose tile body using a single formulation. In order to achieve this, several body recipes were prepared using mainly local raw materials with clearly defined physical and chemical properties at different sieve residues and single fast fired under industrial conditions in the first part of the study. In the second part, the most suitable formulations with the corresponding sieve residues were determined and further fired at different peak temperatures under laboratory conditions in order to establish their vitrification ranges and optimum firing temperatures. The tested peak firing temperatures were varied at 20 °C intervals from 1120 to 1200 °C for multipurpose wall tile body and from 1140 to 1220 °C for multipurpose floor tile body. The physical and thermal properties of the fired bodies such as water absorption, linear firing shrinkage, bulk density and linear thermal expansion coefficient were measured. The vitrification behaviour of the multipurpose bodies was also evaluated using a double-beam optical non-contact dilatometer. Furthermore, the fired bodies were subjected to colour measurements. Particular consideration was given to the phase and microstructural evolution of the developed tile bodies. X-ray diffraction (XRD) was used to analyse the phases formed before and after firing. Scanning electron microscopy (SEM) in combination with energy dispersive X-ray spectroscopy (EDS) was further employed in order to observe the microstructural and microchemical characteristics of the fired bodies with respect to peak firing temperature. The preliminary experimental results showed that it was possible to obtain a multipurpose body with the properties in accordance with ISO-EN 10545.     

Relationship between certain ceramic roofing tile characteristics and biodeterioration

This paper examines the relationship of certain red ceramic roofing tile properties to roofing tile biodeterioration. The following properties were studied: apparent porosity, roughness, and the presence or absence of two types of coatings.The effect of apparent porosity was studied by varying the peak firing temperature of a standard industrial red ceramic roofing tile composition and by preparing several clay mixtures, of different chemical and mineralogical composition, that were fired at various peak temperatures. The effect of roofing tile roughness was determined by either polishing or sanding fired standard red roofing tiles. A waterproof ceramic glaze coating and a photocatalytic coating were formulated to analyse the effect of the presence of different types of coatings. Roofing tile bioreceptivity was evaluated with a method developed in a previous study using the cyanobacteria Oscillatoria sp, which enabled roofing tile resistance to microbial colonization to be determined.As expected, bioreceptivity rose as apparent porosity (measured as water absorption) increased, enabling possible water retention, which favours biological growth. Similarly, greater roughness encouraged micro-organism adhesion and raised bioreceptivity. It was found that, after prolonged exposure periods (several months) under very favourable conditions for biological colonization, roofing tiles coated with the waterproof ceramic glaze were colonized. However, glazed standard red roofing tiles covered with a TiO₂ photocatalytic coating exhibited practically no biological growth under the test conditions used, even after long exposure times, owing to the chemical-physical effect of the TiO₂-based coating.     

Application of grits waste as a renewable carbonate material in manufacturing wall tiles

This work focuses on the reuse of grits waste, from cellulose industry, as a raw material to replace traditional carbonate material in ceramic wall tiles. Wall tile formulations bearing up to 15?wt% of the grits waste were prepared for replacement of calcareous. The tile manufacturing route consisted of dry powder granulation, uniaxial pressing, and firing at temperatures ranging from 1100?°C to 1180?°C by using a fast-firing cycle. The wall tile specimens were tested to determine their physical and mechanical properties (linear shrinkage, water absorption, apparent porosity, apparent density, breaking strength, and flexural strength). The firing behavior, phase transformations, and microstructure were evaluated by dilatometry, XRD, and SEM. The results showed that the fired wall tile specimens are composed of anorthite and quartz, as major mineral phases, and mullite as a minor phase. It was found that the grits waste had a positive influence on the properties and microstructure of the wall tile specimens. The results also revealed that the grits waste from cellulose industry could be used as a total replacement of traditional calcareous material in wall tile formulations.     

Revisiting pyroplastic deformation. Application for porcelain stoneware tile bodies

In this research an analysis of firing deformation tendency in porcelain stoneware tile compositions was carried out based on pyroplastic deformation measurements. The effect of the amount and nature of some fluxing additives as well as some process variables were addressed. Firing diagram, pyroplastic deformation and microstructure examination of fired specimens of the different compositions were carried out.Findings allowed to verify the effect of particle size and unfired bulk density on pyroplastic deformation. Finer particle size and/or higher unfired compactness effectively contribute to reduce pyroplastic deformation. However, the joint effect of particle size and bulk density differs from that observed with more fluxing (redware) floor tile compositions. At compositional level, the effect of some alkaline–earth containing fluxing compounds on the pyroplastic deformation was observed. Thus, Magnesite showed a high fluxing efficiency with moderate deformation while Dolomite displayed a detrimental effect on both densification range and pyroplastic deformation.     

Effect of calcination temperature on use of high-boron-content waste for low-temperature wall tile production

The effects of the calcination temperature on raw-colemanite-waste properties and calcined waste content on wall tile production were investigated. Waste containing 11.24% B₂O₃ calcined between 500 and 800°C was added to wall tile granules in various ratios (0–100 wt.%) to produce a low-temperature-sintered wall tile by adding the maximum content of boron waste, as determined through optimal calcination. The low-temperature (850–1000°C) sinterability of the samples and the effect of the calcined colemanite-waste content on the wall tile properties were investigated. The samples were characterised using X-ray fluorescence, X-ray powder diffraction, differential thermal analysis, thermogravimetric analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy, and colourimetry. The waste calcined at 800°C exhibited a substantially different phase distribution, bond structure, morphology, and colour. The wall tile produced using 40 wt.% colemanite waste calcined at 800°C and subsequently sintered at 950°C exhibited the optimal properties. The linear firing shrinkage, water absorption, and flexural strength of the optimised wall tile were 0.88%, 16.04%, and 36.07 MPa, respectively. The optimised wall tile exhibited major albite, quartz, and diopside phases and 64% higher strength. The sample calcined at 800°C showed that high colemanite-waste content could be incorporated into ceramic bodies.     

Fracture properties of spray-dried powder compacts: Effect of granule size

Inappropriate mechanical properties of spray-dried powder compacts lead to significant green product losses, entailing considerable costs in ceramic tile manufacture as well as serious environmental problems. In addition, green strength can be indicative of how well a ceramic processing system is working.In this study, granules were prepared by spray drying a red clay slurry used in floor tile manufacture. The resulting granules were characterised and their porosity, morphology, and mechanical behaviour were determined.The study analyses the fracture properties of green ceramic materials using Linear Elastic Fracture Mechanics (LEFM), which has been widely used for fired materials, but whose application to green compacts has drawn much less attention. Two types of tests for determining fracture parameters (fracture toughness, fracture energy, and crack size) in green materials are also critically examined. Finally, the fracture parameters have been correlated to the microstructural characteristics of the compacts, in particular to granule size and the topography of the fracture.     

Incorporation of the ash from cellulignin into vitrified ceramic tiles

The incorporation of the ash from cellulignin, a catalytic biofuel, into a clay/feldspar body was investigated. The cellulignin was obtained by acidic prehydrolysis and was then burnt in boilers leaving behind the ash as a solid residue. Characterization tests of the ash employed X-ray diffraction, particle size distribution, mercury porosimetry, chemical analysis, thermal analysis and high-resolution scanning electron microscopy. The ash/clay/feldspar compositions were fired at 1200 °C and the linear shrinkage, water absorption and flexural strength were determined. Solution and leaching tests were conducted to evaluate the environmental safety of the final ceramics. The results showed that the ash is mainly composed of quartz with partially nanometric particle size, high surface area and high content of alkaline and alkaline earth oxides. These are advantages for a potential use of this ash as a flux. The partial replacement of feldspar by ash promoted a better vitrification decreasing the open porosity and increasing the mechanical strength. Heavy metals present in the ash became inert after the firing stage.     

High-Temperature Reactions of Clay Mineral Mixtures and Their Ceramic Properties: I, Kaolinite-Mica-Quartz Mixtures with 25 Weight % Quartz

The mineralogy and ceramic properties (linear shrinkage and porosity) of fired compacts of quartz, kaolinite, and mica containing 25% of quartz and variable proportions of kaolinite and mica were studied systematically in relation to composition and firing temperature. A procedure for the quantitative determination of components by X-ray diffraction measurements is outlined and applied to the determination of quartz and mullite in the fired samples. For a mixture containing 25%, quartz, 75% kaolinite, the amount of mullite developed at 1300°C. is 41% and this contains 85% of the total Alsoa available. In micarich mixtures, mullite develops at lower temperatures and in smaller proportions. The shrinkage and porosity vary systematically with the percentage of mica in the samples and with firing temperature. The formation of cristobalite depends on the kaolinite content and is not related to the quartz content. Mullite and cristobalite develop at about 1100°C. from the transitory Si-Al spinel-type phase derived from kaolinite.     

Effect of microstructure on cutting processability of porcelain tile subjected to different firing cycles

The fast firing technique is one of the most important ways to save energy consumption and improve production efficiency in the porcelain tile industry. In the actual production, excessively short firing cycle time easily causes the cutting edge defects. This work examines the effect of microstructure on cutting processability of a representative composition of a commercial porcelain tile fired at 1200 °C with two different firing cycles as follows: 40 min and 60 min. The phase composition and microstructure were investigated by using a combination of techniques such as X-ray diffraction (XRD) and scanning electron microscopy (SEM). The result indicated that it was beneficial to extend firing cycle (from 40 min to 60 min) for the cutting processability of porcelain tiles, which was due to the formation of positive microstructures such as secondary mullite needles and small-volume residual quartz.     

Effect of slurry properties and operational conditions on the structure and properties of porcelain tile granules dried in an acoustic levitator

Spray-drying is a unit operation highly important in many industrial applications. In this work, the influence of the drying conditions on the final grain properties has been investigated in single droplet experiments. Porcelain tile suspensions like those used in industry have been used. The experiments have been carried out in an acoustic levitator modified to work at high temperature conditions. The effect of the flocculation state, initial solid mass load, primary particle size, air temperature and initial droplet volume on the mean porosity of the grain and its mechanical strength has been studied. The most important parameters to be considered for the porosity are the primary particle size, the initial solid mass load and the flocculation state. For the mechanical strength the significant effects are the primary particle size, the initial solid mass load, the air temperature and the cross effect of flocculation state and initial solid mass load.     

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.     

An estimate of quartz content and particle size in porcelain tiles from young's modulus measurements

The influence of quartz particle size, weight content and firing temperature on the Young's modulus of porcelain tiles was studied. To simulate a porcelain tile microstructure, an albite glass matrix with added crystalline quartz particles was developed. Average particle size of quartz (3.4 and 31 µm) and volume content (18.5 and 37.6 vol%) were varied. An acoustic impulse excitation technique was used to measure the elastic modulus from room temperature up to 700 °C. Results showed that quartz has a major influence on the elastic modulus of porcelain tiles. At temperatures below 573 °C, a hysteresis area between the Young's modulus curves during heating and cooling was closely related to quartz particle size. Between 573 and 700 °C, the variation of the Young's modulus was related to the quartz volume fraction. By using those correlations, a prediction of quartz content and quartz particle size in commercial porcelain materials can be carried out from Young´s modulus data.     

Properties of Triaxial Porcelain Bodies: Interpretation of Statistical Modeling

The effect of raw materials type and content on the properties of clay–feldspar–quartz compositions was studied using the statistical design of mixture experiments. Based on wall and floor tile industrial practice, 10 mixtures of three raw materials were selected and processed. Characterization results were used to calculate statistically significant and valid regression equations, relating fired body properties with clay, feldspar, and quartz contents in the unfired mixture. Such statistical modeling is discussed against quantitative X-ray diffraction and scanning electron microscopy results. The glassy phase present was found to control the microstructure and the mechanical strength of the fired ceramic body.     

Effect of pyrophyllite on vitrification and on physical properties of triaxial porcelain

Quartz was progressively replaced by pyrophyllite in a conventional porcelain mix with a composition of 50% clay, 25% quartz and 25% feldspar. The addition resulted in early vitrification and decreased thermal expansion of the sintered specimen. Addition of up to 15% pyrophyllite decreased the fired shrinkage by 6% and improved the fired strength by around 29% compared to the standard body. The gradual increase in flexural strength with incorporation of pyrophyllite was primarily due to the elimination of stresses in the structure with a decreasing quartz content as well as to the increasing amount of secondary mullite distributed throughout the matrix forming an interlocking network. However, the firing temperature and the generation of the correct amount of properly sized mullite needles are vital in achieving the desired strength. Pyrophyllite was found to dissolve in the melt in preference to quartz. Beyond the optimum proportion of pyrophyllite, a large volume of glass formed as well as large elongated pores distributed in the matrix resulting in deterioration of mechanical properties.     

Ceramic and Dielectric Properties of Lead Metaniobate Electrical Ceramics

The effect of firing temperature and time on the weight loss, fired porosity, and dielectric properties of lead metaniobate was investigated. The amount of lead oxide lost was found to be a linear function of firing time and in addition increased rapidly as the firing temperature was increased. Specimens fired for 30 minutes at temperatures below 1275°C. had weight losses of less than 1% based on the amount of available PbO present, whereas specimens fired for the same length of time at temperatures greater than 1275°C. had weight losses up to 3.5%. Both a minimum and a maximum point were found in the fired porosity curve of lead metaniobate in the temperature range 1200° to 1350°C. When firing for 30 minutes, the minimum point occurred at about 1225°C. with a porosity value of 8% and the maximum point at 1300°C. with a porosity of 18%. The effect of porosity and weight loss on the dielectric properties of lead metaniobate is presented. The effect of replacing up to 0.7 mole fraction of the lead ion in lead metaniobate by cadmium was investigated. Cadmium additions lowered the Curie temperature and diluted the ferroelectric properties of lead metaniobate.