Synthesis of High‐Temperature‐Stable TiO2 and its Application on Ag+‐Activated Ceramic Tile

The main purpose of study was to provide a common synergy using Ag⁺‐doped calcium phosphate powder and high‐temperature‐stable TiO₂ for antibacterial and photocatalytic tile applications. Thermally stable SiO₂‐modified TiO₂ active layer was deposited on Ag⁺‐activated ceramic tiles by spray coating. The results showed that a nearly 100% cleanability degree was detected for SiO₂‐modified TiO₂ (TS)‐coated antibacterial tiles when compared uncoated and unmodified TiO₂‐coated tiles. Antibacterial tests and colorimetric analyses indicated that ceramic tiles provide both antibacterial and photocatalytic properties simultaneously.     

Photocatalytic degradation of methylene blue and acetaldehyde by TiO<Subscript>2</Subscript>/glaze coated porous red clay tile

Nanosized TiO₂ sol synthesized by sol-gel method was successfully coated on the porous red clay tile (PRC tile) with micrometer sized pores. PRC tile was first coated with a low-firing glaze (glaze-coated PRC tile) and then TiO₂ sol was coated on the glaze layer. A low-fired glaze was prepared at various blending ratios with frit and feldspar, and a blending ratio glazed at 700 °C was selected as an optimum condition. Then TiO₂ sol synthesized from TTIP was dip-coated on the glazed layer (TiO₂/glaze-coated PRC tile), and it was calcined again at 500 °C. Here, these optimum calcination temperatures were selected to derive a strong bonding by a partial sintering between TiO₂ sol particles and glaze layer. Photocatalytic activity on the TiO₂/glaze-coated PRC tile was evaluated by the extent of photocatalytic degradation of methylene blue and acetaldehyde. Methylene blue with the high concentration of 150 mg/l on the surface of TiO₂/glaze-coated PRC tile was almost photodegraded within 5 hours under the condition of average UV intensity of 0.275 mW/cm₂, while no photodegradation reaction of methylene blue occurred on the glaze-coated PRC tile without TiO₂. Another photocatalytic activity was also evaluated by measuring the extent of photocatalytic degradation of gaseous acetaldehyde. The photodegradation efficiency in TiO₂/glaze-coated PRC tile showed about 77% photocatalytic degradation of acetaldehyde from 45,480 mg/l to 10,536 mg/l after the UV irradiation of 14 hours, but only about 16% in the case of the glaze-coated PRC tile.     

Preparation and antibacterial activity of Ag/TiO2-functionalized ceramic tiles

An Ag/TiO₂ coating was deposited onto glazed ceramic tiles by a sol-gel and spraying method at high temperatures. The coating was characterized by X-ray diffraction, scanning electron microscopy, and atomic force microscopy. The results showed that silver was present in rutile-TiO₂, and the temperature did not change the phase composition of the samples. The Ag/TiO₂ coating had a higher roughness than the TiO₂ coating. The tape test (D 3359–08) showed that the coatings prepared at 950 °C and 1000 °C had good adhesion to the ceramic tile substrate. The antibacterial activity of the coating was tested by photocatalytic sterilization experiments. The results showed that the Ag/TiO₂ coating had a higher antibacterial activity than the TiO₂ coating, and the sterilization efficiency of Escherichia coli, Staphylococcus aureus, Shigella, and Salmonella exceeded 99.655% under 2 h of visible light irradiation. This research provides a method to create Ag/TiO₂ coatings with good thermal resistance, adhesion, and antibacterial activity. This improves the low photocatalytic activity caused by the anatase-to-rutile transformation of TiO₂ at high temperatures and the poor adhesion at low temperatures.     

Functionalised exposed building materials: Self-cleaning,photocatalytic and biofouling abilities

With the advent of urbanisation, there was a considerable and progressive worsening of urban air quality. Amongst the solutions proposed by scientific research, photocatalysis proved itself to be one of the most promising. In the present work, commercial glazed ceramic tiles were functionalised with a micrometric TiO₂ layer adopting an industrial-like process. It was purposely chosen to avoid the use of nanoparticles because they might be inhaled and come into direct contact with the cells of the human organism during the industrial processing. Additionally, the self-cleaning, photocatalytic – the former by means of liquid-solid phase photocatalytic tests and water contact angle measurements; the latter against nitrogen oxides abatement – and biofouling abilities of the functionalised materials were thoroughly investigated. Results showed that the functionalised glazed ceramic tile possessed excellent self-cleaning and photocatalytic properties. As per the algal growth, surface roughness showed itself to be a key-point: the TiO₂ surface layer, giving the material a higher surface roughness compared to the untreated one, had an accelerated algal growth process.     

Preparation of photocatalytic TiO2 coatings by gel-dipping with polysaccharides

Commercial tiles are being produced in vast quantities. The main properties of tiles are well established but there is an increasing interest in producing ceramics with tailored-properties and advanced functionalities. One way of adding value to commercial tiles is to deposit a photocatalytic coating to obtain ‘smart’ tiles for environmental reasons, e.g. for the (photo) degradation of organic pollutants in air or in a liquid. Here, we show the manufacture of ‘smart’ tiles by formation of TiO₂ coatings onto commercial tiles by a colloidal processing route based on the immersion of the substrate into a homogeneous aqueous ceramic suspension and its consolidation by agar thermogelation. The effect of the processing parameters (withdrawal rate, solid loading and gelling agent content) and the grain size on the photocatalytic activity of the final coated tiles is reported and discussed. Final coatings properties depend on the viscosity of the suspension, particle size, withdrawal rate, solid loading and gelling agent content, and hence, this dependence affects the photocatalytic activity of the coatings.     

Stray Field Magnetic Resonance Imaging (STRAFI) of Water Transport in Ceramic Substrates

Measurements of water transport in ceramic tiles made using the stray field magnetic resonance imaging technique (STRAFI) are reported. STRAFI represents one method of accomplishing magnetic resonance imaging (MRI) of solids and confined liquids.Water was demonstrated to saturate a sample, cored from an unglazed wall tile, within 4 minutes of exposure. The sample was in constant contact with water at the upper surface and open to air at the bottom. The water ingress was characteristically Fickian in its dynamics. Samples cored from glazed wall and floor tiles were demonstrated to be waterproof (down to 50 m spatial resolution) up to 20 h. Water was shown to ingress samples from abraded, glazed floor tiles, in which the glaze layer was damaged. In this situation, a dynamic equilibrium was established between water entering the upper surface and evaporating from the bottom surface. A gradient of water content through the tile developed. These observations held not only for the abraded tiles, but also for certain household tiles of lower porosity than the unglazed wall tile.     

A procedure to evaluate the resistance to biological colonization as a characteristic for product quality of ceramic roofing tiles

Ceramic roofing tiles suffer deterioration through time due to environmental exposure. Biological colonization affects the appearance and integrity of building materials, such as roofing tiles. The resistance to biocolonization represents an important property affecting the product quality of ceramic roofing tiles. While natural colonization of roofing tiles by organisms is a progressive, heterogeneous, and slow process, laboratory assessment of this phenomenon requires a sensitive procedure that can be carried out within a reasonable period of time. Different microorganisms have been evaluated and the use of phototrophs, specifically the cyanobacterium Oscillatoria, presented several advantages such as good adherence, homogeneous growth on surfaces, and the chlorophyll-autofluorescence which can be used for a sensitive detection. Colonization by Oscillatoria on roofing tiles was assessed by measuring the autofluorescence of cells. This study proposes the use of specific cyanobacterial cells and a simple method for monitoring biofilm formation and biological colonization of roofing tiles.     

Frost resistance of clay roofing tiles: Case study

In order to give required protection of the buildings, clay roofing tiles should be resistant to freezing conditions. In the present study, clay roofing tiles were fired at different temperatures. Afterwards, direct and indirect test methods were used to evaluate their frost resistance. The direct method in standard EN 539-2 was applied, ASTM C 1167-03 was used for indirect methods, and Maage factor was calculated from Hg-porosimetry curve. It was confirmed that the temperature of firing is the main influential parameter as it affects the porosity of a ceramic body. The comparison between indirect and direct methods of prediction and test of frost resistance has also shown good correlation.     

Investigation of the durability of porous mineral substrates with newly designed TiO2-LDH coating

Porous building materials constantly deteriorate due to damaging actions of many environmental factors, such as inorganic and organic contaminants. One of the most effective procedures used for the protection of building materials is the deposition of protective coating on their surface. Four types of porous building materials (clay roofing tiles, bricks, renders, and façade paints) and one glass substrate (as the reference material) were chosen as the model substrates for durability investigation. A TiO₂-layer double hydroxide (TiO₂-LDH) suspension was applied by a spray technique onto the surface of the chosen substrates and investigated with the main aim to improve the material surface properties. In order to test the durability of the designed photocatalytic coating, two adhesion tests were performed: tensile/pull-off test with the appropriate adhesive, based on standardized method and the second one, based on the modified test with semitransparent pressure-sensitive tapes. For that purpose, the equipment and some accessories were modified or produced. The investigation of the most important surface properties (self-cleaning effect and photocatalytic activity as the function of UV/vis irradiation time) of the coated mineral substrates were performed before and after the tape adhesion test. The following characterization methods were used: UV/vis spectrophotometry, contact angle measurement, Vickers-microhardness and surface roughness, as well as FTIR analysis (using DRIFT mode). The obtained results indicate good durability of the developed protective TiO₂-LDH coatings as well as a strong impact on the surface characteristics, photocatalytic and self-cleaning properties of the porous building materials.     

Zircon-free frits suitable for single fast-firing opaque wall tile glazes and their industrial productions

Wall tile glazes with a smooth surface texture, high glossiness, and whiteness are usually based on zirconium containing frits. However, these frits are quite expensive and therefore, there have recently been certain attempts to lower the production cost such as taking suitable glass–ceramic glaze systems into an account. With the present work, the frit-based glaze compositions belonging to the K₂O–MgO–CaO–ZnO–Al₂O₃–B₂O₃–SiO₂ glass–ceramic system were studied to prepare newly synthesized wall tile glazes for industrial single fast-firing. The design of a glass–ceramic glaze for this type of tiles should ensure that the selected frit precursor is technically and commercially compatible with the manufacturing conditions generally used in the production of glazed ceramic wall tiles. The aim of the study is to develop zircon-free, frit-based, glossy opaque glass–ceramic glazes for wall tiles by optimizing the CaO/MgO and adjusting the Al₂O₃/alkali ratios in the starting frit compositions. Frit production, glaze preparation, application, and single fast-firing of wall tiles were, first of all, conducted under laboratory working conditions and then, successful recipes were adapted to the relevant industry. The frit crystallization capability and crystallization temperature range were determined by differential thermal analysis (DTA). Thermal expansion coefficient values of glazes were determined by a dilatometer. Characterization of single fast-fired glass–ceramic glazes was made by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques. Colour and gloss analyses of the final glazes were measured with a spectrophotometer and a gloss meter, respectively.     

干压琉璃瓦的研制

介绍了利用当地原料生产干压琉璃瓦的生产工艺,并对原料的性能、釉料配方进行了研究,并在生产线上生产出合格的干压琉璃瓦产品。     

Underglaze engobe for ceramic facing tiles

A formula for white underglaze engobe is developed based on porcelain-faience waste (after the first firing) to be used on facing tiles with a dark-colored ceramic base. Applying this engobe to a dried tile ensures good sinterability of the engobe to the tile at higher temperatures of the first firing. This makes it possible to simplify the engobe composition and to improve the quality parameters of the tile itself and of the glaze coating.     

干压琉璃瓦的研制

介绍了利用当地原料生产干压琉璃瓦的生产工艺,并对原料的性能、釉料配方进行了研究,并在生产线上生产出合格的干压琉璃瓦产品。     

Photocatalytic effects of TiO2 mesoporous coating immobilized on clay roofing tiles

The objective of this study was to examine the effect of the hydroxyl radicals (free and bound) produced by a TiO₂ mesoporous coating immobilized on the surface of clay roofing tiles. The efficiency of the coating was determined by microbiological and photochemical tests. In the microbiological test (pour plate method), use was made of the test bacteria Pseudomonas aeruginosa, while the photochemical test involved the degradation of para-chlorobenzoic acid, monitored by HPLC method. Both experiments were carried out without and with a scavenger (methanol and tert-butanol). The results of the measurement of the photocatalytic efficiency, and the observed changes in the measured contact angle (sessile drop method), imply the existence of a photo-induced hydrophilicity of the TiO₂ coated porous substrates. The newly designed coating represents a medium which efficiently hinders bacterial adhesion. The experiments demonstrated the existence of self-cleaning and slight self-disinfecting properties of the mesoporous coating.     

Photocatalytic ceramic tiles: Challenges and technological solutions

Titania-functionalized ceramic tiles are gaining space on the market of the self-cleaning photocatalytic building materials after a decade of industrial attempts and investigation on different technological issues. The present paper overviews the latest research on photocatalytic ceramic tiles in terms of process parameters, durability, cleanability and photoactivity, addressing challenges and solutions reported by academic and industrial sources. A special attention is paid to the superhydrophilicity and photocatalytic performance achievable on ceramic surfaces and their complex dependence on several factors (titania crystalline phase, deposition technique; firing temperature; thickness, roughness, specific surface area of the photoactive film; and so on). In particular, the methods used to deposit the titania layer, its degree of adhesion and effects on tile appearance (color, brightness, and roughness) are reviewed. Moreover, manufacturing a photocatalytic ceramic tile with a single firing step is still a challenge. Despite the international standards available on photocatalytic performance, the experimental parameters from one research to another may be quite different, therefore a performance comparison becomes virtually impossible. Nevertheless, among the available commercial products declared as photocatalytic ceramic tiles, just some of them revealed to be photoactive. From the data available, superhydrophilicity of tiles corresponded to contact angles with water in the 10–15° range. Specific photoactivity measured as methylene blue (MB) degradation resulted typically in the 2.8–3.4 mol/m²h range; photonic efficiency was between 0.025 and 0.030%; while MB index was in the 15–20 range. Finally, the relationship of dye degradation with the self-cleaning property is also a question that remains unanswered.     

Effect of water absorption on frost resistance of clay roofing tiles

Abstract

High frost resistance is one of the signs of good quality in clay roofing tile products. The present paper deals with the question of whether the water absorption of clay roofing tiles affects frost resistance. The results show that clay roofing tiles with high water absorption can be just as frost proof as tiles with lower absorption. Median pore radius is found to be an important factor in determining frost resistance: increasing the median pore radius increases frost resistance.     

Development of an optical fiber monolith reactor for photocatalytic wastewater Treatment

A photocatalytic reactor, which employs a ceramic multi-channel monolith as a support for TiO₂ and bare quartz fibers inserted inside the monolithic channels as both a light-transmitting conductor and a support for TiO₂, was constructed and tested for water treatment by investigating the photocatalytic degradation of o-dichlorobenzene (DCB) and phenanthrene (PHE). This configuration provides a higher surface area for catalyst coating per unit reactor volume compared to the continuous annular reactor (CAR) and optical fiber reactor (OFR). The light distribution profile inside each cell of the monolith is analyzed. Exponential decay of light was observed in propagation along the quartz fiber core and penetration into the TiO₂ film. Optimum thickness of TiO₂ layer on the optical fiber was found to be ≈ 0.4 μm in this study. The kinetics of DCB and PHE degradation were pseudo-first order. The effect of the water flow velocity was investigated and showed that the operation was in the mass transfer control regime. Overall rate constants were extracted from the experimental data; and these were then used to calculate the apparent quantum efficiency of photocatalytic degradation. Greater apparent quantum efficiency was observed for the optical fiber monolithic reactor (OFMR) compared with that of the CAR.     

Antibacterial activity of silver photodeposited nepheline thin film coatings

Antibacterial characteristic of silver makes this material very appealing for surface coating on various substrates. In this study, we investigated different silver containing powder for this purpose. Specifically we examined the antibacterial activity of Ag/nepheline compared with Ag/TiO₂ and Ag/SiO₂. Our analysis suggested “Ag/nepheline” composite thin film is an appropriate coating for production of antibacterial ceramic tiles in large scale. In our investigation, FactSage software was used for the thermodynamic analysis. Nano-silver was obtained from silver nitrate solution by ultraviolet illumination of distilled water. In this process, silver was doped on micronized TiO₂, SiO₂, or nepheline. The silver composites and monolithic silver were sprayed with water on raw tiles and sintered in a furnace. Exploring the results suggested the best component for achieving antibacterial tile is Ag/nepheline.     

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.     

Durability of SiO2–TiO2 Photocatalytic Coatings on Ceramic Tiles

The aim of this investigation was the evaluation of the durability of photocatalytic sol–gel coating deposited on industrial ceramic tiles. In particular, the effect of substrate roughness on photocatalytic performance before and after different aging tests was determined. The results showed that the photodegradation process was clearly affected by the surface roughness of the substrate. In particular, the smoother surface had a higher photocatalytic activity, faster hydrophilicity but a lower durability to abrasion with respect to the matt surface.