S. N. Misra

STUDIES ON VARIOUS FUNCTIONAL PROPERTIES OF TITANIA THIN FILM DEVELOPED ON GLAZED CERAMIC WALL TILES

A sol-gel based TiO2 thin film was applied on glazed wall tiles for studying its various functional properties. Thin film was deposited by spin coating on the substrate and subjected to curing at different temperatures such as 600°C, 650, 700°C, 750°C and 800°C with 10 minutes soaking. The gel powder was characterized by FTIR, DTA/TG and XRD. Microstructure of thin film was analyzed by FESEM and EDX. Surface properties of the coatings such as gloss, colour difference, stain resistance, mineral hardness and wettability were extensively studied. The antibacterial activity of the surface of coated substrate against E. coli was also examined. The durability of the coated substrate in comparison to the uncoated was tested against alkali in accordance with ISO: 10545 (Part 13):1995 standard. FESEM images showed that thin films are dense and homogeneous. Coated substrates after firing results in lustre with high gloss, which increased from 330 to 420 GU as the curing temperature increases compared to that of uncoated one (72 GU). Coated substrate cured at 800°C shows higher mineral hardness (5 Mohs’) compared to uncoated one (4 Mohs’) and films cured at all temperatures showed stain resistance. The experimental results showed that the resistance towards alkali attack increase with increase in curing temperature and alkali resistance of sample cured at 800 °C was found to be superior compared to uncoated substrate. Contact angle of water on coated surface of substrates decreased with increase in temperature. Bacterial reduction percentages of the coated surface was 97% for sample cured at 700°C and it decreased from 97% to 87% as the curing temperature increased to 800 °C when treated with E. coli bacteria.

Studies on Chemical Resistance of Sol-Gel Derived TiO2-Fe2O3 Thin Film Coatings on Glazed Ceramic Wall Tiles

ABSTRACT Present study reports improvement in chemical resistance of glazed wall tile by solgel derived TiO2-Fe2O3 thin film coatings on the glazed surface. Effect of firing temperature on the chemical resistance of the coating was estimated after firing at different temperatures (600°, 700° and 800°C). The chemical durability of the coated substrate in comparison to the uncoated was tested against acidic attack by immersing them in 3% (v/v) hydrochloric acid solution and 10 wt% citric acid solution and basic attack by immersing them in 20 wt% potassium hydroxide solution in accordance with IS: 13630 (Part 8): 2006 standard. Further, the coated surface was also tested against basic attack in 1 N sodium hydroxide and 2.5 wt% detergent solution for seven days. The chemical durability was quantitatively estimated by measuring gloss at the surface at regular time intervals. Acid resistance was found to be good for coated substrate fired at all test temperatures. The coated substrate fired at 800°C showed high alkali resistance as compared to the uncoated substrate. FESEM and IR studies substantiate the corrosion resistance of the coated surface fired at 800°C. GRAPHICAL ABSTRACT

Irreversible Dilatometry as a Tool for Body Composition and Firing Schedule Design in Traditional Ceramics

Traditional ceramic products are made up of clay, quartz and feldspar raw materials. The technical properties of these products depend on physico-chemical aspects of ingredient materials, their reaction kinetics during firing and ultimate microstructure development. Irreversible dilatometry is an uncommon but powerful technique to study the densification behaviour of ceramics. Differential coefficient of expansion (DCE) is the derivative of percentage of linear change (PLC). DCE is taken as indicator of phase development and other thermal reactions. One white burning and one red burning clay commonly used for manufacturing ceramic tile bodies were studied for irreversible dilatometry. The dilatometric behaviour of individual clays and their combined effect on a ceramic tile body were correlated. Red clay was found to be more thermally stable than white clay in 550°-650°C temperature range because of lesser dimensional vibrations. DCE curves of experimental bodies illustrated that the bodies were in the thermally induced dimensional vibration phases in the temperature ranges of 500 °-650°C and 800°-1000°C, hence these regions are critical and taken care while designing firing schedule. The study showed that the improved performance obtained by irreversible dilatometry can be utilized for designing compatible firing schedule and to achieve better productivity.

Effect of Curing Temperature on Surface Characteristics of TiO2-Fe2O3 Multi Oxide Thin Film Deposited over Glazed Ceramic Wall Tiles

The effects of curing temperature on surface characteristics of TiO2-Fe2O3 multi-oxide thin film coated glazed wall tile were studied. The thin film was developed by sol-gel method using spin coating technique and subsequently cured at 600°, 700° and 800°C by fast firing. DTA/TG of the gel as well as XRD of the calcined gel powder was carried out. The surface characteristics of the thin film were characterized using optical microscopy, FESEM-EDX and gloss meter. The mineral hardness test and stain resistance test were also carried out. The results indicated that the surface characteristics of the thin film coated glazed wall tile changed with the increasing curing temperature. The FESEM investigation showed that density of the film and interface reaction between glaze and thin film increased with higher curing temperatures. Furthermore, increasing curing temperature of thin film coated substrate resulted in significant improvement in gloss and hardness of the coated surface. Thus, this study exhibits the potential application of TiO2-Fe2O3 thin film coating on the glaze not only as decorative coating but also for improving surface characteristics of glazed wall tiles.

CORRELATION BETWEEN CHROMOPHORE IMPURITY CONTENT AND FIRED COLOUR DATA OF KAOLIN CLAY

Different kaolin clay specimen exhibit varying colours after firing depending upon the relative presence of different mineral impurities, physical state of mineral constituents etc. Spectrophotometers used for determining colour values generate many sets of colour data. Interpretation of such colour values is a subjective matter. Increase in darkness, yellowness etc as a consequence of increase in chromophore impurity content in kaolin clay have been shown. However, the inverse of above ie; gradual change in colour values along with gradual change in chromophore impurity content over a realistic range has not been studied. Whether the colour data of kaolin clay after firing can be taken up as a function of impurity content needs to be investigated. Thus, to identify the correlation between kaolin clay impurity content and its fired colour data the present investigation examined the hypotheses i) The colour development after firing of kaolin clay is an indicator of chromophore impurity content present therein and ii) All the colour variables (L, a, b, ISO2470, redness) constituting a colour data set of pressed kaolin clay specimen after firing will vary in similar manner such that to represent variation in impurity content. The study indicated that the colour values obtained by spectrophotometry of clay specimens after firing represent the chromophore impurity present therein in a less reliable manner. To relatively estimate the quantity of chromophore impurity present in a clay sample from its fired colour, the sample should be mixed with 50% by weight of potash feldspar, pressed in to tablet suitable for colour measurement and fired at or above 1220°C to vitrify. After that the ‘L’, ‘a’ and ‘ISO2470’ values obtained truly represent the chromophore present therein.

Studies on thermal reactions and sintering behaviour of red clays by irreversible dilatometry

Thermal behavior of clays strongly influences that of ceramic bodies made thereof and hence, its study is must for assessing its utility in ceramic products as well as to set the body composition. Irreversible dilatometry is an effective thermal analysis tool for evaluating thermal reactions as well as sintering behavior of clays or clay based ceramic bodies. In this study, irreversible dilatometry of four red clay samples (S, M, R and G) of Gujarat region, which vary in their chemical and mineralogical compositions was carried out using a Dilatometer and compared. Chemical analysis and XRD of red clays were carried out. XRD showed that major clay minerals in S, M and R clays are kaolinite. However, clay marked R and G showed presence of both kaolinite and illite and /muscovite. Presence of non-clay minerals such as hematite, quartz, anatase were also observed in all clays. XRD results were in agreement with chemical analyses results. Rational analyses showed variation in amount of clay and non-clay minerals in red clay samples. Evaluation of dilatometric curves showed that clay marked as S, M and R exhibit patterns typical for kaolinitic clays. Variation in linear expansion (up to 550°C) and shrinkage (above 550°C) between these three clays was found to be related to difference in amount of quartz and kaolinite respectively. However, dilatometric curve of G exhibit a pattern similar to that for an illitic clay. This study confirmed that sintering of investigated kaolinitic and illitic and / muscovitic red clays initiates at above 1060°C and 860°C respectively and this behaviour strongly depends upon type and amount of minerals and their chemical compositions.Thermal behavior of clays strongly influences that of ceramic bodies made thereof and hence, its study is must for assessing its utility in ceramic products as well as to set the body composition. Irreversible dilatometry is an effective thermal analysis tool for evaluating thermal reactions as well as sintering behavior of clays or clay based ceramic bodies. In this study, irreversible dilatometry of four red clay samples (S, M, R and G) of Gujarat region, which vary in their chemical and mineralogical compositions was carried out using a Dilatometer and compared. Chemical analysis and XRD of red clays were carried out. XRD showed that major clay minerals in S, M and R clays are kaolinite. However, clay marked R and G showed presence of both kaolinite and illite and /muscovite. Presence of non-clay minerals such as hematite, quartz, anatase were also observed in all clays. XRD results were in agreement with chemical analyses results. Rational analyses showed variation in amount of clay and non-clay miner...

Beneficiation of Low Grade Kaolin by High Shear Agitation with Dispersant (HSD) Pre-Treatment for High Yield and Improved Fired Colour

Crude kaolin contains various amounts of discolouring elements such as anatase (TiO2), mica and iron oxide (Fe2O3), which give low brightness and are detrimental in use. In addition, the anatase (titaniferrous) and mica can also contain iron contaminants. Beneficiation of two crude low grade china clays, marked as KY and SR, was attempted through imitating existing industrial practice of levigation and hydrocyclone classification, and through an innovative technique of high shear agitation with dispersant (HSD) pre-treatment. HSD treated clays were subjected to impurity removal by sieving, demagnetizing and coarse/heavy impurity removal by sedimentation under gravity techniques. The results in terms of yield of clay (% on feed basis), grade of clay (kaolinite%) and effect of purified clays on the whiteness of porcelain were compared. It was found that by use of HSD pre-treatment, SR dump clay could be purified to contain 90.7% kaolinite and 0.75% free silica with a striking yield of 62.32% as compared to 88.90% kaolinite, 3.34% free silica and 30.2% only as yield by levigation and hydrocyclone. The KY dump clay was purified to contain 85.51% kaolinite and only 5.57% free silica with 44.3% yield by HSD pre-treatment as compared to 72.29% kaolinite, 16.29% free silica and 30.4% only as the yield by levigation and hydrocyclone classification. The kaolinite enrichment and removal of free silica to a major extent and chromophore impurities (although to a minor extent) in these dump clays after beneficiation rendered them suitable for polished vitrified porcelain tiles application as far as the development of white fired colour in the tiles body is concerned.

Studies on surface characteristics and chemical resistance of zirconia nano coating developed on glazed ceramic wall tiles

In this study, sol-gel based ZrO2 nano coating was made on the surface of glazed ceramic tile by spin coating. Further, various surface characteristics were studied after curing at 550°C, 650°C and 700°C, 750°C and 800°C. FTIR, DTA/TG of the gel powder and XRD of calcined gel powder were carried out. The surface of the coating has been characterised using optical microscope and SEM. Properties of coated glazed surfaces such as gloss, colour difference, wetting characteristics and stain resistance were evaluated. Chemical resistance studies (both acid and alkali) of ceramic tiles were also carried out. Experimental results showed that gloss and contact angle of water on the surface of the coated samples significantly increased compared to uncoated substrate. Coated substrates cured at all temperatures exhibited good acid resistance. It has also observed that curing temperature has a strong influence on alkali resistance and coated substrate cured at 650°C and 700°C showed superior alkali resistance than uncoated substrate. In this paper, an effort has been made to explore and validate the potential application of ZrO2 nano coating on the glazed ceramic wall tiles w.r.t improved gloss, hydrophobic properties and chemical resistance.