Development of spinel opaque glazes for ceramic tiles

The feasibility of developing fast-firing opaque wall tile glazes obtained from zircon-free frits was studied. The structural and morphological characteristics of the glazes were determined by differential scanning calorimetry, an optical dilatometer, X-ray diffraction and scanning electron microscopy. The studied glaze was characterized by a high whiteness value L* greater than 94, very low values of a* and b* which is about ?0.65 and 0.01, respectively, and a high gloss value above 98%. The opaque effect is due to the presence of spinel crystals with a size range of 0.2–1.0 μm, which is formed by devitrification during fast-firing. The Vickers micro-hardness of the studied glaze is higher than the one of the commercial zircon based glass-ceramic glazes. This type of frit can be an alternative one for fabricating opaque ceramic glazes.     

Crystallization of Zircon in Stoneware Glazes

High levels of zircon are required to impart opacity in glazes. Zircon additions of <3 wt% dissolve into the glassy phase; additions of >12% cause all the zircon to crystallize from the glaze. Dynamic high-temperature X-ray diffraction has shown that, during heating, a portion of the zircon dissolves and subsequently recrystallizes, using undissolved zircon crystals as seeds. This recrystallization does not occur at lesser zircon levels, because of a lack of seed crystals. When zirconia is added to the glaze, zircon is formed as elongated crystals at the glaze surface. Lesser zircon levels have been observed in the glazes that have zirconia additions.     

High wear resistance white ceramic glaze containing needle like zircon single crystals by the addition of sepiolite n-ZrO2

Sepiolite with homogeneous zirconia nanoparticles distribution has been added to a transparent ceramic glaze to study opacification, mechanical and wear resistance properties. It has been observed that monodispersed zircon single crystals with needle-like shape have been formed in the ceramic glaze. These in situ zircon single crystals give white color and increase opacification (L = 94 vs L = 90), mechanical properties (hardness and toughness) and wear resistance by a factor of 4 compared to the commercial crystalline glaze containing a similar fraction of micrometer commercial zircon.     

Preparation of separative-phase fancy glaze derived from iron ore slag

The separative-phase fancy glaze was successfully prepared by using the iron ore residue as the ceramic colorant. A possible coloring mechanism was proposed to explain the variation of glaze colors and patterns with the increasing of firing temperature. Effects of the firing temperature on the chromaticity, precipitated phase and microstructure of separative-phase fancy glaze were investigated. The results indicated that with increasing the firing temperature, the content of whitlockite decreased while the size of phase separation droplets in glazes increased. The residual whitlockite weakened coloring of Fe₂O₃ and formed glaze patterns. In addition, the increased size of phase separation droplets weakened the structural color, which increased the L* and b* value of glazes. Therefore, the color of separative-phase fancy glaze got more yellow and brown gradually.     

Clustering of zircon in raw glaze and its influence on optical properties of opaque glaze

The cluster of zircon (ZrSiO₄) is always observed on the surface of a zircon-containing raw glaze. This work studied the cluster's formation mechanism and its influence on optical properties of opaque glaze by comparing a zircon-containing raw glaze with a zirconium-based frit one. It was observed that the cluster of zircon occurs during the densification of the raw glaze. We found evidences that this phenomenon is caused by the releasing of gas when the glaze is vitrifying. The optical analysis revealed that the cluster of zircon has a significant effect on the scattering of light and also on the color of the studied glazes.     

Development of TiO2 white glazes for ceramic tiles

The objective of this work was the use of titania polymorphs (rutile and anatase) in substitution of zirconia as the main component for producing white opacity in ceramic glazes for tile coatings. Initially, total zirconia (12% mass fraction) was replaced in the standard frit by rutile and by anatase in mass fractions of 5%, 10% and 15%, forming two frit groups processed as ceramic glazes. The glaze color was determined by spectrophotometry and the glaze microstructure by XRD and SEM. The results showed the frit containing 10% anatase formed a totally white glaze presenting excellent coating capacity. The frits containing rutile produced yellow opacity. The results of microscopy and X-rays diffraction revealed that opacity was caused by tiny rutile crystals in the anatase frits and by titanite crystals in the rutile frits.     

Compositional modifications to floor tile glazes opacified with zircon

Abstract

In the ceramic tile industry opaque glazes with considerable zircon content are widely used. However, the high cost of zircon limits its wide use in relevant glaze compositions. In the present study, a model opaque glaze was modified by changing the alumina/silica ratio, adding potassium oxide, or using a higher content of opaque frit while gradually eliminating the zircon content in the glaze batch. After glaze preparation, application, and single firing of glazed floor tiles under industrial conditions glazes were characterised by XRD, SEM, and EDX. The optimum alumina/silica ratio was found to be 0·26. Colour parameters L, a, and b of starting and final glazes showed that an increase in opaque frit content gives more positive improvement in opacity and in dry abrasion resistance than potassium oxide addition. Removal of zircon from the glazes resulted in a decrease of ～13–18% in glaze cost without detrimental effect on opacity.     

我国陶瓷色釉料专利信息分析

本文对我国1985~2007年申请的陶瓷色釉料(含颜料和相关添加剂)专利数据进行了系统分析,以便业内同仁了解我国陶瓷色釉料专利的现状,掌握陶瓷色釉料研发动态。     

Colouring of opaque ceramic glaze with zircon pigments: Formulation with simplified Kubelka-Munk model

In this study a simplified Kubelka-Munk model is proposed for colour matching purposes. Opaque glazes were prepared to determine the absorption optical constants from the reflectance curves measured with a spectrophotometer. After the physical and chemical characterization of the glaze components (frit and pigments), to analyze the spectrophotometric results a simplification of the Kubelka-Munk model was suggested. To experimentally verify the model, two target green colour were reproduced in laboratory by adding in an opaque glaze a yellow praseodymium-doped zircon ((Zr,Pr)SiO₄) and blue vanadium-doped zircon ((Zr,V)SiO₄) pigments. The results were in good agreement with the experimental reflectance curves and the prediction of colour green glazes was possible with a reduced number of experiments.     

Development of sapphirine opaque glazes for ceramic tiles

The purpose of this work is to produce more excellent opaque wall tile glazes by using sapphirine instead of zirconium silicate as an opacifier. In order to achieve it, the chemical compositions were precisely adjusted in the system of SiO₂-Al₂O₃-MgO-K₂O-Na₂O-B₂O₃. The morphological characteristics of the glaze were determined by differential scanning calorimetry (DSC), X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). And the optical properties of the glaze were characterized by a spectrophotometer and a gloss meter. The results reveal that well-shaped crystals of sapphirine (Mg₂Al₄SiO₁₀) with needle-like morphology were formed as only crystal phase. The glaze is provided with better opacity whiteness and gloss compared with commercial zircon-based glass-ceramic glazes, and it is mainly composed of cheap mineral raw materials. Those features make it as an alternative one for improving the properties of conventional opaque ceramic glazes.     

Development of gold-bronze metallic glazes in a clay-based system for stoneware bodies

In this study, a triaxial glaze system consisting of red clay, kaoline, quartz, MnO, CuO and CoO is systematically developed to produce gold-bronze raw metallic glazes for stoneware bodies. At first, all of the glazed samples in the developed system were fired in an electrically-heated kiln at 1160 °C. Then, the selected successful gold-bronze metallic glazes were applied onto 3-D forms of stoneware bodies and fired at the same conditions. Microstructural characterizations of the glazes are done with scanning electron microscopy (SEM) and energy dispersive x-ray analyses (EDS). This study revealed that triaxial blending of the ceramic raw materials is a beneficial method for glaze production and gold-bronze surfaces are obtained in glazes G 9, G 26, and G 34. It is observed that chemical composition of the glazes directly influence the color and the amount of CuO is more significative than MnO for achieving gold-bronze effect.     

Fe—Mn—Cr—Ni系黑色料制备工艺的研究

以废钢渣为主要原料，添加部分化工原料，制备出了Ｆｅ－Ｍｎ－Ｃｒ－Ｎｉ系无钴黑色料。采用现代测试技术对其最佳制备工艺及基础釉的应用性进行了检测。结果表明，在确定料合成温度后，废钢渣的预处理及色料的粒度对色料的呈色影响显著，此系色料不适应于锌釉和镁釉。     

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.     

钒—锆蓝陶瓷色料的制备及其性能

本文论述了锆基陶瓷色料的制备工艺过程,矿化剂的作用机理以及着色离子在ＺｒＳｉＯ４晶体结构中的价态、取位。为获得性能稳定、呈色效果好的锆基陶瓷色料提供理论指导。     

Grain growth of zircon pigment in tile glaze

Abstract

Glazes for ceramic materials are often opacified by a zircon pigment. The increase in optical density is related to the number and size of pigment particles, which are well dispersed in the glass. Mechanical dispersion by grinding of a fine zircon powder in a raw glaze mixture results in an unoptimised pigment dispersion in the melted glassy phase at high temperature. A significant reduction in the number of particles and a simultaneous large increase in their size is observed. In this case the optical glaze density does not attain the expected value and a very large quantity of zircon must be added. In the present work it is shown that a large part of the zircon reacts with the glass phase during firing. Simultaneously, the remaining zircon grains undergo a large increase in grain size by Ostwald ripening through the liquid phase. This process is characterised by a low activation energy (79 ± 1 kJ mol^-1) and a short diffusion path for Zr through the liquid phase between neighbouring grains. The path length is shorter than the size of the larger grains. In the usual firing range, both populations of smaller and larger grains vary in size, the smaller grains favouring growth of the larger grains.     

Colour in ceramic glazes: Efficiency of the Kubelka–Munk model in glazes with a black pigment and opacifier

In this study the efficiency of the Kubelka–Munk model (already known and consolidated in other industrial sectors) was evaluated in the prediction of the colour of an opaque ceramic glaze obtained by a mixture of black pigment (spinel Ni–Fe–Cr) and zircon opacifier (ZrSiO₄). Glazes with different percentages of black pigment and opacifier were prepared to determine the absorption and scattering optical constants from the reflectance curves measured with a spectrophotometer. After the physical and chemical characterization of the glaze components (frit, pigment and opacifier), suggestions for the adaptation of the Kubelka–Munk model were made to facilitate the experimental procedure of analysis. The result obtained with the adapted Kubelka–Munk model was in good agreement with the experimental reflectance curves. The reproduction of the desired colour was possible with a reduced number of experiments and the model made it possible to correlate the colour with the added pigments concentration facilitating the formulation step.     

釉里红的研究

在已有的研究基础上,本实验通过改变釉里红釉的色料、盖釉和底釉的配方及组合方式,探讨了影响釉里红呈色及流动状态的因素。实验结果表明：CuO含量不仅影响釉里红釉的呈色,还对釉料的高温流动性有明显的影响。底釉、盖釉配料中的熔剂对釉里红呈色的影响十分明显。     

微晶玻璃釉的研究

用不同组成的微晶玻璃水淬料,施于陶瓷坯上经核化、晶化,同时完成烧成,而获得微晶玻璃釉层.其工艺制度可以结合DTA分析,通过实验来确定.微晶玻璃釉要和坯料相匹配:釉和坯的膨胀系数相近,微晶玻璃的晶化温度和坯的烧成温度要相一致.     

Submicro-zirconia crystal-intergrown zircon opaque glaze

Zircon opaque glaze is widely used in sanitary and building ceramic products due to its high-temperature stability. Massive amounts of zircon are consumed by the ceramic industry yearly. In this work, a method to reduce zircon consumption and enhance opaque effect was proposed by intergrowth of submicro zirconia. Alumina was added to a K–Na–Ca–Al–Si–Zr system glaze to prepare a 5 wt % content highly opaque glaze, where zirconia coexisted with zircon. The crystallization behavior, opacification properties, and Vickers hardness of the glaze were investigated. Back-scattered electron images showed that when Al₂O₃ addition increased into more than 13 wt %, abundant of submicro zirconia crystals would intergrow with zircon crystals. The glaze containing 13 wt % Al₂O₃ had an L* value of 96.76 ± 0.27 after being fired at 1220 ℃.     

Examining correlations between composition,structure and properties in zircon-containing raw glazes

The effects of additions of zircon (5–17 wt%) to conventional single firing ceramic glazes is examined. The structural and morphological characteristics of the glazes were determined by Scanning Electron Microscopy, X-ray diffraction, infra-red spectroscopy, as well as ²⁷Al and ²⁹Si magic angle spinning (MAS) NMR. The presence of zircon microcrystals was revealed by X-ray diffraction (XRD) combined with scanning electron microscopy (SEM) and EDAX microanalysis. The chemical durability of the glasses is revealed to be acceptable for certain practical applications. The color characteristics of the glazes obtained were estimated in the HunterLab system (L*C*h*, emission spectra). The outcomes of the study established correlations between composition, structure and some of the physical properties.