Anorthite-based transparent glass-ceramic glaze for ceramic tiles: Preparation and crystallization mechanism

A series of high hardness anorthite-based transparent glass-ceramic glaze was successfully developed for ceramic tiles. These glazes were prepared by mixing a high-calcium frit (denoted as HCa) that can crystallize anorthite with other fluxes. The effect of HCa content on the crystalline phase, microstructure and properties of the glaze was studied. In addition, the phase transformation, microstructure evolution and crystallization kinetics of anorthite from frit glaze were investigated in detail. The results revealed that when the HCa content was 45–55 wt%, the glazes had excellent transparency with a hardness of 6.4–7.3 GPa, which was higher than conventional glazes. The XRD and SEM tests showed the crystallization of single-phase lamellar-shaped anorthite crystals up to 20–40 μm in length. Anorthite was found to crystallize directly from the frit glaze at 850 °C. The laminated anorthite was composed of thinner lamellae, and cracks were observed inside the large crystals. The activation energy of anorthite crystallization was about 420 kJ/mol, and the Avrami index (n) was 2.03?2.36. The n value indicates that the crystal is grown in two dimensions, which explains the formation of lamellar-shaped anorthite in SEM.     

Feasibility of Using Cordierite Glass-Ceramics as Tile Glazes

Basic principles of fabricating tile glazes based on cordi-eritic glass-ceramics are explained. Glass compositions from the MgO—Al₂O₃—SiO₂ three-component phase dia-gram have been melted with and without the nucleating agent TiO₂. Additionally, a sodium borosilicate glass that is commonly used in the tile glaze industry has been wet milled, together with the previous compositions, to produce a coating slip. Studies are focused on the role of the nucle-ating agent and glassy formulation in the crystallization of the glass-ceramic system using differential thermal analysis, X-ray diffractometry, and scanning electron mi-croscopy. When added to a borosilicate glass, only one composition is capable of crystallizing cordierite under fast-firing cycle used for "monoporosa" production. The porosity of the glaze layer is sufficiently low and the crystal size is small to ensure good mechanical and chemical prop-erties. The presence of cordierite crystals in the glaze should enhance abrasion and acid resistance, in compari-son to a traditional matte glaze that contains mostly ensta-tite or diopside crystals.     

Floor tile glass-ceramic glaze for improvement of glaze surface properties

Simultaneous improvement of surface hardness and glossiness of floor tile glaze, without changing its firing temperature, was the main purpose of the present paper. Thus, various glazes in the system of CaO–MgO–SiO₂–Al₂O₃–ZrO₂ were prepared and their crystallization behaviors within a fast firing cycle were investigated. With increasing amounts of calcium and magnesium oxides to base glass, the optimum glass-ceramic glaze was obtained. The results showed that with increasing of CaO and MgO part weights in frit, the crystallization peak temperature was gradually decreased and the intensities of diopside and zirconium silicate were increased. The comparison of micro hardness for the optimum glass ceramic glaze derived in this work with a traditional one used in floor tile industries indicates an improvement of 21%. It was found that the glaze hardness not only depend on the amount and type of crystalline phases, but also on the residual glass composition. Furthermore, it was observed that the glaze micro hardness is only slightly affected by thermal expansion mismatch of body and glaze.     

SiO2-Al2O3-MgO-K2O-(F)系玻璃陶瓷的分相和析晶

应用差热分析、X射线衍射分析、扫描电子显微镜等技术，研究了氟含量在SiO2—Al2O3—MgO—K2O系玻璃陶瓷分相及析晶中的作用。结果表明：当玻璃中不含氟时，试样在高温发生整体析晶，析出晶相为堇青石(Mg2Al4Si5O18)。当玻璃中含有质量分数为1．0％的氟时，玻璃的玻璃转变温度及析晶温度都有所降低，但首先在玻璃表面析出云母晶体，玻璃内部发生分相。随着析晶温度的升高，试样内部析出相互交错条状云母晶体。当玻璃中氟的质量分数达到4．0％时，云母晶体呈针片状整体析出，而且析晶温度进一步降低。     

Cathode-Ray Tube panel glass replaces frit in transparent glazes for ceramic tiles

The disposal of Cathode Ray Tubes (CRT) from end-of-life personal computers and TV screens represents a serious problem in electronic-waste management. As an assembly of different materials, finding a use for each of a monitor's parts is a critical step forward a solution. However, the CRT panel is a silicate glass with a relatively high proportion of alkaline and alkaline-earth oxides, for which recycling is a natural task, and the replacement of frit in ceramic glazes arises as an interesting alternative. In this context, we investigated the effect of CRT panel glass in glazes for ceramic tiles based on a comparative analysis. We replaced up to 40?wt% of commercial transparent frit with CRT panel glass in the formulation of one reference slurry. Chemical analyses were conducted by X-ray fluorescence (XRF) and inductively coupled plasma optical emission (ICP-OES) spectrometry. The thermal expansion coefficient and the glass transition and dilatometric softening temperatures were characterized by dilatometry and compared to such properties calculated as a function of composition, using the SciGlass software and database. 20- and 30-min firing cycles were applied in a fast-firing roller kiln, replicating industrial conditions. The samples transparency was measured by spectrophotometry and compared to the colorimetric parameters of a standard glaze. The maximum content of panel glass possible to add in the transparent glaze formulation without affecting the expected properties was 20?wt%, above which transparency decreased due to heterogeneities. The reformulation of a ceramic glaze with waste CRT panel glass was successful, thus suggesting an interesting approach for disposal of other electronic wastes.     

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.     

Sealing Glass‐Ceramics with Near Linear Thermal Strain,Part I: Process Development and Phase Identification

A widely adopted approach to form matched seals in metals having high coefficient of thermal expansion (CTE), e.g. stainless steel, is the use of high CTE glass‐ceramics. With the nucleation and growth of Cristobalite as the main high‐expansion crystalline phase, the CTE of recrystallizable lithium silicate Li₂O–SiO₂–Al₂O₃–K₂O–B₂O₃–P₂O₅–ZnO glass‐ceramic can approach 18 ppm/°C, matching closely to the 18 ppm/°C–20 ppm/°C CTE of 304L stainless steel. However, a large volume change induced by the α‐β inversion between the low‐ and high‐ Cristobalite, a 1^st order displacive phase transition, results in a nonlinear step‐like change in the thermal strain of glass‐ceramics. The sudden change in the thermal strain causes a substantial transient mismatch between the glass‐ceramic and stainless steel. In this study, we developed new thermal profiles based on the SiO₂ phase diagram to crystallize both Quartz and Cristobalite as high expansion crystalline phases in the glass‐ceramics. A key step in the thermal profile is the rapid cooling of glass‐ceramic from the peak sealing temperature to suppress crystallization of Cristobalite. The rapid cooling of the glass‐ceramic to an initial lower hold temperature is conducive to Quartz crystallization. After Quartz formation, a subsequent crystallization of Cristobalite is performed at a higher hold temperature. Quantitative X‐ray diffraction analysis of a series of quenched glass‐ceramic samples clearly revealed the sequence of crystallization in the new thermal profile. The coexistence of two significantly reduced volume changes, one at ~220°C from Cristobalite inversion and the other at ~470°C from Quartz inversion, greatly improves the linearity of the thermal strains of the glass‐ceramics, and is expected to improve the thermal strain match between glass‐ceramics and stainless steel over the sealing cycle.     

Synthesis and Characterization of Crystallizable Anorthite-Based Glass for a Low-Temperature Cofired Ceramic Application

We report successful identification and preparation of a glass composition in the CaO–Al₂O₃–SiO₂ phase diagram with a judicious choice of fluxes that met all dielectric, electrical, and thermal property requirements for low-temperature cofired ceramic (LTCC) applications. The glass composition sintered at 900°C attains good density (2.45 g/cc) and does not precipitate any crystalline phase. However, when this glass powder is sintered at the same temperature in the presence of 30 vol% cordierite, crystallization of the anorthite phase is observed, which improves the properties of the composite for LTCC application.     

Improvement of Mechanical Properties of Machinable Glass-Ceramics through Postmachining Heat Treatments

A mica-based machinable glass-ceramic has been converted to a glass-ceramic containing cordiertie and body-centered cubic chondrodite through heat treatment at temperatures higher than that used for the crystallization of mica. The machinability is lost, microhardness increases, and the thermal expansion coefficient decreases with the change of the crystalline phase from mica to cordierite and chondrodite.     

Crystallization of Bismuth Borosilicate-Based Dielectric Thick Films on a LiZn Ferrite Substrate

The compatibility and crystallization of dielectric thick films, consisting of a bismuth borosilicate glass and crystalline cordierite, on a LiZn ferrite substrate were investigated by focusing on phase development and microstructural changes. Significant diffusion of Li and Fe from the substrate to the dielectric was confirmed as unexpected crystalline phases such as Li₂Al₂Si₃O₁₀ and Fe₂O₃ were found in the thick films fired at 850°C. The crystallization was believed to be initiated from the film interface and developed further toward the film surface as evidenced from cross-sectional microstructures of the films with additional firings. The degree of crystallization and the relative contents of the observed phases were dependent on the ratio between the glass and cordierite and the number of refirings.     

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.     

The influence of TiO2 content on the properties of glass ceramics: Crystallization,microstructure and hardness

The effects of compositional variation, crystallization behavior, crystalline phases and microstructure formed in the SiO₂3Al₂O₃3CaO (SAC) glass system using various amounts of TiO₂ as nucleating agent were investigated by Differential Thermal Analysis (DTA), X-ray powder diffraction (XRD), Scanning Electron Microscope (SEM), Energy-dispersive X-ray spectroscopy (EDAX) and Fourier transform infrared spectroscopy (FTIR) techniques. The crystallization kinetics and mechanical properties of SAC glass ceramics were studied using crystallization peak temperature (T_p) of three different glasses as obtained from DTA, the activation energy (E) and Avrami exponent (n) were also determined. The crystallization peak temperature (T_p) and activation energy (E) were found to increase with the increase in TiO₂ content. The major crystalline phases were anorthite and wollastonite along with gehlenite and titanite as the minor crystalline phases present in the glass ceramic system. The studies showed that the three dimensional crystalline structure and the microhardness increased with the increase of TiO₂ content in the glass ceramics system.     

Effect of iron oxide content on the crystallisation of a diopside glass–ceramic glaze

The effect of iron oxide content on the crystallisation of a diopside glass–ceramic glaze was investigated using a glass–ceramic frit in the K₂O–ZnO–MgO–CaO–Al₂O₃–SiO₂ system and a granite waste glass. Measurements by X-ray diffraction (XRD) combined with scanning electron microscopy (SEM) and EDX microanalysis showed that the distribution of Fe³⁺ ions among different crystalline phases such as franklinite (ZnFe₂O₄) and hematite Fe₂O₃ depends on the iron content in the original diopside mixture. Thus, the original glaze crystallises to franklinite or hematatite when iron content is greater than 2 and 15%, respectively.     

Experimental Study of the Aging and Self-Healing of the Glass/Ceramic Sealant Used in SOFCs

High operating temperatures of solid oxide fuel cells (SOFCs) require that the sealant must function at a high temperature between 600°C and 900°C and in the oxidizing and reducing environments of fuel and air. This paper describes tests to investigate the temporal evolution of the volume fraction of ceramic phases, the evolution of micro-damage, and the self-healing behavior of the glass–ceramic sealant used in SOFCs. It was found that after the initial sintering process, further crystallization of the glass–ceramic sealant does not stop, but slows down and reduces the residual glass content while boosting the ceramic crystalline content. Under a long-term operating environment, distinct fibrous and needle-like crystals in the amorphous phase disappeared, and smeared/diffused phase boundaries between the glass phase and ceramic phase were observed. Meanwhile, the micro-damage was induced by the cooling down process from the operating temperature to room temperature, which can potentially degrade the mechanical properties of the glass/ceramic sealant. The glass/ceramic sealant exhibited self-healing upon reheating to the SOFC operating temperature, which can restore the mechanical performance of the glass/ceramic sealant.     

花型结晶釉的制备及显微结构表征

针对传统结晶釉产品普遍存在的烧成温度高、保温时间长、连续化生产难等问题,以钾长石、方解石、氧化锌、玻璃粉为主要原料,在1 220 ℃成功烧成K₂O-Na₂O-CaO-ZnO-SiO₂-Al₂O₃系陶胎结晶釉,重点研究了窑炉冷却制度和着色剂对釉面效果的影响。结果表明:冷却过程中,1 100 ℃“定点保温”3 h,2%(质量分数)NiO和2%(质量分数)CuO的着色剂组合可使陶胎釉面呈现直径约4.5 cm、白色花边、绿色内簇的花状粗晶;在速率为125 ℃/h的“缓速冷却”制度下,可生成内部绿色放射状晶簇、宏观尺寸约8 mm、美观自然且边界清晰的“梅花状”晶体。采用场发射扫描电镜(FESEM)、能谱仪(EDS)、XRD等分析对典型“梅花状”晶体的显微结构、化学组成等进行了表征,发现其内部存在着六边形柱状、针状等同晶异构硅锌矿晶体。六边形柱状晶体主要聚集在“梅花”中心,由于垂直釉面方向空间受限而长大缓慢,其尺寸普遍在2 μm左右;针状晶体主要平行于釉面并向“花瓣”放射生长。底釉非晶玻璃相中存在大量纳米级分相微球结构,呈现出豆绿乳浊效果。Fe₂O₃、CuO、MnO、NiO的两两组合可使陶胎釉面呈现窑变多色的釉面结晶效果,其中Fe₂O₃与MnO,以及NiO与CuO的着色组合效果最佳。     

Reinforcement of single-firing ceramic glazes with the addition of polycrystalline tetragonal zirconia (3Y–TZP) or zircon

The addition of fine-grained polycrystalline tetragonal zirconia (3%Y₂O₃–TZP, or 3Y–TZP) to conventional, single-firing, ceramic glazes was studied with the aim to enhance their hardness, fracture toughness and wear resistance for floor tile applications. The stability of the added tetragonal zirconia towards solution in the glaze and/or zircon crystallization was found strongly dependent on glaze composition, firing treatment, and on the way of preparing the samples (uniaxially-pressed pellets or thin-layer coatings). 3Y–TZP remained stable in fast-fired pellets, but partial crystallization of prismatic zircon microcrystals (2–3 μm) occurred in samples prepared as thin-layer coatings. Addition of 10–30 wt.% of 3Y–TZP to a conventional single-firing glaze that was industrially enameled (thin films) onto low-porous floor tiles, promoted an important enhancement of Vickers microhardness (H_v from 6.0 to 8.4 GPa), fracture toughness (K_IC from 1.35 to 2.23 MPa m^1/2), and wear resistance (PEI abrasion number from 2 to 5). The achieved reinforcement was higher with 3Y–TZP than with zircon addition, and must be attributed to the stress-induced transformation-toughening mechanism promoted by the undissolved stabilized tetragonal zirconia, and also to partial zircon crystallization. The possibility of obtaining ceramic coatings mechanically reinforced with 3Y–TZP additions, while also maintaining a glossy aspect, was also confirmed.     

浅谈瓷釉制备工艺与搪玻璃设备质量的关系

本文简要介绍了瓷釉制备工艺与搪玻璃设备质量的关系,只有采用合理的瓷釉制备工艺,才能制得性能良好的瓷釉,也只有采用性能良好的瓷釉,才能生产出高质量的搪玻璃设备。     

Crystallization mechanisms of cordierite glass-ceramics with “surface-center” crystallization behavior

Cordierite glass-ceramics usually begin to crystallize from the surface. As an efficient nucleating agent, TiO₂ can promote the rapid transformation of glass to bulk crystallization, but it is easy to cause the increase of dielectric constant and light absorption. High crystallinity cordierite glass-ceramics were prepared by optimizing the heat treatment process without or with different nucleating agents in stoichiometric cordierite glasses. The results show that the crystallization mechanisms of glasses without and with ZrO₂+P₂O₅ as nucleation agents are controlled by surface crystallization. While, the glass with TiO₂+ZrO₂+P₂O₅ as nucleation agents have the tendency to be bulk crystallization. The studied glasses are crystallized from surface and have different crystallization orientations with the inner glass. The thickness of crystalline layer increased with the increasing of heating temperatures, but the “surface-center” crystallization process cannot complete by further increasing heating temperatures because of softening deformation of glasses. At 1020 ℃, the glasses complete the “surface-center” crystallization for long durations. The glasses without nucleation agents and with ZrO₂+P₂O₅ require 10 h, but the glass with TiO₂+ZrO₂+P₂O₅ complete for 5 h. Although all the three glasses complete the “surface-center” crystallization, the glasses with nucleation agents show the higher crystallinity upon the same heat treatments. Finally, glass-ceramics with excellent performance were obtained, for example, the Z1# glass-ceramic have the high microhardness ∼7.4 GPa, low thermal expansion coefficient ∼1.4☓10⁻⁶ ℃⁻¹ at 20–300 ℃, and relatively high thermal conductivity ∼2.4 W/mK. It also exhibits low dielectric constant and loss, which was ∼4.5 and ∼1.2☓10⁻³ at 1 MHz, ∼ 4.9 and 2.3☓10⁻³ at 10.5 GHz..     

White scheelite-zircon glass ceramic enamels: Clues for their optimization as cool surfaces

White enamels were prepared from scheelite and zircon glasses. By modifying the amount of WO₃ and ZrO₂, different crystalline shapes and percentages were obtained. It was found that the high refractivity of zircon hinders the crystallization of scheelite and thus the mixture of the two glasses lead to non-crystallized regions which in turn influence the glaze optical properties. In these non-crystallized areas the infrared characterization revealed a large amount of non-bridging oxygens leading to an increase of the band-gap energy and a decrease in the both the solar reflectance and whiteness of the enamels. It was concluded that by reducing the percentage of these non-crystalline regions, the scheelite/zircon glass ceramic enamels could be potential candidates for reducing the Urban Heat Island effect.     

常温远红外陶瓷粉和远红外日用陶瓷的研究

远红外日用陶瓷不仅对食物、饲料、水有活化作用，加速酒的发酵和成熟，而且对人体还具有保健功能。本研究采用液相法制备出纳米远红外陶瓷粉，把远红外陶瓷粉按适当比例掺入普通陶瓷釉浆中，制成常温下具有高效发射锭红外线功能的日用陶瓷产品。如瓷碗、盘、茶杯、酒具等。脸用XRD分析其物相和SEM观察其显微结构、结果表明，当远红外陶瓷粉在基釉中的添加量为10wt％时，可提高日用陶瓷釉面的光泽度和显微硬度，且釉面质量优良。经中国计量科学研究院测试，远红外陶瓷粉的法向全辐射发射率94％，远红外日用陶瓷的法向全辐射发射率达到83％以上。