THE EFFECT OF HEAT-TREATMENT AND COMPOSITION OF SEMI-PORCELAIN BODIES ON CRAZING

Limits of Investigation.—The investigation was confined to practical semi-porcelain bodies and glazes, therefore, the results may be applicable only to this branch of the whitewares industry. Effect of Thickness of Glaze.—The thicker the glaze the greater the tendency to craze. The glaze on several pieces of dinner ware may appear to the eye to be of uniform thickness, but still have sufficient variation in thickness as to show difference in crazing behavior. It being impossible to obtain a uniform thickness of glaze by hand dipping there is a need for a mechanical dipper. An improved type of biscuit kiln which will produce ware with a uniform absorption is another need. Effect of Glaze Composition.—When sufficient change was made in the composition of a typical semi-porcelain glaze to cause a marked decrease in its crazing tendency, it was at the expense of other desirable properties. Effect of Body Composition.—The addition of 10.0% to 20.0% of “Hercules” clay to a general ware body greatly decreased its tendency to craze. No other change in body composition was found feasible, for when the change was sufficient to cause a decrease in the crazing it was at the sacrifice of other essential properties. Effect of Variation in Absorption.—Contrary to the general opinion among potters, the tendency to craze was not increased by every increase in absorption. An absorption of about 7.0% to 12.0% showed the most resistance to crazing. Effect of the Time-temperature of the Gloss Burn.—Tendency to craze is decreased by increasing the maturing time-temperature portion of the gloss burn.     

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.     

烧成制度与化学组成对分相-析晶乳浊釉的釉面性状的影响

采用DSC、XRD和TEM等测试手段，研究了分相一析晶乳浊熔块在热处理过程中的相变过程，并在此基础上研究了不同的烧成制度对釉面乳浊度的影响。结果发现：缓冷釉样的乳浊效果明显优于急冷釉样；而在晶体完全溶解的温度点保温会减弱釉面乳浊效果。不同组成对釉面光泽度影响的研究表明：引入高折射率的ZnO、CaO和MgO以及添加表面能很低的B2O3和P2O5都可以有效提高釉面光泽度。     

无锆乳浊釉的研制

本文以粘土、钾长石、石英、硅灰石、氧化锌、滑石、硼钙石等为原料,形成K2O-CaO-MgO-ZnO-B2O3-Al2O3-SiO2系统釉料,运用四角配料的方法进行配制,获得釉面平整、白度和光泽度高的无锆乳浊釉。采用XRD、SEM等测试手段,研究了该釉的微观结构和乳浊机理。     

A PRELIMINARY STUDY OF THE RESISTANCE TO ABRASION OF CERAMIC GLAZES,ITS CONTROL AND METHODS OF DETERMINATION1

Two test methods, one using an Ingersoll glarimeter to obtain results of a high degree of accuracy, and the other simpler “alternate method” for plant control, are described in detail. Tests on commercial hotel chinaware showed the average resistance of foreign ware was higher than that of the domestic and the variation from the average was, in general, less. Experimental glazes were prepared to study the effect on resistance, of: (1) varying SiO₂ and Al₂O₃ content, (2) glaze thickness, and (3) firing treatment. Data obtained are insufficient to justify definite conclusions regarding the effect of varying SiO₂ and Al₂O₃, but do show the resistance of well-matured glazes to be inversely proportional to thickness, a decrease in resistance as the tendency to matt increases, a markedly increased resistance by the higher glost fire. That type of body affects resistance less than do glaze composition and temperature of glost fire.     

Effect of ZnO/MgO ratio on the crystallization and optical properties of spinel opaque glazes

The effect of the ZnO/MgO ratio on the crystallization and optical properties of glass‐ceramic glazes from the SiO₂–Al₂O₃–ZnO–MgO–CaO–K₂O–Na₂O–B₂O₃ system was studied. The glazes with different ZnO/MgO ratios were characterized by differential scanning calorimetry, X‐ray powder diffraction, Raman spectroscopy, scanning electron microscopy, energy dispersive spectroscopy analysis and a spectrophotometer. The results reveal that the A glaze without ZnO content contains forsterite and sapphirine. The B and C glazes with intermediate ZnO/MgO ratio contain enstatite and spinel solid solution. The D to F glazes with higher ZnO/MgO ratio crystallize spinel solid solution as the only crystalline phase. The amount of spinel solid solution, lightness values (L*), gloss values and the reflectance of the studied glazes increase with the ZnO/MgO ratio.     

Sintering behaviour of nanostructured glass-ceramic glazes

The thermal behaviour of a glass-ceramic glaze based on the system SiO₂–CaO–ZnO–Al₂O₃ has been evaluated. Frit and kaolin were ball milling using dispersants and binders, and deposited on a green clay based ceramic support. The evolution of the glaze during the sintering step was observed that consisted of a glassy matrix, particles from kaolin and particles from frit. Particles from frit formed a nanostructure of interconnected nanoparticles. Pyroxenes devitrified from the glassy matrix and at higher temperatures they were dissolved in the glassy matrix. Both successes contributed to the final observed nanostructure produced by a spinodal decomposition process in which the crystalline phase had a pyroxene composition.     

NOTE ON COBALT STAIN IN WHITE WARE BODIES

Faulty methods of adding cobalt. —Cobalt oxide or directly added cobalt sulphate frequently causes a blue-gray cast when the body is hard fired. Correct preparations of stain from cobalt sulphate. —To 750 ounces of pure water add 15 ounces pure cobalt sulphate (CoSO₄+ 7H₂O) and stir until dissolved. Then add 7.5 ounces of carbonate of soda (Na₂CO₃) and stir thoroughly. Adding stain to body. —Ball clay must be thoroughly blunged with body before adding stain. If used in a casting slip, add the stain as a part of the casting solution. Proportions stain to body. —For a body containing 10 per cent ball clay add 75 ounces stain solution to each 1500 pounds body, i. e., ½ ounce stain for each 10 pounds body. For bodies with higher ball clay content increase the stain addition in the same ratio up to 15% ball clay. Stain in glazes. —Add 10 ounces stain to each 100 pounds dry glaze batch when same is thoroughly wet in mill. For glaze high in lead, the amount of of stain required is increased.     

HIGH FIRE PORCELAIN GLAZES1

Field covered.—The glazes studied covered the field 3.0 to 13.0 equivalents SiO₂ and 0.3 to 3.25 equivalents A1₂O₃ between the A1₂O₃:SiO₂ ratios of 1:4 and 1:20. The RO was maintained at 0.7 CaO and 0.3 K₂O. Deformation temperatures.—The deformation temperatures were determined by cones in a small gas furnace heated at the rate of 5O°C per hour. The deformation temperatures are shown graphically by isotherms. The results of the part of the field previously covered by Stull and Howat agree with their work. It was found that there is a deformation eutectic axis at a slight inclination to the ordinate representing A1₂O₂ up to 7.0 equivalents SiO₂. Above 7.0 equivalents the inclination rises, and at 11.0 equivalents SiO₂ it increases much more. Firing tests.—The glazes were applied to porcelain cups biscuited at cone 08, and fired to cones 10, 12, 14 and 16. The cone 10 test was made only for comparison, since Stull and Howat had previously covered a small part of the field at cones 9 and 11. The glazes are plotted both by empirical formulas and batch weights, showing the location of the best glazes at the different temperatures. In agreement with Stull's statement, increase in Al₂O₃ in this type of glaze decreases crazing. Increase in SiO₂ will not decrease crazing but if carried far enough will cause crazing to occur. From cone 12 to cone 16 the best glazes have A1₂O₃ and SiO₂ contents corresponding to the approximate formula A1₂O₃= 0.3 + 1/12 SiO₂.     

FURTHER STUDIES OF PORCELAIN GLAZES MATURING AT HIGH TEMPERATURES1

The investigation covers three fields of glazes: Series A contains 21 glazes with variations in composition as shown in the formula . Series B contains 10 glazes, each having the formula but having their clay content varying triaxially between Florida kaolin, North Carolina kaolin, and Kentucky ball clay No. 4. Series C contains 20 glazes with variations in composition as shown in the formula . The method of experimentation consists of grinding the corner glazes of each series wet, for 18 hours, cross blending the corner glazes to produce the intermediate glazes, applying the glazes by dipping to green porcelain discs, and firing them in commercial periodic and tunnel kilns to temperatures between cone 16½ and cone 19 flat. The glazes were examined with the naked eye and a 10 X pocket lens. The triaxial replacement of CaO by MgO and BaO , as tested, makes practically no change in the appearance of the glazes. With the pocket lens the bubbles in the glazes appear smaller and more numerous, near the BaO apex. When fired in the periodic kilns for 42 hours the transparency of all the glazes in- creases with the temperature. The glazes fired in the tunnel kiln to cone 19 flat in 31 hours are more opaque and smoother than in the periodic kiln at three cones lower temperature. The triaxial replacement of the Florida kaolin, by North Carolina kaolin and Kentucky ball clay No. 4 produces relatively little change in the fired appearance. The glazes containing all ball clay or a mixture of ball clay and North Carolina kaolin overfire at a lower temperature than do those containing all kaolin or a mixture of Florida kaolin and ball clay. The best glazes with 0.2 K₂O and 0.8 CaO have approximately an alumina: silica ratio of 1:9 and 1:11 for the field covered. These glazes are generally more trans- parent than the glazes with 0.3 K₂O; otherwise the results are similar. The conclusions are : (1) that the nature of the firing conditions are of the utmost importance in the development of a glaze, and (2) that an intelligent choice between glazes of equally desirable appearance requires a resort to petrographic method and mechanical tests.     

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.     

EFFECT OF OPACIFIERS ON FUSED VISCOSITY OF FELDSPATHIC GLAZES*

A study has been made of the fusion characteristics of feldspar, flint, kaolin, and whiting used in glaze compositions with zine oxide and various opacifiers. The fusion characteristics of tin oxide, Opax, Zircopax, and various combinations of opacifiers are given. All heat-treatments mentioned are at cone 12. Isoviscosity triaxial diagrams show the fields of good glazes in each series, and the rclative effects of composition changes on the physical properties are outlined.     

EFFECTS OF LITHIA SUBSTITUTION FOR SODA IN VITREOUS ENAMEL*

Lithia, as lithium carbonate, was substituted progressively for soda in the composition of a white cover frit. Substitutions were made on both weight and mol bases. Mol replacement of soda by lithia has resulted in improved fusibility, gloss, and opacity; higher gouge, surface abrasion, and acid resistance; and lower thermal expansion coefficient. Weight replacement has caused increased fusibility and gloss; a small decrease in surface abrasion resistance; marked decreases in opacity and in gouge and acid resistance; little change in thermal expansion coefficient, and a noticeable lowering of the transformation temperature.     

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.     

Study of sauce glazed wares from Yaozhou kilns (Northern Song Dynasty, 960–1127 CE): Probing the morphology and structure of crystals in the glazes

Sauce glaze is one of the main varieties of glazes produced in the Yaozhou kilns during the Song Dynasty. It is famous for its reddish-brown color and high gloss. In this work, the elemental composition, morphology, structure, and light reflectivity of glazes of archeological sherds were systematically studied. A large number of ε-Fe₂O₃ dendritic crystals were observed in the glazes. Alkali etching was implemented to remove the glassy matrix surrounding these crystals to further investigate their microstructure. SEM observations emphasize that they are composed of well-arranged parallel branches separated by about 230 nm, each of which consisting of offset stacks of many small flake-shaped crystals, with the offset ranging from 100 to 110 nm. Based on these results, the origin of the reddish-brown color and high gloss was discussed. In addition, cordierite crystals were observed for the first time in the sauce glaze from Yaozhou kilns.     

组成对分相-析晶乳浊釉显微结构及表面性质的影响

采用X射线衍射、透射电镜和扫描电镜等测试手段,研究了不同组成对分相-析晶乳浊釉显微结构及釉面性状的影响.研究表明:B2O3和P2O5能促进分相形成,并且由于分相具有很小的表面张力而使其液滴易于长大.适量引入CaO能使液滴尺寸增大,体积分数提高,但过量引入会由于析晶而使体积分数降低.控制分相液滴尺寸接近可见光波长以及使釉中析出适量钙钠长石晶体可获得最佳的乳浊效果,而液滴过大或过小都难以获得较佳的乳浊效果.     

一种岩板用的6°丝光高耐磨保护釉

使用常用陶瓷原料钾长石、钠长石、烧滑石、方解石、氧化锌高岭土、氧化铝,并引入少量熔块,制备一种6°丝滑高耐磨仿古保护釉,探究随着BaO含量增多,析出晶体钡冰长石(K_0.6Ba_0.4Al_1.42Si_2.58O_8)增多,对光泽度,摩擦系数,耐磨性能,硬度,防污性能的影响。采用XRD、SEM、耐磨仪、光度计、硬度仪进行测试与表征。结果证明,随着BaO含量增多,釉面光泽度和防污性能下降,但其耐磨度、硬度得到优化;但BaO含量为8.51%时,釉面效果丝滑,光泽度为6°,其耐磨度可达到4级,硬度5级。     

THE RESISTANCE OF SINGLE CLAY BODIES TO THE ACTION OF STEAM1

Twelve whiteware bodies were made, consisting of 51.41%, clay, 10.69% North Carolina feldspar, and 37.9% flint, one clay being used in each body. Twelve clays were studied. The specimens made from these bodies were fired in the regular tunnel bisque kiln to cone 9, glazed on one side, and fired to cone 4 in the glost kiln. The trial pieces were then subjected to the autoclave test, with the steam at a pressure of 100 pounds per square inch, maintained for a period of 3 hours. Of three American ball clays none was found to have caused crazing. In the case of four domestic kaolin bodies, one crazed in part, two were noncrazing, and one shivered. Of five imported kaolins, one of the bodies was noncrazing. While lower absorptions bring about a craze-resisting condition, it was shown that of two single clay bodies with practically the same absorption, one may resist the steam action and one may not. The structure of the clay is an important factor in this connection.     

Lead Free Cu-Containing Frit for Modern Metallic Glaze

A lead-free frit containing high amount of copper and its glaze conceived for fine porcelain stoneware tiles were investigated. The glazes obtained under industrial firing were studied using X-ray photoelectron spectroscopy, X-ray diffraction, optical and scanning electron microscopy with energy dispersion spectroscopy. The mechanism of the red color formation on the surface was explained. The results indicated that the glaze presents a metallic gloss and iridescent colors on the surface, mainly associated to the formation of CuO crystallites and Cu metallic particles. Moreover, the Cu glaze showed a good chemical durability; this is particularly interesting because commercial Cu frits usually present poor chemical properties.