Recrystallization of Cerium Oxide in Porcelain Enamels

The effect of cerium oxide incorporated as the principal opacifying agent in the frit batch on the properties of white cover-coat porcelain enamels was studied. The effect of several variables on the opacity of the enamel was investigated as a function of firing temperature. Variables studied included (a) the amount of cerium oxide added, (b) the manner in which cerium oxide was incorporated into the enamel, i.e., mill addition, frit addition, or combination of both, (c) composition of the base glass, (d) weight of application, and (e) type of mill addition. Porcelain enamels were produced which had good acid resistance, high gloss, and a reflectance of 80% or more. Mill-added cerium oxide seemed to be less effective than that which was incorporated in the porcelain enamel as a component of the frit. The spectrophotometric analysis indicated good color stability of cerium oxide enamels.     

Hematite crystal growth in high-temperature lead-free multicomponent alkali borosilicate glass frit for red overglaze enamels

To elucidate the crystal growth process of hematite in high-temperature lead-free multicomponent alkali borosilicate glass, which is essentially important to control the color of red overglaze enamels, frit and hematite mixture is heat-treated and subjected to microscopic observations. Hematite particles slightly grew due to sintering at low temperature. Once the glass matrix formed near the softening point of frit, hematite dissolved into glass fluid. Hematite crystal growth concomitantly ensued with decrease in the number of hematite particles via Ostwald ripening as the temperature increased. The grown particles exhibited an anisotropic morphology with straight outlines reflecting crystal planes, the morphology of which is completely different from those grown by sintering and particles prior to heating. These results suggest that comprehensive understanding of frit and hematite from the perspectives of glass science and chemistry as well as powder technology are important to truly control the color of red overglaze enamels.     

EFFECT OF VARIATIONS IN COLOR STAINS AND FRITS ON COLORS PRODUCED IN PORCELAIN ENAMELS*

A representative series of colors, blue, brown, green, red, and yellow, was selected for this investigation. Variations of the constituents for these five stains were made and the resulting colors produced in the enamels were measured by means of spectrophotometric curves. The influence of additions of barium oxide, lead oxide, and zinc oxide to the frit was also studied. The addition of lead oxide to the frit tended to give greater solution of the blue stains. The barium oxide additions dissolved the lead antimonate yellow the most, while the lead oxide had the least effect on the yellow stains. Variations in calcination temperatures of the red stains produced decided changes in color. The additions of lead oxide darkened the color produced with the red stains.     

Chemical reaction between lead-free multicomponent alkali borosilicate glass frit and hematite during heat treatment

A mixture of a lead-free multicomponent alkali borosilicate glass frit containing zinc ions and hematite was heat-treated under various conditions to elucidate the reaction between the two components, which is essentially important for controlling the color of red overglaze enamels. Above the glass transition temperature, the interaction between the frit fluid and hematite was evident, as the viscosity of the frit decreased. Moreover, hematite dissolved, the iron ions diffused into the glass matrix and they precipitated on residual hematite, resulting in enhanced crystal growth through Ostwald ripening. Concurrently, the iron and zinc ions reacted to form zinc ferrite. During cooling, the supersaturated iron ions were consumed for precipitation of hematite and zinc ferrite. Because frit and hematite dramatically react during heat treatment, conventional modification of hematite alone is insufficient. Development of the frit exhibiting low reactivity toward hematite through precise control of physical properties is a future challenging issue.     

ABRASION RESISTANCE OF PORCELAIN ENAMELS*

The abrasion resistances of enamels, differing in composition and properties, were determined by the test for resistance of porcelain enamels to surface abrasion (a standard of the Porcelain Enamel Institute, March, 1942). Four to five classes of abrasion resistance were obtained, but for the most part, the results fell within relatively narrow limits. Differences in abrasion index, in general, were not distinguishable by visual inspection. No one class or kind of enamel was superior. While changes in abrasion index were affected by changes in frit formula, it seems that many compositions will give comparable results.     

ALUMINIUM FLUORIDE IN CAST-IRON ENAMELS1

Aluminium fluoride was used in cast-iron enamels, replacing cryolite. The fluxes were increased, when substituting aluminium fluoride for cryolite, to care for the extra alumina introduced by the fluoride. The costs of an enamel containing cryolite and one containing aluminium fluoride are compared.     

GOUGE RESISTANCE OF PORCELAIN ENAMELS*

An exploratory study was made to determine possibilities of the Porcelain Enamel Institute rolling-ball gouge test as well as to discover some of the factors influencing the gouge resistance of enamels as shown by the test. The test results compare favorably with deep-scratch and gouge defects encountered in actual enamel practice. The accuracy of test results, moreover, compares favorably with other such physical tests designed for use with porcelain enamel. The gouge resistance is shown to be a function of enamel thickness and of bubble structure. Factors which increase or decrease bubble structure, such as mill additions, frit compositions, and firing treatment, are shown to affect gouge resistance.     

MOLYBDENUM IN ENAMELS: III,TYPICAL MOLYBDENUM ENAMELS*

Compositions and characteristics of various types of enamels using the most successful mill additions in Parts I and II are reported. The enamels used in this paper are (1) clear enamels (regular) for ground or colored coats, (2) clear enamels (acid resisting) for colored coats, (3) high lead clear enamels maturing below 1000°F., (4) raw or partially fritted enamels for ground or colored coats, and (5) white antimony enamels for direct application to the metal base. Reported for the first time are some white enamels containing molybdenum in the frit, which adhere to sheet steel without additions of molybdenum compounds to the mill.     

Color Stability of Clear and Opaque Titania Enamels Containing Various Color Oxides

A study was made of the spectrophotometric characteristics of a clear and an opaque titania-bearing enamel. Three and six per cent additions of green, blue, brown, and red oxides were made to the base enamels. After firing the enameled samples over a range of time and temperature, spectrcphotometric and X-ray data were obtained. The results indicate that the lack of stability of the opaque colored enamels is due to the change from a blue-white to a cream-white color on increased firing treatment. The addition of a cream component tends to shift the hue of the fired enamel toward the red end of the visible spectrum. The green and the blue colors were much less stable than the red. X-ray data show that the total anatase present decreases, which is evidence that a cream-white color developed. X-ray data did not indicate any change in crystal structure of the anatase, rutile, or color oxide. Titania present in the glass of the clear enamel did not cause color instability.     

Drastic enhancement of mechanical strength and thermostability of bright yellowish-red hematite/alumina composites having a unique disk-like structure via silica coating

Surface coating is a key technique used to enhance various properties of functional inorganic materials. We adopted a silica-coating treatment for preparing bright yellowish-red pigments using hematite/alumina composites, which have a unique porous disk-like structure. This treatment enhanced color, mechanical strength, and thermostability. The porous disk-like structure comprising Al-substituted hematite particles and alumina nanoparticles, which is fragile to mechanical impact and/or high-temperature heating, was a key factor to obtain high chroma bright-red color in the present system. Silica-coated samples having various Si molar ratios [x=Si/(Fe + Al + Si)] were prepared, and mechanical-strength and thermostability tests were conducted. The mesopores generated by an assembly of hematite particles and alumina nanoparticles were gradually filled with amorphous silica, thus achieving significant enhancement in mechanical strength and thermostability in color. The composite pigment can be used as a colorant for red overglaze enamels for porcelain, and shows significant potential for various other industrial coloring applications.     

CALCIUM OXIDE AS A SET-UP AGENT FOR ACID-RESISTING ENAMELS*

A study was made of the effect produced by calcium oxide in the set, color, luster, texture, and acid resistance of white and colored enamels.     

EFFECT OF COMPOSITION ON PROPERTIES OF TITANIUM ENAMELS*

The development of a superopaque, acid-resistant titanium enamel is described. Different components of the batch were varied systematically and the properties, such as reflectance, color, flow, gloss, and acid resistance, were determined. Variations in composition, reflectance curves, and spectrophotometer curves are given for all of the enamels investigated. The stability of this type of enamel during firing and smelting was also studied. Spectrophotometric analyses of this type of enamel show a characteristic low reflectance in the short-wave length region of the visible spectrum, differing in this respect from superopaque antimony and zirconia enamels. Additions of as much as 0.5% Fe₂O₃ and 0.2% V₂O₅ to the titanium enamel did not cause any appreciable variations in color. Although some differences in the spectrophotometer curves were noted over the field of enamels investigated, the only major change in color occurred when minute amounts of Cr₂O₃ were present. X-ray diffraction patterns of enamels show that rutile crystals in most cases, or sometimes anatase, are the crystals causing opacity.     

不同颜色色浆对氟树脂/铝低红外发射率涂层的影响

研究了大红、深黄、水紫、黑色4种颜色色浆对氟树脂/铝低红外发射率涂层光泽、附着力、硬度、粗糙度、耐冲击性、色差、红外发射率、耐腐蚀性等性能的影响。研究结果显示:深黄色色浆涂层的发射率最低,约为0.1;不同色浆对氟树脂涂层色差明度影响不同,相对于其他色浆,水紫能够使涂层偏暗;大红、深黄、水紫色浆的涂层硬度均为6H;加深黄色浆的涂层附着力最好,其次是大红色浆和水紫色浆;深黄色浆对涂层的耐冲击性影响最大,其次是大红色浆和水紫色浆;相对于大红、深黄、黑色色浆,水紫色浆涂层具有最低的粗糙度,表面比较光滑;水紫色浆和深黄色浆的红外波峰比较持平,有利于减小表面发射率;水紫色浆氟树脂涂层的耐腐蚀性能最好。耐盐水腐蚀测试后4种涂层均没有明显失光,水紫涂层没有发生明显变色,深黄和黑色涂层起泡密度较低。水紫色浆因其粒径均匀细小,在氟树脂涂料中易分散,与氟树脂相容性好,因此具有相对较优的综合性能。     

EFFECT OF COEFFICIENT OF EXPANSION OF GROUND- AND COVER-COAT ENAMELS ON THERMAL-SHOCK AND IMPACT RESISTANCE *

Four antimony cover-coat enamels, four fluoride cover-coat enamels, and four ground-coat enamels were formulated to give varying coefficients of expansion. The calculated values were 250, 275, 300, and 325 × 10^–7. The observed coefficients of expansion are included in the paper. The enamels were applied to standard 2-quart pudding pans and were tested for thermal shock and impact resistance using the standard methods of the Enameled Utensil Manufacturers’Council. The results show that thermal-shock resistance is controlled chiefly by the coefficient of expansion of the ground-coat and cover-coat enamels. The best results were obtained by using a cover-coat enamel with a low coefficient of expansion and a ground coat with a high coefficient of expansion. No conclusive evidence was found to indicate any effect of the coefficient of expansion of the ground- and cover-coat enamels on impact resistance. The solubility resistance and reflectance curves for the enamels are also included.     

EFFECTS OF VARIOUS CLAYS USED IN MILL ADDITIONS ON PROPERTIES OF A TITANIA-OPACIFIED ENAMEL*

In the course of investigations made in connection with the development of titania-opacified enamels, it was observed that color, reflectance, and acid resistance were influenced by the clay used in the mill additions. In a subsequent search for a clay which would produce the best over-all enamel properties, a study of the effects of twenty clays of different types was made under standardized conditions of milling, spraying, and firing. Coatings sprayed at 30 gm. per sq. ft. were examined for bisque strength, brushing behavior, and tearing. After firing for 3 minutes at 1540°F., and at 1640°F., the reflectance, color, gloss, and acid resistance of the enamels were observed. It has been concluded that the success or failure of an enamel is determined to an important degree by the clay used in the mill addition.     

Systematic Study of Simple Titania-Bearing Porcelain Enamels

An extensive composition study of titania enamels and their properties is described. The compositions investigated contained only six constituents, namely, Na₂O, K₂O, SiO₂, B₂O₃, TiO₂, and F₂. Systematically and over a wide range, the contents of SiO₂, B₂O₃, TiO₂, and alkali were varied. One hundred enamels in all were made and the resulting properties were determined. Properties noted included flow, expansion, color, percentage of anatase, gloss, reflectance, and acid resistance at various firing temperatures.
Enamel Y12, representing a small area in this large composition field, exhibited the properties requisite for a good hollow–ware white cover–coat enamel. Compared with previously studied titania enamels, this enamel is "softer"; i.e., it fires at lower temperatures, has the desired higher flow and expansion, yet still possesses the required properties of color stability, reflectance, gloss, acid resistance, and workability.     

Li_2O-Na_2O-B_2O_3-SiO_2系无铅低温透明熔块的研制

探索用"Li2O-Na2O-B2O3-SiO2"新的配方系统配制无铅低温透明熔块的方法。制得使用温度为740~780℃的低温无铅透明熔块,以熔块配制成的低温透明熔块釉可作为生产陶瓷装饰色料中的低温熔剂。     

EFFECT OF GROUND COATS ON REFLECTANCE OF COVER ENAMELS *

The problem of color variation in white cover-coat enamels has received considerable attention, but variations in color due to base coat have had little or no consideration. An attempt was made to determine the effect of the base coat by comparing color variations in opaque and superopaque enamels applied over blue, white, gray, red, yellow, and green base coats in weights ranging from 10 to 120 gm. per sq. ft. The resultant finishes were compared visually and with the aid of the Hunter multipurpose reflectometer. Over the entire range studied, the base coat was found to have a marked effect on the color characteristics of the finish coat. This is true particularly in the lower ranges of application including normal production application weights. Base coats that decreased the reflectance of the cover coat in the blue field, were found to give higher apparent opacity than those which maintained a relatively high blue reflectance.     

Role of P2O5 in TiO2-Opacified Porcelain Enamels

Phosphorus pentoxide is known to affect the reflectance and color of TiO₂-opacified porcelain enamels. It has been postulated that P₂O₅, impedes the anatase-to-rutile phase transformation. This hypothesis was tested by applying recently developed analytical procedures based on X-ray diffraction analysis to a typical porcelain enamel cover coat system. The inversion of anatase to rutile was not significantly affected by P₂O₅. Instead, in the range 0.5 to 4%, as P₂O₅ concentration was increased in the frit, the rate of crystallization of both anatase and rutile also increased, with the rate of increase of anatase being about twice that of rutile.     

EFFECT OF SOLUBLE SALTS ON THE PROPERTIES OF ENAMELS1

Enamels, in common with other types of glasses, are more or less soluble in water, depending on their compositions. The nature and quantity of salts dissolved from the enamel glass during milling have a very definite bearing on the suspension, work ability, and other properties of the enamel, such as pitting and crawling. Those enamels which produce mill liquors which are excessively alkaline have very poor floating qualities. The ratio of free alkali to boric oxide dissolved from the enamel frit is an important factor in the flotation properties of the enamel. The poor floating powers of certain enamels can be corrected by the addition of suitable electrolytes. The kind and quantity of salts dissolved from the frit will determine the selection of the proper electrolyte. Enamel compositions having minimum solubility for good suspension and other properties are given. The value of an enamel clay cannot be determined by floating the clay in water. Tests must be made with the clay in the type of enamel with which it is to be used. Any studies on the effect of aging of enamels on their working properties must give consideration to the constitution and quantity of the individual salts dissolved from the enamel frit, and to the action of carbon dioxide in neutralizing part of the free alkali.