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.     

Interaction between lead‐free multicomponent alkali borosilicate glass frits and hematite in red overglaze enamels

Japanese traditional red overglaze enamel decorations on porcelain known as akae are produced using lead‐containing frits, leading to a problem of lead release. Although many lead‐free frits have been developed, a well‐colored akae has not yet been realized, mainly because of no information on the reaction between lead‐free frits and hematite during the heating process in akae production. To reveal the effect of such interaction between the frits and hematite in akae on the color tone, various akae test pieces were prepared and investigated. On using low‐melting‐point lead‐free alkali borosilicate glass system, which contain zinc oxide, the formation of zinc ferrite proceeds simultaneously with the dissolution and particle growth of hematite in the frit melt. The particle growth rate due to dissolution and precipitation in the frit melt is faster than that due to sintering of particles caused by heat treatment of hematite powder in dry process. The dissolving capacity and promoting effect of particle growth depended on frit compositions. We also showed that the composition of akae glass layer varies because of ions diffusing from the glaze layer. Compositional changes in the akae glass could strongly affect the reactivity between the frits and hematite, resulting in variation in the color tone, the crystal phases formed, and their segregated states.     

Influence of viscosity and composition of alkali borosilicate lead-free frit on its reaction with hematite,and the color control of red overglaze enamels

Inspired by the ion diffusion at the interface between the red glaze and glaze layers, which was confirmed by the study of overglaze painting on porcelain test pieces, we developed frits with compositions in which a lime glaze was systematically added to a lead-free multicomponent alkali borosilicate glass frit. When the mixed powder of the frit and hematite was heat-treated, the excessive reaction with hematite was suppressed as the lime glaze content increased, due to the increase of the frit viscosity. The dissolution of hematite was suppressed in the sample with the same viscosity at a higher heat treatment temperature, i.e., with a higher lime glaze content, confirming that the composition of the frit strongly affects the dissolution of hematite. We attempted to improve the chroma of lime-glaze-added samples, and the highest chroma in this system was achieved by adjusting the amount of initial hematite and heat treatment temperature.     

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.     

Non-invasive Raman identification of crystalline and glassy phases in a 1781 Sèvres Royal Factory soft paste porcelain plate

A Raman study of a Sèvres soft paste (frit) porcelain plate allowed the identification of both the crystalline and amorphous phases. Cristobalite and pseudowollastonite gave main Raman signatures in the body where also tridymite, amorphous alkali silicate glass and lead arsenate apatite were detected. Na_0.4K_0.1Ca_0.5Pb₄(AsO₄)₃ lacunar apatite is identified as opacifier in blue and green overglaze enamel. Pb-Sb-reach pyrochlore (Naples Yellow) pigment was found in yellow and green overglaze enamels. The orange hue is obtained by superposing a hematite bearing red paint stroke over the yellow. These results are compared to those previously obtained by detailed OM, SEM, XRD and XRF analyses. Some of the phases identified by XRD (quartz, tridymite) are hardly detected by Raman and vice versa cristobalite was not found by XRD, most probably due to its low amount.     

Multinuclear core/shell hematite/glass particles for peeling-free red overglaze enamels on porcelain

For red overglaze enamel decoration, a type of colored ceramic coating for ceramics, a partial peeling might occur in mass-produced ceramic ware products. In this study, multinuclear core/shell hematite/glass composite particles, comprising a hematite core and a glass shell, where hematite particles are highly dispersed in a glass matrix, were developed to prepare a red coating material that could achieve a bright red-colored overglaze enamel without peeling. A peeling-free, bright yellowish red-colored overglaze enamel could be obtained when using the composite particles as the red paint. The former function (preventing peeling) can be derived from micrometric size of the shell glass particles and the latter function (high chroma and lightness) is caused by highly dispersive hematite particles in the shell glass particles. Our results suggest that the composite particles are suitable for mass-production due to their peeling-free nature, indicating a potential to be widely used as coloring for ceramic coating products.     

Stability of Acid-Resistant Red Porcelain Enamels

The comparative acid resistance of a series of enamels was determined by the loss-in-weight test and by the spot test. The stability of the red color oxide in these enamels was also studied by varying the alumina, fluoride, soda, and potassia contents in the frit. Improved acid resistance was obtained with no alumina and no fluoride in the frit. The stability of the red color was markedly influenced by the fluoride content; the absence of fluoride in the frit gave very poor stability.     

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.     

Sintered glass-ceramics from incinerator fly ashes. Part II. The influence of the particle size and heat-treatment on the properties

A composition obtained by mixing MSW ashes with sand and glass cullet was melted at 1500 °C and quenched in water. The obtained frit was sieved and separated in different fractions: L (large, 2–5 mm), I (intermediate, 1–2 mm) and S (small, <1 mm). The sintering of the glass particles, carried out in an alumina mould, occurred in the 700–950 °C range. The curve of the crystal growth rate as a function of the temperature was obtained by means of 1 h heat-treatment in the 850–1050 °C range. The crystal growth started at 850 °C and the maximum rate, 0.013 mm/min, occurred at 1020 °C. The ferrobustamite crystal phase was evaluated by XRD analysis and observed by optical microscopy. The mechanical, thermal and chemical properties of the L, I and S glass-ceramics were measured and discussed. They resulted to be influenced by the grain size of the glass particles and by the percentage of crystal phase.     

Correlation between the Izumiyama porcelain ceramics and the red-overglaze enamels of the Kakiemon-style porcelains

The Kakiemon-style porcelains made from 17th century at Arita are famous Japanese porcelains, characterized mainly by their colored underglaze and overglaze and by their original design of coloring spatial patterns in the porcelain surface. Raw materials of the red-overglaze enamels have been investigated by means of X-ray diffraction and X-ray absorption spectra using synchrotron radiations. It is found that Izumiyama porcelain ceramics of yellow color can produce the Kakiemon red-overglaze enamels by thermal treatment and water-washing, where Izumiyama is a collecting place of the raw porcelain ceramic at Arita. The brightness of the red-overglaze enamels is related on the local structure around Fe ions and the electronic band states of Fe ions near a Fermi level in α-Fe₂O₃, in addition to the spatial density of the α-Fe₂O₃ fine particles. The structural and electronic properties are slightly affected by an electron-hybridization between Fe ions of α-Fe₂O₃ and oxygen ions of the (SiO₂–Al₂O₃) complexes in the red overglaze.     

Microstructure of Titania-Opacified Porcelain Enamels

The microstructure of TiO₂−opacified porcelain enamels was examined by optical microscopy and by transmission electron microscopy. The mosaic pattern found appears to correspond to the positions of the frit particles from which the enamel was made. Significant differences were observed in the crystallization behavior of adjoining frit particles. There is evidence that rutile grows from frit particle surfaces, whereas anatase is body-nucleated. The anatase-to-rutile inversion is a ripening process rather than a phase transformation. Processes occurring during the firing of a TiO₂ enamel include crystallization from single-phase glass, crystallization from multiphase glass, and a ripening process.     

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.     

Role of α-Fe2O3 Morphology on the Color of Red Pigment for Porcelain

To produce a new red pigment for Japanese porcelains, some hematite (α-Fe₂O₃) powders produced by different methods were investigated by mixing them with lead-free frit powders and firing them on white porcelain plates at 800°C. Commercial hematite powders and uniform α-Fe₂O₃ powders 155 and 53 nm in diameter which were prepared using conventional- and microwave-hydrothermal reactions, respectively, were used as sources of red pigments. The morphology and dispersion of the above α-Fe₂O₃ powders were found to have a significant effect on the tone of red color for porcelain pigment.     

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.     

Microstructural and Microchemical Characterization of Roman Period Terra Sigillate Slips from Archeological Sites in Southern France

Terra Sigillata is a fine ware produced during the Roman period. Its great success was because of its remarkable gloss (or slip), which provides a bright deep red color. Transmission electron microscopy and X-ray powder diffraction techniques were used to characterize the microstructure and microcomposition of Roman period Terra Sigillata slip from two sites in southern France. Investigations on eight samples are presented. The slip coatings have similar structures and compositions, consisting of sub-micrometric hematite (≤μm) and nanometric corundum (few tens nm) crystals in a glass matrix with inclusions of spinel and quartz crystals of varying size depending on the extent of preparation by eleutriation. The firing temperature, determined in previous studies, was in the range of 1020°–1080°C. The matrix does not contain iron or other metallic ions. Hematite and corundum crystals are homogeneously dispersed in the matrix and, together, confer the specific red-orange color to the sigillata.     

鹤壁集窑黑,红彩陶瓷的显微结构特征

鹤壁集窑是我国著名的民窑之一,它位于河南省的西北部。鹤壁集窑的黑、红彩装饰技艺的发展在陶瓷和艺术史上占有重要地位。本文对红彩、褐红彩的装饰技术和呈色机理作了研究,发现: 1.北宋样品都有两层化妆土,这在胎釉之间起到过渡作用,它不仅可以增加陶瓷外观白度,而且能使釉减少应力并避免产生裂纹。 2.北宋、金和部分元代样品都是釉下彩。釉下彩样品的色层物相都是以磁铁矿为主,花纹呈黑色。但是部分元代样品色层在釉上,部分釉上彩色层物相是以赤铁矿为主,花纹呈铁红色。两个元代样品釉上色层物棚的含磁铁矿量和赤铁矿接近,花纹呈褐红色。     

Characteristics of thick film resistors embedded in low temperature co-fired ceramic (LTCC) substrates

Commercial thick film resistors were embedded in low temperature co-fired ceramic (LTCC) substrates, and co-fired with substrates at temperatures between 800 and 900 °C. Adding glass frit and amorphous SiO₂ to calcium borosilicate glass ceramic substrates has not only lowered the shrinkage of the substrates, but also improved adhesion and maintained structure integrity of the resistor films. During sintering, the conductive phase particles in the resistor became agglomerated and sedimented, and glass diffused into the LTCC substrate layer. Increasing the dwelling time, the overall resistivity of the co-fired films decreased due to sedimentation of agglomerated conductive particles. The liquid eutectic phases penetrated into the substrates added with either SiO₂ or glass frit that the volume fraction of conductive particles was increased. The resistivity of the embedded resistors was determined by the volume fraction of conductive particles, which was influenced by the conductive particles sedimentation, microstructure of resistor films, and inter-diffusion between the resistors and substrates.     

Effects of BaO–SiO2 glass particle size on the microstructures and dielectric properties of Mn-doped Ba(Ti,Zr)O3 ceramics

The sintering behavior, microstructures and dielectric properties of Mn-doped Ba(Ti, Zr)O₃ (BTZ) ceramics with different particle sizes of BaO–SiO₂ glass (D50 ranging between 185 and 1200 nm) were investigated. From the metallographic observation, adding finer glass frit revealed more homogeneous compositional distribution. It was found that better spreading of the glass phase could be achieved by adding finer glass particles that could penetrate the BTZ ceramic interface more easily, thus enhancing the grain growth. The extent of the incorporation between glass and ceramic increased with smaller glass particles, and the Curie temperature was altered accordingly. Microstructural evaluation conducted by using X-ray diffraction (XRD) and transmission electron microscopy (TEM) with an energy-dispersive X-ray spectrometer (EDS) indicated the glass particle size has a dramatic influence on the sintering behavior and microstructure of Mn-doped BTZ ceramics. The relationship between microstructures and dielectric properties was also discussed in this study.     

Immobilization of hospital waste incineration ashes in glass-ceramic composites

In the paper process of sintering of hospital incineration ash as a counterpart of low-level active waste with borosilicate glass frit is presented. It is shown that low porosity glass-ceramic waste-form can be obtained at a temperature range of 850–900 °C. In the sinter, the main crystal phases are wollastonite and aegirine-augite pyroxenes which have a large isomorphous capacity of binding hazardous elements. The crystal phases are fully encapsulated by the glass that provides additional protection against environmental influence. Thus, multibarrier material can be obtained at a temperature considerably lower than vitrification. This, in turn, can improve the economics of immobilization process.     

Microstructure and mechanical properties of dental 3Y-TZP ceramics by using CaO-P2O5 glass as additive

This study investigated the effects of glass frits on the sintering and mechanical properties of dental 3Y-TZP ceramics. The glass frits, which consisted of MgO, CaO, Al₂O₃, SiO₂, and P₂O₅, were selected to lower the sintering temperature of zirconia via liquid phase sintering.The results of the experiment showed that these glass frit additives neither destroy the stability of the high temperature t-phase nor induce grain growth. All the mechanical properties and the relative densities were strongly correlated with the addition of glass frits. At lower sintering temperatures, the presence of glass additives resulted in an increase in mechanical properties. At higher sintering temperatures, the presence of glass additives decreased the mechanical properties.