Well-Dispersed α-Fe₂O₃Particles for Lead-Free Red Overglaze Enamels through Hydrothermal Treatment

Abstract

The traditional Japanese overglaze ceramic, akae porcelain, typically known for Kakiemon-style wares, has been prized around the world for over 400 years. The red color of akae porcelain provides an attractive contrast to white porcelain. In recent years, because the use of leaded frit in making akae has been restricted by law owing to the effects of lead on human health and the environment, lead-free glass frit mixtures for overglaze ceramic wares have been developed in various porcelain production areas throughout Japan. However, current lead-free frit for red overglaze enamels produces a color that is duller than that of conventional leaded frit. Therefore, the development of red pigments that are suitable for use with lead-free frit is strongly desired. In this study, we used a hydrothermal process to prepare nanosized iron oxide and oxyhydroxide powders, which showed good particle dispersion in molten lead-free frit. The precursor paste was prepared by reacting iron nitrate with ammonium hydrogen carbonate and heated in a sealed vessel at 80–150 °C. The sample powder prepared at 90 °C was almost monophasic α-Fe 2 O 3 (hematite) and exhibited the brightest red color (highest L *, a *, and b * values). This powder featured primary particles of ∼15 nm in diameter that aggregated to form secondary spherical particles of ∼100 nm in diameter. This powder was mixed with lead-free frit and applied as a red paint to a porcelain test piece. The resultant akae showed a bright red color with high L *, a *, and b * values that exceeded the values of akae prepared using conventional hematite powder. Microscopic analysis revealed that the hematite particles were well dispersed in the resultant glass layer, indicating that the hematite powders have good dispersibility in molten frit.

Sol-Gel Synthesis And Characterization Of New Inorganic Pigments Containing Oxides of Iron, Aluminum, Strontium and Silicate

“…Various studies on the synthesis of new red materials that do not harm the environment continue Red iron oxide (α-Fe 2 O 3 ) pigments have attracted more attention due to their good light fastness, tinting strength, hiding power, durability and low toxicity, and have been widely used in coatings, plastics, ceramics, and other fields. [9,10]. Iron makes up about 6.3% of the Earth's crust; however it is never found in pure form, but instead, combined with other elements, especially oxygen, yielding iron oxides.…”

Enhancing Heat Resistance of Red Color by Coating Fe₂O₃ Nanoparticles with Mesostructured Silica

“…As a non-toxic and safe material for the human body and the environment, it is widely used in different areas other than ceramics, such as resin and paint. Although there are many types of red, such as yellowish and blackish red, the color of α-Fe2O3 is known to vary significantly according to the size and shape of the particles [7][8][9][10][11]. Previous studies have applied different synthesis methods, such as the hydrothermal method, and produced various α-Fe2O3 particles and colors [7][8][9][10][11].…”

“…Although there are many types of red, such as yellowish and blackish red, the color of α-Fe2O3 is known to vary significantly according to the size and shape of the particles [7][8][9][10][11]. Previous studies have applied different synthesis methods, such as the hydrothermal method, and produced various α-Fe2O3 particles and colors [7][8][9][10][11]. Katsuki et al [7,8] demonstrated that α-Fe2O3 nanoparticles display a bright red (vermilion), but they tend to coarsen easily and lose this bright red and become closer to black when sintered by heat treatment.…”

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

“…Although the overglaze enamels are depicted by red, green, yellow, blue, purple, and gold colors, they are known as “ akae ,” which means red overglaze enamels, because of difficulties in controlling the red color . We have conducted comprehensive research on lead‐free akae with the aim of controlling its color tone …”

“…By focusing on a red pigment mainly comprising α‐Fe 2 O 3 (hematite), microtubule materials composed of silicate‐coated hematite nanoparticles, composite materials of alumina/hematite nanoparticles having high thermal stability with respect to color, and well‐dispersed hematite nanoparticles that are suitable for akae have been synthesized. We also converted a wet‐synthesized Al‐substituted hematite into a commercial reality, and the effects of dispersion and aggregation of the hematite particles on the color tone of powders and red overglaze enamels was clarified .…”