Wear resistant unfritted white glazes in floor tile production

Translated from Steklo i Keramika, No. 4, pp. 18–20, April, 1989.     

Production and characterisation of iron-chromium pigments and their interactions with transparent glazes

In this study, production and characterisation of pigments by using less expensive raw materials such as limonite and chromite was undertaken. The resulting pigments were characterised by using X-ray diffraction (XRD) and UV-Vis spectrophotometer. The colour of glazed tiles containing 3 wt.% pigment change from dark brown to light brown depending on the calcination temperature and limonite content. With pigments prepared with 50% limonite content calcined at 1250 °C, the chocolate brown colour was obtained corresponding to the commercial brown pigments. An iron-chromium black pigment was synthesised from a mixture of pure chromium (III) oxide (Cr₂O₃) and iron (III) oxide (Fe₂O₃) powders and was used to determine possible interactions between a pigment and a transparent glaze. The interactions were studied using a scanning electron microscope (SEM) attached with an energy dispersive X-ray spectrometer (EDX). The results showed that black pigment particles give brown colour to the glaze. EDX analysis on pigment crystals embedded in the glaze clearly showed that Zn and Mg diffused into pigment crystals and caused a change of colour from black to brown.     

Karrooite green pigments doped with Co and Zn: Synthesis,color properties and stability in ceramic glazes

The solid-state synthesis and stabilization of Co doped (Mg_1−xCo_xTi₂O₅), Zn doped (Mg_1−xZn_xTi₂O₅) and Co- and Zn-codoped karrooite solid solutions (Mg_0.8−xZn_0.2Co_xTi₂O₅ and (Mg_0.5Zn_0.5)_1−xCo_xTi₂O₅) were investigated. In addition, the optical spectra, color properties and technological performance of (Co,Zn)-karrooite compositions as new green ceramic pigments were also analyzed. XRD characterization revealed for the first time the high solid solubility of Zn²⁺ in MgTi₂O₅ karrooite at 1200 ºC (between 60 and 80 mol% per Mg or karrooite formula unit). In contrast, the reactivity and stabilization of karrooite phase decreased in the case of Co²⁺ doping. Interestingly, codoping with Zn²⁺ ions at high molar ratios (Zn:Mg ratio equal to 1:1) enhanced the reactivity and enabled the stabilization of (Co,Zn)-MgTi₂O₅ karrooite solid solutions, even with high Co²⁺ loadings (20 mol% per karrooite formula unit). The (Co,Zn)-MgTi₂O₅ pigments exhibited yellowish-green colors associated to Co²⁺ ions allocated in octahedral M1 and M2 sites of karrooite lattice, and becoming more intense and less yellow the higher the Co content. However, Zn²⁺ codoping produced less saturated green colors with similar green but lower yellowish hues. The obtained pigments were not stable enough within the tested ceramic glazes, giving rise to turquoise colorations due to cobalt leaching and incorporation into tetrahedral sites of the glassy phase. The stability of Co-karrooite green pigments was higher in a Ca- and Zn-enriched ceramic glaze (B) fired at a higher temperature (1050 °C).     

The mechanism for the colour change of iron chromium black pigments in glazes through transmission electron microscopy techniques

Black iron-chromium (Fe-Cr) bearing oxide pigments are generally utilised as effective colourants in a wide variety of applications. However, in the case of their use within ZnO-containing glazes, they yield an undesirable brown colour instead of expected black colour. In order to understand the colour change in this system, we report the use of focused ion beam (FIB) sample preparation technique followed by the use of analytical transmission electron microscopy (TEM) characterisation techniques. According to the results, the formation of a reaction layer between the pigment and glaze was identified with an average composition of Zn_0.48Fe_0.79Cr_1.32O₄. Additionally, the valance of Fe was determined as 3+ in the pigment grain, whereas 2+ in the reaction layer and the glaze, respectively. Therefore, it was concluded that the colour change is occurring as result of the valence variation of Fe, the formation of Zn_0.48Fe_0.79Cr_1.32O₄ compound and the outward diffusion of Fe into the glaze.     

The stability of gahnite doped with chromium pigments in glazes from the French manufacture of Sèvres

The French manufacture of Sèvres, famous for its production of fine porcelain artifacts, has been synthesizing pink pigments mainly composed of the spinel phase ZnAl_2?xCr_xO₄ with x varying from 0.25 to 0.41 since the middle of the 19th century. This kind of pigment is mixed with an uncolored frit to obtain decorations for porcelain artifacts. However, the pink color of the pigment is altered in a particular uncolored frit and a brownish color appears. The mechanism of this color change was investigated. Observations under a scanning electron microscope revealed the formation of a phase rich in Cr resulting from reactions between the uncolored frit and the pigment during firing. X‐ray diffraction combined with Rietveld refinements and X‐ray absorption near edge structure measurements at the Cr K‐edge showed that the new formed phase belongs to the same spinel phase ZnAl_2?xCr_xO₄ than the pigment, but with a higher Cr content x. We showed that its formation and thus the stability of the pigment is driven by the Al content in the uncolored frit.     

抗高铁氧化物熔渣的镁炭砖

通过选用特殊加工的电熔镁砂,改变镁炭砖的粒度组成及添加剂,开发了新型抗高铁熔渣的镁炭砖。在使用中,该砖具有较强的对熔渣的亲合力,挂渣效果好,同时与传统镁炭砖相比又具有很强的抗侵蚀性和较高的高温强度。该砖在天津钢管公司150tUHP电炉上使用,表现出对高铁氧化物熔渣极强的适应性,1999年初使用炉龄首次突破400炉大关。     

Activating crystallization in zirconia glazes

Translated from Steklo i Keramika, No. 4, pp. 23, April, 1992.     

Phase formation in titanium glazes

Phase formation in titanium-containing systems is examined. The results of studies of phase formation under crystallization are reported for the SiO₂−TiO₂−CaO−Al₂O₃−B₂O₃−Na₂O system. The principal phases in the compositions studied were found to be sphere, anorthite, and rutile. Translated from Steklo i Keramika, No. 1, pp. 17–20, January, 1997.