The basic trends in production of ceramic pigments based on silicates of different crystal structure are examined. The features of synthesis of the pigments and formation of chromophore phases are demonstrated. The use of natural silicate and aluminosilicate materials will allow expanding the raw materials base, reduce the temperature of synthesis, and produce pigments of a broader palette for decorating porcelain and faience articles.S. G. Tumanov proposed the current classification of ceramic pigments [1], basing it on the crystal structures of refractory, chemically stable minerals of the spinel, corundum, baddeleyite, garnet, and other types. The chromophore ions Co 2+ , Ni 2+ , Cr 3+ , Fe 3+ , V 3+ , and Mn 3+ , whose properties (radius and charge) are close to the ions replaced in the structure of the lattice, can be incorporated in these crystal structures in high-temperature synthesis. This approach made it possible to use purposeful synthesis to obtain a broad palette of ceramic pigments.However, the raw-material base for synthesis of ceramic pigments has expanded significantly in recent years, which will allow refining the structural approach and proposing new variants for pigment synthesis. In particular, the use of silicates and aluminosilicates of different structures as raw materials has increased significantly [2 -5]. The solid-phase reactions take place at relatively low temperatures. Not only incorporation of transition element ions in the crystal structures of silicates but also formation of chromophore phases, the products of the reaction, take place during synthesis of pigments.The silicates used in synthesis of pigments can be divided into two groups [6]: silicates with silica motifs of finite size: with isolated [SiO 4 ] 4-tetrahedrons (island structures); with groups of [SiO 4 ] 4-tetrahedrons of finite size; silicates with silica motifs of infinite size in one or more directions: with like chains or ribbons of [SiO 4 ] 4-tetrahedrons (chain or ribbon structures); with two-dimensional layers of [SiO 4 ] 4-tetrahedrons (layered structures); with three-dimensional backbones of [SiO 4 ] 4-tetrahedrons (backbone structures). Island structures have minerals of the olivine (forsterite, fayalite), garnet (grossularite), monticellite, akermanite, rankinite, and other groups. Pigments with the structure of forsterite, 2MgO × SiO 2 , were synthesized by partial substitution of MgO by CoO, and NiO and [SiO 4 ] 4-tetrahedrons by Fe 2 O 3 , Cr 2 O 3 [7]. In incorporation of CoO in the structure of forsterite, pink to purple pigments are obtained as a function of the amount of coloring oxide [8], and in incorporation of NiO, the pigment is green. Incorporation of Fe 2 O 3 decreased the synthesis temperature and increased the degree of sintering. Judging by the absorption spectra, partial incorporation of [CoO 6 ] in the crystal structure of forsterite instead of [MgO 6 ] took place. The green coloring of nickel-containing forsterite is due to formation of Ni 2 SiO 4 and [NiO 6 ].Pigments of forsterite st...
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The results of a study of the possibility of bulk dyeing of ceramic brick by incorporating manganese and iron ore and metallic slags and sludges from electroplating plants in the pastes are reported. It was found that low-melting clays should first be bleached with chalk or fireclay or kaolin impregnated with solutions of transition metal salts in order to attain a broad color scale for the articles. Using natural raw materials and soluble salts of 3d elements significantly expands the raw-materials base, reduces the cost of the ceramic articles by replacing expensive materials, and combines synthesis of pigments and firing of the articles.
The results of an investigation of the possibility of synthesizing pigments with corundum -spinel structure are presented, and the methods for directed regulation of structure-and phase-formation processes so as to produce pigments with the highest physical -chemical indicators are developed. The relation between the temperature -time parameters of synthesis and the content of modifying oxides and mineralizers with the type and amount of color carrying phases, which give saturated color and a range of pigments colors, are determined.At the present time ceramic pigments are synthesized on the basis of crystallized compounds which can withstand high temperatures, the dissolving action of glazes and fluxes, and corrosive media. Spinel of the first and second types, corundum, zircon, perovskite, and others, are used as the crystalline acceptor-lattices. When transition metal ions (Cr, Fe, Ni, Co, Mn, and others) are incorporated into the crystal lattice of these minerals, the crystal acquires coloration which is due to the absorption of light because of either d -d transitions of electrons or charge transfer. The ions named above are introduced into the crystal lattice by means of solid-phase reactions, which occur at temperatures 1200 -1300°C in the presence of mineralizers (H 3 BO 3 , NaF, and CaF 2 ).Isomorphic solid solutions with different compositions are formed when during the synthesis process transitionmetal oxides partially or completely substitute for the oxides in the crystalline acceptor-lattices.The purpose of the present work is to develop methods of directed regulation of the structure and phase formation processes during the synthesis of pigments with corundumspinel structure which possess a high light reflection coefficient, and high thermal and chemical stability and to determine how the temperature -time parameters of synthesis and the content of the trace modifier-oxide additives and the mineralizers are related with the amount of the color-carrying phases formed, which make it possible to obtain pigments with saturated color and a wide color range.Technical grade alumina (Al 2 O 3 ) was used as the initial component for synthesizing pigments. The following additional components were introduced into the pastes: mineralizer (H 3 BO 3 ), modifiers (ZnO, CaO, CdO, SrO), and chromophore oxides (Cr 2 O 3 , Fe 2 O 3 ). The powders of the initial components were carefully milled and mixed together. The prepared samples were calcined in an electric furnace at temperature 1100, 1150, and 1200°C with a holding period of 1 h at the maximum temperature.It was determined that as a result of heat treatment of technical-grade alumina at 1200°C in the presence of a modifier aluminum oxide transforms from the g into the b form and then into a-Al 2 O 3 .Mineralizers have a large effect on the crystal lattice of the synthesized material as well on the color of pigments. The effect of the mineralizers is to form a liquid phase, which loosens the crystal lattice, putting it into an active state. It is known [1] that ...
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