Effect of Underglaze Paints as Cobalt and Nickel Salt Solutions on Porcelain Structure
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EFFECT OF UNDERGLAZE PAINTS AS COBALT AND NICKEL SALT SOLUTIONS ON PORCELAIN STRUCTURE T. L. Neklyudova,1, 2 L. Kh. Yugai,1 and Yu. N. Kryuchkov1 Translated from Steklo i Keramika, No. 6, pp. 30 – 35, June, 2020. The effect of underglaze paints in the form of cobalt and nickel salt solutions, especially in the porcelain-glaze contact zone, on the formation of the structure of a porcelain article was determined. In this zone the salts change the character and size of the new crystalline formations. As the color of the glassy layer of the glaze attests, the cobalt ions form compounds which are more soluble than nickel ions in the glass phase of porcelain and glaze. As the content of the salts increases, a crystalline paint layer forms on both sides of the article. Key words: porcelain, glaze, surface, underglaze paint, solution, salts, ions, new crystalline formations.
thite crystals. The composition of the porcelain and glaze, the viscosity, wetting power, and surface tension of the glaze, and the firing regimes affect the development of an intermediate layer with expressed crystallization [3]. When the porcelain glaze is overburned, the growth of mullite needles in the contact zone is intensified and they can even penetrate the entire layer of glaze. In addition the mullite needles are arranged chaotically or grow into the glaze. In normally fired glaze the mullite crystals formed in the contact interaction zone near the porcelain-glaze boundary do not exceed 30 ìm in size, as shown as an example for the glaze represented in Fig. 1 and used in the present work. The objective of the present work was to study the action of underglaze paint in the form of salt solutions on the formation of porcelain structure and the contact layer with the glaze. The chemical composition of the porcelain body includes (weight content, %): 59.5 SiO2; 28.2 Al2O3; 0.34 Fe2O3; 0.45 TiO2; 0.3 CaO; 0.2 MgO; 2.2 K2O; 0.4 Na2O; and, 7.2 LOI. Forty-percent salt solutions, prepared using distilled water, were deposited on porcelain after biscuit firing (with water absorption 22%). Cobalt and nickel sulfate, specifically, CoSO4 × 7H2O and NiSO4 × 7H2O, were used. The salt solutions were brushed on from the exterior side of the samples in one, two, three, and four layers. The amount of salt (%) on average per unit mass of material was determined according to the increase in the mass of the samples. The mass content of salt for the layers from the 1st to the 4th, respectively, was, %: 0.89, 1.48, 2.2, and 2.88 for CoSO4 × 7H2O and 0.96, 1.76, 2.15, and 3.0 for NiSO4 × 7H2O. Next, the samples were coated with a transparent feldspar glaze. The
Underglaze decoration of porcelain is usually accomplished by using coloring substances capable of withstanding high firing temperatures in different gaseous environments as well as the action of the glaze melt. One of the varieties of underglaze paint is a water solution of metal salts and their mixtures. Even though the pallet is limited, salt solutions afford the possibility of creating a ‘watercolor
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