Phase composition and structure of dull low-melting glazes

Abstract

The possibility of producing dull low-melting glazes for ceramic products to be fired according to a slow firing regime based on the system Na 2 O -MgO -CaO -B 2 O 3 -Al 2 O 3 -SiO 2 is demonstrated. The results of studying glaze glasses and coatings by x-ray phase analysis, electron microscopy, infrared microscopy, etc. are described. A correlation between the structure and the phase composition of coatings and their qualitative characteristics is established. The main properties of synthesized dull glazes are specified.Household majolica and pottery are becoming increasingly popular. Producers appreciate the possibility of using inexpensive local argillaceous materials, whereas consumers appreciate high artistic qualities reviving the traditions of folk crafts. Dull glazes used for decorating majolica products impart diverse types of textures to the majolica surface and conceal the heterogeneity in color tones that is typical of majolica. Furthermore, a glaze coating can improve the service properties of an article and decrease its disadvantages, such as high porosity, high water permeability, and low mechanical strength.One of the best methods for obtaining a dull glaze surface is based on inducing a crystalline phase in the coating, whose refractive index differs significantly from that of the matrix glass. The dullness of such coating is determined by the diffuse reflection of light from the faces of the emerging crystals, and the degree of dullness depends mainly on the size and quantity of crystals.The development of glazes not containing expensive or toxic components is of special interest. The research in the synthesis of opaque zirconium-free glazes performed at the NIIstroikeramika Institute [1] and at the Kharkov State Polytechnic University [2], as well as our studies [3], indicate that glaze coatings with a dull texture can be obtained in the system R 2 O -RO -B 2 O 3 -Al 2 O 3 -SiO 2 [R 2 O) Na 2 O, K 2 O; RO) MgO, CaO] due to the formation of opacifying phases represented by wollastonite and diopside under optimum temperatures. According to the authors of [1, 3], a silky-dull coating surface can be ensured by the formation of a finely dispersed structure with crystal sizes not more than 10 mm. However, the known compositions are intended for construction ceramics whose technology involves fast firing.The purpose of the present study is to obtain dull glazes based on the system Na 2 O -MgO -CaO -B 2 O 3 -Al 2 O 3 -SiO 2 by a slow-firing regime, which would be formed due to the crystallization processes.For our study we selected a range of compositions containing a constant quantity of Na 2 O and Al 2 O 3 equal to 10 and 3%, respectively (here and elsewhere mol.%, unless otherwise specified). The following contents of the components were studied (%): 0 -10.0 MgO, 2.5 -22.5 CaO, 4.5 -19.5 B 2 O 3 , and 50.0 -65.0 SiO 2 .Experimental glaze glasses were obtained by melting batches whose components included quartz sand, boric acid, soda ash, chalk, dolomite, alumina, and magnesia. Synthesis was performe...

Structure property relations in multicomponent oxide systems with additions of TiO2 and ZrO2 for glaze applications

“…At around 790 cm 1 , the characteristic symmetric Si-O-Si stretching vibrations of SiO 4 units are observed [12]. The band at 460 cm 1 is assigned to asymmetric deformation vibrations (δ) of SiO 4 units [13].…”

Evaluation of borax solid wastes in production of frits suitable for fast single-fired wall tile opaque glass-ceramic glazes

“…The development of glazes not possessing expensive or toxic components is of special interest (Moreva and Levitskii 2006). When compared to raw glazes fritted ones decrease melting temperatures and consequently, the glaze maturation time is narrowed, smooth and bright surfaces can easily be formed.…”