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Whiteware and Glazes
Published in Debasish Sarkar, Ceramic Processing, 2019
Glazes are traditionally glassy materials generally applied to sanitary ware and earthenware to render the ware impervious, remove surface defects, and improve the aesthetic value. In general, glazes are lustrous and glossy constituting numerous tiny crystals embedded in the glassy matrix obtained by cooling metal salts/oxides from an elevated temperature, which melts on the surface of the ceramic objects. Sometimes, an intermediate coating, known as “engobe,” is applied between the glaze and body to conceal the body color and improve adhesion between the glaze and the body during firing. Glazes are traditionally prepared using principle raw materials and the oxide minerals consist of silica, boron oxide, alumina, lime, magnesia, lead oxide, zinc oxide, potash, soda and their combination thereof. However, other oxides and various pigments have also been explored to develop glaze compositions.
Properties and applications of engineering materials
Published in Alan Darbyshire, Charles Gibson, Mechanical Engineering, 2023
Alan Darbyshire, Charles Gibson
Whiteware includes china pottery, porcelain, earthenware, stoneware, decorative tiles and sanitary products. Firing takes place at temperatures between 1,200°C and 1,500°C after which some of the products are glazed with a thin layer of molten glass. Selected and refined clays are used for whiteware to which crystalline ceramics such as sodium borate (borax) and sodium aluminium fluoride (cryolite) have been added. These assist the bonding process by acting as a flux and they also lower the vitrification temperature.
Inorganic Polymers
Published in Charles E. Carraher, Carraher's Polymer Chemistry, 2017
Many ceramic products are coated with a glassy coating called a glaze. The glaze increases the resistance of the material to gas and solvent permeability and makes the surface smoother in art objects used for decoration.
Microstructure and mechanical properties of SiO2-Al2O3-CaO-ZrO2 based glazes containing zircon and diopside phases
Published in Journal of Asian Ceramic Societies, 2023
A glaze is a glassy coating formed on the surface of ceramic products. The glaze exhibits excellent surface hardness and high chemical and abrasion resistance, and it improves the mechanical properties of ceramic products [1]. Based on the temperature used for sintering the ceramic, glaze is categorized as either high-fire glaze (sintering temperature above 1250°C) or low-fire glaze (sintering temperature below about 1050°C). Glazes are further divided into transparent or opaque and glossy or matte, based on the method of application [2]. Among these, various colors of opaque glaze can be realized by mixing with various coloring oxides. The opaque glaze protects the ceramic body from external contamination and performs various aesthetic functions. Further, it reduces the surface defect and enhances the mechanical properties of the product [3,4].
A case-practice-theory-based method of implementing energy management in a manufacturing factory
Published in International Journal of Computer Integrated Manufacturing, 2021
Shuaiyin Ma, Yingfeng Zhang, Shan Ren, Haidong Yang, Zhenfei Zhu
Fourthly, the ceramic bodies are glazed with a decorative effect. The glaze is sprayed onto the dried ceramic bodies. Similar to the slurry, water, raw mineral and chemical materials are mixed and milled into the glaze during the preparation stage. The requirement of the glaze is higher than that of the slurry because the glaze can directly affect the surface effect of the ceramic products. If the particle size of the glaze is not qualified, the material might not be absorbed by the ceramic bodies, resulting in rough and uneven surfaces (Gabaldón-Estevan et al. 2016).
Chemical durability of lead-bearing glazes in sulphuric acid solutions — Laboratory experiments performed on Zsolnay architectural ceramics from Budapest (Hungary)
Published in International Journal of Architectural Heritage, 2018
Ágnes Baricza, Bernadett Bajnóczi, József Kovács, Zoltán May, Máté Szabó, Csaba Szabó, Mária Tóth
The total amount of silica and stabilizers such as alumina, magnesium, and calcium are the main components responsible for the chemical durability of glazes (Casasola, Rincon, and Romero 2012; Rhodes and Hopper 2000; Schreiner 2004). Thus, the lower silica and alumina content (<60 wt. %) results in lower chemical durability of the glazes (Cox and Gillies 1986). In addition, the use of potassium instead of sodium in the silicate network further decrease the durability, based on the fact that sodium-bearing glass is approximately twice as durable as glass with the comparable amount of potassium (Schreiner 2004). The lead component of the glaze can also influence the chemical durability based on its dual role in the glaze. According to Fayon et al. (1998), at high lead content (> 60 mol % = ~ 85 wt. % in lead silicate glass) Pb-O-Pb bonds begin to form in the glaze, and lead builds up its own stable network, which makes the glaze durable against chemical attack; however, in glazes with <60 mol % PbO content Si is the main network former. Other authors observed different lead concentration values for the change from the network modifier to the network former role of lead. Schultz-Münzenberg, Meisel, and Gütlich (1998) stated that the change in the role of lead occurs at about 50 mol % PbO (~ 79 wt. % PbO), but based on Wang and Zhang’ study (Wang and Zhang 1996) the boundary is only at 40 mol % PbO (~ 71 wt. % PbO). In addition, Mizuno et al. (2005) suggest that even in low PbO glasses (<35 mol % PbO = ~ 61 wt. % PbO) lead can be network former as well, via creating isolated plumbate units (Pb2O4) in the silicate network and resulting in increased durability and decreased mobility of these units based on their structural position. Despite the stability of these plumbate units in the network, they also decrease the chemical resistance at the same time via making partial breakage in the silicate network, and thus facilitate the migration of the other mobile components (Na, K, etc.) (Rahimi, Sadrnezhaad, and Raisali 2009). Therefore, the question about the role of lead is an open issue in the deterioration of vitreous materials, and it also has to be considered that usually lead silicate model glasses, in which vitreous material consists only of SiO2 and PbO components, were evaluated.