In the ceramic industry, boron products are mostly used in ceramic glaze and enamel productions. Enamel and glazing have a glassy form and used for coating purposes. Enamels are usually used in metal plating, while the glazing is used in coating of the ceramic products.
Boron products gain importance in the main composition of ceramic glazes thanks to their binding properties. As a result of the addition of boron products to the composition, the melting and adhesion processes generally take place at relatively lower temperatures in plating. Borates reduce glass fluidity and surface tension and ensure rapid production of glazing and formation of a smooth surface. Besides, boron products increase ceramic products' breaking and scratch resistance against physical impacts through enhancing mechanical and chemical resistance, strengthen it resistance in chemical environments and also serve as an environment for coloring additives.
In the technical sense, glazing is a thin glassy plating used for the protection of ceramic materials processed at high temperatures against both physical and chemical effects and also, for the beautification of their external appearance. Fritting is the process of melting all or a portion of the glazing composition in glass melting furnaces in order to make water-soluble materials, used in glazing, water-insoluble and to render toxic materials such as PbO harmless and the product obtained is defined as frit. In practice, it is used either by itself or with other water-insoluble substances (floater, colourant etc.). Glazing and frit composition varies according to the application conditions. Frit is stated to be used in more than 80.000 different compositions still in use in industry. Glazing has coloring additives in frit and is used in goods such wet floor tiles, floor and wall tiles, table and ceramics used for sanitary purposes. If baked at an adequately high temperature, silica and alumina may provide the formation of glazing. However, ceramic furnaces cannot reach the desired temperature due to both theoretical and financial reasons. Thus, it is required to add some compounds lowering the melting temperature into the glazing and frit composition. These compounds can be listed as Li20, K20, CaO, ZnO, Na20 and B2O3. Boric acid, boric oxide, borax, colemanite and other sodium borates are used in the production of ceramic glazes. Since it prevents spilling of the frits, the colemanite is generally used in the production of especially dull, pink glassy and maroon glazes.
Boron is used in glazes and frits for the following purposes:
• As flux, reduces melting, formation and liqidus temperatures of the glass
• Enhances wetting of the bottom coating material and ensures formation of the plating at lower temperatures
• Ensures that the thermal expansion of the glaze is in harmony with the ceramic
• Ensures formation of the glass at early stages of melting
• Increases refractive index and brightness of the glaze and improves positively its overall appearance
• Reduces viscosity and surface tension and ensures maturation of the glaze.
• Increases mechanical strength and scratch resistance of the plating
• Improves resistance against the effects of chemicals and water
• Forms the base for the addition of colorants
Glazes are also defined by their ignition and maturing temperatures. The glazes with lower maturation temperatures typically contain B2O3. The B203 is used at a rate up to 20% in enamels and up to 25% in glazes. Besides, the glazes contain colemanite at a rate between 3-24%. If the boron compounds used in glazes are of a water-soluble type such as boric acid and borax, it is required to frit and render them water-insoluble before their use in glazes. However, any compound with a low water solubility such as colemanite doesn’t require fritting.