The selection of glass composition must first meet the quality requirements of the product, have sufficient thermal stability and chemical stability, meet the production process requirements, be easy to melt and clarify, have few defects, achieve the beautiful color and luster required by tableware glass, and also consider the use of low-cost raw materials while reducing pollution.
Composition of tableware glass
The composition of tableware glass can be divided into several types, such as ordinary soda-lime tableware glass, lead crystal glass, lead-free crystal glass, opalescent glass, and colored glass.
Composition of ordinary soda-lime tableware glass
In 2005, the Expert Committee and Technical Advisory Committee of the China Daily Glass Association formulated a unified standard for the composition range of domestic tableware glass, see Table 3-6.
The chemical composition range in Table 3-6 is mostly applicable to the components of sodium-lime utensil glass that is mechanically formed at high speed by machine blowing, machine pressing, etc., such as machine-pressed hot water cups. However, it is not applicable to some hand-made utensil glass that requires "long" material properties, because the calcium and magnesium content is too high, the hardening rate is fast, and manual forming is difficult to operate. In order to extend its material properties, the calcium oxide content is often less than 6%; the raw materials of magnesium oxide are prone to high iron content, so it is rarely used in utensil glass. The hand-made utensil glass produced in Shanxi and Hebei is mainly transparent glass material, which is melted in a pool kiln. The potassium and sodium content is relatively low, at about 16%. Northeast handmade glassware is known for its colored glass. Transparent soda-lime glass needs to match the colored glass. However, colored glass is mostly melted in a crucible furnace, which is difficult to melt. This problem is often solved by increasing the alkali content in the glass composition, which is about 18%. The soda-lime glassware used for color matching in Boshan, Shandong, has a potassium and sodium content of about 20%, which is easy to melt. Most of its unique products are ornaments, which are not easy to show the shortcomings of poor thermal stability caused by high alkali. Of course, as the tank kiln gradually replaces the crucible kiln, the alkali content in the glass composition is also decreasing under market demand. The composition of transparent glassware is shown in Table 3-7.
Numbers 1 and 2 are the ingredients of domestic handmade glassware. The iron content is significantly higher than that of numbers 3 to 6. This is related to the selection of raw materials and process control, and also directly affects the whiteness, transparency and overall texture of the final product. The common characteristics of numbers 3 to 6 are low silicon oxide content, calcium oxide content that plays a high-temperature fluxing role is about 7%, and potassium and sodium oxide content reaches about 19%. The melting temperatures of glasses with these ingredients are lower than those of numbers 1 and 2. At the same time, the aluminum oxide content is high. Obviously, the chemical stability of the glass can be improved by increasing the aluminum oxide content. Table 3-8 is the formula of transparent glassware used in production.
Color glass composition
The 632 material formula was successfully developed in February 1963. In 1984, an improved formula was proposed to remove potassium nitrate and luminol, which are more expensive. Arsenic oxide has been replaced by other composite clarifiers, and other ingredients vary according to the actual needs of each factory. Color glass is derived on this basis. Adding a certain amount of colorant to the transparent glass component can achieve the required color.
Color glass coloring is divided into ion coloring and colloidal coloring. Ion-colored color glass mainly introduces divalent or trivalent transition metal oxides and rare earth oxides. The oxide of a single transition metal element conforms to the additivity law. Co2+ and NF+ are stable in valence in glass, while other transition metal elements exist in different valences. In actual production, several metal element oxides are often mixed to achieve the required color. Table 3-9 shows the coloring effect of transition metal element oxides. The basic components are SiO2 72%, CaO 5.5%, ZnO 2.0%, Na2O 18.0%, and Al2Og 1.5%.
For blue, the combination of copper oxide and diamond oxide can eliminate the green component of copper itself, while copper can eliminate the red component of cobalt. The combination of the two can obtain a tone between light blue and light cyan. Between copper oxide and chromium oxide, Increasing the amount of chromium, the mixed green color develops to a yellow tone; conversely, increasing the amount of copper, the mixed color develops to a blue tone. The combination of copper and chromium can produce all shades from yellow-green to blue-green. When manganese oxide and chromium oxide are used together, a small amount of chromium can promote the coloring of manganese, but with the increase of chromium, the glass will appear a significant gray tone, showing a change from brown to black. The combination of "ferromanganese" can produce brown color, which is affected by Due to the mutual influence of valence states, more colorants are added, but the color is not deep. "Cerium-Titanium Yellow" is a unique color that can only be expressed with a fixed combination. Some neutral gray can be obtained by sharing cobalt, nickel, and copper, which varies according to different dosages.
The oxides of rare earth elements are stable in coloring, pure in color and have a two-color effect. The coloring ability is weak, and when it reaches a certain amount, it will show a certain saturated state (Table 3-10). The basic ingredients are SiO: 72%, CaO 5.5%, ZnO 2.0%. Na2O 18.0%, Al2O31.5%.
Rare earth elements are pure and elegant, but due to their high price, they are mostly used in high-end glassware and artworks. The basic ingredients have a certain influence on the color development and addition amount of the colorant.
Colloidal coloring mainly includes gold, silver yellow, copper red and other colors, which do not conform to the additivity law. Glass is colored by the selectivity of light, and the color depends to a large extent on the size of the metal particles dispersed in the glass. If the particles are too small, it is not easy to show, and if the particles are too large, the color is easy to appear. In order to obtain uniformly distributed metal particles with moderate particle size, some reducing raw materials need to be added to the formulation, such as stannous oxide and stannous chloride, which mainly utilize the "metallic properties" of tin ions to make the colloidal particles highly dispersed between the metal bridges of tin ions and inhibit the further growth of colloidal particles. In colloidal colored glasses such as gold red and copper red, these tin-containing substances play the role of "protective glue". The change of glass composition has a great influence on the color rendering effect. For secondary color-developing colloidal colored glass, the SnOz and colorant used in the colored glass are as follows: gold red glass SnOAu=100'(1~4); silver yellow glass SnO:1Ag=(5~10):1. Indium glass, (1~2)1. After cadmium and cadmium compounds are clearly banned, copper red will become the main application direction.