Glass Additives

Glass additives refer to substances added to raw materials during the production and preparation of glass. Glass additives often have specific functions, such as making glass easier to melt and shape, reducing defects in glass products, or improving the performance of glass products. Commonly used glass additives include colorants, opacifiers, clarifiers, bleaching agents, foaming agents, foam stabilizers, etc.

Applications:

Since glass additives have many advantages such as variety, and are very important in the preparation process of glass, they have very great application value.

• Flux: In the preparation process of glass, melting raw materials to prepare shaped glass often needs to be carried out at a higher temperature. High temperature operation has many inconveniences, not only wastes fuel, but also has a high degree of danger. Flux is an additive commonly used in the glass melting process, and its introduction can reduce the glass melting temperature and shorten the glass melting time, thereby promoting glass melting. In addition, some fluxes also have the functions of improving the thermal and chemical stability of the glass, increasing the refractive index of the glass, improving the gloss of the glass, and improving the mechanical strength of the glass. Boron oxide and magnesia slag are both commonly used fluxes in the glass industry. For example, the introduction of a small amount of boron oxide in the soda lime silicate glass composition can reduce the melting temperature by 10% and shorten the glass melting time by 20% to 30%.

Figure 1. Flux for melting glass

• Foam stabilizer: Foam stabilizer refers to a substance that can improve the stability of bubbles and prolong the half-life of bubbles breaking. Foam stabilizers are divided into two categories according to their differences in foam stabilization mechanism. One type of foam stabilizer is to generate free cations under high temperature conditions and reduce the repulsive force of the liquid film anionic surfactant and anionic groups to achieve foam stabilization, such as iron oxide and titanium dioxide. Another type of foam stabilizer can decompose under high temperature conditions, such as trisodium phosphate, tripotassium phosphate, boric acid and so on. Its product has a tetrahedral structure, which is easy to form a continuous network and increase the viscosity of the melt, thereby achieving the stability of the bubbles and the enhancement of the network structure. At present, in the production process of foam glass, products often have defects such as large bubbles, connecting pores, uneven pore distribution, and large pore size differences. These defects are largely related to the type and amount of foam stabilizer. Different foam stabilizers have different pore diameters and pore wall thicknesses. Reasonable selection of foam stabilizers is beneficial to improve the pore structure of glass products, thereby enhancing the thermal insulation performance of glass products.

Figure 2. Foam stabilizer used to make foam glass

• Clarifier: In the preparation process of glass, clarifier is also a very important additive. Initially, arsenic and sodium nitrate were often used as clarifiers in the preparation of glass. Arsenic is a highly dangerous drug, and procurement and transportation are more difficult. At the same time, the price of sodium nitrate has remained high. In view of the above, more and more clarifiers with excellent performance, economical and environmental protection have been developed. At present, the types of glass clarifiers are very rich, including C type, C-F type, F type, E type, S type and O type. Among them, the F-type composite glass additive contains main components such as sodium oxide, calcium oxide, sulfur trioxide, and aluminum oxide. It is an ideal clarifying agent to replace arsenic, and has great application value in the current production and preparation of glass.

Figure 3. Clarifier used to prepare silicate glass infusion bottle

References:

1. J. H. Hong. (2010), "Lead -free low-melting point sealing glass in SnO-CaO-P₂O₅ system." Journal of Non-Crystalline Solids 356, 1400-1403.
2. Zhang Bing. (2008), "Effect of MnO/MnO₂ addition on the properties of low-melting phosphate glasses." Journal of the Chinese Ceramic Society 36(4), 535-538．
3. L, Koudelka. (2000), "Borophosphate glasses of the ZnO-B₂O₃-P₂O₅ system." Materials Letters 42, 194-199.