Ultra clear glass is a type of ultra transparent low iron glass, also known as low iron glass or high transparency glass, and is known as the "Crystal Prince" of the glass family. It has the advantages of low self explosion rate, color consistency, high visible light transmittance, good transparency, and low ultraviolet transmittance. It is a high-quality and multifunctional new high-end glass variety. Mainly used in industries such as solar cells, solar thermal mirrors, high-end building decoration electronic products, and high-end car glass.
As a fundamental product in the solar energy industry, ultra clear glass requires a direct solar transmittance of at least% (equivalent to a standard thickness of 3mm), while the transmittance of ordinary float glass is generally 86%. To achieve this goal, the content of coloring oxidant Fe2O3 must be controlled below 150ppm. It can be said that the process of producing ultra clear glass is the process of controlling the Fe2O3 content.
Reasonable selection of raw materials
Because iron oxides not only affect the color of glass and its transmittance, but also have a strong absorption effect on thermal radiation, most of the radiated heat is absorbed by the surface glass liquid, resulting in a significant temperature gradient between the upper and lower layers of the glass liquid, making it difficult for the glass liquid to circulate in the melting furnace and increasing the difficulty of melting and clarification. In order to effectively reduce the iron content of glass, the first step is to start with raw materials. Effectively selecting raw materials with low Fe2O3 content is a prerequisite for achieving the production of ultra clear glass.
The raw materials used for ultra clear glass include dolomite, limestone, feldspar, and silica sand. Magnesium oxide can effectively control the hardening rate and crystallization performance of glass liquid, mainly due to the high-temperature physical properties of glass, while improving the melting performance of glass to assist in melting. Dolomite is the main raw material for introducing magnesium oxide. Limestone is another important mineral raw material. At present, the Fe2O3 content of limestone supplied for ultra clear glass is below 50ppm.
Among various raw materials, SiO2 is the main component that forms the glass skeleton. The introduced SiO2 siliceous raw material is the most important and widely used raw material in glass production, and it is also the first to be solved and controlled in the production of ultra clear glass.
There are mainly two sources of it. One type is high-quality quartzite, whose own grade meets the requirements of low iron glass production. During the processing, efforts should be made to minimize the mixing of iron. Traditional stone mills can be used, which are only available in a few regions in China such as Fengyang, Anhui. Another method is to use high-quality silica sand for flotation and other mineral processing on ordinary flat glass to meet the requirements. The cost of this sand is relatively high, more than twice that of the aforementioned natural high-quality quartzite. At present, both methods can control the content of Fe2O3 to below 100ppm. In this way, the iron introduced by silica sand can be controlled below 73ppm.
Development opportunities brought by industrial policy orientation
Building energy conservation is a comprehensive system engineering, and the scientific and rational use of processed glass with energy-saving, safety, and environmental protection characteristics is one of the extremely important links in this system engineering.