Real thing!Quality requirements for quartz sand for ultra-white glass

Ultra-clear glass can achieve a transmittance of more than 91.5%, and its optical properties are widely used in solar power generation, solar thermal power generation, information display, architectural decoration, and smart agriculture. The iron content in the ultra-clear glass is 0.015% or less, and the high-quality ultra-clear glass for the photothermal glass for clean energy, the electronic glass for information display, and the like requires higher transmittance, and therefore requires silica sand has a lower iron content, which puts higher demands on the raw materials of glass.

Among the ultra-white glass batch materials, quartz sand generally accounts for more than 60% of the weight ratio, which is the main factor affecting the iron content in the glass, and the melting temperature of the quartz sand is high, which determines the melting speed of the glass, so quartz sand in glass batch materials is the main research object.

What are the requirements for the chemical composition of quartz sand for ultra-white glass?

Ultra-white glass with low iron quartz sand has requirements for iron removal, but also for SiO₂ and Al₂O₃ content. For example, a company uses quartz sand produced by sinonine glass sand washing plant as raw material to produce ultra-white low-iron glass by float method. The requirements for SiO₂ and Al₂O₃ components are as follows.

	SiO2%	Al2O3%	Fe2O3%
Low iron quartz sand	≥99.1±0.3	≤0.6±0.1	≤0.01±0.001

In addition to the main chemical components, other trace elements such as Ti, Cr, Mn in quartz sand also have an impact on the transmittance and melting of ultra white glass. Some studies have suggested that the increase of Ti content in glass can make the glass turn yellow and cause the transmittance of ultraviolet and visible light to decrease significantly. In production, good physical and optical properties of ultra white glass should be guaranteed, and the content of TiO2 in raw materials should be controlled Below 0.022%.

What is the effect of quartz sand size on the production of ultra white glass?

The particle size of quartz sand determines the melting speed of the mixture, and the melting time is directly proportional to the particle size. Botevigin proposed the following equation to calculate the effect of particle size on the glass forming time:

T-glass forming time, min; R is the radius of original quartz particles, cm; K is a constant related to glass composition and test temperature.

It can be seen from the formula that the larger the grain size of quartz sand is, the more difficult it is to melt. At present, the particle size of quartz sand for ultra white glass mainly depends on the upper and lower limits of control particles. The particle size distribution range of superior products in China's silicon raw materials and building materials industry standard is shown in the table below.

Particle size range	+1mm	+710μm	+500μm	-100μm
Weight percentage	0	0.5	5.0	5.0

Although there is no restriction on the distribution of 100-500 μ m in the national standard, it will affect the glass melting and clarification in the actual production, so it is necessary to adjust the corresponding process to adapt to the change of raw materials. Through the influence of the particle size of glass raw materials on the glass melting, it is shown that the presence of quartz sand particles above 0.75mm will seriously affect the glass melting quality, and it is difficult to melt the coarse quartz sand in the production, even it may become scum, which makes the glass appear pimple and wave bar. When the size of quartz sand is less than 0.106mm, the chemical composition fluctuates seriously, SiO₂ content decreases and Fe₂O₃ content increases. During the melting process, due to the effect of surface tension of finely sized powder, it is easy to form agglomeration and lead to the difficulty of melting. At the same time, fine powder is easily brought into the regenerator by indoor airflow, which affects the heat transfer effect and life of the lattice. When the particle size is less than 0.106mm content, too much foam will be generated when the furnace melts, so that the heat radiation can not be easily transmitted into the molten glass, and the bubble discharge is very difficult. Bubbles form on the product.

Why should we pay attention to the shape of quartz sand?

The microstructure of quartz sand is related to its formation process and its chemical composition and impurity content. It is considered that the shape of quartz sand is the best with angular shape, the surface area of angular shape is large, the contact opportunities with cosolvent are more, and it is not easy to layer in the process of mixing and transportation. In the actual production, the attention to the shape of quartz sand is not high. In the production of high-quality glass, we should pay enough attention to the shape of quartz sand.

With the increasing demand for green energy photovoltaic and photothermal power generation, the demand for ultra white glass is also increasing, and the corresponding demand for large-scale ultra white glass raw material quartz sand. Silica sand for ultra white glass shall be improved in processing technology in combination with production requirements of ultra white glass. On the basis of ensuring iron content, chemical composition, particle size and other aspects shall also meet the requirements of glass.