November 28, 2019

How to remove the gas-liquid inclusions of high purity quartz sand?


This paper presents an effective method to remove gas-liquid inclusions from high-purity quartz sand.

Quartz glass is a special glass with single component of SiO2. It has excellent physical and chemical properties such as chemical stability, wide spectral transmission, heat shock resistance, high temperature deformation resistance, radiation resistance, electrical insulation, etc. it provides cutting-edge materials for optical power supply, electronic industry, optical communication, SiO2 film materials, large-scale and ultra large scale integrated circuits, lasers, aerospace, military industry and other fields. The raw material of producing quartz glass is mainly high-purity quartz sand, which is obtained from quartz ore through a series of purification processes.

high purity sand

Quartz ore contains a lot of impurities. The impurities can be divided into structural and non structural impurities. Non structural impurities are impurities beyond quartz crystal, such as surface adherents and associated minerals. At present, impurities removal technologies, such as water quenching, flotation, acid pickling, magnetic separation, high temperature vacuum treatment, chlorination, superconducting separation, electric separation, ultrasonic treatment, doping purification and other means can basically meet the requirements of quartz glass. Structural impurities refer to the impurities formed during the growth of quartz crystal, also known as micro defects, such as gas-liquid inclusions, which can be inherited to quartz glass, leading to the formation of quartz glass bubbles and hydroxyl defects, so it is difficult to make transparent quartz glass, so it can not be applied to the production of high-end quartz glass. Therefore, the removal of gas-liquid inclusions is the key and difficult point to prepare high-end quartz glass.

gas-liquid inclusion

Sinonine master a kind of purification method in the production of high-purity quartz sand, through which the gas-liquid inclusions and other impurities of quartz ore can be removed.

Based on the processing of ordinary quartz ore into high-purity quartz sand by basic silica sand processing plant and purification technology, high-purity quartz sand with relatively less impurities and gas-liquid inclusions is prepared first. On this basis, the following purification steps are included: put quartz sand in the microwave field, the microwave frequency range is 300MHz-300GHz, of which 600MHz-30GHz is the best, 945MHz-2.45GHz  is the best, so that the gas-liquid inclusions and impurities are heated up to over 1000 ℃ by selective heating, while quartz The temperature of SiO2 in the sand almost does not rise until the overall temperature of quartz sand rises to 200 ℃ to 1200 ℃ for 2-30 minutes due to the heat transfer effect of gas-liquid inclusions and impurities, and then it cools rapidly. Then, the gas-liquid inclusions are further destroyed or the impurities are peeled off by external loading. According to the actual situation, the above steps are repeated several times to further remove the gas-liquid inclusions and impurities.

The actual production steps are as follows.

Ordinary quartz ore (water content of gas-liquid inclusions is more than 90%) is selected as raw material and processed according to the following procedures:
 
1.Crush the selected quartz ore using hammer crusher or jaw crusher to less than 50mm and remove obvious non quartz impurities;

2. Put the lump quartz ore into the electric furnace, calcine it at 950 ℃ for 2 hours, cool it out of the furnace, and crush it to about 0.50mm with the rod mill;

3.The pure quartz sand is obtained by magnetic separation, flotation, acid leaching, cleaning and drying;

4.The quartz sand is put into the carrier of the quartz glass container and treated by microwave in the microwave sintering furnace. The microwave frequency is 2.45GHz, and it is washed with deionized water, so that the gas-liquid inclusions and impurities are heated to over 1000 ℃ rapidly by selective heating (the higher is better), while the SiO2 in the quartz sand is almost not heated up. Only because of the heat transfer effect of the gas-liquid inclusions and impurities, the overall temperature of the quartz sand rises to 500 ℃, keep for 20 minutes, and then cool down quickly;

5.The quartz sand treated by microwave was ground to further destroy the gas-liquid inclusions;

6. Through acid leaching, cleaning and drying, high-purity quartz sand products are obtained.

Remarks:high purity quartz sand for quartz glass has strict requirements for gas-liquid inclusions, which can only be put into large-scale production after repeated tests.

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