1. What’s Quartz Glass?
Quartz glass is a kind of special glass which is made of single component-SiO2. Its series of special performance that other material can’t replace, make quartz glass an indispensable material in modern science and technology and modern industry.
2. Raw Material of Quartz Glass
Quartz glass is made of natural quartz powder through high-temperature melting process, or made by silicon compounds through flame hydrolysis process.
Natural quartz powder is processed from natural crystal or pure silica. American Unimin Co. has high-grade ore source and advanced purification technology of quartz glass raw material. Its product-quartz glass raw material-become the world standard raw material of quartz glass, and the representative of high-purity natural quartz powder in the world.
Synthetic quartz glass is prepared by a liquid inorganic or organic silicon compounds (such as silicon tetrachloride) through flame hydrolysis synthetic process.
3. Quartz Glass Preparation Process and Products Characteristics from Different Processes
Quartz glass quality mainly depends on its purity. However besides the influence from quartz raw material purity, the production process of quartz glass is the important factor for its quality.
Quartz glass processes mostly include electric fused process (vacuum electric fused process, two-step melting process, continuous melting process), flame fused process, high-frequency plasma melting process, synthetic quartz glass process.
Electric fused process is electrically powered and heated through resistance, arc, intermediate-frequency induction, high-frequency plasma, etc. to melt quartz powder into quartz glass. The characteristic of quartz glass manufactured by electric fused process is low content of hydroxyl.
3.1 Electric Fused Process
3.1.1 Vacuum Electric Fused Process
Vacuum electric fused process, the major method to produce infrared quartz tube for optical field, is to put quartz powder in the graphite crucible, using vacuum electric furnace as the heating source, to melt the powder into quartz glass.
The quartz glass manufactured by vacuum fused process has characteristic of lower content of hydroxyl, but there exist major defects in terms of bubble, stone, etc.
3.1.2 Two-Step Melting Process
The prepared quartz glass rough ingot is reheated, shaped and processed into the required quartz tube, quartz rod, quartz plate, which is called two-step method. Two-step melting process is characterized by flexible production process, product variety, easily controllable product quality. However, energy consumption is big and resulting in high cost.
Two-step melting process can be divided into contact and non-contact methods.
Contact two-step method is through the former to draw the ingot into the quartz glass products in the required size. This process is featured by simple operation, easily controlled size, but the drawback is easy to scratch the surface of quartz glass products.
Non-contact two-step method is to melt the quartz glass rough ingot in the heating region of the ingot melting furnace, and reduce the diameter by pulling the quartz cylinder, and then draw it to the required size of quartz glass rods through adjusting the traction speed. Quartz ingot neither contacts any substance during the heating period, nor needs molds during shaping stage, which results in good surface quality of the products.
3.1.3 Continuous Melting Process
Continuous melting process refers to use automatic device to feed quartz powder into the top mouth of the furnace, then after the quartz powder melted in the furnace, the quartz glass products are drawn out of the bottom mouth of the furnace continuously. Continuous melting process normally uses tungsten heater-tungsten crucible, thus gas protection is needed. Helium is used as protection gas in foreign countries, which leads to good appearance and low hydroxyl for the products. However due to high price of helium in China, hydrogen is usually used as protection gas, which generates relative worse appearance and high content of hydroxyl for the products.
Continuous melting process has advantages of high degree of mechanical automation, long production cycle, low production cost, which is suitable for large amount of products in the industries of electric light source illumination and electric heating.
3.2 Flame Fused Process
Flame fused process is a kind of technology method to use energy source of hydrogen and oxygen to heat quartz glass raw material to produce quartz glass.
3.2.1 Flame Fused One-Step Method
Quartz powder is fused by flame of hydrogen and oxygen on the special lathe equipment, to directly make quartz tube or quartz crucible. The Products from this process have features of big size tolerance and rough corrugation on the surface. At present, the process has been basically eliminated.
3.2.2 Ingot Making by Vertical Flame Fused Process
Ingot making by vertical flame fused process is to set quartz glass target holder in the furnace, and use hydrogen and oxygen burner to melt the quartz powder to deposit on the target holder, and then form a certain size of quartz ingot.
This process can produce quartz rough ingot which will then be machined to various quartz tubes, instruments, flanges, etc. The quartz ingots produced by this process have high content of hydroxyl.
3.3 High-Frequency Plasma Melting Process
High-frequency plasma melting process is a kind of high-quality quartz glass production process which was introduced from France. This process uses plasma as heat source to melt quartz powder evenly and deposit quartz fume on the mother tube which is rotating and translating at a constant speed. After deposition layer by layer, the OD of the mother tube is increased gradually to finally form a certain dimension of quartz ingot.
High-frequency plasma melting process manufactures quartz rough ingot which will be further machined to reach a certain accurate size through cold-fab, and then be prepared to quartz glass tubes and rods via two-step tubing process.
The products manufactured by the process are high-quality quartz glass with high purity and low hydroxyl, which are used in the industries of optical fiber, laser, semicon and solar energy.
3.4 Synthetic Quartz Glass Process
Synthetic quartz glass process is based on raw material of SiCl4 to synthesize SiO2 through hydrolysis.
The products from this process is featured by high purity with total impurity of metal elements <1×10-6; however due to complex process and high cost, this process hasn’t been widely used yet.
Synthetic quartz glass is mainly applied in the quartz glass for optical communication and far ultraviolet optical quartz glass.
4. High-Quality Quartz Glass
There are strict requirements on material in the industries of optical fiber, semicon and laser light source which needs high-quality quartz glass. High purity, low hydroxyl, high-precision geometric dimension, excellent appearance, etc feature high-quality quartz glass.
High-quality quartz glass needs high-quality quartz/silica sand material and production technology to guarantee, which is integrated by Quick Gem Optoelectronic S & T Co., Ltd. (for short GQOE). QGOE, having decades of rich experience in production of quartz glass, is a high-tech enterprise with strong technology force and standardized management in the same industry at home. It is also the only one in China and one of the three major manufacturers all over the world that can produce substrate tube and jacket tube for optical fiber field.
QGOE adopts two-step method of ingot making by high-frequency plasma and intermediate-frequency non-contact tubing to manufacture quartz glass products based on raw material of high-purity quartz/silica sand (total impurity elements≤20ppm) imported from American Unimin Co. The two-step method combines both high-frequency plasma process and non-contact process, and flexible production, to result in the products reaching the international level of similar products with high purity, low hydroxyl, high-precision dimension, excellent appearance, etc.