Silicon metal is polycrystalline silicon, also known as crystalline silicon or industrial silicon, and its concept is opposite to semiconductor silicon. Silicon metal is a product smelted from quartz and coke in an electric furnace. The silicon content of the main component is about 98%, and the remaining impurities include iron, aluminum, calcium, etc., and the price is relatively high. Silicon metal has many uses, including the preparation of organic silicon, silicon powder, edge skin silicon, black skin silicon, etc., and is also used to prepare high-purity semiconductor materials and alloys for special purposes; among them, silicon powder is also called 180 mesh metal silicon powder, Microsilica fume or microsilica fume is widely used in refractory materials, concrete and other industries.
Microwave ovens have now become an indispensable kitchen appliance in our daily life, but they also have broad application prospects in industrial production processes. Melting polysilicon (metallic silicon) with microwaves is a practical method. The basic idea is to use a quartz crucible as a container. Due to its excellent wave-transmitting properties, metallic silicon can be heated in a microwave oven. The microwave heating method has the characteristics of rapid heating and strong controllability.
A method for microwave heating and melting metal silicon, comprising the following steps:
(1) Metal silicon grinding: choose metal silicon raw materials, immerse in the grinding liquid, and grind on the grinding disc for 1.5~3 hours to obtain metal silicon powder, wash and remove the grinding liquid;
(2) Screening: sieve the metal silicon powder with a multi-stage sieve disc, and select 180 mesh metal silicon powder;
(3) Prepare a special microwave heating furnace: the microwave heating furnace includes a furnace body made of insulating material, a feeding port and an air filling port. A plurality of microwave magnetrons are arranged on the inner wall of the furnace, and the microwave magnetrons are connected with a power supply. There is a high-temperature-resistant wave-transparent crucible in the furnace body, and the sieved 180-mesh metal silicon powder is loaded into the feed port, so that the metal silicon powder fully falls into the high-temperature-resistant wave-transparent crucible;
(4) Heating: Fill inert gas into the gas charging port, exhaust the air in the microwave heating furnace, close the feeding port, and leave only the gas charging port to continue charging inert gas; Minimum, the microwave generated by the microwave magnet control tube penetrates the high temperature wave crucible to heat 180 mesh metal silicon powder;
(5) Temperature control: control the power of the microwave magnetron and observe the temperature indication. The heating rate showed a trend of increasing slowly at first and then decreasing slightly. Increase the initial heating rate from 5-10°C/min to 20°C/min. At -30 °C/min, reduce the heating rate to 3-5 °C/min. When the temperature reaches t1, the power of the microwave magnetron is turned to the minimum, the metal silicon powder is in a molten state, and the control switch maintains heat exchange with the outside world. The temperature in the furnace is stable, just keep the 180-mesh metal silicon powder at t1 for a specified time.
There is also a discharge pipe at the bottom of the microwave heating furnace. The discharge pipe is connected to the intermediate frequency heating furnace backward. t1 is 900-1250°C. After step (5), inert gas is filled into the gas filling port, and the metal silicon powder is pressed into the intermediate frequency heating furnace. Heating furnace, intermediate frequency heating furnace temperature control rate 5-10 ℃ / min, stop heating when the temperature of metal silicon powder reaches t2, metal silicon powder is in a molten state, it takes time to maintain a constant temperature. The combination of medium frequency heating can give full play to the advantages of each heating, combine them effectively, and greatly improve their work efficiency while saving energy.
The appropriate particle size of 180 mesh metal silicon powder is beneficial to its microwave absorption performance, thereby improving microwave heating efficiency. The high temperature wave transparent crucible is a quartz crucible. The melting point of quartz crucible is about 300°C higher than that of silicon powder, and it has good wave-transmitting performance, which is very suitable for this process. The inert gas charged into the gas charging port is argon or nitrogen. After closing the feeding port, the gas charging port continues to be filled with inert gas, and the pressure reaches 3.5-6 bar. The inert protection effect of nitrogen or argon is relatively reliable, and the pressure of 3.5-6 bar makes the compaction force of metal silicon powder sufficient. The topography of the intermediate frequency heating furnace is lower than the discharge pipe of the microwave heating furnace. When the terrain of the intermediate frequency heating furnace is lower than that of the microwave heating furnace, the operation of pressing metal silicon powder into the intermediate frequency heating furnace with inert gas is easier to realize.