RU2245381C1 - Device for cleaning molten metals, mainly silicon - Google Patents

Abstract

FIELD: metallurgy; chemical technology; production of metals of high purity, mainly silicon; cleaning molten metals by electric transfer in magnetic field.

SUBSTANCE: proposed device has heated space with reservoir for initial metal and reservoir for cleaned metal which is provided with tapping hole; these reservoirs are interconnected by means of passage; device is also provided with magnet for generating magnetic field in passage and electrodes located in said reservoirs. Passage is connected with pure metal reservoir in lower point and is inclined towards pure metal reservoir through angle α whose sine is lesser than ratio of height h of pure metal reservoir from bottom to tapping hole to length l of passage. Located in lower point of pure metal reservoir is tube for draining residual metal; this tube is directed downward. Tube may be closed by means of plug for example fitted on rod which is cooled below melting point of metal; tube may also extend beyond zone heated to melting point; it may be provided with heater located along entire length of tube. Metal draining tube may be provided with circular electrode for forming electromagnetic pulse forcing out residual metal from tube.

EFFECT: reduction of labor consumption.

4 cl, 4 dwg

Description

The invention relates to metallurgy, chemical technology, the production of high-purity metals, mainly silicon, in particular to devices for cleaning liquid metals by electric transport in a transverse magnetic field.

A device for cleaning liquid metals by electrotransfer / 1 /, which consists of two containers connected by a channel. In capacities are electrodes connected to a direct current source. When current flows through a liquid metal, electrons scatter on impurities and remove impurities from the metal volume in the longitudinal direction.

To achieve the necessary cleaning, it is necessary to move the impurities along the entire length of the capillary with a drift velocity, which depends on the diffusion coefficient of the impurity in the melt and the driving force of electric transport in the longitudinal direction. Therefore, the performance of such a device is small, and the cost of cleaning is high. Such cleaning devices are advisable to use only for research purposes and in technologies with low demand, where the high price is not significant.

A device / 2 / is known in which there is a channel with electrodes placed in a transverse magnetic field. A constant electric current flows through the channel. In a magnetic field, the current creates transverse driving forces that lead to the transverse transfer of impurities and their removal from the bulk of the metal. As the channel length increases, cleaning performance increases. The performance of the cleaning devices in a transverse magnetic field is hundreds to thousands of times higher than conventional electric transfer. The indicated devices for cleaning by electric transport in a magnetic field are successfully used to obtain high-purity 99.99999% indium and gallium / 3 /. However, these devices are not intended for the purification of liquid metals with a high melting point, including silicon (silicon in the liquid state is a metal).

Closest to the claimed invention is a device / 4 / for cleaning silicon by electric transport in a magnetic field, which is a heated volume with containers: for the starting metal into which the loading is carried out, and for the purified metal, interconnected by a channel placed in a magnetic field. The metal is pumped through the channel and flows from the container for purified metal into the mold, where it hardens. During pumping, the metal passes through the region of crossed electric and magnetic fields. Electric current is supplied by electrodes located in containers. The electrodes are immersed in liquid silicon to the height of the outlet through which the purified metal enters the mold. Electric and magnetic fields make it possible to remove impurities from the bulk of silicon. However, silicon in a liquid state has a density of 2.5 g / cm, and when cooled, a density of 2.3 g / cm. That is, the silicon remaining in the crucible and in the channel expands upon crystallization and breaks the channel and capacities. When stopping the process, this item of equipment has to be replaced each time with a new one. If the metal expands during melting, the destruction of the channel with the metal occurs when the cleaning device is heated. Therefore, it is advisable to drain the liquid metal from the cleaning device when stopped in any case.

The objective of the invention is to eliminate this drawback and to ensure the reliability of the device for cleaning liquid metals. The technical result is a decrease in the complexity of the process.

The technical result is achieved by the fact that in the device for cleaning liquid metals, mainly silicon, containing a heated volume with a container for the source metal and made with an outlet for the capacity of the purified metal, interconnected by a channel, a magnet to create a magnetic field in the channel, and electrodes, located in the containers for the source and purified metal, the channel is connected to the container for purified metal at its lower point and tilts towards the container for purified metal at an angle α, the sine of which it is less than the ratio of the height h of the tank for purified metal from the bottom to the outlet, to the length of 1 channel, and at the lower point of the tank for purified metal there is an overlapping pipe for draining metal residues, directed downward.

The tube for draining metal residues is blocked by a single polished plug made of metal to be cleaned and located on a rod cooled below the melting temperature of the metal.

The tube for draining metal residues can go beyond the zone heated to the melting temperature and has an additional heater located along the entire length of the tube.

An annular electrode is located on the tube for draining metal residues to form an electromagnetic pulse that ejects the metal residues from the tube.

The inventive device has parameters that provide melting and the flow of silicon into the tank for the source metal. The silicon level in the operating mode provides contact of the electrodes in communicating containers with liquid silicon and the flow of current through the channel with liquid silicon. The height of the outlet allows further passage of the purified metal after accumulating it to a certain level. The system must have a certain amount of metal, ensuring the normal operation of the device. Electrodes are immersed in the metal in the containers for the source and purified metal, which provide contact, the passage of current through the metal being cleaned and the cleaning process. The inclination of the channel of the device is necessary to remove residual liquid metal (mainly silicon) after stopping work and opening the tube located at the bottom of the tank. The value of the angle of inclination of the channel should not exceed the limit value at which it becomes impossible for the electrodes to contact the liquid metal, that is, the angle (α) of the inclination of the channel is chosen so that the following relationship is fulfilled: the sine (α) of the angle of inclination of the channel is less than the height ratio ( h) containers for purified metal to the length (1) of the channel. The magnetic field in the channel is created by an electromagnet or a permanent magnet. The electrodes providing the passage of current are made of materials that do not pollute the molten metal. Crystallizers for receiving purified metal do not contaminate the purified metal. Crystallizers can be cooled, have special coatings. Crystallizers can be replaced as they are filled.

The inventive device for cleaning liquid metals, mainly silicon, is shown in figure 1, a General view.

Figure 2, 3, 4 shows fragments of a device for cleaning liquid metals with device options for blocking the tube for draining metal residues.

A device for cleaning liquid metals, mainly silicon, shown in figure 1 contains: 1 - a container for the source metal, 2 - a container for purified metal, 3 - a liquid metal, 4 - a channel, 5 - a magnet to create a magnetic field, 6 - border metal melting zones, 7 - electrodes, 8 - power source, 9 - outlet, 10 - mold for purified metal, 11 - pipe for draining metal residues, 12 - mold, 13 - heated volume.

The device operates as follows.

Silicon enters the tank 1 for the source metal, melts and fills the channel 4 and the tank 2 for the purified metal. Through the electrodes 7, a current is supplied to the metal and the metal is purified in the channel. After reaching the level of molten metal to the height of the outlet 9, the metal enters the mold 10. In the process, the tube 11 for draining the remaining metal is closed. Closing can be carried out by devices made as ordinary taps of pure quartz, graphite, carbide, silicon and the devices shown in figure 2, 3, 4.

In figure 2. a fragment of a device for cleaning liquid metals is presented, comprising: 1 - a container for purified metal, 2 - a channel, 3 - liquid metal, 4 - hardened metal, 5 - a ground plug of purified metal, 6 - a cooled rod, 7 - a conditional boundary of the temperature zone melting, 8 - a device for attaching and moving the cooled rod, 9 - a pipe for draining metal residues. At high temperatures, closing-opening devices, like conventional taps made of pure quartz, graphite, silicon carbide, as a rule, interact with molten metal and may not work. In the case of the use of a single polished plug placed on a cooled rod, the reliability of operation increases and the operability of the device is ensured. When cooling is applied to the material located at the bottom of the tube for draining metal residues, the initially molten metal coming from above gradually crystallizes from below and provides sealing. After removing the cooled rod, the metal heats up, melts and flows out.

Figure 3 presents a fragment of a device for cleaning liquid metals, containing: 1 - a container for purified metal, 2 - channel, 3 - liquid metal, 4 - conditional boundary of the temperature zone of melting, 5 - hardened metal, 6 - heater, 7 - tube for draining metal residues that goes beyond the zone heated to the melting temperature.

In the case of a tube that extends beyond the boundaries of the melting temperature zone, the first portions of molten metal from the device flow out as they enter the tube. The metal crystallizes. The next portion increases the zone of solidified metal and the boundary of the solid-liquid metal remains at the temperature boundary of the melting of the metal during the entire cleaning process. Metal melting in the tube is carried out by an additional heater located along the entire length of the tube.

Figure 4 presents a fragment of a device for cleaning liquid metals, containing: 1 - capacity for purified metal, 2 - channel, 3 - liquid metal, 4 - conditional boundary of the temperature zone of melting, 5 - ring electrode for the formation of an electromagnetic pulse, 6 - tube for draining metal residues.

In some cases, at high surface tension coefficients of the liquid metal, a noticeable part of the metal may remain in the tube. When a powerful electromagnetic pulse is applied to an electrode located around the tube, a current pulse in the liquid metal that is opposite in direction is created and the liquid metal is ejected from the tube.

In accordance with the Lenz rule, a change in the vortex magnetic field in the circuit induces a current in the conductor (in the liquid metal) in the opposite direction with the magnetic field, resulting in mechanical ponderomotive forces that repel the two conductors from each other.

The current pulse supplied to the electrode creates forces acting on the liquid metal and pushes the metal out of the tube.

Sources of information

1. Overview of electronic technology: Clean materials in electronic technology (new cleaning methods). I.V. Zakurdaev, D.P. Muzlov, E.B. Trunin, A.V. Zhevnyak. M. Electronics, 1980, no. 12 (754), ser. Technology, organization of production and equipment, 53 p.

2. Trunin E.B. The transfer of impurities in liquid metals during the flow of current in a transverse magnetic field. High Purity Substances, 1988, No. 1, pp. 77-80.

3. Trunin E.B., Trunina O.E. Obtaining high purity indium and gallium by electric field transport in a magnetic field. // Materials of the XVII Scientific Conference “High-Purity Materials with Special Physical Properties", Suzdal. 2001, p.25.

4. Karabanov S.M., Trunin E. B., Prikhodko V.V. Study of solar-grade silicon production technology by the method of carbothermic reduction. Proceeding of the Seventinth European Photovoltaic Solar Energy Conference. s.77-79. Munich, Germany, October 22-26, 2001.

Claims (4)

1. A device for cleaning liquid metals, mainly silicon, containing a heated volume with a container for the source metal and a container for purified metal made with an outlet, interconnected by a channel, a magnet to create a magnetic field in the channel, and electrodes located in the containers for the source and of purified metal, characterized in that the channel is connected to the container for purified metal at its lower point and tilts toward the container for purified metal by an angle α, whose sine is less than the ratio cells h of the container for purified metal from the bottom to the outlet to the length l of the channel, at the lower point of the vessel for purified metal there is an overlapping downward discharge pipe for draining metal residues. 2. The device according to claim 1, characterized in that the tube for draining metal residues is blocked by a single, polished plug made of metal to be cleaned. 3. The device according to claim 1, characterized in that the tube for discharging metal residues extends beyond the zone heated to the melting temperature, and has an additional heater located along the entire length of the tube. 4. The device according to claim 1, characterized in that on the tube for discharging metal residues there is a ring electrode for generating an electromagnetic pulse to eject metal residues from the tube.

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