SE448164B - PROCEDURE FOR PROVIDING A BED OF PURE SILICONE CRYSTALS - Google Patents

Description

l4 l5 20 25 30 35 40 448 164 according to which it was found that a relatively large case, amounting to the volume of the melt during the treatment in two sharply densely melted alloy and the other consists of the zone crystallization, from 5 - 20 ° C, divides the total delimited regions. One is of crystallized solid phase. According to this patent, the separation process can be significantly accelerated and the purity of the German phase can be increased if the molten alloy is kept in continuous motion during the treatment and so much heat per unit time is separated from the melt, by means of a cooled surface or crystallization surface. on the crystallization surface for a relatively short time and in the form of a very compact layer. In addition, prior art (U.S. Pat. No. 3,008,887) states that elemental silicon containing traces of .. .___.__.> .- <__. - _-.-.__ ~ _..... - _ .-____._...._. M ~ _-.- .. V impurities can be removed by subjecting the silicon material to melting in a closed reactor; dissociated atomic hydrogen, which; in water under anhydrous conditions and in the presence of kept in direct contact with the molten silicon material formed, and by removing the vaporized contaminant products obtained by the reaction. According to this patent, such a process is particularly suitable for the purification of boron-contaminated silicon. In addition, U.S. Pat. No. 2,866,701 discloses a process for purifying silicon and ferro-silicon using gaseous carbon dioxide to remove aluminum and calcium by oxidation. However, despite prior art, there is still a great need for a process for producing high purity silicon in an economical manner. The present invention meets this need by providing Risel in significant quantities. Procedural silicon to a purity level in size- a strong economic process for purification of it can be used to increase the purification rate of the order of 99.99% by weight or higher.

According to the present invention there is provided a process for providing a bed of purified silicon crystals, wherein the silicon material is crystallized from a metal solvent and the amount of residual metal solvent in the crystal bed is reduced to a low level, the process comprising the steps of: a) providing a melt body containing silicon and metal, silicon being present in an amount greater than at the eutectic point of the silicon / metal combination and the metal being adapted to act as a solvent for the silicon material; b) removing heat from the body to provide a solid phase containing silicon in crystalline form and to concentrate the impurities in a molten phase; c) subsequently removing a substantial portion of the molten phase from the solid phase containing the silicon crystals; d) subjecting the solid phase to a melting process to melt at least a portion of the solid phase in order to remove a substantial amount of metal-silicon combinations that have adhered to the crystals; and e) separating at least a portion of the molten material from the Hisel crystals.

AAQ 1A4 3 44s 164 v Thus, the process for purifying silicon comprises the provision of a body of molten metal, which contains a significant amount of silicon. Heat is extracted from the body to give a solid phase containing silicon in crystalline form and to concentrate the impurities in the molten phase. In this embodiment of the invention, the heat is extracted mainly from the upper or free surface of the body. While removing heat, the walls defining the body of the molten metal should be maintained at a temperature high enough to prevent significant crystal precipitation on them. After a desired amount of heat has been removed, a substantial portion of the molten phase or metal solvent is removed from the solid phase.

A fraction or part of the solid phase is remelted for the purpose of removing metal-containing impurities from the crystals, and at least one fraction solvent n the crystals. In the accompanying drawings: Fig. 1 is a phase diagram of an aluminum-silicon-iron system; Fig. 2 schematically shows a cross-sectional elevational view of a crystallization furnace for use in the process of the present invention; Fig. 3 is a cross-sectional elevational view of a crystallization furnace illustrating a device for introducing gases into the furnace; and Fig. 4 is a diagram showing the yield of silicon and the iron boundaries plotted against the original amount of silicon in an alloy.

A material which can be given highly purified silicon in accordance with the present invention can be cm Si, the remainder being the impurities with respect to silicon. It should be noted that 99.0% by weight of Si has a melting point of about 140 ° C. In order to work at a lower tt at least one metal, consisting of tin, aluminum, silver or lead, is present in or added to the silicon material, thereby acting as a solvent for the silicon material. For example. Thus, if silver can be enriched in the range between about 830 and e degree of purification or enriched for the recovery of P55 temperatures, it is preferred a zinc, the metal ag is added to give a degreasing having a melting point of l400 ° C. In addition, alloys such as tin-lead alloys are used as solution material. Typically, the tin-lead alloy can vary between about 20-50% lead and 50-80% tin. A suitable composition is about 80% tin and 20% lead. It will be appreciated that other metal compounds such as tin-zinc can be used and are included within the scope of the invention. Of the group of net numbers that can be used, aluminum is preferred.

A silicon-rich alloy, which can be used in the present invention, may contain up to 87.4% by weight of aluminum. Small amounts of aluminum are because smaller amounts result in higher melting points. Thus, with respect to aluminum, in order to obtain an efficient operation, a typical silicon-rich alloy can vary between 20 - 80% by weight Si, whereby when the silicon to be purified has a purity of 99.0% by weight, the aluminum can which are added as above be of commercial purity, e.g. 99.5% by weight of aluminum. But aluminum with a purity of 99.9% by weight is preferred because then fewer impurities are added to the system. Furthermore, it will be appreciated that aluminum silicon carrying up to about 99.0 weight- usually less preferred n are aluminum and impurities. '- «» w v-v -_ .. »__. ..s ....-_....

Asaï-.e-Iiia ..-__ -, ssseex :. jg L, 5 l0 l5 20 i 2, i j 30 i ip 35 vi k »vill; 2. v al '(in 448 164 alloys, containing large quantities of silicon, can be used without adversely affecting the quality of the purified silicon obtained from the process. Other materials which can be considered as contaminants with respect to silicon should is controlled very carefully in some cases, so that silicon of a high degree of purity can be maintained economically, thus, in 5 when aluminum is used as a solvent metal, iron, it should be controlled in the body by molten material or alloy, so that during the fractional crystallization process the ¿double saturation line AB Fig. 1, is not reached By checking the iron content of the molten alloy L, intermetallic crystals such as FeSi2Al4 are avoided, which helps to guarantee a silicon product of high purity. For illustrative purposes, the iron content of the molten body, which is to be subjected to fractional crystallization, is not allowed to exceed 8.8% by weight as it is desirable to reduce the temperature of the molten alloy to a near its eutectic temperature of about 577 ° C. It will be appreciated that in the process of the present invention, it is normally desirable to approach the eutectic temperature in order to obtain a high yield of silicon crystals. However, the higher the temperature above the eutectic temperature when the fractional crystallization process is stopped, the greater the amount of iron that can be tolerated in the molten alloy. If e.g. If the crystallization process is stopped at about 660 ° C, the level of iron can be as high as 1.5% by weight without phases containing intermetallic crystals such as e.g. FeSi2Al¿, and related purity problems: It is thus clear that it is best to avoid such ferrous phases. It should be noted that if the iron content is controlled to be present in the alloy, as above, the iron content may be reduced in one step of the process of the present invention to less than about 1 ppm after the treatment with e.g. HCl. However, if the iron content is allowed to exceed these limits, then there can be a significant increase in the level of contamination found in the silicon crystals. If e.g. iron is present in a content of 3% by weight in the alloy to be subjected to fractional crystallization, then the amount of iron present in the crystal bed will be very high and even after leaching the iron level tends to be higher than desired starting from _ from obtaining purified silicon.

From what has been said above, it is understood that control of contaminants, such as Iron is very important in the process of the present invention in order to obtain high yields of a high purity silicon product economically. It will thus be appreciated that it is important to control the iron content of the material constituting the molten body which is to be subjected to fractional crystallization. Thus, if 99.0 weight Si and aluminum of commercial purity were used to form the molten body, the iron content of both the silicon material and the aluminum material should be checked in order to obtain maximum yield. Dm e.g. the iron content is high in the silicon source used, the aluminum source used should be selected with respect to iron in order to maximize the yield of silicon which is cannulated through the process without encountering the f: mmrem .g 25 30 35 40 'used in semiconductor applications, required it is normal for the boron content to be 448,164 less preferred iron-aluminum silicon crystal phases. Referring to Fig. 3, the importance of fixing the iron control can be seen more clearly. If it e.g. it is desirable to purify 99.0% by weight of Si with 0.5% by weight of iron therein, the residue being contaminated, it can be determined how much aluminum must be added and the iron content therein which can be tolerated so that the silicon material can be purified in accordance with the preferred embodiment of the present invention. Thus, it can be seen from Fig. 3 that if the aluminum added to the silicon material has an Fe content of 0.04% by weight, then the initial amount of silicon in the alloy can be as high as 63% by weight, whereby a yield of purified silicon is obtained of about 58% without causing harmful amounts of iron. If, by comparison, the iron content of the aluminum material is 0.2% by weight, then the initial amount of silicon in the alloy is about 59% and the yield of renadic silicon is about 53%. Fig. 3 assumes that the molten alloy is cooled to some degree above the eutectic temperature. The higher the crystallization process is held above it, the amount that can be tolerated in the process is that during the crystallization process. eutectic temperature, the greater as mentioned above.

Another contaminant that should be reduced at rest can be considered harmful in electrolytic photocells. Since purified silicon should be very low and often one has, however, to a low level is boron, since its presence is required that the content is 0.1 ppm or less for certain applications. found that although the fractional crystallization results in a significant removal of boron, it may be desirable to supplement such a method. Thus, an addition of a metal consisting of titanium, vanadium or zirconium to the silicon-rich aluminum alloy can lower the boron content to a very low level. the addition of titanium, vanadium or zirconium to the silicon-rich alloy in molten form results in precipitation of a boron-containing reaction product. The reaction product falls to the bottom of the molten alloy and can be removed or separated from it.

The preferred metal used to treat the melt for the purpose of removing boron is titanium. The amount of titanium added should not exceed 0.2% by weight and preferably not 0.1% by weight. It is important that these limits be maintained because titanium can result in the formation of intermetallic crystals in excess amounts similar to those which occur with the fractional crystallization step in a manner such as iron.

In the treatment of a silicon-rich aluminum alloy to remove boron, the alloy is first melted and the temperature is kept relatively close to the melting point. In order to remove boron, effective removal at lower temperatures is facilitated. Thus, the temperature should not normally exceed the melting point of the silicon-rich alloy by more than about 100 ° C. It should be noted that the melting point of an aluminum-silicon system can vary from between about 580 ° C to 1420 ° C, depending on the purity of the silicon alloy to be enriched. It should also be noted that in a silicon-aluminum system with a melting point of about 580 ° C, the alloy has a high content of aluminum and a low content of silicon. amma f. . »Få l0 l5 20 25 30 35 40 448 164 _. kiael system with a melting point at about 580 ° §, the silicon material should comprise l2.6% by weight, the remainder being aluminum and impurities. Furthermore, it should also be noted that in order to carry out a fractional crystallization according to the present invention, the silicon content should also be greater than about 12.6% by weight in an aluminum-silicon system.

The metal can be added in excess of the amount required to react E since the excess can be advantageously removed in the step of the fractionated 4 n product, the molten alloy in order to Dvs in an aluminum with boron, crystallization. In order to remove the reaction, it is allowed to stand or be kept in a dormant state for about 1-4 hours. allow the reaction product to settle. It can then be separated from the melt. Other methods of removing the reaction product, such as filtering or transporting the reaction product to the surface of the melt with a cooling gas, which are discussed later, are considered to be within the scope of the invention.

It is preferred to remove boron from the silicon-rich alloy, rather than at a later time when the silicon material has been mainly enriched as this prevents the possibility of contamination with the boron-removing metal after the crystallization step.

Another component that is undesirable or insufficiently removed during the fractional crystallization is phosphorus, which is important for solar applications. In silicon materials to be contaminated with respect to silicon is removed to a very low level.- used for solar applications, phosphorus of In accordance with one aspect of the present invention, it has been discovered that if the silicon-rich alloy in a molten state is treated with a source of chlorine, phosphorus is removed to a very low level. A preferred source of chlorine which is suitable for use in the present invention is Cl 2. But also other chlorine-containing materials such as COC1 and_CCl4 can be used. Preferably the source of chlorine is in gaseous form. lf * In the process for treating silicon for the purpose of removing phosphorus, the silicon material is first dissolved in a molten metal solvent, e.g. aluminum, such as be-. W written earlier, to give a molten body of about 50% by weight and e.g. 50% by weight of aluminum. * Chlorine gas is added to the bottom of the molten body and bubbled through it (see Fig. 3) for a certain period of time, to remove phosphorus by concentrating it at the surface of the melt with foam which may be present. Then the molten peak can be fractionally crystallized in order to form silicon crystals. In addition to iron and boron, other contaminants are controlled. For example, as previously mentioned, titanium should be controlled. Other examples of metals which should be carefully controlled are manganese and chromium, where the maximum amounts should be less than about 2% by weight and 0.4% by weight, ie, impurities other than the solvent metal, eg aluminum, with respect to silicon should be kept at a level which does not allow them to form intermetallic compounds during the fractional crystallization step in the same manner as discussed with respect to Iron. The formation of such impurities may be subjected to d '* e: Jissamæ fl- ze 40 7 448 164 result 1 means difficulty in obtaining the desired titanium can not be easily removed by treating equilibrium to remove But the fact is that if, as mm as discussed earlier, degree of purity. For example. it has been found that the crystal bed with hydrochloric acid, which is a used and significant amounts of iron from the crystals. kept well above the eutectic temperatures, the acid can be formed without the formation of intermetallic compounds ç in aluminum iron, during the process the temperature amounts of impurities are tolerated in the system during the crystallization and without the accompanying problems with respect to the purification.

As for the fractional crystallization part of the invention, it is understood that in one embodiment heat is taken from the molten, silicon-rich body to give a solid phase containing silicon in crystalline form with a high degree of purity by concentrating the impurities with respect to silicon in the molten phase. The limits of the present invention with respect to the starting temperatures are controlled in one respect by the amount of silicon present in the molten alloy. Ie. the higher the silicon content h thus the initial temperature from which the greater the yield, the higher the melting point of the alloy and the body is cooled. The higher the kitel content in the starting alloy, of purified silicon crystals, especially when the temperature is reduced to or near the eutectic temperature of the system. At e.g. an alloy concentration of about 90% by weight:% Si, the starting temperature, or melting point, will be about 1370 ° C. Carrying out the process at this temperature may prove to be black solely due to material limitations and the tendency to form oxides or nitrides. Otherwise such a process is considered completely possible and it can give large yields of silicon crystals with a high purity.

In a preferred embodiment of the fractional crystallization process from which silicon is to be recovered, avwf-gka. e ii-ašäa, a body 8 of the silicon-rich metal is provided, in a molten state (Fig. 2), the body having a free upper surface 10 from which heat can be extracted in order to form a solid phase containing silicon crystals.

The body is contained in a vessel 60, which has an insulating wall 62 which can be heated if desired. Preferably, little or no heat is allowed to be lost through the walls of the vessel to avoid freezing or silicon crystals forming on the walls. The container preferably has a layer 64 containing powdered alumina, which forms a barrier against the molten metal which may disappear through the inner wall 66. The wall 66 should comprise a material which does not act as a source of contamination for the molten body 8. When the solvent is molten aluminum, the wall is 1! 66 preferably made of high purity alumina-based refractories, i.e. at least 90% by weight of alumina and preferably 92-99% by weight. Such a refractory material can be obtained from Norton Company, Worchester, Massachusetts, under the name Älundum VA-112 or LA-85215. This material is provided in path 66 in powder form, compressed, and then sintered to give it rigidity. This gives a monolithic lining through which molten aluminum is less likely to pass and which is thus suitable for use in the embodiment described below. i ~ v. 10 448 164 The heat removal through the free surface 10 from the silicon-rich body of molten metal can be conveniently controlled with cooling gas. That is, a gas such as air can be dropped against or passed over the surface 10 by means of a gas cooling device 24 for the purpose of solidifying silicon crystals in a layer at or substantially parallel and adjacent the surface 10, as shown schematically in Fig. 2. In an alternative embodiment, heat may be removed by bubbling gas through the body 8 substantially as shown in Fig. 3. The fused metal body 8 is provided in a vessel or container similar to that shown in Figs. 2. In the body there is a gas dispersing device 50 which allows an inert gas, e.g. argon or a gas that is inert with respect to silicon and aluminum, is introduced or bubbled through the body to remove heat. In addition, there is a lid 52 which prevents the gases from escaping to the atmosphere. Thus, in accordance with the invention, gas may be introduced through line 54 and passed to the space 56 from which it is introduced into the molten metal.

The gas cools the metal and crystals of silicon 51 are considered to be formed in close proximity to the gas bubbles and the molten metal interface, as depicted in Fig. 3. In addition to allowing gas cooling, the dispersing device 50 can be used to remove silicon crystals by mounting by means of by a device that allows it to be taken upwards out of the vessel (not shown). Remelting substantially all of the crystals for the purpose of removing them from the vessel may be uneconomical due to the high tempe- .__- Tw- -n-aw -a - »~ -_, ......- v ._, ~ ,, _, _______ rations required. .

During heat removal from the body, it is beneficial to have a certain amount of mixing movement. Such a satisfactory mixing motion can be obtained by subjecting the formed crystals to a packing motion using the blade 26 (Fig. 2), by means of which the crystals at or near the surface §Å¿ of the molten metal are forced downwards. That is, the packing motion breaks up massive crystal formations that can form at the surface and displaces such crystals downward, allowing new silicon-rich metal to come up to the surface. A packing movement can be performed during the crystallization in the order of 10 - 40 times per minute. Furthermore, it will be appreciated that other types of mixing motion may be utilized. For example. For example, the mixing motion obtained by introducing cooling gas into the body of molten metal (Fig. 3) can be used. Referring to Fig. 2, the blade 6 is shown mounted on a shaft 28 which may be used for packing purposes in accordance with the invention.

As recently observed, it should be noted that the crystals formed have a density which is generally similar to the density of the molten metal and thus tends to flow, especially when aluminum is used as the solvent metal. Thus, there does not appear to be a significant accumulation of crystals at the bottom of the vessel, not even after the packing movement has passed them in that direction. Instead, the crystals appear to be randomly distributed in the body of molten metal with the higher concentrations accumulated at or near the surface. After the crystallization has proceeded to a desired stage, the remaining molten metal is separated from the silicon crystals, preferably by draining. This can be accomplished by removing the port 34 from the opening 36 and allowing residual molten metal containing contaminants to be drained. This is an important part of the invention because in this way a significant amount of the contaminants are removed. Furthermore, it is understood that one is removed in this way, whereby the uneconomical from the crystals using a large part of the solvent metal can and Difficult step of trying to leach metal in solid form of large quantities of e.g. hydrochloric acid is avoided. In the process of the invention, it is preferred to remove as much loose metal, including contaminants. as possible while the temperature of the crystal body is preferably kept above 2, at the eutectic temperature. It should be noted that it is advantageous to keep it unclean in order to melt the metal temperature slightly above the eutectic temperature by means of resistance wires.ll0 which l gnM¿å facilitate draining. This can be done in tubes 100, Fig. 2. In addition, it is preferred that the remaining crystals be subjected to a compressive movement during tapping in order to obtain a higher removal of molten metal. During compression, it is preferred that the temperature of the silicon crystals be maintained above corresponding to melting at it (above 578 ° C for the silicon-aluminum mixture), typically about can be advantageous, '11 eutectic temperature 5-50 ° C, although higher temperatures are not considered negative but which will be explained later. By draining the crystals in this way, a significant portion of the remaining molten metal is removed, but a residual amount of the molten metal wets or adheres to the crystals and may constitute up to 50% by weight of the bed with typical amounts of about 30% by weight. -%, to some extent depending on the alloy used. It is desirable that the molten metal be reduced to a minimum after it is not only a silicon contaminant but also contains many contaminants. Thus, it has been discovered that compression or packing of the crystals helps to remove residual molten metal in the crystal bed. The compaction can be carried out quickly using the blade 26, Fig. 2. Thus, in order to facilitate the draining of molten metal from the vessel 60, the blade 26 is lowered in contact with the crystal bed and a pressure is applied. A suitable hydraulic device can be used for the lowering and application of a controlled pressure. e 4 A pressure that gives suitable results is in the order of 0.7 - 2.1 kp / cm.

As described above, when the molten metal is drained from the vessel, a certain amount remains attached to the surface of the crystals. Thus, in order to economically obtain high-purity silicon, the amount of metal remaining must be reduced as far as possible. In the aluminum-silicon mixture, the remaining phase consists of the crystal bed: fff for the most part of aluminum and silicon. The aluminum present in phase ö can be removed by treatment with a solution of hydrochloric acid. However, in an important part of the invention, the silicon crystals, on which the aluminum-silicon phase has solid, are subjected to a controlled heating in order to remelt the phase and a smaller part of the silicon crystals. This gives a silicon crystal bed where the solvent metal usually does not constitute more than 15% by weight of the bed. The remelting can be performed by melting an upper part of the crystal bed, the part being allowed to be discharged through the remaining part of the bed so as to remove a part of the aluminum-silicon phase attached to the silicon crystals. However, the heating of the crystals which by direct action of gas-fired flames on the top of the crystal bed can result in oxide formations, freezing at the bottom of the bed and the need to remelt all the crystals A for a removal.

In a preferred embodiment, the body is exposed to silicon crystals containing the metal-silicon phase, e.g. aluminum-silicon, for a heating process, which § is effective by heating the whole body more uniformly than top heating. it is preferred to check the heat supply to ensure that the whole body is heated at approximately the same speed. This can e.g. obtained by means of electric heating. When an electric current is passed through the body, it is preferably heated (unlike the silicon crystals) and part of the solid or aluminum silicon phase melts. A representative heating occurs because the resistance of the aluminum-silicon phase, which remains between or adheres to the crystals, is much less than that of the silicon crystals. Typically, the aluminum-silicon phase comprising impurities has a resistance in the order of about 30 microohm cm and the silicon crystals have a much higher resistance, i.e. over 3000 microohm cm. the silicon phase which remains between or on the crystals pine bed and has a relatively high ka current preferably go Thus, since aluminum is considered to be more or less interconnected in crisis electrical thermal conductivity, the electricity is passed through the aluminum silicon phase, allowing a more uniform heating than peak - t to the solvent metal phase results in a heating. A strong concentration of heat is only slightly reduced because only a higher level of purity, while the yield of crystals a smaller part of the crystals, will dissolve.

The preferred method of heating residues in the crystal bed is induction heating, although there may be times when resistance heating is quite possible. Referring to Fig. 2, a coil F 80 is shown which is made to operate in conjunction with a vessel for fractional crystallization for the purpose of electrically inducing heat in the bed. Fig. 2 shows the vessel 60 with the induction coil 80 placed just above and around the drain hole 36 on one side and which extends to the bottom on the opposite side. The coil is shown wound around the vessel and extends upwards along the sides to a height which approaches the height g of the crystal bed. From Fig. 2 it can be seen that the induction coil can be placed under the insulating phase which attaches to or ___- ß,, * e layer az. While induction heating is used for the purpose of obtaining more uniform heating, it should be noted that in some cases larger amounts of heat may be found at or near the wall of the vessel than in the bed. This phenomenon, which can be controlled to a certain extent, can have the advantage that any crystals or any alloy phase that adheres to the vessel wall can easily melt, which facilitates the removal of Jasse. . e, _ a fi ee; __ ef_, 1u 15 20 25 30 40 11 448 164 of the remainder of the krista11 bed, _if so desired, without risk of damage to the e1dfasta wall.

Heating in the vicinity of the wall in an induction system depends to some extent on the frequency of the current in the induction coils. For example. are high-frequency systems e.g. 10,000 Hz, more likely to produce larger amounts of heat to or near the wall than low frequency systems, e.g. 180 Hz. The frequency used in commercial operation preferably ranges from about 60 Hz to about 180 Hz, with the higher frequencies being less preferred due to the loss of uniform heating. However, high frequencies are required when a single vessel is used to obtain a suitable vessel which can only have a load capacity of 2.25-5 kg of heating. For example. which has been found to be more efficient at requiring a frequency of 1,000 - 10,000 Hz, than alternative heating methods.

To facilitate the extraction, the silicon crystals are preferably subjected to a compression, substantially similar to that previously described. In one embodiment of the remelting step, the compressive pressure can be applied substantially simultaneously with the melting step, i.e. It is of value if both a significant amount of remelted material can be exposed, as well as silicon from the partially redesigned aluminum-silicon phase, heating is utilized. can be used simultaneously, whereby eff is squeezed out of the crystals containing impure solution phase, melting crystals. The compressed agitation is carried out after in each case the remaining solution metal usually constitutes not more than 10% by weight of the bed and preferably the solution metal is reduced to not make up more than 2% by weight of the crystal bed.

During heating of the crystals and unclean crystals, the molten part can be drained from the crystal bed substantially continuously or in some cases at periodic intervals. The temperature of the crystal bed, at which the molten part is removed, is preferably in the range of 0-130,000. The periodic tapping has the advantage that this can facilitate the heating to be started. phase, which remains between the council of the middle 75 to place the crystals in the bed in a melt of increasing purity. the purification by allowing a melt of higher purity to come into contact with the crystals in the bed. Although not desirable in some theory, it is contemplated that by coming into contact with the crystals, a mass transfer of the crystals to the liquid is obtained, thereby increasing the purity of the crystals. The following examples further illustrate the invention.

EXAMPLEb11 a melt of high purity impurities from 1 previously.

Silica of about 99.0% by weight of purity to obtain a mixture of 907 kg of about 25 .mu.l, the remainder being impurities. The silicon material is dissolved in aluminum, at 850 ° C in a container. mainly the aluminum material by heating to specificity, especially when the induction compression and heating to necessarily bind the invention purity were added to aluminum of about 99.9% by weight of silicon and about 74% by weight of carbon dioxide. 12 448 164 as shown in Fig. 2. The height of the melt in the vessel was about 45.7 cm After the silicon material dissolved, the mixture was cooled at a rate of about 2 ° C per minute 585%. The cooling was effected by means of in until the temperature of the mixture was about air, which was allowed to fall towards the surface of the liquid mixture, mainly as shown in Fig. 2. During the cooling and to facilitate the removal of heat, a packing sheet, shown in Fig. 2, was passed. , downwards at a rate of 30 times per minute to remove crystals from the surface and to give a certain mixing motion.A sample of formed crystals was removed from the vessel and was found to contain about 74% by weight of aluminum. The bed while maintaining the bed at a temperature of about 580 ° C to facilitate the removal of aluminum. Analyzes ; showed that after draining, the remaining aluminum in the crystal bed amounted to about 49% by weight. From this experiment it appears that a favorable effect is obtained by draining in comparison with only lifting the silicon crystals out of the vessel. Thus, the amount of aluminum to be removed from the crystals after draining has decreased. EXAMPLE 2 This example was carried out as Example 1, except that after draining, the bed of crystals and the aluminum contained therein were partially remelted by allowing a gas-fired flame to act on the surface of the bed. The amount of aluminum contained in the bed was reduced on average to about 42% by weight. But in some areas of the bed, the aluminum content had fallen sharply. For example, at the center at the top of the bed, the aluminum content was 7% by weight and peripheral areas at the top were found to have aluminum contents of about 19% by weight. This example shows that the aluminum content of the crystal bed can be significantly lowered F W by applying heat. The differences in the amount of aluminum that arose É if “fÜli- ii were attributed to the difficulty of heating the total bed uniformly. For example. found that during the remelting, the temperature adjacent to the surface was above 900 ° C, while the temperature at the bottom was only about 70,000.

Examples: This example was performed to determine whether the crystal bed and the aluminum contained therein could be heated more uniformly in order to obtain a more efficient separation of aluminum and impurities from the silicon crystals. Thus, a melt containing 33.4% by weight of silicon (metallurgical purity) was prepared, the remainder being aluminum and impurities, which melt was provided in a small vessel with a capacity of 2.25 kg. Thereafter, heat was extracted from the unit, the temperature was lowered to about 58006 and the alloy was drained. Because the unit was so small, only a relatively small amount of molten material was removed. The remaining crystals and the alloy were then subjected to induction heating in order to achieve greater separation of the aluminum from the silicon crystals. Using a 30 kw induction source with l0.000 Hz, the temperature in the bed was increased more or less uniformly to about ll00 ° C. After draining, only about 35% by weight of aluminum remained in the crystal bed. The result of this example clearly shows that the aluminum alloy, which can be heated uniformly in 448 using a content contained in the crystal bed, can be separated from the silicon crystals. With 907 kg capacity, a slightly larger separation from such a vessel, a 250 kw induction source can be used at about i aaaaen can be najas: iii about iooo ° c on about so-45 min. leaf sheets to compress the crystals un induction heating, should only l2,0 wt.% aluminum, in It should be noted that materials drained as a result of induction heating may contain high levels of silicon, eg some melting a later melt for crystallization 164 t give a molten part as light t larger vessels, t. When using a l80 H ;, at which the temperature l During use of a packer the initial drain and under: on a calculated basis, weight% remain, as it can v silicon crystals.Such material can incorporate As in one of the above, it is stated that in a process for purifying silicon by crystallization, the solvent metal, e.g. al level in the crystal bed. Aluminum that remains in the bed can be used with the use of hydrochloric acid, whereby you economically occur losses of aluminum due to the acid. At a higher degree of purity, the molten material is useful when e.g. aluminum castings, we economy, for the system. Although the invention has described the accompanying claims intended to cover other embodiments as the invention. uminium, is removed to a very low easily dissolved from crystal- maintains a system which is very because only a very small amount of hydrochloric acid is required and it does not need large amounts to dissolve in vapor, 2 the cases where aluminum is used as solvent to give silicon which is drained only after crystallization- I "lk further improves joke with preferred embodiments, they fall within the scope of upp- z-í- fi xw- il: J l, š f'-

Claims (10)

1. -. e-.å-f 10 15 20 25 30 35 40 / '/' I - f -. . . . / /, f / / / '' _ / / / /// /// / //////////////, / Ä /, / Å 50 56 '34 The numbers mom pacman indicate lmernanoneil ldenxiilerlngukod, INXD code. A process for obtaining silicon is crystallized from a metal solvent and the amount present in the crystal bed is reduced to a low level, a) a molten body being provided containing silicon, preferably in an amount of 20-. 80% by weight and metal, preferably aluminum, silicon being present in an amount greater than the amount at the silicon-metal eutectic point. The metal is adapted to act as a solvent for silicon, the metal mixture preferably having a melting point between about 600 contain a bed of purified silicon crystals where the metal solvent grinding, then and wherein silicon and 120 ° C; b) heat extraction and to concentrate the impurities in a molten phase; s from the body to give a solid phase containing silicon in crystalline form, characterized in that c) a substantial part of the holding silicon crystals; d) the solid phase is subjected to the molten solid phase in order to remove a vase which is attached to the crystals; and e) at least a portion of the molten material is separated from the crystals of silicon. 2. A method according to claim 1, characterized in that walls, which delimit the body, are kept at a temperature high enough to prevent any significant precipitation of crystals thereon. 3. A method according to claim 1 or 2, characterized in that heat is removed from the body by bubbling a gaseous agent through it, or that the body has a free surface and that heat is removed via it in order to give a solid phase containing silicon in crystalline form. 4. A method according to claim 3, characterized via the free surface by a gas, preferably vi 5. A method according to any one of the preceding claims, characterized in that during the removal of heat, the body is subjected to a mixing movement, which is preferably performed by the body being packaged to move crystals from the surface of the body. Method according to any one of the preceding claims, characterized in that the molten phase is removed from the solid phase by draining while maintaining the temperature of the body above the eutectic temperature, the body preferably being maintained at a temperature of between 577 and 650 ° C . A method according to any one of the preceding claims, characterized by setting a packing motion to thereby minimize the melting phase and then removing it from the solid phase inside to melt at least a portion of the final amount of the metal-silicon mixture, e.g. by removing heat s air, is blown towards it. that the solid phase releases the amount of liquid phase remaining in the solid phase. 8. A method according to any one of the preceding claims, characterized in that after a substantial amount of the molten phase is removed from the solid letter within parentheses anoer interner-emil dnkumonikmuww ”fl _ 1219131171 * ~ _. . The solid phase is heated, preferably at a temperature of 750 DEG-300 DEG C., in order to remove substantially all of the crystals, whereby the solid phase is heated to melt at least a portion of the crystals. of the excessive amount of the metal-silicon combination, which cover Nä is developed in the solid phase by passing an electric current through, step by step, by inductive heating. Oh Process according to any one of the preceding claims, characterized in that: in the material forming the molten body, which is to be subjected to the fractions for fractional crystallization, of intermetallic impurities, turns 10 in the body are controlled so that the double saturation line AB in Fig. 1 is avoided. _ü fl A method according to claim 9, characterized in that at least one of the following impurities in the body is controlled, wherein the amount of iron impurities Å in gl is controlled to be not higher than 0.8% by weight, titanium to a level of not Fi f greater than about 0,2% by weight, manganese to a level of not more than about 2,0% by weight and / or chromium to a level of not more than about 0,4% by weight. controlled to a level that avoids formation id preferably the level of iron impurities e i .i ie - v. i Vi 0 f. l fi f. {it “ß ï <__ ß--: a¿ ~: {1§« i_ «.