DD287468A5 - METHOD FOR THE PRODUCTION OF FINE-COAL, HIGH-PURITY, REACTIONALLY SILICIUM - Google Patents

Abstract

The invention relates to a process for the production of feinstkoernigem, high-purity, responsive silicon, which is mainly used as a base material for the production of silicon nitride, for powder metallurgy production of high-quality construction ceramic components and as a base material for solar cells and semiconductor devices. The starting material is optionally comminuted dry at high stress intensity by methods known per se and nasal-chemically purified by methods known per se, wherein the metallurgical silicon with the addition of at least one modifier ground to the desired fineness without solidified agglomerates, the very fine-grained silicon in the presence of at least one Modified modifier nas-chemically to form a coarse structured, rapidly disintegrating foam and then subjected to a washing and drying process. {Silicon, feinstkoernig, high purity, reactive; dry grinding; Cleaning, nasochemical; Modifiers; agglomerates; Foam, coarse textured and decay quickly}

Description

Field of application of the invention

The invention relates to a process for the production of fine-grained, high-purity, reactive silicon metallurgical silicon, which is mainly used as a base material for the production of silicon nitride, for powder metallurgy production of high-quality construction ceramic components and as a base material for solar cells and semiconductor devices.

Characteristic of the known state of the art

According to data in the literature, for ultrafine grinding of silicon in ball and vibratory mills, longer grinding times of more than 15 h are required, the milled product containing a large proportion of coarser particles. The literature also reports on the occurrence of agglomeration in the milled product (RP Herbell, TK Glasgow, NW Orth: "Demonstration of a Silicon Nitride Attrition Mill for Production of Fine Pure Si and Si ₃ N ₄ Powders", Ceramic Bulletin 63 [1984 No. 9, pp. 1176-1178; PCT WO 84/01373; GB 1452578) .This agglomeration can even lead to the prevention of regrind transport in continuous mills.

The dry fine grinding of the pre-shredded material takes place here in ball, jet or vibratory mills at comparatively low stress intensity. It is known that, by dry pulverization of pre-shredded silicon at high stress intensity, e.g. In vibratory mills a significant shortening of the grinding time can be achieved. However, the problems due to the presence of oversize particles and agglomerates are still present and present an obstacle to the effective technical implementation of the dry micronization of silicon. For example, an additional classification process is required to achieve a desired grain size range of sufficient fineness.

To avoid the disturbing agglomeration in the milling of metals, a method has been proposed in which water-soluble compounds such. B. NaCl added to the millbase and then eusgelaugt from the ground product. However, the required high levels increase the milling energy consumption and the throughput of silicon decreases. In addition, loss of material already occurs by reacting the leaching agent with the silicon to form hydrogen and silanes, and there are special expenses for the treatment of the solutions with the leached compounds (DD-59464).

Also known is the use of grinding aids such. B. Kuhn: "Ultrafina Particles", published by Wiley in 1963.) The disadvantage, however, is that it produces powders with a low specific surface area (US-3476326). ,

For the production of high-purity silicon powder of metallurgical silicon as a base material for ceramic powder or compact molded body as well as for solar cells and semiconductor devices is a complex intensive chemical

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Cleaning process required. In the case of wet-chemical cleaning, mineral acids, especially hydrofluoric acid and hydrofluoric-mineral acid mixtures are preferably used according to the literature (NP Tucker: "Alloys of Iron Research, Part VII: Preparation of High Purity Silicon" J. Iron and Steel Inst. London, 115 (1927), pp. 412-416; US-2972521; JM Juveja, TK Mukherjeo: "A Study of the Purification of Metallurgical Grade Silicon", Hydrometallurgy 16 (1986) 1, pp. 69-75; No. 4,333,174, US-4,304,763, US-4,379,777, DE-2722783, DD-240728, DD-240729, DD-240730, DE-3317286, US-4588571, US-4539194). The chemical reaction of the impurities in the silicon with the leaching agents leads to the development of hydrogen and silanes. In the wet-chemical cleaning of fine-grained silicon, a stable foam is thereby formed in the reaction vessel, which also accumulates a large proportion of silicon particles at its interfaces and which eludes the action of the leaching agent. This foam causes a relatively slow course of the cleaning process, so that leaching times of several days are required. In the technical. Process of wet chemical silicon cleaning greatly limits the performance and throughput of silicon through foam formation.

Object of the invention

The aim of the invention is an effective process for the production of fine-grained, high-purity, reactive silicon metallurgical silicon, which is characterized by a short-term dry Feinstmahlung and low leaching times.

Explanation of the essence of the invention

The invention has for its object to develop a process for the production of fine-grained, high-purity, reactive silicon from metallurgical silicon, wherein the starting material optionally comminuted by known per se dry at high stress intensity and purified by wet-chemical methods known per se, wherein Fine-grained silicon no solidified agglomerates occur, with relatively little Mahlaufwand very high specific surface areas can be achieved, only a limited surface oxidation takes place and the leaching time is significantly shortened.

According to the invention, this object is achieved in that optionally the metallurgical silicon with the addition of at least one modifier ground to the desired fineness without solidified agglomerates and the very fine-grained silicon in the presence of at least one modifier wet chemical to form a coarse structured, rapidly disintegrating foam and then a wash and drying process. If the starting material is sufficiently fine, the modifier can also be added only during the wet-chemical cleaning. It is essential to the invention that the modifying agents used are nonionic surfactants, preferably alkylphenyl polyglycol ethers and / or alkylpolyglycol ethers. Furthermore, it is essential to the invention that during the grinding, the modifier or the mixture of modifying agents in a concentration of 0.2 to 5 parts by mass in%, based on the millbase, is added and that in the wet-chemical cleaning with mineral acids in aqueous media, the modifying agent or Mixture of modifiers in a concentration of 0.1 to 5 parts by mass in%, based on the solid, added or postdosed. In addition, it is characteristic that in wet-chemical cleaning the separation of the dissolved impurities and of the leaching agent takes place by cross-flow membrane or diafiltration with subsequent ion exchange process.

Through the use of the modifier caking of the ground material is prevented at the Mühlenwandungen and only thereby allows undisturbed operation of the mill. The result is a flowable ground material without solidified agglomerates and oversize particles, so that no Klassieroperationen are required. The modifier causes a very high surface area milled product to be produced with a relatively short milling time. As a result, the impurities distributed in the silicon can be removed during the subsequent chemical cleaning more than with not so finely ground silicon. In this way it is possible to produce silicon of solar quality. In chemical cleaning with mineral acids in aqueous media, the modifier causes a change in the foam occurring during leaching. It becomes large pores, drains quickly and disintegrates quickly. Thus, the process of chemical cleaning in a technologically reasonable time (about 4 to 6 hours) to realize. In contrast, without modifier addition a lye ··. from 3 to 4 days, because then a foam is formed, which is very stable and decomposes only slowly. Furthermore, the surface modification is limited by covering the solid surface by the Modifizierungsmittelzusatz both during grinding and during the leaching. Compared to the prior art, the invention u.a. following advantages:

- Shortening of grinding time and leaching time

- Prevention of the formation of solidified agglomerates of the ground material

- Limitation of surface oxidation

- Production of high-purity silicon of solar quality possible

- undisturbed operation of the grinding unit at high stress quality. The invention will be explained in more detail with reference to an embodiment.

embodiment

Metallurgical silicon of 2.8 wt.% Fe was continuously added in a tubular vibrating mill under inert gas atmosphere (N 2) at a flow rate of 7.8 kg / h, a mill scale fill of 75 with the addition of 1 wt.% Of alkylphenyl polyglycol ether containing 72.5 wt.% Ethoxy groups Volume fractions in% steel balls and a vibration amplitude of 5 mm dry ground and then with 6% hydrofluoric acid with further addition of 0.45 parts by weight in% of

above-mentioned Modifier at a solids content of 300g / l of a stirring leach at room temperature. In contrast to milling and leaching without additives, leaching produced a coarsely structured, rapidly disintegrating foam, which reduced the leaching time from 75 h to 4 h. Thereafter, the separation of the silicon was carried out by filtration and washing with leachant and deionized water. Finally, the solid was dried. Grinding in the tube mill was not possible without the addition of the modifier, since there was no more material transport due to the strong formation of solidified agglomerates. Although the utilization of high stress intensity in an exclusively discontinuously operable pot vibration mill leads to the desired fineness, the product yield was significantly reduced and economically unacceptable as a result of caking on the grinding pot wall and the grinding balls

 The purified silicon powder had the following characteristics:

Sbet: 5.1 mVg X97: 13.0 pm xw: 4.8 μπΊ Fe: 0.03% Ca: 0.04% al: 0.02% O ₂ : 1.1%

Claims (6)

1. A process for the production of fine-grained, high-purity, reactive silicon from metallurgical silicon, the starting material optionally du / ch per se known methods crushed dry at high stress intensity and purified by wet-chemical methods known per se, characterized dadu.ch that the metallurgical If desired, silicon is ground to the desired fineness without solidified agglomerates with the aid of at least one modifying agent, and the fine-grained, metallurgical silicon is wet-chemically cleaned in the presence of at least one modifier to form a coarsely structured, rapidly disintegrating foam and subsequently subjected to a washing and drying process. 2. Move! · ^; Tach claim 1, characterized in that are used as modifying agent nonionic surfactants. 3. The method according to claim 1 and 2, characterized in that are used as non-ionic surfactants Alkylphenylpolyglykolether and / or alkyl polyglycol ethers. 4. The method according to claim 1 to 3, characterized in that when grinding the modifier or the mixture of modifying agents in a concentration of 0.2 to 5 parts by mass in%, based on the millbase, is added. 5. The method of claim 1 to 4, characterized in that in the wet chemical cleaning with mineral acids in aqueous media, the modifier or the mixture of modifying agents in a concentration of 0.1 to 5 parts by mass in%, based on the solid, added or postdosed becomes. 6. The method according to claim 1 to 5, characterized in that in the wet-chemical cleaning, the separation of the dissolved impurities and the leachant from the solid by Querströmembran- or diafiltration with subsequent ion exchange process.