DD290860A5 - METHOD FOR PRODUCING FINE-CORROSIVE SINTERICTIC SILICON CARBIDE, BORCARBID, SILICON NITRIDE AND / OR REACTIVE SILICON - Google Patents

Abstract

The invention relates to a process for the production of feinstkoernigem sinter-active silicon carbide, boron carbide, silicon nitride and / or reactive silicon, which are used primarily for powder metallurgy production of high-quality construction ceramic components. The process is characterized in that the starting material is ground dry and / or wet at high stress intensity, using as grinding fluid in the nasal addition water without the addition of antioxidants and surfactants or organic liquids, and the chemical cleaning of Feinstmahlprodukte by leaching with aqueous solutions of mineral or mineral acid mixtures and / or alkali hydroxides, washing and addition of ion exchangers. {Process; silicon carbide; boron carbide; silicon nitride; Silicon, very fine-grained, sinter-active; high stress intensity; chemical cleaning; Ion exchangers}

Description

Field of application of the invention

The invention relates to a process for the production of very fine sintered silicon carbide, boron carbide, silicon nitride and / or reactive silicon, which are mainly used for powder metallurgy production of high-quality construction ceramic components.

Characteristic of the known state of the art

Since the properties of sintered bodies are very much influenced by the nature of the starting powders, they must meet certain requirements with regard to grain size and particle size distribution as well as with regard to impurity contents.

In the internationally used methods for producing sintered silicon carbide, boron carbide, silicon nitride and reactive silicon powders from coarse-grained material, the treatment is carried out by dry and / or wet comminution, classification and chemical cleaning (US Pat. Herbell, Th., Glasgow, Th., Et al.: Demonstration of a Silicon Nitride Attrition for Production of Fine Pore Silicon and Silicon Nitride Powders, Am.Ceram.Soc.bull.63 (1984) 9 p. 1176 Shaffer, PTB: "Fine SiC-Powders for High Performance Ceramics, their Production and Characterization", Proceed, of the 9th Ann. Conf. On Composites and and Advanced Ceramic Mat., Feb. 20-23, 1985 in Columbus, Ohio: The Am.Ceram.Soc., 1985, pp. 1135-1145; U.S. Pat.

The dry grinding of the vorzurkleinerten material is carried out according to the information in the literature in ball, jet or vibratory mills usually at comparatively low stress intolerance. In technical swing mills z. B. worked with amplitudes below 4mm or low acceleration values. Agitator ball mills are used above all for wet grinding. While in the grinding of silicon carbide and boron carbide except organic liquids and water with the addition of antioxidants and surfactants can be used (DE3123924, DE-OS3543708, EP0193970), high-quality silicon nitride is prepared solely by grinding in organic liquids because of its easy hydrolyzability (Freedmann, MR ; Kiser, JD, et al.: Factors influencing the ball milling OfSi ₃ N ₄ in water In: Proceedings of the 9th annual conference on composites and advanced ceramic materials, 20-23-18-85 in Columbus, Ohio: The Americ. Ceram. Soc. [1985] p. 1124-1134).

The grind with comparatively low stress intensity has the disadvantage that the impurities enclosed in the coarse grain are exposed only unspecified and thus only a starting material with a high degree of purity can be used. In addition, due to the longer milling time required at low stress intensity, the formation of oxidation products of the Feinstmahlprodukte takes place to an increased extent.

The wet grinding in organic liquids has the disadvantage that high demands of occupational health and safety must be observed. Since in Feinstmahlprodukt still in any case impurities such. 8. SiO ₂ , Fe and Mahlabrieb, are present in impermissibly high levels, a wet chemical treatment of Feinstmahlprodukte to remove the impurities is necessary. While the grinding abrasion is usually achieved by a hydrochloric acid treatment, a treatment with hydrofluoric acid-nitric acid mixtures is generally carried out to dissolve the SiO ₂ and Si impurities (DE-OS2452799, US4123286, DE-AS2848452, US4238434, US4318876, US4525461). In addition, hydrochloric acid-hydrofluoric acid mixtures were used to dissolve the contaminants of silicon carbide, boron carbide and silicon nitride powders (G. Schwier: Forschungsbei icht T84-211 of the Federal Ministry for Research and Development of the Federal Republic of Germany, 1984, p 11, Gläser, WD Bunk, W., Böhme, M .: Ceramic Components for Vehicle Gas Turbines, Springer-Verlag Berlin, Heidelberg, New York 1978, Vol. 1: For the production of high-purity Si ₃ N 4 Heißpreßpulver and SiC Sinterpi'lver , Pp. 81-86). Also known is the wet chemical treatment of coarse-grained products of SiC production for abrasive grain mixtures with sodium hydroxide (Ulimann's Encyclopedia of Industrial Chemistry, Volume 15, (1964), p. 695, Winnacker-Kuchler: Chemical Technology, Volume 1 [1970], p. 463). The use of various mineral acids and mineral acid mixtures to dissolve technical silicon impurities, also by use during a grinding operation, is also known (U.S. Pat. No. 2,797,221, U.S. Pat. No. 4,304,763, U.S. Pat. No. 4,379,777, DE-OS2722783, DE-OS2729464 , DD-WP240728, DD-WP240729, DD-WP240730, Juneja, JM, et al: A Study of the Purification of Metallurgical Grade Silicon, Hydrometallurgy 18 [1986], pp. 68-75). In describing the known methods of wet chemical treatment, the literature has generally considered only the leachant system for solving the impurities contained in the silicon carbide, boron carbide, silicon nitride and silicon powders to evaluate their technical feasibility and their economics. However, the process stages for separating the dissolved impurities from the solid are particularly complicated. These washing processes are referred to only briefly in the literature in connection with decantation, filtration and centrifuging. However, they are of paramount importance in achieving high purities of the silicon carbide, boron carbide, silicon nitride and silicon fine powders. Due to the easy adsorbability of dissolved impurities on the large surface of the finest-grained, purified powder cleaning is possible with the usual methods only with a considerable consumption of washing solution and wash water.

Object of the invention

The object of the invention to provide an effective method for the preparation of sinter-active feinstkörnigem ¹ silicon carbide, boron carbide, silicon nitride and / or to develop reactive silicon.

Explanation of the essence of the invention

The invention has for its object to develop a process for the production of fine-grained sintered silicon carbide, boron carbide, silicon nitride and / or reactive silicon, in which relatively heavily contaminated starting material can be used, the grinding time is shortened and the subsequent washing and separation processes so be guided that with the least possible consumption of wash solutions and wash water, low solids losses and short treatment times, a final product is obtained which contains only the permissible contamination levels for sintered silicon carbide, boron carbide, silicon nitride and / or reactive Siliziumfeinstpulver. According to the invention, this object is achieved in that the silicon carbide, boron carbide, silicon nitride and / or silicon is ground dry and / or wet at high stress intensity, as the grinding fluid in the wet grinding of silicon carbide, boron carbide and / or low quality silicon nitride water without the addition of surfactants and antioxidants and in the wet grinding of high quality silicon nitride and silicon organic liquids are used t and that are used as a leaching agent aqueous solutions of mineral acids or mineral acid mixtures and / or alkali metal hydroxides, the dissolved impurities from the solid by filtration and washing with pure leachant and subsequently be separated with deionized water or so that after settling of the solid, the leaching solution is decanted and the settled solid dispersed at least once in pure leachant and after settling of the solid What Then the sediment is decanted, the settled solid is then dispersed at least once in deionized water and / or water-miscible organic solvents and decanted after settling the solid, the settled solid is then dispersed in deionized water and / or water-miscible organic solvents, and coarse-grained ion exchangers are added to this suspension, which after exchange of the dissolved impurities and foreign ions in the suspension for H ⁺ and / or OCT ions are separated from the purified suspension, and the purified solid is finally dehydrated and / or dried. It is essential to the invention that the silicon carbide and boron carbide used as starting material have a comparatively high proportion of foreign phases in the range of 0.1-0.5% by weight of Fe, 0.1-5% by weight of Al and 0.01-1% by mass. % Ca, the silicon nitride has a proportion of foreign phases up to 2Ma .-% Fe, 0.3Ma .-% Al, 0.3Ma .-% Ca (Si ₃ N ₄ > 96%) and technical silicon a proportion of foreign phases up to 3 Ma .-% Fe, 0.3 Ma .-% Al, 0.3 Ma .-% Ca may have. Furthermore, it is essential to the invention that in the wet grinding an organic grinding fluid is used, which is not or only to a small extent miscible with water. It is also characteristic that the silicon carbide, boron carbide, silicon nitride and / or silicon is dry pre-ground in a vibratory mill at high acceleration or in a jet mill and optionally the subsequent Naßfeinstmahlung done in a stirred mill or a vibratory mill with Stahlmahlkörpern. Due to the intensive comminution the foreign phases are exposed, so that thereby the chemical cleaning is made possible. It is also essential to the invention that the settling of the solid from the suspension and the decantation of the aqueous phase take place in a centrifuge.

It is essential to the invention that the cations are exchanged for H ⁺ ions and subsequently optionally the anions for OhT ions in the solid suspension by addition of cation exchangers, the order of addition of cation and anion exchangers being selectable or else a mixture of cations - And anion exchangers can be added. It is also possible that the treatment of the solid suspension with ion exchangers takes place only after oiger leaching stage. By using the ion exchangers, practically complete removal of the dissolved impurities and the residual ions of the leaching agent is achieved

 The invention will be explained in more detail below with reference to FIG. 3 Aucführungsbeispielen.

Embodiment 1

After the Acheson process produced a-silicon carbide grain size 0 to 100 .mu.m was dry pre-ground in a pot vibration mill for 1.5 hours with a Mahlkörperfüllung of 80Vol .-% steel balls and a Schwingungsamplitute of 7.5 mm, then in a stirred ball mill for 40 min at a Solid: Water ratio of 1: 1 and a Mahlkorperfüllung of 60VoI .-% steel balls bsi high stirrer speed milled and dried. The dry cleaning of the ground product was carried out by leaching with a hydrofluoric acid-nitric acid-water mixture, in which the solid was added to a content of 250g / l and treated with stirring. After centrifuging the suspension and decanting the leaching solution, the settled solid was first dispersed in dilute hydrofluoric acid and then in deionized water. The washings were each separated by centrifugation. Finally, the solid suspension was added to a coarse-grained cation exchange resin loaded with H ⁺ ions and stirred. After ion exchange, the resin was separated again by means of a sieve. Subsequently, the ion exchange process in the suspension was repeated with a coarse-grained anion exchange resin loaded with OH.sup. + Ions. At the end, the purified suspension was dewatered and the SiC was dried.

The following results were achieved:

characteristic value in mVg starting product inventively in pm treated SiC Sbet in% by weight 0.2   5.3 deodorant Inma .-% 63 0.7 Fe Inma .-% 0.32 0.02 Ca in% by weight 0.056 0.03 al 0.47 0.02 O ₂ 0.37 0.4

Embodiment 2

RoIi-Si ₃ N ₄ was dry pre-ground in an opposed jet mill at an operating pressure of 0.4 MPa and a throughput of 10 kg / hr, and then vortexed in a stirred ball mill for 45 minutes at a solids to liquid ratio. 1: 1, a Mahlkörper'üllung of 50% steel ball in n-butano! ground and then dried. The chemical cleaning was carried out by leaching with a hydrofluoric acid-nitric acid-water mixture, in which the solid was added to a content of 250g / l and treated with stirring. After centrifuging the suspension and decanting the leaching solution, the settled solid was first dispersed in dilute hydrofluoric acid and then in acetone. The washings were each separated by centrifugation. Finally, a mixture of coarse-grained H ⁺ -loaded cation exchange resin and coarse-grained OH ~ -loaded anion exchange resin was added to the solid suspension and stirred. After ion exchange, the exchange resin was separated by means of a sieve. At the end, the dispersant was separated from the purified suspension and the Si ₃ N ₄ dried.

The following results were achieved:

characteristic value inmVg starting product inventively in pm treated Si ₃ N ₄ Sbet in% by weight 0.1 12.1 d _M in% by weight 0.45 Fe in% by weight 0.1 0.03 Ca in% by weight 0.04 0.02 al in% by weight 0.05 0.02 O ₂ 1.1 ... 1.4 1.5 Si 1.0 0.08

Embodiment 3

ROh-Si ₃ N ₄ from technical Si (Si metal Si-96-0.3) was ground and purified analogously to Example 2.

The following results were achieved:

characteristic value starting product inventively treated Si ₃ N ₄ Sbet in mVg 0.1 16.1 dgo in μιη 250 0.68 Fe inMa .-% 1.85 0.03 Al in% by weight 0.2 0.02 Ca inMa .-% 0.2 0.02 O ₂ in% by weight n.d. 1.5

The invention has the following advantages over the prior art:

- Use of more contaminated starting material possible

- Shortening of grinding time

- Lower demands of occupational health and safety in the Mahlu.ig when using water without the addition of antioxidants and surfactants as grinding liquid! tit

- Lower consumption of washing solution and washing water

- lower solids losses during dry cleaning

- Ensuring the virtually complete removal of the ions from the suspension

- Shortening of treatment time during dry cleaning

Claims (9)

1. A process for the production of fine-grained sintered silicon carbide, boron carbide, silicon nitride and / or reactive silicon with Fe, Al and Ca contents of <0.15Ma .-%, wherein the coarse-grained starting material by per se known methods of comminution and Classification is prepared and then the cleaning of Feinstmahlprodukte by wet chemical treatment with leaching agents and the separation of the dissolved impurities by washing the solid, characterized in that the silicon carbide, boron carbide, silicon nitride and / or silicon dry and / or wet milled at high stress intensity is used as the grinding liquid in the wet grinding of Silici carbide, boron carbide and / or lower quality Siliziumnitrid Wasssr without the addition of surfactants and antioxidants and in the wet grinding of silicon nitride high quality and silicon organic liquids, and that as a leaching w aqueous solutions of mineral acids or mineral acid mixtures and / or alkali hydroxides are used, the dissolved impurities are separated from the solid by filtration and washing with pure leachant and subsequently with deionized water or so that after settling of the solid, the leach solution is decanted and the settled solid at least once dispersed in pure leachant and after settling of the solid, the wash solution is dispersed, the settled solid then at least once in deionized water and / or mixed with water-miscible organic solvents and decanting the sediment after settling the solid, the settled solid then in deionized water and / or water-miscible organic solvents is dispersed and coarse-grained ion exchangers are added to this suspension, after replacing the dissolved impurities and foreign ions in the suspension against H ⁺ - and / or OH ~ ions are separated from the purified suspension, and the purified solid is finally dehydrated and / or dried. 2. The method according to claim 1, characterized in that the silicon carbide and boron carbide used as a starting material, a comparatively high proportion of foreign phases in the range of 0.1 to 0.5Ma .-% Fe, 0.1 to 5Ma .-% Al and 0 , 01 to 1 wt .-% Ca, the silicon nitride a relatively high proportion of foreign phases in the range of 0.1 to 2Ma .-% Fe, 0.1 to 0.3 Ma .-% Al and 0.01 to 0.3Ma % Of Ca and the technical silicon contains a proportion of foreign phases up to 3% by mass of Fe, up to 0.3% by mass of Al and up to 0.3% by mass of Ca. 3. The method according to claim 1, characterized in that the organic grinding liquid used in the wet grinding is not or only to a small extent miscible with water. 4. The method according to claim 1, characterized in that the silicon carbide, boron carbide, silicon nitride and / or silicon is dry pre-ground in a vibratory mill at high acceleration or in a jet mill and optionally the subsequent Naßfeinstmahlung in a stirred mill or in a vibrating mill with Stahlmahlkörpern. 5. The method according to claim 1, characterized in that the settling of the solid from the suspension and the decantation of the aqueous phase take place in a centrifuge. 6. The method according to claim 1, characterized in that in the solid suspension by addition of cation exchangers first the cations against H ⁺ ions and subsequently optionally the anions by addition of cation exchangers, first the cations against H ⁺ ions and subsequently optionally the anions by addition of anion exchangers, the anions are exchanged for OH ~ ions. 7. The method according to claim 1, characterized in that in the solid suspension by the addition of Anionenaustsuschern first the anions are exchanged for OH ~ ions and subsequently optionally by the addition of cation exchangers, the cations against H ⁺ ions. 8. The method according to claim 1, characterized in that the solids suspension is added to a mixture of cation and anion exchangers. 9. The method of claim 1,6,7 and 8, characterized in that the treatment of the solid suspension with ion exchangers takes place only after a leaching.