DE941608C - Process for the preparation of disilicides and diborides - Google Patents

Description

Process for the production of, disilicides and diborides The hard materials, Compounds of transition metals from IV. To VI. Group of the periodic table (i.e. Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W) with carbon, nitrogen, silicon and boron and especially the disilicides and Dibori.de have proven to be high-melting, Proven heat-resistant and oxidation-resistant materials. From the known. procedure the implementation is now used to represent this group of compounds. the hard material forming Metals and alloys with vaporous halogen compounds of boron or silicon for the formation of the diborides and disilicides of particular technical interest. By Such "vapor deposition processes" can not only be used for thin parts made of hard material Metals and alloys completely into the desired disilicides or diborides be implemented, but it also succeeds in the boride or silicide formation on the Surface of didker sized metal parts. They also offer the volatile Halogen compounds an easier cleaning option, and you get on this Ways to the purest hard materials free of foreign metals.

However, it has been found that the reactions of the volatile halides with the hard material forming metals and alloys often quite slow and incomplete run and also a locally very different course of the reaction exhibit. At Ader, this requires: Desired complete conversion of the metals .in the hard materials a disproportionately long reaction time.

In the case of layer formations made of hard materials, this fact causes uneven layers Layer thicknesses with all the resulting disadvantages.

According to the process according to the invention, the formation of the disilicides and diboride through. Implementation of the vaporous halides of boron and silicon with the hard material forming metals of the IV. to VI. Group of the periodic table thereby accelerated and made more effective that the volatile halogen compounds before the vapor deposition reaction by reaction with large-area boron or silicon or their alloys activated and then with the metals without cooling implemented. The reaction takes place by passing over the halide stream, preferably in an inert or reducing carrier gas, over boron or silicon in one Heating zone.

It was found that the best activation takes place at high temperatures and the activated chlorides must not be cooled before the vapor deposition reaction, at least not below the temperature of the vapor deposition reaction. Apparently, the catalytic reduction occurs during. the evaporation reaction. favors the figuratively unstable halogen compounds, with a possible thermal decomposition of the halogen compounds being superimposed. As is well known, chain-like silicon chlorides are formed by: Treating silicon tetrachloride with excess silicon. These S, siliconchlori @ de, such as. B. Si2C16, are cleavable at a higher temperature by z. B. C16 slowly disintegrates at 300 ' , rapidly at 80o ° into Si and Si C14. The finely divided Si that forms during this disintegration and the low-value halogen compounds that are formed, which are stable at low temperatures, make it easier to capture the image of the desired metal disiccides.

In addition, the inventive method has: the Advantage that there is circulation of the vapor deposition atmosphere during activation also a regeneration of the evaporation reaction. Halogen or Hydrogen halide permitted. 'The one according to the invention is perfectly suitable Process for the production of easily compressible hard material powder. For this purpose, the hard material forming Metals and alloys in powder form of the desired grain size of the 'treatment exposed. Only on the largest possible exposed surface with constant Renewal of the vapor deposition atmosphere and maintenance of the temperature must be ensured will. The advantage is a slight, even movement of the metal powder. For Such hard material formations aus.den corresponding metal powders could z. B. that so-called; Fluidized bed can be applied with success.

As an example it should be given that at 120o ° molybdenum powder differs from the average Grain size of i, u with H C1-free silicon chlorides activated at 130 ° over silicon powder in a few minutes you can be converted into Mo: can. The obtained disilicide powder can be pressed directly and further processed by powder metallurgy, without prior Comminution, sieving or similar process steps. In this :, way can Advantageous heating conductors, furnace components, protective tubes, nozzles, B @ renn: er heads, parts turbines and internal combustion engines, in short all workpieces are produced, which are used up to temperatures around 17-5o °. Appears particularly cheap the resistance of Mo S12 workpieces to V2 05 corrosion, because this Materials are also used in internal combustion engines operated with crude oil can; without the dreaded accelerated oxidation by slagging occurring.

Claims (3)

PATENT CLAIMS: i. Process for the production of disilicides and diborides of transition metals from IV. To VI. Group of the. Periodic, system of the corresponding pure or alloyed metals through. Reaction with vaporous halogen compounds of silicon or boron, characterized in that the hollow halogen compounds are activated prior to the reaction with the hard material forming metals by reaction with large surface boron or silicon or alloys of these semimetals at a temperature above the reaction temperature of the halogen compounds with the metals and then without Cooling can be implemented with the metals. 2. Method according to Claim i, characterized in that the activation is carried out by transferring of the halide stream, preferably in an inert or reducing carrier gas, takes place via the large-area boron or silicon in a heating zone. 3. The method according to claim i or z, characterized in that the halogen atmosphere is recycled after the reaction with the disilizidurnd diboride-forming metals in the circuit for activation and is thereby regenerated. q .. Process according to claim i or the following claims for - production of compressible disilicide and diboride powder, characterized in that the dis: ilicide and diboride-forming metals or alloys in powder form, preferably with slight movement, are exposed to the action of activated halogen compounds. . Attracted publications: magazine for änorgan. and alpgemeine Chemie, 1937 vol. 232, p. 241 ff; F. E phraim: Inorgan. Chemie, 2nd and 3rd edition 1923, pp. 618 bis. 61g.