DE1024937B - Process for the production of powdery silicon or boron - Google Patents

Description

Process for the production of powdered silicon or boron die The invention relates to a method for the direct production of powdered elemental Silicon and boron in a pure, especially oxygen and carbon-free state, for the direct production of silicide and boride hard materials without a comminution process can be used. The difficulties in producing the purest boron and Powdered silicon is known. Mostly one assumes impure, mostly carbonaceous ones Pre-products that are subjected to a grinding process. This crushing process always causes oxidation on the surfaces. It is also known that The storage of ground powder absorbs a high degree of oxygen. Even the production of the finest hard material powders, as they are not for the production brittle sintered bodies would be required, can be done by grinding coarse grains Reaction material can only be achieved very imperfectly. Also due to the wear and tear of the Mill material, these powders are heavily contaminated, and it must then the most diverse washing processes are carried out in order to achieve a purer, To obtain sinterable powder. However, experience has shown that oxygen uptake can not completely avoided at all - ,, verden.

The invention., The production of powdery silicon and boron in a pure, especially oxygen and carbon-free state with economical portable means possible.

This is achieved according to the invention in that the halides of silicon or boron with a deficit of diluted mercury alloys the alkali and / or alkaline earth metals are reduced and the floating, powder interspersed with salt by-products and mercury particles by dissolving and / or These by-products can be removed by evaporation.

This reduction takes place at room temperature and is possible despite the reduction in the reducing power of the alkali or alkaline earth metals due to dissolution in excess mercury.

The reduction at the lowest possible temperatures is particularly important in the case of the volatile halides, because reductions at higher temperatures under pressure. In no case were low-value intermediates found with incomplete reduction.

Silicon and boron show when the method is carried out according to the invention no affinity for mercury. They swim in the mercury together with the as a finely divided alkali or alkaline earth chloride by-product.

When the reduction is carried out at low temperature, there is an intimate one Mixing of the liquid reactants is necessary. If you reduce z. B. S 'C14 at 25 ° C with 0.5a / a sodium amalgam while stirring at a speed of 600 / minute, so the entire reaction mixture is completely reacted in 15 minutes. One lets against it the mixture is under occasional shaking, so the implementation needs the same Temperature about 10 hours until the sodium amalgam has completely reacted.

B C13 can e.g. B. at -I-5 ° C with stirring in 2 hours will. At 50 ° C, however, in a closed vessel, the reaction is shaking completed in minutes. The implementation takes place with the formation of a pasty Porridge, which is a suspension of the reaction products in the residual amalgam. With an equivalent approach, this suspension remains in place even after the reaction has ended. It it was found, however, that the reduction products float after Completion of the reduction, d. H. after complete consumption of the reducing metal; in the Mercury occurs when a slight excess of the chloride to be reduced is used will. This fact is an important feature of the present invention.

The floating powder is an intimate mixture of finely divided powder Boron or silicon and alkali or alkaline earth chloride and some mercury powder The semi-metals obtained are very reactive. You can either post distilling off the adhering mercury powder directly as active semi-metal powder when diluted with salts in finely divided form to the most varied of reactions be used. That way you can one z. B. produce hard materials. The implementation with oxide-free molybdenum or tungsten powder sets z. B. from 600 ° C, i.e. at unusually low temperatures for hard material formations. It result Hard powder with grain sizes around a few microns. After the salts have been dissolved out with dilute hydrochloric acid, these can be `` purest '' directly without any comminution Powder can be used for the production of sintered bodies.

However, the active boron and silicon can also be heat-treated in the alkali salt will. At 1000 ° C e.g. B. reduced silicon is deactivated at room temperature to such an extent that that it is no longer pyrophoric in the strict sense. While the not heat treated Silicon already burns up at 300 ° C in air to form silica and also under water Development of hydrogen at least until the protective layer has formed capable of decomposing the individual grains, the heat-treated silicon is already stable against water. The salt by-product can thus be dissolved out with water.

The grain sizes of the silicon heat-treated at 1000 ° C are z. B. at 10% less than 2 microns, 10% 2 to 4 microns, 50% 4 to 10 microns, 20% above 10 microns.

Nevertheless, the silicon powder is still very reactive. When glowing in air z. B. it burns at 700 ° C to Si 0z. If you use z. B. Magnesium amalgam As a reducing agent, the salt of the resulting semi-metal powder can be used in a high vacuum be evaporated. In the reduction of boron chloride and subsequent leaching of the For heat-treated goods, care must be taken that the leaching liquid is not alkaline which causes losses under borate formation.

Claims (2)

PATENT CLAIMS: 1. A process for the production of powdered silicon or boron by reducing the halides in question with metals, characterized in that the halides of silicon or boron are reduced with a deficit of diluted mercury alloys of the alkali and / or alkaline earth metals and the floating ones with salt by-products and mercury particles permeated powder are freed from these by-products by dissolving and / or evaporating. 2. The method according to claim 1, characterized in that prior to separation of the salt by-products a heat treatment is carried out on the powders in the molten by-products will.