DE880132C - Process for the production of metal powder - Google Patents

Description

As is known, metal powder, particularly iron powder, is nowadays produced on a large scale by attrition λ'οη hydrogen-containing electrolyte iron or a other similar metallic product in ball mills or by pulverization in vortex mills made of coarser, malleable metal granulate. There is a disadvantage to this method then that the material of the mills, which consists of a hard alloy or hard ceramic mass,

ίο like porcelain, is mixed into the metal powder will.

These disadvantages are avoided in powder production according to the present invention. The procedure persists in that one made with anodes, which consist of the pure or impure metal, in powder form is to be, the melt or the anhydrous solution of a salt of a in relation to this metal less noble Metal or a more electropositive radical.

The cathode should preferably also consist of the metal which is to be produced in powder form. The electrolysis, if it is to be carried out at high temperature, is preferably carried out in a double-walled one and / or a double-bottomed metallic electrolysis vessel carried out, the gap is kept filled with a reducing gas. That The inner vessel consists of or is coated with the metal that is to be pulverized. To the This metal can also be replaced by the noblest constituent of it, provided it is an alloy in powder form should be produced. You can also connect the electrolysis vessel to the cathode. In the electrolysis vessel One electrolyzes a molten salt or an anhydrous salt solution, which is called electropositive Component contains a metal or more metals or radicals that are less noble than the metal that to be produced in powder form. Find an electronegative component as an electronegative component

Basic material or an electronegative radical, preferably a halogen or one of another electronegative Basic substance and a halogen built-up radical, application.

As a less noble metal than z. B. Iron are preferred in the manufacture of iron or powder from metals with the same heat of formation in halogen compounds potassium, sodium, barium, Calcium or magnesium and as an electronegatiyer

ίο constituent fluorine, chlorine or bromine or an electronegative radical, e.g. B. SiF ₆ or BF _{4 is} used. These electrolyte salts, which contain a less noble metal or a more electropositive radical than the metal to be pulverized, can also occur in various stages of saturation, but not in such a way that they are partially reduced by the metal to be pulverized, or under such conditions that the salt which is newly formed during the electrolysis and which is in a lower saturation stage is oxidized, as a result of which concentrations of the ions of the metal to be pulverized which are unsuitable for powder formation arise or the resulting powder is oxidized. An example of a compound that meets these requirements is vanadium trichloride in relation to silver with the exclusion of air. During the electrolysis of VCl ₃ , V-metal is formed at the cathode, which reduces VCl ₃ to VCl ₂ . From VCl ₂ in melt or solution, AgCl is reduced to Ag, whereby VCl _{3 is formed} back. VCl ₄ and VCl ₆ , on the other hand, cannot be used since they are reduced _{from Ag to VCl 3.}

To avoid contamination of the metal powder by absorbing sulfur and phosphorus it is preferable to use pure salts made from these substances.

In order to avoid contamination at all, it is important that both the anode and the cathode consist of such pure metals that are desired in powder form, e.g. B. electrolyte iron. A possible content of hydrogen in the electrolyte iron does not cause any disadvantage, since the hydrogen is made free by electrolysis.

When producing pure metal powder from impure metals, anode and cathode are useful separated by a diaphragm.

To prevent the powder from picking up oxide during its manufacture in the molten salt and in order to avoid the formation of larger metal powder it is important that both the anode and also the cathode, also the bath vessel and the electrolyte salts are free of oxides or other compounds of the metal or alloy intended for pulverization, so that a preceding Annealing of the apparatus and electrodes in a hydrogen atmosphere can be useful.

In addition to treating the device and the electrodes with hydrogen, there are further measures to avoid oxidation and partial gasification of the Pulvtrs advantageous by z. B. the Electrolyte one or more such metals, which are less noble than the metal from which the powder is made is to be produced, adds in metallic form, which theoretically all conceivable possibilities for Oxidation of the powder can be eliminated during manufacture.

To illustrate the process, the pulverization of iron in a molten salt is used, for example described.

70 Example 1

Pulverization of iron

The aforementioned double-walled and double-bottomed electrolysis vessel is preferably with a Mixture of potassium and sodium chloride, which is melted down, whereupon the vessel is filled with a tightly fitting lid is covered. In the cover there are feed-through tubes for the electrodes and gas supply pipes or gas discharge pipes attached. The electrodes become as tight as possible attached to each other.

The decomposition products produced during electrolysis react with one another in the melt in such a way that that sponge iron or iron powder is deposited on the cathode; a division occurs into dust-fine powder, whereby depending on the hold of the metal a larger or smaller part of the resulting Sponge iron or iron powder falls on the bottom of the electrolyzer.

Depending on whether the sponge or powder is deposited on the cathode, the product will scraped off to avoid short circuits, which is achieved by influencing a seal in the Electrolysis room introduced, externally influenceable scraper or by using rotating Cathodes can be achieved, which cooperate with a scraping device.

Before the electrolysis, the air is removed from the apparatus by means of a hydrogen stream expelled by oxidations of the powder and the apparatus to eliminate the formation of coarse powder.

It has been shown to be expedient, especially when producing iron powder from electrolytic iron anodes, to give the electrode space below the electrodes a lower temperature than in the electrolysis zone in order to prevent the resulting powder from sintering together. A salt bath with a low melting point is preferably used, which has approximately the following composition: KBr + NaCl + BaCl ₂ , whereby any temperature difference between the electrolysis zone and the floor space can be achieved by extending the electrolysis vessel below the electrodes.

By using anodes made of different metals, but each one for itself, such as Iron, chromium and "nickel" are obtained with a suitable current density on the various anodes an alloy e.g. Stainless steel in the form of powder deposits on the cathode.

The method is particularly useful for production of iron powder, chrome steel powder and stainless steel powder, but can also be used to advantage Manufacture of powder from other metals, e.g. B. for the production of nickel, chromium and copper powders be used.

Further exemplary embodiments relating to the production of powders from copper, Nickel is given to stainless steel, chrome and soft iron. In all manufacturing processes an electrolysis vessel with double walls and a double bottom, i.e. an inner vessel with a smaller one Cross-section used in an outer vessel with a larger cross-section. Near the bottom of the outer vessel made of a refractory material

ίο or made of aluminized iron, hydrogen is introduced into the space between the walls. The hydrogen is discharged at the top. Both vessels have flange connections, the seal is made by one between the Flanged sealing ring. The cover, which is also sealed with a sealing ring, is with continuous tubes for electrodes and powder scrapers. The powder scrapers are insulated from the surrounding pipes; Everyone

Feed-through pipes are sealed by means of stuffing boxes. On the lid are pipes for introducing hydrogen into the inner vessel and for discharging the Provided hydrogen from this vessel.

Before the start of the electrolysis, the air is expelled from the inner vessel. In the same vessel Cathodes can be provided in the form of one or more sieve bottom containers, or the inner vessel serves as a cathode itself. The purpose of the sieve bottom containers is to collect the metal powder that has formed.

The molten salt flows when the sieve bottom container is lifted for the most part, while the powder remains in the container.

Example 2

Pulverization of copper

Outer diameter of the outer vessel 184 mm, inner diameter of the outer vessel 170 mm, outer diameter of the inner vessel (bath vessel) 165 mm, inner diameter of the inner vessel 155 mm. The inner vessel contains a pressed-in copper container with the outer diameter of 154 mm and an inner diameter of 153 mm.

Introduced molten salt BaCl ₂ +

KBr + NaCl 17.4 kg

Height of the molten salt 350 mm

Specific weight of the molten salt

at i8 ° C ₃ o ₅

Melting point of the molten salt 490 ° C

! temperature of the molten salt. . about 508 to 550 ⁰ C

Mean temperature of the molten salt. . 520 ⁰ C

¥ # luäinen the molten salt at 500 ⁰ C 6.3 1
Iblosfen dimensions, 8 χ 60 χ 280 mm

Copper sheet

Anode weight before pulverization 1.2 kg

Anode area, total ο Λ? ^

Anodic surface. (effective in the bathroom) 3 ^ 75 dm ²

Anode length under the bath surface. 250 mm

_{Anode distance} from the floor I20 mm

Anode weight loss on pulverization; 0.545 kg

Anodic current density 14 amps / dm ²

Cathode made of two bars of Cu, diameter 10 mm, length less than Surface of molten salt 250 mm,

Surface 1.57 dm ²

Cathodic current density 30 Amp./dm ²

Distance between electrodes 30 to 40 mm

Pulverization time 11.5 hours

Amp-hours 542.45

Amperage 47.6 amps.

Bath voltage 2.16 V

Current yield 84.3 ° / "

Obtained mixture of copper powder

and salt 2.64 kg

Copper powder obtained from the mixture 0.545 kg

Number of powder swabs 16

80 Example 3

Pulverization of nickel

Salt bath 2 KBr + KCl + NaCl + 2 NaF 8.8 kg

Height of the molten salt 250 mm

Specific weight of the molten salt

at 18 ° C 2.5

Melting point of the molten salt 475 ° C

Volume of the molten salt at 500 ⁰ C. 4.2 1

The molten salt temperature is around 507 ° C

Anode dimensions, five pieces 2 X 60 χ 250 mm made of sheet nickel

Anode area (effective in the bath) 1.96 dm ²

Anode length below the surface ... 160 mm

Anode distance from the floor 90 mm

Loss of anode during pulverization. 0.678 kg

Anodic current density 75 Amp./dm ²

Cathodic current density 12.5 amps / dm ²

Electrode gap, 37.5 to 62.5 mm

Anode weight before pulverization i, 335 kg Anode weight after pulverization 0.657 kg Anode weight loss on pulverization 0.678 kg

The pulverization takes 5 hours.

Amp-hours 750

Current 150 amp.

Bath voltage 3.58 V.

Current efficiency 85.4%

Obtained mixture of nickel powder

and salt 2.69 kg

Nickel powder obtained from the mixture 0.678 kg

Example 4

Stainless steel pulverization

The pulverization was carried out using the same molten salt as in Example 3. Anode dimensions:

Diameter 38 mm

Length 295 mm

Anode weight before pulverization 2.635 kg

Anode surface (in the bath at the beginning

of the experiment effective) 2.03 dm ² ia, s

Anode length below the bath surface ... 160 mm

Anode distance from the floor 90 mm

Anode weight loss on pulverization 0.625 kg

Anodic current density 92.6 Amp./xlm ²

Distance of the anode from the wall of the

Cathode 48.5 mm

Distance of the anode from the bottom of the

Cathode 90 mm

Cathodic current density 14-77 Amp./dm ²

Pulverization time 9 hours

Ampere hours 1584

Current 176 amps.

Bath voltage 3.28 V.

Current yield 42%

Preserved mixture of stainless

Steel powder and salt 2.635 kg

Metal powder obtained from the mixture 0.625 kg

The temperature of the pulverization ot about 484 ⁰ C

ao (powder scraper not used.)

Example 5

Pulverization of chromium * 5

Salt bath KCl + KF 7.6 kg

Height of the salt bath 250 mm

Specific weight of the molten salt

at 18 ° C 2.175

Melting point of the salt melt 480 ⁰ C

Volume of the molten salt at approximately

600 ° C 4.2 1

Temperature of the molten salt about 600 ° C

Anode material, pieces connected by welding with

the dimensions 30 χ 30 χ 300 mm

Anode area, effective 2 dm ²

Anode length below the bath surface 160 mm anode distance from the wall of the

Cathode 46.5 to 52.5 mm

Anode distance from the floor 90 mm

Anode weight loss on pulverization 0.582 kg

Anodic current density 29 Amp./dm ²

Cathodic current density 5 Amp./dm ²

Pulverization time 11.5 hours

Amp-hours 667

Amperage 58 amps.

Bath voltage 1.74 V

Current yield 85.2 ° / "

Obtained mixture of chromium powder

and salt 2.8 kg

Chromium powder obtained from the mixture 0.58 kg

(Powder scraper not used.)

Example 6

Pulverization of soft iron

The pulverization was carried out in a non-nickel-plated vessel made of soft iron (make Sandviken 2 M. F.) executed.

Molten salt KCl -f- NaCl 7 kg

Height of the molten salt 250 mm

Specific weight of the molten salt

at 18 ° C 2.0

Melting point of the molten salt approximately 590 ^° C

Temperature of the molten salt 713 ° C

Anode material, two pieces 5 60 χ 240 mm (Sandviken

2 M. F. sheet) 1.1 kg

Anode area, effective 1.96 dm ²

Anode length under the bath surface 160 mm
Anode distance from the cathode bottom 90 mm anode distance from the cathode wall 37.5 to 62.5 mm

Anode weight loss on pulverization 0.314 kg

Anodic current density 75 Amp./dm ²

Cathodic current density 12.5 amps / dm ²

Powdering time 3 hours

Amp-hours 450

Current 150 amp.

Bath voltage 3.6 V

Current efficiency 66.1 ° / ₀

Obtained mixture of iron powder

and salt 1.150 kg

Fe powder obtained from the mixture 0.314 kg

(Powder scraper not used.)

Claims (6)

PATENT CLAIMS: 1. A process for the production of metal powder, characterized in that one with anodes, which consist of the pure or impure metal to be produced in powder form, which Melt or the anhydrous solution of a salt of a less noble metal in relation to this metal Metal or a more electropositive radical. 2. The method according to claim 1, characterized in that that a melt of a halogen salt, preferably an alkali chloride, is electrolyzed. 3. The method according to claim 1, characterized in that that one has an electrolyte made up of oxides or other compounds of the anode metal with the exception of that at the anode salt formed during the electrolysis is free, electrolyzed. 4. The method according to claim 1, characterized in, that the electrolysis is carried out with a diaphragm arranged between the cathode and anode. 5. The method according to claim 1, characterized in that that the electrolysis takes place in a closed space with an indifferent or reducing gas, e.g. B. hydrogen gas is kept filled. 6. The method according to claim 1, characterized in that that the electrolysis takes place in an apparatus with double walls and / or double bottom, its space with a reducing gas, e.g. B. hydrogen, is carried out. I 5204 6.