SU833377A1 - Method of producing metallic powder - Google Patents

Description

(54) METHOD FOR PRODUCING METAL POWDER

This invention relates to metallurgy powders, in particular to the production of metal powders,. Electroerosion is known for producing fine powders of metals, based on the fact that a spark discharge in a liquid causes the material of the electrodes to melt and splash at the point of contact. Microscopic metal droplets form a fine powder that is carried by the flow of a liquid. It is filtered and dried. In order to achieve repetitive discharges, it is necessary that a short circuit does not occur between the electrodes and at the same time that the gap between the electrodes is not too large, but sufficient to break down the applied electrical voltage | 1. The disadvantage of this method is low productivity. Closest to the present invention is a method for producing powders, in which pieces of metal to be dispersed fall asleep, with two electrodes obliquely immersed in a liquid so that the distance between their lower ends is less than the distance between the edges. A fluid is pumped from the bottom up. When voltage pulses are applied to the electrodes at the points of contact between each other and from the electrode, spark discharges occur in the liquid, dispersing the metal of both the pieces and the electrodes. The discharge occurs mainly at the lower ends of the electrodes. As they wear out.} Of the ends of the electrodes, they are fitted to the reactor with spring-loaded pushers, which ensures that the operation of the reactor is unaffected. To prevent contamination of the product, the electrode array is made from the same material. from which I made pieces of dispersible metal. The resulting powder is transported by the flow of liquid, then it is filtered and dried. In order to prevent metal pieces from sticking together, they are periodically mixed with a fluid flow, increasing its speed for a short time. As a result of increasing the fluid velocity for a short time, its consumption is relatively small f2. The disadvantage of this method is that only metals that form on its surface an oxide film with high contact resistance (aluminum, zinc J. Spark discharge between the pieces of metal in this method then occurs that the surface oxide film forms a dielectric gap between the contacting pieces, preventing short circuits. If metals that do not form a dielectric surface film with high contact resistance (stainless steel, nickel, silver, etc.) are dispersed in this way, then the contact resistance of the circuit is too small, therefore the probability of short circuit between the electrodes increases and the probability of spark discharges decreases as a result It is often repeated short circuit performance dispersing It appears small and the energy consumption per unit product large. The purpose of the invention is to improve the performance of dispersing corrosion-resistant metals and alloys. The aim is to achieve that in a method for producing a metal powder that includes electroerosine dispersion of metal particles between the electrodes in running water and subsequent separation of powder particles from the pulp, the metal particles are dispersed between aluminum They are treated with an alkali or acid before discharging the powder, and the dispersion is carried out in the presence of aluminum particles. When 8 4 at least one aluminum electrode is included in a discharge circuit consisting of particles of any metal, the oxide film covering this electrode prevents the occurrence. in the discharge circuit of a short circuit, even if the contact resistance between all other metal particles between the electrodes is absent, the result is that the short circuit mode between the electrodes is excluded. Loading a mixture of metal particles and aluminum particles between the electrodes further enhances the contact resistance of the discharge circuit, reduces the likelihood of local short circuits between the individual particles in the reactor and increases the uniformity of dispersion of all the metal particles. The method is carried out as follows. Metal particles to be dispersed or a mixture of metal particles and aluminum pieces in a weight ratio of metal: aluminum (9-1): (1-1), respectively, are loaded into the reactor with electrodes made of aluminum. Water is pumped through the reactor to remove the electric erosion products and cool the reactor during operation. The electrodes are supplied with voltage pulses from a current generator. At the same time, at the points of contact of the particles with each other and with the electrodes, spark discharges occur in the water (Particle) in the reactor are mixed either periodically with a fluid flow, for which periodically briefly increase its velocity, or continuously using a mechanical agitator or rotating the reactor. A stream of water carries pulp out of the reactor consisting of an aluminum hydroxide gel with a dispersed metal powder suspended in it and puffs of hydrogen formed during the interaction of the dispersible aluminum with water to form aluminum hydroxide. From the reactor, the pulp enters the settling vessel, in which hydrogen is separated and removed by blowing the vessel with nitrogen or air. Then, the pulp is separated by filtration from water, which is recycled. An alkali or acid solution is added to the resulting paste with a humidity of 80-90% and the mixture is stirred while heating until complete dissolution of aluminum hydroxide. The alkali or acid is chosen depending on the metal of the powder so that the aluminum hydroxide gel is dissolved in it and the metal is not. The aluminum hydroxide gel, obtained by electrically aerosolized dispersion of aluminum in water, dissolves with almost all the liquor and acids without sediment, which ensures the complete removal of aluminum hydroxide during the subsequent washing of the powder with water. The resulting aluminate solution is separated from the metal powder and sent to extract from it the active aluminum hydroxide, which is a valuable by-product, used in chemical industry. The wet powdered metal is mixed with pure hot water, the mixture is neutralized with acid or alkali and separated from the liquid. Then the powder is washed with hot water from salt residues, separated from water and dried. The result is a pure metal powder with a dispersion of 0.01-10 microns with spherical particles. Example 1. A reactor with flat aluminum electrodes (iOOx.OO mm) lowered into the reactor by an angle of 30 ° to the vertical (growing angle Bcipa electrodes 60) and with a distance between the lower ends of the electrodes 50 mm is loaded with 2 kg of stainless steel particles St 118N9T with dimensions of 3-5 mm. Loading is performed up to 1/3 of the height of the electrodes (70 mm). A flow of water at a flow rate of 0.5 m is periodically fed upwards through the strainer bottoms. Periodically (once per minute) the flow rate of water is increased to 10 m / h for 5 s. In this case, a flowing fluidized bed appears in the reactor, mixing the particles. A voltage pulse of 600 V is applied to the electrodes with a pulse repetition rate of 5 kHz from a 30 kW generator. In this case, spark discharges between particles in water arise in the reactor. The pulp carried out by the flow of water from the reactor is collected in a 1-m-settling vessel, which is purged with nitrogen. Then the pulp is filtered on the press filter from the water, which is returned to the cycle. The result is a paste with a humidity of 80%, consisting of a mixture of stainless steel powder and aluminum hydroxide with a 2: 3 ratio (calculated on the dry matter). Take 1 kg of the obtained wet paste and mix with 2 liters of 20% sodium hydroxide at 70-80 ° C and stir the mixture for 1 hour until the aluminum hydroxide gel is completely dissolved. The solution is separated from the powder in a centrifuge. The obtained wet powder is mixed with 1 liter of hot water and the mixture is neutralized with hydrochloric acid. Then, the powder is separated from the liquid by centrifugation and washed three times with water, for which the powder is alternately mixed with 1 liter of hot water, stirred for 10 minutes, and separated from the water in a centrifuge. The resulting powder is dried in a stream of air at 100-150C. The result is 80 g of stainless steel powder with a dispersion of 0.01-10 microns with spherical particles. Example 2 A mixture of stainless steel particles St 1XI8H9T (1 kg) and aluminum particles (1 kg) is loaded into the reactor described in example 1. All other operations are carried out as in example 1. Example 3. The reactor described in example 1 load 2 kg. Particles of iron brand Armco. All operations were carried out as in Example 1, with the difference that the aluminum hydroxide gel was dissolved in a 20% potassium hydroxide solution. As a result, iron powder is obtained. Example A. A mixture of particles of iron (1.7 kg) and particles of aluminum (0.3 kg) is loaded into the reactor described in example 1. All other operations are carried out in the same manner as in Example 3, Example 5. 2 kg of nickel particles are loaded into the reactor described in Example 1. All operations are carried out as in Example 1, with the difference that the aluminum hydroxide gel is dissolved in a 20% hydrochloric acid solution, and neutralization of the water of the first wash is carried out with sodium hydroxide solution. The result is nickel powder, Example. A mixture of nickel particles (1.2 kg) and aluminum particles (0.8 kg) is loaded into the reactor described in example 1. All other operations are carried out as in Example 1.

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Example 7. To disperse tungsten having a density of 19.1 g / cm, the reactor described in Example 1 is unsuitable, since the limiting flow rate of water (l5) developed in it is insufficient for mixing tungsten particles, therefore, tungsten particles mm) in an amount of 1 kg is dispersed in a reactor consisting of a 80 mm length vinyl-plastic pipe with two aluminum electrodes at its ends. The interelectrode distance is 100 mm. The pipe is filled with particles no larger than 1/1 of its volume, horizontally and continuously rotates around an axis. At the same time, the particles loaded into it are mixed. There are holes in the electrodes, through which water is supplied to the reactor from one end (Yu l / h), and pulp flows from the other end.

The electrodes are supplied with voltage pulses of 300 V with a repetition rate and J pulses 2 kHz from a 1 kW generator. The pulp is collected in a vessel with a capacity of 10 liters and defended for 6 hours while it is not left out of the hydrogen pulp. Then the pulp is filtered from the water on a vacuum filter. The result is a paste with a moisture content of 85%, consisting of a mixture of tungsten powder and aluminum hydroxide with a ratio of 1: 1, respectively (in terms of dry substance). Then take 1 kg of the resulting wet paste and mix it with 2 liters of 20% potassium hydroxide solution. The mixture is stirred for 1 hour at 70-80 ° C until the aluminum hydroxide gel is completely dissolved. Next, the operations are carried out as in Example 1. As a result, 75 g of rolfram powder are obtained.

Example 8. In the reactor described in example 7, load a mixture of parts of tungsten (900 g) and aluminum particles (100 g). All other operations are carried out as in Example 7.

Example 9, In the reactor described in example 7, load 1 kg hour TIC alloy POS-40, containing 40 (

eight .

wt.% tin and 60 wt.% lead. All operations are carried out as in Example 7. The result is a powder from POS-40 alloy.

Example 10 A mixture of alloy particles is loaded into the reactor described in example 7. POS-40 (900 g) and aluminum particles (100 g). All other operations are carried out as in Example 7.

The values of the measured specific energy consumption of the generator for dispersion and dispersion performance, proposed and in a known manner are presented in the table.

The expected economic effect from the implementation of the proposed method for producing nickel powder, for example, is determined as follows.

The initial raw material - nickel LF (GOST-849-70) - costs 3400 rubles / ton. The power consumption for dispersion is 20 kW. h / kg When the cost of electricity is 1 cop. per 1 kWg h this corresponds to 200 rubles per ton of powder. In addition, 0.5 tons of aluminum worth 1000 rubles per ton and 4 tons of sodium hydroxide (NaOH) worth 23 rubles per ton are used to prepare 1 ton of nickel powder. The total cost of raw material for the preparation of 1 ton of powder is 4820 rubles. Taking into account the cost of the entire process, the cost of nickel powder obtained by the proposed method is no more than 5500 rubles / ton. -02 (GOST 14086-68), is 11,100 RUR / t. Therefore, the economic effect from the introduction of the proposed method is 5,500 rubles / ton.

Thus, the proposed method allows increasing the productivity of dispersing corrosion-resistant metals and alloys that do not form a dielectric film with high contact resistance on their surface.

Claims (2)

Claim 1. A method for producing metal powder comprising a dispersion of spark erosion in flow vo de metal particles ₄₀ between the electrodes: and subsequent vvdelenie of pulp powder, characterized in that, in order to increase productivity dispersing _corrosion-45 onnostoykih metals and alloys, the dispersion of metal particles is carried out between aluminum electrodes, and the pulp is treated with alkali or acid before powder separation, 2. The method according to nJ, characterized in that the dispersion is carried out in the presence of aluminum particles.