RU2030972C1 - Method for making dispersed metallic powder - Google Patents

Abstract

FIELD: powder metallurgy. SUBSTANCE: first water solution of alkali is prepared. Then metallic salt is treated with this solution to extract hydroxide of corresponding metal. Extracted metallic hydroxide is filtered and washed. These operations are combined with the milling of extracted material. Further metallic hydroxide is dried and after that recovered to a metal. For this purpose hydrogen is passed through extracted material during its heating to a temperature exceeding the threshold of recovery of metallic hydroxide. EFFECT: enhanced quality. 6 cl

Description

 The invention relates to powder metallurgy, in particular to the production of metal powders, and can be used to obtain dispersed powders of iron, nickel, cobalt, copper, tungsten, molybdenum, etc.

 A known method for producing dispersed metal powder of Nickel (particle size 0.1-2.0 μm), which is as follows (see, for example, Mao Minghua, Tu Taozhi, Gao Wengkao Preparation of ultrafine nickel pewder from slurries of basic nickel carbonate by hydrogen reduction auder pressure // Selec. pap. Eng. Chem and met. (China), 1989 - Beijing, 1990 - p. 50-55).

An aqueous suspension of basic nickel carbonate having the formula: m˙Ni (OH) ₂ ˙NiCO ₃ ˙nH ₂ O is poured into an autoclave. In the liquid phase is reduced in hydrogen Ni ²⁺ ions at a temperature less than 175 ^C and a pressure of at least 25 kgf / cm ^2. The resulting product is filtered, washed and dried in air. However, this method is inefficient, and to increase the speed of the process requires the introduction of an expensive catalyst PdCl ₂ . In addition, the process in a steel autoclave at elevated temperatures and pressures requires special safety measures during operation.

There is another method for producing a dispersed metal powder of copper (particle size 0.2-1.0 μm), which consists in the following. The reaction of carbonate, hydroxide or copper oxide with formic acid produces copper formate with a particle size of approximately 800 μm. The resulting product was thermally decomposed in nitrogen or hydrogen at a heating rate of 3 ° ^C / min and a temperature of 150-300 ^C to produce copper powder. Target copper yield of more than 90%. The resulting powder is washed with water or an organic solvent, adding a substance that prevents the oxidation of copper in the solution. The powder is crushed after dehydration at a temperature of 130 ^o C. However, the grinding operation after dehydration of the product can significantly change the shape and morphology of the powder particles, as well as lead to a significant dispersion of its particle size distribution and change its technological properties. This, in turn, leads to a limitation of the applications of such powders and excludes the possibility of obtaining products with stable properties with guaranteed properties using them.

Another method for producing dispersed metal powder is known (see, e.g., J. Saida, A. Inoue, T. Masumoto. Preparation of ultra-fine amorphous powders by the chemical reduction method and the properties of their sintered products // Mater. Sci . and Eng. a [Pap] 7th Int. conf. "Struct. mater: properties, microstruct. and process", Stockholm, Aug. 13-17, 1990. Pt. 1, 1991-133. - c.771-774 ), which consists in the fact that 0.1 mol of aqueous solutions of salts of iron, cobalt, nickel is treated with 1 mol of an aqueous solution of potassium borohydride reduction reagent (KVN ₄ ), adding it to the solution periodically after 600 s and constantly stirring. The product obtained by the reaction is separated by filtration, quickly dehydrated and washed with a large amount of distilled water, then with acetone and dried in air.

 However, this method also does not allow to conduct the process productively and to vary particle sizes over a wide range, for example, to obtain particles larger than 50 nm. In addition, the accompanying salts, impurities that are not removed during the preparation process, can contaminate the final product or go into wash water, creating environmental difficulties.

 The objective of the invention is the creation of such a method of producing a dispersed metal powder, which would, along with high productivity and process stability, provide the ability to manufacture a wide range of dispersed powders by particle size while maintaining their narrow fractional composition.

 This problem is solved in that in the method for producing a dispersed metal powder, which consists in first preparing an aqueous solution of a reagent, then the metal salt is treated with the resulting solution, then filtered, washed and dried in air, according to the invention, an alkali solution is used as a reagent followed by the production of metal hydroxide, and the filtration and washing operation is combined with the grinding operation of the obtained metal hydroxide, which, after drying in air, is reduced by passing of hydrogen therethrough when heated to a temperature above the recovery metal hydroxide threshold. This allows you to get a wide range of dispersed powders with a narrow fractional composition and various particle shapes from round or ellipsoidal to needle-shaped.

 It is advisable to use a solution of caustic soda as alkali. This makes it possible to reduce the cost of the process by using the widely available and cheap reagent.

 It is possible to use ammonia solution as alkali. This allows you to use for the preparation of aqueous solutions of alkali already prepared with a higher concentration of ammonia solutions produced by industry.

Advantageously the metal hydroxide to metal recovery performed at a temperature above the threshold of a corresponding metal hydroxide on recovery of about 100-400 ^C. This allows to carry out the process at a low temperature, which increases the lifespan and reliability of the equipment and easy maintenance.

 It is desirable to increase the temperature of reduction of metal hydroxide to metal stepwise. This provides the possibility of strict control of the mechanism of ongoing processes and ensuring their reproducibility.

 It makes sense to remove residual moisture during the reduction of metal hydroxide to metal to carry out a stepwise increase in temperature with at least two time delays. This makes it possible to exclude the growth of particles and prevent a change in their composition during the reduction of metal hydroxide due to the exact observance of the equilibrium process conditions.

It is desirable to implement a time delay at a temperature of from about 100 to 160 ^{° C} with a duration from about 30 to 90 minutes, and the other - under the reduction temperature of duration of about 40 to 120 minutes. This allows you to remove residual hygroscopic moisture at the first exposure temperature and to guarantee the completeness of the process of reduction of hydroxide to metal at a second exposure temperature.

 It is advisable to regenerate the dispersed metal by passivation with nitrogen or argon, and during passivation, another exposure time of about 60 to 90 minutes is carried out. This avoids the ignition of metal powder in contact with air and eliminates its oxidation during transportation and storage.

 It is possible to carry out the process of passivation of iron powder in a mixture of argon and air. This allows one to obtain α-Fe particles surrounded by oxide layers, which are characterized by high values of coercive force.

Desirably, hydrogen is used to recover the metal hydroxide to metal had a dew point of about -40 to ^-60 ° C. This process provides increased speed of recovery toward the process expense hydroxide equilibrium shift to the metal and reducing the oxygen content in the final product.

 A patented method for producing dispersed metal powder is as follows. In a separate container, a predetermined concentration of an aqueous reagent solution is prepared. A salt of the corresponding metal is introduced in portions into the prepared aqueous solution. At room temperature, under stirring, a treatment is carried out to obtain hydroxide. The hydroxide is separated from the main solution by filtration, washed intensively, crushed during filtration and washing, removed from the container and the finished product is dried at room temperature in air with periodic stirring. Alkali is used as a reagent; the prepared alkali aqueous solution corresponds to a concentration of about 6 to 15 mol / L. In relation to the amount of salt loaded, the alkali solution is administered with approximately 1.5-2.0 times a single excess relative to the stoichiometric calculation.

However, it is possible to use hydrochloric acid for the same purpose. After processing it ferric chloride FeCl ₃ at 24 hours exposure and subsequent aging at ¹⁰⁰ ° C for one week to give particles Fe ₂ O ₃ and β-FeOOH.

 Similarly, particles of chromium oxide, Al hydroxide, Ti oxide, etc. were obtained (Atsushi Maramatsu, Hiroshi Sasaki. Production of ultrafine particles of metals or metal oxides by wet method and surface properties of particles. // J. Iron and Steel Just. Gap., 1991- 77, N9, pp. 10-17).

 The dried hydroxide is placed in thin layers on mesh trays, heated to a temperature above the temperature of the threshold for the reduction of hydroxide to metal with continuous passage of hydrogen through it. Alternatively, it is possible to treat the hydroxide in suspension at a reduction temperature and a continuous stream of hydrogen. As alkali, you can use widely available caustic soda. Moreover, it can be both in the form of a solid substance, and in the form of an aqueous solution. Along with availability, this alkali does not form complex compounds with processed salts and their transition products.

 It is sometimes advantageous to use an ammonia solution as alkali. Usually, this is convenient in cases where there is no dissolution of the resulting metal in an ammonia solution. Moreover, the resulting ammonium chloride has a high dissolving ability of such toxic elements as zinc, lead, cadmium, which makes the process environmentally controlled.

The reduction of hydroxide to metal is advisable to carry out with a stepwise rise in temperature with exposure in time to remove hygroscopic moisture, for example, 100-160 ^about C, the exposure time of 30-90 minutes

Reducing the temperature below 100 ^{° C} is impractical because it leads to slow down the moisture removal process, the temperature rise above 160 ^{° C} is undesirable because of the intense evaporation, which may lead to caking of the powder.

 Reducing exposure at a temperature of moisture removal to less than 30 minutes is undesirable, since the process of removing moisture does not go completely; an increase in exposure over 90 minutes is impractical from the point of view of the efficiency of the process. At optimal temperature and time parameters, the recovery process is intensified during subsequent heating, since the equilibrium constant of the reaction, determined by the ratio of the partial pressures of hydrogen and water, shifts toward reduction. The second temperature-time exposure is expediently carried out directly at the reduction temperature of the metal hydroxide to ensure the completeness of the recovery process, but the exposure time must be selected taking into account the dependence of the growth of powder particles on the duration of heating.

 To exclude ignition of particles of a metal dispersed powder and to protect it from oxidation during storage, it is advisable to passivate the reduced powder until it comes in contact with air. Moreover, it is convenient to passivate with nitrogen, since the explosiveness of the hydrogen medium used in the reduction of hydroxide is excluded.

 It is possible to carry out passivation in an argon medium, especially in the case when the presence of even small traces of nitrides in solid solutions of the resulting metals is undesirable.

 Sometimes it is advisable to obtain passivation in magnetic mixtures of α-Fe in a mixture of argon and air.

 It is advantageous, from the point of view of the completeness of the process, to carry out another time delay of about 60 to 90 minutes at the passivation temperature.

 Moreover, reducing exposure to less than 60 minutes is unacceptable, since the passivation process does not have time to go through to the end; an increase in exposure of more than 90 minutes is undesirable due to the cost of the process.

It is advantageous to bias the equilibrium of the reaction of the metal hydroxide to restore constants toward restoring apply dehumidified hydrogen having a dew point of about -40 to -60 ° ^C.

Increasing the dew point of more than -40 ^{° C} is limited by the fact that in this case, the recovery process does not pass through and the oxygen content in the final product is increased; lowering the dew point less than ^-60 ° C is impractical because such gas drying difficulties associated with its industrial implementation and thus increasing production costs.

 It is also possible to use sodium formate (HCOONa) to obtain nickel and copper powders from their hydroxides. In the same way, you can get iron powder.

PRI me R 1. For the preparation of 6 mol of a solution of ammonia was taken 0.75 l of ammonia water 25% concentration and 0.8 l of distilled water. 360 g of FeCl ₃ ˙ 6H ₂ O salt was introduced into the prepared 1 L of the solution, which corresponded to the condition of a 1.5-fold excess of alkali with respect to the stoichiometric amount. After 1 h, filtration, 6-fold washing to pH7 and grinding to a particle size of iron hydroxide of 100-150 μm were carried out. Hydroxide with a mass fraction of hygroscopic moisture of 2-10% was separated from the washing solution and dried for about 24 hours at room temperature. The dried hydroxide was reduced in a stream of hydrogen with a dew point of -40 ^{° C} at a temperature of 480 ^C, which is 200 C above ^the threshold of reduction of iron at a hydrogen flow rate of 0.25 m ³ / h. The reduction temperature was increased stepwise. At a temperature of 130 ^{° C} and 980 made by soaking 1.5 and 10 hours, respectively. The particle size of the obtained iron powder is 80-90 nm, the spread is less than 6%. No NH ₄ cations or Cl anions were detected. When the recovery process (5 h) and the temperature drops to 250 ^{° C} overlap hydrogen, allowed to extract at 250 ^{° C} - 60 minutes, filled working space of the furnace with nitrogen and further cooling to room temperature, the powder was carried out under nitrogen.

PRI me R 2. For the preparation of 6 mol of a solution of caustic soda took 240 g of dry alkali and 1 liter of distilled water. 600 g of CuSO ₄ ˙ 5H ₂ O salt was introduced into the prepared solution, which met the condition of a 1.6-fold excess of alkali with respect to the stoichiometric amount, after 1.5 hours filtration was carried out, 6-fold washing to pH and simultaneous grinding to particle size copper hydroxide up to 800 nm. Hydroxide with a mass fraction of hygroscopic moisture of 6% was separated from the washing solution and dried for 24 hours at room temperature. The dried hydroxide was reduced in a stream of hydrogen with a dew point of -40 ^{° C} at a temperature of ^{250 °} C, 100 ° C above ^the recovery threshold copper at a hydrogen flow rate of 0.2 ^m3 / h. At a temperature of 130 ^{° C} and 250 made by soaking 1 hour. Upon completion of the recovery process (5 h) and the temperature drops ^to 200 ° C overlap hydrogen and further cooling of the powder was carried out in a stream of nitrogen to room temperature. The particle size of the obtained copper powder is 46-49 nm, the spread is less than 6%. Na cations and SO ₄ anions were not detected.

PRI me R 3. For the preparation of 15 mol of sodium hydroxide solution was taken 600 g of dry alkali and 1 liter of distilled water. 500 g of NiCl ₂ ˙ 4H ₂ O salt was introduced into the prepared solution, which corresponded to the condition of an approximately 2-fold excess of alkali with respect to the stoichiometric amount. After 1 h, filtration, 6-fold washing to pH7 and simultaneous grinding of nickel hydroxide to 200 nm were carried out. Hydroxide with a mass fraction of hygroscopic moisture of 3% was separated from the washing solution and dried for 24 hours at room temperature. The dried hydroxide was reduced in a stream of hydrogen with a dew point of -50 ° ^C at a temperature of 500 ^C, which is 250 C above ^the recovery threshold nickel at a hydrogen flow rate of 0.25 m ³ / h. At a temperature of 140 ^{° C} and 500 made extracts 1.5 and 1 hour respectively. When the recovery process (4.5 hr) and the temperature drops to 350 ^{° C} overlap hydrogen and further cooling of the powder was carried out under argon. The particle size of the obtained nickel powder is 100-120 nm, the spread is less than 2%. Na cations and Cl anions were not detected.

Dispersed metal powders obtained by the claimed method can be used, for example:
as catalytic additives in various processes, for example, during sintering of doped powder systems;
as anti-friction additives to oils and coolants in metal processing;
as fillers for conductive pastes;
as magnetic carriers in ferrography;
as additives when creating special paints;
as additives that accelerate plant growth;
as substances for the manufacture of protective screens against infrared radiation;
as a ferromagnetic powder for magnetic recording devices, in night vision devices, etc.

 The inventive method for producing dispersed metal powder can be widely used in materials science as activating additives when creating new powder materials with a fine-grained structure; chemistry of paints; electronics as components of pastes in the manufacture of printed circuit boards and the creation of "clean" rooms; in mechanical engineering as additives to lubricating oils and coolants; military equipment for producing materials with nanocrystalline structures and a high complex of physico-mechanical properties, as well as for the manufacture of invisible objects; space - for the manufacture of solar panels and the development of gradient materials; medicine as additives to pharmaceuticals, agriculture as additives to animal feed and fertilizer additives to increase crop yields.

Thus, the claimed method of producing a dispersed metal powder provides the ability to produce powders with a particle size of from about 10 nm to 1 μm with a narrow dispersion of particles in fractions within each batch. The specific surface of such powders can be adjusted from about 3 to 70 m ² / g. The high productivity of the process, due to the combination of filtration, washing and grinding operations, as well as the regulation of the hydrogen reduction process, makes it possible to obtain a relatively cheap product with guaranteed properties. Significant adjustable process parameters make it possible to widely automate it using a computer, which guarantees its stability, and this, in turn, makes it possible to obtain dispersed metal powders with predetermined characteristics. Carrying out the process of producing hydroxide at room temperature creates the conditions for cheaper instrumentation of the process.

Claims (6)

 1. METHOD FOR PRODUCING A DISPERSED METAL POWDER, comprising treating a metal salt hydrate with an alkali solution, filtering, washing, drying the precipitated metal hydroxide, restoring it with hydrogen when heated to a temperature above the metal hydroxide reduction threshold and subsequent passivation of the powder, characterized in that the filtering and washing the hydroxide metal is carried out simultaneously with grinding.  2. The method according to claim 1, characterized in that the heating to a reduction temperature is carried out stepwise.  3. The method according to p. 2, characterized in that to remove residual moisture, stepwise heating is carried out with at least two excerpts. 4. The method according to claim 3, characterized in that the first exposure is carried out at 100 - 160 ^o With a duration of 30 - 90 minutes, and the second at a recovery temperature of 40 to 120 minutes.  5. The method according to claim 1, characterized in that the passivation is carried out with a mixture of argon and air. 6. The method according to claim 1, characterized in that hydrogen for recovery is used with a dew point temperature of -40 to -60 ^o C.