RU2625155C1 - Production method of nanostructured powder of the nickel-cobalt solid solution - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method includes the interaction of crystalline slightly soluble nickel and cobalt carbonates with the reducing agent in the form of the aqueous solution of hydrazine hydrate in the concentration of 9.6 wt %.

EFFECT: monophasic powder production that does not contain oxide and hydroxide impurities.

4 dwg, 2 tbl

Description

The invention relates to powder metallurgy, in particular to the field of producing monophasic nanostructured powders of nickel-cobalt (Ni-Co), which may find application as new objects for electronics, the electrical industry, the production of magnetic fluids, as catalysts for the chemical industry, and for targeted drug delivery, in magnetic resonance imaging and biology.

A known method of producing metal nanoscale powders (patent RU No. 2432231, IPC B22F 9/14, B82B 3/00, publ. 10/27/2011) by heating the source metal or at least two metals in an inert gas stream to the temperature of evaporation of the starting metals to form metal vapors in an inert gas stream and the release of metal powder at a temperature below the melting point of the starting metals. In this case, the heating of the starting metals is carried out by an electron beam with an energy of 0.4-3 MeV and a power of not more than 200 kW at a pressure close to atmospheric, the inert gas flow rate is 0.5-25000 l / min.

The disadvantages of this method include:

- high energy costs associated with the need to heat the starting metals having sufficiently high evaporation temperatures;

- high consumption of inert gas (up to 25000 l / min);

- a large spread in particle sizes: for example, for nickel - from 20 to 200 nm; for an alloy of nickel with titanium, the particle size is 50-300 nm;

- the need to use special expensive equipment.

A known method of producing ultrafine metal powder (patent RU No. 2170647, IPC B22F 9/22, publ. 07.20.2001), including chemical precipitation of at least one metal hydroxide with an alkali solution to form a suspension, diafiltration of the resulting suspension with separation of the solution of at least one metal hydroxide and its reduction to obtain a metal powder and the subsequent passivation of the specified powder, while simultaneously with diafiltration carry out sorption purification of the suspension. In this case, the reduction of metal hydroxide and the passivation of the metal powder is carried out with active stirring of the material. The method allows to obtain nanosized metal powders of iron, copper, nickel, cobalt, tungsten, molybdenum and their alloys.

The disadvantages of this method are:

- multi-stage, as well as a significant duration of the process (for example, only the stage of precipitation of hydroxides takes 1.5-2 hours);

- the need to strictly control the pH of the reaction medium to prevent the dissolution of metal hydroxides and reduce metal loss with the mother liquor during filtration;

- the need for ion-exchange purification using cationic and anion-exchange resins, the preparation of which for work and regeneration after cleaning is a rather laborious and lengthy process;

- the use of high-temperature dehydration (up to 180 ° C) of hydroxides in a drying plant;

- hydrogen used as a reducing agent is explosive and requires the observance of special safety measures when working with it.

Closest to the proposed invention is a nanostructured solid solution powder of cobalt-nickel and a method for its production (patent RU No. 2568858, IPC B22F 1/00, B22F 9/24, B82Y 40/00, publ. 20.11.2015), carried out by the interaction of precursors cobalt and nickel, which are used as aqueous solutions of salts (chlorides, nitrates, sulfates) of cobalt and nickel, a mixture of which interacts with reagents and stabilizer at elevated temperatures. At the same time, reductant hydrazine hydrate and alkali are used as reagents, and potassium sodium tartrate is used as a stabilizer. This method allows to obtain nanostructured Co-Ni systems representing a solid solution with a cubic face-centered lattice. Particles of such a system consist of primary cobalt-nickel nanoblocks 5–20 nm in size, agglomerated into secondary particles of 100–200 nm in spherical shape.

The main disadvantages of this method are:

- the use of alkali as a reagent leads to the formation of intermediate products in the form of mixed hydroxides of cobalt and nickel, which subsequently lead to contamination of the final products with oxide and hydroxide phases;

- the need to use a stabilizer (tartrate ligands) to reduce the amount of by-products - mixed hydroxide and the metal phase of the solid solution with a hexagonal close-packed structure;

- Co-Ni solid solutions are not formed in the entire composition range, radiographically pure solid solutions are formed only at a relatively high nickel content in the system (≥60%) (Zakharov Yu.A. Phase composition and morphology of nanopowders of the cobalt-nickel / Yu system. A. Zakharov, R. P. Kolmykov, V. M. Pugachev, S. Yu. Lirschikov // Bulletin of the Kemerovo State University. - 2014. - No. 3-3 (59). - S. 194-200);

- the use of a concentrated solution of hydrazine hydrate (64%), which is a toxic substance. The introduction of this method in industry can adversely affect the environmental environment.

The objective of the invention is the implementation of a simplified method for producing nanostructured powder of a solid solution of Ni-Co in the entire range of compositions that do not contain oxide-hydroxide impurities, while reducing the total resource and energy consumption.

The problem is solved by obtaining a nanostructured powder of a nickel-cobalt solid solution in a manner involving the interaction of nickel and cobalt salts with an aqueous solution of hydrazine hydrate as a reducing agent. At the same time, their crystalline poorly soluble carbonates are used as nickel and cobalt salts, and an aqueous solution of hydrazine hydrate is taken in a concentration of 9.6 mass. %

In FIG. Figure 1 shows the diffraction patterns of nanostructured Ni-Co powders of various compositions:

a) Ni / Co = 0.05 / 0.95 mass. % respectively;

b) Ni / Co = 0.25 / 0.75 mass. % respectively;

c) Ni / Co = 0.5 / 0.5 wt. % respectively;

g) Ni / Co = 0.75 / 0.25 mass. % respectively.

In FIG. Figure 2 shows the characteristic mass distribution function of particles of a nanostructured Ni-Co solid solution powder according to the small-angle X-ray scattering method:

a) peak corresponding to the size of nanocrystallites;

b) peaks corresponding to the sizes of nanocrystallites and sizes of agglomerates of the initial particles (from left to right).

In FIG. 3 shows a raster electron micrograph of a nanostructured Ni-Co powder for a composition of 50/50 mass. %

и ГЦК

типов от состава системы.In FIG. 4. The dependence of the molar volume of Ni-Co hcp solid solutions is given

and fcc

types of system composition.

A significant reduction in resource and energy consumption in obtaining powders with a narrow particle size distribution, in obtaining a monophasic solid solution (metals) in the entire range of compositions not contaminated with oxide-hydroxide impurities, is achieved by treating a homogeneous mechanical mixture of hard hardly soluble nickel and cobalt carbonates of a given composition with water a solution of hydrazine hydrate when heated, washing with water and subsequent drying.

When implementing the method, the obtained Ni-Co powder has high purity — the total mass content of nickel and cobalt in it reaches 99.999 mass. % This method of obtaining has several advantages: the availability and low cost of preparative and hardware-based synthesis, the ease of scaling of the process, the production of high purity powders, low energy consumption of the method and, consequently, reducing the cost of the final product.

The nanostructured Ni-Co system consists of nanocrystallites 5–20 nm in size (according to the broadening of diffraction profiles — Fig. 1, according to the small-angle X-ray scattering method — FIG. 2a), which are composed of low-porous sphere-like agglomerates 100–200 nm in size (electron microscopic photographs - Fig. 3, according to the method of small-angle scattering of x-rays - Fig. 2b).

Depending on the incorporated composition, the nanostructured Ni-Co system is a solid solution with a hexagonal close-packed (hcp) or face-centered cubic (fcc) lattice, at the nodes of which nickel and cobalt atoms alternate, which is confirmed by X-ray phase analysis (Fig. 1). Reflections of any other crystalline structures, including oxide and hydroxide phases, were not detected. By the method of X-ray fluorescence and chemical analysis of the powders, it was found that the metal content in the powder corresponds to the inherent value. The straightforward dependence of the calculated lattice parameters on the composition of the powders proves the formation of a solid solution obtained by the proposed method (Fig. 4).

The powder particles have a high pycnometric density of 6-8 g / cm ³ and exhibit mechanical strength when subjected to ultrasound. According to the results of studies by the method of small-angle scattering of x-rays, the specific surface area varies in the range of 4-9 m ² / g. The specific surface determined by the Brunauer-Emmett-Taylor method is 2-4 m ² / g. The reasons for the underestimation of the experimental values of the specific surface determined by the BET method may be the presence in the samples of sections (both inside and outside) that are inaccessible to the adsorbed gas.

The method is implemented as follows.

A mechanical mixture is prepared containing crystalline sparingly soluble salts: m1 nickel carbonate and m2 cobalt carbonate. The resulting mixture is thoroughly triturated for 3-5 minutes until a homogeneous fine powder is formed. After which the mixture of precursors is quantitatively transferred into a heat-resistant beaker, 9.6 masses are added. % aqueous solution of hydrazine hydrate. The suspension is placed in a thermostat heated to 80 ° C, equipped with a mechanical stirrer. Constant mixing is necessary for uniform formation of components throughout the reaction volume. The duration of the reaction of recovery is 15-25 minutes. Across the entire volume, nanodispersed Ni-Co particles are uniformly formed, the formation of which is visually fixed. After settling, the obtained black powder is washed with decantation with distilled water, dried at a temperature of 105 ° C and stored in an airtight package. By X-ray phase analysis, it was found that when stored for two years, the powders do not oxidize and their phase composition does not change.

With a decrease in the concentration of reducing agent below 9.6 mass. % there is a noticeable slowdown in the recovery process, as well as incomplete recovery of the original carbonates. The increase in the concentration of the reducing agent does not lead to a significant increase in the efficiency of the process both in completeness and in speed (table 1). In addition, the use on an industrial scale of hydrazine hydrate with a high concentration will adversely affect the ecological state of the environment.

The essence of the invention is illustrated by the following examples.

Example 1

To obtain the composition of the nanostructured powder of a solid solution of Ni-Co 5/95 mass. %, respectively, poorly soluble crystalline carbonates are mixed: 0.1003 g of nickel carbonate and 1.9057 g of cobalt carbonate. A mixture of two sparingly soluble salts is thoroughly triturated in a chemical mortar for 3-5 minutes until a homogeneous powder is formed. After that, the mechanical mixture of precursors is quantitatively transferred into a heat-resistant beaker, 100 ml of 9.6 mass are added. % aqueous solution of hydrazine hydrate and heated in a thermostat at 80 ° C with constant stirring until complete recovery of salts. The end of the recovery process is visually fixed by the formation of nanodispersed Ni-Co particles in the form of a black powder. Recovery time is 15 minutes. After settling, the obtained black powder is washed by decantation with distilled water to a neutral wash water medium, dried in an oven at a temperature of 105 ° C to constant weight. Keep powders in sealed packaging.

Examples 2-19 of the method for producing nanostructured powder of a solid solution of Ni-Co in the concentration range of Ni (100-x) / Co (x), where x is from 5 to 90%, are performed analogously to example 1 and are shown in table 2.

The use of the invention provides:

- obtaining a monophasic nanostructured powder of a solid solution of Ni-Co in the entire range of compositions not contaminated with oxide-hydroxide impurities with a purity of up to 99.999%;

- achieving a narrow particle size distribution;

- simplification of the method of producing nanostructured powder of a solid solution of Ni-Co by eliminating alkali and stabilizers in the process, thus reducing the staging, eliminating the formation of intermediate polluting products, as well as reducing the total resource and energy consumption when producing powders, leading to a decrease the cost of the final product;

- the use of dilute solutions of the reducing agent (9.6 wt.% versus 64 wt.% hydrazine hydrate in the closest analogue), which do not have a technogenic impact on the environment when this method is introduced into the industry.

Claims (1)

A method of producing a nanostructured powder of a nickel-cobalt solid solution, comprising reacting nickel and cobalt salts with an aqueous solution of hydrazine hydrate as a reducing agent, characterized in that crystalline sparingly soluble carbonates are used as nickel and cobalt salts, and an aqueous solution of hydrazine hydrate is used at a concentration of 9.6 wt.%.

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