RU2621508C2 - Electrochemical method for holmium and nickel intermetallic compounds nanopowders production in halide melts - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to electrochemical production of holmium and nickel intermetallic compounds nanopowders, which can be used as catalysts in chemical and petrochemical industries, hydrogen energy for reversible sorption of hydrogen, as well as for magnetic material creation. Electrolysis of a molten mixture containing potassium chloride, sodium chloride, holmium (III) chloride and nickel (II) chloride is performed in a quartz cell on a tungsten electrode at a temperature of 973°K and a current density of 0.5÷1.9 A/cm².

EFFECT: decreased temperature of electrolysis and obtaining of nickel and holmium intermetallic compounds nanopowders.

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Description

The invention relates to the electrochemical production of ultrafine powders of holmium and nickel intermetallic compounds in halide melts and can be used as catalysts in the chemical and petrochemical industry, in hydrogen energy for reversible sorption of hydrogen, as well as for the creation of magnetic materials.

A known method of producing holmium and nickel intermetallic compounds by diffusion saturation of a nickel electrode with holmium ions in a melt in KCl-HoCl ₃ [Qiqin Y. Electrochemistry of deposition of rare earth metals and their alloys in molten salts. Proceedings of 6th International Symposium on Molten Salt Chemisry and Technology. Shanghai, China, Okt. 2001, p. 383-390].

Also known is a production method, Su YZ, Yang QQ, Liu GK. Electroreduction of Ho ³⁺ on nickel catode in molten KCI-HoCl ₃ // J. Rare Eartns, 2000. - V. 18. - N 1. P. 34-38] at a temperature of 1093 ° C.

The disadvantage of these analogues is the high temperature of the process, as well as the inability to obtain nanosized powders, because this method receive only diffusion coatings.

The closest to the claimed technical solution in terms of technical nature and the technical result achieved is a method for producing holmium and nickel intermetallic compounds by diffusion saturation of metallic nickel with holmium in a KCl-NaCl melt (Samodelkina O.V. Reduction of praseodymium, neodymium, terbium and holmium chlorides in ionic melts: Dis ... Candidate of Chemical Sciences: 02.00.05. Ekaterinburg, 2004, 127 pp. RSL OD, 61: 04-2 / 562). In this way, only diffusion coatings can be obtained.

The essence of the diffusion saturation of an electropositive metal with an electronegative REM from the melt is as follows: the electropositive metal (nickel) is in the melt of an alkali metal salt with the addition of a rare earth metal (HoCl ₃ ) in contact with a metal alkali metal. This creates a short-circuited galvanic cell in which sodium is the anode and nickel is the cathode. Saturation was carried out in the temperature range 1073–1173 K for 20 minutes.

The disadvantage of the prototype is the inability to obtain ultrafine powders of intermetallic holmium and nickel. Another disadvantage of this method is the limitation of the rate of the process of diffusion of holmium on the surface of metallic nickel.

The objective of the invention is to obtain nanosized powders of holmium and nickel intermetallic compounds in halide melts, lowering the temperature of electrolysis and reducing energy consumption.

The problem is solved as follows.

Electrochemical high-temperature synthesis of holmium and nickel intermetallic compounds in galvanostatic mode is carried out in a KCl-NaCl-HoCl ₃ -NiCl ₂ melt in the following ratio of components, mol. %:

HoCl ₃ - 0.5-3.0;

NiCl ₂ - 0.5-2.5;

the rest is an equimolar mixture of KCl and NaCl.

The electrolysis is carried out in a high-temperature quartz cell in an inert gas - argon atmosphere at a temperature of 973 K. A high-purity tungsten rod with a diameter of 3 mm served as the cathode. A glass-carbon crucible served as the anode and at the same time a container for the melt.

The electrochemical synthesis of holmium and nickel intermetallic compounds is carried out in the galvanostatic mode in the KCl-NaCl-HoCl ₃ -NiCl ₂ melt as follows: first, the salts used are prepared. Potassium and sodium chlorides are recrystallized, dried thoroughly in the process of evacuation by stepwise heating to 573-423 K and melted at the melting points of these salts. Then, nickel chloride is dried in an atmosphere of carbon tetrachloride, gradually increasing the temperature to 673 K. The source of holmium ions is anhydrous holmium (III) chloride (99.99%). Nickel is anhydrous nickel (II) chloride. Weights of anhydrous chlorides are carried out in the MbraunLabStar glove box.

Next, electrolysis of the molten mixture of KCl-NaCl containing holmium (III) chloride is carried out - 0.5 ÷ 3.0 mol. % and nickel (II) chloride - 0.5 ÷ 2.5 mol. % at a current density of 0.5 ÷ 1.9 A / cm ² .

On the tungsten electrode, a metal-salt "pear" is formed (Fig. 1).

Leaching of the cathode deposit is carried out in hot distilled water, which allows you to separate the target product from the salt phase. After repeated washing in distilled water, the precipitate is dried in a vacuum oven at temperatures of 373-423 K.

Depending on the composition of the electrolysis bath and the electrolysis parameters, a mixture of phases of metallic nickel, holmium and intermetallic compounds HoNi, HoNi ₅ , HoNi _{3 is formed} .

In FIG. Figure 2 shows the X-ray diffraction pattern of the galvanostatic electrolysis product (phase composition of the cathode deposit) obtained from the KCl-NaCl-HoCl ₃ -NiCl ₂ melt on a tungsten electrode. C (HoCl ₃ ) = 2.5 mol. %, C (NiCl ₂ ) = 0.5 mol. % i _k = 1.2 A / cm ² . T = 973 K. S = 2.43 cm ² . Standard lines: 1 - HoNi, 2 - HoNi ₅ , 3 - HoNi ₃ .

To determine the optimal concentrations of HoCl ₃ and NiCl _2, it is necessary to take into account that, in the beginning, a more electropositive component, nickel, is released.

The electrochemical reduction of holmium ions begins as nickel chloride is produced. The optimal concentration of Nickel chloride is about 0.5 mol. % At higher nickel chloride concentrations, the precipitate contains metallic nickel. The dependence of the composition of the cathode deposits on the content of nickel chloride, holmium chloride and their ratio in the KCl-NaCl melt (1: 1) was studied (table 1).

Table 1 presents the dependence of the phase composition and particle size of the products of galvanostatic electrolysis on the composition of the electrolysis bath KCl-NaCl-HoCl ₃ -NiCl ₂ . The duration of electrolysis is 60 minutes T = 973 K, S = 2.43 cm ² , i = 1.2 A / cm ² .

The content of intermetallic compounds increases both with an increase in the concentration of holmium chloride in the melt, and with an increase in the ratio of concentrations of holmium chloride and nickel (Fig. 3). When the concentration ratio of [HoCl ₃ ]: [NiCl ₂ ] = 1: 1, the phase of metallic nickel prevails in the cathode deposit. With an increase in this ratio, the proportion of metallic nickel decreases, and the content of intermetallic compounds HoNi, HoNi ₃ , HoNi ₅ increases. Provided that [HoCl ₃ ]: [NiCl ₂ ] is greater than 5, no metallic nickel phase is detected in the cathode deposit, but a mixture of intermetallic phases is formed. Moreover, the phase with a high content of holmium prevails.

In FIG. Figure 3 shows the dependence of the composition of the products of galvanostatic electrolysis on the ratio of the components of the electrolysis bath KCl-NaCl-HoCl ₃ -NiCl ₂ : 1 - HoNi, 2 - HoNi ₅ , 3 - HoNi ₃ , 4 - Ni.

A series of experiments was conducted in the galvanostatic mode at various initial current densities (0.5 ÷ 2.0) A / cm ² in an electrolysis bath of the optimal composition KCl-NaCl-NiCl ₂ (0.5 mol.%) - HoCl ₃ (2, 5 mol%) (table 2).

At an initial current density of 0.5 A / cm ² in the cathode deposit, the phase of metallic nickel and the phase of intermetallic compounds with a high nickel content prevail. With an increase in the initial current density, the nickel content in the cathode deposit decreases, and the holmium content increases.

At an initial current density of 1.2 A / cm ^{2, there is no} phase of metallic nickel in the cathode deposit, and phases with a high holmium content are contained in a greater amount of intermetallic phases.

At an even higher current density (~ 2.0 A / cm ² ), a phase of metallic holmium already appears in the cathode deposit.

Table 2 shows the dependence of the phase composition and particle size of the products of galvanostatic electrolysis in the KCl-NaCl-HoCl ₃ -NiCl ₂ melt on the current density. The duration of electrolysis is 60 minutes C (HoCl ₃ ) = 2.5 mol. %, C (NiCl ₂ ) = 0.5 mol. %

Table 3 presents the dependence of the phase composition of the products of galvanostatic electrolysis in the KCl-NaCl-HoCl ₃ -NiCl ₂ melt _on the synthesis temperature. The duration of electrolysis is 60 minutes C (HoCl ₃ ) = 2.5 mol. %, C (NiCl ₂ ) = 0.5 mol. %

In FIG. _Figure 4 presents the result of a variance analysis of powders of holmium and nickel intermetallic compounds obtained by galvanostatic electrolysis of the melt (KCl-NaCl) _eut. -HoCl ₃ -NiCl ₂ in a ratio of 5: 1 at a current density of 1.2 A / cm ² and a temperature of 973 K.

The structure, morphology, and elemental composition of the obtained samples (quantitative and qualitative) were studied on a VEGA3 LMH scanning scanning electron microscope. The obtained images confirm the process of joint electrowinning of holmium and nickel (Fig. 5, 6).

In FIG. 5 is a sample map obtained using a VEGA3 TESCAN scanning scanning electron microscope. Phase composition: HoNi, HoNi ₅ , HoNi ₃ .

In FIG. Figure 6 shows a photo of the product of galvanostatic electrolysis (KCl-NaCl-HoCl ₃ -NiCl ₂ ) obtained on a VEGA3 TESCAN scanning scanning electron microscope.

Example 1

High-temperature electrochemical synthesis of holmium and nickel intermetallides is carried out in a molten mixture of KCl-NaCl-HoCl ₃ -NiCl ₂ in the following ratio of components, mol. %: HoCl ₃ - 0.5; NiCl ₂ - 0.5; the rest is an equimolar mixture of KCl and NaCl.

The cathode is a tungsten rod with a diameter of 3 mm, an area of 2.43 cm ² . A glass-carbon crucible serves as an anode and at the same time a container under the galvanostatic electrolysis mode. The electrolysis was carried out at a temperature of 973 K. The initial density of the cathode current was 1.2 A / cm ² . The electrolysis lasts 60 minutes, after which the melt is poured out and the metal-salt “pear” that has fallen on the alundum substrate is removed. Leaching of the cathode deposit in hot distilled water made it possible to separate the target product from the salt phase. After repeated washing in distilled water, the precipitate was dried in a vacuum oven at temperatures of 373-423 K. According to x-ray phase analysis, the cathode precipitate consists of intermetallic compounds Ni, HoNi, HoNi ₅ , HoNi ₃ . According to the analysis of particle size distribution, the volume fraction of particles of the target product up to 100 nm is 22%.

Example 2

High-temperature electrochemical synthesis of holmium and nickel intermetallides is carried out in a molten mixture of KCl-NaCl-HoCl ₃ -NiCl ₂ in the following ratio of components, mol. %: HoCl ₃ - 2.5; NiCl ₂ - 0.5; the rest is an equimolar mixture of KCl and NaCl.

The cathode is a tungsten rod with a diameter of 3 mm, an area of 2.43 cm ² . A glass-carbon crucible serves as an anode and at the same time a container under the galvanostatic electrolysis mode. The electrolysis was carried out at a temperature of 973 K. The initial density of the cathode current was 1.2 A / cm ² . The electrolysis lasts 60 minutes, after which the melt is poured out and the metal-salt “pear” that has fallen on the alundum substrate is removed. Leaching of the cathode deposit in hot distilled water made it possible to separate the target product from the salt phase. After repeated washing in distilled water, the precipitate was dried in a vacuum oven at temperatures of 373-423 K. According to x-ray phase analysis, the cathode precipitate consists of intermetallic compounds HoNi, HoNi ₅ , HoNi ₃ . According to the analysis of particle size distribution, the volume fraction of particles of the target product up to 100 nm is 69%.

Example 3

High-temperature electrochemical synthesis of holmium and nickel intermetallides is carried out in a molten mixture of KCl-NaCl-HoCl ₃ -NiCl ₂ in the following ratio of components, mol. %: HoCl ₃ - 2.5; NiCl ₂ - 0.5; the rest is an equimolar mixture of KCl and NaCl.

A tungsten rod with a diameter of 3 mm and an area of 2.43 cm ² served as a cathode. A glass-carbon crucible served as the anode and at the same time a container under the galvanostatic electrolysis mode. The electrolysis was carried out at a temperature of 973 K. The initial density of the cathode current of 0.5 A / cm ² . The electrolysis lasts 60 minutes, after which the melt is poured out and the metal-salt “pear” that has fallen on the alundum substrate is removed. Leaching of the cathode deposit in hot distilled water made it possible to separate the target product from the salt phase. After repeated washing in distilled water, the precipitate was dried in a vacuum oven at temperatures of 373-423 K. According to x-ray phase analysis, the cathode precipitate consists of Ni, HoNi ₅ , HoNi, HoNi ₃ , HoNi ₂ . According to the analysis of particle size distribution, the volume fraction of particles of the target product up to 100 nm is 34%.

Example 4

High-temperature electrochemical synthesis of holmium and nickel intermetallides is carried out in a molten mixture of KCl-NaCl-HoCl ₃ -NiCl ₂ in the following ratio of components, mol. %: HoCl ₃ - 2.5; NiCl ₂ - 0.5; the rest is an equimolar mixture of KCl and NaCl.

A tungsten rod with a diameter of 3 mm and an area of 2.43 cm ² served as a cathode. A glass-carbon crucible served as the anode and at the same time a container under the galvanostatic electrolysis mode. The electrolysis was carried out at a temperature of 973 K. The initial cathodic current density of 1.9 A / cm ² . The electrolysis lasts 60 minutes, after which the melt is poured out and the metal-salt “pear” that has fallen on the alundum substrate is removed. Leaching of the cathode deposit in hot distilled water made it possible to separate the target product from the salt phase. After repeated washing in distilled water, the precipitate was dried in a vacuum oven at temperatures of 373-423 K. According to x-ray phase analysis, the cathode precipitate consists of Ho, Ni, HoNi ₅ , Ho ₂ Ni ₁₇ . According to the analysis of particle size distribution, the volume fraction of particles of the target product up to 100 nm is 79%.

Example 5

High-temperature electrochemical synthesis of holmium and nickel intermetallides is carried out in a molten mixture of KCl-NaCl-HoCl ₃ -NiCl ₂ in the following ratio of components, mol. %: HoCl ₃ - 2.5; NiCl ₂ - 0.5; the rest is an equimolar mixture of KCl and NaCl.

A tungsten rod with a diameter of 3 mm and an area of 2.43 cm ² served as a cathode. A glass-carbon crucible served as the anode and at the same time a container under the galvanostatic electrolysis mode. The electrolysis was carried out at a temperature of 1073 K. The initial density of the cathode current of 1.2 A / cm ² . The electrolysis lasts 60 minutes, after which the melt is poured out and the metal-salt “pear” that has fallen on the alundum substrate is removed. Leaching of the cathode deposit in hot distilled water made it possible to separate the target product from the salt phase. After repeated washing in distilled water, the precipitate was dried in a vacuum oven at temperatures of 373-423 K. According to x-ray phase analysis, the cathode precipitate consists of HoNi, HoNi ₂ . An analysis of the particle size distribution showed that, at a temperature of 1073 K, nanosized powders of holmium and nickel intermetallic compounds are not formed.

EFFECT: obtaining nanosized powders of holmium and nickel intermetallic compounds from KCl-NaCl-HoCl ₃ -NiCl ₂ melt on a tungsten electrode.

Claims (3)

A method for the electrochemical preparation of nanosized powders of holmium and nickel intermetallic compounds, comprising electrolysis of a molten mixture containing potassium chloride, sodium chloride and holmium (III) chloride in an atmosphere of purified and dried argon in a high-temperature quartz cell, characterized in that the molten mixture of potassium chloride, sodium chloride and holmium (III) chloride additionally contains nickel (II) chloride, in the following ratio of components, mol.%: HoCl ₃ 0.5 ÷ 3.0 NiCl ₂ 0.5 ÷ 2.5 equimolar mixture of KCl and NaCl rest the electrolysis is carried out at a temperature of 973 K and a current density of from 0.5 to 1.9 A / cm ² using a tungsten electrode.

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