RU2582414C1 - Method of producing tantalum powder - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to production of high-purity tantalum hydride powder using a method. Method involves activation of a tantalum ingot by heating to 700-900°C, hydrogenation using saturated titanium hydride as hydrogen source, grinding produced tantalum hydride to given dispersity and dehydrogenation of tantalum powder obtained using unsaturated titanium hydride. Activation of tantalum ingot by heating is carried out in a hydrogen atmosphere at pressure of 0.01-0.3 MPa, which is produced by desorption of hydrogen from a saturated hydride of a multicomponent intermetallic compound La_1-yR_yNi₄Co, where R denotes rare earth metals of cerium group and/or mischmetal, 0 < y ≤ 1, to provide beginning of hydrogenation of tantalum ingot with hydrogen. Simultaneously with activation of tantalum ingot, saturated titanium hydride is heated to its decomposition with release of hydrogen and upon achieving excess pressure of hydrogen of 0.2-0.3 MPa, continuing initiated hydrogenation of tantalum ingot with hydrogen released during decomposition of titanium hydride.

EFFECT: reduced duration of hydrogenation and dehydrogenation, safer process and reduced loss of hydrogen.

1 cl, 3 dwg, 1 tbl, 2 ex

Description

The invention relates to the field of powder metallurgy and can be used to obtain high-purity tantalum powders by the hydride method.

The hydride method for producing powders of transition metals, including tantalum, involves activation of a compact material by heating, hydrogenation (with the aim of converting a metal from plastic to brittle) by cooling in a hydrogen atmosphere, mechanical crushing, grinding and separation (sieving, classification) of synthesized hydride for obtaining powders of the desired degree of dispersion, as well as dehydrogenation in order to remove hydrogen and reduce its residual content to the values required by consumers.

A known method of producing tantalum powders from compact metals, comprising the following operations:

1) heating the ingot in vacuum at temperatures of 800-1400 ° C, hydrogenation at a hydrogen pressure of 300-400 mm RT. Art. (40-53 kPa), carried out during cooling at least in three stages with holding for several hours at temperatures of 600-1000, 200-500 and 60-120 ° С;

2) crushing the embrittled material to obtain a coarse powder, which, if necessary, is further crushed to the required degree of dispersion (not more than 150 microns);

3) dehydrogenation of the powder in high vacuum at temperatures of 600-1200 ° C (US Patent 3635693, IPC B22F 9/00, US Cl. 75 / 0.5 BB, publ. Jan. 18, 1972).

The main disadvantages of this method are the large consumption of hydrogen per unit of output due to the lack of utilization of the gas pumped out by vacuum pumps and the contamination of the metal powder by interstitial impurities entering it with oil vapors released during the operation of these pumps.

Inadequate purification of the hydrogen used for hydrogenation can also lead to contamination of the obtained powder with impurities. Often, it causes an increase in the induction period of the reaction and requires an increase in the temperature of hydrogenation (Metal hydrides / under the editorship of V. Mueller, D. Blackledge, J. Libowitz; trans. From English; under the editorship of R.A. Andrievsky, K.G. Weaver, Moscow: Atomizdat, 1973, 432 p.). In addition, the speed of hydrogenation and dehydrogenation processes, as well as the yield of the product, directly depend on the purity of hydrogen. Among the known methods for producing high-purity hydrogen, the most effective, convenient, and economical method is the thermal decomposition of hydrides (Preparative chemistry of hydrides / MM Antonova, R.A. Morozova. Kiev: Nauk. Dumka, 1976, 99 pp.).

The processes of hydrogenation-dehydrogenation of transition metals are reversible, which makes it possible to use the Me-H system not only as a source of pure hydrogen, but also as an absorber of this gas, carrying out the above process of producing powders by the hydride method in a closed hydrogen cycle. For this purpose, a titanium sponge is most often used, which forms non-stoichiometric TiH _x hydrides in a wide concentration range (0 <x≤2) and in a saturated state serves as a source of high-purity hydrogen, and in an unsaturated state it is an absorber that provides the sorption of the main amount of gas released from the powder upon decomposition of hydride.

A known method of producing vanadium powder from a compact metal by hydrogenation-dehydrogenation in a closed cycle through hydrogen. According to this method, the ingots are activated by heating to 600-800 ° C, hydrogenated by cooling from the indicated temperature level to 50-200 ° C in a hydrogen atmosphere, which is created by thermal decomposition of titanium hydride with its unsaturation. Then the synthesized hydride is ground, subjected to classification and dehydrogenated by heating to 650-800 ° C with the removal of hydrogen and holding at this temperature to a residual pressure of 0.05-0.50 mm RT. Art. In this case, unsaturated titanium hydride is used to absorb hydrogen released during dehydrogenation of the powder (Method for producing vanadium powder: RU patent No. 2196024, IPC B22F 9/16, C22B 34/22, publ. 10.01.2003).

There is also a method of producing powders of rare metals by hydrogenation-dehydrogenation of compact materials using hydrogen in a closed cycle. This method includes the technological operations of hydrogenation, grinding, classification and dehydrogenation (the technological scheme is shown in Fig. 1). In this case, pure hydrogen enters the system from saturated titanium hydride, and the removal of hydrogen released during the dehydrogenation of the powder is ensured by the absorption of this gas by unsaturated TiH _x (Research and development of IHTREMS KSC RAS in the field of materials science for solving problems of special equipment / V.T. Kalinnikov, A.G. Kasikov, V.M. Orlov, N.N. Grishin, B.M. Freudin // Chemical Technology. 2009.V. 10, No. 3. P. 177-182). The method adopted for the prototype.

When using TiH _x in the production of rare metal powders, the important advantages of the technologies described above are provided largely due to the high affinity for hydrogen and the high hydrogen intensity of titanium (in saturated TiH ₂ hydride contains about 4 wt.% Hydrogen). However, these methods of producing powders have significant disadvantages. Firstly, due to the high formation temperatures (above 400 ° C) and decomposition (550-950 ° C) of titanium hydride, heating it to a predetermined temperature level requires a lot of time and high energy costs, which significantly lengthens the hydrogenation of a compact metal, reduces their productivity and increases the cost of the product. Secondly, if only one sorbent, TiH _x , is involved in the process, potential emergencies that can occur when it overheats due to the inertia of the furnaces and the difference in the rates of hydrogen evolution and absorption by the hydrated metal are not excluded. This can lead to a sharp jump in pressure (above a safe level).

The technical result of the claimed invention is to reduce the time required for hydrogenation and dehydrogenation operations, reduce energy costs and thereby increase the economic efficiency of the process used to obtain high-purity tantalum powders, as well as increase the safety of this process and reduce hydrogen losses by providing the possibility of additional absorption of excess gas.

The technical result is achieved in that in a method for producing tantalum powders, including activation of a tantalum ingot by heating to 700-900 ° C, hydrogenating it using saturated titanium hydride as a hydrogen source, grinding the obtained tantalum hydride to a predetermined degree of dispersion, and dehydrogenating the obtained tantalum powder with using unsaturated titanium hydride, according to the invention, the activation of the tantalum ingot by heating is carried out in a hydrogen atmosphere at an excess pressure of 0.01-0.3 MPa, which is created by hydrogen desorption from the saturated hydride of the multicomponent intermetallic compound La _1-y R _y Ni ₄ Co, where R are the rare-earth metals of the cerium group and / or mischmetal, (0 <y≤1), with the onset of hydrogenation of the tantalum ingot with hydrogen, while simultaneously with the activation of the tantalum ingot, saturated titanium hydride is heated to its decomposition temperature with hydrogen evolution and, when an excess pressure of hydrogen of 0.2-0.3 MPa is reached, the hydrogenation of the tantalum ingot released during decomposition of titanium hydride is continued.

(The technological scheme for producing powders is shown in Fig. 2.)

The invention consists in the following.

Activation of the initial tantalum ingot is carried out by heating it to a temperature of 700-900 ° C in an atmosphere of pure hydrogen at an excess pressure of 0.01-0.3 MPa (0.1-3.0 kgf / cm ² ), which is created by desorption of this gas from saturated hydride of the multicomponent intermetallic compound La _1-y R _y Ni ₄ Co (R - rare-earth metals of the cerium group, or or mischmetal, 0 <y≤1). Since the additional doping of La _1-y R _y Ni ₄ Co with other rare-earth metals increases the equilibrium pressure of hydrogen sorption-desorption by this IC, the absorption-gas evolution processes are carried out at room temperature (without heating).

Simultaneously with the activation of the tantalum ingot, saturated titanium hydride is heated until its decomposition temperature (550-950 ° C) is achieved, which provides the necessary pressure and the amount of hydrogen released. By the time the ingot begins to absorb hydrogen, the excess pressure of hydrogen released during the decomposition of titanium hydride reaches the required values: 0.2-0.3 MPa (2-3 kgf / cm ² ), and in the future, this gas is used for the process.

The use of IC La _1-y R _y Ni ₄ Co at the first stage of the process can significantly reduce the duration of hydrogenation of a tantalum ingot by eliminating equipment downtime during heating of titanium hydride to the required temperature, and reducing energy costs due to the fact that La ₁ sorption and desorption of hydrogen _-y R _y Ni ₄ Co are carried out at temperatures close to room temperature. In addition, the presence of a second sorbent avoids sudden pressure surges in the system (due to the reversibility of the hydrogen sorption-desorption processes La _1-y R _y Ni ₄ Co at room temperature, if the pressure rises, the IC will begin to absorb gas) and, therefore, increase the safety of the process process.

It is known to use the intermetallic compound LaNi ₄ Co in the hydrogenation of niobium with hydrogen, which is liberated during the decomposition of IC hydride.

Niobium ingots were placed in a retort, which was then sealed, evacuated, filled with hydrogen released from saturated LaNi ₄ Co IC hydride, heated in an electric furnace to 750 ± 50 ° С, and held at this temperature for 4-5 hours. The hydrogenation process that began was continued by stepwise lowering the temperature: first to 450 ± 50 ° C (with holding at this level for about 5 hours), then to 80-100 ° C (together with the furnace, for 20-30 hours), and after retort extraction from the furnace to room temperature (Development of oxide-semiconductor capacitors based on niobium / A.V. Elyutin, Yu.B. Patrikeev, N.S. Vorobyova // GIREDMET - 70 years in the metallurgy of rare metals and semiconductors: anniversary collection M.: TsINAO, 2001.S. 291-306).

The disadvantages of this method include:

1) the hydrogen capacity of the LaNi ₄ Co IC, lower than that of titanium hydride (at room temperature in the range of 0.2-1.0 MPa, it is 1.4-1.8 wt.%), Which requires participation in the hydrogenation processes dehydrogenating more of this sorbent;

2) the low pressure of hydrogen desorption from the IM hydride LaNi ₄ Co at temperatures close to room temperature is lower than the values required for hydrogenation of tantalum. To create and maintain the required pressure, this hydride needs to be heated to temperatures of about 100 ° C, using electric energy or hot water for this purpose, which complicates the hardware circuit of the process and increases energy costs;

3) lower sorption activity of the IMC at an absolute pressure below 0.1 MPa, which does not completely absorb the hydrogen released from the powder during dehydrogenation, and requires evacuation of the latter to more completely remove this interstitial impurity.

Thus, the closed cycle is not fully realized, since the part of the hydrogen that is lost when the gas is pumped out by the pumps is greater than when using titanium hydride.

Examples of the method.

Tantalum powder was obtained by hydrogenation-grinding-dehydrogenation. The starting material was cathode ray ingots weighing about 150 kg.

Tantalum powders were obtained by a known method (example 1) and the claimed method (example 2). The compact metal was activated by heating to 700–900 ° C. Moreover, in the first case, the process was carried out first in vacuum (up to 300-350 ° С), and then in hydrogen released from saturated titanium hydride, heated to a temperature of 550-900 ° С (depending on the degree of titanium saturation with hydrogen). In the second case, a hydrogen atmosphere was created before the temperature began to rise, using for this purpose the gas generated during the decomposition of the hydride of the IMC La _1-y R _y Ni ₄ Co. Saturated TiH _{x was} heated at the same time as the hydrogenated metal, and when the excess pressure of hydrogen released during its decomposition reached 0.2-0.3 MPa, this gas was fed into the reaction zone.

For the implementation of hydrogenation-dehydrogenation processes, a setup was used, the circuit diagram of which is shown in Fig. 3. A tantalum ingot was loaded into a steel retort 1, which was placed in an electric furnace 2, sealed and evacuated using a fore-vacuum (3) and diffusion (4) pumps. IMS saturated hydride was in retort 5, the amount of hydrogen released from it was measured by counter 6, the readings of which correspond to the volume occupied by the gas under normal conditions. Retort 1 was gradually heated to a temperature at which the hydrogenation process began, as evidenced by the pressure drop recorded by the manovacuum meter 7. The hydrogen-rich titanium sponge (TiHx) was in the third retort (8), placed in an electric furnace 9, and heated there to a temperature ensuring the excess hydrogen pressure necessary for hydrogenation of tantalum, as measured by a manovacuum meter (10).

After exposure at high temperatures, which ensures the diffusion of hydrogen from the surface into the thickness of the metal ingot, the temperature in retort 1 was gradually reduced until it was completely cooled. The final stage of the tantalum hydrogenation process was carried out at temperatures below 200 ° C. In this range, the hydride phases are intensively formed in the metal - hydrogen system and the concentration of this interstitial element is achieved, which is necessary for embrittlement of tantalum; therefore, the hydride obtained is easily ground.

After grinding to the required particle size dispersion, tantalum hydride was sent for dehydrogenation to a retort 11 (heated by an electric furnace 12) equipped with a manovacuum meter 13, and the hydrogen released was put into a retort 14 (equipped with a manovacuum meter 15 and heated by an electric furnace 16) with an unsaturated titanium sponge to absorb it and further use for hydrogenation of the next tantalum ingot. The hydrogen consumed during the activation process from retort 5 was replenished due to the gas coming from titanium hydride at the initial stage of the dehydrogenation process. The pressure in this retort was measured by a manovacuum meter 17.

The gas flows in the system were regulated using valves 18. The technical hydrogen required for the initial hydrogenation of the titanium sponge and IC La _1-y R _y Ni ₄ Co was supplied from a standard gas cylinder 19 through a reducer 20. To prevent contamination of the resulting powder with oil vapors released during the operation of the vacuum pump, they were frozen using a trap 21 cooled with liquid nitrogen.

Obtaining tantalum powder

Example 1. The activation of the tantalum ingot was carried out by heating first to 350 ° C in vacuum, and then to 800 ° C in hydrogen released from saturated titanium hydride (retort 8), at an excess pressure of 0.2-0.3 MPa before hydrogenation . After that, the temperature was maintained for 3.5–4 h, and then the heating of the electric furnace 2 was turned off and the hydrogenation process was continued with the gradual cooling of retort 1 and the continuous flow of hydrogen from saturated TiH _{x into it} . The duration of activation before the start of hydrogenation was 9-10 hours, the duration of the entire high-temperature phase of the process was 12.5-14 hours.

Example 2

Activation of the tantalum ingot began at an overpressure of about 0.01-0.02 MPa. This gas was supplied from a retort 5 filled with IH hydride La _0.78 Ce _0.22 Ni ₄ Co. In this case, the tantalum ingot was gradually heated from room temperature to 750 ° C, due to which the pressure increased to approximately 0.25 MPa. At the same time, saturated TiH _{x was} heated (in retort 8), creating the same excess pressure of hydrogen. The activation time before the start of hydrogenation did not exceed 3.5–4 h, exposure at the reached temperature lasted about the same, and the total duration of the high-temperature phase of the process was 7–8 h.

Then, in both cases, the temperature in retort 1 was reduced stepwise to room temperature for about 40 hours. After unloading from the retort, the synthesized tantalum hydride was crushed in a ball mill to a powder with a particle size less than 250 μm, subjected to classification, and then dehydrogenated in retort 11 at a temperature of 850- 900 ° C to a residual pressure (0.1 ± 0.02) mm Hg. Art. The result was a tantalum powder containing less than 0.01 mass. % hydrogen.

The table below compares the time spent on the implementation of the individual stages and the hydrogenation process as a whole for the known (1) and claimed (2) methods for producing tantalum powders.

The data presented in the table indicate that the use of IC in the first stage of hydrogenation reduces the duration of its high-temperature stage by 1.5-2 times, and the duration of the entire process by 9-17%.

Claims (1)

A method of producing tantalum powders, including activation of a tantalum ingot by heating to 700-900 ° C, hydrogenating it using saturated titanium hydride as a hydrogen source, grinding the obtained tantalum hydride to a predetermined degree of dispersion, and dehydrogenating the obtained tantalum powder using unsaturated titanium hydride, characterized in that the activation of the tantalum ingot by heating is carried out in a hydrogen atmosphere at an excess pressure of 0.01-0.3 MPa, which is created by desorption of hydrogen from saturated hydride nogokomponentnogo intermetallic compound La _1-y R _y Ni ₄ Co, where R - cerium group rare earth metals and / or mischmetal, 0 <y≤1, beginning with providing an ingot of tantalum hydrogenation with hydrogen at the same time with the activation of tantalum ingot was heated saturated titanium hydride up to the temperature of its decomposition with the evolution of hydrogen and when an excess pressure of hydrogen of 0.2-0.3 MPa is reached, the hydrogenation of the tantalum ingot initiated by decomposition of titanium hydride with hydrogen continues.

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