RU2647971C2 - Method for obtaining the tantalum dust of a regulate size - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to the metallothermic production of tantalum dust by reduction from a complex fluoride salt of tantalum in hot solution of halogen salts of alkali metals. Method comprises scaling of complex fluoride banding and reducing agent into a hot solution of alkali metal halogen salts and stirring the hot solution to ensure the reduction of the tantalum dust. Scaling of the complex fluoride salt of tantalum and a reducing agent into the hot solution of halogen salts of alkali metals is carried out by at least twenty portions. Average excess amount of the reducing agent presenting in the reactional hot solution from the stoichiometrically necessary to restore a single scale of the complex fluoride salt of tantalum is set from minus 250 % to plus 100 %. Sulfur content in the reactional hot solution is maintained at not more than 0.085 mass% in terms of the sulfate ion.

EFFECT: improved management of the reduction process is provided.

3 cl, 2 dwg, 4 tbl, 19 ex

Description

The invention relates to powder metallurgy, in particular, to a method for producing primary tantalum powder of controlled fineness by metallothermal reduction from a complex fluoride compound in a melt of alkali metal halide salts. The powder can be used for the manufacture of radio capacitors.

A known method of producing tantalum powder (United States Patent No. 4582530 "Method of making a valve metal powder for electrolytic condensers and the like" / Hans J. Heinrich, Meinhard Aits. 1986. IPC B22F 9/16; B22F 9/20; C22B 34 / 24; C22C 1/04; C22B 34/00; B22F 009/00), which includes the following operations:

- the formation of a mixture of a double fluoride salt of a valve metal and metallic sodium or potassium, or an alloy of sodium with potassium;

- adding an effective amount of sulfur to the mixture;

- heating the reaction mixture to form a melt;

- leaching of salt reaction products.

Tantalum acts as a valve metal.

Sulfur is introduced into the reaction mixture in the form of elemental sulfur, sulfur, an inorganic or organic compound in an amount of from 50 ppm to 500 ppm (from 0.005% to 0.05%) of the amount of the valve metal.

The disadvantage of this method is that the method does not allow to obtain a powder with a specific surface area of more than 0.6 m ² / g

Also known is a method for producing tantalum powder (United States Patent No. 5234491 “Method of producing high surface area, low metal impurity” / Hongtu Chang. 1993. IPC B22F 9/24; B22F 9/16; C22B 34/24; C22B 34/00 ; B22F 009/18), which includes the following operations:

- adding to the reactor a component having a greater chemical activity than the material of the reactor in an amount sufficient to remove part of the water and air from the reactor;

- reduction of tantalum from the compound with a reducing agent to obtain tantalum powder.

The method is primarily aimed at reducing the corrosive effects of gases released from salts during their heating and melting on the material of the crucible or lining of the crucible.

As the active component, alkali or alkaline earth metals are used. Preferably, metallic sodium (lumpy) is used, which is loaded onto the bottom of the crucible under a layer of salts.

The resulting oxide of the active component present in the melt acts as crystallization centers and contributes to a finer powder.

The disadvantage of this method is that the active component loaded into the crucible has a reduced specific surface area, and, accordingly, the rate of absorption of gases by it is low. The efficiency of using alkali or alkaline earth metals as an active component increases only with an increase in temperature in the crucible above the boiling point of the active component (for sodium, 883 ° С).

A known method of producing tantalum powder (United States Patent No. 5442978 "Tantalum production via a reduction of K ₂ TaF ₇ , with diluent salt, with reducing agent provided in a fast series of slug additions" / Richard Hildreth, Malcolm Shaw, Terrance B. Tripp , Leo G. Gibbons. 1995. IPC B22F 9/24; B22F 9/16; C22B 34/24; C22B 34/00; B22F 009/00), which aims to reduce the corrosive effects of the gases released from salts by the crucible material heating and melting them. As an active component added to the crucible, finely divided tantalum powder acts.

The disadvantage of this method is that tantalum powder is added directly to the reactor (crucible), which is associated with the risk of contamination of the resulting powder with impurities contained in the added powder. The tantalum powder added to the reactor must have an increased purity and, accordingly, has an increased cost.

Closest to the proposed invention is a method for producing tantalum powder (United States Patent No. 4684399 "Tantalum powder process" / Roger M. Bergman, Charles E. Mosheim. 1987. IPC B22F 9/24; B22F 9/16; C22B 5/04; C22B 5/00; C22B 34/24; C22B 34/00; C22B 034/20), according to which tantalum powder is obtained by metallothermal reduction from a compound by continuous or batch loading of a tantalum compound and a reducing agent into a reactor during a reduction reaction.

Potassium or sodium fluorotantalate, tantalum chloride or a mixture of these compounds can act as a tantalum compound, and sodium, potassium, or an alloy of these metals can be used as a reducing agent. Potassium fluorotantalate and sodium are preferably used. Potassium fluorotantalate is used in solid form, and sodium in the form of a melt.

Sodium is loaded into the reactor at a rate of from 0.09 kg / min to 6.8 kg / min.

Potassium fluorotantalate is loaded into the reactor in portions from 1/20 to 1/2 of the full charge.

The temperature in the reactor is maintained in the range from 600 ° C to 950 ° C.

This method is taken as a prototype.

The disadvantage of the prototype is that the regulation of the size of the powder is carried out by changing the amount of halide salts or compounds of tantalum (potassium fluorotantalate), as well as by changing the number of servings. A change in the mass of halide salts or potassium fluorotantalate leads to a change in the technical and economic indicators of the process for the powder of each size class. An increase in the portion mass makes it difficult to maintain the temperature of the reaction melt at a predetermined level - when loading the reducing agent, the melt needs to be cooled, and when loading the tantalum compound (potassium fluorotantalate), it must be heated, which also increases the duration of the process and energy consumption.

The task of the invention is to change the algorithm for loading reagents and the amount of sulfate ion in the reaction melt.

The technical result of the invention is to simplify and increase the efficiency of managing the recovery process.

The essence of the invention lies in the fact that, in contrast to the known method of metallothermal production of tantalum powder by reduction from a complex fluoride salt of tantalum in a melt of alkali metal halide salts, which includes loading the complex fluoride salt and a reducing agent into a melt of alkali metal halide salts and mixing the melt to ensure tantalum recovery , loading complex fluoride salts and a reducing agent in the melt of halides of alkali metals is carried out not less than twenty in portions, while the average for the process excess of the reducing agent present in the reaction melt, from the stoichiometrically necessary to restore one loaded portion of the complex tantalum fluoride salt, is from minus 250% to plus 100%, and the sulfur content in the reaction melt is maintained no more than 0.085% (wt. .) in terms of sulfate ion.

During the reduction, potassium fluorotantalate or sodium fluorotantalate can act as the initial complex tantalum fluoride salt, sodium, potassium, or an alloy of sodium with potassium as a reducing agent, and potassium chloride, potassium fluoride, sodium chloride, and sodium fluoride as halide salts of alkali metals or a mixture of at least two of these salts. Preferably, the starting complex tantalum fluoride salt is potassium fluorotantalate, sodium is the reducing agent, and the reaction melt consists of potassium chloride and potassium fluoride.

It was found that the size of the obtained powder depends on the concentration of potassium fluorotantalate and sodium in the reaction melt, referred to the mass of a portion of potassium fluorotantalate. With an increase in the concentration of potassium fluorotantalate, the size of the obtained powder increases, and with an increase in the concentration of sodium, it decreases. As will be shown in the examples below, with a change in the concentration of reagents, the fineness of the obtained powder changes monotonously.

For the convenience of practical use, the specific concentration of potassium fluorotantalate and the specific concentration of sodium are expressed in terms of the specific concentration of one reagent, namely sodium. The specific concentration of sodium is expressed as the excess of the stoichiometrically necessary for the recovery of one loaded portion of potassium fluorotantalate.

A positive excess indicates the presence of excess sodium in the melt, and a negative excess indicates the presence of excess potassium fluorotantalate.

порции фтортанталата калия рассчитывают следующим образом:Excess sodium from stoichiometrically necessary to recover boot

portions of potassium fluorotantalate are calculated as follows:

,

,

Where

ω - excess sodium,%

- масса натрия;

- mass of sodium;

m _ftk is the mass of potassium fluorotantalate;

0.2933 is the proportionality coefficient connecting the mass of potassium fluorotantalate with the mass of sodium stoichiometrically necessary for tantalum reduction (calculated from the reaction equation);

n is the total number of servings.

In the last portion, all excess sodium, which is necessary for the guaranteed complete progress of the reduction reaction, is loaded into the crucible. Since the mass of excess sodium can be comparable with the mass of sodium necessary to restore one portion of potassium fluorotantalate, the last portion is not taken into account.

The excess sodium calculated for all portions taken into account (n-1) is averaged.

It is established that an increase in the average excess of sodium over a process of more than 100% leads to an increase in the oxygen content in the resulting powder. Due to evaporation, excess sodium enters the potassium fluorotantalate loading port, which causes it to become clogged with the reduced product. When the average sodium excess for the process is reduced to less than “minus” 250%, the content of alkali metals in the resulting powder increases.

Sulfur contained in the reaction melt, for example, in the form of a sulfate ion, acts as a surfactant. The surface properties of the contacting phases affect the rate of formation and growth of crystals (Khamsky EV "Crystallization in the chemical industry." - M .: Chemistry, 1969, p. 55, 103, 104), in our case, powder particles.

When carrying out the reduction in accordance with this invention, an increase in the sulfur content in the reaction melt leads to an acceleration of immersion in the melt of the product being restored on the surface. When immersed in the melt, the reduced product cools and the growth of powder particles stops.

It was established that the powder obtained as a result of reduction in a salt melt with a high sulfur content has an increased activity during sintering (a “structurally sensitive” property). In this case, the sulfur content in the resulting powder is lower than the sensitivity used by the analysis methods, for example, less than 0.001%. The greater activity during sintering is due to the lower thermal effect obtained by the powder during reduction.

Preferably, the reduction is carried out in a melt with a minimum sulfur content.

With an increase in sulfur content in the reaction melt of more than 0.085% (mass.) In terms of sulfate ion, the resulting powder is characterized by increased sintering activity and is not suitable for the production of agglomerated condenser powders.

The course of the reduction reaction, which proceeds with the release of heat, leads to an increase in the temperature of the reaction melt, and the loading of potassium fluorotantalate, due to the expenditure of heat for heating and melting the salt, leads to a decrease in temperature. As will be shown below in the examples, the number of portions of at least twenty allows maintaining a constant temperature of the melt with an accuracy of ± 10 ° C, without resorting to artificial cooling or heating.

The salts used to create the reaction melt contain volatile impurities (water, free acids, etc.).

For example, in the potassium salt of chloride grade “ChP”, the content of free acid (Hcl) is allowed up to 0.002%, the loss on ignition is up to 0.5%. Complete dehydration of potassium chloride salt is achieved at a temperature of 550-600 ° C. At this temperature, corrosion of most structural materials, including nickel and tantalum, is inevitable. The ingress of corrosion products of steels, alloys and nickel into the crucible leads to contamination of the resulting powder. The interaction of tantalum with water (oxidation) leads to its embrittlement and, accordingly, to a decrease in the working life of the equipment.

To protect against corrosion, finely dispersed tantalum powder is applied to the internal surfaces of the device, in addition to the internal surface of the crucible and the surfaces of the screens facing the mirror of the reaction melt. The powder is applied in the form of a suspension with a brush, roller or spray at the rate of at least 0.1 kg of powder per 1 m ^{2 of} surface and dried, while the mass of the powder should be at least 0.4 kg per 100 kg of alkali metal halides loaded into the crucible. After drying, the fine powder adheres to the surface on which it is applied as it happens, for example, with clay. To increase the adhesion and mechanical strength of the coating, a neutral salt, such as potassium chloride, can be added to the pulp.

Powder coating has a barrier function, protecting the surface on which it (coating) is applied from corrosion.

Fine powder is also a getter. Since the powder coating is located on the heat supply side, as well as due to the increased specific surface area, the powder is oxidized primarily and absorbs gases released from salts. Thus, while maintaining a reduced partial pressure of corrosive gases inside the device, elements of internal equipment that do not apply powder are protected from corrosion.

In FIG. Figure 1 shows a schematic diagram of a recovery apparatus that was used in carrying out the restoration.

The device comprises a resistance furnace (1) equipped with a forced air cooling system (2) for heating and cooling the retort (3). The retort has a thermally insulated cover (4) with nozzles for loading reagents (5). The device is equipped with a device for maintaining and regulating the inert gas pressure, including a sodium vapor condenser (18), an exhaust valve (6) and an automatic valve for supplying inert gas (7).

An oil trap was used as an exhaust valve, and a second-stage reducer of an insulating breathing apparatus (AP-2000) was used as an automatic valve for supplying inert gas.

For mixing the reaction melt (16), the apparatus is equipped with a stirrer (8), driven by a mechanism (9), which allows the stirrer to be moved up and down along the axis of rotation.

To control the temperature of the melt, the device has a thermocouple (10) connected to the device through a separate port. The reaction crucible of the device is made in the form of a separate removable structural element (11). The crucible is lined with nickel (12) and, over nickel, with tantalum (13). A cap (14) is mounted on top of the crucible, and a shield (15) is mounted on the lid above the crucible. The screen consists of two parts: conical, located above the crucible and cylindrical, embedded in the pipe, on which the seal and centering unit of the mixer shaft is located (17).

Recovery was carried out as follows. In a crucible (11), salts were loaded in layers. The loaded crucible was placed in a retort (3), a cap (14) was placed on top of the crucible. The retort with the crucible was closed with a lid on which a stirrer (8), a shield (15), a thermocouple (10) and a capacitor (18) were already installed and fixed. Using a vacuum pump, air was pumped from the retort and filled with argon. After filling with argon, an exhaust valve (6) and an automatic valve for supplying argon (7) were installed on the condenser (18). The prepared retort was placed in the furnace (1) and the heating was turned on. To remove the bulk of the volatile impurities contained in the salts, the retort was held for some time at a temperature of 300-500 ° C, after which the temperature in the furnace was increased and the salts were melted. After the salts were melted, the stirrer (8) and the thermocouple (10) were lowered into the melt and stirring was turned on. To achieve the required reduction temperature, the melt (16) was cooled using a forced air cooling system (2). Then the cooling was stopped and the reagents were charged. After completion of the recovery, the stirrer and thermocouple were lifted from the melt, and the retort was kept for some time in the furnace for better separation of the melt, after which it was removed from the furnace and cooled. After cooling, the retort was disassembled and the crucible removed. Using a tilter, the crucible was turned over. If the ingot did not fall out, then with the help of a hook-ejector, the crucible was lifted and dropped onto a steel plate to knock out the ingot. The ingot was separated: the part of the ingot containing no powder was crushed and disposed of separately, and the part of the ingot containing the powder was also crushed and subjected to hydrometallurgical treatment. Salt products were dissolved in water, and the powder was treated with a mixture of hydrochloric and hydrofluoric acids, washed until neutral, and dried. Retort, as well as, if necessary, other parts of the device were cleaned, washed, dried and prepared for the next restoration.

Examples 1 to 7

In all examples, the reaction melt was composed of potassium chloride qualification “ChP” in the amount of 69.3 kg and potassium fluoride anhydrous grade (grade) “Special” in the amount of 54.5 kg. The total mass of 123.8 kg, the ratio of KCl: KF-1: 1 (mol).

In the potassium salt of chloride grade “ChP”, the sulfur content in terms of sulfate ion is allowed to be no more than 0.002%. According to the supplier’s specification, in the potassium salt of anhydrous fluoride grade (grade) “Special”, a sulfur content of not more than 0.002% (not more than 0.006% in terms of sulfate ion) is allowed.

Thus, in examples 1 to 7, the sulfur content in the reaction melt did not exceed 0.004% in terms of sulfate ion.

Recovery was carried out as described above. In example 1, the first portion of potassium fluorotantalate (FTK) was loaded at a temperature of 825-835 ° C, in examples 2 and 3 at a temperature of 810-820 ° C, and in examples 4 to 7 at a temperature of 795-810 ° C. After cooling the melt to 780 ° C, a portion of sodium was charged. The subsequent portions of potassium fluorotantalate were loaded after the melt temperature stopped growing after the sodium portion was loaded (not more than 800 ° С). Thus, during the recovery, the temperature was maintained in the range from 780 ° C to 800 ° C. In total, 68.6 kg of potassium fluorotantalum (salt: FTK-1.8 ratio) and 20.8-21.2 kg of sodium were charged for each recovery. The number of servings of sodium and, accordingly, acts of recovery is twenty.

The mass of portions of potassium fluorotantalate and sodium, as well as the average over the process excess of sodium present in the reaction melt, from the stoichiometrically necessary to restore the loaded portion of potassium fluorotantalate, are shown in table 1. Table 1 also shows the total excess of sodium, from the stoichiometrically necessary to restore all potassium fluorotantalate and the total specific surface area of the obtained powder (BET).

A diagram of the dependence of the fineness of the powder obtained in all examples on the average excess of sodium present in the reaction melt on the stoichiometrically necessary to restore the loaded portion of potassium fluorotantalate is shown in FIG. 2.

Examples 8 and 9

In examples 8 and 9, the recovery was carried out in the same way as in examples 2 and 3, with the difference that 85.75 kg of potassium fluorotantalum (salt: FTK-1.44 ratio) and 25.78-25 were charged to each recovery. 94 kg of sodium. The number of servings of sodium and, accordingly, acts of recovery is twenty-five.

The mass of servings of potassium fluorotantalate and sodium, as well as the average for the process excess of sodium present in the reaction melt, from the stoichiometrically necessary to restore the loaded portion of potassium fluorotantalate, are shown in table 2. Table 2 also shows the total excess of sodium, from stoichiometrically necessary to restore all potassium fluorotantalate and the total specific surface area of the obtained powder (BET).

Examples 10 to 14

In Examples 10-14, 100 g of 10-aqueous sodium sulfate was added to the reaction melt. Thus, taking into account the possible sulfur content in the starting salts, the content of sulfate ion in the reaction melt was not more than 0.028%.

Recovery was carried out as in examples 4 to 7.

The mass of servings of sodium and the average for the process excess of sodium present in the reaction melt, from the stoichiometrically necessary to restore the loaded portion of potassium fluorotantalate, are shown in table 3. Table 3 also shows the final excess of sodium, from the stoichiometrically necessary to restore all potassium fluorotantalate, as well as total specific surface area of the obtained powder (BET).

The weight of all servings of potassium fluorotantalate is 3.43 kg.

Examples 15 to 19

In Examples 15-19, 100 g of anhydrous sodium sulfate was added to the reaction melt. Thus, taking into account the possible sulfur content in the starting salts, the content of sulfate ion in the reaction melt was not more than 0.058%.

Recovery was carried out as in examples 10 to 14.

The mass of servings of sodium and the average for the process excess of sodium present in the reaction melt, from the stoichiometrically necessary to restore the loaded portion of potassium fluorotantalate, are shown in table 4. Table 4 also shows the final excess of sodium, from the stoichiometrically necessary to restore all potassium fluorotantalate, as well as total specific surface area of the obtained powder (BET).

As can be seen from the tables and FIG. 2, with an increase in the excess of sodium present in the reaction melt from the stoichiometrically necessary to restore one loaded portion of potassium fluorotantalate, the size of the resulting powder monotonously decreases (specific surface area increases). With an increase in the sulfate ion content in the reaction melt, the fineness of the resulting powder also decreases.

With an increase in the load mass of potassium fluorotantalate for the reduction process from 68.6 kg to 85.75 kg (1.25 times), a significant increase in the particle size of the obtained powder did not occur.

Claims (3)

1. The method of metallothermal production of tantalum powder by reduction from a complex fluoride salt of tantalum in a melt of alkali metal halides, comprising loading the complex fluoride compound and a reducing agent into a melt of alkali metal halides and mixing the melt to ensure recovery of tantalum powder, characterized in that the complex fluoride salt is charged tantalum and a reducing agent in the melt of halides of alkali metals is carried out in at least twenty portions, while the average for process excess of the reducing agent present in the reaction melt, from the stoichiometrically necessary to restore one loading portion of the complex tantalum fluoride salt, is set from minus 250% to plus 100%, and the sulfur content in the reaction melt is supported by not more than 0.085 wt.% in terms of sulfate ion . 2. The method according to p. 1, characterized in that potassium fluorotantalate or sodium fluorotantalate is used as a complex fluoride salt, sodium, potassium or an alloy of sodium with potassium is used as a reducing agent, and potassium chloride and potassium fluoride are used as alkali metal halide salts. , sodium chloride, sodium fluoride or a mixture of at least two of these salts. 3. The method according to p. 1, characterized in that the average process excess of the reducing agent present in the reaction melt is calculated from (n-1) portions, where n is the total number of portions.

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