CN114433861A - A kind of method for preparing cobalt powder from cobalt oxalate - Google Patents

Abstract

The present invention provides a method for preparing cobalt powder from cobalt oxalate, which comprises the following steps: Step 1, the cobalt oxalate powder is heated to a reduction temperature under the condition that hydrogen is introduced. In step 2, the cobalt oxalate powder and hydrogen are reacted at the reduction temperature to obtain the cobalt powder, and then cooled to normal temperature. The reduction temperature has a corresponding relationship with the content of the crystal form in the cobalt powder, and the crystal form of the cobalt powder is controlled within a certain proportion range by controlling the reduction temperature. The preparation method of the present invention has the advantages of simple process and relatively accurate control of the crystal form ratio.

Description

A kind of method for preparing cobalt powder from cobalt oxalate

technical field

The invention relates to the field of preparing cobalt powder by hydrogen reduction, in particular to a method for preparing cobalt powder by hydrogen reduction of cobalt oxalate.

Background technique

Because of its unique chemical properties, cobalt is often used as an important constituent phase in cemented carbide, diamond tools and magnetic materials. Cobalt is an allotropic polymorphic metal that can undergo crystal transformation under certain conditions. Studies have shown that cobalt has two stable crystal forms: a face-centered cubic structure (FCC) in a stable state at high temperature, and a hexagonal close-packed structure (HCP) in a stable state at room temperature. Face-centered cubic cobalt has 12 slip systems and has better plasticity, which can make cemented carbide show better toughness when dealing with external impact. Close-packed hexagonal cobalt has only 3 slip systems, showing more brittleness, which is beneficial to the crushing and mixing between cobalt powder and tungsten carbide during ball milling. In order to meet the needs of ball milling without affecting the properties of the alloy, it is particularly important to control the relative content of the crystal form during the preparation of cobalt powder. However, there are only qualitative studies in the current method, and it is difficult to control the phase composition ratio of the final product to a relatively high level. within a small range.

Patent application number CN101653830B discloses a method for preparing ultrafine cobalt powder with hexagonal close-packed structure (HCP) or face-centered cubic structure (FCC) by hydrogen reduction. The method adopts the combination of high-pressure hydrogen reduction and high-temperature solid-phase hydrogen reduction. The method for obtaining cobalt powder with a close-packed hexagonal structure or a face-centered cubic structure at a secondary hydrogen reduction temperature is relatively complicated, and the preparation process is relatively complicated, and there is no disclosure of a technical solution that can obtain a ratio of the close-packed hexagonal structure to the face-centered cubic structure within a narrow range. .

In order to solve the above problems, we have been looking for an ideal technical solution.

SUMMARY OF THE INVENTION

The purpose of the present invention is to aim at the deficiencies of the prior art, thereby providing a method for preparing cobalt powder from cobalt oxalate, which can control the crystal form ratio in the cobalt powder within a relatively small range.

In order to achieve the above object, the technical scheme adopted in the present invention is:

A method for preparing cobalt powder from cobalt oxalate, which comprises the following steps: step 1, the cobalt oxalate powder is heated to a reduction temperature under the condition of introducing hydrogen to prevent the cobalt oxalate hydrate from being decomposed into cobalt powder or cobalt oxide; step 2, the The cobalt oxalate powder and hydrogen are reacted at the reduction temperature T to obtain the cobalt powder, and then cooled to normal temperature; the reduction temperature T and the content X of the close-packed hexagonal phase in the cobalt powder correspond to the following table, and the center of the cobalt powder The content of the cubic phase is Y, Y=1-X:

content reduction temperature 85%<X≤100% 280℃≤T≤300℃ 70%＜X≤85% 300℃＜T≤330℃ 55%＜X≤70% 330℃＜T≤340℃ 40%＜X≤55% 340℃＜T≤370℃ 25%＜X≤40% 370℃＜T≤390℃ 10%＜X≤25% 390℃＜T≤440℃ 0%＜X≤10% 440℃＜T≤550℃

The reaction equipment can be quartz tube slide rail tube furnace, single tube furnace, double tube furnace, fifteen tube furnace and other common reduction furnaces in metal powder smelting industry. ), the best purity is >99% (V/V).

As a further improvement of the technical solution, when the temperature is above 400°C, preventing the cobalt powder from cooling too fast will cause the phase transition of the cobalt powder, the crystal form ratio of the cobalt powder cannot be accurately controlled, and the cooling rate during cooling is ≤10°C/min. More preferably, the temperature is close to the phase transition temperature of cobalt powder at 400-430°C, and the cooling rate during cooling is ≤10°C/min.

As a further improvement of the technical scheme, when the temperature of the reaction system is 400-430°C, the cooling rate during cooling is 1-5°C/min.

As a further improvement of the technical solution, when the temperature of the reaction system is 400-430°C, the cooling rate during cooling is 1-3°C/min.

As a further improvement of the technical solution, the Fisher particle size of the cobalt oxalate powder is 1.3-2.0 μm.

As a further improvement of the technical solution, the general industrial cobalt oxalate contains a large amount of adsorbed water, and it also includes the step of first placing the cobalt oxalate powder in an inert atmosphere and warming up to the dehydration temperature to remove the adsorbed water, and the inert atmosphere can be nitrogen. Or a group zero element gas. In order to be heated evenly, the temperature can be raised slowly, and dehydration can be carried out during the heating process.

As a further improvement of the technical solution, in order to ensure the removal of water absorbed by cobalt oxalate, the dehydration temperature is 100-150°C.

As a further improvement of the technical solution, in order to heat the raw material uniformly, the heating rate in the step of removing the adsorbed water is 3-10°C/min.

As a further improvement of the technical solution, in order to heat the raw material uniformly, the temperature rising rate is 3-8°C/min.

As a further improvement of the technical solution, to maintain the stability of the reduction reaction temperature and reduce the generation of side reactions, the rate at which hydrogen is introduced into the reaction system in the second reaction process is 1-2 L/min.

As a further improvement of the technical solution, when the temperature of the reaction system is above 150°C, the cooling rate during step 2 cooling is 1-5°C/min; preferably, the cooling rate during step 2 cooling is 1-3°C/min.

Compared with the prior art, the present invention has outstanding substantive features and significant progress. Specifically, the preparation method of the present invention has a simple process and only needs to control the reduction temperature to obtain cobalt powder with a crystal form ratio within a relatively small range. The invention has the advantages of simple process and relatively accurate control of the crystal form ratio.

Detailed ways

The technical solutions of the present invention will be further described in detail below through specific embodiments.

In each embodiment, adopt the inner diameter 89mm quartz tube slide rail tube furnace to carry out hydrogen reduction cobalt carbonate to prepare cobalt powder, and select 5cm*4cm*3cm stainless steel boat, the stainless steel boat is made of Cr25Ni20, and 25g is loaded in the boat. The cobalt oxalate powder was shaken to level, the water content of the cobalt oxalate powder was 2.3% (adsorbed water), and the Fischer particle size of the cobalt oxalate was 1.57 μm.

The crystal form of cobalt powder was characterized by Bruker D8 Advance X-ray diffractometer, and the crystal form ratio was calculated according to the standard YB/T5320-2006.

The moisture content of cobalt oxalate was determined by drying and weighing, and the Fisher particle size of cobalt oxalate powder and cobalt powder was determined by WLP-208A average particle size analyzer.

Example 1

Pour argon gas into the furnace for 30min, check that the oxygen content in the exhaust gas is less than 0.1%, and slowly heat up to 120°C for dehydration, and the heating rate is 5°C/min.

Switch to feed hydrogen into the furnace and continue to heat up, the hydrogen flow rate is 1.5 L/min, the heating rate is 5 °C/min, the temperature is increased to the set reduction temperature of 350 °C, and the reduction temperature is 350 °C for 165min.

After the reaction, the product was cooled with the furnace, and the cooling rate was less than 3°C/min. After cooling to room temperature, the hydrogen was turned off and the product was taken out for vacuum sealing.

The obtained cobalt powder has a Fisher particle size of 0.9 μm, and the results of XRD detection and quantitative calculation are: HCP content 47.4%, FCC content 52.6%.

Example 2

Pour argon gas into the furnace for 30min, check that the oxygen content in the exhaust gas is less than 0.1%, and slowly heat up to 120°C for dehydration, and the heating rate is 5°C/min.

Switch to feed hydrogen into the furnace and continue to heat up, the hydrogen flow rate is 1.5 L/min, the heating rate is 5 °C/min, the temperature is increased to the set reduction temperature of 400 °C, and the reduction temperature is 400 °C for 165min.

After the reaction, the product was cooled with the furnace, and the cooling rate was less than 3°C/min. After cooling to room temperature, the hydrogen was turned off and the product was taken out for vacuum sealing.

The obtained cobalt powder has a Fisher particle size of 0.96 μm, and the results of XRD detection and quantitative calculation: the HCP content is 18.9%, and the FCC content is 81.1%.

Example 3

Pour argon gas into the furnace for 30min, check that the oxygen content in the exhaust gas is lower than 0.1%, and slowly heat up to 120 °C, and the heating rate is 5 °C/min.

Switch to feed hydrogen into the furnace and continue to heat up, the hydrogen flow rate is 1.5 L/min, the heating rate is 5 °C/min, the temperature is increased to the set reduction temperature of 480 °C, and the reduction temperature is 480 °C for 165min.

After the reaction, the product was cooled with the furnace, and the cooling rate was less than 3°C/min. After cooling to room temperature, the hydrogen was turned off and the product was taken out for vacuum sealing.

The obtained cobalt powder has a Fisher particle size of 1.95 μm, and the XRD detection and quantitative calculation show that the HCP content is 5.2%, and the FCC content is 94.8%.

Example 4

Pour argon gas into the furnace for 30min, check that the oxygen content in the exhaust gas is lower than 0.1%, and slowly heat up to 120 °C, and the heating rate is 5 °C/min.

Switch to feed hydrogen into the furnace and continue to heat up, the hydrogen flow rate is 1.5 L/min, the heating rate is 5 °C/min, the temperature is increased to the set reduction temperature of 500 °C, and the reduction temperature is 500 °C for 165min.

After the reaction, the product was cooled with the furnace, and the cooling rate was less than 3°C/min. After cooling to room temperature, the hydrogen was turned off and the product was taken out for vacuum sealing.

The obtained cobalt powder has a Fisher particle size of 2.03 μm, and the XRD detection and quantitative calculation show that the HCP content is 4%, and the FCC content is 96%.

Example 5

Pour argon gas into the furnace for 30min, check that the oxygen content in the exhaust gas is lower than 0.1%, and slowly heat up to 120 °C, and the heating rate is 5 °C/min.

Switch to feed hydrogen into the furnace and continue to heat up, the hydrogen flow rate is 1.5 L/min, the heating rate is 5 °C/min, the temperature is increased to the set reduction temperature of 300 °C, and the reduction temperature is 300 °C for 165min.

After the reaction, the product was cooled with the furnace, and the cooling rate was less than 3°C/min. After cooling to room temperature, the hydrogen was turned off and the product was taken out for vacuum sealing.

The obtained cobalt powder has a Fisher particle size of 0.84 μm, which is detected by XRD and quantitatively calculated: the content of HCP is 100%, and the content of FCC is 0%.

Finally it should be noted that: the above embodiment is only used to illustrate the technical scheme of the present invention and not to limit it; although the present invention has been described in detail with reference to the preferred embodiment, those of ordinary skill in the art should understand that it is still possible to The specific embodiments of the invention are modified or some technical features are equivalently replaced; without departing from the spirit of the technical solutions of the present invention, all of them should be included in the scope of the technical solutions claimed in the present invention.

Claims (10)

1. a method for preparing cobalt powder by cobalt oxalate, is characterized in that, it comprises the steps: step 1, cobalt oxalate powder is warming up to reduction temperature under the condition of feeding hydrogen; step 2, described cobalt oxalate powder and hydrogen are The cobalt powder is obtained by reacting at the reduction temperature T, and then cooled to normal temperature; wherein, the corresponding relationship between the reduction temperature T and the content X of the close-packed hexagonal phase in the cobalt powder is shown in Table I, Table I content reduction temperature 85%<X≤100% 280℃≤T≤300℃ 70%＜X≤85% 300℃＜T≤330℃ 55%＜X≤70% 330℃＜T≤340℃ 40%＜X≤55% 340℃＜T≤370℃ 25%＜X≤40% 370℃＜T≤390℃ 10%＜X≤25% 390℃＜T≤440℃ 0%＜X≤10% 440℃＜T≤550℃ . 2. the method for preparing cobalt powder from cobalt oxalate according to claim 1, is characterized in that, when reaction system temperature is above 400 DEG C, the cooling rate during step 2 cooling≤10 DEG C/min; When the temperature is 400-430°C, the cooling rate during cooling in step 2 is ≤10°C/min; preferably, the cooling rate is 1-5°C/min. 3. the method for preparing cobalt powder from cobalt oxalate according to claim 2, is characterized in that, described cooling rate is 1-3 ℃/min. 4. The method for preparing cobalt powder from cobalt oxalate according to any one of claims 1-3, wherein the cobalt oxalate powder has a Fisher particle size of 1.3-2.0 μm. 5. The method for preparing cobalt powder from cobalt oxalate according to claim 4, characterized in that, it further comprises the step of first placing the cobalt oxalate powder in an inert atmosphere and warming up to a dehydration temperature to remove adsorbed water. 6. The method for cobalt cobalt oxalate powder according to claim 5, wherein the dehydration temperature is 100-150 °C. 7. The method for preparing cobalt powder from cobalt oxalate according to claim 5 or 6, characterized in that, in the step of removing adsorbed water, the heating rate is 3-10°C/min. 8 . The method for preparing cobalt powder from cobalt oxalate according to claim 7 , wherein the heating rate is 3-8° C./min. 9 . 9. the method for preparing cobalt powder from cobalt oxalate according to claim 5, is characterized in that, in step 2 reaction process, the speed that hydrogen passes into reaction system is 1-2L/min. 10. the method for preparing cobalt powder from cobalt oxalate according to claim 5, is characterized in that, in step 2, when reaction system temperature is above 150 ℃, the cooling rate during cooling is 1-5 ℃/min; Preferably step 2 The cooling rate during cooling is 1-3°C/min.