WO2012162936A1

WO2012162936A1 - Coated cobalt powder and preparation method thereof

Info

Publication number: WO2012162936A1
Application number: PCT/CN2011/077727
Authority: WO
Inventors: 郭苗苗; 马哲波; 何显达; 周继峰; 傅月; 刘琮
Original assignee: 深圳市格林美高新技术股份有限公司; 荆门市格林美新材料有限公司
Priority date: 2011-05-30
Filing date: 2011-07-28
Publication date: 2012-12-06
Also published as: CN102303114B; EP2716387B1; EP2716387A1; EP2716387A4; US20140113140A1; CN102303114A

Abstract

Provided are a coated cobalt powder and a preparation method thereof, the coated cobalt powder consisting of cobalt powder, and paraffin wax, polyethylene glycol or polyethylene coated on the outer surface of the cobalt powder. Using the coated cobalt powder to replace traditional cobalt powder as the raw material for preparing hard alloys, the dusts generated during production can be reduced, and the environment in a production shop can be improved; simultaneously, the paraffin wax, the polyethylene glycol or the polyethylene coated on the surface of the cobalt powder can effectively prevent the cobalt powder from being oxidized by the oxygen or water vapor in the air, thus improving the quality of the cobalt powder. The preparation process of the coated cobalt powder is free from contamination and the coated cobalt powder is suitable for industrialized production.

Description

Coated cobalt powder and preparation method thereof. The present application claims to Chinese Patent Application No. 201110142262.8, filed on May 30, 2011, entitled "A coated cobalt powder and its preparation method" Priority is hereby incorporated by reference in its entirety. Technical field

The present invention relates to a raw material cobalt powder in the field of cemented carbide, and more particularly to a coated cobalt powder and a method for preparing the same. Background technique

Cemented carbide is usually composed of refractory metal carbides and bonding metals (such as cobalt and nickel). The preparation methods mainly include: mixing metal carbides and bonding metals, ball milling (mixing and mixing), molding (adding Steps of molding agent, granulation, press molding, removal of molding agent, and sintering.

Among them, molding is an important part in the process of preparing cemented carbide. Since cemented carbide is mainly composed of refractory metal carbide with high hardness, high modulus of elasticity and high compressive strength, the powder is hard to be plastically deformed during pressing, and molding is difficult. Moreover, there are fine defects (holes, inclusions, delamination and cracks) in the formed blank, which are not easily eliminated during the sintering process and may seriously affect the quality of the product. The addition of a molding agent can help improve the performance of the blank and sintered product. At the same time, the molding agent must be completely removed, and any residue will bring hidden dangers to the quality of the sintered product.

At present, the molding agents commonly used at home and abroad are mainly paraffin wax (polymerization agents such as polyethylene glycol PEG and polyethylene PE have also been reported). Usually, the paraffin wax is mixed with the wet-milled and dried cemented carbide powder in the form of paraffin gasoline, and the paraffin is dispersed in the cemented carbide. It has also been reported that ball blends such as refractory metal carbides, binder metals and paraffin are directly formed by ball milling. But in these methods, the bond gold Genus (eg, cobalt, nickel, etc.) is easily oxidized by oxygen or water vapor in the air before being incorporated into paraffin, especially for fine particles and ultrafine particles, and the quality control of the cemented carbide powder is difficult. In addition, a large amount of respirable dust is easily generated in the mixing ingredients and the ball milling process before the molding agent is added, which contaminates the production environment of the cemented carbide workshop and seriously jeopardizes the health of the production workers. Summary of the invention

In order to solve the above problems, the present invention aims to provide a coated cobalt powder and a preparation method thereof. The coated cobalt powder is composed of cobalt powder and paraffin wax, polyethylene glycol or polyethylene coated on the outer surface of the cobalt powder. The coated cobalt powder replaces the conventional cobalt powder as a raw material for preparing the cemented carbide, thereby reducing the dust generated in the production process, improving the environment of the production workshop, and simultaneously, paraffin wax and polyethylene glycol coated on the surface of the cobalt powder. Or polyethylene can effectively prevent cobalt powder from being oxidized by oxygen or water vapor in the air, thereby improving the quality of the cobalt powder.

In one aspect, the present invention provides a coated cobalt powder consisting of cobalt powder and paraffin wax, polyethylene glycol or polyethylene coated on the outer surface of the cobalt powder, the paraffin, polyethylene glycol or polyethylene constituting cobalt The powder quality is 1.5% to 2.5%.

Among them, paraffin has the advantages of no mechanical impurities, low molecular weight, saturated linear hydrocarbons, high temperature and complete residue, and no residue; polyethylene glycol (PEG) is completely soluble in water and compatible with many substances. Large substance shows maximum compatibility, non-toxic, non-irritating; Polyethylene (PE) is a crystalline raw material, minimal hygroscopicity, good molecular chain flexibility, low bond force, low melt viscosity, and extremely fluid it is good. Paraffin wax, combined.

The invention provides for the first time a cobalt powder coated with an appropriate amount of paraffin, polyethylene glycol or polyethylene on the outer surface, which can be used as a raw material for preparing a cemented carbide instead of the conventional cobalt powder. The particle size of the coated cobalt powder of the invention is larger than the particle size of the original cobalt powder, and the paraffin wax, polyethylene glycol or polyethylene in the coated cobalt powder is coated on the surface of the original cobalt powder. Preferably, paraffin, polyethylene glycol or polyethylene comprises 2% by mass of the cobalt powder. The dust generated during the production process improves the environment of the production workshop. At the same time, paraffin, polyethylene glycol or polyethylene coated on the surface of the cobalt powder can effectively prevent the cobalt powder from being oxidized by oxygen or water vapor in the air, thereby increasing the cobalt powder. the quality of.

In a second aspect, the present invention provides a method for preparing coated cobalt powder, comprising the steps of: taking cobalt powder and cobalt powder with a mass of 1.5% to 2.5%, and pouring the paraffin into an organic solvent to form a paraffin-organic The solvent mixture, the paraffin-organic solvent mixture is added to the cobalt powder, placed in a planetary power mixer, stirred and mixed, and vacuum dried to obtain a waxed cobalt powder.

Among them, the organic solvent is an organic solvent having a high solubility to paraffin and a low boiling point. Preferably, the organic solvent is n-hexane, n-heptane, toluene or ethyl acetate. More preferably, the organic solvent is ethyl acetate because, by contrast, ethyl acetate has the advantages of low boiling point, easy drying, high flash point, relatively safe, moderate solubility to paraffin, and relatively inexpensive. In the reaction, the organic solvent is recovered by condensation and is suitable for industrial production. Different grades of paraffin have different dissolution temperatures and mixing temperatures. Preferably, the solid-liquid ratio (g/mL) of the cobalt powder to ethyl acetate is 20 to 50:1. More preferably, when ethyl acetate is used as the organic solvent to dissolve paraffin No. 52, the solid-liquid ratio (g/mL) of ethyl acetate and cobalt powder is 20 to 25:1. Preferably, the temperature of the organic solvent is from 2 to 50 °C. Preferably, the paraffin wax comprises 2% by mass of the cobalt powder.

If the mixing time is too short, the coating effect is not uniform, and if the mixing time is too long, the time cost of industrial production will increase. Preferably, the mixing and mixing time is l~5h, and the stirring speed is 40~100 rpm. More preferably, the mixing time is 1 to 2 hours. There is no obvious requirement for temperature and pressure during the mixing and mixing process. Low temperature (2~50 °C) can be used under normal pressure. Subsequently, preferably, the vacuum drying temperature is 40 to 55 °C. After the waxy cobalt powder is obtained, the organic solvent is recovered by condensation and recycled.

In a third aspect, the present invention provides a method for preparing coated cobalt powder, comprising the steps of: taking cobalt powder and cobalt powder with a mass of 1.5% to 2.5%, respectively, into a planetary power mixer, and vacuum or nitrogen protection. The mixture was stirred and mixed under a protective condition to obtain a waxed cobalt powder. Preferably, the paraffin wax comprises 2% by mass of the cobalt powder. The method does not involve the process of dissolving paraffin by an organic solvent, but directly melts the paraffin with a certain stirring mixing temperature while stirring and mixing. Preferably, the stirring mixing temperature is 55 to 60 °C. Preferably, the mixing and mixing time is 1 to 5 hours, and the stirring speed is 40 to 100 rpm. More preferably, the stirring and mixing time is 1-2 hours. According to a fourth aspect, the present invention provides a method for preparing a coated cobalt powder, comprising the steps of: respectively taking cobalt powder and polyethylene powder having a mass of 1.5% to 2.5% of polyethylene powder, and putting it into a planetary power mixer; The mixture was stirred and mixed to obtain a coated cobalt powder with polyethylene glycol added or a coated cobalt powder with polyethylene. Preferably, the mixing and mixing time is 1 to 5 hours, and the stirring speed is 40 to 100 rpm. More preferably, the stirring and mixing time is 1 to 2 hours. There is no obvious requirement for temperature and pressure during the mixing and mixing process. Low temperature (2~50 °C) can be used under normal pressure. Subsequently, preferably, the vacuum drying temperature is 40 to 55 °C. The present invention provides for the first time a coated cobalt powder and a preparation method thereof, which have the following beneficial effects:

The dust improves the environment of the production workshop. At the same time, paraffin, polyethylene glycol or polyethylene coated on the surface of the cobalt powder can effectively prevent the cobalt powder from being oxidized by oxygen or water vapor in the air, thereby improving the quality of the cobalt powder. The preparation process of the coated cobalt powder of the invention is non-polluting and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the results of dust test of raw cobalt powder and waxed cobalt powder; FIG. 2 is an electron micrograph of waxed cobalt powder (organic solvent is ethyl acetate); FIG. 3 is waxed cobalt powder (organic solvent is positive) Electron micrograph of alkane);

Figure 4 is an electron micrograph of the original cobalt powder. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following are preferred embodiments of the present invention, it should be noted that Many modifications and refinements can be made by the skilled artisan without departing from the principles of the invention, and such modifications and refinements are also considered to be within the scope of the invention.

Embodiment 1

A preparation method of coated cobalt powder comprises the following steps: 9.6 g of paraffin is poured into 20 mL of ethyl acetate at 25 ° C to form a paraffin-ethyl acetate mixture, added to 480 g of cobalt powder, and placed in a planetary power mixture. The mixing time was 1.5 h, the stirring speed was 60 rpm, and then vacuum drying at 50 ° C to obtain a waxed cobalt powder.

The waxed cobalt powder can be used to prepare a cemented carbide. The method for preparing a cemented carbide comprises the steps of: mixing a tungsten carbide and a waxed cobalt powder; adding a small amount of paraffin as a molding agent; stirring and mixing; press molding; low temperature dewaxing; and high temperature sintering.

Among them, by reasonably controlling the total amount of paraffin added, the paraffin wax in the wax-added cobalt powder and the subsequently added paraffin wax can be completely removed in the low-temperature dewaxing step, without affecting the sintering of the cemented carbide. Cobalt powder can reduce the dust generated during the preparation of cemented carbide and improve the environment of the production workshop. At the same time, it can effectively prevent the cobalt powder from being oxidized by oxygen or water vapor in the air, thereby improving the quality of the cobalt powder and greatly improving the quality of the cobalt powder. The added value of cobalt powder makes the cobalt powder more competitive.

After the paraffin is removed, the cobalt powder is used as a binder in the firing process, and the high-temperature sintering is interspersed between the tungsten carbide crystal lattices, and its morphology has little effect on the difference in the quality of the cemented carbide.

Embodiment 2

A preparation method of coated cobalt powder comprises the following steps: respectively, 500 g of cobalt powder and 10 g of paraffin are placed in a planetary power mixer, stirred and mixed under a nitrogen protection condition, and the mixing temperature is 58 ° C, and the mixing time is stirred. For 3 h, the stirring speed was 60 rpm, and a waxed cobalt powder was obtained.

In the method, the paraffin wax is directly melted by using a stirring mixing temperature of 58 ° C, and the mixture is stirred and mixed so that the paraffin wax is uniformly coated on the outer surface of the cobalt powder. Embodiment 3

A preparation method of coated cobalt powder comprises the following steps: respectively, 500 g of cobalt powder and 10 g of polyethylene glycol are placed in a planetary power mixer, the mixing time is 4 h, the stirring speed is 50 rpm, and then 45 ° C was vacuum dried to obtain a coated cobalt powder with polyethylene glycol.

Paraffin wax, polyethylene glycol and polyethylene are all well-known molding agents in the preparation of cemented carbides, and therefore the present invention provides only a representative effect of the wax-added cobalt powder.

Effect embodiment

First, the experimental method

Paraffin wax with a mass ratio of 2% of cobalt powder is poured into 20~30mL organic solvent (n-hexane, n-heptane, toluene, ethyl acetate) at 2~50°C, and added to 600g cobalt powder. Cobalt powder, which can be purchased directly, also referred to as the original cobalt powder, is stirred at 100 rpm for 1~5h on a planetary power mixer at 0.6~1 atmosphere pressure, vacuum dried at 50 °C, numbered and mark. The specific optimization process is as follows. The waxed cobalt powders obtained in different batch tests are respectively numbered with different letters (for example, the number is ethyl acetate A refers to ethyl acetate as the organic solvent and according to the corresponding in Table 1 The test conditions were prepared by adding waxy cobalt powder).

Second, the experimental results

1. Effect of different organic solvents on waxing effect

Paraffin wax has different solubility in different organic solvents, so it is important to choose a suitable organic solvent. This test examines the effect of different organic solvents (n-hexane, toluene, ethyl acetate, and n-heptane) on the waxing effect. The results are shown in Table 1 (wherein, paraffin wax is No. 52 paraffin, FSSS is Fischer particle size value, "paraffin%" is the percentage of paraffin wax in the mass of cobalt powder, the same below; in addition, n-hexane A and n-hexane B respectively represent n-hexane The organic solvent was reacted with the original cobalt powder 1, and toluene, ethyl acetate VIII, ethyl acetate B and n-heptane were reacted with the original cobalt powder 2, respectively. Table 1. Physical and chemical indicators of waxed cobalt powder prepared by different organic solvents

Conclusion: Hexane, toluene, ethyl acetate and n-heptane can be used as the solvent for the paraffin wax in the waxed cobalt powder. Considering the preference of industrial production, the boiling point is low, easy to dry, high flashing point, relatively safe, An organic solvent in which the solubility of paraffin is moderate and relatively inexpensive, and ethyl acetate is preferred in the present invention.

2. Effect of different mixing conditions on waxing effect

In this experiment, ethyl acetate was used as an organic solvent to dissolve paraffin No. 52. The effects of different mixing conditions (mixing time, mixing temperature, mixed pressure and mixed solid-liquid ratio) on the waxing effect were investigated. The results are shown in Tables 2~4.

Table 2. Physical and chemical indicators of waxed cobalt powder prepared at different mixing times

Analysis: It can be seen from Table 2 that when the stirring time is 0.5h, the mixing is uneven, resulting in the addition of paraffin content higher than the theoretical 2%, and the hydrogen loss content is also obviously high, and the stirring time is lh and above. The mixing effect is relatively uniform, and the paraffin content fluctuates around 2%, so preferably, the waxing mixing time is l~2h. Table 3. Physical and chemical indicators of waxed cobalt powder prepared at different mixing temperatures

Analysis: It can be seen from Table 3 that under the mixing temperature of 2~50 °C and the mixed pressure of one atmosphere, the indexes of the waxed cobalt powder mixed for 2 hours have little difference, so the mixing test is for the environment. The requirements (temperature and pressure) are not very sensitive, and can be carried out at low temperature (2~50 °C) under normal pressure.

Table 4. Physical and chemical indicators of waxed cobalt powder prepared under different mixed solid-liquid ratios

Analysis: It can be seen from Table 4 that according to the solubility of paraffin wax No. 52 in ethyl acetate is 450 g/l, the theoretical solid-liquid ratio (g/mL) is 22.2, possibly due to the phenomenon of supersaturated solution. Therefore, when the solid-liquid ratio is increased to 25, the paraffin wax is still completely dissolved, and is not precipitated in the cobalt powder of 2 to 50 ° C, so that it can be uniformly added to the surface of the solid cobalt powder, so preferably, ethyl acetate and cobalt powder are used. The solid-liquid ratio (g/mL) is 20 to 25:1. Considering the difference between the dissolution temperature and the mixing temperature of each type of paraffin, when other types of paraffin are used, the solid-liquid ratio (g/mL) of ethyl acetate and cobalt powder is 20 to 50:1.

Conclusion: Ethyl acetate is used as the organic solvent. Preferably, the mixing time is 1-2 hours. The solid-liquid ratio (g/mL) of ethyl acetate and cobalt powder is 20~50:1, low temperature (2~50°C). It can be carried out under normal pressure.

Third, the characterization results

Taking the original cobalt powder 2, a sample of the waxed cobalt powder was prepared in accordance with the above preferred conditions for the following characterization experiments. Specifically, as shown in Table 5. Table 5. Preparation conditions for waxed cobalt powder samples

1, anti-oxidation experiment

The change in hydrogen loss with time was measured simultaneously with the above-mentioned sample of the wax-added cobalt powder (the organic solvent was ethyl acetate) and the original cobalt powder before the waxing. The results are shown in Table 6.

Table 6. Changes of hydrogen loss with time before and after cobalt powder addition at different temperatures

Analysis: Because paraffin wax is present in the wax-coated cobalt powder sample, it may affect the oxygen-sulfur meter, so the hydrogen loss value is used instead of the oxygen content. It can be seen from Table 6 that in the environment of 20 ° C and 40 ° C, the hydrogen loss of the waxed cobalt powder sample is lower than that of the original cobalt powder, indicating to some extent the sample of the waxed cobalt powder. It has oxidation resistance.

2, dust test

A sample of 100 g of the original cobalt powder and the waxed cobalt powder (the organic solvent was ethyl acetate) was placed in a jar, and shaken up and down for 1 min. The original cobalt powder on the left and the waxed cobalt powder sample on the right. The test results are shown in Figure 1. Figure 1 is a graph showing the results of the dust test of the original cobalt powder and the waxed cobalt powder sample.

Analysis: It can be seen from Fig. 1 that the original cobalt powder dust adheres more on the bottle wall, which is l.lg. After waxing, it is less on the bottle wall, 0.8g, and the dust is reduced after waxing 36 %.

3. Dispersion experiment

The ease with which the powder is dispersed in the air is called the degree of dispersion. The measurement method is that after 10 g of the original cobalt powder and the waxed cobalt powder are respectively dropped from a certain height, the percentage of the sample outside the tray is measured as a percentage of the total amount of the original cobalt powder and the waxed cobalt powder. See Table 7 for the results. The degree of dispersion is related to the dispersibility, floatability and spatterability of the sample. Table 7. Experimental results of dispersion of raw cobalt powder and waxed cobalt powder

Analysis: It can be seen from the figure that the dispersion of cobalt powder after the addition of paraffin wax is significantly reduced, from 5.3% of the original cobalt powder to 1.6% or even lower to 0.9%, indicating that the wax produced by the waxy cobalt powder is more than the original cobalt. Less powder.

4, electron microscopy

The results of the electron microscope scan are shown in Fig. 2, Fig. 3 and Fig. 4. Figure 2 is an electron micrograph of a sample of waxed cobalt powder (organic solvent is ethyl acetate N), Figure 3 is an electron micrograph of waxed cobalt powder (organic solvent is n-hexane A), and Figure 4 is an electron microscope of the original cobalt powder. Figure.

Analysis: As can be seen from Fig. 2, Fig. 3 and Fig. 4, the particle size of the waxed cobalt powder is larger than that of the original cobalt powder, and the paraffin wax in the waxed cobalt powder is wrapped around the surface of the original cobalt powder.

Claims

Rights request

A coated cobalt powder characterized by comprising cobalt powder and paraffin wax, polyethylene glycol or polyethylene coated on the outer surface of the cobalt powder, wherein the paraffin, polyethylene glycol or polyethylene accounts for Cobalt powder quality

1.5%~2.5%.

The coated cobalt powder according to claim 1, wherein the paraffin, polyethylene glycol or polyethylene accounts for 2% by mass of the cobalt powder.

3. A method for preparing coated cobalt powder, comprising the steps of: taking cobalt powder and cobalt powder with a mass of 1.5% to 2.5%, and pouring the paraffin into an organic solvent to form a paraffin-organic solvent mixture; The paraffin-organic solvent mixture is added to the cobalt powder, placed in a planetary power mixer, stirred and mixed, and vacuum dried to obtain a waxed cobalt powder.

The method of producing coated cobalt powder according to claim 3, wherein the organic solvent is n-hexane, n-heptane, toluene or ethyl acetate.

The method for producing coated cobalt powder according to claim 4, wherein the solid powder ratio of the cobalt powder to the ethyl acetate is 20 to 50:1.

The method for preparing coated cobalt powder according to claim 3, wherein the stirring and mixing time is l~5h, and the stirring speed is 40~100 rpm.

7. A method for preparing coated cobalt powder, comprising the steps of: taking cobalt powder and cobalt powder with a mass of 1.5% to 2.5%, respectively, into a planetary power mixer under vacuum or nitrogen protection conditions; Stirring and mixing were carried out to obtain a waxy cobalt powder.

The method for producing coated cobalt powder according to claim 7, wherein the stirring and mixing temperature is 55 to 60 °C.

The method for preparing coated cobalt powder according to claim 7, wherein the stirring and mixing time is l~5h, and the stirring speed is 40~100 rpm.

10. A method for preparing coated cobalt powder, comprising the steps of: respectively taking cobalt powder and polyethylene powder of polyethylene powder or polyethylene having a mass of 1.5% to 2.5%, stirring and mixing in a planetary power mixer, vacuum drying, System Polyethylene glycol coated cobalt powder or polyethylene coated cobalt powder