Heterogeneous precipitation process for modified tin oxide powder doped with low and medium melting point oxides

Abstract

The application discloses a modified tin oxide powder doped with low-melting-point oxides and prepared by a heterogeneous precipitation method, and relates to the field of powder metallurgy. In the application, bismuth oxide is coated on the surface of tin oxide slurry with a D50 particle size of 0.5-3 microns prepared by a traditional acidification method, and then calcination is carried out at 900-1200 DEG C, liquid-phase sintering of the tin oxide is carried out by using the liquid-phase state of the bismuth oxide at the temperature, and then cooling is carried out, so that the modified tin oxide powder doped with low-melting-point oxides is obtained, and the modified tin oxide powder has a spherical shape, a concentrated and uniform particle size distribution and the characteristics of more concentrated particle size distribution, better particle size uniformity and easier dispersion and uniformity. Compared with the tin oxide powder prepared by a traditional acidification method, the low-melting-point oxide modified tin oxide powder prepared by the application has the characteristics of more concentrated particle size distribution, better particle size uniformity and easier dispersion and uniformity, and is beneficial to preparation of silver-tin oxide material with good uniformity and stable quality.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of powder metallurgy, in particular to a heterogeneous precipitation preparation process of modified tin oxide powder doped with low-melting-point oxides. BACKGROUND

[0002] Silver tin oxide material is one of the main materials of silver-based electrical contact materials used in the low-voltage electrical industry at present. The performance of the material mainly depends on the selection of oxides and the production and processing technology, and the morphology and particle size of tin oxide are the main factors affecting the performance of silver tin oxide.

[0003] At present, the processes for producing tin oxide mainly include gasification method, acidification method, high-energy mechanical ball milling method, etc. Since the gasification method and high-energy mechanical ball milling method for producing tin oxide require special equipment and have high energy consumption, the acidification method for preparing tin oxide is the mainstream process in many enterprises at present.

[0004] The acidification method for preparing tin oxide is to melt the metal tin, pass it into water to form tin flowers, react with nitric acid to form metatungstic acid, and then wash, dry, calcine and ball mill to obtain tin oxide. However, when the acidification method is used to prepare tin oxide, the temperature is high during the calcination stage, and the formed tin oxide crystals have a large size and a multi-rib shape in morphology, and the particle size distribution is 10-20 μm. Even if the subsequent ball milling process is adjusted to control different size requirements, the multi-rib crystals are broken into small particles with a particle size distribution of 0.1-7 μm and a large span of particle size distribution and many sharp corners, which is still not conducive to the improvement of the processing performance of the tin oxide material. SUMMARY

[0005] In order to improve the problem that the existing tin oxide material has a large particle size distribution span and a multi-rib structure, which is not conducive to processing, the present application provides a heterogeneous precipitation preparation process of modified tin oxide powder doped with low-melting-point oxides.

[0006] In a first aspect, the present application provides a heterogeneous precipitation preparation process of modified tin oxide powder doped with low-melting-point oxides, which adopts the following technical scheme:

[0007] A heterogeneous precipitation preparation process of modified tin oxide powder doped with low-melting-point oxides, comprising the following steps:

[0008] S1, dissolving: dissolving low-melting-point oxides or their corresponding salts in acid to obtain a salt solution;

[0009] S2, mixing: ball milling the tin oxide prepared by the traditional acidification process into a tin oxide slurry with a D50 particle size of 0.5-3 μm; adding the salt solution into the tin oxide slurry, stirring uniformly to obtain a premixed slurry;

[0010] S3, precipitating: adding alkali to the premixed slurry to adjust the pH to generate a tin oxide slurry doped with precursors;

[0011] S4, drying: washing and drying the tin oxide slurry doped with precursors to obtain a tin oxide powder doped with precursors;

[0012] S5, calcining: calcining the tin oxide powder doped with precursors at 900-1200°C for 10-15h to obtain a modified tin oxide powder doped with low-melting oxides.

[0013] The present application uses a heterogeneous precipitation method to coat low-melting oxides on the surface of tin oxide with a D50 particle size of 0.5-3 μm prepared by traditional acidification method, and then calcines at 900-1200°C. The low-melting oxides are in a liquid phase at this temperature, which is used for liquid-phase sintering of tin oxide, and then cooled to obtain a modified tin oxide powder doped with low-melting oxides. Since the spherical droplets of low-melting oxides in a liquid phase can be wrapped on the surface of fine tin oxide particles, it is beneficial to the growth of tin oxide particle grains, and can control the morphology of tin oxide particles in the growth process to be spherical, thereby achieving the purpose of controlling the morphology and size of the modified tin oxide powder doped with low-melting oxides. Taking bismuth oxide modified tin oxide powder as an example, the chemical reaction equation involved is as follows:

[0014] .

[0015] In addition, one of the key points for obtaining the modified tin oxide powder doped with low-melting oxides with a spherical morphology and a concentrated and uniform particle size distribution is that in step S2, the D50 particle size of the tin oxide slurry is controlled to be 0.5-3 μm, which is beneficial to the wrapping of low-melting oxides on tin oxide particles and improves the uniformity of wrapping. Another key point for obtaining the modified tin oxide powder doped with low-melting oxides with a spherical morphology and a concentrated and uniform particle size distribution is the control of the calcination temperature in step S5. If the calcination temperature is too high, it is easy to cause hardening, and if the calcination temperature is too low, it is not conducive to the uniform coating of low-melting oxides on tin oxide.

[0016] In some specific embodiments, the low-melting oxides or their corresponding salts include but are not limited to bismuth oxide, antimony oxide, and sodium antimonate.

[0017] In some specific embodiments, the acid in S1 is concentrated nitric acid.

[0018] In some specific embodiments, the D50 particle size of the tin oxide slurry includes, but is not limited to, 0.5 μm, 0.75 μm, 1 μm, 1.25 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm.

[0019] In some specific embodiments, the weight ratio of the low-melting point oxide or its corresponding salt in S1 to the tin oxide prepared by the traditional acidification method in S2 is (0.2-0.5):(9.5-9.8).

[0020] For example, the weight ratio of the low-melting point oxide or its corresponding salt to the tin oxide prepared by the traditional acidification method in S2 is 0.2:9.8 or 0.3:9.7 or 0.4:9.6 or 0.5:9.5.

[0021] In the present application, the low-melting point oxide or its corresponding salt is mixed with the tin oxide prepared by the traditional acidification method in a specific weight ratio. The low-melting point oxide in the range of the weight ratio can effectively regulate the growth behavior of the tin oxide particles, which is conducive to obtaining the modified tin oxide powder doped with the low-melting point oxide, which has a morphology of quasi-spherical shape and a uniform and concentrated particle size distribution.

[0022] In some specific embodiments, the weight ratio of the tin oxide prepared by the traditional acidification process in S2 to water is 1:(3-4).

[0023] If the amount of water added is too much, the ball milling time will increase and the energy consumption will increase. If the amount of water added is too little, it is not conducive to improving the uniformity of the particle size distribution of the tin oxide slurry.

[0024] In some specific embodiments, in S3, the base is at least one of ammonia, sodium hydroxide solution, and potassium hydroxide solution.

[0025] In some specific embodiments, in S3, the pH is adjusted to be greater than 8 by adding a base.

[0026] Adjusting the pH of the premixed slurry to be greater than 8 can effectively promote the precipitation reaction of the low-melting point oxide precursor and improve the uniform distribution of the low-melting point oxide precursor in the tin oxide slurry. This technical means ensures the coating effect of the low-melting point oxide on the tin oxide particles in the subsequent calcination process, thereby further improving the morphology and particle size distribution of the prepared modified tin oxide powder, making it more quasi-spherical and more uniform and concentrated in particle size, which is conducive to improving the processing performance and quality stability of the silver-tin oxide material.

[0027] In some specific embodiments, in S4, the tin oxide slurry doped with the precursor is washed with deionized water until the pH of the tin oxide slurry doped with the precursor is between 6.5 and 7.5, and the washing step is ended.

[0028] In some specific embodiments, in S4, the drying temperature is controlled to be 100-200℃.

[0029] In some specific embodiments, in S5, before calcining the precursor-doped tin oxide powder, the precursor-doped tin oxide powder is first crushed, and the crushed precursor-doped tin oxide powder is sieved through a 100-mesh sieve, and the sieved precursor-doped tin oxide powder is calcined, which is beneficial to improve the particle size uniformity of the modified tin oxide powder doped with low-melting-point oxides and reduce the distribution span of the particle size.

[0030] In a second aspect, the application provides a modified tin oxide powder doped with low-melting-point oxides, which adopts the following technical scheme:

[0031] A modified tin oxide powder doped with low-melting-point oxides is prepared by the heterogeneous precipitation process of any one of the above-mentioned modified tin oxide powders doped with low-melting-point oxides.

[0032] In summary, the application at least has the following beneficial technical effects:

[0033] 1. The modified tin oxide powder doped with low-melting-point oxides has a spherical shape, which solves the problem of the multi-angled shape of the tin oxide prepared by the traditional acidification method, and is beneficial to the processing of silver-tin oxide materials.

[0034] 2. The point particle size of the modified tin oxide powder doped with low-melting-point oxides prepared by the above-mentioned process is more uniform and concentrated, which is beneficial to the preparation of silver-tin oxide materials with good uniformity. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 FIG. 1 is an SEM image of the modified tin oxide powder doped with bismuth oxide in Example 1 of the application.

[0036] Figure 2 FIG. 4 is an SEM image of the tin oxide (after ball milling) prepared by the traditional acidification process in Comparative Example 1 of the application.

[0037] Figure 3 FIG. 5 is an SEM image of the tin oxide (before ball milling) prepared by the traditional acidification process in Comparative Example 2 of the application.

[0038] Figure 4 FIG. 6 is a particle size distribution graph of the modified tin oxide powder doped with bismuth oxide in Example 1 of the application.

[0039] Figure 5 FIG. 7 is a particle size distribution graph of the tin oxide (after ball milling) prepared by the traditional acidification process in Comparative Example 1 of the application. DETAILED DESCRIPTION

[0040] The application will be further described in detail below in connection with specific examples. Examples

[0041] Example 1

[0042] A process for preparing modified tin oxide powder doped with low-melting-point oxide by heterogeneous precipitation includes the following steps:

[0043] S1, dissolving: 0.2 kg of bismuth oxide crystals is dissolved in concentrated nitric acid to obtain a salt solution;

[0044] S2, mixing: 39.2 kg of water is added to 9.8 kg of tin oxide prepared by a traditional acidification process, and the raw materials are ball milled by a ball mill to obtain tin oxide slurry with a D50 particle size of 2.9 μm. Then the tin oxide slurry is poured into a reaction kettle, and the ultrasonic and stirrer are turned on. The salt solution is slowly added to the tin oxide slurry. After the addition of the salt solution is completed, the stirring is continued for 10 min to obtain a premixed slurry;

[0045] S3, precipitation: ammonia solution is added to the premixed slurry to adjust the pH to greater than 8 to form tin oxide slurry doped with a precursor;

[0046] S4, drying: the tin oxide slurry doped with the precursor is washed with deionized water until the pH is between 6.5 and 7.5, and then dried at 100°C to obtain tin oxide powder doped with the precursor;

[0047] S5, calcination: the tin oxide powder doped with the precursor is crushed, and the crushed tin oxide powder doped with the precursor is sieved through a 100-mesh sieve. The sieved tin oxide powder doped with the precursor is calcined at 900°C for 15 h to obtain modified tin oxide powder doped with bismuth oxide.

[0048] Example 2

[0049] A process for preparing modified tin oxide powder doped with low-melting-point oxide by heterogeneous precipitation includes the following steps:

[0050] S1, dissolving: 0.5 kg of sodium antimonate crystals is dissolved in concentrated nitric acid to obtain a salt solution;

[0051] S2, mixing: 38 kg of water is added to 9.5 kg of tin oxide prepared by a traditional acidification process, and the raw materials are ball milled by a ball mill to obtain tin oxide slurry with a D50 particle size of 2.9 μm. Then the tin oxide slurry is poured into a reaction kettle, and the ultrasonic and stirrer are turned on. The salt solution is slowly added to the tin oxide slurry. After the addition of the salt solution is completed, the stirring is continued for 10 min to obtain a premixed slurry;

[0052] S3, precipitation: adding sodium hydroxide solution to the premixed slurry to adjust the pH to be greater than 8, to generate a tin oxide slurry doped with precursors;

[0053] S4, drying: washing the tin oxide slurry doped with precursors with deionized water until the pH is between 6.5-7.5, and then drying at 200°C to obtain a tin oxide powder doped with precursors;

[0054] S5, calcination: crushing the tin oxide powder doped with precursors, and passing the crushed tin oxide powder doped with precursors through a 100 mesh sieve, and taking the sieved tin oxide powder doped with precursors to be calcined at 1200°C for 10h, to obtain a modified tin oxide powder doped with antimony oxide.

[0055] Comparative Example

[0056]

Comparative Example 1

[0057] A tin oxide powder, specifically a tin oxide powder with a D50 particle size of 2.9μm obtained by drying the tin oxide slurry in the S2 step of Example 1.

[0058]

Comparative Example 2

[0059] A tin oxide powder, specifically a tin oxide powder (before ball milling) prepared by a traditional acidification process used in the S2 step of Example 1.

[0060] Performance test results

[0061] 1. The SEM images of the modified tin oxide powder doped with bismuth oxide prepared in Example 1, Comparative Example 1, and Comparative Example 2 were detected respectively, wherein the SEM image of the modified tin oxide powder doped with bismuth oxide prepared in Example 1 is shown in Figure 1 , the morphology of the obtained modified tin oxide powder doped with bismuth oxide is spherical, without sharp edges and corners, which is beneficial to the processing of silver tin oxide materials. The SEM image of the tin oxide powder (after ball milling) prepared by the traditional acidification method in Comparative Example 1 is shown in Figure 2 , the particle size of the tin oxide powder after ball milling is smaller, but most of the particles still have obvious multi-rib structure, and when applied to the processing of silver tin oxide materials, there is still a problem of poor uniformity. The SEM image of the tin oxide powder (before ball milling) prepared by the traditional acidification method in Comparative Example 2 is shown in Figure 3 , which is a multi-rib crystal with large size in morphology, and it is difficult to achieve uniform dispersion when applied to the processing of silver tin oxide materials.

[0062] 2. The particle size distribution of the modified tin oxide powder doped with bismuth oxide prepared in Example 1 and the tin oxide (before ball milling) prepared by the traditional acidification process in Comparative Example 2 was detected respectively, wherein the particle size distribution of the modified tin oxide powder doped with bismuth oxide prepared in Example 1 is shown in Figure 4 , the particle size distribution of the tin oxide (before ball milling) prepared by the traditional acidification process in Comparative Example 2 is shown in Figure 5 , and the specific particle size distribution in Example 1 and Comparative Example 2 is shown in Table 1 below.

[0063] Table 1

[0064]

[0065] According to the data recorded in Table 1, it can be seen that in the modified tin oxide powder doped with bismuth oxide prepared in Example 1, 10% of the particle volume is less than or equal to 0.834 μm, 50% of the particle volume is less than or equal to 2.965 μm, and 90% of the particle volume is less than or equal to 6.721 μm. In the tin oxide (before ball milling) prepared by the traditional acidification process in Comparative Example 2, 10% of the particle volume is less than or equal to 1.847 μm, 50% of the particle volume is less than or equal to 7.650 μm, and 90% of the particle volume is less than or equal to 17.522 μm. The particle size distribution range of the modified tin oxide powder doped with bismuth oxide prepared in Example 1 is narrower and the uniformity is better.

[0066] In summary, compared with the tin oxide powder prepared by the traditional acidification process, the modified tin oxide powder doped with bismuth oxide prepared by the process of the present application has the characteristics of more concentrated particle size distribution, better particle size uniformity and easier dispersion, which is beneficial to prepare silver tin oxide material with good uniformity and stable quality.

[0067] The specific embodiment is only an explanation of the present application, which is not a limitation of the present application. Those skilled in the art can make modifications to the specific embodiment without creative contribution after reading the present specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A heterogeneous precipitation preparation process for modified tin oxide powder doped with medium- and low-melting-point oxides, characterized in that, Includes the following steps: S1. Dissolution: Dissolve low- or medium-melting-point oxides or their corresponding salts in acid to obtain a salt solution; S2. Mixing: The tin oxide obtained by the traditional acidification process is ball-milled with water to form a tin oxide slurry with a D50 particle size of 0.5μm~3μm; the salt solution is added to the tin oxide slurry and stirred evenly to obtain a premixed slurry; the weight ratio of tin oxide to water obtained by the traditional acidification process is 1:(3-4). S3, Precipitation: Add alkali to the premixed slurry to adjust the pH to >8, and generate tin oxide slurry doped with precursors; S4. Drying: The tin oxide slurry doped with the precursor is washed and dried to obtain tin oxide powder doped with the precursor. S5. Calcination: The tin oxide powder doped with the precursor is crushed and passed through a 100-mesh sieve. The tin oxide powder doped with the precursor after sieving is calcined at 900℃~1200℃ for 10-15h to obtain modified tin oxide powder doped with medium and low melting point oxides. The weight ratio of the low-to-medium melting point oxide or its corresponding salt described in S1 to the tin oxide prepared by the conventional acidification method described in S2 is (0.2-0.5):(9.5-9.8). The medium- and low-melting-point oxides or their corresponding salts include bismuth oxide, antimony oxide, or sodium antimonate.

2. The heterogeneous precipitation preparation process of modified tin oxide powder doped with medium and low melting point oxides according to claim 1, characterized in that: The acid mentioned in S1 is concentrated nitric acid.

3. The heterogeneous precipitation preparation process of modified tin oxide powder doped with medium and low melting point oxides according to claim 1, characterized in that: In S3, the alkali is at least one of ammonia water, sodium hydroxide solution, and potassium hydroxide solution.

4. The heterogeneous precipitation preparation process of modified tin oxide powder doped with medium and low melting point oxides according to claim 1, characterized in that: In step S4, the tin oxide paste doped with the precursor is washed with deionized water until the pH of the tin oxide paste doped with the precursor is between 6.5 and 7.5, at which point the washing step ends.

5. The heterogeneous precipitation preparation process of modified tin oxide powder doped with medium and low melting point oxides according to claim 1, characterized in that: In S4, the drying temperature is controlled at 100℃~200℃.

6. A modified tin oxide powder doped with medium- and low-melting-point oxides, characterized in that: It is prepared by a heterogeneous precipitation process of modified tin oxide powder doped with medium and low melting point oxides as described in any one of claims 1-5.

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