Spherical zinc sulfide as well as preparation method and application thereof

Abstract

The invention relates to spherical zinc sulfide as well as a preparation method and application thereof. The preparation method of the spherical zinc sulfide comprises the following steps: mixing and reacting a zinc sulfate solution and a sodium sulfide solution; carrying out filter pressing and washing on the zinc sulfide precipitate obtained by the reaction, adding water again to pulpify a filter cake, pumping the slurry into a spray dryer, and carrying out spray drying to obtain powder; and finally, calcining the powder to obtain the spherical zinc sulfide powder. The preparation method comprises the following steps: firstly synthesizing nano-scale zinc sulfide, then atomizing the nano-scale zinc sulfide into small liquid particles with the diameter of 2-5 microns in a spray drying process, meanwhile, forming a spherical aggregate through high-temperature drying and shrinkage, and then forming compact spherical zinc sulfide particles through high-temperature melting and calcining.

Description

Technical Field

[0001] The invention relates to the technical field of zinc sulfide preparation, and in particular to spherical zinc sulfide, a preparation method thereof and applications thereof. Background Art

[0002] Zinc sulfide (ZnS) is an inorganic compound with the chemical formula ZnS. It is mostly white powder in appearance, so it is mostly used as a white pigment. The thermal conductivity of zinc sulfide is 27w / m·k, and it can be used as a thermal conductive material. When used as a thermal conductive material, the filling rate of the spherical type is relatively high. Therefore, filling the material with spherical zinc sulfide of different particle sizes can make the material have a higher thermal conductivity. Under the same conditions, the thermal conductivity of the material can be significantly improved compared to ordinary thermal conductive materials.

[0003] The prior art lacks a method for preparing spherical zinc sulfide. Summary of the invention

[0004] The present invention firstly proposes a method for preparing spherical zinc sulfide. The prepared spherical zinc sulfide has different particle sizes and a narrow particle size range, so that the zinc sulfide has a higher filling rate when used as a filler; when the prepared spherical zinc sulfide is used as a thermal conductive filler, the spherical zinc sulfides of different particle sizes cooperate with each other to fully fill the voids of the polymer material, so that the void rate of the prepared thermal conductive material is lower, thereby the thermal conductive material has good thermal conductivity.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A method for preparing spherical zinc sulfide comprises the following steps:

[0007] Mix the zinc sulfate solution with the sodium sulfide solution;

[0008] After the mixed solution reacts, sodium sulfide is continuously added to the solution to precipitate free zinc ions; this process is generally controlled so that the pH value becomes 6 to 7 after the sodium sulfide is added; the zinc ion concentration in the solution can be detected after the sodium sulfide is added to determine whether the amount of sodium sulfide added is sufficient; the zinc ion concentration can be allowed to be 100 ppm; the mixed solution reaction is preferably completed through an ultra-gravity reactor.

[0009] The zinc sulfide precipitate obtained by the reaction is filtered and washed, and the filter cake is re-slurried, and the slurry is pumped into a spray dryer for spray drying to obtain a powder;

[0010] Finally, the powder is calcined to obtain spherical zinc sulfide powder.

[0011] Preferably, in the present invention, a zinc sulfide growth inhibitor is added to the solution before filter pressing and washing, and the zinc sulfide growth inhibitor forms a precipitate on the surface of zinc sulfide to coat the surface of zinc sulfide and prevent the zinc sulfide from growing coarse during calcination.

[0012] The zinc sulfide growth inhibitor used in the present invention is sodium silicate, or aluminum sulfate, or sodium metaaluminate, and the pH value is controlled to form a precipitation layer on the surface of zinc sulfide to prevent the zinc sulfide from growing. Among them, when the zinc sulfide growth inhibitor is sodium silicate, sodium hydroxide is used to adjust the solution pH to 8-9 at the same time. Under this condition, sodium silicate will form Si(OH)4 precipitation on the surface of zinc sulfide, which is coated on the surface of zinc sulfide to prevent the zinc sulfide from growing coarse during calcination. When the zinc sulfide growth inhibitor is aluminum sulfate, sodium hydroxide is added dropwise at the same time to control the pH to be kept at 8-9. Under this condition, aluminum sulfate and sodium hydroxide form aluminum hydroxide and aluminum hydroxide, which are coated on the surface of zinc sulfide to prevent the zinc sulfide from agglomerating and growing coarse during calcination. Aluminum oxide has a high melting point, so its effect on the growth inhibition of zinc sulfide is better than that of sodium silicate. When the zinc sulfide growth inhibitor is sodium aluminate solution, sulfuric acid solution is added dropwise while the sodium aluminate solution is added to keep the solution pH at 8-9. Under this condition, the boehmite structure is formed on the surface of zinc sulfide, and it is continuously coated with a uniform surface, which prevents the zinc sulfide from agglomerating and growing thick during calcination.

[0013] The spherical zinc sulfide prepared by the present invention is used as a filler for a thermally conductive material. Since the spherical shape has a higher filling rate, the thermally conductive material prepared by the spherical zinc sulfide products of different particle sizes has a lower porosity and can have good thermal conductivity. The thermal conductivity of the material prepared by using the spherical zinc sulfide products of different particle sizes of the present invention as a filler is better than that of the material prepared by using the non-spherical zinc sulfide as a filler.

[0014] The advantages of the present invention are:

[0015] The invention first synthesizes nanometer-level zinc sulfide, then atomizes it into small liquid particles with a diameter of 2 to 5 μm in spray drying, simultaneously forms spherical agglomerates through high-temperature drying and shrinkage, and then forms dense spherical zinc sulfide particles through high-temperature melting and calcination. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is an electron microscope photograph of the spherical zinc sulfide obtained in Example 1;

[0017] Figure 2 is an electron microscope photograph of the spherical zinc sulfide obtained in Example 2;

[0018] Figure 3 is an electron microscope photograph of the spherical zinc sulfide obtained in Example 3;

[0019] Figure 4 is an electron microscope photograph of the spherical zinc sulfide obtained in Example 4;

[0020] Figure 5 This is an electron microscope photograph of the zinc sulfide prepared in Comparative Example 1. DETAILED DESCRIPTION

[0021] In order to make the technical personnel in the field understand the present invention more clearly and intuitively, the present invention will be further described below in conjunction with the accompanying drawings. The experimental methods without specific conditions in the following examples are selected according to conventional methods and conditions, or according to the product instructions.

[0022] Example 1

[0023] Take 10L of 1.0mol / L zinc sulfate solution and 10L of 1.0mol / L sodium sulfide solution and mix them. Pump the solutions into the ultra-gravity reactor at the same time. The slurry synthesized in the ultra-gravity reactor flows back into the reaction tank. Continue to add sodium sulfide to fine-tune the pH value to 6-7. Test whether there is excessive residual zinc ion (the residual amount is generally allowed to be within 100ppm). Then filter press and wash, re-slurry the filter cake, slurry to a concentration of 200-250g / L and pump it into a spray dryer for spray drying. The average particle size of the dried powder is about 2.3um. The powder is then sent to a kiln at 600-700℃ and calcined for 30 minutes. After cooling, the median particle size of the zinc sulfide is tested to be 1.8um, and the particle shape is spherical. The electron microscope photo is as follows Figure 1 shown.

[0024] Example 2

[0025] Take 10L of 1.0mol / L zinc sulfate solution and 10L of 1.0mol / L sodium sulfide solution and mix them. Pump the solutions into the supergravity reactor at the same time. The slurry synthesized in the supergravity reactor flows back into the reaction tank. Continue to add sodium sulfide to fine-tune the pH value to 6-7. Test whether there is excessive residual zinc ion (generally the residual amount is allowed to be within 100ppm). Then add sodium silicate (2.6% SiO2) solution to the solution and adjust the pH value to 8.0 (using sodium hydroxide solution). In this process, Si(OH)4 precipitation is formed on the surface of zinc sulfide, and the amount of silicon added is within 1% to 10% of the mass of zinc sulfide (in terms of SiO2). Then filter press and wash, re-slurry the filter cake with water, slurry to a concentration of 200-250g / L and pump it into a spray dryer for spray drying. Then the powder was sent into a kiln at 600-700℃ and calcined for 30 minutes. After cooling, the median particle size of zinc sulfide was tested to be 1.1um, and the particle shape was spherical. The electron microscope photo is as follows: Figure 2 shown.

[0026] Example 3

[0027] Take 10L of 1.0mol / L zinc sulfate solution and 10L of 1.0mol / L sodium sulfide solution, and pump the solutions into the supergravity reactor at the same time. The slurry synthesized in the supergravity reactor flows back into the reaction tank, and sodium sulfide is added to fine-tune the pH value to 6-7, and test whether there is excessive residual zinc ion (generally the residual amount is allowed to be within 100ppm). Then add 500g of aluminum sulfate solution (100g / L) to the solution, and at the same time add sodium hydroxide solution (95g / L) to the tank to control pH=8.2-8.3. In this process, aluminum precipitates on the surface of zinc sulfide particles as aluminum hydroxide and Al(OH)3. Then filter press and wash the zinc sulfide, add water again to slurry the filter cake, and pump it into a spray dryer for spray drying after slurrying to a concentration of 200-250g / L. Then the powder was sent into a kiln at 600-700℃ and calcined for 30 minutes. After cooling, the median particle size of zinc sulfide was 0.9um and the particle shape was spherical. The electron microscope photo is as follows: Figure 3 shown.

[0028] Example 4

[0029] Take 10L of 1.0mol / L zinc sulfate solution and 10L of 1.0mol / L sodium sulfide solution, and pump the solutions into the supergravity reactor at the same time. The slurry synthesized in the supergravity reactor flows back into the reaction tank, and sodium sulfide is added to fine-tune the pH value to 6-7, and test whether zinc ions are residual (generally the residual amount is allowed to be within 100ppm). Then add 570g of sodium aluminate solution (100g / L) to the solution, and add sulfuric acid solution (20g / L) to the tank to control pH=8.0-9.0. After stirring for 10min, add 50g of polyvinyl alcohol. During this process, aluminum precipitates as boehmite on the surface of zinc sulfide particles. Then filter press and wash the zinc sulfide, add water again to slurry the filter cake, and pump it into a spray dryer for spray drying after slurrying to a concentration of 200-250g / L. Then the powder was sent into a kiln at 700-800℃ and calcined for 60 minutes. After cooling, the median particle size of zinc sulfide was 0.9um and the particle shape was spherical. The electron microscope photo is as follows: Figure 4 shown.

[0030] Comparative Example 1

[0031] The difference between this comparative example and Example 1 is that the zinc sulfide solution is directly reacted with the sodium sulfide solution, filtered and washed, and then dried and calcined. It is not subjected to other treatments such as spray drying. The calcination temperature is 800-900°C, and after 30 minutes, it is cooled and crushed. The electron microscope photo of the obtained zinc sulfide is as follows: Figure 5 As shown. Figure 5 It can be seen that the zinc sulfide prepared by this method is irregular in shape.

[0032] The shape characteristics of each embodiment and comparative example are shown in Table 1. The purity and particle size detection standard of zinc sulfide adopts GB / T 31194-2014, and the thermal conductivity is measured by a thermal conductivity measuring instrument.

[0033] Table 1

[0034]

[0035] The zinc sulfide prepared in Example 1 and Comparative Example 1 was used as filler to prepare thermal conductive ink together with epoxy resin. The thermal conductivity of the thermal conductive ink prepared by the zinc sulfide prepared in the ordinary comparative example 1 was between 1.6 and 1.8 w / m·k, calculated by adding 60% zinc sulfide. The thermal conductivity of the thermal conductive ink prepared by the spherical zinc sulfide prepared in Example 1 reached more than 2 w / m·k.

[0036] Therefore, the present invention not only prepares spherical zinc sulfide, but also can significantly improve the thermal conductivity of the product and extend the service life of the product when the spherical zinc sulfide is used as a filler.

[0037] The above description of the embodiments is to facilitate the understanding and application of the present invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the embodiments herein, and improvements and modifications made to the present invention by those skilled in the art based on the disclosure of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing spherical zinc sulfide, characterized in that: The steps include: The zinc sulfate solution and the sodium sulfide solution are mixed and reacted; The zinc sulfide precipitate obtained by the reaction is filtered and washed, and water is added again to slurry the filter cake, and the slurry is pumped into a spray dryer for spray drying to obtain a powder; Finally, the powder is calcined to obtain spherical zinc sulfide powder.

2. The preparation method according to claim 1, characterized in that After the mixed solution reacts, the zinc ions in the solution are detected, and when the zinc ions are excessive, sodium sulfide is continuously added to the solution to precipitate free zinc ions.

3. The preparation method according to claim 1, characterized in that: The mixed solution reaction is completed through a supergravity reactor.

4. The preparation method according to claim 1, characterized in that: Before filter pressing and washing, a zinc sulfide growth inhibitor is added to the solution. The zinc sulfide growth inhibitor forms a precipitate on the surface of zinc sulfide, covers the surface of zinc sulfide, and prevents the zinc sulfide from growing coarse during calcination.

5. The preparation method according to claim 4, characterized in that: The zinc sulfide growth inhibitor is sodium silicate, aluminum sulfate or sodium aluminate, and the pH value of the solution is controlled to form a precipitation layer on the surface of the zinc sulfide to prevent the zinc sulfide from growing.

6. The preparation method according to claim 5, characterized in that: The zinc sulfide growth inhibitor is sodium silicate. The solution is adjusted to an alkaline environment with sodium hydroxide. Sodium silicate forms Si(OH)4 precipitation on the surface of zinc sulfide and coats the surface of zinc sulfide to prevent the zinc sulfide from growing coarse during calcination.

7. The preparation method according to claim 5, characterized in that: The zinc sulfide growth inhibitor is aluminum sulfate. A sodium hydroxide solution is added dropwise while the aluminum sulfate solution is added to adjust the solution pH to 8-9. Aluminum oxyhydroxide and aluminum hydroxide formed by aluminum sulfate are coated on the surface of zinc sulfide to prevent the zinc sulfide from agglomerating and growing thick during calcination.

8. The preparation method according to claim 5, characterized in that: The zinc sulfide growth inhibitor is a sodium aluminate solution. A sulfuric acid solution is added dropwise while the sodium aluminate solution is added dropwise to adjust the solution pH to 8-9, thereby generating a boehmite structure that covers the surface of the zinc sulfide to prevent the zinc sulfide from agglomerating and growing thick during calcination.

9. Spherical zinc sulfide obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the spherical zinc sulfide obtained by the preparation method according to any one of claims 1 to 8 as a filler for thermal conductive materials.

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