A preparation method of coated spherical magnesium oxide powder

Abstract

The present invention discloses a method for preparing coated spherical magnesium oxide powder. The method comprises first uniformly mixing magnesium oxide with a coupling agent to obtain a primary modified magnesium oxide powder, then mixing with a water-soluble surface treatment agent to obtain a secondary modified magnesium oxide powder, then adding water to form a slurry, and spray drying to form spherical magnesium oxide agglomerates with a D50 of 10 to 150 μm. Finally, a flame melting method is used for spheroidization to obtain spherical magnesium oxide powder. The present invention sequentially coats the magnesium oxide powder with different modifiers, effectively suppressing the occurrence of its hydrolysis reaction during the slurrying process, reducing heat loss during the spheroidization process, and obtaining a spherical magnesium oxide product with high sphericity and high moisture resistance.

Description

Technical Field

[0001] The invention belongs to the field of preparation of thermal conductive fillers and relates to a method for preparing coated spherical magnesium oxide powder. Background Art

[0002] In recent years, crystalline silica and alumina have been commonly used as thermally conductive fillers. However, silica's low thermal conductivity makes it inadequate for addressing the increased heat generation associated with today's high integration, high power consumption, and high-speed development. While alumina offers improved heat dissipation compared to silica, its high hardness can easily cause wear and tear on equipment such as mixers and molding machines. Magnesium oxide, with its high thermal conductivity, low hardness, and excellent cost-effectiveness, holds promise as a thermally conductive filler to meet these development needs. However, compared to silica and alumina, magnesium oxide powder is highly hygroscopic and readily reacts with water to form magnesium hydroxide, necessitating further improvements in its moisture resistance.

[0003] Patent CN109095482A uses an oxygen-natural gas flame fusion method to melt magnesium oxide powder to form spherical droplets, which are then cooled and shaped to form spherical magnesium oxide particles. The magnesium oxide powder prepared by this method has good sphericity and fluidity, but poor moisture resistance. Patent CN100500770C uses magnesium oxide and a silicon compound or aluminum salt to mix wet processes to prepare composite oxides such as forsterite (Mg2SiO4) and spinel (Al2MgO4), and collects magnesium oxide powder by cooling in a propane-oxygen flame. Although the moisture resistance of the composite oxide prepared by this method is improved, its sphericity is poor, and there are gaps in the particles, showing a high specific surface area. Patent JP2023059538A uses spherical magnesium carbonate as a magnesium source and obtains spherical magnesium oxide particles with high sphericity and high moisture resistance by mixing and calcining with silicon compounds, aluminum compounds, boron compounds, phosphorus compounds, halogen compounds, titanium compounds and iron compounds. However, direct mixing and calcining with magnesium carbonate as a magnesium source will release a large amount of carbon dioxide. However, this method has high requirements on the sphericity of the raw materials and the product yield is less than 50%. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing coated spherical magnesium oxide powder with high sphericity and excellent moisture resistance.

[0005] The technical solutions for achieving the purpose of the present invention are as follows:

[0006] A method for preparing coated spherical magnesium oxide powder comprises the following steps:

[0007] (1) Primary modification: uniformly mixing magnesium oxide with an average particle size of 0.1-10 μm with a coupling agent to obtain a primary modified magnesium oxide powder, wherein the coupling agent is selected from one or more of an aluminate coupling agent, a titanate coupling agent, a borate coupling agent, and a silane coupling agent;

[0008] (2) Secondary modification: uniformly mixing the primary modified magnesium oxide powder with a water-soluble surface treatment agent to obtain a secondary modified magnesium oxide powder, wherein the water-soluble surface treatment agent is selected from one or more of polyacrylamide, polyacrylic acid, polyvinyl pyrrolidone, polyvinyl alcohol, polymaleic anhydride, polyquaternary ammonium salt and polyethylene glycol;

[0009] (3) Slurry preparation: Add the secondary modified magnesium oxide powder into water and stir to obtain a uniformly dispersed slurry;

[0010] (4) Spray granulation: The slurry is spray-dried to obtain spherical magnesium oxide agglomerates with a D50 of 10 to 150 μm;

[0011] (5) Spheroidization: Spherical magnesium oxide agglomerates are put into the flame zone formed by the combustion of oxygen and fuel gas for spheroidization to obtain spherical magnesium oxide powder.

[0012] Preferably, in step (1), the purity of magnesium oxide is above 95%.

[0013] Preferably, in step (1), the mixing time is 3-20 min, and the amount of the coupling agent added is 0.1% to 10% of the mass of the magnesium oxide, more preferably 5% to 10%.

[0014] Preferably, in step (2), the mixing time is 3-20 min, and the amount of the water-soluble surface treatment agent added is 0.1% to 10% of the mass of the magnesium oxide, more preferably 5% to 10%.

[0015] Preferably, in step (1) or (2), the mixing equipment used is a device conventionally used in the art, such as a two-dimensional mixer, a three-dimensional mixer, a V-shaped mixer, a double-cone mixer, a zero-gravity mixer, a conical mixer, a plowshare mixer, etc.

[0016] Preferably, in step (3), the solid content of the slurry is 1% to 50%, more preferably 10% to 30%.

[0017] Preferably, in step (5), the fuel gas is selected from one or more of natural gas, propane, hydrogen and acetylene.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] Magnesium oxide easily absorbs water in water to form magnesium hydroxide, which is easily severely hydrolyzed during pulping and spray granulation. In the process of spheroidization, magnesium hydroxide needs to absorb a large amount of heat to decompose the raw material into magnesium oxide and water. The present invention first performs a primary modification on the magnesium oxide raw material by mixing it with a coupling agent. The coupling agent is coated on the surface of magnesium oxide. On the one hand, it improves its moisture resistance by coating on the surface of magnesium oxide and reduces its water absorption rate in the slurry. On the other hand, it is converted into corresponding aluminum, titanium, boron or silicon oxides during the high-temperature spheroidization process, further improving the sphericity and moisture resistance of spherical magnesium oxide. In addition, since most coupling agents are hydrophobic, it is impossible to uniformly disperse magnesium oxide powder in water to form a uniformly dispersed slurry. The present invention mixes the once-modified magnesium oxide with a water-soluble surface treatment agent for secondary modification, thereby improving the dispersibility and solubility of magnesium oxide powder. In summary, the present invention uses different modifiers to coat magnesium oxide powder in sequence, which can effectively inhibit the occurrence of its hydrolysis reaction during the pulping process, reduce the heat loss during the spheroidization process, and obtain a spherical magnesium oxide product with high sphericity (sphericity of 0.96 to 1.00) and high moisture resistance. DETAILED DESCRIPTION

[0020] The present invention will be further described in detail below with reference to specific embodiments.

[0021] In the following examples and comparative examples, the testing methods for various properties are as follows:

[0022] 1. Sphericity determination

[0023] The sphericity of magnesium oxide powder was measured using a microscopic particle imager (Winner99E, Jinan Micro-Nano Particle Instrument Co., Ltd.) by combining computer images with particle size and shape analysis theory using an image acquisition system and analysis software.

[0024] 2. Particle size distribution determination

[0025] The volume-based cumulative 50% particle size (D50) of the magnesium oxide powder was measured by a laser diffraction scattering method using a particle size distribution analyzer (Mastersizer 3000, Malvern Panalytical Ltd).

[0026] 3. Moisture resistance test

[0027] The moisture resistance of the magnesium oxide powder was evaluated using the weight gain rate in a constant temperature and humidity chamber test. 10.00 g of the magnesium oxide powder was placed in a constant temperature and humidity chamber (LHS-50CL, Yiheng Scientific Instrument Co., Ltd.) at 85°C and 85% RH for 168 hours, and the weight gain rate was measured.

[0028] Example 1

[0029] Magnesium oxide powder with a purity of 98% and an average particle size of 1 μm was mixed with an aluminate coupling agent to obtain sample A, wherein the amount of the aluminate coupling agent added was 5% by mass of the magnesium oxide. Sample A was mixed with polyacrylic anhydride to obtain sample B, wherein the amount of the polyacrylic anhydride added was 5% by mass of the magnesium oxide. Sample B was dispersed in pure water, stirred and dispersed uniformly to obtain a slurry with a solid content of 10%. Spherical magnesium oxide agglomerates with an average particle size of 10 μm were prepared from the slurry using a spray drying device, and the agglomerates were supplied to a high-temperature flame formed by the combustion of natural gas and oxygen for melting and spheroidization to obtain spherical magnesium oxide powder.

[0030] Example 2

[0031] Magnesium oxide powder with a purity of 98% and an average particle size of 1 μm is mixed with an aluminate coupling agent, wherein the amount of the aluminate coupling agent added is 10% by mass of the magnesium oxide; sample A is mixed with polyacrylic anhydride to obtain sample B, wherein the amount of the polyacrylic anhydride added is 5% by mass of the magnesium oxide; sample B is dispersed in pure water, stirred and dispersed uniformly to adjust the solid content of the slurry to 10%; spherical magnesium oxide agglomerates with an average particle size of 10 μm are prepared from the slurry using a spray drying device, and the agglomerates are supplied to a high-temperature flame formed by the combustion of natural gas and oxygen for melting and spheroidization to obtain spherical magnesium oxide powder.

[0032] Example 3

[0033] Magnesium oxide powder with a purity of 98% and an average particle size of 1 μm was mixed with tetrabutyl titanate to obtain sample A, wherein the amount of tetrabutyl titanate added was 5% by mass of the magnesium oxide; sample A was mixed with polyacrylic anhydride to obtain sample B, wherein the amount of polyacrylic anhydride added was 5% by mass of the magnesium oxide; sample B was dispersed in pure water, stirred and dispersed evenly to obtain a slurry with a solid content of 30%; spherical magnesium oxide agglomerates with an average particle size of 60 μm were prepared from the slurry using a spray drying device, and the agglomerates were supplied to a high-temperature flame formed by the combustion of natural gas and oxygen for melting and spheroidization to obtain spherical magnesium oxide powder.

[0034] Example 4

[0035] Magnesium oxide powder with a purity of 98% and an average particle size of 3 μm was mixed with vinyltrialkoxysilane to obtain sample A, wherein the amount of vinyltrialkoxysilane added was 10% by mass of the magnesium oxide; sample A was mixed with polyacrylic anhydride to obtain sample B, wherein the amount of polyacrylic anhydride added was 5% by mass of the magnesium oxide; sample B was dispersed in pure water, stirred and dispersed evenly to obtain a slurry with a solid content of 10%; spherical magnesium oxide agglomerates with an average particle size of 30 μm were prepared from the slurry using a spray drying device, and the agglomerates were supplied to a high-temperature flame formed by the combustion of natural gas and oxygen for melting and spheroidization to obtain spherical magnesium oxide powder.

[0036] Example 5

[0037] Magnesium oxide powder with a purity of 98% and an average particle size of 3 μm was mixed with an aluminate coupling agent to obtain sample A, wherein the amount of the aluminate coupling agent added was 10% of the mass of the magnesium oxide; sample A was mixed with polyvinyl alcohol to obtain sample B, wherein the amount of the polyvinyl alcohol added was 10% of the mass of the magnesium oxide; sample B was dispersed in pure water, stirred and dispersed uniformly, and the solid content of the slurry was adjusted to 30%; spherical magnesium oxide agglomerates with an average particle size of 50 μm were prepared from the slurry using a spray drying device, and the agglomerates were supplied to a high-temperature flame formed by the combustion of natural gas and oxygen for melting and spheroidization to obtain spherical magnesium oxide powder.

[0038] Example 6

[0039] Magnesium oxide powder with a purity of 98% and an average particle size of 10 μm was mixed with an aluminate coupling agent to obtain sample A, and the amount of borate coupling agent added was 10% of the mass of the magnesium oxide; sample A was mixed with polyvinyl alcohol to obtain sample B, and the amount of polyvinyl alcohol added was 10% of the mass of the magnesium oxide; sample B was dispersed in pure water, stirred and dispersed evenly, and the solid content of the slurry was adjusted to 30%; spherical magnesium oxide agglomerates with an average particle size of 50 μm were prepared from the slurry using a spray drying device, and the agglomerates were supplied to a high-temperature flame formed by the combustion of natural gas and oxygen for melting and spheroidization to obtain spherical magnesium oxide powder.

[0040] Comparative Example 1

[0041] Magnesium oxide powder with a purity of 98% and an average particle size of 3 μm is directly supplied to a high-temperature flame formed by the combustion of natural gas and oxygen for melting and spheroidization to obtain spherical magnesium oxide powder.

[0042] Comparative Example 2

[0043] Magnesium oxide powder with a purity of 98% and an average particle size of 3 μm is dispersed in pure water, stirred and dispersed evenly, and the solid content of the slurry is adjusted to 30%. Spherical magnesium oxide agglomerates with an average particle size of 60 μm are prepared from the slurry using a spray drying device, and the agglomerates are supplied to a high-temperature flame formed by the combustion of natural gas and oxygen for melting and spheroidization to obtain spherical magnesium oxide powder.

[0044] Comparative Example 3

[0045] Sample A was obtained by mixing magnesium oxide powder with a purity of 98% and an average particle size of 3 μm with an aluminate coupling agent, where the amount of the aluminate coupling agent added was 5% of the mass of the magnesium oxide. Sample A was dissolved in pure water, and the product had poor dispersibility.

[0046] Comparative Example 4

[0047] Sample A was obtained by mixing magnesium oxide powder with a purity of 98% and an average particle size of 3 μm with polyvinyl alcohol, where the amount of polyvinyl alcohol added was 5% of the mass of the magnesium oxide. Sample A was dispersed in pure water, stirred and dispersed evenly, and the solid content of the slurry was adjusted to 10%. Spherical magnesium oxide agglomerates with an average particle size of 10 μm were prepared from the slurry using a spray drying device, and the agglomerates were supplied to a high-temperature flame formed by the combustion of natural gas and oxygen for melting and spheroidization to obtain spherical magnesium oxide powder.

[0048] The experimental conditions and product properties of each embodiment and comparative example are shown in Table 1.

[0049] Table 1

[0050]

[0051] As can be seen from Table 1, the spherical magnesium oxide powder obtained by flame melting the raw magnesium oxide in Comparative Example 1 is poor in sphericity, only 0.71, and exhibits extremely poor moisture resistance. Comparative Example 2 prepares the raw magnesium oxide into a slurry and then flame melts it into balls. The sphericity of the spherical magnesium oxide powder obtained is increased to 0.86, but the corrosion resistance is still poor. Comparative Example 3 only uses an aluminate coupling agent for one modification. Due to the hydrophobic surface, the dispersion in water is poor and the next step of flame melting cannot be performed. Comparative Example 4 modifies the raw magnesium oxide with a water-soluble surface treatment agent. Although the dispersion of the raw material in water is improved, the sphericity of the spherical magnesium oxide powder obtained is only 0.92, which cannot reach above 0.96, and the resistance performance is not improved. In summary, the present invention uses different modifiers to coat magnesium oxide powder in sequence, which can effectively inhibit the occurrence of its hydrolysis reaction during the pulping process, reduce the heat loss during the spheroidization process, and obtain a spherical magnesium oxide product with high sphericity (sphericity of 0.96 to 1.00) and high moisture resistance.

Claims

1. A method for preparing coated spherical magnesium oxide powder, characterized in that: The following steps are involved: (1) Primary modification: uniformly mixing magnesium oxide with an average particle size of 0.1-10 μm with a coupling agent to obtain a primary modified magnesium oxide powder, wherein the coupling agent is selected from one or more of an aluminate coupling agent, a titanate coupling agent, a borate coupling agent and a silane coupling agent; (2) Secondary modification: uniformly mixing the primary modified magnesium oxide powder with a water-soluble surface treatment agent to obtain a secondary modified magnesium oxide powder, wherein the water-soluble surface treatment agent is selected from one or more of polyacrylamide, polyacrylic acid, polyvinyl pyrrolidone, polyvinyl alcohol, polymaleic anhydride, polyquaternary ammonium salt and polyethylene glycol; (3) Slurry preparation: Add the secondary modified magnesium oxide powder into water and stir to obtain a uniformly dispersed slurry; (4) Spray granulation: The slurry is spray-dried to obtain spherical magnesium oxide agglomerates with a D50 of 10-150 μm; (5) Spheroidization: Spherical magnesium oxide agglomerates are placed in a flame zone formed by the combustion of oxygen and fuel gas for spheroidization to obtain spherical magnesium oxide powder.

2. The preparation method according to claim 1, characterized in that In step (1), the purity of magnesium oxide is above 95%.

3. The preparation method according to claim 1, wherein In step (1), the mixing time is 3-20 min, and the amount of coupling agent added is 0.1% to 10% of the mass of magnesium oxide.

4. The preparation method according to claim 1, wherein In step (2), the mixing time is 3-20 min, and the amount of the water-soluble surface treatment agent added is 0.1% to 10% of the mass of the magnesium oxide.

5. The preparation method according to claim 1, characterized in that In step (1), the amount of the coupling agent added is 5% to 10% of the mass of the magnesium oxide; in step (2), the amount of the water-soluble surface treatment agent added is 5% to 10% of the mass of the magnesium oxide.

6. The preparation method according to claim 1, characterized in that In step (1) or (2), the mixing equipment used is a two-dimensional mixer, a three-dimensional mixer, a V-shaped mixer, a double-cone mixer, a zero-gravity mixer, a cone mixer or a plowshare mixer.

7. The preparation method according to claim 1, characterized in that In step (3), the solid content of the slurry is 1% to 50%.

8. The preparation method according to claim 1, characterized in that In step (3), the solid content of the slurry is 10% to 30%.

9. The preparation method according to claim 1, characterized in that In step (5), the fuel gas is selected from one or more of natural gas, propane, hydrogen and acetylene.

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