CN109835927B

CN109835927B - High-temperature-resistant and high-hydrophobicity electric-grade magnesium oxide powder and preparation method thereof

Info

Publication number: CN109835927B
Application number: CN201711211163.4A
Authority: CN
Inventors: 苏宏久; 任高远; 王树东
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2017-11-28
Filing date: 2017-11-28
Publication date: 2021-09-17
Anticipated expiration: 2037-11-28
Also published as: CN109835927A

Abstract

The invention provides high-temperature-resistant and high-hydrophobicity electric-grade magnesium oxide powder and a preparation method thereof. The product of the invention is characterized in that the inside of the particle is high-purity magnesium oxide, and the outside is an inorganic silicon oxide coating. The preparation process comprises the following steps: pulverizing and sieving to obtain fused magnesite with a certain mesh number, and ageing and growing the fused magnesite with a silicon solution. The method specifically comprises the following operations: crushing and screening fused magnesia; then adding at least one organic silicon solvent and the fused magnesia for mixing and stirring; then adding an inducer; aging for a period of time, filtering, drying, and finally roasting to obtain the high-temperature-resistant and high-hydrophobicity electric-grade magnesium oxide powder. The method has the advantages of simple operation and low energy consumption, and the prepared electrical grade magnesium oxide has excellent hydrophobicity and high temperature resistance.

Description

High-temperature-resistant and high-hydrophobicity electric-grade magnesium oxide powder and preparation method thereof

Technical Field

The invention relates to the field of material preparation, in particular to high-temperature-resistant and high-hydrophobicity electric magnesium oxide powder and a preparation method thereof.

Background

The electric-grade magnesia powder has excellent insulativity and heat conductivity, and is mainly used for manufacturing electric appliance elements with heating function. The electric smelting magnesia is produced by crushing, processing and granularity proportioning and then a series of treatments

Can be widely used as the insulating filling material of the electric heating element.

The factors influencing the electrical magnesium oxide powder mainly comprise heat conductivity, insulating strength, moisture absorption rate, hydration rate, content of magnetized substances and the like. Because the raw materials of the electrical-grade magnesia powder mainly come from the fused magnesia, the fused magnesia on the market has low magnesia content, high moisture absorption rate and high hydration rate, can damage the electrical performance of an electric heating element after being used, is easy to leak electricity and even explode tubes, and has great potential safety hazard. In addition, the electric heating element preparation material and the filler may contain a small amount of organic matters, and the organic matters can be decomposed, diffused and carbonized at high temperature to cause the magnesium oxide to turn black, thereby influencing the electric performance of the electric heating element. The application of the high-temperature resistant hydrophobic electric magnesium oxide powder is very wide, and the high-temperature resistant hydrophobic electric magnesium oxide powder is mainly suitable for civil use: the insulating property at high temperature of high-grade stainless steel tubes such as microwave furnace tubes, bread machine tubes, oven heating tubes and the like and British rice tubes is directly related to the quality of electric heating products. The high-end product can also be used for manufacturing insulating materials in the fields of aviation, aerospace, nuclear power and the like.

At present, Chinese patent CN107204213A discloses a method for producing electrical grade magnesium oxide powder, which comprises the following steps: the fused magnesia is crushed, screened and treated by alkali liquor; after drying, adding inorganic fillers such as kaolin and the like, and screening to remove magnetism; and finally, spraying silicone oil on the surface of the magnesium oxide powder in a spraying manner to obtain the electrical magnesium oxide powder. The patent CN16967309A discloses a production method of an electrical grade magnesium oxide powder for a water boiling aluminum pipe, which comprises the steps of firstly crushing and screening an electrical melting magnesium block, adding an organic silicon material for mixing, curing at normal temperature, adding an inorganic nano material as an oil absorbent, curing in a kiln at 80-150 ℃, finally curing at high temperature of 200-250 ℃ and naturally cooling to obtain the electrical grade magnesium oxide powder. Patent CN103922615A discloses a method for preparing high-grade electrical grade magnesium oxide from low-grade electric melting magnesium oxide. And heating the capacitance magnesium oxide powder to 800-2000 ℃, preserving the heat for a certain time, and quenching to obtain the electrical magnesium oxide powder. Patent CN103523791B discloses a method for preparing an electrical grade magnesium oxide additive, which can greatly reduce the leakage current of electrical grade high temperature magnesium oxide after being mixed with electric melting magnesium oxide. The specific process is as follows: firstly, a certain proportion of magnesium oxide and silicon dioxide are mixed and calcined at high temperature, then cooled, and then a boron compound is added and mixed, and then the mixture is calcined at high temperature. Finally, crushing and screening the obtained cooled substance to obtain the required product. Patent CN103971786B discloses a method for preparing high temperature resistant insulating magnesium oxide powder with electrical grade organic coating for electric oven, which can be used to make electric heating elements without 1050 degree annealing. Patent US4677026 discloses a method for preparing moisture-proof electrical magnesium oxide powder, wherein 600 ℃ organosilicon steam is introduced into a fluidized bed containing electric melting magnesium oxide, and the organosilicon is pyrolyzed and then covers the surface of electric melting magnesium oxide particles, thereby forming a moisture-proof insulating electrical magnesium oxide powder product.

China has developed to become a manufacturing base of global household appliances, and simultaneously, the fields of the heavy industry and the aerospace production are gradually expanded, and simultaneously, China is also a production base of the electric heating insulating material. However, the prior art is backward, equipment is not too much, so that the electrical grade magnesium oxide produced in China is high in cost and low in product quality, and generally mainly comprises medium-low temperature magnesium oxide powder. Therefore, the research and development of high-quality high-temperature-resistant and good-moisture-resistance electrical-grade magnesium oxide powder become urgent.

Disclosure of Invention

Aiming at the problems of the prior patent, the high temperature resistance of the electric-grade magnesium oxide powder is difficult to overcome, and the preparation process of the high-temperature-resistant electric-grade magnesium oxide is complicated, the energy consumption is high, and the environmental pollution is serious. In order to overcome the defects and shortcomings in the prior art, the invention provides high-temperature-resistant and high-hydrophobicity electric-grade magnesium oxide powder and a preparation method thereof.

The invention relates to high-temperature-resistant and high-hydrophobicity electric-grade magnesium oxide powder, wherein high-purity magnesium oxide is arranged in the electric-grade magnesium oxide powder, and an inorganic silicon dioxide coating is arranged outside the electric-grade magnesium oxide powder.

The invention relates to high-temperature-resistant and high-hydrophobicity electric magnesium oxide powder, which is characterized in that high-purity magnesium oxide is arranged inside the electric magnesium oxide powder, and the purity of the magnesium oxide is 96-99.9%;

the invention relates to high-temperature-resistant and high-hydrophobicity electrical magnesium oxide powder, wherein the thickness of an inorganic silicon dioxide coating on the exterior of the electrical magnesium oxide powder is 0.1-100 nm; the mass ratio of the silicon oxide to the magnesium oxide is 0.1-10%;

a preparation method of high-temperature-resistant and high-hydrophobicity electric-grade magnesium oxide powder is realized by the following steps:

(1) crushing the fused magnesia into 40-325 meshes to prepare fused magnesia powder with the magnesia content of 95-98 percent;

(2) mixing an organic silicon solution and an alcohol solvent, and fully stirring to prepare a solution A;

(3) mixing an alkaline inducer, deionized water and an alcohol solvent, and fully stirring to prepare a solution B;

(4) mixing the fused magnesia powder prepared in the step (1) with the solution A and stirring for 20-30 minutes to prepare slurry C;

(5) adding the solution B into the slurry C in a certain proportion within a certain time, and uniformly stirring;

(6) aging for 30-180 minutes at 20-80 ℃, standing and filtering;

(7) drying the filtered solid particles for 5-24 hours at 40-200 ℃;

(8) and roasting the dried solid for 2-10 hours at 800-2000 ℃.

In the step (2), the organic silicon solution is selected from one or more of methyl orthosilicate, ethyl orthosilicate, propyl orthosilicate and butyl orthosilicate.

The alcohol in the step (2) is selected from one or more of methanol, ethanol, n-propanol, isopropanol and ethylene glycol.

And (3) selecting one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, ammonia water, triethylamine and pyridine as the alkaline inducer.

The alcohol in the step (3) is selected from one or more of methanol, ethanol, n-propanol, isopropanol and ethylene glycol.

The feeding time range of the step (5) is 1-120 minutes.

The mixing proportion in the step (5): the mol ratio of the organic silicon solution (calculated by SiO 2), the alkaline inducer and the deionized water is 1: (0.001-100): (1-600).

The invention has the following advantages and beneficial effects for the prior art:

1. the high-temperature-resistant and high-hydrophobicity electric grade magnesium oxide prepared by the invention can resist the high temperature of 2000 ℃, and the moisture-proof insulating property is more than 1000 MOmega.

2. The invention has simple operation, low energy consumption and no environmental pollution.

3. The method is easy to enlarge industrialization, has no complex post-treatment process, and greatly reduces production cost.

Drawings

FIG. 1 is a flow chart of the preparation of the present invention.

Detailed Description

The following detailed description of the present invention will be made with reference to the accompanying drawings and examples, which are not intended to limit the present invention. The details and forms of the present invention may be modified by those skilled in the art within the principle of the present invention, and such modifications are within the scope of the present invention.

For the convenience of understanding and showing the present invention, the preparation process of the present invention is shown in FIG. 1. The high temperature resistance and waterproof performance of the sample are tested in SU304 stainless steel tube with diameter of 6.6mm and length of 500mm, and the heating power of the electric heating furnace wire is 500W. The hydrophobicity test is to test the insulating properties at 50% and 90% humidity, respectively.

Example 1

And (3) crushing and screening the fused magnesia to 40-325 meshes to prepare the fused magnesia powder. 1kg of fused magnesia powder, 50g of tetraethoxysilane and 2kg of ethanol are taken and fully and uniformly stirred to prepare slurry; 3g of concentrated ammonia water and 3kg of ethanol are fully mixed and added into the magnesia powder slurry, and the time is controlled to be 30 minutes. After the feeding is finished, the mixture is aged in a water bath at 50 ℃ for 1 hour, and is kept stand and filtered. The filtered solid was placed in an oven and dried at 150 ℃ for 10 hours. After natural cooling, the mixture is placed into a kiln for roasting for 6 hours under the condition of 1200 ℃. The resulting product was tested by SEM and had a silica coating thickness of 35nm and a SiO2 content of 2.1% of MgO.

Example 2

And (3) crushing and screening the fused magnesia to 40-325 meshes to prepare the fused magnesia powder. Taking 0.5kg of fused magnesia powder, 150g of methyl orthosilicate and 3kg of methanol, and fully and uniformly stirring to prepare slurry; 1.5g of concentrated ammonia water and 5kg of methanol are fully mixed and added into the magnesia powder slurry, and the time is controlled to be 55 minutes. After the feeding is finished, the mixture is aged in a water bath at 30 ℃ for 3 hours, and is kept stand and filtered. The filtered solid was placed in an oven and dried at 40 ℃ for 24 hours. After natural cooling, the mixture is placed into a kiln for roasting for 10 hours at 1100 ℃. The resulting product was tested by SEM and had a silica coating thickness of 40nm and a SiO2 content of 1.6% of MgO.

Example 3

And (3) crushing and screening the fused magnesia to 40-325 meshes to prepare the fused magnesia powder. 3.2kg of fused magnesia powder, 80g of tetraethoxysilane and 4.5kg of ethanol are taken, and the mixture is fully and uniformly stirred to prepare slurry; 6.5g of concentrated ammonia water and 2.6kg of ethanol are fully mixed and added into the magnesia powder slurry, and the time is controlled to be 35 minutes. After the feeding is finished, the mixture is aged in a water bath at 80 ℃ for 2 hours, and is kept stand and filtered. The filtered solid was placed in an oven and dried at 60 ℃ for 24 hours. After natural cooling, the mixture is put into a kiln for roasting for 3 hours at the temperature of 1800 ℃. The resulting product was tested by SEM and had a silica coating thickness of 30nm and a SiO2 content of 1.1% of MgO.

The high temperature resistant and highly hydrophobic electrical magnesium oxide powder prepared in the examples 1, 2 and 3 of the present invention was compared with the general uncoated electrical magnesium oxide powder, and after the powder was respectively prepared into a standard electric heating element, the component content, mesh number analysis and electrical insulation analysis were tested, and the comparison results are shown in tables 1, 2 and 3.

Table 1 table for analyzing components of each example

Sample batch number	MgO	CaO	Fe2O3	SiO2	Al2O3	L.O.I
							Example 1	95.93	0.67	0.36	2.75	0.26	0.03
Example 2	95.84	0.67	0.36	2.85	0.26	0.02
							Example 3	96.34	0.56	0.36	2.45	0.26	0.03
Uncoated MgO	97.02	0.82	0.4	1.46	0.26	0.04

TABLE 2 mesh number analysis table (content%)

TABLE 3 electric insulation Performance analysis Table (M. OMEGA.) for each example

Insulation performance of sample	Normality	Tidal state
			Example 1	3500	3500
Example 2	4500	4000
			Example 3	4000	3500
Uncoated MgO	40	15

Note: sample tube SU304 steel tube

Length: 500mm 110V/500W.

Claims

1. A preparation method of high-temperature-resistant and high-hydrophobicity electric-grade magnesium oxide powder is characterized by comprising the following steps of: the method comprises the following steps:

(1) crushing fused magnesia to 40-325 meshes to prepare fused magnesia powder with the magnesia content of 95-98 percent;

(6) aging for 30-180 minutes at 20-80 ℃, standing and filtering;

(7) drying the filtered solid particles for 5-24 hours at 40-200 ℃;

(8) roasting the dried solid for 2-10 hours at 800-2000 ℃;

the electrical grade magnesium oxide powder is internally provided with high-purity magnesium oxide and externally provided with an inorganic silicon dioxide coating.

2. The method for preparing high temperature resistant and high hydrophobicity electrical grade magnesium oxide powder according to claim 1, wherein: the interior of the electrical grade magnesia powder is high-purity magnesia, and the purity of the magnesia is 96-99.9%.

3. The method for preparing high temperature resistant and high hydrophobicity electrical grade magnesium oxide powder according to claim 1, wherein: the thickness of the external inorganic silicon dioxide coating of the electrical grade magnesium oxide powder is 0.1-100 nm; the mass ratio of the silicon oxide to the magnesium oxide is 0.1-10%.

4. The method for preparing high temperature resistant, highly hydrophobic electrical grade magnesium oxide powder according to claim 1, wherein: in the step (2), the organic silicon solution is selected from one or more of methyl orthosilicate, ethyl orthosilicate, propyl orthosilicate and butyl orthosilicate.

5. The method for preparing high temperature resistant, highly hydrophobic electrical grade magnesium oxide powder according to claim 1, wherein: the alcohol in the step (2) is selected from one or more of methanol, ethanol, n-propanol, isopropanol and ethylene glycol.

6. The method for preparing high temperature resistant, highly hydrophobic electrical grade magnesium oxide powder according to claim 1, wherein: and (3) selecting one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, ammonia water, triethylamine and pyridine as the alkaline inducer.

7. The method for preparing high temperature resistant, highly hydrophobic electrical grade magnesium oxide powder according to claim 1, wherein: the alcohol in the step (3) is selected from one or more of methanol, ethanol, n-propanol, isopropanol or ethylene glycol.

8. The method for preparing high temperature resistant, highly hydrophobic electrical grade magnesium oxide powder according to claim 1, wherein: the feeding time range of the step (5) is 1-120 minutes.

9. The method for preparing high temperature resistant, highly hydrophobic electrical grade magnesium oxide powder according to claim 1, wherein: the mixing proportion in the step (5): the organosilicon solution is SiO₂The mol ratio of the alkali inducer to the deionized water is 1: 0.001 to 100: 1-600, wherein the volume ratio of the alcohol solvent in the total solution is 60-85%.