CN100457834C - Alumina insulating coating and preparation method thereof - Google Patents

Abstract

The invention discloses an aluminum oxide insulating coating and a preparation method thereof. The coating comprises an aluminum oxide coating on a substrate, in particular, the thickness of the aluminum oxide coating is 5 to 30 μm, and the coating is composed of 2 to 8 layers of α-Al ₂ O ₃ particles with a particle size of 20 to 150 nm and a product of boehmite sol at high temperature; the method comprises a sol-gel method, in particular, the steps of: (1) mixing nano-scale α-Al ₂ O ₃ powder, aqueous boehmite sol and inorganic acid or inorganic acid salt or organic acid or organic acid salt in a ratio of 1 to 20:100:0.1 to 5, then ball milling the mixture for 5 to 10 hours and leaving the mixture for 5 to 24 hours to obtain a composite slurry; (2) coating the substrate with the composite slurry, then drying the mixture at 80 to 120°C for 10 to 30 minutes, and then heat treating the mixture at 400 to 700°C for 5 to 20 minutes; and (3) repeating step (2) 2 to 8 times to obtain the aluminum oxide insulating coating. It has high breakdown voltage and DC resistance and can be widely used in the field of high voltage resistant electrical insulation.

Description

Aluminum oxide insulating coating and preparation method thereof

technical field

The invention relates to an insulating coating and a preparation method, in particular to an aluminum oxide insulating coating and a preparation method thereof.

Background technique

Alumina insulating coatings have broad application prospects in nuclear energy, metallurgy, mining and other fields due to their advantages of high temperature resistance, acid and alkali corrosion resistance, wear resistance, and high dielectric strength. At present, people have made some efforts in order to obtain it. For example, in the "Research on the Properties of Plasma Sprayed Ceramic Coatings" in the "Journal of Dalian Railway Institute", Volume 21, No. 2, published in June 2000, it was once disclosed a method of using plasma Body spraying is a method of spraying aluminum oxide on No. 45 steel, and the thickness of the aluminum oxide coating is 40-90 microns. But this aluminum oxide coating and its spraying method all have weak point, at first, aluminum oxide coating is piled up in lamination, bonding strength is low, and there is a large amount of pores in the coating, causes coating to loosen, thereby causes Its dielectric breakdown strength is low, and it is difficult to be used as a high-performance insulating coating; secondly, the plasma spraying method has high requirements on equipment, and the second is that the spraying parameters, which are the key factors affecting the quality of the coating, are not easy to grasp. But the preparation period is also long, and it is not suitable for large-scale industrial production.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide an aluminum oxide insulating coating that can be used at relatively high temperatures, is convenient to use and has excellent insulating properties and a preparation method thereof.

The aluminum oxide insulating coating includes an aluminum oxide coating on the substrate, especially the thickness of the aluminum oxide coating is 5-30 μm, which consists of 2-8 layers of α-Al ₂ O ₃ with a particle size of 20-150 nm Particles and boehmite sols are formed at high temperatures.

The preparation method of aluminum oxide insulating coating comprises sol-gel method, particularly it is finished by the following steps: (1), nanoscale α-Al ₂ O ₃ powder and aqueous boehmite sol and mineral acid or Inorganic acid salts or organic acids or organic acid salts are mixed according to the ratio of 1 to 20:100:0.1 to 5, and then ball milled for 5 to 10 hours and then placed for 5 to 24 hours to obtain a composite slurry; (2). Coat the substrate with the slurry, then dry it at 80-120°C for 10-30 minutes, and then heat-treat it at 400-700°C for 5-20 minutes; (3), repeat steps 2-8 of (2) Second, an alumina insulating coating is obtained.

As a further improvement of the preparation method of the alumina insulating coating, the particle size of the nanoscale α-Al ₂ O ₃ powder is 20-150nm; the composition of the water-based boehmite sol is γ-AlOOH, concentration 1 to 10 wt%, and a pH value of 2 to 5; the inorganic acid is nitric acid or sulfuric acid or hydrochloric acid; the inorganic acid salt is aluminum sulfate or aluminum nitrate or aluminum chloride; the organic acid is acetic acid or oxalic acid or citric acid; the organic acid salt is aluminum acetate or aluminum oxalate or aluminum citrate; the ball mill is to place the mixed slurry in a ball mill tank to mix and grind on a planetary ball mill; Coating is by dipping or spin coating or spraying.

Compared with the beneficial effects of the prior art, firstly, after characterizing and testing the prepared aluminum oxide insulating coating and its section using a field emission scanning electron microscope, an X-ray diffractometer and a coating thickness gauge, From the obtained scanning electron microscope photos, X-ray diffraction patterns and thickness values, it can be known that the insulating coating is dense and free of cracks, which is composed of α-Al ₂ O ₃ particles with a particle size of 20-150nm and boehmite sol at high temperature. The product is uniformly distributed in it, and its thickness is 5-30 μm; second, use an automatic high-voltage breakdown device and an insulation resistance tester to conduct power-frequency AC shocks on the prepared alumina insulating coating at different temperatures. The test of breakdown voltage and DC insulation resistance, wherein the thickness of the coating is 21.5μm, and the area of the electrode is 0.25cm ² , the results are as follows:

It can be seen from the table that the coating has a high breakdown voltage and DC resistance, and its insulation performance is excellent; third, nano-scale α-Al ₂ O ₃ powder and water-based boehmite sol and inorganic acid or inorganic Salts or organic acids or organic acid salts as raw materials for the preparation of insulating coatings can play the role of nano-α-Al ₂ O ₃ ceramic particles: 1) prevent the coating from cracking during drying and heat treatment, 2) can obtain comparative Thick coating, 3) increase the packing density between particles, thereby increasing the density of the coating, 4) make the main phase of the coating be α-phase alumina, and the α-phase has a very good quality in many alumina phases The characteristics of insulation performance, and can also play the role of water-based boehmite sol: 1) As a high-temperature "binder", the nano-ceramic particles in the system are tightly bonded together, 2) Boehmite is the form of alumina A precursor, which can be completely transformed into alumina during heat treatment, is the same substance as the added alumina ceramic particles, which properly alleviates the characteristics of cracks in the coating caused by the mismatch of thermal expansion coefficients of materials, and can also play an important role in inorganic Acid or inorganic acid salt or organic acid or organic acid salt: 1) It can regulate the gelation time of boehmite colloid, so as to obtain a composite slurry with a certain viscosity, which is convenient for coating construction. 2) Due to the addition of these substances, The number of charges in the system increases, and the electrostatic stabilization mechanism is used to disperse the nanoparticles uniformly in the slurry system. 3) This additive will either completely decompose or produce a material in the same phase as alumina at high temperature, and will not leave any effect on the coating. 4) These additives will have a weak corrosion and oxidation effect on the substrate, and can form a thin and dense oxide film on the surface of the metal substrate. This film matches the aluminum oxide coating and improves the coating. Layer adhesion properties. Therefore, the contradiction between the thickness of one coating and the cracks caused by the mismatch of the thermal expansion coefficient of the material is properly resolved, and the insulating coating of the required thickness can be obtained with only a small number of coating times; Fourth, it has been tested by other instruments , the insulating coating also has high wear resistance, corrosion resistance, oxidation resistance, and heat resistance properties, which is convenient for large-scale use in a wider application field; fifth, the preparation process is simple and easy to operate, and the equipment requirements Not high, suitable for large-scale industrial production.

Description of drawings

The preferred modes of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Figure 1 shows the use of (a) pure water-based boehmite sol, (b) 10 parts of nano-sized α-Al ₂ O ₃ powder and 100 parts of water-based boehmite sol, and (c) 10 parts of nano-sized α -The single coating thickness of the coating prepared by the slurry of Al ₂ O ₃ powder and 100 parts of aqueous boehmite sol and 2 parts of inorganic acid or salt of inorganic acid or organic acid or salt of organic acid. It can be seen from the figure that after one coating, the coating thickness of (c) is about 5 μm, which is the largest among the three samples;

Figure 2 is a photo taken after observing the surface and cross-sectional morphology of the insulating coating with the Sirion 200 FEG type field emission scanning electron microscope of FEI Company of the United States, where (a) is the insulating coating The surface topography of the layer, (b) is the cross-sectional topography of the insulating coating;

Fig. 3 is the phase diagram of the insulating coating using the X'pert-PRO type X-ray diffractometer of the Netherlands Philips company to distinguish the coating, wherein the abscissa is a 2θ angle, and the ordinate is a relative intensity, as can be seen from this, The main phase of the coating is α-Al ₂ O ₃ phase structure, and there is a small amount of γ-Al ₂ O ₃ phase structure formed by heat treatment of boehmite sol;

Figure 4 is a graph of the relationship between the AC dielectric breakdown voltage and temperature obtained after measuring the power frequency AC breakdown voltage of the insulating coating using the CW2672H automatic high-voltage breakdown device of Changzhou Micro & Special Motor General Factory, where the abscissa is temperature , the ordinate is the breakdown voltage, and the coating thickness is 21.5 μm.

Detailed ways

Firstly, α-Al ₂ O ₃ powder with a particle size of 20-150 nm, aqueous boehmite sol, inorganic acid, inorganic acid salt, organic acid, and organic acid salt are prepared by conventional methods or purchased from the market. then:

Embodiment 1: Complete the preparation according to the following steps: 1), mix nanoscale α-Al ₂ O ₃ powder with aqueous boehmite sol and inorganic acid according to the ratio of 1:100:0.1, wherein, nanoscale α- The particle size of the Al ₂ O ₃ powder is 150nm, the composition of the water-based boehmite sol is γ-AlOOH, the concentration is 1wt%, the pH value is 2, and the inorganic acid is nitric acid (or sulfuric acid or hydrochloric acid), and then the mixed slurry Put it in a ball mill tank, mix and grind on a planetary ball mill for 5 hours, and then place it for 5 hours to obtain a composite slurry; 2), after polishing, degreasing and cleaning the copper substrate, apply it with a composite slurry, and apply The method is spraying (or dipping or spin coating), then drying it at 80°C for 30 minutes, and then heat-treating it at 400°C for 20 minutes; 3), repeat the steps of 2) twice, and the obtained 2. The aluminum oxide insulating coating shown in Figure 3 and Figure 4.

Embodiment 2: Complete the preparation according to the following steps: 1), mix nanoscale α-Al ₂ O ₃ powder with water-based boehmite sol and inorganic acid according to the ratio of 5:100:1.5, wherein, nanoscale α- The particle size of the Al ₂ O ₃ powder is 110nm, the composition of the water-based boehmite sol is γ-AlOOH, the concentration is 3wt%, the pH value is 3, and the inorganic acid is nitric acid (or sulfuric acid or hydrochloric acid), and then the mixed slurry Put it in a ball mill tank, mix and grind on a planetary ball mill for 6 hours, and then place it for 10 hours to obtain a composite slurry; 2), after polishing, degreasing and cleaning the copper substrate, apply it with a composite slurry, and apply The method is spraying (or dipping or spin coating), then drying it at 90°C for 25 minutes, and then heat-treating it at 480°C for 17 minutes; 3), repeat the steps of 2) 4 times, and obtain a similar Figure 2 and the aluminum oxide insulating coating shown in Figure 3 and Figure 4.

Embodiment 3: Complete preparation according to the following steps: 1), mix nanoscale α-Al ₂ O ₃ powder with water-based boehmite sol and inorganic acid according to the ratio of 10:100:3, wherein, nanoscale α- The particle size of the _Al2O3 powder is _85nm , the composition of the water-based boehmite sol is γ-AlOOH, the concentration is 5wt%, the pH value is 3.5, and the inorganic acid is nitric acid (or sulfuric acid or hydrochloric acid), and then the mixed slurry Put it in a ball mill tank, mix and grind on a planetary ball mill for 7.5 hours, and place it for 15 hours to obtain a composite slurry; 2), after polishing, degreasing and cleaning the copper substrate, apply it with a composite slurry, and apply The method is spraying (or dipping or spin coating), then drying it at 100°C for 20 minutes, and then heat-treating it at 550°C for 13 minutes; 3), repeat the steps of 2) 5 times, and obtain a similar Figure 2 and the aluminum oxide insulating coating shown in Figure 3 and Figure 4.

Embodiment 4: Complete the preparation according to the following steps: 1), mix nanoscale α-Al ₂ O ₃ powder with aqueous boehmite sol and inorganic acid according to the ratio of 15:100:4, wherein, nanoscale α- The particle size of the Al ₂ O ₃ powder is 55nm, the composition of the water-based boehmite sol is γ-AlOOH, the concentration is 8wt%, the pH value is 4, and the inorganic acid is nitric acid (or sulfuric acid or hydrochloric acid), and then the mixed slurry Put it in a ball mill tank, mix and grind it on a planetary ball mill for 9 hours, and place it for 20 hours to obtain a composite slurry; 2), after polishing, degreasing and cleaning the copper substrate, apply it with a composite slurry, and apply The method is spraying (or dipping or spin coating), then drying it at 110°C for 15 minutes, and then heat-treating it at 630°C for 9 minutes; 3), repeat the steps of 2) 6 times, and obtain a Figure 2 and the aluminum oxide insulating coating shown in Figure 3 and Figure 4.

Example 5: Complete the preparation according to the following steps: 1), mix nanoscale α-Al ₂ O ₃ powder with aqueous boehmite sol and inorganic acid according to the ratio of 20:100:5, wherein, nanoscale α- The particle size of the Al ₂ O ₃ powder is 20nm, the composition of the water-based boehmite sol is γ-AlOOH, the concentration is 10wt%, the pH value is 5, and the inorganic acid is nitric acid (or sulfuric acid or hydrochloric acid), and then the mixed slurry Put it in a ball mill tank, mix and grind on a planetary ball mill for 10 hours, and then place it for 24 hours to obtain a composite slurry; 2), after polishing, degreasing and cleaning the copper substrate, apply it with a composite slurry, and apply The method is spraying (or dipping or spin coating), then drying it at 120°C for 10 minutes, and then heat-treating it at 700°C for 5 minutes; 3), repeat the steps of 2) 8 times, and obtain a similar Figure 2 and the aluminum oxide insulating coating shown in Figure 3 and Figure 4.

Then replace the inorganic acid with inorganic acid salt or organic acid or organic acid salt, wherein the inorganic acid salt is aluminum sulfate or aluminum nitrate or aluminum chloride, the organic acid is acetic acid or oxalic acid or citric acid, and the organic acid salt is aluminum acetate Or aluminum oxalate or aluminum citrate, and select semiconductor or superconductor again as substrate, repeat above-mentioned embodiment 1～5, also make as or approximate to the aluminum oxide insulating coating shown in Fig. 2 and Fig. 3, Fig. 4 .

Apparently, those skilled in the art can make various changes and modifications to the alumina insulating coating and its preparation method of the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims (6)

1, a kind of preparation method of alumina insulating coating comprises sol-gel method, it is characterized in that finishing according to the following steps:

1.1, be α-Al of 20～150nm with particle diameter ₂O ₃Powder and water-based boehmite sol and organic acid or organic acid salt are according to 1～20: 100: 0.1～5 ratio is mixed mutually, its ball milling was placed after 5～10 hours obtained composite mortar in 5～24 hours again;

1.2, use the composite mortar coated substrate, again with its in 80～120 ℃ dry 10～30 minutes down, afterwards, with it in 400～700 ℃ of following thermal treatments 5～20 minutes;

1.3, repeat 1.2 step 2～8 time, make alumina insulating coating.

2, the preparation method of alumina insulating coating according to claim 1, the composition that it is characterized in that the water-based boehmite sol is that γ～AlOOH, concentration are that 1～10wt%, pH value are 2～5.

3, the preparation method of alumina insulating coating according to claim 1 is characterized in that organic acid is acetic acid or oxalic acid or citric acid.

4, the preparation method of alumina insulating coating according to claim 1 is characterized in that organic acid salt is Burow Solution or oxalic acid aluminium or Tiorco 677.

5, the preparation method of alumina insulating coating according to claim 1 is characterized in that ball milling is to place ball grinder to mix and grinding mixed slurry on planetary ball mill.

6, the preparation method of alumina insulating coating according to claim 1 is characterized in that being applied to dipping or spin coating or spraying.

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