A preparation method and coating of protective coating based on fused quartz

Abstract

The present invention discloses a preparation method and coating of a high-temperature protective coating based on fused quartz, namely, coating a layer of silicon dioxide nanoparticles / organic polymer film on the surface of a substrate, wherein the average particle size of the silicon dioxide particles is less than 100 nanometers, and after drying and annealing to remove the organic polymer, high-temperature sintering is performed to allow the silicon dioxide nanoparticles to fuse with each other and eventually form a dense, amorphous fused quartz coating on the surface of the substrate; the coating prepared by the method can provide excellent high-temperature anti-oxidation protection performance of thousands of degrees Celsius for a material with a thickness of a few atomic layers on the surface of the substrate, and is suitable for special protection requirements such as thermal shock, anti-oxidation, and anti-corrosion in extreme high-temperature environments.

Description

Technical Field

[0001] The present invention relates to the technical field of high-temperature protective coatings, and in particular to a high-temperature impact-resistant, oxidation-resistant and corrosion-resistant protective coating based on fused quartz and a preparation method thereof. Background Art

[0002] At present, commercial glasses such as silicate glass and high borosilicate glass are mainly manufactured by adding various additives such as silicate, boron oxide, sodium oxide, etc., in order to reduce the melting point of the glass and enhance its processability. However, the melting point of these doped glasses is only a few hundred degrees Celsius, and they cannot withstand high temperatures of thousands of degrees Celsius. They are even more difficult to withstand ultra-high temperature shocks. They are extremely easy to break in extreme environments such as ultra-fast heating and cooling rates and strong temperature gradients. At the same time, doping will also reduce the corrosion resistance of the glass. Therefore, existing commercial glass coatings cannot meet the protection needs of workpieces in extreme environments.

[0003] At present, the commonly used high temperature resistant coatings are divided into three categories: organic high temperature resistant coatings, inorganic high temperature resistant coatings, and organic-inorganic composite high temperature resistant coatings. Among them, organic coatings and organic-inorganic composite coatings have good packaging airtightness, but poor thermal stability. Inorganic coatings are mostly ceramic materials with stable mechanical properties, but high brittleness and poor airtightness.

[0004] Fused quartz is an amorphous, high-purity silica glass. It is different from crystalline quartz glass and traditional low-melting-point doped glass. It has unique physical properties: a melting point of about 1700°C, extremely low thermal expansion coefficient, high inertness, high temperature shock resistance, and high transmittance in a wide range of ultraviolet-visible-infrared bands. It is often used in optical fields such as lenses and laser optical fibers, and has the advantages of high temperature shock resistance, corrosion resistance, and oxidation resistance. However, the high melting point, high hardness and other difficult-to-process characteristics of fused quartz also limit the application range of this material, especially its rare application in protective coatings. Summary of the invention

[0005] In response to the protection needs of ultra-high temperature extreme environments above 1000°C, the present invention provides a coating based on fused quartz to provide physical and chemical protection such as anti-oxidation and anti-corrosion for substrate surface materials in ultra-high temperature environments.

[0006] Specifically, the above invention object is achieved through the following technical solutions:

[0007] First, the present application provides a method for preparing a protective coating based on fused quartz, and the specific steps are as follows:

[0008] 1) Dissolve the organic polymer in a solvent and disperse the organic polymer in a solvent having an average particle size of less than 100 nanometers and a specific surface area of ​​less than 100 m 2 / g of silicon dioxide nanopowder, thereby preparing a slurry of silicon dioxide / organic polymer / solvent components;

[0009] The solid content ratio of silicon dioxide to organic polymer in the slurry is not less than 0.6;

[0010] The organic polymer is selected from polymethyl methacrylate (PMMA), polyvinyl butyral (PVB), polyvinyl alcohol (PVA), polyethylene glycol (PEG), etc. or a combination thereof, which are easy to be removed by annealing.

[0011] As the solvent, various organic or inorganic solvents such as water, ethanol, methanol, acetone, chloroform, anisole, etc., which can fully dissolve the selected organic polymer, are used.

[0012] In a preferred embodiment of the present application, in the above slurry, based on the mass percentage of the whole slurry, the organic polymer accounts for 15%, the silicon dioxide nanopowder accounts for 15%, and the balance is the solvent.

[0013] 2) directly coating the slurry on the substrate surface and drying to remove the solvent to form a silica / organic polymer composite cured coating, ensuring that the coating thickness is less than 200 microns to avoid cracks caused by internal stress during the subsequent heat treatment process;

[0014] The above-mentioned "slurry coating" means that the slurry can be applied to the substrate surface by drip coating, scraper coating, spin coating, spray coating, etc. The above-mentioned "drying" means that the organic solvent can be removed by natural drying, heating drying, air drying, infrared drying, etc.

[0015] The above-mentioned "substrate surface" can be metals such as nickel, titanium, tungsten, molybdenum and their various alloys with ultra-high temperature thermal stability, or various inorganic non-metals such as silicon carbide, silicon nitride, aluminum oxide, zirconium oxide, carbon materials or their composite materials.

[0016] 3) removing the organic polymer in the coating by annealing to form a porous coating in which the silicon dioxide nanoparticles are bonded to each other;

[0017] 3) Annealing conditions are based on the characteristics of the selected organic polymer and use a corresponding annealing temperature or annealing atmosphere, including vacuum, nitrogen, air, etc., to achieve a removal rate of more than 95% of the organic polymer. The annealing temperature can be 400° C. or above.

[0018] 4) High-temperature sintering causes the nanoparticles to melt and fuse with each other, eventually forming a dense amorphous silicon dioxide coating, i.e., a fused quartz coating, on the surface of the substrate; the coating has high chemical inertness, high melting point, and high density, and can provide efficient thermal and chemical protection for the substrate surface material.

[0019] The above sintering temperature is not less than 1700°C, such as 1700-1800°C.

[0020] Secondly, the present application provides a protective coating obtained by the above preparation method, and the coating is amorphous.

[0021] The preparation method of the high-temperature anti-oxidation protective coating based on fused quartz provided by the present invention has a simple process and low cost. It can avoid the peeling and damage of the substrate surface material and the coating caused by annealing in the entire preparation process, and even does not damage the single atomic layer material on the substrate surface. It can be attached to the substrate surface to form a high-quality protective coating, which can effectively improve the anti-oxidation performance of the substrate surface in a high-temperature environment, and can even provide high-temperature and anti-oxidation protection of thousands of degrees Celsius for a small number of atomic layer materials, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 These are camera images and scanning electron microscope images of the coating / substrate at different sintering temperatures in the examples of the present invention.

[0023] Figure 2 The following are actual photos and typical Raman spectra of the fused quartz coating prepared by sintering at 1700°C in an example of the present invention.

[0024] Figure 3 This is a typical Raman spectrum of the fused silica coating prepared by sintering at 1800°C in an example of the present invention.

[0025] Figure 4 These are Raman spectra of a few atomic layers of graphene on the substrate surface before and after coating preparation in an example of the present invention.

[0026] Figure 5 This is the Raman spectrum of graphene with and without coating protection in an air environment at 1000°C in an example of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other. The technical scheme of the present invention is further described below in conjunction with examples.

[0028] Example 1 Preparation of protective coating

[0029] Step 1: dissolving polymethyl methacrylate (PMMA) particles in anisole to obtain a PMMA solution, and uniformly dispersing amorphous silicon dioxide nanopowder (purchased from Evonik Industries AG, Germany) in the PMMA solution to obtain a composite slurry; the composite slurry includes, by weight percentage of the composite slurry, 15% PMMA, 15% SiO2 nanopowder (average particle size of about 40nm, specific surface area of ​​35-65m 2 In specific implementation, when the average particle size of the organic polymer dispersed in the solvent is less than 100 nanometers, the purpose of the invention can be achieved.

[0030] Step 2: Evenly scrape the composite slurry obtained in step 1 onto the surface of the substrate, with a coating thickness of 90 μm;

[0031] The substrate used in this embodiment is aluminum oxide, and there is 1-2 atomic layers of graphene on the surface of the substrate. The method for preparing graphene on the surface of the substrate is a conventional method in the art. This embodiment is prepared according to the method disclosed in the document "Materials Letters, 2013, 110: 225-228". The use of graphene with a thickness of a few atomic layers is only for the convenience of verifying the atomic-level process compatibility and excellent protective effect of the obtained coating on the substrate surface material.

[0032] In a specific implementation, the substrate surface can be made of metals such as tungsten, nickel, titanium and their alloys with ultra-high temperature thermal stability, or inorganic non-metallic materials such as silicon carbide, silicon nitride, aluminum oxide, zirconium oxide, and carbon materials.

[0033] Step 3: Then heat and dry on a hot plate at 150°C for 5 minutes to obtain a uniform SiO2 / PMMA composite film;

[0034] Step 4: Annealing at 400° C. in a vacuum atmosphere in a tube furnace for 3-5 hours to remove PMMA from the SiO2 / PMMA composite film to obtain a loose and porous SiO2 coating.

[0035] Step 5: The sample is subjected to high-temperature vacuum sintering. The sintering device is constructed according to the method disclosed in the document "Science, 2020, 368:521". The sintering temperatures are 1400°C, 1600°C, 1700°C, and 1800°C, respectively, and are maintained for 10 seconds (in a specific implementation, the sintering temperature can be higher than 1700°C, and the time can be maintained for more than 10 seconds) to obtain a coating.

[0036] Figure 1AC are the physical photos, 10-micron SEM photos and 1-micron SEM photos of the protective coating obtained at a sintering temperature of 1400°C; DF are the physical photos, 10-micron SEM photos and 1-micron SEM photos of the protective coating obtained at a sintering temperature of 1600°C; GI are the physical photos, 10-micron SEM photos and 1-micron SEM photos of the protective coating obtained at a sintering temperature of 1800°C.

[0037] Figure 2 In the figure, A is a photo of the protective coating obtained at a sintering temperature of 1700°C, and B is a photo of the coating obtained at the sintering temperature characterized by the characteristic peaks of the Raman spectrum, which can be verified to be amorphous fused quartz.

[0038] Figure 3 The coating obtained by sintering at 1800°C was characterized by the characteristic peaks of Raman spectroscopy and was verified to be amorphous fused quartz.

[0039] It can be seen that only when the sintering temperature is above 1700°C (including 1700°C) can a transparent and dense amorphous protective coating be produced on the substrate surface, that is, a protective coating based on fused quartz be formed. When the sintering temperature is lower than 1700°C, the formed coating is opaque.

[0040] The performance of the fused quartz protective coating prepared in this example and its preparation process were characterized: Figure 4 In the figure, A and B are the Raman spectra of graphene on the substrate surface before and after coating preparation (sintering temperature of 1700°C), respectively. It can be seen that the entire coating preparation process in the embodiment does not cause any damage to the graphene with a thickness of 1-2 atomic layers on the substrate surface, and the relative height of the graphene Raman characteristic peak is almost the same with or without coating.

[0041] Analysis of the protective performance of the coating against high temperature oxidation: The graphene sample protected by fused quartz was heated to 1000°C in an air environment and maintained for 10 minutes. The Raman spectrum is shown in Figure 5 shown. Figure 5 In the figure, A and B are the Raman spectra of graphene with protective coating (sintered at 1700°C) and graphene without coating obtained in the example, respectively; it can be seen that the Raman characteristic peak of graphene in A has no obvious change, indicating that graphene has not been damaged by high-temperature oxidation. However, after the sample without protective coating in B was treated under the same conditions at 1000°C, there was no graphene Raman characteristic peak, indicating that the graphene without coating protection was completely oxidized and disappeared at high temperature. This proves the application prospect of the protective coating obtained in this example in the field of high-temperature protection.

Claims

1. A method for preparing a protective coating based on fused quartz, characterized in that: The specific steps are as follows: 1) dissolving an organic polymer in a solvent and dispersing silicon dioxide nanopowder therein to obtain a slurry of silicon dioxide / organic polymer / solvent components; The organic polymer is polymethyl methacrylate; The solvent is anisole; The slurry comprises, by mass percentage, 15% polymethyl methacrylate, 15% silicon dioxide nanopowder, and the remainder anisole; 2) coating the slurry on the surface of the substrate to obtain a coating; then drying, annealing and sintering to obtain the protective coating based on fused quartz, wherein the protective coating is amorphous; the sintering is high-temperature vacuum sintering, the sintering temperature is not less than 1700°C, and the sintering time is 10s; the annealing refers to annealing in a vacuum atmosphere or a nitrogen atmosphere; the annealing temperature is not less than 400°C; the coating thickness is less than 200 microns; the substrate surface material is graphene with a thickness of a few atomic layers.

2. The method for preparing a protective coating based on fused quartz according to claim 1, characterized in that: Step 1) The average particle size of the silicon dioxide nanopowder is less than 100 nanometers and the specific surface area is less than 100m 2 / g.

3. The method for preparing a protective coating based on fused quartz according to claim 1, characterized in that: Step 2) The drying refers to at least one of natural drying, heating drying, air drying, and infrared drying.

4. A protective coating based on fused quartz prepared by the method according to any one of claims 1 to 3.

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