Silicon oxide coated metal powder based on polysilazane as well as preparation method and application of silicon oxide coated metal powder

Abstract

The invention relates to silicon oxide coated metal powder based on polysilazane and a preparation method and application of the silicon oxide coated metal powder, belongs to the technical field of functional material preparation, and solves at least one of the following problems existing in a silicon oxide coated metal powder preparation method in the prior art: (1) high-temperature conversion is needed; (2) equipment dependence or environment dependence exists in a low-temperature conversion method; and (3) agglomeration after powder coating. The method comprises the steps that metal powder and a polysilazane polymer precursor solution are mixed and dispersed, so that polysilazane is subjected to a growth reaction on the surface of the metal powder, and dispersion liquid is obtained; carrying out solid-liquid separation on the dispersion liquid; the metal powder with the polysilazane layer growing on the surface is placed in a high-humidity environment to be subjected to a hydrolytic condensation reaction; and drying the reacted product to obtain the silicon oxide coated metal powder. According to the method, complex processes such as high-temperature heat treatment and ultraviolet radiation are avoided, and the agglomeration phenomenon of the metal powder is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of functional material preparation, and in particular to a polysilazane-based silicon oxide-coated metal powder, a preparation method thereof, and applications thereof. Background Art

[0002] Metal powders, typically composed of micron- or nanometer-sized particles, possess unique physical and chemical properties and are widely used in fields such as biomedicine, materials science, and electronics. Silicon oxide has excellent surface chemical properties, high biocompatibility, controllable porosity, and good transparency, among other outstanding properties. Coating metal micro- and nanoparticles with silicon oxide can impart even more superior properties, such as improving their compatibility within the body, their dispersibility and filling properties in resin and other material systems, their catalytic activity and lifespan, and their stability, insulation, and corrosion resistance. However, large-scale production of silicon oxide-coated metal powders using simple and mild processes remains a significant challenge.

[0003] Using tetraethyl orthosilicate (TEOS) as raw material, adopting sol-gel method to wrap silicon oxide layer on metal powder surface is currently a typical process. However, TEOS is weak in metal surface adhesion, and it is necessary to first prepare a transition interface layer on the metal surface to facilitate the growth of TEOS on the metal surface, so as to improve the coating quality and adhesion of the silicon oxide layer on the metal powder surface. For example, CN116730398A discloses a silicon dioxide-coated carbonyl iron powder and a preparation method thereof, which prepares an iron phosphate transition layer between the silicon oxide coating layer and the carbonyl iron powder particles through a chemical reaction of phosphoric acid and iron, reduces the possibility of cracks or defects in the silicon oxide layer, and improves the bonding force between the silicon oxide layer and the carbonyl iron powder. Although this technology of adding an interface layer between the silicon oxide layer and the metal powder can solve the problem that the sol-gel method silicon oxide layer has poor quality and low adhesion on the metal powder surface, it can increase the complexity of the process steps. In addition, using TEOS as raw material, the technology of adopting the sol-gel method to prepare the silicon oxide layer usually requires high temperature heat treatment. For example, CN114682266B discloses a mesoporous silica-coated nano-alumina-supported nickel-molybdenum catalyst, its preparation method, and application. This method requires calcining at 450-550°C for 4-12 hours to obtain the mesoporous silica-coated nano-alumina-supported nickel-molybdenum catalyst. Another example is CN115285997B, which discloses a method for preparing wide-temperature-range, oxidation-resistant silica-coated molybdenum disilicide powder. This method requires heat-treating the sample in air at 1200±5°C for 1-3 hours to vitrify and densify the silica coating, resulting in the final product.

[0004] In recent years, methods for preparing high-quality silicon oxide layers using polysilazane as a raw material have gradually attracted widespread attention. However, PHPS-derived silicon oxide layers generally require high-temperature conversion, and existing low-temperature conversion methods have problems such as equipment dependence and environmental dependence. For example, JP2008088031A discloses a method for preparing a silicon dioxide film, which uses laser beams or microwaves to irradiate a polysilazane film to convert the polysilazane into silicon dioxide. However, it is clear that this method is difficult to achieve large-scale production applications. In addition, whether it is high-temperature conversion or conversion using laser beams or microwaves, it is a conversion in a solid phase state. Obviously, when this conversion method is applied to the conversion of polysilazane on the surface of a powder, it is difficult to avoid adhesion between the powders, which may cause agglomeration problems after the powder is coated. Summary of the Invention

[0005] In view of the above analysis, the embodiments of the present invention aim to provide a polysilazane-based silicon oxide-coated metal powder, a preparation method and application thereof, so as to solve at least one of the following problems existing in the existing silicon oxide-coated metal powder preparation method: (1) high-temperature conversion is required; (2) low-temperature conversion methods are equipment-dependent or environmental-dependent; (3) powder agglomeration problem after coating.

[0006] In one aspect, the present invention provides a method for preparing a silicon oxide-coated metal powder based on polysilazane, the preparation method comprising:

[0007] Step 1: Mixing and dispersing metal powder and polysilazane polymer precursor solution to allow polysilazane to grow on the surface of the metal powder to obtain a dispersion;

[0008] Step 2: performing solid-liquid separation on the dispersion obtained in step 1 to obtain metal powder with a polysilazane layer grown on the surface;

[0009] Step 3: placing the metal powder with the polysilazane layer grown on its surface obtained in step 2 in a high humidity environment to perform a hydrolysis condensation reaction;

[0010] Step 4: Dry the product after the hydrolysis and condensation reaction in step 3 to obtain silicon oxide-coated metal powder.

[0011] Preferably, in step 1, the polysilazane polymer precursor solution comprises polysilazane, a solvent and a catalyst, wherein, in terms of mass percentage, the content of polysilazane is 0.01% to 5%, the content of the solvent is 95% to 99.99%, the content of the catalyst is 0% to 0.5%, and the sum of the mass percentages of each component is 100%.

[0012] Preferably, the viscosity of the polysilazane polymer precursor solution is 2 cP to 50 cP.

[0013] Preferably, the catalyst is aminosilane.

[0014] Preferably, the average particle size of the metal powder is 5 nm to 100 μm.

[0015] Preferably, the mass ratio of the polysilazane polymer precursor solution to the metal powder is 1:1 to 50:1.

[0016] Preferably, the reaction temperature of the growth reaction is 20° C. to 80° C., and the reaction time is 1 h to 5 h.

[0017] Preferably, in step 3, the reaction temperature of the hydrolysis condensation reaction is 20° C. to 80° C., and the reaction time is 10 min to 5 h.

[0018] In a second aspect, the present invention also provides silicon oxide-coated metal powder prepared by the above method.

[0019] In a third aspect, the present invention further provides applications of the silicon oxide-coated metal powder in the fields of nanocomposites, thermally conductive and insulating composite materials, coatings and adhesives, and temperature sensors.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] 1. The method of the present invention is applicable to various metal powders, does not require surface activation treatment, and avoids complex processes such as high-temperature heat treatment and ultraviolet irradiation. Furthermore, by dispersing the powder in an aqueous solution and simultaneously converting the surface coating to silicon oxide, the method effectively prevents metal powder agglomeration.

[0022] 2. The present invention uses polysilazane as a silicon oxide precursor to coat the metal powder with a silicon oxide layer. The Si-H and Si-N chemical bonds in the polysilazane structure are highly chemically active and react chemically with the metal surface. This allows the silicon oxide layer on the metal surface to bond to the metal via Si-O-metal chemical bonds, resulting in excellent adhesion.

[0023] 3. The present method for preparing silicon oxide by converting polysilazane has the advantages of a low conversion temperature and a flexible liquid-phase process. Therefore, the metal powder surface can be coated with a silicon oxide layer at a relatively low temperature. The low conversion temperature (less than 80°C) has little effect on the thickness of the silicon oxide layer, and the thickness of the silicon oxide layer can be adjusted simply by adjusting the solution concentration. In addition, polysilazane-derived silicon oxide has excellent properties such as high hardness, high modulus, high density, and good wear resistance.

[0024] 4. The present invention uses aminosilane catalysts to achieve the conversion of polysilazane to silicon oxide under mild conditions. The large number of Si-N and Si-H bonds in polysilazane undergo hydrolysis and condensation reactions with water under alkaline conditions to form silicon oxide. Therefore, compared to traditional sol-gel methods represented by TEOS, the present invention achieves the conversion of polysilazane to silicon oxide in aqueous solution. Under the action of the catalyst, the polysilazane on its surface can be rapidly converted to silicon oxide, effectively avoiding the agglomeration of metal powders and significantly improving the quality and efficiency of the silicon oxide layer coated on the metal powder surface.

[0025] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be described in the following description, and some advantages will become apparent from the description or be learned through practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like parts throughout the drawings.

[0027] Figure 1 These are the appearance photos of the powder in Examples 1-4 before and after coating with silicon oxide (Figures a, c, e, and g are before coating, and Figures b, d, f, and h are after coating).

[0028] Figure 2 This is a transmission electron microscope image of the cross-sectional morphology sample of the iron powder coated with silicon oxide in Example 1 prepared by focused ion beam (FIB) processing technology.

[0029] Figure 3 These are the XPS test results of the silicon oxide-coated metal powders obtained in Examples 1-4.

[0030] Figure 4 This is the result of further peak separation of the O1s orbital in the XPS spectrum of the silicon oxide-coated metal powder obtained in Example 1-4.

[0031] Figure 5 These are the Fourier transform infrared spectroscopy test results of the metal powder before and after being coated with silicon oxide in Example 2.

[0032] Figure 6 These are scanning electron microscope images of the powder of Example 2 before and after being coated with silicon oxide.

[0033] Figure 7 These are scanning electron microscope images of the powder of Example 3 before and after being coated with silicon oxide.

[0034] Figure 8These are scanning electron microscope images of the powder of Example 4 before and after being coated with silicon oxide.

[0035] Figure 9 These are the XRD test results of the silicon oxide-coated metal powder in Example 3-4.

[0036] Figure 10 These are the Fourier transform infrared spectroscopy test results after the hydrolysis and condensation reaction of PHPS with different catalyst contents in Example 5.

[0037] Figure 11 The adhesion test results of Example 6 and Comparative Example 1 were obtained by cross-hatch method.

[0038] Figure 12 This is a scanning electron microscope image of the silicon oxide-coated tungsten powder in Example 7 after oscillation.

[0039] Figure 13 Graph showing the relationship between the thickness of the silicon oxide coating and the concentration of the polysilazane solution in Example 8.

[0040] Figure 14 This is the load-displacement curve of the silicon oxide coating in Example 9.

[0041] Figure 15 Schematic diagram of the principle of the method for powder coating silicon oxide using PHPS in the present invention. DETAILED DESCRIPTION

[0042] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, and are not used to limit the scope of the present invention.

[0043] In one aspect, the present invention provides a method for preparing a silicon oxide-coated metal powder based on polysilazane, the preparation method comprising:

[0044] Step 1: Mixing and dispersing metal powder and a polysilazane polymer precursor solution to allow polysilazane to undergo a growth reaction on the surface of the metal powder to obtain a dispersion; the growth reaction refers to a chemical reaction between chemical bonds such as Si-H and Si-N in the polysilazane structure and the metal surface, thereby forming a polysilazane layer on the surface of the metal powder;

[0045] Step 2: performing solid-liquid separation on the dispersion obtained in step 1 to obtain metal powder with a polysilazane layer grown on the surface;

[0046] Step 3: placing the metal powder with the polysilazane layer grown on its surface obtained in step 2 in a high humidity environment to perform a hydrolysis condensation reaction;

[0047] Step 4: Dry the product after the hydrolysis and condensation reaction in step 3 to obtain silicon oxide-coated metal powder.

[0048] Compared with the prior art, the preparation method of silicon oxide coated metal powder based on polysilazane provided by the present invention uses polysilazane as a precursor of silicon oxide to coat the surface of the metal powder with a silicon oxide layer, such as Figure 15 As shown, chemical bonds such as Si-H and Si-N in the polysilazane structure have good chemical activity and can react chemically with the metal surface, so that the silicon oxide layer on the metal surface can be combined with the metal in the form of Si-O-metal chemical bonds, thus having excellent adhesion. This method is applicable to various metal powders, and does not require activation treatment of the powder surface, and avoids complex processes such as high-temperature heat treatment and ultraviolet irradiation. The method adopts a scheme of dispersing the powder in an aqueous solution and simultaneously converting the surface coating layer into silicon oxide, which effectively avoids the agglomeration of the metal powder.

[0049] Illustratively, in step 1, before mixing the metal powder and the polysilazane polymer precursor solution, the metal powder is washed with a ketone solvent, an alcohol solvent, and deionized water in sequence, and then dried in a vacuum oven.

[0050] Specifically, the metal powder to be treated is added to a sample bottle, and a ketone solvent is added to disperse the metal powder in the ketone solvent and fully mix it for a period of time, and then the metal powder is filtered to obtain the metal powder; the obtained metal powder is added to the sample bottle again, and an alcohol solvent is added to disperse the metal powder in the alcohol solvent and fully mix it for a period of time, and then the metal powder is filtered to obtain the metal powder; the obtained metal powder is added to the sample bottle again, and deionized water is added to disperse the metal powder in the deionized water and fully mix it for a period of time, and then the metal powder is transferred to a vacuum oven for drying after filtration to obtain the cleaned metal powder. This step is to use a ketone solvent, an alcohol solvent and deionized water to clean the metal powder to remove pollutants such as organic matter, oil or impurities on the surface of the metal powder, so as to facilitate the subsequent growth of a silicon oxide layer on the surface of the metal powder.

[0051] Illustratively, the ketone solvent is selected from one or more of acetone, butanone, methyl ethyl ketone, cyclohexanone, and isophorone; and the alcohol solvent is selected from one or more of methanol, ethanol, and isopropanol.

[0052] Illustratively, the added mass of the ketone solvent, alcohol solvent and deionized water is 1 to 100 times that of the metal powder, more preferably 5 to 10 times, for example, 6 times, 7 times, 8 times, 9 times.

[0053] Exemplarily, the cleaning time for each step is 1 min to 99 min, more preferably 15 min to 30 min.

[0054] Illustratively, the drying temperature of the vacuum oven is 60°C to 120°C, more preferably 80°C to 100°C, for example, 83°C, 85°C, 88°C, 90°C, 93°C, 96°C, or 98°C.

[0055] Exemplarily, the drying time of the vacuum oven is 1 hour to 48 hours, more preferably 8 hours to 16 hours, such as 10 hours, 12 hours, or 14 hours.

[0056] Illustratively, the metal powder is one or more of iron powder, copper powder, aluminum powder, cobalt powder, nickel powder, molybdenum powder, tungsten powder, silver powder, gold powder and oxides thereof.

[0057] Illustratively, the shape of the metal powder can be any one of spherical powder, flaky powder and fibrous powder, preferably spherical powder or flaky powder.

[0058] Illustratively, the average particle size of the metal powder is 5 nm to 100 μm, preferably 1 μm to 50 μm, more preferably 2 μm to 20 μm, such as 5 μm, 8 μm, 10 μm, 13 μm, 16 μm, or 18 μm.

[0059] Exemplarily, in step 1, the polysilazane polymer precursor solution includes polysilazane, a solvent, and a catalyst, wherein, in terms of mass percentage, the content of polysilazane is 0.01% to 5%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, and 4%; the content of the solvent is 95% to 99.99%, for example, 96%, 97%, 98%, and 99%; the content of the catalyst is 0% to 0.5%, for example, 0.1%, 0.2%, 0.3%, and 0.4%. The catalyst only affects the conversion rate, so the catalyst content can be 0%. Too high a catalyst content will result in too fast a conversion rate and uncontrollable conversion process; the sum of the mass percentages of each component is 100%. For example, in the polysilazane polymer precursor solution, the mass percentage of polysilazane is 1%, the mass percentage of the solvent is 98.95%, and the mass percentage of the catalyst is 0.05%.

[0060] It should be noted that the polysilazane has the structure shown in the formula:

[0061]

[0062] Wherein, R1 and R2 are the same or different and are independently selected from one of hydrogen, methyl, ethyl, vinyl, phenyl, and amino groups; preferably, R1 and R2 are both H, i.e., the polysilazane is perhydropolysilazane (PHPS); n is selected from an integer between 10 and 3000, preferably an integer between 20 and 100. Because the method of the present invention is a liquid-phase film-forming method, excessively low or high molecular weight will affect film-forming properties. If the molecular weight is too low, the coating is prone to defects such as holes; if the molecular weight is too high, the precursor solution will have poor fluidity, affecting film formation.

[0063] Illustratively, the polysilazane has a linear or cyclic structure, and formula (I) only lists its structural units, which does not mean that the polysilazane has a linear structure.

[0064] Illustratively, the solvent of the polysilazane polymer precursor solution is selected from one or more of hydrocarbon solvents, ether solvents, ketone solvents, benzene derivative solvents, and ester solvents.

[0065] Illustratively, the hydrocarbon solvent is selected from one or more of n-hexane, n-octane, n-decane, chloroform, dichloromethane, dichloroethylene, petroleum ether, and mineral oil; the ether solvent is selected from one or more of ethyl ether, ethylene glycol dimethyl ether, dibutyl ether, and n-butyl ether; the ketone solvent is selected from one or more of acetone, butanone, methyl ethyl ketone, cyclohexanone, and isophorone; the benzene derivative solvent is selected from one or more of toluene, o-xylene, m-xylene, p-xylene, and chlorobenzene; the ester solvent is selected from one or more of ethyl acetate, butyl butyrate, amyl acetate, and octyl acetate.

[0066] Exemplarily, the catalyst is aminosilane. Aminosilane catalysts enable the conversion of polysilazane to silicon oxide under mild conditions. Specifically, the large number of Si-N and Si-H bonds in polysilazane undergo hydrolysis and condensation reactions with water under alkaline conditions to form silicon oxide, achieving the conversion of polysilazane to silicon oxide. Furthermore, under the action of the catalyst, the polysilazane on the surface of the metal powder can be rapidly converted to silicon oxide, effectively avoiding the agglomeration of the metal powder and significantly improving the quality and efficiency of the silicon oxide layer coated on the metal powder surface.

[0067] Exemplarily, the aminosilane is selected from one or more of (3-aminopropyl)trimethoxysilane, (3-aminopropyl)triethoxysilane, di(3-trimethoxysilylpropyl)amine, N-[3-(trimethoxysilyl)propyl]n-butylamine, and aminoethylaminopropyltrimethoxysilane.

[0068] Exemplarily, the viscosity of the polysilazane polymer precursor solution is 2 cP to 50 cP. Examples include 5 cP, 10 cP, 15 cP, 20 cP, 25 cP, 30 cP, 35 cP, 40 cP, and 45 cP. Since viscosity is primarily affected by molecular weight, its impact is similar to that of molecular weight; excessively low or high viscosity can affect film-forming properties. If the viscosity is too low, defects such as holes may easily appear in the coating; if the viscosity is too high, the precursor solution may have poor fluidity, affecting film formation.

[0069] Illustratively, the mass ratio of the polysilazane polymer precursor solution to the metal powder is 1:1 to 50:1, more preferably 5:1 to 10:1, for example 6:1, 7:1, 8:1, or 9:1.

[0070] In a preferred embodiment, in step 1, the cleaned metal powder is added to a polysilazane polymer precursor solution, and the metal powder is dispersed in the polysilazane polymer precursor solution by oscillation or magnetic stirring to perform a growth reaction of a polysilazane layer on the surface of the metal powder.

[0071] Specifically, in step 1, a certain amount of polysilazane is placed in a sample bottle, a solvent is added to dissolve it at the desired concentration, and a catalyst is added to obtain a polysilazane polymer precursor solution. The cleaned metal powder is added to the sample bottle and mixed with the polysilazane polymer precursor solution. The metal powder is dispersed in the polysilazane polymer precursor solution by oscillation or magnetic stirring, and a polysilazane layer is grown on the surface of the metal powder to obtain a mixed solution in which the metal powder is uniformly dispersed in the polysilazane polymer precursor solution. The purpose of this step is to cause the silicon oxide precursor polysilazane to grow on the surface of the metal powder.

[0072] Illustratively, the stirring speed of the magnetic stirring is 100 rpm to 800 rpm, preferably 300 rpm to 500 rpm; the stirring time of the magnetic stirring is 10 min to 12 h, preferably 1 h to 4 h.

[0073] Illustratively, the oscillation frequency is 40 rpm to 300 rpm, preferably 70 rpm to 200 rpm; the oscillation time is 10 min to 12 h, preferably 1 h to 4 h.

[0074] Illustratively, the reaction temperature of the growth reaction is 20°C to 80°C (eg, 30°C, 40°C, 50°C, 60°C, 70°C), and the reaction time is 1h to 5h (eg, 2h, 3h, 4h).

[0075] Illustratively, in step 2, the solid-liquid separation is performed by filtration separation or centrifugal separation.

[0076] Illustratively, in step 2, the filtration separation includes: transferring the dispersion obtained in step 1 to a sand core funnel, and the filter cake obtained after suction filtration is the metal powder with a polysilazane layer grown on the surface.

[0077] Illustratively, in step 2, the centrifugal separation includes: transferring the dispersion obtained in step 1 into a centrifuge tube, removing the supernatant after centrifugation, and obtaining a metal powder with a polysilazane layer grown on the surface.

[0078] Illustratively, step 3 includes placing the metal powder with a polysilazane layer grown on its surface obtained in step 2 in a high humidity environment, so that the polysilazane on the surface of the metal powder undergoes a hydrolysis and condensation reaction, thereby achieving silicon oxide coating on the metal surface.

[0079] Specifically, step 3 involves transferring the metal powder with the polysilazane layer grown on its surface obtained in step 2 to a high-humidity environment. More specifically, a certain amount of deionized water can be directly added to the powder. The purpose of this step is to hydrolyze and condense the polysilazane layer on the metal surface, thereby achieving a silicon oxide coating on the metal surface.

[0080] Illustratively, in step 3, the high humidity environment refers to a relative humidity of 60% to 100%; the humidity can be achieved by controlling the humidity of the reaction environment or by directly adding water to the powder; the reaction temperature of the hydrolysis condensation reaction is 20°C to 80°C (for example, 30°C, 40°C, 50°C, 60°C, 70°C), and the reaction time is 10 min to 2 h.

[0081] Illustratively, in step 3, the mass ratio of the deionized water to the metal powder with a polysilazane layer grown on the surface is 1:1 to 50:1; preferably 5:1 to 10:1, for example, 6:1, 7:1, 8:1, or 9:1.

[0082] Illustratively, step 4 includes: filtering or centrifuging the mixture obtained in step 3 and drying it in a vacuum oven to obtain silicon oxide-coated metal powder.

[0083] Specifically, step 4 includes: transferring the mixture obtained in step 3 to a sand core funnel, the filter cake obtained after filtration is the silica-coated metal powder, and the silica-coated metal powder is transferred to a vacuum oven for drying to obtain dry silica-coated metal powder; or, step 4 includes: transferring the mixture obtained in step 3 to a centrifuge tube, removing the supernatant after centrifugation to obtain silica-coated metal powder, and transferring the metal powder to a vacuum oven for drying to obtain dry silica-coated metal powder.

[0084] Illustratively, in step 4, the drying temperature of the vacuum oven is 60°C to 120°C, preferably 80°C to 100°C.

[0085] Illustratively, in step 4, the drying time in the vacuum oven is 1 h to 48 h, preferably 8 h to 16 h.

[0086] In a second aspect, the present invention also provides a silicon oxide-coated metal powder prepared by the above method. The silicon oxide coating layer has excellent adhesion to the surface of the metal powder and has excellent properties such as high hardness, high modulus, high density, and good wear resistance.

[0087] Illustratively, the average thickness of the silicon oxide coating layer of the silicon oxide-coated metal powder is 5 nm to 300 nm.

[0088] In a third aspect, the present invention further provides the use of the aforementioned silicon oxide-coated metal powder in at least one of the following fields: nanocomposites, thermally conductive and insulating composite materials, coatings and adhesives, and temperature sensors. In these applications, the silicon oxide-coated metal powder can improve the powder's dispersibility, enhance its interfacial bonding strength, improve its sintering properties, increase its surface catalytic activity sites, improve its thermal conductivity and insulation properties, enhance its biocompatibility, and improve its corrosion and oxidation resistance.

[0089] The polysilazane-based silicon oxide-coated metal powder and its preparation method of the present invention are further described below through specific examples.

[0090] In the following examples and comparative examples, the elemental composition of the metal powder was analyzed using an ESCALab 250Xi multifunctional electron spectrometer, the adhesion was tested using the cross-hatch method in accordance with GB / 9286-1998, the micromorphology was observed using a Hitach SU 8020 scanning electron microscope, the cross-sectional morphology samples were prepared using focused ion beam (FIB) processing technology and observed using a JEOL JEM-F200 transmission electron microscope, and the chemical structure of the silicon oxide layer was tested using a BRUKERALPHA Ⅱ Fourier transform infrared spectrometer.

[0091] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0092] Example 1

[0093] This embodiment provides a polysilazane-based silicon oxide-coated metal powder and a preparation method thereof.

[0094] Step 1): 5 g of black iron powder (particle size 10-20 μm) was added to a sample bottle, followed by addition of 50 mL of acetone, washing for 1 hour, filtering, transferring the iron powder to another sample bottle, adding 50 mL of ethanol, washing for 1 hour, filtering, transferring the iron powder to another sample bottle, adding 50 mL of deionized water, washing for 1 hour, filtering, and transferring the iron powder to a vacuum oven at 80°C for 12 hours to obtain clean iron powder;

[0095] Step 2): The iron powder cleaned and dried in step 1) is added to a perhydropolysilazane (PHPS) polymer precursor solution, wherein the solvent is n-butyl ether; the PHPS concentration is 0.5 wt %, the molecular weight of PHPS is 980, and the viscosity of the PHPS polymer precursor solution is 5 cP; (3-aminopropyl)trimethoxysilane is used as a catalyst, and the content is 0.05 wt %. The resulting mixture of iron powder and PHPS polymer precursor solution is continuously stirred at room temperature for 2 hours at 300 rpm using a magnetic stirrer to induce a PHPS layer growth reaction on the surface of the iron powder, thereby obtaining a mixed solution in which the iron powder is uniformly dispersed in the PHPS solution.

[0096] Step 3): The dispersion obtained in step 2) is transferred to a sand core funnel, and filtered to obtain iron powder with a PHPS layer grown on the surface.

[0097] Step 4): The iron powder with the PHPS layer grown on the surface obtained in step 3) is transferred to a constant temperature and humidity chamber with a humidity of 70% for hydrolysis and condensation reaction at a reaction temperature of 25° C. for 30 minutes to obtain silicon oxide-coated iron powder.

[0098] Step 5): The powder obtained in step 4) was transferred to a vacuum oven and dried at 80° C. for 12 h to obtain dry silicon oxide-coated iron powder.

[0099] The apparent morphology of the iron powder obtained in Example 1 before and after silicon oxide coating ( Figure 1 In (a) and (b), the appearance of the iron powder before and after the silicon oxide coating treatment is basically the same, with no obvious color change and no effect on the fluidity of the powder.

[0100] The cross-sectional morphology of the iron powder coated with silicon oxide obtained in Example 1 was prepared by focused ion beam (FIB) processing technology and observed by transmission electron microscope (TEM) of JEOL JEM-F200. Figure 2 As shown, a coating layer with a thickness of ∼10 nm can be observed, and the silicon oxide layer has no obvious defects such as holes and has excellent density.

[0101] The iron powder obtained in Example 1 was subjected to XPS elemental analysis test ( Figure 3), we can observe the peaks belonging to Si and O elements, and further perform peak separation on the O1s orbital ( Figure 4 In (a), a peak attributable to silicon oxide can be observed, indicating that the silicon oxide layer is coated on the surface of the iron powder.

[0102] The iron powder obtained in Example 1 was subjected to Fourier transform infrared spectroscopy test ( Figure 5 ), compared with the iron powder before treatment, the iron powder after silicon oxide coating treatment can be observed to have infrared characteristic peaks belonging to Si-O-Si.

[0103] Example 2

[0104] This embodiment provides a polysilazane-based silicon oxide-coated metal powder and a preparation method thereof similar to Example 1. The difference from Example 1 is that in step 1), 5 g of copper powder (particle size 5-15 μm) is taken.

[0105] The silicon oxide coated copper powder obtained in Example 2 was subjected to SEM micromorphology observation ( Figure 6 The morphology of copper powder before and after silicon oxide coating is as follows: Figure 1 (c) and (d) are shown; the XPS elemental analysis test of copper powder is as follows Figure 3 As shown, the O1s orbital is further processed as follows Figure 4 b; the copper powder Fourier transform infrared spectroscopy test results are shown in Figure 5 shown.

[0106] Example 3

[0107] This embodiment provides a polysilazane-based silicon oxide-coated metal powder and a preparation method thereof similar to that of Example 1, except that, in step 1), 5 g of molybdenum powder (particle size 5-20 μm) is taken;

[0108] XRD test of silicon oxide coated molybdenum powder prepared in Example 3 ( Figure 9 ), the characteristic peaks attributed to amorphous silicon oxide can be observed. The apparent morphology of molybdenum powder before and after silicon oxide coating is as follows Figure 1 As shown in (e) and (f); XPS elemental analysis test of silicon oxide coated molybdenum powder is as follows Figure 3 As shown, the O1s orbital is further processed as follows Figure 4 As shown in (c), the SEM micromorphology of silicon oxide coated molybdenum powder is as follows Figure 7 shown.

[0109] Example 4

[0110] This embodiment provides a polysilazane-based silicon oxide-coated metal powder and a preparation method thereof similar to that of Example 1. The difference from Example 1 is that in step 1), 5 g of tungsten powder (particle size 5-20 μm) is taken.

[0111] The XRD test results of the silicon oxide coated tungsten powder in Example 4 are as follows: Figure 9 As shown in Figure 2, characteristic peaks attributable to amorphous silicon oxide can be observed. The apparent morphology of tungsten powder before and after silicon oxide coating is shown in Figure 2. Figure 1 As shown in (g) and (h); XPS elemental analysis test of silicon oxide coated tungsten powder is as follows Figure 3 As shown, the O1s orbital is further processed as follows Figure 4 As shown in (d), the SEM micromorphology of silicon oxide coated tungsten powder is as follows Figure 8 shown.

[0112] Example 5

[0113] This example studies the effect of a catalyst on the hydrolysis and condensation reaction of PHPS. A preparation method similar to that of Example 1 is used, except that (3-aminopropyl)trimethoxysilane is added as a catalyst at a mass ratio of 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, and 10% relative to the mass of PHPS to promote the hydrolysis and condensation reaction of PHPS in water.

[0114] The obtained silicon oxide coated iron powder was tested by Fourier transform infrared spectroscopy ( Figure 10 ), it can be seen that when no catalyst is added, PHPS will not be converted into silicon oxide at room temperature within 24 h. However, after adding the catalyst, the characteristic peak of Si-O bond can be observed, indicating the conversion of PHPS to silicon oxide, and the degree of conversion increases with the increase of catalyst amount.

[0115] Example 6

[0116] This embodiment provides a polysilazane-based silicon oxide-coated metal powder and its preparation method similar to that of Example 1. The difference from Example 1 is that the silicon oxide layer is prepared using a copper sheet as a substrate, which facilitates the use of the cross-hatch method for adhesion testing. Figure 11 b.

[0117] Example 7

[0118] This example studies the wear resistance of PHPS-derived silicon oxide coatings. The preparation method is similar to that of Example 4. The difference is that the prepared silicon oxide-coated tungsten powder is oscillated at 60 rpm for 1 hour at room temperature. During this process, the powder is subjected to external forces such as friction. The SEM micromorphology of the powder after oscillation is shown in Figure 2. Figure 12 Compared with the microstructure before oscillation ( Figure 8 ), there is no peeling, stratification or shedding on the powder surface after oscillation, indicating that the PHPS-derived silica coating has good wear resistance.

[0119] Example 8

[0120] This example illustrates the effect of precursor solution concentration on the thickness of PHPS-derived silicon oxide coatings. A preparation method similar to that of Example 1 was used. PHPS precursor solutions with concentrations of 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, and 10 wt% were prepared for coating preparation, and a sheet substrate was used for coating preparation to facilitate coating thickness measurement.

[0121] PHPS-derived SiO measured by spectroscopic ellipsometry x The relationship between the coating thickness and the concentration of PHPS precursor solution is shown in the figure Figure 13 As shown in the figure, it can be clearly seen that the thickness of the silicon oxide coating is linearly related to the concentration of the precursor solution. As the concentration of the precursor solution increases, the coating thickness increases in direct proportion. Therefore, the coating thickness can be controlled by adjusting the concentration of the precursor solution.

[0122] Example 9

[0123] This embodiment adopts a preparation method similar to that of Example 1, except that, in order to facilitate the nanoindentation test of the coating, a sheet-like substrate is used to prepare the coating.

[0124] PHPS-derived SiO obtained by nanoindentation testing x Load-displacement curve of the coating and PHPS-derived SiO calculated from the load-displacement curve x The hardness and modulus of the coating are as follows Figure 14 As shown in the figure, it can be seen that the coating has high nanoindentation hardness and modulus, with the hardness reaching 3.62GPa and the modulus reaching 30.06GPa.

[0125] Comparative Example 1

[0126] This comparative example employed existing methods to prepare a silicon oxide-coated copper sheet. The silicon oxide layer was prepared using a sol-gel method using TEOS as the raw material. The specific preparation process was as follows: a solution (4.28 g) was prepared with a molar ratio of TEOS:H₂O:C₂H₅OH:HCl = 1:4:10:0.01. The solution was stirred at room temperature for 24 hours. The solution was then spin-coated onto the copper sheet at a speed of 1000 rpm for 30 seconds and cured at room temperature.

[0127] Silicon oxide layer bonding strength test of Example 6 and Comparative Example 1:

[0128] The samples of Example 6 and Comparative Example 1 were tested using the cross-hatch method according to the GB / 9286-1998 standard. The morphology of the sample of Comparative Example 1 under a microscope is as follows: Figure 11 As shown in a, it can be clearly observed that the silicon oxide coating prepared on the copper sheet using the sol-gel method using TEOS as the raw material cracked and fell off, indicating that its adhesion was poor. The cross-hatch test results of the silicon oxide coating prepared using PHPS as the raw material in Example 6 are shown in FIG. Figure 11 As shown in (b), the adhesion grade is 0, indicating that the PHPS-based silicon oxide coating has excellent adhesion on Cu.

[0129] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing silicon oxide-coated metal powder based on polysilazane, characterized in that: The preparation method comprises: Step 1: Mixing and dispersing metal powder and polysilazane polymer precursor solution to allow polysilazane to grow on the surface of the metal powder to obtain a dispersion; Step 2: performing solid-liquid separation on the dispersion obtained in step 1 to obtain metal powder with a polysilazane layer grown on the surface; Step 3: placing the metal powder with the polysilazane layer grown on its surface obtained in step 2 in a high humidity environment to perform a hydrolysis condensation reaction; Step 4: Dry the product after the hydrolysis and condensation reaction in step 3 to obtain silicon oxide-coated metal powder.

2. The preparation method according to claim 1, characterized in that In step 1, the polysilazane polymer precursor solution includes polysilazane, a solvent and a catalyst, wherein, by mass percentage, the content of polysilazane is 0.01% to 5%, the content of the solvent is 95% to 99.99%, the content of the catalyst is 0% to 0.5%, and the sum of the mass percentages of each component is 100%.

3. The preparation method according to claim 2, characterized in that The viscosity of the polysilazane polymer precursor solution is 2 cP to 50 cP.

4. The preparation method according to claim 2, characterized in that The catalyst is aminosilane.

5. The preparation method according to claim 1, characterized in that The average particle size of the metal powder is 5 nm to 100 μm.

6. The preparation method according to claim 1, characterized in that The mass ratio of the polysilazane polymer precursor solution to the metal powder is 1:1 to 50:

1.

7. The preparation method according to claim 1, characterized in that The reaction temperature of the growth reaction is 20° C. to 80° C., and the reaction time is 1 hour to 5 hours.

8. The preparation method according to claim 1, characterized in that In step 3, the reaction temperature of the hydrolysis condensation reaction is 20° C. to 80° C., and the reaction time is 10 min to 5 h.

9. The silicon oxide-coated metal powder obtained according to the preparation method according to any one of claims 1 to 8.

10. Use of the silicon oxide-coated metal powder according to claim 9 in at least one of the fields of nanocomposites, thermally conductive and insulating composite materials, coatings, adhesives, and temperature sensors.

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