A catalytic porous coating on the surface of an internal combustion engine and a preparation method thereof

Abstract

The embodiment of the present invention discloses a catalytic porous coating on the surface of an internal combustion engine and a preparation method thereof, comprising: cleaning and drying the surface of a workpiece to be processed to obtain a pre-treated workpiece to be processed; placing the workpiece to be processed in an electrolyte, operating by plasma micro-arc oxidation, and coating the surface of the workpiece to be processed to form a dense layer; adding nano-catalytic materials to the electrolyte for dispersion, and under the conditions of plasma micro-arc oxidation operation, the intensity of the plasma spectrum reaches not less than 2 / 5 of the peak value, and the coating of the transition layer is completed; adjusting the processing parameters of the plasma micro-arc oxidation operation, continuing the plasma micro-arc oxidation operation, and completing the preparation of the catalytic porous coating on the surface of the internal combustion engine when the intensity of the ion emission spectrum reaches 7 / 10 to 4 / 5 of the peak value. The coating carrier finally prepared by the present invention has the properties of high strength, high porosity and a large number of honeycomb holes, which solves the problem of insufficient specific surface area of ​​the current internal combustion engine catalytic carrier.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of catalytic combustion of internal combustion engines, and specifically to a catalytic porous coating on the surface of an internal combustion engine and a preparation method thereof. Background Art

[0002] Automobile exhaust pollution is one of the main sources of ambient air pollution, especially in densely populated urban areas, where exhaust emissions directly lead to the deterioration of local urban ambient air quality. With the national "dual carbon" strategic goal, the standards for automobile fuel consumption and exhaust pollutants are becoming increasingly stringent, so reducing automobile exhaust emissions is an important issue that needs to be addressed. At present, lightweight automotive materials and new energy power have become important trends in the development of the automotive industry.

[0003] The degree of combustion in automobile engines is a key factor in determining exhaust emissions and fuel utilization. In order to improve the degree of combustion in the engine cylinder, the industry often applies heavy metal catalysts on the surface of the engine cylinder, piston, and combustion chamber, but this type of technology has disadvantages such as catalyst poisoning and aging failure; another type of pre-combustion PRL (platinum, rhenium, rhenium) three-way catalytic technology is to continuously spray a small amount of platinum, rhenium, and rhenium catalytic liquid into the combustion chamber through a steam injector to improve the combustion efficiency of the fuel, thereby greatly reducing the emission of toxic gases and fuel consumption and extending the life of the engine. For three-way catalytic technology, in terms of the selection of catalyst types, precious metal catalysts have better effects, but precious metals are expensive and difficult to be widely promoted. Therefore, for a long time, researchers in the industry have been trying to find cheap catalytic materials that can replace precious metals from base metals (such as Fe, Co, Ni, Cu, etc.) and their oxides.

[0004] At present, the field often uses deposition precipitation method, spraying method, micro-arc oxidation and other technical means to prepare permanent catalytic coating on the contact surface of the combustion chamber, without the need for steam injection of catalytic combustion agent, thereby reducing fuel costs and improving combustion rate. For example, the deposition precipitation method is used to load CuO onto the TiO2 carrier, which can reduce the complete conversion temperature of CuO to CO to 110 degrees Celsius. The good activity of lattice oxygen makes it have very high low-temperature oxidation catalytic performance. Moreover, the greater the degree of oxidation dispersion of other catalytic metals such as CuO and CeO2, the lower its reduction temperature, and TiO2, Fe2O3, Al2O3 ceramics can all be used as catalytic loads. However, with this type of coating method, the contact area between the catalytic element and the combustion chamber is limited, and increasing the contact area between the catalytic element and the combustion chamber becomes a key factor in determining the catalytic effect.

[0005] Liquid-phase plasma technology can realize the preparation of porous coatings, which have the significant advantage of high specific surface area and are ideal carriers for catalytic substances. However, in the middle and late stages of the liquid-phase plasma discharge, as the thickness of the coating increases, the breakdown discharge phenomenon becomes more and more obvious. This type of discharge is prone to form large-sized through holes and closed holes. On the one hand, such holes reduce the mechanical strength and thermal fatigue resistance of the coating. The micro-collapse failure of the thermal protection coating during service will cause damage to the internal combustion engine; on the other hand, the generation of such large-sized holes or closed holes will reduce the specific surface area. Therefore, in order to improve the level of catalytic combustion, the small-sized honeycomb microporous structure is a key indicator of the catalytic carrier coating, and it is also a key technical bottleneck in realizing the industrial application of liquid-phase plasma catalytic coatings. Summary of the invention

[0006] To this end, an embodiment of the present invention provides a catalytic porous coating on the surface of an internal combustion engine and a preparation method thereof. By preparing open small-sized holes, a porous ceramic coating carrier containing a catalyst is prepared on the workpiece to be processed at the inner wall of the engine cylinder, the top of the piston, etc., to form a functional multilayer structure composed of a dense layer / transition layer / open microporous catalytic layer, so that the finally prepared coating carrier has the properties of high strength, high porosity and a large number of honeycomb holes, thereby solving the problem of insufficient specific surface area of ​​the current internal combustion engine catalytic carrier.

[0007] In order to achieve the above object, the embodiments of the present invention provide the following technical solutions:

[0008] In one aspect of an embodiment of the present invention, a method for preparing a catalytic porous coating on the surface of an internal combustion engine is provided, comprising:

[0009] S100, pretreatment of the workpiece to be processed: cleaning and drying the surface of the workpiece to be processed to obtain a pretreated workpiece to be processed;

[0010] S200, preparation of a dense layer: placing the pre-treated workpiece obtained in step S100 in an electrolyte, and performing plasma micro-arc oxidation to form a dense layer on the surface of the workpiece;

[0011] S300, preparation of transition layer: adding nano-catalytic material to the electrolyte in step S200 for dispersion, and performing plasma micro-arc oxidation operation until the intensity of the plasma spectrum reaches no less than 2 / 5 of the peak value, thereby completing the plating of the transition layer;

[0012] S400, the preparation of the coating is completed: the processing parameters of the plasma micro-arc oxidation operation are adjusted, and the plasma micro-arc oxidation operation is continued until the intensity of the plasma spectrum reaches 7 / 10 to 4 / 5 of the peak value, and the plasma micro-arc oxidation operation is stopped to complete the preparation of the catalytic porous coating on the surface of the internal combustion engine.

[0013] As a preferred embodiment of the present invention, in step S200, the electrolyte is an alkaline electrolyte system.

[0014] As a preferred embodiment of the present invention, the electrolyte is a silicate electrolyte system;

[0015] The electrolyte is an aqueous solution including sodium silicate nonahydrate with a concentration of 10-25 g / L, disodium ethylenediaminetetraacetate with a concentration of 1-3 g / L, sodium hydroxide with a concentration of 1-4 g / L, and sodium polyphosphate with a concentration of 1-7 g / L.

[0016] As a preferred solution of the present invention, step S200 specifically includes:

[0017] S201, placing the workpiece to be processed in an electrolyte and connecting it to the anode of a power supply, and connecting the electrolytic cell to the cathode of the power supply;

[0018] S202, extending the plasma spectrum collection device to a fixed position, and deducting the background spectrum of the test environment;

[0019] S203, adopting a constant current and constant frequency output mode to perform plasma micro-arc oxidation operation to form a dense layer on the surface of the workpiece to be processed; wherein,

[0020] The processing parameters of plasma micro-arc oxidation operation are: discharge frequency is 50-200 Hz, current density is set to 10-16 A / dm 2 , the negative-to-positive current ratio is 1-1.2, the negative-to-positive pulse duty cycle is 50-60%, and the coating time is 10-20 minutes.

[0021] As a preferred solution of the present invention, before step S100, or between step S100 and step S200, the method further includes obtaining a plasma discharge spectrum of the pre-treated workpiece, and obtaining a peak intensity of the plasma spectrum according to the plasma discharge spectrum.

[0022] As a preferred embodiment of the present invention, the nano-catalytic material in step S300 is nano-copper oxide particles with a particle size of no more than 80 nm, and the content of the nano-catalytic material in the electrolyte after the nano-catalytic material is added is 1-3 g / L.

[0023] As a preferred embodiment of the present invention, in step S400, the final processing parameters of the adjusted plasma micro-arc oxidation operation are: the discharge frequency is 1200-1400 Hz, the current density is 8-12 A / dm 2 .

[0024] As a preferred solution of the present invention, in step S400, the adjustment of the processing parameters of the plasma micro-arc oxidation operation is a fluctuation adjustment, so that the intensity of the plasma spectrum is maintained at 2 / 5 to 4 / 5 of the peak value.

[0025] In another aspect of the embodiments of the present invention, there is also provided a catalytic porous coating on the surface of an internal combustion engine, which is prepared by the preparation method described above.

[0026] The embodiments of the present invention have the following advantages:

[0027] Plasma micro-arc oxidation operation is used to prepare a dense layer, and a support structure that can play a corrosion-resistant and supporting role is constructed for the entire coating system; on this basis, catalytic materials are introduced to construct a catalytic transition layer. This process is the process in which the workpiece gradually reaches mid-term discharge in a new electrolyte after the catalytic elements are added; further, based on the adjustment of the processing parameters of the plasma micro-arc oxidation operation, the open micropores formed in the outermost layer are densely distributed, and the densely distributed micropores can greatly increase the specific surface area of ​​the coating, and allow it to load more nano-catalytic materials, further improving the subsequent catalytic combustion level. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0029] The structures, proportions, sizes, etc. illustrated in this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with the technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantial technical significance. Any structural modification, change in proportion or adjustment of size shall still fall within the scope of the technical contents disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0030] Figure 1 A schematic diagram of the structure of a catalytic porous coating on the surface of an internal combustion engine provided by an embodiment of the present invention;

[0031] Figure 2 A flow chart of a preparation method provided by an embodiment of the present invention;

[0032] Figure 3 This is a plasma discharge spectrum provided by an embodiment of the present invention.

[0033] In the figure:

[0034] 1-workpiece to be processed; 2-dense layer; 3-transition layer; 4-open microporous catalytic layer. DETAILED DESCRIPTION

[0035] The following is a description of the implementation of the present invention by specific embodiments. People familiar with the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] The present invention provides a method for preparing a catalytic porous coating on the surface of an internal combustion engine, which is based on plasma electrolytic oxidation (PEO) technology. The main process is: first, before formally preparing the dense layer 2 / transition layer 3 / open microporous catalytic layer, a set of spectral peak intensity calibration tests must be performed to obtain a plasma discharge spectrum spectrum. The parameters and environment of this set of tests are consistent with all parameters in the subsequent dense layer 2 preparation process. The purpose of the calibration test is to obtain the peak intensity of the plasma spectrum and provide a reference for the subsequent 2 / 5 and other spectral intensity nodes. During this experiment, when the concentrated discharge phenomenon first appears (at about 35 to 55 minutes, the concentrated discharge phenomenon will appear, and this process can be distinguished by the naked eye. The specific progress of this process can be referred to the literature of our research group Fangtao Xu, Yuan Xia, Guang Li. et al., "The mechanism of PEO process on Al-Si alloys with the bulk primary silicon[J]., published in "Applied Surface Science," 2009, 255(23):9531-9538.), the Al spectrum peak intensity at this time is recorded and agreed to be the peak intensity (generally, the Al spectrum peak intensity in the wavelength range of 394 to 466 nm will have a peak intensity).After the peak intensity calibration test is completed, the formal preparation process of the multilayer coating is started. First, the silicate electrolyte is re-prepared, the workpiece 1 to be processed is washed and placed in the electrolyte, the power is started, a high-frequency pulse positive voltage is applied to the workpiece 1 to be processed, and a high-frequency pulse negative voltage is applied to the electrolytic tank. At the same time, a plasma spectrum feedback device is used to monitor the characteristic peaks of the liquid phase plasma spectrum in real time. In the preparation of the dense layer 2, no nano powder containing catalytic elements is added; the workpiece 1 to be processed is washed and placed in the electrolyte, the power is started, a high-frequency pulse positive voltage is applied to the workpiece 1 to be processed, and a high-frequency pulse negative voltage is applied to the electrolytic tank. At the same time, a plasma spectrum feedback device is used (it should be noted that the position of the plasma spectrum feedback device should be consistent with that set during the aforementioned calibration), and the characteristic peaks of the liquid phase plasma spectrum are monitored in real time to prepare the dense layer 2; after the preparation of the dense layer 2 is completed, the catalytic element nano powder is introduced into the electrolyte, and when the Al element spectrum peak reaches the B-type discharge (it should be noted that the three discharge modes of type A, type B and type C here are conventionally understood and determined by those skilled in the art, for example, reference can be made to Alexander Sobolev, Tamar Peretz, Konstantin Borodianskiy. et al. published a document titled "Synthesis and growth mechanism of ceramic coatings on an Al-Cu alloy using plasma electrolytic oxidation inmolten salt[J]." in Journal of alloys and compounds, 2021, 869-159309) and it is 2 / 5 of the characteristic peak of the Al element (i.e., the peak intensity obtained by previous calibration), the transition layer 3 is prepared; taking the spectrum in the middle stage of discharge (mainly type A and type C discharge at this time, about 2 / 5 to 4 / 5 of the characteristic peak of the Al element during the later continuous breakdown discharge) as the feedback reference, the pulse frequency and pulse current are controlled in real time to maintain the characteristic peak of the spectrum within a certain range, extend the arcing time in the middle stage of discharge, reduce the continuous discharge of harmful type B large holes, and increase the number of small-sized honeycomb holes. When the Al element spectrum peak exceeds 4 / 5 of the peak intensity of the Al element spectrum peak of type B discharge (i.e., the peak intensity obtained by previous calibration), the open microporous catalytic layer is prepared. The functional multilayer structure composed of the dense layer 2 / transition layer 3 / open microporous catalytic layer prepared by the above method can greatly increase the specific surface area of ​​the obtained coating carrier and keep it high in strength. Figure 1 As shown, the structure of the finally prepared internal combustion engine surface catalytic porous coating is as follows Figure 1 shown.

[0037] The following is a detailed description through specific embodiments. The workpiece 1 to be processed is generally the inner wall of an internal combustion engine or a piston or other parts.

[0038] 1) Pretreatment: First, a metal cleaning agent of a certain concentration is prepared with deionized water to remove oil stains on the surface of the workpiece 1; then, 2000-mesh sandpaper is used to perform matte polishing on the workpiece 1; the workpiece 1 is placed in an anhydrous ethanol / acetone solution prepared in a ratio of 15:1, and ultrasonic cleaning is performed for 10 minutes; deionized water is used to perform ultrasonic cleaning on the workpiece 1 for 2 minutes, and after further cleaning the surface, the workpiece 1 is dried to obtain a clean workpiece 1 with a certain roughness of the surface.

[0039] 2) Preparation of electrolyte and clamping: In the preparation of the electrolyte, the solutes include: sodium silicate nonahydrate with a concentration of 12 g / L, disodium ethylenediaminetetraacetic acid with a concentration of 2.5 g / L, sodium hydroxide with a concentration of 1.5 g / L, and sodium polyphosphate with a concentration of 5 g / L. The solvent is deionized water. The electrolyte is placed in an electrolytic cell, the electrolytic cell is connected to the negative electrode of the micro-arc oxidation power supply, and the workpiece 1 to be processed is connected to the positive electrode of the power supply.

[0040] 3) Spectral peak intensity calibration test: After the power supply is connected, turn on the power supply, circulating water and ventilation cabinet; install the plasma spectrum acquisition equipment, place the capture probe of the spectrum acquisition equipment on the top of the workpiece 1 to be processed, and subtract the background spectrum; use constant current and constant frequency mode output, the frequency is set to 50Hz, and the positive current density is 15A / dm 2 , the negative-to-positive current ratio is set to 1.2, the negative-to-positive pulse duty cycle is 55%, and when the concentrated discharge phenomenon first occurs, the Al spectrum peak intensity (24000) with a wavelength of 396.152nm is calibrated as the peak intensity, such as Figure 3 shown.

[0041] 4) Preparation of dense layer 2: Repeat the operating steps of 1) and 2), and repeat the experimental environment and test parameters of 3), with a deposition time of 15 minutes.

[0042] 5) Preparation of transition layer 3:

[0043] A 50 nm CuO (catalyst) spherical particle powder was dissolved into the electrolyte at a ratio of 1.5 g / L. The powder was dispersed using a stirring device and the Al element spectrum peak was monitored. When the Al element spectrum intensity reached 2 / 5 of the calibrated peak intensity, the transition layer 3 was prepared.

[0044] 6) Preparation of open microporous catalytic layer: Adjust the discharge frequency to 400 Hz and the discharge current to 12 A / dm 2When the Al element spectrum intensity rises to 3 / 5 of the later discharge peak value (i.e. the calibrated peak intensity), the frequency is set to 800Hz and the discharge current is set to 10A / dm 2 ; When the Al element spectrum intensity rises to 4 / 5 of the calibrated peak intensity, set the frequency to 1200Hz and the discharge current to 8A / dm 2 When the Al element spectrum rises to 4 / 5 of the calibrated peak intensity again, the power is turned off and the preparation of the open microporous catalytic layer is completed.

[0045] Through the above technical solution, the preparation method of the present invention has the following advantages:

[0046] (1) Liquid plasma spectrum feedback control

[0047] In the present invention, in the preparation process of the transition layer 3 and the open microporous catalytic layer, it is necessary to pay close attention to the discharge stage, especially in the preparation process of the open microporous layer, it is necessary to focus on maintaining the discharge in the mid-term stage, and try to dominate with type A and type C discharge forms. However, in the preparation process of traditional micro-arc oxidation plasma coating, large-pore concentrated discharge dominated by type B discharge will inevitably appear in the late stage of deposition. This process is destructive to the coating structure and mechanical properties. Therefore, in this process, liquid plasma spectral feedback control technology is adopted. According to the early discharge parameter collection, the discharge frequency and current are adjusted to extend the mid- and late-stage discharge time, increase the density and quantity of the open microporous catalytic layer, and maximize the specific surface area.

[0048] (2) High frequency liquid plasma discharge power supply

[0049] In order to better control the energy of a single discharge pulse, the present invention adopts a high-frequency liquid plasma discharge power supply, which can increase the power supply discharge frequency from 50Hz to 2000Hz. The pulse width of a single pulse discharge can vary between 250 and 2.5μs, thereby controlling the single pulse energy to a great extent and providing a broad regulation space for maintaining stable discharge in the middle and late stages.

[0050] (3) Functional structure design of support layer / transition layer 3 / open microporous catalytic layer

[0051] In this structure, the support layer can play a role in corrosion resistance and support; then the catalytic elements are introduced to construct the transition layer 3. This process is the process in which the workpiece 1 to be processed gradually reaches mid-term discharge in the new electrolyte after the catalytic elements are added; the outermost layer is an open microporous catalytic layer, the surface of which contains a large number of catalytic nanoparticles, and the densely distributed micropores can greatly increase the specific surface area of ​​the coating.

[0052] Although the present invention has been described in detail above by general description and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. A method for preparing a catalytic porous coating on the surface of an internal combustion engine, characterized in that: include: S100, pretreatment of the workpiece to be processed: cleaning and drying the surface of the workpiece to be processed to obtain a pretreated workpiece to be processed; S200, preparation of a dense layer: placing the pre-treated workpiece obtained in step S100 in an electrolyte, and performing plasma micro-arc oxidation to form a dense layer on the surface of the workpiece; S300, preparation of transition layer: adding nano-catalytic material to the electrolyte in step S200 for dispersion, and performing plasma micro-arc oxidation operation until the intensity of the plasma spectrum reaches no less than 2 / 5 of the peak value, thereby completing the plating of the transition layer; S400, the preparation of the coating is completed: the processing parameters of the plasma micro-arc oxidation operation are adjusted, and the plasma micro-arc oxidation operation is continued until the intensity of the plasma spectrum reaches 7 / 10 to 4 / 5 of the peak value, and the plasma micro-arc oxidation operation is stopped to complete the preparation of the catalytic porous coating on the surface of the internal combustion engine; The electrolyte is a silicate electrolyte system; The electrolyte is an aqueous solution including sodium silicate nonahydrate with a concentration of 10 to 25 g / L, disodium ethylenediaminetetraacetate with a concentration of 1 to 3 g / L, sodium hydroxide with a concentration of 1 to 4 g / L, and sodium polyphosphate with a concentration of 1 to 7 g / L; In step S200, the processing parameters of the plasma micro-arc oxidation operation are: the discharge frequency is 50 to 200 Hz, and the current density is set to 10 to 16 A / dm 2 , the negative-to-positive current ratio is 1-1.2, the negative-to-positive pulse duty cycle is 50-60%, and the coating time is 10-20 minutes; In step S400, the final processing parameters of the adjusted plasma micro-arc oxidation operation are: the discharge frequency is 1200-1400 Hz, the current density is 8-12 A / dm 2 .

2. A preparation method according to claim 1, characterized in that: Step S200 specifically includes: S201, placing the workpiece to be processed in an electrolyte and connecting it to the anode of a power supply, and connecting the electrolytic cell to the cathode of the power supply; S202, extending the plasma spectrum collection device to a fixed position, and deducting the background spectrum of the test environment; S203, adopting a constant current and constant frequency output mode to perform plasma micro-arc oxidation operation to form a dense layer on the surface of the workpiece to be processed.

3. A preparation method according to claim 1 or 2, characterized in that: Before step S100 , or between step S100 and step S200 , the method further includes obtaining a plasma discharge spectrum of the pre-processed workpiece, and obtaining a peak intensity of the plasma spectrum according to the plasma discharge spectrum.

4. A preparation method according to claim 1 or 2, characterized in that: The nano-catalytic material in step S300 is nano-copper oxide particles with a particle size of no more than 80 nm, and the content of the nano-catalytic material in the electrolyte after the nano-catalytic material is added is 1-3 g / L.

5. A preparation method according to claim 1 or 2, characterized in that: In step S400, the processing parameters of the plasma micro-arc oxidation operation are adjusted in a fluctuating manner so that the intensity of the plasma spectrum is maintained at 7 / 10 to 4 / 5 of the peak value.

6. A catalytic porous coating on the surface of an internal combustion engine, characterized in that: The method is prepared by any one of claims 1 to 5.

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