Co-permeation agent, coating and preparation method of co-permeation agent

Abstract

The invention provides a co-permeation agent, a coating and a preparation method of the co-permeation agent. The co-permeation agent comprises the following components in percentage by mass: 10-50% of an aluminum supply agent, 0.5-4% of an activating agent, 0.5-2.5% of silicon powder, 0.2-4% of a carbon supply agent, 0.5-8% of a decoking agent and the balance of aluminum oxide. A coating prepared from the co-permeation agent is high in content of catalytic active elements, and the loss of decoking elements is not obvious.

Description

Technical Field

[0001] The present invention belongs to the technical field of coating materials, and particularly relates to a co-permeation agent, a coating and a preparation method thereof. Background Art

[0002] Ethylene, as an important basic raw material in the petrochemical industry, is the basis for the production of various important organic chemical products. At present, most of the ethylene production adopts the thermal cracking process of tubular cracking furnaces. After the raw materials are pyrolyzed at high temperatures, a series of complex chemical reactions will occur, resulting in varying degrees of coking on the inner walls of the radiant section furnace tubes of the cracking furnace and the inner walls of the quench boiler casings. As the coke layer continues to thicken, the inner diameter of the tube decreases, the pressure drop of the fluid inside the tube increases, the heat transfer resistance of the furnace tube increases, and the heat outside the tube cannot be transferred to the pyrolysis raw materials inside the tube in time, seriously affecting the pyrolysis depth of the raw materials. In addition, the temperature of the outer surface of the furnace tube continues to rise, and local overheating may occur, resulting in a shortened service life of the furnace tube. When the temperature exceeds the maximum design temperature of the furnace tube material, the furnace needs to be shut down for coke cleaning. Therefore, how to effectively inhibit the coking rate during the raw material pyrolysis process is one of the key issues for extending the operation cycle of the device.

[0003] As the most effective means to inhibit coking in ethylene cracking furnaces at present, the coating technology for cracking furnace tubes mainly prepares one or more layers of coatings on the surface of the cracking furnace tubes by physical or chemical methods. These coatings can not only play a shielding role for catalytic coking active elements such as iron and nickel in the furnace tube substrate, but also reduce the corrosion of the cracking furnace tubes caused by carburization during ethylene production. This technology can effectively inhibit the coking of cracking furnace tubes, greatly improve the operation cycle of the cracking furnace, and the reduction of the coke generation amount on the inner surface of the furnace tube can further reduce the operation energy consumption of the cracking furnace. Through years of research at home and abroad, a variety of coating technologies for cracking furnace tubes have been proposed. These coating technologies mostly play a shielding role for iron and nickel elements in the furnace tube substrate, and obtain good coking inhibition performance for cracking furnace tubes by preventing the generation of catalytic coking. However, for the free radical coking and condensation coking generated during the pyrolysis process, these coating technologies are mostly difficult to effectively inhibit. To obtain a better coking inhibition effect, researchers have newly proposed a coating with a self-cleaning coking function, which reduces the coke generation amount during pyrolysis by adding a carbon donor and self-cleaning coking elements, and at the same time further extends the operation cycle of the cracking furnace.

[0004] The existing catalytic coatings for cracking furnace tubes have good coking inhibition performance and anti-carburization performance. During application, they can well protect the substrate of the cracking furnace tubes. However, in the process of preparing catalytic coatings by the traditional powder-pack cementation method, due to the differences in the diffusion rates among the elements in the infiltrant and the diffusion rates of the infiltrant elements relative to the substrate elements, it leads to a large difference in the element diffusion rates during high-temperature infiltration, resulting in a coating structure with relatively many pore structures. The existence of this structure is not conducive to improving the overall mechanical strength of the coating. At the same time, since the diffusion rate of the catalytic active components is slower than that of the infiltrant elements, the catalytic active components in the prepared coating tend to concentrate in the outer surface area of the coating. This makes the high-temperature stability of the catalytic active components relatively low during the application of the coating. With the loss of catalytic active elements, the catalytic conversion performance of the catalytic coating for coke gradually decreases.

[0005] CN104264205B discloses a composite coating for inhibiting furnace tube coking, its preparation method and application. Mainly through the method of co-electrodeposition composite electroplating, chromium, Me and rare earth oxide Re x O y and other substances are used to prepare a composite coating on the material surface. Cr 2 O 3 in the coating of this invention can, to a certain extent, inhibit the erosion of carbon on the furnace tube. However, at high temperatures, H 2 O will accelerate the evaporation of chromium oxide, causing the chromium oxide layer to become thinner and reducing the protection effect of the composite coating.

[0006] CN107236925A discloses a solid powder silicon-aluminum co-cementation process for improving the anti-carburization protection of ethylene cracking furnace tubes, forming a surface infiltration layer composed of NiAl and FeAl intermetallic compounds on the surface of the ethylene cracking furnace tubes. The silicon-aluminum layer adopted in this invention has good anti-carburization ability. However, the higher the silicon element concentration, the faster the diffusion rate. Therefore, during the interdiffusion process of Si and other elements, a serious Kirkendall effect will occur, resulting in voids being formed at the front of the silicon infiltration layer.

[0007] CN112853260B discloses a preparation method for a powder-pack infiltration coating. Metal powder, alumina, activator, silicon powder, rare earth and graphite powder are mixed evenly and placed in an infiltration box with the workpiece for sealing treatment, and then the infiltration box is subjected to element diffusion infiltration chemical heat treatment. Although expandable graphite is added to the infiltrant in this invention, with the reaction with oxygen, the carbon concentration is reduced, and stable nitrides cannot be formed. Moreover, the reduction of the carbon concentration also cannot ensure the inhibitory effect of carbon on the diffusion rates of elements such as Si and Al.

[0008] CN114540749A discloses a self - defouling coating, its preparation method and application. The self - defouling coating includes a barrier coating composed of Cr, Si, Al, Zr and their oxides and halides, and a defouling coating composed of Cr, Si, Al, self - defouling elements and their oxides and halides. The preparation process of the self - defouling coating is to first apply the barrier coating by the thermochemical embedding method, then apply the defouling coating, and finally perform a stabilization treatment to obtain a cracking furnace tube coating with strong coking inhibition performance and good coating stability. Although the invention adopts a barrier coating and a self - defouling coating, and both coatings contain Cr, Si, and Al elements, at high temperatures, when Si exists as a substitutional solid solution in Cr and Fe, due to the large difference in the local diffusion rates of Si atoms and Cr and Fe atoms, and the higher the Si concentration, the faster the diffusion rate. Therefore, in the inter - diffusion process between Si and other elements such as Cr and Fe, a more serious Kirkendall effect will occur, resulting in the formation of pores at the front of the silicon - infiltrated layer. Summary of the Invention

[0009] In order to solve the above problems in the prior art, the object of the present invention is to provide a co - infiltration agent, a coating and its preparation method. The co - infiltration agent of the present invention contains a defouling agent, an aluminum - supplying agent, and a carbon - supplying agent is introduced. The coating prepared therefrom has a high content of catalytically active elements and the loss of defouling elements is not obvious.

[0010] To achieve the above object, according to one aspect of the present invention, a co - infiltration agent is provided, which includes, by mass percentage:

[0011] 10 - 50% of an aluminum - supplying agent, 0.5 - 4% of an activator, 0.5 - 2.5% of silicon powder, 0.2 - 4% of a carbon - supplying agent, 0.5 - 8% of a defouling agent, and the balance of alumina.

[0012] The present invention introduces a carbon - supplying agent into the infiltration agent. The carbon - supplying agent can decompose under high - temperature action and provide active carbon atoms. The introduction of carbon atoms can reduce the diffusion rates of elements such as Si and Al. When the co - infiltration agent of the present invention is applied to substrates such as steel and alloys, it can make the diffusion rates of elements such as Si and Al match those of matrix elements such as Fe, Ni, and Cr, reduce the influence of the Kirkendall effect, and make the prepared coating have a dense microstructure.

[0013] At the same time, due to the more uniform diffusion of Si in the coating, the splash of the molten pool during the welding process is avoided, and the welding performance of the coating furnace tube is also improved.

[0014] At the same time, the present invention can make the structure of the prepared coating smooth and dense by matching the diffusion speed of Al and Si elements with the elements contained in the decoking agent and the elements contained in the matrix. Compared with the catalytic coating prepared by the traditional powder embedding co-infiltration method, under the condition of using the same infiltration agent content of catalytic active elements, the content of catalytic active elements in the coating prepared by this method is higher than that of the coating prepared by the traditional method. In addition, the high-temperature stability of the decoking elements in the coating is more excellent, and the loss of the decoking elements is not obvious during the use of the coating.

[0015] The carbon-containing compounds in the carbon supplying agent used in the present invention will decompose under high temperature, and the generated nitrogen atoms will combine with aluminum atoms under high temperature to form aluminum nitride on the surface of the substrate. Since aluminum nitride has high thermal conductivity and heat shock resistance, the overall high-temperature thermal stability of the coating can be further improved.

[0016] In particular, the present invention allows the infiltrant to contain a carbon supplying agent, and the carbon powder in the carbon supplying agent can generate CO gas at high temperature. Therefore, the present invention can control the concentration of the CO atmosphere more directly and stably.

[0017] Under the action of high temperature, the carbon-containing compounds in the carbon supply agent will decompose into carbon dioxide, thereby forming a reaction balance between carbon monoxide and carbon. The resulting reducing gases such as CO can, on the one hand, eliminate the oxygen contained in the infiltrant, eliminate the oxidizing effect of oxygen on the infiltrant, and improve the overall utilization efficiency of the infiltrant; on the other hand, the resulting reducing gas will form a balanced relationship with the carbon component after high-temperature activation, thereby maintaining the carbon concentration in the co-infiltrating system and thus ensuring the inhibitory effect of carbon on the diffusion rate of elements such as Si and Al during the high-temperature co-infiltrating process.

[0018] In some preferred embodiments of the present invention, the amount of each component in the co-permeation agent, by mass percentage, includes: 15% to 35% of aluminum supply agent, 1% to 3% of activator, 1% to 2% of silicon powder, 1% to 4% of carbon supply agent, 1.5 to 6% of coke removal agent, and the balance of aluminum oxide. The above-mentioned dosage ratio is preferred, which is more conducive to improving the comprehensive performance of the obtained coating.

[0019] In some preferred embodiments of the present invention, the carbon supplying agent includes carbon powder and / or a carbon-containing compound.

[0020] In some preferred embodiments of the present invention, the mass percentage of the carbon-containing compound in the carbon supply agent is ≤85%, and more preferably, the mass percentage is 15% to 75%. The carbon supply agent will generate a CO atmosphere at high temperature, and such a ratio is preferred, and the resulting CO atmosphere is more stable.

[0021] In some preferred embodiments of the present invention, the carbon-containing compound includes one or a combination of two or more of ammonium bicarbonate, diammonium bicarbonate, and ammonium acetate.

[0022] In some preferred embodiments of the present invention, the toner includes graphite powder.

[0023] In some preferred embodiments of the present invention, the coke cleaning agent includes one or a combination of two or more of potassium aluminosilicate, barium carbonate, potassium carbonate, and cerium oxide. In the present invention, the selection of the coke cleaning agent is not limited thereto, and elements having the function of catalytic gasification of coke scale are selected as the selection conditions.

[0024] In some preferred embodiments of the present invention, the aluminum supplier is one or a combination of two or more of pure aluminum powder, ferroaluminum alloy, aluminum-silicon alloy, and aluminum-chromium alloy.

[0025] In some preferred embodiments of the present invention, the activator is one or a combination of two or more of silicon chloride, aluminum fluoride, and aluminum chloride.

[0026] In some preferred embodiments of the present invention, the powder particle size of the co-permeation agent is -150 to +400 mesh.

[0027] According to another aspect of the present invention, a method for preparing a coating is further provided, and the method includes:

[0028] The surface of the substrate is subjected to a purification treatment to obtain a treated sample piece;

[0029] The above-mentioned co-permeation agent and the treated sample are subjected to a sealing treatment in a permeation box to obtain an intermediate sample piece;

[0030] The intermediate sample piece is subjected to elemental diffusion infiltration chemical heat treatment.

[0031] During the elemental diffusion infiltration chemical heat treatment, the carbon supplier will decompose to generate reducing gases such as CO. On the one hand, the above-mentioned reducing gases can eliminate the oxygen contained in the permeation agent, eliminate the oxidation effect of oxygen on the permeation agent, and improve the overall utilization efficiency of the permeation agent; on the other hand, the reducing gases will also form an equilibrium relationship with carbon, maintaining the diffusion inhibition effect of carbon on elements such as Si and Al.

[0032] In some preferred embodiments of the present invention, the elemental diffusion infiltration chemical heat treatment is carried out in a heat treatment furnace;

[0033] Preferably, the furnace inlet temperature is 150 to 350 °C;

[0034] Preferably, the heat preservation temperature is 700 to 950 °C, and the time is 4 to 10 h;

[0035] Preferably, the heating rate is 5 to 10 °C / min.

[0036] Preferably, after the heat preservation is completed, it is cooled with the furnace.

[0037] In some preferred embodiments of the present invention, the volume percentage of the co-permeation agent in the permeation box is 40-60%.

[0038] Further, for the sealing treatment, high-temperature refractory mud is used to coat the connection part of the permeation box to prevent air from entering.

[0039] In some preferred embodiments of the present invention, the material of the base material is heat-resistant steel or superalloy.

[0040] In some preferred embodiments of the present invention, by mass percentage, the base material includes:

[0041] Ni: 8-50%, Cr: 12-45%, C: 0.2-1.5%, Si: 0-3%, Mn: 0-2%, P: 0-0.1%, S: 0-0.1%, Nb: 0-2%, with the balance being Fe.

[0042] In some preferred embodiments of the present invention, the base material includes HP40, HK40, TP310S, Cr25Ni35Nb, Cr35Ni45Nb, etc.

[0043] According to another aspect of the present invention, there is also provided a coating prepared from the above co-permeation agent, or a coating prepared by the above preparation method.

[0044] The present invention has the following beneficial technical effects compared with the prior art:

[0045] 1. The high-temperature thermal stability of the coating is improved; 2. The welding performance of the coating furnace tube is improved; 3. The catalytically active elements in the coating are higher, and the loss of decoking elements is not obvious during use. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Shows the scanning electron microscope image of the cross-section after carburizing on the coating surface in Example 3.

[0047] Figure 2 Shows the scanning electron microscope image of the cross-section after carburizing on the surface without coating in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0048] In order to have a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solutions of the present invention are described in detail below, but it should not be construed as a limitation on the implementable scope of the present invention.

[0049] For the carburizing of the coating and elemental analysis and characterization in the present invention, a Hitachi S3400 scanning electron microscope is used, and the electron microscope scanning voltage is 15 kV.

[0050] The coking performance of the coating material was tested using a hanging slice coking performance evaluation device. In this device, the coating sample slice was suspended in a tubular reactor, and steam cracking reaction conditions under high temperature were simulated by introducing steam and hydrocarbon raw material gas into the reaction tube. In each embodiment of the present invention, the same conditions for evaluating the coking performance of the hanging slice were adopted. The specific evaluation test conditions were as follows: Naphtha was used as the cracking raw material to test the coking performance of the coating hanging slice. The reaction conditions were that the mass ratio of naphtha to deionized water was 2:1, the naphtha flow rate was 8 mL / min, the deionized water flow rate was 3 mL / min. After mixing the two, they were preheated to 360 °C and then introduced into the reaction tube for cracking reaction. The reaction temperature of the cracking furnace was maintained at 840 °C, the reaction pressure was 30 kPa, and the cracking reaction time was 5 h. After the reaction ended, the coating hanging slice was taken out, and the total mass Wtotal of the coked coating hanging slice was weighed using an electronic balance. After deducting the mass W0 of the sample slice before the evaluation test through formula (1), the coking amount Wcoke of the coating hanging slice was obtained.

[0051] Wcoke = Wtotal - W0 (1)

[0052] In order to better express the catalytic conversion effect of the coating on coke, the present invention uses the coking inhibition rate to describe the coke inhibition performance of the coating material. The calculation formula of the coking inhibition rate is shown in formula (2):

[0053] S = (Wreference - Wcoke) / Wreference × 100% (2)

[0054] Among them, S is the coking inhibition rate, Wcoke is the coking amount of the coating hanging slice, and Wreference is the coking amount of the reference coating hanging slice.

[0055] The stability performance of the coating was tested using a hanging slice coking performance evaluation device. The specific test method was to use multiple cycle evaluations for testing. The number of cycles was 5 times, and the single evaluation time was 6 h. The reaction conditions adopted for the evaluation were that the mass ratio of naphtha to deionized water was 2.5:1, the naphtha flow rate was 11 mL / min, the deionized water flow rate was 3 mL / min. After mixing the two, they were preheated to 360 °C and then introduced into the reaction tube for cracking reaction. The reaction temperature of the cracking furnace was maintained at 850 °C, and the reaction pressure was 30 kPa. After the reaction ended, the coating hanging slice was taken out and placed in a muffle furnace for roasting in an air atmosphere. The roasting temperature was 900 °C, and the roasting time was 6 h. After the furnace temperature dropped to room temperature, it was taken out and rehung into the device for testing in the next evaluation cycle under the same reaction conditions.

[0056] The penetrant raw materials used in each embodiment and comparative example of the present invention were all purchased from commercially available products. The percentage ratios involved in each embodiment and comparative example of the present invention are all mass percentage ratios unless otherwise specified.

[0057] Preparation of the substrate sample slice

[0058] Take Cr25Ni35Nb, HP40, TP310S, Cr35Ni45Nb, HK40 alloy substrates, and uniformly process the above alloy substrates into a number of substrate samples with a size of 30mm×15mm×5mm for standby.

[0059] Example 1

[0060] Take the Cr25Ni35Nb substrate sample for coating preparation. The specific preparation process is as follows:

[0061] Weigh the co-permeation agent (20% aluminum-silicon alloy powder, 2% silicon chloride, 5% cerium oxide, 2.5% silicon powder, 2% carbon-supplying agent, among which ammonium bicarbonate in the carbon-supplying agent accounts for 38%; alumina: the balance) according to the ratio, stir and mix it, then put it into a ball mill for ball milling and mixing for 2h at a rotation speed of 300r / min and a ball-to-material ratio of 1:2; polish and clean the substrate sample, and clean it with a Scotch-Brite pad and acetone; fill the permeation agent and the substrate sample into the permeation box, and the filling ratio of the permeation agent is 40vol%. Seal it with high-temperature refractory mud and dry it at 80°C for 2 hours; place the permeation box in a heat treatment furnace preheated to 200°C, heat it to 750°C at a rate of 10°C / min and hold for 5 hours, and after the holding is completed, take it out after cooling in the furnace to obtain a coated sample. The thickness of the sample coating is 85μm, the surface layer components are mainly alumina and aluminum nitride, and the cerium element content is 1.7%.

[0062] Example 2

[0063] Take the HP40 substrate sample for coating preparation. The specific preparation process is as follows:

[0064] Weigh the co-permeation agent (20% aluminum-chromium alloy, 4% aluminum chloride, 3% potassium carbonate, 1% silicon powder, 1.5% carbon-supplying agent, among which ammonium bicarbonate in the carbon-supplying agent accounts for 35%; alumina: the balance), with the particle size of each powder less than 75um, according to the ratio, stir and mix it evenly; polish and clean the substrate sample, and clean it with anhydrous ethanol; fill the permeation agent and the substrate sample into the permeation box, and the filling ratio of the permeation agent is 40vol%. Seal it with high-temperature refractory mud, and then dry it at 80°C for 2 hours; place the permeation box in a heat treatment furnace at 250°C, heat it to 850°C at a rate of 8°C / min and hold for 4 hours, and after the holding is completed, take it out after cooling in the furnace to obtain a coated furnace tube. The thickness of the sample coating is 115μm, the surface layer components are mainly alumina and aluminum nitride, and the potassium content is 0.6%.

[0065] Example 3

[0066] Take the Cr25Ni35Nb substrate sample for coating preparation. The specific preparation process is as follows:

[0067] Weigh the co-permeation agent (28% aluminum-silicon alloy, 3% aluminum fluoride, 5% cerium oxide, 2% silicon powder, 3% carbon provider, among which ammonium acetate in the carbon provider accounts for 43%, and the balance is aluminum oxide) according to the ratio, mix them and grind them in a grinder until the powder particle size is less than 100 mesh. Sandblast and clean the substrate sample with a pneumatic grinding wheel, and wipe it clean with acetone. Fill the permeation agent and the substrate sample into the permeation box, and the filling ratio of the permeation agent is 40 vol%. Seal it with high-temperature refractory mud, and then dry it at 80 °C for 2 hours. Heat the heat treatment furnace to 200 °C, put the permeation box into it, heat it to 820 °C at a rate of 6 °C / min and hold for 10 hours. After the holding is completed, take it out after cooling with the furnace to obtain the coated sample. The thickness of the furnace tube coating is 120 μm, and the surface components are mainly aluminum oxide and aluminum nitride, and the cerium content is 2.1%.

[0068] The scanning electron microscope image of the cross-section after carburizing on the surface of the coating in Example 3 is as Figure 1 shown.

[0069] Example 4

[0070] Take a TP310S substrate sample for coating preparation. The specific preparation process is as follows:

[0071] Weigh the co-permeation agent (25% iron-aluminum alloy powder, 3% silicon chloride, 4% potassium aluminosilicate, 0.8% silicon powder, 2.3% carbon provider, among which ammonium bicarbonate in the carbon provider accounts for 43%, and the balance is aluminum oxide) according to the ratio, stir and mix it, and then put it into a ball mill for ball milling and mixing for 2 h at a rotation speed of 300 r / min and a ball-to-material ratio of 1:2. Sandblast and clean the substrate sample, and clean it with a white cleaning cloth and acetone. Fill the permeation agent and the substrate sample into the permeation box, and the filling ratio of the permeation agent is 40 vol%. Seal it with high-temperature refractory mud and dry it at 80 °C for 2 hours. Place the permeation box in a heat treatment furnace preheated to 200 °C, heat it to 830 °C at a rate of 9 °C / min and hold for 6 hours. After the holding is completed, take it out after cooling with the furnace to obtain the coated furnace tube. The thickness of the sample coating is 110 μm, and the surface components are mainly aluminum oxide and aluminum nitride, and the potassium element content is 0.8%.

[0072] Example 5

[0073] Take a Cr35Ni45Nb substrate sample for coating preparation. The specific preparation process is as follows:

[0074] Weigh the co-permeation agent (23% aluminum-chromium alloy powder, 2.5% aluminum chloride, 6% barium carbonate, 2.3% silicon powder, 0.8% carbon-supplying agent, among which ammonium bicarbonate in the carbon-supplying agent accounts for 45%, and the balance is alumina) according to the ratio. After stirring and mixing it, put it into a ball mill for ball milling and mixing for 2 h at a rotation speed of 300 r / min with a ball-to-material ratio of 1:2. Grind and clean the substrate sample with a pneumatic grinding wheel and wipe it clean with acetone. Fill the permeation agent and the substrate sample into the permeation box, and the filling ratio of the permeation agent is 50 vol%. Seal it with high-temperature refractory mud and dry it at 80 °C for 2 hours. Place the permeation box in a heat treatment furnace preheated to 200 °C, heat it to 770 °C at a rate of 5 °C / min and hold for 6 hours. After the holding is completed, take it out after cooling with the furnace. Obtain a coated sample. The thickness of the sample coating is 103 μm, the surface components are mainly alumina and aluminum nitride, and the barium element content is 1.3%.

[0075] Example 6

[0076] Take a HK40 substrate sample for coating preparation. The specific preparation process is as follows:

[0077] Weigh the co-permeation agent (20% pure aluminum powder, 1% silicon chloride, 3.5% cerium oxide, 1.5% silicon powder, 4% carbon-supplying agent, among which ammonium acetate in the carbon-supplying agent accounts for 20%, and the balance is alumina) according to the ratio. After stirring and mixing it, put it into a ball mill for ball milling and mixing for 2 h at a rotation speed of 300 r / min with a ball-to-material ratio of 1:2. Grind and clean the substrate sample with a pneumatic grinding wheel and wipe it clean with acetone. Fill the permeation agent and the substrate sample into the permeation box, and the filling ratio of the permeation agent is 60 vol%. Seal it with high-temperature refractory mud and dry it at 80 °C for 2 hours. Place the permeation box in a heat treatment furnace preheated to 200 °C, heat it to 820 °C at a rate of 7 °C / min and hold for 4 hours. After the holding is completed, take it out after cooling with the furnace to obtain a coated sample. The thickness of the sample coating is 113 μm, the surface components are mainly alumina and aluminum nitride, and the cerium element content is 1.2%.

[0078] Example 7

[0079] Take a Cr25Ni35Nb substrate sample for coating preparation. The specific preparation process is as follows:

[0080] Weigh the co-permeation agent (29% aluminum-chromium alloy powder, 4% aluminum fluoride, 1.5% potassium carbonate, 2% silicon powder, 3.8% carbon-supplying agent, among which ammonium acetate in the carbon-supplying agent accounts for 50%; alumina: the balance) according to the ratio. After stirring and mixing it, put it into a ball mill for ball milling and mixing for 2 hours at a rotation speed of 300 r / min and a ball-to-material ratio of 1:2. Grind and clean the substrate sample piece with a pneumatic grinding wheel and wipe it clean with acetone. Fill the permeation agent and the substrate sample piece into the permeation box, and the filling ratio of the permeation agent is 40 vol%. Seal it with high-temperature refractory mud and dry it at 80 °C for 2 hours. Place the permeation box in a heat treatment furnace preheated to 200 °C, heat it to 750 °C at a rate of 8 °C / min and hold for 5 hours. After the holding is completed, take it out after cooling with the furnace to obtain a coated sample piece. The thickness of the sample piece coating is 90 μm, the surface layer components are mainly alumina and aluminum nitride, and the potassium element content is 0.9%.

[0081] Example 8

[0082] Take a HK40 substrate sample piece for coating preparation. The specific preparation process is as follows:

[0083] Weigh the co-permeation agent (30% iron-aluminum alloy powder, 1.5% silicon chloride, 3% cerium oxide, 1% silicon powder, 0.2% carbon-supplying agent, among which ammonium bicarbonate in the carbon-supplying agent accounts for 60%; alumina: the balance) according to the ratio. After stirring and mixing it, put it into a ball mill for ball milling and mixing for 2 hours at a rotation speed of 300 r / min and a ball-to-material ratio of 1:2. Grind and clean the substrate sample piece with a pneumatic grinding wheel and wipe it clean with acetone. Fill the permeation agent and the substrate sample piece into the permeation box, and the filling ratio of the permeation agent is 60 vol%. Seal both ends with high-temperature refractory mud and dry it at 80 °C for 2 hours. Place the permeation box in a heat treatment furnace preheated to 200 °C, heat it to 750 °C at a rate of 10 °C / min and hold for 5 hours. After the holding is completed, take it out after cooling with the furnace to obtain a coated sample piece. The thickness of the sample piece coating is 104 μm, the surface layer components are mainly alumina and aluminum nitride, and the cerium element content is 1.4%.

[0084] Example 9

[0085] Take a Cr35Ni45Nb substrate sample piece for coating preparation. The specific preparation process is as follows:

[0086] Weigh the co-permeation agent (25% pure aluminum powder, 2.8% aluminum chloride, 5% barium carbonate, 0.5% silicon powder, 3.5% carbon provider, among which ammonium bicarbonate in the carbon provider accounts for 23%; alumina: the balance) according to the ratio. After stirring and mixing it, put it into a ball mill for ball milling and mixing for 2 h at a rotation speed of 300 r / min and a ball-to-material ratio of 1:2. Grind and clean the substrate sample with a pneumatic grinding wheel and wipe it clean with acetone. Fill the permeation agent and the substrate sample into the permeation box, and the filling ratio of the permeation agent is 50 vol%. Seal it with high-temperature refractory mud and dry it at 80 °C for 2 hours. Place the permeation box in a heat treatment furnace preheated to 200 °C, heat it to 700 °C at a rate of 9 °C / min and hold for 8 hours. After the holding is completed, take it out after cooling with the furnace to obtain a coated sample. The thickness of the sample coating is 106 μm, the surface components are mainly alumina and aluminum nitride, and the barium element content is 1.1%.

[0087] Example 10

[0088] Take an HP40 substrate sample for coating preparation. The specific preparation process is as follows:

[0089] Weigh the co-permeation agent (33% aluminum-iron alloy powder, 3.3% silicon chloride, 4.3% potassium aluminosilicate, 1.8% silicon powder, 2.7% carbon provider, among which ammonium acetate in the carbon provider accounts for 65%; alumina: the balance) according to the ratio. After stirring and mixing it, put it into a ball mill for ball milling and mixing for 2 h at a rotation speed of 300 r / min and a ball-to-material ratio of 1:2. Grind and clean the substrate sample with a pneumatic grinding wheel and wipe it clean with acetone. Fill the permeation agent and the substrate sample into the permeation box, and the filling ratio of the permeation agent is 60 vol%. Seal it with high-temperature refractory mud and dry it at 80 °C for 2 hours. Place the furnace tube in a heat treatment furnace preheated to 200 °C, heat it to 950 °C at a rate of 8 °C / min and hold for 4 hours. After the holding is completed, take it out after cooling with the furnace to obtain a coated sample. The thickness of the sample coating is 110 μm, the surface components are mainly alumina and aluminum nitride, and the potassium element content is 1.3%.

[0090] Example 11 - Coating Furnace Tube Preparation

[0091] The workpiece material is a Cr35Ni45Nb alloy furnace tube with an inner diameter of 40 mm, a wall thickness of 5 mm, and a length of 4 m. The coating preparation process is as follows:

[0092] Co-permeation agent (28% aluminum-silicon alloy, 3% aluminum fluoride, 5% cerium oxide, 2% silicon powder, 3% carbon-supplying agent, among which ammonium acetate in the carbon-supplying agent accounts for 43%, and alumina: the balance), weighed according to the ratio, stirred and mixed, then put into a ball mill for ball milling and mixing for 2 h at a rotation speed of 300 r / min and a ball-to-material ratio of 1:2. The inner wall of the centrifugally cast furnace tube was polished and cleaned with a pneumatic grinding wheel and wiped clean with acetone; the permeation agent was filled into the inner cavity of the furnace tube, and the filling ratio of the permeation agent was 40 vol%. Seal both ends with high-temperature refractory mud and dry at 80 °C for 2 hours. Place the furnace tube in a heat treatment furnace preheated to 200 °C, heat it to 760 °C at a rate of 10 °C / min and hold for 10 hours. After holding, cool it in the furnace and take it out to obtain a coated furnace tube. The thickness of the furnace tube coating is 85 μm, the surface layer components are mainly alumina and aluminum nitride, and the cerium element content is 1.9%.

[0093] Example 12 - Preparation of Coated Furnace Tube

[0094] The workpiece material is HP40 alloy tube, with an inner diameter of 40 mm, a wall thickness of 5 mm, and a length of 4 m. The coating preparation process is as follows:

[0095] Weigh the co-permeation agent (29% aluminum-chromium alloy powder, 4% aluminum fluoride, 1.5% potassium carbonate, 2% silicon powder, 3.8% carbon-supplying agent, among which ammonium acetate in the carbon-supplying agent accounts for 50%, and alumina: the balance) according to the ratio, stir and mix it evenly; polish and clean the inner wall of the furnace tube and wash it with absolute ethanol; fill the permeation agent into the furnace tube, and the filling ratio of the permeation agent is 40 vol%. Seal both ends with high-temperature refractory mud, and then dry at 80 °C for 2 hours; place the permeation box in a heat treatment furnace at 250 °C, heat it to 850 °C at a rate of 8 °C / min and hold for 8 hours. After holding, cool it in the furnace and take it out to obtain a coated furnace tube. The thickness of the furnace tube coating is 115 μm, the surface layer components are mainly alumina and aluminum nitride, and the potassium element content is 0.5%.

[0096] Example 13 - Preparation of Coated Furnace Tube

[0097] The workpiece material is Cr25Ni35Nb alloy tube, a centrifugally cast furnace tube, with an inner diameter of 41 mm, a wall thickness of 5 mm, and a length of 5 m. The coating preparation process is as follows:

[0098] Weigh the co-permeation agent (30% iron-aluminum alloy powder, 1.5% silicon chloride, 3% cerium oxide, 1% silicon powder, 0.2% carbon provider, among which ammonium bicarbonate in the carbon provider accounts for 60%; alumina: the balance) according to the ratio, mix them and grind through a grinder, with the powder particle size less than 100 mesh; polish and clean the inner wall of the centrifugal casting furnace tube with a pneumatic grinding wheel and wipe it clean with acetone; fill the permeation agent into the furnace tube, and the filling ratio of the permeation agent is 60 vol%. Seal both ends with high-temperature refractory mud and then dry at 80°C for 2 hours; heat the heat treatment furnace to 200°C, put the furnace tube in, heat it to 820°C at 7°C / min and hold for 10 hours. After the holding is completed, take it out after cooling in the furnace to obtain the coated furnace tube. The thickness of the furnace tube coating is 120 μm, and the surface components are mainly alumina and aluminum nitride, and the cerium element content is 1.8%.

[0099] Comparative Example 1

[0100] Take a Cr25Ni35Nb substrate sample for coating preparation. The specific preparation process is as follows:

[0101] Weigh the co-permeation agent (28% aluminum-silicon alloy, 3% aluminum fluoride, 5% cerium oxide, 2% silicon powder, alumina: the balance) according to the ratio, stir and mix it, then put it into a ball mill for ball milling for 2 h at a rotation speed of 300 r / min and a ball-to-material ratio of 1:2; polish and clean the substrate sample with a pneumatic grinding wheel and wipe it clean with acetone; fill the permeation agent and the substrate sample into the permeation box, and the filling ratio of the permeation agent is 40 vol%. Seal it with high-temperature refractory mud and dry at 80°C for 2 hours; heat the heat treatment furnace to 200°C, put the permeation box in, heat it to 820°C at 9°C / min and hold for 10 hours. After the holding is completed, take it out after cooling in the furnace to obtain the coated sample. The thickness of the sample coating is 114 μm, and the cerium element content is 1.65%.

[0102] The scanning electron microscope image of the cross-section after carburizing on the surface of the coating obtained in Comparative Example 1 is as Figure 2 shown.

[0103] Comparative Example 2

[0104] Take a Cr25Ni35Nb substrate sample for coating preparation. The specific preparation process is as follows:

[0105] Weigh the co-permeation agent (28% aluminum-silicon alloy, 3% aluminum fluoride, 5% cerium oxide, 2% silicon powder, 3% carbon provider, where the carbon provider only contains graphite, and the balance is aluminum oxide) according to the ratio, mix it, and grind it with a grinder until the powder particle size is less than 100 mesh. Clean the substrate sample with a pneumatic grinding wheel and wipe it clean with acetone. Fill the permeation agent and the substrate sample into the permeation box, and the filling ratio of the permeation agent is 40 vol%. Seal it with high-temperature refractory mud and then dry it at 80°C for 2 hours. Heat the heat treatment furnace to 200°C, put in the permeation box, heat it to 820°C at a rate of 10°C / min and hold for 10 hours. After the holding is completed, take it out after cooling in the furnace to obtain the coated sample. The coating thickness of the furnace tube is 103 μm, and the surface components are mainly aluminum oxide and aluminum nitride, and the cerium content is 1.3%.

[0106] Comparative Example 3

[0107] Take a Cr25Ni35Nb substrate sample for coating preparation. The specific preparation process is as follows:

[0108] Weigh the co-permeation agent (28% aluminum-silicon alloy, 3% aluminum fluoride, 5% cerium oxide, 2% silicon powder, 3% carbon provider, where the carbon provider only contains ammonium bicarbonate, and the balance is aluminum oxide) according to the ratio, mix it, and grind it with a grinder until the powder particle size is less than 100 mesh. Clean the substrate sample with a pneumatic grinding wheel and wipe it clean with acetone. Fill the permeation agent and the substrate sample into the permeation box, and the filling ratio of the permeation agent is 40 vol%. Seal it with high-temperature refractory mud and then dry it at 80°C for 2 hours. Heat the heat treatment furnace to 200°C, put in the permeation box, heat it to 820°C at a rate of 8°C / min and hold for 10 hours. After the holding is completed, take it out after cooling in the furnace to obtain the coated sample. The coating thickness of the furnace tube is 106 μm, and the surface components are mainly aluminum oxide and aluminum nitride, and the cerium content is 1.4%.

[0109] Comparative Example 4

[0110] After degreasing and derusting the surface of the HK40 alloy, put it into the permeation box together with the pack cementation agent (200-mesh powder). The components of the permeation agent are (by mass percentage): 20% silicon powder, 20% chromium powder, 3% ammonium chloride, 0.4% sodium fluoride, 0.2% cerium oxide, and the balance is high-temperature calcined Al 2 O 3 powder. Put the sealed permeation box into a muffle furnace and hold it at 1000°C for 2 h. Cool it to room temperature at a rate of 10°C / min, take out the permeation box, soak the alloy in a 20% concentration KOH aqueous solution, then wash it with deionized water and dry it. Subsequently, put the alloy into a tubular heat treatment furnace, and use a mixed gas of 60% argon, 10% hydrogen and 30% methanol, and continuously introduce it into the heat treatment furnace. Heat it to 950°C at a heating rate of 15°C / min and hold for 10 h. After the holding is completed, cool it to room temperature in the furnace and stop the gas supply.

[0111] Test Example 1

[0112] The coking performance evaluation experiment was carried out on the coating specimens prepared in Comparative Example 1 and Example 3. The coking inhibition rates of each coating specimen are shown in Table 1.

[0113] Table 1

[0114]

[0115] Test Example 2

[0116] The stability test was carried out on the catalytic coating specimens of Comparative Example 1 and Example 3. The coked specimens obtained from the test were subjected to air calcination treatment to fully remove the coke attached thereto. The specific calcination conditions were as follows: the temperature was raised to 900 °C at a heating rate of 5 °C / min in an air atmosphere, and maintained at this temperature for 5 h. Then, the calcination furnace was naturally cooled to room temperature, the specimens were taken out and subjected to EDS elemental analysis. The analysis results are shown in Table 2.

[0117] Table 2

[0118]

[0119] Test Example 3

[0120] The carburization and elemental analysis characterization of the coatings of Example 3 and Comparative Examples 1 to 4 were carried out using a Hitachi S3400 scanning electron microscope, and the electron microscope scanning voltage was 15 kV.

[0121] The statistical results of the mass percentage content of the surface elements of the coatings of Example 3 and Comparative Examples 1 to 4 are shown in Table 3.

[0122] Table 3

[0123]

[0124] It can be seen from Table 1 that the catalytic coating specimens prepared by the method of the present invention have better coking inhibition effect than the catalytic coating specimens prepared by the traditional powder embedding method. The coking inhibition rate of the coating specimens prepared by the present invention is 3 percentage points higher than that of the traditional method. On the one hand, this is because after the element diffusion rate is optimized, the overall co-permeation effect of the coating elements is improved; on the other hand, it is also because the heat penetration efficiency of the catalytic active components of the coating specimens prepared by the method of the present invention is higher than that of the traditional method. This can also be seen from the EDS elemental analysis results of the coating surface. The content of the catalytic active elements in the coating prepared by the method of the present invention is 0.4 percentage points higher than that of the traditional method.

[0125] As can be seen from Table 2, after the coating specimens prepared by the method of the present invention are used in multiple reaction-coking cycles, the content of catalytic active elements in the coating decreases less than that of the catalytic coating prepared by the traditional method. After the stability test, the catalytic active component in the catalytic coating specimen prepared by the present invention decreases from 2.1 wt% to 1.82 wt%.

[0126] As can be seen from Table 3, the carbon donors used in the present invention contain higher Al and Si elements compared to the coatings prepared by using only graphite or only carbon-containing compounds or introducing carbon-containing gases as carbon donors. This shows that the carbon donors used in the present invention can produce reducing gases and form an equilibrium relationship with the graphite components activated at high temperature. The stable carbon concentration in the co-permeation system can ensure the inhibitory effect of carbon elements on the diffusion of elements such as Si and Al into the workpiece during the high-temperature co-permeation process. Compared with other methods, the carbon donors used in the present invention have a more obvious inhibitory effect on the diffusion of Al and Si elements.

[0127] The coating furnace tube prepared in Example 11 and a Cr35Ni45Nb alloy furnace tube of the same specification were subjected to an anti-carburization experiment. A mixed gas of 2% CH 4 -98% H 2 was used, and the holding time at 1050 °C was 120 h. The weight gain due to carburization was only about 1 / 10 of that of the uncoated furnace tube.

[0128] Through Figure 1 and Figure 2 it can be seen that the carburization effect of the coated furnace tube is effectively inhibited compared to the uncoated furnace tube. In summary, through analysis, the coated furnace tube prepared by the present invention has excellent high-temperature protection performance for the substrate. At the same time, it has an efficient conversion function for coke.

[0129] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be considered within the protection scope of the present invention.

Claims

1. A co-permeation agent, characterized in that, by mass percentage, it includes: 10 - 50% of aluminum-providing agent, 0.5 - 4% of activator, 0.5 - 2.5% of silicon powder, 0.2 - 4% of carbon-providing agent, 0.5 - 8% of coke-removing agent, and the balance of alumina.

2. The co-permeation agent according to claim 1, characterized in that, the carbon-providing agent includes carbon powder and / or carbon-containing compound.

3. The co-permeation agent according to claim 2, characterized in that, the mass percentage of the carbon-containing compound in the carbon-providing agent ≤ 85%.

4. The co-permeation agent according to claim 2, characterized in that, the carbon-containing compound includes one or a combination of two of ammonium bicarbonate and ammonium acetate.

5. The co-permeation agent according to claim 2, characterized in that, the carbon powder includes graphite powder.

6. The co-permeation agent according to claim 1, characterized in that, the coke-removing agent includes one or a combination of two or more of potassium aluminosilicate, barium carbonate, potassium carbonate, and cerium oxide.

7. The co-permeation agent according to claim 1, characterized in that, the aluminum-providing agent is one or a combination of two or more of pure aluminum powder, ferro-aluminum alloy, aluminum-silicon alloy, and aluminum-chromium alloy.

8. The co-permeation agent according to claim 1, characterized in that, the powder particle size of the co-permeation agent is -150 mesh to +400 mesh.

9. The co-permeation agent according to claim 1, characterized in that, the activator is one or a combination of two or more of silicon chloride, aluminum fluoride, and aluminum chloride.

10. A method for preparing a coating, characterized in that, it includes: performing a purification treatment on the surface of the substrate to obtain a treated sample piece; performing a sealing treatment on the co-permeation agent according to any one of claims 1 to 9 and the treated sample in a permeation box to obtain an intermediate sample piece; performing an element diffusion chemical heat treatment on the intermediate sample piece.

11. The preparation method according to claim 10, characterized in that, the element diffusion chemical heat treatment is performed in a heat treatment furnace; preferably, the furnace inlet temperature is 150 - 350 °C; preferably, the holding temperature is 700 - 950 °C, and the time is 4 - 10 h; preferably, the heating rate is 5 - 10 °C / s.

12. The preparation method according to claim 10, characterized in that, the volume percentage of the co-permeation agent in the permeation box is 40 - 60%.

13. The preparation method according to claim 10, characterized in that, the material of the substrate is heat-resistant steel or superalloy.

14. The preparation method according to claim 10, characterized in that, by mass percentage, the substrate includes: Ni: 8 - 50%, Cr: 12 - 45%, C: 0.2 - 1.5%, Si: 0 - 3%, Mn: 0 - 2%, P: 0 - 0.1%, S: 0 - 0.1%, Nb: 0 - 2%, with the balance being Fe.

15. A coating is prepared from the co-permeation agent according to any one of claims 1 to 9, or obtained by the preparation method according to any one of claims 10 to 14.

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