CN113046815A - Preparation method of double-pulse electroplated nickel-graphene composite coating of continuous casting crystallizer - Google Patents

Preparation method of double-pulse electroplated nickel-graphene composite coating of continuous casting crystallizer Download PDF

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CN113046815A
CN113046815A CN202110138369.9A CN202110138369A CN113046815A CN 113046815 A CN113046815 A CN 113046815A CN 202110138369 A CN202110138369 A CN 202110138369A CN 113046815 A CN113046815 A CN 113046815A
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nickel
electroplating
graphene composite
composite coating
graphene
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冯团辉
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Xuchang University
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Xuchang University
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    • CCHEMISTRY; METALLURGY
    • C25ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25DPROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D15/00Electrolytic or electrophoretic production of coatings containing embedded materials, e.g. particles, whiskers, wires
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22DCASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/04Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
    • B22D11/059Mould materials or platings
    • CCHEMISTRY; METALLURGY
    • C25ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25DPROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D3/00Electroplating: Baths therefor
    • C25D3/02Electroplating: Baths therefor from solutions
    • C25D3/12Electroplating: Baths therefor from solutions of nickel or cobalt
    • CCHEMISTRY; METALLURGY
    • C25ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25DPROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/18Electroplating using modulated, pulsed or reversing current
    • CCHEMISTRY; METALLURGY
    • C25ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25DPROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/34Pretreatment of metallic surfaces to be electroplated

Abstract

The invention discloses a preparation method of a double-pulse electroplated nickel-graphene composite coating of a continuous casting crystallizer, which comprises the following steps: step S1, electroplating pretreatment of the crystallizer copper plate; step S2, preparing a graphene oxide solution by using a Hummers method; step S3, electroplating a nickel interface electroplated layer; step S4, double-pulse electroplating of the nickel-graphene composite coating; s5, carrying out reduction treatment on the nickel-graphene composite coating; s6, when the reduced thickness of the nickel-graphene composite plating layer does not reach the design thickness, executing S4 and S5; when the design thickness is reached, executing the next step; step S7, after the electroplating is finished, hydrogen removal and stress removal treatment are carried out; the raw materials of the plating solution such as graphene oxide, sodium saccharin, sodium allylsulfonate, softening agent and the like are continuously added in the electroplating process, so that the internal performance of the electroplated layer is more uniform and consistent, the heat-conducting performance in a high-temperature area is uniform, the overall abrasion resistance of the electroplated layer is consistent, the surface quality of the produced billet is superior, and the final corrosion resistance of the electroplated layer can be further improved.

Description

Preparation method of double-pulse electroplated nickel-graphene composite coating of continuous casting crystallizer
Technical Field
The invention belongs to the field of electroplating, and particularly relates to a preparation method of a double-pulse electroplating nickel-graphene composite coating of a continuous casting crystallizer.
Background
The continuous casting crystallizer is the core equipment of the whole continuous casting production, and the quality of the continuous casting crystallizer directly influences the quality of a casting blank and the operation efficiency of a continuous casting machine. When the surface of the continuous casting crystallizer works, the continuous casting crystallizer is directly contacted with high-temperature liquid molten steel with the temperature of more than 1500 ℃, is subjected to the corrosion of the molten steel and the action of complex thermal stress, and is required to have the performances of high mechanical strength, good thermal conductivity, alternating thermal stress resistance, high hardness, high wear resistance, corrosion resistance and the like, so the surface of the crystallizer generally needs to be treated by a plating layer. In the existing crystallizer surface treatment technology, the technology is mature, the equipment investment is low, the production cost is low, and the utilization rate of raw materials is high. Wherein, the electroplated single metal coating, such as the conventional pure Ni coating, has good bonding force with the matrix, but the coating has low hardness and is not wear-resistant, thereby influencing the service life of the crystallizer; the binary or ternary composite plating layers of Ni-Co and the like have long service life, but have high Co content, high cost, larger alloy brittleness, poor alternating thermal stress resistance, poor corrosion resistance, limited application and various production procedures.
Disclosure of Invention
The invention provides a preparation method of a double-pulse electroplated nickel-graphene composite coating of a continuous casting crystallizer, which solves the problems.
In order to solve the above problems, the technical scheme provided by the invention is as follows: the preparation method of the double-pulse electric nickel-graphene composite coating of the continuous casting crystallizer comprises the following steps:
step S1, electroplating pretreatment of the crystallizer copper plate: sequentially degreasing and deoiling a continuous casting crystallizer copper plate matrix, mechanically blasting sand, electrolytically degreasing and deoiling, fixing an electroplating auxiliary tool, and performing hydrochloric acid spraying and activating treatment;
step S2, preparing a graphene oxide solution by using a Hummers method: taking natural flake graphite as a raw material, mixing the natural flake graphite with concentrated sulfuric acid, NaNO3 and KMnO4 for reaction, and preparing a graphene oxide solution by adopting a Hummers method;
step S3, electroplating nickel interface electroplated layer: using a crystallizer copper plate as a cathode and a nickel cake as an anode, in a plating bath of a nickel-containing composite plating solution without graphene oxide, adjusting the pH value of the plating solution to 4.0-5.5 by sulfamic acid, controlling the temperature to be 45 +/-5 ℃, and stirring by using a mechanical pump; firstly, DC plating a pre-plated nickel layer with a certain thickness (0.1-1mm) to ensure the bonding strength;
step S4, double-pulse electroplating of the nickel-graphene composite coating: step S4, preparing 50-500mg/L graphene oxide solution again in the plating tank, adjusting the pH value of the plating solution to 4.0-5.5 by sulfamic acid, controlling the temperature to be 45 +/-5 ℃, fully and uniformly stirring, electroplating a nickel-graphene composite plating layer by adopting double pulses, and automatically stopping electroplating for one period when the thickness of the nickel-graphene composite plating layer reaches a certain thickness of 20-25 mu m;
and step S5, reduction treatment of the nickel-graphene composite coating: lifting the crystallizer copper plate obtained in the step S4 after the electroplating is stopped out of the electroplating bath, putting the crystallizer copper plate into a hydrazine hydrate solution with the temperature of 80-90 ℃ and the concentration of 1-3%, and lifting out after the heat preservation reaction for 10-20 min;
step S6, when the reduced thickness of the nickel-graphene composite plating layer does not reach the design thickness, executing steps S4 and S5; when the reduced thickness of the nickel-graphene composite coating reaches the designed thickness, executing the next step;
further, the design thickness is between 0.2mm and 2 mm.
And step S7, after the electroplating is finished, the crystallizer copper plate is subjected to heat preservation for 3 hours at the temperature of 250-300 ℃, and hydrogen removal and stress removal treatment are carried out to ensure the service performance.
Preferably, the nickel-graphene composite coating contains 99-99.5% of nickel and 0.5-1% of graphene by mass, and the thickness of the nickel-graphene composite coating is 0.2-3 mm.
Preferably, when the crystallized copper plate interface nickel-plating interface electroplated layer is electroplated, adding the graphene oxide when the nickel interface electroplated layer reaches a certain preset thickness.
Further, a thickness of 50 μm is preset.
Further, the method for adding graphene oxide comprises the following steps: adding a graphene oxide solution into the electroplating bath, preparing the concentration of the plating bath according to 100mg/L, simultaneously supplementing raw materials such as saccharin sodium, sodium allylsulfonate, sodium dodecyl sulfate, a softening agent and the like, ensuring that the actual concentration reaches the set concentration, and stirring for 20 minutes by using a mechanical pump to start electroplating.
Further, the nickel composite electroplating solution comprises the following components: 50-200mg/L of graphene oxide, 250-500 g/L of nickel sulfamate, 10-30 g/L of nickel chloride, 3-10 g/L of nickel bromide, 20-40 g/L of boric acid, 2-5 g/L of saccharin sodium, 0.5-3 g/L of sodium allylsulfonate, 0.2-1 g/L of sodium dodecyl sulfate and 5-10ml/L of a softening agent.
Further, a method for adding sodium dodecyl sulfate to the nickel composite electroplating solution comprises the following steps: the surface tension of the nickel composite plating solution is detected before plating, and then sodium dodecyl sulfate is added once before plating according to the detection result of the surface tension of the nickel composite plating solution, so that the surface tension of the plating solution is controlled to be 25-32 mN/m.
Preferably, in the nickel composite plating solution of step S3, during the double pulse plating of the nickel-graphene composite plating layer of step S4, the saccharin sodium, the sodium allylsulfonate, and the softening agent are continuously added to the predetermined amounts in the amounts of 3 to 20g/KAH, 15 to 80g/KAH, and 1.5 to 10g/KAH, respectively, and are additionally added when the detected content is less than 8 to 10% of the predetermined amount.
Further, the specific electroplating process of the double-pulse electroplating nickel-graphene composite coating comprises the following steps: using a crystallizer copper plate as a cathode and a nickel cake as an anode, adjusting the pH value of the electroplating solution to 4.0-5.5 by sulfamic acid in a plating tank of the graphene oxide and nickel-containing electroplating solution, controlling the temperature to be 45 +/-5 ℃, stirring by a mechanical pump,
further, the pulse power supply is a double-pulse power supply with alternating positive and negative waveform currents, the pulse frequency is 1000Hz, the positive pulse current density is controlled to be 5.0-10.0A/dm 2, the positive pulse time is 100ms, the reverse pulse current density is 0.2-1.4A/dm2, the reverse pulse time is 10ms, the positive duty ratio is 30-40%, and the reverse duty ratio is 20-30%.
Preferably, the reduction treatment process of the nickel-graphene composite plating layer in step S6 is as follows: and (3) lifting out the crystallizer copper plate with the nickel-graphene composite coating reaching a certain thickness, putting the crystallizer copper plate into a hydrazine hydrate solution prepared in advance, reacting at the temperature of 80-90 ℃ for 10-20 minutes, lifting out, and then lifting into an electroplating bath again for electroplating.
Preferably, the concentration of the prepared hydrazine hydrate solution is 1-3%, and the holding container is a steel container.
Preferably, in step S4: and when the thickness of the nickel-graphene composite coating does not reach the preset value, the crystallizer copper plate treated by hydrazine hydrate is re-placed into the electroplating bath, and the step S4 of double-pulse electroplating of the nickel-graphene composite coating is continuously executed until the thickness of the nickel-graphene composite coating reaches the design requirement.
Preferably, the degreasing and deoiling treatment of the copper plate matrix of the continuous casting crystallizer in the step S1 is carried out for 10-20 minutes by adopting hot alkaline solution at 50-60 ℃.
Preferably, the Hummers method in step S2 is to prepare the graphene oxide solution by:
the Graphite Oxide (GO) solution is prepared by mixing and reacting 500-mesh 1000-mesh natural crystalline flake graphite with the purity of more than 99.0% with concentrated sulfuric acid, NaNO3 and KMnO 4.
Preferably, the ratio of graphite: concentrated sulfuric acid: NaNO 3: the proportion of KMnO4 is as follows: 23: 1: and 6, carrying out.
Preferably, the nickel-graphene composite coating contains 99-99.5% of nickel and 0.5-1% of graphene by mass, and the thickness of the nickel-graphene composite coating is 0.2-3 mm.
Compared with the prior art, the method has the beneficial effects that by adopting the scheme, the method for preparing the double-pulse electroplated nickel-graphene composite coating of the continuous casting crystallizer provided by the invention solves the problems of incomplete reduction and low compactness of graphene oxide in the traditional graphene-nickel coating by adopting a double-pulse electroplating method and a multi-layer step composite electroplating method, the hardness of the composite coating can be flexibly adjusted according to the requirement, the prepared nickel-graphene composite coating has high bonding strength with a substrate, the coating structure is compact and good in stability, the crystal grains of the composite coating are obviously refined compared with a pure nickel coating, the elongation change is small, the hardness of the composite coating is obviously improved, the microhardness can be adjusted within the range of 600 + 1000HV, the concentration of the graphene oxide is higher, and the hardness of the composite coating is higher;
the friction coefficient of the nickel-graphene composite coating is reduced by 10-20% compared with that of a pure nickel coating, and the friction coefficient is reduced by 0.05-0.15, because the prepared graphene oxide contains multilayer graphite, the self-lubricating property of the multilayer graphite can obviously reduce the friction coefficient of the coating, the wear resistance is obviously improved, and the nickel-graphene composite coating has obvious benefits on prolonging the service life of a continuous casting crystallizer;
the nickel-graphene composite coating has good hot corrosion resistance and thermal cracking resistance under high temperature conditions, has good thermal conductivity, and does not influence the heat transfer process of a crystallizer. The addition of the flaky graphene hinders the diffusion of high-temperature metal atoms, so that the excellent anti-corrosion capability is shown, the service life of the crystallizer copper plate is prolonged, and the service life is prolonged by more than 30%.
The nickel-graphene composite plating layer has obvious cost advantage, the natural graphite is used as the raw material to prepare the graphene oxide solution, the cost is low, the concentration of the added graphene solution is only 50-500mg/L, and the hardness of the composite plating layer can be increased by 50-100HV when the concentration is increased by 100 mg/L; when the concentration of the graphene oxide in the plating solution is 50mg/L, the surface hardness of the composite plating layer can reach 500 plus 600HV, and when the concentration of the graphene oxide in the plating solution reaches 500mg/L, the surface hardness of the composite plating layer can reach 900 plus 1000HV, so that compared with the traditional alloy plating layers of Ni-Co, Ni-CO-W, Ni-Co-Mn and the like, the cost is obviously reduced, the addition of precious metals is reduced, the cost is reduced, and the service life is prolonged;
the nickel-graphene electroplating layer has the advantages of low manufacturing cost, high hardness, high elongation, good thermal conductivity, alternating thermal stress resistance, excellent high-temperature corrosion resistance and excellent wear resistance, is suitable for continuous casting production under various complex conditions, reduces the cost by about 30 percent compared with a nickel-cobalt electroplating layer, and prolongs the service life by more than 30 percent;
the invention takes the nickel cake as the anode, limits the mass fraction of the nickel cake to be 0.010-0.05%, can activate the anode material nickel, reduces the activation potential of the nickel anode and reduces the internal stress of the electroplated layer;
the raw materials of graphene oxide, saccharin sodium, sodium allylsulfonate, softening agent and the like in the plating solution are continuously added in the electroplating process, the internal performance of the electroplated layer prepared by the method is more uniform and consistent, the heat conduction performance of a high-temperature area is more uniform, the whole abrasion resistance of the electroplated layer is more consistent, the surface quality of the produced billet is more excellent, and the final corrosion resistance of the electroplated layer is further improved.
Detailed Description
In order to facilitate an understanding of the invention, the invention is described in more detail and preferred embodiments are given below with reference to specific examples. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
Graphene is a new material which is discovered only in 2004 and is formed by tightly packing carbon atoms into a single-layer two-dimensional honeycomb lattice structure, is one of the known materials with the highest strength, has good toughness and can be bent, the theoretical Young modulus of the graphene reaches 1.0TPa, and the inherent tensile strength is 130 GPa. The graphene has very good heat conduction performance, and the heat conduction coefficient of pure defect-free single-layer graphene is as high as 5300W/mK, so that the graphene is a carbon material with the highest heat conduction coefficient. Meanwhile, the graphene also has high corrosion resistance and high temperature resistance, the pyrolysis temperature of the C-C bond forming the graphene is above 3000 ℃, the graphene does not react with acid and alkali, and the graphene is stable in the atmospheric environment. The graphene serving as a material for enhancing the strength of the nickel-based plating layer can not only increase the strength and the wear resistance of the plating layer, but also has good heat conductivity and high temperature resistance without influencing the continuous casting production, and is an ideal plating layer material of the copper plate of the continuous casting crystallizer. The graphene can be prepared from natural graphite by a chemical method, and has the advantages of wide source, low price and higher economic feasibility.
Example 1: the preparation method of the double-pulse electroplated nickel-graphene composite coating of the continuous casting crystallizer comprises the following steps:
step S1, electroplating pretreatment of the crystallizer copper plate: sequentially degreasing and deoiling a continuous casting crystallizer copper plate matrix, mechanically blasting sand, electrolytically degreasing and deoiling, fixing an electroplating auxiliary tool, and performing hydrochloric acid spraying and activating treatment;
step S2, preparing a graphene oxide solution by using a Hummers method: taking natural flake graphite as a raw material, mixing the natural flake graphite with concentrated sulfuric acid, NaNO3 and KMnO4 for reaction, and preparing a graphene oxide solution by adopting a Hummers method;
step S3, electroplating nickel interface electroplated layer: using a crystallizer copper plate as a cathode and a nickel cake as an anode, in a plating bath of a nickel-containing composite plating solution without graphene oxide, adjusting the pH value of the plating solution to 4.0-5.5 by sulfamic acid, controlling the temperature to be 45 +/-5 ℃, and stirring by using a mechanical pump; firstly, DC plating a pre-plated nickel layer with a certain thickness (0.1-1mm) to ensure the bonding strength;
further, in order to enhance the bonding strength between the crystalline copper plate and the plating layer, when the nickel-plated interface electroplated layer is electroplated on the interface of the crystalline copper plate, graphene may not be added temporarily, and graphene oxide is added when the nickel-plated interface electroplated layer reaches a certain thickness;
further, the nickel composite electroplating solution comprises the following components: 50-200mg/L of graphene oxide, 250-500 g/L of nickel sulfamate, 10-30 g/L of nickel chloride, 3-10 g/L of nickel bromide, 20-40 g/L of boric acid, 2-5 g/L of saccharin sodium, 0.5-3 g/L of sodium allylsulfonate, 0.2-1 g/L of sodium dodecyl sulfate and 5-10ml/L of a softening agent;
further, a method for adding sodium dodecyl sulfate to the nickel composite electroplating solution comprises the following steps: the surface tension of the nickel composite plating solution is detected before plating, and then sodium dodecyl sulfate is added once before plating according to the detection result of the surface tension of the nickel composite plating solution, so that the surface tension of the plating solution is controlled to be 25-32 mN/m.
Step S4, double-pulse electroplating of the nickel-graphene composite coating: step S4, preparing 50-500mg/L graphene oxide solution again in the plating tank, adjusting the pH value of the plating solution to 4.0-5.5 by sulfamic acid, controlling the temperature to be 45 +/-5 ℃, fully and uniformly stirring, electroplating a nickel-graphene composite plating layer by adopting double pulses, and automatically stopping electroplating for one period when the thickness of the nickel-graphene composite plating layer reaches a certain thickness of 20-25 mu m;
and step S5, reduction treatment of the nickel-graphene composite coating: lifting the crystallizer copper plate obtained in the step S4 after the electroplating is stopped out of the electroplating bath, putting the crystallizer copper plate into a hydrazine hydrate solution with the temperature of 80-90 ℃ and the concentration of 1-3%, and lifting out after the heat preservation reaction for 10-20 min; the purpose of the step is to reduce the functional groups and metal oxides which are not reduced by the graphene oxide in the composite coating and increase the compactness of the coating;
s6, when the reduced thickness of the nickel-graphene composite plating layer does not reach the design thickness, executing S4 and S5; when the reduced thickness of the nickel-graphene composite coating reaches the designed thickness, executing the next step;
and step S7, after the electroplating is finished, the crystallizer copper plate is subjected to heat preservation for 3 hours at the temperature of 250-300 ℃, and hydrogen removal and stress removal treatment are carried out to ensure the service performance.
In example 2, when a nickel interface plating layer is plated on the interface of the crystalline copper plate, graphene oxide is added when the thickness of the nickel interface plating layer reaches a certain preset thickness.
The method for adding graphene oxide in step S4 includes: adding a graphene oxide solution into the electroplating bath, preparing the concentration of the plating solution according to 100mg/L, simultaneously supplementing raw materials such as saccharin sodium, sodium allylsulfonate, sodium dodecyl sulfate, a softening agent and the like, ensuring that the actual concentration reaches the set concentration, and stirring for 20 minutes by using a mechanical pump to start electroplating.
Example 3, in the nickel composite plating solution of step S3, during the double pulse plating of the nickel-graphene composite plating layer of step S4, saccharin sodium, sodium allylsulfonate, and softener were continuously added to predetermined amounts in the amounts of 3 to 20g/KAH, 15 to 80g/KAH, and 1.5 to 10g/KAH, respectively, and were then added when the detected content was less than 8 to 10% of the predetermined amount.
Example 4, the specific electroplating process of the double-pulse electroplating of the nickel-graphene composite plating layer in step S4 is as follows: using a crystallizer copper plate as a cathode and a nickel cake as an anode, adjusting the pH value of the electroplating solution to 4.0-5.5 by sulfamic acid in a plating bath of the graphene oxide and nickel-containing composite electroplating solution, controlling the temperature to be 45 +/-5 ℃, stirring by a mechanical pump,
further, the pulse power supply is a double-pulse power supply with alternating positive and negative waveform currents, the pulse frequency is 1000Hz, the positive pulse current density is controlled to be 5.0-10.0A/dm 2, the positive pulse time is 100ms, the reverse pulse current density is 0.2-1.4A/dm2, the reverse pulse time is 10ms, the positive duty ratio is 30-40%, and the reverse duty ratio is 20-30%.
Example 5, the reduction treatment process of the nickel-graphene composite plating layer in step S6 is as follows: lifting out a crystallizer copper plate with a nickel-graphene composite coating layer reaching a certain thickness, putting the crystallizer copper plate into a hydrazine hydrate solution prepared in advance, reacting at the temperature of 80-90 ℃ for 10-20 minutes, then lifting out, and then lifting into an electroplating bath again for electroplating; through the strong reduction treatment of hydrazine hydrate, the functional groups and metal oxides of graphene oxide in the plating layer can be further reduced, and the confidentiality of the plating layer is increased.
Further, the concentration of the prepared hydrazine hydrate solution is 1-3%, and the holding container is a steel container.
Further, when the thickness of the nickel-graphene composite plating layer does not reach the preset value in the step S4, the crystallizer copper plate treated by hydrazine hydrate is transferred into the electroplating bath again, and the step S4 of double-pulse electroplating of the nickel-graphene composite plating layer is continuously performed until the thickness of the nickel-graphene composite plating layer reaches the design requirement.
Example 6, degreasing and degreasing the copper plate matrix of the continuous casting crystallizer in step S1, and treating the copper plate matrix with hot alkaline solution at 50-60 ℃ for 10-20 minutes.
Preferably, the Hummers method in step S2 is to prepare the graphene oxide solution by:
the Graphite Oxide (GO) solution is prepared by mixing and reacting 500-mesh 1000-mesh natural crystalline flake graphite with the purity of more than 99.0% with concentrated sulfuric acid, NaNO3 and KMnO 4.
Further, graphite: concentrated sulfuric acid: NaNO 3: the proportion of KMnO4 is as follows: 23: 1: and 6, carrying out.
Example 7: the method for preparing the graphene oxide solution by using the Hummers method comprises the following steps:
the first step is as follows: introducing 460ml of concentrated sulfuric acid (more than or equal to 95.0%) into a beaker, cooling the beaker to 0 ℃, respectively adding 20g of natural flake graphite and 10g of NaNO3 (the purity is more than or equal to 99.0%) under the stirring action of a magnetic stirrer, uniformly mixing the two solids, then gradually adding 60g of KMnO4 (the purity is more than or equal to 99.0%) into the beaker while stirring, controlling the temperature of the reaction solution to be between 5 and 15 ℃, and completing the reaction at the low temperature stage after the reaction solution is added and stirred for 0.5 to 1 hour after the temperature of the reaction solution is slowly increased and the temperature of the KMnO4 is prevented from being too high and causing the cup overflow phenomenon. The above quantities can be increased or decreased according to proportion;
the second step is that: after the low-temperature reaction is finished, placing the beaker filled with the reaction product in a constant-temperature water bath, gradually heating to 35 ℃, and continuing stirring for reaction for 20-40min when the temperature is raised to about 35 ℃, thus finishing the oxidation medium-temperature reaction of the graphite;
the third step: and in the high-temperature reaction stage of the graphite, gradually and slowly heating the water bath to 100 ℃, stirring in the whole heating process, adding a certain amount of deionized water to control the reaction speed if the reaction speed is too high, heating to 100 ℃, then continuously stirring for 30min until the graphite is completely oxidized, gradually changing the solution from black to golden suspension, adding deionized water to dilute the reaction solution to 900-1000 ml, then adding 10-30ml of 5% dioxygen (H2O2), and stirring in the water bath at 100 ℃ for reaction for 10-20min to promote the complete oxidation of the graphite.
The fourth step: finally, filtering the oxidized graphene solution subjected to the high-temperature reaction of the graphite by using filter paper while the solution is hot;
further, the filtering method comprises the following steps:
step B1, washing with 5% hydrochloric acid (HCl),
step B2, fully washing with deionized water until the filtrate is free of SO42- (detected by BaCI2 solution) and Cl- (detected by AgNO3 solution);
and step B3, dissolving the filtered graphene oxide in 2000ml of ionized water, heating to 80 ℃, putting the graphene oxide into an ultrasonic cleaning machine for ultrasonic treatment for 2-3 hours, promoting the undissociated graphene to be further dispersed, and increasing the dispersion uniformity of the graphene.
Through the steps, the concentration of the yellow graphene oxide solution uniformly dispersed in water is about 10g/L, and the solution is sealed and stored, and is diluted according to the proportion when in use. The graphene oxide solution has good stability, and no matter how long the graphene oxide solution is kept stand, the graphene oxide solution cannot be precipitated or layered, namely the qualified graphene oxide solution is obtained.
In the double-pulse electroplating process in the nickel composite electroplating solution, saccharin sodium, sodium allylsulfonate and a softening agent are continuously added to a specified amount according to the adding amounts of 3-20g/KAH, 15-80g/KAH and 1.5-10g/KAH respectively, and 8-10% of the detected content is lower than the specified amount and then is supplemented.
Further, according to the requirement of the thickness of the copper plate plating layer of the crystallizer, the electroplating is circularly carried out according to the step S4 and the step S5 until the thickness of the plating layer reaches the requirement.
Furthermore, in the double-pulse electroplating process, stirring is required to be kept constantly, graphene oxide is supplemented timely, and the stability of the concentration of the graphene oxide in the electroplating process is ensured. And supplementing the graphene oxide once according to the total electroplating thickness of 50 mu m, wherein the supplementing amount is 0.1-0.2g/L each time.
Furthermore, the hardness of the nickel-graphene composite coating is in direct proportion to the concentration of the configured graphene oxide, the hardness is increased by about 50-100HV when the concentration of the graphene oxide is increased by 50mg/L, the concentration of the graphene oxide can be adjusted according to the design hardness requirement during electroplating, and the concentration of the graphene can be properly increased during the last coating, so that the surface hardness of the coating is ensured.
Further, the mass fraction of S in the nickel cake in the step S3 is 0.015-0.06%.
Note that: the nickel-graphene pre-plated layer, the thickness of the nickel-graphene composite plating layer and the hardness of the composite plating layer in the nickel-graphene plating layer can be designed according to needs, and the hardness of the nickel-graphene composite plating layer can also be designed according to a certain gradient.
Example 8: in order to ensure the bonding strength and toughness, the coating is divided into an interface nickel plating layer and a nickel-graphene composite coating, the total thickness is 0.5mm, the thickness of the nickel plating layer adjacent to the copper plate interface is 0.3mm, the thickness of the nickel-graphene composite coating is 0.2mm, the hardness of the composite coating is required to be gradually increased, and the surface hardness reaches 800 plus 900 HV. The specific production process comprises the following steps:
(1) firstly, preparing 10g/L graphene oxide dispersion liquid in batches by using a Hummers method, and storing for later use.
(2) Pretreatment of matrix electroplating: sequentially degreasing and deoiling a continuous casting crystallizer copper plate matrix, mechanically blasting sand, electrolytically degreasing and deoiling, fixing an electroplating auxiliary tool, and performing hydrochloric acid spraying and activating treatment;
(3) in the electroplating bath, nickel composite electroplating solution is prepared. The nickel composite electroplating solution comprises the following components: 350g/L of nickel sulfamate, 20g/L of nickel chloride, 4g/L of nickel bromide, 30g/L of boric acid, 3g/L of sodium saccharin, 1.5g/L of sodium allylsulfonate, 0.6g/L of sodium dodecyl sulfate and 8ml/L of softener. In order to enhance the bonding strength between the crystalline copper plate and the composite coating, graphene oxide is not added temporarily when the interface of the crystalline copper plate is electroplated with the nickel coating.
(4) After the surface tension of the plating solution was measured before plating, sodium lauryl sulfate was added thereto at a time before plating based on the result of the surface tension measurement, so that the surface tension of the plating solution was controlled to 27 mN/m.
(5) Electroplating a crystalline copper plate interface with a nickel coating: the method comprises the steps of taking a crystallizer copper plate as a cathode and a nickel cake as an anode, adjusting the pH value of an electroplating solution to be 4.0-5.5 by sulfamic acid in a plating tank of the nickel-containing electroplating solution without graphene oxide, controlling the temperature to be 45 +/-5 ℃, stirring by a mechanical pump, controlling the pulse frequency to be 1000Hz, the forward pulse current density to be 8A/dm2, the forward pulse time to be 100ms, the reverse pulse current density to be 0.2A/dm2, the reverse pulse time to be 10ms, the forward duty ratio to be 40% and the reverse duty ratio to be 20% in a pulse power supply, controlling the thickness of the plating layer according to the current passing amount, and automatically stopping electroplating when the thickness of the plating layer reaches 0.2 mm.
(6) Adding a graphene oxide solution into the electroplating bath, preparing the concentration of the plating solution according to 100mg/L, simultaneously supplementing raw materials such as saccharin sodium, sodium allylsulfonate, sodium dodecyl sulfate, a softening agent and the like, ensuring that the actual concentration reaches the set concentration, and stirring for 20 minutes by using a mechanical pump to start electroplating.
(7) In another steel container, preparing hydrazine hydrate aqueous solution according to 2% concentration, and heating to 80-90 deg.C for standby.
(8) Electroplating a nickel-graphene composite coating: the method comprises the steps of using a crystallizer copper plate as a cathode, using a nickel cake as an anode, adjusting the pH value of an electroplating solution to be 4.0-5.5 by sulfamic acid in a plating tank of a nickel-containing electroplating solution with the graphene oxide concentration of 100mg/L, controlling the temperature to be 45 +/-5 ℃, keeping a mechanical pump for stirring in the electroplating process, using a pulse power supply as a double-pulse power supply with alternating positive and negative waveform currents, controlling the pulse frequency to be 1000Hz, the forward pulse current density to be 8A/dm2, the forward pulse time to be 100ms, the reverse pulse current density to be 0.5A/dm2, the reverse pulse time to be 10ms, the forward duty ratio to be 40% and the reverse duty ratio to be 30%, controlling the thickness of a plating layer according to the current passing amount, and stopping electroplating.
(9) And (3) carrying out reduction treatment on the nickel-graphene composite coating, namely hanging out a crystallizer copper plate with the thickness of the nickel-graphene coating reaching 25 micrometers, hanging the crystallizer copper plate into a prepared 2% hydrazine hydrate solution, reacting at the temperature of 80-90 ℃ for 10 minutes, then hanging the crystallizer copper plate out, then hanging the crystallizer copper plate into an electroplating bath again, carrying out further electroplating according to the process of the step (8), and hanging the crystallizer copper plate into the hydrazine hydrate electroplating bath for reduction when the total thickness of the composite coating reaches 50 micrometers.
(10) When the nickel-graphene composite coating reaches 50 micrometers, most of graphene oxide prepared in the electroplating bath is generally consumed, and a graphene oxide solution needs to be supplemented. And (3) configuring the concentration of the oxidized graphite for the second time according to 200mg/L, stirring for 10-20 minutes, then putting the crystallizer copper plate into the plating tank again, performing electroplating and reduction according to the circulation of the steps S4 and S5, and controlling the concentration of the oxidized graphene in the plating tank to be 400mg/L when the final plated layer is 100 mu m. When graphene oxide is prepared, the graphene oxide remained in the previous coating is generally converted into 50mg/L, so that the phenomenon that the hardness of the coating is too high due to too high concentration of the prepared graphene oxide is prevented. The specific process concentration for controlling the concentration of the oxidized graphene and the concentration of different electroplated layers are shown in the following table:
in the electroplating process, except for supplementing the concentration of the graphene oxide, raw materials such as saccharin sodium, sodium allylsulfonate, sodium dodecyl sulfate, a softening agent, hydrazine hydrate and the like are continuously supplemented, so that the stable concentrations of the plating solution and the hydrazine hydrate in the electroplating and reducing processes are ensured. Sodium saccharin, sodium allyl sulfonate and softener were added in amounts of 5g/KAH, 20g/KAH and 150ml/KAH, respectively, to prescribed amounts. The hydrazine hydrate is supplemented in a manner that 0.5% of hydrazine hydrate needs to be newly supplemented every time the nickel-graphene plating layer with the thickness of 100 mu m is subjected to reduction treatment.
After the electroplating is finished, the crystallizer copper plate is kept at the temperature of 300 ℃ for 3h, and hydrogen removal and stress removal treatment are carried out to ensure the service performance.
The nickel-graphene composite coating of the copper plate of the continuous casting crystallizer prepared by the process steps has good binding force with a matrix, compact coating, high outer surface hardness, good inner layer toughness, average surface hardness of 892HV, gradually reduced hardness from the surface of the composite coating to the interface of the copper plate of the crystallizer, and increased toughness, and meets the requirements of the coating of the crystallizer on good hardness and good toughness. Meanwhile, the nickel-graphene coating on the surface of the coating contains multiple layers of graphene, so that the coating has good lubricity, the measured friction coefficient of the surface is about 0.50-0.52, and the friction coefficient is reduced by 0.10-0.15% compared with that of a pure nickel or Ni-Co coating, so that the problem of wear resistance of the coating is well solved. The nickel-graphene composite coating also shows good high-temperature corrosion resistance, the graphene has good high-temperature resistance, the corrosion speed of the composite coating is greatly reduced when the composite coating is in contact with liquid metal, the service life of the coating is greatly prolonged, and through field test tests, the thickness corrosion speed of the crystalline copper plate coating adopting the nickel-graphene composite coating is reduced by 36% compared with that of the traditional pure nickel coating, the service life of a continuous casting crystallizer is prolonged by more than 30%, the requirements of production practice are met, and the method has good market popularization value.
The coating of the copper plate of the continuous casting crystallizer adopts a pure nickel + graphene coating, but the method and the process can also be suitable for preparing a multi-alloy coating and a graphene composite coating of the copper plate of the continuous casting crystallizer, such as Ni-Co, Ni-Co-Mn, Ni-Co-Fe and other multi-alloy coatings, so that the multi-alloy coating and the graphene composite coating of the continuous casting crystallizer also belong to the protection range of the patent.
It should be noted that the above technical features are combined with each other to form various embodiments which are not listed above, and all the embodiments are regarded as the scope of the present invention described in the specification; also, modifications and variations may be suggested to those skilled in the art in light of the above teachings, and it is intended to cover all such modifications and variations as fall within the true spirit and scope of the invention as defined by the appended claims.

Claims (10)

1. The preparation method of the double-pulse electroplated nickel-graphene composite coating of the continuous casting crystallizer is characterized by comprising the following steps of:
step S1, electroplating pretreatment of the crystallizer copper plate: sequentially degreasing and deoiling a continuous casting crystallizer copper plate matrix, mechanically blasting sand, electrolytically degreasing and deoiling, fixing an electroplating auxiliary tool, and performing hydrochloric acid spraying and activating treatment;
step S2, preparing a graphene oxide solution by using a Hummers method: taking natural flake graphite as a raw material, mixing the natural flake graphite with concentrated sulfuric acid, NaNO3 and KMnO4 for reaction, and preparing a graphene oxide solution by a Hummers method;
step S3, electroplating nickel interface electroplated layer: using a crystallizer copper plate as a cathode and a nickel cake as an anode, in a plating bath of a nickel-containing composite plating solution without graphene oxide, adjusting the pH value of the plating solution to 4.0-5.5 by sulfamic acid, controlling the temperature to be 45 +/-5 ℃, and stirring by using a mechanical pump; firstly, plating a pre-plated nickel layer with a certain thickness (0.1-1mm) by adopting double-pulse electroplating to ensure the bonding strength;
step S4, double-pulse electroplating of the nickel-graphene composite coating: preparing 50-500mg/L of graphene oxide solution again in the electroplating bath in the step S3, adjusting the pH value of the electroplating solution to 4.0-5.5 by sulfamic acid, controlling the temperature to be 45 +/-5 ℃, fully and uniformly stirring, electroplating a nickel-graphene composite coating by adopting double pulses, and automatically stopping electroplating for one period when the thickness of the nickel-graphene composite coating reaches a certain thickness of 20-25 microns;
and step S5, reduction treatment of the nickel-graphene composite coating: lifting the crystallizer copper plate obtained in the step S4 after the electroplating is stopped out of the electroplating bath, putting the crystallizer copper plate into a hydrazine hydrate solution with the temperature of 80-90 ℃ and the concentration of 1-3%, and lifting out after the heat preservation reaction is carried out for 10-20 min;
s6, when the reduced thickness of the nickel-graphene composite plating layer does not reach the design thickness, executing S4 and S5; when the reduced thickness of the nickel-graphene composite coating reaches the designed thickness, executing the next step;
step S7, after the electroplating is finished, the crystallizer copper plate is insulated for 3 hours at the temperature of 250-300 ℃ for dehydrogenation and stress relief treatment.
2. The method for preparing a double-pulse electroplated nickel-graphene composite coating of a continuous casting crystallizer as claimed in claim 1, wherein when the interface nickel-plated interface electroplated coating of the crystallized copper plate is electroplated, the graphene oxide solution is added when the interface nickel-plated interface electroplated coating reaches a certain preset thickness.
3. The method for preparing a nickel-graphene composite plating layer by double pulse electroplating of a continuous casting crystallizer as claimed in claim 1, wherein in the nickel composite electroplating solution in step S3, during the double pulse electroplating of the nickel-graphene composite plating layer in step S4, saccharin sodium, sodium allylsulfonate and softener are continuously added to a predetermined amount according to the addition amounts of 3-20g/KAH, 15-80g/KAH and 1.5-10g/KAH, respectively, and are added when the detected content is lower than 8-10% of the predetermined amount.
4. The method for preparing the double-pulse electroplated nickel-graphene composite coating of the continuous casting crystallizer as claimed in claim 1, wherein the reduction treatment process of the nickel-graphene composite coating in step S6 is as follows: and (3) lifting out the crystallizer copper plate with the nickel-graphene composite coating layer reaching a certain thickness, putting the crystallizer copper plate into a prepared hydrazine hydrate solution, reacting at the temperature of 80-90 ℃ for 10-20 minutes, lifting out, and then lifting into an electroplating bath again for electroplating.
5. The method for preparing the double-pulse electroplated nickel-graphene composite coating of the continuous casting crystallizer as claimed in claim 5, wherein the concentration of the prepared hydrazine hydrate solution is 1-3%, and the holding container is a steel container.
6. The method for preparing a double-pulse electroplated nickel-graphene composite coating of a continuous casting crystallizer as claimed in claim 1, wherein in step S4: and when the thickness of the nickel-graphene composite coating does not reach a preset value, the crystallizer copper plate treated by hydrazine hydrate is transferred into the electroplating bath again, and the step S4 of double-pulse electroplating of the nickel-graphene composite coating is continuously executed until the thickness of the nickel-graphene composite coating reaches the design requirement.
7. The method for preparing a double-pulse electroplated nickel-graphene composite coating of a continuous casting crystallizer according to claim 1, wherein the degreasing and deoiling treatment of the copper plate matrix of the continuous casting crystallizer in the step S1 is performed for 10-20 minutes by using a hot alkaline solution at 50-60 ℃.
8. The method for preparing the nickel-graphene composite coating by double pulse electroplating of the continuous casting crystallizer according to claim 1, wherein the specific method for preparing the graphene oxide solution by the Hummers method in the step S2 is as follows: the Graphite Oxide (GO) solution is prepared by mixing and reacting 500-mesh 1000-mesh natural crystalline flake graphite with the purity of more than 99.0% with concentrated sulfuric acid, NaNO3 and KMnO 4.
9. The method for preparing the double-pulse electroplated nickel-graphene composite coating of the continuous casting crystallizer as claimed in claim 9, wherein the graphite: concentrated sulfuric acid: NaNO 3: the proportion of KMnO4 is as follows: 23: 1: and 6, carrying out.
10. The nickel-graphene composite coating according to any one of claims 1 to 9, wherein the nickel-graphene composite coating contains 99 to 99.5% of nickel and 0.5 to 1% of graphene by mass, and the thickness of the nickel-graphene composite coating is 0.2 to 3 mm.
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