CN113279030B - Molten salt electrodeposition method of niobium coating - Google Patents

Molten salt electrodeposition method of niobium coating Download PDF

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CN113279030B
CN113279030B CN202110567587.4A CN202110567587A CN113279030B CN 113279030 B CN113279030 B CN 113279030B CN 202110567587 A CN202110567587 A CN 202110567587A CN 113279030 B CN113279030 B CN 113279030B
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molten salt
coating
niobium
electroplating
plated part
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CN113279030A (en
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朱利安
白书欣
王震
叶益聪
胡双鹏
王淑祥
万红
李顺
唐宇
刘希月
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National University of Defense Technology
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    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D3/00—Electroplating: Baths therefor
    • C25D3/66—Electroplating: Baths therefor from melts
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D21/00—Processes for servicing or operating cells for electrolytic coating
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    • C25D21/14—Controlled addition of electrolyte components

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Abstract

The invention provides a molten salt electrodeposition method of a niobium coating, which adopts a NaCl-KCl-CsCl system as a supporting electrolyte, K2NbF7The support electrolyte and the active salt are pretreated to be active salt, the pretreated support electrolyte is heated to 750 ℃ to be fully melted under the protective atmosphere of argon gas, chlorine gas is introduced to carry out chlorination treatment, and the cooled support electrolyte and the active salt are uniformly mixed in a crucible to obtain molten salt; and the plated part is pretreated; and then vacuumizing to enable the pressure of an electroplating device to be lower than 100Pa, introducing inert gas, putting the pretreated plated part into the prepared molten salt in the electroplating device, controlling the electroplating temperature to be 650-850 ℃, and selecting a corresponding current form and electroplating time according to the thickness of the required coating to carry out electroplating to obtain the plated part with the niobium coating on the surface. The method is environment-friendly, efficient and low in cost, and the prepared niobium coating is good in uniformity.

Description

Molten salt electrodeposition method of niobium coating
Technical Field
The invention relates to the technical field of molten salt electrochemistry and surface coatings, in particular to a molten salt electrodeposition method of a niobium coating.
Background
Niobium (Nb) is a refractory metal with a body-centered cubic structure, has good physical and chemical properties, and has high melting point (2468 ℃) and relatively low density (8.57 g/cm)3) High-temperature strength, high thermal conductivity, small thermal neutron capture section, high superconducting critical temperature (9.2K), good corrosion resistance, weldability, ductility and excellent biocompatibility [ tindoline, tantalum niobium and alloy and application thereof [ J]Rare metals and cemented carbides, 1998 (02): 48-54]Therefore, niobium and its alloy are often used to manufacture superconductor, chemical reaction tank, biological implant, rocket engine combustion chamber, reactor heat exchanger and nuclear reactor cladding material, etc. which are used under special working conditions.
The current methods for preparing niobium coatings mainly include spray coating, physical vapor deposition, chemical vapor deposition, and fused salt electrodeposition. The spraying method has low cost and high efficiency, the obtained coating is thicker, but the coating has lower density and higher surface roughness, and the method is mainly used for strengthening the surface of steel; the coating prepared by the physical vapor deposition method is smooth and compact, but the equipment is expensive and the cost is high, and the method is mainly used for preparing a nano-scale film; the chemical vapor deposition method has the advantages of simple equipment, high deposition rate, good plating winding performance and the like, but has high deposition temperature, long period, poor quality consistency and difficult industrialization; the molten salt electrodeposition method has complex molten salt treatment and larger pollution, but has good plating property, controllable deposition rate and coating thickness and high repeatability, and is expected to realize large-scale industrial production.
The molten salt is composed of active salt and supporting electrolyte, NbCl5High steam pressure, low stability and strong hygroscopicity, and the active salt is generally K with better stability2NbF7The supporting electrolyte systems include chloride systems, fluoride systems, and fluorochloride systems. The stability of Nb-containing complex in the perfluorinated system molten salt is good, and the continuous and compact Nb coating is favorably prepared, and the continuous and compact Nb coating is prepared by adopting a LiF-NaF-KF system by Mellors and the like, is a typical columnar crystal, has the density of more than 99.8 percent of theoretical density, and has the thickness of 6.35 mm. [ MELLORS G W, SENDERROFF S.ELECTRODE POSITION of Coherent Deposits of Refractory Metals:I.Niobium[J].Journal of the Electrochemical society,1965,112(3):266.]However, the perfluoride system has high F content, high toxicity and great environmental pollution. Full chloride systems (LiCl-KCl and NaCl-KCl) are low in toxicity and environment-friendly, but the complex stability is poor, and the adhesion and the bonding force of the prepared Nb coating are poor. Therefore, Kolosov et al uses a fluorochloride molten salt system (NaCl-KCl-NaF) to reduce the toxicity of the molten salt, ensure the stability of the complex, and prepare a continuous, dense, and good-bonding niobium coating [ KOLOSOV N, SHEVYREV A. displacement of superconducting Nb3Sn and high-purity Nb coatings on the rotor of a cryogenic gyroscope[J].Inorganic Materials,2012,48(2):132-137.]But is still more environmentally polluting than perchloro systems.
Therefore, providing a method for preparing a niobium coating with environmental friendliness, high efficiency, low cost, fast deposition rate and good uniformity is a technical problem of great concern to those skilled in the art.
Disclosure of Invention
The invention aims to provide a preparation method of a niobium coating, which is environment-friendly, efficient, low in cost and good in uniformity. A NaCl-KCl-CsCl system with low toxicity and environmental friendliness is adopted, and the reverse polarization effect of cesium ions is weaker than that of sodium and potassium ions, so that a complex containing cesium ions in the second coordination sphere is more stable in a melt, the problem of lower stability of the complex in a full chloride system is solved, a continuous compact coating can be prepared, and meanwhile, the system is low in melting point and working temperature, and the volatilization of molten salt and working energy consumption can be reduced.
The technical scheme of the invention is as follows:
a molten salt electrodeposition method of a niobium coating comprising the steps of:
step one, molten salt preparation: adopts NaCl-KCl-CsCl system or single CsCl as supporting electrolyte, K2NbF7Is active salt, the supporting electrolyte and the active salt are pretreated, the pretreated supporting electrolyte is heated to 750 ℃ in the protective atmosphere of argon gas and is fully melted, chlorine gas is introduced for chlorination, and the cooled supporting electrolyte and the active salt are mixedUniformly mixing the active salts to obtain molten salt;
secondly, pretreating the plated part and the crucible;
step three, electroplating: and (3) placing the molten salt in a crucible of an electroplating device, vacuumizing to enable the pressure of the electroplating device to be lower than 100Pa, introducing inert gas, placing the plated part pretreated in the step two in the electroplating device into the molten salt prepared in the step one, controlling the electroplating temperature to be 650-850 ℃, and electroplating by selecting a corresponding current form and electroplating time according to the thickness of the required coating to obtain the plated part with the niobium coating on the surface.
Further, in the NaCl-KCl-CsCl system, the mass ratio of NaCl is 0-45%, KCl is 0-50%, and CsCl is 20% -100%. Further, in the NaCl — KCl-CsCl system, the mass ratio of NaCl: KCl: CsCl ═ 1: 1-2: 0.5-20.
Further, the concentration of niobium ions in the molten salt prepared in the first step is 1-6 wt.%.
Further, the pretreatment of the supporting electrolyte comprises: drying the components of the supporting electrolyte in a baking oven at 200 ℃ for 8h to remove crystal water, grinding and mixing; the pretreatment of the active salt comprises: will K2NbF7Drying in a vacuum drying oven at 110-130 deg.C and vacuum degree of less than 100Pa for 8 hr.
Further, the chlorination treatment specifically comprises: and introducing chlorine into the molten salt for chlorination for 1-30 min, introducing argon for bubbling for 1-30 min to make the molten liquid colorless and transparent, and finally cooling under the condition of argon protection to obtain the chlorinated molten salt.
Further, the pretreatment of the plated part is specifically as follows: and (3) polishing the plated part, and then carrying out degreasing, acid washing, water washing, organic solvent cleaning and drying treatment to obtain the plated part substrate with a smooth surface and no oxide.
Furthermore, the plating piece is made of any one of niobium, molybdenum, nickel and rhenium.
Further, when the thickness of the desired coating is less than 30 μm, the current is in the form of a steady state current or a pulsed current; when the desired coating thickness is greater than 50 μm, the current is in the form of a pulsed current.
Further, the cathode current density of the steady-state current is 10mA/cm2-100mA/cm2(ii) a The average current density of the pulse current is 5mA/cm2-200mA/cm2The duty ratio is 30-90%, and the frequency is 0.1-100 Hz.
Further, in the second step, the crucible is made of materials or active materials niobium, wherein platinum, glassy carbon and molybdenum are stable in molten salt.
The invention can achieve the following technical effects:
1. the method adopts NaCl-KCl-CsCl system molten salt as electrolyte, overcomes the problem that a chloride system cannot prepare a continuous compact niobium coating, reduces the cost of raw materials, and improves the safety and the environmental protection. By K2NbF7The niobium element is directly added into the molten salt as a source of the niobium element, the operation is convenient, and the concentration of niobium ions is convenient to control. The niobium ions in the molten salt are supplemented in the form of an active anode.
2. The niobium coating prepared by molten salt electroplating has high speed, the average deposition speed can reach 10-80 mu m/h, and the thickness of the coating is easy to control. The thickness uniformity of each part of the plating piece is good. The current efficiency is close to 100%, and the metal coating is compact and smooth and is well combined with the matrix.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 is a process flow diagram of the preparation method of the present invention.
FIG. 2 is a schematic view of an electroplating apparatus used in the embodiment of the present invention.
Fig. 3 is an SEM image of the surface of the coating layer obtained in example 1 of the present invention, in which (a) is the surface topography of the coating layer magnified 1000 times and (b) is the surface topography of the coating layer magnified 10000 times in fig. 3.
FIG. 4 is a SEM photograph of a cross section of the coating layer obtained in example 1 of the present invention.
FIG. 5 is an SEM image of the surface of the coating obtained in example 2 of the present invention, wherein (a) in FIG. 5 is the surface topography of the coating magnified 1000 times and (b) is the surface topography of the coating magnified 5000 times.
FIG. 6 is a SEM photograph showing a cross-section of the coating layer obtained in example 2 of the present invention.
Fig. 7 is an SEM image of the surface of the coating layer obtained in example 3 of the present invention, in which (a) is the surface topography of the coating layer magnified 1000 times and (b) is the surface topography of the coating layer magnified 5000 times in fig. 7.
FIG. 8 is a SEM photograph showing a cross-section of a coating layer obtained in example 3 of the present invention.
FIG. 9 is an SEM image of the surface of the coating obtained in example 4 of the present invention, wherein (a) in FIG. 9 is the surface topography of the coating magnified 1000 times and (b) is the surface topography of the coating magnified 5000 times.
FIG. 10 is a SEM photograph showing a cross-section of the coating layer obtained in example 4 of the present invention.
FIG. 11 is a photograph of the surface of the coating layer obtained in comparative example 1 of the present invention.
Fig. 12 is an XRD pattern of black powder obtained in comparative example 1 of the present invention.
Fig. 13 is an SEM image of the surface of the coating obtained in comparative example 2 of the present invention.
FIG. 14 is an SEM photograph of dendrites washed and dropped in comparative example 2 of the present invention.
FIG. 15 is a SEM photograph showing a cross-section of the coating layer having no dendrite region in comparative example 2 of the present invention.
Illustrated in FIG. 2 is:
1-stainless steel flange; 2-quartz cylinder; 3-a crucible; 4-resistance furnace; 5-a nickel rod; 6-a thermocouple; 7-a cooling water pipe; 8-plating parts.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In addition, the technical solutions in the embodiments of the present invention may be combined with each other, but it must be based on the realization of the technical solutions by those skilled in the art, and when the technical solutions are contradictory to each other or cannot be realized, such a combination of the technical solutions should not be considered to exist, and is not within the protection scope of the present invention.
The drugs/reagents used are all commercially available without specific mention.
The technical scheme of the invention comprises three basic steps of molten salt preparation, electroplating pretreatment and electroplating, and the plated part can be cleaned after the electroplating is finished.
The electroplating device adopted by the invention is shown in figure 2 and mainly comprises a stainless steel flange 1, a quartz cylinder 2, a crucible 3 and a resistance furnace 4. The quartz cylinder 2 is arranged in a hearth of the resistance furnace 4 and wound with the cooling water pipe 7, and the crucible 3 is positioned inside the quartz cylinder 2. The crucible 3 is connected with a nickel rod 5, and the outside of the crucible is connected with the positive pole of a power supply. The plating part 8 is connected with the nickel rod 5 and is externally connected with the negative pole of a power supply. A thermocouple 6 is used to monitor and control the molten salt temperature.
When the electroplating device is adopted, firstly, the device is vacuumized to enable the pressure of the device to be lower than 100Pa, the electroplating device is cleaned by argon with the purity of 99.999% for three times, the resistance furnace 4 is heated under the protection of flowing argon, the temperature is raised to the experimental temperature and kept, the plated part 8 is inserted into the molten salt in the crucible 3 after the molten salt is fully melted, the power supply is started to start electroplating after the temperature is kept for a period of time (5-15 minutes), and the plated part is lifted out of the liquid level and cooled along with the furnace after the electroplating is finished. Ultrasonically cleaning the molten salt on the surface of the plated part and then drying.
Referring to fig. 1, the molten salt electrodeposition method of a niobium coating provided by the invention specifically comprises the following steps:
firstly, preparing molten salt. A NaCl-KCl-CsCl system or a single CsCl system is adopted as a supporting electrolyte, and the mass percentages of the NaCl, the KCl and the CsCl in the NaCl-KCl-CsCl system are as follows: 1-2: 0.5-20, K2NbF7Is active salt, contains K2NbF7The concentration of niobium ions in the molten salt is 1-6 wt.%. Due to K2NbF7Sensitive to oxygen and easy to react with chlorine, the supporting electrolyte and the active salt need to be treated respectively, and all components of the supporting electrolyte are dried in a drying oven at 200 ℃ for 8h to remove crystal waterThe mixture was then ground and placed in a quartz cell and the mixed salt was heated to 750 ℃ under an argon protective atmosphere. After the mixed salt is fully melted, introducing chlorine into the molten salt for chlorination treatment for 1-30 min, introducing argon for bubbling for 1-30 min to prevent the residual chlorine from reacting with the active salt, so that the molten liquid is colorless and transparent, and finally cooling under the protection of argon to obtain the treated molten salt, wherein K is used as a protective agent2NbF7The potassium fluoroniobate can be produced with water at high temperature, and is dried for 8 hours in a vacuum drying oven with the temperature of 110-130 ℃ and the vacuum degree of less than 100Pa, and then ground and mixed evenly in a glove box under the argon atmosphere.
And secondly, pre-treating the plated part and the crucible. After polishing, the plated part is degreased, pickled, washed, cleaned by organic solvent and dried by a common method to obtain a plated part matrix with smooth surface and no oxide. The plating piece can be niobium, molybdenum, nickel and rhenium. Due to K2NbF7The crucible is sensitive to oxygen, an oxide crucible cannot be selected, and because niobium and carbon easily generate niobium carbide at high temperature and a graphite crucible which is easy to fall powder cannot be selected, materials such as platinum, glassy carbon, molybdenum and the like which are stable in molten salt or an active material niobium can only be selected as the crucible, and the treatment mode is the same as that of a plated part.
And thirdly, electroplating. Placing the molten salt in a crucible of an electroplating device, vacuumizing to make the pressure of the device lower than 100Pa, introducing argon with the purity of 99.999 percent, repeating for three times, further reducing the oxygen content in the device, and preventing K2NbF7Reacting with oxygen, placing the plated part in the molten salt obtained in the first step, controlling the electroplating temperature to be 650-850 ℃, selecting the electroplating time according to the required thickness of the coating, wherein the thickness of the coating is less than 30 mu m, the current form can be steady-state current or pulse current, the quality difference of the coating is not large, and the cathode current density of the steady-state current is 10mA/cm2-100mA/cm2The average current density of the pulse current is 5mA/cm2-200mA/cm2The duty ratio is 30-90%, the frequency is 0.1Hz-100Hz, the coating thickness is more than 50 μm, pulse current is selected, because the coating surface dendritic crystal obtained by steady-state current is more, the plating piece is lifted out of the liquid level after the electroplating is finished, and the plating piece is cooled along with the furnace in the flowing atmosphere of argon. Ultrasonically cleaning the sample with water to remove the residual molten salt on the surface, and dryingAnd (4) finishing.
To further illustrate the process of the present invention, reference is made to the following specific examples:
example 1:
a molten salt electrodeposition method of a niobium coating comprising the steps of:
1. preparing molten salt: respectively weighing NaCl, KCl and CsCl according to the mass ratio of the raw materials of 1:1.28:3.41, placing the NaCl, KCl and CsCl in a 200 ℃ oven for drying treatment for 8 hours to remove crystal water, then grinding and mixing the NaCl, KCl and CsCl in a quartz cup, cleaning the quartz cup with an argon cleaning device for three times, and heating the quartz cup to 750 ℃ under the protective atmosphere of argon for melting. And introducing chlorine into the molten salt for chlorination treatment for 10 minutes, introducing argon for bubbling for 15 minutes, and finally cooling under the condition of argon protection. Will K2NbF7Drying in a vacuum drying oven at 120 deg.C and vacuum degree of 100Pa for 8 hr, adding into supporting electrolyte to contain K2NbF7The concentration of niobium ions in the molten salt was 2.4 wt.%.
2. Plating the workpiece and treating the crucible before plating. The plating part adopts molybdenum, the plating part is ground flat by using No. 1200 abrasive paper before electroplating, ethanol is ultrasonically cleaned for 5 minutes, the plating part is dried by hot air, the crucible adopts a niobium crucible, the plating part is ground flat by using No. 1200 abrasive paper, 35 percent HF and 10 percent HNO3Chemical cleaning with mixed acid for 1 minute, ultrasonic cleaning with ethanol for 5 minutes, and drying with hot air.
3. And (4) electroplating. The treated molten salt and the assembled electrode were placed in the apparatus shown in FIG. 2, evacuated to 20Pa, and the apparatus was purged three times with 99.999% argon gas and heated to 700 ℃ in a flowing argon atmosphere. And after the molten salt is fully melted, inserting the plated part into the molten salt, and preserving the heat for 5 minutes to start electroplating. Selecting steady-state current with cathode current density of 30mA/cm2Plating time was 1 hour.
4. And (5) cleaning the plated part. And taking out the plated part after the electroplating is finished, cooling the plated part to room temperature along with the furnace under the protection of Ar gas, washing and drying to obtain the plated part plated with the niobium coating.
Fig. 3 is an SEM picture of the coating surface obtained in example 1, which shows that the coating surface is uniform and flat, the grains are in a hexagonal star shape, and small grains are included between large grains. Fig. 4 is an SEM picture of the coating section obtained in this example 1, and it can be seen that the coating section has no obvious pores and good compactness, and can be divided into a fine equiaxed crystal nucleus layer and a columnar crystal continuous growth layer column near the substrate, and the thickness of the niobium layer is about 22 μm.
Example 2:
essentially the same procedure as in example 1, except that: the temperature in step 3 was adjusted to 800 ℃.
FIG. 5 is an SEM image of the surface of the coating obtained in example 2, and it can be seen that the surface of the coating is uniform and has undulations, and the grains are shell-shaped. FIG. 6 is an SEM image of the coating cross section obtained in this example, which shows that the coating cross section has no obvious pores, good compactness, coarse grains, and a thickness of the Nb layer of about 26 μm.
Example 3:
essentially the same procedure as in example 1, except that: the steady state current of the step 3 is adjusted to be pulse current, and the average current density is 50mA/cm2The duty cycle is 50% and the frequency is 0.5 Hz.
Fig. 7 is an SEM picture of the surface of the coating obtained in example 3, and it can be seen that the surface of the coating is uniform and the grains have irregular polygonal shapes. Fig. 8 is an SEM picture of the coating cross section obtained in this example, which shows that the coating cross section has no obvious pores, good compactness, fine columnar crystals, and a thickness of the niobium layer of about 50 μm.
Example 4:
essentially the same procedure as in example 1, except that: the supporting electrolyte contains no NaCl and KCl, and only CsCl.
Fig. 9 is an SEM picture of the surface of the coating obtained in example 4, and it can be seen that the surface of the coating has small undulation and uniform morphology, and the grains have irregular polygonal shapes. FIG. 10 is an SEM image of the cross section of the coating obtained in this example, which shows that the coating has no obvious pores on the cross section, good compactness and a thickness of the Nb layer of about 25 μm.
Comparative example 1:
essentially the same procedure as in example 1, except that: the pressure in step 3 reached 150 Pa.
K2NbF7Sensitive to oxygen and with plating temperatures as high as 700 ℃ aggravates the reaction, since the device pressure is only as high as150Pa, more oxygen remained in the device, and K2NbF7The reaction occurs to generate fluoroxyniobate, which causes oxide generation during electroplating. Fig. 11 is a macroscopic surface optical picture of the coating obtained in comparative example 1, and it can be seen that the surface layer of the coating is black, and black powder is obtained upon ultrasonic cleaning. FIG. 12 is an XRD pattern of black powder obtained in comparative example 1, and it is understood that the formation of niobium oxide by electroplating is caused by an excessively high pressure.
Comparative example 2:
essentially the same procedure as in example 1, except that: the time of step 3 was adjusted to 5 hours to obtain a coating thickness of greater than 50 μm.
Because concentration polarization is generated during electrodeposition, and when steady-state current is adopted, the concentration polarization degree is increased along with the prolonging of the electrodeposition time, dendritic crystals and even powder are obtained by electrodeposition, and the coating is difficult to continuously thicken, and a great number of dendritic crystals exist on the surface of the coating as shown in an SEM picture of the surface of the coating obtained in comparative example 2 in FIG. 13. FIG. 14 is a graph showing dendrites dropped by ultrasonic cleaning of the coating obtained in comparative example 2. FIG. 15 is a SEM image of a cross-section of the dendrite free region coating of comparative example 2, in which the thickness of the niobium layer was about 70 μm, and a large number of dendrites were generated to cause a great difference in the thickness of the coating from the theoretical thickness of 120 μm.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (7)

1. A molten salt electrodeposition method of a niobium coating, comprising the steps of:
step one, molten salt preparation: adopts NaCl-KCl-CsCl system or single CsCl as supporting electrolyte, K2NbF7Is active salt, and the supporting electrolyte and the active salt are pretreated, the pretreated supporting electrolyte is heated to 750 ℃ in the protective atmosphere of argon gas and is fully melted, chlorine gas is introduced for chlorination, and the cooled supporting electrolyte and the active salt are uniformly mixed to obtain the catalystTo molten salt;
secondly, pretreating the plated part and the crucible;
step three, electroplating: placing the molten salt in a crucible of an electroplating device, vacuumizing to enable the pressure of the electroplating device to be lower than 100Pa, introducing inert gas, placing the plated part pretreated in the step two in the electroplating device into the molten salt prepared in the step one, controlling the electroplating temperature to be 650-850 ℃, and electroplating according to the thickness of the required coating by selecting a corresponding current form and electroplating time to obtain the plated part with the niobium coating on the surface;
wherein in the NaCl-KCl-CsCl system in the first step, the mass ratio of NaCl is 0-45%, KCl is 0-50%, and CsCl is 20-100%; the concentration of niobium ions in the molten salt prepared in the first step is 1-6 wt.%;
when the thickness of the required coating is less than 30 μm, the current is in the form of steady-state current or pulse current; when the thickness of the desired coating is greater than 50 μm, the current is in the form of a pulsed current.
2. The molten salt electrodeposition method of niobium coating of claim 1, wherein the pretreatment of the supporting electrolyte comprises: drying the components of the supporting electrolyte in a baking oven at 200 ℃ for 8h to remove crystal water, grinding and mixing; the pretreatment of the active salt comprises: will K2NbF7Drying for 8h in a vacuum drying oven at the temperature of 110-130 ℃ and the vacuum degree of less than 100 Pa.
3. The molten salt electrodeposition method of niobium coating according to claim 1, characterized in that the chlorination treatment is specifically: and introducing chlorine into the molten salt for chlorination treatment for 1-30 min, introducing argon for bubbling for 1-30 min to make the molten liquid colorless and transparent, and finally cooling under the condition of argon protection to obtain the chlorinated molten salt.
4. The molten salt electrodeposition method of a niobium coating as claimed in claim 1, wherein the pretreatment of the plated part is specifically: and (3) polishing the plated part, and then carrying out degreasing, acid pickling, water washing, organic solvent cleaning and drying treatment to obtain the plated part substrate with a smooth surface and no oxide.
5. The molten salt electrodeposition method of a niobium coating as claimed in claim 1, wherein the material of the plating member is any one of niobium, molybdenum, nickel and rhenium.
6. The molten salt electrodeposition method of niobium coating of claim 1, wherein the steady state current cathode current density is 10mA/cm2-100mA/cm2(ii) a The average current density of the pulse current is 5mA/cm2-200mA/cm2The duty ratio is 30-90%, and the frequency is 0.1-100 Hz.
7. The molten salt electrodeposition method of a niobium coating as claimed in any one of claims 1 to 6, wherein in the second step, the crucible material is selected from platinum, glassy carbon, molybdenum or niobium as an active material.
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