CN111206269A - Preparation method of electroplating black chromium with high heat radiation coefficient - Google Patents
Preparation method of electroplating black chromium with high heat radiation coefficient Download PDFInfo
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- CN111206269A CN111206269A CN201911316738.8A CN201911316738A CN111206269A CN 111206269 A CN111206269 A CN 111206269A CN 201911316738 A CN201911316738 A CN 201911316738A CN 111206269 A CN111206269 A CN 111206269A
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- C—CHEMISTRY; METALLURGY
- 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
- C25D3/02—Electroplating: Baths therefor from solutions
- C25D3/04—Electroplating: Baths therefor from solutions of chromium
- C25D3/06—Electroplating: Baths therefor from solutions of chromium from solutions of trivalent chromium
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D15/00—Electrolytic or electrophoretic production of coatings containing embedded materials, e.g. particles, whiskers, wires
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- 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
- C25D21/10—Agitating of electrolytes; Moving of racks
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/04—Electroplating with moving electrodes
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/18—Electroplating using modulated, pulsed or reversing current
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/34—Pretreatment of metallic surfaces to be electroplated
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/48—After-treatment of electroplated surfaces
- C25D5/50—After-treatment of electroplated surfaces by heat-treatment
Abstract
The invention relates to the technical field of plating materials, in particular to a method for preparing electroplating black chromium with high thermal emissivity. Under the assistance of a cathode rotation electroplating process and a pulse current electroplating process, the invention absorbs a layer of modified carbon nano tubes on the surface of the X-ray tube copper sleeve rotor in an oriented and ordered manner, and the composite electroplating black chromium has excellent high thermal radiation coefficient, firm coating combination and few defects compared with the traditional electroplating black chromium, thereby meeting the use requirements of high temperature resistance and vacuum working state required in the X-ray tube.
Description
Technical Field
The invention relates to the technical field of plating materials, in particular to a preparation method of electroplating black chromium with high thermal emissivity.
Background
The rotating anode X-ray tube is a high vacuum electric vacuum device, the working principle of the rotating anode X-ray tube is that high voltage (generally 125-150 kV) is applied to the anode and cathode ends of the X-ray tube, electron beams emitted by a cathode bombard an anode target surface (the target surface material is generally tungsten) to generate X-rays under the action of a high vacuum high voltage electric field, but the X-rays only account for about 1% of electron energy, and 99% of the X-rays are converted into heat. Since the X-ray tube is a vacuum device, the thermal conduction within the tube is rather undesirable.
In order to conduct a large amount of heat generated by the rotating anode X-ray tube during working to an insulating medium oil layer outside the vacuum tube in time, a black chromium plating process is adopted on the surface of the anode rotor. The common black chromium coating is generally used at normal temperature, only plays roles of surface decoration, shading and the like, and is not suitable for the use requirements of high temperature resistance and vacuum working state required by the black chromium coating of the anode rotor of the rotary anode X-ray tube.
Because the surface working temperature of the anode rotor can reach 600-700 'C, the black chromium coating has higher technical requirements relative to common use, namely the coating has to resist high temperature (about 600-700' C); under the high vacuum condition, the plating layer must be firmly combined with the anode rotor substrate and not fall off; the coating must have a high thermal emissivity.
Therefore, it is highly desirable to prepare an electroplated black chrome with high emissivity to meet practical production requirements.
Disclosure of Invention
The invention aims to solve the problem of low emissivity of a black chromium plating layer electroplated on a medical X-ray bulb tube in the prior art, and provides a preparation method of the electroplated black chromium with high emissivity, the electroplated black chromium prepared by the method has the characteristics of high hardness, high density, high emissivity, few crack defects and the like, and the specific technical scheme is as follows:
a preparation method of electroplating black chromium with high heat radiation coefficient specifically comprises the following steps:
s1: treating the surface of a substrate: before electroplating, the surface of the substrate is polished, then the surface of the substrate is cleaned by using a detergent and deionized water, and finally the residual stress on the surface of the substrate is eliminated.
S2: preparing trivalent chromium plating solution: the plating solution comprises the following components: 100-110g/L CrCl 3. H2O, 50-60g/L NH4Cl, 55-65g/L NaCl, 60-70g/L HCOONa, 10-20g/L CON2H4, 10-20g/L NH4Br and deionized water as solvent.
Compared with the standard chromium plating solution only containing sulfuric acid and chromic acid in the formula, a certain amount of methanol and formic acid are added into the trivalent chromium solution taking urea as a complex, the deposition speed of the chromium layer is greatly improved to 20-100 mu m/h, meanwhile, the thickness of a plating layer can reach 200 mu m, and the data shows that the trivalent chromium solution process taking urea as a complex can gradually replace the co-registration chromium plating solution process.
S3: preheating and adding modified carbon nanotubes: preheating an electroplating device with a rotary cathode structure, updating the solution around the cathode by adopting a bottom flushing mode, and adding the modified carbon nano tube according to the proportion of 2-5g/L to realize the self-assembly of the modified carbon nano tube on the surface of the matrix.
The cathode rotates, namely the cathode has a certain rotating speed relative to the anode, and plays a certain role in stirring the electroplating solution, so that the convection of the solution and the diffusion of ions are promoted, the influence of concentration polarization is reduced, and the influence of reaction heat on the solution in the cathode area can be reduced as much as possible. Generally, the mass transfer process can be accelerated by adopting the cathode rotation electroplating process, and the influence of polarization is reduced by reducing concentration polarization, so that the current efficiency is improved. However, the effect of cathode rotation in the chromium electroplating process is different, and the cathode polarization effect is increased while hydrogen is driven. The hydrogen-expelling effect is caused by the fact that during the rotation of the cathode, the solution flow rate inside the diffusion layer is greater than that of the other parts, wherein the flow rate is greater closer to the cathode. This causes hydrogen to be generated on the surface of the cathodeThe air bubbles are difficult to adsorb on the surface for a long time, and the generation of pockmarks is avoided. On the other hand, the stirring makes the flow rate large, reducing the possibility that hydrogen ions are adsorbed on the surface of the cathode to obtain electrons. The cathode polarization is increased because the chromium is deposited from the chromate CrO4 2-Ion-completed, not by dichromate ion Cr2O7 2-And (4) completing. The rotation of the cathode and the increase of the solution convection velocity only lead the concentration of the dichromate ions on the surface of the cathode to be improved, and the concentration of the chromate ions is not greatly changed. Chromate CrO4 2-The ion generation requires a certain increase in pH. As can be seen from the hydrogen-expelling effect, the hydrogen ions in the cathode region are difficult to obtain electrons, so that the rising speed of the PH value becomes slow, and the chromate CrO4 2-Slow generation of ions, CrO4 2-The ion concentration decreases. The continuous deposition of chromium consumes CrO continuously4 2-Ions, causing a further reduction in their concentration. CrO in the cathode region4 2-Ion concentration and CrO in bulk solution4 2-The ion concentration difference is further increased, so that concentration polarization is increased, and cathode polarization is increased. During electrodeposition, the formation of crystal nuclei originates from the cathode overpotential. The greater the cathodic polarization, the greater the cathodic overpotential. Meanwhile, the nucleation speed of the crystal nucleus is accelerated along with the increase of the overpotential. The cathode rotation has the effect of refining the grains.
S4: and (3) formal black chromium electroplating:
s41: in the early stage of forward plating, reverse small current is used in a short time to remove the oxide film on the surface of the matrix, so that fine concave-convex parts are formed on the surface of the body, and the binding force of the plating layer is increased.
S42: in the middle stage of forward plating, forward large current 2 times of the plating current is used for continuously impacting the surface of the substrate for 2min, so that the polarization effect is increased, more crystal nuclei are formed during plating, and the effect of refining crystal grains is achieved.
S43: and (3) at the later stage of positive plating: connecting the matrix with a rotary cathode of an electroplating pulse power supply, putting the matrix into an electrolytic bath in an electrified manner, and electroplating under the following process parameters: the temperature of the plating solution is 45 ℃, the flushing speed is 4L/min, the cathode rotation speed is 300r/min, the current density is 50A/dm2, the current pulse frequency is 5.5KHz, and the current duty ratio is 75%.
Compared with direct current, pulse current has two more adjustable parameters besides two parameters of voltage and current: pulse frequency and duty cycle. The pulse current can be divided into a pulse-on phase and a pulse-off phase within one period. During the pulse on time, the peak current density at the cathode surface far exceeds the average current density due to the duty cycle. Higher peak current density can produce high overpotential, so that more chromium can be deposited in unit time, the nucleation speed of the chromium exceeds the growth speed of the chromium, and finally the obtained coating has fine grains. Meanwhile, the proportion of hydrogen evolution reaction in the chromium plating process can be reduced due to high overpotential, the hydrogen evolution amount is reduced, and the occurrence of bad conditions such as pinholes, pits and the like is effectively avoided. CrO in solution during pulse off time4 2-Rapidly moving to the cathode processing area to enable CrO in the diffusion layer4 2-The concentration of the ions can be increased back to some extent, so that the influence of concentration polarization can be greatly eliminated. Meanwhile, in the turn-off time, the current density is 0, so that the deposition of chromium on the surface of the cathode can be fully ensured, the recrystallization of the chromium layer is facilitated, and the hydrogen bubbles adsorbed on the surface have sufficient time to be adsorbed and desorbed. The pulse frequency allows this process to be performed periodically so that it is present throughout the plating process. In addition, the pulse current has an influence on the uniformity of the plating. This effect can be explained by the double layer capacitance effect. A large number of ions are adsorbed on the surface of the electrode due to the charge. And because of the requirement of electric neutrality, ions with opposite electric potentials tend to exist in the area near the electrode. These ions and electrodes exhibit opposite polarities, and thus both constitute an electric double layer, and can be similarly considered as a capacitor. In the case of electroplating with a pulse current, the electric double layer is charged first in the pulse-on phase and then discharged in the pulse-off phase. This charging and discharging process can have an effect on chromium deposition, especially during the discharge phase. During the electric double layer discharge phase, the discharge area occurs near the electrodes, and thus the deposition processWithout passing through the interior of the solution, the effects of conductivity and solution resistance are negligible, so that the current at the cathode surface is uniformly distributed in the process. This results in a uniform distribution of the chromium layer deposited on the cathode surface during the discharge.
S5: and (3) discharging and cleaning: taking out the matrix from the electrolytic cell, firstly washing the matrix for more than 30s by using tap water, then washing the matrix for more than 30s by using deionized water, and finally drying the matrix by using compressed air;
s6: and (3) dehydrogenation treatment: the assembly was placed in a vacuum oven and heat treated at 300 ℃ for 7 h.
Further, in step S1, the surface of the substrate is polished by using 80-100 mesh quartz sand, so that the roughness of the surface of the substrate reaches Ra ═ 0.4, and at this roughness, more active sites can be provided for the deposition of chromium atoms and the adsorption of modified nano carbon fibers, and the bonding strength between the substrate and the black chromium layer is enhanced.
Further, in step S1, the composition of the detergent is: 100g/L of sodium hydroxide, 25g/L of sodium carbonate decahydrate, 8g/L of sodium silicate and deionized water as a solvent. The alkaline solution cleaning mainly has the functions of cleaning oil stains and harmful impurities on the surface of a substrate and avoiding the influence of the impurities on the dispersing capacity and the covering capacity of a plating solution, which causes the grey of a plating layer and the corrosion of the substrate and an anode.
Further, in step S3, the self-assembly of the modified carbon nanotube on the surface of the substrate specifically includes the following steps:
s31: modification of carbon nanotubes: doping B atoms on the surface of the carbon nano tube by using a chemical vapor deposition method to form an electron-deficient structure, so that the Fermi level of the carbon nano tube is improved, the energy gap is reduced, and the adsorption capacity between the carbon nano tube and metal atoms is improved.
A tiny energy gap of about 0.2eV exists between a front conduction band and a valence band of the pure carbon nanotube for adsorbing metal atoms. The Fermi level of the carbon nano tube is reduced to be below the top of the valence band after B atoms are doped, and B3+In place of C3+The rear carbon nanotube forms an electron-deficient state, and the 2p orbital electron of the B atom forms an acceptor level in the vicinity of the fermi level.
The B-doped carbon nanotube forms an electron-deficient structure, and after the Cu atom is adsorbed, the 3d orbital electron and the 4s orbital electron of the Cu atom are filled near the Fermi level, so that holes formed after the B atom is doped are reduced. The energy band structure and state density analysis shows that doping changes the energy band structure of the carbon nano tube by increasing or reducing the Fermi level of the carbon nano tube and provides a half-full energy band near the Fermi level, free electrons provided by adsorbed Cu atoms are filled near the Fermi level of the carbon nano tube, and particularly charge transfer between the Cu atoms and the carbon nano tube is improved after doping B atoms.
S32: the electric field force in the electrolytic bath is used as a driving force, and the polarized carbon nano tubes overcome the influence of self gravity, electrostatic force and external viscous resistance and are directionally arranged on the surface of the matrix.
For chromium plating solutions, the dispersion of the modified carbon nanotubes in the polymer can be assumed to be a dilute solution of metal cylinders. The solution is subject to dynamic phenomena under the influence of an external electric field. The modified carbon nanotube has extremely strong dielectric property, so that the modified carbon nanotube can generate polarization effect under the condition of an external electric field, and has extremely high polarizability. The polarized modified carbon nanotube can be regarded as an electric dipole, and the electric intestinal force acting on positive and negative charges forms a couple. The moment of the electric field can make the electric distance of the dipole turn to the direction parallel to the electric field, so that the modified carbon nano tubes can be directionally and orderly arranged along the direction of the electric field in the parallel uniform electric field. Setting corresponding electric field parameters can control the forward rotation of the modified carbon nano tubes, thereby realizing the directional ordered arrangement of the modified carbon nano tubes on the surface of the matrix.
Further, in step S31, the modified carbon nanotube has a diameter of 20-30nm, a length of 10-30 μm, a B atom content of 3-3.2%, and a purity of > 95%.
Furthermore, in order to improve the air tightness of the prepared black chromium layer and eliminate cracks of the chromium layer, the surface of the chromium layer is extruded by using diamond, so that a residual profit layer is formed on the surface of the matrix while no cracks exist on the surface of the chromium layer, and the fatigue strength of the matrix is improved.
Further, in order to solve the problem of the occurrence of the unavoidable poor plating layer during electroplating, the hard plating layer on the surface of the substrate needs to be deplated, and the specific process comprises the following steps: preparing 50g/L NaOH solution at 20-35 deg.CUnder the circumstance, 3-550A/dm is used2The power density of (3) is removed.
Compared with the prior art of plating black chromium on the surface of the rotor of the X-ray tube, the invention has the beneficial effects that:
under the assistance of a cathode rotation electroplating process and a pulse current electroplating process, the invention absorbs a layer of modified carbon nano tubes on the surface of the rotor of the X-ray tube in an oriented and ordered way, and the composite electroplating black chromium has excellent high thermal radiation coefficient, firm coating combination and few defects compared with the traditional electroplating black chromium due to the excellent heat conductivity and heat resistance of the carbon nano tubes, thereby meeting the use requirements of high temperature resistance and vacuum working state required in the X-ray tube.
Detailed Description
In order to further illustrate the adopted mode and the obtained effect of the invention, the technical scheme of the invention is clearly and completely described by combining the embodiment and the experimental example.
Example one
The reagents used in example one were all commercially available; the base material is a copper sleeve; the pulse power supply is produced by Shanghai Suo Yiyi electronic technology company Limited; the electroplating equipment used was manufactured by Tianyi corporation, Changzhou. The specific technical scheme of the embodiment is as follows:
s1: surface treatment of the copper bush: before electroplating, the surface of the copper bush is polished, then the surface of the copper bush is cleaned by using a detergent and deionized water, and finally the residual stress on the surface of the copper bush is eliminated.
S2: preparing trivalent chromium plating solution: the plating solution comprises the following components: 105g/L CrCl3 & H2O, 54g/L NH4Cl, 58g/L NaCl, 66g/L HCOONa, 15g/L CON2H4, 17g/L NH4Br and deionized water as a solvent.
Compared with the standard chromium plating solution only containing sulfuric acid and chromic acid in the formula, a certain amount of methanol and formic acid are added into the trivalent chromium solution taking urea as a complex, the deposition speed of the chromium layer is greatly improved to 80 mu m/h, meanwhile, the thickness of a plating layer can reach 200 mu m, and the data show that the trivalent chromium solution process taking urea as the complex can gradually replace the co-registration chromium plating solution process.
S3: preheating and adding modified carbon nanotubes: preheating an electroplating device with a rotary cathode structure, updating the solution around the cathode by adopting a bottom flushing mode, and adding the modified carbon nano tubes according to the proportion of 2g/L to realize the self-assembly of the modified carbon nano tubes on the surface of the copper sleeve.
The cathode rotates, namely the cathode has a certain rotating speed relative to the anode, and plays a certain role in stirring the electroplating solution, so that the convection of the solution and the diffusion of ions are promoted, the influence of concentration polarization is reduced, and the influence of reaction heat on the solution in the cathode area can be reduced as much as possible. During electrodeposition, the formation of crystal nuclei originates from the cathode overpotential. The greater the cathodic polarization, the greater the cathodic overpotential. Meanwhile, the nucleation speed of the crystal nucleus is accelerated along with the increase of the overpotential. The cathode rotation has the effect of refining the grains.
S4: and (3) formal black chromium electroplating:
s41: in the early stage of forward plating, the reverse small current is used in a short time to remove the oxide film on the surface of the copper sleeve, so that fine concave-convex parts are formed on the surface of a machine body, and the binding force of a plating layer is increased.
S42: in the middle stage of forward plating, forward large current 2 times of the plating current is used for continuously impacting the surface of the copper sleeve for 2min, so that the polarization effect is increased, more crystal nuclei are formed during plating, and the effect of refining crystal grains is achieved.
S43: and (3) at the later stage of positive plating: connecting the copper sleeve with a rotary cathode of an electroplating pulse power supply, putting the copper sleeve into an electrolytic bath in an electrified manner, and electroplating under the following process parameters: the temperature of the plating solution is 45 ℃, the flushing speed is 4L/min, the cathode rotation speed is 300r/min, the current density is 50A/dm2, the current pulse frequency is 5.5KHz, and the current duty ratio is 75%.
A large number of ions are adsorbed on the surface of the electrode due to the charge. And because of the requirement of electric neutrality, ions with opposite electric potentials tend to exist in the area near the electrode. These ions and electrodes exhibit opposite polarities, and thus both constitute an electric double layer, and can be similarly considered as a capacitor. In the case of electroplating with a pulse current, the electric double layer is charged first in the pulse-on phase and then discharged in the pulse-off phase. This charging and discharging process can have an effect on chromium deposition, especially during the discharge phase. During the double layer discharge phase, the discharge area occurs near the electrodes, so that the deposition process does not need to pass through the interior of the solution, and the influence of the conductivity and the solution resistance is negligible, so that the current at the cathode surface is uniformly distributed during the process. This results in a uniform distribution of the chromium layer deposited on the cathode surface during the discharge.
S5: and (3) discharging and cleaning: taking out the copper bush from the electrolytic bath, firstly washing the copper bush with tap water for more than 30s, then washing the copper bush with deionized water for more than 30s, and finally drying the copper bush with compressed air;
s6: and (3) dehydrogenation treatment: the assembly was placed in a vacuum oven and heat treated at 300 ℃ for 7 h.
Example two
The second embodiment is the same as the first embodiment except that:
in step S3, the ratio of the modified carbon nanotubes in the plating solution was 3 g/L.
EXAMPLE III
The third embodiment is the same as the first embodiment except that:
in step S3, the ratio of the modified carbon nanotubes in the plating solution is 4 g/L.
Example four
The second embodiment is the same as the first embodiment except that:
in step S3, the ratio of the modified carbon nanotubes in the plating solution is 5 g/L.
EXAMPLE five
And the fifth embodiment is that on the basis of the first embodiment, in order to improve the air tightness of the prepared black chromium layer and eliminate cracks of the chromium layer, diamond is used for extruding the surface of the chromium layer, so that a residual profit layer is formed on the surface of the base body while the surface of the chromium layer has no cracks, and the fatigue strength of the base body is improved.
EXAMPLE six
The fifth embodiment is that on the basis of the first embodiment, aiming at the problem of unavoidable poor plating layer generated in electroplating, the hard plating layer of the copper sleeve is deplated, and the specific process comprises the following steps: preparing 50g/L NaOH solution, and deplating at 20-35 ℃ and with the power density of 3-550A/dm 2.
Experimental example 1
The carbon nanotubes prepared in examples 1 to 4 were subjected to the charge amount test, and the test results are shown in table 1:
TABLE 1 Effect of doping with B atoms on the amount of charge and Effect of carbon nanotubes
| Carbon nanotube | Cu atom/e | Doping with B atoms/e |
| Pure carbon nanotube | 1.40 | — |
| B-doped carbon nanotubes | 1.49 | 0.14 |
The data in table 1 indicate that the Cu atom is positively charged, indicating the loss of an electron; doping B atoms into positive charges, indicating that a multi-electron state is formed around the B atoms; the above phenomena indicate that after doping with B atoms, the adsorption energy between the Cu atoms and the carbon nanotubes is improved by enhancing the ionic bond bonding between the two atoms.
Experimental example two
The black chromium plate prepared in examples 1 to 4 was subjected to emissivity test, and the test results are shown in table 2:
TABLE 2 influence of doped modified carbon nanotubes on the emissivity of electroplated black chromium
The data in Table 2 show that when the doping amount of the modified carbon nanotube is increased within the range of 2-4g/L, the emissivity of the electroplated black chromium is increased; however, when the doping amount of the modified carbon nanotube reaches 5g/L, the emissivity of the electroplated black chromium is rather reduced because the excessive modified carbon nanotube and CrO increase along with the increase of the doping amount of the modified carbon nanotube4 2-Forming a competitive relationship, and seizing active sites on the surface of the Cu atomic matrix together to block the deposition of Cr, so that the emissivity of the electroplated black chromium is reduced.
Experimental example III
The X-ray tube manufactured by the black chromium plating process in the embodiments 1 and 2 is tested in a high-temperature working state at 600-700 ℃ in a high vacuum state, then an anode rotor is dissected and taken out, and samples are randomly selected to carry out black chromium plating adhesion strength and plating thickness detection. The test proves that the coating meets the GB/T5270-2005 standard of the test method for the adhesion strength of the metal coating on the metal substrate by electrodeposition and chemical deposition, the surface coating does not peel off, and the thickness of the black chromium coating is about: 0.75 μm (according to GB/T6462-2005 "microscope method for measuring the thickness of metal and oxide coatings").
Finally, it should be noted that: the above examples and experimental examples are only used to illustrate the technical solution of the present invention, but not to limit the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (7)
1. A preparation method of electroplating black chromium with high heat radiation coefficient is characterized by comprising the following steps:
s1: treating the surface of a substrate: before electroplating, firstly polishing the surface of a substrate, then cleaning the surface of the substrate by using a detergent and deionized water, and finally eliminating the residual stress on the surface of the substrate;
s2: preparing trivalent chromium plating solution: the plating solution comprises the following components: 100-110g/L CrCl3·H2O, 50-60g/L NH4Cl, 55-65g/L NaCl, 60-70g/L HCOONa, 10-20g/L CON2H410-20g/L NH4Br, deionized water as solvent;
s3: preheating and adding modified carbon nanotubes: preheating an electroplating device with a rotary cathode structure, updating a solution around a cathode in a bottom flushing mode, and adding a modified carbon nano tube according to the proportion of 2-5g/L to realize the self-assembly of the modified carbon nano tube on the surface of a substrate;
s4: and (3) formal black chromium electroplating:
s41: in the early stage of forward plating, removing an oxide film on the surface of the substrate by using a reverse small current in a short time;
s42: in the middle stage of forward plating, continuously impacting the surface of the substrate for 2min by using a forward large current 2 times as large as the electroplating current to increase the polarization effect;
s43: and (3) at the later stage of positive plating: connecting the matrix with a rotary cathode of an electroplating pulse power supply, putting the matrix into an electrolytic bath in an electrified manner, and electroplating under the following process parameters: the temperature of the plating solution is 45 ℃, the flushing speed is 4L/min, the cathode rotation speed is 300r/min, and the current density is 50A/dm2The current pulse frequency is 5.5KHz, and the current duty ratio is 75 percent;
s5: and (3) discharging and cleaning: taking out the matrix from the electrolytic cell, firstly washing the matrix for more than 30s by using tap water, then washing the matrix for more than 30s by using deionized water, and finally drying the matrix by using compressed air;
s6: and (3) dehydrogenation treatment: the matrix is placed in a vacuum furnace and heat treated for 7h at 300 ℃.
2. The method of claim 1, wherein in step S1, the surface of the substrate is polished with 80-100 mesh quartz sand to achieve Ra 0.4.
3. The method for preparing black chromium electroplating solution with high emissivity of claim 1, wherein in step S1, the detergent comprises the following components: 100g/L of sodium hydroxide, 25g/L of sodium carbonate decahydrate, 8g/L of sodium silicate and deionized water as a solvent.
4. The method for preparing black chromium electroplating solution with high emissivity coefficient as claimed in claim 1, wherein the step S3, the self-assembly of the modified carbon nanotubes on the surface of the substrate specifically comprises the following steps:
s31: modification of carbon nanotubes: b atoms are doped on the surface of the carbon nano tube by using a chemical vapor deposition method to form an electron-deficient structure, so that the Fermi level of the carbon nano tube is improved, the energy gap is reduced, and the adsorption capacity between the carbon nano tube and metal atoms is improved;
s32: the electric field force in the electrolytic bath is used as a driving force, and the polarized carbon nano tubes overcome the influence of self gravity, electrostatic force and external viscous resistance and are directionally arranged on the surface of the matrix.
5. The method of claim 4, wherein in step S31, the modified carbon nanotubes have a diameter of 20-30nm, a length of 10-30 μm, a B atom content of 3-3.2%, and a purity of > 95%.
6. The method of claim 1, wherein the diamond is pressed on the surface of the chrome layer to improve the airtightness of the prepared black chrome layer and to eliminate cracks of the chrome layer.
7. The method of claim 1, wherein the problem of poor plating layer which is inevitable during electroplating is solved by the method of claim 1The method comprises the following specific processes of deplating the hard coating on the surface of the substrate: preparing 50g/L NaOH solution, and using 3-550A/dm at 20-35 deg.C2The power density of (3) is removed.
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| CN113774438A (en) * | 2021-08-24 | 2021-12-10 | 上原汽车铭牌（惠州）有限公司 | Trivalent chromium electroplating solution formula for automobile mark production and trivalent chromium electroplating process |
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| KR20110083147A (en) * | 2010-01-13 | 2011-07-20 | 신양에너지 주식회사 | Black metal plating method using the same for copper plate with low emissivity and high absorption of solar energy |
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| CN113774438A (en) * | 2021-08-24 | 2021-12-10 | 上原汽车铭牌（惠州）有限公司 | Trivalent chromium electroplating solution formula for automobile mark production and trivalent chromium electroplating process |
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