The main factors affecting the distribution of the plating layer are the cathodic polarization of the plating solution, the conductivity, the current efficiency of the cathode, the geometry of the electrode and the plating bath, and the surface state of the base metal.
1. Cathodic polarization Cathodic polarization is the slope of the cathodic polarization curve, which is the degree to which the cathodic potential changes with the cathodic current density (dφ/dDK). Since the slope of each point on any cathodic polarization curve is different, the polarization at each point is not the same. When the other conditions are not changed, the polarizability of the plating solution is better. Therefore, any factor that can increase the cathodic polarization (such as selecting appropriate complexing agents and additives, etc.) can improve the dispersibility and coverage of the coating.
2. Electroplating solution conductivity In general, increasing the conductivity increases the coverage. When the cathodic polarizability of the plating solution is large, increasing the conductivity can significantly improve the dispersibility and coverage. If the polarizability is very small or even close to zero, increasing the conductivity may not improve the dispersion capability. For example, the degree of polarizability at the time of chrome plating is almost equal to zero, so even if the chromium plating solution has good conductivity, the dispersion thereof And coverage is poor.
3. Cathode Current Efficiency The effect of cathodic current efficiency on the dispersion capability depends on the degree to which the cathodic current efficiency varies with cathodic current density. Generally can be divided into three situations:
(1) The current efficiency of the cathode varies little with the change in current density (eg, sulphate copper plating, galvanization), and the current efficiency has almost no effect.
(2) Cathode current efficiency decreases as the current density increases (for example, all plating solutions using a complexing agent), the cathodic current efficiency can improve dispersion and coverage. Due to the large current density, the current efficiency is low, and the current efficiency is high where the current density is small, so that the actual current density at the cathodes is redistributed more uniformly. That is, the ability to disperse has increased.
(3) Cathode current efficiency increases with increasing current density (eg, chrome plating), which can reduce dispersion and coverage. Because the current density at the cathode is high, the current efficiency is high, and the current density is low where the current density is small, so that the actual current density at the cathodes is redistributed more unevenly, that is, the dispersibility is reduced.
4. Electrode and plating cell geometry factors The shape and size of the electrode, the distance between the electrodes, the position of the electrode in the plating bath, and the shape of the plating bath all affect the uniform distribution of the coating on the cathode surface. In order to improve the uneven current distribution on the electrode caused by this, the auxiliary cathode and the pictorial anode are often used in electroplating, and the distance between the cathode and the anode is appropriately increased.
5. Surface state of the base metal Since the overpotential of hydrogen on the rough surface is smaller than the smooth surface, hydrogen easily precipitates on the rough surface and the deposit is not easily deposited. Therefore, improving the smoothness of the base metal can often improve the covering ability. In addition, if the matrix metal contains impurities with low hydrogen overpotential (such as carbon impurities in cast iron), hydrogen easily precipitates on these impurities and the deposited layer is difficult to deposit. If the overpotential of hydrogen on the base metal is less than the overpotential on the plating metal, more hydrogen gas will escape during the plating process immediately after the tank. If plating is applied locally at this time, hydrogen evolution is less and the current efficiency is high because the plating is applied first, which will reduce the dispersion ability. At this time, in order to plate uniform continuous plating, a large current density “impact” is often used at the beginning of power supply, so that the surface of the substrate metal is quickly plated with a layer of metal with a large hydrogen overpotential, and then the normal Electroplating at the current density, which can eliminate the adverse effect of the base metal on the dispersibility and coverage
158.The Status and Development Trend of New Surface Functional Coating Technology
I. Technical Overview
New surface functional coating technologies, including low-temperature chemical surface coating technology and ultra-deep surface modification technology, which use physical, chemical or physical chemistry to change the "surface and composition of materials and their parts", its characteristics It is to maintain the inherent characteristics of the matrix material, but also to provide a variety of properties required for the surface, so as to meet the special requirements of various technologies and service environment for the material, so it is the most active technical field of manufacturing and materials disciplines, but also involves surface treatment Interdisciplinary with coating technology. Its greatest advantage lies in its ability to produce extremely thin surface layers that are difficult or even impossible to obtain with a minimum of material and energy consumption. This results in maximum economic benefits. It is a high-quality, highly effective surface modification and coating. technology.
High-quality, high-efficiency surface modification and coating technology has a wide range: such as thermal chemical surface technology; physical vapor deposition; chemical vapor deposition; physical chemical vapor deposition technology; high-energy isotopic surface coating technology; diamond thin film coating; Multi-layer composite coating technology; surface modification and coating performance prediction and cropping technology; performance testing and life assessment and so on.
The new low-temperature chemical vapor deposition technology introduces plasma-enhanced technology to reduce its temperature to less than 600 degrees and obtain a new process of hard wear-resistant coating. The high-strength, high-performance coating process produced at high speed and heavy load Difficult processing has its special role.
The ultra-deep surface modification technology can be applied to most heat treatment parts and surface treatment parts, and can replace the high-frequency quenching, carbonitriding, ion nitriding and other processes to get a deeper penetration layer, higher wear resistance, products Sudden increase in life span can produce breakthrough functional changes.
Second, the status quo and development trends at home and abroad
With the development of basic industry and high-tech products, the demand for high-quality, high-efficiency surface modification and coating technology has been extended in depth. At home and abroad in the situation where this field and related disciplines promote each other, such as “thermal chemical surface modification” There have been breakthroughs in the development of "high-energy plasma surface coatings," "diamond thin-film coating technologies," and "surface modification and coating process simulation and performance prediction."
1. Status and Development Trend of Thermochemical Surface Modification Technology
In recent years, foreign emphasis has been placed on "carburizing, carbonitriding and other technologies under controlled atmosphere conditions and vacuum conditions, and has achieved industrialization. However, it is rarely used in China, and related technological research work is not enough. Carburizing and vacuum carburizing technologies significantly shorten the production cycle, save energy, and save time. At the same time, they can improve the quality of work pieces, prevent oxidation, decarburization, ensure the corrosion resistance and fatigue resistance of the parts, and reduce the machining allowance after heat treatment. Clearance time.
At present, research results on the control and monitoring of carbon potential in the world and the control of the fabric layer type have been applied to actual production and computerized online dynamic control.