100 Questions on Basic Electroplating Knowledge (Part 6)
26.Known current density and plating time, how to find the thickness of the plating layer?
Answer: First of all, according to the type of plating the current efficiency of the process, while checking the table to get the electrochemical equivalent of the metal and the density (specific gravity), and then calculated according to the following formula: ■ Plating thickness d formula (d: microns).
Plating thickness d formula (d: micron)
d=(C×Dk×t×ηk×100)/(60×r)
■Plating time t calculation formula (t: minutes)
t=(60×r×d)/(C×Dk×ηk×100)
■Cathode current density Dk calculation formula (Dk: A/dm2)
Dk=(60×r×d)/(C×t×ηk×100)
■Cathode current efficiency calculation formula:
ηk=(60×r×d)/(C×t×Dk×100)
C=electrochemical equivalent (g/ampere-hour)
Dk=cathodic current density (amperes/square decimeter)
t=plating time (min)
ηκ=cathodic current efficiency (%)
r = plating layer metal density (g / cm 3)
Example: nickel plating solution is known to be 95% current efficiency, cathode current density of 2.5A / d ㎡, plating 20 minutes after the resulting thickness of the plating layer is how much? Check the table to get the nickel electrochemical equivalent of 1.095 density 8.8
d = (C × Dk × t × ηk) / 60r = 1.095 × 2.5 × 20 × 95% × 100 / (60 × 8.8) = 9.85um
27.What are anodic and cathodic plating, and for iron substrate, zinc, copper, nickel, chromium, copper-tin alloy, etc. plating belongs to that category of plating?
Answer:According to the electrochemical relationship between the plated metal and the base metal, the plating can be divided into anodic plating and cathodic plating, under general conditions, the electrode potential of the plated metal is negative than that of the base metal, it is called anodic plating, and vice versa, it is called cathodic plating. Zinc plating electrode potential than the electrode potential of the iron substrate is negative, so the zinc plating is anodic plating. Copper, nickel, copper-tin alloy plating potential than the potential of the iron substrate is positive. Therefore, it is cathodic plating. Chromium plating according to the standard potential, than the iron is negative, but because the chromium plating is easy to purify, so that the potential tends to be positive, so also belongs to the cathodic plating. Since the potential of a metal changes depending on the conditions, whether the plating is anodic or cathodic may also change. For example, under normal conditions, tin plating is cathodic for iron, but in organic acids, it becomes anodic.
28.What is the protective effect of anodic plating and cathodic plating on the base metal?
Answer:The protection principle of anodic plating is based on the potential of the plating is negative compared to the base metal, its electrolytic pressure is larger, it becomes the anode in the corrosion battery, thus delaying the corrosion of the base metal. Even when the base metal is slightly exposed, the plating can still play a protective role, so the number of pores on the anodic plating, the impact on the protective performance is very small, in terms of thickness, the greater the thickness of the plating, the stronger the protection. Cathodic plating on the base metal only plays a purely mechanical isolation role, not like anodic plating electrochemical protection, so it must be in the plating porosity is very little in the case of protection, otherwise, in the plating porosity or damage, the base metal will be used as a corrosive battery anode, accelerating the corrosion of the base metal. Generally the porosity of the plating layer decreases with the increase of the thickness of the plating layer, so the greater the thickness, the stronger the protective performance of the cathodic plating layer.
29.Plated parts plating before the general quality requirements?
Answer:Before plating, the plated parts must be free of oxidized skin, rust, stains and oil, and the surface can be completely wetted by water without hanging water droplets.
30.After the plating of plated parts, why do I need to rinse with water?
Answer:Because after the product is plated out of the tank, there is a large amount of plating solution adhering to the surface and holes, and the plating solution itself usually has a certain degree of corrosiveness. If it is not cleaned, it will corrode the plating layer and the substrate, which will affect the appearance and protection performance of the product. Therefore, after the plated parts out of the tank, should be rinsed with clean water, and then dry.
