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Q: What are the characteristics of the plating?

07/08/2025 07:40:18 1    answers in: Other
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Characteristics of Zinc Plating
Zinc is stable in dry environments and rarely tarnishes. However, once exposed to water or humid atmospheres, zinc reacts with oxygen or carbon dioxide to form an oxide or alkaline zinc carbonate film. This film provides protection, preventing further oxidation. Zinc is highly susceptible to corrosion in environments containing acids, alkalis, and sulfides. To enhance its corrosion resistance, zinc coatings are typically passivated, such as in chromic acid or chromate solutions. The resulting passivation film effectively prevents zinc from reacting with moisture. Dehydrogenation treatment is required for spring parts, thin-walled parts, and steel parts requiring high mechanical strength, while this step is generally not required for copper and copper alloy parts.

Characteristics of Cadmium Plating
Cadmium plating performs well in marine atmospheres or in hot water above 70°C, offering strong corrosion resistance and lubricity. It dissolves slowly in dilute hydrochloric acid but is highly soluble in nitric acid and insoluble in alkalis. Cadmium coatings are softer than zinc coatings, less susceptible to hydrogen embrittlement, and offer stronger adhesion. Under certain electrolytic conditions, they can even be more aesthetically pleasing. However, please note that the gases and soluble cadmium salts produced by cadmium during melting are toxic.
Under normal conditions, cadmium acts as a cathodic coating on steel, but it becomes anodic in marine and high-temperature atmospheres. Therefore, cadmium coatings are often used to protect parts from corrosion in seawater or similar salt solutions, as well as in atmospheres saturated with seawater vapor. Cadmium plating is used on many parts in the aviation, marine, and electronics industries. It can also be used for polishing, phosphating, and as a paint primer, but is not suitable for food containers.


Characteristics of Chromium Plating
Chromium is very stable in humid atmospheres, alkalis, nitric acid, sulfides, carbonate solutions, and organic acids, but is soluble in hydrochloric acid and hot concentrated sulfuric acid. Under direct current, if a chromium coating acts as an anode, it may dissolve in caustic soda solutions. Advantages of chromium coatings include strong adhesion, high hardness, good wear resistance, and high light reflectivity. It also has high heat resistance, retaining its original color below 480°C, but oxidizing above 500°C and significantly decreasing its hardness at 700°C. However, the chromium layer is hard but brittle and easily flakes off, especially when subjected to alternating shock loads. Chromium is also porous. Metallic chromium readily forms a passive film in air, changing its potential, making it a cathodic coating on iron.


Characteristics of Nickel Plating
Nickel exhibits excellent chemical stability at room temperature and resists discoloration. It only oxidizes at temperatures above 600°C. It dissolves slowly in sulfuric and hydrochloric acids but is soluble in dilute nitric acid. Furthermore, nickel readily forms a passive film in concentrated nitric acid, providing excellent corrosion resistance.
Characteristics of nickel plating include high hardness, easy polishing, high light reflectivity, and aesthetic appeal. However, it also suffers from the disadvantage of porosity. To overcome this drawback, multilayer metal plating is used, often with nickel as the intermediate layer. Nickel is a cathodic coating on iron and an anodic coating on copper.

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