Electroplating Process and Components
– Electroplating is a process for producing a metal coating on a solid substrate through the reduction of cations of that metal by means of a direct electric current.
– The part to be coated acts as the cathode (negative electrode) of an electrolytic cell.
– The electrolyte is a solution of a salt of the metal to be coated.
– The anode (positive electrode) is usually either a block of that metal or of some inert conductive material.
– The current is provided by an external power supply.
– The electrolyte in the electrolytic plating cell should contain positive ions (cations) of the metal to be deposited.
– These cations are reduced at the cathode to the metal in the zero valence state.
– The anode can be made of the metal that is intended for coating onto the cathode.
– When the anode is made of the coating metal, the opposite reaction may occur at the anode, turning it into dissolved cations.
– The plating is most commonly a single metallic element, not an alloy.
Plating Bath and Techniques
– Plating baths often include cyanides of other metals in addition to cyanides of the metal to be deposited.
– These free cyanides facilitate anode corrosion and help maintain a constant metal ion level.
– Non-metal chemicals such as carbonates and phosphates may be added to increase conductivity.
– Stop-offs, such as tape, foil, lacquers, and waxes, are applied to prevent plating on certain areas of the substrate.
– The ability of a plating to cover uniformly is called throwing power.
– A strike deposit is a very thin plating used as a foundation for subsequent plating processes.
– It is formed using high current density and a bath with low ion concentration.
– Strikes can be used to improve adhesion between different metals.
– Pulse electroplating involves alternating the electrical potential or current between two different values.
– This results in a series of pulses that can change the composition and thickness of deposited films.
Different Electroplating Methods
– Brush electroplating involves using a brush saturated with plating solution.
– The brush is connected to a low voltage direct current power source.
– Advantages include portability and low masking requirements.
– Disadvantages include greater operator involvement and limited plate thickness.
– Barrel plating is commonly used for large numbers of small objects.
– Objects are placed in a barrel-shaped cage and immersed in a chemical bath.
– Electrical currents run through the pieces in the barrel to complete circuits.
– Provides uniform and efficient plating process, but finish may suffer from abrasion.
– Unsuitable for highly ornamental or precisely engineered items.
Cleanliness and Test Cells
– Cleanliness is essential for successful electroplating.
– Cleaning methods include solvent cleaning, alkaline detergent cleaning, and acid treatment.
– The waterbreak test is commonly used to test cleanliness.
– Surfactants such as soap can reduce test sensitivity.
– Electroplating can displace hydrophilic contaminants easily.
– Test cells are used to measure parameters like throwing power.
– Throwing power measures the uniformity of electroplating current and metal thickness.
– Micro throwing power refers to coating small recesses.
– Various conventions exist for measuring throwing power.
– Cell performance parameters are measured in small test cells.
Effects, Disadvantages, and History of Electroplating
– Electroplating changes the chemical, physical, and mechanical properties of the workpiece.
– Examples of chemical changes include improved corrosion resistance.
– Examples of physical changes include a change in outward appearance.
– Examples of mechanical changes include a change in tensile strength or surface hardness.
– Electroplating can reduce contact resistance and prevent oxidation.
– Disadvantages of electroplating include lower deposition speed, consumption of relatively expensive chemicals, limited choice of coating metals, process limited to very thin coatings, and immersion coating process stopping after the substrate is completely covered.
– Different methods of electroplating include immersion coating processes, sputtering, physical vapor deposition, chemical vapor deposition, and gilding.
– The history of electroplating dates back to Boris Jacobi in Russia and Luigi Valentino Brugnatelli in 1805.
– The electroplating industry was founded in Birmingham by George Elkington and Henry Elkington.
– Electroplating technology spread globally with the development of electric generators.
– Applications and innovations in electroplating include decorative plating of gold and silver, commercial plating of nickel, brass, tin, and zinc, development of hard chromium plating and bronze alloy plating, and use in the aviation industry for corrosion protection and enhanced wear properties. Source: https://en.wikipedia.org/wiki/Electroplating
Electroplating, also known as electrochemical deposition or electrodeposition, is a process for producing a metal coating on a solid substrate through the reduction of cations of that metal by means of a direct electric current. The part to be coated acts as the cathode (negative electrode) of an electrolytic cell; the electrolyte is a solution of a salt of the metal to be coated; and the anode (positive electrode) is usually either a block of that metal, or of some inert conductive material. The current is provided by an external power supply.
Electroplating is widely used in industry and decorative arts to improve the surface qualities of objects—such as resistance to abrasion and corrosion, lubricity, reflectivity, electrical conductivity, or appearance. It is used to build up thickness on undersized or worn-out parts, or to manufacture metal plates with complex shape, a process called electroforming. It is used to deposit copper and other conductors in forming printed circuit boards, and copper interconnects in integrated circuits. It is also used to purify metals such as copper.
The aforementioned electroplating of metals uses an electroreduction process (i.e. negative or cathodic current on the working electrode). The term "electroplating" is also used occasionally for processes, that occur under electrooxidation (i.e positive or anodic current on the working electrode). One such example is the formation of silver chloride on silver wire in chloride solutions to make silver/silver-chloride (AgCl) electrodes. Although such processes are more commonly referred to as anodizing rather than electroplating.
Electropolishing, a process that uses an electric current to selectively remove outermost layer from the surface of a metal object, is the reverse of the process of electroplating.
Throwing power is an important parameter that provides a measure of the uniformity of electroplating current, and consequently the uniformity of the electroplated metal thickness, on regions of the part that are near to the anode compared to regions that are far from it. It depends mostly on the composition and temperature of the electroplating solution, as well as on the operating current density. A higher throwing power of the plating bath results in a more uniform coating.
