Plating - An in Depth Look

Plating usually describes a process of metal finishing that deposits a metallic coating onto some form of substrate. Plating is done to protect, beautify, increase corrosion or wear resistance, affect conductivity of heat or electricity and or solder-ability of an item.  For our purposes, plating can be generally described by two different processes, electroplating and electroless deposition. Electroless plating involves the use of an aqueous solution containing metallic ions that is designed to deposit the metal onto a substrate through autocatalytic reduction of the metallic ions in the solution. 

Electroplating is a process where a metal in solution is deposited onto an electrode that is negatively charged relative to the solution. The item being plated can be referred to as the cathode.  The solution is charged through the use of an anode.   Since the metal in solution is in ionic form and contains a positive charge, it migrates toward the negatively charged cathode.  Once the metallic ion has reached the cathode it picks up the electrons and is deposited onto the cathode (item being plated).  The metallic coating accumulates one atom at at time.  Faraday's law states that for each  Faraday of  electricity (96,5000 Coulombs of electrons), one gram of metal will be deposited on the cathode.  The plating industry uses amperes as the measure of current flowing through the system.  One Ampere = 1 Coulomb of electrons for 1 second therefore it is possible to determine the amount of metal deposited onto the cathode by factoring the amperes by the amount of time the current is flowing. 

 It is important to note that the actual amount of metal deposited by the system is a product of time, the total current flowing through the solution, and bath efficiency; also called the cathode efficiency.  Since bath efficiency can range from less than 10% to more than 90%, it is important to understand the chemistry of the bath to monitor it's efficiency.  For example the metallic content affects the cathode efficiency of our 24K Bright Gold Solution near the range of the stock solution we provide.  Due to cost factors we typically offer this solution with approximately one-third Troy oz fine gold per gallon, (~ 2.8g/qt.). 

The depletion table for this solution indicates that increasing the gold content above this level has diminishing effect on the bath efficiency.  However, as gold is depleted from this solution the bath efficiency can fall off significantly. 

There are many factors that affect the properties of the deposit.  A few of the main factors are;  Current density, which is the ratio of the system amperage over the unit area of the anode or cathode.  The temperature of the solution.   The pH of the solution.  The concentration of metallic ions.  Relative movement of the solution and cathode.