(2) Faraday's law

In electroplating, there is none other than Faraday's law as important and used as the foundation of various calculations. The law is composed of the following two sections.

Faraday discovered this law in 1834. He has defined 1 ampere per 1 second of electricity as 1 Coulomb, an amount of electricity needed to generate 1 chemical equivalent of various atoms or group as 96,540 Coulombs, and named this amount of electricity 1 Faraday.
The chemical equivalent is a product of dividing the plating metal atomic weight by the valence of the metal ions in the plating bath. In case if bright nickel in Watts bath, this will be 58.71/2＝29.36（g）. In other words, 1 Faraday of electricity value, 29.36g of nickel will be precipitated with this nickel plating.

Calculation example 1

With silver nitrate solution, how much silver will be precipitated by 1 hour electrolysis at 1 ampere?

　AgNO₃ →　Ag+ + NO^3-
Since Ag is monovalent and the atomic weight is 107.88, the amount of precipitation will be
(107.88 x 60 sec. X 60 min.) / (96,540 x 1 valency) = 4.023g

Calculation example 2

How much nickel will precipitate on cathode by electrolyzing Nickel sulfate solution ( NiSO4) at 1 ampere for 1 hour?

　NiSO₄　→ Ni²+ + SO₄^2-
Ni is divalent, and the atomic weight is 58.71, therefore...
(58.71 × 60sec. × 60min.) / (96,540×2)＝1.095g

When this is expressed in a plating thickness, since specific gravity of nickel is 8.9g/cm3, the thickness per 1dm2 is...
　　1.095 (g/10¹⁰μm²) / 8.9 (g/10¹²μm³)
　　＝0.123×10² (μm/Ah・dm²)
　　＝12.30 (μm/Ah・dm²)

When this is converted into per one minute (AM),
it will be 12.3/60=0.205 (μm/AM・dm²)

In general, a concept of "Current density" is used to determine the strength of the electrical current. This indicates the strength of current applied per unit area of the product, and typically represented with A/dm2 (Amperes per 1 square decimeter 100x100mm).
Therefore, surface area of the product to be plated is calculated, and the applicable current density multiplied constitutes the current (A) to be applied per one product.