As previously discussed, each element involved in the electroforming process can be compared to a component of a DC circuit. For instance, if either the anode or cathode is not immersed in the electrolyte, the electrical current is interrupted.
In fact, the amount of current flowing through the circuit is directly proportional to the number of cations reduced at the cathode — this is described by Faraday’s First Law of Electrolysis.
It was also mentioned that, as long as the circuit remains complete, the amount of current is directly proportional to the applied voltage. However, according to Ohm’s Law (V=I·R), the total resistance of the system must also be considered.
The total resistance R can be broken down into two main components:
- Rp — Resistance of the metallic part being electroformed:
where ρ is the resistivity of nickel (Ω·m), which increases with temperature, L is the length of the part being electroformed (m), and Ap is the cross-sectional area (m²);
- Re — Resistance of the electrolyte:
where k is the electrical conductivity of the solution (S·m⁻¹), d is the distance between the electrodes (m), and Ae is the cross-sectional area of the electrodes (m²).
The conductivity of the electrolyte is directly proportional to its ionic concentration. By combining the two previous formulas, we can identify the key factors that reduce resistance and therefore improve efficiency — allowing more current to flow and resulting in greater metal ion deposition at a given voltage:
- high conductivity of the solution (i.e., high ionic concentration);
- short distance between electrodes;
- homogeneous crystalline structure (absence of welds or cold spots, especially at contact points);
- large cross-sectional area of the part being electroformed;
- large cross-sectional area of the electrodes.
However, it‘s crucial to stay within recommended parameters. An overly concentrated electrolyte can generate excessive stress on the deposit, particularly at the early stages when the layer is still thin. This stress can compromise the integrity of the electroformed part. The recommended electrolyte concentration is between 28° and 35° Baumé.
Voltage and current