Theory of operation

Electroforming:

• produces a metallic layer on another solid metallic substrate through the process of metal cation reduction, using a direct current supplied by a voltage generator;
• it is based on electrolysis, introduced by the physicist Michael Faraday in the 19th century. It is a process that triggers a non-spontaneous chemical reaction by applying direct current to a solution (electrolyte) containing water and charged particles (ions);
• cations are positively charged ions;
• anions are negatively charged ions.

When suspended in the electrolyte:

• cations move toward the negative electrode (cathode);
• anions move toward the positive electrode (anode).

At the respective electrodes:

• cations gain electrons (reduction occurs at the cathode);
• anions lose electrons (oxidation occurs at the anode).

The attractive force between the two opposite charges depends on the electric potential difference.

The electrolyte commonly used for nickel electroforming is nickel sulfamate, a complex salt in which the Ni²⁺ cation is associated with 2 sulfamate anions, becoming NH2SO3-.

The image shows the elements that have just been discussed, as they appear in practice:

• the component undergoing electroforming — whether a metal master, metal mother, or stamper — is connected to the cathode (negative electrode). It is mounted on the shaft of a motor that rotates it continuously;
• the negative terminal of the power supply is connected to the motor shaft;
• the anode (positive electrode) consists of pellets or crowns of pure nickel (Ni or Ni(s)), held within a titanium basket. Titanium is chosen for its strength and resistance to corrosion;
• the positive terminal of the power supply is connected to the basket;
• the electrolyte is a nickel sulfamate solution.

During electroforming, assuming a non-zero direct current:

1. at the anode, metallic nickel (Ni) is oxidized to Ni²⁺ ions;
2. at the cathode, Ni²⁺ ions from the electrolyte are reduced back to metallic nickel (Ni);
3. the concentration of Ni²⁺ ions in the electrolyte remains stable;
4. the electrons lost by nickel at the anode are transferred to the cathode.

The reduced nickel deposits uniformly onto the cathode, aided by the continuous rotation of the part being coated. A rubber ring — visible in the image — helps prevent deformation of the part during high-current or high-speed electroforming, when the attractive force betweeen the electrodes becomes significant.