Give the properties and uses of silicon iron alloy and nickel iron alloy.

Silicon Iron alloy: Pure iron has low resistivity that results in higher eddy current losses. These losses can be minimized through increasing the resistivity of the material that is achieved through adding 1 to 4 percent of silicon to iron. Silicon raises the electrical resistivity of iron. This decreases hysteresis loss. The magnetostriction consequence is also decreased. Silicon also enhances resistance to corrosion and oxidation and raises hardenability.

Silicon Iron alloy is utilized in the form of thin sheets termed as laminations. These laminations are used in transformers, large turbo- generators and small machines.

Nickel Iron alloy: A group of iron alloys having between 40 to 90 percent nickel have much higher permeabilities at lower losses and low flux densities than ordinary iron. The significant alloys are mumetal and permalloy. Mumetal has lower permeability but higher resistivity. Addition of small amounts of another element to nickel iron alloys enhances their magnetic properties. Nickel enhances strength, toughness and resistance to fatigue. This also lowers the critical cooling rate and therefore increases hardenability.

Nickel Iron alloy is broadly used in transformer cores and loading coils instrument transformers, magnetic circuits of instruments, for telephone circuits, for magnetic screens of electronic equipments.