Short Answer:

Spark plugs are made of different materials that can withstand high temperature and pressure inside the engine cylinder. The main body is made of steel, the insulator is made of ceramic (usually aluminum oxide), and the electrodes are made of metals such as copper, nickel, platinum, or iridium.

Each part of the spark plug is carefully chosen for durability and performance. The metal shell gives strength, the ceramic insulator prevents current leakage, and the electrode materials ensure long life and strong spark generation for efficient combustion.

Detailed Explanation :

Spark Plugs Made of

A spark plug is an essential component of the ignition system in petrol engines. It is used to ignite the compressed air-fuel mixture inside the engine cylinder by producing an electric spark. Since it operates under very high temperature and pressure, it must be made of materials that are strong, heat-resistant, corrosion-resistant, and electrically efficient.

The materials used in spark plugs are selected based on the part’s function — mechanical strength for the outer shell, electrical insulation for the insulator, and high conductivity for the electrodes. The combination of these materials ensures reliable ignition, long service life, and improved engine performance.

Main Parts and Their Materials

Metal Shell (Body):
The outer metal shell of the spark plug is usually made of steel or nickel-coated steel. This part provides the main structure and strength to the plug. It is threaded to fit into the engine cylinder head and acts as the grounding path for the electric spark.
The steel is often nickel-plated to prevent rusting and corrosion due to exposure to heat, fuel, and gases. This helps in maintaining durability even in harsh engine conditions.
Insulator:
The insulator surrounds the central electrode and isolates it electrically from the outer metal shell. It is made of aluminum oxide ceramic (Al₂O₃) because of its excellent electrical insulation and high heat resistance.
Ceramic can withstand very high temperatures (up to 1200°C) and provides mechanical strength. It also resists the buildup of carbon or dirt, ensuring clean and efficient spark operation.
Central Electrode:
The central electrode is the part through which the spark passes to the ground electrode. It must conduct electricity efficiently and resist heat and erosion caused by repeated sparking.
Common materials used for the central electrode include:
- Copper Core: Excellent conductor of electricity and heat; commonly used in standard spark plugs.
- Nickel Alloy Tip: Provides better resistance to corrosion and erosion.
- Platinum or Iridium Tip: Used in high-performance spark plugs due to their high melting point and durability. Platinum and iridium allow finer electrodes that produce stronger sparks and last longer.
Ground (Side) Electrode:
The ground electrode is welded to the metal shell and positioned close to the central electrode, forming the spark gap. It is usually made of nickel-steel alloy or coated with platinum or iridium in premium spark plugs.
These metals resist wear and maintain a stable spark gap for longer durations. In modern spark plugs, iridium or platinum electrodes can last up to 100,000 kilometers or more.
Sealing Gasket:
The gasket seals the joint between the metal shell and insulator to prevent gas leakage. It is generally made of copper or soft metal alloy that can withstand high temperature and pressure while ensuring a tight seal.
Terminal Stud:
The terminal stud connects the spark plug to the ignition cable or coil wire. It is made of steel or nickel-plated brass, ensuring good electrical contact and corrosion resistance.

Material Properties Required

Each material used in spark plug construction must possess special properties to perform its role effectively. The required properties are:

High electrical conductivity: For efficient current flow (copper, nickel).
High melting point: To resist heat damage (platinum, iridium).
Corrosion resistance: To prevent rust or fuel reaction.
Thermal shock resistance: To withstand sudden temperature changes.
Good insulation: To prevent current leakage (ceramic insulator).

These combined characteristics make the spark plug capable of continuous operation in the extreme environment of the engine cylinder.

Modern Spark Plug Materials

Modern spark plugs have evolved significantly with the use of precious metals like platinum and iridium. These materials offer several advantages:

They produce a stronger spark even at lower voltages.
They reduce electrode wear, increasing plug life.
They improve fuel efficiency and engine performance.
They maintain a consistent spark gap for a long time.

For example:

Copper Spark Plug: Used in older engines; provides good conductivity but wears out faster.
Platinum Spark Plug: Longer life (up to 60,000 km); better heat resistance.
Iridium Spark Plug: Longest life (up to 100,000 km); strong spark and efficient combustion.

Performance and Durability

The choice of materials directly affects spark plug performance.

A copper-core electrode helps remove heat quickly, preventing overheating.
A ceramic insulator ensures no current leakage and maintains spark efficiency.
Platinum and iridium tips help maintain constant spark strength, ensuring smooth engine running and reduced fuel consumption.

Due to these material combinations, modern spark plugs provide higher reliability, lower maintenance needs, and consistent engine operation under all conditions.

Conclusion

Spark plugs are made of specially selected materials that can withstand extreme engine conditions. The main body is made of steel, the insulator from ceramic (aluminum oxide), and the electrodes from metals like copper, nickel, platinum, or iridium. Each material is chosen for its strength, conductivity, and heat resistance. The combination of these materials ensures long life, efficient combustion, and better engine performance. Modern spark plugs, especially those using platinum or iridium, offer superior durability and reliability compared to conventional ones.