The spark plug is perhaps the most underrated component in the ignition system of an internal combustion engine. At first glance, this is a simple device consisting of metal and ceramics, but the stability of spark formation and the combustion efficiency of the fuel-air mixture depend on its internal structure. Understanding that what are spark plugs made of?, allows the car owner to make an informed choice when purchasing, avoiding cheap analogues that can damage the engine.
Structurally, the product is a complex composite, where each element performs a strictly defined function under the influence of extreme temperatures and high pressure. The materials are selected to withstand heat up to 2500 degrees Celsius and voltages of tens of thousands of volts. In this article we will analyze in detail the chemical composition and physical properties of the components, without which the operation of a modern internal combustion engine would be impossible.
Center electrode: spark core
The main element that forms the discharge is the central electrode. The durability of the spark plug and the stability of the spark depend on its material. In budget models of the mass segment it is most often used Nickel alloy. This solution is time-tested: nickel has good corrosion resistance and an affordable price. However, it has a significant drawback - it quickly burns out under high thermal loads, which leads to an increase in the gap and misfire.
To increase the resource, manufacturers introduce precious metals. Iridium and platinum have become the standard for premium candles. Iridium, for example, has a melting point of 2454 degrees Celsius, which is significantly higher than nickel. This makes it possible to make the central electrode extremely thin, only 0.4–0.6 mm, which reduces the breakdown voltage and makes it easier to start the engine in cold weather.
There are also copper cores hidden inside a nickel shell. Copper has excellent thermal conductivity, quickly removing heat from the working part, but by itself it is too soft and susceptible to erosion. Therefore, pure copper is practically not used as a working end.
⚠️ Attention: Using spark plugs with an inappropriate heat rating or electrode material can lead to hot ignition, when the mixture is ignited not by the spark, but by the hot electrode. This threatens to destroy the piston group.
When choosing between materials, it is worth considering the recommendations of your car manufacturer. Engineers calculate the ignition system for specific spark formation parameters.
Side electrode and coating technologies
The side electrode, often called the "ground", works in tandem with the central one. At the moment of sparking, it is its edge that is subject to the greatest thermal and chemical attack. Traditionally, this element is made of steel with the addition of nickel or manganese to increase heat resistance. The shape of the ground electrode also matters: a V-shaped notch or U-shaped groove helps the spark jump more easily into the combustion chamber, improving ignition of lean mixtures.
Modern technologies involve the application of special spraying. For example, yttrium coating often used in candles in the mid-price segment. Yttrium increases oxidation resistance and reduces the rate of metal erosion. In expensive models you can find platinum or palladium soldering on the end of the side electrode, which is especially important for circuits with two or four side electrodes.
In multi-electrode spark plugs, the spark always jumps to the side electrode that has the least resistance at the moment. This ensures uniform wear of all electrodes and extends the overall service life of the product.
When installing multi-electrode spark plugs, do not try to adjust the gap mechanically by hitting the side electrode on hard surfaces - this may damage the ceramic insulator or break the seal of the housing.
The galvanic pair must provide a stable discharge without excessive voltage drop.
Insulator: dielectric protection
The bulk of the spark plug body is occupied by the insulator. Its task is to prevent high voltage leakage to the housing and ensure heat removal from the central electrode. The main material here is aluminum oxide (alumina) of high purity. This is snow-white ceramics that can withstand enormous electrical loads and sudden temperature changes.
The surface of the insulator is often coated with a special glaze. This layer not only gives the spark plug a neat appearance, but also performs a critical function: it prevents the deposition of conductive dust and oil deposits that could create a conductive bridge between the central contact and the housing. In damp weather or when the engine is dirty, it is the glaze that saves the engine from “tripping.”
The shape of the insulator is also thought out to the smallest detail. The ribs (corrugations) on the outer surface increase the length of the leakage current path. The longer this path along the surface, the less likely there is a breakdown to ground, especially in conditions of high humidity in the engine compartment.
| Material | Melting point | Main function | Application |
|---|---|---|---|
| Aluminum oxide | ~2050 °C | Electrical insulation, heat sink | The bulk of the insulator |
| Nickel alloy | ~1450 °C | Spark Formation | Budget electrodes |
| Iridium | ~2454 °C | Reduced erosion, thin electrode | Premium candles |
| Copper | ~1085 °C | Heat sink (inside the electrode) | Electrode core |
The ceramic insulator removes up to 80% of the heat perceived by the spark plug, so a violation of thermal contact (for example, due to carbon deposits) leads to overheating and glow ignition.
Housing and sealing elements
The metal body of the spark plug is made of low carbon steel. This material was not chosen by chance: it must be strong enough to withstand the tightening torque and pressure in the cylinder, but at the same time have a certain plasticity. The steel is nickel-plated or galvanized to protect against corrosion, which is inevitable in the engine compartment.
At the bottom of the body there is a threaded seat. The threads often have a special coating that makes it easier to unscrew the spark plug even after prolonged use. However, there is an important nuance here: some manufacturers apply graphite lubricant to the threads, others leave the metal clean.
The spark plug is sealed in the cylinder head in two ways. Most modern cars use a disposable metal ring (washer), which, when tightened, is deformed, filling micro-irregularities. In some old or specific engines, a conical coupling is used, where the role of the seal is played by the spark plug body itself, which fits tightly to the seat.
Internal structure and conductive sealant
If you look inside the candle, through the ceramic insulator, you can see the central rod. It connects the top terminal to the bottom electrode. But simply inserting a metal rod is not enough - there is a gap between it and the walls of the ceramic insulator.
To provide electrical contact and mechanical fixation, it is used conductive sealant (glass mass). This is a special mixture that is baked at high temperatures to form a monolith. It performs two functions: it transmits high voltage from the contact to the electrode and removes heat from the central rod to the ceramic and then to the body.
The quality of this sealant directly affects the reliability of operation. If the technology is broken, microcracks or air voids may form inside the candle. This leads to internal breakdown when a spark jumps inside the insulator and not at the electrodes. It is difficult to distinguish such a spark plug visually, but the engine will run unstable.
☑️ Signs of a high-quality internal device
Influence of materials on engine life and operation
The materials from which the candle is made dictate its lifespan. Nickel spark plugs last an average of 20–30 thousand kilometers. Iridium and platinum analogues are capable of traveling 60, 90 and even 120 thousand kilometers. However, the numbers in the manual are relevant only for ideal conditions: high-quality fuel and a working engine.
When using fuel with a high content of ferrocene additives or sulfur, a conductive coating quickly forms on the electrodes, which can “short-circuit” even the most expensive iridium spark plug. In such cases, the electrode material ceases to be a guarantee of durability.
It is also worth considering the thermal regime. A thin iridium electrode warms up faster and self-cleans better in city mode (“start-stop”) than a massive nickel electrode. Therefore, for modern small-displacement direct injection turbo engines, the choice of spark plug material becomes a critical engine tuning parameter.
⚠️ Warning: Do not attempt to clean spark plugs with sandblasting or sandpaper if they have precious deposits. You will irreversibly destroy the working layer of metal, and the spark plug will stop performing its functions after a few hundred kilometers.
Frequently asked questions (FAQ)
Is it possible to visually determine the electrode material?
Partially yes. Iridium and platinum spark plugs are often marked on the ceramic insulator or in the model name (for example, "Iridium", "Platinum"). Also, their central electrode is much thinner (less than 1 mm) than that of conventional nickel electrodes. However, the exact chemical composition can only be determined in a laboratory or by trusting the manufacturer’s packaging.
Why are copper spark plugs considered inferior to iridium spark plugs if copper conducts current better?
Copper does have better electrical and thermal conductivity, but it is very soft and has a low melting point compared to the required arcing loads. Therefore, copper is used only as a core inside a nickel shell. A pure copper electrode would simply melt or erode within a couple of thousand kilometers.
Does the color of the insulator affect the composition of the candle?
No, white insulator color is standard for aluminum oxide. A change in color (the appearance of a brown coating, black dots) indicates the operating mode of the engine or breakdowns, but not the material used to make the ceramic itself.
Is it worth paying extra for iridium on an old car?
If the engine is in good condition and you use high-quality fuel, iridium spark plugs will provide a more stable start and smooth operation. However, if the engine consumes oil or has problems with the ignition system, the life of expensive spark plugs will be reduced to the level of conventional ones, and overpaying will be inappropriate.