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Iridium-based spark plug. Spark plugs are devices used in combustion engines to provide sparks to ignite the fuel-air mixture when the engine is started. The spark is produced using a high voltage, which causes the air between the two electrodes to become ionised in a similar process to the formation of lightning. Here, the spark gap and tip is at lower right. This is an iridium spark plug from the Japanese NGK company. It has a laser-welded tip made of an alloy of the transition metal iridium (Ir). This durable alloy has a high melting point, ensuring that this spark plug has a longer lifetime than those using less durable materials.
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