Spark of Destruction
The plugs inside your car fire a charge hot enough to wear away metal. Hereâ€™s how to re-create that process, only bigger
by Mike Walker
Make Your Own Sparks
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A Spark plug is one of those humble, anonymous things without which the world would grind-or rather coast-to a halt. And like many underappreciated cogs in the machine, it has a really hard life. A good modern plug will endure 300 million sparks (around 20 per second) over 100,000 miles, each one triggering an explosion around its head as the fuel combusts, driving the engine´s pistons (and thus, your car). But the spark itself is far more destructive than the bang. Cylinders, pistons and valve heads made of steel easily withstand the explosive abuse, but spark plugs made of steel would last just about long enough to get your car to the shop to buy new spark plugs.
On a molecular level, every spark is a hot tongue of superheated plasma crashing into the electrode at nearly the speed of light, heating a microscopic spot on the surface to thousands of degrees and blasting away a few billion atoms. Worse, the spark brings with it corrosive gases eager to react with the metal surface, forming insulating coatings that render it useless for sparking. What you need is a metal with a high melting point that stays shiny (clean metal sparks better) under extreme conditions. The technical term for such a metal is â€expensive.â€
Early spark plugs made of copper, nickel or chromium alloys were ill prepared for these conditions, making their lives nasty, brutish and short. But over time, parts makers started using corrosion-resistant noble metals like gold, platinum, palladium and iridium. High-end plugs today cost $10 instead of $2, but they last nearly the life of the car. Modern metallurgy has given today´s spark plug a much different life than its ancestors. Now it´s nasty, brutish and long.
- Get a Wimshurst machine [see image above] of the size intended for classroom demonstrations (starting around $120; try scientificsonline.com), which generates static electricity with two counter-rotating plastic-and-aluminum disks.
- Connect two of the most expensive coins you can find to simulate gold, palladium or platinum spark-plug tips. (The electrodes that come with the machine simulate cheap nickel-chromium tips.)
- Crank it up, and watch the sparks fly! With a machine this size, touching the electrodes is a shocking, but rarely harmful, adventure.
ACHTUNG! Don´t try this at home without proper lab-safety procedures and equipment. Find more on Gray´s scientific pursuits at periodictabletable.com.