Cadmium: The Dark Knight of Metallurgy
The value of cadmium in harsh environment applications
By John Gentry, CEO of Positronic
You may have seen it in a movie – the medieval swordsmith at his forge. He hammers away at a glowing bar of iron, shaping it blow by blow. But before he puts an edge on it, he dips the blade into a curious bucket of black, then returns it to the forge. What is that about?
It didn’t take our ancestors long to discover that the biggest threat to their iron implements was not some foe on the battlefield, but the simple forces of air, salt and water. Corrosion was the real enemy, always lurking. By adding carbon – the black substance derived from coal – to his refining process, the blacksmith hardened iron into steel, improving its strength, not its ability to withstand the elements.
Ever since, protecting metal has been a common human endeavor, whether it’s a sword, a saw, a car, or fence. We’ve worked hard to prevent the rusty nail, but rust remains a menace.
And we’re surrounded by iron. It’s one of the most common elements in the world. It’s in our blood stream. We use it to make steel, and steel to make everything from sky scrapers to shoehorns. We use it here at Positronic, to build electronic connectors.
We’ve been trying for millennia to find better ways to prevent rust and corrosion. Today, you can go to the hardware store and buy galvanized nails, which include the most common shield: zinc.
Why is that? Well, the answer gets into chemistry, but a simple experiment helps to illustrate. Zinc is known as a sacrificial metal. Take a hunk of steel, clamp on some zinc, and put that in a corrosive environment – with moisture or water vapor. The steel should rust, but it doesn’t. The zinc starts to disappear, giving up metal in place of the steel. The zinc sacrifices itself, protecting and prolonging the life of the steel, at the expense of its own.
If you look around, you’ll notice many steel products have a yellow tint. That’s because we put a chromium film on top of zinc, to further increase protection. We do this if we know the piece will be subjected to the elements.
But now we come to the star of the story. Or to stay on theme, the heroic knight.
When we consider applications where we need the best protection – in aircraft, defense, or anything that goes near the ocean (especially military) – the more protective element is cadmium.
Cadmium is sacrificial like zinc, but it does a better job, especially in harsh environments. In the world of metallurgy, we use test chambers to replicate certain climate conditions. If you put an uncoated nail in a salt water mist chamber, for instance, it will rust in minutes. Add zinc, and it won’t rust for about 96 hours. Add cadmium, and it won’t rust for 500 hours – five times the protection!
Because of its qualities, we have many customers who purchase products with cadmium. This includes military uses in harsh environments – aircraft, vehicles, electronic equipment, weapons. Commercial aviation also uses cadmium, protecting planes in temperatures and humidity extremes, guarding against corrosion caused by condensation, moisture, and air.
Cadmium really is part of protecting human lives. So why isn’t it a household name? Turns out, the hero has a dark side. Sacrificial as it is, you might say cadmium is the dark knight of metallurgy. We discovered decades ago that it has certain levels of toxicity. Consequently, cadmium use has declined. Some countries have completely banned it.
There is a worldwide movement to consider the end-of-life of electronic products. As an item breaks down or decomposes over time, will any of its elements end up in our ground water? It’s an important question, for our children’s sake. Certainly, customers need to know what’s in their products, because everything has an end of life.
Is there a suitable replacement for cadmium? Stainless steel is one. It has non-corrosive, anti-rusting attributes and delivers secure electrical connections in the most demanding applications. Stainless steel resists corrosion because it contains a minimum of 10.5 percent chromium, forming an inert layer of chromium oxide. We love stainless steel, and use it regularly in components. But that’s another story.
The industry has developed other alternatives as well. They’re sacrificial and, while less protective than cadmium, are good enough for many applications. But they are not yet widely available, so they are very expensive.
Cadmium remains an important ingredient in our business of making failsafe electronic connectors for the harshest applications, where failure isn’t an option. For the time being, it looks to stay that way – a small part, carefully considered, but absolutely vital to protecting lives.
And now you know the rest of the story: cadmium, the dark knight. Sacrificial, life-saving, and heroic. Handle with care.
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