Rust

 

 

“Thin layers of paint skillfully applied are all that stand between the chaos of rust and the fragile order of a still-floating steel ship. The average large cargo ship requires 28 tons of paint—repainted every 5-10 years. If the ship carries 20,000 containers, they require 550 tons of paint.

 

No wonder everyone longs for a single comprehensive protective coating that can last indefinitely with no need for maintenance at all, please.  A coating that comes close to that ideal is hot-dip galvanized steel.  The magic ingredient is zinc.  When you dip ordinary steel in an ultrahot bath of molten zinc (840 degrees Fahrenheit), you get an inexpensive product with impressive properties.  The inner surface of the thin zinc layer bonds tightly with the steel as an alloy, and the exterior reacts with air to form non-corroding zinc carbonate.

 

Painted steel is a little cheaper than galvanized at first, but over time it costs three times more because it has to be periodically repainted, and galvanized doesn’t.  Of the roughly two billion tons of steel produced annually in the world, as much as a fifth is galvanized steel, used primarily in construction.

 

The magic ingredient of stainless steel is the metal chromium.  When it makes up more than eleven percent of the alloy, the chromium forms a micro-thin layer of chromium oxide that is stable and highly corrosion-resistant.  The protective coating has the ultimate in self-healing properties because it forms instantly whenever the underlying steel is exposed to the air.  Thus stainless steel requires even less maintenance than galvanized steel.

 

Comparing stainless to galvanized steel, the stainless is more expensive, stronger, and far more resistant to corrosion over time.  It is usually the best choice for particularly corrosive environments such as saltwater and for uses such as medicine and food handling that have to be highly sanitary.  The shininess of stainless is considered a feature for its looks and because it can be cleaned as perfectly as glass.

 

However, stainless steel still requires some maintenance, even in ordinary use.  Experts advise that dirt and other contaminants that accumulate on the surface can lead to corrosion, so it is vital to keep it clean.  But be aware that detergents, alcohol-based cleaners, and steel wool scrubbers can damage the chromium oxide protective coating, so stick with soap and water.  And don’t let stainless have direct contact with certain other metals such as aluminum or galvanized steel, because it will cause them to weaken from galvanic corrosion.  (Metals corrode by losing electrons to “nobler” metals in the galvanic series.  Zinc loses electrons to iron, which loses electrons to copper, and so on.)”