Story and Photography by Ryan Lee Price
updated November 2016
Left unchecked and in constant contact with oxygen and moisture, rust will eventually convert all available iron into… more rust.
Approximately 4.6 billion years ago, when the solar system birthed, hydrogen (H), carbon (C), nitrogen (N), oxygen (O) and iron (Fe) swirled around in space. As soon as these atoms emerged, iron reacted with oxygen, forming iron oxide. This prevented carbon or nitrogen from reacting with oxygen and forming carbon dioxide and nitrogen oxide, both of which are hazardous gases for human beings. Instead, carbon and nitrogen reacted with hydrogen to form methane and ammonia, and these two compounds eventually formed DNA, which led to all life on Earth.
The 117 elements on the periodic table that are known to exist in this universe make millions of combinations to form the many thousands of materials that surround us every day. Most of those molecules are carbon and silicon based—the building blocks of life—but the air in Earth’s atmosphere contains not only oxygen, nitrogen and hydrogen and a host of other elements, but also lots of moisture. Without moisture (and sunshine), Earth would experience no weather and iron wouldn’t rust.
Low carbon steel, which is an alloy made up of iron and traces of carbon (less than 0.1 percent), accounts for 90 percent of all steel production. Generally speaking, the average car body is made from this kind of steel. The carbon content in iron has a significant impact on the characteristics of the final alloy, as there are approximately 3,000 types of steel, from stainless steel (think DeLorean) to aluminum (the hood of a 2008 Chevrolet Tahoe Hybrid). Some of today’s cars, such as the Volvo XC90, BMW E60, and Porsche Cayenne, are using boron (B) in their steel alloys, creating a much more durable steel.
Chemical reactions happen all the time, as each element in the periodic table meets other elements, like a big singles’ bar. Sometimes the elements get together and sometimes they don’t, but when it comes to iron and oxygen, they always bond (which is the reason why iron in your diet helps promote good circulation). Add moisture to the mix, and rust is the result:Two parts of iron (Fe) plus three parts of oxygen (O) equal Fe2O3, or iron oxide, which is found naturally in roughly 16 forms and is relatively harmless by itself. But unfortunately, oxygen carries with it, by way of the moisture in the air, water (H2O), which reacts with iron to form rust. The oxygen and moisture combine with iron to create a hydrated iron oxide— Fe2O3 x H2O—on the surface of the metal. This is rust: cancer in the automotive world.This type of iron oxide— Fe2O3 x H2O—is bulky and porous, and it allows more oxygen access to the iron surrounding it, causing similar chemical reactions. The resulting reactions of water, oxygen and iron, if allowed to continue, will completely convert the remaining iron to hydrated iron oxide, which is weak and flaky and will compromise the structural integrity of the original metal. Only iron-based alloys (like steel and chrome) rust, while all other types of metals (like copper and zinc) corrode.How do you stop rust? Just keep oxygen away from your car. No oxygen, no chemical reaction, no problem. However, since oxygen makes up roughly 21 percent of the air we breathe, and there is moisture in that air, rust happens. Even on the sunniest days and over the hottest deserts, air is full of water.Assuming the problem has gone beyond preventative measures, the only way to further keep oxygen and moisture from reaching the iron and creating rust is to mechanically or chemically remove all the existing rust before the surface can be sealed again. If any rust remains and paint is applied over the surface, enough moisture and oxygen still exist on the metal to continue the rusting process (i.e., paint bubbles). There are four main methods for dealing with rusty metal: mechanical removal, specialty paints, acids, and chemical converters. With the exception of chemical conversion, many procedures for removing rust involve toxic chemicals and/or require special equipment. The mechanical removal of rusted panels can take on several forms, from merely sanding and grinding to cutting out and replacing a section of rusted sheet metal. Mechanical Removal—The most common methods of removing rust are by using grinders, wire brushes, sandpaper and sand blasting. For minor rust, sandpaper will effectively remove surface rust (or steel wool on chrome), while sandblasting will take care of more developed rust. One of the most popular ways to eradicate existing rust and to prevent new rust from forming is specialty paints that create a non-porous surface that cannot be penetrated by oxygen or moisture.
Special Paints—A few paints on the market claim the ability to encapsulate rust. They have chemical structure that dries to an incredible rock-hard, non-porous finish that won't chip, crack, or peel, and it prevents rust from recurring by protecting metal from further exposure to moisture.
Acids—Acids (specifically phosphoric acid) dissolve the rust and leave behind a thin oxide coating on the surface. It is important to rinse off the metal before the acid begins to attack the metal. This is similar to paint stripping. In this process, the metal is dipped in large tanks of caustic soda. After the paint is dissolved, the metal is put in another tank of alkaline solution and the rust is removed through electrolysis. An over-the-counter multi-purpose phosphoric acid based cleaner and pre-paint conditioner will achieve similar results.Chemical Conversion—Blacksmiths were the first to discover that when they coated their tools with oil and then heated them in an oven their tools weren’t susceptible to rust. Typically, chemical converters are solutions or primers designed to be applied directly to a rusty surface to convert residual rust on steel surfaces to harmless and adherent chemical compounds that provide a protective film (usually phosphates) on the metal surface that protect against rust.
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Not only is Ryan Lee Price a freelance writer specializing in automotive journalism and a former long-time magazine editor, he is part of the technical editorial team that provides content for most all of the Chilton products. He currently resides in Corona, California, with his wife Kara and their two children.