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About Rust and Rust Protection in cars and other items

Rust is acompounds of iron (Fe) and oxygen (O) and often also hydrogen (H). According to the composition rust may be yellow, reddish, brownish or blackish.

Iron in cars and other constructions will easily rect with water and oxygen to form rust, if the iron is not protected.

Since the rust is not strong as the iron itself, but breaks away and leave holes and areas with reduced thickness, rust is a sort of corrosion that seriously weakens the constrution.

Common components of rust are hydrated iron(III) oxides Fe2O3·nH2O and iron(III) oxide-hydroxide (FeO(OH) and iron-hydroxide Fe(OH)3). Rusting is the common term for corrosion of iron and its alloys, such as steel.  In these oxides iron has the valence and oxidation number III. These kind of exids are mechanically weak, tend to draw more water into themsleves and flake off.

Rust is a major problem of constructions composed of iron or ferrous materials.

In certain metals compounds of metal and oxygen form a water-tight and air-tight layer that prevents further corrosion inside the metal. Stainless steel is made with alloys so thet such layers are formed.

The rust on iron, however, form flakes that loosen and crack so that oxygen and humidity reaches steadily further into the construction. Finally there will be holes or the material breaks apart.

Conditions that promote rusting

The presense of humidity and oxygen together disposes for formation of rust. If the matrial is often warm it will rust faster. Presense of dissolved salts, sulphur dioxide or carbon dioxide in the water accelerates the rusting heavily.

Treatment of cars and other constructions to hinder rusting

Rust can often be prevented by galvanization where a layer of another metal is deposited onto the iron. This is done either by electolysis or by dipping the iron in melted metal. The metal used must be of the kind that form oxide layers thet are unpermeateable to water and air, for example zink or crome.

Rust can also be prevented by alloying the iron with a metal that form a tight oxygen layer at the surface. Iron-based metals with such composition is called stainless steal.

In cars it is not practicle to make the whole vehicle of stailess steel, because of the costs and because that kind of steal do not have the right mechanical properties. Galvanizing all parts or specially exposed parts is a common procedure done allready by the fabricant.

Zink is a common substances used for galvanization. For visible parts that one wishes to be blank, crome is often used.

The metal can also be protected with a water-tight grounding with a paint layer above. In cars this is usually done even if the metal in the car is galvanized. The paint is of cource used for decorative purposes, but also that is a part of the protection.

Alternatively, iron constructions can be protected with a layer of petroleum-based products, particularly the vital carrying parts and underside of cars. This is often adviceable to do at the lower parts of the car where the impacts easily penetrates the grounding and galvanization. This layer should be reposited yearly.

Using such a protective product is especially important in old cars that do not always have galvanized constructions, or will often also have injuries to the galvanization covering the iron parts.

Repair of rusted constructions

Ideally all rust should be scrubbed off, then a water-tight grounding substance should be deposited upon the metal and then it should be painted.

If it is imprctical to remove all rust, at least all lose rust must be scrached off. Then you must use a product upon the rusty parts that combines with the remaining rust and make a strong protective layer.

Then you can paint upon the treated parts or you can use an oil-based sheet for further protection.

Chemical reactions during rusting

By rusting electrons are tranfered from iron to oxygen and under combination of the resulting oxygen ions with water to OH-.

2 Fe > 2 Fe2+ + 4 e−

O2 + 4 e- + 2 H2O > 4 OH-

These reactions are strongly accelerated by low Ph. Then the resulted iron ions react once more with oxygen to form Fe3+.

2 Fe2+ + O2 > 2 Fe3+ + O2−

Then the ironIII-ions and OH- ions combine to form one component of the rust, iron-III-hydroxide.

Fe3+ + 3 OH- > Fe(OH)3.

Then also this reaction will occur:

Fe3+ + O2- + OH- > FeO(OH).

Additionally, the following multistep acid-base accelerated reactions affect the over-all result:

Fe2+ + 2 H2O > Fe(OH)2 + 2 H+ Fe3+ + 3 H2O > Fe(OH)3 + 3 H+

As do the following dehydration equilibria:

Fe(OH)2 > FeO + H2O Fe(OH)3 > FeO(OH) + H2O 2 FeO(OH) > Fe2O3 + H2