Preventing Corrosion: What product(s) to buy

 

Writer:  Ron Knight (Chemist)

Corrosion, rust, oxidation or whatever you want to call it has been around since the beginning of time. If you have been to Georgia, Oklahoma or any of a number of states and have asked yourself why the soil is red? The answer is iron oxides (rust).. Iron oxides occur when iron, oxygen and water combine and the resulting color of this mixture is red/orange.

Since man started to use iron, rust has been and will always be a problem. Over the millennium, man has tried to control rust by the use of corrosion preventative compounds. Some of the earliest attempts were the use of animal fats and coal/oil tars. These attempts worked better than nothing and the reason that they worked was they provided a barrier to keep water away from the metal. Over the years as technology improved these “barrier” products improved. One of the best-known products is Cosmoline. Cosmoline is a mixture of waxy long chain hydrocarbons not too unsimilar to the old “tar” products. While Cosmoline is best known for its use in WW II to protect about anything metal, it is thought that the ancient Egyptians used a product amazing similar in their mummification process.

It has been a long time since WWII and now there are a LOT of products on the market.   New ingredients become available daily. Corrosion preventative products that were “state of the art” a few years ago may not be the best product on the market today. The question is what should I use and the best answer can be found through research. Steps to consider when choosing the best product for your application/situation should include:

Type of metal to be protected

Iron/steel, aluminum, copper etc

Environment

Acid fumes, saltwater spray etc.

Hot/cold, wet (humid)/dry

Temperature extremes

Dusty

How long protection should last

Long term, short term (shipping)

Solvent base desired

Water, oil or solvent

Type of coating/film

Hard, soft, flexible, self-healing

There are some terms that you will find that may be confusing. A lot of products on the market will use the term “water displacing”. Boats displace water. A floating object will displace (push aside) a fluid whose weight is equal to the weight of the floating object. Displacing water does not mean that the water is removed. The term to look for is hydrophobic. There are several definitions for hydrophobic and they include: lacking affinity for water; tending to repel and not absorb water; tending not to dissolve in, mix with or be wetted by water. For corrosion preventative compound to drive off water it must be a hydrophobic.

Look for the specific gravity (S.G.) of a product. Water has a S.G. of 1.0; simply put if something has a S.G. less than 1.0 it will float and if it has a S.G. greater than 1.0 it will sink. The vast majority of products that are on the market have a specific gravity 0.8/0.9; there are even some products that have a S.G. less than 0.7. Question—how does the product get under and drive off water if it floats on water? Try to find a product that sinks under existing water (has a S.G. greater than 1.0).

When you find a product or are currently using a product, go online and get the MSDS for the product. The MSDS will give you the S.G. and it will also list some of the ingredients. Following the name of the ingredients there will be a CAS number. If you “Google” CAS number xxxxx-xx-x, it will give you the specifications of that CAS number. See what ingredients are in the product. There are products that say they are (or contain) lubricants but no lubricants are listed on the ingredient sheets. One product has a lubricant listed but the product is essentially wheel bearing grease and mineral spirits. This may have been acceptable in the past but not today.

One year I made four presentations on corrosion preventative compounds. Some of the people in attendance were at all four presentations and ask the same questions. The real answer to selecting a product that will work the best for your situation is: do the research; buy the product AND USE IT!! Nothing works if you leave it in the can.

Next time: A discussion on contact angles of liquids

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