Why does salt rust metal?

In this brief article, we will answer the question why does salt rust metal, explained effects of rusting and three ways to prevent rusting

Why does salt rust metal?

Salt accelerates the rusting process by lowering the electrical resistance of water, this makes the ion exchange easy and rusts form quickly over the metal surface.

What is rusting?

Rusting is an oxidation process in which a reddish-brown compound forms on the surface of metals. The reddish-brown compounds are usually the oxide of metal and usually iron-oxide. It forms when moisture, oxygen from air and iron reacts with each other.

If salts are present, the reaction is fastened or accelerated because it helps in ion-exchange. When iron reacts with chlorides underwater the product is also called rust. The exchange of ions causes the reaction to speed up in the presence of salt water.

Salt water vs Fresh water

Salt water is known to accelerate rusting and initiate rusting as well. But fresh water doesn’t have the same effect as salt water. Current flows more easily in salt water and ion exchange happens quickly too. As fresh water doesn’t have ions in it so it becomes hard for current to pass.

That’s why in sea water things rust faster than when they are submerged in fresh water. In salt water the ion exchange is also assisted by air. The presence of salt provides more cations and anions than fresh water. All of this makes salt water a better medium for rusting.

How metals rust?

Rusting is not an overnight process it happens slowly but once it starts it keeps gaining acceleration. Rusting can only happen in the presence of oxygen and water. Water actually helps iron to react with oxygen or chlorides present in the solution.

During the initial stage of rusting, iron loses its electrons and gets reduced while oxygen gains them. The resulting compound is ferrous hydroxide, ferric hydroxide and hydrogen. Slowly all the compounds are converted to rust and surface starts to look reddish-brown

How long does rusting takes:

Rusting is a slow process and might take years or days depending upon the available condition. If salt water is present, the process speeds up and only salt water takes about a year to form ½ mm long rust on the surface.

The process is quite slow and might not gain speed. It won’t show that a metal has started to rust until it’s too late. That’s why it is called slow death of metal because it takes so much time but once it starts there is no saving the metal.

Effects of rust on surface:

Rust is a common process that happens when air oxygen reacts with metal in presence of air oxygen. But it is not a good process for metal surfaces, in fact it actually destroys metal surfaces. Rusting can cause the metal frame to break down easily.

If two metals have rust in between them, they will stick to each other instead of sliding over each other. Rust also disintegrates the shape of metal and forms holes on the surface of metals. It also affects them, magnetic properties of metal especially that of iron

Other FAQs about Salt which you may be interested in.

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Effects of rust on health:

Drinking water contaminated with rust or stored in a rusty container can cause diarrhea, stomach ache, nausea, and vomiting. In severe cases the result can be very dangerous as liver failure or even cardiovascular complications.

How to prevent rusting?

Rusting is a slow death of metal and destroys the metal completely. If consumed, rust also affects human health. Using rusted utensils is prohibited when making food especially on industrial scale. Once rusting starts it is impossible to stop so it is better to prevent it.

Galvanization:

Coating metals with a protective layer of zinc is called galvanization. This prevents the formation of rust as the metals don’t get direct exposure to salt water or oxygen. It is done by special paints or air sprays which coats the surface of metal with zinc.

Keeping utensils dry:

In the food industry, everything you use is cleaned and washed properly. So the chance of rusting is very high as oxygen is always present. One way to prevent it, is drying the utensils after washing them. If there is no moisture available, the rusting will not happen.

Don’t use saltwater:

Salt water is antiseptic and used to kill microbes from the surface. It is preferred in many ways but it is better to use clean fresh water to wash something. Salt water also has a tendency to speed up the rusting process. That’s why it is better to use fresh water.

If still utensils develop a rust it is best to discard it or change it. In case of consumption it is better to consult a doctor.

Conclusion:

In this brief article, we have answered the question why does salt rust metal, explained effects of rusting and three ways to prevent rusting

References:

https://sciencing.com/effects-saltwater-metals-8632636.html

Hi, I am Charlotte, I love cooking and in my previous life, I was a chef. I bring some of my experience to the recipes on this hub and answer your food questions.