It reduces the magnetic, thermal, and electrical conductivity of metals. It makes jewelry unattractive and unusable. Posing a safety hazard in infrastructures and transportation are just some negative effects. Metal corrosion comes in different forms, and rusting is one of them. Humans have found different ways to make metals resistant to it. We all take advantage of it to produce safe products that will last for years or decades.
However, resistance is not equivalent to immunity. Metals and alloys can still corrode after several years, although some can last up to centuries. Therefore, it’s important to know which types rust and corrode quickly and which ones can remain in good condition for years. This way, you’ll know what type of material to look for when buying certain items. That way, you can rest assured that it won’t be a problem for you any time soon.
What causes it?
When the iron in the metal comes in contact with air and water, an electrochemical reaction happens. It results in the formation of an oxide. Rust is the product of such a reaction, an iron oxide in its hydrated form. Depending on the type of iron oxide formed, the color may vary. Orange and brown are various colors it comes in or a mix of these colors. However, we’re most familiar with red rust. Its scientific name is iron oxide trihydrate or hydrated ferric oxide with a chemical formula of Fe2O3•H2O.
In a nutshell, this is what happens:
iron + oxygen + water → iron oxide trihydrate
If one element lacks the equation, the process won’t occur. Therefore, it only happens to materials that contain iron and only if water or moisture is present. Water facilitates the transfer of electrons between iron and the environment, basically the oxidation of iron. Let me discuss it briefly below:
- When exposed to a strong oxidizing agent such as oxygen, the iron readily gives up its electrons. The iron goes into the aqueous solution as a cation.
Fe → Fe2+ + 2e–
Balanced equation: 2Fe → 2Fe2+ + 4e–
- The oxygen and water react with the surface of the metal, and the oxygen gets dissolved in the water. It forms hydroxide ions.
O2 + 2H2O + 4e– → 4OH–
- And then, the iron ion and the hydroxide ion react to form iron hydroxide.
2Fe2+ + 4OH– → 2Fe(OH)2
- Lastly, the iron hydroxide reacts with oxygen to form red rust.
This whole chemical reaction is summarized in the image below. The red brick represents the rust formed.
Image source: Spennemann, D.H.R. from Research Gate
The process is sped up when the metal is exposed to better electrolytes, such as saltwater and acidic environments. This is because more oxidizing agents are available to attack the iron, corroding the metal faster.
Other metals also undergo this type of corrosion. Still, the result cannot be classified as rust simply because those are not iron oxides. For example, silver reacts with sulfur. The oxide called silver sulfide is formed, commonly known as silver tarnish.
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Steel is an alloy of iron and carbon and may also contain minute amounts of silicon and phosphorus. It can also contain sulfur and oxygen. With around 98-99% iron content, steel readily rusts upon exposure to water and air. This posed a problem in products made of steel since rusting decreases the products’ lifespans. To increase the resistance to corrosion and other damage, elements that protect it from oxidation were used to coat the alloy. It was also incorporated during steel manufacture.
Stainless steel is an example of an alloy resistant to rusting and corrosion, containing a high percentage of chromium. It is usually around 10-30%. This element gives the alloy a remarkable increase in heat and corrosion resistance. How does chromium impart rust resistance?
Chromium is an element that is more reactive than iron. Meaning before it can oxidize to form rust, chromium reacts first with oxygen to form an oxide layer on the surface. This acts as a protective layer on the surface. It works to prevent oxygen from contacting the underlying layer, thereby resisting oxidation and corrosion.
Alongside chromium, other alloying elements such as nickel and molybdenum. Other examples are titanium and aluminum. They are also added to increase corrosion and resistance to specific environmental conditions or impart other characteristics. Ductility and electrical conductivity are examples.
Does it tarnish?
As mentioned, materials with iron can rust. Since stainless steel has this in it, the process can occur. Due to the previously mentioned components of this alloy, stainless steel does not rust nor tarnish readily. It is why it’s called “stainless.” The protective layer prevents oxidation, thus preventing the formation of tarnish. This makes this alloy one of the most widely used materials for engineering and practical products.
It takes continuous or frequent exposure to extreme conditions such as contact with damaging chemicals and saline before it corrodes. Mechanical damage that compromises the chromium oxide layer can also impart faster corrosion and oxidation, like scratches.
Suppose you purchased something supposedly stainless steel, but it tarnishes within a month. You must have been tricked into thinking that the item is made up of this superior material. The metal is probably just coated thinly with something that will make it look like it. I suggest reading the item’s reviews and for you to buy from highly reputed stores.
How to remove it from stainless steel appliances
To prevent rust from forming on stainless steel appliances, you must do regular cleaning and maintenance. You must wipe off any residual moisture from the item after use. Air out the bathroom and kitchen to let the moisture dry on its own. Also, avoid exposing the appliances to rain and direct sunlight.
It is important to remove any developing rust immediately to avoid further degradation. Avoid using bleach and abrasive cleaners on stainless steel since these will damage the alloy. Here are examples of routine cleaning processes you can do every 3 months to lengthen the lifespan of your appliances.
- For appliances with oil and grease marks:
- Saturate a soft cloth with solvents like isopropyl alcohol or acetone.
- Rub the saturated cloth on the affected areas until all grease marks are gone.
- Wash the item with mild soap and rinse properly with water.
- Wipe it dry with a soft cloth.
- For appliances with discoloration
- Make a baking soda and warm water mixture (1:1 ratio) or washing soda and warm water mixture. Apply it to the affected areas.
- Let the mixture stay on for a few minutes, 15-30 mins, in my opinion. You can extend it if the discoloration is stubborn.
- Rinse the item with water and wash with mild soap.
- Rinse with water and dry properly.
- Localized stains
- Soak a soft cloth with an oxalic acid solution or other commercially available removers.
- Apply the solution to the affected areas.
- Leave the oxalic acid on for a few minutes until it dissolves the particles. For removers, follow the instructions that come with them carefully.
- Rinse the item properly with water, making sure no solution is left.
- Dry the item with a soft cloth.
If you don’t want to go to such lengths to avoid it, make sure any vulnerable item is kept away from moist or wet environments. Clean items made up of metal regularly to avoid tarnishing. Suppose you notice your home frequently gathering dust. I suggest looking into UV light sanitizers for your HVAC and furnace systems. Avoid multiple exposures of your tool to water due to frequent cleaning.
Lastly, store all susceptible items in areas with proper temperature and humidity. If you noticed that your central home AC is not blowing cold air, you should resolve it quickly. Hot and humid areas do not bode well with avoiding rust.
Whereas stainless steel has a higher amount of chromium, this type has a higher concentration of carbon. The concentration is up to 2.5%, whereas the regular type has0.05-0.3%. The increase in carbon content imparts toughness and strength, making it more functional. It forms a strong crystal lattice of carbon molecules. This cross-linking of carbon molecules gives it high stability even at high temperatures. It is ideal for high-temperature applications such as waste oil heaters.
Like other types, carbon steel contains iron. Therefore, it can rust when exposed to water and air. This alloy may also contain molybdenum and chromium. It does not form a protective oxide layer upon exposure to air.
Depending on the carbon content, its properties may differ:
- Low-carbon (<0.25%) – high ductility and toughness. Low hardness and cost.
- It is the most widely used type.
- It can be easily cut and bent. It can be welded using engine-driven welders.
- It is used for automobile parts like idle air control valves and structural shapes. It’s great for pipes and infrastructures.
- Medium-carbon (0.25-0.60%) – medium strength, ductility, and toughness. Low hardenability.
- It’s resistant to wear.
- It is harder to weld or bend.
- It is used for railway tracks and gears.
- High-carbon (0.6-1.25%) – high strength and hardness. Low ductility.
- It has high wear resistance. It is extremely hard and brittle after heat treatment.
- It is used for cutting machinery and high-strength wires.
High-carbon steel is indeed a good material for cutting machinery. Still, it will not handle tougher metals like tungsten or titanium. You’re better off using plasma cutters instead!
Carbon fiber comprises organic polymers characterized by thin crystalline carbon filaments. The arrangement of carbon molecules makes it five times stronger than steel. It is easy to manipulate to suit different applications, unlike the latter. It also remains lightweight and is 5 times lighter than steel and 2 times lighter than aluminum. It has high tensile strength, making it ideal for many manufacturing processes.
What’s great is that carbon fibers are not as affected by heat as other metals and are resistant to rust and corrosion. It has an epoxy resin that is chemically inert and will not react with oxygen, preventing oxidation. Here are some applications of carbon fibers:
- Watersports accessories/products
- Drone parts
This type is used in biomedical applications, a variety that prioritizes corrosion and oxidation resistance over strength. This alloy does contain iron, but it also has other alloying elements like chromium. It usually has at least 13% chromium. It also has nickel, molybdenum, and carbon to resist corrosion. Examples of surgical stainless steel are austenitic 316 stainless and martensitic 440. 420 is another type.
Since it comes in contact with bodily fluids, it must be resistant to oxidation. Examples of items that must be made up of this material include forceps and needle holders. Piercing needles and dental implants are other examples, although there are many.
Aluminum is the most abundant metallic element in the Earth’s crust. It is a lightweight, low-density metal that is soft and malleable. It has excellent thermal and electrical conductivity. This silvery-white material is one of the most important and widely used nonferrous metals. It is used in a vast array of applications:
- A coating or component of food containers and kitchen utensils
- A reflective coating for light and heat
- Electrical transmission lines
- Parts for various forms of transport
Alone, aluminum is too soft to be used in the manufacture of airplane parts and other forms of transport. It becomes strong when alloyed with other elements like copper and manganese but stays lightweight. Magnesium and silicone will also give it important properties.
Does aluminum rust?
Since aluminum is a nonferrous metal, it does not. Even aluminum alloys do not usually contain iron, so those won’t either. Like other metals, aluminum oxidizes and forms an oxide upon reacting with oxygen. It is even more reactive than iron, so it oxidizes faster. If this is the case, why is it used to manufacture important items such as airplane parts?
Upon oxidation, the aluminum oxide that forms on the surface protects the metal from further oxidation and corrosion. This hard layer acts as a resistant shield that prolongs the lifespan. A further study noted that exposure to water strengthens the aluminum oxide even more. This is the opposite of other metals, wherein their corrosion processes speed up when exposed to water.
It turns out that when the aluminum oxide layer comes in contact with water molecules, its structure changes and becomes chemically inert. It will not react anymore with other water molecules or atmospheric oxygen, making it corrosion-resistant. This is why aluminum can be used to manufacture fuel transfer tanks and waste oil heaters. Whether you store oil or water in it, you won’t have to worry about any unwanted reactions.
However, aluminum is not immune to all damages despite its high inherent resistance to oxidation and corrosion. It also needs regular maintenance to ensure that the oxide layer is not compromised. Usually, the oxide layer will repair itself once exposed to oxygen. It will be jeopardized when exposed to chlorides and sulfides instead. Saltwater and polluted air both threaten aluminum oxide, containing chlorides and sulfides. Aluminum will undergo various corrosion, such as galvanic corrosion and pitting without a protective oxide layer.
If aluminum is maintained regularly and kept away from unfavorable conditions, it will stay strong and last for years. Make sure also to read our article on welding aluminum and the various joints to choose from. If you do so, make sure you also have the right welding glasses to keep your eyes safe!
I briefly touched on the process of galvanizing metals in this article when I talked about zinc. Galvanized steel is carbon steel coated in zinc, wherein zinc acts as the sacrificial metal to protect the layer underneath. It will not rust because the coating protects against corrosion and damage despite containing iron. Galvanizing can be applied in various fields due to different available galvanization methods. It is done to make corrosion-resistant material for roofing and automotive parts.
How long does it take for galvanized steel to experience it?
Zinc is more reactive than iron, so it will react first to form a layer of zinc oxide on the surface upon exposure to oxygen. This layer protects the iron from oxidizing, thereby preventing the damaging process. When the coating or oxide layer is compromised, moisture and air can contact the layer underneath. This will lead to rusting.
Suppose we are talking about the natural deterioration process of the zinc coating. It will take years before the layer underneath rusts because the zinc oxide can repair itself if the zinc coating gets exposed to air. Properly galvanized steel can last up to 20-50 years in average environments. It depends on the thickness of the coating.
However, suppose extreme environmental conditions and mechanical damage are considered. It may corrode quickly, even more so if the coating is thin. Examples of such conditions are saltwater and acidic environments.
By itself, zinc is pretty weak and brittle. It has low to moderate tensile strength and conductivity. It forms alloys with high impact strength and ductility when alloyed with other elements. It also has corrosion and rust resistance. As mentioned in the previous section, zinc acts as a sacrificial metal to form a protective layer of zinc oxide. Even if alloyed with iron, it will take years before zinc alloys rust.
Copper is extremely ductile and malleable and has a high thermal and electrical conductivity. This is why it is widely used to create electrical wires and motors. You can also find it in heat exchangers. Since copper does not have any iron, it does not rust. It oxidizes and undergoes a series of chemical reactions upon exposure to air, forming a green layer called patina.
But you don’t have to worry about this patina. It protects the copper from corrosion! This is why copper is also used in manufacturing roofing materials. The layer of patina protects the underlying material from moisture and air.
This patina cannot protect the copper from other forms of corrosion, such as pitting and galvanic corrosion. Exposure to acids and heavy-metal salts can corrode copper.
Tungsten is a highly durable metal with the highest tensile strength (142,000 psi) and melting point (3687 K) among natural metals. Because of the durability of tungsten, it is used to alloy with other metals for added strength and corrosion resistance. Pure tungsten does oxidize readily upon exposure to air, developing colorful tarnish or patina. This poses a problem, especially in making jewelry.
This is why tungsten carbide is most widely used for high-quality jewelry. It is an alloy of tungsten and carbon with a nickel binder. It does not readily oxidize or tarnish, except at very high temperatures. You won’t have to worry about stains around your finger. Furthermore, this alloy does not contain any iron. It will not rust. The durability of tungsten is also retained in tungsten carbide, imparting scratch resistance. The nickel binder allows the alloy to hold a shape so that the jewelry will last longer. Due to its high durability, tungsten carbide is also used in making aircraft and bullets. You can also find it in metallic cement.
How to remove rust from metal in general
If rusting is only minimal at the surface, mechanical and chemical means can remove rust from metal. The most common mechanical option is to rub it off with fine steel wool or wire brush and then rinse the metal. Use warm soap and water. Another method is to scrape off stains, which is a much more efficient method to get rid of rust from large metal surfaces.
However, this method is best suited for scratch-resistant metals. Those with coatings are better treated with various solutions or homemade concoctions instead.
Easy-to-make homemade solutions include:
- baking soda and warm water
- washing soda and warm water
- baking soda and lemon vinegar
Mix your combo of choice in a 1:1 or 2:1 ratio to make a paste, and then apply it to the affected areas. Leave it on for a few minutes to let the damaged part dissolve, rinse the item with water. Wash it with mild soap, and then do a thorough rinse before drying it. If the whole item is affected, soak it in white vinegar. Let it sit for a few hours or overnight, and then rinse it thoroughly with water. If any stubborn parts are left, try scrubbing it with fine steel wool right after soaking it in white vinegar.
Rust removers are commercially available, and these solutions vary per application. Some can be used on fabrics only, while some can be used on a certain type of metal only. One example of rust removers is WD-40.
Does WD 40 work?
WD-40 is a widely used rust remover. It does remove exactly that. It diffuses through the porous iron oxide layer. It expands to gas as it reacts with the material it is applied to. It can be used on iron or chrome. It’s also great on stainless steel without compromising the metal underneath. However, it is important to do a test patch first since some metals get damaged upon the usage of WD-40.
It has a multi-use-product spray variant, which is very easy to use. Spray it on the affected surface and scrub it with a wire brush. You can opt for the WD-40 Specialist Penetrant, which penetrates rust and grime better. Use it for grooves that are hard to reach and stubborn parts.
The list of metals that do not rust is short. It consists of precious metals, namely platinum, gold, and silver. Since these elements are found in their purest forms, they’re not contaminated with iron. Thus, they’re considered to be free from rust.
Galvanized steel delays the rusting process, making it ideal for outdoor use. It’s also affordable, hence remains a popular choice for the outdoors. Typically, galvanized steel will last over 95 years in a suburban environment.
Carbon fiber is celebrated for its multiple benefits, but about two disadvantages might affect its popularity. Firstly, carbon fiber is heavy on the pocket. Especially in comparison to aluminum and steel, carbon fiber installation comes at a much higher price. Secondly, it’s an excellent heat and electricity conductor. Suppose you’re planning to install carbon fibers in a project that uses either heat or electricity. In that case, it might not be the ideal choice.
Carbon fiber is amongst the most durable structural materials available. With proper care, it’s guaranteed to last over 50 years. The carbon fiber itself is robust, but the resin holding it together is prone to degradation.
Tungsten carbide may be ideal when working with high heat tolerance or highly coarse materials, but it’s not all good news. The material can prove quite expensive and difficult to sharpen. The shape of the cutting edges is also limited due to the slightly low strength of the carbide. It’s also more brittle than other materials used for the same task.