Rust can negatively affect various characteristics of a metal or product. It can reduce the product’s lifespan, produce holes and cracks in metals, reduce magnetic properties, and decrease a metal’s electrical and thermal conductivity, among many others. Furthermore, rust can also be bad to our health and the environment: it can put our safety in jeopardy due to the degradation of metals in infrastructures like pipes, power supplies, bridges, buildings, etc.
Image source: ThoughtCo
What causes rust?
Rust is another name for the chemical called iron oxide (in its hydrated form), which we commonly see as the reddish-brown or yellowish-brown coating/flaky substance on iron or steel. Rusting is one of the most common examples of metal corrosion, and it happens with materials/metal made up of (or containing) iron or iron-alloys. This phenomenon results from electrochemical reactions such as oxidation (loss of electron; gain of oxygen).
When the metal is exposed to moist air or wet environments,the iron reacts with oxygen gas in the presence of water, forming an oxide layer, a.k.a. rust. Depending on the chemical composition of the iron oxide, its color may vary from yellow, orange, brown, red, or green (or a mix of these colors). The most common one that we see is red rust, which is iron (III) oxide trihydrate or hydrated ferric oxide with a chemical formula of Fe2O3•H2O. In a nutshell, this is what happens:
iron + oxygen + water → iron (III) oxide trihydrate
Water is necessary for this reaction to occur, facilitating the transfer of electrons. Feeling confused? Let me delve a bit into the chemical reaction above. I’ll be brief to prevent you from snoozing!
- When exposed to a strong oxidizing agent such as oxygen, the iron in the metal readily gives up its electrons (e–), and the iron goes into the aqueous solution (water) as a cation (Fe2+).
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, forming hydroxide ions (OH –).
O2 + 2H2O + 4e– → 4OH–
- And then, the iron ion (Fe2+) and the hydroxide ion (OH –) reacts to form iron hydroxide [Fe(OH)2].
2Fe2+ + 4OH– → 2Fe(OH)2
- Lastly, the iron hydroxide [Fe(OH)2] reacts with the oxygen to form red rust (Fe2O3•H2O).
This whole electrochemical 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 of rusting is sped up when the metal is exposed to better electrolytes, such as saltwater and acidic solutions/environments. This is because there are more available oxidizing agents that can attack the iron, corroding the metal at a faster rate.
Now, let’s face the other questions that are related to rusting:
Do all metals rust? If not, what are the types of metal that can rust? Does acetone remove rust? What can you do to prevent rusting? Does metal corrosion manifest the same (e.g., only rusting) for all types of metal? Or are there different types of metal corrosion?
Types of metal
There are various types of metals, and some of them are prone to oxidation and corrosion, while some are not.
Noble metals, also called as precious metals, are metals with high resistance to oxidation and corrosion even in moist air and in high temperatures. Because of these properties, these metals are very expensive and are widely used in making jewelry. Here are some examples of noble metals:
Despite not being considered as noble metals, other transition metals can also resist oxidation and corrosion. Some examples are:
In contrast to noble metals, base metals are prone to oxidation and corrosion. Here are some examples:
- and other transition metals
An alloy is a combination of metal and another element, which can either be metal or non-metal.
Humans found a way to turn metals that are usually easily corroded into something resistant to oxidization/corrosion by mixing them with other metals or elements. Example of such corrosion-resistant alloys are:
- Stainless steel
However, not all alloys are made to be resistant to rusting or corrosion. Here are some examples of alloys that are predominantly made up of base metals, and thus, are also considered to be base metals.
- Brass – an alloy of copper and zinc
- Bronze – an alloy of copper and tin; metals like aluminum, manganese, nickel, and zinc, and non-metals like arsenic, phosphorus, and silicon are often added.
Although many metals mentioned above can corrode through oxidation, bear in mind that not all oxidation processes produce rust. For example, silver tarnish is also an example of metal corrosion that happens due to oxidation. But for now, we’ll limit our discussion to rusting.
So, among these metals, which are the ones that can rust?
As mentioned earlier, rust forms through the oxidation of iron; therefore, rusting can only occur to iron and metals that contain iron, such as iron alloys.
Basically, these alloys have iron as their most predominant component. Due to the abundance of iron, these alloys are can rust. Most iron alloys are steels, containing carbon as the major non-metal alloying element, and may also contain small amounts of silicon, phosphorus, sulphur, and oxygen. However, depending on the type of steel, the ratio or percentage of elements of their composition may differ.
Here are some examples of iron alloys:
- Carbon steel
- Stainless steel
- Silicon steel
- Tool steel
- Bulat steel
- Damascus steel
- Crucible steel
- HSLA steel
- Maraging steel
- Wootz steel
- Anthracite iron
- Cast iron
- Pig iron
- Wrought iron
- Ferroalloys (alloys with names starting in “ferro-” such as ferroboron, ferrochrome, etc.)
Bronze is an alloy which is traditionally composed of copper and tin, but nowadays are made with addition of other metals (like aluminum, manganese, nickel, and zinc) or non-metals (arsenic, phosphorus, and silicon). This alloy has been widely used for millennia, used to build sculptures, tools, weapons, and bells.
Does bronze rust?
Since bronze does not have iron in it, it will not rust. It is also much more resistant to corrosion and harder than pure iron and copper, thanks to alloying copper with tin. Although bronze does not rust and is wear- and corrosion-resistant, this does not mean that it can never be corroded.
Bronze disease is a form of metal corrosion that affects bronze, and it manifests as a green fuzz. In previous times, people thought that it is caused by bacteria (hence the term “disease”), but it turns out that it is caused by a series of complex chemical reactions involving the chlorides of the copper of the bronze and water. These chemical reactions, however, are still not fully understood. What’s currently known is that the cuprous chloride in the bronze reacts with water, creating hydrochloric acid that damages the bronze, which then will react with copper. It would take years before this happens to bronze (think tens to hundreds of years), but it can be sped up if the environment favors it.
Bronze disease in ancient coin
Image source: Joukowsky Institute – Brown University
However, do not confuse a layer of green patina with bronze disease! Patina is not destructive to bronze and may even protect it from further exposure to moisture. Over time, a layer of protective brown patina naturally forms on the bronze’s surface through oxidation, and as more time passes, the patina becomes green.
Green patina on a bronze watch
Image source: Fratello Watches
Nickel, one of the most abundant elements here on earth, is widely used for its properties as a good heat and electricity conductor and its high heat and corrosion resistance. This silvery-white metal does not rust, since it is pure metal with no iron in it.
Due to these wonderful properties of nickel, it is alloyed to a lot of different metals to increase rust-resistance. This metal is beneficial to use in industrial processes, especially ones involving water since it won’t easily oxidize nor rust. An example is how nickel alloys are used in making fuel tanks for heat and corrosion resistance.
Image source: Nornickel
Cast iron is an iron-carbon alloy, and as mentioned before, it will rust. You might be wondering why then it is famous in cooking. This is because cast iron has a high volumetric heat capacity. When cast iron is heated, it stays hot for a longer amount of time compared to other pan materials.
Cast iron skillets have a protective layer of carbonized oil against rusting. However, this coating can be chipped away through time and repetitive use. Making sure that your pan or skillet is not left to soak and is not stored in a moist environment is your best bet in preventing rusting. If your cast iron pan gets rust, you can remove it through vinegar soak or by scrubbing it all off using fine steel wool.
Image source: Stephanie Staton – Hobby Farms
Chrome is mostly used for electroplating (chrome plating), done to lengthen the lifespan of metals or plastics. Chromium is a transition metal that is steely grey in color, lustrous, hard, and brittle. It acts as a protective layer against corrosion and rusting. Thus, chrome does not rust.
Chrome plating involves the application of chromium onto the surface of an object (metal or non-metal) as a finishing process. The layer of chromium is applied via electroplating, making use of an electrical charge, which is applied to a solution of chromium anhydride. This triggers a chemical reaction and the chromium deposits itself onto the surface of the submerged object. This results in a silvery chrome layer that readily protects the underlying surface from corrosion since chrome is impermeable to oxygen and thus prevents oxidation.
However, if the chrome layer is compromised and the underlying material contains iron, rusting can occur. Without the chrome plating, the metal underneath will come in contact with moisture and oxygen—the perfect recipe for rust.
Image source: Alchemist-hp
Despite being brittle, tungsten is still one of the most durable elements: it has the highest tensile strength (142,000 psi) and melting point (3687 K) among natural metals. These characteristics make tungsten favored by jewelry makers, producing rings that are strong and can last for years, with its hardness and high temperature resistance. Because of the durability of tungsten, it is used to alloy with other metals for added strength and corrosion resistance. Although this metal is highly durable, in some forms, it still can be cut by plasma cutters and polished by diamond wheels.
Furthermore, tungsten does not contain iron, so it does not rust. Pure tungsten does, however, oxidizes in the air, developing colorful tarnish or patina.
Tungsten carbide with nickel binder, on the other hand, does not readily oxidize and tarnish, except at very high temperatures (around 1100 K above). This type of tungsten alloy is the one widely used for high quality jewelry, one that doesn’t stain around the finger and lasts long.
Tungsten cube of high purity alongside tungsten rods with evaporated crystals and colorful tarnish.
Image source: Alchemist-hp
Damascus steel can rust since it is an iron alloy. Famous for its watery light and dark pattern (known as the “damask” pattern) Damascus steel has been valued for years since the ancient period, used to forge the blades and weapons of warriors. This steel was originally cast from wootz, another type of steel from India, which is made by melting iron and steel together with charcoal (carbon) and uses Sorel metal (Fe-C alloy) as a raw material.
During the 19th century, the mining region in India where the wootz came from changed, bringing impurities, and thus changing the steel ingots for making Damascus steel. Due to these impurities, the original manufacture of wootz Damascus steel with its watery patterns was never replicated again.
However, since the composition of this steel was shed to light and the truth about the significance of wootz ingots, it led to the successful reproduction of Damascus steel, albeit manufactured differently. The damask pattern of the original steel was copied onto the new ones through layering iron and steel and forging the two together by hammering at high temperatures, forming a welded bond. After multiple layers of forge welding, the watery pattern is replicated.
This synthetic gemstone rivals the beauty of diamonds. It is made from melting zirconium oxide powder, together with stabilizers like magnesium and calcium, and then crystals will start to form and stabilize upon removal from heat. The cubic zirconia crystals are then cut and polished, and the resulting pieces sparkle just like diamonds, but usually having more “colors” than the natural gem.
Notice how there is no iron whatsoever introduced in the process of making cubic zirconia. Thus, the crystal itself does not rust. However, if you’re thinking about jewelry, the metal that holds the cubic zirconia may rust, depending on what type of metal it is.
Image source: Essilux
Rhodium is commonly used for plating material, giving a protective coat that shields the underlying material from scratches, just like chrome. Just like how wide belt sanders can give wood a beautiful finish, rhodium plating gives jewelry a strong shine, reflecting up to 80% of light, and smoothens chips and scratches.
This noble metal is one of the most expensive ones, with its pure form being even more costly than gold. It is a silvery-white, hard, and chemically inert transition metal. It is highly corrosion-resistant and doesn’t rust. With these great properties, it is used as an alloying agent to form furnace coils, electrodes, laboratory apparatus, etc. This metal has a high melting point and is brittle, which is why it is widely used as an alloying agent and electroplating material.
Although the metal itself is corrosion-resistant, if the coating of rhodium done on the material is thin, it can wear off over time. If the underlying material contains iron, the jewelry or equipment will rust.
Before and after pictures of rhodium plating on jewelry
Image source: Mark Lloyd Jewellery
Chromoly will rust since it is an iron alloy, but not as readily as other steel alloys containing iron. Two of its major alloying elements are chromium and molybdenum (which is why it is named “chromoly”), and these contribute to the corrosion resistance of chromoly steel, increasing its hardness and melting point. To protect this alloy steel from rusting, this steel is treated with coatings. This steel is what you’ll mostly find in bicycle tubing or frame because it is more lightweight than other steel frames. Also, due to its high melting point, it can be used in making furnace equipment, such as waste oil heaters.
Chromoly bike frame
Image source: Sprocket Store
Sheet metal is basically metal processed into thin, flat pieces (below 6mm). Depending on the material, metal sheets can be easily cut by engine-driven welders. Making sheet metal may involve shearing, punching, cutting, folding, and splicing of steel, among many others.
Regular steel is an alloy of carbon and iron, which will readily rust. With that being said, sheet metals that do not rust are commonly made up of galvanized or stainless steel, both of which have corrosion and rust-resistant properties. One example use of stainless steel is the manufacture of car parts, such as idle air control valves, while galvanized steel is commonly used for roofing materials. Galvanized steel is made by coating regular steel or iron with a protective zinc coating to shield the underlying steel from oxidation and corrosion. Once this layer is degraded, the steel underneath will rust.
Image source: Thomas
Most people confuse galvanized steel with Galvalume. Both are coatings, applied to metals to protect them from corrosion and oxidation, but these two are different things.
Galvalume is a metal alloy invented and introduced by Betlehem Steel in the market in 1972. This alloy coating contains zinc, aluminum, and silicon. The combination of zinc and aluminum enhances its corrosion and heat resistance. Galvalume is widely used in roofing materials, and it lasts longer than galvanized metals. It is made by hot-dipping the carbon steel base sheet with aluminum and zinc alloy until it reaches the right percentage of alloys.
Unpainted Galvalume roof
Image source: Construction Magazine
Does acetone remove rust?
If you failed to safeguard your tools or jewelry against rusting, fortunately, you can easily remove rust with acetone! This is one of the easiest fixes against rusting of various surfaces, one that you can do on your own without needing any special equipment. All it takes is letting the item sit in the acetone for a few hours until the rust chips away, and then scrub off the remaining rust. If submerging the item in acetone is not applicable, you can just douse a scouring pad with acetone and use it to scrub the rust off. Just remember to oil your equipment afterwards to protect it from further oxidation.
However, bear in mind that acetone can also damage paint, so you’ll have to look for other remedies to remove rust for equipment marked with paint, such as precision tools. Furthermore, acetone may react with the metal or coating and produce toxic fumes, so you have to be careful and choose which metals can be mixed with acetone.
Other methods to remove rust include mechanical means by using fiberwheel/abrasive buff wheel attached to a rotary tool, and chemical removal by using safe rust removers like Evapo-Rust, WD-40 Rust Remover, and POR-15 Rust Remover.
How to prevent rusting
Prevention is better than cure, as one might say. If buying rust-resistant materials is not an option for you, you’ll just have to take care of our equipment of jewelry properly to avoid rusting. First and foremost, avoid exposing the metal to moist or wet environments. If you notice your home frequently gathering dust, I suggest you look into UV light sanitizers for your HVAC and furnace systems to avoid multiple exposures of your tool to water due to frequent cleaning.
Also, it’s important to oil your tools regularly to prevent rusting. Oil protects the surface of your equipment from getting in contact with moisture, thereby avoiding oxidation. I always make sure to oil my engine-driven welder after cleaning its parts to ensure that it won’t rust.
It is also important to store your metallic equipment 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. Our two most popular articles include this one on oxy torches and this one on gauge wire.