Rusting can cause an array of problems, from producing cracks and holes in metals up to reducing the magnetic properties and electrical or thermal conductivity of metals. Although rust is non-toxic, its presence in infrastructures, such as bridges, cars, power supplies, etc., can jeopardize our safety. Since rusting is a natural phenomenon, all metals containing iron must be regularly checked to avoid any safety hazards.
What causes metal to rust?
Rusting is the most common example of metal corrosion, and it happens to metals made up of (or containing) iron. When the iron in the metal comes in contact with air and water, an electrochemical reaction occurs, and an oxide forms: iron oxide (in its hydrated form).
Yes, rust is just the common name for iron oxide. Depending on the type of iron oxide formed, the color of rust may vary, from yellow, orange, brown, red, or green (or a mix of these colors). The most common one 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 (air) + water → iron (III) oxide trihydrate
Without moisture or water, this chemical reaction won’t happen, so it’s important to safeguard the metal from direct exposure to moist or wet environments. Water facilitates the transfer of electrons between the iron and the environment, which is basically the oxidation of iron. Let me discuss it briefly below:
- 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 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 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 to attack the iron, corroding the metal at a faster rate.
Other metals also undergo this type of corrosion (oxidation), but the resulting oxides cannot be classified as rust, simply because those are not iron oxides. For example, silver reacts with sulfur, and the oxide called silver sulfide is formed, which is commonly known as silver tarnish.
Brass is an alloy of copper and zinc, with the former usually being the main component. Depending on the proportions of copper and zinc, brass’s color may change from bright gold up to reddish-gold or silver. Other elements, non-metal or metal (e.g., tin, lead, nickel, silicon, or arsenic) may also be added depending on what is needed.
Copper is extremely ductile and has a high thermal and electrical conductivity, but it is soft and malleable by itself. The addition of zinc, however, improves the strength and ductility of the brass. The resulting alloy has a low melting point and high workability and durability, the perfect material for musical instruments, decorative items, plumbing, locks, etc.
Does brass rust?
Brass does not contain iron unless it is one of the added components for certain applications. If iron is added, it is usually at a very low concentration, so it can be negligible. Therefore, it does not rust.
However, brass does corrode and/or oxidizes! The resulting oxide just isn’t iron oxide, so you cannot classify it as rust. It’s more suitable to call it as tarnish, rather than rust.
Here’s one example of how brass corrodes: selective leaching.
When the zinc in brass leaches off, it is called dezincification. And when zinc is lost and copper is left behind, the alloy weakens because zinc is the one that contributes to the durability/strength of brass. If copper is the one that leaches off, it’s called decuprification. Either way, the structural integrity of brass will be compromised.
Dezincification is more common since zinc is more reactive (more likely to oxidize) than copper. Once this happens, pink or reddish discoloration on brass appears. Exposure to moisture or water (especially salt water) will also quicken this type of corrosion, since the zinc will oxidize faster. For example, in musical instruments, the dezincification occurs in areas where the brass instruments were held (sweat as the source of moisture)—musicians call this phenomenon “red rot.”
What is the blue-green layer that forms on brass?
Although this phenomenon is also caused by oxidation, the blue-green/green layer that you see on brass is not a sign of corrosion! It’s called patina, a naturally-occurring film layer on most metals. The patina is not detrimental to the alloy—it may actually become a shield against air and moisture. Many people even consider this color change as attractive on brass and accelerate the oxidizing process by applying solutions to it for an “aged/vintage look.”
How to remove “rust” from brass
As mentioned, the “rust” that people see in bronze isn’t actually rust. Since selective leaching doesn’t happen quickly and is accompanied by the weakening of brass, it’s most probably just patina that you’re seeing. Patina can be easily removed by scrubbing with hot, soapy water. But if that doesn’t work well, it’s probably mild dezincification you’re dealing with. Try using an abrasive slurry like a baking soda and lemon/vinegar paste. Leave it on for 5-10 minutes and then rub it in for a few seconds. Alternatively, you can also use commercial abrasive polish such as calcium carbonate silver polish. Rinse the brass properly and coat it with a bit of mineral oil. Lastly, just like how wide belt sanders give wood the perfect, smooth finish, use a microfiber cloth to buff the brass and bring back its shine.
To avoid patina formation or tarnishing and dezincification, you should regularly keep brass clean and dust-free. Avoid exposing it to moisture, especially with salts or acids, such as sweat. Also, any commercial polish used on brass must be rinsed off properly. A coating (e.g., wax or clear lacquer) must be applied to protect the surface from further tarnishing.
Severe dezincification that extends deeply into the alloy is hard to solve, and you might just end up discarding the item in the end.
Zinc is mostly used to galvanize steel, applied as a coating that’s metallurgically bonded to the steel, protecting it from corrosion like oxidation or rusting. Zinc acts as a sacrificial metal, reacting with oxygen to form a zinc oxide layer that prevents rusting or formation of iron oxide.
By itself, zinc is pretty much a weak and brittle metal, with low to moderate tensile strength and conductivity. However, when alloyed with other metals (such as copper to make brass), the resulting alloy usually has high impact strength and ductility, and it is more corrosion-resistant.
Zinc itself doesn’t rust, but if alloyed to iron or ferroalloys, rusting may occur. Also, if the zinc layer of galvanized steel is compromised, rusting may occur since the underlying metal that contains iron (steel) will be exposed to air and water.
Titanium is a strong, lustrous, and corrosion-resistant metal. It’s high resistance to corrosion is due to its ability to form titanium dioxide (TiO2) upon oxidation; this strong oxide layer protects the titanium metal underneath from corrosion caused by most acids, alkalis, and saltwater. Furthermore, other salts that would usually speed up the corrosion of some metals actually inhibits corrosion of titanium (e.g., FeCl3 and CuCl2). Just like tungsten, titanium is one of the most durable natural metals on earth. However, despite being resistant to most corrosion like oxidation, titanium isn’t immune to pitting and saltwater corrosion at elevated temperatures.
Titanium itself doesn’t rust. The commercially available forms of titanium are usually alloys, and if iron is one of the alloy’s component, rusting can happen.
If you’re looking for a tool to cut this strong metal with, oxy torches or plasma cutters can still do the job. But if you’re dealing with metals that are not as tough as titanium or tungsten, these engine-driven welders will be perfect for you.
Tin (Sn), if not alloyed with iron, will not rust. This soft, pliable silvery white metal is used to electroplate or coat steel and other metals (just like zinc), or as an alloy component (as in bronze, the alloy of copper and tin) to prevent corrosion and rusting. This is why it is used to coat metal that is used as food storage (i.e., tin cans) because it does not rust, corrode, or react readily with water and oxygen at room temperatures. However, at elevated temperatures, tin can still corrode and react with water and oxygen and form oxides.
Pure tin is commonly mistaken with tin-coated steel (e.g., tin can, tin roof, etc.), and thus, is called tin, too. The latter can rust (because steel contains iron) if the tin coating is compromised.
How to remove rust from tin
As mentioned, rust can readily form when the steel underneath the tin coating is exposed to water and air. To remove rust, you can also use abrasive tools, just like in removing patina or tarnishes. The most common method is to rub the rust off with fine steel wool, rinsing the metal with warm soap and water.
Using abrasive methods, although effective in removing rust, can also further damage the tin coating. A gentler approach is the use of a lemon juice/vinegar and baking soda paste, as discussed previously. Apply the paste to affected areas, rub it in for a few moments, and leave it on for a few minutes. Scrub off the paste gently with a sponge, and see if the rust has softened or come out. If not, repeat the soaking process. Then, rinse the item with warm soapy water.
Sterling silver is an alloy of silver and another metal, which is usually copper. The standard purity of sterling silver is 92.5% (by weight of silver), hence the name “925 sterling silver” for jewelry. The other metal component (copper, nickel, zinc, or germanium) constitutes only 7.5% by weight— this proportion retains the silvery color of the alloy.
Sterling silver does not rust, but it is not immune to other forms of corrosion.
The addition of copper makes sterling silver more susceptible to oxidation and corrosion because copper is a more reactive metal between the two. This is the reason why sterling silver tarnishes more easily than fine or pure silver. But the addition of copper is necessary for silver to be workable and turned into something of use. Fine silver, which is 99.9% pure silver, is too soft to be used in making tools or jewelry; the addition of copper, however, increases its durability and hardness.
Like in brass musical instruments, when sterling silver jewelry gets in contact with moisture like our sweat, it will tarnish. The presence of salt in our sweat speeds up the process of oxidation. Although tarnish is not necessarily something to panic about because you can easily have it cleaned/removed, further neglect of the item is not the right way to go.
When tarnish is not cleaned immediately, and the item is not protected against further exposure to air and moisture, oxidation will further damage the metal, making it more vulnerable to other forms of corrosion such as pitting.
Lead, a bluish-white to silvery-grey metal, is soft, highly malleable, and ductile. Although it is a poor conductor of heat and electricity, it is resistant to corrosion. Lead has been used for years to make pipes, pewter, paint, insecticides, etc. but has been banned due to leaching and its detrimental effect on health. Currently, lead is widely used in the manufacture of roofing, glass windows, car batteries, pigments, weights, glasses, and ammunition.
Lead does not rust but tarnishing is a common problem with this metal. When freshly cut, this metal is actually a lustrous silver with a bluish tinge. But when exposed to moist air, it tarnishes to a dull silver-grey color, which is the color that we commonly see.
Powder coated steel
Coating metals to increase their corrosion resistance or retain their luster has been widely practiced, as mentioned in galvanizing steel and lacquer-coating of brass. Powder coating also has the same purpose. It is done to materials such as steel as a resilient, protective layer. Thus, the resulting powder coated steel has improved corrosion resistance and durability, thereby extending its lifespan.
Powder coating is one of the processes in the manufacture of fuel transfer tanks, which increases the quality of the tank’s finish. Also, some car parts like valve covers are powder coated for more protection to avoid damage to idle air control valves.
Powder coating, unlike galvanization, is a dry coating process. Zinc is applied as a liquid for adhesion purposes (steel is hot-dipped in molten zinc), while powder coating is applied dry and adhered to the steel with the help of electrostatics. One of the many advantages of powder coating is it can come in different colors, chemical compounds, and thickness. Powder coating materials can either be thermoplastics or thermosets.
- these coating materials are usually plastic polymers that are soft when heated and hardens upon cooling
- coating material can be altered (post-curing alterations) and removed even after setting on the substrate/steel
- more ductile and has better chemical resistance
- examples: nylon, polyester, polyvinyl chloride, polysulfones, etc.
- these coating materials/polymers form strong cross-links within their molecular structure when set/cured; coating material can’t be altered post-curing
- cross-linking in molecules give stability even at high temperatures; ideal for high temperature applications like waste oil heaters
- examples: epoxy, silicone, phenolic, polyurethane, etc.
Powder coating is resistant to chipping, abrasion, peeling, cracking, and chemical damage, but it is not immune to damages forever. Although it can last up to 20 years, powder coating can slowly deteriorate. When enough damage/wear is accumulated, the coating will be compromised, and the steel underneath will rust upon exposure to moist air.
How to remove rust stains
One of the hassles of rust is when it gets onto clothing or other fabrics; it’s a very stubborn stain and will not disappear with usual laundering tricks, sticking to the fabric even after using bleach. But here’s the good news: rust-stained fabrics can still be saved with the use of lemon juice, salt, baking soda, and hydrogen peroxide!
The first thing that I tried is the salt and lemon combo. If the fabric isn’t colorfast, test the lemon juice on it first to check if any bleaching or fading will occur. If there isn’t any, then you can proceed.
- Put salt on the stained area, and then wet the salted areas with lemon juice. Make sure to not miss any stains!
- Pick a sunny spot outside, lay down the fabric (with the stained area facing the sun), and let the sun do its work.
- Once the fabric is dry, wash the garment as usual but use a heavy-duty laundry detergent.
If this technique doesn’t work, try the baking soda and hydrogen peroxide combo next! However, this may cause bleaching/fading, so only do this on white and colorfast fabrics.
- In a bowl, add in 1-2 spoonful—depending on how much you think you’ll need to cover the stain—of baking soda.
- Add a few drops of hydrogen peroxide and mix periodically until you get a paste consistency.
- Apply this paste onto the stained areas, let it sit for 30-60 minutes, and then rinse the fabric with water.
- Launder the fabric as usual using a heavy-duty detergent.
It’s best to air dry the fabric first if you’re not too sure whether you’ve taken out all the stains. This is because the blast of hot air in dryers may set the rust stain onto the fabric. But if you’re sure that you got all stains out, feel free to use the dryer!
If both home remedies didn’t work, try using a commercially available rust remover. Make sure that the fabric is colorfast (or else, the dye will be washed away along with the rust) and choose a rust remover one that is applicable to fabrics. All rust removers come with their own set of precautions and instructions, so read and follow them carefully.
Almost all rust removers follow the same procedure: apply it on the stained area, let it sit for a few minutes, and then rinse with water. After that, you can launder the fabric as usual.
Does rustoleoum stop rust
If you’re no stranger to automobile work, you’re probably familiar with rust protectors, converting primers, rust removers, etc. In my experience, Rust-Oleum products work best on metal that hasn’t rusted that much yet. Like I’ve always mentioned, prevention is better than cure. Rustoleoum products work best on clean metal that has little to no rust.
However, applying rust inhibitors on metal that is already heavily rusted won’t successfully stop rusting. Applying thick coats of rusteloeum on moderately or heavily rusted metal might slow down rusting, but you’ll see some bubbles or cracks soon enough, and rusting spots will appear sooner rather than later.
When it comes to stopping rusting, you might need two to three products: metal/converting primer or rust reformer, rust protector, and a top coating or paint. Results may vary depending on the extent of rusting on metal, and you’ll still need to remove the existing rust before applying all coats.
In all instructions of various metal primers and rust inhibitors, it is recommended that you remove a significant amount of rust first until you achieve a smooth, clean metal surface. Metal primers or converting primers are usually applied first, to ready the surface for adhesion of further coatings of other rust protectors. These primers usually include ingredients that bond with the rust or simply turn the surface of the metal into a waterproof, paintable surface. Once the primer coat is set, another coating (or two) is usually applied which will act as a protection layer.
To sum it up, yes, rustoleoum may stop rusting from worsening, but it doesn’t work like magic, wherein one coat or spray will magically melt all rust and stop it from reoccurring. It’s more of a preventive measure rather than a cure. You’ll have to remove existing rust, clean the metal, prime the surface, and apply a protective coat.
If you don’t want to go through such lengths (and extra cost) to avoid rusting, make sure that any item that may rust is kept away from moist or wet environments. Clean items made up of metal regularly to avoid tarnishing. 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.
Lastly, store all items that are susceptible to rusting 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. We also have a bunch of articles on topics like gauge wire and other things.