What speeds up oxidation?
Rate of Rust Formation
Rusting can happen quickly or slowly, depending on the material thats rusting, and the environment. Rust is the oxidation of iron along with the absorption of water to make Fe2O3 with water molecules attached. Here are some things that can affect the rusting rate:
1) The iron can have additives to prevent rusting. Stainless steel has added nickel and chromium which bind to the iron atoms and keep them from oxidizing. I havent seen stainless steel rust even over long periods of time.
2) The iron can be painted or coated with oil, preventing oxygen and water from coming into contact. This can slow or halt rusting.
3) The air can be devoid of humidity and in some place it doesnt rain much. Cars last longer out in the desert because its so dry, rusting is slowed.
4) Hot iron rusts faster than cold iron — typically heat speeds up chemical reactions. This is one reason why mufflers and exhaust manifolds in cars get rusty very quickly (unless they are coated or made out of non-rusting materials).
5) Thin iron can rust through (get holes in it) faster than thick iron. The rusting rate may be the same, but you may notice it sooner in thin metal sheeting than on a thick piece of iron because the former will have a hole in it sooner. Some kinds of steel wool also rust quickly (they are commonly exposed to water so this doesnt help), although other steel wools are made of stainless steel or coated.
6) The rate of rusting or corrosion in water can be affected by the electrical environment. If you have two different metals in electrical contact, and both in contact with salty water, then effectively a battery is made. Current flows, and the energy comes from the corrosion of the metals. Some companies sell blocks of zinc that you can attach to boats so that the zinc corrodes first, protecting the other metals.
7) Some questioners on this site have found that rusting rates in iron submerged in water are affected by dissolved impurities. Vinegar and bleach have been tried and seem to affect the rusting rate.
Fresh iron exposed to a hot atmosphere with plenty of oxygen and water will form a thin layer of rust immediately (although if you look at a very short time after exposing the iron surface, you will have a very small amount of rust). Any of the above variables can affect the rusting rate however. Can you think of more?
(published on 10/22/2007)
Follow-Up #1: rusting stainless
I read what Tom said about the rate of rusting and stainless steel does rust! I did an experiment on rusting stainless steel and it rusted in water, salt water, vinegar, lemonade and red cordial. I just thought I’d add that to what Tom said before Beth
— Beth
Melbourne Victoria Australia
The rate of stainless steel rusting is very sensitive to what type of stainless it is. The amounts of chromium, nickel etc. in different steels vary a lot, and so does the uniformity of the mixing of the different elements. When a ‘stainless’ steel has pockets of nearly pure iron, it will rust.
(published on 10/22/2007)
Follow-Up #2: contact rust?
I just wanted to add that contact with other metals will contaminate the Stainless at almost any grade. I see lots of stainless tubes where some pipe-fitter leaves the chain-fall lead laying on it and the next morning there is a rust layer on the s.s. surface. Although some maybe transfer, that s.s. has been contaminated by the carbon in the chain. I think that rust rates are also related to whether the metal is a ferrous or nonferrous, but that is pure opinion, and I am just a dumb irish welder. S-
— Scott George (age 31)
Smith Valley, Nv, USA
You know more about this than we do.
I wonder if there’s a connection with the effect by which when two metals are in electrical contact, one will corrode much faster than the other. Ships use this to protect the hull by attaching a more easily dissolved metal.
(published on 02/28/2010)
Follow-Up #3: Danger of wet electrical fuse boxes
I have 2 metal cabnets with alot of copper fusses and there has been at least 6 days of rain hitting them and there in a confined space, i was just wondering what is the possibilities of getting rust in such a short time. my email is ## i just trying to find out if you need more information i could provide it thankyou
— Jose Sanchez (age 25)
Ohio, il, usa
I wouldn’t worry about rust too much. The conducting elements in wires and fuses are mainly copper. However, water and electricity don’t mix. There is always danger of shock. Don’t get your hands in that fuse box when it’s wet.
(published on 06/29/2010)
Follow-Up #4: rusting rate vs. oxygen pressure
Does air pressure affect rust formation? This pertains to steel tanks that hold compressed air. Would increased air pressure increase, decrease or not effect rust formation on steel? Thanks
— Mark Johnson (age 35)
woodland, ca, usa
I’d assume that higher oxygen pressure would increase the rate of oxidation, i.e. rusting. Chemical rates don’t always follow such simple rules, but it would be surprising if it didn’t happen this way.
(published on 01/04/2013)
Follow-Up #5: battery corrosion
I was wondering about rust and corrosion rates with batteries. Does the electric charge of the battery increase the rate of corrosion? Like for example could small amounts of rust form on a battery within say an hour?
— Ryan (age 26)
Billings, MT USA
I’m not sure about the rates, but you could check that pretty easily. I did just notice that the contacts with the negative sides of some bicycle light batteries were much more corroded than the positive contacts. Clearly the electrical charges are playing a role, just as you guessed. (I put some bulb contact grease, available at auto stores, on the contacts after cleaning them up.)
(published on 05/17/2019)
What speeds up oxidation?
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Speeding Up Key Oxygen-Oxygen Bond-Formation Step in Water Oxidation
New molecular catalysts could drive reaction needed to efficiently store solar energy in chemical bonds of clean fuels
May 16, 2016
enlarge The research team, left to right: Brookhaven Lab research collaborator David Szalda, Baruch College; David Shaffer, Yan Xie, and Javier Concepcion, Brookhaven Lab. Not pictured: Anna Lewandowska-Andralojc, Adam Mickiewicz University.
UPTON, NY—For years, scientists have been trying to emulate photosynthesis, the process by which plants, algae, and some bacteria harness light from the sun to chemically transform water and carbon dioxide into energy that is stored for later use. An artificial version of photosynthesis could provide a clean, renewable source of energy to help satisfy society’s growing demands. For artificial photosynthesis to become a viable alternative to fossil fuels, the efficiency and speed of water oxidation—the reaction that turns water into oxygen gas, hydrogen ions, and electrons—is one of the processes that must be improved. Now, a team of scientists from the U.S. Department of Energy’s Brookhaven National Laboratory, Adam Mickiewicz University, and Baruch College, City University of New York, has synthesized two new molecular catalysts for water oxidation. The catalysts—complexes of ruthenium surrounded by binding molecules (ligands) containing phosphonate groups—accelerate the formation of the oxygen-oxygen bond, usually the most energy-intensive and slowest step of water oxidation. Initial studies, described in a paper published on May 11 in Angewandte Chemie International Edition, demonstrated that these ruthenium complexes could offer a low-energy pathway to faster water oxidation. «Storing solar energy as hydrogen fuel or carbon-based fuels like methanol requires catalysts that can oxidize water at fast rates, with high efficiency, and for long periods of time,» said Javier Concepcion, an author of the paper and a chemist in the artificial photosynthesis group at Brookhaven Lab. «Our ruthenium complexes catalyze the oxygen-oxygen bond formation faster than any other known catalysts, generating hundreds of oxygen molecules per molecule of catalyst per second. With these catalysts, the electrical potential required to start the reaction is approximately 10 times less than that of a AA battery.»
Forming the oxygen-oxygen bond
In water oxidation, four protons and four electrons—required in a subsequent reaction to convert carbon dioxide into usable energy—are removed from two water molecules, and an oxygen-oxygen bond is formed. For water oxidation to occur, the bonds between hydrogen and oxygen atoms in the two water molecules must be broken. In the case of artificial photosynthesis, a chemical catalyst triggers this molecular breakup. «Water is a very stable molecule, so getting two water molecules to react with each other is very difficult,» explained first author Yan Xie, a doctoral candidate at Stony Brook University and a research assistant in Brookhaven’s artificial photosynthesis group. «Our ruthenium complexes provide the reactivity needed to break those bonds.» The paper describes details of the series of steps through which the catalyst initiates and completes the reaction. In short, one of the water molecules binds to the ruthenium complex and loses protons as the complex is oxidized (loses electrons), resulting in an electron-deficient ruthenium-oxo group. Then, with the assistance of a phosphonate group, the other water molecule reacts with this highly reactive ruthenium-oxo to release molecular oxygen (O2). «The phosphonate group accepts protons, or hydrogen ions, from water,» said coauthor David Shaffer, a research associate in Brookhaven’s Chemistry Department. «It is positioned near the active site of the ruthenium complex where water oxidation occurs. Incorporating the phosphonate group and ruthenium in a single complex makes it easy for the water molecule to find that one site and react.» Eventually, the protons are transferred from the phosphonate group to the surrounding solution.
Studying the electrochemistry of the ruthenium complexes
To determine the efficiency and rate of water oxidation with the ruthenium catalysts, the team studied the electrochemistry of each oxidation state by applying different voltages and measuring the amount of current flowing through the system at various pH values (the concentration of protons in the solution). «The voltage at which catalysis starts tells you about the energy efficiency of water oxidation, while the current tells you how quickly water oxidation is occurring,» explained Concepcion. «Our ruthenium complexes minimize the amount of energy lost as heat, both in terms of the voltage and the rate that would be required for the catalyst, if incorporated into a device, to make use of all incoming sunlight.» The team also used computational modeling to study the activation parameters—the energy and molecular order—required to break and make bonds during the key reaction between the water molecule and the ruthenium-oxo group. The computational studies showed why the phosphonate group resulted in faster catalysis. «Phosphonate is a good proton acceptor, so it energetically favors the reaction. Because it is part of the ligand, it is already positioned and ready to interact with water, removing the need for a more ordered arrangement of molecules,» said Concepcion. From separate studies, the scientists were able to tell that one of the oxidation steps—not the oxygen-oxygen bond-formation step—was limiting the rate of the catalysis. The team is now developing second-generation catalysts to optimize this step. Eventually, they hope to make equally reactive catalysts using metals such as iron and cobalt that are more abundant and less expensive than ruthenium, but whose chemistries are much more complicated. «By incorporating these catalysts into systems capable of absorbing sunlight and combining them with catalysts that reduce carbon dioxide or water into fuels, artificial photosynthesis could become a practical approach for storing solar energy as fuels,» said Concepcion. The research was supported by the DOE Office of Science. Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.
Related Links
- Scientific paper: «Water Oxidation by Ruthenium Complexes Incorporating Multifunctional Bipyridyl Diphosphonate Ligands»
