Tag Archives: rust

Rust and salt water — the new way to generate electricity

While renewable energy keeps expanding across the globe, a new discovery by scientists at Caltech and Northwestern University could soon lead to new ways of developing a sustainable power production.

Credit: Flickr

A new study found that thin films of rust—iron oxide—can generate electricity when saltwater flows over them. The study was published at Proceedings of the National Academy of Sciences and led by Tom Miller and Franz Geiger.

Thanks to a chemical reaction that changes the elements, the interaction between metal compounds and saltwater commonly generates electricity. However, harnessing that electricity has proven challenging.

Researchers have now discovered that rust, or iron oxide, converts the kinetic energy of flowing saltwater into electricity, with no chemical reaction involved.

The discovered phenomenon has previously been observed in thin films of graphene — sheets of carbon atoms arranged in a hexagonal lattice. The effect is around 30 percent% at converting kinetic energy into electricity. For comparison, the best solar panels are about 20% efficient.

“A similar effect has been seen in some other materials. You can take a drop of saltwater and drag it across graphene and see some electricity generated,” Miller said, adding that the iron oxide films discovered would be relatively easy to produce and scalable to larger sizes

In order to make sure that the rust formed in a consistent and thin layer, the researchers used physical vapor deposition (PVD). The technique turns normally solid materials into a vapor that condenses on the desired surface. They created a layer that it’s around 10,000 times thinner than a human hair.

Using saltwater solutions over the layer, the ions in the water attracted electrons in the iron under the layer of rust and dragged those electrons along with them, generating an electrical current. The process could be used in the future to generate energy on items like buoys floating in the ocean, researchers claimed.

“For perspective, plates having an area of 10 square meters each would generate a few kilowatts per hour—enough for a standard US home,” Miller said. “Of course, less demanding applications, including low-power devices in remote locations, are more promising in the near term.

The discovery could be useful in specific scenarios where there are moving saline solutions, like in the ocean or the human body, the researchers think.

“For example, tidal energy, or things bobbing in the ocean, like buoys, could be used for passive electrical energy conversion,” he said. “You have saltwater flowing in your veins in periodic pulses. That could be used to generate electricity for powering implants.”

While this is still very early days for this technology, it’s an exciting approach that’s worth keeping an eye on in the future.

What is oxidation?

Rust, patina, fire, rancid food — they all have oxidation in common. So let’s take a look at exactly what that is.

Rust.

Image via Pexels.

Life as we know it today couldn’t exist without oxygen. So, we’re lucky that there’s so much of it around. But this reliance on oxygen has been, at times, called a ‘deal with the devil’. The same property that makes the gas vital to most Earth-borne life — its unquenchable thirst for electrons — slowly kills the very life it supports.

Today, I thought we’d take a deeper look into this life-giving-life-taking dynamic by asking:

What is oxidation

Oxidation is the process in which one atom strips electrons from another, claiming them for its own. It is one side of redox type reactions. These reduction-oxidation reactions stand apart from other types of chemical interactions because they involve changes to multiple atoms’ electron envelopes. Reduction is the process via which an atom ceeds electrons to another.

The term draws its name from oxygen because it was the first known oxidative element. In fact, for quite a good stretch of time in the 18th century, ‘oxidation’ referred solely to the addition of oxygen to a compound. A good example of this traditional definition for oxidation can (annoyingly) display itself on the body of our cars: rust (iron oxide).

Since then, we’ve learned that oxidation isn’t limited to either iron or oxygen. Most elements can be oxidized, given proper coaxing, in a variety of environments. Many can be made to oxidize their peers. Some flake and break apart when oxidized, others tend to become more resistant to further oxidation. The process comes in many forms and involves many players. As such, we’ve expanded the definition of oxidation to include any and all reactions in which an element sheds electrons and increases its oxidation state.

Putting the ox in redox

Oxidation and reduction.

Image via Texample.net.

Oxidation and reduction always, always, occur together.

For purely theoretical approaches, half-reactions can be used to explain half of a redox reaction — be it the oxidation or the reduction component. These are pretty helpful in simplifying the whole process, to make it easier to teach or understand. But keep in mind the first line: in real life, oxidation and reduction always come together.

Quite simply, an electron won’t want to leave its hosting atom. It won’t go into the wild willy-nilly. There’s nothing to satisfy its electrical imbalance there. But having a more inviting host nearby to move on to can draw it out. Oxidation, then, cannot occur unless there’s an electron-thirsty atom around. On the other hand, without an electron donor, there’s no transfer. Reduction, then, can’t occur if there’s nobody to strip electrons from.

Think of it as a marketplace. You need buyers to have sellers and vice-versa; one simply can’t happen without the other.

Ok, so why do we call it ‘reduction’? Again, it’s history at work. We weren’t able to properly understand chemistry for quite a long time, but we were able to observe and measure some of its effects. ‘Reduction’ is actually a metallurgic term. Smelters (or blacksmiths, I guess?) could see that refining a one-pound piece of ore would net less than a pound of metal. They didn’t know why, but they could see the drop in quantity, so they referring to it as ‘reducing the ore to its base metal’.

Spoiler alert: that lost mass is oxygen (or hydrogen and oxygen) being chemically ripped apart from metallic oxides/hydroxides in furnaces. But the name stuck. Somewhat confusingly, in my view, as an atom gains electrons when it’s reduced. It loses electrons during oxidation.

A useful trick to help you remember this is the OIL RIG — Oxidation is Loss, Reduction is Gain.

Let’s see it in action

Banded Iron Formation.

Banded Iron formation showing layers of iron ore from the Karijini National Park, Western Australia. As you can see, it’s very oxidized.
Image credits Graeme Churchard / Wikimedia.

Imagine we’re working at a steel mill, and we get a shipment of iron ore (Fe) and coal (C). When we toss them into the furnace, this happens:

2Fe2O3+3C4Fe+3CO2

This iron starts out with an oxidation state of +3 (each atom is donating 3 electrons) and its oxygen starts out with an oxidation state of -2 (each atom is accepting 2 electrons). The carbon in the coal has a neutral electric charge (oxidation state is 0 for all pure elements). Oxygen, however, likes binding to carbon much more than it likes binding to iron. It will give iron back its electrons, and go bind with carbon, taking its electrons instead. This changes iron’s oxidation state from +3 to 0 — since it’s now a pure element so there’s nobody to donate to — and carbon’s from 0 to -4 (as it binds to two oxygen atoms, each taking up 2 electrons).

Oxygen likes binding to carbon more than iron because the former has more electrons to give. It thus holds a more powerful electronegative charge, which means it pulls on oxygen more strongly than iron does. Carbon is the reducing agent here, while oxygen is the oxidizing agent.

Caution to the wise

Another definition of oxidation, one that you may encounter especially in organic chemistry, is the loss of hydrogen. Again, somewhat confusing, but it does make sense. Let’s look at the oxidation of ethanol (the thing we use to get drunk) into ethanal (acetaldehyde) to make this simpler.

CH3CH2OH + [O] → CH3CHO + H2O

Hydrogen is the simplest atom — it’s one proton orbited by an electron. It usually cedes said electron when linking to other chemical species via covalent bonds. To oversimplify things, hydrogen usually helps reduce an element’s need for electrons when tying chemically to it.

In the above example, the addition of oxygen to ethanol takes out two hydrogen atoms to form water; overall, then, the ethanol gains in oxygen (which is oxidation) as it transforms to ethanal. Alternatively, you can see the loss of hydrogen as a loss of the electrons it shared with the rest of the molecule (which, again, is oxidation).

Oxidation and you

Examples of oxidation abound. Iron rusts, alcohol sours into vinegar, the carbon in firewood gets reduced by oxygen as it burns. It keeps your car running by enabling combustion. It makes bronze statues that stately shade of green.

It’s also inside you. Your cells oxidize nutrients to produce energy, water, and CO2. So it keeps your internal combustion going, too. Free radicals in your body damage cells by oxidizing atoms in your molecules (antioxidants help prevent this type of chemical damage). Some oxidizers also see use as disinfectants.

Oxidative processes make the butt of jokes for many a disgruntled student. They cause extensive, expensive damages to our infrastructure, our property, our bodies. Oxidation is likely one of the main drivers of aging, as the same gas which keeps us going slowly rusts our bodies from the inside out.

Oxidation is a simple process, but it takes many forms in various settings — too varied to treat in a single article, much less in one you’d stay awake through. But it directly underpins life as we know it, and likely death as we know it, too. So we shouldn’t take it lightly.

Unexpected deep-Earth oxidized iron surprises geologists

Researchers drilling into the Earth’s mantle have made an unexpected finding: analyzing rocks which came from 550 km below the surface, they discovered highly oxidized iron, similar to the rust we see on our planet’s surface.

Diamonds with garnet inclusions can form at depths down to 550 kilometers below the surface. Image credits: Jeff W. Harris, University of Glasgow.

If there’s something you don’t expect to find kilometers beneath the surface, it’s rust. The oxidized iron was found as inclusions in diamonds and garnets coming from the deep mantle. Of course, researchers didn’t drill 550 km (the deepest borehole “only” went 12 km deep) but reaching the top of the mantle enables geoscientists to analyze rock samples that migrated from deeper parts.

It’s quite a unique opportunity, as geoscientists don’t know that much about how oxidation happens in the deep Earth — actually, they weren’t even sure whether it takes place at those depths in the first place.

“On Earth’s surface, where oxygen is plentiful, iron will oxidize to rust,” explained Thomas Stachel, professor in the Department of Earth and Atmospheric Sciences at the University of Alberta, who co-authored the study. “In the Earth’s deep mantle, we should find iron in its less oxidized form, known as ferrous iron, or in its metal form. But what we found was the exact opposite–the deeper we go, the more oxidized iron we found.”

Most of us are familiar with oxidized iron through a process we commonly see on the surface: rust. Image via Pixabay.

The discovery suggests that some oxidation does happen, even at those ungodly depths. Researchers believe the main culprit is molten carbonate, which was carried in sinking slabs of ancient seafloor. However, it’s hard to explain exactly how oxidation happened there in the first place. It’s counterintuitive and hard to explain why the deeper they went, the more oxidized iron they found. Nevertheless, it raises some intriguing possibilities.

“It’s exciting to find evidence of such profound oxidation taking place deep inside the Earth,” said Stachel, Canada Research Chair in diamonds.

Unfortunately, this study raises more questions than it answers. We know a lot about the carbon cycle on the Earth’s surface, but what happens in the mantle? This study seems to indicate that carbon can go down as far as 550 kilometers below the surface, where it interacts with the rocks and crystallizes as diamonds. But diamonds can migrate even deeper in the mantle. Does this mean, that the carbon cycle too extends this low? The study seems to suggest it, but if this is the case, then where does the oxygen come from, and how is the process different from what happens at the surface? Those are all questions to be answered by future research.

The study “Oxidized iron in garnets from the mantle transition zone,” was published in Nature Geoscience (doi: 10.1038/s41561-017-0055-7).

The ‘orange goo’ in Alaska is actually fungal spores

The orange goo that collected on the shores of Alaska and baffled scientists at first was believed to be a mixture of microscopic eggs and/or embryos deposited by some sort of crustacean. However, researchers at NOAA’s Center for Coastal Environmental Health and Biomolecular Research, based in Charleston, South Carolina conducted another examination and concluded that in fact it is of fungal origin.

The material is consistent with a species that causes a plant disease, “rust”, which infects plants and impregnates them with a rust-like colour.

The spores are unlike others we and our network of specialists have examined; however, many rust fungi of the Arctic tundra have yet to be identified,” Steve Morton, a scientist with the NOAA Charleston lab, said in a statement.

When the material first washed up on the shore, locals were afraid it was pollution, and for good reason – the Red Dog Mine is the biggest zinc producer in the world. However, the material is harmless to humans, even though it can be deadly for plants.

“Rust is a disease that only affects plants, so there’s no cause for alarm,” she said, adding that details about its origins remained a mystery. “There just has not been a lot of research done on rust fungi in the Arctic. This is one that we’ve never encountered before that we know of,” she said.