This weeks short read: Thermodynamics and Red Mud

[SteamyTea]

Heating and cooling seem to be fundamentally different, not opposites

Conventional thermodynamics says that heating and cooling are essentially mirror images of each other, but an experiment with a tiny silica sphere suggests otherwise

By Alex Wilkins

29 January 2024

 

 

 

Conventional thermodynamics explains why hot tea gets cold – but those laws don’t tell the full story

In Green/Shutterstock

 

Heating something up will always be quicker than cooling it down on a microscopic scale, according to a proposed new principle of thermodynamics. The two processes, long thought of as two sides of the same coin by physicists, seem actually to be fundamentally different.

While most people have an intuitive understanding of what temperature is, physicists have argued over a precise definition for centuries. A school textbook might say it is a measure of how much atoms jiggle around in a system. But thermodynamics, the study of the relationship between heat and other forms of energy, describes temperature as a measure of how many different arrangements of values, such as speed or energy, all the atoms in a system can have. These arrangements are called microstates.

Based on this understanding, conventional thermodynamics says that heating and cooling are essentially mirror images of each other. However, this theory assumes that temperature changes happen either slowly or over small increments.

When systems heat up or cool down over very large intervals, the physics is less well understood – and the outcomes can be counterintuitive. For example, hot water freezes faster than cold water, a phenomenon called the Mpemba effect.

Now, Aljaz Godec at the Max Planck Institute for Multidisciplinary Sciences in Göttingen, Germany, and his colleagues have found that a microscopic sphere of silica that is rapidly heated or cooled by an electric field appears to do so in a lopsided way, heating up faster than it cools.

“This is very surprising,” says Godec. “So far, we know that this is true because we have shown it, but I don’t think we can claim that we understand why this is the case.”

Godec and his team placed the tiny sphere in water and trapped it in place using a laser. They then applied an electric field to heat or cool it and measured how much the particle jiggled and moved. They repeated this process tens of thousands of times.

Measuring a single particle in this way is equivalent to measuring a single microstate. This is impossible to do for a material consisting of many particles because of the vast number of possible configurations they can take. But by making many measurements for a single microscopic particle, the team was able to map out the possible number of microstates it can take.

The researchers then measured how many different microstates the particle would have to go through when transitioning between two temperatures by heating or cooling. They found it had to travel through fewer possible microstates when heating up as opposed to when cooling down, which translated to a faster heating speed.

While it isn’t clear why there should be this fundamental difference, it should be present in any system that heats or cools by a sufficiently large amount, says Godec, though it would usually be difficult to see. This is because such large temperature changes normally induce phenomena in the system itself, such as freezing or boiling, that obscure this newly observed effect. Despite this, the asymmetry could be important for improving the efficiency of microscopic systems such as tiny heat engines or motors, he says.

“It’s really interesting work,” says Janet Anders at the University of Exeter, UK. “It’s really important to think about what this could explain in nature.”The effect that Godec and his team have discovered could almost be considered an extra law of thermodynamics, says Anders. It expands upon the second law of thermodynamics, which says that hot things always cool unless you do something to stop them. “The second law doesn’t say anything about speed; it says something about possibility,” she says. “This second-and-a-half law, as I’m calling it, says you can do all these things, but some of them will take a lot longer than the inverse.”

 

Journal reference:

Nature Physics DOI: 10.1038/s41567-023-02269-z

 

Toxic mud from aluminium production can be used to make greener steel

Producing steel generates huge amounts of CO2 emissions. These could be reduced with a technique that repurposes the hazardous red mud generated when refining aluminium

By Andrew Rosenblum

24 January 2024

 

 

 

Aluminium refinement produces a hazardous red sludge

Ajdin Kamber/Shutterstock

 

The huge reservoirs of hazardous red mud that are produced as part of refining aluminium could be used to make greener steel.

There are roughly 4 billion tonnes of red mud stored around the world, which is an environmental hazard that can lead to deadly accidents. And producing a tonne of steel generates nearly 2 tonnes of CO2 – that is because most steel production involves burning fossil fuels to react carbon with the oxygen in iron ore, yielding iron but also carbon dioxide.

 

Read more

A hydrogen fuel revolution is coming – here's why we might not want it

 

Isnaldi Souza Filho at the Max Planck Institute for Iron Research in Germany and his colleagues have come up with a way to tackle both problems. They have devised a method to extract iron from red mud by exposing it to a plasma of hydrogen and argon, and then using this iron to produce steel.

Key to the process is that red mud contains between 30 and 60 per cent iron oxide by weight, alongside hazardous elements such as arsenic and lead.

The researchers heated up red mud in a device called an electric arc furnace to a temperature of roughly 1850°C (3362°F), with a blend of argon and hydrogen to react with the oxygen. The resulting melt was then cooled, crushed and separated into iron pellets ready to be turned into steel.

Co-author Matic Jovičević-Klug, also at the Max Planck Institute for Iron Research, says that given the amount of red mud there is, the process could produce between 748 million and 942 million tonnes of steel, which would result in over a billion tonnes less of CO2 compared with conventional methods. However, this scale would still only be a fraction of the steel produced globally each year.

Using green hydrogen as part of the refining process is not a new idea, says Mark Jacobson at Stanford University in California. In 2021, a Swedish consortium called HYBRIT demonstrated a trial run that lowered the carbon footprint of steelmaking by up to 98 per cent. What is new is using the hazardous red mud as a feedstock, he says. “Whether it is less expensive than the first process is difficult to tell,” says Jacobson. “The authors claim it is inexpensive, but more information is needed to determine this.”

 

Journal reference:

Nature DOI: 10.1038/s41586-023-06901-z

 

 

Toxic mud from aluminium production can be used to make greener steel

Producing steel generates huge amounts of CO2 emissions. These could be reduced with a technique that repurposes the hazardous red mud generated when refining aluminium

By Andrew Rosenblum

24 January 2024

 

 

 

Aluminium refinement produces a hazardous red sludge

Ajdin Kamber/Shutterstock

 

The huge reservoirs of hazardous red mud that are produced as part of refining aluminium could be used to make greener steel.

There are roughly 4 billion tonnes of red mud stored around the world, which is an environmental hazard that can lead to deadly accidents. And producing a tonne of steel generates nearly 2 tonnes of CO2 – that is because most steel production involves burning fossil fuels to react carbon with the oxygen in iron ore, yielding iron but also carbon dioxide.

 

Isnaldi Souza Filho at the Max Planck Institute for Iron Research in Germany and his colleagues have come up with a way to tackle both problems. They have devised a method to extract iron from red mud by exposing it to a plasma of hydrogen and argon, and then using this iron to produce steel.

Key to the process is that red mud contains between 30 and 60 per cent iron oxide by weight, alongside hazardous elements such as arsenic and lead.

The researchers heated up red mud in a device called an electric arc furnace to a temperature of roughly 1850°C (3362°F), with a blend of argon and hydrogen to react with the oxygen. The resulting melt was then cooled, crushed and separated into iron pellets ready to be turned into steel.

Co-author Matic Jovičević-Klug, also at the Max Planck Institute for Iron Research, says that given the amount of red mud there is, the process could produce between 748 million and 942 million tonnes of steel, which would result in over a billion tonnes less of CO2 compared with conventional methods. However, this scale would still only be a fraction of the steel produced globally each year.

Using green hydrogen as part of the refining process is not a new idea, says Mark Jacobson at Stanford University in California. In 2021, a Swedish consortium called HYBRIT demonstrated a trial run that lowered the carbon footprint of steelmaking by up to 98 per cent. What is new is using the hazardous red mud as a feedstock, he says. “Whether it is less expensive than the first process is difficult to tell,” says Jacobson. “The authors claim it is inexpensive, but more information is needed to determine this.”

 

Journal reference:

Nature DOI: 10.1038/s41586-023-06901-z