Materials Science

[Recusant]

An intriguing field, and why not a thread?

A new ceramic which will probably soon be coming to a device near you . . .

"Researchers develop thermoformable ceramics, 'a new frontier in materials'" | Phys.org

It was one of those happy accidents of science. Northeastern professor Randall Erb and Ph.D. student Jason Bice were working on a product for a university client—and wound up with an entirely new class of material.

Their discovery of an all-ceramic that can be compression-molded into complex parts—an industry breakthrough—could transform the design and construction of heat-emitting electronics, including cellphones and other radio components.

"Our research group's lives are very much situated at the bleeding edge of technology," says Erb, an associate professor of mechanical and industrial engineering who heads the DAPS Lab at Northeastern. "Things break a lot, and every once in a while one of those breaks turns out to be good fortune."

Last July, Erb was in his Northeastern lab with Bice, who has since earned a mechanical engineering Ph.D. They were testing an experimental ceramic compound as part of a hypersonic project for an industrial partner when something appeared to go wrong.

"We blasted it with a blowtorch and, while we were loading it, it unexpectedly deformed and fell out of the fixture," Erb says. "We looked at the sample on the floor thinking that it was a failure."

Closer examination gave way to a revelation.

"We realized it was perfectly intact," Erb says. "It was just shaped differently."

[Continues . . .]

[hermes2015]

Thanks for that interesting link. So many important discoveries are the result of happy accidents. First class scientists are open minded and alert, so they notice interesting results in "failed" experiments. The accidental discovery of mauveine by Perkin when he was in his tens is a classic example.

https://www.vox.com/science-and-health/2018/3/12/17109258/sir-william-henry-perkin-google-doodle-birthday-180-mauveine-purple-dye

[Recusant]

This one is cool; a new material composed of bosons.

"Scientists Discover a Weird Material Made of Subatomic Particles" | Science Alert

Scientists are always looking for the next weird and wonderful material, and they've just found it: A bosonic correlated insulator to give it its technical name, which is both a new material and, indeed, a whole new state of matter.

It's a lattice formed from a layer of tungsten diselenide and a layer of tungsten disulfide placed on top of each other but not fully aligned.

That slight misalignment creates what's known as a moiré pattern, and here has revealed some interesting properties.

To understand what's special about the material, you need to understand what bosons and fermions are. At the quantum level, particles are grouped into two main types: bosons (force carriers like photons) that can share the same quantum state, and fermions (matter particles like electrons), which can't. Usually, fermions are easier to work with.

"Conventionally, people have spent most of their efforts to understand what happens when you put many fermions together," says condensed matter physicist Chenhao Jin from the University of California, Santa Barbara (UCSB).

"The main thrust of our work is that we basically made a new material out of interacting bosons."

[Continues . . .]

The paper is behind a paywall.

Abstract:

A panoply of unconventional electronic states has been observed in moiré superlattices. Engineering similar bosonic phases remains, however, largely unexplored.

We report the observation of a bosonic correlated insulator in tungsten diselenide/tungsten disulfide (WSe2/WS2) moiré superlattices composed of excitons, that is, tightly bound electron-hole pairs. We develop a pump probe spectroscopy method that we use to observe an exciton incompressible state at exciton filling νex = 1 and charge neutrality, indicating a correlated insulator of excitons.

With varying charge density, the bosonic correlated insulator continuously transitions into an electron correlated insulator at charge filling νe = 1, suggesting a mixed correlated insulating state between the two limits. Our studies establish semiconducting moiré superlattices as an intriguing platform for engineering bosonic phases.

[Tank]

My mind is officially blown!

[Recusant]

My mind is officially blown!

Yeah, I got a little frisson myself when I read the article. 

[Recusant]

Thanks for that interesting link. So many important discoveries are the result of happy accidents. First class scientists are open minded and alert, so they notice interesting results in "failed" experiments. The accidental discovery of mauveine by Perkin when he was in his tens is a classic example.

https://www.vox.com/science-and-health/2018/3/12/17109258/sir-william-henry-perkin-google-doodle-birthday-180-mauveine-purple-dye

Missed this first time around--thanks in return for your link!  Interesting that our idea of mauve is distinctly different from the color produced by the original dye. I did a bit of further looking and learned that Perkin's original mauve fades fairly quickly, which may have something to do with it. I had always thought the 1890s being the "Mauve Decade" referred to the more subdued tone, but perhaps not. 

[Icarus]

Here is another important development aimed at heat mitigation.

[Recusant]

Here is another important development aimed at heat mitigation.

Ah, hoping you still have  the link for that video, Icarus. Sounds intriguing.

[Tank]

I can't see it either. What was the subject.

[Icarus]

Purdue University engineering school has developed a white paint that can reject a huge proportion of th suns heat. It is different from ordinary white paint which might be capable of rejecting nine percent of the heat. The new paint can reject something on the order of ninety percent.  Something about the way that the particulate matter is distributed and variously sized in the paint.

I will root around on the internet and see if I can find the descriptive article. By now, if this is for real, the report will appear in various scientific journals.

[hermes2015]

Is it this one?

[Icarus]

That is not the one that I tried to post.

This one is detailed beyond need for the casual viewer. I did watch the whole deal and managed to recall some of the chemistry that I had long forgotten.

In any case, the end product may well be important for our survival. Imagine that most of the worlds roofs were coated with this stuff. Air conditioners would not run so much. That would reduce the demand for electricity, thus reduce the carbon output of the generating facilities, affect the world economy and more.

Thanks for the help Hermes.

[Recusant]

I think I read about this a few months ago. Still worthwhile for this thread.

"We Finally Know How Ancient Roman Concrete Was Able to Last Thousands of Years" | Science Alert

The ancient Romans were masters of building and engineering, perhaps most famously represented by the aqueducts. And those still functional marvels rely on a unique construction material: pozzolanic concrete, a spectacularly durable concrete that gave Roman structures their incredible strength.

Even today, one of their structures – the Pantheon, still intact and nearly 2,000 years old – holds the record for the world's largest dome of unreinforced concrete.

The properties of this concrete have generally been attributed to its ingredients: pozzolana, a mix of volcanic ash – named after the Italian city of Pozzuoli, where a significant deposit of it can be found – and lime. When mixed with water, the two materials can react to produce strong concrete.

But that, as it turns out, is not the whole story. In 2023, an international team of researchers led by the Massachusetts Institute of Technology (MIT) found that not only are the materials slightly different from what we may have thought, but the techniques used to mix them were also different.

The smoking guns were small, white chunks of lime that can be found in what seems to be otherwise well-mixed concrete. The presence of these chunks had previously been attributed to poor mixing or materials, but that did not make sense to materials scientist Admir Masic of MIT.

"The idea that the presence of these lime clasts was simply attributed to low quality control always bothered me," Masic said back in January 2023.

"If the Romans put so much effort into making an outstanding construction material, following all of the detailed recipes that had been optimized over the course of many centuries, why would they put so little effort into ensuring the production of a well-mixed final product? There has to be more to this story."

Masic and the team, led by MIT civil engineer Linda Seymour, carefully studied 2,000-year-old samples of Roman concrete from the archaeological site of Privernum in Italy. These samples were subjected to large-area scanning electron microscopy and energy-dispersive x-ray spectroscopy, powder X-ray diffraction, and confocal Raman imaging to gain a better understanding of the lime clasts.

One of the questions in mind was the nature of the lime used. The standard understanding of pozzolanic concrete is that it uses slaked lime. First, limestone is heated at high temperatures to produce a highly reactive caustic powder called quicklime, or calcium oxide.

Mixing quicklime with water produces slaked lime, or calcium hydroxide: a slightly less reactive, less caustic paste. According to theory, it was this slaked lime that ancient Romans mixed with the pozzolana.

Based on the team's analysis, the lime clasts in their samples are not consistent with this method. Rather, Roman concrete was probably made by mixing the quicklime directly with the pozzolana and water at extremely high temperatures, by itself or in addition to slaked lime, a process the team calls "hot mixing" that results in the lime clasts.

"The benefits of hot mixing are twofold," Masic said.

"First, when the overall concrete is heated to high temperatures, it allows chemistries that are not possible if you only used slaked lime, producing high-temperature-associated compounds that would not otherwise form. Second, this increased temperature significantly reduces curing and setting times since all the reactions are accelerated, allowing for much faster construction."

And it has another benefit: The lime clasts give the concrete remarkable self-healing abilities.

When cracks form in the concrete, they preferentially travel to the lime clasts, which have a higher surface area than other particles in the matrix. When water gets into the crack, it reacts with the lime to form a solution rich in calcium that dries and hardens as calcium carbonate, gluing the crack back together and preventing it from spreading further.

[Continues . . .]

The paper is open source:

"Hot mixing: Mechanistic insights into the durability of ancient Roman concrete" | Science Advances

Abstract:

Ancient Roman concretes have survived millennia, but mechanistic insights into their durability remain an enigma. Here, we use a multiscale correlative elemental and chemical mapping approach to investigating relict lime clasts, a ubiquitous and conspicuous mineral component associated with ancient Roman mortars.

Together, these analyses provide new insights into mortar preparation methodologies and provide evidence that the Romans employed hot mixing, using quicklime in conjunction with, or instead of, slaked lime, to create an environment where high surface area aggregate-scale lime clasts are retained within the mortar matrix.

 Inspired by these findings, we propose that these macroscopic inclusions might serve as critical sources of reactive calcium for long-term pore and crack-filling or post-pozzolanic reactivity within the cementitious constructs. The subsequent development and testing of modern lime clast–containing cementitious mixtures demonstrate their self-healing potential, thus paving the way for the development of more durable, resilient, and sustainable concrete formulations.

[Tank]

Wow

[Recusant]

Missed this one the first time around. May be an early inkling of an important development, or maybe not.

"A Cracked Piece of Metal Healed Itself in Experiment That Stunned Scientists" | Science Alert

In a study published last year, a team from Sandia National Laboratories and Texas A&M University was testing the resilience of the metal, using a specialized transmission electron microscope technique to pull the ends of the metal 200 times every second.

They then observed the self-healing at ultra-small scales in a 40-nanometer-thick piece of platinum suspended in a vacuum.

Cracks caused by the kind of strain described above are known as fatigue damage: repeated stress and motion that causes microscopic breaks, eventually causing machines or structures to break.

Amazingly, after about 40 minutes of observation, the crack in the platinum started to fuse back together and mend itself before starting again in a different direction.

[. . .]

While the observation is unprecedented, it's not wholly unexpected. In 2013, Texas A&M University materials scientist Michael Demkowicz worked on a study predicting that this kind of nanocrack healing could happen, driven by the tiny crystalline grains inside metals essentially shifting their boundaries in response to stress.

Demkowicz also worked on this study, using updated computer models to show that his decade-old theories about metal's self-healing behavior at the nanoscale matched what was happening here.

That the automatic mending process happened at room temperature is another promising aspect of the research. Metal usually requires lots of heat to shift its form, but the experiment was carried out in a vacuum; it remains to be seen whether the same process will happen in conventional metals in a typical environment.

A possible explanation involves a process known as cold welding, which occurs under ambient temperatures whenever metal surfaces come close enough together for their respective atoms to tangle together.

Typically, thin layers of air or contaminants interfere with the process; in environments like the vacuum of space, pure metals can be forced close enough together to literally stick.

[Continues . . .]

The paper is behind a paywall.

Abstract:

Fatigue in metals involves gradual failure through incremental propagation of cracks under repetitive mechanical load. In structural applications, fatigue accounts for up to 90% of in-service failure. Prevention of fatigue relies on implementation of large safety factors and inefficient overdesign. In traditional metallurgical design for fatigue resistance, microstructures are developed to either arrest or slow the progression of cracks. Crack growth is assumed to be irreversible. By contrast, in other material classes, there is a compelling alternative based on latent healing mechanisms and damage reversal.

Here, we report that fatigue cracks in pure metals can undergo intrinsic self-healing. We directly observe the early progression of nanoscale fatigue cracks, and as expected, the cracks advance, deflect and arrest at local microstructural barriers. However, unexpectedly, cracks were also observed to heal by a process that can be described as crack flank cold welding induced by a combination of local stress state and grain boundary migration.

The premise that fatigue cracks can autonomously heal in metals through local interaction with microstructural features challenges the most fundamental theories on how engineers design and evaluate fatigue life in structural materials. We discuss the implications for fatigue in a variety of service environments.