#Material Science

[mostlysignssomeportents]

Circular battery self-sufficiency

I'm coming to DEFCON! On FRIDAY (Aug 9), I'm emceeing the EFF POKER TOURNAMENT (noon at the Horseshoe Poker Room), and appearing on the BRICKED AND ABANDONED panel (5PM, LVCC - L1 - HW1–11–01). On SATURDAY (Aug 10), I'm giving a keynote called "DISENSHITTIFY OR DIE! How hackers can seize the means of computation and build a new, good internet that is hardened against our asshole bosses' insatiable horniness for enshittification" (noon, LVCC - L1 - HW1–11–01).

If we are going to survive the climate emergency, we will have to electrify – that is, transition from burning fossil fuels to collecting, storing, transmitting and using renewable energy generated by e.g. the tides, the wind, and (especially) the Sun.

Electrification is a big project, but it's not an insurmountable one. Planning and executing an electric future is like eating the elephant: we do it one step at a time. This is characteristic of big engineering projects, which explains why so many people find it hard to imagine pulling this off.

As a layperson, you are far more likely to be exposed to a work of popular science than you are a work of popular engineering. Pop science is great, but its role is to familiarize you with theory, not practice. Popular engineering is a minuscule and obscure genre, which is a pity, because it's one of my favorites.

Weathering the climate emergency is going to require a lot of politics, to be sure, but it's also going to require a lot of engineering, which is why I'm grateful for the nascent but vital (and growing) field of popular engineering. Not to mention, the practitioners of popular engineering tend to be a lot of fun, like the hosts of the Well That's Your Problem podcast, a superb long-form leftist podcast about engineering disasters (with slides!):

https://www.youtube.com/@welltheresyourproblempodca1465

If you want to get started on popular engineering and the climate, your first stop should be the "Without the Hot Air" series, which tackles sustainable energy, materials, transportation and food as engineering problems. You'll never think about climate the same way again:

https://pluralistic.net/2021/01/06/methane-diet/#3kg-per-day

Then there's Saul Griffith's 2021 book Electrify, which is basically a roadmap for carrying out the electrification of America and the world:

https://pluralistic.net/2021/12/09/practical-visionary/#popular-engineering

Griffith's book is inspiring and visionary, but to really get a sense of how fantastic an electrified world can be, it's gotta be Deb Chachra's How Infrastructure Works:

https://pluralistic.net/2023/10/17/care-work/#charismatic-megaprojects

Chachra is a material scientist who teaches at Olin College, and her book is a hymn to the historical and philosophical underpinnings of infrastructure, but more than anything, it's a popular engineering book about what is possible. For example, if we want to give every person on Earth the energy budget of a Canadian (like an American, but colder), we would only have to capture 0.4% of the solar energy that reaches the Earth's surface.

Now, this is a gigantic task, but it's a tractable one. Resolving it will require a very careful – and massive – marshaling of materials, particularly copper, but also a large number of conflict minerals and rare earths. It's gonna be hard.

But it's not impossible, let alone inconceivable. Indeed, Chachra's biggest contribution in this book is to make a compelling case for reconceiving our relationship to energy and materials. As a species, we have always treated energy as scarce, trying to wring every erg and therm that we can out of our energy sources. Meanwhile, we've treated materials as abundant, digging them up or chopping them down, using them briefly, then tossing them on a midden or burying them in a pit.

Chachra argues that this is precisely backwards. Our planet gets a fresh supply of energy twice a day, with sunrise (solar) and moonrise (tides). On the other hand, we've only got one Earth's worth of materials, supplemented very sporadically when a meteor survives entry into our atmosphere. Mining asteroids, the Moon and other planets is a losing proposition for the long foreseeable future:

https://pluralistic.net/2024/01/09/astrobezzle/#send-robots-instead

The promise of marshaling a very large amount of materials is that it will deliver effectively limitless, clean energy. This project will take a lot of time and its benefits will primarily accrue to people who come after its builders, which is why it is infrastructure. As Chachra says, infrastructure is inherently altruistic, a gift to our neighbors and our descendants. If all you want is a place to stick your own poop, you don't need to build a citywide sanitation system.

What's more, we can trade energy for materials. Manufacturing goods so that they gracefully decompose back into the material stream at the end of their lives is energy intensive. Harvesting materials from badly designed goods is also energy intensive. But if once we build out the renewables grid (which will take a lot of materials), we will have all the energy we need (to preserve and re-use our materials).

Our species' historical approach to materials is not (ahem) carved in stone. It is contingent. It has changed. It can change again. It needs to change, because the way we extract materials today is both unjust and unsustainable.

The horrific nature of material extraction under capitalism – and its geopolitics (e.g. "We will coup whoever we want! Deal with it.") – has many made comrades in the climate fight skeptical (or worse, cynical) about a clean energy transition. They do the back-of-the-envelope math about the material budget for electrification, mentally convert that to the number of wildlife preserves, low-income communities, unspoiled habitat and indigenous lands that we would destroy in the process of gathering those materials, and conclude that the whole thing is a farce.

That analysis is important, but it's incomplete. Yes, marshaling all those materials in the way that we do today would be catastrophic. But the point of a climate transition is that we will transition our approach to our planet, our energy, and our materials. That transition can and should challenge all the assumptions underpinning electrification doomerism.

Take the material bill itself: the assumption that a transition will require a linearly scaled quantity of materials includes the assumption that cleantech won't find substantial efficiencies in its material usage. Thankfully, that's a very bad assumption! Cleantech is just getting started. It's at the stage where we're still uncovering massive improvements to production (unlike fossil fuel technology, whose available efficiencies have been discovered and exploited, so that progress is glacial and negligible).

Take copper: electrification requires a lot of copper. But the amount of copper needed for each part of the cleantech revolution is declining faster than the demand for cleantech is rising. Just one example: between the first and second iteration of the Rivian electric vehicle, designers figured out how to remove 1.6 miles of copper wire from each vehicle:

https://insideevs.com/news/722265/rivian-r1s-r1t-wiring/

That's just one iteration and one technology! And yeah, EVs are only peripheral to a cleantech transition; for one thing, geometry hates cars. We're going to have to build a lot of mass transit, and we're going to be realizing these efficiencies with every generation of train, bus, and tram:

https://pluralistic.net/2024/02/29/geometry-hates-uber/#toronto-the-gullible

We have just lived through a massive surge in electrification, with unimaginable quantities of new renewables coming online and a stunning replacement of conventional vehicles with EVs, and throughout that surge, demand for copper remained flat:

https://www.chemanalyst.com/NewsAndDeals/NewsDetails/copper-wire-price-remains-stable-amidst-surplus-supply-and-expanding-mining-25416#:~:text=Global%20Copper%20wire%20Price%20Remains%20Stable%20Amidst%20Surplus%20Supply%20and%20Expanding%20Mining%20Activities

This isn't to say that cleantech is a solved problem. There are many political aspects to cleantech that remain pernicious, like the fact that so many of the cleantech offerings on the market are built around extractive financial arrangements (like lease-back rooftop solar) and "smart" appliances (like heat pumps and induction tops) that require enshittification-ready apps:

https://pluralistic.net/2024/06/26/unplanned-obsolescence/#better-micetraps

There's a quiet struggle going on between cleantech efficiencies and the finance sector's predation, from lease-back to apps to the carbon-credit scam, but many of those conflicts are cashing out in favor of a sustainable future and it doesn't help our cause to ignore those: we should be cheering them on!

https://pluralistic.net/2024/06/12/s-curve/#anything-that-cant-go-on-forever-eventually-stops

Take "innovation." Silicon Valley's string of pump-and-dump nonsense – cryptocurrency, NFTs, metaverse, web3, and now AI – have made "innovation" into a dirty word. As the AI bubble bursts, the very idea of innovation is turning into a punchline:

https://www.wheresyoured.at/burst-damage/

But cleantech is excitingly, wonderfully innovative. The contrast between the fake innovation of Silicon Valley and the real – and vital – innovation of cleantech couldn't be starker, or more inspiring:

https://pluralistic.net/2024/05/30/posiwid/#social-cost-of-carbon

Like the "battery problem." Whenever the renewables future is raised, there's always a doomer insisting that batteries are an unsolved – and unsolvable – problem, and without massive batteries, there's no sense in trying, because the public won't accept brownouts when the sun goes down and the wind stops blowing.

Sometimes, these people are shilling boondoggles like nuclear power (reminder: this is Hiroshima Day):

https://theconversation.com/dutton-wants-australia-to-join-the-nuclear-renaissance-but-this-dream-has-failed-before-209584

Other times, they're just trying to foreclose on the conversation about a renewables transition altogether. But sometimes, these doubts are raised by comrades who really do want a transition and have serious questions about power storage.

If you're one of those people, I have some very good news: battery tech is taking off. Some of that takes the form of wild and cool new approaches. In Finland, a Scottish company is converting a disused copper mine into a gravity battery. During the day, excess renewables hoist a platform piled with tons of rock up a 530m shaft. At night, the platform lowers slowly, driving a turbine and releasing its potential energy. This is incredibly efficient, has a tiny (and sustainable) bill of materials, and it's highly replicable. The world has sufficient abandoned mine-shafts to store 70TWh of power – that's the daily energy budget for the entire planet. What's more, every mine shaft has a beefy connection to the power grid, because you can't run a mine without a lot of power:

https://www.euronews.com/green/2024/02/06/this-disused-mine-in-finland-is-being-turned-into-a-gravity-battery-to-store-renewable-ene

Gravity batteries are great for utility-scale storage, but we also need a lot of batteries for things that we can't keep plugged into the wall, like vehicles, personal electronics, etc. There's great news on that score, too! "The Battery Mineral Loop" is a new report from the Rocky Mountain Institute that describes the path to "circular battery self-sufficiency":

https://rmi.org/wp-content/uploads/dlm_uploads/2024/07/the_battery_mineral_loop_report_July.pdf

The big idea: rather than digging up new minerals to make batteries, we can recycle minerals from dead batteries to make new ones. Remember, energy can be traded for materials: we can expend more energy on designs that are optimized to decompose back into their component materials, or we can expend more energy extracting materials from designs that aren't optimized for recycling.

Both things are already happening. From the executive summary:

The chemistry of batteries is rapidly improving: over the past decade, we've reduced per-using demand for lithium, nickle and cobalt by 60-140%, and most lithium batteries are being recycled, not landfilled.

Within a decade, we'll hit peak mineral demand for batteries. By the mid-2030s, the amount of new "virgin minerals" needed to meet our battery demand will stop growing and start declining.

By 2050, we could attain net zero mineral demand for batteries: that is, we could meet all our energy storage needs without digging up any more minerals.

We are on a path to a "one-off" extraction effort. We can already build batteries that work for 10-15 years and whose materials can be recycled with 90-94% efficiency.

The total quantity of minerals we need to extract to permanently satisfy the world's energy storage needs is about 125m tons.

This last point is the one that caught my eye. Extracting 125m tons of anything is a tall order, and depending on how it's done, it could wreak a terrible toll on people and the places they live.

But one question I learned to ask from Tim Harford and BBC More Or Less is "is that a big number?" 125m tons sure feels like a large number, but it is one seventeenth of the amount of fossil fuels we dig up every year just for road transport. In other words, we're talking about spending the next thirty years carefully, sustainably, humanely extracting about 5.8% of the materials we currently pump and dig every year for our cars. Do that, and we satisfy our battery needs more-or-less forever.

This is a big engineering project. We've done those before. Crisscrossing the world with roads, supplying billions of fossil-fuel vehicles, building the infrastructure for refueling them, pumping billions of gallons of oil – all of that was done in living memory. As Robin Sloan wrote:

Did people say, at the dawn of the automobile: are you kidding me? This technology will require a ubiquitous network of refueling stations, one or two at every major intersection … even if there WAS that much gas in the world, how would you move it around at that scale? If everybody buys a car, you’ll need to build highways, HUGE ones — you’ll need to dig up cities! Madness!

https://www.robinsloan.com/newsletters/room-for-everybody/

That big project cost trillions and required bending the productive capacity of many nations to its completion. It produced a ghastly geopolitics that elevated petrostates – a hole in the ground, surrounded by guns – to kingmakers whose autocrats can knock the world on its ass at will.

By contrast, this giant engineering project is relatively modest, and it will upend that global order, yielding energy sovereignty (and its handmaiden, national resliency) to every country on Earth. Doing it well will be hard, and require that we rethink our relationship to energy and materials, but that's a bonus, not a cost. Changing how we use materials and energy will make all our lives better, it will improve the lives of the living things we share the planet with, and it will strip the monsters who currently control our energy supply of their political, economic, and electric power.

If you'd like an essay-formatted version of this post to read or share, here's a link to it on pluralistic.net, my surveillance-free, ad-free, tracker-free blog:

https://pluralistic.net/2024/08/06/with-great-power/#comes-great-responsibility

[abiwaif]

One more final to go (tomorrow) and I will have completed all my ungrad work. I should have my grades by Friday, but I am not expecting anything but straight A's. I will get to graduate with high honors. Not bad for a smol, cult-raised girl who was told she would fail in college. (I have been liberated from the cult once I turned 18).

Many have asked so I will state it here. I have a consulting job lined up for the Summer (along with the intention to have some fun) and in the Fall I start my PhD track in Physics/Material Science researching new, stronger, lighter aluminum alloys (primarily for space exploration, but who knows).

[andmaybegayer]

I usually tell the attendees at one of my metal forming conferences, that in order to form aluminum, you must think like aluminum. Aluminum reacts completely differently from steel in a drawing or forming operation. This certainly doesn't mean that aluminum is bad -- it just means that it is different.

obsessed with the tone of this introductory paragraph

[bouquetofgemstones]

4.2.2025: We had a gloriously sunny winter morning today. The majority of the day was spent editing the article. And by editing, I mean I didn't write a single sentence. The main part I need to rewrite is the first paragraph of the introduction, which is also the part I find the hardest. I just don't understand how to start articles. But that's okay, I've now highlighted all of the parts that will need to be reworded and I think I also managed to figure out what I want the first paragraph to be about. I now just need to put that into words.

Listened to: Debussy, Satie, Tchaikovsky

[bakingmakingmachine]

An SEM image of a guitar string held down with carbon tape to a sample mount.

[fuckterfs-deactivated20221212]

so I've been told that titanium is more durable than steel but also sucks at holding an edge because it's not as hard, but then why are pairs of scissors titanium coated? and why do the vendors of titanium coated scissors say the titanium edge lasts longer than if it was steel? is it all a sham? are they lying so they can sell more scissors? or is the edge retention problem not a thing in scissors because scissors work differently to knives? material scientists and or blacksmiths and or engineers of tumblr please explain

[blatentmisinformation]

Due to concerns over children consuming pieces of drywall containing potentially toxic products, all modern drywall recipes are non toxic and in theory edible.

[noosphe-re]

[tropylium]

[wayti-blog]

"Scientists are a step closer to unraveling the mysterious forces of the universe after working out how to measure gravity on a microscopic level."

"(...) now physicists at the University of Southampton, working with scientists in Europe, have successfully detected a weak gravitational pull on a tiny particle using a new technique.

They claim it could pave the way to finding the elusive quantum gravity theory.

The experiment, published in Science Advances, used levitating magnets to detect gravity on microscopic particles—small enough to border on the quantum realm.

Lead author Tim Fuchs, from the University of Southampton, said the results could help experts find the missing puzzle piece in our picture of reality.

He added, "For a century, scientists have tried and failed to understand how gravity and quantum mechanics work together. Now we have successfully measured gravitational signals at a smallest mass ever recorded, it means we are one step closer to finally realizing how it works in tandem.

"From here we will start scaling the source down using this technique until we reach the quantum world on both sides. By understanding quantum gravity, we could solve some of the mysteries of our universe—like how it began, what happens inside black holes, or uniting all forces into one big theory.""

continue reading article

[mostlysignssomeportents]

Deb Chachra's "How Infrastructure Works": Mutual aid, the built environment, the climate, and a future of comfort and abundance

This Thursday (Oct 19), I'm in Charleston, WV to give the 41st annual McCreight Lecture in the Humanities. And on Friday (Oct 20), I'm at Charleston's Taylor Books from 12h-14h.

Engineering professor and materials scientist Deb Chachra's new book How Infrastructure Works is a hopeful, lyrical – even beautiful – hymn to the systems of mutual aid we embed in our material world, from sewers to roads to the power grid. It's a book that will make you see the world in a different way – forever:

https://www.penguinrandomhouse.com/books/612711/how-infrastructure-works-by-deb-chachra/

Chachra structures the book as a kind of travelogue, in which she visits power plants, sewers, water treatment plants and other "charismatic megaprojects," connecting these to science, history, and her own memoir. In so doing, she doesn't merely surface the normally invisible stuff that sustains us all, but also surfaces its normally invisible meaning.

Infrastructure isn't merely a way to deliver life's necessities – mobility, energy, sanitation, water, and so on – it's a shared way of delivering those necessities. It's not just that economies of scale and network effects don't merely make it more efficient and cheaper to provide these necessities to whole populations. It's also that the lack of these network and scale effects make it unimaginable that these necessities could be provided to all of us without being part of a collective, public project.

Think of the automobile versus public transit: if you want to live in a big, built up city, you need public transit. Once a city gets big enough, putting everyone who needs to go everywhere in a car becomes a Red Queen's Race. With that many cars on the road, you need more roads. More roads push everything farther apart. Once everything is farther apart, you need more cars.

Geometry hates cars. You can't bargain with geometry. You can't tunnel your way out of this. You can't solve it with VTOL sky-taxis. You can't fix it with self-driving cars whose car-to-car comms let them shave down their following distances. You need buses, subways and trams. You need transit. There's a reason that every plan to "disrupt" transportation ends up reinventing the bus:

https://stanforddaily.com/2018/04/09/when-silicon-valley-accidentally-reinvents-the-city-bus/

Even the cities we think of as motorists' paradises – such as LA – have vast, extensive transit systems. They suck – because they are designed for poor people – but without them, the city would go from traffic-blighted to traffic-destroyed.

The dream of declaring independence from society, of going "off-grid," of rejecting any system of mutual obligation and reliance isn't merely an infantile fantasy – it also doesn't scale, which is ironic, given how scale-obsessed its foremost proponents are in their other passions. Replicating sanitation, water, rubbish disposal, etc to create individual systems is wildly inefficient. Creating per-person communications systems makes no sense – by definition, communications involves at least two people.

So infrastructure, Chachra reminds us, is a form of mutual aid. It's a gift we give to ourselves, to each other, and to the people who come after us. Any rugged individualism is but a thin raft, floating on an ocean of mutual obligation, mutual aid, care and maintenance.

Infrastructure is vital and difficult. Its amortization schedule is so long that in most cases, it won't pay for itself until long after the politicians who shepherded it into being are out of office (or dead). Its duty cycle is so long that it can be easy to forget it even exists – especially since the only time most of us notice infrastructure is when it stops working.

This makes infrastructure precarious even at the best of times – hard to commit to, easy to neglect. But throw in the climate emergency and it all gets pretty gnarly. Whatever operating parameters we've designed into our infra, whatever maintenance regimes we've committed to for it, it's totally inadequate. We're living through a period where abnormal is normal, where hundred year storms come every six months, where the heat and cold and wet and dry are all off the charts.

It's not just that the climate emergency is straining our existing infrastructure – Chachra makes the obvious and important point that any answer to the climate emergency means building a lot of new infrastructure. We're going to need new systems for power, transportation, telecoms, water delivery, sanitation, health delivery, and emergency response. Lots of emergency response.

Chachra points out here that the history of big, transformative infra projects is…complicated. Yes, Bazalgette's London sewers were a breathtaking achievement (though they could have done a better job separating sewage from storm runoff), but the money to build them, and all the other megaprojects of Victorian England, came from looting India. Chachra's family is from India, though she was raised in my hometown of Toronto, and spent a lot of her childhood traveling to see family in Bhopal, and she has a keen appreciation of the way that those old timey Victorian engineers externalized their costs on brown people half a world away.

But if we can figure out how to deliver climate-ready infra, the possibilities are wild – and beautiful. Take energy: we've all heard that Americans use far more energy than most of their foreign cousins (Canadians and Norwegians are even more energy-hungry, thanks to their heating bills).

The idea of providing every person on Earth with the energy abundance of an average Canadian is a horrifying prospect – provided that your energy generation is coupled to your carbon emissions. But there are lots of renewable sources of energy. For every single person on Earth to enjoy the same energy diet as a Canadian, we would have to capture a whopping four tenths of a percent of the solar radiation that reaches the Earth. Four tenths of a percent!

Of course, making solar – and wind, tidal, and geothermal – work will require a lot of stuff. We'll need panels and windmills and turbines to catch the energy, batteries to store it, and wires to transmit it. The material bill for all of this is astounding, and if all that material is to come out of the ground, it'll mean despoiling the environments and destroying the lives of the people who live near those extraction sites. Those are, of course and inevitably, poor and/or brown people.

But all those materials? They're also infra problems. We've spent millennia treating energy as scarce, despite the fact that fresh supplies of it arrive on Earth with every sunrise and every moonrise. Moreover, we've spent that same period treating materials as infinite despite the fact that we've got precisely one Earth's worth of stuff, and fresh supplies arrive sporadically, unpredictably, and in tiny quantities that usually burn up before they reach the ground.

Chachra proposes that we could – we must – treat material as scarce, and that one way to do this is to recognize that energy is not. We can trade energy for material, opting for more energy intensive manufacturing processes that make materials easier to recover when the good reaches its end of life. We can also opt for energy intensive material recovery processes. If we put our focus on designing objects that decompose gracefully back into the material stream, we can build the energy infrastructure to make energy truly abundant and truly clean.

This is a bold engineering vision, one that fuses Chachra's material science background, her work as an engineering educator, her activism as an anti-colonialist and feminist. The way she lays it out is just…breathtaking. Here, read an essay of hers that prefigures this book:

https://tinyletter.com/metafoundry/letters/metafoundry-75-resilience-abundance-decentralization

How Infrastructure Works is a worthy addition to the popular engineering books that have grappled with the climate emergency. The granddaddy of these is the late David MacKay's open access, brilliant, essential, Sustainable Energy Without the Hot Air, a book that will forever change the way you think about energy:

https://memex.craphound.com/2009/04/08/sustainable-energy-without-the-hot-air-the-freakonomics-of-conservation-climate-and-energy/

The whole "Without the Hot Air" series is totally radical, brilliant, and beautiful. Start with the Sustainable Materials companion volume to understand why everything can be explained by studying, thinking about and changing the way we use concrete and aluminum:

https://memex.craphound.com/2011/11/17/sustainable-materials-indispensable-impartial-popular-engineering-book-on-the-future-of-our-built-and-made-world/

And then get much closer to home – your kitchen, to be precise – with the Food and Climate Change volume:

https://pluralistic.net/2021/01/06/methane-diet/#3kg-per-day

Reading Chachra's book, I kept thinking about Saul Griffith's amazing Electrify, a shovel-ready book about how we can effect the transition to a fully electrified America:

https://pluralistic.net/2021/12/09/practical-visionary/#popular-engineering

Chachra's How Infrastructure Works makes a great companion volume to Electrify, a kind of inspirational march to play accompaniment on Griffith's nuts-and-bolts journey. It's a lyrical, visionary book, charting a bold course through the climate emergency, to a world of care, maintenance, comfort and abundance.

If you'd like an essay-formatted version of this post to read or share, here's a link to it on pluralistic.net, my surveillance-free, ad-free, tracker-free blog:

https://pluralistic.net/2023/10/17/care-work/#charismatic-megaprojects

My next novel is The Lost Cause, a hopeful novel of the climate emergency. Amazon won't sell the audiobook, so I made my own and I'm pre-selling it on Kickstarter!

[abiwaif]

Senior Year about to Begin

Since many of you have been asking, here is my class schedule that begins Monday, August 26. Yes, I will be quite busy but I thrive in such an atmosphere. In addition to my classes, I will also be a TA for one of my professors, so there is that too!

Statistical Learning I

Computational Physics

Partial Differential Equations I

Soft Matter and Biological Physics

Mechanics

[andmaybegayer]

For a different project I was reading about developments in induction heating technologies and realized I had a small misunderstanding about how induction stoves work.

So, the classic misunderstanding is in why steel works on an induction hob but aluminium doesn't. Most people assume this is because you need a magnetic material in order to induce a current, but if you know your physics you know this isn't true. You can induce a current in any conductor, and indeed inducing currents in aluminium is something that happens in industry all the time.

So then you get to my understanding of why you can't use aluminium and copper, which is that they're too good at conducting electricity. Induction generates a voltage that pushes a current through the material. Aluminium and copper are much better conductors than steel, so the generated potential is lower and the overall current is lower as a result of material interactions with the field, so you don't get nearly as much heat out of induction on aluminium as on steel. This was what I thought. This is also wrong, although it's closer.

The actual answer is one step deeper. Induction hobs have to operate at pretty high frequencies, usually 24-ish kHz, both for audible noise reasons and, crucially, because they rely heavily on the skin effect. Interestingly this makes that first wrong explanation kind of more correct, I'll get to that in a moment.

The skin effect is a thing that happens when you have an alternating current in a bulk material; the AC signal sets up magnetic fields that force current to flow in a thin layer closer to the surface of the solid rather than flowing evenly throughout the material. This increases the effective resistance of the material, since you end up with a reduced effective surface area through which current can flow. The skin effect gets more pronounced at higher frequencies, and it's part of why you'll see bundles of smaller cables used to conduct high power AC: each cable has its own skin that can carry more current than the same quantity of material in one bulk cable.

In the right kinds of steel and iron, 24kHz is enough to generate a current carrying skin only a few tenths of a millimeter thick, which has a high enough resistance to generate the heat needed for cooking. Ferromagnetic materials have very high magnetic permeability, which causes them to experience much stronger skin effects. Copper and aluminium, between their high conductivity and lower magnetic permeability, have much weaker skin effects, their skins at 24kHz are much thicker, and so you just can't kick up enough resistance to the current to generate heat, it just spins around in there getting kind of warm but you'd have a hard time actually cooking with it. Indeed, non-magnetic stainless steel also won't work on induction hobs, because it also has a much thicker skin effect.

So you have the "real answer" being a fun hybrid of the two incorrect explanations.

The main side effects I take away from this are twofold.

1) you can absolutely make an induction hob that will heat copper and aluminum and non-magnetic stainless steels, you just need a high enough frequency to generate a strong enough skin effect to generate heat. Panasonic makes one that uses 60+kHz induction under the brand "Met-all".

2) if you physically constrain the current by having a really thin piece of metal, you can induction heat it anyway. When I read this, I stopped, took out a piece of aluminium foil, and stuck it on my induction cooktop. It almost immediately got incredibly hot and I pulled it away before anything bad happened. Turns out you could definitely melt and maybe even vaporize aluminium this way. So don't do that. Apparently people do this with lightweight titanium cookware too, which would not be able to sustain the necessary currents in a large bulk solid but can if you thin the base of the pan out enough.

[bouquetofgemstones]

16.5.2025: Today I read the second, shorter article for the learning diary and it was so much clearer! I have over a page of notes on it now, I can totally write two pages on this. So I basically just wasted a whole day yesterday reading a thing I won't even use.

This morning I watched a panel on academic careers, and it was pretty interesting. It was also really validating, bc most of them said that they'd just sort of ended up becoming professors as a result of taking whatever career opportunities felt interesting in the moment. And like all of my big life decisions were made fully based on vibes and I don't really have plans for my career, so it feels nice to know that that's how it's supposed to be.

Listened to: lofi

[bakingmakingmachine]

Using optical emission spectroscopy to find out what makes up our samples!