A Transistor, But For Heat Instead Of Electrons

December 20, 2023 by Donald Papp 31 Comments

Researchers at UCLA recently developed what they are calling a thermal transistor: a solid-state device able to control the flow of heat with an electric field. This opens the door to controlling the transfer of heat in some of the same ways we are used to controlling electronics.

Heat management can be a crucial task, especially where electronics are involved. The usual way to manage heat is to draw it out with things like heat sinks. If heat isn’t radiating away fast enough, a fan can be turned on (or sped up) to meet targets. Compared to the precision and control with which modern semiconductors shuttle electrons about, the ability to actively manage heat seems lacking.

This new device can rapidly adjust thermal conductivity of a channel based on an electrical field input, which is very similar to what a transistor does for electrical conductivity. Applying an electrical field modifies the strength of molecular bonds in a cage-like array of molecules, which in turn adjusts their thermal conductivity.

It’s still early, but this research may open the door to better control of heat within semiconductor systems. This is especially interesting considering that 3D chips have been picking up speed for years (stacking components is already a thing, it’s called Package-on-Package assembly) and the denser and deeper semiconductors get, the harder it is to passively pull heat out.

Thanks to [Jacob] for the tip!

Tech In Plain Sight: Super Glue

December 11, 2023 by Richard Baguley 68 Comments

Many inventions happen not by design but through failure. They don’t happen through the failure directly, but because someone was paying attention and remembered the how and why of the failure, and learns from this. One of these inventions is Super Glue, the adhesive that every tinkerer and engineer has to hand to stick pretty much anything to anything, quickly. Although it was a complete failure for the original uses it was developed for, a chemist with good memory and an eye for a helpful product created it in a process he described as “one day of synchronicity and ten years of hard work.”

Super Glue was initially invented in 1942, when the chemist Harry Coover was working on a team trying to develop a clear plastic gun sight that would be cheaper than the metal ones already in use. The team cast a wide net, trying a range of new materials. Coover was testing a class of chemicals called cyanoacrylates. They had some promise, but they had one problem: they stuck to pretty much everything. Every time that Coover tried to use the material to cast a gun sight, it stuck to the container and was really hard to remove.

When the samples he tried came into contact with water, even water vapor in the air, they immediately formed an incredibly resilient bond with most materials. That made them lousy manufacturing materials, so he put the cyanoacrylates aside when the contract was canceled. His employer B. F. Goodrich, patented the process of making cyanoacrylates in 1947, but didn’t note any particular uses for the materials: they were simply a curiosity.

It wasn’t until 1951 when Coover, now at Eastman Kodak, remembered the sticky properties of cyanoacrylates. He and his colleague Fred Joyner were working on making heat-resistant canopies for the new generation of jet fighters, and they considered using these sticky chemicals as adhesives in the manufacturing process. According to Coover, he told Joyner about the materials and asked him to measure the refractive index to see if they might be suitable for use. He warned him to be careful, as the material would probably stick in the refractometer and damage it. Joyner tested the material and found it wasn’t suitable for a canopy but then went around the lab using it to stick things together. The two realized it could make an excellent adhesive for home and engineering use. Continue reading “Tech In Plain Sight: Super Glue” →

Dry Ice From Seashells, The Hard (But Cheap) Way

December 6, 2023 by Dan Maloney 11 Comments

[Hyperspace Pirate] wants to make his own dry ice, but he wants it to be really, really cheap. So naturally, his first stop is… the beach?

That’s right, the beach, because that’s where to find the buckets of free seashells that he turned into dry ice. Readers may recall previous efforts at DIY dry ice, which used baking soda and vinegar as a feedstock. We’d have thought those were pretty cheap materials for making carbon dioxide gas, but not cheap enough for [Hyperspace Pirate], as the dry ice he succeeded in making from them came out to almost ten bucks a pound. The low yield of the process probably had more to do with the high unit cost, in truth, so cheaper feedstocks and improved yield would attack the problem from both ends.

With a supply of zero-cost calcium carbonate from the beach and a homemade ZVS-powered induction heater tube furnace at the ready, [Hyperspace Pirate] was ready to make quicklime and capture the CO₂ liberated in the process. That proved to be a little more difficult than planned since the reaction needed not just heat but a partial vacuum to drive the CO₂ off. An oil-free vacuum pump helped, yielding a little CO₂, but eventually he knuckled under and just doused the shells in vinegar. This had the fun side effect of creating calcium acetate, which when distilled not only corrodes the copper still plumbing but also makes a lousy but still flammable grade of acetone. Once enough CO₂ was stored in a couple of beach balls, the process of cooling and condensing it into dry ice was pretty much the same as the previous method, except for taking advantage of the Joule-Thomson cryocooler he built a while back.

The result is a hundred or so grams of dry ice snow, which isn’t great but still shows promise. [Hyperspace Pirate] feels like the key to improving this process is more heat to really drive the calcination reaction. Might we suggest a DIY tube furnace for that job?

Continue reading “Dry Ice From Seashells, The Hard (But Cheap) Way” →

Simple Chemistry To Metallize And Etch Silicon Chips

December 3, 2023 by Dan Maloney 5 Comments

We’ve been eagerly following [ProjectsInFlight]’s stepwise journey toward DIY semiconductors, including all the ups and downs, false leads, and tedious optimizations needed to make it possible for the average hacker to make chips with readily available tools and materials.

Next up is metallization, and spoiler alert: it wasn’t easy. In a real fab, metal layers are added to chips using some form of deposition or sputtering method, each of which needs some expensive vacuum equipment. [ProjectsInFlight] wanted a more approachable way to lay down thin films of metal, so he turned to an old friend: the silver mirror reaction. You may have seen this demonstrated in high school chemistry; a preparation of Tollen’s reagent, a mix of sodium hydroxide, ammonia, and silver nitrate, is mixed with glucose in a glass vessel. The glucose reduces the reagent, leaving the metallic silver to precipitate on the inside of the glass, which creates a beautiful silvered effect.

Despite some issues, the silvering method worked well enough on chips to proceed on, albeit carefully, since the layer is easily scratched off. [ProjectsInFlight]’s next step was to find an etchant for silver, a tall order for a noble metal. He explored piranha solutions, which are acids spiked with peroxide, and eventually settled on plain old white vinegar with a dash of 12% peroxide. Despite that success, the silver layer was having trouble sticking to the chip, much preferring to stay with the photoresist when the protective film was removed.

The solution was to replace the photoresist’s protective film with Teflon thread-sealing tape. That allowed the whole process from plating to etching to work, resulting in conductive traces with pretty fine resolution. Sure they’re a bit delicate, but that’s something to address another day. He’s come a long way from his DIY tube furnace used to put down oxide layers, and suffering through the search for oxide etchants and exploring photolithography methods. It’s been a fun ride so far, and we’re eager to see what’s next.

Continue reading “Simple Chemistry To Metallize And Etch Silicon Chips” →

The Slow March Of Sodium-Ion Batteries To Compete With Lithium-Ion

November 26, 2023 by Maya Posch 56 Comments

The process of creating new battery chemistries that work better than existing types is a slow and arduous one. Not only does it know more failures than successes, it’s rare that a once successful type gets completely phased out, which is why today we’re using lead-acid, NiMH, alkaline, lithium, zinc-air, lithium-ion and a host of other battery types alongside each other. For one of the up-and-coming types in the form of sodium (Na)-based batteries the same struggles are true as it attempts to hit the right balance between anode, cathode and electrolyte properties. A pragmatic solution here involves Prussian Blue for the cathode and hard carbon for the anode, as is the case with Swedish Northvolt’s newly announced sodium-ion battery (SIB) which is sampling next year.

Commercialization of different SIB battery chemistries by various companies. (Credit: Yadav et al. 2022) — Commercialization of different SIB battery chemistries by various companies. (Credit: Yadav et al., 2022)

The story of SIBs goes back well over a decade, with a recent review article by Poonam Yadav and colleagues in Oxford Open Materials Science providing a good overview of the many types of anodes, cathodes and electrolytes which have been attempted and the results. One of the issues that prevents an SIB from directly using the carbon-based anodes employed with today’s lithium-ion batteries (LIB) is its much larger ionic radius that prevents intercalation without altering the carbon material to accept Na+ ions.

This is essentially where the hard carbon (HC) anode used by a number of SIB-producing companies comes into play, which has a far looser structure that does accept these ions and thus can be used with SIBs. The remaining challenges lie then with the electrolyte – which is where an organic form is the most successful – and the material for the sodium-containing cathode.

Although oxide forms and even sodium vanadium fluorophosphate (NVPF) are also being used, Prussian Blue analogs (PBAs) are attractive for being very low-cost and effective as cathode material once processed. An efficient way to process PB into fully sodiated and reduced Prussian White was demonstrated a few years ago, followed by successive studies backing up this assessment.

Although SIBs are seeing limited commercial use at this point, signs are that if it can be commercialized for the consumer market, it would have similar capacity as current LIBs, albeit with the potential to be cheaper, more durable and easier to recycle.

Radioactive Water Was Once A (Horrifying) Health Fad

November 10, 2023 by Donald Papp 24 Comments

Take a little time to watch the history of Radithor, a presentation by [Adam Blumenberg] into a quack medicine that was exactly what it said on the label: distilled water containing around 2 micrograms of radium in each bottle (yes, that’s a lot.) It’s fascinatingly well-researched, and goes into the technology and societal environment surrounding such a product, which helped play a starring role in the eventual Food, Drug, and Cosmetic Act of 1938. You can watch the whole presentation in the video, embedded below the break. Continue reading “Radioactive Water Was Once A (Horrifying) Health Fad” →

William Blake Was Etching Copper In 1790

October 30, 2023 by Kristina Panos 11 Comments

You may know William Blake as a poet, or even as #38 in the BBC’s 2002 poll of the 100 Greatest Britons. But did you know that Blake was also an artist and print maker who made illuminated (flourished) books?

Blake sought to marry his art with his poetry and unleash it on the world. To do so, he created an innovative printing process, which is recreated by [Michael Phillips] in the video after the break. Much like etching a PCB, Blake started with a copper sheet, writing and drawing his works backwards with stopping varnish, an acid-resistant varnish that sticks around after a nitric acid bath. The result was a raised design that could then be used for printing.

Cleaning up the ink smudges before printing.

Blake was a master of color, using few pigments plus linseed or nut oil to create pastes of many different hues. Rather than use a brayer, Blake dabbed ink gently around the plate, careful not to splash ink or get any in the etched-away areas. As this was bound to happen anyway, Blake would then spend more time wiping out the etched areas than he did applying the ink.

Another of Blake’s innovations was the printing process itself. Whereas traditionally, illuminated texts must be printed in two different workshops, one for the text and the other for the illustrations, Blake’s method of etching both in the same plate of copper made it possible to print using his giant handmade press.

Want to avoid censorship and print your own ‘zines? Why not build a proofing press?.

Continue reading “William Blake Was Etching Copper In 1790” →