Making Liquid Oxygen: Far From Easy But Worth The Effort

April 9, 2025 by Dan Maloney 26 Comments

Normally, videos over at The Signal Path channel on YouTube have a certain vibe, namely teardowns and deep dives into high-end test equipment for the microwave realm. And while we always love to see that kind of content, this hop into the world of cryogenics and liquid oxygen production shows that [Shahriar] has other interests, too.

Of course, to make liquid oxygen, one must first have oxygen. While it would be easy enough to get a tank of the stuff from a gas supplier, where’s the fun in that? So [Shahriar] started his quest with a cheap-ish off-the-shelf oxygen concentrator, one that uses the pressure-swing adsorption cycle we saw used to great effect with DIY O₂ concentrators in the early days of the pandemic. Although analysis of the machine’s output revealed it wasn’t quite as capable as advertised, it still put out enough reasonably pure oxygen for the job at hand.

The next step in making liquid oxygen is cooling it, and for that job [Shahriar] turned to the cryocooler from a superconducting RF filter, a toy we’re keen to see more about in the future. For now, he was able to harvest the Stirling-cycle cryocooler and rig it up in a test stand with ample forced-air cooling for the heat rejection end and a manifold to supply a constant flow of oxygen from the concentrator. Strategically placed diodes were used to monitor the temperature at the cold end, a technique we can’t recall seeing before. Once powered up, the cryocooler got down to the 77 Kelvin range quite quickly, and within an hour, [Shahriar] had at least a hundred milliliters of lovely pale blue fluid that passed all the usual tests.

While we’ve seen a few attempts to make liquid nitrogen before, this might be the first time we’ve seen anyone make liquid oxygen. Hats off to [Shahriar] for the effort.

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Make DIY Conductive, Biodegradable String Right In Your Kitchen

March 28, 2025 by Donald Papp 3 Comments

[ombates] shares a step-by-step method for making a conductive bio-string from scratch, no fancy equipment required. She demonstrates using it to create a decorative top with touch-sensitive parts, controlling animations on an RGB LED pendant. To top it off, it’s even biodegradable!

The string is an alginate-based bioplastic that can be made at home and is shaped in a way that it can be woven or knitted. Alginate comes primarily from seaweed, and it gels in the presence of calcium ions. [ombates] relies on this to make a goopy mixture that, once extruded into a calcium chloride bath, forms a thin rubbery length that can be dried into the strings you see here. By adding carbon to the mixture, the resulting string is darkened in color and also conductive.

There’s no details on what the actual resistance of a segment of this string can be expected to measure, but while it might not be suitable to use as wiring it is certainly conductive enough to act as a touch sensor in a manner similar to the banana synthesizer. It would similarly be compatible with a Makey Makey (the original and incredibly popular hardware board for turning household objects into touch sensors.)

What you see here is [ombates]’ wearable demonstration, using the white (non-conductive) string interwoven with dark (conductive) portions connected to an Adafruit Circuit Playground board mounted as an LED pendant, with the conductive parts used as touch sensors.

Alginate is sometimes used to make dental molds and while alginate molds lose their dimensional accuracy as they dry out, for this string that’s not really a concern. If you give it a try, visit our tip line to let us know how it turned out!

Benchtop Haber-Bosch Makes Ammonia At Home

March 21, 2025 by Dan Maloney 23 Comments

Humans weren’t the first organisms on this planet to figure out how to turn the abundance of nitrogen in the atmosphere into a chemically useful form; that honor goes to some microbes that learned how to make the most of the primordial soup they called home. But to our credit, once [Messrs. Haber and Bosch] figured out how to make ammonia from thin air, we really went gangbusters on it, to the tune of 8 million tons per year of the stuff.

While it’s not likely that [benchtop take on the Haber-Bosch process demonstrated by [Marb’s lab] will turn out more than the barest fraction of that, it’s still pretty cool to see the ammonia-making process executed in such an up close and personal way. The industrial version of Haber-Bosch uses heat, pressure, and catalysts to overcome the objections of diatomic nitrogen to splitting apart and forming NH₃; [Marb]’s version does much the same, albeit at tamer pressures.

[Marb]’s process starts with hydrogen made by dripping sulfuric acid onto zinc strips and drying it through a bed of silica gel. The dried hydrogen then makes its way into a quartz glass reaction tube, which is heated by a modified camp stove. Directly above the flame is a ceramic boat filled with catalyst, which is a mixture of aluminum oxide and iron powder; does that sound like the recipe for thermite to anyone else?

A vial of Berthelot’s reagent, which [Marb] used in his recent blood ammonia assay, indicates when ammonia is produced. To start a run, [Marb] first purges the apparatus with nitrogen, to prevent any hydrogen-related catastrophes. After starting the hydrogen generator and flaring off the excess, he heats up the catalyst bed and starts pushing pure nitrogen through the chamber. In short order the Berthelot reagent starts turning dark blue, indicating the production of ammonia.

It’s a great demonstration of the process, but what we like about it is the fantastic tips about building lab apparatus on the cheap. Particularly the idea of using hardware store pipe clamps to secure glassware; the mold-it-yourself silicone stoppers were cool too.

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Big Chemistry: Glass

March 5, 2025 by Dan Maloney 12 Comments

Humans have been chemically modifying their world for far longer than you might think. Long before they had the slightest idea of what was happening chemically, they were turning clay into bricks, making cement from limestone, and figuring out how to mix metals in just the right proportions to make useful new alloys like bronze. The chemical principles behind all this could wait; there was a world to build, after all.

Among these early feats of chemical happenstance was the discovery that glass could be made from simple sand. The earliest glass, likely accidentally created by a big fire on a sandy surface, probably wasn’t good for much besides decorations. It wouldn’t have taken long to realize that this stuff was fantastically useful, both as a building material and a tool, and that a pinch of this and a little of that could greatly affect its properties. The chemistry of glass has been finely tuned since those early experiments, and the process has been scaled up to incredible proportions, enough to make glass production one of the largest chemical industries in the world today.

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Integrated Micro Lab Keeps Track Of Ammonia In The Blood

February 17, 2025 by Dan Maloney 6 Comments

We’ve all got our health-related crosses to bear, and even if you’re currently healthy, it’s only a matter of time before entropy catches up to you. For [Markus Bindhammer], it caught up to him in a big way: liver disease, specifically cirrhosis. The disease has a lot of consequences, none of which are pleasant, like abnormally high ammonia concentration in the blood. So naturally, [Markus] built an ammonia analyzer to monitor his blood.

Measuring the amount of ammonia in blood isn’t as straightforward as you think. Yes, there are a few cheap MEMS-based sensors, but they tend to be good only for qualitative measurements, and other solid-state sensors that are more quantitative tend to be pretty expensive since they’re mostly intended for industrial applications. [Marb]’s approach is based on the so-called Berthelot method, which uses a two-part reagent. In the presence of ammonia (or more precisely, ammonium ions), the reagent generates a dark blue-green species that absorbs light strongly at 660 nm. Measuring the absorbance at that wavelength gives an approximation of the ammonia concentration.

[Marb]’s implementation of this process uses a two-stage reactor. The first stage heats and stirs the sample in a glass tube using a simple cartridge heater from a 3D printer head and a stirrer made from a stepper motor with a magnetic arm. Heating the sample volatilizes any ammonia in it, which mixes with room air pumped into the chamber by a small compressor. The ammonia-laden air moves to the second chamber containing the Berthelot reagent, stirred by another stepper-powered stir plate. A glass frit diffuses the gas into the reagent, and a 660-nm laser and photodiode detect any color change. The video below shows the design and construction of the micro lab along with some test runs.

We wish [Markus] well in his journey, of course, especially since he’s been an active part of our community for years. His chemistry-related projects run the gamut from a homebrew gas chromatograph to chemical flip flops, with a lot more to boot.

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Improving Aluminium-Ion Batteries With Aluminium-Fluoride Salt

February 11, 2025 by Maya Posch 43 Comments

There are many rechargeable battery chemistries, each with their own advantages and disadvantages. Currently lithium-ion and similar (e.g. Li-Po) rule the roost due to their high energy density at least acceptable number of recharge cycles, but aluminium-ion (Al-ion) may become a more viable competitor after a recently published paper by Chinese researchers claims to have overcome some of the biggest hurdles. In the paper as published in ACS Central Science by [Ke Guo] et al. the use of solid-state electrolyte, a charge cycle endurance beating LiFePO₄ (LFP) and excellent recyclability are claimed.

It’s been known for a while that theoretically Al-ion batteries can be superior to Li-ion in terms of energy density, but the difficulty lies in the electrolyte, including its interface with the electrodes. The newly developed electrolyte (F-SSAF) uses aluminium-fluoride (AlF₃) to provide a reliable interface between the aluminium and carbon electrodes, with the prototype cell demonstrating 10,000 cycles with very little cell degradation. Here the AlF₃ provides the framework for the EMIC-AlCl₃ electrolyte. FEC (fluoroethylene carbonate) is introduced to resolve electrolyte-electrode interface issues.

A recovery of >80% of the AlF₃ during a recycling phase is also claimed, which for a prototype seems to be a good start. Of course, as the authors note in their conclusion, other frameworks than AlF₃ are still to be investigated, but this study brings Al-ion batteries a little bit closer to that ever-elusive step of commercialization and dislodging Li-ion.

Make Custom Shirts With A 3D Print, Just Add Bleach

February 10, 2025 by Donald Papp 38 Comments

Bleach is a handy way to mark fabrics, and it turns out that combining bleach with a 3D-printed design is an awfully quick-working and effective way to stamp a design onto a shirt.

Plain PLA stamp with bleach gives a slightly distressed look to this design.

While conceptually simple, the details make the difference. Spraying bleach onto the stamp surface helps get even coverage, and having the stamp facing “up” and lowering the shirt onto the stamp helps prevent bleach from running where it shouldn’t. Prompt application of hot air with a heat gun (followed by neutralizing or flushing any remaining bleach by rinsing in plenty of cold water) helps keep the edges of the design clean and sharp.

We wondered if combining techniques with some of the tips on how to 3D print ink stamps would yield even better results. For instance, we notice the PLA stamp (used to make the design in the images here) produces sharp lines with a slightly “eroded” look overall. This is very much like the result of inking with a stamp printed in PLA. With a stamp printed in flex filament, inking gives much more even results, and we suspect the same might be true for bleach.

Of course, don’t forget that it’s possible to 3D print directly onto fabric if you want your designs to be a little more controlled (and possibly in multiple colors). Or, try silkscreening. Who knew there were so many options for putting designs onto shirts? If you try it out and learn anything, let us know by sending in a tip!

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