The (Copper) Crystal Method

July 3, 2016 by Al Williams 43 Comments

One of the staples of kitchen chemistry for kids is making sugar crystals or rock candy. Why not? It is educational and it tastes good, too. [Science with Screens] has a different kind of crystal in mind: copper crystals. You can see the result in the video below.

To grow pure metal crystals, he used copper wire and copper sulfate. He also used a special regulated power supply to create a low voltage to control the current used to form the crystal. The current needed to be no more than 10mA, and an LM317 holds the voltage constant. However, that regulator only goes as low as 1.25V, so diodes cut a volt off the output.

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Reverse Engineering The McDonald’s French Fry

June 25, 2016 by Gerrit Coetzee 88 Comments

McDonald’s is serious about their fries. When they were forced by shifting public opinion (drunkenly swaggering around as it always does) to switch from their beef tallow and cottonseed oil mixture to a vegetable oil mixture; they spent millions to find a solution that retained the taste. How they make the fries is not the worlds most closely guarded secret, but they do have a unique flavor, texture, and appearance which is a product of lots of large scale industrial processes. [J. Kenji López-Alt] decided to reverse engineer the process.

His first problem was of procurement. He could easily buy cooked fries, but he needed the frozen fries from McDonald’s to begin his reverse engineering. McDonald’s refused to sell him uncooked fries, “They just don’t do that,” one employee informed him. He reached out to his audience, and one of them had access to a charlatan. The mountebank made quick work of the McDonald’s employees and soon [J. Kenji] had a few bags of the frozen potato slivers to work with.

What follows next was both entertaining and informative. At one point he actually brought out a Starrett dial caliper to measure the fries; they were 0.25in squares in cross section. Lots of research and experimentation was done to get that texture. For example, McDonald’s fries aren’t just frozen raw potatoes. They are, in fact; blanched, flash fried, frozen and then fried again. Getting this process right was a challenge, but he arrived at similar fries by employing his sous vide cooker.

He then wanted to see if he could come up with a french fry recipe that not only allowed the home chef to make their own McDonald’s fries, but improve on them as well. It gets into some food chemistry here. For example he found that the same effect as blanching could be produced by boiling the fries; if you added vinegar to keep the cell walls from disintegrating.

The article certainly shows how knowledge of the chemistry behind cooking can improve the results.

Single Molecule Detects Light

June 23, 2016 by Al Williams 12 Comments

Everything is getting smaller all the time. Computers used to take rooms, then desks, and now they fit in your pocket or on your wrist. Researchers that investigate light sensors have known that individual diarylethene molecules can exist in two states: one where it conducts electricity and one where it doesn’t. A visible photon causes the molecule to be electrically open and ultraviolet causes it to close. But there’s a problem.

Placing electrodes on the molecule interferes with the process. Depending on the kind of electrode, the switch will get stuck in the on or off position. Researchers at Peking University in Beijing determined that placing some buffering material between the molecule and the electrodes would reduce the interference enough to maintain correct operation. What’s more the switches remain operable for a year, which is unusually long for this kind of construct.

Using chemical vapor deposition and electron beam lithography, the team produced over 40 working single molecule switches. These devices could be useful in optical computing and other applications. Future work will include developing multilevel switches comprised of multiple molecules.

If you want something more macroscopic, you might try using an LED to sense light. A switch is fine, but sometimes you want to generate a signal.

Disposable Diapers Are A Tribute To Material Science

June 14, 2016 by Mike Szczys 53 Comments

It’s a really tough problem that has been solved to an amazing level. How do you capture and contain urine from a floppy, curved, and moving human infant? Ah, but the problem is a bit harder than that. You also want to keep that liquid away from the soft skin of the newborn and keep the exterior of your overall system dry too. From an R&D point of view the nice thing is that the customer base is huge — everyone needs some type of diapers. And what we have achieved thus far is a huge accomplishment of material science. [Bill Hammack], The Engineer Guy, takes on the engineering of baby diapers in his latest video.

A diaper uses three inner layers to sweep urine away from baby’s skin. The first layer actually repels water — being injected between skin and this layer, liquid passes through the holes in the material. But the moisture repellent property prevents it from moving in the opposite direction because of the next two layers encountered. The second layer uses capillary action to pull the moisture toward the third (and to act as a one-way moisture valve). The third layer contains a super-absorbent polymer. That layer starts off very thin and swells with absorption.

Bill explores just a bit about how these materials are actually manufactured. The layers are non-woven to form the necessary structures. The absorption layer uses cotton fibers to ensure moisture doesn’t form a dam between polymers. Whether you have a little one in your own household or not, the science behind this solved problem is fascinating and well worth the six minutes you’ll spend on the video below.

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Mining Platinum From The Road

June 6, 2016 by Jenny List 94 Comments

For several decades now all petrol-driven motor vehicles have had to feature a catalytic converter in their exhaust systems to meet the requirements of emissions legislation. These feature a high surface area coated with platinum, palladium, and rhodium, which catalyses the high-temperature breakdown of the exhaust gasses.

When a vehicle reaches the end of its life its catalytic converter is recycled and those metals are recovered, but this recovery does not account for all the metal. [Cody Reeder] noticed that the weight of platinum in a catalytic converter taken from a scrap vehicle is significantly less than that of a new one. Some of that metal has escaped, so where has it gone?

The answer to that question is that it has become detached from the converter and blown out through the rear of the exhaust pipe. Therefore in the area around a busy highway with many thousands of cars passing there must be a reasonable concentration of platinum. The video below the break details [Cody]’s quest to verify that theory, and it opens with him and a friend sweeping dust from beside a freeway in the early hours. The resulting bags contain a lot of gravel and bits of tire, plus a few cigarette butts and a large amount of very fine dust. He sieves away the debris, and heats a sample of dust in a furnace with a flux mixture containing lead oxide. He hopes that as this oxide degrades to metallic lead it will dissolve any platinum and settle in the bottom of his crucible, and indeed when he pours out the resulting slag there is a bead of lead. Taking away the lead reveals a speck of impure platinum, which he further purifies and assays to determine the percentage of platinum and to detect the other catalyst metals.

He finally arrives at a figure of 6.7 g per ton of his fine-sifted roadside dirt “ore”, a figure which as he points out would be considered quite valuable were it to be encountered in a mine. His process might be a little difficult for individuals with sweeping brushes to hit pay dirt and a modern gold rush to descend on their local Interstate, but it’s not impossible that a highways agency equipped with sweeper trucks could have the metal extracted at a more profitable level.

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Hack A Bike Electroetching

May 17, 2016 by Al Williams 10 Comments

[Melka] wanted a track bike, but never quite got around to buying a nice one. Then he found an inexpensive abandoned project bike for 10 Euro. He had to do a lot of work to make it serviceable and he detailed it all in a forum post. What caught our eye, though, was his technique for electroetching.

The process is simple, but [Melka] says the procedure caused hydrochloric acid fumes as a byproduct. Your lungs don’t like HCl fumes. Apart from the danger, you probably have everything you need. He used electrical tape to create a stencil on the metal (although he mentioned that Kapton tape might come off better afterward) and a saturated solution of common table salt as the electrolyte.

Power comes from a bench power supply set to about 24V. The positive lead was connected to the metal and the ground to the sponge. From the photos, it looks like the particular piece and solution caused about 600mA to flow. After 10 minutes, the metal etched out to about 0.2 mm. After the etching, [Melka] brazed some brass into the etched area to make an interesting looking logo.

If you have a laser cutter, you can skip the chemicals. We’ve even seen laser etching combine with a 3D printer to produce PCBs. [Melka’s] method is a little messier and probably would not do fine lines readily, but if you need to etch steel and you don’t mind the fumes, it should be simple to try.

Beyond WD-40: Lubes For The Home Shop

May 17, 2016 by Dan Maloney 134 Comments

If your shop is anything like mine, you’ve got a large selection of colorful cans claiming to contain the best and absolutely only lubricant you’ll ever need. I’ve been sucked in by the marketing more times than I care to admit, hoping that the next product will really set itself apart from the others and magically unstick all the stuck stuff in my mechanical life. It never happens, though, and in the end I generally find myself reaching for the familiar blue and yellow can of WD-40 for just about every job.

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