In graduate school, I had a seminar course where one of the sections was about X-ray crystallography. I was excited, because being able to discern the three-dimensional structure of macromolecules just by shining X-rays on them seemed like magic to me. And thanks to a lackluster professor, after the section it remained just as much of a mystery.
If only I’d had [Steve Mould] as a teacher back then. His latest video does an outstanding job explaining X-ray crystallography by scaling up the problem considerably, using the longer wavelength of light and a macroscopic target. He begins with a review of diffraction patterns, those alternating light and dark bands of constructive and destructive interference that result when light shines on two closely spaced slits — the famous “Double-Slit Experiment” that showed light behaves both as a particle and as a wave and provided our first glimpse of quantum mechanics. [Steve] then doubled down on the double-slit, placing another pair of slits in the path of the first. This revealed a grid of spots rather than alternating bands, with the angle between axes dependent on the angle of the slit pairs to each other.
Photograph 51, an X-ray crystallogram of the B-form of DNA, by Gosling and Franklin, 1952. Source: Wikipedia
To complete the demonstration, [Steve] then used diffraction to image the helical tungsten filament of an incandescent light bulb. Shining a laser through the helix resulted in a pattern bearing a striking resemblance to what’s probably the most famous X-ray crystallogram ever: [Rosalind Franklin]’s portrait of DNA. It all makes perfect sense, and it’s easy to see how the process works when scaled down both in terms of the target size and the wavelength of light used to probe it.
Hats off to [Steve] for making something that’s ordinarily complex so easily understandable, and for filling in a long-standing gap in my knowledge.
Continue reading “A Beginner’s Guide To X-Ray Crystallography”
[The Plutonium Bunny] saw homegrown tin crystals on YouTube and reckoned he could do better—those crystals were flimsy and couldn’t stand up outside of the solution in which they were grown. Having previously tackled copper crystals, he applied the same procedure to tin.
Beginning with a 140 ml baby food jar filled with a solution of tin II chloride, 90 grams per liter, with a small amount of HCl as the electrolyte. A wire at the bottom of the jar was connected to a blob of tin and served as the anode, while the cathode, a loop of tin, stuck down from above. A LM317-based adjustable voltage regulator circuit was used to manage the power running through the solution. Because [The Plutonium Bunny]’s technique involves days or even weeks of very low current, he used six diodes to drop the circuit’s voltage from 1.5 V to 0.25 V, giving him around 13 mA.
His first attempt seemed to go well and he got some nice shiny crystal faces, but he couldn’t get the current bellow 10 mA without it dropping to the point where no tin was depositing. Rather than reset the experiment he made some changes to the project: he changed the solution by removing 30 ml of the electrolyte and topping it off with water. He also made a gentle agitator out of a DC motor and flattened plastic tube from a pen, powering it with another low-voltage LM317 circuit so he could get the lowest RPM possible.
With this new setup [The Plutonium Bunny] began to get much better results, proving his hypothesis that low current with a lower concentration of Sn2+ was the ticket for large crystal growth. We featured his copper crystal experiments last year and he’s clearly making good progress! Video after the break.
Continue reading “Grow Your Own Tin Crystals”
[Collin] loves piezos – and why not?
According to him, they are about as close to magic as you can find in the world. We can’t really disagree on that one – there’s something oddly enchanting about piezoelectric materials.
Most commercially used piezoelectric devices that you find today are constructed out of man-made ceramic materials such as Lead zirconate titanate, and can be found in grill starters, gas-powered water heaters, etc. While they are common, it’s not exactly easy to synthesize these sorts of ceramic materials at home.
You can however, create piezoelectric crystals in your kitchen, using just a few simple ingredients. In his video, [Collin] shows us how to create Rochelle Salt, one of the first known materials found to exhibit piezoelectricity. The recipe calls for three ingredients, cream of tartar, sodium carbonate (soda ash), and water – that’s it. The procedure is quite simple, requiring you to heat a solution of water and cream of tartar, adding the soda ash a little at a time once it reaches the proper temperature. The solution is filtered after it turns clear and then left to sit overnight while the crystals form.
Take a look at the video embedded below to see how his Rochelle Crystals turned out, and be sure to try this out with your kids if they are interested in electronics. Making crystals that generate electricity when tapped is far cooler than making rock candy any day, trust us on this.
Continue reading “Cooking Up Piezo Crystals At Home”