Experiment 66: Growing Large, Solid Tin Crystals

Encouraged by the success of my copper crystal growing experiment, I planned another metal crystal experiment - tin!  There are actually plenty of videos on growing tin crystals, but they all make terribly unsatisfactory small, flimsy crystals that can't even support their own weight out of water.  Using the same method I used for growing large, solid copper crystals, I successfully did the same for tin.

For this experiment, I initially used tin II chloride (about 90 grams per liter) acidified with a bit of HCl as the electrolyte.  A blob of tin and a strip of tin functioned as the anode and cathode, respectively.  As in my copper crystal experiment, the anode was on the bottom of my glass jar cell while the cathode poked into the electrolyte from the top.

The same sort of LM317 adjustable voltage regulator circuit was used, including the string of six diodes on the output.  Each diode drops a certain amount of voltage, so with a series of diodes, the lowest achievable voltage drops from the LM317's 1.25V down to about 0.25V.  This is critical for getting very low currents and slow crystal growth, which lead larger, more solid crystals.

I kept a thorough log of my observations during the experiment in a lab notebook, and the text of this may be viewed here.  The first try at growing the crystal worked fairly well, producing a solid result with some shiny crystal faces.  I couldn't really get the current to below 10mA or else it would drop almost discontinuously to 5mA.  I tried running the cell at 5mA, but I don't think tin was actually depositing.  A weird grey gunk started to grow at the cathode, and this turned out to be very brittle and crumbly out of water.  Upping the voltage just slightly to get ~10mA fixed the problem and tin crystals started growing again.  I also had to swirl the solution around a few times, and I think that this caused debris from the anode to get kicked up, which could have caused more small crystals to form, which is undesirable.  There was also some cloudiness at the end of this run, which may have been SnCl2 hydrolyzing in a not-acidic-enough electrolyte.  This should be avoided for best results.

To improve the experiment, I grabbed a small DC motor (probably scavenged from some dead electronics) and made a stir stick using an old plastic tube from a pen.  I powered the motor with another LM317 circuit so that I could get the lowest RPM.  This functioned as a very gentle agitator for the electrolyte cell to ensure the concentrations of tin chloride remained well-mixed.  Otherwise, the denser, more concentrated SnCl2 coming off the anode would stay at the bottom while the cathode would deplete the upper part of the cell of its SnCl2.  This seemed to work OK.  The resulting crystal did not have any grey gunk, but many of its crystals were smaller, though very solid.  There may have been more HCl in the solution than with the previous run; I had to re-acidify it to dissolve the cloudiness observed after the first run.

One interesting thing I noticed is that the tin anode made crackling noises as it cooled from being cast, and after using it as an anode, electrochemical etching showed some really neat crystals inside.
 I wonder if more metals would do this.

Still not quite satisfied with the crystals, I removed 30mL of the electrolyte from my cell (a tall glass baby food jar with a ~140mL capacity) and replaced it with tap water and a few drops of HCl (to ensure the solution stayed clear) for a new concentration of about 60g/L.  I used the same stirring technique as before, but this time, the crystal grew extremely quickly, taking less than 48 hours to grow to the bottom of the cell.  It also formed absolutely enormous crystal faces, with unblemished, flat, shiny parts a few centimeters long.  Through all three crystal growing runs, the current stayed below 15mA and the voltage was (according to the voltmeter) between 40 and 150 millivolts.  Thus, it seems that low current along with low(er) Sn2+ and HCl concentration is key to growing large crystals.

Once again, a microwave turntable motor was used for making 360° video of the crystals.  Unlike the copper crystals, these tin crystals do not tarnish, so they will retain their awesome shininess indefinitely.  :)  Perhaps it is time to try some new metals for crystal growing...

Cast a Mini Aluminum Skillet - Start to Finish

This actually happened a while ago but I just got around to posting the video.  I used a small cast iron skillet as a mold to make an aluminum skillet from melted-down vacuum cleaner parts.  Amazing!  A cast vacuum cleaner from the 1960s becomes a fully functional skillet useful for camping or making eggs.

I thought it would be helpful to explain how to do metal casting rather than only showing the pouring of the molten aluminum, so there are tips throughout the video aimed at those beginning casting.

MEL Science Chemistry Kits Review

Disclaimer: I was in no way compensated for this review, other than MEL Science generously sending me two free chemistry experiment kits along with their starter kit.

With the disclaimer out of the way, let's begin the review!  The basic concept is that upon subscription to MEL Science, they send you two chemistry kits each month.  You can then do experiments at home without needing to buy everything individually.
My first impression was that everything in the kit was well packed.  I did not find anything broken or damaged, and all the glassware was neatly padded so as to make breaking nearly impossible.  The starter kit has some good beginning materials - disposable plastic beakers (no more beaker-scrubbing!), a solid fuel stove, some glassware, etc.  It also has an instruction booklet on using the kits along with a detailed website that discusses the chemistry going on behind the scenes in the experiments.

The experiments themselves are on a variety of topics - I was sent one on combustion (The Chemistry of Monsters) and one on electrochemistry/redox reactions (Tin).  I enjoyed that the kits didn't require a lot of set-up work.  There wasn't anything to weigh out, plug in, or lay out.  In perhaps five minutes' time, I was doing actual experiments.

The tin dendrites experiment seemed to work well.  The dendrites grew beautifully, and the included macro lens took some stunning shots with my iPad 4 (sadly the MEL Science app does not support the iPad 4).

I tried one other experiment for the video, the sugar snake experiment from The Chemistry of Monsters.  As seen in the video, the hexamine solid fuel didn't quite fill the included mold, so its depression didn't hold all the sugar/sodium bicarbonate mix and the snake didn't work as well as pictured on the MEL website.  That was a small disappointment, but the sugar snake was still quite an intriguing experiment.  This simply shows that you may get different results as you try the experiments

In general, the MEL Science experiments seem to be "real"/unadulterated chemistry - they do dangerous and unique things like lighting off a Zn/S mixture and also have complicated concepts such as concentration cells.  They are meant to be suitable for most ages, so they won't be a substitute for a rigorous class in chemistry.  If, however, you are looking to explore, enjoy, and learn some unique chemistry, a subscription to MEL Science may be what you're looking for.

Experiment 65: Manganese Thermite from Batteries

A while ago, in Experiment 46: Manganese Dioxide Thermite, I attempted to make manganese metal for my element collection using thermite with manganese dioxide scavenged from batteries.  The experiment failed.  The batteries simply have too many contaminants (carbon, zinc oxide, etc.) to sustain a thermite reaction.

After reading some posts on ScienceMadness.org, I determined which steps would need to be taken to purify the manganese dioxide.  I first washed the manganese-containing battery paste with water and vinegar, then dissolved everything in HCl.  I filtered off my now-MnCl2 solution from the carbon, but it was contaminated with iron.  NurdRage's selective precipitation procedure came in handy for resolving that issue, and finally, I got a pretty pink solution - pure MnCl2!

I added NaOH to that solution to make manganese hydroxide, which oxidizes rapidly in air to Mn2O3, an oxide suitable for thermite.  After baking my hydroxide slush in the oven to help along the oxidation, I mixed my Mn2O3 with aluminum powder and lit it using a magnesium ribbon.  Unlike my previous manganese thermite attempts, this one violently flared up and reacted quite vigorously.
 Even better, I recovered some very beautiful shiny lumps of manganese metal.  While the thermite only gave a 23% yield on account of being so violent, it added another element to my collection, which is something to celebrate for sure.