Experiment 62: Explosive Copper Thermite!

Copper thermite is notorious for being violent and even explosive, so naturally, it was next on my list of thermites to try.  I began by weighing my 49.25g of copper (II) oxide made in Experiment 54: Making Copper Oxide for Thermite.  I divided this mass by 4.42 (derived from stoichiometry) to get the required mass of homemade aluminum powder, which was 11.12g.  I mixed them thoroughly to ensure a fast reaction and then set aside 45g for later.  With the 15g I now had, I used a homemade electric match (wire filament + kitchen match) to ignite it with the press of a button.  I wanted to capture the reaction on slow-motion, but my Nikon 1 J1 only records slow-motion for five seconds, so I had to have the thermite ignite at a precise time.  The electric match was better for this than a magnesium ribbon.

I was quite impressed by the speed and violence of the reaction.  It was all over in less than a fifth of a second, and the cloud of smoke it created made a smoke ring at least a yard in diameter.  It was quite amazing to see.

https://www.youtube.com/watch?v=LEvCJHDvyIQ

I wanted to make molten copper with the rest of the thermite.  Since my unmodified copper thermite blew everything out of the paper cup I put it in, I diluted my copper thermite with 17g of borax powder in a 2.5:1 ratio.  In a previous small-scale test, the borax had slowed the reaction and acted as a flux to liquefy the alumina slag created by the thermite.  This helped separate the molten copper from the slag.  Since this thermite reacted more slowly, I ignited my large batch of it using a magnesium ribbon.  It started off well, but then the thermite fizzled and continued to sputter for a few minutes.  Since my small-scale test of the composition worked well, I think that the large batch didn't perform because I had lightly pressed the thermite down before igniting it.  Maybe this didn't let the fire travel quickly enough.

Although the slow thermite was a bit of a disappointment, it did make solid copper pebbles, which is more or less what I was aiming for.  I used a hammer to pulverize the slag and then washed the mix with water to float away the less-dense slag.  This actually separated the copper out quite well, and in the end, I recovered 3.55g of copper granules.  This is a 9% yield, which isn't terrible, considering the thermite seemed to sputter instead of flaring up nicely.  In any case, my expectations were "blown away" by the fast copper thermite smoke ring, so I consider this experiment a success.

Experiment 61: Single-Transistor Ion Chamber for Detecting Radiation

Radiation fascinates me, but it isn't very interesting unless you can detect it somehow.  Geiger counters cost a lot, so I built something a radiation detector using a soup can and a single transistor.

The ion chamber I built uses a thin whisker wire inside a metal can to collect charge from ions made by passing radiation.  The transistor (I used a BC547B, but any small NPN signal transistor should work) amplifies the difference in charge between the can and the wire and sends this out as a voltage read out on a multimeter.  The other components of this simple radiation detector are a 4.7kOhm resistor, a 9V battery clip, and a 9V battery for power.  My whisker wire was simply some bare wire that held its shape when straightened.  I got my design from this YouTube video, and the video's instructions seemed fairly clear.

I learned some important things through researching this ion chamber.  When picking a can, it is important to pick one without a coating on the inside (or sand it off).  Any coating interferes with picking up charge from the air, which hampers the detector's performance.  I sanded my can's inside to be sure it would work.  Also, the transistor gets epoxied to can.  The epoxy shouldn't touch any of the transistor leads (only the plastic), and the leads shouldn't touch the can.  Either of those situations would cause unwanted electrical conductivity.  The only electrical connection to the can is made through the 4.7kOhm resistor.  If there is a coating on the outside of the can, it should be sanded off to help make a good electrical connection with the resistor.  When attaching the whisker wire, it is important to make sure it doesn't touch the can as it goes from the transistor's base through the hole in the can bottom (see picture at right).

One problem with this design is its sensitivity to external electromagnetic fields.  Simply moving sometimes causes the measured voltage to fluctuate.  To help prevent this, the detector may be closed off with an aluminum foil "lid" with the radiation source inside.  I also made an electronics cover using the bottom of another soup can and taped it over the electronics with some foil tape (as seen in the two pictures below).

Using the detector is simple.  With a 9V battery connected, exposing the detector chamber to radiation creates an increased voltage readout on a connected multimeter.  I have tested this detector with an americium source and with uranium ore, and while both work, the americium definitely has a greater effect.  Sadly, I do not have any other radioactive items to test; if I did, I would check whether this ion chamber can sense beta and gamma radiation.  Still, I am truly amazed at what can be accomplished with just a soup can and a single transistor.

Experiment 60: Anodizing Titanium into Rainbow Colors

A very long time ago, I received some scrap rods of titanium.  One of titanium's really neat properties (it has several) is that it can be anodized into a rainbow of colors.  Unlike aluminum anodizing, where the created aluminum oxide layer is colorless and a dye is needed, titanium anodizes to create what is known as thin film interference.  Basically, light waves entering the transparent oxide layer created by anodizing interfere with each other, making new waves and colors.  Other metals like niobium and tantalum also have this effect.  I thought anodizing titanium looked really fun, so I slapped together an anodizing experiment.

For my anodizing bath, I used 200mL of tap water with 8 grams of Borax dissolved in it.  Then, I sanded my titanium and cleaned it with acetone.  It is important to not leave fingerprints on the surface.

I looked at this image to see which voltages anodized titanium to nice colors.  Then, I connected the number of 9V batteries necessary to achieve that voltage.  Some batteries were at a bit less than 9V, so my first voltage I used was 24V (three batteries).  I connected my titanium to the positive on my battery series and clipped a piece of aluminum to the negative.  After putting both electrodes in my anodizing bath for half a minute, the titanium had turned a bright blue color!

I wanted to try making a pattern, so I cleaned my blue titanium with acetone again and then cut a tiny square of electrical tape into the letters "Ti."  I carefully applied the tape letters to the titanium, being sure not to leave skin oil on the metal.  Then, I put the titanium back into the bath, this time using 57V (seven batteries).  I wasn't happy with the faint yellow color that voltage made, so I tried again with 73V (nine batteries).  That gave a nice pink color, so I took the titanium out and removed the tape.  The pattern had worked, and I now had beautiful blue letters on a pink background.  The experiment only took half an hour, but it had great results!

Experiment 59: Stripping the Copper Coating from Pennies

After seeing a neat YouTube video (everything starts this way, doesn't it?) showing a chemist removing the copper plating from a zinc-core penny to make a solid zinc penny, I decided to try the experiment myself.  Upon further research, I saw that Theodore Gray the element collector also had a solid zinc penny, but he had used cyanide to remove the copper plating.  Since I didn't feel like exposing myself to extremely toxic salts, I decided to go with the YouTube method.

The reaction uses calcium hydroxide and elemental sulfur to oxidize away the penny's copper plating but not the underlying zinc.  If I remember correctly (I did this experiment some time ago), the reaction smells awful, so it is best performed outside.  I didn't have any calcium hydroxide, so I substituted in sodium hydroxide drain cleaner and used gardening sulfur as my source of sulfur.  After that, I simply followed the video's directions.

The pennies come out of the solution blackened with copper oxide, so I tried to remove it with a scrubbing pad.  That got rid of the copper oxide, but it also scratched the zinc pennies, making them less shiny than they otherwise might have been.  I would recommend going with the YouTube video's recommended cleaning method using ceramic cooktop cleaner.  I suppose the dullness could also be because of my substitutions, but the reaction still worked well using sodium hydroxide, so I doubt that was the case.  Nonetheless, I was really impressed that a reaction could remove only the copper on a penny while leaving the zinc untouched.  After polishing the pennies with a Dremel wheel, I was left with ten solid zinc pennies.

Platings provide opportunities to observe the subtle differences in colors of transition metals.  While nearly all transition metals are some color of gray, some have different hues.  I had some pennies with a layer of zinc or nickel plated over the copper, so I put them together with the solid zinc penny for a nice comparison.  Nickel definitely has a golden hue compared to zinc, which I find interesting.