Experiment 50: Silicon Thermite

A thermite is always a special reaction to perform for a 50th experiment!  I enjoy isolating elements at home for my periodic table collection, so I used silicon dioxide (common name: sand) and homemade ball-milled aluminum powder to make small beads of pure silicon.

Iron thermite uses aluminum powder and iron oxide, but silicon thermite needs an additional ingredient besides silicon dioxide to be successful.  Adding sulfur creates more heat in a side reaction with aluminum, thus helping the reaction keep going.  I used a 12:10:9 mass ratio of S:SiO2:Al.  All the materials were finely powdered, and the silicon dioxide came as 400 mesh chromatography media from some company online.  They had a free samples program, so I readily agreed to get free chemicals!

After mixing the ingredients, I placed them in a flowerpot and lit them with a magnesium ribbon fuse.  The reaction was extremely bright and wonderful, but I'll let the video speak for itself:
As seen in the video, the reaction also makes aluminum sulfide, which hydrolyzes in water to make toxic, smelly hydrogen sulfide gas.  This is the active ingredient in many stink bombs, so it really stinks!  Plan on taking a shower and washing your clothes before social interactions if you repeat this experiment.

When the reaction had cooled, I put the slag pieces in water and hydrolyzed off all the aluminum sulfide.  I then sifted the silicon beads out from the resulting aluminum oxide powder.  I may have lost some, but I still got a decent number of small beads of silicon.  They weren't very shiny, so I soaked them in dilute hydrochloric acid for an hour or so until I could see the pretty crystals inside.  They turned out quite nicely, and I was happy to isolate another element in my backyard!

Experiment 49: Exploding Bridgewire Detonators!

An exploding bridgewire detonator (EBW) is a type of explosives detonator that explodes by passing a large electric current through a tiny metal wire very quickly.  The resistance of the wire causes it to vaporize at high speeds, creating a shockwave which initiates any explosives nearby.  These are used for plutonium A-bombs because the explosives that compress the plutonium-gallium core need to fire at the same time, to a precision of a few microseconds.  Normal fuses and blasting caps have too large an uncertainty in initiation time.

I use alligator clip lead wire as my bridgewire.  Alligator clip wires have many strands of very fine wire, so a single strand works well for the bridgewire.  Larger diameter wires can carry more current with less resistance, so they don't explode as well.  I usually crimp larger wires to the ends of the bridgewire; these serve as long leads for the detonator.  When the wire is connected, I tape the thicker leads a distance apart so they don't short.

The power supply for an EBW is a capacitor.  I asked Walgreens for used-up disposable cameras, and they gave me five of them.  I removed the flash capacitors from them and soldered them in parallel, making sure to connect all the white (-) sides together.  I zapped myself a few times desoldering the capacitors, and while it is OK to be haphazard with single capacitors, the five-capacitor bank could possibly kill someone if used improperly.  Be careful with large capacitor banks.
I used the charging circuit board from one of the cameras to charge my capacitor bank.  Charging five capacitors with a single board takes a few minutes, but it still works well.  I also made a detonator button to act as a switch for dumping the current from the capacitors through the wire.  This is explained in the video.  Once the capacitors are charged to 300V and the EBW is connected, I press the detonator button and everything goes boom.

This homemade EBW has many uses.  I have used it many times to ignite nitrocellulose, sometimes with highly explosive results.  EBWs are also good for making loud noises, so wear hearing protection.  These devices are very fun and simple to build, even if not used for high explosives.

Experiment 48: Integrated Circuit Silicon Chips

After seeing a really neat video by Ben Krasnow on YouTube about decapping integrated circuits to reveal the tiny silicon chips inside, I was intrigued.  By dissolving away the black epoxy surrounding the chip innards, Ben Krasnow uncovered the silicon wafer square that actually holds all the circuitry for the IC.  I thought this was pretty cool, and since I had nitric acid, I decided to give it a shot.

I started by sanding down the metal pins and most of the epoxy.  This made it so the nitric acid would have less material to dissolve, so I wouldn't need as much acid.  Once I had my chips prepared, I put them in a glass beaker on my hotplate.  With the chips on medium heat, I slowly dripped nitric acid onto the black epoxy.  It is absolutely critical to add the nitric acid extremely slowly!  If it is added too quickly, there will be billowing clouds of nitrogen dioxide, which has an awful odor.  Additionally, adding the acid too quickly can cause thermal shock on the hot beaker, which may make it crack (personal experience).

The experiment used substantially more nitric acid than I expected, but after a while of slowly dripping the acid onto the epoxy and regulating the heat to prevent excess boiling, I saw what looked like a silicon chip.  The epoxy hadn't actually dissolved, though.  It had disintegrated into a thick black paste, which made finding the extremely small silicon chips difficult.  I let the beaker cool and then poured everything into water to dilute any remaining acid.  From two ICs, I got three silicon chips.  I cleaned them with acetone and then put them on a slide for inspection.

I was shocked by how much detail fit onto a chip only a few millimeters square.  All these pictures were taken by simply lining my Nikon J1 up with my microscope eyepiece.  The results were pretty impressive (the text is even readable at the top of the left picture):