Experiment 64: Homemade Napalm with Household Materials

A while ago, I saw a neat YouTube video on making napalm from Styrofoam and gasoline.  Making napalm is as easy as pushing Styrofoam into gasoline until it won't dissolve anymore.  I waited until I got a large block of Styrofoam from an appliance box and then tried making napalm in my own backyard.  :)

The Styrofoam dissolved surprisingly quickly, and it tripled the volume of the gasoline.  I only used about 10mL of gasoline, but that was plenty to make a good volume of napalm.  It had a consistency like silly putty, and it was very stretchy.  While saturated with gasoline, the napalm was slippery, but when it dried just a bit, it became tenaciously sticky.

I split my napalm into three blobs and lit one on an overturned paint can.  For its villainous reputation, napalm really isn't that interesting.  It just burns... and burns and burns and burns.  Each small chunk of napalm burned for over four minutes.

While the napalm itself wasn't super exciting, it did provide a neat photo opportunity.  I used my Nikon 1 J1 in manual mode to capture some really neat images of the flames.  The photos were all underexposed slightly to make the fire stand out, and I used a fast shutter speed to ensure sharp detail in the flames and toxic black smoke.  I took a lot of pictures as the napalm burned and then picked the best ones; at times, the flames had very beautiful contours.  Although napalm may be unexciting as far as fireballs go, it certainly provides a good subject for the amateur photographer.

Casting a 3D Aluminum Puzzle Cube

As I was searching for another casting project to hone my skills on, my eyes fell upon an injection-molded 3D puzzle cube made by Proto Labs.  The cube had nine plastic parts that all fit together to make the cube.  It fit the bill for an interesting casting project, so I started by planning out how each piece would be oriented in the casting flask.  I wanted to be able to pull them straight out of the sand without having undercuts.  The plastic parts were hollow with one side missing, so I had to put tape over the missing side so that I would cast solid aluminum parts.

After all the pieces were taped, I laid them in a circle in my casting flask.  I positioned them close together so that the aluminum would only have to travel a short distance to fill the mold.  Then, I dusted the parts in baby powder and sprinkled on casting sand, packing as I went.  To make the other half of the mold, I first flipped the initial mold half over and then cut away sand that had gotten under the yellow piece.  The yellow piece was tricky because it had an overhang/undercut in all orientations.  Thus, I had to cut away the sand under the overhang so that I could later pull the piece straight out of the mold.

With the first half complete, I dusted everything with baby powder again and then packed sand into the second half of the mold, which fit on the first half with wooden pegs.  When both casting flasks were finished, I pried the halves apart and carefully teased the pieces free from the sand.  I then cut a sprue and gate system to feed metal to the pieces.  The sprue and gate system should have rounded corners as much as possible to minimize sand erosion by molten aluminum.  I did not make any vents for the casting, as the pieces were fairly small.

Outside, I melted a full crucible of aluminum and heated it for three minutes after the last piece of scrap melted to bring it up to pouring temperature.  Then, I sprinkled sodium carbonate and sodium chloride on in a 50/50 ratio and scraped off the dross/flux mix.  I poured the shiny liquid aluminum down the sprue, and half an hour later, I broke open the mold to reveal a casting that looked somewhat like an ancient Mayan symbol.

Using a hacksaw with a metal blade, I cut each piece free from its gate and began filing.  Injection molding is quite different from sand casting, so the pieces weren't designed to be sand cast, and they were fairly rough straight from the mold.  My strategy for filing them was to file two pieces until they fit together and then file additional pieces to fit the previously filed ones.  I began with the orange and red pieces and ended with the green piece, since it holds the cube together.  I found that filing the edges and corners of the pieces greatly improved the cube's appearance, so I did that, using a Dremel tool to get in the hard-to-reach corners.  In total, I filed for 12 hours.  It was quite awful.

When all the pieces fit, I sanded them with progressively finer grits to remove the scratch marks left from filing and sanding.  I finished by sanding everything with a worn-out sanding sponge, which gave the cube a nice shine.  When looked at from a corner, the cube appears to be a 3D maze, which I think is pretty neat.  Although the cube was a lot of work and took an obscene amount of filing to finish, it was well worth it in the end.  Nothing worthwhile is ever easy... still, I'm never doing this much filing again!

Experiment 63: Purifying Potassium Chlorate from Matches

For a while, I have wanted to make flash powder, a mixture of potassium chlorate or perchlorate and aluminum powder.  Like nitrocellulose, it burns with a flash when unconfined, but it will explode if confined.  One easy (if expensive and time-consuming) way to get potassium chlorate is through purification from match heads, so I decided to try the process on a handful of matches.  I used this video as a reference for the experiment.

I began the experiment by crushing around 50 match heads into a powder.  For cardboard matches, I simply snipped the head off and then pulverized it, but for wooden kitchen matches, I crushed the powder off the match and discarded the matchstick.  Once I had a fine powder, I poured in about 100mL of water and stirred to thoroughly dissolve the potassium chlorate.

There were a lot of bits of floating cardboard, so I filtered the mixture through a coffee filter to separate the green-colored solution from the insolubles.  I also washed the cardboard with water to recover any soaked-up chlorate solution.  Then, I boiled the green liquid down to about 1/10 of its original volume and set the beaker aside to cool.  When it had cooled to room temperature, I placed it in an ice bath to precipitate as much chlorate as possible.  As the solution cools from boiling to freezing temperatures, the potassium chlorate's solubility drops, so it precipitates as solid crystals.

I filtered off my crystals using another coffee filter and then washed these with acetone to remove some of the green dye; obviously, I didn't get all of it.  Potassium chlorate is not soluble in acetone, so this step does not remove any potassium chlorate.  Then, I let my crystals dry and weighed them.  From around 50 matches, I got 1.5g of fairly pure potassium chlorate.  Combined with aluminum powder, this is sure to make a brilliant flash.

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.

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.

Experiment 58: Alpha Particle Spark Detector

I wanted to "see" nuclear radiation, so I looked online for experiments similar to making a Geiger counter.  One of the ones I found was an alpha particle spark detector, which shows passing alpha particles as high-voltage sparks.  A wire grid hovers a few millimeters above a plate charged to a high voltage, and when an alpha particle shoots by, it ionizes the air between the grid and the plate, which allows a spark to jump across.  I enjoy this device because it helps me visualize alpha radiation emanating from a source.

I made extensive use of this tutorial, which was the only one at the time.  To generate the high voltages required for this experiment, I powered a CCFL inverter with 12V from my lab power supply.  While the inverter's 900V is high voltage, it isn't high enough for this experiment, so I fed the inverter output into a Cockcroft–Walton voltage multiplier, as per the tutorial.  I used 0.01uF ceramic capacitors and 1N4007 diodes for my multiplier, which had four stages.  When powered with my lab power supply, that increases the voltage about eight-fold, generating the approximately 10kV necessary for a successful spark detector.  I also tried to round off the solder joints to minimize sharp edges that might cause performance-harming corona discharge.

When detecting alpha radiation, it is nice to have frequent small sparks that represent individual alpha particles, rather than one large spark every now and then.  To achieve this affect, I placed a 10 mega-Ohm high voltage resistor (from Vishay) on the high voltage output of my voltage multiplier.  This makes each spark smaller, but it also enables a greater number of sparks at a time.  The resistor also limits the current--larger currents might burn out the extremely thin wire grid.  A normal-voltage resistor might possibly work, but it could fail under 10kV.

Before building the wire grid and plate assembly, I picked out a case for my project.  Previously, I had gotten a sleek enclosure from OKW Enclosures, so I decided to use it in this project.  Because the enclosure was an oval, I picked an oval-shaped piece of aluminum for my high voltage plate.  I needed a good electrical connection for the high voltage, so I tried soldering to the aluminum.  After many failed attempts, I found online instructions that suggested scratching the aluminum under a pool of molten solder.  This eventually made the solder wet the aluminum, and soldering a wire to the plate underside was simple with that done.  After sanding the top to a near-mirror finish, I used four bolts and springs to attach the plate to the enclosure top.  The wire grid sits a few millimeters above the plate, and the bolts and springs let me adjust this distance so that the spark detector does not spark while idle.  I adjust the bolts until the detector only sparks in the presence of alpha radiation.

For my wire grid, I bolted small strips of copper-clad PCB stock to the enclosure top on each side of the aluminum plate.  I used the bolts protruding through the enclosure top's underside as my feedthroughs for the ground connection.  (The wires are ground and the aluminum plate is high voltage.)  I made multiple small cuts in the PCB strips to make individual (but still connected) pads to solder my wire grid to.  I didn't cut all the way through the fiberglass, nor did I separate the pads completely.  They still have copper connecting them in the back, but they are more thermally isolated, which makes soldering easier.  After tinning each pad and using soldering flux, I soldered 10 strands of flexible copper alligator clip lead wire from one pad to its corresponding pad across the aluminum plate.  I tried to make each wire tight so that it would not sag closer to the aluminum plate and create sparks without alpha particles present.  The distance between each wire was 4mm, and the distance from the wires to the aluminum plate was 3mm.  Each wire had a diameter of 0.08mm; such a small diameter is necessary to create the concentrated electric fields which make the spark effect.

As I put everything inside the enclosure, I tried to be sure that none of the high voltage (900V or 10kV) wire were close together or overlapping.  When I finally applied power, I found out that the aluminum plate was too close to the copper pads.  I sanded the plate's sides using 80 grit sandpaper, and eventually, I stopped the continuous sparking that had been I had noticed.  Some of the wires had low spots that sparked even without alpha particles, so I gently pushed those up with a q-tip.

Eventually, I got all the bugs worked out and tested the spark detector using an Am-241 source from a smoke detector.  It worked wonderfully, making a beautiful storm of sparks and small pinging sounds.  If you open the picture on the right and look closely, you can see small sparks on the finished detector as I hold the Am-241 source above it.  Because uranium undergoes primarily alpha decay, this detector also works with uranium ore, although not quite as vigorously, since the source material is more spread out.  This project is one of my favorites because I can "see" radiation with it.  Each spark happens at the actual location of an alpha particle, thus showing me the distribution of the radioactivity, which I think is really neat.

Experiment 57: Microwave Furnace Melting Metal

A while ago, I saw a YouTube video showing someone smelting gold from ore using a common household microwave.  Intrigued, I researched microwave furnaces further.  Amazingly, the microwave found in nearly any kitchen can melt metals like gold, copper, and aluminum!  Microwave furnaces work by surrounding the crucible or the metal to be melted with something that absorbs microwaves (a susceptor) and turns them into heat.  Some common microwave susceptors are charcoal and silicon carbide, as well as water--food gets hot in a microwave because of its water content.

To make my microwave furnace, I grabbed the alumina-silica light-density firebrick that was my arc furnace body and cleaned the metal residue from its inside.  The furnace body is simply one brick with a 2" diameter hole 1.5" deep in it and another brick as the lid.  Each brick is about 4" by 4" by 2.5", so this leaves a 1" thick bottom on the furnace body.

I added a 1/8" layer of crushed lump charcoal to the bottom of the furnace's inside and put my soup can crucible on top of that.  Then, I added some aluminum TIG welding filler rod scraps and set the furnace in an experiments-only microwave.  With everything in place, I nuked my furnace for six minutes on high heat.  Amazingly, the aluminum was completely molten and glowed bright orange!  I was quite impressed, so I tried zinc in the microwave furnace.  After four minutes, it was a mere puddle.

I read on a forum somewhere that charcoal can heat things to at least 1000°C as a microwave susceptor, so I suppose I shouldn't be surprised that the furnace works so well.  With a simple soup can as its crucible, though, it has limitations.  I tried melting copper, and while the copper melted (around 20 minutes on high), it also ate through the steel and leaked out everywhere.  A graphite crucible might be a better choice.  However, I am still impressed that a common microwave can melt a metal like aluminum in less than ten minutes!

Experiment 56: Homemade Lab Centrifuge

I had an old (possibly from the 1960s) Hoover vacuum cleaner motor lying around, so I decided to turn it onto a lab centrifuge for chemistry experiments.  The motor was enormous and spun with such ferocity that I thought it would might go airborne and kill me, which scared me thoroughly.  For that reason, I used large bolts to attach it to a thick plastic/wood board, which I clamp to a table when I use the centrifuge.

The vacuum cleaner creates suction by spinning a cast aluminum turbine.  The aluminum turbine blades were relatively flat on top, so I decided to make this the centrifuge top.  I cut some plywood into a disc with a hole it in to go around the motor output shaft.  If the disc ever flew off in operation, someone could get seriously hurt, so I cut some scrap sheet steel into a large washer to go between the end nut of the motor output shaft and the plywood.  Once everything was assembled, I tightened the nut until everything was snugly in place.
Previously, I had requested and received free samples of 2mL plastic centrifuge tubes from a laboratory supply company, so I designed my tube holders around those.  I cut and drilled six wood cubes with holes sized for my centrifuge tubes and then glued these around the plywood disc.  Centrifuges can self-destruct if they are off-balance, so I carefully measured 60° increments around the circle so that the disc would be balanced.  To finish off the centrifuge, I added a cord and on/off switch salvaged from the old vacuum cleaner.

For being made from a vacuum cleaner, this centrifuge works surprisingly well.  I have successfully separated oil from mayonnaise, although mustard does not separate.  This centrifuge is extremely useful for settling precipitates out of solutions.  If I mix copper sulfate and sodium carbonate solutions, I get clear sodium sulfate in solution and blue copper carbonate precipitate.  By placing a sample of solution in the centrifuge, I can settle all the blue precipitate out and see the true color of the solution--it should be clear if I have used enough sodium carbonate.  One thing this centrifuge can't do is enrich uranium, but if that's the only complaint, I would say it works pretty well!

Experiment 55: Fresnel Lens Solar Death Ray!

A very long time ago, one of my friends introduced me to The King of Random's videos on YouTube.  I was impressed, and it wasn't long before I found his video on making a solar death ray using a Fresnel lens from a rear projection TV and some cheap wood boards.  I had to try it!

After finding a rear projection TV on craigslist for free and just barely managing to compress it into a minivan for transport, I began searching for its Fresnel lens.  The TV was absolutely enormous, and it was really heavy as well.  I eventually found out how to take off the lens and carefully set it aside so it wouldn't get scratched.  Other useful things I found in the TV were castor wheels (used in my ball mill), mirrors (CO2 laser, perhaps?), and various circuit boards and lenses that I haven't used yet.

The Fresnel lens itself is quite floppy, and it is also large and unwieldy, which isn't good.  The King of Random's video showed how to build a nice frame for the lens that held it rigidly but still allowed for easy rotation to follow the sun.  I followed his instructions closely, and the frame turned out to be inexpensive and very helpful.  I also used this Instructable to find the lens focal length so I knew where to put objects for best burning performance.  My death ray's focal length is about 35".  I put a board across the two cross-pieces on the frame so that objects can rest there at a fixed distance from the lens (instead of me holding them in midair).  Finally, I scratched each lens side with my fingernail to find out which side had grooves on it.  The grooves should face the sun for best performance.  In use, I also try to line the lens up so that it is perpendicular to the sun's rays that are hitting it.

Concentrating over a square yard of sunlight into a square inch makes a very bright spot of light, which can be problematic for unprotected eyeballs.  I bought some #10 shade cheap-o welding goggles from Harbor Freight and use them every time I play with the death ray.  It is impossible to see what is happening otherwise, although my iPad can see details inside the bright spot.

I love using my Fresnel lens.  It creates a searing-hot spot of intensely focused sunlight, capable of melting or burning many things.  Over the years, I have melted over a quarter's worth of zinc pennies using this Fresnel lens.  Yes, melting metal with sunlight!  While this lens cannot melt iron or rocks as some videos show, I have melted and compressed HDPE milk jug shreds into a usable billet by placing them in a soup can "oven" under the death ray spot.  My Fresnel lens has even burnt all the way through inch-thick wood boards!  This death ray cost less than $20 to make and uses freely available energy to do incredibly destructive things, which is exactly why I love it!

Experiment 54: Making Copper Oxide for Thermite

Next on my list of thermite reactions I want to try is copper.  For that, I will need copper (II) oxide to react with my homemade ball-milled aluminum powder.  I saw a nice video by zhmapper on YouTube about making copper (II) oxide, so I decided to try his method myself.

To start, I made concentrated solutions of copper sulfate (root killer) and sodium carbonate (washing soda).  I used about a 2:1 mass ratio of these solids and completely dissolved each.  Baking soda (sodium hydrogen carbonate) would work just as well, but the ratio might be different.  With my solutions prepared, I mixed them thoroughly together.  This made a lot of bubbles, so I had to quickly transfer my experiment to a larger container.  When the solutions mix, they make copper carbonate, which can be decomposed into copper (II) oxide.  I knew that I had added enough sodium carbonate because the blue color of the solution became clear (once the blue copper carbonate had settled out).

The byproduct of the reaction is sodium sulfate, so I filtered this off, along with the excess water, using simple coffee filters.  When the copper carbonate dried, I was left with a robin's-egg-blue powder.  To transform the copper carbonate into copper (II) oxide by releasing CO2 gas, I heated the powder in a soup can.  My hot plate wasn't hot enough, so I put the can in a bonfire for 15 minutes.  When everything had cooled, I was left with a dark black powder--the copper (II) oxide.  I also noticed some pink inside the can, so I wonder if the fire was somehow reducing some of the copper oxide back into copper metal.

Untouched, the copper oxide would probably work.  I have heard that copper thermite is very energetic, so it probably doesn't require extra fine ingredients.  However, I want the best performance from this reaction, so I milled the powder by hand using some steel ball bearings in a plastic jar.  Shaken enough, the bearings break up any clumps.  I also ran a magnet in a plastic bag over the powder to remove magnetic particles that came from the soup can.  I was left with 55 grams of fine copper (II) oxide powder for an exciting thermite reaction.

Experiment 53: Growing Large Copper Crystals

For a very long time, I have been fascinated with crystals of pure metals.  Many people have grown crystals of copper sulfate, but crystals of metallic copper are a rare thing.  After seeing The Backyard Scientist's video as well as this more crystalline crystal, I had to try it myself.
The basic principle of copper crystal growing is to very slowly electrolyze a solution of copper sulfate with two copper electrodes.  I used a normal copper wire as my cathode (-) and a flat spiral of thick copper wire as my anode (+).  The cathode just poked into the solution ~5mm, and the anode rested on the bottom of my glass jar electrolysis cell, connected to my breadboard via a soldered-on insulated wire.  In a Sciencemadness forum post, The Backyard Scientist says he used 100g/L copper sulfate and 60ppm chloride ions to prevent spindly dendrites from forming (thick crystals are more impressive).  I initially thought dilute copper sulfate would conduct less electricity and thus grow the crystals more slowly, thus helping to form larger crystals.  It turns out that if the solution is too dilute, the growing crystal will "use up" all the Cu2+ ions in the immediate vicinity and will get weird polyp-like black growths instead of shiny crystalline copper.  I ended up using 40g/L of copper sulfate for the final iteration of my experiment; concentrated solutions (or frequent stirring) are key to success.  My chloride ion source was simply table salt, and I used tap water for my electrolyte bath.  There was some gunk in the root killer copper sulfate, so I filtered my solution before use.

While a dilute solution is actually not good for making beautiful crystals, very low currents and voltages are.  My electrodes were spaced about 7cm apart, and my voltage varied throughout the experiment‐it was usually around 0.28V.  The key is to keep the current very low.  I never let the current exceed 10mA for the entire experiment.  To achieve the very low voltages necessary for low currents, I made an LM317 constant voltage circuit and put five 1N4007 diodes in series on the positive output of the circuit to drop the voltage down lower.  Basically, the LM317 can only regulate down to an output voltage of 1.25V, but I wanted the ability to go to around 0.25V, so I put a bunch of diodes on the output so that each of them dropped the voltage down a little bit.constant voltage circuit.  Oh well!

 Turning the potentiometer on the circuit still changes the voltage, only everything is shifted down a volt.  I used a 7.5V wall wart power supply to power the LM317; anything within the specified input voltage will do fine.  One odd thing I noticed was that while reading the voltage between the two electrodes, if I connected the ammeter, the measured voltage would increase.  I have no idea why this happened, since my circuit should have been a

With everything connected and my electrolyte prepared (filled to ~1/2" of top of glass jar), I turned on the power and adjusted the potentiometer until my multimeter read less than 10mA on the output.  I recorded the voltage and nearly everything I did in an experiment log which may be viewed here.  If you would like to repeat this experiment, definitely read it through.  With my electrolysis power on, I just had to wait.  Every few days, I checked on the experiment.  At times, I had to gently swirl the solution to mix the Cu2+ ions up again.  When I swirled the solution, the current would increase and the voltage would decrease.  I could tell when the solution was becoming depleted around the crystal because it would be a lighter blue than the rest of my electrolysis cell.  I also covered the jar to prevent dust from entering and added water to balance evaporation.  After waiting for six weeks (yes, 42 days), I pulled out an unbelievably shiny bloom of huge copper crystals!

Over six weeks, my crystal grew to 14 grams and a nick in the anode wire insulation allowed the wire to corrode almost through.  In a previous run of this experiment, I had noticed that the crystal dulled and darkened after exposure to air.  I wanted to preserve the extremely shiny pink color of my new crystal, so I cut the cathode wire ~1/2" from the crystal and hot-glued this to the inside of a small spice jar lid.  One note on cutting thick wire with side cutters-be careful to hold the crystal at all times!  My first crystal shot a yard away and smashed against the wall when the cutters made it through the wire.  My new crystal had already darkened some, so I dipped it in plain vinegar, which restored its ultra-shiny pink color well.  I then filled the spice jar with mineral oil and sealed the crystal in to keep its shine.

For photography, I brought the crystal display outside for the bright sunlight and set it on a microwave turntable motor connected to 120VAC.  The motor was an AC motor rated for 3rpm, so it slowly rotated the crystal for the video.  The effect was rather nice, and I was exuberantly happy to be the new owner of such a rare and amazingly beautiful crystal.

Experiment 52: Highly Flammable Nitrocellulose

Nitrocellulose is simply cotton that has had its hydroxide groups replaced with nitrate groups.  This simple substitution makes it highly flammable and even explosive.  After seeing some YouTube videos demonstrating its highly combustible properties, I decided to make some.

First, I selected some 100% cotton string, a piece of white paper towel, and some cotton balls as my sources of cellulose.  I very carefully made a 2:1 volume mixture of concentrated sulfuric and nitric acid in a small glass beaker.  After stirring gently, I placed this beaker in a bucket of snow to cool the nitration.  I nitrated my three sources of cotton separately, one after the other.  To nitrate each batch, I placed it in the acid mixture for 15 minutes.  After the time was up, I transferred the now-nitrocellulose to a saturated baking soda solution to neutralize remaining acid.  Finally, I thoroughly washed the nitrocellulose with plain water and let it dry.

One interesting thing I noticed was that the cotton balls almost seemed to freeze in the mixture.  It was quite cold when I did the experiment, but the stiffening could also have been caused by close packing.  I had just enough acid to cover three cotton balls at a time, so they were squished.

The homemade nitrocellulose is quite inflammable.  I have even held pieces in my hand and lit them without hurting myself.  While the paper towel and the cotton seem to burn extremely quickly without any residue, the string burns slower and leaves some charred material behind.  A cotton ball that I nitrated at the end of the run also left some residue--perhaps the acid was nearly used up.  The best cotton burns so quickly that it can detonate under the right conditions.
I created these "right conditions" by compressing the nitrated cotton balls in a spent brass shell casing and initiating detonation with a homemade bridgewire detonator.  I first made an insulating sleeve out of a straw to go on the inside of the shell; this protected the bridgewire from shorting on the casing.  Then, I packed the shell half full with nitrocellulose.  I inserted the bridgewire (also stuffed with nitrocellulose) and then packed the shell the rest of the way.  I left 3/8" at the top and crimped this over with some pliers to seal the shell, creating containment for the combustion gasses.

I put the device in a cardboard box with a polycarbonate viewing window and set it off from another room using my flash capacitor bank.  I was wearing hearing protection (a must for explosions), but from family member accounts, the ensuing explosion was frighteningly loud.  The shell casing was completely blown to pieces, with brass shrapnel flying through the cardboard box and also embedding itself a centimeter into a nearby block of wood.  I was quite impressed by the detonation-it was much more powerful than I had expected.

If you read the preceding two paragraphs, please don't do anything stupid.  While exploding bridgewire detonators are incredibly safe (as they contain no primary explosives), shrapnel is much more dangerous than a simple fireball.  If you repeat this experiment, make sure you will be protected from potential shrapnel.

Laser Cutter Update: Great Improvements and Laser Art

A while ago, my church did a silent auction to raise money for students going to a youth conference.  I wanted to donate some laser art, so I found neat designs online and used Inkscape's "Trace Bitmap" and "Object to Path" tools to create a path from an image.  Then, I used a laser engraver plugin to transform the path into g-code for my laser cutter.  I tried cutting the design from black paper, but it didn't work!  My laser cutter (PiKnife) messed up the movements and cut things out in wrong places, making the entire cutout worthless.  I was quite disappointed, so I tried to figure out what the problem was.

One problem PiKnife had a lot was that the stepper motors would sometimes stick and jitter.  Eventually, I noticed that pressing on the input and output wires plugged into the ribbon cable going to the Raspberry Pi would cause this problem, so I deduced that the issue must stem from bad connections.  To fix the connections, I wrote down where everything was in the ribbon cable and then used male-to-female breadboard jumpers to wire each input and output directly into the Pi's GPIO header.  This eliminated the uncertainty of plugging wires directly into a ribbon cable.

Amazingly, that fixed the problem entirely!  I set a new piece of paper on the laser cutter, pressed enter to begin the program, and didn't have an issue again!  While it took five and a half hours to complete the design, it showed the true capability of PiKnife.  It can cut extremely complex shapes for a long duration without problems.
With mere hours to spare, I completed the laser art and entered it in the silent auction.  I also made a sped-up video (above) of the laser cutter working, which turned out well.  Perhaps now that PiKnife really works it is time to expand into the CO2 laser range...

Experiment 51: Electric Resistance Furnace

Electric resistance furnaces differ from electric arc furnaces (like the one I made in Experiment 32) in that they use resistive heating (like a toaster) instead of giant lightning bolts to melt metal.  I had a hotplate that died (because a container holding hot sodium hydroxide solution broke on it), so I decided to use its heating elements to make a small furnace.

First, I played with the resistance wire to see what sort of current made it glow.  I found that 12 volts made a 7" piece glow red hot.  However, it didn't melt the wire, which was good.  I calculated the current using Ohm's law and determined how much wire I would need to use to get the same current at 120 volts.  Actually, the math is pretty simple--I needed to use ten times as much, or 70".

I used a hollowed-out low density soft alumina-silica firebrick as the furnace body.  It had seen previous service as an arc furnace, so it was fairly beat up and I didn't care if it broke.  I also used another piece of firebrick as an insulating lid.  Fitting 70" of resistance wire in a 2" diameter hole was difficult, but coiling the wire seemed to work well.  For connecting the mains electricity to the ends of the wire, I made clamps using small nuts and bolts that sandwhiched the wire snugly.

My crucible was a cut-off soup can bottom, and my metal of choice was aluminum.  Plugging the furnace into the outlet made the heating elements glow, but the really neat thing about this furnace was that it was silent.  I even read a book while I waited for my metal to melt!  An hour later, I checked on the melt, and the aluminum was undoubtedly molten!  I wanted to grow aluminum crystals inside a blob, so I tried pouring the molten aluminum onto some glass to insulate it better.  That was a rather bad idea, because the glass exploded, and molten aluminum was dispersed about the room.  Oops!

Even though the crystal growing didn't work out, I was quite impressed that aluminum could be melted silently with just some electricity!  Of all the metal-melting methods I have tried (there are at least 14 of them), this is one of the quietest.

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):

Experiment 47: Metal Polishing with Toothpaste

Recently, I cast a fancy flower-shaped dinner plate out of aluminum.  I had to redo the casting twice to get something I was satisfied with, but eventually I got a good replica of the glass plate I used as a pattern.  Fancy plates are usually shiny, though, and my plate still had the rough texture of the casting sand.  To fix this, I sanded it with 80 grit sandpaper for a while and then sanded with progressively finer grits until I reached 1500 grit.  Each finer grit sandpaper removes the scratches left by the previous one until the scratches are too small to see.  The plate still wasn't very shiny at 1500 grit, but I didn't have any polishing compound, so I looked online for an alternative.

Toothpaste is used for brushing teeth, and it works for this because it has extremely fine abrasives in it that polish your teeth.  I squirted a bit of toothpaste onto my plate and then used a cloth rag to rub it around.  I scrubbed until the toothpaste became grey with aluminum and then washed it off.  I repeated this process for about two hours.

Finally, at the end of the laborious process of sanding and polishing, I cleaned the plate off with a toothbrush and soap to remove the minty fresh smell.  After drying the plate, I was stunned to see that it was really and truly shiny!  I hadn't expected a lot from the toothpaste, but it did a dazzling job of shining up the cast plate.  I was quite pleased with the end result of the casting, sanding, and polishing.