Piezo Explosive Popper
Kids love things that go boom. Throw in some flames and you’ve got one of the most popular experiments in Reeko’s Mad Scientist Lab. The piezo popper, also known as the film cannon, binaca bomb, or photo flash, lets us release energy from a rapidly combusting fuel-air mixture and use that expanding air to blow the top off a film canister. The force of the mini-explosion will be so great that we’ll be able to propel the canister over 3 stories in the air!
- Take apart the fireplace lighter and look for the “igniter” part. The igniter is the “clicker” mechanism and will have a button that is pressable and two metal connection points. The clicker button will be used to trigger the explosion.
- Take two pieces of equal length wire, about 10 inches in length, and solder the wires to the two connection points on the igniter. Solder one wire to each of the connection points.
- Cut a small slit in the film canister lid and run the two wires through the slit in the lid. Bend the wires so they are only 1/8 inch apart. A spark jumping between the wires will be the ignition source for our explosion.
- Spray the inside of the film canister with two squirts of breath spray. Binaca mouth freshener works best because it has both alcohol and isobutane. Hair spray also works very well as it contains alcohol, butane, isobutane, and propane that are used as propellants in the hair spray container. These substances, primarily the alcohol, will be ignited causing a rapid release of energy and heat which will propel the lid off the canister.
- Quickly put the lid back on the film container. You must put the lid on quickly before the alcohol evaporates.
- Aim the canister away from you and press the igniter button. The igniter will spark, igniting the alcohol and butane in the spray gas, to create a rapid expansion of air which will blow the lid off the canister.
The entire process is fairly simple. An igniter creates an explosion which blows the lid off the film case. The details of the entire process are intricate though and first we must understand piezoelectricity.
Fireplace lighters, BBQ grill lighters, push button cigarette lighters, piezoelectric tweeters in stereo speakers, phonograph needles (ask Dad about these), quartz crystals used in digital clocks, and even some biological materials such as bone DNA and some proteins, use something called piezoelectricity to create a electric voltage. Some crystalline materials (like quartz, Rochelle salt and certain ceramics) exhibit piezoelectric behavior. When pressure is applied to these substances, a charge separation within the crystal and a voltage across the crystal is produced that is sometimes extremely high. Strangely, piezoelectric materials work in the opposite way too, producing a very odd effect. If a charge is applied across a piezoelectric crystal, the crystal will change shape. This change in shape is small but near instantaneous. Given this odd effect, piezoelectric materials can be used in very small speakers, such as a beeper used in a digital alarm clock, to vibrate rapidly creating sound waves.
The igniter in our experiment is what we call a piezoelectric generator. Piezoelectric substances are materials that generate electricity when pressure is applied to the substance. The piezoelectric material in a fireplace lighter is a man-made ceramic material that is created by placing the ceramic material under a high voltage electric field. This forced electric field aligns the charges in the material giving the material its piezoelectric properties.
A fireplace lighter has a “hammer” that strikes the piezoelectric material causing it to release a quick, burst charge. This charge arcs across the two wires causing a spark which ignites the alcohol/propane/butane mixture causing a flash point explosion inside the film case. As with any fuel-air explosion, tremendous amounts of heat are generated. As the fuel-air mixture burns, energy is released which heats up the gasses that result from the burning fuel. The gases that are heated up are water vapor (H2O) and carbon dioxide (CO2). These heated gases expand at a very rapid rate which pushes on all sides of the canister. The lid being the weakest contact on the canister, will blow off the film can and fly through the air with a loud bang (and quick burst of flames).