Pyrotechnics Concepts

• Pyrotechnics is the science of utilizing a self sustaining exothermic reactions in order to produce heat, light, sound, smoke or any combination of the former
• It is mainly utilized in the entertainment industry, but items in the military, industry, and NASA have used it, for example in matches, candles, explosive bolts and fasteners, airbags, and mining, quarrying, etc
• The field that specializes in the use of explosions, flashes, smoke, flames etc. in front of an audience is called proximate pyrotechnics

Components of High Energy Mixtures

• Four Parts: Oxidizers, fuels, binders, and retardants

• Oxidizers

• Oxygen rich ionic compounds that release oxygen when reacted, which is then used to reduction with the fuel.
• Common anions are nitrate, chlorate, perchlorate, chromate, oxide, and dichromate ions
• Examples include potassium nitrate (saltpeter), one of the oldest oxidizers, potassium chlorate, one of the best and controversial oxidizer due to its intense reactivity, and potassium perchlorate, which is one of the most common oxidizer due to its relative safetiness compared to potassium chlorate, etc.

• Fuels

• Acts as an electron donor and reacts with the oxygen provided from the oxidizer to produce an oxidized product and heat
• Heat is then used for a make a variety of effects, such as color, motion, smoke, or sound
• Fuels can be categorized into 3 main groups: metals, non-metallic elements, and organic compounds
• Metals

• Good metal fuels are ones that resist air oxidation and moisture, has a high heat output and can be easily oxidized
• Aluminum and magnesium are most common, along with titanium, zirconium, and tungsten being common in the military

• Nonmetals

• Same as metals, needs to be able to resist air and moisture, high heat output, and readily oxidized
• Sulfur, boron, silicon, and phosphorus are good elements

• Organic

• Along with producing heat, organic compounds can also release a ton of gas by producing carbon dioxide and water vapor
• This comes from the redox reaction between the carbon and the oxygen, with the carbon oxidizing and the oxygen undergoing reduction in order to form carbon dioxide, which is why hydrocarbons, carbohydrates, etc combust

• Binders

• Organic polymers that hold the components together in a homogenous blend
• Composition can separates since the different compounds and elements can be varying particle sizes and densities, which means that a binder is used to keep everything together as one composition.
• Since its an organic compound, it can double as the fuel of the blend
• Dextrin is a commonly used binder in the firework industry

• Retardants

• Retardants are used in order to slow down a reaction without affecting the overall performance
• Retardants can be compounds that decompose with the absorption of heat, aka endothermic decomposition, or inert diluents such as clay and diatomaceous earth, which can absorb heat and separate reactants.

• DEMO: Gunpowder

• Gunpowder is made up of 75% potassium nitrate, 15% charcoal, and 10% sulfur
• The potassium nitrate acts as the oxidizer, releasing oxygen for the reaction when decomposed
• Charcoal acts as a fuel and a source of carbon
• Sulfur acts as a fuel and is used to lower the ignition temperature since it undergoes an exothermic reaction
• Redox reaction, carbon and sulfur undergo oxidation and the oxygen from potassium nitrate gets reduced

• Burning Behavior

• There are 2 overarching factors that come in mind when talking about burning behavior: homogeneity and confinement

• Particle size and surface area play hand in hand for homogeneity, since by decreasing particle size, there is an increase in contact between the fuel and oxidizers and in surface area, which allows for greater efficiency for the reaction rate between oxidizers and fuels
• Confinement plays another role since the degree of confinement affects temperature of the reaction. When the composition is restrained in a tighter confinement, the increase in temperature creates an exponential increase in reaction rate due to the lack of energy being lost to the surrounding environment. Furthermore, the buildup of pressure due to gases being released from the reaction can lead to an increase in reaction rate, since its compresses the reactants together for a greater collision rate.

• Color and Light Production

• Color

• When certain elements and compounds are heated up, they emit spectral lines in the visible region, and each element is able to produce its own unique color. The color producing elements also follow a specific temperature range; high enough to in order to energize the electrons into an excited state, which produces the color, but low enough to prevent dissociation. The heat is of course provided from the redox reaction in the high energy composition.

• Smoke and Sound

• Smoke

• Colored smoke mixtures are created when the colored dyes are evaporated and ejected into the air upon ignition of the composition, which then condenses and forms a smoke of the dye particles.

• Sound

• 2 types of sounds: Loud explosive noise or whistling sound
• Loud explosive noises:

• Created from igniting an explosive mixture under confinement in a tube
• Potassium chlorate and Potassium perchlorate are commonly used as oxidizers for compositions called “flash and sound” mixtures, since they produce a flash of light and a loud bang

• Whistles

• Whistle mixes are created from tightly compacting a fuel-oxidizer mixture into a tube along with an air pocket above it.
• When the composition burns at a certain pulsating frequency, the surface pulsates, creating pulses of sound waves and the tube provides resonance.

Works cited:

http://www.newworldencyclopedia.org/entry/Pyrotechnics

http://explodder.info/book/piro/Conkling_Chemistry%20of%20pyrotechnics.pdf

http://pyrotechnicmagazine.com/?p=1281

http://www.compoundchem.com/2014/07/02/the-chemistry-of-gunpowder/

Images

https://en.wikipedia.org/wiki/Pyrotechnics#/media/File:Pyrotechnics.jpg

http://www.wisegeek.com/what-is-gunpowder.htm#

https://commons.wikimedia.org/wiki/File:ThermiteFe2O3.JPG

http://pyrodata.com/definitions/Binder

https://commons.wikimedia.org/wiki/File:Et_baal.jpg

...