The Chemistry of fireworks is a very interesting field. A look at an amusement park or a baseball game, or such events such as New Year's Eve or Christmas Eve are just a few ways to show how much fun that comes our way from fireworks. This however is an intricate science requiring application of physical science. For instance, to produce a red chrysanthemum spray and an accompanying explosion requires certain components and materials such as an oxygen producer, color ejector, binder, fuel and propellants. There are three conspicuous and identifiable forms of energy produced by fireworks. These are heat, light and sound. The loud sound experienced in such events is attributed to the rapid release of energy into the atmosphere; hence the air expands at a greater rate than the speed at which sound travels. Therefore, a sonic boom which is a shock wave is produced.
The chemistry behind fireworks is a series of oxidation and reduction reactions which result in the desired sound and light. This happens as propellants push the firework into the sky. Oxidation reactions ensure that the oxygen needed to exhaustively burn the mixture of reducing agents and excite the atoms in the light-emitting compounds is produced. Oxidizers used such as chlorates, nitrates and percolates and reducing agents such as carbon and sulfur are available of the shelf for home-made users. The combination of reducing agents with oxygen is there responsible for the energy dissipated during the reaction. Black powder, which mainly contains nitrates, is the most used oxidizer. A look at an explosion under the use of potassium nitrate so as to provide nitrate ions (NO3-) after decomposition can be represented as:
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decomposition of potassium nitrate
Potassium nitrate potassium oxide + nitrogen gas + oxygen gas.
The reaction is more controlled since when reacting, nitrates only release two in every three oxygen atoms, hence, the reaction is not exhaustive and vigorous since not all the oxygen atoms are actively used up. However, nitrates do not provide enough power to propel the firework into the sky and also ignite the package. Therefore, they cannot be used in star explosions since they cannot produce temperatures high enough to energize most color metal salts.
Star reactions need a temperature ranging from 1700 to 2000°C. This was enabled by the Italians in the 1830's whereby trhey came across more explosive oxidizers, chlorates (ClO3-), which give up all their committed oxygen atoms upon reaction. This can be illustrated by the equation below which is highly spectacular, vigorous and releases more energy.
reaction of chlorates
Potassium chlorate potassium chloride + oxygen gas.
However, chlorates have the major demerit of being highly unstable, hence they can be dangerous to handle. On the merit side, chlorate can be easily ignited. For instance, dropping them on the ground can lead to a major explosion. This is since chlorates have the maximum potential of bonding with four oxygen atoms but they however bond with three. The fourth oxygen atom is left free, unsaturated and reactive. This makes chlorates better oxidizing agents. Further, in comparison to the slow-burning rate previously availed by nitrates, chlorates provide a faster reaction leading to a loud and exceedingly dangerous explosion. This was solved by the use of perchlorates which are more stable when releasing oxygen. The oxygen atoms in perchlorates are fully bonded hence stable. When reacting, perchlorates are able to release all their oxygen atoms.
reaction of perchlorates
So, perchlorates are not only more stable, but more oxygen-rich than chlorates. They, like chlorates, produce more vigorous reactions which produce hot, rapidly expanding oxygen atoms than nitrates in their star compartments.
Carbon and sulfur in charcoal are the most common reducing agents. They are contained in black powder and react to produce carbon dioxide and sulfur dioxide respectively.
Combustion of sulfur and carbon
The magnanimous amount of energy released in these reactions and the hot rapidly expanding oxygen gas provide a basis for propulsion and consequent explosion.
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The chemistry of fireworks, so as to come up with a varying degree of colors has generated a lot of interest. Color is generated through two mainstream ways: Incandescence and luminescence. Incandescence entails the production of light by means of heat. When a substance glows as a result of heat, it first emits infrared wavelengths, then red light. Orange light is then produced as the object becomes progressively hotter, followed by yellow and finally white light. Under a controlled environment, the glow of reducing agents such as charcoal can be regulated at a certain temperature, hence emitting a particular color at the desired time. Temperature regulators that are most common are magnesium, aluminum and titanium. Luminescence is the production of light through other means other than heat. These can therefore occur at colder temperatures lower than room temperature since it is independent of any heat. An electron in an atom is first excited and destabilized by absorption of energy. The atom is then relegated to a lower energy state hence releasing the energy within via photons, the basics of light. The energy possessed by these photons consequently determines its wavelength or color. A major challenge in producing color through luminescence is that some salts used are unstable at room temperatures such as Barium chloride. Therefore, this problem must be solved by use of a combination of these salts with more stable compounds such as chlorinated rubber. For instance, in the combustion of the pyrotechnic composition between barium chloride and chlorinated rubber, a green color is produced. Other salts such as copper chloride which gives a blue color must be regulated not to attain high temperatures yet the brightness of the resultant blue color must be achieved.
The quality of the resultant color produced by various factors can be compromised by various factors. First, pure colors require pure ingredients. No traces of impurities such as the dominant impurity, sodium, which gives a yellow-orange color, should be present since it easily overpowers all other colors. Secondly, the cost of the firework when the client is buying off the shelf often alludes to quality. Finally, it is important to note the date of manufacture and the skill and popularity attached to the manufacturer by other users.
strontium salts, lithium salts
lithium carbonate, Li2CO3
strontium carbonate, SrCO3 = bright red
calcium chloride, CaCl2
calcium sulfate, CaSO4·xH2O, where x = 0,2,3,5
incandescence of iron (with carbon), charcoal, or lampblack
sodium nitrate, NaNO3
white-hot metal, such as magnesium or aluminum
barium oxide, BaO
barium compounds + chlorine producer
barium chloride, BaCl+ = bright green
copper compounds + chlorine producer
copper acetoarsenite (Paris Green), Cu3As2O3Cu(C2H3O2)2 = blue
copper (I) chloride, CuCl = turquoise blue
mixture of strontium (red) and copper (blue) compounds
burning aluminum, titanium, or magnesium powder or flakes
How fireworks work.
It is crucial to evaluate how both sparklers, which ensure production of bright light, and firecrackers, which enable the production of explosions, function. Firecrackers consist of black powder, commonly referred to as black powder in a tight paper tube with a fuse at one end so as to light the powder. Black powder contains sulfur, charcoal and potassium nitrate. Further, some explosions are brightened the more by use of aluminum. On the other hand, sparklers are used to produce exceptionally bright and showery light for a longer period of time that can last up to a minute. There are commonly referred to as 'snowball sparklers' since they are accompanied by a ball of sparks surrounding the burning epicenter.
A sparkler constitutes various compounds. Key among them is oxidizers, fuel, binder such as starch or sugar and iron or steel powder. They are mixed in water to form slurry which is then coated on a wire through dipping. This is then dried. It is then ready for use whereby it can be lit in order to burn end to end like a cigarette. In sparklers, oxidizers and fuel are carefully proportioned with other compounds so as it burns slowly rather than explode as is the case with firecrackers.
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Fireworks however are more complex in their manufacture. Bright shimmering sparks have to be induced by adding steel or iron, aluminum, magnesium and zinc. These metal flaks heat up to attain high temperatures that ensure production of light by incandescence beyond which they burn exhaustively. To create a wide range of colors, various chemical addictives are used.
These are large, conspicuous and colorful fireworks that can be observed on major celebrations such as the Fourth of July. The aerial firework shell contains: stars which are small cylinders, cubes or spheres that contain the compounds needed; container which has the pasted paper for instructions and things such as company name and an accompanying string; the bursting charge located at the center of the shell; and a fuse which ensures delay in time till the firecracker attains the right altitude. A lifting charge is located below the shell. A mortar is used to launch an aerial firecracker. This is a small, steel pipe containing black powder that serves as the lifting charge. When this is fired, the shell fuse is lit which burns progressively up to the desired height, then explodes. A simple shell, such as those used in an aerial display, contains stars in the blue balls, and a grey part containing black powder and the center tube containing the bursting charge. Multi-break shells burst over two or three phases. They have a variety of colors and compositions so as to contain various degrees of light and sparks. Multi-break shells have various compartments or sections in one with different fuses. Each shell bursts and consequently ignites the other through break charges, each with a different effect and possible color.
The pattern painted in the sky by an aerial shell chiefly depends on the order and arrangement of star pellets in the shell. For instance, equally spaced pellets in a circle with the accompanying black powder produce a mid-air display of minor star explosions uniformly spaced in a circle. A specific figure can therefore be created by arranging the star pellets in the outline of the figure desired. Place explosive charges in the interior of the figure so as to blow them outside into a large figure as desired. Then, surround this with a layer of break charge so as to separate them with the rest of the shell contents. This break charges must be set to explode at the desired time.
There are several shell names in the market:
Contains large comets, or charges in the shape of a solid cylinder, that travel outward, explode and then curve downward like the limbs of a palm tree
Explodes in a spherical shape, usually of colored stars
Explodes to produce a symmetrical ring of stars
Contains stars (high charcoal composition makes them long-burning) that fall in the shape of willow branches and may even stay visible until they hit the ground
Bursts into a circle of maroon shells that explode in sequence
Bursts into a spherical pattern of stars that leave a visible trail, with an effect somewhat suggestive of the flower
Like a chrysanthemum shell, but has a core that is a different color from the outer stars
Makes a loud bang
Bursts to send small tubes of incendiaries skittering outward in random paths, which may culminate in exploding stars
Fireworks are used in most of today's' public celebrations. However, they are dangerous if mishandled. Over 8000 United States are reported to suffer every year due to fireworks. Of whom more than half are children. The most common hazard experienced by more than a third of the cases is burns which have been reported to occur from illegally acquired fireworks. Hence, there are a number of regulations that have been put in place to ensure mishandling reduces. The statute organization chiefly responsible for consumer fireworks is the National Council on Fireworks Safety. It educates the public on how to responsibly handle and use fireworks.
The National Fire Protection Association is responsible for enforcing rigorous safety regulations for big fireworks displays. Spectators are required to watch at least 840 feet from the launching zone based on the height and burst diameter of the largest of shells. Secondly, shells cannot be launched if the winds at that particular time are stronger than 20 miles per hour, since they would be carried away over the set diameter thereby causing harm to onlookers. However, despite all these regulations that have been put in place, many accidents still do occur at informal and poorly regulated places.
Manufacturers are also required by law to set up buildings in the manufacturing plants that are separated by concrete blast walls from any other buildings with roofs weakened so as any resultant explosion travels upwards instead of outwards. Further, mechanization in the industry is limited and work is mainly done by hand since machines may produce sparks or static charges that would be disastrous in causing explosions. However, some disasters have occurred between 1970 and 1995 resulting in the death of more than 20 factory employees
Environmentally Friendly Fireworks
Most animals are scared by the explosions resulting from displays. Most regulations and rules bar people from attending such events with their pets in tow. Sadly, cases of pets getting lost at such events have been reported. Wide research is continuing on hoe to combine various elements into pyrotechnic compounds and mixtures have been made. This produces minimal smoke and particulate matter. This shall replace oxidizers such as perchlorates which are environmentally harmful.