The science behind the 4th of July...
HOW FIREWORKS LIGHT UP THE SKY
Here are some interesting facts about fireworks you can impress your family and friends with as you watch the show.
Fireworks manufacturing
Manufactures all have their own recipes for creating their fireworks; but the basic chemistry behind is the same for any fireworks.
Manufacturers start by combining a mixture of metals and oxidizers such as chlorates, perchlorates, or nitrates. The type of metals used influences the fireworks colours while the oxidizers provide the oxygen needed to achieve the required temperature for the reaction. Water is also added to the mixture to bind the metals and oxidizers together. This damp mixture is then cut into smaller pieces known as “stars”.
The manufacturers then fill a fireworks shell with “stars” and black powder, a mixture of potassium nitrate, charcoal, and sulfur. A time-delay fuse is also inserted into the shell which ignites the black powder and stars causing the shell to burst open.
Firework colours
There are 5 basic colours for fireworks, and each colour is produced by a different metal:
Red—strontium
Green—barium
Yellow—sodium
Blue—copper
White—aluminum, magnesium, or titanium
Dr. Paul Worsey teaches commercial pyrotechnics operations at the University of Misouri-Rolla in the United States said in an issue of JOM that the art of fireworks lies in getting the right temperature for the reaction to occur.
“Some colours are pretty easy, and those colours would be red and green,” says Worsey, “but you can tell how good a firework manufacturer is by the quality of their blues.” Blue is such a difficult colour to produce because the reaction temperature has to be perfect.
In the same issue of JOM, Phil Grucci executive VP of the New York based fireworks manufacturing company Fireworks by Grucci explained that too much or too rich of an oxidizer that’s combined with the copper causes the mixture to burn at temperatures that are too high—causing a washed out powder blue colour. But burning the mixtures at temperatures that are too low may result in an orange-red colour, rather than blue—or the mixture may even fail to ignite.
Aside from the basic fireworks colours, other colours can be made by mixing the elements that create the primary colours. For example, purple explosions are created when a copper oxidizer (used to make blue fireworks) is combined with a certain amount of strontium (used to make red fireworks). Pastel explosions can be made by adding white-light generating elements such as aluminium, magnesium or titanium to the firework’s composition.
Fireworks effects
The metal used influences not just the colour but also the look of a firework. For example,
a “salute” firework is a quick burst of light with a loud sound and contains finely ground metal powders. The fine powder explodes in a burst of light and burns out quickly. The silver colour of a “salute” is made by combining an oxidizer and aluminum powder. Titanium is also added to the firework mixture to produce a sparkling effect.
In comparison, a waterfall (or willow) firework explodes in the air and leaves a trail of colour then as it slowly falls to the ground. This type of longer lasting firework uses charcoal and flakes of metal because they burn at a slower rate.
Fireworks shapes
Some fireworks create familiar shapes like as rings, stars, and hearts as they explode. The trick behind these fireworks is the plastic mold that’s placed inside the fireworks shell. The “star” is arranged inside the shell using a plastic mold of the same shape as the fireworks explosion (e.g. ring, star, heart). When the fireworks explode, the “star” will break out of the mold and form the desired shape.