MicroCT of a Sparkler
Image of the Month: Sparkler
Since this Saturday marks the 4th of July, we wanted to join in the celebration. As most people go to see a fireworks show during this time of the year, we decided to have our own celebration a little early. Our warmup to the holiday involved scanning a sparkler. With a burning interest to learn more, a little research, and microCT scanning we bring to light the microstructure of a sparkler.
A Brief History
You light the sparkler and watch the snowball shaped sparks scatter, exciting children and providing a radiant light display. Something so simple such as fire and light still fascinates humans after thousands of years. Though the Chinese are credited for first inventing gun powder and fireworks around 2,000 years ago, it was actually the Germans (though debated) that made the first recorded sparkler. Known as wunderkerzen (quite literal translation of sparkler), they were developed in the 1850’s by using iron and gunpowder paste that was coated over wire3.
Since that time the chemical makeup has changed slightly to produce the sparkler we know today. All sparklers are similar and their chemical composition comprises of a fuel, oxidizer, metal powder and a binder. The fuel is usually charcoal and sulfur, the oxidizer is a chemical such as potassium nitrate or barium nitrate, the metal powder can be iron, steel, zinc, etc., and the binder is usually a slurry of starch and water. There are various compositions available but to explain the process we are sticking to the barium nitrate and iron mixture.
What Causes the Spark?
The process of a sparkler is a chain of chemical reactions that progressively get hotter until the metal powder is hot enough to ignite and spark. Let’s take for instance the one kind of sparkler. The fuel, say charcoal and sulfur and oxidizer such as barium nitrate are mixed to a certain proportion such that the sparkler will burn slowly and not just explode in your hand. What happens is the charcoal, sulfur, and barium nitrate mixture will light first. In particular, the barium nitrate will heat to high enough temperatures to ignite the metal powder, such as iron. This gives a sparkler its name for the usual orange and white sparks. All this is awesome but none of this would happen without something to hold the constituents together. The binder of starch and water keeps everything tidy and ready for your sparkling display. If desired, other chemicals can be added to the mixture for the addition of color, similar to fireworks1, 2.
Scanning the Spark
Using microCT imaging, the chemical composition comes to light, even before the sparkler is burned. The first image (Figure 1) shows the sparkler tip before it is burned. Notice the bright specs throughout sparkler. Our hypothesis was that is the metal powder distributed in the matrix of the fuel, oxidizer, and binder. Since the goal of a sparkler is to get the temperature high enough to ignite the metal, these should in theory burst out and cause the sparks. To test the hypothesis we did what a scientist would do, burn it and see what happens.
Figure 1. Image of sparkler before burning
After burning and scanning the results were quite impressive (Figure 2). All the same scan settings were used as the unburned sparkler to ensure an adequate comparison. The results supported our hypothesis as the white specs had burned up in the process leaving nothing but the charred fuel and binder with various cavities. These likely being where the metal powder had exploded out of the sparkler.
Figure 2. Image of sparkler after burning
We hope you enjoyed our celebration of a sparkler and we wish you great 4th of July. As always, be safe with any fireworks or sparklers and make sure to follow all handling instructions.
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1. Brain, Marshall. (2000, June 30). How Fireworks Work. HowStuffWorks.com. Retrieved from http://science.howstuffworks.com/innovation/everyday-innovations/fireworks.htm.
2. How Does a Sparkler Work? (2009, December 23). Audio blog post. BASF. Canada. Retrieved from http://www.basf.ca/group/corporate/ca/en/news-and-media-relations/podcasts/chemical-reporter/sparkler.
3. Karen. (2014, June 30). Bits and Tidbits about Sparklers. CountyFairs USA. Retrieved from https://www.countyfairsusa.net/bits-tidbits-sparklers/.