It all started 1400 years ago with a legend. For months there has been a storm with torrential rainfall in the city of Liu Yang (Hunan region, China). People suffered from hunger and disease. To put an end to the misery, the monk Li Tian used bamboo pipes filled with saltpetre, charcoal and sulphur to drive out evil spirits and the dreadful thunderstorms. The first firecracker was developed. There is no scientific evidence as to whether this myth actually occurred, but to this day the monk is revered in the area. Today, we want to talk about the probably simplest form of a firework: The sparkler.
It usually consists of a long steel wire coated with an ignitable paste composed of metal powder, an oxidizer and a binder. While the grain size of the powder is crucial for the characteristic sparkling, barium nitrate is usually used as an oxidizing agent to provide the oxygen that is necessary for the reaction. When the sparkler is ignited, the metallic component produces small glowing sparks that are fired in all directions. Depending on the metal powder used, these sparks light up in different colours and can reach temperatures of up to 2000 °C. That means the sparks are extremely hot.
But why not burn yourself if you get hit by a spark? The reason is the difference between temperature and heat. Every object has a so-called thermal energy which depends on its temperature, its mass and the specific heat capacity, i.e. the type of material. The larger the mass of a body, the higher its thermal energy. The heat capacity indicates how well a material can store heat. The sparks of a sparkler have a very small mass. As a result, their thermal energy is relatively low. The tiny sparks cannot store the heat for a long time and cool down on the skin so quickly that they cannot cause severe damage. A sparkler is not dangerous when used safely. So nothing gets in the way of a sparkling Christmas eve.
About the author
Anna Ritscher studied chemistry in Vienna and completed her PhD in Berlin, focusing on solid state chemistry. Currently, she is working at Biotop, of which she is a co-founder, developing modular lab spaces and citizen science projects.