Exploring the Phenomena of Sparking and Crackling in Relit Candles
Introduction to Candle Relighting
When you attempt to relight a candle, you might notice an unusual occurrence: the wick begins to spark and make a crackling noise. This intriguing phenomenon can be attributed to several factors involving the wick, its material, and the conditions under which the candle was originally burned. Let's dive into the scientific details behind this interesting observation.
Residual Carbon
After a candle has been burnt, the wick is primarily composed of carbon, which can be in a form that has not been fully combusted. When you reheat this carbon with the flame from a lighter, the sudden ignition of these carbon particles can result in small sparks and crackling sounds. This process is a classic example of incomplete combustion, where the residual carbon does not burn completely until it reaches a certain temperature.
Moisture and Thermal Expansion
The wick can absorb moisture, which can be present in the air or carried in from where the candle was stored. When you heat the wick, the moisture rapidly vaporizes, leading to small explosions or popping sounds as steam escapes. This rapid evaporation can also cause the wick and any residual materials to expand quickly, contributing to the crackling noise. The sudden expansion of heated materials can create vibrations that manifest as sound.
Combustion of Residual Wax
If there is any leftover wax on the wick, it can ignite when exposed to the flame, adding to the crackling and sparking sounds as it burns. This wax combustion is part of the larger chemical reaction that occurs during the burning process. The interplay between the wick material and the residual wax can significantly influence the way the candle behaves when relit.
Flashback and Glass Explosions
A further phenomenon that can occur when relighting a candle is a flashback. This happens when the flame is hotter in the center of the candle, and the wax pool becomes cooler as it spreads to the edge. This temperature gradient allows the hot, splattering of water/wax and fire combination to reach out towards the glass container. This can cause the candle to break or "explode." The primary cause of black smoke is an overly long wick. When a candle burns, the wax near the flame melts and the liquid wax is pulled up the wick to feed the flame. If the wick is too long, the chemical reaction is thrown off, producing excess soot and smoke.
Wick Material and Contaminants
When lighting the wick of a candle, the wax has not yet melted from the heat of the flame, so there is no fuel to burn at that moment. However, the only thing left to burn is the wick itself. Depending on the wick material, contaminants left behind from snuffing out the flame, inefficient burn soot, and other factors can cause the wick to sputter and spark. Once the wax has melted and begins to wick upwards and evaporate to burn, the candle reaches a steady state burn and will no longer sputter. However, if there are impurities in the wax, the candle can continue to sputter.
Conclusion
The complex interplay of factors behind the sparking and crackling sounds during candle relighting is a fascinating area of study in the field of combustion science. Understanding these phenomena can help us better appreciate the chemistry behind our daily activities and use candles more effectively.