How many times we happened to turn on a candle or fire in the fireplace with a match? Although today they are replaced by the most modern lighters, the matches remain the fascinating objects present in our homes. Behind the simple gesture of turning them on, there is an interesting chemical and physical process which makes the match almost a magical tool. The match, introduced by the English chemist John Walker in 1827, is nothing more than a small wooden or paper stick rolled with a particular head, the most important part. This in fact contains chemicals which, thanks to thefrictionactivate and trigger a reaction it produces heat And finally, one flame. When we crawl the head against the rough surface of the abrasive strip on the box, the heat that is generated starts a combustion reaction between the substances that make up the match and the oxygen present in the air: red phosphorus, Potassium chlorate And antimony sulphideperfectly calibrated in the right proportions, they are the protagonists of this daily magic of chemistry.
The chemistry of the matches
A traditional match puts together More chemical componentseach with a precise function, to obtain, after rubbing Of the matte head on a rough surface, a sufficiently stable and long -lasting flame (we are talking about a few seconds anyway) to be able to turn on stove, candles or what we want. The substances present in the matches are mixed in the right proportions and are almost all found in the head. They include:
- a fuel, like the antimony sulphide that, as if it were petrol or diesel, burns reacting with oxygen and freeing heat;
- a oxidant, Usually chlorate potassium, capable of oxidizing, providing oxygen, another chemical compound such as the antimony sulphide helping it to burn;
- a compound like ammonium phosphate which prevents the match smokes too much after ignition;
- paraffin wax, to direct the flame along the body of the match;
- pigment or dyes;
- glue, which holds together the various parts of the head and the abrasive strip.
To this chemical mixture, the two components of the Abrasive strip on which we crawl the match, also essential for the lighting of traditional matches:
- glass powder: to increase friction and clutch in rubbing;
- red phosphorus: In the clutch it turns into white phosphorus, a more unstable form that reacts with the oxygen of the air.
The phases of the ignition
The steps really fundamental To obtain a long -lasting flame to start a larger combustion are three:
- aabrasive action that triggers the flame: in this passage the kinetic energy of rubbing turns into thermal energy, that is heat.
- sufficient heat to support and feed the flame;
- The right proportion of substances that burn without giving toxic fumes o too vigorous or weak flames;
Specifically: the heat produced during the clutch transforms red phosphorus into white phosphorus, which, being very volatile, reacts with the oxygen present in the air. The heat decomposes the chlorate potassium, which in turn provides the necessary oxygen for the ignition of the fuelthe antimony sulfide, leading to the formation of a stable flame and burning the wood of the match.
As the antimony sulphide oxidizes, sulfur oxides are formed, which give the characteristic smell of burned matches, until the fuel is exhausted. The smoking formed by combustion is not a gas, but a colloida system consisting of gas and small particles not burned deriving from incomplete combustion, which, dispersed in the air, form the smoke we see.
Phosphorus and safety
This complex phosphoric -based ignition mechanism it has not always been so sure. Originally the white phosphorusextremely reactive but also a lot toxiccapable of causing serious damage to health, especially for those who worked in the production of matches. To make their use safer, a chemically variant went down to red phosphorus more stable and less dangerousthen became the standard in modern manufacture.
The distinction between white and red phosphorus also led to a differentiation in the types of matches. In the first Capocchia matchesphosphorus is already present on the head of the stick: they were easier to turn onbecause they only light up by rubbing the head on any rough surface, but also less sure. Today there are the so -called safety matchesin which red phosphorus is not found in the head but, as we have seen, in the abrasive strip of the box, making it Impossible accidental ignition. This evolution not only has improved daily security, But he also made the matches a more reliable and regulated product, without losing its “old -fashioned” charm.
