La chimie - tout est dans le mélange!

unfall bei chemie-experiment, verrußte kidsPyrotechnic mixtures almost always function according to the principle of a REDOX reaction. Simply put, one substance releases oxygen, i.e. is reduced, while another substance takes up oxygen, i.e. is oxidised. However, since a pyrotechnic mixture rarely consists of only two components, the reactions that take place in it are quite complicated.

Take normal black powder as an example, a mixture of 75% potassium nitrate, 15% sulphur and 10% charcoal powder. Potassium nitrate (chemical formula: KN03) is a compound of potassium (K), nitrogen (N) and oxygen (O). As can be seen from the 3 behind the "O", it "consists" of 3/5 oxygen and also releases this very easily to oxidisable substances such as sulphur, charcoal, etc. when starting energy in the form of heat or friction is added to the finished mixture.

On this basis, most mixtures can be made: oxygen-releasing substance + easily combustible (oxidisable) substance. However, one must pay attention to the so-called "chemical" equilibrium, i.e. there must not be more oxygen-releasing substance in a mixture than is necessary for the combustion of the combustible substance, as such an excess would hinder the reaction. The correct ratio can be calculated using the reaction equation, but first you have to come up with a complete reaction equation before you can then do your calculations using the molecular weight (molar mass). But a perfect equilibrium does not mean that a mixture will work well - sometimes you have to do many experiments before you succeed.

But there are more factors that play a role, such as particle size. Suppose you want to make black powder and you pulverise your basic ingredients in a mortar and mix them; you will find that the end product burns quite slowly. If you were to put it in a firecracker, there would be no bang but perhaps a "poof", but nothing more. The powder that can be produced with the help of a mortar may look very fine at first glance, but this "fineness" is not sufficient to ensure a fast reaction. The finer a powder is, the larger its surface area and the better it can react. A kilo of wood in the shape of a cube will not burn if you hold a lighted match to it, but a kilo of wood wool will! Nevertheless, you should know what reaction you want to achieve - making a sparkler with iron dust makes no sense, it would burn with a bright flash in two seconds, whereas with coarse iron powder it burns calmly and sparkles away. So for a flash powder that is supposed to burn abruptly, you will always use dust-fine ingredients.

The procedure of mixing is also an important factor for a good mixture. But it is also a significant safety aspect, because any kind of energy you add to a mixture can make it react. There are mixtures that are so insensitive that you can hit them with a hammer and need a sparkler to ignite them. Other mixtures, on the other hand, explode at the slightest touch.

The colours

nico_europe_chemie_farben_in_reagenzgläschenThe beautiful thing about fireworks are always the different colours: Blue, red, green, purple, yellow, etc. What looks so beautiful is sometimes very difficult to achieve. A flame can be created by the salts of metals like: Sodium (yellow), Barium (green), Strontium (red), Potassium (violet), Copper (blue). The metals mentioned are not the only ones that can cause flame colouring, but they are the most common. And as always, when it comes to colour, you have to know what you want to achieve.

If you take a mixture of sulphur, potassium nitrate, strontium nitrate and sodium nitrate, it will always burn yellow, because the sodium produces a very intense yellow and so completely covers the red of the strontium and the violet of the potassium. If you add magnesium to a mixture of strontium nitrate and sulphur, then this mixture will look much less red because the magnesium gives off a very bright white light and so the red fades away to some extent.

All colours, except blue, can be produced very easily. One simply uses the nitrate of the corresponding metal. However, the use of copper nitrate does not produce blue colour in pyrotechnic mixtures. To produce blue, one must use different copper salts in the same mixture and add exact amounts of organic chlorine compounds. The blue colouring is only produced when chlorine is present in addition to copper during combustion. In these mixtures there is a fine balance that cannot be calculated. It can only be achieved by experimentation!

Chemicals

ALUMINIUM Al - Fuel
Used for white or silver sparks or in flash bang sets.

AMMONIUM NITRATE NH4NO3 - Oxidising agent
Very hygroscopic. Rarely used in pyrotechnics.

BARIUM NITRATE Ba(NO3)2 - Oxidising agent, colouring agent
Toxic. Green colouring agent.

BORIC ACID - Corrosion Inhibitor
Boric acid is finely powdered and used in small quantities in mixtures of nitrates with metal powders to prevent corrosion and premature reactions.

CALCIUMCARBONATE CaCO3 - Colouring agent
Orange-red colouring agent.

CALCIUM SULPHATE CaSO4 - Colouring agent
Except in chlorate sets for orange-red flashing effects and luminous stars.

DEXTRIN - Binder
Yellowish, fine powder. For stars and sparklers.

IRON Fe - Fuel
Fine to coarse powder or filings (also steel filings) for golden sparks in fountains and sparklers.

CHARCOAL C – Fuel
Used as the main ingredient of black powder. The quality and origin of the charcoal is crucial for the quality of black powder. Very finely powdered charcoal is needed for black powder and somewhat coarser powder for long sparks.

POTASSIUM CHLORATE KClO3 - Strong oxidising agent
Potassium chlorate is a very strong oxidising agent. Mixtures of potassium chlorate and flammable substances are very sensitive to contact. Potassium chlorate must never be mixed with sulphur, sulphates, sulphides, metal powders or even red phosphorus. Such mixtures usually explode on contact.

POTASSIUM NITRATE KNO3 - Oxidising agent
Main component of black powder and commonly used oxidant in pyrotechnics.

COPPER CARBONATE BASIC CuCO3 * Cu(OH)2 - Colouring agent - Toxic
Greenish powder. Blue colouring agent.

COPPER CHLORIDE CuCl, CuCl2 - Colouring agent - Toxic
Hygroscopic. Greenish powder. Blue colouring agent.

COPPER OXIDE CuO, Cu2O - Colouring agent - Low toxicity
Black or red powder. Blue colouring agent.

LAMPBLACK C – Fuel
Sometimes used to create long glowing orange sparks.

LINSEED OIL or VARNISH – Binder, corrosion inhibitor
In a few blends, linseed oil or varnish is used as an air-drying binder. More often, however, it is used to coat metal powders to protect them from premature oxidation.

LITHIUM CARBONATE Li2CO3 - Colouring agent
White powder. Red colouring agent.

MAGNESIUM Mg – Fuel
Produces a blinding white flame that can damage the retina! Therefore, do not look into the flames!

SODIUM HYDROGEN CARBONATE (NATRON) NaHCO3 – Colouring agent
Yellow colouring agent.

SODIUM NITRATE NaNO3 - Oxidising agent - Colouring agent
Similar to potassium nitrate, but strongly hygroscopic. Used together with potassium perchlorate in whistle sets.

PHOSPHORUS red/white - Fuel - Toxic
Red phosphorus is rarely used in pyrotechnics, almost exclusively in mixtures for friction heads, and even then only rarely. Pyrotechnic mixtures with phosphorus are unstable and there is a risk of white phosphorus forming when they burn. White phosphorus is HIGHLY TOXIC and can ignite spontaneously at elevated room temperatures; it is therefore stored under water.

POLYVINYL CHLORIDE (PVC) - Colour improver
Chlorine donor. Essential ingredient in blue mixtures.

SULPHUR S – Fuel
Yellow, fine powder. Only use washed sulphur powder, as the so-called sulphur bloom has a high content of sulphuric acid. Important ingredient of black powder.

SHELLAC – Fuel, Binder
Orange-coloured resin obtained from the shellac louse.

STRONTIUM NITRATE Sr(NO3)2 - Oxidising agent - Colouring agent
Hygroscopic, similar to potassium nitrate. Red colouring agent

CLAY
The nozzles in rockets and fountains are almost always made of clay.

VASELINE - Corrosion inhibitor
Sometimes used to protect metal powder from oxidation.

ZINC Zn – Fuel
Mostly fine powder (zinc dust), used in smoke mixtures.

nico europe info chemie junge frau im weißen kittel mit mundschutz und handschuhen hält reagenzgläschen mit blauer flüssigkeit hoch, vor ihr weitere gläser und kolben mit diversen bunten flüssigkeiten und pipetten

Dangerous chemicals

Chlorates

Should generally not be used as they are highly reactive and tend to react undesirably with many substances. There is a reason why chlorates are no longer used in professional fireworks!

They should generally not be mixed with the following:

• Acidic components:
(Releases HIGHLY REACTIVE hyper-chloric acid, which can lead to spontaneous combustion and explosion.)

• Sulphates, sulphides and sulphur:
(Often contain traces of sulphuric acid, see above.)

• Ammonium compounds:
(Can together form HIGHLY EXPLOSIVE ammonium chlorate.)

• Finely powdered organic substances:
(Danger of spontaneous combustion.)

Nitrates

Never mix with unphlegmatised metal powders, especially copper (catalytic decomposition possible), especially ammonium nitrate!

Chromium compounds

Almost all chromium compounds, e.g. also ammonium dichromate, are classified as carcinogenic! Furthermore, A-dichromate reacts very violently with organic solvents.

Heavy metal compounds

Are sometimes used in old blends. E.g. copper acetoarsenate (Paris green) for blue flames. Or lead nitrate for special fountains (heavy metal fumes are produced when burning - TOXIC!). Also applies to heavy metal azides (e.g. lead azide).

Mercury fulminate

Is HIGHLY TOXIC, extremely sensitive and the manufacturing process produces large amounts of toxic mercury waste.

Organic and inorganic peroxides

Almost always toxic and unpredictably explosive!

Literature reference

A substantial part of this article is taken from the z-netz.alt.pyrotechnik-FAQ.
Author is Mr Solon Luigi Lutz.