pyrotechnics-revived/chapters/99-1-chemical-aluminium.md

## Aluminium powder

**Formula**

$Al$

**Pyrotechnic use**

Fuel

**Synonyms**

Aluminium metal

**Description**

Aluminium powder is one of the most often used fuels in pyrotechnics. A wide
range of effects are possible with different types of powder, with differences
in particle size, shape and impurities. The finest powders (e.g., German Dark
and XD-30) can be 'airfloat', and are commonly used in flash compostions. Fine
aluminium is also used in small percentages in some hobby-rocket fuels. Courser
powders are generally used for sparkling effects. With these larger particle
types, many effects--such as flitter, glitter, firefly and snowball--can be
achieved.

**Sources**

Aluminium powder is sometimes sold as a pigment in (art) paint stores. This
powder, known as 'aluminium bronze', is a flaky powder with a stearin coating.
It is quite expensive but readily available and a source for small quantities.
Aluminium grit and turnings can sometimes be found in machine shops were
aluminium is processed. If fine enough this can be used as is, but it can also
be ball milled into flakes. These flakes are quite reactive as they have a
large surface area and can be used for several effects. Sanding aluminium
chunks can also make aluminium powder. I've heard of people building a machine
to do this, and the results can be quite good depending on the sanding paper
used and the set-up. Another source of usable aluminium powder is to burn
tetra-paks, and then powder the resultant aluminium residue in a ball mill.
Aluminium powder can also be found inside an Etch A Sketch. In Boating stores,
it can be found as a two component epoxy for protection of boat hulls against
UV radiation, mesh size is questionable.

**Dark (Pyro) Aluminium type**

It is a very fine powder and dark grey in colour. Nominal mesh size is 200 but
it contains particles of 2µ. There is a wide variety of uses for dark
aluminium, for example: flash powders, star compositons, fountains, waterfalls,
torches, flares, etc. For all this purposes it is generally used as a fuel.
Many powders sold as "dark" aren´t really dark aluminium but the atomized type
(often 63µ) and although the color of the former may vary it has to be dark
grey and not light grey or even whitish grey (some of the best dark aluminium
comes from Eckart Germany and this powder is nearly black in color = German
Dark). Under the microscope it´s possible to identify atomized and dark powders
quite well: the former are spherical in shape while the latter are irregular
and angular. Dark alu is generally the most expensive of all the alu powders.

**Atomatized Aluminium powder type**

Atomized Aluminuim is increasingly used in fireworks although there are only
limited uses for it (this is because spherical or spindle shaped particles are
more difficult to ignite than a flake). In practice no material coarser than
120 mesh can be used and commercial atomized powders are generally 300+ mesh
and light grey to grey in colour. It is needed for glitter effects and other
special stars, to give an example only.

**Flake Aluminium type**

There are mainly three different types of flake alu (all silver in colour). The
first is "bronze" also known as paint grade aluminium. This fluffy powder is
used for making paint and the particle size is very fine (sometimes less than
2µ). Paint aluminium generally contains grease or stearine (the content varies
from one to four percent by weight) which decreases its reactivity.
Nevertheless aluminium bronze is easily obtained from an artist supply and
produces quite good silver effects. It can be used wherever "bright" aluminium
is mentioned in a composition. Generally it´s a dirty business to work with
fatty aluminium. It only passes the mesh when accompanied by another material.
The second flake aluminium is the real "bright" or "brilliant" powder we can
subsitute with bronze for most purposes. Bright alu usually passes 120 mesh
(nominal mesh Flake Aluminiumsize 120-200) and like "bronze" is very fluffy and
leafing mass. The main difference to the latter is that brilliant powders
contain less grease/stearine (0,5% by weight max) or are coated with another
material which means that they aren´t as fatty to handle as bronze grades. They
are used as a fuel for many purposes and to obtain silver effects. The third
flake grade is called "flitter" which means flake powders of a larger mesh size
than bright aluminium. It is sold as "fine", "middle" and "coarse"
flake/flitter. Some people think that using flitter larger mesh variations are
allowed. Sometimes this might be true but corresponding to the correct mesh
size often makes the critical difference. As a rule of thumb fine flitter is:
80-120 mesh, middle flitter is: 30-80 mesh and coarse flitter (=coarse flake)
is 10-30 mesh.

Aluminium Particle Types: <PICTURE>

**Hazards**

Aluminium is a neurotoxin that alters the function of the blood-brain barrier.
Additionally small particles that are airborne act as tiny razors when they
come in contact with lung or eye tissue, and a dust mask and goggles should be
worn at all times when working with aluminium powder. Mixtures containing
nitrates and aluminium powder are prone to heating up spontaneously and may
ignite, especially when wet. This is caused by the reduction of the nitrate by
aluminium, forming amides. These very basic compounds react further with
aluminium powder in a very exothermic reaction that can cause spontaneous
ignition. An ammonia smell is often produced in this reaction. Adding 1 to 2%
boric acid to compositions containing nitrates and aluminium is common practice
and will often prevent spontaneous ignition.