From: Subject: Philistiniphony Date: Mon, 22 Jan 2007 00:34:18 -0800 MIME-Version: 1.0 Content-Type: multipart/related; type="multipart/alternative"; boundary="----=_NextPart_000_001C_01C73DBD.0D20B8B0" X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3028 This is a multi-part message in MIME format. ------=_NextPart_000_001C_01C73DBD.0D20B8B0 Content-Type: multipart/alternative; boundary="----=_NextPart_001_001D_01C73DBD.0D20B8B0" ------=_NextPart_001_001D_01C73DBD.0D20B8B0 Content-Type: text/html; charset="utf-8" Content-Transfer-Encoding: quoted-printable Content-Location: http://web.archive.org/web/20040904092635/http://members.ozemail.com.au/~gmillar/ =EF=BB=BF Philistiniphony =0A= =0A= <BODY BGCOLOR=3D"#FFFFFF">=0A= =0A= <H1>You are viewing with the wrong browser. You need Netscape 2.0 or = later.</H1>=0A= =0A= ------=_NextPart_001_001D_01C73DBD.0D20B8B0 Content-Type: text/html; charset="utf-8" Content-Transfer-Encoding: quoted-printable Content-Location: http://web.archive.org/web/20040828200127/members.ozemail.com.au/~gmillar/submenu.html =EF=BB=BF Philistiniphony

------=_NextPart_001_001D_01C73DBD.0D20B8B0-- ------=_NextPart_000_001C_01C73DBD.0D20B8B0 Content-Type: text/html; charset="utf-8" Content-Transfer-Encoding: quoted-printable Content-Location: http://web.archive.org/web/20040806174619/members.ozemail.com.au/~gmillar/pyrotechnics/colours.html =EF=BB=BF Colour and light

Colour and Light=20

There are three main types of light production in pyrotechnics:

  1. Incandescence (or blackbody radiation)=20
  2. Atomic emmision=20
  3. Molecular Emmision

Incandescence

This is when solid or liquid particles of matter are heated to a very = high=20 temperature (at least 1500oC, preferably about 2-3000) and = give off=20 the excess energy as light. The substance gives of light throughout the=20 spectrum, at higher temperatures with a shorter wavelength, at lower=20 temperatures with a longer wavelength. The intensity is proportional to=20 T4 where T is the temperature of the = substance.

An everyday example of this is an incandescent light bulb. The = filament is=20 heated to a very high temperature and it glows with a yellowish-white = light.

When metals are oxidised, the resulting metal oxide is heated to a = very high=20 temperature, causing it to emit incandescent light. This is what is seen = in=20 flares, for instance, a typical flare might contain magnesium and an = oxidiser,=20 which would burn with a bright white light. If the particles of metal = are made=20 larger they continue to burn once expelled into the atmosphere. This is = what=20 produces sparks and showers.

Atomic and Molecular Emission

This is when certain chemicals are vaporised in a pyrotechnical flame = such=20 that the atoms become excited, causing the electrons in their shells to = jump=20 from their ground state (up to the next shell) and the compound to = become=20 ionised. When they return to the ground state again they emit a photon = at a=20 certain wavelength. Each time this happens it is called the nth=20 ionisation energy, therefor what has just been described would be the = 1st=20 ionisation energy.

This is the way by which spectacular and colourful fireworks of today = produce=20 colour.

Molecular emission is basically the same, however, if the substance = is heated=20 too high the molecule decomposes and no light is emitted.

This emmision of light occurs the same way as in a flourescent/gas=20 discharge/cathode ray tube (they are all basically the same thing). As = the=20 electrons flow from the cathode to the anode, the atoms are caused to go = into an=20 excited state, emitting a photon when they go back to the ground = state.

Sodium is one of the strongest atomic light emiters. It produces a=20 yellow-orange light having a wavelength of 589nm. It is so strong that = when=20 included with other colour emiters it often washes them out completely. = The US=20 Military uses sodium nitrate as an oxidiser mixed with magnesium to = provide=20 light for night-time operations.

Colours are normally achieved from the ionised salt of a particular = metal.=20 Some of the more commonly used metal compounds and their ions for some = of the=20 more commonly radiated colours are listed below:

Name Formula Ion Formed Colour Wavelength
strontium chloride SrCl2 SrCl+ red 605-682nm
calcium chloride CaCl2 CaCl+ orange ?
barium chloride BaCl2 BaCl+ green 507-532nm
copper(II) chloride CuCl2 CuCl+ blue ?

These are ions which are not stable at room temperature, are only = stable at=20 very high temperatures and as a result cannot be included as is into a=20 pyrotechnic composition. For this reason they are synthesized in fast = chemical=20 reactions within the flame. The chemicals normally used are a nitrate of = the=20 metal and a chlorine donor. Chlorine donors also decrease incandescent = light and=20 hence make the coloured light more visible.

Chlorate and perchlorate oxidizers are really the only oxidisers = which serve=20 a dual purpose as a donor and oxidiser.

Blue is the most difficult colour to produce, because the copper = compounds=20 used are destroyed if the temperature is too high, but if the temprature = is too=20 low, not enough light is produced. This is the same for all colours, but = blue=20 has a narrow range of temperature which works. A good measure of the = quality of=20 a pyrotechnic demonstration is the quality of the blue which is = produced.

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