Flame composition

As far as flame composition is concerned, it may be noted that an acetylene-air mixture is suitable for the determination of some 30 metals, but a propane-air flame is to be preferred for metals which are easily converted into an atomic vapour state. For metals such as aluminium and titanium which form refractory oxides, the higher temperature of the acetylene-nitrous oxide flame is essential, and the sensitivity is found to be enhanced if the flame is fuel-rich. 

Alteration of flame composition or of flame temperature can be used to reduce the likelihood of stable compound formation within the flame. 

The negative ion concentrations all show very definite maxima on the fuel-rich side of stoichiometric flame composition. 

The LIF technique is extremely versatile. The determination of absolute intermediate species concentrations, however, needs either an independent calibration or knowledge of the fluorescence quantum yield, i.e., the ratio of radiative events (detectable fluorescence light) over the sum of all decay processes from the excited quantum state—including predissociation, col-lisional quenching, and energy transfer. This fraction may be quite small (some tenths of a percent, e.g., for the detection of the OH radical in a flame at ambient pressure) and will depend on the local flame composition, pressure, and temperature as well as on the excited electronic state and ro-vibronic level. Short-pulse techniques with picosecond lasers enable direct determination of the quantum yield [14] and permit study of the relevant energy transfer processes [17-20]. 

Mixtures of ammonium perchlorate with fuels can produce high temperatures when ignited, and the hydrogen chloride (HCl) liberated during the reaction can aid in the production of colors. These two factors make ammonium perchlorate a good oxidizer for colored flame compositions (see Chapter 7). 

Barium nitrate is a white, crystalline, non-hygroscopic material with a melting point of approximately 592°C. It is commonly used as the principal oxidizer in green flame compositions, gold sparklers, and in photoflash mixtures in combination with potassium pert hlorate. ... 

The numerous requirements for a good oxidizer were discussed in detail in Chapter 3. An oxidizer for a colored flame composition must meet all of those requirements, and in addition must either emit the proper wavelength light to yield the desired color or not emit any light that interferes with the color produced by other components. 

Applications involving colored flame compositions will reqnire either a long-burning composition or a mixture that bums rapidly to give a burst of color. 

T. Shimizu, "Studies on Blue and Purple Flame Compositions Made With Potassium Perehlorate," Pyrotechnica VI, Pyrotechnica Publications, Austin, Texas, 1980. 

Black powder] as a propellant, 136-137 as an igniter, 125 burning rate of, 114, 115, 117 composition of, 1 factories, 3 gas production by, 33 history of, 3-5 properties of, 1-2 thermogram of, 43 Blue flame compositions, 160-162 Bond... 

With good fuels (charcoal or active metals), potassium nitrate will burn well. Its use in colored flame compositions is limited, primarily due to low reaction temperatures. Magnesium may be added to these mixtures to raise the temperature (and hence the light intensity), but the color value is diminished by "black body" emission from solid MgO. 

Potassium chlorate was used in the first successful colored-flame compositions in the mid-1800 s and it remains in wide use today in colored smoke, firecrackers, toy pistol caps, matches, and color-producing fireworks. 

Several formulas for blue flame compositions are given in Table 711- An extensive review of blue and purple flames, concentrating on potassium perchlorate mixtures, has been published by Shimizu [131. 

In many instruments, the computer will control the instrument settings (if a coded hollow-cathode lamp or a procedure that has been stored in the memory is being used, the computer may set the wavelength automatically). In addition, the recommended flame composition and the height at which readings will be taken may also be optimized. 

Glyde, E.D., Lewis, G., and Robertson, J. (1984) Smoke and flame compositions based on amorphous phosphorus. Proc.9th Inti. Pyrotech. Seminar, Colorado, USA, Aug. 06-10,1984, pp. 819-836. 

The diagram is quite convenient for designing colour flame compositions. For example, when a red colour represented by Pi is mixed with a green the new colour moves along the straight line P -Pilike P The coordinates have the following relations ... 

Bonfire smoke is produced under the same principle described for black and white smoke. But the difference is that in the case of the bonfire the particles of smoke only absorb the moisture little and do not always grow to a visible size. The smoke therefore sometimes looks almost violet in the distance. The moisture in the air has a great influence upon the growth of the particles of the A-substance when it is hygroscopic. For example, in dry weather a zinc chloride smoke looks thin. A composition which contain ammonium perchlorate, e.g. a colour flame composition or a rocket propellant, has smoke which is almost invisible in dry weather, but it looks quite dense in wet weather. This is due to HCl in the burning gas. A particle of water mist dissolves 00 times its volume of HCl gas at normal temperature. if there is some water mist in the air, the... 

It is used for coloured flame compositions, but the burning rate is not so great as it is with potassium chlorate compositions. On burning it does not smell of chlorine gas. The available oxygen per 1 gram of potassium perchlorate -amounts to 0. 62grams, which is I.I8 times more than that of potassium chlorate. 

It is well suited to ammonium perchlorate compositions or high temperature flame compositions, where HCl gas is produced in the flame. 

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