HEAT AND DELAY COMPOSITIONS

For "gasless" heat and delay compositions, little external pressure effect is expected. This result, plus the increase in burning rate observed with an increase in loading pressure, can be considered good evidence for the absence of any significant gas-phase involvement in a particular combustion mechanism. 

Mixtures of this type were originally developed as first fires and delay compositions. They contained 5-10% boron, and barium chromate. As actual heat sources, the mixtures of zirconium and barium chromate were developed and were known under designations such as Z-2 or Z-3. These are often used as heat paper on a substratum of silica fibers. 

The combinations of boron with oxidizers other than lead compounds seem to be less subject to accidental ignition than comparable mixtures of sensitive metals and oxidizers. Boron is used extensively in first fires and delay compositions and may be useful as a specialty heat source. Because of the small amount of boron required in combination with heavy metal oxides, certain mixtures can be used... 

The burning of a column of delay composition takes place by the passage of a reaction front along the column. The temperature profile of this reaction front can be measured by the use of suitable thermocouples and recording instruments. By analysing the shape of the front it can be shown that the reaction is a solid/solid reaction initiated by thermal conduction of heat through the unreacted material. It follows that to obtain reproducible reaction rates there must be (1) constant amount of solid to solid contact and (2) constant thermal conductivity. 

Some delay compositions are difficult to ignite and ordinary fuseheads may not be adequate for this purpose. In such cases special fuseheads are used which commonly contain cerium powder, or some similar additive which burns with the evolution of a large amount of heat. 

In the design of the detonator attention must also be paid to the effects of the liberation of gas which, though small, is still sufficient to require attention. As the speed of the delay composition is affected by pressure, it is necessary that the free space in the detonator should be carefully controlled. Also, the plug which seals the leading wires in place must withstand this pressure for more than the delay period of the detonator. This task is made more difficult by conduction, along the metal walls of the detonator shell, of heat liberated by the fusehead and the delay composition. Plastic plugs in particular are liable to soften and be ejected from the detonator with probable failure of burning of the delay column. 

Detonators, Initiators, Delay Compositions and Heat-Generating Pyrotechnics... 

Additional experiments have been conducted that varied A from 0.7 to 3.0, holding all other feed conditions constant.8 Dual steady-state operation was observed for the entire range tested providing more evidence that the water amount in the feed composition is probably the dominant factor. This type of experiment was repeated for a different CO feed concentration and nearly the same behavior was recorded. This dual steady-state nature persists for a wide range of lambda, which points to the fact that dual steady state is more influenced by feed composition and more specifically by water amount. Since water has high heat capacity, this may temper the heat rise and delay the onset of H2 oxidation reaction. 

Phenolic resins exhibit excellent dimensional stability with a constant use temperature range of 180-200 °C, excellent resistance to chemicals, moisture, and heat and favorable behaviour against fire and smoke. The predominant consideration in the use of phenolic resins as a matrix resin in fibre-reinforced composites is fire behaviour. Phenolic-based composites perform better under fire conditions compared with epoxy- or vinyl ester-based composites. This is due to their delayed ignitability coupled with low heat release, low smoke evolution with little or no toxic gas emission, and capability to provide significant strength retention (70%)... 

Discussion of the test objectives by user and producer is essential. Communication facilitates agreement regarding frequency of sampling, specimen location, orientation, and surface finish. Testing must be sufficient to guarantee quality without excessive cost or delay. Tests are often performed on each heat and heat treat lot to verify that the material composition and annealing practice were satisfactory. The specimen location may be chosen to provide a typical sample (generally midradius of a bar) or to evaluate... 

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