I know many pyrotechnic composition's burn rate increase with pressure. Just how is this? i do not understand. What i mean is how does it begin to burn so fast that a "firecracker" vilently explodes. I understand why the case explodes, but am wondering why the Bp begins to burn so fast in it. Is it the particles being pushed together or something. I just cant visualize it.

You sort of have it right, an increase in pressure causes two main things to happen 1) The concentration of the reactants increases and 2) The movement of the particles increase. Both these things increase the number of collisions between reactants thus increasing the rate of reaction. This goes for all reactions not just explosive ones.

 

~Scott

Maybe this is not the increase in burn rate that makes black powder to explode but just that everything will explode violently if pressure of gases inside has reached critical limit. That may be very slow reaction where gases build up with months but if pressure in container gets too high, sudden explosion will result.

 

One more reason may be that initial pressure wave makes another parts of powder to ignite even before direct burning reaches them.

in a firecracker it`s the powders surface area and the space between each particle that increases the burn rate. the powder is fery fine and is never pressed tightly, so that the flame can propogate easily.

if it were the same composition packed as a solid grain, it would become a tiny rocket engine instead.

ya, i use fine BP or granulated BP. Granulated seems to be way better becasue it burns a a amazingly higher rate.

 

I dont make flash powder firecrackers, too dangerous.