[whiteleoaprd96]

I really need this for my project guys. I can't find an answer. So here goes:

Why does cornstarch burn in separate and fine dust but not when it clumped in a group?

Why does it even burn? (I sorta get that its a "binder" which is used in pyrotech)

I would really appreciate it if you could give an answer before the end of January 9, 2012 (Philippine time, which means, January 8 to Americans, you guys could figure the rest)

*It'd really help if you'd give a chemical formula, as this is for my project which was given in short-notice.
TNX!

[Borek]

It burns even clumped, just not that fast.

Check what it is in chemical terms.

[fledarmus]

This might help:

http://en.wikipedia.org/wiki/Dust_explosion

Especially the mechanism section.

[whiteleoaprd96]

so fledarmus, does that mean it burns it finer particles because when you blow it, the surface area increases, which makes burning possible through the presence of oxygen in the air?

[Borek]

so fledarmus, does that mean it burns it finer particles because when you blow it, the surface area increases, which makes burning possible through the presence of oxygen in the air?

Exactly.

[vmelkon]

I think a more detailed explanation can be given.

The surface area would always be the same but when the dust is floating in air, you have enough oxygen surrounding each particle.

If the starch is in a pile, there is some oxygen around it but when you burn it, probably the oxygen gets consumed and the CO2 created can't easily leave the pile.

The surface area is slightly reduced because the particle are in contact to each other but IMO (my imagination), this plays less of a role.

A microscope would help here

There is one here (Cornstarch at 500x magnification)
http://wildcatphysics.blogspot.com/2010/07/week-4-adventures.html