Whats the ideal mixture ratio & mesh size for the iron oxide powder (F304) & aluminum powder to make thermite?

For mesh size, generally speaking, the finer the powder the better. The mesh size determines how quickly the thermite reaction can spread, and so a finer mesh will light easier and burn faster. There really is not an ideal size; just as fine as you can make it.





The proper stoichiometry for the reaction in terms of mass is 3:8, aluminum powder to Iron Oxide. Keep in mind that this is in terms of mass, not volume, and so the mixture will look like it has about a 50:50 volume ratio.





Because coarse thermite is so difficult to light, I would recommend buying the Aluminum powder that you use in the reaction.