thermitequestion

I want to make some aluminum powder to use in thermite, I've seen people in youtube making it from powdered aluminum foil. I was wondering if i can make aluminum powder by grinding aluminum beams from windows/doors or aluminum cans using angle grinder (disc cutter). . I heard that if you mix the aluminum powder with a little charcoal it will keep it from oxydising? I Can i remove the O from the aluminum with some chemical?s aluminum oxide combined with iron oxide reactive thermite?