I want to make some aluminum powder to use in thermite, the premade stuff is too expensive for my country. I was wondering if i can make aluminum powder by grinding aluminum beams from windows/doors or aluminum cans using angle grinder (disc cutter). Will grinding produce the aluminum powder or the friction and the heat will  oxydise it  into aluminum oxide. I heard that if you mix the aluminum powder with a little charcoal it will keep it from oxydising?