When I ballmill some potassium chlorate (for example), I mostly add 0,5 - 1% of anti cake. This makes sure that when it is used maybe one year later, it's still airfloat.
Unfortunately I dont know what exactly I'm using. Silicon dioxide, that's all I know, got the bag as a gift a long time ago.
When looking for some Silicon dioxide anti cakes, I found there are hydrophilic and hydrophibic ones. My first guess would be that hydrophobic is the right stuff for our needs, but I never stuck my nose deep enough into the chemistry of silicon to get a precise understanding of the whole thing.
Some stuff that should be treated with it is hygroscopic.
-> What would you use/ do you recommend?