Metal oxide reaction with water

[Zero86]

Hello,

I'm quite new to this forum, I am currently a student in a radiography program and for fun I was wanting to try to make some x-ray attenuation materials to x-ray in our lab.

I purchased a few metal oxides, Bi2O3 and Sb2O3 which they currently use to make protection vest out of, when mixing these powders together in an epoxy I noticed I couldn't get a very even mixture unless I mixed the two compounds together in water first making them hydroxides and then dehydrated the mixture, when doing so i also noticed the loading capacity increased compared to that our adding the two compounds directly to the epoxy. My question would be why would adding water to the compounds and then removing the water increase the amount I can add to the epoxy, after removing the water from the newly made hydroxides am I left with a new compound other then Bi2O3/Sb2O3?