The nanofluid dispersion was purchased to Nanophase according a previous post, and according to their products and the white color, this stuff should be composed of aluminum oxide, the most classical nanofluid, or zinc oxyde (you talk about it in your paper, you probably forgot to erase some info...). They have tin oxyde too, that gives a white color, but I doubt about its use here. Hence, no problem of corrosion because nanoparticles are already in an oxidized form.