γ-Fe2O3with condensed phosphates as antisintering agents

Magnetic and rheological properties for pure and phosphates surface modified γ-Fe2O3were determined in order to evaluate different kinds of phosphate ions, as antisintering agents, during the transformation of α-FeOOH into γ-Fe2O3via Fe3O4. The magnetic data show that hexametaphosphate (HMP) and tripolyphosphate (TPP) ions, which adsorb onto the α-FeOOH precursor surface, behave like effective antisintering additives in the same way as silica Coating. On the contrary, no antisintering properties are shown by pyrophosphate (PP) ions. The wettability and the specific surface area of the HMP and TPP modified γ-Fe2O3, are higher than those of the pure and PP treated γ-Fe2O3, since the increase of surface roughness produces a much higher "real surface area".