Calorimetric characterization of magnetic pigment surfaces

One of the most direct and sensitive ways of studying pigment surface properties is to measure the enthalpy changes which accompany the immersion of pigments in liquids. Different wetting liquids were used to test for H donor and H acceptor properties as well as to probe the polarity of the pigments´ surfaces. The measurements were performed in an isoperibol batch calorimeter. Results are presented for γ-Fe ₂O₃, CrO₂, Co-modified γ-Fe₂ O₃, and barium ferrite pigments. It is found that Co-modified γ-Fe₂O₃ pigments are very polar, whereas CrO₂ pigments have low polarities: H donor and H acceptor properties are less pronounced. It is found that barium ferrite pigments act very much like γ-Fe₂O₃ pigments. It is shown that the effects of surface treatment can clearly be monitored by calorimetry