Adsorption of H2O, H2S, and N-2 on MnZn ferrite

MnZn ferrites show extensive subcritical crack growth. In this process wate r plays an important role. The fracture surfaces of MnZn ferrites with thre e different stoichiometries were investigated with adsorption isotherm meas urements, temperature-programmed desorption, diffusive reflection infrared Fourier transform spectroscopy (DRIFT), low-energy ion spectroscopy (LEIS), and x-ray photoelectron spectroscopy (XPS). The XPS results confirmed the presence of Mn, Zn, Fe, and O atoms in the surface region, but LEIS indicat ed that the outer layer of the fracture surfaces contained no Zn atoms. DRI FT confirmed that hydroxyl groups were present on the fracture surfaces. Ex periments with H2S, for which the XPS is more sensitive, indicated that at low coverage pairs of S atoms bridge a pair of Fe atoms. With increasing co verage the S bridge shifts to one Fe atom while at the highest coverage eac h Fe atom is bonded to one S atom. In experiments with N-2 the highest nitr ogen absorption is found for the lowest oxygen concentration in the ferrite , which is probably related to the polarity of the surface. Both the adsorp tion and desorption tests indicated that N-2 had a larger adsorption affini ty to MnZn ferrite surfaces than H2O.