The surface chemistry of amorphous zinc polyphosphates of different compositions (ranging from zinc metaphosphate to zinc orthophosphate) has been investigated by means of X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary-ion mass spectroscopy (ToF-SIMS). The identification of the chain length of zinc polyphosphates by XPS was on the basis of the integrated intensity ratio of the bridging (P-O-P) and nonbridging (P = O and P-O-M) oxygen peaks used for fitting the oxygen 1s signal, the shift of the P 2p(3/2) signal towards lower binding energies and the modified Auger parameter towards higher values as the zinc content increases. The discrimination of the polyphosphate chain lengths was also achieved by ToF-SIMS, by comparing the intensities of selected characteristic phosphate fragments. Both techniques appear to be suitable for the investigation of polyphosphate glasses in applications such as tribology, where there is a need to identify the chain length present in the outermost monolayer of the film. Fourier-transform infrared (FT-IR) spectroscopy was used to characterize the bulk compounds. The FT-IR studies showed that long-chain structures linked through P-O-P bonds predominate in the metaphosphate composition, while when the zinc content is increased, the chains become shorter, ultimately being replaced by PO(4) monomers in the orthophosphate composition.

Zinc polyphosphate glasses are the principal component of the antiwear tribofilms formed on steel surfaces in the presence of additives, such as zinc dialkyldithiophosphates. In this work, amorphous, zinc metaphosphate glasses have been synthesized and characterized by means of X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), elemental analysis, and X-ray photoelectron spectroscopy (XPS). Tribological tests were performed by rubbing steel balls against the zinc metaphosphate discs in a poly-aolefin (PAO) bath at room temperature. XPS was used in order to characterize the tribostressed areas on both metaphosphate discs and steel balls. A transfer film, constituted of iron and zinc polyphosphates, was formed on the contact area of the balls. This transfer film was found to reduce friction and prevent ball wear. A reduction in the relative intensities of XPS signals related to bridging-oxygen species and a binding energy shift of 0.4 eV of the P 2p toward lower values demonstrated the presence of shorter-chain-length phosphates inside the tribo-tracks on the discs. Furthermore, iron was transferred to the glass during the tribological tests. A tribochemical reaction between zinc metaphosphate and iron oxide has been proposed as an explanation for the depolymerization of the glass and the formation of iron phosphate.

Electroless Ni-P alloys are produced as coatings on a broad variety of substrates. They exhibit a corrosion resistance that is superior to pure nickel but do not form a NiO oxide film (passive film) as pure nickel does. Despite the fact that many mechanisms have been proposed to explain this superior corrosion behaviour, no consensus has yet been reached. In this work electrochemical and XPS surface analytical methods have been combined in order to gain a deeper insight into the mechanisms underlying the corrosion resistance of electroless deposited Ni-P alloys with phosphorus content between 18 and 22 at.%. The anodic polarization curves in acidic and neutral solutions confirm a broad current plateau followed by a region with increasing current density. During potentiostatic polarization in the plateau region the current decays according to a power law with exponent ca. -0.5 indicating diffusion-limited dissolution of nickel. XPS/XAES measurements performed after potentiostatic polarization show that phosphorus is present in three different chemical environments. Based on the Auger parameter concept and on the chemical state plot, the three phosphorus states were assigned to phosphorus in the bulk alloy, phosphates and an intermediate phosphorus compound attributed to elemental phosphorus. Angle-resolved XPS analysis has shown that the elemental phosphorus is enriched at the interface between the alloy and the outermost surface in contact with the corrosive solution. These results suggest the following conclusions: the high corrosion resistance of electroless deposited Ni-P alloys can be explained by a strong enrichment of elemental phosphorus at the interface which limits the dissolution of nickel via a diffusion mechanism. A complementary explanation--not yet advanced--for the high corrosion resistance may lie in the electronic state of nickel in the Ni-P alloys.