Depolymerization of sodium polyphosphates on an iron oxide surface at high temperature.

Density functional theory (DFT) and first principles molecular dynamics (FPMD) studies of pyrophosphate cluster Na4P2O7 and triphosphate cluster Na5P3O10 absorbed and decomposed on an Fe2O3(0001) surface have been conducted. Comparative analyses of the structure properties and adsorption processes during the simulation at elevated temperature have been carried out. The results depict the key interactions including the covalent P-O bonds, pure ionic Na-O or Fe-O interactions. The iron oxide surface plays an important role in the bridging bond decomposition scheme which can both promote and suppress phosphate depolymerization. It is found that the chain length of polyphosphates does not have considerable effects on the decomposition of phosphate clusters. This study provides detailed insights into the interaction of a phosphate cluster on an iron oxide surface at high temperature, and in particular the depolymerization/polymerization of an inorganic phosphate glass lubricant, which has an important behavior under hot metal forming conditions.

Thin film lubrication of hexadecane confined by iron and iron oxide surfaces: A crucial role of surface structure.

A comparative analysis of thin film lubrication of hexadecane between different iron and its oxide surfaces has been carried out using classical molecular dynamic simulation. An ab initio force-field, COMPASS, was applied for n-hexadecane using explicit atom model. An effective potential derived from density functional theory calculation was utilized for the interfacial interaction between hexadecane and the tribo-surfaces. A quantitative surface parameterization was introduced to investigate the influence of surface properties on the structure, rheological properties, and tribological performance of the lubricant. The results show that although the wall-fluid attraction of hexadecane on pure iron surfaces is significantly stronger than its oxides, there is a considerable reduction of shear stress of confined n-hexadecane film between Fe(100) and Fe(110) surfaces compared with FeO(110), FeO(111), Fe2O3(001), and Fe2O3(012). It was found that, in thin film lubrication of hexadecane between smooth iron and iron oxide surfaces, the surface corrugation plays a role more important than the wall-fluid adhesion strength.

Simultaneous measurement of pure curvature and twist distribution fields by a five-aperture shearing and two-fourier filtering technique.

A five-aperture shearing and two-Fourier filtering technique to measure simultaneously pure curvature and twist distribution fields of a deformed object is proposed. In this method the slope fringes that are contained in the patterns of curvature and twist fringes can be completely eliminated. Thus patterns of pure curvature and twist fringes with a good contrast can be obtained. A theoretical analysis and experimental results are given.