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Authors: Nicolas Maier, Klaus G. Nickel, Christine Engel, Andreas Mattern
Abstract: Cordierite Mg2Al4Si5O18 is a material for diesel particulate filters (DPF) with high potential. Its resistance to a simplified model ash has been tested on single crystals at temperatures up to 1050°C, which are realistic for use under ‘worst case’ conditions. A mixture of Ca, Mg and Zn phosphates, which are typical main constituents of many DPF ashes, was used as model ash. Single crystals were examined in order to investigate the orientation dependence of attack due to the strongly anisotropic nature of the Cordierite crystal lattice. Strong corrosion by the ash occurs at 1050 °C, connected to excessive ash melting. The molten ash attacks Cordierite by fast dissolution of the substrate with melt (super)saturation within minutes. Anisotropy of the dissolution process could not be detected. The initial kinetics are dominated by saturation effects, which slow down corrosion. The saturated melt attacks Cordierite by reaction processes leading to the formation of new crystalline phases. This process is much slower than the initial dissolution process but may significantly contribute to the destruction of Cordierite substrates if large contact areas between ash melt and Cordierite exist.
Authors: Marju Mannila, Antti Häkkinen
Abstract: The object of the research was to compare the corrosion resistance of three types of multioxide technical ceramics in hydrofluoric acid containing aqueous media according to a full factorial experimental plan with pH and fluoride ion concentration as variables. The samples were a silicon carbide doped aluminum silicate material, and two membrane coated aluminum silicates with one containing a membrane on both sides of the ceramic plate. The substrates contained more additives on alumina, while the membrane coats were of higher grade aluminum oxide. The samples were shaken in containers for up to two weeks, and their remaining hardness and weight losses were measured. Daily samples drawn from the liquid phase were analyzed for dissolved components. With respect to all measured properties, fluoride concentration affected the materials more detrimentally than alterations in pH.
Authors: Shahin Khameneh Asl, Mohammad Reza Saghi Beyragh, Mahdi Ghassemi Kakroudi
Abstract: Interest in nanomaterials has increased in recent years. This is due to the potential of size reduction to nanometric scale to provide properties of materials such as hardness, toughness, wear, and corrosion resistance. The current study is focused on WC-Co cermet coats, materials that are extensively used in applications requiring wear resistance. In this work, WC-17Co powder was thermally sprayed onto mild steel using High Velocity Oxy Fuel (HVOF) spray technique. The nanostructured specimen was produced from sprayed sample by heat-treating at 1100°C in a vacuum chamber. Their structures were studied by using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Polarization and electrochemical impedance spectroscopy (EIS) tests were performed on the both types of coated samples in 3.5% NaCl solution. The amorphous phase in WC-17Co coating was transformed to crystalline phases by heat treatment at high temperatures. The heat treatment of these coatings at high temperature also resulted in partially dissolution of WC particles and formation of new crystalline phases. Generation of these phases produced the nanostructured coating with better mechanical properties. Comparative electro chemical test results showed that, the heat treatment could improve corrosion resistance of the nanostructured WC-17Co coat than the as sprayed coats.
Authors: H.H. Seleem, A.M. Rashad, B.A. El-Sabbagh
Abstract: The current work reports the influence of synthetic seawater on some of the durability aspects of an ordinary concrete mixture (control) and six pozzolan-concrete mixtures. Three types of pozzolanic materials were employed; silica fume (SF), ground granulated blast furnace slag (GGBS) and metakaolin (MK). The pozzolanic materials were employed as an addition to cement in binary and ternary combinations. All mixtures were tested for strength deterioration ratio (SDR) after 3, 6, and 12 months of exposure to synthetic seawater, permeability was measured after 6 and 12 months of exposure. It was found through this investigation that pozzolans increase the ability of concrete to withstand aggressive environment and prevent most of the deterioration signs. The pozzolanic materials serve also to increase the strength and to minimize the strength loss (SDR) upon exposure to seawater. The pozzolanic materials led to reduce concrete permeability compared to control.
Authors: Philip Egberts, Roland Bennewitz
Abstract: Scratches on KBr(100) surfaces were produced and examined with an atomic force microscope (AFM) operated in an ultra-high vacuum (UHV) environment. Scratches with lengths on the order of 100s of nanometers and depths on the order of atomic layers were investigated. Non-contact AFM topographic images of scratches revealed screw and edge dislocation activity around the scratch sites, illuminating the role of plastic deformation in wear processes. Friction coefficients of approximately 0.3 were measured during scratching, more comparable to macroscopic friction experiments than those measured in low-load, single asperity experiments.
Authors: Seung Min Yeo, Emerson Escobar Nunez, Andreas A. Polycarpou
Abstract: With increasing importance of advanced coating materials for use in interacting parts of air-conditioning compressors, several commercially available polymer-based coatings (PTFE/ Pyrrolidone-1, 2, PTFE/MoS2-1, 2, Fluorocarbon, PEEK/PTFE and PEEK/Ceramic coatings) were tribologically evaluated. Friction and wear behavior of these coatings, deposited on gray cast iron were in-situ measured using a specialized pin-on-disk tribometer. The experiments were performed under compressor specific conditions, namely under oscillatory motion simulating piston-type compressor and unidirectional motion simulating swash plate-type compressor operation. Also, the tribological properties of newly developed ATSP-based coatings deposited on aluminum substrates were evaluated under ball-on-disk, unidirectional sliding experiments. Polymer-based coatings exhibited excellent frictional properties, while their wear resistance was also acceptable, even though lower compared to hard coatings. However, the wear debris generated at the interface acted as a third-body solid lubricant with a beneficial role in their overall performance. ATSP coatings blended with fluoroadditives showed superior frictional behavior than pure ATSP coatings, and their wear rate was extremely low compared to commercially available PTFE-based coatings.
Authors: Giuseppe Pezzotti
Abstract: Photo- and electro-stimulated probes have been employed for quantitatively evaluating highly graded residual stress fields generated at the surface of alumina hip joints. Optical calibrations revealed large differences in probe size, which strongly affected the detected magnitude of residual stress. A comparison between the responses of Raman and fluorescence probes in polycrystalline alumina showed that the depth of those probes spread to an extent in the order of the tens of microns even with using a confocal probe configuration. On the other hand, the electro-stimulated luminescence emitted by oxygen vacancy sites (F+ center) in the alumina lattice represented a suitable choice for confining to a shallow volume the stress probe. The electron probe enabled confining the measurement depth to the order of the tens of nanometers. Maps of surface residual stress were collected on both main-wear and non-wear zones of an alumina femoral head. A comparison among stress maps taken at exactly the same location, but employing different probes, clarified the averaging probe effects on surface stress magnitude.
Authors: Volker Presser, Klaus G. Nickel, Christoph Berthold

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