Corrosion behavior of T24, T92, VM12, and AISI 304 steels exposed to KCl–NaCl–K2SO4–Na2SO4 salt mixtures

The corrosion mechanisms of T24, T92, VM12, and AISI 304 steels are studied under the influence of NaCl–KCl, NaCl–Na₂SO₄, and KCl–K₂SO₄ salt mixtures in a dry air atmosphere at 650°C for 15 days. NaCl–KCl was the most aggressive deposit and AISI 304 stainless steel exhibited the highest corrosion resistance. There was no relation between the Cr content of the ferritic steels and their corrosion resistance in NaCl–KCl. In contrast, the resistance of high-Cr steels was better when exposed to NaCl–Na₂SO₄ and KCl–K₂SO₄. The high-Cr and the low-Cr steels were more susceptible to NaCl–Na₂SO₄ and to KCl–K₂SO₄, respectively.     

Excimer Laser Processing of Metals

Laser processing of materials is a new technique for modifying the near-surface region without altering bulk characteristics. The use of excimer lasers is attractive in terms of its potential applications, including its combined utilization with other surface treatment techniques, and from the standpoint of physical metallurgy research. We describe herein some of our current research and its projections toward surface-related properties improvement.     

Dual FastSLAM: Dual Factorization of the Particle Filter Based Solution of the Simultaneous Localization and Mapping Problem

The process of building a map with a mobile robot is known as the Simultaneous Localization and Mapping (SLAM) problem, and is considered essential for achieving true autonomy. The best existing solutions to the SLAM problem are based on probabilistic techniques, mainly derived from the basic Bayes Filter. A recent approach is the use of Rao-Blackwellized particle filters. The FastSLAM solution factorizes the Bayes SLAM posterior using a particle filter to estimate over the possible paths of the robot and several independent Kalman Filters attached to each particle to estimate the location of landmarks conditioned to the robot path. Although there are several successful implementations of this idea, there is a lack of applications to indoor environments where the most common feature is the line segment corresponding to straight walls. This paper presents a novel factorization, which is the dual of the existing FastSLAM one, that decouples the SLAM into a map estimation and a localization problem, using a particle filter to estimate over maps and a Kalman Filter attached to each particle to estimate the robot pose conditioned to the given map. We have implemented and tested this approach, analyzing and comparing our solution with the FastSLAM one, and successfully building feature based maps of indoor environments.     

Effect of functional monomer on the stability and film properties of thermosetting core-shell latexes

Functionalized core-shell latexes were prepared by copolymerization of butyl acrylate and methyl methacrylate with 2-hydroxyethyl methacrylate (HEMA) or methacrylic acid (MAA), which were added during the first or second stages of polymerization, respectively. The HEMA and MAA concentrations were increased while the equivalent ratio of functional groups remained constant. Colloidal stability, particle size, particle size distribution, film properties and morphology were studied as functions of functional monomer content. The upper limit functionality content was limited by the stability of the system during synthesis. A bimodal particle size distribution was observed for high concentrations of functional monomers. Increase in carboxyl and hydroxyl functionalities improved tensile strength and modulus for un-crosslinked films, and generally higher tensile strength, tensile modulus and storage modulus at high temperature were obtained after the functional latexes were crosslinked with a cycloaliphatic diepoxide.     

Using OR to adapt supply chain management best practices to humanitarian logistics

The demand for humanitarian aid is extraordinarily large and it is increasing. In contrast, the funding for humanitarian operations does not seem to be increasing at the same rate. Humanitarian logistics has the challenge of allocating scarce resources to complex operations in an efficient way. After acquiring sufficient contextual knowledge, academics can use operations research (OR) to adapt successful supply chain management best practices to humanitarian logistics. We present two cases of OR applications to field vehicle fleet management in humanitarian operations. Our research shows that by using OR to adapt supply chain best practices to humanitarian logistics, significant improvements can be achieved.     

Oxidation Resistance of Thermal Barrier Coatings Based on Hollow Alumina Particles

Thermal barrier coatings were synthesized in a single step process from a slurry containing Al microspheres onto different Ni-based superalloys. Upon growth of the coating a top coat of hollow alumina spheres linked to an aluminium diffused coating through an alumina TGO formed. The isothermal and cyclic oxidation tests at different temperatures (900 till 1100 °C) up to 1000 h or 1500 cycles revealed progressive growth of different thermal oxides depending on the substrate composition. Faster degradation of the coatings occurred in the titanium-rich substrates (e.g. IN-738LC and PWA1483) compared to the titanium-poor ones (CM-247LC and René N5). By comparing with conventional low activity aluminide coatings, it appeared that the incorporation of alloying elements (notably Ti and Ta) to the diffused layers upon the high activity slurry coating process is responsible for such fastest degradation.     

Cathodic electrodeposition of cerium-based oxides on carbon steel from concentrated cerium nitrate solutions: Part I. Electrochemical and analytical characterisation

In this work the elaboration by cathodic electrodeposition of cerium-based oxides on carbon steel from relatively concentrated cerium nitrate solutions is investigated. In particular, the study presented here (Part I) focuses on the electrochemical and analytical characterisation of the films and on the correlations between the electrochemical features and the characteristics of the layers. The effect of other parameters such as concentration, temperature, pH and additives to improve the behaviour of the film against corrosion will be investigated in part II of the study.The electrochemical characterisation will reveal that Ce(IV)–steel interactions can be responsible for some weak electrochemical waves appearing in the cyclic voltammograms that often are attributed to oxygen or nitrates reduction. This results from the oxidation of Ce(III) solutions to Ce(IV) in contact with air. Furthermore, the deposits strongly depend on the applied current density. Low current densities do not render fully covering deposits on the steel and a carbonated green rust will appear. On the contrary, the increase of the current density leads to denser layers of relatively small crystallite size that readily covers the steel surface. The deposits have a needle-like morphology and the Ce content achieves a plateau of about 20–22 at.%. However, a significant network of cracks appears probably occurring during the deposition process itself. The differential scanning calorimetry (DSC) results indicate that the deposits are not fully crystalline after 550 °C in contrast with the X-ray diffraction (XRD) patterns that unambiguously show a fluorite-type CeO₂ phase whose crystallite size decreases with increasing the current density. The rinsing medium also brings about different features of the films. Rinsing with water allows to incorporate more nitrates and to adsorb CO₂ than when rinsing with ethanol. However, R-OH bonds will be trapped in the latter.     

Cyclic and Isothermal Oxidation at 1,100 °C of a CVD Aluminised Directionally Solidified Ni Superalloy

CVD aluminide coatings deposited on a Directionally Solidified (DS) substrate were oxidized at 1,100 °C up to 240 h under isothermal and cyclic oxidation conditions to study the growth mechanisms of the oxide scales and the possible degradation of the coatings. The specimens were investigated using light and scanning electron (SEM) microscopy, energy-dispersive spectrometry (EDS) and X-Ray Diffraction (XRD). The results indicate that the coatings provide a much greater beneficial effect under isothermal conditions than upon cycling. The cycled specimens undergo oxide-scale spallation and increased roughening, which can derive from growth and thermal stresses as well as from the NiAl → Ni₃Al phase transformation associated with Al depletion. Under isothermal conditions, typical oxide scales formed with the appearance of some rumples. However, the origin of rumpling is uncertain from these experimental results.     

The adhesion of copper films deposited onto aluminum nitride

Good adhesion between copper film and AlN substrate is obtained when the surface of AlN is laser-irradiated prior to copper film deposition and post deposition annealing is conducted. Surface chemistry of AlN substrates before and after laser irradiation and the interfacial reactions of copper film/AlN couples were studied with Auger Electron Spectroscopy (AES) to understand the adhesion mechanisms. The surface of as-received AlN substrates was covered with a thin sheath of Al₂O₃. Laser irradiation removed the surface Al₂O₃ layers, smoothened the surface, and decomposed AlN leaving metallic aluminum on the surface. The interfacial reactions in the copper film/AlN couple are affected by the amounts of oxygen and metallic aluminum available at the interface. The adhesion mechanism is the formation of a Cu-O-Al compound at the interface of copper film/AlN couple. Since copper does not react with AlN, laser induced decomposition of AlN seems to be the driving force for the formation of the compound. This revised version was published online in September 2006 with corrections to the Cover Date.