Dissolution of chromium-enriched inclusions and pitting corrosion of resulfurized stainless steels

The dissolution of MnS inclusions enriched in chromium (30 to 40 wt pct Cr) and the corrosion susceptibility of resulfurized stainless steel were studied in various NaCl- and NaClO₄-based solutions by X-ray photoelectron spectroscopy, secondary ion mass spectroscopy, scanning electron microscopy (SEM), and the electrochemical microcell technique. It has been shown that chromium-enriched inclusions do not undergo dissolution under free corrosion conditions. By contrast, electrochemical dissolution of inclusions occurs at high potential values (above 500 mV vs saturated calomel electrode) in all the solutions, followed by stable pitting. It has also been shown that some areas containing chromium-enriched inclusions exhibited stable pitting at low potentials (below 100 mV vs saturated calomel electrode) in the electrolytes with chloride ions. Field-emission SEM experiments have revealed that the matrix undergoes dissolution around these inclusions. An assumption is proposed for describing pitting corrosion mechanisms.     

Selection of Contributing Natural Poles for the Characterization of Perfectly Conducting Targets in Resonance Region

In the resonance region, the radar scattering response of any target can be modeled by natural poles, with the formalism of the singularity expansion method. The mapping of poles gives useful information for the discrimination of radar targets. In this paper, we show that a reduced number of natural poles is sufficient to characterize such objects. Furthermore, we propose a procedure for selecting the poles that actually contribute to the scattering response. Results are presented for various perfectly conducting (PC) canonical targets and for a PC complex shape target.     

Microwave-assisted polymerization process: A way to design new, high molecular weight poly(arylimidazole)s

In this paper, the microwave-assisted synthesis of high molecular weight poly(arylimidazole)s is described. These polymers were obtained by a one-pot polycondensation reaction involving a bis(α-diketone), an aromatic dialdehyde and ammonium acetate. Depending on the dialdehyde monomer, different poly(arylimidazole)s structures were synthesized. Structural characterization (¹H and ¹³C NMR), thermal properties (T_g, thermal stability) as well as a molecular weight determination of the polymers are reported.     

On the effective Lewis number formulations for lean hydrogen/hydrocarbon/air mixtures

Decades of research have underlined the undeniable importance of the Lewis number (Le) in the premixed combustion field. From early experimental observations on laminar flame propagation to the most recent DNS studies of turbulent flames, the unbalanced influence of thermal to mass diffusion (i.e. Le ≠ 1), known as nonequidiffusion, has shed the light on a wide range of combustion phenomena, especially those involving stretched flames. As a result the determination of the Lewis number has become a routine task for the combustion community. Recently, the growing interest in hydrogen/hydrocarbon (HC) fuel blends has produced extensive studies that have not only improved our understanding of H₂/HC flame dynamics, but also, in its wake, raised a fundamental question: which effective Lewis number formulation should we use to characterize the combustion of hydrogen/hydrocarbon/air blends? While the Lewis number is unambiguously defined for combustible mixtures with a single fuel reactant, the literature is unclear regarding the appropriate equivalent formulation for bi-component fuels. The present paper intends to clarify this aspect. To do so, effective Lewis number formulations for lean (φ = 0.6 and 0.8) premixed hydrogen/hydrocarbon/air mixtures have been investigated in the framework of an existing outwardly propagating flame theory. Laminar burning velocities and burned Markstein lengths of H₂/CH₄, H₂/C₃H₈, H₂/C₈H₁₈ and H₂/CO fuel blends in air were experimentally and numerically determined for a wide range of fuel compositions (0/100% → 100/0% H₂/HC). By confronting the two sets of results, the most appropriate effective Lewis number formulation was identified for conventional H₂/HC/air blends. Observed deviations from the validated formulation are discussed for the syngas (H₂/CO) flame cases.     

Experimental study of carrier transport in multi-layered structures

Gate stress measurements are applied to Flash cell array structures. The counter intuitive V_t shift is associated to the charge redistribution in the ONO layer. This redistribution of charge follows Poole–Frenkel conduction mechanisms. In multi-level Flash, the total charge in the nitride layer need to be minimized, and well-controlled, in order to achieve good data retention of the device.     

Modulation of dopamine release in the nucleus accumbens by 5-HT1B agonists: involvement of the hippocampo-accumbens pathway

Changes in extracellular levels of dopamine (DA), DA metabolites DOPAC and HVA, and the serotonin metabolite 5-HIAA, were measured by microdialysis in the rat nucleus accumbens (n. acc) after treatments with serotonin (5-HT)1A (8-OH-DPAT) or 5-HT1B (RU 24969 and S-CM-GTNH2) receptor agonists. Subcutaneous injections of RU 24969 (0.02-2 mg/kg) dose-dependently decreased 5-HIAA levels (0 to -38%), and also induced long-lasting increases in DA levels (0 to +37%) and DOPAC (+11% at the dose 0.5 mg/kg) in the shell of the n. acc, whereas 8-OH-DPAT (0.25 and 0.5 mg/kg) reduced 5-HIAA levels (-25%) and very slightly increased DOPAC at the lower dose (+4%), but had no effect on DA levels. Three weeks after interruption of the subicular efferent projections, the increase in DA levels previously observed after systemic injections of RU 24969 was abolished. Microinjections of RU 24969 (10 micrograms/microliter) or S-CM-GTNH2 (3 micrograms/microliter) into the ventral subicular area reproduced the effects of systemic injections of RU 24969 cn DA levels and increased DOPAC (+13%; +19%, respectively) and HVA levels (+23%; +24%), with no significant change in 5-HIAA. It is concluded that: (1) serotonin interacts with the mesolimbic dopaminergic system through 5-HT1B, but not 5-HT1A, receptors: and (2) serotonin interaction with the mesolimbic dopaminergic system involves postjunctional 5-HT1B heteroreceptors located in the ventral subicular area, which modulate the activity of glutamatergic hippocampo-accumbens pathways and only secondarily alter DA levels in the n. acc. The possible relevance of these results for schizophrenia is discussed.     

Anomalous corrosion resistance behavior of Mo-containing SS in alkaline media: The role of microstructure

Electrochemical and microscopy techniques were used to investigate the role of the microstructure in the corrosion behavior of Mo-containing stainless steel grades in alkaline chloride rich media. It is shown that under certain conditions, Mo containing grades can be even less corrosion resistant than Mo free ones. This anomalous behavior is straightforwardly related to the austenite phase. On the other hand, results show that Mo confirms its clearly beneficial effect in ferritic and duplex steels. Current transient analysis indicated that the protection mechanism in those cases appears to be related to an inhibited pit initiation rather than faster repassivation kinetics.     

On melting of silicon carbide under pressure

The melting of silicon carbide has been studied at pressures 5?C8 GPa and temperatures up to 3300 K. It has been found that SiC melts congruently, and its melting curve has negative slope of ?44 ± 4 K/GPa.     

In Situ Film-Forming and Friction-Reduction Mechanisms for Carbon-Nanotube Dispersions in Lubrication

Current requirements in automotive lubrication impose extremely complex formulation. For environmental reasons, it is important to reduce or eliminate the presence of sulphur and phosphorus contained in tribological additives. For that purpose, multi-walled carbon nanotubes have been dispersed in oil in various concentrations. The lubrication mechanisms of such dispersions in mixed and EHL regimes have been investigated by means of the IRIS tribometer that allows us simultaneous contact visualization, film thickness and friction measurement under controlled contact kinematics. The lubricant film-forming capability has been determined as a function of the entrainment velocity and the nanotube content: the presence of carbon nanotubes within the contact results in a local increase in the film thickness and it can be shown that the contact acts as a filter of carbon-nanotube aggregates. Introduction of sliding results in a diminution of the number of aggregates passing through the contact. Moreover, a reduction in friction and a drift in the wear onset have been observed under controlled contact kinematics: this behaviour originates from the transient propagation of carbon-nanotube aggregates through the contact and a friction law is proposed taking into account the contact heterogeneity.