Tribological behavior of composites fabricated by reactive SPS sintering in Ti-Si-C system

In this study, wear and friction behavior of two based-composites from the Ti-Si-C system, (40 wt% TiC; 28 wt% Ti₅Si₃; 17 wt% Ti₃SiC₂) and (18 wt% TiC; 26 wt% Ti₅Si₃; 41 wt% Ti₃SiC₂) reinforced by 15 wt% of large size SiC (100-150 µm) particles were investigated. The four-phase composites exhibited approximatively the same friction coefficient (µ ~ 0.9) under high loads (10 N and 7 N). The composite with high Ti₃SiC₂ showed higher wear rate values by one order of magnitude. However, under 1 N, the composite with high TiC content showed a higher running-in period and a lower steady state µ value (0.37 after 1000 m sliding distance). Scanning electron microscopy, Energy Dispersive X-Ray and Raman spectroscopy analysis of the worn surfaces of the two composites revealed that oxidation was the dominant wear mechanism. The oxidation process and the removal kinetics of the oxides during sliding controlled the tribological behavior of the composites. The influence of processing variables on microstructures development and wear mechanisms of the composites is discussed.     

An experimental investigation on the rate of CO<Subscript>2</Subscript> absorption into aqueous methyldiethanolamine solutions

In this paper, the CO₂ absorption rates into aqueous solutions of Methydiethanolamine (MDEA) at various concentrations of 1, 2, 3 and 4 M and temperatures varying from 293 to 323 K were measured by using a laboratory stirred reactor. The kinetics experiments were conducted under a pseudo first order regime. The data were analyzed by means of chemical absorption theory and the kinetic parameters associated with the reaction, such as the reaction order and the reaction rate constants, were evaluated. The effect of temperature on the reaction rate constant was assessed and the activation energy was evaluated at about 44.12 kJoule/mol.     

Flocculation and viscoelastic behavior of industrial papermaking suspensions

The effects of the surface charge type and density C496, C492 and A130LMW polyacrylamides (PAMs) on the rheological behavior of real industrial papermaking suspensions were quantitatively related to the degree of flocculation for the same industrial papermaking suspensions. The floc sizes were larger but less dense when anionic PAM was used, and this due to the repulsive forces between the anionic PAM and colloidal particles, leading to the development of open structure flocs of less density. On the other hand, rheological measurements showed that the papermaking suspension is thixotropic with a measurable yield stress. The results showed that the magnitude of the critical stress, τ _c , complex viscosity, η*, elastic modulus, G′, and viscous modulus, G″, depend on the number of interactions between the PAM chains and particle surface and the strength of those interactions. Cationic PAM showed higher values of η*, G′, G″ and τ _c compared to anionic PAM. This behavior is in good agreement with Bingham yield stress, τ _B , adsorption and effective floc density results. Similar to oscillatory measurements, creep measurements also showed that the deformation was much lower for the cationic PAM based suspensions than for the anionic PAM based suspensions. Furthermore, the results revealed that increasing the cationic PAM surface charge decreases the floc size but increases the adsorption rate, elasticity and effective floc density proposing differences in the floc structures, which are not revealed clearly in the Bingham yield stress measurements.     

Kinetic of CO2 absorption and carbamate formation in aqueous solutions of diethanolamine

The absorption rates of CO₂ into aqueous solutions of Diethanolamine (DEA) with varying concentrations from 0.2 to 4M and temperature range from 293 to 323 K were measured by using a laboratory stirred reactor. The CO₂ partial pressure was varied in a range that the reaction would occur in pseudo first order regime. Experimental data were analyzed and the kinetic parameters associated with the reaction were determined. The activation energy for the deprotonation of the intermediate zwitterion was estimated at about 11.4 kcal/mol. The contribution of carbamate formation to the overall absorbed CO₂ was experimentally evaluated and found to be of the order of 100%.     

Platinum degradation mechanisms in proton exchange membrane fuel cell (PEMFC) system: A review

Proton Exchange Membrane Fuel Cells (PEMFCs) have the perspective to intensely decrease global emission through environmentally-friendly potential. This review paper summarizes the degradation of platinum catalyst layer that has become a significant issue in the improvement of PEMFCs. The review intends to categorise and provide a clear understanding between disintegration and agglomerate that occurs during platinum degradation. In each process, different degradation mechanisms and their migration processes are presented. The improvement in platinum degradation as a function of increasing the performance of PEMFC is established. Prospects for addressing platinum degradation through the exploration of further experimental and numerical research are recommended. Lastly, this paper through recommendation attempts to prevent platinum degradation and reduces high costs associated with the replacement of catalysts in the PEMFCs.     

Radionuclide cisternography in spontaneous intracranial hypotension

A case of secondary syphilis acquired by nonsexual household contact in a prepubertal girl is presented.     

Fabrication of polysulfone nanocomposite membranes with silver‐doped carbon nanotubes and their antifouling performance

In this study, polysulfone (PSf)/silver‐doped carbon nanotube (Ag‐CNT) nanocomposite membranes were prepared by a phase‐inversion technique; they were characterized and evaluated for fouling‐resistant applications with bovine serum albumin (BSA) solutions. Carbon nanotubes were doped with silver nanoparticles via a wet‐impregnation technique. The prepared Ag‐CNT nanotubes were characterized with scanning electron microscopy (SEM)/energy‐dispersive X‐ray spectroscopy, X‐ray diffraction, Raman spectroscopy, and thermogravimetric analysis. The fabricated flat‐sheet PSf/Ag‐CNT nanocomposite membranes with different Ag‐CNT loadings were examined for their surface morphology, roughness, hydrophilicity, and mechanical strength with SEM, atomic force microscopy, contact angle measurement, and tensile testing, respectively. The prepared composite membranes displayed a greater rejection of BSA solution (≥90%) and water flux stability during membrane compaction with a 10% reduction in water flux values (up to 0.4% Ag‐CNTs) than the pristine PSf membrane. The PSf nanocomposite membrane with a 0.2% Ag‐CNT loading possessed the highest flux recovery of about 80% and the lowest total membrane resistance of 56% with a reduced irreversible fouling resistance of 21%. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44688.     

Global stabilization of discrete-time homogeneous systems

The feedback stabilization of continuous time Δ^r-homogeneous systems has been studied by several authors, see for instance (Dayawansa and Martin, Proceedings of the 28th C.D.C., Tampa, Florida, December, 1989, Hermes, J. Differential Equations 92 (1991) 76–89, Hermes, Systems Control Lett. 24 (1995) 7–11, Kawski, Proceedings of the 27th C.D.C., Texas, 1988, Texas, Kawski, Control Theory and Advanced Technology, vol. 6, MITA Press, Tokyo, 1996, pp. 497–516, Sepulchre and Aeyels, Math. Control Signal Systems 9 (1996) 34–58). In (Kawski, Analysis of Controlled Dynamical Systems, Birkhauser, Basel, 1991, Kawski, Proceedings of IFAC NOLCOS, 1995), Kawski gave an intrinsic concept of homogeneity with respect to general smooth dilations. In this note, we define the homogeneity of transition maps w.r.t. continuous dilations and we show how one can construct a global stabilizing feedback control for discrete-time homogeneous systems which are locally asymptotically stabilizable.     

Friction and wear properties of MoAlB against Al2O3 and 100Cr6 steel counterparts

The present work investigates, for the first time, the dry sliding friction and wear behaviour of fully dense, predominantly single-phase MoAlB ceramics against alumina (Al₂O₃) and 100Cr6 steel counterparts. Against Al₂O₃, the friction coefficient (μ) increased with increasing load and the wear was highly dependent on the load applied. A transition from mild wear under 1 N and 4 N to severe wear at 10 N occurred. Scanning electron microscopy revealed that abrasion is the dominant wear mechanism. Against steel, μ decreased with increasing load and the wear rates were low, under all applied loads. The morphologies of the worn surfaces against steel were characterized by the appearance of a rippled layers. Atomic force microscopy and Raman spectroscopy were used to propose a possible formation mechanism of such patterns. X-ray photoelectron spectroscopy revealed the rippled surfaces to be composed of Fe₂O₃ and a mixture of MoO_x.