Sulfonated hexagonal boron nitride is explored as a potential filler to prepare Nafion hybrid membranes for direct methanol fuel cell (DMFC) applications. The layered morphology of h-BN effectively ...suppresses the methanol crossover in the Nafion-h-BN membrane, while the presence of sulfonic acid groups improves the proton conductivity by providing an additional pathway for proton transport. Consequently, the Nafion-h-BN hybrid membranes display a significantly reduced methanol crossover current density. On the other hand, the optimized Nafion-h-BN hybrid membrane displays a proton conductivity of 214 mS cm
−1
, which is ∼58% higher than that of the pristine Nafion membrane. The single-cell DMFC employing Nafion-h-BN (0.75 wt%) membrane delivers a peak power density of 165 mW cm
−2
at 70 °C, while only a peak power density of 65 mW cm
−2
is achieved with the pristine Nafion under similar operating conditions.
Sulfonated hexagonal boron nitride is explored as a potential filler to prepare Nafion hybrid membranes for direct methanol fuel cell (DMFC) applications.
Sulfonated graphitic carbon nitride (s-GCN) is first realized as an effective bifunctional filler in modifying the Nafion membrane for direct methanol fuel cell (DMFC) application. Carbon nitride ...with amino (−NH2) and imino (−NH) functional groups was successfully synthesized through one-step calcination of melamine (C3H6N6) and thereafter surface functionalized to incorporate sulfonic acid (−SO3H) groups. The proton transfer in the Nafion–s-GCN hybrid membrane is enhanced by the presence of sulfonic acid groups in the filler and also by acid–base interaction between −NH2 groups present on the GCN with −SO3H groups of hybrid membrane. The Nafion–s-GCN hybrid membrane with an optimized filler content exhibits a proton conductivity of 183 mS cm–1, which is about 36% higher in relation to the pristine Nafion membrane. In addition, porous nature of GCN nanosheets in the hybrid membrane enhances movement of hydronium ions while acting as a barrier for methanol molecule. As a result, the Nafion–s-GCN hybrid membranes displayed much lower methanol crossover current density than that of the pristine Nafion membrane. The DMFC comprising Nafion–s-GCN (0.5 wt %) hybrid membrane delivers a peak power density of 125 mW cm–2 at 70 °C under ambient pressure, while a peak power density of 65 mW cm–2 is realized for pristine Nafion membrane under similar operating conditions.
The effect of post-weld solution along with different double aging treatments on precipitation of various strengthening phases in Alloy 718 weld is carried out in the current assessment. The ...formation of intermetallic phases in the weld zone deteriorates the mechanical properties and quality of the weld joint. The high-temperature solution treatment at 1165 °C/1 h has dissolved the intermetallic phases and makes a suitable quantity of alloying elements accessible for precipitation of the strengthening phases. To analyze the impact of aging temperature and holding time on
δ
,
γ'
and
γ"
phase precipitation, four different heat treatment paths are designed. The heat treatment holding time is reduced by 53% on the welded component by applying a higher aging temperature compared to the conventional standard aging temperatures. The variation in aging temperature and holding time followed by solution treatment changes the platelet morphology of the
δ
phase to needle shape in the grain boundary. Significant enhancement in the tensile strength (21%) and weld hardness (121%) is witnessed due to duplex aging treatment compared to as-welded condition. The XRD analysis confirms the precipitation of
γ'
and
γ''
strengthening phases inside the grain and
δ
particles in the grain boundaries.
Graphical abstract
Sulfonic acid functionalized graphene (S-graphene) is explored as a potential inorganic filler as well as a solid acid proton conducting medium to realize a hybrid membrane with Nafion for a direct ...methanol fuel cell (DMFC). The simple, but effective, functionalization of graphene is performed by sulfonic acid containing aryl radicals to increase the number of sulfonate groups per unit volume of graphene domain. Nafion–S-graphene hybrid membranes increase compactness of ionic domains and enhanced proton conductivity while restricting the methanol crossover across the membrane. DMFCs with a Nafion–S-graphene (1 wt %) hybrid membrane deliver a peak power density of 118 mW cm–2 at a load current density of 450 mA cm–2 while operating at 70 °C under an ambient pressure. By contrast, operating under identical conditions, a peak power density of 54 mW cm–2 at a load current density of 241 mA cm–2 is obtained with the pristine recast Nafion membrane. The Nafion–S-graphene hybrid membranes are extremely beneficial and useful for DMFCs in addressing many critical problems associated with commercial Nafion membranes.
Nitrogen and fluorine co-doped graphite nanofibers (N–F/GNFs) were synthesized using melamine and ammonium fluoride as precursors, respectively, for use as metal-free catalysts for oxygen reduction ...reaction (ORR). The N–F/GNF catalyst undergoes structural transformation resulting in wrinkled graphene structures with many open-edge sites when F is doped into N/GNF. The developed catalyst has no effect on CH3OH or CO, which makes it highly desirable as a metal-free electrocatalyst for the ORR. The developed catalyst was subjected to 20,000 repeated potential cycles, no degradation of ORR activity was observed in acidic media. X-ray photoelectron spectroscopy analysis of the N–F/GNF catalyst reveals the presence of active pyridine and graphitic type N with highly active semi-ionic C–F bond in the graphitic structure. First-principles density functional theory calculations further support the formation of graphene structures from the GNF with the interlayer distance increasing from 3.9 to 5.1Å. The Bader charge analysis predicts the site specificity of F doping in N-doped GNF. This N–F/GNF catalyst delivers a peak power density of 165mWcm−2 at a load current density of 850mAcm−2 in a H2/O2 polymer electrolyte fuel cell, as a nonmetallic electrocatalyst in acidic media.
Comparison of fluidization index in circular, square and rectangular cross sectional shape fluidized bed column. Display omitted
•Experiments were done using square and rectangular cross sectional ...shape columns.•Fine magnetite particles (−45μm) were used for the study.•Stability region increases with increase of equivalent aspect ratio.•Rectangular shape column will provide better stability to fluidized bed.
Dry coal washing is gaining popularity on account of its ability to produce clean coal without the use of water which is becoming to be a costly resource for beneficiation. Air dense medium fluidized bed separation (ADMFBS) is one of the dry beneficiation techniques which is used for cleaning of coal. Fine magnetite particles are used as medium to make pseudo-fluid by fluidization method. The effectiveness of ADMFBS depends on stability of the fluidized bed. In the present work, an attempt has been made to study the stability characteristics of different cross-sectional shapes of fluidized bed having same cross-sectional area. Different indicators like fluidization index, particulate expansion function, pressure drop of bed and distributor, minimum fluidization and bubbling velocities were used to characterize the stability of fluidized bed. The effect of different operating and design parameters on the homogeneity and stability of the fluidized bed was studied. It was observed that cross sectional shape of the fluidized bed column has a significant effect on the stability of the bed. Moreover, rectangular cross-sectional shape provides better stability properties compared to square or circular shape.
The present work addresses the weldability of dissimilar materials Inconel 718 and AISI 316L stainless steel through metallurgical and mechanical characterization of the joint. The 3D heat transfer ...model analyzes the solidification behavior for a pulsed arc energy source. However, intermetallic formation deteriorates the welded joint properties and promotes solidification cracking in the weld zone. We attempt to join these dissimilar materials without using any filler materials and allowing solidification with the use of a pulse current. The use of a pulse current during microplasma arc welding assists in the formation of a beneficial microstructure that produces strong welds. Since the solidification parameters (
G
·
R
and
G
/
R
) largely define the weld microstructure, their effect on the weld joint properties is investigated herein. With an increase in the pulse current, the (
G
/
R
) decreases and enables the formation of an equiaxed solidified structure in the weld zone. A reduction in the amount of various intermetallic phases is observed in the equiaxed regions compared to amount present in areas with a columnar structure. The tensile strength of the joint is superior to that of AISI 316L stainless steel, and failure is observed in the heat-affected zone of this material. The best joint efficiency herein of 108 pct and elongation of 35.3 pct is achieved for the welding condition having the lowest (
G
/
R
) value. An improvement in the elongation is achieved for the weld joint with a reduction in the (
G
/
R
) value.
Clival and Paraclival Lesions: A Pictorial Review Palsetia, Delnaz R.; Vijan, Antariksh V.; Gala, Foram B. ...
The Indian journal of radiology & imaging,
04/2023, Letnik:
33, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
The clivus is a midline anatomical structure in the central skull base. It is affected by a wide range of non-neoplastic, benign and malignant pathologies, some of which typically affect the ...clivus because of its strategic location and embryological origins. Clival lesions may often be asymptomatic with occasional complaints like headache or cranial neuropathy in few. Cross-sectional imaging techniques, namely, computed tomographic scan and magnetic resonance imaging, thus, play a key role in approximating to the final diagnosis and estimating the disease extent. In this article, we highlight the important imaging features of various clival and paraclival pathologies to facilitate effective diagnosis, therapeutic planning, and management.
While young muscle is capable of restoring the original architecture of damaged myofibers, aged muscle displays a markedly reduced regeneration. We show that expression of the "anti-aging" protein, ...α-Klotho, is up-regulated within young injured muscle as a result of transient Klotho promoter demethylation. However, epigenetic control of the Klotho promoter is lost with aging. Genetic inhibition of α-Klotho in vivo disrupted muscle progenitor cell (MPC) lineage progression and impaired myofiber regeneration, revealing a critical role for α-Klotho in the regenerative cascade. Genetic silencing of Klotho in young MPCs drove mitochondrial DNA (mtDNA) damage and decreased cellular bioenergetics. Conversely, supplementation with α-Klotho restored mtDNA integrity and bioenergetics of aged MPCs to youthful levels in vitro and enhanced functional regeneration of aged muscle in vivo in a temporally-dependent manner. These studies identify a role for α-Klotho in the regulation of MPC mitochondrial function and implicate α-Klotho declines as a driver of impaired muscle regeneration with age.
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