Slow strain rate tensile (SSRT) tests were performed on tempered 13 wt% Cr martensitic stainless steel (MSS) with hydrogen charging during straining and also separately on hydrogen pre-charged ...tensile specimens. Microstructural characterization of tempered MSS showed lath martensitic structure with sub-micron sized M23C6 type carbides at lath interfaces and high angle grain boundaries. There was no change in the yield strength but loss in ductility was observed with increase of absorbed hydrogen quantity/pre-charging duration. Fracture surface examination showed increased brittle (intergranular) zone with increase of absorbed hydrogen. Compared to hydrogen pre-charging, effect of hydrogen charging during straining was more pronounced on the mechanical properties as both ductility and yield strength decreased. A change in the fracture mode form ductile dimples to mixed and intergranular fracture was observed with the increase of cathodic current density. Hydrogen enhanced decohesion embrittlement (HEDE) is the dominant mechanism for hydrogen pre-charged and also with hydrogen charging during straining conditions.
Metal oxide nanomaterials approaching grain size less than the Debye length are potential candidates for highly sensitive gas sensors owing to their large surface-to-volume ratio. Hence, research ...efforts are directed towards cost-effective synthesis of metal oxide nanomaterials for gas-sensor applications. In this context, we report on the facile synthesis and gas sensing studies of NiO nanoparticles (crystallite size ~ 10 nm), prepared by low-cost co-precipitation (NiO_A) and thermochemical (NiO_B) methods. XRD and FESEM confirmed the formation of cubic NiO nanoparticles. UV–Vis spectrometry and photoluminescence studies validated the optical band gap and abundance of defects/vacancies of the NiO nanoparticles. Gas sensors fabricated by spray coating of these nanoparticles on glass substrates revealed high sensitivity, selectivity and reversibility for NO
2
at 180 °C. A plausible sensing mechanism has been suggested based on the interaction of NO
2
with nickel vacancies. Higher sensitivity of co-precipitated nanoparticles has been attributed to the abundance of adsorption sites brought about by the smaller size grains.
In the present study, microstructures and texture of Cr clads developed on V plate using laser-assisted Directed Energy Deposition (DED) at different laser power and scan speeds have been ...investigated using scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and transmission electron microscopy (TEM) techniques. This investigation has shown that at low laser power grains at the interface region of clad and substrate show equiaxed morphology with random orientation and at high laser power grains have columnar morphology with strong rotated cube texture {110}, while middle region of all clads showed columnar morphology. In the top region of the clad, at low laser power the grain morphology remained columnar and at high laser power, columnar grains transformed to equiaxed morphology. Theoretically estimated temperature profiles and energy calculations have shown that the equiaxed grains developed at low laser power is due to incomplete melting of powder particles and transformation of columnar to equiaxed grains at the top region of clad at high laser power was due to constitutional super cooling resulted by compositional dilution. A process parameter map between laser energy density and number of powder particles has been developed to predict the microstructure of clads at a given laser power and scan speed. The experimental observation of all the clads showed that the clads developed at high laser power and low scan speed exhibit superior physical integrity and higher micro-hardness which is favorable for the development of crack-free transition joints of V and Cr. The optimized laser parameters can be used to develop the SS-Ti joint by DED process using V and Cr interlayers.
The present study aims at understanding the sorption performance of gamma irradiated bentonite clay (Bentoγ) for cesium (Cs) ions as compared to native bentonite (BentoN). BentoN was irradiated up to ...a dosage of 100 KGy using high intensity 60Co source. The uptake of Cs using both BentoN and Bentoγ clay sorbents was investigated from aqueous medium over a wide concentration range (50–1000 mg L-1) in batch mode and the distribution coefficients for Cs were determined. Batch studies revealed that maximum sorption of cesium occurred within 10 min of contact with the sorbent at a solution pH 6. The sorption data was analyzed using non-linear Langmuir and Freundlich adsorption isotherms. The characterization of bentonite using different physicochemical techniques like SEM, XRD and FTIR illustrated that there were minor structural changes after irradiation. The effect of gamma irradiation on the structural properties of constituent clay minerals of bentonite and the resultant reduction in the sorption capacity of the sorbent has been correlated in order to get an insight into the sorption mechanism.
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•Cesium sorption using bentonite clay before and after gamma irradiation was examined.•Structural changes in clay after irradiation were observed.•Cesium sorption capacity of clay reduced after gamma irradiation.•Cs sorption mechanism with respect clay structure is discussed.
In the present study, Be-free Zr-based bulk metallic glasses (Zr
46
Cu
36
Ag
8
Al
8,
Zr
52
Ti
6
Al
10
Cu
18
Ni
14
and Zr
62.5
Cu
22.5
Fe
5
Al
10
) and tungsten fiber reinforced Be-free Zr-metallic ...glass matrix composites were produced using suction casting and melt infiltration techniques, respectively. X-ray diffraction and transmission electron microscopy analyses revealed that the structure of the BMG’s was completely amorphous, whereas in composites the matrix contained crystalline phases (Zr
2
Cu and Al
2
Zr) along with the amorphous phase. Mechanical properties of composites were found to be superior to those of BMGs, due to the generation of multiple shear bands in the composites caused by the presence of tungsten fibers and crystalline phases in the metallic glass matrix. The present study shows that if the matrix in the composite is partly crystalline consisting of ductile crystalline phase in the amorphous matrix will have better properties than the fully amorphous matrix composites.
Evidences of both sluggish eutectoid and active eutectoid (not suppressible under rapid cooling) transformations have been found for the first time in a single hyper-eutectoid Ti-Cu alloy. Both of ...these types of eutectoid reactions have been investigated in detail, at different length scales, by coupling scanning electron microscopy (SEM),transmission electron microscopy (TEM) and atom probe tomography (APT). The unique three phase crystallographic relationship between the parent β (bcc) and the two product phases, α (hcp) and Ti2Cu, has been established. The extent of partitioning of the solute (Cu) between the two product phases has been determined by APT and is rationalised in terms of thermodynamic considerations. Based on the observed lattice site correspondence and the extent of solute partitioning, a possible mechanism of active eutectoid transformation is proposed.
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Structure of metallic glasses fascinates as the generic amorphous structural template for ubiquitous systems. Its specification necessitates determination of the complete hierarchical structure, ...starting from short-range-order (SRO) → medium-range-order (MRO) → bulk structure and free volume (FV) distribution. This link has largely remained elusive since previous investigations adopted one-technique-at-a-time approach, focusing on limited aspects of any one domain. Reconstruction of structure from experimental data inversion is non-unique for many of these techniques. As a result, complete and precise structural understanding of glass has not emerged yet. In this work, we demonstrate the first experimental pathway for reconstruction of the integrated structure, for
and
glasses. Our strategy engages diverse (× 7) multi-scale techniques XAFS, 3D-APT, ABED/NBED, FEM, XRD, PAS, FHREM on the same glass. This strategy complemented mutual limitations of techniques and corroborated common parameters to generate complete, self-consistent and precise parameters. Further, MRO domain size and inter-void separation were correlated to identify the presence of FV at MRO boundaries. This enabled the first experimental reconstruction of hierarchical subset: SRO → MRO → FV → bulk structure. The first ever image of intermediate region between MRO domains emerged from this link. We clarify that determination of all subsets is not our objective; the essence and novelty of this work lies in directing the pathway towards finite solution, in the most logical and unambiguous way.
Pd/reduced graphene oxide (Pd-RGO) composites were successfully prepared from graphite and PdCl2 precursors using wet impregnation and reverse micro emulsion methods. From hydrogen adsorption studies ...it is confirmed that spillover of hydrogen from Pd to graphene layers occurs at room temperature. However, at low temperatures there is negligible spillover effect and this is explained based on lower kinetic energy available with hydrogen atoms to overcome the activation barrier involved in diffusion. Detailed 13C MAS NMR and Raman spectroscopic studies confirmed that small amounts of structural units (functional groups) like carboxylate and polyacetylenic linkages are retained in Pd-RGO samples prepared by wet impregnation and reverse micro-emulsion methods, respectively. Such structural moieties facilitate the atomic scale mixing of Pd with the graphene layers thereby improving the spillover efficiency.
•Spillover of hydrogen from Pd to graphene layers occurs at room temperature.•Carboxylate and polyacetylenic linkages are retained in Pd-RGO samples.•Organic structural units facilitate spillover of hydrogen from Pd to graphene.
The present manuscript deals with the hydrogen absorption properties of multiwalled carbon nano-tubes (MWCNTs) doped with Pd nanoparticles by the conventional wet impregnation method and the polyol ...method. In the latter method Pd nanoparticles are doped into CNTs based on polyhydroxy organic compounds (polyol) mediated functionalization. The polyol medium reduces palladium chloride to palladium nanoparticles, and also acts as a capping agent to stabilize the Pd nanoparticles. The samples have been characterized using X-ray diffraction (XRD), Energy Dispersive X-ray (EDX) and Infrared (IR) spectroscopy. Hydrogen absorption studies clearly illustrate that Pd doped MW-CNT's prepared by polyol mediated functionalization show much higher hydrogen storage capacity compared to the sample prepared by wet impregnation route. To determine the cause of this behavior, Transmission Electron Microscopic (TEM) studies of the samples were carried out. The results indicate that the dispersion of Pd nanoparticle on the MW-CNT is much better for the sample prepared by the polyol route. An attempt was made to determine the existence of any metal-support interaction using Thermogravimetric Analysis (TGA). The investigation reveals that the higher dispersion of Pd nanoparticles on the CNT support plays a major role for the hydrogen adsorption.
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•Large scale synthesis of MW-CNT using CVD method.•Dispersion of Pd on MW-CNT using different routes.•Polyol method shows better hydrogen storage capacity.•Higher dispersion of Pd leads to better hydrogen sorption.
Nanocomposites of CdO–CdS have been prepared in ethylene glycol water mixture followed by heating at 300 °C. TEM and XRD studies confirmed the atomic scale mixing of CdO and CdS nanoparticles, ...leading to the formation of CdSO3 phase at the interfacial region between CdO and CdS. Photocatalytic studies for hydrogen generation from water show an enhanced activity for CdO–CdS composites compared to individual components namely CdO or CdS nanoparticles. Based on optical absorption, surface area measurements, steady state and time resolved fluorescence studies, it is established that, enhanced absorption in the visible region, higher surface area and increase in lifetime of the charge carriers are responsible for the observed increase in hydrogen yield from water when composite sample was used as the photocatalyst compared to individual components. The composite sample when combined with Pt as co-catalyst exhibit a large increase in the photocatalytic activity.
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•CdO–CdS nanocomposites have been prepared at a relatively low temperature of 300 °C.•CdO–CdS nanocomposites show enhanced hydrogen evolution.•Lifetime of charge carriers in composite sample is higher compared to CdO and CdS.
