3 research outputs found
Phase Composition and Temperature Effect on the Dynamic Youngâs Modulus, Shear Modulus, Internal Friction, and Dilatometric Changes in AISI 4130 Steel
Elastic properties of materials and their changes with temperature are important for their applications in engineering. In the present study the influence of phase composition and temperature of AISI 4130 alloy on Youngâs modulus (Ed), shear modulus (Gd), and damping (Qâ1) was carried out by the impulse excitation technique (IET). The material characterization was performed using confocal microscopy, XRD, SEM, HV, and dilatometry. A stable structure, composed of ferrite (BCC) and pearlite (α-Fe + Fe3C), was obtained by annealing. Metastable structure of martensite (BCT) was obtained by quenching. The Ed, Gd, and Qâ1 were measured by varying the temperature from RT to 900 °C. The values of Ed and Gd, at RT, were determined as 201.5 and 79.2 GPa (annealed) and 190.13 and 76.5 GPa (quenched), respectively. In the annealed steel, the values Ed and Gd decrease linearly on heating up to 650 °C, with thermal expansion. In the quenched steel, weak changes occurred in the dilatometric curve, Ed, Gd, and Qâ1, in the range of 350â450 °C, which indicated decompositions of the martensitic phase. A sharp decrease in the moduli and high peak of Qâ1 were observed for both samples around 650â900 °C, revealing low lattice elastic stability of the phases during transformations α(BCC) + Fe3CÎł(FCC)
Znâdoped MnOx nanowires displaying plentiful crystalline defects and tunable small cross-sections for an optimized volcano-type performance towards supercapacitors
Abstract MnOx-based nanomaterials are promising large-scale electrochemical energy storage devices due to their high specific capacity, low toxicity, and low cost. However, their slow diffusion kinetics is still challenging, restricting practical applications. Here, a one-pot and straightforward method was reported to produce Zn-doped MnOx nanowires with abundant defects and tunable small cross-sections, exhibiting an outstanding specific capacitance. More specifically, based on a facile hydrothermal strategy, zinc sites could be uniformly dispersed in the α-MnOx nanowires structure as a function of composition (0.3, 2.1, 4.3, and 7.6 wt.% Zn). Such a process avoided the formation of different crystalline phases during the synthesis. The reproducible method afforded uniform nanowires, in which the size of cross-sections decreased with the increase of Zn composition. Surprisingly, we found a volcano-type relationship between the storage performance and the Zn loading. In this case, we demonstrated that the highest performance material could be achieved by incorporating 2.1 wt.% Zn, exhibiting a remarkable specific capacitance of 1082.2 F.gâ1 at a charge/discharge current density of 1.0 A gâ1 in a 2.0 mol Lâ1 KOH electrolyte. The optimized material also afforded improved results for hybrid supercapacitors. Thus, the results presented herein shed new insights into preparing defective and controlled nanomaterials by a simple one-step method for energy storage applications
Facile Gram-Scale Synthesis of NiO Nanoflowers for Highly Selective and Sensitive Electrocatalytic Detection of Hydrazine
The design and development of efficient and electrocatalytic
sensitive
nickel oxide nanomaterials have attracted attention as they are considered
cost-effective, stable, and abundant electrocatalytic sensors. However,
although innumerable electrocatalysts have been reported, their large-scale
production with the same activity and sensitivity remains challenging.
In this study, we report a simple protocol for the gram-scale synthesis
of uniform NiO nanoflowers (approximately 1.75 g) via a hydrothermal
method for highly selective and sensitive electrocatalytic detection
of hydrazine. The resultant material was characterized by scanning
electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction.
For the production of the modified electrode, NiO nanoflowers were
dispersed in Nafion and drop-cast onto the surface of a glassy carbon
electrode (NiO NF/GCE). By cyclic voltammetry, it was possible to
observe the excellent performance of the modified electrode toward
hydrazine oxidation in alkaline media, providing an oxidation overpotential
of only +0.08 V vs Ag/AgCl. In these conditions, the peak current
response increased linearly with hydrazine concentration ranging from
0.99 to 98.13 ÎŒmol Lâ1. The electrocatalytic
sensor showed a high sensitivity value of 0.10866 ÎŒA L ÎŒmolâ1. The limits of detection and quantification were
0.026 and 0.0898 ÎŒmol Lâ1, respectively. Considering
these results, NiO nanoflowers can be regarded as promising surfaces
for the electrochemical determination of hydrazine, providing interesting
features to explore in the electrocatalytic sensor field