• Journal of Powder Materials
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• v.10 no.3
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• pp.172-175
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• 2003

Mechanically-alloyed NiAl powder was sintered by Spark-Plasma Sintering (SPS) process. Densification and behavior mechanical property were determined from the experimental results and analysis ,such as changes in linear shrinkage, shrinkage rate, microstructure, and phase during sintering process, Victors hardness, and transver.ie-rupture-strength (TRS). Above 97% relative density was obtained after sintering at 115$0^{\circ}C$ for 5 min. Crystallite size determined by the Scherrer method was approximately 50 nm. From the X-ray diffraction analysis it was confirmed that the sintered bodies were composed mainly of NiAl phase together with Ni$_3$Al phase. Measured Vickers hardness and TRS value were 555$\pm$10 $H_v$ and 1393$\pm$75 MPa , respectively.

• Bulletin of the Korean Chemical Society
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• v.31 no.10
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• pp.2835-2840
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• 2010

A series of $MoO_3/CeO_2-ZrO_2$ catalysts with different Mo content (8 - 20 wt %) were prepared by simple co-precipitation followed by impregnation method and were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), energy dispersive spectroscopic (EDS) techniques. The prepared materials were tested for catalytic activity by the synthesis of benzimidazole derivatives using condensation of aromatic aldehydes and o-phenylenediamine by conventional and microwave method. Obtained results reveal that the catalytic activity increases with increase in Mo wt % loading. The best catalytic activity was obtained with 20 wt % $MoO_3/CeO_2-ZrO_2$. The particle size or crystallite size was estimated using Debye-Scherrer equation. After completion of reaction, the catalyst can be recovered efficiently and reused with consistent activity.

• Journal of the Korean Ceramic Society
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• v.55 no.5
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• pp.498-503
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• 2018

Using the thermal ablation method, the oxidation behavior of $SiC_f/SiC$ composites was investigated in air and in the temperature range of $1,300^{\circ}C$ to $2,000^{\circ}C$. At the relatively low temperature of $1,300^{\circ}C$, passive oxidation, which formed amorphous phase, predominantly occurred in the thermal ablation test. When the oxidation temperature increased, SiO (g) and CO (g) were formed by active oxidation and the dense oxide layer changed to a porous one by vaporization of gas phases. In the higher temperature oxidation test, both active oxidation due to $SiO_2$ decomposition on the surface of the oxide layer and active/passive oxidation transition due to interfacial reaction between oxide and base materials such as SiC fiber and matrix phase simultaneously occurred. This was another cause of high temperature degradation of $SiC_f/SiC$ composites.

• Journal of Magnetics
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• v.22 no.2
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• pp.188-195
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• 2017

The ferromagnetic resonance and other magnetic properties dependence on $Ni^{2+}/Fe^{3+}$ ratio and crystallite size were investigated for nano nickel ferrite ($NiFe_2O_4$). The crystallite size was controlled by controlling the nickel content in the starting material solution. The XRD and TEM were utilized to measure the crystallite size through Scherrer formula and particle size respectively. The most frequent particle sizes were lower than crystallite size, which ranged from 16.5 to 44.65 nm. The general behavior of M-H loop shapes and parameters showed superparamagnetic one. The saturation magnetization had a maximum value at $Ni^{2+}/Fe^{3+}$ molar ratio equal to 0.186. The FMR signals showed, generally, broad linewidths, where the maximum width and minimum resonance field were for the sample of the lowest crystalline size. Furthermore, FMR resonance field shows linear dependence on crystalline size. The fitting relation was estimated to express this linear dependency on the base of behavior coincidence between particle size and the inverse of saturation magnetization. The given interpretations to understand the intercept and the slope meanings of the fitted relation were based on Larmor equation, and inhomogeneous in the anisotropy constant.

• Journal of Magnetics
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• v.22 no.2
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• pp.169-174
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• 2017

In this work, lithium ferrite ($Li_{0.5}Fe_{2.5}O_4$) nanoparticles were prepared via mechanochemical processing and subsequent heat treatment at a relatively low ($600^{\circ}C$) calcining temperature. The raw materials used were high purity $Fe_2O_3$ and $Li_2CO_3$ that were milled for between 2 and 20 h. The milled powders were then calcined at temperatures of 500 and $600^{\circ}C$ for 5 h in air. XRD results show that optimum conditions to obtain single phase lithium ferrite nanoparticles with a mean crystallite size of about 23 nm, using Scherrer's formula, are 10 h milling and calcination at $600^{\circ}C$. Saturation magnetization and coercivity of the single phase Li ferrite nanoparticles are 44.6 emu/g and 100 Oe respectively, which are both smaller than those of the bulk Li ferrite. The Curie temperature of the single sample was determined by a Faraday balance, which is $578^{\circ}C$ and smaller than that of bulk Li ferrite.

• Transactions on Electrical and Electronic Materials
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• v.11 no.1
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• pp.29-32
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• 2010

In this study, transparent and conductive Al-doped zinc oxide (AZO) films were prepared on a glass substrate by an radio frequency (RF) magnetron sputtering method using a 150-nm-thick AZO target (Al: 2 wt.%) at room temperature. We investigated the effects of RF power between 100-350 W (in steps of 50 W) on the structural, electrical, and optical properties of the AZO films. The thickness and cross-sectional images of the films were observed by field emission scanning electron microscopy. The thicknesses of all films were kept constant at 150 nm and grown on a glass substrate. The grain sizes of the AZO films were determined with the X-ray diffraction by using the Scherrer' equation, and their electrical properties were investigated using a Hall effect electronic transport measurement system. The transmittance of the AZO films was also measured by an ultraviolet-visible spectrometer.

• Korean Journal of Materials Research
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• v.19 no.6
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• pp.330-336
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• 2009

The size of crystallites in mono-dispersed cubic silver bromide grains was measured by applying a powder X-ray diffraction method and Scherrer's equation to grains that were suspended in swollen gelatin layers. In order to evaluate the existence of defects, the measured crystallite size was compared to those measured by using a scanning electron microscope. In the case of the grains prepared by the controlled double jet method, the size of crystallites was equal to the edge length of the grains that had edge lengths smaller than 400 nm. This result proved the usefulness of the above-stated method for measuring the size of crystallites and also evaluating the presence of any crystal defect in each grain. In the case of the grains, which were precipitated in the presence of a sensitizing dye and potassium iodide, the size of crystallites was smaller than the edge's length, indicating the discontinuities in the grains introduced during the precipitation process.

• Nuclear Engineering and Technology
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• v.53 no.9
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• pp.2816-2829
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• 2021

Decay heat residuals of spent nuclear fuel (SNF), i.e., the differences between calculations and measurements, were obtained previously for various spent fuel assemblies (SFA) using the Polaris module of the SCALE code system. In this paper, we compare decay heat residuals to their uncertainties, focusing on four PWRs and four BWRs. Uncertainties in nuclear data and model inputs are propagated stochastically through calculations using the SCALE/Sampler super-sequence. Total uncertainties could not explain the residuals of two SFAs measured at GE-Morris. The combined z-scores for all SFAs measured at the Clab facility could explain the resulting deviations. Nuclear-data-related uncertainties contribute more in the high burnup SFAs. Design and operational uncertainties tend to contribute more to the total uncertainties. Assembly burnup is a relevant variable as it correlates significantly with the SNF decay heat. Additionally, burnup uncertainty is a major contributor to decay heat uncertainty, and assumptions relating to these uncertainties are crucial. Propagation of nuclear data and design and operational uncertainties shows that the analyzed assemblies respond similarly with high correlation. The calculated decay heats are highly correlated in the PWRs and BWRs, whereas lower correlations were observed between decay heats of SFAs that differ in their burnups.

• Nuclear Engineering and Technology
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• v.53 no.10
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• pp.3164-3170
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• 2021

The increasing interest that GEANT4 is gaining nowadays, because of its special capabilities, prompted us to address its reliability in neutronic calculation for the realistic and complex spallation target MEGAPIE of the Paul Scherrer Institute of Switzerland. In this paper we have specifically addressed the neutronic characterization of the active zone of this target. Three physical quantities are evaluated: neutron flux spectra and total neutron fluxes on target's z-axis, and the neutron yield as a function of the target's altitude and radius. Comparison of the obtained results with those of the MCNPX reference code and some experimental measurements have confirmed the impact of the geometrical and proton beam models on the neutron fluxes. It has also allowed to reveal the intrinsic influence of the code type. The resulting differences reach a factor of ~2 for the beam model and 4-18% for the other parameters cumulated. The analysis of the neutron yield has led us to conclude that: 1) Increasing the productivity of the MEGAPIE target cannot be achieved simply by increasing the thickness of the target, if the irradiation parameters are not modified. 2) The size of the spallation area needs to be redefined more precisely.

• Korean Journal of Materials Research
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• v.32 no.2
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• pp.80-84
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• 2022

Copper nanoparticles (CuNPs) are considered of great importance due to their high catalytic and antimicrobial activities. This study focuses on the preparation and characterization of CuNPs, and on their antibacterial/antifungal activities. A copper salt (copper sulfate pentahydrate) as precursor, starch as stabilizing agent, and ascorbic acid as reducing agent were used to fabricate CuNPs. The resulting product was characterized via different techniques such as X-ray diffractrometry (XRD), Fourier Transform Infrared (FTIR) spectroscopy, and Scanning electron microscopy (SEM) to confirm its characteristic properties. Employing the Scherrer formula, the mean crystallite sizes of copper (Cu) and cuprous oxide (Cu₂O) nanocrystals were found to be 29.21 and 25.33 nm, respectively, as measured from the main X-ray diffraction peaks. The functional groups present in the resulting CuNPs were confirmed by FTIR. In addition, the engineered CuNPs showed antibacterial and antifungal activity against tested pathogenic bacterial and fungal strains.