• Journal of Magnetics
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• v.21 no.3
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• pp.308-314
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• 2016

Cobalt-, zinc-, and nickel-zinc-substituted nano-size manganese ferrite powders, $MnFe_2O_4$, $Mn_{0.8}Co_{0.2}Fe_2O_4$, $Mn_{0.8}Zn_{0.2}Fe_2O_4$ and $Mn_{0.8}Ni_{0.1}Zn_{0.1}Fe_2O_4$, were fabricated using a sol-gel method, and their crystallographic and magnetic properties were subsequently studied. The $MnFe_2O_4$ ferrite powder annealed at temperatures above 523 K exhibited a spinel structure, and the particle size increased as the annealing temperature increased. All ferrites annealed at 773 K showed a single spinel structure, and the lattice constants and particle size decreased with the substitution of Co, Zn, and Ni-Zn. The $M{\ddot{o}}ssbauer$ spectrum of the $MnFe_2O_4$ ferrite powder annealed at 523 K only showed a doublet due to its superparamagnetic phase, and the $M{\ddot{o}}ssbauer$ spectra of the $MnFe_2O_4$, $Mn_{0.8}Co_{0.2}Fe_2O_4$, and $Mn_{0.8}Zn_{0.2}Fe_2O_4$ ferrite powders annealed at 773 K could be fitted as the superposition of two Zeeman sextets due to the tetrahedral and octahedral sites of the $Fe^{3+}$ ions. However, the $M{\ddot{o}}ssbauer$ spectrum of the $Mn_{0.8}Ni_{0.1}Zn_{0.1}Fe_2O_4$ ferrite powder annealed at 773 K consisted of two Zeeman sextets and one quadrupole doublet due to its ferrimagnetic and paramagnetic behavior. The area ratio of the $M{\ddot{o}}ssbauer$ spectra could be used to determine the cation distribution equation, and we also explained the variation in the $M{\ddot{o}}ssbauer$ parameters by using this cation distribution equation, the superexchange interaction and the particle size. Relative to pure $MnFe_2O_4$, the saturation magnetizations and coercivities were larger in $Mn_{0.8}Co_{0.2}Fe_2O_4$ and smaller in $Mn_{0.8}Zn_{0.2}Fe_2O_4$, and $Mn_{0.8}Ni_{0.1}Zn_{0.1}Fe_2O_4$. These variations could be explained using the site distribution equations, particle sizes and magnetic moments of the substituted ions.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.12a
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• pp.212-212
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• 2003

• Proceedings of the Korean Magnestics Society Conference
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• 2003.12a
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• pp.250-250
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• 2003

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.448.2-448.2
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• 2006

• Journal of the Korean Applied Science and Technology
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• v.18 no.3
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• pp.167-173
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• 2001

The spinel $LiMn_{2}O_{4}$ powders were synthesized at $480^{\circ}C$ for 12 h in air by a sol-gel method using manganese acetate and lithium hydroxide as starting material and the $Fe_{3}O_{4}$ powders were synthesized by the precipitation method using $0.2M-FeSO_{4}{\cdot}H_{2}O$ and 0.5M-NaOH. The synthesized $Fe_{3}O_{4}$ powders were mixed at portion of 5, 10, 15 and 20 wt% about $LiMn_{2}O_{4}$ powders through ball-milling followed by drying at room temperature for 48 h in air. The mixed catalysts were reduced at $350^{\circ}C$ for 3 h by hydrogen and the decomposition rate of carbon dioxide was measured at $350^{\circ}C$ using the reduced catalysts. As the results of $CO_{2}$ decomposition experiments, the decomposition rates of carbon dioxide were 85% in all catalysts but the initial decomposition rates of $CO_{2}$ were slightly high in the case of the $5%-Fe_{3}O_{4}$ added catalyst.

• Journal of Powder Materials
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• v.25 no.1
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• pp.36-42
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• 2018

In order to expand the application of oxide dispersion-strengthened (ODS) steel, a composite material is manufactured by adding mechanically alloyed ODS steel powder to conventional steel and investigated in terms of microstructure and wear properties. For comparison, a commercial automobile part material is also tested. Initial microstructural observations confirm that the composite material with added ODS steel contains i) a pearlitic Fe matrix area and ii) an area with Cr-based carbides and ODS steel particles in the form of a $Fe-Fe_3C$ structure. In the commercial material, various hard Co-, Fe-Mo-, and Cr-based particles are present in a pearlitic Fe matrix. Wear testing using the VSR engine simulation wear test confirms that the seatface widths of the composite material with added ODS steel and the commercial material are increased by 24% and 47%, respectively, with wear depths of 0.05 mm and 0.1 mm, respectively. The ODS steel-added composite material shows better wear resistance. Post-wear-testing surface and cross-sectional observations show that particles in the commercial material easily fall off, while the ODS steel-added material has an even, smooth wear surface.

• Nuclear Engineering and Technology
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• v.31 no.6
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• pp.595-607
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• 1999

The reaction cross-sections of $^{nat}$Ti(p,X)$^{48}$ V, $^{nat}$Fe(p,X)$^{56}$ Co, $^{nat}$Cu(p,X)$^{65}$ Zn and $^{nat}$Mo(p,X)$^{96}$ Tc for TLA application are calculated in the frame of the ECIS-GNASH code system up to 60 MeV. The calculated results are compared with the experimental data taken from the EXFOR at the NEA Data Bank. A preliminary calculation with the global optical parameters of Varner et al. shows considerable differences from the experimental data at low energy range. The global optical parameters for the imaginary volume potential and the diffuseness of the imaginary potential are adjusted to achieve a better description of the experimental data in the vicinities of peak position below 16 MeV. 16 MeV.

• Journal of Energy Engineering
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• v.10 no.4
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• pp.370-378
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• 2001

Characteristics and synergistic effects of the coliquefaction of Alaskan subbituminous coal, wasted tire, and polypropylene were investigated in a tubing-bomb reactor at 41$0^{\circ}C$, and the coliquefaction reactions were performed at 37$0^{\circ}C$~45$0^{\circ}C$ to evaluate the coliquefaction mechanism. The coliquefaction kinetic model based on the free-radical theory was proposed and simulated by the non-linear parameter estimation method. Simulated results represented experimental ones successfully with the correlation coefficient of 0.99. When a catalyst was not used, the conversions were decreased as tetralin increase due to the decrease of liquefaction of polypropylene. When naphthenate catalysts of Mo, Co, and Fe were used, the coliquefaction conversions were increased with the increase of the liquefaction of polypropylene. When Co-naphthenate catalyst was used, the increase of the coliquefaction conversion were as high as 21~23%.

• Transactions of Materials Processing
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• v.31 no.5
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• pp.273-280
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• 2022

Although the mechanical properties of high-entropy alloys depend on the annealing conditions, limited works were established to investigate the annealing effect on the mechanical properties of Mo-added high-entropy alloys. Therefore, in the present work, the annealing effects on the microstructural evolution and mechanical properties of Mo-added high-entropy alloy were investigated. As a result, incomplete recrystallization from the limited annealing time not only suppresses deformation-induced phase transformation during cryogenic tensile test but also induces a deformation instability that results into the ductility reduction compare with the fully recrystallized sample. This result represents adjustment of annealing time is useful to control both transformation-induce plasticity and deformation instability of high-entropy alloys, and this can be applied to control the mechanical properties of metallic alloys by combining pre-straining and subsequent annealing.

• Transactions of Materials Processing
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• v.24 no.1
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• pp.44-51
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• 2015

The current study seeks to examine the effects of V and C additions on the mechanical and low thermal expansion properties of a high strength invar base alloy. The base alloy (Fe-36%Ni-0.9%Co-2.75%Mo-0.7Cr-0.23Mn-0.17Si-0.3%C, wt.%) contains $Mo_2C$ carbides, which form as the main precipitate. In contrast, alloys with additions of 0.4%V+0.3%C (alloy A) or 0.4%V+0.45%C (alloy B) contain $Mo_2C$+[V, Mo]C carbides. The average thermal expansion coefficients of these high strength invar based alloys were measured in the range of $5.16{\sim}5.43{\mu}m/m{\cdot}^{\circ}C$ for temperatures of $15{\sim}230^{\circ}C$. Moreover, alloy B showed lower thermal expansion coefficient than the other alloys in this temperature range. For the mechanical properties, the [V, Mo]C improved hardness and strengths(Y.S. and T.S.) of the high strength invar base alloy. T.S.(tensile strength) and Y.S.(yield strength) of hot forged alloy B specimen were measured at 844.6MPa and 518.0MPa, respectively. The tensile fractography of alloy B exhibited a ductile transgranular fracture mode and voids were initiated between the [V, Mo]C particles and the matrix. Superior properties of high strength and low thermal expansion coefficient can be obtained by [V, Mo]C precipitation in alloy B with the addition of 0.4%V and 0.45%C.