• Korean Journal of Materials Research
• /
• v.31 no.2
• /
• pp.61-67
• /
• 2021

Fabrication of a ferromagnetic composite powder for the magnesium and BaFe12O19 system by mechanical alloying (MA) is investigated at room temperature. Mixtures of Mg and BaFe12O19 powders with a weight ratio of Mg:BaFe12O19 = 4:1, 3:2, 2:3 and 1:4 are used. Optimal MA conditions to obtain a ferromagnetic composite with fine microstructure are investigated by X-ray diffraction, differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM) measurement. It is found that Mg-BaFe12O19 composite powders in which BaFe12O19 is dispersed in Mg matrix are successfully produced by MA of BaFe12O19 with Mg for 80 min. for all compositions. Magnetization of Mg-BaFe12O19 composite powders gradually increases with increasing the amounts of BaFe12O19, whereas coercive force of MA powders gradually decreases due to the refinement of BaFe12O19 powders with MA time for all compositions. However, it can be seen that the coercivity of Mg-BaFe12O19 MA composite powders with a weight ratio of Mg:BaFe12O19=4:1 and 3:2 for MA 80 min. are still high, with values of 1260 Oe and 1320 Oe compared to that of Mg:BaFe12O19=1:4. This clearly suggests that the refinement of BaFe12O19 powders during MA process for Mg:BaFe12O19=4:1 and 3:2 tends to be suppressed due to ductile Mg powders.

• Korean Journal of Materials Research
• /
• v.11 no.5
• /
• pp.378-384
• /
• 2001

In this study, nanostructured Fe-Ce powder with grain size of 10nm was produced by MA (mechanical alloying) process and was consolidated by PECS (pulse electric current sintering) process for the fabrication of bulk nanostructured Fe-Co softmagnetic alloy. PECS process was performed at 700, 800, 900 and $^1000{\circ}C$ with holding time ranging from 0 to 15min. The effectiveness of PECS Process to Produce nanostructured bulk specimens was estimated. The optimal PECS process condition for nanostructured Fe-Co powders was found through observing the change of relative density and microstructure with sintering temperature and holding time. The magnetic properties of the sintered specimens were evaluated through the measurement of coercivity and saturation magnetization.

• Composites Research
• /
• v.14 no.5
• /
• pp.1-11
• /
• 2001

The particulates reinforced metal matrix composites(PMMC) have a number of interesting mechanical properties. including high strength and good resistance to wear at high temperature and low thermal expansion. The equipment structure to obtain the homogeneous distribution in composites are proposed for the continuous pouring of reinforcement at the desired temperature. The particulates reinforced metal matrix composites(A357/SiCp) were fabricated by the process of the combined stirring method with the various fabrication process. The combined stirring method to niform distribution of particle is consisted of two stirring force both electro-magnetic stirring generated from induction heating and mechanical stirring with graphite stirrer. PMMC billets were fabricated with the volume fractions ranged from 0% to 20% and particle sizes ranged from 14${\mu}{\textrm}{m}$ to 25${\mu}{\textrm}{m}$. It is important to cont the size of primary $\alpha$-Al solid particles because it could become the cause of the particle pushing or capture phenomena from the fact that secondary dendrite arm spacing size depends on the cooling rate during the solidification in hypoeutectic Al-Si alloy. Therefore, the effect of primary $\alpha$-Al on the reinforcement distribution in matrix alloys has been investigated. The microstructure of PMMC fabracated with various volume fractions(0%, 10%, and 20%) and particle size were observed.

• Korean Journal of Materials Research
• /
• v.9 no.3
• /
• pp.274-281
• /
• 1999

Usually sputtering and electroless plating methods were used for manufacturing metal-alloy thin film magnetic memory devices. Since electroless plating method has many merits in mass production and product variety com­pared to sputtering method, many researches about electroless plating have been performed in the United State of America and Japan. However, electroless plating method has not been studied frequently in Korea. In these respects the purpose of this research is manufacturing Co-Mn-P alloy thin film on the corning glass 2948 by electroless plating method using sodium hypophosphite as a reductant, and analyzing deposition rate, alloy composition, microstructure, and magnetic characteristics at various pH's and temperatures. For Co-P alloy thin film, the reductive deposition reaction 0$\alpha$urred only in basic condition, not in acidic condition. The deposition rate increased as the pH and temperature increased, and the optimum condition was found at the pH of 10 and the temperature of $80^{\circ}C$. Also magnetic charac­teristics was found to be most excellent at the pH of 9 and the temperature of $70^{\circ}C$, resulting in the coercive force of 8700e and the squareness of 0.78. At this condition, the contents of P was 2.54% and the thickness of the film was $0.216\mu\textrm{m}$. For crystal orientation, we could not observe fcc for $\beta$-Co. On the other hand,(1010), (0002), (1011) orientation of hcp for a-Co was observed. We could confirm the formation of longitudinal magnetization from dominant (1010) and (1011) orientation of Co-P alloy. For Co-Mn-P alloy deposition, coercive force was about 1000e more than that of Co P alloy, but squareness had no difference. For crystal orientation, (l01O) and (lOll) orientation of $\alpha$-Co was dominant as same as that of Co- P alloy. Likewise we could confirm the formation of longitudinal magnetization.

• Journal of Conservation Science
• /
• v.30 no.4
• /
• pp.335-343
• /
• 2014

This study classified the result of non-metallic inclusion analysis and result of microstructure investigation on the ironware excavated in the Baekje region into Han River, Geum River, and Yeongsan River to estimate the iron making temperature and study the characteristics of regional and temporal characteristics of the heat treatment technology and steel making technology. Regardless of era, bloom iron and sponge iron are judged to be the major method for making as a directreduction process in all three regions. The result of the reinterpretation of the non-metallic inclusion by the oxide ternary constitutional diagram suggest that the temperature inside of the furnace is estimated to be between $1,100{\sim}1,300^{\circ}C$ while making the steel. The magnetic iron ores are the major raw material of steel ore and irons with high $TiO_2$ are estimated to use iron sands. Ironware with $CaO/SiO_2$ rate higher than 0.4% are considered to have artificially added the flux of calcareous materials. It was found that the iron making method is the solid caburizing-steel which caburizes low-carbon steels by the CO gas and $CO_2$ gas created when heating the forging furnace with charcoal. Also, the ironware manufacturers in the Baekje during 3rd century recognized the heat treatment technology as they performed carburizing process and quenching to intentionally increase the strength of necessary parts.

• Geophysics and Geophysical Exploration
• /
• v.14 no.1
• /
• pp.105-115
• /
• 2011

Although there are many possible mechanisms for the intrinsic seismic attenuation in composite materials that include fluids, relative motion between solids and fluids during seismic wave propagation is one of the most important attenuation mechanisms. In our previous study, we conducted ultrasonic wave transmission measurements on an ice-brine coexisting system to examine the influence on ultrasonic waves of the unfrozen brine in the pore microstructure of ice. In order to elucidate the physical mechanism responsible for ultrasonic wave attenuation in the frequency range of 350.600 kHz, measured at different temperatures in partially frozen brines, we employed a poroelastic model based on the Biot theory to describe the propagation of ultrasonic waves through partially frozen brines. By assuming that the solid phase is ice and the liquid phase is the unfrozen brine, fluid properties measured by a pulsed nuclear magnetic resonance technique were used to calculate porosities at different temperatures. The computed intrinsic attenuation at 500 kHz cannot completely predict the measured attenuation results from the experimental study in an ice-brine coexisting system, which suggests that other attenuation mechanisms such as the squirt-flow mechanism and wave scattering effect should be taken into account.

• Journal of the Korean Magnetics Society
• /
• v.17 no.1
• /
• pp.18-21
• /
• 2007

The hexagonal $HoMn_{1-x}-Fe_xO_3$(x=0.00, 0.05) thin films were prepared using pulsed laser deposition(PLD) method on $Pt/Ti/SiO_2/Si$ substrate. The microstructure and magnetic properties have been studied by x-ray diffraction(XRD), atomic force microscopy (AFH), scanning electron microscope(SEM:), x-ray photoelectron spectroscopy(XPS), and conversion electron $M\"{o}ssbauer$ spectroscopy(CEMS). From the analysis of the x-ray diffraction patterns, the crystal structure for all films was found to be a hexagonal($P6_3cm$), which was preferentially grown along(110) direction. The lattice constant $c_0$ of the film with x=0.05 was close to that of single crystal, whereas lattice constant $a_0$ with respect to single crystal shows a slight decrease. This difference of lattice parameters between film and single crystal was caused by the lattice mismatch between the film and $Pt/Ti/SiO_2/Si$ substrate. Conversion electron $M\"{o}ssbauer$ spectrum of $HoMn_{0.95}Fe_{0.05}O_3$ thin film shows an asymmetry doublet absorption ratio at room temperature, which is due to the oriented direction of crystallographic domains. This is corresponding with analysis of x-ray diffraction. The quadrupole splitting(${\Delta}E_Q$) at room temperature is found to be $1.62{\pm}0.01mm/s$. This large ${\Delta}E_Q$ was caused by asymmetry environment surrounding Fe ion.