• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.12
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• pp.6187-6195
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• 2012

Recycling process of iron should be developed for efficient recovery of neodymium(Nd), rare metal, from acid-leaching solution of neodymium magnet. In this study, $FeCl_3$ solution as iron source was used for synthesis of iron nanoparticle with the condition of various factors, etc, reductant, surfactant. $Na_4O_7P_2$ and polyvinylpyrrolidone(PVP) as surfactants, $NaBH_4$ as reductant, and palladium chloride($PdCl_2$) as a nucleation seed were used. Iron powder was analyzed with instruments of XRD, SEM and PSA for measuring shape and size. Iron nanoparticles were made at the ratio of 1 : 5(Fe (III) : $NaBH_4$) after 30 min of reduction time. Size and shape of iron particles synthesized were round-form and 50 nm ~ 100 nm size. Zeta-potential of iron at the 100 mg/L of $Na_4O_7P_2$ was negative value, which is good for dispersion of metal particle. When $Na_4O_7P_2$(100 mg/L), PVP($FeCl_3$ : PVP = 1 : 4, w/w) and Pd($FeCl_3$ : $PdCl_2$ = 1 : 0.001, w/w) were used, iron nanoparticles which are round-shape, well-dispersed, near 100 nm-sized can be made.

• Proceedings of the Korean Institute of Resources Recycling Conference
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• 2004.12a
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• pp.27-34
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• 2004

This experiment was carried out to examine the effects of morphology on properties of La-Co substituted SrM ferrite. The magnetic properties of calcined and sintered materials varied with the substitutional amount of La and Co elements in Sr-ferrite. In the substituted SrM ferrite, the atomic fraction x of La is directly related to the mole ratio n of iron oxide and the atomic fraction y of Co by equation x=2ny. The HcJ values of the calcined powder were about 270 kA/m and 240 kA/m with x=0.3 and K=0.2, respectively at stoichiometriy, n=6.0. Crystallites of the sintered material were grown with a plate shape, and their size decreased with increasing mole ratios. Such a shape was caused by the initial state of crystallite formed after calcination. In case of x=0.3 and n=6.0, Br was 415 mT and HcJ was 355 kA/m, and in x=0.2 and n=6.0, Br was 410 mT and HcJ was 370kA/m. The squareness in 2nd quarter of BH curve with x=0.2 was smoothly improved compared with x=0.3

• Korean Journal of Materials Research
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• v.22 no.11
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• pp.569-574
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• 2012

Large single grain $Gd_{1.5}Ba_2Cu_3O_{7-y}$ (Gd1.5) bulk superconductors were fabricated by a top-seeded melt growth (TSMG) process using an $NdBa_2Cu_3O_{7-y}$ seed. The seeded Gd1.5 powder compacts with a diameter of 50 mm were subjected to the heating cycles of a TSMG process. After the TSMG process, the diameter of the single grain Gd1.5 compact was reduced to 43 mm owing to the volume contraction during the heat treatment. The superconducting transition temperature ($T_c$) of the top surface of the single grain Gd1.5 sample was as high as 93.5 K. The critical current densities ($J_cs$) at 77 K and 1T and 1.5 T were in ranges of 25,200-43,900 $A/cm^2$ and 10,000-23,000 $A/cm^2$, respectively. The maximum attractive force at 77 K of the sample field-cooled using an Nd-B-Fe permanent magnet (surface magnetic field of 0. 527 T) was 108.3 N; the maximum repulsive force of the zero field-cooled sample was 262 N. The magnetic flux density of the sample field-cooled at 77 K was 0.311T, which is approximately 85% of the applied magnetic field of 0.375 T. Microstructure investigation showed that many $Gd_2BaCuO_5$ (Gd211) particles of a few ${\mu}m$ in size, which are flux pinning sites of Gd123, were trapped within the $GdBa_2Cu_3O_{7-y}$ (Gd123) grain; unreacted $Ba_3Cu_5O_8$ liquid and Gd211 particles were present near the edge regions of the single grain Gd1.5 bulk compact.

• Progress in Superconductivity and Cryogenics
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• v.19 no.1
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• pp.30-35
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• 2017

The effects of the crystallographic orientation and sample thickness on the magnetic levitation forces (F) and trapped magnetic field (B) of single grain YBCO bulk superconductors were examined. Single grain YBCO samples with a (001), (110) or (100) surface were used as the test samples. The samples used for the force-distance (F-d) measurement were cooled at 77 K without a magnetic field (zero field cooling, ZFC), whereas the samples used for the B measurement were cooled under the external magnetic field of a Nd-B-Fe permanent magnet (field cooling, FC). It was found that F and B of the (001) surface were higher than those of the (110) or (100) surface, which is attributed to the higher critical current density ($J_c$) of the (001) surface. For the (001) samples with t=5-18 mm, the maximum magnetic levitation forces ($F_{max}s$) of the ZFC samples were larger than 40 N. About 80% of the applied magnetic field was trapped in the FC samples. However, the F and B decreased rapidly as t decreased below 5 mm. There exists a critical sample thickness (t=5 mm for the experimental condition of this study) for maintaining the large levitation/trapping properties, which is dependent on the material properties and magnitude of the external magnetic fields.

• Progress in Superconductivity
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• v.13 no.2
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• pp.133-138
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• 2011

To reduce the processing cost of the single grain REBCO (RE: Rare-earth elements) bulk superconductors, a cost-effective process should be developed. One possible way of developing the cost-effective process is the use of low-cost precursor powders. In this study, the single grain YBCO superconductors were fabricated using a home made powder. $YBa_2Cu_3O_{7-y}$ (Y123) powders were synthesized at $850-900^{\circ}C$ in air by the powder calcination method with repeated crushing and heat treatment steps. The processing parameters for the fabrication of single grain Y123 bulk superconductors, $T_{max}$ (maximum temperature), $T_p$ (peritectic temperature) and a cooling rate through $T_p$ were optimized. To enhance the flux pinning capacity of the single grain Y123 samples, $Y_2BaCuO_5$ (Y211) particles were dispersed in the Y123 matrix by adding $Y_2O_3$ powder to the calcined Y123 powder. Applying the optimized processing condition, the single grain Y123 superconductors with $T_c=91\;K$ and $J_c=1.5{\times}10^4\;A/cm^2$ at 2 T were successfully fabricated using a home made powder. The levitation forces and trapped magnetic field at 77 K measured using a Nd-B-Fe permanent magnet of 5300 G were 47 N and 3000 G, respectively, which are comparable to those obtained for the samples fabricated using a commercial grade Y123 powders.

• The KSFM Journal of Fluid Machinery
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• v.17 no.3
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• pp.19-24
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• 2014

Development of long-term mobile energy sources for mobile robots or small-sized unmanned vehicles are actively increasing. The micro gas turbine generator (MTG) is a good candidate for this purpose because it has both of high energy density and high power density, and 500W class MTG is under development. The designed MTG can be divided into 2 main parts. One part consists of motor/ generator and compressor, and the other one consists of combustor, recuperator and turbine. 500W class MTG is designed to operate at ultra-high speed of 400,000 rpm in high turbine temperature over $700^{\circ}C$ to improve the efficiency. Because the magnetism of NdFeB permanent magnet for the motor/generator could be degraded if the temperature is over $150-200^{\circ}C$, MTG needs the thermal insulation to block the heat transfer from combustor/turbine side to motor/generator side. Moreover, the motor/generator is allocated to get the cooling effect from the rapid air flow by the compressor. This study presents the experimental results to verify whether the thermal insulator and air flow are effective enough to keep the motor/generator part in the low temperature less than $100^{\circ}C$. From the motoring test by using the high temperature test rig, it was confirmed that the motor/generator part could maintain the temperature less than $50^{\circ}C$ under the condition of 1.0 bar compressed air.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.51 no.11
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• pp.601-611
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• 2002

As resent trends in structural construction have been to build taller and larger structures than any time in the past, they have had high flexibility and low damping that can cause large vibration response under severe environmental loading such as earthquakes, winds, and mechanical excitations. The damper with mass and sqring is one aproach to safeguarding the structure against excessive vibrations. In this paper, a large capacity hybrid-type linear motor damper(LMD) was designed and fabricated for the application to the vibration control of a large building structure model. It has been designed to be able to move the damper mass, 1,500 kg up to ${\pm}250mm$ strokes at the first mode natural frequency of the building structure model, ${\pm}0.51Hz$. Linear motor is consisted of the fixed coil and the movable NdFeB permanent magnets field part. The PM field part composed magnet modules and iron yoke, is the damper mass itself, 1500kg. LMD therefore has a simplified structure and requires a few elements in the driving system, being compared with a rotary motor damper and a hydraulic damper. However, the manufacture of large PM linear actuator is difficult because of the limit of PM size and the attraction and repulsion at the assembly of PM. Therefore, large damper system is manufactured and tested for dynamic characteristics and frequency response.

• Korean Journal of Materials Research
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• v.12 no.3
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• pp.215-219
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• 2002

For the purpose of annihilating tumor in body, hematoporphyrin as a photosensitizer was coated onto magnetic particles of $Fe_3O_4$ prepared by coprecipitation which could be concentrated around the tumor by magnetic field. The photosensitizer was applied differently before, during and after adsorbing the 1st surfactant on the particles. Its added amount was $5{\times}10^{-4}/mol$, and the coating reaction proceeded at temperatures of 60, 70 and 8$0^{\circ}C$. The amounts of photosensitizer coated on the magnetic particles were obtained by calculating an optical density with the maximum UV spectrum. As a result of the UV analysis, the coating amount of photosensitizer increased with higher reaction temperatures. When applied at 8$0^{\circ}C$ after adsorbing the 1st surfactant, the photosensitizer was coated with a maximum value of $3.8{\times}10^{-3}/mo1/$\ell$$. The TGA analysis revealed that the ferrofluids included the particles of 30.115 g/$\ell$. It was suggested that the magnetite particles was coated with photosensitizer of $1.26{\times}10^{-4}/mo1/g$. A small-sized device for magnetic field and light emission was designed, in which LED sheets coverts the permanent magnet of Nd-Fe-B. The LED sheet was connected in series circuit and also protected with a silicon tube. The power was supplied with rechargable battery of 9V and 100-120mA.

• Progress in Superconductivity
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• v.14 no.1
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• pp.39-44
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• 2012

The fabrications condition and superconducting properties of top-seeded melt growth (TSMG) processed $GdBa_2Cu_3O_{7-y}$ (Gd123) bulk superconductors were studied. Processing parameters (a maximum temperature ($T_{max}$), a temperature for crystal growth ($T_G$) and a cooling rate ($R_G$) through a peritectic temperature ($T_P$) for the fabrication of single grain Gd123 superconductors were optimized. The magnetic levitation forces, trapped magnetic fields, superconducting transition temperature ($T_c$) and critical current density ($J_c$) of the Gd123 bulks superconductors were estimated. Single grain Gd123 bulk superconductors were successfully fabricated at the optimized processing condition. The $T_c$ of a TSMG processed Gd123 sample was 92.5 K and the $J_c$ at 77 K and 0 T was approximately $50kA/cm^2$. The trapped magnetic field contour and magnetic levitation forces were dependent on the top surface morphology of TSMG processed Gd123 samples. The single grain Gd123 samples, field-cooled at 77 K using a Nd-B-Fe permanent magnet with 5.27 kG and 30 mm dia., showed the trapped magnetic field contour of a single grain with a maximum of 4 kG at the sample center. The maximum magnetic levitation forces of the single grain Gd123 sample, field-cooled or zero field-cooled, were 40 N and 107 N, respectively.

• Resources Recycling
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• v.2 no.2
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• pp.27-38
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• 1993

In this study, we investigated the grinding and sedimentation(elutriation) process of the dusts for the effective separation of high purity iron and iron oxides. For characterization of the dust, particle size distribution and chemical composition, were examined. The results obtained in this study may be summarized as follows : 1. The converter CF(clarifier) dust of the Pohang 1st, 2nd steel making factory and EC(Evaporation Cooler), EP(Eltrostatic precititator) dust of the Kwangyang 2nd steel making factory are composed $\alpha$-Fe(21~50%), FeO(wustite)$Fe_3$$O_4$(magnetite), $Fe_2$$O_3$, CaO, $Al_2$$O_3$, $SiO_2$, and etc. 2. Pure iron has ductile characteristic in nature, particle size of the pure iron increase by increasing the grinding time. On the other hand, it is conformed that bo고 particles of hematite and magnetite become less than 325 mesh after 10 minutes grinding. 3. By applying the elutriation technique for the EC dust of the Kwangyang 2nd steel making factory, the iron powder of high content more than 99.17% of pure Fe was recovered with 37.8% yield at grinding time for 40 minutes. 4. By applying the elutriation technique for the CF dust of the Pohang 2nd steel making factory, the iron powder of high content more than 98.38% of pure Fe was recovered with 44.42% yield at grinding time for 40 minutes. 5. When magnetic separation was performed using plastic bonding magnet of 70 gauss, more than 98% Fe grade of iron powder was recovered in the size range +65 -200 mesh but the recovery of it was low.