• Archives of Metallurgy and Materials
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• v.65 no.4
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• pp.1273-1276
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• 2020

Liquid metal extraction (LME) process results in 100% neodymium (Nd) extraction but the highest extraction efficiency reported for Dysprosium (Dy) so far is 74%. Oxidation of Dy is the major limiting factor for incomplete Dy extraction. In order to enhance the extraction efficiency and to further investigate the limiting factors for incomplete extraction, experiments were carried out on six different particle sizes of under 200 ㎛, 200-300 ㎛, 300-700 ㎛, 700-1000 ㎛, 1000-2000 ㎛ and over 2000 ㎛ at 900℃ with magnesium-to-magnet scrap ratio of 15:1 for 6, 24 and 48 hours, respectively. This research identified Dy₂Fe₁₇ in addition to Dy₂O₃ phase to be responsible for incomplete extraction. The relationship between Dy₂Fe₁₇ and Dy₂O₃ phase was investigated, and the overall extraction efficiency of Dy was enhanced to 97%.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.6
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• pp.225-228
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• 2005

We have grown the long persistent $SrAl_2O_4:Eu^{2+},\;Dy^{3+}$ phosphor single crystal by Verneuil method. The obtained single crystals were long persistent phosphorescence peaking at ${\lambda}=520nm$ with a size of about 5 mm diameter, 55 mm length. The melting temperature of $SrAl_2O_4:Eu^{2+},\;Dy^{3+}$ measured $T_{mp}=1968^{\circ}C$. The optimum composition was $SrCO_3:Al(OH)_3:Eu_2O_3:Dy_2O_3$ = 1 : 2 : 0.015 : 0.02. Flow rate of $H_2:O_2$ is about 4 : 1. Growthing rate is about 5 mm/hr. The spectra of the phosphorescence from the crystals are quite similar to those obtained with sintered powders used for luminous pigments. The crystalline structure of long persistent $SrAl_2O_4:Eu^{2+},\;Dy^{3+}$ phosphor single crystal was determined by X-ray diffraction.

• Journal of the Korean Society of Safety
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• v.35 no.3
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• pp.49-57
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• 2020

In comparison with the existing static reliability analysis methods, the dynamic reliability analysis(DyRA) method is more suitable for estimating the failure probability of a structure subjected to earthquake excitations because it can take into account the frequency characteristics and damping capacity of the structure. However, the DyRA is known to have an issue of numerical stability due to the uncertainty in random sampling of the earthquake excitations. In order to solve this numerical stability issue in the DyRA approach, this study proposed two earthquake-scale factors. The first factor is defined as the ratio of the first earthquake excitation over the maximum value of the remaining excitations, and the second factor is defined as the condition number of the matrix consisting of the earthquake excitations. Then, we have performed parametric studies of two factors on numerical stability of the DyRA method. In illustrative example, it was clearly confirmed that the two factors can be used to verify the numerical stability of the proposed DyRA method. However, there exists a difference between the two factors. The first factor showed some overlapping region between the stable results and the unstable results so that it requires some additional reliability analysis to guarantee the stability of the DyRA method. On the contrary, the second factor clearly distinguished the stable and unstable results of the DyRA method without any overlapping region. Therefore, the second factor can be said to be better than the first factor as the criterion to determine whether or not the proposed DyRA method guarantees its numerical stability. In addition, the accuracy of the numerical analysis results of the proposed DyRA has been verified in comparison with those of the existing first-order reliability method(FORM), Monte Carlo simulation(MCS) method and subset simulation method(SSM). The comparative results confirmed that the proposed DyRA method can provide accurate and reliable estimation of the structural failure probability while maintaining the superior numerical efficiency over the existing methods.

• The Korean Journal of Nuclear Medicine
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• v.28 no.2
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• pp.227-233
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• 1994

Irradiation of 20mg of natural $Dy(NO_3)_3$ in a neutron flux of $2{\times}10^{13}n/cm^2$ sec for 4 hours gave 5.76 Ci of $^{165}Dy$(specific activity, 610mCi/mg Dy) with high radionuclidic purity (>99.9 %). $^{165}Dy-MA$ was prepared in a quantitative yield by reacting the aqueous solution of $^{165}Dy(NO_3)_3$ with sodium borohydride solution in 0.2N NaOH. Coulter particle analyzer exhibited mean particle size of $2.6{\mu}m$ (range $1{\sim}6{\mu}m$), Even though the $^{165}Dy-MA$ suspension in saline was stored at $37^{\circ}C$ for 24 hours or autoclaved at $121^{\circ}C$ for 30minutes, there was no significant change in particle size and leakage problem indicating the prepared $^{165}Dy-MA$ is sufficiently stable. In-vivo retention studies were carried out by administering $^{165}Dy-MA$ into the knee joint space of normal rabbits. Gamma camera analysis showed high retention in joint space of normal rabbits. Gamma camera analysis showed high retention in joint space even at 24 hours after administration (> 99.9%). The ease with which the $^{165}Dy-MA$ can be made in the narrow size range and their high invitro and vivo stability make them attractive agents for radiation synovectomy.

• Journal of the Korean institute of surface engineering
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• v.51 no.5
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• pp.271-276
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• 2018

The effects of activator ion on the structural, morphological, and optical properties of $LaNbO_4:RE^{3+}$ (RE = Dy, Dy/Sm, Sm) phosphors were investigated. X-ray diffraction patterns exhibited that all the phosphors showed a monoclinic system with a main (112) diffraction peak, irrespective of the concentration and type of activator ions. The grain size showed a slightly decreasing tendency as the concentration of $Sm^{3+}$ ions increased. The excitation spectra of the $LaNbO_4:Dy^{3+}$, $Sm^{3+}$ phosphor powders consisted of a strong charge transfer band centered at 259 nm in the range of 220-290 nm and five weak peaks. The emission spectra of the $La_{0.95}NbO_4$:5 mol% $Dy^{3+}$ phosphors exhibited two intense yellow and blue bands centered at 575 nm and 479 nm respectively, which resulted from the $^4F_{9/2}{\rightarrow}^6H_{13/2}$ and $^4F_{9/2}{\rightarrow}^6H_{15/2}$ transitions of $Dy^{3+}$. As the concentration of $Sm^{3+}$ was increased, the intensity of the yellow emission band was gradually decreased, while those of orange and red emission bands centered at 604 and 646 nm began to appear and reached maxima at 5 mol%, and then decreased rapidly with further increases in the $Sm^{3+}$ concentration. These results indicated that white light emission could be realized by controlling the concentrations of the $Dy^{3+}$ and $Sm^{3+}$ ions incorporated into the $LaNbO_4$ host crystal.

• Journal of the Korean institute of surface engineering
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• v.54 no.3
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• pp.112-118
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• 2021

Dy³⁺- and Eu³⁺-codoped BaWO₄ phosphors for white light-emitting diode were synthesized with different activator ions via a solid-state reaction process. The structural, morphological, and optical properties of the BaWO₄:Dy³⁺,Eu³⁺ phosphors were investigated as a function of Eu³⁺ concentration at a fixed concentration of Dy³⁺ ions. XRD patterns exhibited that all the synthesized phosphors had a tetragonal system, irrespective of the concentrations of Dy³⁺ and Eu³⁺ ions. The excitation spectra of the synthesized phosphors were composed of three intense bands centered at 251, 355, and 393 nm and several weak peaks. For the BaWO₄:Dy³⁺,Eu³⁺ phosphors synthesized with 1 mol% of Eu³⁺, the emission spectra under ultraviolet excitation at 393 nm showed two strong blue and yellow bands at 485 and 577 nm corresponding to the ⁴F_9/2⁶H_15/2 and ⁴F_9/2⁶H_13/2 transitions of Dy³⁺ ions, respectively and several weak bands in the range of 600-700 nm resulting from the 4f transitions of Eu³⁺ ions. As the concentration of Eu³⁺ ions increased, intensities of the blue and yellow emission bands gradually decreased while those of the red emissions increased rapidly and the energy transfer efficiency from Dy³⁺ to Eu³⁺ ions was 95.3% at 20 mol% of Eu³⁺. The optimum white light emission with x=0.363, y=0.357 CIE 1931 chromaticity coordinates was obtained for the sample doped with 5 mol% Dy³⁺ and 1 mol% of Eu³⁺.

• Journal of the Korean Ceramic Society
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• v.19 no.4
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• pp.316-320
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• 1982

The effect of the additive on dielectric properties of $BaTiO_3$ containing 0.030 mol% $Dy_2O_3$ was investigated function of frequency from 5$\times$104 to 0.3$\times$107cps and temperature from 25 to 1$25^{\circ}C$. The dielectric constant increased with increasing $Dy_2O_3$ concentration from 0 to 0.05mol% due to space charge polarization. However, the dielectric constant decreased for further increase of $Dy_2O_3$ concentration due to density increase. The dielectric constant exhibits rapid change at the Curie temperature and the Curie temperature drops from 122 to 116$^{\circ}C$ with increasing amount of $Dy_2O_3$ concentration.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1171-1172
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• 2006

Addition of 2.0wt%$Dy_2O_3$ or 0.3wt%Sn proved to be very effective in improving the permanent magnetic properties of NdFeNbB magnets. $Dy_2O_3$ additions result in the increase in the Hci and temperature dependence due to formation of (NdDy)-rich phase and grain refinement of $\Phi$ phase. This improvement of the coercivity stability of the magnets from the addition of Sn is attributed to the smoothing effect of the Sn addition at the grain boundaries. The magnetic properties, the temperature dependence and Curie temperature of NdFeNbB with $Dy_2O_3$ and Sn combined addition were found to be considerably improved.

• Nuclear Engineering and Technology
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• v.34 no.2
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• pp.154-164
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• 2002

Neutron cross section data on Dy-160, Dy-161, Dy-162, Dy-163 and Dy-164 were calculated and evaluated in the energy range of 1 keV to 20 MeV using a spherical optical model, statistical model and pre-equilibrium model. The energy dependent optical model potential parameters were obtained based on the recent experimental data. The width fluctuation correction in Hauser-Feshbach particle decay and the quantum mechanical approach in pre-equilibrium analysis were introduced and gave a better cross section calculation in EMPIRE-II. The total, elastic scattering and threshold reaction cross sections were evaluated and compared with the evaluated files. The model calculated (n, tot), (n, ${\gamma}$) and (n, p) cross sections were in good agreement with the experimental data in the measured energy range. The results will be applied to ENDF/B-VI for data improvement.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.10
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• pp.897-901
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• 2003

The microstructure and varistor characteristics of ZnO-Pr$_{6}$O$_{11}$-CoO-Cr$_2$O$_3$-Dy$_2$O$_3$(ZPCCD)-based ceramics were investigated with Dy$_2$O$_3$ content in the range of 0.0∼2.0 mol%. As Dy$_2$O$_3$ content is increased, the average grain size was decreased in the range of 18.6∼4.7 $\mu$m and the density was decreased in the range of 5.53∼4.34 g/cm$^3$. While, the varistor voltage was increased in the range of 39.4∼436.6 V/mm and the nonlinear exponent was in the range of 4.5-66.6 with increasing Dy$_2$O$_3$ content. The addition of Dy$_2$O$_3$ highly enhanced the nonlinear properties of varistors, compared with the ceramics without Dy$_2$O$_3$ Particularly, the ceramics with Dy$_2$O$_3$ content of 0.5 mol% exhibited the highest nonlinearity, in which the nonlinear exponent is 66.6 and the leakage current is 1.2 $\mu$A.A.A.