• The Korean Journal of Ceramics
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• v.5 no.3
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• pp.255-259
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• 1999

The effects of $SiO_2$ and MnO addition on the sinterability and the electrical properties of 0.4mol% Nb-doped SrTiO3 varistor were investigated. The $SiO_2$ content was fixed at 0.3mol% and the MnO content varied from 0 to 1.0mol%. With 0.3 mol% $SiO_2$ and 0.3 mol% MnO addition, optimum density was obtained by sintering at $1200^{\circ}C$ without excess liquid phase. Impedance spectroscopy was performed on the sintered specimens with 0.3 mol% $SiO_2$ and various MnO contents. It was found that the resistivities of grains was increased with increasing MnO content. The dielectric constant was measured to be above 50000 in the specimen with 0.3~1.0mol% Mn content. The non-linear coefficient increased substantially with MnO addition, and it varied from 1 to 9 depending on the MnO content.

• Journal of Magnetics
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• v.20 no.4
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• pp.336-341
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• 2015

MnBi alloys were fabricated by arc melting and annealing at 573 K. The heat treatment enhanced the content of the low-temperature phase (LTP) of MnBi up to 83 wt%. The Bi-excess assisted LTP MnBi alloys were used in the hybridization with the Nd-Fe-B commercial Magnequench ribbons to form the hybrid magnets (100-x)NdFeB/xMnBi, x = 20, 30, 40, 50, and 80 wt%. The as-milled powder mixtures of Nd-Fe-B and MnBi were aligned in a magnetic field of 18 kOe and warm-compacted to anisotropic and dense bulk magnets at 573 K by 2,000 psi for 10 min. The magnetic ordering of two hard phase components strengthened by the exchange coupling enhanced the Curie temperature ($T_c$) of the magnet in comparison to that of the powder mixture sample. The prepared hybrid magnets were highly anisotropic with the ratio $M_r/M_s$ > 0.8. The exchange coupling was high, and the coercivity $_iH_c$ of the magnets was ~11-13 kOe. The maximum value of the energy product $(BH)_{max}$ was 8.4 MGOe for the magnet with x = 30%. The preparation of MnBi alloys and hybrid magnets are discussed in details.

• Journal of Welding and Joining
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• v.13 no.3
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• pp.147-156
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• 1995

The change of microstructure in the bonded interlayer and tensile properties of joints were studied for liquid phase diffusion bonding using STS-310 and Incoloy-825 as base metal and base metal+B alloy as insert inetal. Main experimental results obtained in this study are as follows. 1) The optimum amount of B addition into the insert metal was found to be about 4mass%. 2) When isothermal solidification was completed, the microstructure in the bonded interlayer was the same with that of the base metal because of the grain boundary migration in the bonded interlayer. 3) All of the tensile specimen fractured at base metal and joints bonded at optimum condition exhibited tensile properties in excess of base metal requirements. 4) It was determined that fine car-borides and bordes such as M$_{23}$(C,B)$_{6}$, Cr$_{2}$B, and CrB in STS-310S and TiB in Incoloy-825 exist at the grain boundary around bonded interlayer. These precipitates almost disappeared after homogenizing treatment at 1373K for 86.4ks.s.

• Journal of the Korean Ceramic Society
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• v.27 no.2
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• pp.187-194
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• 1990

Effects of MnO2 addition ranged from 0.0wt% to 5.0wt% on the microstructure and dielectric and piezoelectric properties of the Pb(Zr0.52 Ti0.48)O3 Ceramics have been investigated. The solubility limit of MnO2 in Pb(Zr0.52 Ti0.48)O3 is about 0.5wt%, and MnO2 as a valence state of Mn3+ is substituted for (Zr, Ti) lattice site in PZT solid-solution. The addition of MnO2 up to 0.5wt% in Pb(Zr0.52 Ti0.48)O3 brings increase of density, but decreased of grain size and tetragonality. Dielectric constant slightly decreases, but both coupling factor(Kp) and mechanical quality factor(Qm) increase with the addition of MnO2. However, excess amount of MnO2 addition more than 0.75wt% results in rapid decrease of resistance. Dielectric constant and tan $\delta$ increase due to the second phase and inhomogeneous Mn distribution.

• Journal of the Korean Magnetics Society
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• v.5 no.1
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• pp.21-26
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• 1995

The systematic variation of complex permeability and complex permittivity and their relationship with micro-wave absorbing properties are investigated in sintered Ni-Zn ferrites of non-stoichiometric composition. The specirrens of ${(Ni_{0.5}Zn_{0.5}O)}_{1-x}(Fe_{2}O_{3})_{1+x}$ spinels were prepared by a conventional ceramic processing technique. In the present study. complex permeability and permittivity can be controlled by the variation of ${\alpha}-Fe_{2}O_{3}$ contents in the spinel lattice. The primary effect of the excess ${\alpha}-Fe_{2}O_{3}$ is to increase the dielectric constant. while the notable decrease of magnetic loss is observed in the iron-deficient ferrites. The results suggest that the matching fre-queocyand matching thickness could be controlled by the variation of ${\alpha}-Fe_{2}O_{3}$ contents in the Ni-Zn ferrite.

• Korean Journal of Materials Research
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• v.21 no.10
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• pp.542-545
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• 2011

Half-Heusler alloys are a potential thermoelectric material for use in high-temperature applications. In an attempt to produce half-Heusler thermoelectric materials with fine microstructures, TiCoSb was synthesized by the mechanical alloying of stoichiometric elemental powder compositions and then consolidated by vacuum hot pressing. The phase transformations during the mechanical alloying and hot consolidation process were investigated using XRD and SEM. A single-phase, half- Heusler allow was successfully produced by the mechanical alloying process, but a minor portion of the second phase of the CoSb formation was observed after the vacuum hot pressing. The thermoelectric properties as a function of the temperature were evaluated for the hot-pressed specimens. The Seebeck coefficients in the test range showed negative values, representing n-type conductivity, and the absolute value was found to be relatively low due to the existence of the second phase. It is shown that the electrical conductivity is relatively high and that the thermal conductivities are compatibly low in MA TiCoSb. The maximum ZT value was found to be relatively low in the test temperature range, possibly due to the lower Seebeck coefficient. The Hall mobility value appeared to be quite low, leading to the lower value of Seebeck coefficient. Thus, it is likely that the single phase produced by mechanical alloying process will show much higher ZT values after an excess Ti addition. It is also believed that further property enhancement can be obtained if appropriate dopants are selectively introduced into this MA TiCoSb System.

• Journal of the Korean Chemical Society
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• v.37 no.8
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• pp.717-722
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• 1993

Reactions of [PtCl$_4$]$^{2-}$ with excess of dithiocarbamates in water lead to facile replacement of the chloro ligand by dithiocarbamato ligand to give [Pt(A)], [Pt(B)$_2$]Cl$_2$, [Pt(C)$_2$], and [Pt(D)(CH$_2$=CH$_2$)Cl]Cl. The complexes of platinum have been characterized by elemental analyses, infrared and UV-visible spectra, and conductivity measurements. Platinum(II)-dithiocarbamate complexes were soluble in polar solvents such as water, alcohol, acetone, dimethylformamide, and dimethylsulfoxide etc. The possible structure was proposed on the basis of elemental analyses and physical properties.

• Korean Journal of Materials Research
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• v.3 no.5
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• pp.529-537
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• 1993

The mecllanical properties of AI/TiCp composite fabrication by liquid mixing was investigat ed. The composites, containing 10 wt% Tic. were producwi using induction furnace with mechanical stirring. The amounts of' 1.5wt% Mg were, added to wetting agents. Thr presence of aluminum in TiC composites showed rnhanced strengrh without loss of ductility at room and clrvated temperatures. Espe cially, wear resistance was found to dramatically irnprovc. I3ul excess stirring d~terrninrd the mect~ani~ cal properties. Approximate values at present work were 500 rpm. There was no inrerfacial reaction of any kind and the interface remains clearly deineated.

• Korean Journal of Materials Research
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• v.17 no.9
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• pp.480-483
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• 2007

Hydroxyapatites were prepared by the different $SiO_2$ addition at $1450^{\circ}C$ for 2h. With the increase of $SiO_2$ addition, microstructure, bulk density, porosity, mechanical strength of $hydroxyapatite/{\beta}-TCP$ composite were investigated. When the sintered HAp contained 1 wt% $SiO_2$, the each properties of the HAp were increased. But the excess addition of $SiO_2$ content above 1wt% the each property were decreased. This results were due to the ${\beta}-TCP$ phase. The ${\beta}-TCP$ phase appeared at 3 wt% $SiO_2$ addition and the ${\beta}-TCP$ phase was enhanced by the $SiO_2$ increasing.

• Korean Chemical Engineering Research
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• v.56 no.5
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• pp.663-678
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• 2018

Refractive index and speeds of sound for the binary mixture of isomer of butanol (1) + cyclohexane, benzene and toluene (2) were measured at 308.15 K. The measured data were used to calculate deviation in refractive index ${\Delta}n$, ultrasonic speed ${\Delta}u$, isentropic compressibility $K_s^E$, available volume $V_a$, excess intermolecular free length $L_f$ and molecular association $M_A$. All the derived properties were correlated with polynomial equation. Ultrasonic speed data were predicted using various empirical correlations like Nomoto, van Dael, impedance dependence and theoretically with Schaaff's collision factor theory (CFT). Jacobson free length theory (FLT) was used to calculate $L_f$. The measured refractive index was also correlated with various mixing rules. The deviation in refractive index Δn and ultrasonic speed ${\Delta}u$ was used to determine the intermolecular interactions.