• Journal of the Mineralogical Society of Korea
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• v.14 no.2
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• pp.128-136
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• 2001

The K-Ba complete solid solution of 7 synthetic hollandite-type minerals ($K_{2x}$ $Ba_{1-x}$ $Cr_2$/$Ti_{6}$ $O_{16}$ , x=0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0, respectively) are studied by the X-ray powder diffraction and Rietveld refinement to find structural transformation during substitution of $Ba^{2+}$ by $K^{+}$ in A site of the tunnel structure of hollandite. Rietveld indices indicate that $R_{wp}$ with respect to $R^{exp}$ ($R_{wp}$ $R_{exp}$ ) are in the range of 15.66%/20.90% and 14.74%/l9.37%, $R_{B}$ and S(Goodness of Fitness) are 6.45~8.97%, 1.45~1.63, respectively. Unit cell parameters of synthetic hollandites, space group 14/m, are a=10.1194(2)~10.0599(2)$\AA$, c=2.9572(6)~2.9512(7)$\AA$, and V=302.75~298.66$\AA^{3}$. Rutile formed as an impurity in those with more than 50% K contents in hollandite series. Substitution of Ba by K ion in a tunnel structure results in constant decrease of cell parameters, but is not sufficient enough to change the hollandite structure. Our data indicate that transformation of tetragonal 14/m to lower symmetry of monoclinic 12/m in hollandite structure may at least be affected by other cation substitution in same A site and/or by cation substitution in B site.

• Nuclear Engineering and Technology
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• v.51 no.4
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• pp.1069-1074
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• 2019

A novel fabrication method of oxide dispersion strengthened (ODS) steel cladding tubes for advanced fast reactors has been investigated using the cold spray powder-based materials deposition process. Cold spraying has the potential advantage for rapidly fabricating ODS cladding tubes in comparison with the conventional multi-step extrusion process. A gas atomized spherical 14YWT (Fe-14%Cr, 3%W, 0.4%Ti, 0.2% Y, 0.01%O) powder was sprayed on a rotating cylindrical 6061-T6 aluminum mandrel using nitrogen as the propellant gas. The powder lacked the oxygen content needed to precipitate the nanoclusters in ODS steel, therefore this work was intended to serve as a proof-of-concept study to demonstrate that free-standing steel cladding tubes with prototypical ODS composition could be manufactured using the cold spray process. The spray process produced an approximately 1-mm thick, dense 14YWT deposit on the aluminum-alloy tube. After surface polishing of the 14YWT deposit to obtain desired cladding thickness and surface roughness, the aluminum-alloy mandrel was dissolved in an alkaline medium to leave behind a free-standing ODS tube. The as-fabricated cladding tube was annealed at $1000^{\circ}C$ for 1 h in an argon atmosphere to improve the overall mechanical properties of the cladding.

• Korean Journal of Materials Research
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• v.21 no.8
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• pp.468-475
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• 2011

[ $LaMeO_3$ ](Me = Cr, Co) powders were prepared using the polymeric precursor method. The effects of the chelating agent and the polymeric additive on the synthesis of the $LaMeO_3$ perovskite were studied. The samples were synthesized using ethylene glycol (EG) as the solvent, acetyl acetone (AcAc) as the chelating agent, and polyvinylpyrrolidone (PVP) as the polymer additive. The thermal decomposition behavior of the precursor powder was characterized using a thermal analysis (TG-DTA). The crystallization and particle sizes of the $LaMeO_3$ powders were investigated via powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and particle size analyzer, respectively. The as-prepared precursor primarily has $LaMeO_3$ at the optimum condition, i.e. for a molar ratio of both metal-source (a : a) : EG (80a : 80a) : AcAc (8a) inclusive of 1 wt% PVP. When the as-prepared precursor was calcined at $700^{\circ}C$, only a single phase was observed to correspond with the orthorhombic structure of $LaCrO_3$ and the rhombohedral structure of $LaCoO_3$. A solid-electrolyte impedance-metric sensor device composed of $Li_{1.5}Al_{0.5}Ti_{1.5}(PO_4)_3$ as a transducer and $LaMeO_3$ as a receptor has been systematically investigated for the detection of NOx in the range of 20 to 250 ppm at $400^{\circ}C$. The sensor responses were able to divide the component between resistance and capacitance. The impedance-metric sensor for the NO showed higher sensitivity compared with $NO_2$. The responses of the impedance-metric sensor device showed dependence on each value of the NOx concentration.

• Journal of the Korea Institute of Building Construction
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• v.23 no.2
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• pp.153-164
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• 2023

The objective of this study is to examine the removal rate of air pollutants, specifically sulfur oxides (SO_x) and nitrogen oxides(NO_x), using concrete permeable blocks containing zeolite beads coated with materials capable of eliminating these pollutants. Titanium dioxide(TiO₂) powder and coconut shell powder were utilized for the removal of SO_x and NO_x and were applied as coatings on the zeolite beads. Concrete permeable block specimens embedded with the coated zeolite beads were produced using an actual factory production line. Test results demonstrated that the concrete permeable block containing zeolite beads coated with coconut shell powder in the surface layer achieved SO_x and NO_x removal rates of 12.5% and 99%, respectively, exhibiting superior performance compared to other blocks. Additionally, the flexural strength and slip resistance were 5.3MPa and 65BPN or higher, respectively, satisfying the requirements specified in KS F 4419 and KS F 4561. Conversely, the permeability coefficient exhibited low permeability, with grades 2 and 3 before and after contaminant pollution, according to the standard for 'design, construction, and maintenance of pavement using permeable block'. In conclusion, incorporating zeolite beads coated with coconut shell powder in the surface layer enables simultaneous removal of SO_x and NO_x, irrespective of ultraviolet rays, while maintaining adequate flexural strength and slip resistance. However, the permeability is significantly reduced, necessitating further improvements.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.1
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• pp.51-53
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• 2008

A new nano-particle deposition system (NPDS) was developed for a ceramic and metal coating process. Nano- and micro-sized powders were sprayed through a supersonic nozzle at room temperature and low vacuum conditions to create ceramic and metal thin films on metal and polymer substrates without thermal damage. Ceramic titanium dioxide ($TiO_2$) powder was deposited on polyethylene terephthalate substrates and metal tin (Sn) powder was deposited on SUS substrates. Deposition images were obtained and the resulting chemical composition was measured using X-ray photoelectron spectroscopy. The test results demonstrated that the new NPDS provides a noble coating method for ceramic and metal materials.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.466-467
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• 2006

The anatase particle was facetted at the free surface and a neck formation between the anatase particles prior to the phase transformation occured. This resulted in the severe lattice distortion at the region of the interface near the neck and this can act as the nucleation sites for the phase transformation. The grain growth of rutile particles after the phase transformation grew very fast by the sweeping phenomena of grain boundary. Therfore, It leaded to the microstructure without the rutile phase located in anatase particle.

• Journal of the Korean Ceramic Society
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• v.39 no.6
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• pp.558-565
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• 2002

Coal fly ash, produced from a power plant in Korea was used for the production of glass-ceramics and the physical properties of glass-ceramics were evaluated. CaO and TiO$_2$ were added into the fly ash during the melting process to reduce the viscosity of molten glass and to induce internal crystallization of glass, respectively. Glass-ceramic was produced through a single stage heat treatment (at 950∼1050$\^{C}$ for 37∼240 min) after preparing glass (iota fly ash powder. As a result, a new tiny rod type crystals (a=7.4480, b=10.7381, c=4.3940 A, $\alpha$=94.9, $\beta$=98.6, γ=108.5°) was found in the glass-ceramics, which showed attractive mechanical properties, high hardness (7.1∼7.6 GPa) and wear resistance (by erosion test). Thus a glass-ceramic produced from thermal power plant fly ash and cell as a source for CaO exhibits a suitable treatment for the recycling and exploitation of waste materials and would be acceptable for a new application far building materials.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.656-658
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• 2004

Pb$(Zr_{0.8}Ti_{0.2})TiO_3$ powder were prepared by the sol-gel method using a solution of Pb-acetate, Zr n-propoxide and Ti iso-propoxide. PZT thick film were fabricated by the screen printing method, and the structural and ferroelectric properties asafunting of the sintering temperature were studied. PZT film thickness, obtained by four screen printing, was approximately $70\sim90{\mu}m$. The relative dielectric constant and the dielectric loss of the PZT thick film sintered at $1050^{\circ}C$t were approximately 676 and 1.4%, respectively. The remanent polarization and the coercive field of the PZT thick film sintered at $1050^{\circ}C$ were $21.15{\mu}C/cm^2$ and 10.1 kV/cm, mapetively

• Journal of Electrical Engineering and Technology
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• v.4 no.4
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• pp.527-530
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• 2009

$(Ba_{0.57}Sr_{0.33}Ca_{0.10})TiO_3$(=BSCT) powders, prepared by the sol-gel method, were doped using $MnCO_3$ as the acceptor and $Dy_2O_3$ as the donor. This powder was mixed with an organic vehicle. BSCT thick films were fabricated by the screen-printing techniques on the alumina substrate. The structural and dielectric properties of BSCT thick films were investigated with variation of the $Dy_2O_3$ amount. As a result of the differential thermal analysis (DTA), the exothermic peak was observed at around $670^{\circ}C$ due to the formation of the polycrystalline perovskite phase. All the BSCT thick films showed the XRD patterns of a typical polycrystalline perovskite structure. The average grain size of BSCT thick films decreased with an increasing amount of $Dy_2O_3$. The relative dielectric constant and dielectric loss of the BSCT thick film doped $Dy_2O_3$ 0.1mol% were 4637.4 and 1.6% at 1kHz, respectively.

• Korean Journal of Materials Research
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• v.25 no.8
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• pp.386-390
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• 2015

Fe-base superalloy powders with $Y_2O_3$ dispersion were prepared by high energy ball milling, followed by spark plasma sintering for consolidation. High-purity elemental powders with different Fe powder sizes of 24 and 50 mm were used for the preparation of $Fe-20Cr-4.5Al-0.5Ti-O.5Y_2O_3$ powder mixtures (wt%). The milling process of the powders was carried out in a horizontal rotary ball mill using a stainless steel vial and balls. The milling times of 1 to 5 h by constant operation (350 rpm, ball-to-powder ratio of 30:1 in weight) or cycle operation (1300 rpm for 4 min and 900 rpm for 1 min, 15:1) were applied. Microstructural observation revealed that the crystalline size of Fe decreased with an increase in milling time by cyclic operation and was about 15 nm after 3 h, forming a FeCr alloy phase. The cyclic operation had an advantage over constant milling in that a smaller-agglomerated structure was obtained. The milled powders were sintered at $1100^{\circ}C$ for 30 min in vacuum. With an increase in milling time, the sintered specimen showed a more homogeneous microstructure. In addition, a homogenous distribution of Y-compound particles in the grain boundary was confirmed by EDX analysis.