• Journal of Powder Materials
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• v.26 no.4
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• pp.311-318
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• 2019

The objective of this study is to investigate the influence of powder shape and densification mechanism on the microstructure and mechanical properties of Ti-6Al-4V components. BE powders are uniaxially and isostatically pressed, and PA ones are injection molded because of their high strengths. The isostatically compacted samples exhibit a density of 80%, which is higher than those of other samples, because hydrostatic compression can lead to higher strain hardening. Owing to the higher green density, the density of BE-CS (97%) is found to be as high as that of other samples (BE-DS (95%) and P-S (94%)). Furthermore, we have found that BE powders can be consolidated by sintering densification and chemical homogenization, whereas PA ones can be consolidated only by simple densification. After sintering, BE-CS and P-S are hot isostatically pressed and BE-DS is hot forged to remove residual pores in the sintered samples. Apparent microstructural evolution is not observed in BE-CSH and P-SH. Moreover, BE-DSF exhibits significantly fine grains and high density of low-angle grain boundaries. Thus, these microstructures provide Ti-6Al-4V components with enhanced mechanical properties (tensile strength of 1179 MPa).

• Journal of Powder Materials
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• v.28 no.5
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• pp.375-380
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• 2021

In this study, we investigate the effect of the duration of mechanical alloying on the microstructures and mechanical properties of ODS ferritic/martensitic steel. The Fe(bal.)-10Cr-1Mo pre-alloyed powder and Y₂O₃ powder are mechanically alloyed for the different mechanical alloying duration (0 to 40 h) and then constantly fabricated using a uniaxial hot pressing process. Upon increasing the mechanical alloying time, the average powder diameter and crystallite size increased dramatically. In the initial stages within 5 h of mechanical alloying, inhomogeneous grain morphology is observed along with coarsened carbide and oxide distributions; thus, precipitate phases are temporarily observed between the two powders because of insufficient collision energy to get fragmented. After 40 h of the MA process, however, fine martensitic grains and uniformly distributed oxide particles are observed. This led to a favorable tensile strength and elongation at room temperature and 650℃.

• Applied Chemistry for Engineering
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• v.9 no.7
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• pp.1011-1017
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• 1998

$YBa_2Cu_3O_{6+x}(Y123)-Ag$ high-Tc superconducting wires were fabricated by plastic extrusion technique using pyrophoric synthetic and mechanical mixing powder with and without Ag addition(20 wt.%). This method involves powder preparation, plastic paste making, die extrusion, binder burn-out and the sintering process. In order to fabricate a good-quality superconducting body, it is required to use homogeneous and fine-size power as a starting materials. $Y_2O_3-BaCO_3-CuO$ precursor powders with/without Ag addition were prepared both by pyrophoric synthetic(PS) and mechanical mixing(MM) method of raw powders. The formation kinetics of the powder mixtures into Y123 phase was investigated at various temperatures and times in air atmosphere. The powder prepared by PS method was more easily converted into a Y123 phase than the MM powder. The fine size and good chemical homogeneity of the powder prepared by PS method is attributable to the fast formation into a Y123 phase. The critical current density($J_c$) of the Y123-Ag superconducting wires made by plastic extrusion method were in the range of $150A/cm^2{\sim}230A/cm^2$. depending on the charateristics of starting material powders. $J_c$ of the wire prepared by pyrophoric synthetic powder with 20 wt.% Ag addition was $230A/cm^2$.

• Resources Recycling
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• v.27 no.6
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• pp.44-52
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• 2018

In this study, copper was recovered from copper containing sludge by selectively controlling electro-refining process conditions in copper sulfate electrolyte solution. Electro-refining process was performed by LSV (Linear Sweep Voltammetry) result according to copper sulfate electrolyte solution concentration, applied current density, additive type and concentration. SEM (Scanning Electron Microscope) and PSA (Particle Size Analyzer) were used to analyze the shape and size of copper powder. In the 0.1 ~ 0.4 M copper sulfate electrolyte solution without organic additives, the copper powder size decreased as the applied current density became closer to the limiting current density and the copper powder size tended to decrease in 0.2 ~ 0.3 M copper sulfate electrolyte solution. In addition, when the shape and size of the copper powder were analyzed by adding various types and concentrations of organic additives to the previous experimental, fine spherical copper powder having the smallest size (nm) was obtained under the condition of cellulose type additive 2,000 ppm.

• Journal of Powder Materials
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• v.16 no.6
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• pp.438-441
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• 2009

Mg-Cu composites were successively fabricated using a combination of rapid solidification and extrusion processes. In addition, the microstructural variation of the composite was investigated by performing the extrusion repeatedly. It resulted that the composite formed an uniform and dense structure by the extrusion, and the microstructure became fine as the extrusion conducted repeatedly. The microstructural variation was known to be dependent on the number of extrusion and the area reduction ratio. The tensile strength was also measured as a function of the microstructural variation.

• Journal of the Korean Ceramic Society
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• v.26 no.5
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• pp.631-636
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• 1989

Submicron high-purity mullite powder was prepared by a colloidal sol-gel route. Boehmite and silica were the starting materials. 2wt% $\alpha$-Al2O3 or ZrO2 was used as a seeding material. The gelled powder was calcined at 130$0^{\circ}C$ for 100min and attrition milled for 3hrs. The mullite powder obtained was composed of submicrometer and uniform particles with a narrow size distribution. It was hot-pressed at 1$600^{\circ}C$ for 1hr under 10MPa or was sintered at 1$650^{\circ}C$ for 4hrs. The bulk densities of the products made by both processes were 3.14 and 3.12g/㎤. the mechanical, thermal and electrical properties of the sintered mullite were characterized by bending strength, thermal expansion coefficient, thermal conductivity, dielectric constant and dielectric loss, etc.

• Transactions of the Korean hydrogen and new energy society
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• v.4 no.1
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• pp.41-50
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• 1993

The hydrogen absorption and desorption characteristics of microencapsulated (CFM)$Ni_{4.7}Al_{0.2}Fe_{0.1}$ and $MmNi_4Fe$ powder with Ni and/or Cu by means of chemical plating method have been investigated. Initial hydrogen absorption rate and activation property were increased remarkably by encapsulation and subsequent compacting. Pellets abtained by compacting of Cu-encapsulated fine powder have fairly good strength even after 30 cycles of hydriding and dehydriding. Encapsulated alloy powder and their compacts show a good resistance to degradation by $O_2$ or CO in hydrogen.

• Journal of environmental and Sanitary engineering
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• v.11 no.1
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• pp.63-70
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• 1996

The synthesis of high purity and ultra-fine $BaTiO_3$ by precipitation with gaseous $NH_3$ as precipitator was investigated to find an alternative process to solve various problems of recent wet methods. A synthesis process for $BaTiO_3$ powder using $NH_3$ gas as a precipitator in a bubble column reactor was experimentally successful in developing the production process of piezoelectric ceramic $BaTiO_3$ powder. And a 2.33m1/sec is approprite for the feed flow rate, $BaTiO_3$ powder produced under above the condition is spherical type, its particle size was about $0.2{\mu}m$.

• Proceedings of the KIEE Conference
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• 1991.07a
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• pp.213-216
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• 1991

In this study, PZT powder was synthesized by coprecipitation method us ing $Pb(NO_3)2$, $ZrOCl_2{\cdot}8H_2O$ and $TiCl_4$ as starting raw materials. Homogeneous and fine-grained PZT powder was obtained by the coprecipitation method. PZT powder was characterized by DTA, SEM and XRD analysis. The XRD peaks were observed at $600(^{\circ}C)$ and over.

• Journal of the Korean Ceramic Society
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• v.33 no.4
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• pp.455-463
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• 1996

Aluminium nitride (AlN) powder was prepared by using aluminium (III) complexes with dibasic carboxylate ligands(adipato)(hydroxo) aluminium(III) and (hydroxo)(succinato)aluminium (III) as a precursor. The AlN pow-der was obtained by calcining the complexes without mixing any carbon source under a flow of ammonia at 120$0^{\circ}C$ Contary to the conventional carbothermal reduction and nitridiation the process of decarboniza-tion of the residual carbon was not required because of the reaction of ammonia with carbon at temperature >100$0^{\circ}C$. Fine AlN powder was also prepared by calcining a mixture of an (adipato)(hydroxo)aluminium(III) complex and carbon under a flow of nitrogen at 140$0^{\circ}C$ The AlN powders prepared were ultrafine and their morphology was almost the same as that of powders of two precursors.