• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.3 no.1
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• pp.57-65
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• 2005

This study suggested a new method for the solidification of molten salt waste generated from the electro-metallurgical process in the spent fuel treatment. Using binary material system, sodium silicate and phosphoric acid, metal chlorides were converted into metal phosphate in the micro-reaction module formed by SiO$_{2} particles. The volatile element in the reaction module would little vaporized below 1100$^{circ}$C After the gel product was mixed with borosilicate glass powder and thermally treated at 1000$^{circ}$C, li exists as Li$_{3}$PO$_4$ separated from glass phase and, Cs and Sr would be incorporated into an amorphous phase from XRD analysis. In case of the addition of ZrCl$_{4}$ to the binary system, the gel products were transformed into NZP structure considered as an prospective ceramic waste form after heat-treatment above 700 $^{circ}$C. From these results, the gel-route pretreatment can be considered as an effective approach to the solidincation of molten salt waste by the confirmed process or waste form and this also would be an alternative method on the ANL method using zeolites in USA by the confirmation of its chemical durability as an future work.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.5
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• pp.345-349
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• 2000

$Al_2O_3/ZrO_2$eutectic fibers were grown by micro-pulling down technique and investigated their microstructure as a function of solidification rate. $Al_2O_3/ZrO_2$eutectic fibers 0.2~2 mm in diameter and 500 mm in length have been grown with a pulling rate of 0.1~15 mm/min. The eutectic microstructures changed as a function of fulling rate from rod-shaped to cellular shape containing some thin lamellar pattern via uniform lamellar structure. Typical lamellar thickness decreased from about 380 nm to 110 nm as the pulling rate increased from 1 mm/min to 15 mm/min. The interlamellar spacing fitted with the inverse-square-root dependence on pulling rate according to $\lambda$= $1{\times}v^{-1/2}$, where $\lambda$ has the dimension in $\mu\textrm{m}$ and v is $\mu\textrm{m}$/s. Hardness value reached 13.1 GPa at 15 mm/min of pulling rate and tensile strength 900 MPa at 10 mm/min were also increased as the interlamellar spacing decreased.

• Journal of Korea Foundry Society
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• v.35 no.5
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• pp.120-127
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• 2015

The effects of Ti, B and Zr on grain refinement and castability were investigated in Al-4wt%Mg-0.9wt%Si-0.3wt%Mn-0.15wt%Fe alloy. Measurement of cooling curve and micro-structure observation were performed to analyze the effects of the addition of minor elements Ti, B and Zr during solidification. The prominence of effect on grain refinement was in increasing order for Ti, Zr and B element. Fine grain size and an increase of the crystallization temperature for ${\alpha}$-Al solution were evident as the amount of addition elements increased in this study. Addition of 0.15wt% Ti was most effective for grain refinement, and the resulting grain size of ${\alpha}$-Al solution for shell mold and steel mold were $72.3{\mu}m$ and $23.5{\mu}m$, respectively. Fluidity and shrinkage tests were perform to evaluate the castability of the alloy. Maximum fluidity length and minimum ratio of micro shrinkage were recorded for 0.15wt% Ti addition due to the effect of the finest grain size.

• Economic and Environmental Geology
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• v.37 no.1
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• pp.99-106
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• 2004

Pollution reduction and/or control technology becomes one of the pressing post-semiconductor research field to lead an advanced industrial structure. Soil/groundwater remediation techniques may act as a core technology which will create many demands on pollution reduction areas. A plenty numbers of abandoned metal mines were left without any remediation action in Korea, and it may be potential sources of heavy metal and As contamination in the ecosystem. In order to bring this soil contamination to a settlement, the emerging soil/groundwater remediation techniques should be introduced. Main research topics in the United States and Europe move towards the clean remediation technology without any secondary impact and the feasible application of developing technique into the field scale study. With these advantages, several soil/groundwater techniques such as electrokinetic soil processing, permeable reactive barrier, stabilization/solidification, biosorption, soil flushing with biosurfactant, bioleaching and phytoremediation will be summarized in this paper.

• Korean Journal of Materials Research
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• v.28 no.6
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• pp.317-323
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• 2018

Crystal structure of the $L1_2$ type $(Al,X)_3Ti$ alloy (X = Cr,Cu) is analyzed by X-ray diffractometry and the nonuniform strain behavior at high temperature is investigated. The lattice constants for the $L1_2$ type $(Al,X)_3Ti$ alloys decrease in the order of the atomic number of the substituted atom X, and the hardness tends to increase. In a compressive test at around 473K for $Al_{67.5}Ti_{25}Cr_{7.5}$, $Al_{65}Ti_{25}Cr_{10}$ and $Al_{62.5}Ti_{25}Cu_{12.5}$ alloys, it is found that the stress-strain curves showed serration, and deformation rate dependence appeared. It is assumed that the generation of serration is due to dynamic strain aging caused by the diffusion of solute atoms. As a result, activation energy of 60-95 kJ/mol is obtained. This process does not require direct involvement. In order to investigate the generation of serrations in detail, compression tests are carried out under various conditions. As a result, in the strain rate range of this experiment, serration is found to occur after 470K at a certain critical strain. The critical strain increases as the strain rate increases at constant temperature, and the critical strain tends to decrease as temperature rises under constant strain rate. This tendency is common to all alloys produced. In the case of this alloy system, the serration at around 473K corresponds to the case in which the dislocation velocity is faster than the diffusion rate of interstitial solute atoms at low temperature.

• Composites Research
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• v.14 no.5
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• pp.1-11
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• 2001

The particulates reinforced metal matrix composites(PMMC) have a number of interesting mechanical properties. including high strength and good resistance to wear at high temperature and low thermal expansion. The equipment structure to obtain the homogeneous distribution in composites are proposed for the continuous pouring of reinforcement at the desired temperature. The particulates reinforced metal matrix composites(A357/SiCp) were fabricated by the process of the combined stirring method with the various fabrication process. The combined stirring method to niform distribution of particle is consisted of two stirring force both electro-magnetic stirring generated from induction heating and mechanical stirring with graphite stirrer. PMMC billets were fabricated with the volume fractions ranged from 0% to 20% and particle sizes ranged from 14${\mu}{\textrm}{m}$ to 25${\mu}{\textrm}{m}$. It is important to cont the size of primary $\alpha$-Al solid particles because it could become the cause of the particle pushing or capture phenomena from the fact that secondary dendrite arm spacing size depends on the cooling rate during the solidification in hypoeutectic Al-Si alloy. Therefore, the effect of primary $\alpha$-Al on the reinforcement distribution in matrix alloys has been investigated. The microstructure of PMMC fabracated with various volume fractions(0%, 10%, and 20%) and particle size were observed.

• Journal of Welding and Joining
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• v.24 no.2
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• pp.71-78
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• 2006

It has been reported that good quality weld beads are not easily obtained during the $CO_2$ CW laser welding of primer coated plate. However, by introducing a small gap clearance in the lap position, the zinc vapor can escape through it and sound weld beads can be acquired. Therefore, this study examines for keyhole behavior by observing the laser-induced plasma and investigates the relation between keyhole behavior and formation of weld defect. Laser-induced plasma has accompanied with the vaporizing pressure of zinc ejecting from keyhole to surface of primer coated plate. This dynamic behavior of plasma was very unstable and this instability was closely related to the unstable motion of keyhole during laser welding. As a result of observing the composition of porosity, much of Zn element was found from inner surface of porosity. But Zn was not found from the dimple structure fractured at the weld metal. By analyzing of vaporizing element in laser welding, a component ratio of Zn was decreased by introducing a small gap clearance. Therefore we can prove that the major cause of porosity is the vaporization of primer in lap position. Mechanism of porosity-formation is that the primer vaporized from the lap position accelerates dynamic behavior of the key hole and the bubble separated from the key hole is trapped in the solidification boundary and romaines as porosity.

• Journal of Korea Foundry Society
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• v.40 no.2
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• pp.16-24
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• 2020

The effect of a heat treatment on the microstructure and mechanical properties of Inconel 713C alloy vacuum investment castings were investigated. The microstructure of the as-cast state was observed, showing well-developed dendrite structures and distributed carbide particles and solidified massive precipitates in the grain or grain boundary during solidification, in this case the γ′ phase and MC particles. During a heat treatment, the γ phase matrix was reinforced by solid solution elements, carbide particles from the film morphology precipitated along the grain boundary, and many micro-precipitates of second γ′ phases 0.2 ㎛~2 ㎛ in size were newly formed in the γ phase matrix according to SEM-EDS analysis results. The tensile strength at a high temperature (850℃) decreased slightly becoming comparable with the room-temperature result, while the hardness value of the specimen after the vacuum heat treatment increased by approximately 19%, becoming similar to that of the as-cast condition. However, the impact values at room temperature and low temperature (-196℃) were approximated; this alloy was mostly not affected by an impact at a low temperature. In the observations of the fracture surface morphologies of the specimens after the tensile tests, the fractures at room temperature were a mix of brittle and ductile fractures, and an intergranular fracture in the inter-dendrite structure and some dimples in the matrix were observed, whereas the fractures at high temperatures were ductile fractures, with many dimples arising due to precipitation. It was found that a reinforced matrix and precipitates of carbide and the γ′ phase due to the heat treatment had significant effects, contributing greatly to the excellent mechanical properties.

• Journal of Powder Materials
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• v.17 no.4
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• pp.302-311
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• 2010

In this research, the refinement behavior of the coarse magnesium powders fabricated by gas atomization was investigated as a function of milling time using a short duration high-energy ball milling equipment, which produces fine powders by means of an ultra high-energy within a short duration. The microstructure, hardness, and formability of the powders were investigated as a function of milling time using X-ray diffraction, scanning electron microscopy, Vickers micro-hardness tester and magnetic pulsed compaction. The particle morphology of Mg powders changed from spherical particles of feed metals to irregular oval particles, then platetype particles, with increasing milling time. Due to having HCP structure, deformation occurs due to the existence of the easily breakable C-axis perpendicular to the base, resulting in producing plate-type powders. With increasing milling time, the particle size increased until 5 minutes, then decreased gradually reaching a uniform size of about 50 micrometer after 20 minutes. The relative density of the initial power was 98% before milling, and mechanically milled powder was 92~94% with increase milling time (1~5 min) then it increased to 99% after milling for 20 minutes because of the change in particle shapes.

• Korean Journal of Materials Research
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• v.27 no.9
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• pp.495-500
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• 2017

Oxide layers were formed by an environmentally friendly plasma electrolytic oxidation (PEO) process on AZ91 Mg alloy. PEO treatment also resulted in strong adhesion between the oxide layer and the substrate. The influence of the KF electrolytic solution and the structure, composition, microstructure, and micro-hardness properties of the oxide layer were investigated. It was found that the addition of KF instead of KOH to the $Na_2SiO_3$ electrolytic solution increased the electrical conductivity. The oxide layers were mainly composed of MgO and $Mg_2SiO_4$ phases. The oxide layers exhibited solidification particles and pancake-shaped oxide melting. The pore size and surface roughness of the oxide layer decreased considerably with an increase in the concentration of KF, while densification of the oxide layers increased. It is shown that the addition of KF to the basis electrolyte resulted in fabricating of an oxide layer with higher surface hardness and smoother surface roughness on Mg alloys by the PEO process. The uniform thickness of the oxide layer formed on the Mg alloy substrates was largely determined by the electrolytic solution with KF, which suggests that the composition of the electrolytic solution is one of the key factors controlling the uniform thickness of the oxide layer.