The effect of the alloy systems Al-Mg alloy and Al-Si alloy in this study on the characteristics of die-casting were investigated using solidification simulation software (MAGMAsoft). Generally, it is well known that the casting characteristics of Al-Mg based alloys, such as the fluidity, feedability and die soldering behaviors, are inferior to those of Al-Si based alloys. However, the simulation results of this study showed that the filling pattern behaviors of both the Al-Mg and Al-Si alloys were found to be very similar, whereas the Al-Mg alloy had higher residual stress and greater distortion as generated due to solidification with a larger amount of volumetric shrinkage compared to the Al-Si alloy. The Al-Mg alloy exhibited very high relative numbers of stress-concentrated regions, especially near the rib areas. Owing to the residual stress and distortion, defects were evident in the Al-Mg alloy in the areas predicted by the simulation. However, there were no visible defects observed in the Al-Si alloy. This suggests that an adequate die temperature and casting process optimization are necessary to control and minimize defects when die casting the Al-Mg alloy. A Tatur test was conducted to observe the shrinkage characteristics of the aluminum alloys. The result showed that hot tearing or hot cracking occurred during the solidification of the Al-Mg alloy due to the large amount of shrinkage.

The particle size of MgO was examined as a function of the Na content in Mg(OH)2 powders and the calcination temperature. Mg(OH)2 suspension was obtained by dropwise precipitation of Mg(NO3)2·6H2O and NaOH solutions. The suspension was diluted by varying the dilution volume ratio of distilled water to Mg(OH)2 suspension to change the Na salt concentration in the suspension. Mg(OH)2 slurry was filtered and dried at 60˚C under vacuum, and then its Mg(OH)2 powder was calcined to produce MgO with different amount of Na content at 500~900˚C under air. Investigation of the physical and chemical properties of the various MgO powders with dilution ratio and calcination temperature variation was done by X-ray diffraction, transmission electron microscopy, BET specific surface area and thermal gravimetric analysis. It was observed that MgO particle size could depend on the condition of calcination temperature and dilution ratio of the Mg(OH)2 suspension. The particle size of the MgO depends on the Na content remaining in the Mg(OH)2 powder, which powder was prepared by changing the dilution ratio of the Mg(OH)2 suspension. This change increased as the calcination temperature increased and decreased as the dilution ratio increased. The growth of MgO particle size according to the increase of temperature was more effective when there was a relatively high content of Na. The increase of Na content lowered the temperature at which decomposition of Mg(OH)2 to MgO took place, thereby promoting the crystal growth of MgO.

This study was performed to investigate the FSH levels for superovulation procedure in Korean Native Cattle (Hanwoo). The effectiveness of 200 mg and 400 mg of FSH to initiate superovulation was examined in Hanwoo. Donors, at random stages of the estrous cycle, received a CIDR. 7 days later, 200 mg FSH group was treated with 40, 30, 20, 10 mg FSH levels in declining doses twice daily by intramuscular injection for 4 days. Also, 400 mg FSH group was treated with 80, 60, 40, 20 mg FSH levels. On the 3rd day administration of FSH, 25 mg PGF2α was administered and CIDR was withdrawn. Donors were artificially inseminated twice at 12 hr intervals. The donor cattle received 250 μg GnRH at time of 1st insemination and embryos were recovered 8 days after the 1st insemination. As a results, average number of CL treated with FSH 200 mg was higher as 20.9±1.20 than 15.8±0.63 for donors treated with FSH 400 mg, respectively(p<0.05). Treated group of 200 mg FSH level increased (p<0.05) the number of embryos recovered per procedure compared to 400 mg FSH level (18.2±1.18 vs. 12.38±0.52, respectively). When treatment of 200 mg FSH was performed, average transferable embryos/ova increased (p<0.05) to 14.1±1.12 from 6.8±0.33 of treated of 400 mg FSH. Group of 200 mg FSH increased (p<0.05) to 8.3±0.76 from 2.0±0.26 in morula stage compare to 400 mg FSH group. Mean of total early blastocyst and expanded blastocyst stage embryos was similar (p<0.05) between the 200 mg and 400 mg FSH levels group (4.7±1.19 vs. 2.9±0.18 and 1.2±0.40 vs. 1.9±0.17). These results suggest that 200 mg FSH level-based superovulation protocol with CIDR may be effectively used for production of superior embryos in Hanwoo. In other words, the less level of FSH may be effectively applied for Hanwoo (Korean Native Cattle), because Hanwoo was smaller body size than beef or daily cow.

In order to improve the weak mechanical properties of cast Mg alloys, Mg- (at%) alloy powders were synthesized using gas atomization, a typical rapid solidification process. The powders consist of fine dendrite structures less than 3 in arm spacing. In order to fabricate a bulk form, the Mg powders were compacted using magnetic pulse compaction (MPC) under various processing parameters of pressure and temperature. The effects of the processing parameters on the microstructure and mechanical properties were systematically investigated.

The structure and dielectric properties of poled<001>-oriented 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-0.3PT) crystals have been investigated for orientations both parallel and perpendicular to the [001] poling direction. An electric field induced monoclinic phase was observed for the initial poled sample. The phase remained stable after the field was removed. A quite different temperature dependence of dielectric constant has been observed between heating and cooling due to an irreversible phase transformation. The results of mesh scans and temperature dependence of the dielectric constant demonstrate that the initial monoclinic phase changes to a single domain tetragonal phase at 370K and to a paraelectric cubic phase at 405K upon heating. However, upon subsequent cooling from the unpoled state, the cubic phase changes to a poly domain tetragonal phase and to a rhombohedral phase. In the ferroelectric tetragonal phase with a single domain state, the dielectric constant measured perpendicular to the poling direction was dramatically higher than that of the parallel direction. A large dielectric constant implies easier polarization rotation away from the polar axis. This enhancement is believed to be related to dielectric softening close to the morphotropic phase boundary and at the phase transition temperature.

Melt foaming method is one of cost-effective methods to make metal foam and it has been successfully applied to fabricate Mg foams. In this research, AZ31 Mg alloy ingot was used as a metal matrix, using AlCa granular as thickening agent and CaCO3 powder as foaming agent, AZ31 Mg alloy foams were fabricated by melt-foaming method at different foaming temperatures. The porosity was above 41.2%~73.3%, pore size was between 0.38~1.52 mm, and homogenous pore structures were obtained. Microstructure and mechanical properties of the AZ31 Mg alloy foams were investigated by optical microscopy, SEM and UTM. The results showed that pore structure and pore distribution were much better than those fabricated at lower temperatures. The compression behavior of the AZ31 Mg alloy foam behaved as typical porous materials. As the foaming temperature increased from 660˚C to 750˚C, the compressed strength also increased. The AZ31 Mg alloy foam with a foaming temperature of 720˚C had the best energy absorption. The energy absorption value of Mg foam was 15.52 MJ/m3 at a densification strain of 52%. Furthermore, the high energy absorption efficiencies of the AZ31 Mg alloy foam kept at about 0.85 in the plastic plateau region, which indicates that composite foam possess a high energy absorption characteristic, and the Vickers hardness of AZ31 Mg alloy foam decreased as the foaming temperature increased.

Magnesium hydroxide sulfate hydrate whiskers (, abbreviated 513 MHSH) were prepared using hydrothermal reaction with magnesium oxide (MgO) and magnesium sulfate () as the starting materials. The effects of the molar ratio of /MgO and amount of were studied. As a result, 513 MHSH whiskers co-existed with hexagonal plate at low concentration of . The molar ratio of /MgO was 7:1, uniform 513 MHSH whiskers were formed without impurity such as . Appropriate amount of has affected to formation of high quality MHSH. Their morphologies and structures were determined by powder X-ray diffraction (XRD) scanning electron microscopy (SEM) and thermo-gravimetric analyzer (TGA).

The influence of sulfate on the selective catalytic reduction of on the Ag/ catalyst was studied when was used as a reducing agent. Various preparation methods influenced differently on the activity. Among the methods, cogelation precipitation gave best activity. When sulfates were formed on the surfaces of samples prepared by impregnated and deposition precipitation, activity was enhanced as long as suitable forming condition is satisfied. The major sulfate formed in Ag/ catalyst was the aluminum sulfate and it seems that this sulfate acted as a promoter. When Mg was added to the Ag/ catalyst it promoted activity at high temperature. Intentionally added sulfate also enhanced activity, when their amount was confined less than 3 wt%.

We investigate grain growth behavior of poly-crystalline Mg sheet having strong basal fiber texture using phase field model for grain growth and micro-elasticity. Strong initial basal texture was maintained when external load was not imposed, but was weaken when external biaxial strain was imposed. Elastic interaction between elastic anisotropy of Mg grain and external load is the reason why texture evolution occurs.

Precipitation of the ordered icosahedral quasicrystal in Mg-6wt%Zn-1wt%Y alloy has been characterized bytransmission electron microscopy observations. The lamellar-type icosahedral qusicrystal phases (I-phase) with the face-centeredicosahedral (FCI) structure are observed in alloy after solution treatment at 550oC. In the alloy annealed at 400oC, polygon-shaped I-phases are observed in the α-Mg matrix. The interfaces of the I-phase with the matrix are facetted and the facets areon five-fold and two- fold plane of the I-phase. The orientation relationship of the I-phase with the matrix is determined tobe [I5]I//[001]Mg, (2f)I//()Mg and [I2]I//[311]Mg, (5f)I//()Mg. The icosahedral grains are occasionally found to be twinnedwith one of the five-fold axis as the twin axis. The twin boundaries appear to be fairly straight and perpendicular to the five-fold twin axis. The icosahedral twin can be expressed as a rotation of 63.4o or 116.6o around two fold zone axis.

Magnesium hydroxide-melamine core-shell particles were prepared through the coating of melamine monomer on the surface of magnesium hydroxide in the presence of phosphoric acid. The melamine monomer was dissolved in hot water but recrystallized on the surface of magnesium hydroxide by quenching to room temperature in the presence of phosphoric acid. The core-shell particle was applied to low-density polyethylene/ ethylene vinyl acetate (LDPE/EVA) resin by melt-compounding at 180˚C as flame retardant. The effect of magnesium hydroxide and melamine content has been studied on the flame retardancy of the core-shell particles in LDPE/EVA resin according to the preparation process and purity of magnesium hydroxide. Magnesium hydroxide prepared with sodium hydroxide rather than with ammonia solution revealed higher flame retardancy in core-shell particles with LDPE/EVA resin. At 50 wt% loading of flame retardant, core-shell particles revealed higher flame retardancy compared to that of the exclusive magnesium hydroxide in LDPE/EVA composite, and it was possible to satisfy the V0 grade in the UL-94 vertical test. The synergistic flame retardant effect of magnesium hydroxide and melamine core-shell particles was explained as being due to the endothermic decomposition of magnesium hydroxide and melamine, which was followed by the evolution of water from the magnesium hydroxide and porous char formation due to reactive nitrogen compounds, and carbon dioxide generated from melamine.

The hydrogen energy had recognized clean and high efficiency energy source. The research field of hydrogen energy was production, storage, application and transport. The commercial storage method was using high pressure tanks but it was not safety. However metal hydride was very safety due to high chemical stability. Mg and Mg alloys are attractive as hydrogen storage materials because of their lightweight and high absorption capacity (about 7.6 wt%). Their range of applications could be further extended if their hydrogenation properties and degradation behavior could be improved. The main emphasis of this study was to find an economical manufacturing method for Mg-Ti-Ni-H systems, and to investigate their hydrogenation properties. In order to examine their hydrogenation behavior, a Sievert's type automatic pressure-compositionisotherm (PCI) apparatus was used and experiments were performed at 423, 473, 523, 573, 623 and 673 K. The results of the thermogravimetric analysis (TGA) revealed that the absorbed hydrogen contents were around 2.5wt.% for (Mg8Ti2)-10 wt.%Ni. With an increasing Ni content, the absorbed hydrogen content decreased to 1.7 wt%, whereas the dehydriding starting temperatures were lowered by some 70-100 K. The results of PCI on (Mg8Ti2)-20 wt.%Ni showed that its hydrogen capacity was around 5.5 wt% and its reversible capacity and plateau pressure were also excellent at 623 K and 673 K.

Na+ ion conductivity can be improved by the substitution of an Mg atom for an Al atom to form a nonstoichiometric Na+ β-alumina. We performed a first principles study to investigate the most stable substitution site of an Mg atom and the resulting structural change of the nonstoichiometric Na+ β-alumina. Al atoms were classified as four different layers in the spinel block that are separated by conduction planes in the nonstoichiometric Na+ β-alumina. The substitution of an Mg atom for an Al atom at a tetragonal site was more favorable than that at an octahedral site. The substitution in the spinel block was more favorable than that close to the conduction plane. This result was well explained by the volume changes of the polyhedrons, by the standard deviation of the Mg-O distance, and by the comparison with bulk MgO structure. Our result indicates that the most preferable site for the Mg atom was the tetrahedral site at the spinel block in the nonstoichiometric Na+ β-alumina.

Creep tests were conducted under a condition of constant stress on two aluminum-based alloys containing particles: Al-5% Mg-0.25% Fe and Al-5% Zn-0.22% Fe. The role of grain boundary sliding was examined in the plane of the surface using a square grid printed on the surface by carbon deposition and perpendicular to the surface using two-beam interferometry. Estimates of the contribution of grain boundary sliding to the total strain, εgbs/εt reveal two trends; (i) the sliding contribution is consistently higher in the Al-Mg-Fe alloy, and (ii) the sliding contribution is essentially independent of strain in the Al-Mg-Fe alloy, but it shows a significant decrease with increasing strain in the Al-Zn-Fe alloy. Sliding is inhibited by the presence of particles and its contributions to the total strain are low. This inhibition is attributed to the interaction between the grain boundary dislocations responsible for sliding and particles in the boundaries.

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.

The long-period stacking order (LPSO) structures and stacking faults (SFs) in rapidly solidified powder metallurgy (RS P/M) Mg97Zn1Y2 alloy were investigated by high resolution transmission electron microscopy (HRTEM) observations. The 18R-type LPSO structure with a stacking sequence of ACBCBCBACACACBABAB and a period of 4.86 nm was observed in the as-extruded RS P/M Mg97Zn1Y2 alloy. After annealing at 773 K for 5 hr, the 18R-type LPSO structure was transformed to the 14H-type LPSO structure with a stacking sequence of ABABABACBCBCBC and a period of 3.64 nm. The 24R-type LPSO structure containing 24 atomic layers of ABABABABCACACACABCBCBCBC with period of 6.18 nm coexists with the 14H-type LPSO structure in the same grains. The LPSO structures contain intrinsic Type II SFs such as BCB/CABA and ABA/CBCB stacking sequences of a closely packed plane.

The aging characteristics of gas atomized Mg-6 wt.% Al-1 wt.% Zn alloy were investigated and compared to those of cast Mg-6 wt.% Al alloy. The gas atomized Mg-6 wt.% Al-1wt.% Zn alloy powders had spherical morphology between 1 and 100 in diameter. After compaction under the pressure of 700 MPa at for 10 min, the Mg-6 wt.% Al-1 wt.% Zn alloy showed a grain size of approximately 40 which is smaller than that of the cast Mg-6 wt.% Al alloy, and a relative compact density of approximately 93%. After ageing, the Mg-6 wt.% Al-1 wt.% Zn alloy showed much faster peak hardness than cast Mg-6 wt.% Al alloy. The Mg-6 wt.% Al-1 wt.% Zn alloy showed the new fine precipitations with ageing time, while the cast Mg-6 wt.% Al alloy was almost similar morphology.

The ultrafine titanium carbonitride particles () below 100nm in mean size were successfully synthesized by Mg-thermal reduction process. The nanostructured sub-stoichiometric titanium carbide () particles were produced by the magnesium reduction at 1123K of gaseous and the heat treatments in vacuum were performed for five hours to remove residual magnesium and magnesium chloride mixed with . And final phase was obtained by nitrification under normal gas at 1373K for 2 hrs. The purity of produced particles was above 99.3% and the oxygen contents below 0.2 wt%. We investigated in particular the effects of the temperatures in vacuum treatment on the particle refinement of final product.

Magnesium and its alloys are attractive as light weight structural/functional materials for high performance application in automobile and electronics industries due to their superior physical properties. In order to obtain high quality products manufactured by the magnesium powders, it is important to control and understand the densification behavior of the powders. The effect of the sheath surrounding the magnesium powders on the plastic deformation and densification behavior during equal channel angular pressing was investigated in the study by experimental and the finite element methods. A modified version of Lee-Kim's plastic yield criterion, notably known as the critical relative density model, was applied to simulate the densification behavior of magnesium powders. In addition, a new approach that extracts the mechanical characteristics of both the powder and the matrix was developed. The model was implemented into the finite element method, with which powder compaction under equal channel angular pressing was simulated.