• Progress in Superconductivity and Cryogenics
• /
• v.16 no.1
• /
• pp.19-22
• /
• 2014

The effects of Mg content on the pore formation, density and critical properties were investigated in in-situ reacted $MgB_2$ superconductors. The $Mg_{1+x}B_2$, (x=-0.2, 0.0, 0.05, 0.3, 1.0) bulk samples with different Mg contents were heat-treated at $900^{\circ}C$ for 1 h in an Ar atmosphere. The dimensional changes of a pellet's mass and volume after heat-treatment were measured. After heat-treatment process, the sample mass was decreased by Mg evaporation, but the sample volume was expanded by pore formation at the Mg site; therefore, the apparent density was decreased. Spherical pores the same as Mg particles were developed after heat-treatment in all samples, and the pore density was increased with increasing Mg content. As the x of Mg content was increased to 1.0, the apparent density of $Mg_{1+x}B_2$ samples was decreased due to a relatively larger reduction in a mass change. The critical current density of Mg excessive sample of x=0.05 showed the highest values over the applied magnetic fields because the excessive Mg may compensate Mg loss and enhance grain connectivity.

• The Korean Journal of Physiology and Pharmacology
• /
• v.3 no.1
• /
• pp.59-68
• /
• 1999

Chemically induced hypoxia has been shown to induce a depletion of ATP. Since intracellular free $Mg^{2+}\;([Mg^{2+}]_i)$ appears to be tightly regulated following cellular energy depletion, we hypothesized that the increase in $[Mg^{2+}]_i$ would result in $Mg^{2+}$ extrusion following hormonal stimulation. To determine the relation between $Mg^{2+}$ efflux and cellular energy state in a hypoxic rat heart and isolated myocytes, $[Mg^{2+}]_i,$ ATP and $Mg^{2+}$ content were measured by using mag-fura-2, luciferin-luciferase and atomic absorbance spectrophotometry. $Mg^{2+}$ effluxes were stimulated by norepinephrine (NE) or cAMP analogues, respectively. $Mg^{2+}$ effluxes induced by NE or cAMP were more stimulated in the presence of metabolic inhibitors (MI). Chemical hypoxia with NaCN (2 mM) caused a rapid decrease of cellular ATP within 1 min. Measurement of $[Mg^{2+}]_i$ confirmed that ATP depletion was accompanied by an increase in $[Mg^{2+}]_i.$ No change in $Mg^{2+}$ efflux was observed when cells were incubated with MI. In the presence of MI, the cAMP-induced $Mg^{2+}$ effluxes were inhibited by quinidine, imipramine, and removal of extracellular $Na^+.$ In addition, after several min of perfusion with $Na^+-free$ buffer, a large increase in $Mg^{2+}$ efflux occurred when $Na^+-free$ buffer was switched to 120 mM $Na^+$ containing buffer. A similar $Mg^{2+}$ efflux was observed in myocytes. These effluxes were inhibited by quinidine and imipramine. These results indicate that the activation of $Mg^{2+}$ effluxes by hormonal stimulation is directly dependent on intracellular $Mg^{2+}$ contents and that these $Mg^{2+}$ effluxes appear to occur through the $Na^+-dependent\;Na^+/Mg^{2+}$ exchange system during chemical hypoxia.

• Korean Journal of Metals and Materials
• /
• v.50 no.12
• /
• pp.949-953
• /
• 2012

$MgH_2$ was employed as a starting material instead of Mg in this work. A sample with a composition of 94 wt% $MgH_2-6$ wt% Ni (called $MgH_2-6Ni$) was prepared by reactive mechanical grinding. The hydriding and dehydriding properties were then examined. An $MgH_2-Ni$ hydrogen storage alloy that does not require an activation process was developed. The alloy was prepared in a planetary ball mill by grinding for 4 h at a ball disc revolution speed of 250 rpm under a hydrogen pressure of about 12 bar. The sample absorbed 3.74 wt% H for 5 min, 4.07 wt% H for 10 min, and 4.41 wt% H for 60 min at 573 K under 12 bar $H_2$, and desorbed 0.93 wt% H for 10 min, 1.99 wt% H for 30 min, and 3.16 wt% H for 60 min at 573 K under 1.0 bar $H_2$. $MgH_2-6Ni$ after reactive mechanical grinding contained ${\beta}-MgH_2$ (a room temperature form of $MgH_2$), Ni, ${\gamma}-MgH_2$ (a high pressure form of $MgH_2$), and a very small amount of MgO. Reactive mechanical grinding of Mg with Ni is considered to facilitate nucleation, and to reduce the particle size of Mg. $Mg_2Ni$ formed during reactive mechanical grinding also increases the hydriding and dehydriding rates of the sample.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.23 no.4
• /
• pp.189-194
• /
• 2013

Single phase crystalline powders of $Mg_3Sb_2$ and $Mg_3Bi_2$ were prepared by mechanical alloying Mg, Sb and Bi metals with planetary ball milling for 24~48 h. The compositions of starting raw materials for single phase $Mg_3Sb_2$ and $Mg_3Bi_2$ were 3Mg : 1.8Sb and 3Mg : 1.6Bi, respectively. Two types of mechanically alloyed powders obtained were mixed at some ratios for the fabrication of $Mg_3Sb_2-Mg_3Bi_2$ composites and then hot pressed under uniaxial pressure of 70 MPa at 723 K for 1 h. The main phase of composites was a stable phase similar to $Mg_3Bi_2$ phase with a small amount of Bi phase. The distributions of Sb and Bi elements on EDS mapping images were discontinuous and their compositional contours were clear, which means that the hot pressed specimens were composites composed of two compounds of $Mg_3Sb_2$ and $Mg_3Bi_2$.

• Journal of Korean Society on Water Environment
• /
• v.31 no.6
• /
• pp.625-631
• /
• 2015

In this study, low cost bio-flocculants, chitosan, cationic starch and Mg-sericite, were used as a flocculant to harvest freshwater microalgae, Chlorella vulgaris. Chitosan, cationic starch and Mg-sericite separated successfully >98% of C. vulgaris at following optimal parameters: 90 mg/L chitosan at pH 6-7, 70 mg/L cationic starch at pH 9-10 and 50 mg/L Mg-sericite at pH 4-5. A relatively high correlation coefficient (R²) of 0.9993 for chitosan, 0.9971 for catonic starch and 0.9924 for Mg-sericite was obtained. The investigated flocculants amount increased linearly with increasing the microalgae amount. The biopolymer, Mg-sericite, was more effective than that of other investigated flocculants. These results indicated that a bio-flocculants, chitosan, cationic starch and Mg-sericite, could prove to be an effective flocculant for economical production of microalgae biomass. In addition, Mg-sericite was more effective comparing to the other investigated flocculants.

• Journal of Korea Foundry Society
• /
• v.36 no.4
• /
• pp.117-125
• /
• 2016

The effects of the Zn content on the microstructure and corrosion behavior in 1M NaCl solution were investigated in Mg-(0~6)%Zn casting alloys. The MgZn phase was scarcely observed in the Mg-1%Zn alloy, while the Mg-(2~6)%Zn alloy consisted of ${\alpha}$-(Mg) and MgZn phases. With an increase in the Zn content, the amount of the MgZn phase was gradually increased. Immersion and electrochemical corrosion tests indicated that the Mg-1%Zn alloy had the lowest corrosion rate among the alloys, and a further increase in the Zn content resulted in the deterioration of the corrosion resistance. Microstructural examinations of the corroded surfaces and EIS analyses of surface corrosion films revealed that the best corrosion resistance at 1%Zn was associated with the absence of MgZn phase particles in the microstructure and the contribution of Zn element to the formation of a protective film on the surface. A micro-galvanic effect by the MgZn particles led to the increased rate of corrosion at a higher Zn content.

• Journal of Korean Society of Environmental Engineers
• /
• v.33 no.4
• /
• pp.275-280
• /
• 2011

In the present work, the aerobic particle's characteristics were enhanced. A polymer was used to make aerobic granular sludge in short period of time. And operation parameters were calculated for organic matter removal in domestic wastewater using a sequencing batch reactor (SBR). The experiment for sewage (Influent concentration of 63~72 mg COD/L) by using mature aerobic granular sludge showed the organic matter removal rate k and oxygen utilization coefficient a', b' were $10.161d^{-1}$ and 0.87 mg $O_2/mg$ $COD_r$, 0.11 mg $O_2/mg$ MLVSS d respectively. Therefore, it was more effective than K value $5{\sim}8d^{-1}$ of conventional activated sludge process. The sludge synthetic value and sludge auto-oxydation value were 0.45 mg VSS/mg $COD_r$ and 0.05 mg VSS/mg MLVSS d respectively. Consequently, mortality rates of microorganisms was lower than conventional activated sludge process.

• Resources Recycling
• /
• v.10 no.5
• /
• pp.16-21
• /
• 2001

Ultrafine $Mg(OH)l_2$and MgO powders were recovered from the waste solution containing $Mg^{++}$ which was a by-product of SHS (Self-propagating High temperature Synthesis)process. The optimum experimental conditions to prepare $Mg(OH)_2$were 13.0 of pH and 0.7M of $Mg^{++}$ content with addition of 9M of KOH as a pH regulator in acid leaching solution. Complete pre-cipitation of Mg(OH)$_2$from $Mg^{++}$ was realized at that condition. The dehydration reaction of the prepared Mg(OH)$_2$was studied by DSC, and the result was used for calcination process. In order to obtain MgO powder, dried Mg(OH)2 powder was calcined at $400~450^{\circ}C$. Particle size and shape of the prepared $Mg(OH)_2$and MgO powder was similar to those of the commercial powders.

• Journal of environmental and Sanitary engineering
• /
• v.23 no.1
• /
• pp.17-23
• /
• 2008

Using the ethanol extract, Achyranthis Radix, various chemical characteristics were investigated. The nutritional compositions of the Achyranthis Radix extract were as follows;moisture 42.3%, crude protein 101.1%, crude fat 2.07%, ash 8.94%, and carbohydrate 36.5%. Among the free sugars, the maximum lactose concentration in the Achyranthis Radix extract was obtained at 0.0526 mg% and fructose, maltose, arabinose, and glucose were followed: 0.3654 mg%, 0.1160 mg%, 0.0365 mg% and 0.027 mg%, respectively. The total amino acid concentration of the Achyranthis Radix extract was 8908.3 mg% and concentrations of lysine, aspartic acid, glutamic acid, and arginine were 989.1 mg%, 954.4 mg%, 841.4 mg% and 763.2 mg%, respectively. Among various long chain fatty acids, the maximum concentrations of palmitic acid and linoleic acid were obtained at 47.8% and 31.058%, respectively. However, in the case of organic acid, only the oxalic acid and malic acid were determined. The potassium concentration in the Achyranthis Radix extract was relatively high and the concentrations of Ca, Mg, Fe, Na, Mn, and Zn were as follows: 275.3 mg%, 281.3 mg%, 119.4 mg%, 37.75 mg%, 10.43 mg% and 3.11 mg%, respectively. These results suggest that the Achyranthis Radix extract might have a possible positive effect for medical and edible purposes.

• Transactions of the Korean hydrogen and new energy society
• /
• v.9 no.4
• /
• pp.143-150
• /
• 1998

The hydriding and dehydriding properties of a Mg-10wt.%Ni mixture, mechanically-alloyed in order to improve the hydriding and dehydriding kinetics of pure Mg, were investigated. The $Mg_2Ni$ phase develops along with hydriding-dehydriding cycling. The principal effects of mechanical alloying in a planetary mill and hydriding-dehydriding cycling are considered to be the augmentation in the density of defects and the enlargement in the specific surface area. The mechanically-alloyed Mg-10wt.%Ni mixture is activated easily. It has much higher hydriding rate and hydrogen-storage capacity and relatively high dehydriding rate as compared with the pure Mg, the Mg-10wt.%Ni alloy, the Mg-25wt.%Ni alloy and the $Mg_2Ni$ alloy.