• 한국주조공학회지
• /
• 제17권6호
• /
• pp.592-597
• /
• 1997

The microstructure and tensile properties of Mg-Zn-Ca and Mg-Zn-Mn-Ca alloys have been investigated. The alloys were obtained by melting in a low carbon crucible coated with boron nitride under an Ar gas atmosphere to prevent oxidation and combustion. The Mg alloy melt was cast into the metallic mold at room temperature, and cooling part was located at the bottom of mold. The phase formed during solidification of the Mg-Zn-(Mn) alloys containing 0.5%Ca is $Ca_2Mg_6Zn_3$. The yield strength and ultimate tensile strength of the alloys increased with increasing Zn content, but the ductility did not change with increasing Zn content. The addition of Mn improves the yield strength and ultimate tensile strength of the alloys, but the ductility did not change. Tensile fracture of the alloys revealed brittle failure, with cracking along the $Ca_2Mg_6Zn_3$ phase. The variation of stress with strain obeyed the relationship of the ${\sigma}=K{\varepsilon}^n$.

• 한국주조공학회지
• /
• 제17권5호
• /
• pp.502-509
• /
• 1997

The mechanical behavior and microstructural evolution in the ignition-proof Mg-Zn-Ca-Zr alloy produced by the semisolid squeeze casting are clarified and the mechanical properties are also compared with those of squeeze cast Mg-Zn-Ca-Zr alloy. The tensile strength and elongation increase slightly as the solid fraction depending on temperature decreases, while the 0.2% proof stress decreases. The size of primary crystal increases with increasing holding time. The tensile strength and 0.2% proof stress of the semi-solid squeeze cast Mg-Zn-Ca-Zr alloy decrease as the size of primary crystal increases, indicating the dependence of strength on the size of primary crystal. The elongation of the semi-solid squeeze cast Mg-Zn-Ca-Zr alloy is two times as large as the squeeze cast Mg-Zn-Ca-Zr alloy and the tensile strength is unchanged despite the growth of primary crystal, resulting from the refining of the melted ${\alpha}Mg$ phase and the brittle eutectic compound as well as the reduction of solidification shrinkage and porosities.

• 한국주조공학회지
• /
• 제27권5호
• /
• pp.198-202
• /
• 2007

In the present study, the high temperature mechanical properties and creep resistance of Mg-Zn-Y-Ca alloys has been investigated. The Mg-4Zn-0.8Y alloy consists of ${\alpha}$-Mg matrix and icosahedral quasicrystalline phase. Calcium addition into Mg-4n-0.8Y based alloy results in the formation of ${\tau}(Ca_{2}Mg_{6}Zn_{3})$ and $Mg_{2}Ca$ as the second solidification phases. Creep properties of the Mg-Zn-Y and Mg-Zn-Ca based alloys measured at applied stresses between 65 MPa and 85 MPa are significantly improved with adding calcium and yttrium, respectively. The improved creep resistance is due to the formation of thermally stable $Mg_{2}Ca$ phase.

• 한국표면공학회:학술대회논문집
• /
• 한국표면공학회 2015년도 춘계학술대회 논문집
• /
• pp.126-127
• /
• 2015

주방 상태의 Mg, Mg+5wt%.Ca, Mg+5wt%.Ca+1wt%.Zn 합금의 발화 실험 및 TGA를 통해 $450{\sim}600^{\circ}C$에서 고온산화실험을 실시하였다. Ca의 첨가로 내발화성 및 고온산화특성이 향상되었으며, Zn의 첨가는 내발화성과 고온산화특성 모두에 악영향을 미쳤다. 산화시킨 시편의 SEM/EDS, XRD, 및 TEM 분석을 통하여 고온산화 특성을 조사하였다.

• 한국자동차공학회논문집
• /
• 제14권5호
• /
• pp.73-78
• /
• 2006

In this paper, creep tests of Mg-Zn-Mn and Mg-Zn-Mn-Ca alloys, which were casted by mold with Mg-3%Zn-1%Mn and Mg-3%Zn-1%Mn-0.2%Ca, were done under the temperature range of 473-573K and the stress range of 23.42-78.00Mpa. The activation energies and the stress exponents were measured to investigate the creep plastic deformation of those alloys, and the rupture lifes of Mg-Zn-Mn alloy were also measured to investigate the fracture behavior. From the results, the activation energy of Mg-Zn-Mn and Mg-Zn-Mn-Ca alloys under the temperature range of 473-493K were measured as 149.87, 145.98KJ/mol, respectively, and the stress exponent were measured as 5.13, 6.06 respectively. Also the activation energies Mg-Zn-Mn and Mg-Zn-Mn-Ca alloys under the temperature range of 553-573K were obtained as 134.41, 129.22KJ/mol, respectively, and tress exponent were obtained as 3.48, 4.63, respectively. Finally stress dependence of rupture life and the activation energy of rupture life of Mg-Zn-Mn under the temperature range of 473-493K was measured as 8.05, 170.0(KJ/mol), respectively, which were a little higher than the results of steady state creep.

• 동력기계공학회지
• /
• 제10권3호
• /
• pp.45-50
• /
• 2006

In this paper, creep tests of Mg-Zn-Mn and Mg-Zn-Mn-Ca alloy casted by mold under the temperature range of 473.00-573.00K, and the stress range of 23.42-87.00Mpa were done with the equipment of automatic controlled temperature and computer for data acquisition. The activation energies were obtained by relationship between creep rate and temperature, and the stress exponents were obtained by relationship between creep rate and stress. From the experiment results, the activation energies of Mg-Zn-Mn and Mg-Zn-Mn-Ca alloy were 149.87kJ/mol, 147.97kJ/mol, respectively, and the stress exponents of those alloy were 5.13, 5.59, respectively, under the temperature of 473.00-493.00K and the stress range of 62.43-78.00Mpa. And the activation energies of those alloy were 134.41kJ/mol, 129.22kJ/mol, respectively, and the stress exponent of those alloy were 3.48, 3.77, respectively, under the temperature of 553-573Mpa and the stress range of 23.42-39.00Mpa. Also the lifes of Mg-Zn-Mn-Ca alloy were higher than those of Mg-Zn-Mn alloy, and the results of SEM showed fracture surfaces under low temperature had smaller dimples than those under high temperature.

• Nutritional Sciences
• /
• 제5권3호
• /
• pp.155-160
• /
• 2002

The purpose of this study was to investigate the effects of micronutrient supplementation on the growth of preschool children in China. A double-blind, placebo-controlled trial was conducted on 156 growth retarded preschool children who were randomly assigned to the following five groups : supplemental control (S-control; n=28); zinc supplementation (＋Zn; 3.5mg Zn/day, n=34); zinc and calcium supplementation (＋ZnCa; 3.5mg Zn ＋ 250mg Ca/day, n=37); zinc, calcium and vitamin A supplementation (＋ZnCaVA; 3.5mgZn ＋ 250mgCa ＋ 200gVA/day, n=28); and calcium and vitamin A supplementation (＋CaVA; 250mgCa ＋ 200gVA/day, n=29). Another 34 children of normal height were selected as a normal control (N-control). Supplementation continued for twelve months. After supplementation, the height gains in the ＋Zn group (7.84cm per year) and the ＋ZnCa group (7.70 cm per year) were significantly higher than that in the S-control group (6.74 cm per year, P＜0.05). The weight gain in the ＋ZnCaVA group (2.55kg per year) and the ＋CaVA group (2.57 kg per year) was also significantly higher than that in the S-control group (2.19 kg per year, P＜0.05). The average number of days of illness in each group taking supplements was lower than that in the S-control group (13 days per year compared with 23 days per year). No significant differences in bone maturity were observed between the groups. In conclusion, in this study Zinc and Zinc ＋ Calcium supplementation improved the height gain, and vitamin A improved the weight gain, in growth retarded preschool children, but these supplements did not affect the maturity of bone. Micronutrient supplementation also lowered the morbidity of these children.

• Journal of Electrochemical Science and Technology
• /
• 제12권1호
• /
• pp.112-125
• /
• 2021

The new emerging "High entropy materials" attract the attention of the scientific society because of their simpler structure and spectacular applications in many fields. A novel nanocrystalline high entropy (Be,Mg,Ca,Sr,Zn,Ni)3O4 oxide has been successfully synthesized through mechanochemical treatment followed by sintering and air quenching. The present research work focuses on the possibility of single-phase formation in the aforementioned high entropy oxide despite the great difference in the atomic sizes of reactant alkaline earth and 3d transition metal oxides. Structural properties of (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide were explored by confirmation of its single-phase Fd-3m spinel structure by x-ray diffraction (XRD). Further, nanocrystalline nature and morphology were analyzed by scanning electron microscopy (SEM). Among thermal properties, thermogravimetric analysis (TGA) revealed that the (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide is thermally stable up to a temperature of 1200℃. Whereas phase evolution in (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide before and after sintering was analyzed through differential scanning calorimetry (DSC). Electrochemical studies of (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide consists of a comparison of thermodynamic and kinetic parameters of water and hydrazine hydrate oxidation. Values of activation energy for water oxidation (9.31 kJ mol-1) and hydrazine hydrate oxidation (13.93 kJ mol-1) reveal that (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide is catalytically more active towards water oxidation as compared to that of hydrazine hydrate oxidation. Electrochemical impedance spectroscopy is also performed to get insight into the kinetics of both types of reactions.

• Nutritional Sciences
• /
• 제2권2호
• /
• pp.82-87
• /
• 1999

Zinc nutriture in South Koreans was evaluated by estimating Zn, Ca, and phytate intake, and the molar ratios of phytate : Zn and the millimolar ratios of phytate $\times$ Ca Zn. food consumption data from the 95 National Nutrition Survey was used. For the present study, data from the nationwide, large city and urban area level were used. No standard deviation measures were provided in the 95 National Nutrition Survey : only mean values were reported. Nationwide daily intake of Zn and Ca were 10.1 mg/day and 426.5 mg/day, respectively. The estimated daily phytate intake was 1676.6 mg/day nationwide. The molar ratio of phvtate : Zn, the millimolar ratio of phytate $\times$ Ca : Zn and the phytate $\times$ Ca Zn mmol per 4.2 MJ (1000 kcal) were 15.9, 168.9 and 91.8 in nationwide, respectively. The major food groups for zinc intake were meat, poultry products (43%), and cereals and grain products (18%). Sixty two percent of Zinc was from animal food sources. Cereal and grain products supplied most of the phytate intake (46%), followed by seasonings, fruits, and legume products. The major food source of phytate was rice (39%) . The results of the present study suggest that Zn status of Koreans maybe influenced by high dietary intake of phytate and high molar ratios of phytate : Zn and phytate $\times$ Ca : Zn. These results raise concerns about Zn status of Koreans, who consume a diet higher in phytate than Western diets. further research is necessary to confirm whether such poorly available dietary Zn has any impact on the health of Koreans.

• 한국수산과학회지
• /
• 제31권2호
• /
• pp.245-251
• /
• 1998

조피볼락 사료의 각종 미네랄 필수성을 조사하기 위해 주요 mineral 함량이 낮은 조피볼락 근육과 casein을 사료 단백질원으로 선정하여 영양연구용으로 자체 설계된 reference premix중에 P, Ca, Zn, Mg, Fe, K, Mn 및 Se을 각각 첨가하지 않은 premix와 mineral 전부를 첨가하지 않은 사료를 설정하여 모두 10종 실험사료를 제조하였다. 평균체중 4.2g의 조피볼락 치어를 각 수조에 25마리씩 실험사료마다 3반복으로 수용하여 10주간 사육실험하였다. 성장, 사료효율, 영양소이용률, 전어체의 지질 함량에서 mineral premix를 첨가하지 않은 사료가 가장 낮은 것 (P<0.01)으로 나타났다. Reference mineral premix에 P, Ca, Zn, Mg, Fe, K, Mn 및 Se을 각각 첨가하지 않은 실험 사료의 증체율은 모두 reference premix를 첨가한 대조구보다 유의하게 낮았다 (P<0.01). 사료효율은 Mg, Fe, K 및 Se을 첨가하지 않은 실험구가 대조구와 통계적으로 차이가 없었으며, 그외 실험구는 대조구보다 낮은 값을 보였다 (P<0.01). 일일 사료섭취율은 실험구간에 유의차가 없었지만 (P>0.01), P, Ca 및 Zn 무첨가구들의 단백질축적률은 대조구보다 저조한 성적을 보였으며, 지질축적률은 Zn 무첨가구만 대조구와 차이를 보였다 (P<0.01). 각 미네랄을 첨가하지 않은 실험구들의 어체성분은 대조구와 통계적인 차이가 없었다.