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RISS 인기검색어
- 검색키워드
- 저자 : Abdelgawad Mahmoud (검색결과 3 건)
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Effect of magnesia rich spinel on densification and stabilization behavior of monoclinic zirconia
Abdelgawad Mahmoud,El-Gamal S. M. A.,Ewais Emad M. M.,Li Shufeng 한국세라믹학회 2021 한국세라믹학회지 Vol.58 No.3
Fully cubic-stabilized zirconia ceramic composites have been successfully fabricated by conventional sintering technique using commercial monoclinic zirconia, Yttrium oxide and waste-derived magnesia-rich spinel (MMA) powder mixtures. In this study, eff ect of MMA content and sintering temperature on stabilization and densifi cation properties of zirconia has been duly considered. The obtained results showed that m-ZrO 2 in MMA-free Z0 reference specimen is partially stabilized upon temperature rising into tetragonal phase by Y 3+ ions diff usion inside zirconia structure. MMA-free Z0 reference specimen sintered at 1600 ºC showed m- and t-ZrO 2 dual-phase structure with a relative density of 80.2%. Unlike, upon rising the sintering temperature, Z10–Z50 composites containing 10–50 wt% MMA demonstrated higher relative density of more than 99% and showed variant behavior, where their m-ZrO 2 is transformed and stabilized into cubic form by diff usion of Y 3+ , Mg 2+ and Al 3+ ions inside zirconia lattice structure. The outcomes indicate that MMA has significantly improved both the densification and stabilization behavior of m-ZrO 2 through facilitating Y 3+ diff usion inside zirconia lattice structure.
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MgAl2O4-reinforced c-ZrO2 ceramics prepared by spark plasma sintering
El-Amir Ahmed A. M.,Li Shufeng,Abdelgawad Mahmoud,Ewais Emad M. M. 한국세라믹학회 2021 한국세라믹학회지 Vol.58 No.5
c-zirconia ceramic composites have been synthesized by spark plasma sintering (SPS) technique from commercial m-ZrO 2 , Y 2 O 3 and waste-derived magnesium aluminate spinel (MA) powders. In this study, eff ect of MA addition on stabilization and reinforcement of 5 mol% yttria-stabilized zirconia (YSZ) was carefully investigated. Spark plasma sintering of designed powder mixtures at 1400 °C for 30 min and 40 MPa produce fully dense compacts with an average grain size of 0.5–10 μm. The pressure was gradually increased up to 40 MPa using argon gas and was kept until the end of the sintering process. The refi ned microstructure (0.5–10 μm) obtained in this study has achieved superior compaction resistance values that are ten times more than strength values of conventionally sintered specimens. Such improvement in compaction resistance of the sintered specimens was attributed to particle size refi nement and grain boundary enhancement. What’s more, spark-plasma sintered composites containing 10–50 wt% MA revealed higher resistance to low temperature degradation (LTD) than the reference composite that doesn’t contain MA spinel; where about ~ 2.8% of t-ZrO 2 was converted into m-ZrO 2 in case of the latter composite while aging test didn’t infl uence at all on the structure of the former composites. The outcomes indicated that MA has a signifi cant eff ect on m-ZrO 2 stabilization into a cubic phase structure that concurrently owned an enhanced and comparable compression resistance to Yttrium-doped t-ZrO 2 (Y-TZP). In this respect, the ternary oxide ceramic composite systems prepared in this study present huge potential for development c-ZrO 2 -based industrial ceramics with a wide spectrum of mechanical characteristics for high-tech engineering applications of harsh-stress and humid environments.
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A Bioactive Fraction from Streptomyces sp. Enhances Maize Tolerance against Drought Stress
Warrad Mona,Hassan Yasser M.,Mohamed Mahmoud S.M,Hagagy Nashwa,Al-Maghrabi Omar A,Selim Samy,Saleh Ahmed M.,AbdElgawad Hamada 한국미생물·생명공학회 2020 Journal of microbiology and biotechnology Vol.30 No.8
Drought stress is threatening the growth and productivity of many economical crops. Therefore, it is necessary to establish innovative and efficient approaches for improving crop growth and productivity. Here we investigated the potentials of the cell-free extract of Actinobacteria (Ac) isolated from a semi-arid habitat (Al-Jouf region, Saudi Arabia) to recover the reduction in maize growth and improve the physiological stress tolerance induced by drought. Three Ac isolates were screened for production of secondary metabolites, antioxidant and antimicrobial activities. The isolate Ac3 revealed the highest levels of flavonoids, antioxidant and antimicrobial activities in addition to having abilities to produce siderophores and phytohormones. Based on seed germination experiment, the selected bioactive fraction of Ac3 cell-free extract (F2.7, containing mainly isoquercetin), increased the growth and photosynthesis rate under drought stress. Moreover, F2.7 application significantly alleviated drought stress-induced increases in H2O2, lipid peroxidation (MDA) and protein oxidation (protein carbonyls). It also increased total antioxidant power and molecular antioxidant levels (total ascorbate, glutathione and tocopherols). F2.7 improved the primary metabolism of stressed maize plants; for example, it increased in several individuals of soluble carbohydrates, organic acids, amino acids, and fatty acids. Interestingly, to reduce stress impact, F2.7 accumulated some compatible solutes including total soluble sugars, sucrose and proline. Hence, this comprehensive assessment recommends the potentials of actinobacterial cell-free extract as an alternative ecofriendly approach to improve crop growth and quality under water deficit conditions.
ScienceON
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