{"title":"Combustion Synthesis of NbB2–Spinel MgAl2O4 Composites from MgO-Added Thermite-Based Reactants with Excess Boron","authors":"C. Yeh, Yin-Chien Chen","doi":"10.3390/cryst10030210","DOIUrl":null,"url":null,"abstract":"The formation of NbB2–MgAl2O4 composites from the MgO-added thermite-based reaction systems was investigated by self-propagating high-temperature synthesis (SHS). Two thermite mixtures, Nb2O5/B2O3/Al and Nb2O5/Al, were, respectively, adopted in Reactions (1) and (2). The XRD analysis confirmed the combination of Al2O3 with MgO to form MgAl2O4 during the SHS process and that excess boron of 30 atom.% was required to yield NbB2–MgAl2O4 composites with negligible NbB and Nb3B4. The microstructure of the composite reveals that rod-shaped MgAl2O4 crystals are closely interlocked and granular NbB2 are embedded in or scattered over MgAl2O4. With the addition of MgAl2O4, the fracture toughness (KIC) of 4.37–4.82 MPa m1/2 was obtained for the composites. The activation energies Ea = 219.5 ± 16 and 167.9 ± 13 kJ/mol for Reactions (1) and (2) were determined from combustion wave kinetics.","PeriodicalId":0,"journal":{"name":"","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-03-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"11","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.3390/cryst10030210","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 11
Abstract
The formation of NbB2–MgAl2O4 composites from the MgO-added thermite-based reaction systems was investigated by self-propagating high-temperature synthesis (SHS). Two thermite mixtures, Nb2O5/B2O3/Al and Nb2O5/Al, were, respectively, adopted in Reactions (1) and (2). The XRD analysis confirmed the combination of Al2O3 with MgO to form MgAl2O4 during the SHS process and that excess boron of 30 atom.% was required to yield NbB2–MgAl2O4 composites with negligible NbB and Nb3B4. The microstructure of the composite reveals that rod-shaped MgAl2O4 crystals are closely interlocked and granular NbB2 are embedded in or scattered over MgAl2O4. With the addition of MgAl2O4, the fracture toughness (KIC) of 4.37–4.82 MPa m1/2 was obtained for the composites. The activation energies Ea = 219.5 ± 16 and 167.9 ± 13 kJ/mol for Reactions (1) and (2) were determined from combustion wave kinetics.