Reaction chemistry in the Mg–B2O3–MoO3 system reactive mixtures

Mechanochemical synthesis of NbC–NbB2 nanocomposite from the Mg/B2O3/Nb/C powder mixtures

“…No tangible change is observed in the XRD pattern of sample milled for 2.8 h, suggesting that no new phases were formed. The absence of graphite and boron oxide peaks in this sample could be attributed to transformation of crystal state of these phases into the amorphous state as reported in some investigations [18,19]. After 3 h milling, the peaks of as-blended materials disappear completely; meanwhile, new peaks appear to emerge, corresponding to the formation of MgO (JCPDS: 00-004-0829) and NbB 2 (JCPDS: 00-008-0120).…”

“…Thus, the first exothermic peak at 820 1C is attributed to the initiation of B 2 O 3 reduction by Mg (magnesiothermic reaction) according to reaction (3). Taking into account the results obtained hitherto in the combustion reaction of Mg-B 2 O 3 -C and Mg-B 2 O 3 -MoO 2 systems [18][19][20][21] as well, the magnesiothermic reduction of B 2 O 3 was occurred at about 800-850 1C. The presence of unreacted Mg peaks indicates that magnesiothermic reaction does not completely occurred during the thermal process.…”

“…2a, several peaks corresponding to magnesium borate (Mg 3 (BO 3 ) 2 ) compound are observed alongside the weak peaks of NbB 2 . Mg 3 (BO 3 ) 2 appears as major by-product in the Mg-B 2 O 3 system [18][19][20][21]. Once the magnesiothermic reaction is initiated, a rapid raise of temperature in the system occurs which is favorable for formation of magnesium borate from the reaction between the formed MgO and remaining B 2 O 3 .…”

“…2b), indicating that an increase in milling time decreased the tendency for the magnesium borate formation. The quantity of Mg 3 (BO 3 ) 2 mainly depends on excess [18][19][20][21]. The excellent dispersion of powders coupled with the decrease in the particle size of B 2 O 3 powder helps consumption of B 2 O 3 , and prevents the formation of magnesium borate.…”

“…With the advantages of time and energy savings, simplicity, and high-purity products, the mechanochemical process represents an attractive alternative to the conventional methods in producing advanced materials, including borides, carbides, nitrides, intermetallics, etc. We have so far applied the mechanochemical technique to the synthesis of carbides and/ or borides of Mo, Ti, and B [18][19][20][21]. The common point of all these reactions is a great amount of the heat created as a result of the exothermic reaction between metal oxides and aluminum/magnesium during the aluminothermic/magnesiothermic reduction.…”