Investigation of the mechanochemical behavior of the Mg – TiO₂ – H₃BO₃ system

Abstract

MgO – TiB2 nanocomposite was synthesized using mixtures of TiO2, H3BO3 and Mg as raw materials via a mechanochemical process. The phase transformation and structural evaluation were investigated by means of X-ray diffractometry, scanning electron microscopy, transmission electron microscopy and differential thermal analysis techniques. Thermodynamics evaluations indicated the reaction was highly exothermic and should be a mechanically induced self-sustaining reaction. According to X-ray analysis, MgO – TiB2 nanocomposite was formed after 4 h of ball milling. Thermal analysis results revealed that after 3 h milling, the temperature of combustion reaction decreased and all the reactions happened simultaneously. Scanning and transmission electron microscopy observations confirmed the range of particle size was within 100 nm.

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

“…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.…”

Investigation on mechanochemical behavior of Al/Mg–B2O3–Nb system reactive mixtures to synthesize niobium diboride

“…The discovery of superconductivity at 39K in MgB 2 has motivated new investigations on similar transition metal diborides such as those in the Ti-B, Zr-B, Hf-B, Nb-B, and Ta-B systems [5][6][7][8][9][10]. There are relatively few studies available on the synthesis of niobium boride powders compared with investigations of other transition metal borides.…”