One-Pot Synthesis of Alumina-Titanium Diboride Composite Powder at Low Temperature

Abstract

Alumina-titanium diboride (Al2O3-TiB2) composite powders were synthesised via aluminothermic reduction of TiO2 and B2O3, mediated by a molten chloride salt (NaCl, KCl, or MgCl2). The effects of salt type, initial batch composition, and firing temperature/time on the phase formation and overall reaction extent were examined. Based on the results and equilibrium thermodynamic calculations, the mechanisms underpinning the reaction/synthesis processes were clarified. Given their evaporation losses at test temperatures, appropriately excessive amounts of Al and B2O3 are needed to complete the synthesis reaction. Following this, phase-pure Al2O3-TiB2 composite powders composed of 0.3–0.6 μm Al2O3 and 30–60 nm TiB2 particles were successfully fabricated in NaCl after 5 h at 1050 °C. By increasing the firing temperature to 1150 °C, the time required to complete the synthesis reaction could be reduced to 4 h, although the sizes of Al2O3 and TiB2 particles in the resultant phase pure composite powder increased slightly to 1–2 μm and 100–200 nm, respectively.

Low temperature controllable synthesis of transition metal and rare earth borides mediated by molten salt

“…Based on this, Liu et al prepared a hybrid powder composed of 0.3-0.6 µm Al 2 O 3 and 30-60 nm TiB 2 particles in NaCl at 1050 °C for 5 h or 1150 °C for 4 h, using TiO 2 and B 2 O 3 as the main raw materials along with Al. 134 As seen from 22)). In this way, a range of metal boride-MgAl 2 O 4 composite powders also can be readily prepared.…”

“…A few intermediate phases such as KAlF 4 , K 3 AlF 6 and Zr 3 Zr were formed, which were difficult to remove from the final product powder, since they are not water soluble and acid leachable. 133 Recently, Zhang's group have synthesised boride-alumina and boride-magnesioaluminate spinel composite powders, 134,135 via MSM-MRS using Al, further illustrating its feasibility as a reductant in the boride syntheses (see Section 'Molten salt synthesis of metal boride-based composite powder' below).…”

“…Figure 16, Al 2 O 3 particles were dispersed evenly among the TiB 2 particles, both of which did not suffer from heavy agglomerations 134. Interestingly, if MgCl 2 is used to form the salt medium, once Al 2 O 3 is formed via Reaction(21), it can further react with the MgCl 2 to form another important…”

Palladium-Catalyzed Intramolecular Migratory Cycloisomerization of 3-Phenoxy Acrylic Acid Ester <i>via</i> C–O Bond Cleavage and C–O/C–C Bonds Formation for 2,3-Disubstituted Benzofurans Synthesis

“…Colorless oil. 1 Methyl (E)-3-(2-((4-Methoxyphenyl)ethynyl)phenoxy)acrylate (1i) 25) Following the typical procedure A, 2-iodophenol (550 mg, 2.50 mmol) was converted to 1i (458 mg, 59%). Colorless powder.…”

“…Colorless oil. 1 H-NMR (300 MHz, CDCl 3 ) δ: 7.77 (d, J = 12.5 Hz, 1H), 7.52 (dd, J = 7.5, 1.5 Hz, 1H), 7.37 (ddd, J = 7.8, 7.8, 1.5 Hz, 1H), 7.17 (ddd, J = 7.6, 7.6, 1.4 Hz, 1H), 7.06 (dd, J = 8.3, 1.0 Hz, 1H), 5.52 (d, J = 12.5 Hz, 1H), 3.72 (s, 3H), 3.29 (s, 1H); Methyl (E)-3-(2-(Hex-1-yn-1-yl)phenoxy)acrylate (1o) 25) Following the typical procedure A, 2-iodophenol (550 mg, 2.50 mmol) was converted to 1o (525 mg, 81%). Yellow oil.…”