New Methods for Preparing Submicrometer Powders of The Tungstate‐Ion Conductor Sc₂(WO₄)₃ and its Al and In Analogs

Abstract

Two new methods for preparing submicrometer powders of M 2 (WO 4 ) 3 , M = Sc, In, and Al via combustion synthesis are reported. Stoichiometric combinations of trivalent metal nitrates, ammonium metatungstate, and either urea or carbohydrazide as the fuel were reacted at 550°C, producing amorphous or poorly crystallized powders with an average particle size ranging from 164 to 350 nm. Calcining the powders at 800°C for 1 h produced well-crystallized, phase-pure powders with an average particle size ranging from 210 to 711 nm. Powders sintered at 1000°C for 14 h resulted in pellets that were 87%-95% of the theoretical density, which is notably higher than typically obtained from powders prepared by solid-state reaction. Whereas there was little difference in the microstructure of Al 2 (WO 4 ) 3 pellets prepared with the two different powders, the carbohydrazide-derived powders resulted in In 2 (WO 4 ) 3 and Sc 2 (WO 4 ) 3 pellets with a larger grain size than those prepared with urea-derived powders. The electrical conductivity of the sintered pellets, while comparable to that reported for polycrystalline M 2 (WO 4 ) 3 prepared by solid-state reaction, was strongly influenced by grain-boundary effects. P. Davies-contributing editorManuscript No. 32260.

Phase Stability and Miscibility in Ethanol/AOT/n-Heptane Systems: Evidence of Multilayered Cylindrical and Spherical Microemulsion Morphologies

“…The amounts of dried AOT (g) and ethanol (mL) used for each composition are given in Table S1 (Supporting Information). The ethanol/AOT/ n -heptane solutions were stirred for 2 h to ensure that the system reached equilibrium, after which DLS ,− measurements were performed on a Microtrac Nanotrac Wave II instrument, which is capable of measuring particle sizes in solution from 0.8 nm to 6.5 μm. Five 30 s measurements were taken and averaged as a single run for each solution.…”

Mechanisms of pore formation in high-temperature carbides: Case study of TaC prepared by spark plasma sintering

“…TaC 1Àx (henceforth referred to as TaC) was produced by methods we previously developed [41][42][43] to generate powders with average crystallite size of 25 nm from X-ray line broadening, average particle (aggregate) size of 73 nm from dynamic light scattering [44][45][46][47][48][49][50][51][52][53][54][55][56][57], a C/Ta compound ratio of 0.94 (i.e. powders of composition TaC 0.94 ), an oxygen content of $6.1-7.9 wt.%, and a free carbon content of $2.4 wt.% [43].…”

Designing in situ and ex situ bulk metallic glass composites via spark plasma sintering in the super cooled liquid state

“…That is, we use the same parameters used to develop the SAM2X5-630 composite, but with a variety of crystalline powders added to the amorphous metal powder. Figure 8 demonstrates that particle size [99][100][101][102][103][104][105][106][107][108][109][110][111][112][113][114] is an important consideration for developing ex situ composites. Figure 8(a) illustrates the presence of W nanoparticle agglomerates in the microstructure with as little as 4 vol%.…”