Liquid-Feed Flame Spray Pyrolysis as a Method of Producing Mixed-Metal Oxide Nanopowders of Potential Interest as Catalytic Materials. Nanopowders along the NiO−Al₂O₃ Tie Line Including (NiO)_0.22(Al₂O₃)_0.78, a New Inverse Spinel Composition

Abstract

Liquid-feed flame spray pyrolysis (LF-FSP) is a general aerosol combustion route to unagglomerated and often single crystal mixed-metal oxide nanopowders with exact control of composition. LF-FSP of xNi(O 2 CCH 2 CH 3 ) 2 /yAl(OCH 2 CH 2 ) 3 N EtOH solutions at selected x:y ratios provides mixed-metal oxide nanopowders with compositions covering much of the Al 2 O 3 -NiO phase space. All powders were characterized by XRD, BET, FTIR, SEM, TEM, and TGA-DTA. With the exception of pure NiO (specific surface area, SSA, ∼7 m 2 /g), all product powders offer SSAs g 45 m 2 /g (average particle sizes e 30 nm) without microporosity. At NiO/Al 2 O 3 ratios near 1:1, the LF-FSP nanopowders are single phase, bright blue NiAl 2 O 4 inverse spinel. The blue color of these materials is typical of Ni spinels. At higher NiO contents, NiO is the dominant phase with some δ-alumina and intermediate spinels. At low NiO contents, blue powders form but the δ-alumina phase predominates, suggesting incorporation of Ni 2+ in the alumina lattice or formation of traces of NiAl 2 O 4 . Compositions near 20:80 mol NiO/Al 2 O 3 generate an inverse spinel structure, per XRD with peaks shifted ≈4°2θ to higher values from those of pure NiAl 2 O 4 . This contrasts with the published phase diagram, which suggests a mixture of NiAl 2 O 4 spinel, and corundum should form at this composition. This material resists transformation to the expected phases on heating to 1400 °C, indicating a single stable phase which contrasts with the known phase diagram and, therefore, is a new material in NiO-Al 2 O 3 phase space with potential value as a new catalyst.

Nickel/Iron Oxide Nanocrystals with a Nonequilibrium Phase: Controlling Size, Shape, and Composition

“…13−16 Many synthetic methods have been reported for the production of high-purity MMOs, including the mechanical mixing of metal precursors, 17−19 spray pyrolysis, 20,21 sol−gel decomposition, 11,22−24 hydrothermal processing, 24−27 polymerbased processes, 28,29 and solution-phase thermal decomposition of metal−organic precursors. 30,31 However, the use and synthesis of MMOs is complicated by the presence of different metal species.…”

Pressureless Sintering t‐zirconia@δ‐Al2O3 (54 mol%) Core–Shell Nanopowders at 1120°C Provides Dense t‐Zirconia‐Toughened α‐Al2O3 Nanocomposites

“…Here, we report the use of ( t ‐ZrO 2 ) x (δ‐Al 2 O 3 ) 1− x core–shell nanopowders produced by liquid‐feed flame spray pyrolysis (LF‐FSP) 43–48 with average particle sizes (APSs) of 30–50 nm (Fig. 1) to produce fully dense, ultrafine ZTA composites with densities ≥99 at 54 unit mol% t ‐ZrO 2 and with final grain sizes<200 nm by pressureless sintering in air at 1120°C.…”

Spin conversion of positronium inNiO/Al2O3catalysts observed by coincidence Doppler broadening technique

“…1,2 The catalytic property is influenced by various factors, such as the specific surface area, pore structure, and dispersion of the active component on the support. 3 The pore structure of the catalyst support is most important because it provides passage for both reactants and resultants and affects the speed and efficiency of reaction.…”