Iron Precursor Decomposition in the Magnesium Combustion Flame: A New Approach for the Synthesis of Particulate Metal Oxide Nanocomposites

Abstract

Powders of Fe–Mg–O nanocomposite particles have been grown using a novel chemical vapor synthesis approach that employs the decomposition of a metalorganic precursor inside the metal combustion flame. After annealing in controlled gas atmospheres composition distribution functions, structure and phase stability of the obtained magnesiowüstite nanoparticles are measured with a combination of techniques such as inductively coupled plasma‐optical emission spectroscopy, energy dispersive X‐ray spectroscopy, X‐ray diffraction, and scanning and transmission electron microscopy. Complementary Mössbauer spectroscopy measurements reveal that depending on Fe loading and temperature of annealing either metastable and superparamagnetic solid solutions of Fe3+ ions in periclase (MgO) or phase separated mixtures of MgO and ferrimagnetic magnesioferrite (MgFe2O4) nanoparticles can be obtained. The described combustion technique represents a novel concept for the production of mixed metal oxide nanoparticles. Adressing the impact of selected annealing protocols, this study underlines the great potential of vapor phase grown non‐equilibrium solids, where thermal processing provides means to trigger phase separation and, concomitantly, the emergence of new magnetic properties.

Impurity Segregation and Nanoparticle Reorganization of Indium Doped MgO Cubes

“…We start with as‐synthesized powders of In−Mg−O nanocomposite particles that were grown using a newly developed chemical vapor synthesis approach (Figure S1, Supporting Information) ,. The process employs the decomposition of an indium organic precursor inside the Mg vapor combustion flame which is associated with a combustion reaction that exhibits sufficiently high exothermicity and high temperatures (≈2600 K) to completely convert the precursor components into metal oxides.…”

“…As a result, less regular surface features remain on the surface and the particles adopt a roundish shape without sharp edge and corner features. A similar situation was previously observed for Fe 3+ doped MgO nanoparticles, where Fe 3+ ions in the near‐surface region of the nanocrystals promote the formation of terraces, protrusions and step edges of multiple heights. Regular {100} faces being energetically favored in pure MgO nanoparticle systems are significantly less abundant in these doped systems.…”

“…We start with as-synthesized powders of InÀ MgÀ O nanocomposite particles that were grown using a newly developed chemical vapor synthesis approach (Figure S1, Supporting Information). [8,16] The process employs the decomposition of an indium organic precursor inside the Mg vapor combustion flame which is associated with a combustion reaction that exhibits sufficiently high exothermicity and high temperatures ( � 2600 K) to completely convert the precursor components into metal oxides. Using this approach, we obtain powders of highly dispersed and crystalline nanoparticles ( Figure 1a) with an extremely homogeneous distribution of size ( Figure 1b) and composition ( Figure S2, Supporting Information).…”

“…In−Mg−O nanoparticles were produced in a modified metalorganic chemical vapor synthesis (MOCVS) approach (Figure S1, Supporting Information), which provides high control over concentration and homogeneous distribution of indium in In−Mg−O nanoparticle powders ,. In this approach, an indium organic vapor decomposes in the combustion flame related to the Mg metal vapor oxidation reaction with oxygen inside a hot wall reactor system and under reduced pressures.…”

“…InÀ MgÀ O nanoparticles were produced in a modified metalorganic chemical vapor synthesis (MOCVS) approach (Figure S1, Supporting Information), which provides high control over concentration and homogeneous distribution of indium in InÀ MgÀ O nanoparticle powders. [8,16] In this approach, an indium organic vapor decomposes in the combustion flame related to the Mg metal vapor oxidation reaction with oxygen inside a hot wall reactor system and under reduced pressures. The two-zone reactor system ( Figure S1, Supporting Information) consists of two quartz glass tubes, which are mounted concentrically inside a heating coil (first heating zone with an operation temperature T1) followed by a ceramic tube furnace (second heating zone with an operation temperature T2).…”