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31SOLUTION COMBUSTION SYNTHESIS OF NANOSTRUCTURED METASTABLE NITRIDES AND INTERMETALLICS
S. I. Roslyakov*", A. S. Mukasyan"^, and Kh. V. Manukyanc
aNational University of Science and Technology MISiS, Moscow, 119049 Russia ^Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, IN 46556, USA
cNuclear Science Laboratory, Department of Physics, University of Notre Dame, Notre Dame, IN 46556, USA *e-mail: roslyakov.si@misis.ru
DOI: 10.24411/9999-0014A-2019-10140
Solution combustion synthesis (SCS) has attracted considerable attention of scientists from around the world for versatile synthesis of a variety of nanoscale materials [1-5]. SCS is based on generic idea of using exothermic self-sustained combustion reactions, which can be initiated in water solutions of oxidizer (typically metal nitrates) and organic fuel (glycine, urea, citric acid, etc.). One of the unique advantages of SCS is the ability to prepare high-quality multielement compounds with complex crystal structures, such as garnets, perovskites, spinels, silicates, phosphates, and others [4, 6]. The mixing of reactants at the molecular level enables efficient doping of materials, even with a trace amount of elements. Proper selection of fuel and optimization of the process allow for avoidance of secondary calcination step and prepare materials in one technological stage. Finally, the process can be performed in continuous schemes providing high throughput synthesis of nanoscale materials [3]. A limitation of SCS is related to the relatively low level of control over the morphological uniformity of the fabricated materials. The rapid increase in temperature leads to spontaneous nucleation, growth, and agglomeration of the products' particles [1, 5]. The most critical role in determining the morphology of the final products is played by maximum temperature and gas release. Another limitation of synthesis related to chemical nature of the mixture is preparation of predominantly oxide materials. Indeed, it is well-known the high temperature decomposition of metal nitrates leads to the formation of corresponding metal oxides [7, 8].
Several works demonstrate utilization of sulfur-containing organic compounds to produce metals sulfides. Currently, the preparation nanoscale metals and alloys is one of the active direction of SCS research. It was found that under certain conditions (typically excess of fuel) the intermediate gaseous combustion products have a reduction (typically hydrogen-based) nature and thus allow reduction of metal oxides to form metals (Ni, Cu, Co, Pt etc.) or alloys (NiCu, NiCo etc.) during SCS. In our recent works we reported the use of time-resolved X-ray diffraction, high-speed infrared imaging, and thermal analysis with mass spectrometry to reveal the metal formation mechanism during the SCS [9]. Tailoring the synthesis conditions also permitted to achieve highly dispersed supported metallic catalysts with particle sizes below 5 nm [10].
These promising results suggest that by understanding the fundamentals of combustion in reactive solutions we will able to synthesize other compounds including nitrides, intermetallics, carbides, and others, thus significantly widen specter of SCS materials. For example, one can expect that rich amount of carbon and nitrogen in organic fuels could create favorable conditions for carbonization or nitridation of metals. However, attempts to produce carbides or nitrides were not successful yet. In the above context, it is difficult to overestimate the importance of the research targeting routes for spreading the application of SCS to produce wide variety of non-oxide-based compounds.
ÏSHS2019
Moscow, Russia
In this work, we apply thermal analysis, mass- and FTIR spectroscopy and rapid combustion diagnostic techniques to produce new non-oxide phases and establish the mechanism of the ceramic (s-Fe3N) and intermetallic (NiAl) formation during SCS. Here, we report for the first time one step solution combustion synthesis of the nitride and intermetallic by self-sustained reactions of gels containing metal nitrates (Fe(NO3)3, Al(NO3)3) and fuels (C6H12N4, C2H5NO2) in an inert atmosphere. It is also important that the short process durations (seconds), high-reaction temperatures (~ 900 K) and rapid cooling rates (~ 20 K/s) permit formation of metastable s-Fe3N phase. The obtained results indicate that the exothermic high-temperature decomposition of a coordinating compound formed due to the interaction between Fe(NO3)3 and C6H12N4 in the reaction front leads to the formation of nanoscale s-Fe3N particles with sizes of 5-15 nm. The SCS conditions permit well preservation of crystalline nanoparticles of metastable s-Fe3N phase, which possess a good magnetic behavior (Fig. 1).
Fig. 1. A single step combustion method in iron nitrate (Fe(NO3)3) and hexamethylenetetramine (C6H12N4) gels.
The research was supported by the Russian Foundation for Basic Research (project
no. 18-03-00306).
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