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27XV International Symposium on Self-Propagating High-Temperature Synthesis
METAL FOAMS FABRICATED BY SPRAY SOLUTION COMBUSTION SYNTHESIS AND SPARK PLASMA SINTERING
G. V. Trusov*"'A, A. B. Tarasovc, D. O. MoskovskihA, A. S. Rogachevflfi, and A. S. Mukasyan^
aMerzhanov Institute of Structural Macrokinetics and Materials Science, Russian Academy of Sciences, Chernogolovka, Russia
bNational University of Science and Technology MISIS, Moscow, Russia cLomonosov Moscow State University, Moscow, Russia dUniversity of Notre Dame, USA *e-mail: german.v.trusov@gmail.com
DOI: 10.24411/9999-0014A-2019-10177
Nickel are most demanded oxide materials for scientific and industrial applications. They are widely used in different forms and modifications as catalysts, magnetic materials, for medical purposes [1]. Although many different approaches are developed to obtain nickel with required properties, any new technique allowing a direct synthesis of single-phase materials still attracts a big attention. As it has been shown recently, a "solution combustion" technique is one of the most promising candidate for nickel production with controllable properties [2]. The method is based on the usage of highly exothermic self-sustained redox reactions between metal nitrates and organic "fuels", which are mixed on a molecular level in aqueous solution. Heating of reaction solution leads to water evaporation and formation of a homogeneous reactive mixture, followed by reaction initiation with rapid heat release. The intensive adiabatic self-heating of the environment and appearance of a great amount of gaseous products facilitates the formation of oxide nanocrystalline aggregates. The further development of the method requires to overcome aggregation of resulted nanoparticles.
In present work, we have developed the solution combustion reaction in the individual micron-size droplets of ultrasounic-generated aerosols using an oxidizer and fuel, namely nickel nitrate and glycine. An aqueous reaction solution was nebulized in a preheated to 800oC quartz tube furnace to produce gray powder depending on preparation temperature and aerosol flow velocity. Phase composition, morphology and optical properties of resulted powders were studied by XRD, SEM, TEM and BET techniques. The magnetic powder obtained at high temperatures or low flow velocity was found to be a well crystalline single-phase nickel. Powder consisted of non-aggregated hollow micron-sized spheres with a complex internal structure. All products demonstrated high values of specific surface area. A spray solution combustion synthesis (SSCS) approach allows fabrication of hollow metal (Ni) spheres with a unique morphology (Fig. 1). The outer diameters of the spheres range from 0.5 to 5 ^m with average wall thicknesses of ~ 20 nm. The most important feature is that the shell consists of Ni nanoparticles and amorphous areas forming a porous skeleton. Such morphological features play an important role during spark plasma sintering of such particles: this "active" porous nano-shell allows rapid transfer of the matter to make strong necks between the spheres, while sintering of the shell itself leads to the formation of rigid pore-free surfaces. Rapid (15 min) low temperature (763 K) spark plasma sintering (SPS) treatment of these particles leads to the fabrication of high porous (up to 93%) cellular materisls with relatively high mechanical properties (reduced elastic modulus E/p = 5.7 GPa and E/p2 = 81.6 GPa) and thermal conductivity 70 times smaller than for bulk Ni. Thus, it is demonstrated that the combination of SSCS and SPS methods can be considered as a novel technological approach for fabrication of metallic foams [3].
ISHS 2019 Moscow, Russia
Fig. 1. SEM image of the sintered nickel microspheres by spark plasma sintering (SPS) without pressure.
Finally, it is worth noting that SSCS allows fabrication a variety of hollow spherical particles with different non-oxide compositions including Cu, Co, NiCu, NiFe, NiCoCu and etc. It implies that the composition of metallic high porous cellular materials produced by hybrid SSCS + SPS approach can be significantly expanded.
1. S.T. Aruna, A.S. Mukasyan, Combustion synthesis and nanomaterials, Curr. Opin. Solid State Mater. Sci., 2008, vol. 12, no. 3, pp. 44-50.
2. K. Manukyan, A. Cross, S. Roslyakov, S. Rouvimov, A. Rogachev, E.E. Wolf, A. Mukasyan, Solution combustion synthesis of nano-crystalline metallic materials: mechanistic studies, J. Phys. Chem. C, 2013, vol. 117, no. 46, pp. 24417-24427.
3. G.V. Trusov, A.B. Tarasov, D.O. Moskovskikh, A.S. Rogachev, A.S. Mukasyan, High porous cellular materials by spray solution combustion synthesis and spark plasma sintering, J. Alloys Compd, 2019, vol. 779, pp. 557-565.
