The influence of heating conditions of the samples of nickel nanopowders on the modes of their interactions with the air
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RESEARCH PAPER
The influence of heating conditions of the samples of nickel nanopowders on the modes of their interactions with the air Michail I. Alymov & Boris S. Seplyarskii & Sergey G. Vadchenko & Victor A. Zelensky & Nickolai M. Rubtsov Roman А. Kochetkov & Alexander S. Schukin & Ivan D. Kovalev
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Received: 21 July 2020 / Accepted: 16 November 2020 # Springer Nature B.V. 2020
Abstract In the present work, compact samples of pyrophoric nickel nanopowders with an average particle size of 55 nm obtained by the method of chemical metallurgy were investigated. The possibility of passivation of compact samples 3 mm in diameter made of nickel pyrophoric nanopowders in the air is experimentally shown for the first time. The time of complete passivation is only 3–5 s for a relative sample density 0.4–0.5. According to X-ray phase analysis, only Ni phase was observed in passivated samples. It was found that passivated samples maintain thermal stability in the air at slow (< 10 °C/s) heating to ~ 200 °C; it is an important parameter for fire safety at handling of nanopowders. The analysis of passivated samples by the SEM method showed no traces of sintering of nickel nanoparticles, even after testing for thermal stability. The uniform distribution of oxygen within passivated samples according to energy dispersive X-ray analysis data indicates the volumic nature of the interaction of samples with the air during passivation. For the passivated samples, critical heating conditions were determined, under which self-ignition occurs.
Keywords Pyrophoric nickel nanopowder . Passivation . Compact samples . Critical ignition conditions M. I. Alymov : B. S. Seplyarskii : S. G. Vadchenko : V. A. Zelensky : N. M. Rubtsov (*) : R. А. Kochetkov : A. S. Schukin : I. D. Kovalev Merzhanov Institute of Structural Macrokinetics and Materials Science, Russian Academy of Sciences, Chernogolovka, Russia e-mail: [email protected]
Introduction Metal nanopowders are pyrophoric, i.e., they are able to self-ignite upon contact with air due to high chemical activity and large specific surface area (Bouillard et al. 2010; Pivkina et al. 2004; Hosokawa et al. 2007; Rubtsov et al. 2017). In order to make safe the process of further processing of nanopowders into products, these are passivated (Hosokawa et al. 2007; Rubtsov et al. 2017; Flannery et al. 2015; Meziani et al. 2009; Nagarajan and Hatton 2008). Passivation consists in producing a thin protective film on the surface of nanoparticles, which prevents their spontaneous combustion. Usually, passivation lasts tens of hours, which is a limiting factor for the production and use of nanopowders. Processes of passivation of iron and nickel nanopowders were investigated in the works (Alymov et al. 2019; Alymov et al. 2017a, b). We have previously formulated a model of passivation of the pyrophoric nanopowder layer and conducted its analysis by analytical and numerical methods (Alymov et al. 2019). Applicability of theoretical approaches of classical macroscopic theory of thermal explosion (Seplya
