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Journal of Physical Studies 28(1), Article 1702 [9 pages] (2024)
DOI: https://doi.org/10.30970/jps.28.1702 FEATURES OF NiCx (x ≤ 1) FORMATION AT MECHANICAL ALLOYING OF THE EQUIMOLAR Ni–CNT AND Ni–GRAPHITE MIXTURES
Nadia Belyavina
Taras Shevchenko National University of Kyiv, 64/13, Volodymyrska St., 01601 Kyiv, Ukraine,
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Comprehensive theoretical and experimental studies of simultaneous mechanical alloying (MA) of Ni-carbon nanotubes (CNT) and Ni-Graphite mixtures (3:1, 3:2 and 1:1 component ratios) in a high-energy planetary ball mill have shown that the interaction of nickel atoms with CNTs or graphite leads to the formation of nanoscaled NiC$_{x}$ carbide ($x<1$). During mechanical alloying the crystal structure of NiC$_{x}$ carbide undergoes a transformation from the defective $s$-ZnS sphalerite type structure (with up to 2 carbon atoms per carbide lattice) to its internally deformed derivative described as own NiC type structure (2-4 carbon atoms per carbide lattice). Components of the charge (CNT or graphite) demonstrate their features at the formation of NiC$_{x}$ carbide. It means a different crystal lattice size for the same number of carbon atoms in its crystal structure as well as different values of the parameters of its real structure (deformations of the first- and second- order) at the same processing time in the mill. Analysis of the experimental data reveals that the plots of numbers of carbon atoms embedded in the NiC$_{x}$ lattice ($N_{\rm C}$) vs MA milling time ($t$) is fitted well by the following equation: $N_{\rm C}=A[1-\exp(-kt)]$, where $A$ and $k$ are constants. The $A$ constant could be associated with the reaction capacity for CNTs or graphite for formation of NiC$_{x}$ carbide ($A_{\rm CNT} > A_{\rm Gr}$), while the $k$ constant characterizes the rate of this process ($k_{\rm CNT} < k_{\rm Gr}$). The magnetic properties of the final MA powders as well as the microhardness of the samples sintered at high pressure and high temperature depend on the carbon form used (CNT or graphite), too. In our opinion, these features are probably related to the $sp^{2}$/$sp^{3}$ ratio of carbon atoms formed in the initial CNT or graphite powders as well as CNT or graphite powders at mechanical alloying.
Key words: monocarbides, mechanochemical synthesis, X-ray diffraction method, crystal structure.
