Chunfei Wu

Chunfei Wu

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Materials characterisation - Differential scanning calorimetry (DSC) analysis - Solid – Structure and interaction analysis (2) - Research application of DSC

Reaction mechanism of zrb2-zrc formation in ni-zr-b4 c system analyzed by differential scanning calorimetry

https://doi.org/10.3390/ma14216467

“The reaction mechanism of ZrB2-ZrC formation in a 30% Ni-Zr-B4C system under argon was revealed by using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicated that the reaction mechanism in the Ni-Zr-B4C system was complex. Initially, NixZry and NixBy intermetallics were formed via solid-state diffusion reactions between Ni, B4C and Zr. Then, the eutectic reaction between Ni2B and Ni4B3 lead to the formation of Ni-B liquid. The free C atoms dissolved into the Ni-B liquid to form a Ni-B-C ternary liquid, and then part of the Zr powder dissolved into the surrounding Ni-B-C ternary liquid to form Ni-Zr-B-C quaternary liquid. Finally, ZrB2 and ZrC formed and precipitated out of the saturated liquid. The eutectic liquid plays an important role during the formation of ZrB2-ZrC.”

“DSC was carried out on a STA 449C Jupiter (Netzsch, Weimar, Germany) apparatus to reveal the reaction mechanism of the Ni-Zr-B4C system. The heating process was set to a rate of 10 °C/min in flowing argon gas (99.9% in purity, flow rate: 40 mL/min). Following DSC analysis, the sintered powders were crushed, and the phase composition was analyzed by XRD (D8 Advance, Bruker, Ettlingen, Germany, Cu-Kα radiation, λ = 0.15406 nm) at a scanning speed of 6°/min and a scanning range of 20–80°. Microstructures of the reacted samples were characterized by SEM (S-4800, Hitachi, Tokyo, Japan) equipped with an energy-dispersive spectrometer (EDS).”

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Figure 1 displays the DSC curves of the Zr-B4C, Ni-B4C, Ni-Zr and 30 wt.% Ni-Zr-B4C mixtures heated to 1200 °C with a heating rate of 10 °C/min. Moreover, interrupted experiments were performed in order to elucidate the reaction mechanism during the heating process.
Materials 14 06467 g001 550
Figure 1. The DSC curves of the mixtures heated to 1200 °C with a heating rate of 10 °C/min: (a) Zr-B4C; (b) Ni-B4C; (c) Ni-Zr and (d) 30 wt.% Ni-Zr-B4C.
The DSC curve of the Zr-B4C mixture is shown in Figure 1a. A broad exothermic peak appears near 1008 °C. The XRD result of DSC product heated to 1200 °C shows that the product mainly consists of a large amount of ZrB2, ZrC and a small amount of Zr (see Figure 2). The presence of Zr may have been caused by the incomplete reaction of reactants. Hu et al. [1] studied the mechanism of ZrB2 and ZrC generation in the Zr-B4C system and proposed that the solid-phase synthesis reaction was the main formation mechanism. Zhang et al. [2,3,4] investigated the reaction behavior and formation mechanism in the Cu-Zr-B4C system. Effects of heating rate and B4C particle size on the reaction process in the Zr-B4C system were also explored. Either increasing the particle size of B4C or increasing the heating rate may result in a sluggish solid-state reaction between Zr and B4C, which leads to the residual of Zr and B4C in the DSC products. The diffraction peaks of Zr were also found in the XRD patterns of the above research, but the diffraction peaks of B4C were very weak or absent due to the atomic characteristics and crystalline lattice of B4C [1,2,3,4].

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