The Effect of Adding CeO2 Nanoparticles to Cu-Ni-Al Alloy for High Temperatures Applications

Abstract

This work presents the effect of CeO₂ nanoparticles (CeO₂-NPs) on Cu-50Ni-5Al alloys on morphological, microstructural, degradation, and electrochemical behavior at high temperatures. The samples obtained by mechanical alloying and spark plasma sintering were exposed to a molten eutectic mixture of Li₂CO₃-K₂CO₃ for 504 h. The degradation of the materials was analyzed using gravimetry measurements and electrochemical impedance spectroscopy. Different characterization techniques, such as X-ray diffraction and scanning electron microscopy, were used to investigate the phase composition, parameter lattice, and microstructure of Cu-Ni-Al alloys reinforced with CeO₂-NPs. The hardness of the composite was also examined using the Vickers hardness test. Gravimetry measurements revealed that the sample with 1 wt.% CeO₂-NPs presented the best response to degradation with a less drastic mass variation. Impedance analysis also revealed that by adding 1 wt.% CeO₂-NPs, the impedance modulus increased, which is related to a lower porosity of the oxide film or a thicker oxide layer. The microhardness also significantly increased, incorporating 1 wt.% CeO₂-NPs, which reduced with higher CeO₂-NPs content, which is possibly associated with a more uniform distribution using 1 wt.% CeO₂-NPs in the Cu-Ni-Al matrix that avoided the aggregation phenomenon.

Keywords: CeO2–NPs; Cu–Ni–Al; gravimetry measurements; high temperatures; impedance; microhardness.

Figure 1

Sample preparation (powder mixture) and schematic representation of the SPS system (consolidation).

Figure 2

The variation of weight of Cu–50Ni–5Al samples after 504 h of exposure to molten carbonates. () 0 wt.% CeO₂–NPs, () 1 wt.% CeO₂–NPs, () 3 wt.% CeO₂–NPs, () 5 wt.% CeO₂–NPs.

Figure 3

FE–SEM images before Cu–50Ni–5Al: (a) 0 wt.% CeO₂–NPs, (b) 1 wt.% CeO₂–NPs, (c) 3 wt.% CeO₂–NPs, (d) 5 wt.% CeO₂–NPs, and after gravimetric measurements Cu–50Ni–5Al, (e) 0 wt.% CeO₂–NPs, (f) 1 wt.% CeO₂–NPs, (g) 3 wt.% CeO₂–NPs, and (h) 5 wt.% CeO₂–NPs.

Figure 4

EDS surface mapping before Cu–50Ni–5Al: (a) 0 wt.% CeO₂–NPs, (b) 1 wt.% CeO₂–NPs, (c) 3 wt.% CeO₂–NPs, (d) 5 wt.% CeO₂–NPs and after gravimetric measurements Cu–50Ni–5Al; (e) 0 wt.% CeO₂–NPs, (f) 1 wt.% CeO₂–NPs, (g) 3 wt.% CeO₂–NPs, and (h) 5 wt.% CeO₂–NPs.

Figure 5

XRD patterns of Cu–50Ni–5Al samples: (a) 0 wt.% CeO₂–NPs, (b) 1 wt.% CeO₂–NPs, (c) 3 wt.% CeO₂–NPs, (d) 5 wt.% CeO₂–NPs before and after gravimetric measurements.

Figure 6

Microhardness of the samples Cu–50Ni–5Al: () 0% wt.% CeO₂–NPs, () 1% wt.% CeO₂–NPs, () 3% wt.% CeO₂–NPs, and () 5% wt.% CeO₂–NPs before exposure.

Figure 7

Open circuit potential variation of () Cu–50Ni–5Al and () Cu–50Ni–5Al + 1 wt.% CeO₂–NPs exposure to Li₂CO₃–K₂CO₃ at 550 °C and aerated atmosphere over time.

Figure 8

Nyquist diagrams of (a) Cu–50Ni–5Al and (b) Cu–50Ni–5Al + 1 wt.% CeO₂–NPs exposure 1 h to Li₂CO₃–K₂CO₃ at 550 °C, aerated atmosphere, and E = E_OC.

Figure 9

(a,b) Effect of correction of electrolyte resistance on Bode plots and (c) variation of the imaginary part of the impedance of Cu–50Ni–5Al + 1% wt.% CeO₂–NPs exposure 1 h to Li₂CO₃–K₂CO₃ in aerated atmosphere at 550 °C and E = E_OC.