In a recent study published in the journal Applied Sciencea team of researchers decorated graphene nanoplatelets (PNG) with rare earth oxide CeO2 particles to study the decorative effect of PNBs on the reinforcing capacity of PNB/Al composites. It was found that the mechanical properties of composites reinforced with CeO2-GNPs were better than composites reinforced with raw GNPs of the same quality.
What are graphene nanoplatelets?
Graphene nanoplatelets, or GNPs, are tiny stacks of graphene that can replace carbon fiber, carbon nanotubes, nano-clays or other substances. When applied to plastics or resins at a concentration of 2-5% by weight, they make them electrically or thermally conductive and less permeable to gases.
PNBs offer exceptional tensile qualities, strength and stiffness, as well as desirable functional properties such as high thermal and electrical conductivity. They are also lightweight and easy to handle. Due to a distinctive two-dimensional structure, GNPs have a greater surface area, allowing them to perform more efficiently in load-boosting applications. For this reason, GNPs are considered an effective reinforcing agent in composite materials.[if–>
SEM image of graphene multilayer microstructure morphology. Image credit: Guo, Z. et al.
Industrial applications and limitations in the past
In the past, GNPs have been used in research on structural and functional composites as a new essential reinforcement material at the nanoscale. They have also been widely used as effective reinforcement in the development of metal matrix composites. Previously, by reinforcing aluminum matrix composites with GNPs, the tensile strength, yield strength, and microhardness of the composites were all significantly improved.
Despite advances in the field of nano-carbon reinforced aluminum-based materials, the fabrication of graphene-reinforced metal matrix composites remains a significant challenge. This is because the force between the graphene sheets tends to cause them to build up, which weakens the matrix and causes the composites to deform during any load-bearing application.
What did the researchers do?
In this study, the researchers used surface modification techniques in conjunction with hot pressure sintering to address the previously mentioned concerns. The 2024 aluminum matrix alloy was supplemented with natural graphene nanoplatelets and CeO coated graphene nanoplatelets2 rare earth oxide particles.
Comparative tests were carried out to determine the effect of PNBs decorated with rare earth oxides on the mechanical properties and the microstructure of the matrix. At first, GNPs were decorated with rare earth oxide CeO2 particles using the alcohol heating method. Next, a hot pressure sintering process was used to reinforce the aluminum composites with freshly prepared CeO.2– GNP particles.
Additionally, the hardness and tensile strength of CeO2@GNPs/2024 AL composites were reviewed. The sample was subjected to a Vickers hardness test, with a loading force of 0.3 kg and a pressure hold of 15 seconds. The tensile speed was set at 0.5 mm/min for the tensile test. Ten indentation inspection tests were required for each hardness pattern to minimize errors.
What was found?
The alcohol heating approach has been effectively used to prepare GNPs coated with CeO2 particles. Rare earth oxides CeO2 and GNPs were strongly bonded, and this bond was maintained even after the pressure sintering technique was used to fabricate the composites.
The decorating procedure increases the dispersibility of GNPs in the matrix. As the wettability between the GNPs and the matrix improves, it encourages the bonding of the GNPs and the alloy, which reduces structural defects during the process.
The GNP boundary lines in the matrix had no visible pores or defects, such as cracks, along their length. This implies the presence of a healthy interface between the GNP and the Al matrix, which is advantageous for improving the mechanical properties of composite materials.
CEO2-GNPs added to composites made under the same preparation circumstances demonstrated a greater grain refinement effect than natural GNPs. The yield strength and tensile strength of Al composites reinforced with rare earth oxide CeO2 decorated GNPs were 21.1% and 24.7% higher than those of Al composites reinforced with natural GNPs.
TEM images of CeO2– PNB/2024Al composite: (a) wide-angle annular darkfield image; (b,vs) HRTEM image of the regions; (vs) Region A SAED model; (D) SAED models of the region (vs). Image credit: Guo, Z. et al.
Importance of decorating GNPs with CeO rare earth oxide2 Particles
This study presented a new method for improving the mechanical properties of nanoparticle-reinforced aluminum composites. The results show that due to the decorative effect of the rare earth oxide CeO2 particles, the combination of matrix and GNPs has been optimized. When interface bonding and particle distribution in the aluminum matrix are improved, GNPs play a more effective role in a range of reinforcing effects, resulting in dramatic improvements in the mechanical properties of the composite.
Read on: Graphene Oxide Synthesis Techniques: An Overview.
Guo, Z. et al. (2021) Rare Earth Oxide CEO2 2024 aluminum alloy matrix composites reinforced with decorated graphene nanoplatelets made by pressure sintering process. Applied sciences, 11(23), 11177. Available at: https://www.mdpi.com/2076-3417/11/23/11177