The Engineering of Graphene: Comparison
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Please note this is a comparison between Version 2 by Catherine Yang and Version 1 by Tanya Scalia.

For space applications, graphene is used mainly in combination with metals or polymers, giving rise to nanocomposites where the graphene insertion greatly influences the features of the host matrix. The engineering of graphene-based composites and the design of materials with the on-demand combination of tailored properties are therefore a primary goal of space-related technologies. The unusual combination of mechanical, electrical, electronic, optical, and thermal properties of graphene have led to a focus on great efforts in the set-up of techniques for the mass-production of graphene-like nanostructures that are able to offer solutions to a variety of technological problems.

  • graphene
  • nanocomposites
  • materials for space
  • space-related applications

1. Metal-Based Nanocomposites

The aircraft and spacecraft industries rely heavily on aluminium, magnesium, and titanium alloys due to their light weight, high mechanical properties, low cost, and also reasonably good temperature resistance [16][1]. Graphene insertion inside the metals greatly improves several fundamental mechanical properties, such as the ultimate tensile, compressive, and rupture strengths, elongation at failure, Young’s and shear moduli, and density. In this view, the graphene-based nanocomposites meet precisely the demands of the Federal Aviation Administration (FAA) reported in the Metallic Materials Properties Development and Standardization (MMPDS) report [17][2]. Beyond its crucial role in the fabrication phase, graphene was demonstrated to be effective also as an additive in thermal spray metallic coatings for the fast repair of aerospace engine components. In particular, the mixing of multi-layered graphene with Ni-Al powders was found to decrease the structural defects in repair coatings, improving hardness and tensile adhesion strength as well as reducing residual strain and the coefficient of friction [18][3].
The wide range of different uses envisaged for different environments needs the fine tuning of highly specific, and sometimes rather complex, materials. An example is given by graphene layers, functionalised with carboxylic and hydroxyl groups, wrapping the silicon carbide (SiC) particles used as the filler in microstructured aluminium. These nano composites showed an increase in storage modulus and ultimate tensile strength by a factor of ~2.1 and ~3.4, respectively, compared to pure aluminium [19][4].
The improvement of nanocomposite mechanical features is accompanied by the improvement of thermal properties, such as thermal conductivity, specific heat capacity, and the thermal expansion coefficient. These effects can be of great value, as can be appreciated from the results obtained in the case of graphene–magnesium nanocomposites, a material much lighter than any existing alloy used by the aerospace industry [20][5].
However, the achievement of outstanding thermo-mechanical results is not an easy task to obtain just by adding graphene to a metal because the insertion of a nanofiller produces structural modifications in the host metal lattice. To obtain a material with the required properties, a strict control for the material structure is needed at the nanoscale level. An example of how to manage this issue can be found in [21][6]. In this paper, the interface between graphene and copper (Cu) has been deeply analysed by Molecular Dynamics simulations in order to optimise the mutual interactions of the two components. Depending on the texturing of Cu along the (1 0 0), (1 1 0), and (1 1 1) crystallographic orientations, the calculations predicted different melting temperatures for the graphene/Cu hybrids. Also, dramatically different values of mechanical strength were evaluated from the stress-strain curves obtained by applying uniaxial tensile loading along the different directions dictated by the graphene edges. Anjam et al. [21][6] found that, along the armchair direction, the mechanical strength of graphene/Cu (1 0 0), (1 1 0), and (1 1 1), compared with pure Cu, increased by about 380%, 370%, and 450%, respectively, whereas along the zigzag direction, the strength increased by about 1200%, 1000%, and 1480%. These differences were related to the diverse lattice mismatches generated by graphene contacting different Cu planes and to the occurrence of glide and shuffle dislocations. The graphene edges were found to drive the propagation of such dislocations, and to indirectly influence the thermal stability and the mechanical strength of the composites.
Experimental nanostructural studies on graphene-Al nanocomposites for aerospace applications have confirmed the Molecular Dynamics (MD) simulations [22][7]. The enhancement of the mechanical properties exhibited by the graphene-reinforced metal have been ascribed to the lamellar fine grain structure of the nanofiller. Such features minimise point defects, surface defects, and line dislocations of the host structure. Images of single-atomic-thickness graphene embedded in three different grades of aluminium alloy are shown in Figure 1.
Figure 1. Single-layer graphene inserted in various Al alloy matrixes (reproduced from ref. [22] Copyright© 2022 MDPI).
Single-layer graphene inserted in various Al alloy matrixes (reproduced from ref. [7] Copyright© 2022 MDPI).
The strengthening of the composite material is achieved by the transfer of the load from the matrix to the graphene flakes, which, in this view, would act also as a load-bearing component and not just like a control for the dislocation movements. The effective transfer of the strain to the filler enables the processing of Al/graphene powders via the traditional metallurgical routes. The structural components of the external fuel tanks of launch vehicles are fabricated using a microwave powder-sintering method followed by hot extrusion [22][7].
Overall, the most recent research has underlined how the thermo-mechanical properties of graphene-metal materials are driven by their structural features at the nanoscale level, confirming how nanocomposites for aerospace applications must be accurately designed.

2. Polymer-Based Nanocomposites

Graphene-based polymer nanocomposites are currently at the forefront of materials used for aerospace structural components. The obvious mechanical advantages that result from the ingenious coupling of graphene with a suitable polymer have indeed made such light-weight and easily manufactured nanocomposites a standard in the engineering of aerospace structural components. However, the many outstanding properties that graphene transfers to the host polymer have also been exploited in other applications, often still at the research stage, such as those in thermal management or space propulsion [23][8].
The large number of polymers under consideration and the many actual or planned space applications need to put into play all the techniques/protocols settled until now to produce, engineer, and process multifunctional nanocomposites [24][9]. One of the main tasks is the production of nanostructured flexible films with given optical and electromagnetic properties. This task needs a strong control, at the nanoscale level, for the geometry and the aggregation state of graphene nanoplatelets, and moreover for their dispersion inside the polymeric matrix [25][10]. For some applications, such as in gas-permeation barriers, the number of graphene layers coating polyurethane films has also been found to play a fundamental role [26][11].
In this context, the challenge is to develop manufacturing techniques and to envisage other hitherto unexplored approaches that are able to assure the specific performance required in uses that include, among others, sensors, antistatic coatings, and electromagnetic interference shields [23][8].
A further space-specific application of graphene-based nanocomposites is the fabrication of ablative coatings in the hyper-thermal environments experienced by space vehicles and rocket motors. Ablation tests demonstrated that the addition of graphene to elastomeric matrices greatly reduces the temperature rise at the back face of the coatings, highlighting an increase in thermal stability and in the heat absorbance capability of the nanocomposites with the increasing of the filler-matrix ratio [27][12].
Approaches based on multi-scale methods are also widely employed in the case of graphene/polymer nanocomposites to model the structure of the materials and the architecture of the systems following the requirements of the specific spatial uses [28][13]. To design new graphene-based nanocomposite layers for aerospace applications, the synergistic coupling of multi-scale modelling with experiments has proven to be a successful approach [29][14]. This paper describes the Integrated Computational Materials Engineering (ICME) method that has been applied in fabricating large aerospace laminate structures made by graphene/carbon fibre/polymer. This new composite has been designed in the frame of the Composite Exploration Upper Stage (CEUS) NASA project and is used for the forward skirt structure of the Space Launch System. The nanocomposite material, used as the face sheet of the sandwich panels in the barrel section of launch vehicles, improved the resistance to open-hole compression failure in the structure. Moreover, due to the graphene insertion, the panels showed a 22% reduction in weight with respect to the conventional composite ones.
To deeply understand the graphene-induced effects on the mechanical properties of polymers used for aerospace structures, in particular for sandwich panels, a major topic is the precise measurement of graphene-polymer interfacial strength. An interesting approach used to quantify such interactions is illustrated in [30][15]. Here, the interfacial strength of graphene and of oxidized graphene with a poly-epoxy resin matrix are measured using strain sensors pasted on the assembled panels.
It is noteworthy to report that a vehicle made with graphene-polymer composites has been assembled by Orbex, the UK-based private, low cost orbital launch services company [31]. [16] The two-stage rocket Orbex Prime, unveiled in May 2022, has been designed to carry up to 150 kg of payload into a Sun-synchronous orbit. The main structures and the fuel tanks of Orbex Prime are built using polymer/carbon fibre/graphene composites. The design of the Orbex Prime body is shown in Figure 32.
Figure 32.
The design of the Orbex Prime body (credits: Orbital Express Launch Ltd., London, UK).

References

  1. Rambabu, P.; Prasad, N.E.; Kutumbarao, V.V.; Wanhill, R.J.H. Aluminium Alloys for Aerospace Applications. In Aerospace Materials and Material Technologies; Prasad, N.E., Wanhill, R.J.H., Eds.; Springer: Singapore, 2017; pp. 29–52.
  2. Ali, A.M.; Omar, M.Z.; Hashim, H.; Salleh, M.S.; Mohamed, I.F. Recent development in graphene-reinforced aluminium matrix composite: A review. Rev. Adv. Mater. Sci. 2021, 60, 801–817.
  3. Ward, D.; Gupta, A.; Saraf, S.; Zhang, C.; Sakthivel, T.S.; Barkam, S.; Agarwal, A.; Seal, S. Functional NiAl-graphene oxide composite as a model coating for aerospace component repair. Carbon 2016, 105, 529–543.
  4. Singh, S.; Rathi, K.; Pal, K. Synthesis, characterization of graphene oxide wrapped silicon carbide for excellent mechanical and damping performance for aerospace application. J. Alloys Compd. 2018, 740, 436–445.
  5. Das, D.K.; Sarkar, J. Graphene magnesium nanocomposite: An advanced material for aerospace application. Mod. Phys. Lett. B 2018, 32, 1850075.
  6. Anjam, Q.; Hussain, F.; Imran, M.; Amina, N.; Kashif, M. A molecular dynamics study on thermal and mechanical behavior of graphene-copper nanocomposites for automobile & aerospace industry. Dig. J. Nanomater. Biostructures 2021, 16, 1185–1196.
  7. Jayaseelan, J.; Pazhani, A.; Michael, A.X.; Paulchamy, J.; Batako, A.; Hosamane Guruswamy, P.K. Characterization Studies on Graphene-Aluminium Nano Composites for Aerospace Launch Vehicle External Fuel Tank Structural Application. Materials 2022, 15, 5907.
  8. Das, P.; Banerjee, S.; Das, N.C. Polymer-Graphene Composite in Aerospace Engineering. In Woodhead Publishing Series in Composites Science and Engineering, Polymer Nanocomposites Containing Graphene; Rahaman, M., Nayak, L., Hussein, I.A., Das, N.C., Eds.; Woodhead Publishing: Cambridge, UK, 2022; pp. 683–711.
  9. Kausar, A.; Rafique, I.; Muhammad, B. Aerospace Application of Polymer Nanocomposite with Carbon Nanotube, Graphite, Graphene Oxide, and Nanoclay. Polym.-Plast. Technol. Eng. 2017, 56, 1438–1456.
  10. Clausi, M.; Santonicola, M.G.; Laurenzi, S. Steady-shear rheological properties of graphene- reinforced epoxy resin for manufacturing of aerospace composite films. AIP Conf. Proc. 2016, 1736, 020024.
  11. Chaitoglou, S.; Spachis, L.; Zisis, G.; Raptis, I.; Papanikolaou, N.; Vavouliotis, A.; Penedo, R.; Fernandes, N.; Dimoulas, A. Layer-by-layer assembled graphene coatings on polyurethane films as He permeation barrier. Prog. Org. Coat. 2021, 150, 105984.
  12. Iqbal, S.S.; Sabir, A.; Islam, A.; Bukhari, S.Z.U.A.; Yasir, M.; Bashir, M.A.; Bahadur, A. Effect of Graphene for Ablation Study of Advanced Composite Materials for Aerospace Applications. Key Eng. Mater. 2018, 778, 118–125.
  13. Manta, A.; Gresil, M. Graphene in aerospace composites. Proc. AIP Conf. 2018, 1932, 020001.
  14. Tomasi, J.; Pisani, W.A.; Chinkanjanarot, S.; Krieg, A.S.; Jaszczak, D.; Pineda, E.J.; Bednarcyk, B.A.; Miller, S.; King, J.A.; Miskioglu, I.; et al. Modelling-driven damage tolerant design of graphene nanoplatelet/carbon fiber/epoxy hybrid composite panels for full-scale aerospace structures. In Proceedings of the 33rd Technical Conference of the American Society for Composites, Seattle, WA, USA, 24–27 September 2018; pp. 656–675.
  15. Zainab, N.; Zaffar, K. Graphene Effect on Mechanical Properties of Sandwich Panel for Aerospace Structures. KEM 2021, 875, 121–126.
  16. Available online: https://orbex.space/news (accessed on 6 December 2022).
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