Graphene Flagship Partnering Project CERANEA develops graphene-filled ceramic sandwiches that deliver materials with enhanced properties and functionalities. In this article, Csaba Balázsi, CERANEA Project Leader and scientific advisor at Graphene Flagship Partner ELKH CER, to explains the potential applications of ceramic-graphene FGMs in coatings and orthopaedics.
The mineralised structures of some bones, seashells and trees have something in common: their composition varies gradually throughout their volume, providing multiple functional roles at once. These are classified as functionally graded materials (FGMs) and can also be artificially engineered with tailored properties for numerous applications, including biomedical implants, optoelectronic devices, sensors and batteries. For further information see the IDTechEx report on Graphene Market & 2D Materials Assessment 2021-2031.
FGMs are sandwich-structures made of several functional layers. We produce different stacks for novel types of composites, optimised for the desired combinations of electrical, thermal and mechanical properties. These stacks contain graphene, hexagonal boron nitride (hBN) or other layered materials, as well as ceramics, such as silicon nitride, silicon carbide and zirconia. Graphene additives are important fillers that increase the wear resistance and conductivity of ceramic matrices. Graphene also improves the thermal quality and the ability to withstand cracking. The key lies in the careful composition of these composite materials, which defines their porosity and conductivity.
For example, we can create a sandwich-structure made with ceramics as the bottom layer, a mixture of ceramics and graphene as the intermediate layer, and a foam-like structure of graphene as the top layer. As the graphene concentration increases from bottom to top, so does the porosity and conductivity of the material.
The importance of graphene-enabled layered structures
Layered structures can deliver the performance desired by industry. These materials are more resistant than current ceramics against damages caused by electrical arcing, so can be used as long-lasting coatings for contacts, switches or wearable parts. In CERANEA, we are demonstrating the feasibility of producing these coatings at an industrial-scale and in an economically affordable manner. Graphene can replace precious metals, such as gold or silver nanoparticles, leading to a more sustainable and resource-efficient fabrication. These composites will be suitable for engineering applications, such as structural health monitoring systems.
Furthermore, composites with graphene, silicon nitride or silicon nitride-zirconia are being studied as novel biomedical implants in orthopaedics. The shape, morphology and composition of natural bone vary: certain parts are denser, while others are more spongy. Similarly, varying amounts of graphene in the ceramics-graphene composite result in different porosity. For this reason, our sandwich-structures made with ceramics and graphene could be applied to bone reconstruction.
Achievements to date
We devised a new method for preparing multi-layered graphene and GO starting from commercially available micro-sized graphite powder. We mill it to reduce its particle size and promote the intercalation and exfoliation of graphite into multi-layered graphene particles. This simple and efficient process leads to the production of 100 grams of multi-layered graphene in one batch, but it can be easily expanded to 100 kilograms in industrial processes. The graphene particles are then oxidised into GO using a combination of strong oxidising agents, thermal oxidising and sonication. We also carried out comprehensive morphological characterisations to reveal GO's structure and size.
We also studied ceramics based on silicon nitride and zirconia with varying amounts of multi-layered graphene. We identified the optimal graphene, silicon nitride and zirconia 'sandwich' - a layer of 30% multilayer graphene (MLG) by weight sandwiched between two layers of 5% MLG. This configuration resulted in a two-to-three-fold improvement in mechanical properties, compared to the opposite ratio (30-5-30 wt% MLG). Sandwich composites are valuable models for understanding the relation between composition and structure of materials, especially in the context of potential health monitoring applications.
In our most recent publication, we used X-ray microscopy in a state-of-the-art synchrotron source to study our ceramic/graphene composites in 3d, as well as their cracking and degradation mechanisms. Our method for preparing these carbon-rich samples could be relevant for other researchers working in this field.
The Graphene Flagship Partnering Project CERANEA was funded through FLAG-ERA Joint Transnational Call 2017 to develop FGMs with graphene in ceramic matrices. The project involves researchers at the Graphene Flagship Partners Eotvos Lorand Research Network, the Centre for Energy Research (ELKH CER, Hungary) and the Fraunhofer Institute for Ceramic Technologies and Systems (Fraunhofer IKTS, Germany), and Graphene Flagship Associate Member Slovak Academy of Sciences (Slovakia).
To learn more about the Graphene Flagship, click here.
Source: Stone Junction