Recent advances in understanding the reinforcing ability and mechanism of carbon nanotubes in ceramic matrix composites

Ni@CNTs/Al2O3 Ceramic Composites with Interfacial Solder Strengthen the Segregated Network for High Toughness and Excellent Electromagnetic Interference Shielding

Ingenious microstructure design and appropriate multicomponent strategies are still challenging for advanced electromagnetic interference (EMI) shielding materials with excellent shielding effectiveness (SE) and reliable mechanical properties in harsh environments and low filling levels. In this study, nickel@multiwalled carbon nanotubes/alumina (Ni@CNTs/Al₂O₃) ceramic composites with segregated structures and electric/magnetic-coupling networks anchored by CNTs and magnetic Ni nanofillers were prepared by hot-press sintering. CNTs/Al₂O₃ ceramic composites exhibit a percolation threshold of only about 0.32013 vol %, which is lower than those of other reported CNTs/Al₂O₃ composites with segregated or uniformly dispersed structures. The electrical conductivity and EMI SE of 9CNTs/Al₂O₃ ceramic composites with 9 vol % (4.76 wt %) CNT content were 103.1 S/m and 33.6 dB, respectively. In addition, EMI SE and toughness were both enhanced by the synergistic effect of Ni nanoparticles and CNTs. In the unit of a segregated structure, a three-dimensional (3D) electric/magnetic-coupling network effectively captures and attenuates electromagnetic wave energy by electrical conduction, dielectric loss, and magnetic loss. On the other hand, the pull-out of CNTs and deflection of cracks distributed along the segregated structures synergistically enhance the fracture toughness of Ni@CNTs/Al₂O₃ ceramic composites. High-performance 3Ni@5CNTs/Al₂O₃ ceramic composites with 5 vol % (2.64 wt %) and 3 vol % (0.76 wt %) CNT contents have been achieved, whose EMI SE is 41.8 dB, density is 90.99%, flexural strength is 197.83 ± 18.62 MPa, and fracture toughness is 6.03 ± 0.23 MPa·m^1/2. This efficient method provides a promising way to fabricate EMI shielding ceramic composites with high mechanical properties.

Silicon Nitride-Based Composites with the Addition of CNTs-A Review of Recent Progress, Challenges, and Future Prospects

In this overview, the results published to date concerning the development, processing, microstructure characteristics, and properties of silicon nitride/carbon nanotube (Si₃N₄ + CNTs) composites are summarized. The influence of the different processing routes on the microstructure development of the Si₃N₄ + CNTs is discussed. The effects of the CNTs addition on the mechanical properties—hardness, bending strength and fracture toughness—and tribological characteristics—wear rate and coefficient of friction—are summarized. The characteristic defects, fracture origins, toughening and damage mechanisms occurring during the testing are described. The influence of the CNTs’ addition on the thermal and functional properties of the composites is discussed as well. New trends in the development of these composites with significant potential for future applications are outlined.

Boron nitride nanoplatelets as reinforcement material for dental ceramics

OBJECTIVE

The main goal of this research was to demonstrate the potential value of boron nitride nanoplatelets (BNNPs), which have excellent mechanical properties and biocompatibility, as a suitable reinforcement for dental materials.

METHODS

The BNNPs were prepared by exfoliating h-BN via high-energy ball-milling and dispersion on a zirconia matrix. Then the composite powder was consolidated using spark plasma sintering. Fracture toughness, flexural strength and wear resistance were the mechanical properties explored. Agar diffusion-based biocompatibility testing was carried out. Low temperature degradation tests were also performed in a steam environment in an autoclave.

RESULTS

The BNNPs dispersed zirconia exhibited improved strength (up to 27.3%), and fracture toughness was also increased (up to 37.5%) with the addition of 1-1.5 vol.% BNNPs. Tribological properties were also enhanced by the addition of BNNPs. The cytotoxicity tests confirmed that the BNNPs do not have obvious toxicity. The accelerated low-temperature degradation experiment revealed the barrier properties of the BNNPs, whose addition almost fully inhibited the degradation of the zirconia matrix in a humid environment.

SIGNIFICANCE

The main contribution of this study is the introduction of an advanced material, BNNP, which can be used as a biocompatible reinforcement for dental materials, resulting in enhanced mechanical properties of the system due to its unique structure and extraordinary properties.

Development of an Ultra-Low Carbon MgO Refractory Doped with α-Al2O3 Nanoparticles for the Steelmaking Industry: A Microstructural and Thermo-Mechanical Study

The effect of α-Al₂O₃ nanoparticles (up to 5 wt.%) on the physical, mechanical, and thermal properties, as well as on the microstructural evolution of a dense magnesia refractory is studied. Sintering temperatures at 1300, 1500, and 1600 °C are used. The physical properties of interest were bulk density and apparent porosity, which were evaluated by the Archimedes method. Thermal properties were examined by differential scanning calorimetry. The mechanical behavior was studied by cold crushing strength and microhardness tests. Finally, the microstructure and mineralogical qualitative characteristics were studied by scanning electron microscopy and X-ray diffraction, respectively. Increasing the sintering temperature resulted in improved density and reduced apparent porosity. However, as the α-Al₂O₃ nanoparticle content increased, the density and microhardness decreased. Microstructural observations showed that the presence of α-Al₂O₃ nanoparticles in the magnesia matrix induced the magnesium-aluminate spinel formation (MgAl₂O₄), which improved the mechanical resistance most significantly at 1500 °C.

Recent Advances and Future Prospects in Spark Plasma Sintered Alumina Hybrid Nanocomposites

Although ceramics have many advantages when compared to metals in specific applications, they could be more widely applied if their low properties (fracture toughness, strength, and electrical and thermal conductivities) are improved. Reinforcing ceramics by two nano-phases that have different morphologies and/or properties, called the hybrid microstructure design, has been implemented to develop hybrid ceramic nanocomposites with tailored nanostructures, improved mechanical properties, and enhanced functionalities. The use of the novel spark plasma sintering (SPS) process allowed for the sintering of hybrid ceramic nanocomposite materials to maintain high relative density while also preserving the small grain size of the matrix. As a result, hybrid nanocomposite materials that have better mechanical and functional properties than those of either conventional composites or nanocomposites were produced. The development of hybrid ceramic nanocomposites is in its early stage and it is expected to continue attracting the interest of the scientific community. In the present paper, the progress made in the development of alumina hybrid nanocomposites, using spark plasma sintering, and their properties are reviewed. In addition, the current challenges and potential applications are highlighted. Finally, future prospects for developing alumina hybrid nanocomposites that have better performance are set.

Customizable Ceramic Nanocomposites Using Carbon Nanotubes

A novel tweakable nanocomposite was prepared by spark plasma sintering followed by systematic oxidation of carbon nanotube (CNT) molecules to produce alumina/carbon nanotube nanocomposites with surface porosities. The mechanical properties (flexural strength and fracture toughness), surface area, and electrical conductivities were characterized and compared. The nanocomposites were extensively analyzed by field emission scanning electron microscopy (FE-SEM) for 2D qualitative surface morphological analysis. Adding CNTs in ceramic matrices and then systematically oxidizing them, without substantial reduction in densification, induces significant capability to achieve desirable/application oriented balance between mechanical, electrical, and catalytic properties of these ceramic nanocomposites. This novel strategy, upon further development, opens new level of opportunities for real-world/industrial applications of these relatively novel engineering materials.

Advanced Materials for Next-Generation Spacecraft

Spacecraft are expected to traverse enormous distances over long periods of time without an opportunity for maintenance, re-fueling, or repair, and, for interplanetary probes, no on-board crew to actively control the spacecraft configuration or flight path. Nevertheless, space technology has reached the stage when mining of space resources, space travel, and even colonization of other celestial bodies such as Mars and the Moon are being seriously considered. These ambitious aims call for spacecraft capable of self-controlled, self-adapting, and self-healing behavior. It is a tough challenge to address using traditional materials and approaches for their assembly. True interplanetary advances may only be attained using novel self-assembled and self-healing materials, which would allow for realization of next-generation spacecraft, where the concepts of adaptation and healing are at the core of every level of spacecraft design. Herein, recent achievements are captured and future directions in materials-driven development of space technology outlined.

Carbon nanotube, graphene and boron nitride nanotube reinforced bioactive ceramics for bone repair

The high brittleness and low strength of bioactive ceramics have severely restricted their application in bone repair despite the fact that they have been regarded as one of the most promising biomaterials. In the last few years, low-dimensional nanomaterials (LDNs), including carbon nanotubes, graphene and boron nitride nanotubes, have gained increasing attention owing to their favorable biocompatibility, large surface specific area and super mechanical properties. These qualities make LDNs potential nanofillers in reinforcing bioactive ceramics. In this review, the types, characteristics and applications of the commonly used LDNs in ceramic composites are summarized. In addition, the fabrication methods for LDNs/ceramic composites, such as hot pressing, spark plasma sintering and selective laser sintering, are systematically reviewed and compared. Emphases are placed on how to obtain the uniform dispersion of LDNs in a ceramic matrix and maintain the structural stability of LDNs during the high-temperature fabrication process of ceramics. The reinforcing mechanisms of LDNs in ceramic composites are then discussed in-depth. The in vitro and in vivo studies of LDNs/ceramic in bone repair are also summarized and discussed. Finally, new developments and potential applications of LDNs/ceramic composites are further discussed with reference to experimental and theoretical studies.

STATEMENT OF SIGNIFICANCE

Despite bioactive ceramics having been regarded as promising biomaterials, their high brittleness and low strength severely restrict their application in bone scaffolds. In recent years, low-dimensional nanomaterials (LDNs), including carbon nanotubes, graphene and boron nitride nanotubes, have shown great potential in reinforcing bioactive ceramics owing to their unique structures and properties. However, so far it has been difficult to maintain the structural stability of LDNs during fabrication of LDNs/ceramic composites, due to the lengthy, high-temperature process involved. This review presents a comprehensive overview of the developments and applications of LDNs in bioactive ceramics. The newly-developed fabrication methods for LDNs/ceramic composites, the reinforcing mechanisms and the in vitro and in vivo performance of LDNs are also summarized and discussed in detail.

45S5 Bioglass(®)-MWCNT composite: processing and bioactivity

Multi-walled carbon nanotube (MWCNT)-Bioglass (BG) matrix composite was fabricated using a facile and scalable aqueous colloidal processing method without using any surfactants followed by spark plasma sintering (SPS) consolidation. The individual MWCNTs were initially uniformly dispersed in water and then entirely immobilized on the BG particles during the colloidal processing, avoiding their common re-agglomeration during the water-removal and drying step, which guaranteed their uniform dispersion within the dense BG matrix after the consolidation process. SPS was used as a fast sintering technique to minimise any damage to the MWCNT structure during the high-temperature consolidation process. The electrical conductivity of BG increased by 8 orders of magnitude with the addition of 6.35 wt% of MWCNTs compared to pure BG. Short-duration tests were used in the present study as a preliminary evaluation to understand the effect of incorporating MWCNTs on osteoblast-like cells. The analysed cell proliferation, viability and phenotype expression of MG-63 cells showed inhibition on 45S5 Bioglass(®)-MWCNT composite surfaces.