Embedding two-dimensional graphene array in ceramic matrix

Tough and strong bioinspired high-entropy all-ceramics with a contiguous network structure

Developing bioinspired all-ceramics with plastic phases is considered one of the most effective ways to simultaneously achieve enhanced strength and toughness in ceramic materials for high-temperature applications. Here we explore tough and strong bioinspired high-entropy all-ceramics with a contiguous network structure that are able to serve up to 1300 °C. Specifically, we develop the high-entropy all-ceramics, featuring a unique contiguous network distribution of the Cr7C3 plastic phase within the predominant high-entropy carbide (HEC) hard phase, through a high-entropy composition-engineering strategy. The resulting materials exhibit impressive fracture initiation toughness of 12.5 ± 1.5 MPa·m1/2 and flexural strength of 613 ± 52 MPa at room temperature, as well as ~97% strength retention up to 1300 °C due to their good high-temperature stability, surpassing the performance of most other reported bioinspired ceramics. Further experimental and theoretical investigations demonstrate that the Cr7C3 phase can undergo plastic deformation by forming nanoscale shear bands with significant crystal defects, resulting in multiple toughening mechanisms involving crack-bridging of unfractured Cr7C3 ligaments and crack deflection in the HEC/Cr7C3 all-ceramics. This work successfully develops tough and strong bioinspired high-entropy all-ceramics capable of serving up to 1300 °C, offering an innovative strategy that facilitates further design of bioinspired ceramics applicable at higher temperatures.

Enhancing the mechanical and antibacterial properties of hydroxyapatite bioceramics by in situ graphene doping to promote osseointegration in infected bone defects

Hydroxyapatite (HA) bioceramics are extensively utilized in the field of bone repair owing to their remarkable biocompatibility, bioactivity, and osteoconductivity. However, their applications in load-bearing bones are significantly limited because of their inherent brittleness. Achieving a suitable balance between mechanical strength and osteogenic activity remains a critical challenge. In this work, HA ceramics with in situ graphene doping were fabricated via ball-milling and vacuum sintering processes in a convenient way, thereby increasing their fracture toughness and flexural strength to the levels of natural cortical bone. Furthermore, in situ graphene doping imparted outstanding photothermal property to HA bioceramics, achieving wet temperatures exceeding 60 °C under near-infrared radiation at 808 nm and exhibiting excellent antibacterial efficacy with a bacteriostasis rate of approximately 96% against S. aureus. Additionally, HA bioceramics with in situ graphene doping promoted the proliferation and differentiation of bone marrow stem cells (BMSCs). The anti-infective capability and osseointegration potential of these doped HA bioceramics were further validated using an infected bone defect model in the rabbit femur. In summary, these findings indicate that in situ graphene doping holds immense potential for broadening the applications of HA bioceramics in the repair of load-bearing and infected bone defects.

Strong and weak interface synergistic enhance the mechanical and microwave absorption properties of alumina

Multifaceted balance makes the design of ceramics difficult but is urgently needed. This work purposes to grow uniform edge-rich graphene (ERG) on alumina (Al2O3/ERG) in-situ, then constructs a discontinuous conductive, strengthening and toughening network of crosslinked ERG by mixing Al2O3/ERG with Al2O3 and sintering. Under the guarantee of the tight-bound covalent interface, ERG and doping Al2O3 strengthen and toughen the ceramic by synergistic effect of weak and strong interface. And doping Al2O3 interrupts the conductive network of ERG to improve the impedance matching and endow material with moderate electromagnetic wave (EMW) loss capacity. The optimal flexural strength and fracture toughness of the composite ceramic reach 333.04 MPa and 12.43 MPa⋅m1/2, respectively. Meanwhile, it can absorb 80 % or more of the incident EMW in X-band with a matching thickness of 2 mm. This work takes full advantage of ERG to prepare load-bearing EMW absorbing ceramics, which expands the idea for material design.

Properties of a Dental Adhesive Containing Graphene and DOPA-Modified Graphene

Graphene is a promising biomaterial. However, its dispersion in aqueous medium is challenging. This study aimed to modify graphene nanoparticles with L-dopa to improve the properties of experimental dental adhesives. Adhesives were formulated with 0% (control), 0.25%, 0.5%, and 0.75% of graphene, modified or not. Particle modification and dispersion were microscopically assessed. Degree of conversion was tested by Fourier-transform infrared spectroscopy. Flexural strength and modulus of elasticity were evaluated by a 3-point flexural test. Bond strength was tested by shear. To test water sorption/solubility, samples were weighed during hydration and dehydration. Antibacterial activity was tested by Streptococcus mutans colony-forming units quantification. Cytotoxicity on fibroblasts was evaluated through a dentin barrier test. The modification of graphene improved the particle dispersion. Control presented the highest degree of conversion, flexural strength, and bond strength. In degree of conversion, 0.25% of groups were similar to control. In bond strength, groups of graphene modified by L-dopa were similar to Control. The modulus of elasticity was similar between groups. Cytotoxicity and water sorption/solubility decreased as particles increased. Compared to graphene, less graphene modified by L-dopa was needed to promote antibacterial activity. By modifying graphene with L-dopa, the properties of graphene and, therefore, the adhesives incorporated by it were enhanced.

Perspectives Toward Damage-Tolerant Nanostructure Ceramics

Advanced ceramic materials and devices call for better reliability and damage tolerance. In addition to their strong bonding nature, there are examples demonstrating superior mechanical properties of nanostructure ceramics, such as damage-tolerant ceramic aerogels that can withstand high deformation without cracking and local plasticity in dense nanocrystalline ceramics. The recent progresses shall be reviewed in this perspective article. Three topics including highly elastic nano-fibrous ceramic aerogels, load-bearing nanoceramics with improved mechanical properties, and implementing machine learning-assisted simulations toolbox in understanding the relationship among structure, deformation mechanisms, and microstructure-properties shall be discussed. It is hoped that the perspectives present here can help the discovery, synthesis, and processing of future structural ceramic materials that are insensitive to processing flaws and local damages in service.

Orientation of graphene nanosheets in suspension under an electric field: theoretical model and molecular dynamic simulations

Orientation regulation of nanoparticles in a suspension by an electric field is a powerful tool to tune its mechanical, thermal, optical, electrical properties etc. However, how molecular modification can affect the orientation of two-dimensional nanoparticles is still unclear. In this paper, the influence of molecular modification on the orientation of graphene nanosheets (GNS) in water was investigated through theoretical analyses and molecular dynamics (MD) simulations. Firstly, a new orientation angle model was proposed, which considers hydration effects, dipole moments and resistance torque. Then, MD simulations were conducted to investigate the effects of position, direction, type, and number of functional groups on the orientation of GNS. The trend observed in MD simulations is consistent with the proposed theoretical model. The results reveal that, under the combined influence of the dipole moment and hydration effects, the modification with hydrophilic functional groups can reduce the orientation angle from 21.31° to 8.34°, while the modification with hydrophobic functional groups increases it to 26.43°. Among the hydrophilic functional groups, orientation of hydroxylated GNS is the best. With an increase in the number of hydroxyl groups, orientation angle is decreased from 12.61° to 8.34°. This work can provide valuable guidance for the design of high-performance suspensions and composites, such as thermal smart materials with adjustable thermal conductivity and intelligent devices with tailored capabilities.

Nanograded artificial nacre with efficient energy dissipation

The renowned mechanical performance of biological ceramics can be attributed to their hierarchical structures, wherein structural features at the nanoscale play a crucial role. However, nanoscale features, such as nanogradients, have rarely been incorporated in biomimetic ceramics because of the challenges in simultaneously controlling the material structure at multiple length scales. Here, we report the fabrication of artificial nacre with graphene oxide nanogradients in its aragonite platelets through a matrix-directed mineralization method. The gradients are formed via the spontaneous accumulation of graphene oxide nanosheets on the surface of the platelets during the mineralization process, which then induces a lateral residual stress field in the platelets. Nanoindentation tests and mercury intrusion porosimetry demonstrate that the material's energy dissipation is enhanced both intrinsically and extrinsically through the compressive stress near the platelet surface. The energy dissipation density reaches 0.159 ± 0.007 nJ/μm3, and the toughness amplification is superior to that of the most advanced ceramics. Numerical simulations also agree with the finding that the stress field notably contributes to the overall energy dissipation. This work demonstrates that the energy dissipation of biomimetic ceramics can be further increased by integrating design principles spanning multiple scales. This strategy can be readily extended to the combinations of other structural models for the design and fabrication of structural ceramics with customized and optimized performance.

Review of two-dimensional nanomaterials in tribology: Recent developments, challenges and prospects

From our ordinary lives to various mechanical systems, friction and wear are often unavoidable phenomena that are heavily responsible for excessive expenditures of nonrenewable energy, the damages and failures of system movement components, as well as immense economic losses. Thus, achieving low friction and high anti-wear performance is critical for minimization of these adverse factors. Two-dimensional (2D) nanomaterials, including transition metal dichalcogenides, single elements, transition metal carbides, nitrides and carbonitrides, hexagonal boron nitride, and metal-organic frameworks have attracted remarkable interests in friction and wear reduction of various applications, owing to their atomic-thin planar morphologies and tribological potential. In this paper, we systematically review the current tribological progress on 2D nanomaterials when used as lubricant additives, reinforcement phases in the coatings and bulk materials, or a major component of superlubricity system. Additionally, the conclusions and prospects on 2D nanomaterials with the existing drawbacks, challenges and future direction in such tribological fields are briefly provided. Finally, we sincerely hope such a review will offer valuable lights for 2D nanomaterial-related researches dedicated on tribology in the future.

A review of recent advances and applications of machine learning in tribology

In tribology, a considerable number of computational and experimental approaches to understand the interfacial characteristics of material surfaces in motion and tribological behaviors of materials have been considered to date. Despite being useful in providing important insights on the tribological properties of a system, at different length scales, a vast amount of data generated from these state-of-the-art techniques remains underutilized due to lack of analysis methods or limitations of existing analysis techniques. In principle, this data can be used to address intractable tribological problems including structure-property relationships in tribological systems and efficient lubricant design in a cost and time effective manner with the aid of machine learning. Specifically, data-driven machine learning methods have shown potential in unraveling complicated processes through the development of structure-property/functionality relationships based on the collected data. For example, neural networks are incredibly effective in modeling non-linear correlations and identifying primary hidden patterns associated with these phenomena. Here we present several exemplary studies that have demonstrated the proficiency of machine learning in understanding these critical factors. A successful implementation of neural networks, supervised, and stochastic learning approaches in identifying structure-property relationships have shed light on how machine learning may be used in certain tribological applications. Moreover, ranging from the design of lubricants, composites, and experimental processes to studying fretting wear and frictional mechanism, machine learning has been embraced either independently or integrated with optimization algorithms by scientists to study tribology. Accordingly, this review aims at providing a perspective on the recent advances in the applications of machine learning in tribology. The review on referenced simulation approaches and subsequent applications of machine learning in experimental and computational tribology shall motivate researchers to introduce the revolutionary approach of machine learning in efficiently studying tribology.

Two-Dimensional FePS3 Nanosheets as an Integrative Sonosensitizer/Nanocatalyst for Efficient Nanodynamic Tumor Therapy

As the emerging modalities for tumor therapy, sonodynamic therapy (SDT) and chemodynamic therapy (CDT) can generate reactive oxygen species (ROS), typically inducing tumor cell apoptosis. However, the construction of more efficient sonosensitizers integrated with excellent Fenton/Fenton-like catalytic activity to improve the synergistic therapeutic effect of SDT and CDT is still highly challenging. In this study, 2D semiconductor FePS₃ nanosheets (NSs), as one of the metal phosphorus trichalcogenides for both sonosensitizer and Fenton catalyst, are successfully synthesized via an ultrasonic-assisted liquid phase exfoliation method from bulk FePS₃ and further modified with lipoic acid-polyethylene glycol (LA-PEG) to obtain FePS₃ -PEG NSs with desirable biocompatibility. The in vitro and in vivo results demonstrate that the engineered FePS₃ -PEG NSs induce the combinatorial SDT/CDT effect attributing to the enhanced ROS generation and significant glutathione depletion, which can conduct highly efficient and safe tumor inhibition and prolong the life span of tumor-bearing mice. This work provides the paradigm of semiconductor FePS₃ NSs as the integrative sonosensitizer/Fenton nanocatalyst for dual nanodynamic tumor therapy, paving the new way for exploring other 2D metal phosphorus trichalcogenides in biomedicine.

Recent advances in precursor-derived ceramics integrated with two-dimensional materials

This review focused on the recent advances in precursor-derived ceramics integrated with two-dimensional materials. Their fabrication methods, structures and applications were discussed in detail and the perspectives in this field were presented.

Recent advances in 2D graphene reinforced metal matrix composites

The unique combination of excellent mechanical and functional properties makes graphene an ideal component for high-performance 'smart' composites, which are sensitive to thermal, optical, electrical and mechanical excitations, hence being potential in application of a range of sensors. It has confirmed that the addition of graphene into metal matrix can significantly enhance the mechanical property and deliver surprising functional properties. Thus, graphene reinforced metal matrix composites (GMMCs) have long been regarded as potential prospects of nanotechnology applications. Recently, researchers mainly focused on: (i) solving the interfacial issues and realizing controllable alignment of graphene in metal matrix to achieve optimal performance; (ii) reasonable designing of the microstructures basing on usage requirement and then fabricating via efficient technique. Thus, it is necessary to figure out key roles of microstructure in fabrication process, mechanical and multi-functional properties. This review consists of four parts: (i) fabrication process. The fabrication processes are firstly divided into three kinds basing on the different bonding nature between graphene and metal matrix. (ii) Mechanical property. The microstructural characteristics of metal matrix accompanying by the incorporation of graphene and their vital effects on mechanical properties of GMMCs are systematically summarized. (iii) Functional property. The crucial effects of microstructure on electrical and thermal properties are summarized. (iv) Prospect applications and future challenges. Application and challenges basing on the research status are discussed to provide useful directions for future exploration in related fields. All these four parts are discussed with a focus on key role of microstructure characteristics, which is instructive for the microstructures design and fabrication process optimization during academic researches and potential commercial applications.

Designing New-Generation Piezoelectric Transducers by Embedding Superior Graphene-Based Thermal Regulators

Cascaded-piezoelectric-transducers (CPETs) is a key component in modern energy-conversion fields, possessing versatile applications in ultrasonic scalpels, acoustic levitation, and sonar. However, serious self-heating inevitably occurs inside high-power CPETs, severely limiting their practical applications in broader fields. To tackle this, multidirectional heat-escape channels of multidimensional (multi-D, 3D/2D) graphene films are introduced in designing new-type thermal regulators. A porous AlN-ceramic thermal-sink is creatively selected as a template for directly synthesizing graphene via a two-step chemical vapor deposition strategy. This perfect combination of 3D/2D-graphene and the AlN ceramic can integrate their complementary advantages in uniformizing, transmitting, and releasing heat. Amazingly, in the new-generation CPETs embedded with these graphene-based thermal regulators, the self-heating-induced temperature rise can be substantially reduced by ≈60% (far exceeding actual demand standard). As another kernel parameter, electroacoustic-energy-conversion efficiency is dramatically improved in the new-generation CPETs. Briefly, this research realizes the first synthesis of a novel multi-D-graphene/AlN-ceramic hybrid, and propels its brand-new application directions in new-generation energy-conversion- and thermal-management-related territories.

Edge-Rich Reduced Graphene Oxide Embedded in Silica-Based Laminated Ceramic Composites for Efficient and Robust Electrocatalytic Hydrogen Evolution

To mitigate the energy crisis and environmental pollution, efficient and earth-abundant hydrogen evolution reaction (HER) electrocatalysts are essential for hydrogen production through electrochemical water splitting. Graphene-based materials as metal-free catalysts have attracted significant attention but suffer from insufficient activity and stability. Therefore, a novel and economical approach is developed to prepare highly active, robust, and self-supported reduced graphene oxide (rGO)/SiO₂ ceramic composites as electrocatalysts in HER. Through intercalation and pressure sintering, the rGO sheets are parallelly aligned and embedded into a dense and chemically inert SiO₂ matrix, ensuring the electrical conductivity and stability of the prepared composites. After directional cutting, the edges of the oriented rGO sheets become fully exposed on the composite surface, acting as highly electrocatalytic active sites in HER, as confirmed by density functional theory calculations. The 4 vol% rGO/SiO₂ composite displays superior electrocatalytic performance, featuring a low overpotential (134 mV) at a current density of 10 mA cm^-2 , a small Tafel slope (103 mV dec^-1 ), and excellent catalytic durability in 0.5 m H₂ SO₄ . This study provides a new yet cost-effective strategy to prepare metal-free, robust, and edge-rich rGO/ceramic composites as a highly electrocatalytic active catalyst for HER applications.

Anomalous Loss of Stiffness with Increasing Reinforcement in a Photo-Activated Nanocomposite

Hydrogels are commonly doped with stiff nanoscale fillers to endow them with the strength and stiffness needed for engineering applications. Although structure-property relations for many polymer matrix nanocomposites are well established, modeling the new generation of hydrogel nanocomposites requires the study of processing-structure-property relationships because subtle differences in chemical kinetics during their synthesis can cause nearly identical hydrogels to have dramatically different mechanical properties. The authors therefore assembled a framework to relate synthesis conditions (including hydrogel and nanofiller mechanical properties and light absorbance) to gelation kinetics and mechanical properties. They validated the model against experiments on a graphene oxide (GO) doped oligo (ethylene glycol) diacrylate (OEGDA), a system in which, in apparent violation of laws from continuum mechanics, doping can reduce rather than increase the stiffness of the resulting hydrogel nanocomposites. Both model and experiment showed a key role light absorbance-dominated gelation kinetics in determining nanocomposite mechanical properties in conjunction with nanofiller reinforcement, with the nanofiller's attenuation of chemical kinetics sometimes outweighing stiffening effects to explain the observed, anomalous loss of stiffness. By bridging the chemical kinetics and mechanics of nanocomposite hydrogels, the authors' modeling framework shows promise for broad applicability to design of hydrogel nanocomposites.