Mechanical Properties of Silicon Carbide Composites Reinforced with Reduced Graphene Oxide.

This article presents research on the influence of reduced graphene oxide on the mechanical properties of silicon carbide matrix composites sintered with the use of the Spark Plasma Sintering method. The produced sinters were subjected to a three-point bending test. An increase in flexural strength was observed, which reaches a maximum value of 503.8 MPa for SiC-2 wt.% rGO composite in comparison to 323 MPa for the reference SiC sample. The hardness of composites decreases with the increase in rGO content down to 1475 HV10, which is correlated with density results. Measured fracture toughness values are burdened with a high standard deviation due to the presence of rGO agglomerates. The KIC reaches values in the range of 3.22-3.82 MPa*m1/2. Three main mechanisms responsible for the increase in the fracture toughness of composites were identified: bridging, deflecting, and branching of cracks. Obtained results show that reduced graphene oxide can be used as a reinforcing phase to the SiC matrix, with an especially visible impact on flexural strength.

Effect of Anisotropy of Reduced Graphene Oxide on Thermal and Electrical Properties in Silicon Carbide Matrix Composites.

Reduced graphene oxide, due to its structure, exhibits anisotropic properties, which are particularly evident in electrical and thermal conductivity. This study focuses on examining the influence of reduced graphene oxide in silicon carbide on these properties in directions perpendicular and parallel to the direction of the aligned rGO flakes in produced composites. Reduced graphene oxide is characterized by very high in-plane thermal and electrical conductivity. It was observed that the addition of rGO increases thermal conductivity from 64 W/mK (reference sample) up to 98 W/mK for a SiC-3 wt.% rGO composite in the direction parallel to the rGO flakes. In the perpendicular direction, the values were slightly lower, reaching up to 84 W/mK. The difference observed in electrical conductivity values is more significant and is 1-2 orders of magnitude higher for the flakes' alignment direction. The measured electrical conductivity increased from 1.2710-8 S/m for the reference SiC sinter up to 1.55 × 10-5 S/m and 1.2410-4 S/m for the composites with 3 wt.% rGO for the perpendicular and parallel directions, respectively. This represents an enhancement of four orders of magnitude, with a clearly visible influence of the anisotropy of the rGO. The composite's enhanced electrical and thermal conductivity make it particularly attractive for electronic devices and high-power applications.

Synthesis of Ti3SiC2 Phases and Consolidation of MAX/SiC Composites-Microstructure and Mechanical Properties.

The article describes the Ti3SiC2 powder synthesis process. The influence of the molar ratio and two forms of carbon on the phase composition of the obtained powders was investigated. The synthesis was carried out using a spark plasma sintering (SPS) furnace. In addition, using the obtained powders, composites reinforced with SiC particles were produced. The obtained results showed no effect of the carbon form and a significant impact of annealing on the purity of the powders after synthesis. The composites were also consolidated using an SPS furnace at two temperatures of 1300 and 1400 °C. The tests showed low density and hardness for sinters from 1300 °C (maximum 3.97 g/cm3 and 447 HV5, respectively, for composite reinforced with 10% SiC). These parameters significantly increase for composites sintered at 1400 °C (maximum density 4.43 g/cm3 and hardness 1153 HV5, for Ti3AlC2-10% SiC). In addition, the crack propagation analysis showed mechanisms typical for granular materials and laminates.

Novel Alumina Matrix Composites Reinforced with MAX Phases-Microstructure Analysis and Mechanical Properties.

This article describes the manufacturing of alumina composites with the addition of titanium aluminum carbide Ti3AlC2, known as MAX phases. The composites were obtained by the powder metallurgy technique with three types of mill (horizontal mill, attritor mill, and planetary mill), and were consolidated with the use of the Spark Plasma Sintering method at 1400 °C, with dwelling time 10 min. The influence of the Ti3AlC2 MAX phase addition on the microstructure and mechanical properties of the obtained composites was analyzed. The structure of the MAX phase after the sintering process was also investigated. The chemical composition and phase composition analysis showed that the Ti3AlC2 addition preserved its structure after the sintering process. The increase in fracture toughness for all series of composites has been noted (over 20% compared to reference samples). Detailed stereological analysis of the obtained microstructures also could determine the influence of the applied mill on the homogeneity of the final microstructure and the properties of obtained composites.

Cytotoxicity and Antibacterial Activity of Mineral Trioxide Aggregate Cement with Radiopacity Introduced by ZrO2.

The article presents the results of in vitro studies on cytotoxicity and antibacterial activity of new MTA-type cements, developed on the basis of the sintered tricalcium silicate enriched with ZnO, along with an agent introducing the radiopacity in the form of ZrO2. The new materials have been developed to ensure that their physical and chemical properties are suited for endodontic applications. The cements were evaluated via characterisation of setting time, compressive strength, as well as translucency on X-ray images, and bioactivity in the simulated body fluid (SBF). The µCT was used to test the influence of the ZrO2 grains in the powder component on the microstructure of the produced cement. Then, the cytotoxic action of the cements was evaluated by applying a reference L-929 cell line. The conditions of the culture upon contact with the tested materials or with extracts from the cements were assessed using image analysis or an MTT colorimetric assay. Two strains of streptococci, Streptococcus mutans and Streptococcus sanguinis, were used to study the antibacterial activity of the tested cements with ZrO2 acting as the agent introducing the radiopacity. The new cements are characterised by appropriate properties as far as retrograde root canal filling is concerned.

Modelling and Characterisation of Residual Stress of SiC-Ti3C2Tx MXene Composites Sintered via Spark Plasma Sintering Method.

This article presents an attempt to determine the effect of the MXene phase addition and its decomposition during sintering with the use of the spark plasma sintering method on mechanical properties and residual stress of silicon carbide based composites. For this purpose, the unreinforced silicon carbide sinter and the silicon carbide composite with the addition of 2 wt.% of Ti3C2Tx were tested. The results showed a significant increase of fracture toughness and hardness for composite, respectively 36% and 13%. The numerical study involving this novel method of modelling shows the presence of a complex state of stress in the material, which is related to the anisotropic properties of graphitic carbon structures formed during sintering. An attempt to determine the actual values of residual stress in the tested materials using Raman spectroscopy was also made. These tests showed a good correlation with the constructed numerical model and confirmed the presence of a complex state of residual stress.

The 10th anniversary of MXenes: Challenges and prospects for their surface modification toward future biotechnological applications.

A broad family of two-dimensional (2D) materials - carbides, nitrides, and carbonitrides of early transition metals, called MXenes, became a newcomer in the flatland at the turn of 2010 and 2011 (over ten years ago). Their unique physicochemical properties made them attractive for many applications, highly boosting the development of various fields, including biotechnological. However, MXenes' functional features that impact their bioactivity and toxicity are still not fully well understood. This study discusses the essentials for MXenes's surface modifications toward their application in modern biotechnology and nanomedicine. We survey modification strategies in context of cytotoxicity, biocompatibility, and most prospective applications ready to implement in medical practice. We put the discussion on the material-structure-chemistry-property relationship into perspective and concentrate on overarching challenges regarding incorporating MXenes into nanostructured organic/inorganic bioactive architectures. It is another emerging group of materials that are interesting from the biomedical point of view as well. Finally, we present an influential outlook on the growing demand for future research in this field.

Use of Post-Flotation Solidified Tailings from Copper Production for Ceramic Tile Production.

The development of the mining industry has resulted in the accumulation of large amounts of waste, which effectively degrades the environment. The aim of this study is to check whether the addition of post-flotation sludge from copper production to the typical ceramic mass of the "gress porcelanato" will allow to obtain qualified sintered or faience tiles. By adding successive amounts of post-flotation sludge to the high-quality lamellar mass, typical parameters such as firing shrinkage, water absorbability and bending strength after firing were assessed. The structure of the obtained ceramic materials, using scanning electron microscopy (SEM with EDS), was also determined. Obtaining positive results would allow not only to significantly reduce the production costs of ceramic tiles, because the sludge is finely divided and no grinding is necessary, but, above all, will allow to eliminate the environmental risk. The present study has shown that it is possible to introduce up to 20% post-flotation sludge for gres porcellanato tile production and up to 50% post-flotation slugde for faience tile production. Both types of ceramic materials with an appropriate proportion of sludge, meet the requirements of tile standards in terms of mechanical strength and water absorption.

Investigation of MXenes Oxidation Process during SPS Method Annealing.

This paper discusses the effects of the environment and temperature of the Ti3C2 (MXene) oxidation process. The MXene powders were annealed at temperatures of 1000, 1200, 1400, 1600, and 1800 °C in argon and vacuum using a Spark Plasma Sintering (SPS) furnace. The purpose of the applied annealing method was to determine the influence of a high heating rate on the MXene degradation scheme. Additionally, to determine the thermal stability of MXene during the sintering of SiC matrix composites, SiC-C-B-Ti3C2 powder mixtures were also annealed. The process parameters were as follows: Temperatures of 1400 and 1600 °C, and pressure of 30 MPa in a vacuum. Observations of the microstructure showed that, due to annealing of the SiC-C-B-Ti3C2 powder mixtures, porous particles are formed consisting of TiC, Ti3C2sym, and amorphous carbon. The formation of porous particles is a transitional stage in the formation of disordered carbon structures.

Influence of Ti3C2Tx MXene and Surface-Modified Ti3C2Tx MXene Addition on Microstructure and Mechanical Properties of Silicon Carbide Composites Sintered via Spark Plasma Sintering Method.

This article presents new findings related to the problem of the introduction of MXene phases into the silicon carbide matrix. The addition of MXene phases, as shown by the latest research, can significantly improve the mechanical properties of silicon carbide, including fracture toughness. Low fracture toughness is one of the main disadvantages that significantly limit its use. As a part of the experiment, two series of composites were produced with the addition of 2D-Ti3C2Tx MXene and 2D-Ti3C2Tx surface-modified MXene with the use of the sol-gel method with a mixture of Y2O3/Al2O3 oxides. The composites were obtained with the powder metallurgy technique and sintered with the Spark Plasma Sintering method at 1900 °C. The effect adding MXene phases had on the mechanical properties and microstructure of the produced sinters was investigated. Moreover, the influence of the performed surface modification on changes in the properties of the produced composites was determined. The analysis of the obtained results showed that during sintering, the MXene phases oxidize with the formation of carbon flakes playing the role of reinforcement. The influence of the Y2O3/Al2O3 layer on the structure of carbon flakes and the higher quality of the interface was also demonstrated. This was reflected in the higher mechanical properties of composites with the addition of modified Ti3C2Tx. Composites with 1 wt.% addition of Ti3C2Tx M are characterized with a fracture toughness of 5 MPa × m0.5, which is over 50% higher than in the case of the reference sample and over 15% higher than for the composite with 2.5 wt.% addition of Ti3C2Tx, which showed the highest fracture toughness in this series.

Microstructure and Mechanical Properties of Alumina Composites with Addition of Structurally Modified 2D Ti3C2 (MXene) Phase.

This study presents new findings related to the incorporation of MXene phases into ceramic. Aluminium oxide and synthesised Ti3C2 were utilised as starting materials. Knowing the tendency of MXenes to oxidation and degradation, particularly at higher temperatures, structural modifications were proposed. They consisted of creating the metallic layer on the Ti3C2, by sputtering the titanium or molybdenum. To prepare the composites, powder metallurgy and spark plasma sintering (SPS) techniques were adopted. In order to evaluate the effectiveness of the applied modifications, the emphasis of the research was placed on microstructural analysis. In addition, the mechanical properties of the obtained sinters were examined. Observations revealed significant changes in the MXenes degradation process, from porous areas with TiC particles (for unmodified Ti3C2), to in situ creation of graphitic carbon (in the case of Ti3C2-Ti/Mo). Moreover, the fracture changed from purely intergranular to cracking with high participation of transgranular mode, analogously. In addition, the results obtained showed an improvement in the mechanical properties for composites with Ti/Mo modifications (an increase of 10% and 15% in hardness and fracture toughness respectively, for specimens with 0.5 wt.% Ti3C2-Mo). For unmodified Ti3C2, enormously cracked areas with spatters emerged during tests, making the measurements impossible to perform.

Influence of MXene (Ti3C2) Phase Addition on the Microstructure and Mechanical Properties of Silicon Nitride Ceramics.

This paper discusses the influence of Ti3C2 (MXene) addition on silicon nitride and its impact on the microstructure and mechanical properties of the latter. Composites were prepared through powder processing and sintered using the spark plasma sintering (SPS) technic. Relative density, hardness and fracture toughness, were analyzed. The highest fracture toughness at 5.3 MPa·m1/2 and the highest hardness at HV5 2217 were achieved for 0.7 and 2 wt.% Ti3C2, respectively. Moreover, the formation of the Si2N2O phase was observed as a result of both the MXene addition and the preservation of the α-Si3N4→ß-Si3N4 phase transformation during the sintering process.

Future Applications of MXenes in Biotechnology, Nanomedicine, and Sensors.

The past few years have seen significant developments in the chemistry and potential biological applications of 2D materials. This review focuses on recent advances in the biotechnological and biomedical applications of MXenes, which are 2D carbides, nitrides, and carbonitrides of transition metals. Nanomaterials based on MXenes can be used as therapeutics for anticancer treatment, in photothermal therapy as drug delivery platforms, or as nanodrugs without any additional modification. Furthermore, we discuss the potential use of these materials in biosensing and bioimaging, including magnetic resonance and photoacoustic imaging techniques. Finally, we present the most significant examples of the use of MXenes as efficient agents for environmental and antimicrobial treatments, as well as a brief discussion of their future prospects and challenges.

Ti2C MXene Modified with Ceramic Oxide and Noble Metal Nanoparticles: Synthesis, Morphostructural Properties, and High Photocatalytic Activity.

Among two-dimensional (2D) materials, such as graphene, a new family of 2D anisotropic carbides and nitrides of early transition metals (MXenes) is very interesting because of the potential applications in electronics, medicine, and photocatalysis. In this paper, preparation, morphostructural characterization, band gaps determination, and salicylic acid photodegradation ability of Ti2C MXene and six nanocomposites consisting of the MXene modified by TiO2, Ag2O, Ag, PdO, Pd, and Au are reported. It was confirmed using electron diffraction studies, energy dispersive X-ray spectroscopy, and high-resolution transmission microscopy that metals and metal oxides occur on the MXene flakes as nanoparticles in a shape of spots. The band gaps determined experimentally using Tauc's method are placed in the region of 0.90-1.31 eV. In recent years, the method of photocatalytic decomposition of pollutants using semiconductor photocatalysts and UV-vis energy has become increasingly important. The MXene based nanocomposites revealed high activity in the salicylic acid (SA) photodegradation reaction (86.1-97.1% of degraded SA after 3 h, concentration of SA initial solution 100 µM, the circulation rate of the SA solution 0.875 cm3/min). The interfacial charge transfer mechanism and the role of the metallic and metal oxide nanoparticles in the photocatalytic activity of the MXene based nanocomposites are presented and discussed.

2D Ti2C (MXene) as a novel highly efficient and selective agent for photothermal therapy.

Photothermal therapy (PTT) has shown significant potential for anti-cancer modality. In this report, according to our best knowledge, we explore for the first time Ti2C-based MXene as a novel, highly efficient and selective agent for photothermal therapy (PTT). Ti2C superficially modified with PEG was obtained from the layered, commercially available Ti2AlC MAX phase in the process of etching aluminum layers using concentrated HF, and characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HREM) as well as X-ray photoelectron spectroscopy for chemical analysis (ESCA-XPS). The PEG-coated Ti2C flakes showed a satisfactory photothermal conversion efficacy (PTCE) and good biocompatibility in wide range of the tested concentrations. Through in vitro studies, the PEG-modified Ti2C demonstrated notable NIR-induced ability to cancerous cells' ablation with minimal impact on non-malignant cells up to the concentration of 37.5 µg mL-1. The applied doses of Ti2C_PEG in our work were even 24 times lower comparing other MXene-based photothermal agents. This work is expected to expand the utility of 2D MXenes to biomedical applications through the development of entirely novel agents for photothermal therapy. This work is expected to expand the utility of 2D MXenes to biomedical applications through the development of entirely novel agents for photothermal therapy.

Closed Die Upsetting of Aluminum Matrix Composites Reinforced with Molybdenum Disulfide Nanocrystals and Multilayer Graphene, Implemented using the SPS Process-Microstructure Evolution.

New methods for producing composite materials such as SPS (Spark Plasma Sintering) are becoming more and more popular due to the ease of implementation in industrial conditions and the versatility of the materials used for processing. In order to fully exploit the potential of this method, modifications were proposed which consisted in the deliberate induction of deformation during the sintering process. The influence of the manufacturing method on the microstructure of aluminum alloy matrix composites reinforced with layered crystals in the form of nanoflakes was investigated. Composites with the addition of 10 vol % of multilayer graphene and molybdenum disulfide were prepared and their density, hardness, and the influence of the deformation ratio on the changes occurring in the microstructure were examined. The potential of the method to shape the properties of the tested composites and the strong dependence of the obtained results on the morphology of the reinforcing phase was indicated. An interesting phenomenon observed for composites with the addition of MoS2 during the process was the reaction of the components leading to in situ formation of the Al12Mo intermetallic phase.

Tribological Properties of Aluminium Alloy Composites Reinforced with Multi-Layer Graphene-The Influence of Spark Plasma Texturing Process.

Self-lubricating composites are designed to obtain materials that reduce energy consumption, improve heat dissipation between moving bodies, and eliminate the need for external lubricants. The use of a solid lubricant in bulk composite material always involves a significant reduction in its mechanical properties, which is usually not an optimal solution. The growing interest in multilayer graphene (MLG), characterised by interesting properties as a component of composites, encouraged the authors to use it as an alternative solid lubricant in aluminium matrix composites instead of graphite. Aluminium alloy 6061 matrix composite reinforced with 2-15 vol % of MLG were synthesised by the spark plasma sintering process (SPS) and its modification, spark plasma texturing (SPT), involving deformation of the pre-sintered body in a larger diameter matrix. It was found that the application of the SPT method improves the density and hardness of the composites, resulting in improved tribological properties, particularly in the higher load regime.

Recent advances in graphene family materials toxicity investigations.

Recently, graphene family materials (GFMs) have been introduced among all fields of science and still get numerous attention. Also, the applicability of these materials in many areas makes them very attractive. GFMs have attracted both academic and industrial interest as they can produce a dramatic improvement in materials properties at very low filler content. This article presents recent findings on GFMs toxicity properties based on the most current literature. This article studies the effects of GFMs on bacteria, mammalian cells, animals, and plants. This article also reviews in vitro and in vivo test results as well as potential anticancer activity and toxicity mechanisms of GFMs. The effect of functionalization of graphene on pacifying its strong interactions with cells and associated toxic effects was also analyzed. The authors of the article believe that further work should focus on in vitro and in vivo studies on possible interactions between GFMs and different living systems. Further research should also focus on decreasing GFMs toxicity, which still poses a great challenge for in vivo biomedical applications. Consequently, the potential impact of graphene and its derivatives on humans and environmental health is a matter of academic interest. However, potential hazards sufficient for risk assessment first need to be investigated.

Covalent binding of sensor phases--a recipe for stable potentials of solid-state ion-selective sensors.

In this work, a new concept of the solid-state sensors free from EMF instabilities is proposed. In order to prevent the formation of an aqueous layer underneath the ion-selective membrane, instead of improving the hydrophobicity of the monolayer, the moieties terminated with acrylate groups were incorporated within the redox-active monolayer structure. It allowed to "sew" all phases of the sensor (i.e., the transducer, the intermediate layer and the ion-selective membrane) and to obtain a stable and durable ion-selective sensor. It is shown that newly designed monolayer containing both the ferrocene- and the acrylate-terminated molecules does not affect the working parameters of the electrode, such as selectivity or the slope of the calibration curve, although the EMF drift of the sensor is significantly reduced to 0.2 mV per day.