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Publications (90)
MXenes exhibits remarkable electrical, mechanical, and thermal properties, positioning them as strong candidates for high-performance electrodes and interconnects. Deposited 2D MXene thin-films suffer from a persistent issue of crystalline salt...
Platinum (Pt)‐based electrocatalysts are considered benchmark materials for the hydrogen evolution reaction (HER) in acidic solution. However, widespread use is limited by the high price of Pt. Tuning the Pt morphology to increase the catalytic surface area for the same mass loading is therefore essential to increase its utilization. Herein, single...
This study reveals that MAX phase materials can exhibit extraordinary reactivity when subjected to impact loading. This previously unknown behavior was discovered and examined in a case study of Ti 3 SiC 2 subjected to Split Hopkinson pressure bar (SHPB) testing. The employed methodology integrated SHPB coupled with thermal measurements and ex-situ...
Herein, the isothermal oxidation of Mn2AlB2 and Fe2AlB2 MAB phases in air was studied. When oxidized at 700 ◦C, the weight gain kinetics for Mn2AlB2 are sub-cubic up to 96 h as a result of the formation of a Mn2-xAlxO3 protective layer. Severe spallation of the oxides formed was observed at 800 ◦C and 900 ◦C, limiting its service temperature. The o...
A distinguishing feature of MAX phases and their MXene derivatives is their remarkable chemical diversity. This diversity, coupled with the 2D nature of MXenes, positions them as outstanding candidates for a wide range of electrochemical applications. Chemical disorder introduced by a solid solution can improve electrochemical behavior. Up to now,...
Despite its disordered liquid-like structure, glass exhibits solid-like mechanical properties¹. The formation of glassy material occurs by vitrification, preventing crystallization and promoting an amorphous structure². Glass is fundamental in diverse fields of materials science, owing to its unique optical, chemical and mechanical properties as we...
2D materials are emerging as promising nanomaterials for applications in energy storage and catalysis. In the wet chemical synthesis of MXenes, these 2D transition metal carbides and nitrides are terminated with a variety of functional groups, and cations such as Li+ are often used to intercalate into the structure to obtain exfoliated nanosheets....
One of the distinguishing features of MAX phases and their MXene derivatives is their remarkable chemical diversity. This diversity, coupled with the two-dimensional nature of MXenes, positions them as outstanding candidates for a wide range of electrochemical applications. In this study, we report the synthesis of M site T1-xWx solid solution MAX...
Wearable pressure sensors have become increasingly popular for personal healthcare and motion detection applications due to recent advances in materials science and functional nanomaterials. In this study, a novel composite hydrogel is presented as a sensitive piezoresistive sensor that can be utilized for various biomedical applications, such as w...
Optical transparency is of paramount importance for visual armor and certain optical devices when subjected to severe impact conditions. Shock wave loading not only generates high pressure during hypervelocity impacts but also diminishes optical transmittance. To investigate optical transparency of transparent polycrystalline ceramic under harsh sh...
MXenes are a family of 2D transition metal carbides and nitrides with remarkable properties and great potential for energy storage and catalysis applications. However, their oxidation behavior is not yet fully understood, and there are still open questions regarding the spatial distribution and precise quantification of surface terminations, interc...
MXenes have gained significant attention, particularly Ti3C2Tz, as materials with favorable properties for energy storage and conversion applications. The overwhelming majority of electrochemical durability studies are based on durability in the hydrogen evolution window, well below the reversible hydrogen electrode where degradation via electroche...
MgAl2O4 is a versatile and stable oxide that is useful in various applications. However, the presence of impurities originating as a part of the powder synthesis process can potentially impair desired properties. In this work, we performed acidic treatments with mixtures of HNO3 and H2SO4 on commercial MgAl2O4 nanopowders. The treated powder struct...
Alumina forming, oxidation and thermal shock resistant MAX phases are of high interest for high temperature applications. Herein we report on the fabrication of a highly textured Ti2AlC MAX phase and its creep behavior. Creep rates were measured in the temperature range of 1000–1150 °C under a tensile stress range of 15–50 MPa. The minimum creep ra...
Spark plasma sintering (SPS) is an advanced pressure-assisted sintering technology that combines the application of uniaxial pressure with rapid current-induced heating. The so-called high-pressure SPS (HPSPS) approach involves using specialized tooling made of robust materials that can withstand high pressures and temperatures simultaneously. The...
MXenes are a family of 2D transition metal carbides and nitrides with remarkable properties and great potential for energy storage and catalysis applications. However, their oxidation behavior is not yet fully understood, and there are still open questions regarding the spatial distribution and precise quantification of surface terminations, interc...
2D metal carbides and nitrides (MXene) are promising materials platform for on‐chip neural networks owning to their nonlinear saturable absorption effect. The localized surface plasmon resonances in metallic MXene nanoflakes may play an important role in enhancing the electromagnetic absorption; however, their contribution has not been determined d...
Herein the isothermal oxidation of the Mn2AlB2 and Fe2AlB2 MAB phases in air was studied. When oxidized at 700 °C, the weight gain kinetics for Mn2AlB2 are sub-cubic up to 96 h are sub-cubic up to 96 h as a result of the formation of Mn2-xAlxO3 layer. At 800 °C and 900 °C severe spallation of the oxides was observed limiting its service temperature...
The emerging need for green technologies motivates the development of new approaches to manufacture electronic consumables. In case of low-cost mass-production sensors, the problem becomes even more severe due to the generation of environmental waste. Here we demonstrate an RFID-type sensor based on a caramel substrate with a micron-scale conductiv...
As MXenes become increasingly widespread, approaches to utilize this versatile class of 2D materials are sought. Recently, there has been growing interest in incorporating MXenes into metal or ceramic matrices to create advanced nanocomposites. This study presents a facile approach of mixing MXene with ceramic particles followed by pressure-assiste...
Practicality of lithium-sulfur batteries is severely hindered by the notorious polysulfide-shuttle phenomenon, leading to rapid capacity fade. This issue is aggravated with increase in sulfur loading, causing low-coulombic efficiency and cycle life. Herein, we present a facile strategy to combine hydrophobic sulfur and hydrophilic , conductive Ti 3...
Room temperature alkali metal - sulfur batteries are promising alternatives to lithium-ion batteries due to their high capacity and low inherent cost. Herein we report MXene (Ti3C2Tx) as a host to confine sulfur (S8) enabling the use of commercialization-friendly carbonate electrolyte in metal-sulfur batteries. The multilayer MXene structure provid...
The atomically laminated Ti2AlC, Ti3AlC2 and Cr2AlC MAX phases, with A = Al, form adherent, passivating α-alumina, Al2O3, oxide scales when heated in air. The effect of solid solutions on the A layers in affecting the oxidation kinetics remains a subject of open research. Herein we synthesize a dense bulk polycrystalline Ti3Al1−xGaxC2 (x ≈ 0.4) sol...
Neural networks are one of the first major milestones in developing artificial intelligence systems. The utilisation of integrated photonics in neural networks offers a promising alternative approach to microelectronic and hybrid optical-electronic implementations due to improvements in computational speed and low energy consumption in machine-lear...
Practicality of lithium-sulfur batteries is severely hindered by the notorious polysulfide-shuttle phenomenon, leading to rapid capacity fade. This issue is aggravated with increase in sulfur loading, causing low-coulombic efficiency and cycle life. Herein, we present a facile strategy to combine hydrophobic sulfur and hydrophilic, conductive Ti3C2...
Lithium-Sulfur batteries are of great interest owing to sulfur's high theoretical capacity, low-cost and environmental benignity. However, the practicality of these batteries has been impeded due to the infamous “polysulfide-shuttle” effect. Although several research articles in the past decade have focused to mitigate this effect, capacity fade an...
Efficient water splitting for commercial electrolysis devices is predicated on the development of materials, specifically for the catalytic electrodes, that exhibit an optimal balance between activity and stability. Complicating the development of electrocatalytic materials, particularly for oxygen-evolving anodes in acidic polymer electrolyte memb...
The MAX phases comprise of a group of layered ternary carbides that exhibit unique mechanical properties which bridge the gap between their metal and ceramic constituents. To study the effects of the global grain orientation, Ti, Si and TiC powders were hot pressed to synthesize highly oriented bulk Ti3SiC2. X-ray diffraction (XRD) was used to veri...
Recently, a new family of MAX phases with in-plane chemical order, i-MAX, have been discovered which incorporate new elements expanding the family of MAX phases. i-MAX phases remain to be synthesized in single-phase bulk form for characterization. Herein, we show that by reactively hot pressing an intermetallic precursor, Y2.23Al, instead of elemen...
Quaternary MAX phases, (Ta1-xTix)3AlC2 (x = 0.4, 0.62, 0.75, 0.91 or 0.95), have been synthesised via pressureless sintering of TaC, TiC, Ti and Al powders. Via chemical etching of the Al layers, (Ta0.38 Ti0.62)3C2Tz - a new MXene, has also been synthesised. All materials contain an M-layer solid solution of Ta and Ti, with a variable Ta concentrat...
MXene is a recently discovered family of two-dimensional transition metal carbides, nitrides and carbonitrides that have shown a lot of promise in the field of energy storage with applications ranging from high capacity anodes for lithium, sodium, potassium and aluminum ion batteries, supercapacitors and catalysts for hydrogen evolution, among seve...
The thermal stability and decomposition mechanisms of Fe2AlB2 powders, synthesized by reactive powder metallurgy, were studied under nitrogen (N2) or argon (Ar) atmospheres. The effects of using different FeB precursors to synthesize the Fe2AlB2 and hydrochloric acid (HCl) purification treatments on the thermal stability were also investigated. Whe...
Herein we topotactically reacted sulphur, S, with Mo2CTx MXene powders to synthesize Mo2CTx sheets covered by MoS2 nanosheets and tested the resulting material as a hydrogen evolution reaction, HER, electrocatalyst. As a result, a high electrochemical active surface area catalyst was obtained. It allows driving a current density of 10 mA cm-2 at a...
In this work, we investigate the magnetic structures of (Fe1−xMnx)2AlB2 solid-solution quaternaries in the x=0 to 1 range using x-ray and neutron diffraction, magnetization measurements, and mean-field theory calculations. While Fe2AlB2 and Mn2AlB2 are known to be ferromagnetic (FM) and antiferromagnetic (AFM), respectively, herein we focused on th...
In this work, we investigate the magnetic structures of $(Fe_{1-x}Mn_x)_2AlB_2$ solid-solution quaternaries in the $x$ = 0 to 1 range using X-ray and neutron diffraction, magnetization measurements, and mean field theory calculations. While $Fe_2AlB_2$ and $Mn_2AlB_2$ are known to be ferromagnetic (FM) and antiferromagnetic (AFM), respectively, her...
To date, MXene dispersions have been mostly limited to polar solvents. Here, we show that when the lithium cations present between MXene multilayers after etching are exchanged with di(hydrogenated tallow)benzyl methyl ammonium chloride (DHT), they become organophilic and form highly stable colloidal suspensions in nonpolar solvents. The rapid cati...
Herein we report on the phases and microstructures obtained when Ni and commercial Ti2AlC powder mixtures - with Ti2AlC molar fractions of 0.1, 0.5 and 0.64 – are hot pressed (HPed) at 1050 °C for 2 h at a stress of 36 MPa in a vacuum hot press and then further annealed either at 1200 °C for 16 h or at 1350 °C for 16 h under the protection of high...
The first MXene discovered, Ti3C2Tz, was synthesized by etching of the parent MAX phase, Ti3AlC2, in a solution of concentrated hydrofluoric acid. Since then, several other ways of synthesizing MXenes have been reported, such as electrochemical etching in various electrolytes, high-temperature alkali treatment, molten salt synthesis, etc. The major...
Contrary to the characteristic strengthening of polycrystalline ceramics with a decrease in grain size, extremely fine nanocrystalline ceramics exhibit softening, increased plasticity and an inverse Hall-Petch relation. Despite experimental evidence, questions remain regarding the underlying deformation mechanisms governing this abnormal mechanical...
Herein, we present the fabrication of dispersed, 5.0 wt % (1.74 vol %) Ti3C2T
z
MXene epoxy nanocomposites (NCs), and report on their water transport and mechanical properties. To make the composites, Li+ ions between Ti3C2T
z
MXene multilayers, MLs, present after the etching step were exchanged with either 12-aminolauric acid, ALA, or di(hydrogena...
MXenes have shown promise in myriad applications, such as energy storage, catalysis, EMI shielding, among many others. However, MXene oxidation in aqueous colloidal suspensions when stored in water at ambient conditions remains a challenge. It is now shown that by simply capping the edges of individual MXene flakes, Ti3C2Tz and V2CTz, by polyanions...
The MAB phases are atomically layered, ternary or quaternary transition metal (M) borides (TMBs), with the general formula (MB)2zAx(MB2)y (z = 1–2; x = 1–2; y = 0–2), whose structures are composed of a transition M-B sublattices interleaved by A-atom (A = Al,Zn) mono- or bilayers. Most of the MAB phases were discovered before the 1990s, but recent...
MXenes have shown promise in many applications such as energy storage, catalysis, EMI shielding, among many others. However, MXene oxidation in aqueous colloidal suspensions when stored in water at ambient conditions remains a challenge. Herein we show that by simply capping the edges of individual MXene flakes – Ti3C2Tz and V2CTz ‐ by polyanions s...
Herein, we report on the response of the MAX phase, Ti3SiC2, to shock wave compression at strain rates above 104s−1. The shock response was determined by measuring the rear, free surface, and velocity of samples—subjected to impact by high-velocity projectiles launched by a gas-gun—using interferometry. The effects of temperature and sample thickne...
Clay-reinforced nylon-6 nanocomposites (NCs) - characterized by the full exfoliation of the nano-reinforcement – were introduced in the marketplace in the 1990s. Herein we demonstrate, for the first time, that Ti3C2Tz MXene can be incorporated into nylon-6 to synthesize melt-processable nanocomposites with excellent barrier properties (94% reductio...
The Mn+1AXn, or MAX, phases are nanolayered, hexagonal, machinable, early transition-metal carbides and nitrides, where n = 1, 2, or 3, M is an early transition metal, A is an A-group element (mostly groups 13 and 14), and X is C and/or N. These phases are characterized by a unique combination of both metallic and ceramic properties. The fact that...
Spark plasma sintering (SPS) is an effective process for the fabrication of highly transparent oxide ceramics for photonic applications. In the present study, Nd-doped yttrium aluminum garnet (Nd:YAG) ceramics with various dopant concentrations (0.5–5 at.%) were fabricated at 1300–1400 °C using conventional SPS (60 MPa) and high pressure (300 MPa)...
Transparent alumina was fabricated from untreated commercial powder by high-pressure spark plasma sintering (HPSPS) at temperatures of 1000, 1050 and 1100 °C under pressures of 250-800 MPa. It was established that transparency strongly depends on the HPSPS parameters. At all temperatures, there was a certain point when increasing the pressure led t...
Alumina forming, oxidation and thermal shock resistant MAX phases are of a high interest for high temperature applications. Herein we report, on bonding and resulting interactions between a Ni-based superalloy, NSA, and two alumina forming MAX phases. The diffusion couples Cr${_2}$AlC/Inconel-718/Ti${_2}$AlC were assembled and heated to 1000 or 110...
Of all the MXenes, Ti3C2Tz is the most studied and has shown promise in many different applications by virtue of its metal-like conductivity, hydrophilicity and ease by which aqueous stable colloids can be processed. Apart from appreciating that this high stability was due to relatively high negative surface charges on individual flakes, there has...
Applying high pressure during the sintering of ceramic materials is a common practice that allows for a reduction of the sintering temperature and the obtaining of fine-grained microstructures. In this work, we show that the final grain size of submicron alumina increased consistently with applied pressure during low temperature (1000–1050 °C), hig...
Transparent cerium-doped yttrium aluminum garnet (Ce:YAG) phosphors are promising candidates for high-power white light emitting diode applications. In the present study, Ce:YAG powder was synthesized by a co-precipitation method and highly transparent ceramics were fabricated by spark plasma sintering. The effects of temperature and pressure, as w...
Alumina forming, oxidation and thermal shock resistant MAX phases are of a high interest for high temperature applications. Herein we report, on bonding and resulting interactions between a Ni-based superalloy, NSA, and two alumina forming MAX phases. The diffusion couples Cr2AlC/Inconel-718/Ti2AlC were assembled and heated to 1000 or 1100 °C in a...
Herein we report on the reactivity between palladium, Pd, and the MAX phases, Ti2AlC, Ti3AlC2, Ti3SiC2 and Cr2AlC. Diffusion couples of Pd/MAX were heated to 900 °C under uniaxial stress of ∼20 MPa for 2, 4, and 10 h in a vacuum (<1 Pa) hot press. The diffusion couples were examined using X-ray diffraction, scanning electron microscopy and energy-d...
A two-stage processing approach combining spark plasma sintering (SPS) and hot isostatic pressing (HIP) was employed for the fabrication of relatively large (30 mm diameter) and thick (up to 8 mm) samples of transparent polycrystalline magnesium aluminate. The effects of sample thickness, heating rate during SPS, and the temperature and duration of...
Polycrystalline magnesium aluminate (MgAl2O4) spinel (PMAS) exhibits a unique combination of physical, chemical, mechanical, and optical properties, which makes it useful for a wide range of applications, including UV lenses for lithography, electroinsulation, and structural windows for both VIS and IR region radiation and armor applications. Conve...
A spark plasma sintering (SPS) apparatus was successfully employed to perform uniaxial compressive creep tests on pure copper under a stress of 30 MPa in the 400–600 °C temperature range. By utilizing two different configurations, the creep experiments were conducted without or with a low-density pulsed direct electric current (~ 6–7 A/mm2) passing...
Inverse Hall-Petch behavior was observed in a transparent nanocrystalline magnesium aluminate spinel ceramic with grain size lower than 30 nm fabricated by high pressure spark plasma sintering (HPSPS). The ceramic was consolidated from 12 nm powder, synthesized by a solution combustion method and displayed an optical transmission of 80% at 550 nm w...
High-pressure spark plasma sintering of Si3N4 with Y2O3, Al2O3 and LiF additives was employed to fabricate high quality dense ceramics comprising approximately 92% α-Si3N4 phase and 8% β-Si3N4 phase. The relatively high pressure applied (up to 650MPa) had a substantial effect on densification by enhancing particle rearrangement, making it possible...
The effects of LiF on the synthesis and reactive sintering of polycrystalline gahnite (zinc aluminate spinel, ZnAl2O4) were studied using XRD, high-temperature simultaneous thermal analysis and a spark plasma sintering (SPS) apparatus. It was demonstrated that the LiF reduces the onset of synthesis by about 200 °C and plays an important role in the...
Samples of transparent polycrystalline spinel with average grain size varying from 0.14 to 170 μm were prepared by different sintering approaches. The effect of grain size on the flexural strength, hardness and Hugoniot elastic limit (impact loading) was investigated. It was found that values of hardness divided by three for samples with grain size...
A spark plasma sintering (SPS) apparatus was used to perform uniaxial compressive creep tests on dense SPS-processed fine-grained alumina. Experiments were carried out in the 1125–1250 °C temperature range under an applied stress of 80–120 MPa. Creep rates, stress exponent and apparent activation energy were determined. The microstructure of deform...
We report a successful passive Q-switching of a Tm:YLF laser operating at λ = 1.9 μm, using a Co²⁺:AgCl0.5Br0.5 saturable absorber. Approximately 200-ns long, 150 μJ pulses were obtained. Increase in pump energy resulted in repetitive pulsing, with a repetition rate approximately proportional to the pump pulse energy. Room-temperature optical trans...
This chapter discusses the use of high pressure spark plasma sintering to fabricate transparent magnesium aluiminate spinel at low temperature in an experiment. The specimens fabricated under 400 MPa at 1200°C in the experiment displayed very fine microstructure (grain size was about 170 nm) and a unique combination of hardness (about 16 GPa) and i...
Transparent Co2+ doped MgAl2Ob4 spinel was fabricated by SPS consolidation followed by and HIP treatment. It was established that HIP treatment significantly improved transparency of the ceramic in a wide range of wavelengths, especially, in a range, which is relevant for Q-switching. Nonlinear absorption was demonstrated and the ground and excited...
Nano-structured transparent polycrystalline magnesium aluminate spinel (PMAS) was fabricated using a high pressure (up to 1000 MPa) spark plasma sintering (HPSPS) apparatus and various properties of the spinel, such as transparency, micro-structure and mechanical properties (specifically, hardness and fracture toughness), were tested. Using a creep...
A spark plasma sintering (SPS) apparatus was used for the first time as an analytical testing tool for studying creep in ceramics at elevated temperatures. Compression creep experiments on a fine-grained (250 nm) polycrystalline magnesium aluminate spinel were successfully performed in the 1100–1200 °C temperature range, under an applied stress of...
The present study focused on the fabrication of bulk materials from Ti1-xAl x N nano-powders using a spark plasma sintering (SPS) apparatus. Super-saturated Ti1-xAl x N solid solutions containing differing fractions of AlN (10, 20, 30 and 50mol%) were synthesized by high-energy ball milling (HEBM) of pure nitrides. The complete dissolution of AlN i...
High-pressure spark plasma sintering (HPSPS) was employed to fabricate polycrystalline Nd:YAG specimens with desired functional properties. Specimens fabricated under a uniaxial pressure of 300 MPa at 1300°C at a heating rate of 50°C/min and holding time of 60 min displayed submicrometer microstructure and elevated mechanical properties, including...
A high pressure SPS (spark plasma sintering) process was applied for consolidation of un-doped polycrystalline magnesium aluminate spinel. This approach allows fabricating a fully dense transparent ceramic with submicron grain size and high hardness values at a relatively low temperature (1200 °C). The light transmittance of the specimens increases...
