Tamer El-Raghy

Bio: Tamer El-Raghy is an academic researcher from Drexel University. The author has contributed to research in topics: Atmospheric temperature range & Heat capacity. The author has an hindex of 47, co-authored 73 publications receiving 8501 citations.

Synthesis and Characterization of a Remarkable Ceramic: Ti3SiC2

Abstract: Polycrystalline bulk samples of Ti{sub 3}SiC{sub 2} were fabricated by reactively hot-pressing Ti, graphite, and SiC powders at 40 MPa and 1,600 C for 4 h. This compound has remarkable properties. Its compressive strength, measured at room temperature, was 600 MPa, and dropped to 260 MPa at 1,300 C in air. Although the room-temperature failure was brittle, the high-temperature load-displacement curve shows significant plastic behavior. The oxidation is parabolic and at 1,000 and 1,400 C the parabolic rate constants were, respectively, 2 {times} 10{sup {minus}8} and 2 {times} 10{sup {minus}5} kg{sup 2}{center_dot}m{sup {minus}4}{center_dot}s{sup {minus}1}. The activation energy for oxidation is thus {approx}300 kJ/mol. The room-temperature electrical conductivity is 4.5 {times} 10{sup 6} {Omega}{sup {minus}1}{center_dot}m{sup {minus}1}, roughly twice that of pure Ti. The thermal expansion coefficient in the temperature range 25 to 1,000 C, the room-temperature thermal conductivity, and the heat capacity are respectively, 10 {times} 10{sup {minus}6} C{sup {minus}1}, 43 W/(m{center_dot}K), and 588 J/(kg{center_dot}K). With a hardness of 4 GPa and a Young`s modulus of 320 GPa, it is relatively soft, but reasonably stiff. Furthermore, Ti{sub 3}SiC{sub 2} does not appear to be susceptible to thermal shock; quenching from 1,400 C into water does not affect the postquench bend strength.more » As significantly, this compound is as readily machinable as graphite. Scanning electron microscopy of polished and fractured surfaces leaves little doubt as to its layered nature.« less

Processing and characterization of Ti 2 AlC, Ti 2 AlN, and Ti 2 AlC 0.5 N 0.5

Abstract: In this article, we report on the fabrication and characterization of Ti2AlC, Ti2AlN, and Ti2AlC0.5N0.5. Reactive hot isostatic pressing (hipping) at ≈40 MPa of the appropriate mixtures of Ti, Al4C3 graphite, and/or AlN powders for 15 hours at 1300 °C yields predominantly single-phase samples of Ti2AlC0.5N0.5, 30 hours at 1300 °C yields predominantly single-phase samples of Ti2AlC. Despite our best efforts, samples of Ti2AlN (hot isostatic pressed (hipped) at 1400 °C for 48 hours) contain anywhere between 10 and 15 vol pct of ancillary phases. At ≈25 µM, the average grain sizes of Ti2AlC0.5N0.5 and Ti2AlC are comparable and are significantly smaller than those of Ti2AlN, at ≈100 µm. All samples are fully dense and readily machinable. The room-temperature deformation under compression of the end-members is noncatastrophic or graceful. At room temperature, solid-solution strengthening is observed; Ti2AlC0.5N0.5 is stronger in compression, harder, and more brittle than the end-members. Conversely, at temperatures greater than 1200 °C, a solid-solution softening effect is occurring. The thermal-expansion coefficients (CTEs) of Ti2AlC, Ti2AlN, and Ti2AlC0.5N0.5 are, respectively, 8.2 × 10−6, 8.8 × 10−6, and 10.5 × 10−6 °C−1, in the temperature range from 25 °C to 1300 °C. The former two values are in good agreement with the CTEs determined from high-temperature X-ray diffraction (XRD). The electrical conductivity of the solid solution (3.1 × 106 (Θ m)−1) is in between those of Ti2AlC and Ti2AlN, which are 2.7 × 106 and 4.0 × 106 Θ −1 m−1, respectively.

Processing and Mechanical Properties of Ti3SiC2: II, Effect of Grain Size and Deformation Temperature

Abstract: In this article, the second part of a two-part study, we report on the mechanical behavior of Ti3SiC2. In particular, we have evaluated the mechanical response of fine-grained (3–5 μm) Ti3SiC2 in simple compression and flexure tests, and we have compared the results with those of coarse-grained (100–200 μm) Ti3SiC2. These tests have been conducted in the 25°–1300°C temperature range. At ambient temperature, the fine- and coarse-grained microstructures exhibit excellent damage-tolerant properties. In both cases, failure is brittle up to ∼1200°C. At 1300°C, both microstructures exhibit plastic deformation (>20%) in flexure and compression. The fine-grained material exhibits higher strength compared with the coarse-grained material at all temperatures. Although the coarse-grained material is not susceptible to thermal shock (up to 1400°C), the fine-grained material thermally shocks gradually between 750° and 1000°C. The results presented herein provide evidence for two important aspects of the mechanical behavior of Ti3SiC2: (i) inelastic deformation entails basal slip and damage formation in the form of voids, grain-boundary cracks, kinking, and delamination of individual grains, and (ii) the initiation of damage does not result in catastrophic failure, because Ti3SiC2 can confine the spatial extent of the damage.

Two‐Dimensional Nanocrystals Produced by Exfoliation of Ti 3 AlC 2

Abstract: Currently, however, there are relatively few such atomically layered solids. [ 2–5 ] Here, we report on 2D nanosheets, composed of a few Ti 3 C 2 layers and conical scrolls, produced by the room temperature exfoliation of Ti 3 AlC 2 in hydrofl uoric acid. The large elastic moduli predicted by ab initio simulation, and the possibility of varying their surface chemistries (herein they are terminated by hydroxyl and/or fl uorine groups) render these nanosheets attractive as polymer composite fi llers. Theory also predicts that their bandgap can be tuned by varying their surface terminations. The good conductivity and ductility of the treated powders suggest uses in Li-ion batteries, pseudocapacitors, and other electronic applications. Since Ti 3 AlC 2 is a member of a 60 + group of layered ternary carbides and nitrides known as the MAX phases, this discovery opens a door to the synthesis of a large number of other 2D crystals. Arguably the most studied freestanding 2D material is graphene, which was produced by mechanical exfoliation into single-layers in 2004. [ 1 ] Some other layered materials, such as hexagonal BN, [ 2 ] transition metal oxides, and hydroxides, [ 4 ] as well as clays, [ 3 ] have also been exfoliated into 2D sheets. Interestingly, exfoliated MoS 2 single layers were reported as early as in 1986. [ 5 ] Graphene is fi nding its way to applications ranging from supercapacitor electrodes [ 6 ] to reinforcement in composites. [ 7 ] Although graphene has attracted more attention than all other 2D materials combined, its simple chemistry and the weak van der Waals bonding between layers in multilayer structures limit its use. Complex, layered structures that contain more than one element may offer new properties because they

2D metal carbides and nitrides (MXenes) for energy storage

Abstract: The family of 2D transition metal carbides, carbonitrides and nitrides (collectively referred to as MXenes) has expanded rapidly since the discovery of Ti3C2 in 2011. The materials reported so far always have surface terminations, such as hydroxyl, oxygen or fluorine, which impart hydrophilicity to their surfaces. About 20 different MXenes have been synthesized, and the structures and properties of dozens more have been theoretically predicted. The availability of solid solutions, the control of surface terminations and a recent discovery of multi-transition-metal layered MXenes offer the potential for synthesis of many new structures. The versatile chemistry of MXenes allows the tuning of properties for applications including energy storage, electromagnetic interference shielding, reinforcement for composites, water purification, gas- and biosensors, lubrication, and photo-, electro- and chemical catalysis. Attractive electronic, optical, plasmonic and thermoelectric properties have also been shown. In this Review, we present the synthesis, structure and properties of MXenes, as well as their energy storage and related applications, and an outlook for future research. More than twenty 2D carbides, nitrides and carbonitrides of transition metals (MXenes) have been synthesized and studied, and dozens more predicted to exist. Highly electrically conductive MXenes show promise in electrical energy storage, electromagnetic interference shielding, electrocatalysis, plasmonics and other applications.

25th Anniversary Article: MXenes: A New Family of Two‐Dimensional Materials

Abstract: Recently a new, large family of two-dimensional (2D) early transition metal carbides and carbonitrides, called MXenes, was discovered. MXenes are produced by selective etching of the A element from the MAX phases, which are metallically conductive, layered solids connected by strong metallic, ionic, and covalent bonds, such as Ti2AlC, Ti3AlC2, and Ta4AlC3. MXenes ­combine the metallic conductivity of transition metal carbides with the hydrophilic nature of their hydroxyl or oxygen terminated surfaces. In essence, they behave as “conductive clays”. This article reviews progress—both ­experimental and theoretical—on their synthesis, structure, properties, intercalation, delamination, and potential applications. MXenes are expected to be good candidates for a host of applications. They have already shown promising performance in electrochemical energy storage systems. A detailed outlook for future research on MXenes is also presented.

Two-dimensional transition metal carbides.

Abstract: Herein we report on the synthesis of two-dimensional transition metal carbides and carbonitrides by immersing select MAX phase powders in hydrofluoric acid, HF. The MAX phases represent a large (>60 members) family of ternary, layered, machinable transition metal carbides, nitrides, and carbonitrides. Herein we present evidence for the exfoliation of the following MAX phases: Ti2AlC, Ta4AlC3, (Ti0.5,Nb0.5)2AlC, (V0.5,Cr0.5)3AlC2, and Ti3AlCN by the simple immersion of their powders, at room temperature, in HF of varying concentrations for times varying between 10 and 72 h followed by sonication. The removal of the “A” group layer from the MAX phases results in 2-D layers that we are labeling MXenes to denote the loss of the A element and emphasize their structural similarities with graphene. The sheet resistances of the MXenes were found to be comparable to multilayer graphene. Contact angle measurements with water on pressed MXene surfaces showed hydrophilic behavior.

Cation Intercalation and High Volumetric Capacitance of Two-Dimensional Titanium Carbide

Abstract: The intercalation of ions into layered compounds has long been exploited in energy storage devices such as batteries and electrochemical capacitors However, few host materials are known for ions much larger than lithium We demonstrate the spontaneous intercalation of cations from aqueous salt solutions between two-dimensional (2D) Ti3C2 MXene layers MXenes combine 2D conductive carbide layers with a hydrophilic, primarily hydroxyl-terminated surface A variety of cations, including Na+, K+, NH4+, Mg2+, and Al3+, can also be intercalated electrochemically, offering capacitance in excess of 300 farads per cubic centimeter (much higher than that of porous carbons) This study provides a basis for exploring a large family of 2D carbides and carbonitrides in electrochemical energy storage applications using single- and multivalent ions