High-pressure studies of size dependent yield strength in rhenium diboride nanocrystals.

The superhard ReB system is the hardest pure phase diboride synthesized to date. Previously, we have demonstrated the synthesis of nano-ReB and the use of this nanostructured material for texture analysis using high-pressure radial diffraction. Here, we investigate the size dependence of hardness in the nano-ReB system using nanocrystalline ReB with a range of grain sizes (20-60 nm).

Nanostructured Graphene Oxide Composite Membranes with Ultrapermeability and Mechanical Robustness.

Graphene oxide (GO) membranes have great potential for separation applications due to their low-friction water permeation combined with unique molecular sieving ability. However, the practical use of deposited GO membranes is limited by the inferior mechanical robustness of the membrane composite structure derived from conventional deposition methods. Here, we report a nanostructured GO membrane that possesses great permeability and mechanical robustness.

Synthesis and High-Pressure Mechanical Properties of Superhard Rhenium/Tungsten Diboride Nanocrystals.

Rhenium diboride is an established superhard compound that can scratch diamond and can be readily synthesized under ambient pressure. Here, we demonstrate two synergistic ways to further enhance the already high yield strength of ReB. The first approach builds on previous reports where tungsten is doped into ReB at concentrations up to 48 at.

Superhard Tungsten Diboride-Based Solid Solutions.

Solid solutions of tungsten diboride (WB) with increasing substitution of tungsten (W) by tantalum (Ta) and niobium (Nb)-ranging from 0 to 50 at. % on a metals basis-were synthesized through resistive arc melting. Samples were characterized using a combination of powder X-ray diffraction (PXRD) for phase identification, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy for elemental composition, Vickers microindentation for hardness measurements, and thermogravimetric analysis for thermal stability.

Effects of Variable Boron Concentration on the Properties of Superhard Tungsten Tetraboride.

Tungsten tetraboride is an inexpensive, superhard material easily prepared at ambient pressure. Unfortunately, there are relatively few compounds in existence that crystallize in the same structure as tungsten tetraboride. Furthermore, the lack of data in the tetraboride phase space limits the discovery of any new superhard compounds that also possess high incompressibility and a three-dimensional boron network that withstands shear.

Superhard Rhenium/Tungsten Diboride Solid Solutions.

Rhenium diboride (ReB), containing corrugated layers of covalently bonded boron, is a superhard metallic compound with a microhardness reaching as high as 40.5 GPa (under an applied load of 0.49 N).

Superhard Monoborides: Hardness Enhancement through Alloying in W1- x Tax B.

In tungsten monoboride (WB), the boron atoms are linked in parallel serpentine arrays, with tungsten atoms in between. This lattice is metallic, unlike conventional covalent superhard materials such as diamond or cubic boron nitride. By selectively substituting tungsten atoms with tantalum, the Vickers hardness can be increased to 42.

Stabilization of HfB12 in Y1-xHfxB12 under Ambient Pressure.

Alloys of metal dodecaborides-YB12 with HfB12-were prepared via arc-melting in order to stabilize the metastable HfB12 high-pressure phase under ambient pressure. Previously, HfB12 had been synthesized only under high-pressure (6.5 GPa).

Extrinsic Hardening of Superhard Tungsten Tetraboride Alloys with Group 4 Transition Metals.

Alloys of tungsten tetraboride (WB4) with the group 4 transition metals, titanium (Ti), zirconium (Zr), and hafnium (Hf), of different concentrations (0-50 at. % on a metals basis) were synthesized by arc-melting in order to study their mechanical properties. The phase composition and purity of the as-synthesized samples were confirmed using powder X-ray diffraction (PXRD) and energy dispersive X-ray spectroscopy (EDS).

Structure of superhard tungsten tetraboride: a missing link between MB2 and MB12 higher borides.

Superhard metals are of interest as possible replacements with enhanced properties over the metal carbides commonly used in cutting, drilling, and wear-resistant tooling. Of the superhard metals, the highest boride of tungsten--often referred to as WB4 and sometimes as W(1-x)B3--is one of the most promising candidates. The structure of this boride, however, has never been fully resolved, despite the fact that it was discovered in 1961--a fact that severely limits our understanding of its structure-property relationships and has generated increasing controversy in the literature.

Vapor-phase polymerization of nanofibrillar poly(3,4-ethylenedioxythiophene) for supercapacitors.

Nanostructures of the conducting polymer poly(3,4-ethylenedioxythiophene) with large surface areas enhance the performance of energy storage devices such as electrochemical supercapacitors. However, until now, high aspect ratio nanofibers of this polymer could only be deposited from the vapor-phase, utilizing extrinsic hard templates such as electrospun nanofibers and anodized aluminum oxide. These routes result in low conductivity and require postsynthetic template removal, conditions that stifle the development of conducting polymer electronics.

Toward inexpensive superhard materials: tungsten tetraboride-based solid solutions.

To enhance the hardness of tungsten tetraboride (WB(4)), a notable lower cost member of the late transition-metal borides, we have synthesized and characterized solid solutions of this material with tantalum (Ta), manganese (Mn), and chromium (Cr). Various concentrations of these transition-metal elements, ranging from 0.0 to 50.