Heavily Boron Doped Diamond Powder: Synthesis and Rietveld Refinement

Boron-doped diamonds were synthesized by the reaction of an amorphous globular carbon powder (80%) with a powder of 1,7-di (oxymethyl)-M-carborane (20%) in a ‘toroid’-type high-pressure chamber at a pressure of 8.0 GPa and temperature of 1700 °C. The structure was refined by the Rietveld method according to the X-ray powder diffraction data. It was shown that the unit cell parameters of these diamonds have two discrete quantities: around 3.570 Å for small concentrations of B (~1–1.5%) and around 3.578 Å for large concentrations of B (~2–3%). The concentration of the vacancies in the diamonds exceeds the concentration of boron atoms by 2–3 fold. This fact can play an important role in the formation of the structure and in determining the physical properties of diamonds

High-pressure high-temperature synthesis and structure of α-tetragonal boron

ERRATUMThis is an Erratum for the article 2011 Sci. Technol. Adv. Mater. 12 055009The publisher regrets that there is a typographical error on page 2 of this article. The fourth sentence of section 3 should read as follows:The lines characteristic of B–H–B (1700–2000 cm-1) and B–H (2550–2650 cm-1) bonds of decaborane were not found in the Raman spectra of the crystals (figure 3) that confirms the complete decomposition of decaborane [19, 20]

Diamond Composites Produced from Fluorinated Mixtures of Micron-Sized and Nanodiamonds by Metal Infiltration

Improving the operating performance of superhard composites is an important and urgent task, due to a continuing industrial need. In this work, diamond composites with high wear resistance were obtained by sintering fluorinated mixtures of micron-sized diamonds with nanodiamonds at high pressures and temperatures (7–8 GPa, 1550–1700 °C). Aluminum and cobalt powders were added to the diamond mixture to activate the process. The external infiltration of nickel into the diamond layer was carried out additionally during the sintering process, and the effects of nickel infiltration on the structure and properties of composites were studied. The metal melt ensured the mass transfer of carbon within a volume, and the formation of a strong diamond framework. The composition of the additives was selected in such a way that the binding phase became ultimately composed of the intermetallic AlNixCo1−x(x ≤ 1). The Young’s modulus of composites synthesized in this way had a value of 850 GPa, and their wear resistance when turning white granite was more than twice as high as that of premium commercial PDC. The obtained results thus demonstrate that by using nickel to increase melt infiltration into diamond-based composites, the mechanical properties of Al/Co/fluorinated diamond compositions, studied previously, can be further improved

Magnetic Nanoparticles with Fe-N and Fe-C Cores and Carbon Shells Synthesized at High Pressures

Nanoparticles of iron carbides and nitrides enclosed in graphite shells were obtained at 2 ÷ 8 GPa pressures and temperatures of around 800 °C from ferrocene and ferrocene–melamine mixture. The average core–shell particle size was below 60 nm. The graphite-like shells over the iron nitride cores were built of concentric graphene layers packed in a rhombohedral shape. It was found that at a pressure of 4 GPa and temperature of 800 °C, the stability of the nanoscale phases increases in a Fe7C3 > Fe3C > Fe3N1+x sequence and at 8 GPa in a Fe3C > Fe7C3 > Fe3N1+x sequence. At pressures of 2 ÷ 8 GPa and temperatures up to 1600 °C, iron nitride Fe3N1+x is more stable than iron carbides. At 8 GPa and 1600 °C, the average particle size of iron nitride increased to 0.5 ÷ 1 μm, while simultaneously formed free carbon particles had the shape of graphite discs with a size of 1 ÷ 2 μm. Structural refinement of the iron nitride using the Rietveld method gave the best result for the space group P6322. The refined composition of the samples obtained from a mixture of ferrocene and melamine at 8 GPa/800 °C corresponded to Fe3N1.208, and at 8 GPa/1650 °C to Fe3N1.259. The iron nitride core–shell nanoparticles exhibited magnetic behavior. Specific magnetization at 7.5 kOe of pure Fe3N1.208 was estimated to be 70 emu/g. Compared to other methods, the high-pressure method allows easy synthesis of the iron nitride cores inside pure carbon shells and control of the particle size. And in general, pressure is a good tool for modifying the phase and chemical composition of the iron-containing cores

Synthesis of Star-Shaped Boron Carbide Micro-Crystallites under High Pressure and High Temperatures

We synthesized star-shaped pentagonal microcrystals of boron carbide with an extremely low carbon content (~5%), from m-carborane under high pressure (7 GPa) and high temperature (1370⁻1670 K). These crystals have five-fold symmetry and grow in the shape of stars. A 5-fold symmetry in large micron-sized crystals is extremely rare making this a striking observation