Controlled Formation of Silicon-Vacancy Centers in High-Pressure Nanodiamonds Produced from an "Adamantane + Detonation Nanodiamond" Mixture.

Despite progress in the high-pressure synthesis of nanodiamonds from hydrocarbons, the problem of controlled formation of fluorescent impurity centers in them still remains unresolved. In our work, we explore the potential of a new precursor composition, a mixture of adamantane with detonation nanodiamond, both in the synthesis of nanodiamonds and in the controlled formation of negatively charged silicon-vacancy centers in such nanodiamonds. Using different adamantane/detonation nanodiamond weight ratios, a series of samples was synthesized at a pressure of 7.

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.

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.

Nanoengineered Polycrystalline Diamond Composites with Advanced Wear Resistance and Thermal Stability.

Fluorinated grains of micrometer size diamonds overcoated with nanodiamond particles were used as a feedstock for high-pressure, high-temperature synthesis of new polycrystalline diamond composites (PDCs). Such a nanoengineering approach for exploring the interfacial chemistry of diamonds has been implemented in two methods: (i) infiltration of Co from the WC-Co layer into a fluorinated diamond layer with added Al and (ii) sintering of fluorinated micro- and nanosize diamond homogeneous mixtures with added Al and Co. We found that unlike commercial PDCs made with a metallic Co binder for drilling tools, the binding phase in new composites comprises only intermetallic compound AlCo or ternary carbide AlCoC.

WB : Synthesis, Properties, and Crystal Structure-New Insights into the Long-Debated Compound.

The recent theoretical prediction of a new compound, WB, has spurred the interest in tungsten borides and their possible implementation in industry. In this research, the experimental synthesis and structural description of a boron-rich tungsten boride and measurements of its mechanical properties are performed. The ab initio calculations of the structural energies corresponding to different local structures make it possible to formulate the rules determining the likely local motifs in the disordered versions of the WB structure, all of which involve boron deficit.

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

Microcrystals of α-tetragonal (α-t) boron with unit cell parameters =9.05077(6) and =5.13409(6) Å and measured density 2.