M. V. Baidakova

Defects and impurities in nanodiamonds: EPR, NMR and TEM study

Abstract EPR, 13 C NMR and TEM study of ultradisperse diamond (UDD) samples is reported. The compounds show a high concentration of paramagnetic centers (up to 10 20 spin/g), which are due to structural defects (dangling C–C bonds) on the diamond cluster surface. The anomalous reduction in the spin–lattice relaxation time of 13 C (from several hours in natural diamond to ∼150xa0ms in UDD clusters) is attributed to the interaction between the unpaired electrons of the paramagnetic centers and nuclear spins. 13 C NMR line-width reflects the fact that the structure of the UDD surface is distorted in comparison to the ‘bulk’ diamond structure.

The structure of diamond nanoclusters

A model describing the structure of diamond nanoclusters produced by explosive shocks is proposed. The model is based on experimental data obtained from x-ray diffraction and small-angle x-ray scattering. This model considers the diamond nanocluster as a crystalline diamond core coated by a carbon shell having a fractal structure. The shell structure depends both on the cooling kinetics of the detonation products and on the method used to extract from them the diamond fraction.

Diamond-graphite phase transition in ultradisperse-diamond clusters

A systematic study of the diamond-graphite structural phase transition in ultradisperse-diamond clusters obtained by the detonation technique is reported. Samples of two types, differing in the kinetics of detonation-product cooling, were investigated. The phase transition was achieved under heating in an inert atmosphere in the temperature range 720–1400 K. The transition was identified by Raman scattering and x-ray diffraction data. Raman and x-ray characterization showed the ultradisperse diamond, irrespective of the cooling rate used, to be cluster material possessing diamond structure with a characteristic nanocrystal size of 43 Å. The diamond-graphite phase transition in ultradisperse diamond is shown to start from the cluster surface inwards at Tpt≈1200 K, i.e. at substantially lower temperatures than is the case with bulk diamond single crystals.

Structure and defects of detonation synthesis nanodiamond

Abstract Characterization of the structure and defects in detonation synthesis, ultradisperse diamond (UDD) is reported. X-ray and proton nuclear magnetic resonance results on UDD powders are interpreted in terms of the different structure of the shell of UDD particles, produced under different conditions. In spite of the comparable contents of carbon and nitrogen atoms in the precursor, no (

Ultradisperse-Diamond Nanoclusters. Fractal Structure and Diamond–Graphite Phase Transition

A systematic study of the diamond–graphite structural phase transition in ultradisperse-diamond clusters obtained by the detonation technique is reported. Samples of two types, differing in the kinetics of detonation-product cooling, were investigated. The phase transition was achieved under heating in an inert atmosphere in the temperature range 720–1400 K. X-ray characterization showed the ultradisperse-diamond, irrespective of the cooling rate used, to be a cluster material possessing a diamond structure with a characteristic nanocrystal size of 44 A. The diamond–graphite structural phase transition in ultradisperse diamond is shown to start from the cluster surface inwards at Tpt≈1200 K, i.e., at substantially lower temperatures than is the case with bulk diamond single crystals. Ultradisperse-diamond clusters are shown to be fractal objects and the character of variation of the fractal dimension in the course of the diamond–graphite phase transition is studied.

Detonation Nanodiamonds as Catalyst Supports

The article reports on experimental study of catalytic properties of a new system: Pt on detonation nanodiamond (Pt/DND) for the carbon monoxide oxidation reaction. The catalytic activity of Pt/DND structures as a function of platinum content in the catalyst within the 7–80 wt % intervals was studied and the structure of the Pt/DND catalyst was investigated by X-ray diffraction and HRTEM. The Pt/DND catalysts developed demonstrate a high degree of conversion of CO to CO2 at room temperature, a feature making them attractive for commercial applications as catalytic systems for purification of air from carbon monoxide in houses and industrial areas. The new catalysts were incorporated in solid-state electrochemical CO gas sensors. A statement on efficiency of the detonation nanodiamonds as a support for catalytic metals of platinum groups has been done.

Fractal structure of ultradisperse-diamond clusters

Ultradisperse-diamond clusters are shown to be fractal objects, and the character of variation of the fractal dimension in the course of the diamond-graphite phase transition under annealing in an inert atmosphere is studied.

Effect of hydrogen on the structure of ultradisperse diamond

The paper reports on a study of the effect of annealing in hydrogen on the structural phase transition in clusters of ultradisperse diamond (UDD) obtained by the detonation method. The samples studied were of two types, namely, prepared by the “dry” and “wet” techniques, which differ in the cooling rate of the detonation products and, accordingly, in the structure of the diamond nanocluster shell. It is shown that, irrespective of the type of synthesis, the relative content of the diamond (sp3) phase increases within the anneal temperature range of 450 to 750°C, the increase being more pronounced in the samples prepared by “dry” synthesis. A model accounting for the observed structural transformation processes is discussed. A hypothesis of the possibility of compacting UDD clusters into bulk single crystals is put forward.

Structure of Nanodiamonds Prepared by Laser Synthesis

A study is reported of nanodiamonds obtained by a new method—pulsed laser ablation of a specially prepared carbon target. In the mechanism employed to produce a diamond phase, this method is similar to that of detonation synthesis of nanodiamonds. The main structural characteristics of the material have been determined and compared with the corresponding characteristics of detonation nanodiamonds.

Electrosurface properties of single-crystalline detonation nanodiamond particles obtained by air annealing of their agglomerates

A complex study of electrosurface properties has been performed for single-crystalline detonation nanodiamond particles with sizes of 4–5 nm obtained by air annealing of their agglomerates. FTIR spectroscopy and X-ray photoelectron spectroscopy data indicate that the investigated properties result from the presence of two types of ionogenic functional groups on the particle surface, i.e., acidic carboxyl and amphoteric hydroxyl groups. Acid-base potentiometric titration, laser Doppler electrophoresis, and conductometry have been employed to measure the ΓH+(pH) and ΓOH-(pH) adsorption isotherms of potential-determining ions, as well as the pH dependences (in a pH range of 3.5–10.5) of the surface charge density, electrophoretic mobility, and specific surface conductivity of detonation nanodiamond particles in aqueous 0.0001–0.01 M KCl solutions.