Vol 40, No 4 (2018)

Described are unusual nano-microcrystals of natural diamond found in a meteorite crater of Ukraine and advised about the earlier unknown mechanism of diamond polyhedra growth—the formation by globules. It was revealed that diamond nano-microcrystals in a meteorite crater are very similar to globular crystals, and at the same time have octahedral faceting. The morphology and composition of diamond nano-microcrystals are studied by scanning electron microscopy and with an energy dispersive X-ray analyser. These tiny crystals are grown on the grains of impact apographitic diamond from the Bilylivka meteorite crater (Zapadnaya impact crater) on the Ukrainian Shield. Their surface morphology indicates that the nano-microdiamonds are grown, most probably, by a vapor deposition process immediately after the formation of the impact diamond–transformation of the graphite into diamond and lonsdaleite.

Special features of the interactions and phase formations in carbide-oxide mixture WC 33.5 wt % Fe₂O₃ and in the WC–Fe₂O₃–C system when heated in vacuum and in argon have been studied. To add free carbon into carbide-oxide mixture, the K354 soot and saccharose, which dissociated when heated to high-clean carbon. It is established that at the absence of free carbon in the carbide-oxide system the active interaction between carbon of tungsten carbide and oxygen of iron oxide takes place that shows up in the weight loss of the samples. As a results there form the phase of the intermetallide Fe₇, W₆, the phase with a structure of the FeWO₄ and W. The addition of free carbon allows keeping tungsten carbide partly or completely and reducing iron from oxide. At the lack of free carbon some part of the tungsten carbide carbon starts to interact with oxygen and the Fe₃W₃C complex carbide forms in the system, at the excess of carbon the tungsten carbide retained and the bcc-iron forms. The heating in vacuum differs from the heating in argon by two indications: to remove the same amount of oxygen is spent more carbon than in heating in argon; the temperature of the active interaction of carbon with oxygen decreases. The largest (by 300°C) decrease of the temperature is observed when the saccharose is used as the source of free carbon.

The photo-induced periodic nano structure inside 4H–SiC has been induced by a femtosecond double pulse train. The alignment of the periodic structure is in the direction independently from crystal orientation. In particular, FE-SEM analysis revealed that the periodic structure on the fractured surface can be classified into two categories of the polarization-dependent and polarization-independent.

We have studied performance of AS20 diamond powders to be used in grinding wheels and have found the ways to improve it through changing the dimensional and physico-chemical characteristics of the powders. It is demonstrated that the wheel wear is influenced by separating the narrowest range of grain sizes 100/90 and providing a uniform powder with a certain grain shape factor; it is preferable to use diamond grains with higher values of the shape factor. It is shown that after diamond powders are separated into magnetic and non-magnetic fractions there is a difference between the fractions in the physico-chemical state of the grain surfaces, and it is preferable to use non-magnetic fractions in resin-bonded wheels in order to improve the wheel wear resistance.

A ratio between the predicted and actual yields of condensed carbon in post-detonation processes of nanodiamond synthesis has been studied. These values are shown to closely coincide when optimal synthesis conditions are ensured. The yields of condensed carbon and detonation nanodiamonds in the industrial synthesis are 12.0 wt % and 8.16 wt %, respectively; the DND concentration in DS is up to 68 wt %.

The onset of plasticity during nanodeformation of a bulk TiN specimen is studied by the nanoindentation. It is shown that with a high density of dislocations in the specimen surface layer (mechanical polishing) plasticity in TiN initiates smoothly under an average contact pressure of 18.1 GPa. Hence, with a spherical approximation of the Berkovich tip, the yield strength of TiN at the nanoscale is determined to be 14.5 GPa.