Burners (fuel nozzles) for fritmaking furnaces

Translated from Steklo i Keramika, No. 6, p. 31, June, 1992.     

Model of grain-boundary diffusion with allowance for near-boundary layers of equilibrium composition

Fisher model of intercrystalline diffusion is refined based on an analysis of previously obtained results of emission Mössbauer studies of grain boundaries. It is shown that under conditions of dominating intercrystalline diffusion, the existence of monatomic near-boundary layers of equilibrium composition should be taken into account. It has been found that the allowance for these layers does not change the expressions for the distribution of the concentration of the diffusing impurity in a polycrystal in the case of a type-B kinetic regime, whereas in the type-C regime the corresponding expressions change somewhat. The technique that was used previously for the determination of parameters of grain-boundary diffusion and segregation, which is based on the results of emission Mössbauer investigations of grain boundaries, has been modified; the application of the new approach has been demonstrated on the example of processing data of Mössbauer investigations of grain boundaries in polycrystalline Nb at ^119mSn nuclei.     

An Acoustic-Emission Technique of Forced Vibrations Used for Flaw Detection in Thin-Walled Pressure Vessels

An acoustic-emission technique of forced vibrations based on the principles of the acoustic-topographical integral technique of forced vibrations, combined with the acoustic-emission technique, is considered. An example of using this technique for diagnostics of thin-walled cylindrical shells made of aluminum alloys is considered.__________Translated from Defektoskopiya, Vol. 41, No. 3, 2005, pp. 27–31.Original Russian Text Copyright © 2005 by Popov.     

Effect of electric field on the vapor-phase growth of carbon nanostructures

A mathematical model of dc gas discharge plasma has been developed in order to determine the electric field strength at a substrate surface during plasmachemical deposition of carbon nanostructures. A numerical solution of the model equations has been obtained using the experimentally determined boundary conditions and model parameters. A comparison of the solution to experiment confirms the adequacy of the proposed mathematical model, which provides the electric field profiles and the electron and ion density distributions near the substrate surface. Estimations show that, for carbon nanostructures with a characteristic size of about 30 nm, the electric field strength at the surface is sufficiently high to provide for their directional growth along the field.     

Investigation of the nucleation and growth mechanisms of nanocrystalline diamond/amorphous carbon nanocomposite films

Nucleation and growth, but especially the development of the morphology of nanocrystalline diamond/amorphous carbon (NCD/a-C) nanocomposite films have been investigated by systematic variation of three important parameters, namely the deposition time, the growth rate, and the substrate pre-treatment used to enhance the nucleation density. The films have been characterized, among others, by scanning electron microscopy, atomic force microscopy, and Fourier transform infrared spectroscopy. It is shown that, by successive addition of ultradispersive diamond powder to the suspension of nanocrystalline diamond powder in n-pentane used for the ultrasonic pre-treatment, the nucleation density can be enhanced by two orders of magnitude from 1 · 10⁸ cm^− 2 to > 1 · 10¹⁰ cm^− 2. This reduces the thickness required to achieve closed films from 1 µm to 100 nm. However, once coalescence of the individual nodules emerging from the nucleation sites has taken place the films loose “memory” of the nucleation step and start to develop the typical NCD morphology consisting of larger features with diameters of some hundreds of nm which are in turn composed of much smaller features. Irrespective of the feature size and of the parameters used, the films of this investigation possess AFM rms roughnesses of 9–13 nm, indicating that rms values are not sufficient to characterize NCD surfaces.     

Grinding high-quality and art glass with diamond grinding wheels with organic binders

It has been found that using the new organic binder MV1 with grinding powder with grain size 45/38 µm instead of the binder M2-01 with micropowder grain size 30/40 µm increases the productivity of the final diamond grinding of high-quality and art glass by a factor of 2–2.5 without any subsequent chemical polishing and decreases the roughness of the worked surface by 20% with 14–28% higher specific consumption.     

Oxidation of methane in a wide range of pressures and effect of inert gases

The analysis of methane oxidation in a wide range of pressures (0.05–10 atm) demonstrates that the efficiency of CH₃ radicals recombination is of great importance for high selectivity of C₂ hydrocarbons formation. The relative efficiency of different “colliders” assisting the stabilization of exited C₂H*₆ molecules increases in the series: solid surface> Ar> He. The increase of the overall reaction rate upon increasing pressure of the inert gases in the case of catalysts having a higher surface area and more developed pore structure is likely due to the contribution of the surface-induced chain reaction in the volume of pores.