Effect of Molybdenum Additions on Compaction during Sintering of Fine-Grained Iron-Copper Pseudoalloys

The effect of added molybdenum powder on compaction and the properties of sintered fine-grained iron-copper pseudoalloys is studied. The original powder mixtures are prepared by mechanical alloying, and the original powder particle size in mixtures does not exceed 0.5 μm. Specimens are sintered in the range 600-1130°C. It is shown that addition of molybdenum powder to the original charge accelerates compaction of fine pseudoalloys in both the solid phase and liquid-phase sintering compared with compaction of the same pseudoalloys without adding molybdenum. After solid-phase sintering the maximum relative density of specimens is 98.8%, and after liquid-phase sintering it is 99.3%. The main reasons for acceleration of compaction are prolonged retention of a fine-grained structure of sintered specimens up to the melting temperature for the phase based on copper and mutual diffusion between iron and molybdenum; to a significant extent the latter occurs during specimen heating in the solid phase.     

Sintering of Si3N4 Ceramics with Additives Containing Yttrium and Ytterbium Oxides with Microwave and Traditional Heating

Compaction processes, phase transformation, and porous structure evolution are compared for materials based on silicon nitride containing yttrium and ytterbium oxides under microwave and traditional heating conditions. Experiments by microwave heating are performed in a special gyrotron device operating at a frequency of 30 GHz in a nitrogen atmosphere at normal pressure with a constant heating rate of 30, 60, and 90 deg/min. Traditional sintering is carried out in a tubular continuous furnace with a tungsten muffle in a nitrogen atmosphere at normal pressure with a heating rate of 60 deg/min. It is established that under microwave heating conditions compaction of the test materials and the start of the phase transformation occur at temperatures 100-150 deg lower than those typical for traditional heating. In material with a reduced amount of oxide additives compaction is accompanied by an increase in the proportion of large pores which is the reason for a slow-down in compaction both with traditional heating and with microwave one. It is suggested that the reason for acceleration of mass transfer with microwave heating is the specific nature of the interaction of the microwave field with the liquid phase formed, promoting development of non-diffusion transfer of solid-phase elements dissolved within it and the mechanical effect on its particles.     

Effect of Refractory Boride Particles on Crystallization of the Amorphous Alloy Fe85B15

We have studied the characteristic features of the process of transition from the amorphous to the crystalline state in the presence of refractory boride particles of different crystallographic types (zirconium diboride ZrB₂ and lanthanum hexaboride LaB₆), introduced into ribbons of Fe₈₅B₁₅ amorphous alloy directly during ribbon formation. ZrB₂ particles in the base alloy have practically no effect on its thermal stability, defined by the temperature of onset of formation of primary α-Fe crystals, while in the presence of LaB₆ particles the thermal stability is considerably reduced. This qualitatively correlates with the Dankov principle of structural and dimensional correspondence considered in the theory of heterogeneous nucleation. We have shown that the major factor determining the high catalytic activity of LaB₆ particles with respect to nucleation of α-Fe crystallization centers is rapid chemical reaction within the zone where they come in contact with the Fe₈₅B₁₅ melt. The ZrB₂ particles which do not enter into such a reaction, do not affect the course of crystallization processes and the thermal stability of the base amorphous alloy.     

Graphene oxide membranes for electrochemical energy storage and conversion

Graphene oxide (GO) membranes have recently attracted considerable attention for various applications involving filtration. In electrochemical systems, GO membranes serve as a separator or solid-state electrolyte; the roles which have been played for over four decades by the commercial ionic polymers such as Nafion. Owing to the versatility of GO membranes, they have shown an incredible potential for electrochemical energy storage and conversion. In lithium-sulphur batteries and similar electrochemical systems in which the electrode redox system is based on a conversion mechanism and subject to the so-called shuttle effect, a selective membrane can facilitate the transport of the electroactive species such as Li ions while blocking the release of the electroactive material (e.g., polysulphides) into the other half-cell. The same requirement is essential for the fabrication of redox flow batteries. Owing to the growing interest in flexible supercapacitors, there is a desire to replace liquid electrolytes with solid electrolytes, and GO membrane provides an appropriate scaffold for trapping gel electrolytes. The performance of Nafion in fuel cells has also been improved by the preparation of GO/Nafion membranes. All these different applications reveal the practical potential of GO membranes for the future energy storage and conversion.     

Interaction of electromagnetic waves in a waveguide with very thin wires

Absorption and scattering of electromagnetic radiation by thin metal wires in a waveguide are investigated experimentally and theoretically. It is shown that, when the wavelength many times exceeds the diameter of a cylindrical wire, this wire strongly absorbs the radiation and weakly scatters it, and the absorption efficiency factor depends on the wavelength only slightly. This phenomenon can be used for developing radiation absorbers in the meter-wavelength range.     

Surface segregation of Ti atoms during NiTi alloy sputtering

The paper addresses NiTi alloy sputtering by 9 keV He and Ar ions and discusses the experiment performed by V.S. Chernysh et al. about 10 years ago. The binary collision simulation has been applied to extract the concentrations of surface Ni and Ti atoms from the experimental data. The results of simulations favor segregation of Ti for both He and Ar ion bombardment. The effect of non-symmetric surface collisions (Ti on Ni and Ni on Ti) was found to be negligible. A pronounced effect of the interatomic (target–target) potential is noted.     

OM,SEM–EDX,and micro‐FTIR analysis of the Bronze Age pottery from the Băile Figa salt production site (Transylvania,Romania)

This article presents the results of analyses carried out on a lot of 11 fragments of Bronze Age ceramics discovered in the site from B?ile Figa (Beclean town, Transylvania, Romania), where salt exploitation occurred. The samples were analyzed by means of optical microscopy, on the basis of which the morphology and distribution of the inclusions in the ceramic paste was established. Likewise, the samples were analyzed by scanning electron microscopy with energy‐dispersive X‐ray spectrometry, producing microphotographs for each sample, and on the basis of the X‐ray spectra, the elemental composition in gravimetric percentages was established. Through the micro‐Fourier‐transform infrared spectroscopy analysis, on the basis of characteristic group vibrations, it was possible to ascertain the nature of the compounds from the ceramic samples. These analyses will contribute to the reconstruction of the prehistoric technologies for salt exploitation.     

Investigation of Composition of Endometallofullerene Extracts

Gases evolved upon heating endometallofullerene (EMF) extracts with La or Y have been investigated. It has been shown that solvent molecules used to release EMF are observed in extracts up to high temperatures. It has been found that in the dimethylformamide (DMF) extract the EMF molecules are present mainly as the [EMF]^- anions, which were observed in electrospray mass spectra. The treatment of such extracts with iodine results in the anion reduction to neutral molecules.     

Effects of Porous Structure on the Electrical Conductivity of Highly Porous Metal-Matrix Materials

It is shown that high-porosity materials based on tungsten and nickel that have been made with the use of pore-forming agents show an increase in specific conductivity as the ratio between the dimensions of the metal particles and those of the pore-forming ones increases. This result is explained from the viewpoint of the fractal dimensions and the percolation threshold.