Structure and Electrochemical Activity of C60 Fullerite Films

Results are presented from structural and electrochemical researches on C₆₀ films. The fullerite films were made by thermal vacuum evaporation and deposition on NaCl crystals. The substrate temperatures were 293-473 K. The examinations were made in a transmission electron microscope at 100 kV and by x-ray diffraction. Dark-field images were obtained from the individual fullerite particles and particularly from grains in continuous thin films, which showed stacking faults or twin boundaries. The numbers of these defects increase with the substrate temperature. The x-ray diffraction patterns of the fullerite films show extremely diffuse reflections together with a weak reflection around the FCC (111), which may be assigned to a hexagonal close packed HCP modification of fullerite. Rietveld's method was used in processing the x-ray patterns. The best fit between the experimental and theoretical diffraction lines was obtained with the following structure parameters: ratio of FCC phase (a = 1.4117 nm) and HCP phase (a = 0.9756 nm and c = 1.7084 nm) was 46/54 mass%. The electrochemical data indicate that a palladium-activated fullerite film shows prominent hysteresis, which confirms that certain hydride phases are formed at the surface of the C₆₀ film.

     

Experimental Study and Numerical Visualization of Physical Fields of Electromagnetic Pumps Constructed on Permanent Magnets

Pumps with magnet systems constructed on permanent magnets and performed in two manners like two-disk type and the cylindrical rotor type are discussed.First,by way of example we consider the experimental study of disk pump with straight channel;second,we analyse the results of numerical simulation of cylindrical pump in two cases,namely,of straight and U-bend forms of pump channels.At a high speed of pump rotation when induced magnetic field becomes essential in as against the applied field,i.e.when the skin-effect takes place,the pump characteristics are analyzed.Visualization of physical fields of the pumps is reported.     

Synthesis,crystal structure and magnetic properties of the new ternary indides REPd2In4 (RE = La,Ce, Pr,Nd)

The rare-earth-palladium-indides REPd₂In₄ (RE = La, Ce, Pr, Nd) were prepared by arc-melting of the elements and subsequent annealing at 750 °C. The compounds crystallize in a new structure type, space group Pmc2₁, Z = 10, Pearson code oP70. The structures can be described as built of Pd-centered trigonal prisms condensed via common edges. A structural comparison between the new structures and the related isostoichiometric compounds is discussed. The magnetic and electrical transport behavior of the REPd₂In₄ phases was studied from room temperature down to 1.7 and 4.2 K, respectively. While LaPd₂In₄ is a weak diamagnet, CePd₂In₄, PrPd₂In₄, and NdPd₂In₄ exhibit Curie–Weiss paramagnetism and long-range magnetic ordering below 2.4, 2.1 and 5.0 K, respectively. All the compounds studied exhibit metallic character of their electrical conductivity.     

Influence of Particle Size and Mixing Technology on Combustion of HMX/Al Compositions

In this work, two widely used components of high‐energy condensed systems – HMX and aluminium – were studied. Morphology, thermal behaviour, chemical purity and combustion parameters of HMX as a monopropellant and Al/HMX as a binary system were investigated using particles of different sizes. It was shown that in spite of the differences in composition and particle size, combustion velocities are almost identical for micrometer‐sized HMX (m‐HMX) and ultrafine HMX (u‐HMX) monopropellants under pressure from 2 to 10 MPa. Replacement of the micrometer‐sized aluminium with ultrafine one in the system with m‐HMX leads to a burning rate increase by a factor of 2.5 and the combustion completeness raise by a factor of 4. Two mixing techniques to prepare binary Al/HMX compositions were applied: conventional and ‘wet’ technique with ultrasonic processing in liquid. Applying wet mixing results in a burning rate increase of 18% compared to the conventional mixing for systems with ultrafine metal. The influence of the component's particle size and the composition microstructure on the burning rate of energetic systems is discussed and analysed.     

Comparative Study of Microwave Sintering of Zinc Oxide at 2.45, 30, and 83 GHz

Temperature gradients that develop in ceramic materials during microwave heating are known to be strongly dependent on the applied microwave frequency. To gain a better understanding of this dependence, identical samples of ZnO powder compacts were microwave heated at three distinct widely separated frequencies of 2.45, 30, and 83 GHz and the core and surface temperatures were simultaneously monitored. At 2.45 GHz, the approximately uniform "volumetric" heating tends to raise the temperature of the sample as a whole, but the interior becomes hotter than the exterior because of heat loss from the surface. At 30 and 83 GHz, this interior to exterior temperature difference was found to be reversed, especially for high heating rates. This reversal resulted from increased energy deposition close to the sample's surface associated with reduced skin depth. A model for solving Maxwell's equations was incorporated into a newly developed two-dimensional (2-D) heat transport simulation code. The numerical simulations are in agreement with the experimental results. Simultaneous application of two or more widely separated frequencies is expected to allow electronic tailoring of the temperature profile during sintering.     

Development of Hydrogenating Powder Alloys for the Electrodes of Alkali Batteries. Part 3. Production Characteristics of Gas-Atomized Powders of Multicomponent Intermetallic Alloys

Alloy powders containing rare earth metals are prepared by the gas atomization method and their structure, surface, technological, and electrochemical properties are studied. Powders of the alloys LaNi_4.5Al_0.5, LaNi_2.5Co_2.4Al_0.1, and (Mm, La)Ni_3.5Co_0.7Al_0.35Mn_0.4Zr_0.05 are prepared with different particle sizes. The morphology, oxygen content and crystal structure of powders in relation to particle size are studied by x-ray analysis, electron microscopy, and surface dispersion spectroscopy. The hydrogen capacity and electrochemical properties of different fractions are determined. It is established that all of the fractions have similar morphology and alloy lattice parameters. The surface of gas atomized powders with less particle size is less contaminated with oxygen compared with larger fractions. At the same time fractions with a particle size <50 μm have poor activity during gas and electrochemical hydrogenation. DTA curves for fractions of fine particles have an additional exothermic peak that may be caused by thermally induced transformation of the amorphous component into crystalline. The coarse fraction of gas atomized powder has the same hydrogen and electrochemical capacity as for fuzzed alloys.     

Flameless Combustion Synthesis of Ni and Ag Nanoparticles in Ballasted Systems: A Time‐Resolved X‐ray Diffraction Study

The combustion of cellulose nitrate in ballasted mixtures containing an organic binder and nickel hydroxycarbonate or silver carbonate as precursors resulted Ni or Ag nanoparticles. The formation of Ni and Ag nanoparticles from flameless combustion of cellulose nitrate was monitored by time‐resolved X‐ray diffraction. During the formation of the Ag nanoparticles, the diffraction patterns exhibited only signals from decreasing amounts of the precursor and newly simultaneously formed 20–30 nm silver particles. It was detected that in the systems with Ni precursor the formation of the Ni 5–10 nm crystals proceeded by some 2–3 s diffraction‐silent intermediate states of the whole system.     

Reverse-Flow Operation in Fixed Bed Catalytic Reactors

Transition from the usual steady-state mode of continuous processes toward forced unsteady-state conditions (FUSC) has been discussed in chemical engineering literature since the beginning of the 1960s [1-12]. FUSC can be created by periodic variations of temperature, composition, or other parameters to the inlet of a chemical unit.