Solubility of aluminum in cryolite-alumina electrolytes

The complex influence that additives of aluminum, calcium, lithium, and potassium fluorides have on the total solubility of aluminum in the cryolite-alumina melt is studied. The investigations were performed at a constant overheating of the melt saturated by alumina (15°C relative to the liquidus temperature). The aluminum solubility was determined via the prolonged holding of metal in the melt at a specified temperature with the subsequent sampling of the specimen, which was rapidly frozen, and the metal content in it was determined by a gas-volumetric analysis. It was seen that, as the cryolite ratio (CR) decreases from 2.5 to 2.2, the aluminum solubility in the electrolyte drops by a factor of 1.7, while the further decrease in CR to 2.1 does not cause its substantial variation. The introduction of 3 wt % LiF and 5 wt % KF into the melt with a constant overheating of the melt substantially decreases the metal solubility, namely, by a factor of 2.9 and 1.5, respectively.     

An X-ray technique for investigation of the explosive-emission cathode surface

We present the results of pulsed X-ray radiography of an electron beam spot on the anode of a diode employing an explosive-emission cathode. It is demonstrated that this technique can provide objective information on the character of emissive centers on the cathode surface and can be used for preliminary evaluation of the possibility of using a particular explosive-emission cathode type for the formation of desired electron beams in a given diode.     

Simulation of the composition and proportions of anions in polymerized silicate melts

A new statistical model is proposed for describing an equilibrium structure of polymer complexes in a silicate melt. The model makes it possible to calculate the molecular-mass distributions of polyanions of the general formula (Si _i O_{3i + 1 ? j} )^{2(i + 1 ? j} )^?, where i is the number of silicon atoms and j is the number of intramolecular closures of bridging bonds. The proposed model is implemented as the STRUCTON computer program (version 1.1, 2006) intended for calculating the composition and proportions of polyanions at different degrees of polymerization of the system. The executable code is implemented on personal computers. The distributions of Q ⁿ structons, which are obtained experimentally from Raman and NMR spectroscopic data or evaluated theoretically, are used as input parameters for the computer program. The testing calculations are performed with the STRUCTON program for three arbitrary distributions of Q ⁿ particles corresponding to different degrees of polymerization 0.25 ≤ α ≤ 0.49 for the model system containing 104 initial structons. The results of the statistical simulation have demonstrated that a limited ensemble of polymer complexes is formed in the system, so that the mean number of different types of complexes varies from 46 to 141. This result correlates with an increase in the mean size of anions from 1.87 to 8.60 and with a decrease in the total number of polymer particles from 5320 to 1166 in the aforementioned range of degrees of polymerization α.     

Properties of refractory materials for primary aluminum production electrolyzers

Results are provided for a study of changes in the properties of barrier materials during laboratory and industrial tests. Some autopsy results are presented for electrolyzers with a different service life. Directions are indicated for improving barrier layer properties in electrolyzers due to the use of new technology and equipment intended for vibration compaction of materials directly in electrolyzer socles. __________ Translated from Novye Ogneupory, No. 3, pp. 96–102, March 2008.     

Optimization tools of parallel simulation of nanostructures with quantum dots

Tools for optimizing the performance of parallel programs on multi-architectural distributed computing systems are considered. A method for optimizing the embedding of parallel MPI-program into computing clusters with a hierarchical communication network structure is described. An adaptive approach to the delta optimization of restore points is proposed for effective fault-tolerant simulation on distributed computing systems.     

UV Schottky photodiode on boron-doped CVD diamond films

We report on experimental study of photosensitivity and Q-DLTS spectra of polycrystalline CVD diamond UV photodetectors. The measured characteristics of Schottky photodiode on boron-doped diamond films are compared with those obtained for planar photoconductive structures (photoresistor type) based on undoped CVD diamond. The Schottky photodiode exhibited a sharp cut-off in photoresponse with spectral discrimination ratio (between wavelengths of 190 nm and 700 nm) as high as 5 · 10⁵ at zero bias voltage (at zero dark current). The photodiode showed the maximum of photoresponse at wavelength < 190 nm, and a low density of trapping and recombination centers as evaluated with the Q-DLTS technique. The devices demonstrated the photoresponsivity at 190 nm from 0.03 to 0.1 A/W with quantum yield of 0.20 to 0.67 in closed circuit, while the photovoltage ≥ 1.6 V was measured in open circuit regime. Another type of UV detector, the planar photoconductive structures with interdigitizing ohmic electrodes fabricated on undoped diamond film and operated under a bias voltage, revealed a higher density of (surface) defect centers and the maximum photoresponse at  210 nm wavelength. A strong influence of UV light illumination on the Q-DLTS spectra of the planar photoconductive structures was observed. This effect can be used for development of new UV detectors and dosimeters based on the Q-DLTS signal measurements.     

Multilayer structures with quantum dots in the InAs/GaAs system emitting at a wavelength of 1.3 μm

The optical properties of multilayer structures with quantum dots in the heteroepitaxial InAs/GaAs system have been studied. The structures were obtained by the method of submonolayer migration-stimulated epitaxy. It is shown that the optimized growth conditions provide room-temperature luminescence at a wavelength of 1.3 μm.