Tests for Resistance to Cryolite: Methods and Comparative Evaluation

Methods of testing refractory and barrier (shielding) materials used in the lining of aluminum electrolyzers for resistance against corrosive attack of electrolyte components are briefly reviewed. The advantages of a method proposed by Allaire et al. [2] are emphasized vis-a-vis the conventional methods that are used to simulate performance of the aluminum electrolysis cell.     

Current-voltage characteristics of thin-film gas sensor structures based on tin dioxide

The experimental current-voltage (I–U) curves of thin-film structures based on tin dioxide (SnO₂) exhibit nonlinearity in the range of strong applied electric fields. The results of I-U measurements are interpreted within the framework of a model that assumes the drift of adsorbed ions over the film surface. The observed phenomenon can be used both for detecting the impurities in air and for recognizing the types of adsorbed species.     

High-power laser diodes (λ = 808–850 nm) based on asymmetric separate-confinement heterostructures

Symmetric and asymmetric separate-confinement AlGaAs/GaAs heterostructures have been grown by MOCVD in accordance with the concept of design of high-power semiconductor lasers. High-power laser diodes with a 100-μm aperture, emitting in the 808–850-nm range, were fabricated from these structures. The internal optical loss in asymmetric separate-confinement heterostructures with broadened waveguide is reduced to 0.5 cm⁻¹. In the lasers with 1.7-μm-thick waveguide, the output optical power of 7.5 W in CW mode was achieved owing to reduction of the optical emission density at the cavity mirror to 4 mW/cm². Original Russian Text ? A.Yu. Andreev, A.Yu. Leshko, A.V. Lyutetskiĭ, A.A. Marmalyuk, T.A. Nalyot, A.A. Padalitsa, N.A. Ptkhtin, D.R. Sabitov, V.A. Simakov, S.O. Slipchenko, M.A. Khomylev, I.S. Tarasov, 2006, published in Fizika i Tekhnika Poluprovodnikov, 2006, Vol. 40, No. 5, pp. 628–632.     

State of the Art and Trends in the Development of Base Plate Materials for Aluminum Electrolysis Cells

The state of the art and trends in the production and application of barrier materials intended for preventing the infiltration of corrosive components (sodium, sodium fluoride, and molten aluminum) into the heat-insulating layer of refractories for the base plate of aluminum electrolysis cells are discussed. Results for different types of barrier materials tested for cryolitic stability are given; the granular composition and pore structure of some of them are studied. Strengths and weaknesses of the barrier materials are discussed.__________Translated from Novye Ogneupory, No. 2, pp. 16 – 22, February, 2005.     

A study of epitaxially stacked tunnel-junction semiconductor lasers grown by MOCVD

Design parameters of epitaxially stacked tunnel-junction asymmetric separate-confinement laser heterostructures are chosen. Technological modes for fabrication of heterostructures of this kind by metal-organic chemical vapor deposition in the system of AlGaAs/GaAs/InGaAs solid solutions are found. It is demonstrated that high-efficiency GaAs:Si/GaAs:C tunnel stru ctures and asymmetric AlGaAs/GaAs/InGaAs laser heterostructures with low internal optical loss can be fabricated in a single technological process. Conditions are chosen in which a deep mesa can be formed for fabrication of mesa-stripe diode lasers based on epitaxially stacked tunnel-junction laser heterostructures. Mesa-stripe diode lasers with a 150 × 12-μm aperture have been manufactured on the basis of these structures. These samples have a threshold current density J _th of 96 A cm^-2, internal optical loss α_i of 0.82 cm^-1, and differential resistance R = 280 mΩ. Samples containing three laser structures have a slope efficiency of 3 W A^-1 and a maximum peak output power of 250 W in the pulsed operation mode (100 ns, 1 kHz).     

Investigation of phase transformations in iron and cerium using a polyvinylidene fluoride pressure gauge

This paper presents results of studies of shock-induced phase transformations in iron (polymorphic α-ε transition) and cerium (isomorphic γ-α transition) using a polyvinylidene fluoride pressure gauge. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 4, pp. 121–126, July–August, 2007.     

Thermal state of cathode assemblies in high-current plasma systems

A nonlinear thermal problem is solved for composite cathode assemblies of high-current plasma devices. Variability of thermal and electrophysical properties of the structural elements of the assembly, volume (Joule heat generation) and surface (the effect of discharge plasma, convective and radiant heat exchange) sources, and sinks of heat have been taken into account in a two-dimensional statement of the problem. This allowed for a substantial increase in the accuracy of calculating the cathode temperature field. The thermal state of cathode assemblies depending on external parameters of the plasma device has been considered in detail. The effect of Joule heat generation and radiant and convective heat exchange components on the energy balance of electrodes with different geometries has been analyzed.