Electrical output parameters of efficient cylindrical thermionic energy converters

Electrical output parameters are presented for four one-element cylindrical TEC operating with cesium plasmas and electrode gaps from 0.3 to 0.8 mm. The cylindrical emitters have been made by vapor-phase epitaxial deposition of tungsten on cylindrical molybdenum substrates having [111] axial orientation under the conditions where the deposit is automatically formed faced with (110) planes. The average vacuum work function is up to 5.3 eV. The collector is made of a molybdenum-ruthernium alloys. Tests have been made on how the vacuum work function of the emitter influences the output parameters. Calculations combined with experiment have been used to estimate the work functions and electron temperatures in the plasma. Translated from Atomnaya énergiya, Vol. 87, No. 2, pp. 129–133, August, 1999.     

Influence of the Collector Emission Properties on the Efficiency of a Thermionic Energy Converter in the Arc Regime

The effect of the emission properties of the collector surface (electronic work function and transmittance) on the potential jump near the collector in the arc operating regime of a thermionic converter is studied. Two models are examined: neglecting and taking into account the influence of cold emission electrons on the gradient of the electron temperature of the plasma near the collector. The proposed model, which takes account of the influence of cold emission electrons, with a decreasing electronic transmittance and the presence of emission from the collector results in the fact that the useful voltage also decreases substantially. This agrees with the experimental data for oxygen-containing converters with a high collector temperature. 4 figures, 5 references.     

Solar-blind Al x Ga1–x N (x > 0.45) p–i–n photodiodes with a polarization-p-doped emitter

Technical Physics Letters - Polarization-induced p-type doping of AlGaN layers with high aluminum content during plasmaassisted MBE growth has been studied. It is shown that a gradient of the AlN...     

Effect of second phase particles on grain refinement during equal-channel angular pressing of an Al-Mg-Mn alloy

The process of grain refinement under severe plastic deformation was examined in an Al-5.4% Mg-0.5% Mn-0.1% Zr alloy, which was subjected to equal-channel angular pressing (ECAP) in the strain interval from 1 to 12 at a temperature of ∼300 °C. It was shown that the size and distribution of the second phase particles precipitated under homogenization annealing strongly affect grain refinement. Extensive grain refinement under ECAP was provided by a dispersion of Al₆Mn particles with an average size of ∼25 nm that precipitated during the homogenization annealing at an intermediate temperature. The fully recrystallized structure with an average crystallite size of ∼0.55 μm evolves through continuous dynamic recrystallization. In contrast, homogenization annealing at a high temperature leads to the formation of coarse Al₆Mn particles with a plate-like shape. Under further ECAP, the formation of coarse recrystallized grains takes place in this material due to the discontinuous growth of recrystallized grains during the inter-pass annealing between the ECAP passes. The role of second phases in grain refinement is discussed in terms of pinning and driving forces for recrystallization.     

多向锻造和单向轧制304不锈钢高温退火后的晶界面分布

固溶处理后的2组304不锈钢样品分别经应变量ε=2的多向锻造(MF)和单向轧制(DR)后,再经900℃高温退火2—120min.采用电子背散射衍射(EBSD)技术和五参数晶界面分析方法(FPA),研究了样品的晶界特征分布(GBCD)和晶界面分布(GBPD).结果表明,2组样品中∑3~n(n=1,2,3)特殊晶界的比例均不超过45%,并且在退火过程中,非共格∑3晶界逐渐共格化,∑9和∑27晶界比例也随之下降.分别经MF和DR处理后再经120 min退火的样品中,一般大角度晶界(过滤掉Σ3n)一般均以(111)扭转晶界和〈110〉倾侧晶界为主,表明样品中均存在明显的晶界织构(GBT);在某些特定取向差条件下,一般大角度晶界的GBPD在样品中存在显著差异,表明退火之前的加工过程对304不锈钢的GBPD有显著影响.     

Molecular beam epitaxy of AlGaAs/Zn(Mn)Se hybrid nanostructures with InAs/AlGaAs quantum dots near the heterovalent interface

Features of the growth of InAs quantum dots in an Al_0.35Ga_0.65As matrix by molecular beam epitaxy at different substrate temperatures, deposition rates, and amounts of deposited InAs are studied. The optimum conditions for growing an array of low-density (≤2 × 10¹⁰ cm^?2) small (height of no more than 4 nm) self-organized quantum dots are determined. The possibility of the formation of optically active InAs quantum dots emitting in the energy range 1.3–1.4 eV at a distance of no more than 10 nm from the coherent heterovalent GaAs/ZnSe interface is demonstrated. It is established that inserting an optically inactive 5-nm GaAs quantum well resonantly coupled with InAs quantum dots into the upper AlGaAs barrier layer enhances the photoluminescence efficiency of the quantum-dot array in hybrid heterostructures.     

Effect of stresses on the structural changes in high-chromium steel upon creep

The effect of stresses on the microstructure and dispersed particles in a heating-performance Fe?0.12C–0.06Si–0.04Ni–0.2Mn–9.5Cr–3.2Co–0.45Mo–3.1W–0.2V–0.06Nb–0.005B–0.05N (wt %) steel has been studied under long-term strength tests at Т = 650°C under initial applied stresses ranging from 220 to 100 MPa with a step of 20 MPa. Under an applied stress of 160 MPa, which corresponds to a time to fracture of 1703 h, a transfer from short- to long-term creep takes place. It has been shown that alloying with 3% Co and an increase in W content to 3% significantly increase the short-term creep resistance and slightly increase the long-term strength upon tests by more than 10⁴ h. The transfer from short- to the long-term creep is accompanied by substantial changes in the microstructure of the steel. Under long-term creep, the solid solution became depleted of tungsten and of molybdenum down to the thermodynamically equilibrium content of these elements in the solid solution, which leads to the precipitation of a large amount of fine particles of the Laves phase at the boundaries of laths and prior austenitic grains. At a time to fracture of more than 4 × 10³ h, the coalescence of the M₂₃С₆ carbides and Laves-phase particles occurs, which causes the transformation of the structure of fine tempered martensite lath structure into a subgrained structure.