Role of gallium ion on the conducting properties of La0.7(Ba,Sr)0.3Mn1−xGaxO3 (x=0.0, 0.1 and 0.2) perovskite

The transport properties of Ga-doped La_0.7(Ba, Sr)_0.3Mn_1−xGa_xO₃ (x=0.0, 0.1 and 0.2) perovskite materials were investigated by admittance spectroscopy over a wide range of temperatures and frequencies. The electronic conduction was found to be dominated by thermally activated hopping and to depend strongly on Ga-content. Results have shown samples with x=0.0 and 0.1 exhibit a metallic behavior at low temperature and a semiconducting one at high temperature. The temperature (T_MI) of the metal–insulator transition was found to be about 180 and 120 K for samples with x=0.0 and 0.1, respectively. Ga doping leads to a depletion in the number of hopping electrons, which suppresses metallicity and pushes the system in semiconductor side. Besides, the activation energy (E_a) deduced from the variation of conductance as a function of temperature, was found to increase from 89 to 165 meV when x increased from 0.0 to 0.2. This increase can be explained by the decrease of charge carriers with increasing Ga-content.     

Preparation and electrical conductivity of KTaO3-based proton conductor

KTaO₃ and KTa_0.9M_0.1O_3-α (M = Ti, Hf, Zr) were prepared by solid state reaction at 1330 °C for 2 h and characterized by x-ray diffraction. The AC impedance technique was used to analyze the sintered solid electrolytes in 1%H₂/Ar and dry air atmosphere. Among KTa_0.9M_0.1O_3-α (M = Ti, Hf, Zr), KTa_0.9Zr_0.1O_3-α displays the highest conductivity in 1%H₂/Ar atmosphere. The carriers transport numbers of solid electrolytes were measured by concentration cell method. The results show KTa_0.9Zr_0.1O_3-α is a pure proton conductor below 525 °C. Stability tests show that KTa_0.9Zr_0.1O_3-α has good chemical stability against CO₂ and H₂O.     

Transport of lithium through a supported liquid membrane of LIX54 and TOPO in kerosene

A mathematical transport model is developed for the extraction of lithium from dilute synthetic solution, simulating geothermal water, using a supported liquid membrane (SLM) of LIX54 (major component is -acetyl-m-dodecylacetophenone) and TOPO (tri-n-octylphosphine oxide) in kerosene. The model is based on fundamental mass transfer and kinetics mechanisms that account for all possible transport resistances. The model is solved numerically and is used to investigate the effect of various extraction conditions and membrane support characteristics. Reasonable agreement is found between the predicted and the experimental results reported in literature.     

Autogenous healing of engineered cementitious composites under wet-dry cycles

Self-healing of Engineered Cementitious Composites (ECC) subjected to two different cyclic wetting and drying regimes was investigated in this paper. To quantify self-healing, resonant frequency measurements were conducted throughout wetting-drying cycles followed by uniaxial tensile testing of self-healing ECC specimens. Through self-healing, crack-damaged ECC recovered 76% to 100% of its initial resonant frequency value and attained a distinct rebound in stiffness. Even for specimens deliberately pre-damaged with microcracks by loading up to 3% tensile strain, the tensile strain capacity after self-healing recovered close to 100% that of virgin specimens without any preloading. Also, the effects of temperature during wetting-drying cycles led to an increase in the ultimate strength but a slight decrease in the tensile strain capacity of rehealed pre-damaged specimens. This paper describes the experimental investigations and presents the data that confirm reasonably robust autogenous healing of ECC in commonly encountered environments for many types of infrastructure.     

Non-isothermal drying of fired-clay brick, an NMR study

Nuclear magnetic resonance (NMR) was used to measure moisture profiles during non-isothermal drying of fired-clay brick. Drying was induced by a temperature gradient resulting from one-sided heating. A saturated fired-clay brick sample which was closed and isolated on all sides except for the front surface was heated with a halogen lamp of variable intensity. By measuring the moisture profiles in time it was possible to identify two distinct drying stages. In the first drying stage homogeneous drying is observed. When the critical moisture content is reached a drying front enters the sample. The characteristic time t₀ after which this drying front develops depends on the applied heat flux.The total amount of energy needed for evaporation of the moisture in the first drying stage is found to be independent of the heat flux from the lamp. As a result the total amount of moisture as a function of time can be scaled to one master curve using the time t₀. The data from these measurements provided an interesting view on drying processes, not only under isothermal conditions but also under influence of a thermal gradient. By using the power input as a scaling parameter it is shown that both the total mass and the drying front positions as a function of time show the same behaviour in all experiments.     

Transport of zinc complexes through an anion exchange membrane

The transport of zinc complexes ions through an anion exchange membrane was evaluated by the treatment of solutions with and without cyanide. The ionic transport was analyzed as a function of the applied current density and of the cyanide and hydroxyl concentration. Experimental results showed that the ionic transfer in electrodialysis was mainly affected by concentration. There is an ideal molar relationship among the concentration of the cyanide ions, hydroxyl and zinc ions, in solution, in which the zinc transport is maximized. For values above or below this, the transport decreases. Zinc extraction from solution containing CN⁻ was more effective when the current density of 29 mA.cm⁻² was applied. The current–voltage curves (CVC) of the anion exchange membrane show that the electrical resistance of the AMV membrane increases with the presence of the zinc–cyanide complex in the solution.     

CORROSION INHIBITION OF CARBON STEEL IN LOW CHLORIDE MEDIA BY AN AQUEOUS EXTRACT OF HIBISCUS ROSA-SINENSIS LINN

The inhibition efficiency (IE) of an aqueous extract of white flower, namely, Hibiscus rosa-sinensis Linn., in controlling corrosion of carbon steel immersed in an aqueous solution containing 60 ppm of Cl^-has been evaluated by the mass loss method. The flower extract (FE) shows good IE. In the presence of Zn²⁺, excellent IE is shown by the flower extract. A synergistic effect exists between the flower extract and Zn²⁺. The mechanistic aspects of corrosion inhibition have been investigated by polarization study and AC impedance spectra. Polarization study reveals that the formulation consisting of flower extract and Zn²⁺ functions as a mixed inhibitor. AC impedance spectra reveal that a protective film is formed on the metal surface. The active principle in the flower extract is quercetin-3-O-glucoside. This has been confirmed by UV-visible absorption spectra. The protective film formed on the metal surface has been analyzed by FT-IR and AFM spectra. It is found that the protective film consists of Fe²⁺-quercetin-3-O-glucoside complex and Zn(OH)₂.     

Role of diluents in uranium transport across a supported liquid membrane using di(2-ethylhexyl)isobutyramide as the carrier

The extraction and transport behaviour of uranium from nitric acid medium across a supported liquid membrane has been studied using di(2-ethylhexyl)isobutyramide as the carrier. The effects of experimental parameters such as nature of diluents, e.g., n-dodecane, benzene, chloroform, tert-butyl benzene, diethyl benzene, n-octanol, 1,2-dichlorbenzene, and 2-nitrophenyl octyl ether, the membrane thickness, and the nitrate ion concentration, on the extraction/transport behaviour of uranium are reported. The experimentally obtained and the theoretically calculated values of permeability coefficients for uranium transport have been compared for different diluents.     

我国交通运输设备制造业科技投入竞争力研究 --以大中型工业企业为案例的分析

交通运输设备制造业的竞争力,在很大程度上代表了一个国家或一个地区制造业的水平。其中科技投入是重要决定因素。本文以大中型工业企业为案例,实证研究了我国交通运输设备制造业科技投入竞争力建设的行业特征、地区特征和存在问题,为我国机电产业科技竞争力提升提供决策依据。     

消失模铸造传质过程与铸件品质控制

消失模铸造是1 种有利于环保的近净成形铸造方法，在消失模工艺的浇注过程中，模样分解为液态或气态产物。为了生产合格的铸件，须选用具有合适透气性和液态产物浸润能力的涂料，以控制分解产物的传质过程。说明设计在高温下测试涂料透气性的仪器是必要的。