Corrosion behaviour of the extruded and unidirectionally solidified AlAl4Ca eutectic alloy in a neutral sodium chloride solution

The corrosion behaviour of extruded and unidirectionally solidified AlAl₄Ca eutectic alloy in a neutral sodium chloride solution has been compared with the behaviour of commercially pure Al and AlCu alloy. From both anodic and cathodic cyclic linear potentiodynamic measurements and from S.E.M. observations it was possible to point out that the corrosion behaviour of unidirectionally solidified alloy is substantially equal to that of the extruded alloy, slightly different from that of commercially pure Al and better than AlCu alloy. Therefore, the use of this new lamellae-reinforced AlAl₄Ca composite is promising, even though from the corrosion point of view further studies involving different techniques and conditions (solutions, temperature, surface state, stress, etc.) should be undertaken.     

Photoelectrochemical performance of anodic n-TiO2 films submitted to hydrogen reduction

The photoelectrochemical behaviour of semiconducting n-TiO₂ films prepared by anodic oxidation of titanium plates in concentrated alkaline solutions at very high current densities, and subsequently cathodically reduced or thermally reduced in a hydrogen atmosphere, was investigated. The original and reduced films were examined by scanning electron microscopy and X-ray diffraction analysis. Hydrogen reduction improved the photoelectrochemical performance of the oxide giving the best results when reducing the films at 600°C for 2 h. Preliminary water photoelectrolysis experiments showed that hydrogen could be produced at the counter electrode even without applying an external bias voltage, in agreement with the proposed energy diagram for the TiO₂ films.     

A photoelectrochemical and spectroscopic investigation of oxide layers on AISI 301 in sulfate solutions at different pH

Photocurrents flowing at AISI 301 stainless steel electrodes, polarized anodically in sulfate solutions of various pH, were related to the nature of the surface oxides formed in these environments. The oxides were identified by surface Raman and IR spectroscopies. Correlations among pH, surface coverage with different types of oxides and photocurrent were recognized by mapping Raman spectroscopy, optical microscopy and image analysis. A high photoresponse is mainly related to high surface coverage with magnetite, formed at high pH. Exposure to low-pH solutions gives rise to preferential formation of hematite. Magnetite formed at high pH is irreversibly transformed into hematite if the oxide layer is subsequently exposed to a low-pH solution.     

Model and Experimental Characterization of the Dynamic Behavior of Low-Power Carbon Monoxide MOX Sensors Operated With Pulsed Temperature Profiles

Wireless sensor networks for home automation or environment monitoring require low-cost low-power sensors. Carbon monoxide (CO) metal-oxide (MOX) sensors could be suitable in terms of device cost, but they show some severe limits, such as the need to be heated, which means large power consumption and the need for complex and frequent calibration procedures, which increases the overall cost. This paper investigates the possibility to partially overcome these limits by a low-cost detection system based on a suitable commercial sensor (TGS 2442, Figaro, Inc.) and an ad hoc measurement technique exploiting specifically tailored temperature profiles. To this aim, the authors study the dynamic behavior of low-power CO MOX sensors operated with pulsed temperature profiles by means of two approaches: 1) sensor modeling and 2) experimental evaluation. To analyze how the sensor dynamic response changes as a function of the CO concentration, the authors individuate a temperature profile, which ensures satisfactory sensitivity to the target gas and very low power consumption. Moreover, some parameters describing the sensor response shape are selected, which prove to be significant in terms of both robustness to environmental conditions and calibration simplicity.     

Epitaxial growth of antimony electrodeposits on oriented single crystal surfaces of gold and silver

The epitaxial growth of antimony electrodeposits, obtained at 25 and 50° C from a chloride bath on single crystal cathodes of gold and silver, oriented along the (1 0 0), (1 1 0) and (1 1 1) crystallographic planes, has been studied by electron diffraction. Current densities ranging from 10 to 1000 Am^–2 and thicknesses between 1 and 50 m have been investigated. The gold substrate was found to be the more favourable to the formation of oriented crystalline deposits. A tendency to form amorphous antimony was observed on the silver substrate, especially at 25° C. The monocrystalline deposits on (1 0 0) and (1 1 1) planes of gold and silver were oriented with their (1 0 0) plane parallel to the substrate, and the deposits on the (1 1 0) plane of gold and silver with their (1 1 0) and (¯1 1 0) planes parallel to the substrate. The orientation relationships between parallel directions of the deposit and substrate have been determined. The results are discussed in terms of the work of formation of variously oriented nuclei on amorphous substrates, the symmetry elements in the deposit-substrate interface region and the mismatch along the more densely packed parallel directions.     

Substitution of silver by various metal ions in modified AgI solid electrolytes

The substitution process of silver by various metals in RbAg₄I₅ and other solid electrolytes of the AgI-modified type has been investigated. This process is of technological interest since it permits the use of copper, zinc or cadmium instead of silver as anode materials in solid state batteries which utilize these electrolytes.     

高效三功能层单晶薄膜太阳电池的研究

讨论了ZnSe/GaAs/Ge等三功能层梯度掺杂异质单晶薄膜复合光电极的结构,分析了把它用于光电化学太阳电池、光伏太阳电池、肖特基光伏太阳电池时的工作机理及优点.实验结果验证了理论分析.在进一步提高太阳电池转换效率方面,该复合光电极值得进一步研究.     

Electrochemical solar cells with layer-type semiconductor anodes. Performance of n-MoSe2 cells

The output characteristics and the long-term performances of n-MoSe₂ (I^?, I₂) electrochemical solar cells have been investigated. It has been confirmed that, by analogy with other layer-type, d-band transition metal dichalcogenide systems, the surface state of the semiconductor plays a key role in the behaviour of the cell. With ‘smooth’ crystal samples, fill factor and efficiency values of the order of 0.6 and 6%, respectively, have been obtained under AM1 illumination. Such performances are, however, drastically reduced if ‘irregular’ crystal samples are used.Control of these undesirable surface state effects has been attempted by chemical treatments specific to the unsaturated transition metal atoms exposed to the electrolyte at the edge sites. Finally, the stability of n-MoSe₂ I^?, I₂) cells under long time operation, has also been evaluated.     

Epitaxial growth of antimony electrodeposits on oriented single-crystal surfaces of copper

The epitaxial growth of antimony electrodeposits obtained at 25 and 50° C from chloride and citrate baths on copper single-crystal cathodes orientated along (1 0 0), (1 1 0) and (1 1 1) crystallographic planes has been studied by electron diffraction. Current densities ranging from 10 to 1000 A m^–2 and thicknesses between 0.2 and 10m have been investigated. Amorphous electrodeposits were usually obtained from the chloride bath at a temperature of 25° C. The monocrystalline deposits obtained from both baths on (1 0 0) and (1 1 1) copper planes were oriented with their (1 1 0) and ( ) planes and with their (1 0 0) plane, respectively, parallel to the substrate. On the (1 1 0) copper substrate, monocrystalline deposits were only obtained from the citrate bath, their ( ) plane being parallel to the substrate face. For the sake of completeness, some bismuth electrodeposits on the same copper substrate faces were also studied. The results are discussed in terms of work of nucleation, symmetry of the deposit-substrate interface region and mismatch along close packed directions. They are also discussed in connection with the results related to bismuth electrodeposits.     

Corrosion behaviour of the extruded and unidirectionally solidified Al-Al4Ca eutectic alloy in a neutral sodium chloride solution

The corrosion behaviour of extruded and unidirectionally solidified Al-Al₄Ca eutectic alloy in a neutral sodium chloride solution has been compared with the behaviour of commercially pure Al and Al-Cu alloy. From both anodic and cathodic cyclic linear potentiodynamic measurements and from S.E.M. observations it was possible to point out that the corrosion behaviour of unidirectionally solidified alloy is substantially equal to that of the extruded alloy, slightly different from that of commercially pure Al and better than Al-Cu alloy. Therefore, the use of this new lamellae-reinforced Al-Al₄Ca composite is promising, even though from the corrosion point of view further studies involving different techniques and conditions (solutions, temperature, surface state, stress, etc.) should be undertaken.