Estimation of ionic conductivity of CuI through tarnishing studies of copper in iodine atmosphere

The conductivity values of isolated CuI crystal has been reported by a large number of investigators. But the conductivity be-haviour of a growing CuI film on copper has not been explored yet. An attempt has been made in this investigation to provide ionic conductivity values of growing CuI films from the kinetics studies of the film growth process. The conductivity value has been found to be proportional to the square of the partial pressure of iodine in the thinner film range while it is approximately proportional to the square root of the partial pressure in the thicker range. Estimation has been based on the fundamental parabolic equation of Wagner relating the rate constant and conductivity. An analysis of the experimental results indicate that the conductivity value of the growing CuI is of higher magnitude for thicker films than that for the thinner ones.     

Effect of static charge on the tarnishing behaviour of silver in iodine atmosphere at low temperatures

The kinetics of Agl film growth on silver under the action of applied static charge of both the polarities, as well as under normal iodination conditions in the temperature range of 294 to 338 K and in the iodine partial pressure range of 0.03 to 0.22kPa, conform to parabolic rate law. Compared to normal iodination, an enhancement in rate under both positive and negative surface charge conditions at the Ag/Agl interface and a decrease in rate under either surface charge condition at the Agl/l₂ interface have been observed. The increased rate with negative charge at the Ag/Agl interface and the decreased rate with same kind of charge at the Agl/l₂ interface, compared to normal iodination, can be explained on the basis of positive hole transport, while the observed effects with positive charge at either of the interfaces receive reasonable support from cation migration as the rate limiting factor during the film growth process.     

Synthesis of flower-like silver nanoarchitectures at room temperature

Novel flower-like silver nanoarchitectures were synthesized via a facile and environmentally benign route in the presence of citric acid and ascorbic acid. The flower-like structures are composed of nano-petals of ca. 20 nm in thickness. The products were characterized with X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The growth mechanism of flower-like silver nanoarchitectures involves a film-fold process. Some crucial factors affect the nanocrchitectures growth, such as, pH, the concentration of citric acid, and the concentration of ascorbic acid, have also been discussed.     

Morphology and size-controllable preparation of silver nanostructures through a wet-chemical route at room temperature

In this letter a simple wet-chemical route was developed to prepare silver nanostructures. The formation of the silver nanostructures occurs in a single process, carried out by mixing an AgNO₃ aqueous solution and a para-phenylenediamine solution at room temperature without the introduction of other reducing agents and morphology controlling agents. It is found that both the morphology and the size of such silver nanostructures can be facilely controlled by the molar ratio and concentration of the reactants as well as the solvent that was used to dilute para-phenylenediamine aqueous solution. As-formed silver nanostructures were examined by scanning electron microscopy.     

Fabrication of silver nanowire transparent electrodes at room temperature

Silver nanowires (AgNWs) surrounded by insulating poly(vinylpyrrolidone) have been synthesized by a polyol process and employed as transparent electrodes. The AgNW transparent electrodes can be fabricated by heat-treatment at about 200 °C which forms connecting junctions between AgNWs. Such a heating process is, however, one of the drawbacks of the fabrication of AgNW electrodes on heat-sensitive substrates. Here it has been demonstrated that the electrical conductivity of AgNW electrodes can be improved by mechanical pressing at 25 MPa for 5 s at room temperature. This simple process results in a low sheet resistance of 8.6 Ω/square and a transparency of 80.0%, equivalent to the properties of the AgNW electrodes heated at 200 °C. This technique makes it possible to fabricate AgNW transparent electrodes on heat-sensitive substrates. The AgNW electrodes on poly(ethylene terephthalate) films exhibited high stability of their electrical conductivities against the repeated bending test. In addition, the surface roughness of the pressed AgNW electrodes is one-third of that of the heat-treated electrode because the AgNW junctions are mechanically compressed. As a result, an organic solar cell fabricated on the pressed AgNW electrodes exhibited a power conversion as much as those fabricated on indium tin oxide electrodes. These findings enable continuous roll-to-roll processing at room temperature, resulting in relatively simple, inexpensive, and scalable processing that is suitable for forthcoming technologies such as organic solar cells, flexible displays, and touch screens.      

Novel phase-transfer preparation of monodisperse silver and gold nanoparticles at room temperature

In a novel water-cyclohexane two-phase system, the aqueous formaldehyde is transferred to cyclohexane phase via reaction with dodecylamine to form reductive intermediates in cyclohexane; the intermediates are capable of reducing silver or gold ions in aqueous solution to form dodecylamine protected silver and gold nanoparticles in cyclohexane solution at room temperature. The prepared silver and gold nanoparticles are examined by transmission electron microscopy (TEM), UV-Visible spectroscopy (UV-vis), X-photon electron spectroscopy (XPS) and Fourier transfer infrared spectroscopy (FT-IR). It is found that these nanoparticles are monodisperse in size of less than 10 nm and have good stability in cyclohexane due to the adsorbed dodecylamine on nanoparticle surface. Moreover, the synthesis mechanism is revealed via gas chromatography (GC), gas chromatography-mass spectroscopy (GC-MS), nuclear magnetic resonance (NMR) analyses of the solutions during the preparation process.     

X-ray studies of iodine sorption in some silver zeolites

After saturation sorption, in a static system, of molecular iodine onto some silver zeolites at 130° C, powder X-ray diffraction analysis revealed sharp reflections due to crystalline -Agl. However, this -Agl contained only a fraction of the sorbed iodine and it seems likely that this -Agl involves unlocalized ions such that a continuous three-dimensional network of -Agl forms in the zeolite channels. Water in the zeolite channels is probably the underlying cause: heating to 200 to 300° C in air destroyed the sharp -Agl reflections and no such reflections were observed if the sorption was carried out with the zeolites dehydrated beforehand. -Agl formation was enhanced when the zeolite framework was broken down by heating in air at 800° C, heating in water or brine at 200° C, or -irradiation.     

Elastic constants of porous silver compacts after acid assisted consolidation at room temperature

Acid assisted consolidation (AAC) is a technique that provides elevatedlevels of cohesiveness to silver powder compacts without recourse to a high temperature treatment. Ultrasonic techniques were used to measure the elastic constants of high purity silver compacts as a function of several processing variables. The elastic moduli of untreated (NT) samples were found to be significantly lower than those of samples that had undergone AAC and compacted at the same pressure. Post compaction sintering increases the elastic constants of both AAC and NT samples. The results indicate that the elastic constants are dependent not only on the density that was attained but also on the processing route that was followed. The elastic constant of a porous metal, M, can be expressed as M = M ₀ g, where M ₀ is the elastic modulus of the bulk metal, g is a geometrical factor that reflects the interparticle contact area and is a quality factor that depends on the nature of the interparticle interfaces. The results suggest that sound wave velocity is a parameter more appropriate than density for predicting the elastic moduli of porous metallic compacts.     

四方相纳米氧化锆低温稳定机制的研究现状

介绍了近几十年t-ZrO2纳米晶在室温下稳定机制的研究现状,并且重点分析表面能理论和氧空位理论等主要机制,在此基础上对镀膜、水蒸气、杂质离子、形核位置以及结构相似对其稳定性的影响进行进一步的讨论.     

Divacancies at room temperature in germanium

We have studied the annealing of vacancy defects in neutron and proton irradiated germanium. After neutron irradiation the Sb-doped samples were annealed at 473, 673 and 773 K for 30 min. The positron lifetime was measured as a function of temperature (30 - 295 K). A lifetime component of 330 ps with no temperature dependence is observed in as irradiated samples, identified as the positron lifetime in a neutral divacancy. The average positron lifetime in the samples annealed at 473 K has a definite temperature dependence, suggesting that the divacancies become negative as the crystal recovers and the Fermi level moves upward in the band gap. Proton irradiation of germanium at 37 K with subsequent room temperature annealing also resulted in a similar lifetime component 315 ps, in good agreement with the neutron irradiation experiment.     

Visco-elasticity in alumina ceramics at room temperature

The decrease in the fracture strength of alumina ceramics at room temperature has usually been assumed to be caused by the effect of stress corrosion. However, at high temperatures, a viscous deformation will occur due to a glass-like phase which exists in the grain boundary. A study of the relation of the fracture strength of an alumina ceramics smooth specimen at room temperature to the visco-elastic property was performed. Mechanical tests and visco-elastic analysis, has shown that the fracture strength of this kind is controlled by the visco-elasticity.     

A novel ozone detection at room temperature through UV-LED-assisted ZnO thick film sensors

In this work a novel ozone detection at room temperature (RT) has been investigated. Two functional materials, ZnO and (W_0.9Sn_0.1)O_3 − x (WS10) oxides, have been synthesized to prepare thick film gas sensors, both used in conventional heated mode as well as at RT assisted by UV irradiation. As a source of light, a light emitting diode (LED) of 400 nm peak wavelength was used. Under typical operating conditions of the UV-LED, the radiation flux density ? over the sensor was of about 5 · 10¹⁷ photons/cm². Powders and films have been characterized by means of TG-DTA, SEM, TEM and XRD. Finally, electrical measurements have been performed on sensing films with the aim to compare conductive properties, surface barrier heights and ozone sensing features with and without UV irradiation. Despite the fact that two types of conventional heated sensors offered quite similar results with respect to ozone sensing, it turned out that, at RT and with the assistance of UV light, ZnO behaved excellently fast detecting ozone at concentrations down to 10 ppb, while for WS10 under the same operating conditions an opposite result was observed, i.e. very low response and long response time.     

Preparation of cadmium selenide nanocrystals through an ultrasonic activation double-phase approach at room temperature

Cubic phase CdSe nanocrystals were prepared through a novel ultrasonic activation double-phase approach at room temperature. The band-edge emissions with the band centered at 452, 478, 496, and 511 nm and the surface state charge carrier recombination emissions from around 520 to 590 nm were observed for the CdSe with diameters of 1.4, 1.7, 1.9 and 2.1 nm, respectively. Those fluorescence emission spectra calculated chromaticity coordinates fall well within the white, white, green and yellowish green colors with quantum yield of about 1–2%.     

Epitaxial growth of silver on an Si(111) 7×7 surface at room temperature

The growth of silver deposited onto an Si(111) 7 × 7 surface at room temperature was studied by reflection high energy electron diffraction. The reflections of thin silver layers appear at a deposition thickness of 1 monolayer with a high background, and they develop into successive streaks with increasing thickness. The reciprocal lattice of silver is composed of concentric coaxial cylinders. The silver layers have the [111] texture structure in which they have preferentially the epitaxial orientation $\text{[01}\text{1}\text{]}{}_{\mathrm{<mtext>Ag</mtext>}}\text{//[01}\text{1}\text{]}{}_{\mathrm{<mtext>Si</mtext>}}\text{on (111)}{}_{\mathrm{<mtext>Ag</mtext>}}\text{//(111)}{}_{\mathrm{<mtext>Si</mtext>}}$. The grain size of the layers is about ten atomic distances in diameter. Each layer grows continouusly in thickness to give the stacking order of the f.c.c. structure. The growth mode for room temperature condensation is considered to be a special case of the Frank-van der Merwe growth mode.     

Some studies on stresses and strains of aluminium alloy during extrusion-forging at room temperature

The present investigation has been undertaken to evaluate some aspects on extrusion-forging during cold upsetting using a suitable die using aluminium alloy (H9-6063) solid cylinders subjected to different geometrical conditions such as approaching angles namely, 35°, 45°, 50° and 60°, with two different initial protrusion heights namely 8 mm and 10 mm. During the experiments, three geometries such as barreled cylinder, truncated cone part and protruded part or extruded parts were observed. The calculations were made on the assumption that the volume constancy principle holds on and the curvatures of the barrel were in the form of a circular arc. Further, it is established that the protrusion height increases with the increase in the approaching angle for a given extrusion load. The relationship was also established between the various bulge parameters namely the hoop stress, the hydrostatic stress and the stress ratio parameters. In this work an attempt has been made to establish a relationship between the approaching angle and protrusion height and to establish a relationship among various height strains and stress ratio parameters.     

Rapid synthesis of MXenes at room temperature

Ti₃C₂, one of the most studied MXenes (M is an early transition metal, and X is either C or N), has attracted considerable attention due to their excellent electrical conductivity, hydrophilicity, and catalytic activity. To date, most MXenes are prepared from powders and chemical etching under conditions of either long duration (generally ≥8?h) or high temperature (generally ≥35°C). In this study, Ti₃C₂ with –F and –O/–OH terminal groups was successfully obtained by electrochemically etching porous Ti₃AlC₂ sheet electrodes in NH₄HF₂ solution at room temperature. The reaction mechanism and the effect of voltage were demonstrated. Electrochemical etching could induce subsequent over-etching to generate carbide-derived carbons.     

AES and XPS study on the tarnishing of silver in alkaline sulphide solutions

Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) were used to follow the changes that occur on the surfaces of silver sheets when reacting with sulphide solutions of pH 12. The results obtained enabled conclusions to be drawn about the nature of the Ag₂S films. Immersion in dilute sulphide solutions ( 3 × 10^–4 M) resulted in highly irregular films that were interrupted by shallow depressions (cavities). Inside these cavities AES analysis proved the existence of massive carbon species, the presence of which delayed healing of the cavities by the formation of Ag₂S film, thus allowing the silver metal interface to continue in contact with the solution oxygen. This explains why silver electrodes maintain the Ag/Ag₂O potential while immersed in dilute sulphide solutions. Equilibration of silver with more concentrated sulphide solutions (5 × 10^–4 to 5 × 10^–3 M) effected healing of the cavities through the formation of a continuous Ag₂S film. Once this continuous film is formed, the metal interface is no longer accessible to the solution oxygen. At this point the transition of potential from Ag/Ag₂O to Ag/Ag₂S occurs.