Stability of ZnO nanofibers in processing liquid agents

The aim of the research was to determine the impact of developers, removers and solvents on the stability of ZnO nanofibers. Surface imaging of nanofiber morphology was studied using Scanning Electron Microscope. From the obtained results a set of factors which have the least influence on the etching of ZnO nanofibers during device processing was selected. The dependence of the grains size on the fibers robustness in the liquid solutions was investigated. It was found that the nanofibers calcinated at higher temperatures were more stable. This was due to the grain size of the fiber as the fibers calcinated at higher temperatures revealed larger grain size. The studies have shown that smaller grains were dissolved much faster, leaving the porous core of the ZnO nanofiber.     

The effect of copper ions on interaction of UV radiation with methacrylic matrix – EPR study

The role of metal ions introduced to polymer matrix in the photochemical degradation of material is not fully understood. In this paper, we considered the effect of copper ions on the photochemical changes in Methafilcon A after UV-irradiation. The presence of methacrylic acid in the structure of Methafilcon A increases the loading capacity of these ions. In result, there is observed the production much more radicals after UV-irradiation than in pure matrix, without copper ions. When the time of UV-exposure increases, the EPR signal of trapped Cu(II) ions in the material decreases. This proves the transformation of Cu(II) to a diamagnetic state of stable Cu(I)-intermediates or copper oxides. Simultaneously, in the first 5-min of UV-irradiation there is observed a rapid increase in intensity of the radical signal, which disappears when the exposure time is extended. This mechanism of radical generating is quite different than for Methafilcon A matrix without copper ions.     

Friction welding of ductile iron with stainless steel

The study of mechanical properties and microstructure of friction welded coupe of ductile iron with stainless steel are presented. Scanning electron microscopy (SEM) was used for investigation of the fracture morphology and phase transformations taking place during friction welding process. It was concluded that in case of bainitic ductile iron (BDI) the fracture precedes mainly trough the cleavage planes. Moreover, the distribution of selected elements on both side of the joining interface was studied using EDS line and maps spectrometry. The EDS spectrometry showed some enrichment of ductile iron with Cr and Ni atoms close to the joint. The depth of Cr atoms penetration reached 50 μm. The heat generated locally by friction increased the temperature in the area close to the interface even over the melting point of ductile iron. This was confirmed by metallography which revealed the carbide eutectic enriched with Cr in ductile iron.     

Effect of time and polarization on kinetics of the oxygen electrode reaction at an Au∣YSZ interface

The oxygen electrode reaction at the interface gold∣yttria stabilized zirconia was investigate using microelectrodes by chronoamperometry and electrochemical impedance spectroscopy, with emphasis put on effect of prolonged polarization of the electrode. Two interesting phenomena were observed: (a) generally, the long-lasting negative polarization resulted in a slow monotonous decrease of the current flowing through the electrode, (b) the reaction mechanism was less complicated for the polarized then unpolarized electrodes, which resulted in a relatively simply equivalent circuit used for modelling the former ones. On the basis of the data obtained, the apparent exchange currents normalized vs. the three phase boundary length and Tafel slopes were determined. The methods of determining the three phase boundary length were discussed. The reconnaissance data obtained for the Pt microelectrode are also reported.     

Image deformation in field ion microscopy of faceted crystals

We perform detailed numerical simulations of field ion microscopy images of faceted crystals and compare them with experimental observations. In contrast to the case of crystals with a smooth surface, for a faceted topography we find extreme deformations of the ion image. Local magnification is highly inhomogeneous and may vary by an order of magnitude: from 0.64 to 6.7. Moreover, the anisotropy of the magnification at a point located on the facet edge may reach a factor of 10.     

Particle formation in supercritical fluids—Scale-up problem

The process of antisolvent precipitation of particles, termed solution enhanced dispersion by supercritical fluids (SEDS™), is applied to precipitate the model drug, paracetamol, from ethanol solutions. In the SEDS process the substrate solution is quickly mixed in a mixing chamber of the coaxial two-component nozzle with an antisolvent, represented in this case by the supercritical CO₂. Resulting partially mixed, highly supersaturated solution is introduced into the precipitation vessel as a jet, which generates intensive circulation of residual fluids that dilute the fresh supersaturated solution. Nucleation starts in the nozzle chamber, whereas particle growth completes the process in the precipitation vessel. The process is carried out above the mixture critical pressure; the antisolvent is thus completely miscible with the solvent. Under such conditions the macro-, meso-, and micro-mixing processes can affect the particle size distribution (PSD) and should be considered when the process is scaled up. Scaling up considerations of the precipitation process are based on scale-up rules, CFD simulations and experimental data for paracetamol precipitation. In simulations the model presented earlier (Ba?dyga et al., 2004) that is based on the population balance equation and CFD modelling of compressible flow processes is applied. Results of experimental investigations and numerical simulations are applied to verify scale-up strategies for the SEDS processes.     

Impedance spectroscopy studies of electroless Ni–P matrix,Ni–W–P,Ni–P–ZrO2, and Ni–W–P–ZrO2 coatings exposed to 3.5% NaCl solution

Ni–P matrix, ternary Ni–W–P and Ni–P–ZrO₂ coatings, and quaternary Ni–W–P–ZrO₂ coatings were deposited using electroless method from a glycine bath. Their corrosion resistance was evaluated by electrochemical impedance spectroscopy (EIS) for various immersion times in a 3.5% NaCl solution. From among the investigated coatings, the ternary Ni–W–P coatings show the highest resistance to corrosion in the first hour of exposure to the 3.5% NaCl medium. An addition of ZrO₂ adversely affects the performance of both the Ni–P coatings and the Ni–W–P coatings. For all the coatings, including the ones containing tungsten, a marked decrease in pore resistance (R_por) over time is observed. This means that their corrosion resistance and capacity to protect the substrate decline. On the other hand, after 24 h immersion in the 3.5% NaCl solution the Ni–W–P coating shows the highest low‐frequency impedance modulus (|Z|_{f = 0.01 Hz}). As regards corrosion resistance, the Ni–P coatings and the Ni–W–P coatings perform best.     

Stresses and strains in soldered joints

In this article, current thinking on stresses in soldered joints of different physical and mechanical properties was appraised, as well as the possibilities for decreasing them with the use of different techniques, from technological experiments to numerical methods. The influence of individual factors on the size of stresses was analysed, including the solder gap size, the thicknesses of joined elements, area and soldered surface roughness, spacers, and compensation inserts as well as joint geometry. The results of numerical calculations of 2D models of soldered joints for different sizes of surfaces soldered at a constant width of solder gap were also presented. Particular attention was paid to stresses occurring in joints with large soldering surfaces.