RESUMEN
An unstable energy-unbalanced state such as superheating or supercooling is often unexpectedly observed because a factor of energy depends not only on the temperature but is a product of temperature (T) and entropy (S). Thus, at the same temperature, if the entropy is different, the total energy of the system can be different. In such cases, the temperature-change-rate cannot match the entropy-change-rate, which results in a hysteresis curve for the temperature/entropy relationship. Due to the difference between the temperature- and entropy-change-rates, properties of a material, such as the boiling and freezing points, can be extended from point to area. This study confirmed that depending on the heating rate, tin powders exhibit different melting points. Given the contemporary reinterpretation of many energy-non-equilibrium phenomena that have only been discussed on the basis of temperature, this study is expected to contribute to the actual expansion of scientific/engineering applications.
RESUMEN
In this study, the correlation between surface roughness of carbon steel and crystal size of manganese phosphate coatings has been investigated. The microstructure and surface morphology of the coatings were analyzed by SEM, XRD. The surface roughness test was carried out in order to calculate Ra value by atomic force microscopy (AFM). Also, the tribology property of manganese phosphate coating was tested by ball-on disk. XRD showed that (Mn,Fe)5H2(PO4)4·4H2O in manganese phosphate coating layer was formed by the chemical reaction between manganese phosphate and elements in carbon steel. Also, (Mn,Fe)5H2(PO4)4 · 4H2O was observed to be formed in all manganese phosphate conversion coating. With regard to the effects of surface roughness on manganese phosphate coatings, it can be seen that there is an increase of the crystal size on manganese phosphate coating as the surface roughness of carbon steel decreased. The increase of crystal size by the surface roughness had effect on the tribology property and electrochemical property. It was approved that friction coefficient of manganese phosphate coating is remarkably improved as the surface roughness of carbon steel become rough.
RESUMEN
To improve the NO2-sensing performance of single-walled carbon nanotube (SWCNT)-based sensors, zinc oxide (ZnO) nanoclusters (NCs) were functionalized by a microwave (MW)-assisted synthesis technique. Gas sensors based on pristine SWCNTs and ZnO NC-SWCNT composites synthesized using different weight ratios (ZnO/SWCNTs = 0.5:1, 1:1, 2:1, and 3:1) were fabricated, and their ability to sense various gases at room temperature (25 °C) was investigated. The results showed that the sensing performance of the ZnO NC-SWCNT composite synthesized with a weight ratio of 1:1 (denoted as Z-SWCNTs) was significantly enhanced with respect to NO2 response and selectivity. This enhanced sensing performance is thought to be a result of both the modulation of the conduction channel at the ZnO NC-SWCNT heterointerfaces and the generation of defects (or holes) by MW irradiation that act as active sites for the target gases. The results obtained in this work provide not only a facile method of cofunctionalizing oxide NCs and defects but also a new methodology for improving the sensing capabilities of SWCNT-based gas sensors.
RESUMEN
The surface activation agents have been used to form a high quality coating layer on manganese phosphate process. The role of surface activation agents increases the nucleation sites, which leads to obtain a finer phosphate coating. In this study, the effects of surface activation agents on manganese phosphate coating were investigated by changing the chemical composition ratio between sodium pyrophosphate and manganese carbonate. The morphology, chemical composition and corrosion resistance of the coatings were analyzed by SEM, XRD, EDS, XPS and electrochemical polarization method, respectively. Also, the tribology property of manganese phosphate coating was tested by ball-on disk. In the results of EDS analysis, coating layer consists of elements such as Mn, P, Fe, O, and C. XRD showed that (Mn,Fe)5H2(PO4)4 · 4H2O in manganese phosphate coating layer was formed by the chemical reaction between manganese phosphate and elements in carbon steel. With regard to the effects of surface activation agents on the manganese phosphate coatings, it can be seen that there is an increase of the crystal size on phosphate coating as the content of sodium pyrophosphate increased. The increase of sodium pyrophosphate had effect on the tribology property under the condition of spindle oil retention. Corrosion resistance was improved for manganese carbonate (3 g/L) and sodium pyrophosphate (3 g/L) coating with the ratio of 1:1. Also, better tribology property was observed for manganese carbonate (3 g/L) and sodium pyrophosphate (15 g/L) with the ratio of 1:5.
RESUMEN
In this study, the correlation between morphology and friction of manganese phosphate coating layer with additive agent of tartaric acid by 2, 4, 6 g were investigated. The microstructure and morphology of the coatings were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and atomic force microscopic (AFM). Potentiodynamic polarization test was carried out in order to evaluate the corrosion protection properties of manganese phosphate coating in 3.5 wt.% NaCl solution. Also, the tribology property of manganese phophate coating was tested by ball-on disk. In the results of EDS analysis, coating layer consists of elements such as Mn, P, Fe, O, and C. XRD showed that (Mn, Fe)5H2(PO4)4·4H2O in manganese phosphate coating layer was formed by the chemical reaction between manganese phosphate and elements in SM45C alloy. The corrosion resistance of manganese phosphate coating with additive agent was superior than the one without additive agent. Also, in the Fe amount in sludge, manganese phosphate coating layer with additive agent was observed to be considerably decreased.
RESUMEN
Effect of pulse reverse current (PRC) method on brass coatings electroplated from gold solution was investigated by various plating parameters such as plating duration, the anodic duty cycle, the anodic current density and the cathodic current density. The reversed current results in a significant change in the morphology of electrodeposits, improvement of the overall current efficiency and reduction of deposit porosity. With longer pulses, hemispherical surface features are generated, while larger grains result from shorter pulse widths. The porosity of the plated samples is found to decrease compared with results at the same time-average plating rate obtained from DC or Pulse plating. A major impediment to reducing gold later thickness is the corrosion of the underlying substrate, which is affected by the porosity of the gold layer. Both the morphology and the hydrogen evolution reaction have significant impact on porosity. PRC plating affect hydrogen gold and may oxidize hydrogen produced during the cathodic portion of the waveform. Whether the dissolution of gold and oxidation of hydrogen occur depends on the type of plating bath and the plating conditions adapted. In reversed pulse plating, the amount of excess near-surface cyanide is changed after the cathodic current is applied, and the oxidation of gold under these conditions has not been fully addressed. The effects of the current density, pulse-reverse ratio and brightener concentration of the electroplating process were investigated and optimized for suitable performance.