Sharif Digital Repository

In order to improve titanium corrosion behavior, we can increase the thickness of oxide layer on titanium surface during anodizing process and by electrochemistry. In this research, self-color anodizing of Ti in sulfuric acid was done, and anodizing layers were created in different colors. The highest value of chromaticity was 37.8 for the anodized sample in 10 V, and the lowest value was 8.6 at 15 V. The oxide layer thickness was calculated by optical method (light refraction). The anodic film thickness increased by increasing the anodizing voltage. The highest thickness of anodic film was 190 nm in sulfuric acid solution for the anodized sample in 80 V. Corrosion resistance of anodized Ti... 

Ta0.8Hf0.2C ceramic has the highest melting point among the known materials (4000 °C). However, this high melting point makes the ceramic difficult to be sintered at temperatures lower than 2300 °C, pressurelessly. The purpose of this study is to consolidate Ta 0.8Hf0.2C UHTC by pressureless sintering at 2000 °C using MoSi2 as sintering aid. In this regard, effect of different amounts of MoSi2 on sintering behavior of Ta0.8Hf 0.2 UHTC was investigated. It was observed that condensation of the UHTC after sintering at 2000 °C was enhanced by increasing MoSi2 content and the highest relative density of 95% was obtained in the presence of 24 vol.% MoSi2. XRD pattern of the sintered UHTC... 

Electrodes made of group VIII and IB metals were examined for their redox process and electrocatalytic activities towards the oxidation of ethylene glycol in alkaline solutions. The method of cyclic voltammetery (CV) and Open circuit potentials measurement (OCP) was employed. It is found that considerable electrooxidation current are observed for silver and copper but lower anodic overpotential for oxidation is obtained for gold and platinum. Oxide layer produced on the surface of all electrodes in alkaline solution under anodic scan participates in ethylene glycol electrooxidation. Oxidation current observed in the reverse scans for platinum and gold are higher than those observed in... 

In this study, tri-cation phosphate coating of zinc, calcium and iron was applied electrochemically to stainless steel 316 substrates. Cathodic current was used as an accelerator for the phosphating process. The effects of current density on the microstructures of the coatings and the time necessary for the reduction of the oxide layer have been established. For this purpose, analyses such as chronopotentiometery, SEM, EDS and linear polarization were carried out. Results indicated that higher electrophosphating current densities result in finer crystal size of the coating. This effect is detrimental to the quality of the layer. In addition, chemical analyses of the layer revealed that the... 

Layers of cobalt and manganese oxides were co-deposited or deposited on top of each other or next to each other by potentiostatic method onto stainless steel substrate. Deposition potentials of 1 and -1 V for the anodic and cathodic depositions were employed. Specific capacitance values in the range of 38.5-78 F g -1 were found with cobalt oxide on top of manganese oxide having the lowest and manganese oxide on top of cobalt oxide having the highest capacitances. The usefulness of the electrodes was characterized by cyclic voltammetry, charge-discharge cycling, and electrochemical impedance spectroscopy in 2 M NaOH electrolyte for redox supercapacitor applications. The latter presented the... 

The effects of intermediate nickel layer on seal strength and chemical compatibility of seal glass and interconnect materials for solid oxide fuel cells (SOFCs) were investigated. Two types of samples (metal/glass/metal sandwiches and glass coated metals) were prepared with the sheet of AISI 430 (nickel plated and uncoated) and slurry of compliant silicate sealing glass (SCN-1). The joined and coated samples were heated at 850 °C for different time durations (0.5-100 h). Tensile and impact tests were performed and SEM micrographs were used to analyze the glass/metal interaction. The results indicate that nickel plated AISI 430 shows higher adhesion strength at short durations of heating due... 

TiO2 a nanotube array was prepared using an anodization process. The process proceeded in a two-electrode cell containing of platinum sheet as the cathode electrode. Two phosphate-base electrolyte solutions containing different amounts of HF and NH4F were prepared. Different concentration of fluorine ions were examined in respected electrolytes. Current transient techniques were used to produce the TiO2 nanotubes at constant voltage of 18-25V. It was revealed that anodization at 18-22V, in so-called electrolytes would end up to nano-tubular structure. However the tubular structure prepared at 20V and from phosphate electrolyte containing of 0.5 wt% NH4F as well as 0.5 wt% HF, was recognized... 

Recent uses of intelligent composites in biomedical appliances aggrandize the necessity of bonding-strength improvement in NiTi/silicone matrix interface. SEM micrographs and pull-out tests are employed to determine the strength of the NiTi/silicone bonds in a flexible composite piece. Greater adhesion strengths are obtained due to the presence of thin oxide layer, surface roughness and frictional forces between the embedded-wires and the contacting phase. Effect of curing treatment on phase transformation temperatures of the wires is determined by electrical resistivity (ER) measurements. Results show that the curing treatment shifts the transition points of the wires towards higher... 

In this research, the pressureless sintering of ZrB 2 composites were studied to obtain the highest densification and investigate the effects of TiC (2–10% wt) and graphite (1–2% wt) additives on the sinterability. The results showed that by adding TiC, the porosity and water absorption of the samples decreased, resulting in an increase in the density of the samples up to ~98% of the theoretical density. The addition of graphite and TiC reduced the surface oxide layers, improved the density and prevented the grain growth. The graphite additive reacted with B 2 O 3 and ZrO 2 and allowed the system to achieve a complete densification at 2000 °C. Both TiC and graphite additives were completely... 

We conduct an experimental investigation on the pool boiling enhancement in DI water on nanoporous surfaces. The surfaces are modified by anodic oxidation, and cavities with 2 mm diameter and pitches between 2.5 and 5 mm applied on them using EDM method filled with a two-part epoxy with low thermal conductivity properties. The capillary wicking action of the superhydrophilic nanoporous oxide layer enhances the rewetting and spreading of the liquid to dry-spots during boiling. The epoxy disks remain wet and prevent merging bubbles during the pool boiling experiment and a 2-D microflow is induced toward dried regions with synergic effects of nanoporous surface absorption, create a considerable... 

Two-stage chemical deposition (TSCD) technique is used to produce ZnO, Mn2O3 and NiO films on soda-lime glass (SL-G) from an aqueous solution of zinc, manganese and nickel complex, respectively. The TSCD method enables the deposition of metal oxide thin films with a thickness which can be controlled during the preparation procedure. The ZnO, Mn 2O3 and NiO thin films were polycrystalline films which were adherent well to the substrates. The SEM micrographs clearly indicate that the zinc oxide layer is composed of oval shaped crystallites preferably orientated perpendicular to the surface of the substrate. The Mn 2O3 and NiO layers were closely packed on the substrate. These particles seem to... 

Latent thermal energy storage dependent on Phase Change Materials (PCMs) proposes a possible answer for modifying the availability of alternating energy from renewable sources such as wind and solar. They can possibly store large amounts of energy in moderately tiny dimensions as well as through almost isothermal procedures. Notwithstanding, low thermal conductivity values is a significant disadvantage of the present PCMs which critically restrict their energy storage usage. Likewise, this unacceptably decreases the solidification/melting rates, hence causing the system response time to be excessively lengthy. The present examination accomplished a better PCM solidification rate with a... 

Nickel oxide (NiOx) is a promising hole transport material in inverted organic-inorganic metal halide perovskite solar cells. However, its low intrinsic conductivity hinders its further improvement in device performance. Here, we employ a trimercapto-s-triazine trisodium salt (TTTS) as a chelating agent of Ni2+ in the NiOx layer to improve its conductivity. Due to the electron-deficient triazine ring, the TTTS complexes with Ni2+ in NiOx via a strong Ni2+-N coordination bond and increases the ratio of Ni3+:Ni2+. The increased Ni3+ concentration adjusts the band structure of NiOx, thus enhancing hole density and mobility, eventually improving the intrinsic conductivity of NiOx. As a result,... 

CuO nanoparticles with average diameter of about 20. nm were accumulated on surface of sol-gel silica thin films heat treated at 300 °C in air. Heat treatment of the CuO nanoparticles at 600 °C in a reducing environment resulted in effective reduction of the nanoparticles and penetration of them into the film. While the thin films heat treated at 300 °C exhibited a strong antibacterial activity against Escherichia coli bacteria, the reducing process decreased their antibacterial activity. However, by definition of normalized antibacterial activity (antibacterial activity/surface concentration of coppers) it was found that Cu nanoparticles were more toxic to the bacteria than the CuO... 

Abstract: Nickel–titanium (NiTi) nanoparticles are ultrafine smart materials manifesting shape memory effect at very small scales. We have produced NiTi nanoparticles surrounded by an amorphous carbon shell using an innovative spark discharge system. The resulting nanoparticles were studied using various characterization methods to systematically study their size, morphology, size distribution, composition, structure, and thermal behavior. Field-emission scanning electron microscopy and dynamic light-scattering results indicated that the average size of the produced nanoparticles was about 13 nm. High-resolution transmission electron microscopy, energy-dispersive spectroscopy (EDS), and... 

ZnO nanoparticles were fabricated via hydrothermal method and an amorphous TiO2 layer was then coated on the nanoparticles via sol-gel route. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies showed that the synthesized ZnO nanoparticles were hexagonal with wurtzite structure and an average particle size of 38 nm. The thickness of the titanium oxide layer was determined to be 20-40 nm. The photocatalytic decolorization of Methylene blue under UV irradiation indicated that as-prepared TiO 2-capped ZnO is inferior than ZnO particles. Nevertheless, calcinations of the particles at 350 °C for 24 h significantly improved the photo-activity of the ZnO/TiO2 core/shell... 

The most common reasons for hard-tissue implant failure are structural loosening and prosthetic infections. Hence, in this study, to overcome the first problem, different bioinspired coatings, including dual acid-etched, anodic TiO2 nanotubes array, anodic hierarchical titanium oxide (HO), micro- and nanostructured hydroxyapatite (HA) layers, and HA/chitosan (HA/CS) nanocomposite, were applied to the titanium alloy surfaces. X-ray diffraction and FTIR analysis demonstrated that the in situ HA/CS nanocomposite formed successfully. The MTT assay showed that all samples had excellent cell viability, with cell proliferation rates ranging from 120% to 150% after 10 days. The HO coating...