Sharif Digital Repository

Laser shock peening (LSP) is known as a post processing surface treatment which can improve the mechanical properties of some materials. Shock waves are generated by confining the laser-induced plasma to cause a large pressure shock wave over a significant surface area. In the present study, effects of LSP on the electrochemical corrosion and micro hardness properties of 316L stainless steel alloy were investigated by changing the laser parameters such as the laser spot size, the average number of impacts, and the laser intensity. Since laser parameters do not cover the desired region of LSP, we have to use the proper design of experiment method, in which the D-optimal design of MATLAB was... 

Reverse osmosis (RO) membrane process has become the most promising technology for desalination to produce purified water. Among numerous polymeric materials used to fabricate RO membranes, aromatic polyamide thin film composite (TFC) membranes are dominant in commercial RO membrane processes because of their high salt rejection and water permeability as well as their excellent chemical, thermal, and mechanical stability. However, the major hindrance to the effective application of polyamide TFC RO membranes is membrane fouling. Furthermore, polyamide TFC RO membranes have limited stability to chlorine, which is commonly used as disinfect to control membrane biofouling. These two factors... 

In this paper, the effect of ozone on membrane fouling of membrane bioreactor (MBR) systems was investigated. Sludge specification such as soluble microbial product (SMP), extracellular polymeric substance (EPS), viscosity, particle size distribution (PSD), microscopic observations and sludge volume index (SVI) in presence of ozone were determined. Further, EPS, Fourier-transform infrared (FTIR) analysis, excitation-emission matrix (EEM) fluorescence spectroscopy, and gel permission chromatography (GPC) are considered to determine cake layer characteristics. The results indicated COD removal did not show significant difference with ozonation. Ozone also increases the particle size and... 

A new method for fabrication of silver nano-islands on glass fibers using a top-down process is introduced. A thin layer of silver chemically coated on the surface of the glass fibers evolves into silver islands by heat treatment. The effect of the concentration of the initial solution and the temperature were investigated. Segregation was more clearly observed for lower solution concentrations and higher temperatures. The temperature of 500 °C was found optimum where separated islands form. At higher temperatures, the coagulation and burial of silver islands occur. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and diffused reflectance spectroscopy (DRS) were... 

Direct oxidation is a simple and effective method for titanium surface treatment. In this research, a titanium sample was directly oxidized at the high temperature in two different atmospheres, air and pure oxygen, to obtain better atmosphere for titanium surface treatment. The results of the Raman spectroscopy indicated that in both atmospheres, the rutile bioactive phase (TiO2) has been formed on the titanium surface. The results of X-ray diffraction (XRD) also revealed that the surface of oxygen-treated sample was composed of the rutile phase and titanium monoxide (TiO), while at the surface of the air-treated sample, the rutile phase and titanium dioxide had been formed. Further, the... 

In this research, polysulfone (PSf) ultrafiltration (UF) membranes were prepared by a phase inversion method. Surface modification of the PSf membranes was carried out via grafting of acrylic acid as a hydrophilic monomer by free radical graft polymerization initiated by redox reaction. A central composite design (CCD) of response surface methodology (RSM) was applied to design the experiments. The process variables were acrylic acid concentration (CAA), redox system contact time (T1), and acrylic acid polymerization time (T2), while the contact angle (CA), pure water flux (PWF), and flux recovery ratio (FRR) were considered as the responses. Analysis of variance (ANOVA) demonstrated that... 

Hexagonal core–shell SiO2[–MOYI]Cl–]Ag nanoframeworks were synthesized via surface modification of hexagonal silica nanoparticles prepared from perlite (EP) as a cheap and abundant raw material. The prepared samples were well characterized by X-ray diffraction powder (XRD), energy dispersive X-ray (EDX), diffuse reflectance spectroscopy (DRS), Brunauer–Emmett–Teller (BET) specific surface area analysis, fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). The XRD patterns confirmed that Ag and AgCl crystalline phases were successfully loaded on the surface. The TEM images were also implied that the... 

In this study, titanium alloy (Ti-6Al-4V) and austenitic stainless steel (AISI 304) biomedical alloys were subjected to surface severe plastic deformation (SSPD) via severe shot peening (SSP) with the conditions of A28-30 Almen intensity. SSP is widely accepted as much more effective than the conventional surface modification techniques since it forms a nano-grain layer with large number of dislocations and grain boundaries. The SSP treatment in this study was led to a very thin rough layer in Ti-6Al-4V titanium alloy compared to that of AISI 304. The thicker layer of AISI 304 was created by twin-twin intersections and a martensite structure transformations. SSP treatment was resulted in a... 

The purpose of this research is to explain the surface modification of fabricated polyamide reverse osmosis (RO) membranes using UV-initiated graft polymerization at different irradiation times (15, 30, 60, and 90 s) and various acrylamide concentrations (10, 20, and 30 g L−1). Also, coating of membranes surface with various concentrations of TiO2 nanoparticles (10, 20, 30, and 50 ppm) followed by the same UV irradiation times was investigated. After that, the membranes modification was done by grafting of acrylamide blended with TiO2 nanoparticles via UV irradiation. The characterization of membranes surface properties and their performance were systematically carried out. The results... 

Abstract: The effect of de-siliconization on the oxidation behavior of AISI 430 stainless steel used for solid oxide fuel cell interconnect application was investigated. De-siliconization treatment was conducted via heating steel parts in an H2 environment. The de-siliconized substrates were then coated with a Mn1.5Co1.5O4 spinel coating, using wet spray method. For comparison, a similar coating process was applied on the as-received AISI 430 stainless steel specimens. Oxidation kinetics of coated interconnects were evaluated at 700, 800 and 900 °C in air. Results showed that the de-siliconization surface treatment decreased oxidation rates, with kinetic rates (g2 cm−4 s−1) of 4.39 × 10−14... 

In this study, the in-vitro bone regeneration ability of commercial pure titanium (CP-Ti) surface modified via electrospun polyvinylidene/hydroxyapatite (PVP/HA) masking and subsequent Nd-YAG pulsed laser treatment was investigated. The ratio of HA to PVP played a significant role in achieving a perfect homogenous mask on the CP-Ti. In the laser treatment process, the parameter of area scanning speed (ASS) had an important influence on the final surface morphology. A favorable range was defined for this parameter where these two conditions were satisfied: no PVP remaining and no severe substrate melting. Within a favorable range of ASS, as decreasing ASS exchanged the surface structure from... 

The condensation process is of great importance in many heat transfer devices in which a large amount of energy must be transferred. Furthermore, condensation is a crucial part of energy conversion and affects the energy efficiency of thermal desalination plants and solar stills. During the condensation process in solar stills, an essential part of the energy is transferred through the condensation surface to produce fresh water. Therefore, the condensation surface plays a significant role in the working efficiency of solar stills. The wettability of the condensation surface influences the condensation mechanism, which, in turn, affects the efficiency of solar stills. This study aims to... 

Control charts are the most popular statistical process control tools used to monitor process changes. When a control chart indicates an out-of-control signal it means that the process has changed. However, control chart signals do not indicate the real time of process changes, which is essential for identifying and removing assignable causes and ultimately improving the process. Identifying the real time of the change is known as the change-point estimation problem. Most of the traditional methods of estimating the process change point are developed based on the assumption that the process follows a normal distribution with known parameters, which is seldom true. In this paper, we propose... 

The influences of cupric oxide layer thickness, cuprous oxide particles, and pores on mechanical properties and microstructure of alumina-copper eutectic bond have been investigated. The furnace atmosphere in the first stage was argon gas with 2 × 10-6 atm oxygen partial pressure. In the second stage, the furnace atmosphere was same as the first stage unless that in cooling between 900-1000 °C, the hydrogen gas was purged in furnace atmosphere. Finally, in the last stage a vacuum furnace with 5 × 10 -8 atm pressure was chosen for bonding procedure. Peel strength of first stage specimens shows that cupric oxide layer with 320 ± 25 nm thick generates the maximum peel strength (13.1 ± 0.3... 

Arms bearing ureido-pyrimidinone functional groups with self-association capability (through quadruple hydrogen bonds) were successfully grafted onto hydroxyapatite nanoparticles. The supramolecularly modified nanoparticles (nHApUPy) exhibited enhanced colloidal stability compared to the original hydroxyapatite nanoparticles and were uniformly dispersed in supramolecular polycaprolactone in PCL(UPy)2/HApUPy nanocomposites at different filler loadings. The combined atomic force microscopy, mechanical, and rheological analyses confirmed a high degree of compatibility of HApUPy nanoparticles with the polymer matrix. The temperature dependence of the supramolecular structure in PCL(UPy)2/HApUPy... 

Cobalt is the most common binder in cemented carbides industry. However, there are some interests in use of alternatives. The similarity in properties has made nickel the first choice. In the present work, the effect of initial composition on modern hardmetals containing transition metal carbides/carbonitrides that are called "cemented carbonitrides" with nickel as binder was investigated. Change in quantity of additive carbides and tungsten to carbon (C/W) weight ratio through applying metallic tungsten powder in primary powder mixture had some effects on final hardness, transverse rupture strength, and microstructure of studied alloys. Addition of vanadium carbide not more than 0.2 wt.%,... 

Nowadays, gasochromic Pd/WO3 coatings as optically switchable materials have become more applicable for hydrogen sensors and smart windows. In this study, WO3 films were prepared by Pulsed Laser Deposition (PLD) and spin-coating sol-gel techniques. For deposition of Pd, first a layer of PdCl2 was obtained via a simple drop-drying process by dropping PdCl2 solution onto WO3 substrates and drying them at room temperature. Then Pd nanoparticles were synthesized via hydrogen gas exposure that causes reduction of the PdCl2 layer. According to Scanning Electron Microscope (SEM) observations before hydrogen reduction, many individual nanoparticles or fractal-like constructions of palladium were... 

The nanocrystallization process of amorphous Fe73.5Si13.5B9Nb3Cu 1 was investigated by active screen plasma nitriding (ASPN) treatment at temperatures ranging from 410 °C to 560 °C for 3 h in two gas mixtures of 75% N2-25% H2 and 25% N2-75% H2 at 5 mbar atmosphere. The amorphous ribbons were then annealed under vacuum at the same time and temperatures mentioned above. The structure of the samples was analyzed using various techniques such as X-ray diffraction (XRD), atomic force microscopy (AFM) and differential scanning calorimetry (DSC). Microhardness measurements, electrical resistivity and Vibrating Sample Magnetometer (VSM) were used to study mechanical, electrical and magnetic... 

A developed route to form TiO2 self cleaning coatings on polycarbonate substrates is reported. TiO2 coatings on plastics may find widespread application in auto and construction industries if possess desired photocatalytic and mechanical properties. A chemical surface treatment method was used to create hydrophilic groups on the surface. X-ray photoelectron spectroscopy showed the treatment led to the oxidation of surface groups. TiO2 deposition was based on wet coating using an anatase sol of TiO2 nanoparticles of 30 nm size. The sol was synthesized using a sol-gel route. A pre-coat of peroxotitanium complex was employed to improve adhesion and inhibit the substrate degradation. The coating... 

The present study analyzed the dose-dependent cyto- and genotoxicity of graphene oxide and reduced graphene oxide on spermatogonial stem cells (SSCs) for the first time. The results showed that graphene oxide significantly increased oxidative stress at concentrations of 100 and 400 μg/ml, while low concentrations did not have a significant effect. In addition, according to the MTT assay, the cell number decreased in high-concentration (100 and 400 μg/ml) graphene oxide-treated samples compared to untreated cells. However, a reduced graphene-treated sample demonstrated a significant increase in cell number. Moreover, microscopic analysis found high concentrations of graphene nanosheets in...