Iranian Journal of Materials Science and Engineering

A Study on the Nanoscale Austenite Stabilized by Q&P Heat Treatment in a Low-alloy Medium-carbon Steel

Sh. Kheirandish

In this research, the objective was to investigate the stabilized retained austenite in the microstructure resulting from the Q&P heat treatment since the primary goal in Q&P is to create a microstructure consists of stabilized retained austenite and martensite. For this purpose, a low-alloy steel with 0.4wt. % carbon was treated by quench and partitioning (Q&P) process. The Q&P was conducted at different quench temperatures to obtain a considerable amount of retained austenite, while partitioning temperature and time were kept constant. Through analysis of the XRD profiles, volume percent, carbon concentration, and lattice parameters of retained austenite and martensite were calculated. At quench temperature equal to 160°C, 12vol.% austenite was stabilized to the room temperature, which was the highest amount achieved. The microstructural observations carried out on selected samples, revealed that retained austenite has a nanoscale particle size, about 200nm. Distinguishing retained austenite in the SEM micrographs became possible by utilizing SE2 signals via the difference in phases contrast. Two types of morphology, film-like and blocky type, were identified by means of TEM and TKD and a schematic model was proposed in order to explain these morphologies

Growth Inhibitory Effect of Oven Dried Copper Nanoparticles(CUNPS) on Drug Resistant Clinical Isolates

S. Hemalatha

Drug resistant pathogenic microbes have been causing serious health issues resulting in the substantial increase of death rates and morbidity paving the way for nanoparticles to be utilized as antimicrobial agents. This study was performed to evaluate the effectiveness of CuNPs on the growth of drug resistant clinical isolates of Streptococcus pyogenes, Enterococcus faecium and Enterococcus faecalis. Minimum inhibitory concentration of CuNPs against Streptococcus pyogenes, Enterococcus faecium and Enterococcus faecalis was found to be 1.25. 1.25 and 0.625 mg/ml and minimum bactericidal concentration against the same isolates was found to be 2.5, 2.5 and 5 mg/ml respectively. The ratio of MBC/MIC, referred to as tolerance level, was calculated for all the isolates which signifies the bactericidal or bacteriostatic effect of any antimicrobial agent. For Streptococcus pyogenes and Enterococcus faecium, the tolerance level was 2 while as for Enterococcus faecalis, it was 8. Antibiotic susceptibility results were calculated which showed that the isolates were resistant to Ampicillin (10 µg), Amoxycillin (30 µg) and Aztreonam (30 µg). Susceptibility results were followed by calculating multiple antibiotic resistance indices (MARI). MARI is an important tool which gives an idea about the bacterial resistance in a given population. For all the three isolates, MARI results were equivalent to 1 because of their resistance towards all the three antibiotics used. Antimicrobial activity through well-plate method was carried out and inhibitory effect of CuNPs on biofilm formation was evaluated.

Thickness Dependence of Structural and Optical Properties of CdTe Films

M.H. Ehsani

In this work, Cadmium Telluride (CdTe) thin films were deposited on glass substrates at room temperature by vacuum evaporation technique. The deposited CdTe thin films were characterized by X-ray diffraction, UV-Visible spectroscopy and Field emission scanning electron microscope (FESEM) techniques. Structural studies revealed that the CdTe films deposited at various thicknesses are crystallized in cubic structure. The results showed the improvement of the film crystallinity upon grain size increment. Optical constants such as refractive index (n), extinction coefficient (k), real and imaginary parts of dielectric constant, volume energy loss function (VELF), and surface energy loss function (SELF) were calculated using UV-Vis spectra. In addition, band gap and Urbach energies were calculated by Tauc and ASF methods. The band gap energy of the specimens was found to decrease from 1.8 to 1.4eV with increasing the thickness of films. The absorption coefficient, computed and plotted versus the photon energy (hν) and tailing in the optical band gap, was observed which is understood based on Urbach law. Urbach energy variation from 0.125 to 0.620 eV in the samples with higher thicknesses is concluded.

The Failiur Analysis of Nb-Microalloyed δ-TRIP Steel

A. Jenabali Jahromi

The relation between microstructure and the fracture mechanisms of δ-TRIP steel with different Nb-content has been investigated using complementary methods of light microscopy, SEM, EDS, EBSD, X-ray phase analysis and tensile test. The results revealed a close dependency between the presences of constitutive phases i.e. ferrite, bainite, retained austenite and martensite and the mode and characteristics of fracture. All samples revealed almost different fractography pattern which could be associated to the effect of Nb microalloying element. The different fractography patterns were consisted of dimple rupture, riverside and Wallner lines pattern. The proportion of the cleavage fracture in comparison of dimple rapture increased by increasing the Nb-content due to the increase of primary martensite in the microstructure.

Structural and Optoelectrical Properties of Single Phase SnS2 Thin Films at Various Substrate Temperatures by Spray Pyrolysis

E. Borhani

Thin films of SnS₂ were prepared, as the absorber layer in solar cells, using an aqueous solution of SnCl₄ and thiourea by spray pyrolysis technique. Effect of the Substrate temperature on the properties of these thin films was studied. Investigation via XRD showed the formation of polycrystalline SnS₂ along (001) in all layers; there was no sign of other unwanted phases. With increasing of substrate temperature from 325 to 400 ⁰C, the crystallinity of the sample was improved, after that, it deteriorated the crystallinity. Layers had granular morphology and Valley- Hills topography. UV-VIS spectra revealed that the transmittance of all layers was lower than 40% in the visible region and the band gap reduced from 2.8 to 2.55 eV with increment in temperature from 350 to 400 ⁰C. Photoluminescence spectra of the prepared film, which was formed at 400 ⁰C showed a dominant peak at 530 nm, caused recombination of excitons. The least electrical resistivity of the SnS₂ thin film prepared at 400 ⁰C in dark and light environment were 4.6 ×10 ^-3Ωcm and 0.65×10 ^-3Ωcm, respectively; which demonstrated 400 ⁰C was the optimum temperature in point of optoelectrical properties in the SnS₂ thin film.

Thermal Stability and Kinetics of Sodium Alginate and Lignosulphonic Acid Blends

S. Giridhar Reddy

Biodegradable polymer blends are prepared by solution casting method by mixing Sodium alginate (SA) and Lignosulphonic acid (LS) biodegradable polymers. In order to investigate for controlled drug delivery the thermal stability of polymer blends are the primary requirements because they should be stable in aqueous medium. The polymer blends are studied using thermogravimetric analysis. The TGA data are used to analyze degradation temperature and energy of activation using ‘Horowitz and Metzger’ an approximate integral method. The energy of activation reveals that blends are stable as compared to their polymers.

L16 Orthogonal Design Synthesis of NASICON-type Li1.4Al0.4Ti1.6(PO4)3 Solid Electrolyte by Pechini Method for Process Optimization

M. R. Ghaani

Na super ionic conductive (NASICON) materials are ceramics with three-dimensional scaffolds. In this study, Li_1.4Al_0.4Ti_1.6(PO₄)₃ with NASICON structure was synthesized by Pechini method. As a result, a sample having a total conduction of 1.18×10^-3 S cm^-1 was attained. In addition, various parameters were studied to obtain high value of conductivity, by optimizing the process. The optimization was made using L16 Taguchi based orthogonal array, followed by ANOM, ANOVA and stepwise regression. As a result, the optimum synthesis parameters can be obtained, while pH of the solution was adjusted to 7. The ratio between the concentration of citric acid to metal ions and ethylene glycol concentration stuck to 1 and 2.5, respectively. The best heat treatment can be carried out with a combination of pyrolysis at 600 ºC and sintering at 1000 ºC.

Solvation Behavior of Gold Nanorods in Water: A Monte Carlo Simulation Study

H. Esfandiar

Gold nanoparticles have become common in many applications of biotechnology due to their specific properties. Shape and size are important attributes which affect their solubility in water. In this study, the outcomes of Monte Carlo Simulation for the solvation of gold nanorods in aqueous solution with the different radii, in terms of solvation free energy, are discussed. Simulation results show a negative solvation free energy for all the samples with radii of 4 to 9Å. The results show that the absolute values of solvation free energy for gold nanorods with smaller radius are larger, which indicate the dependency between the gold nanorods solvation and their radius.