مجله مواد نوین
سال نهم شماره 4 (پیاپی 36، تابستان 1398)

Lithium-air battery has been a focus of study for the past two decades due to their high theoretical energy density. Solid state electrolytes with high ion conuducting capability still remains a critical challenge in developing lithium-air batteries. Lithium aluminium titanium phosphate with high ion conducting properties and NASICON structure is a hopeful material as solid electrolyte. In this study we have prepared LATP powders by a solution based synthesis method continued by annealing to obtain convenient crystallinity without impurities. Preferred Crystallization temperature was determined to be 800 °C by x-ray diffraction analysis. . The milled powder was used to form pellets, which was then calcined 850 °C for two level of pressing pressure and sintering time. Highest ionic conductivity of 1.07×10-4 was abtained by pressing pressure of 50 Mpa and duel time of 3 hours. Although highest density refered to pressing pressure of 300 Mpa and 3 hours duel time.

Semi-solid powder processing (SPP) is a technology that combines traditional powder metallurgy and semi-solid forming methods and has potential to produce metal matrix composites with low cost and high efficiency. In this research, SPP was used to fabricate magnesium alloy AZ91D matrix composite with high SiC reinforcement loading. First, for preparing powder, AZ91D magnesium alloy chips with average size of 4 × 2 × 1 (mm) were mechanically milled with a planetary ball mill and then, for mechanical alloying, the obtained powder with 50 wt.% (36 vol.%) 2 µm silicon carbide were milled again. The milled powder and also AZ91D/SiC composite powder were investigated by a field emission scanning electron microscopy (FESEM), particle size analyzer (PSA) and X-ray diffractometery (XRD). Spark plasma sintering (SPS) apparatus was used to densify the prepared composite powder by heating the powder mixture to semi-solid temperatures 561 °C (equivalent to liquid fraction of 30% in the whole sample) and 576 °C (equivalent to liquid fraction of 40% in the whole sample) applying pressure simultaneously. Microstructure, density, hardness, compressive strength and also present phases in the sintered samples were studied. The results show composites with few porosities and good mechanical properties can be prepared by SPP.

One of the important parameters to increase the corrosion resistance of base metal is the selection of an appropriate primer. This is an important factor for increasing the adhesion and durability of the coating. In this study, the effect of two different primers on the corrosion resistance of the painted low carbon steel has been investigated. For this purpose, zinc phosphate (which is normally used as a paint primer) and Ni-P nano-structured coating were used. The corrosion resistance was evaluated by potentiodynamic and cyclic polarization tests, electrochemical impedance spectroscopy and salt spray tests. The Scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) were used to characterize the morphology and composition of the coatings. And adhesion of the paint was investigated by pull off test. The results showed that the corrosion resistance of the painted low carbon steel with Ni-P nano-structured primer was more than that of the zinc phosphate primer. So that the polarization resistance increased by about 79.1 kΩ.cm2 and the pitting potential increased to 0.49V for nano-structured coating samples compared to zinc phosphate samples. Also, the results of the paint adhesion test indicated a high adhesion to nano-nickel-phosphorus primer compared to the phosphate-zinc primer.

With the successful application of the protrusion spot friction stir welding technology to 2024 aluminum alloy and low carbon steel plate with a thickness of 1 mm , this technique was expanded to the spot welding of 1 mm thick 6061 aluminum alloy in this study. The effects of the tool dwell time (6, 12, 18 s) and plunging depth (0.1, 0.14 and 0.18 mm) were investigated on the microstructure and mechanical properties of samples. Surface appearance of the welding zone showed that the keyhole was not formed and the appearance of weld was relatively smooth. Microstructure and mechanical results indicated that the welding zone with uniform and refine structure due to dynamic recrystallization presents higher hardness and strength than base metal while can be affected by dwell time. Increasing the plunging depth increases the tensile strength and also decreases the thickness of the upper sheet.Fracture surfaces of the failed specimens present the shear fracture and the interfacial fracture.

Electrolytic plasma oxidation (PEO) oxidation is one of the most important methods for oxidation of materials and coatings. The coatings based on aluminum in the PEO method have two α-Al2O3 and γ-Al2O3 altitudes, which have α-Al2O3 allotropic coatings that have better hardness and abrasion resistance. Therefore, the main objective of the present study is to optimize the alumina of aluminum oxide to increase the amount of α-Al2O3 in the coating produced by the PEO method. In the present study, aluminum 1050 is used as a base metal, and materials such as potassium hydroxide, sodium pyrophosphate, and sodium aluminate are used as electrolytes. To optimize the data, the RSM test design method was used with the Design Expert 7 software. The amount of potassium hydroxide, sodium pyrophosphate and sodium aluminate, independent variables of research and hardness, and the ratio of the highest peak allotropic α-Al2O3 to the highest peak γ- Al2O3 are dependent variables of the research. The results of this study show that the optimal electrolyte composition in order to produce the highest amount of α-Al2O3 phase is 2.9 g / L KOH, 1.15 g / L sodium Sodium pyrophosphate and 0.34 g / L Sodium Aluminate, which is the ratio of peak intensity α -Al2O3 (in the XRD test) on the γ-Al2O3 peak at an optimal level of 622 and a hardness of 1648 Hv.

Tin dioxide (SnO2) and Zn doped SnO2 structures were synthesized by hydrothermal method. In this method, synthesis of metal oxides was done without using any additives only by selection of new precursors in Urea-based solvent. The applied solvent in this work can be used as size and shape directing agent to prevent further particle growth besides solvent role. Also by decomposition of Urea component of the solvent at 200 °C, the medium became alkali and can help to the production of metal oxide. The calcination process was done for the production of SnO2 and Zn-doped SnO2 after synthesis. The obtained products were characterized by using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Fourier transform near IR (FTIR), energy dispersive X-ray (EDS) and UV-Vis spectroscopy.  By this method, the products with average sizes of 16 and 18 nm were obtained, respectively for SnO2 and Zn-doped SnO2. No peaks of crystalline impurity phase were observed in the XRD pattern. The calculation showed 3.6 e.V.  for band gap energy that related to ultraviolet part of the electromagnetic spectrum.                        Keywords: Tin Dioxide, Zinc-doped Tin Dioxide, Urea, Calcination.

Austempered ductile iron (ADI) is well known as useful engineering material and can compete with forged steel in many applications. But its poor machinability have caused to be not quite welcomed by manufacturers. Therefore, it is essential to modify production process to achieve desire machinable ADI by controlling of heat treatment parameters. The present study was, therefore, performed to clarify the influence of austenitizing time on cutting forces in rough turning operations and to obtain the optimum austenitizing duration of improving the machinability. To attain this goal, the samples of ferritic ductile iron (FDI) were austenitized at temperature of 900 oC for 5 to 60 min, followed by austempering into a salt bath at 370°C for 60 min to produce dual matrix structures (DMS) with different ausferrite volume fractions. Image analysis was employed to quantitatively evaluate the microstructure. The hardness were determined via Brinell test method. As a criteria adopting for machinability, cutting forces measured by Kistler dynamometer. The results indicated that the ausferrite fraction and hardness increased by increasing austentizing time according to the Johnson-Avrami model. Increasing austenitizing time to 12 min resulted in 40-50% and 36% improvement on the resultant cutting force and Specific cutting power, respectively, when compared to ADI. The resultant cutting force was correlated with feed rate as a power model with exponents of 0.73, 0.80 and 0.85 for FDI, DMS and ADI, respectively. Obtained results indicates the selection of proper duration of isothermal austenitizing play the key role to achieve ADI with desire machinability.

The microstructure control of sodium beta-alumina electrolyte used in the manufacture of sodium sulfur batteries is important for obtaining appropriate mechanical and ionic conductivity properties. In this research, the effect of particle size of sodium beta-alumina powder on the final microstructure and properties of this ceramic has been investigated. For this purpose, solid-state-synthesized sodium beta-alumina powder was milled by attrition milling for 30 min, 2, 6, and 10 hours. The results showed that the milling time had a significant effect on the powder particle size and consequently on the condensation behavior, microstructure, and finally on the fracture strength and ionic conductivity of sodium beta-alumina electrolyte. By increasing the milling time from 30 minutes to 6 hours and reducing the average particle size of the powder from about 2 to 0.7 microns, the resulting powder condensation behavior improved due to increased sintering diving force, resulting in increased fracture strength and ionic conductivity of up to 65% and 100%, at high temperatures. With increasing the milling time to 10 hours, due to the development of non-uniform microstructure, a decrease in the mechanical and electrical properties of sodium beta-alumina ceramic was observed. The results of this study also showed a linear relationship between the fracture strength and the density of the samples can be established.

in this paper, cause of leakage on the caustic tank bottom is investigate using simulation cathodic protection and develop the NACE formula “current distribution with a close anode-to-structure spacing”. The Finite Element Method is used for numerical solution. Although, field measurements have been under protection of the tank bottom, However, the simulation results showed that only a limited area of the tank bottom was protected, which this area follows the NACE formula and the surrounding areas of the tank have a lower level of protection, that has led to the leakage this areas. There were many ways to increase the protection area, one of them was an increase the anode distance from the tank bottom that the NACE formula indicating this issue but the simulation results showed the opposite of this. Each anode make a potential gradient that can vary from one anode to another. Therefore, NACE formula can be used until; with increase anode distance from tank bottom, tank bottom don’t get out from anode potential gradient. For this reason, in this paper, the NACE formula has been developed by providing a complementary formula and using the specified condition, which has a higher efficiency than the previous formula.

The purpose of this study was to evaluate the simultaneous effect of Hyaluronic acid (HA) - Polyvinyl alcohol (PVA) - Gelatin (Gel), and nano Hydroxyapatite (nHAp), which is mineral in bone. In this study, for the first time, bone scaffold of nHAp and bioresorbable polymers (HA, PVA, and Gel) was prepared by solvent evaporation method. The composite specimens were prepared using nHAp-PVA, nHAp-PVA-Gel and nHAp-PVA-HA, four-component nHAp-PVA-HA-Gel, using a simple liquidation process. Phase and chemical analysis were investigated by FTIR and XRD tests. The distribution and porosity size and their relationship to each other as well as the roughness of porosity were studied using scanning electron microscopy. The compressive strength test was also performed on tablets prepared from this composite. The FTIR test did not indicate the formation of a new chemical compound. The compressive strength indicated that the four minor sample had the highest numerical value. Investigating the SEM analysis of the formation of scaffolds for a four-part sample, which shows porosity percentage, porosity size and bonding, suggest the suitability of this sample for tissue engineering applications. The analysis of the XRD is an amorphous specimen and, given the similarity of the natural bone XRD diagram, this composite can be used as a bone filler.

The research is based on experimental tests, lap joint welding of 5456 aluminum alloy was carried, so that the hard working H321 sheet with the thickness of 5 mm was placed on an annealed sheet with the thickness of 2.5 mm and has been investigating the simultaneous effects of parameters such as rotation speed and welding speed on metallurgical and mechanical properties in friction stir welding process. The results showed that increasing of rotation speed and reducing of welding speed (increase of welding step) causes increased heat input, increase vertical flux, increase hook height and reduction in effective Sheet thickness and it is causing the failure from the thermomechanical zone where the maximum heat input applied also, increasing of welding speed causes reduction in the material mixing and hook height and it causes an interface failure. It was observed with an examination of the results due to the differences in thickness of the sheets, existence of hook defect and its appropriate height and orientation is useful in this joint and causes an increase in strength and failure was in the base metal of the sheet with a thickness 2.5 mm in a tensile test.

In this research, the effect of billet preheat temperature on the forming force value in hot backward extrusion process for a preform made of vanadium micro alloyed steel is studied. The plastic deformation behavior of steel using hot compression test at temperatures of 850℃ to 1250℃ under different strain rates is obtained. Then on the basis of these data, the hot backward extrusion process for the desired vessel in the same temperature range is simulated using finite element method. The results of the hot compression test and finite element, show that with increasing the preheat temperature from 850℃ to 1250℃, the maximum stress reduced from 200 MPa to 42 MPa and the required force for hot extrusion process is reduced from 247 to 43 Ton, respectively. In addition, the microstructure of the samples was examined by optical microscopy and no defect was observed in microstructure. Finally, according to result of calculated force in hot extrusion process on billet with 1200℃ preheat temperatures was carried out in the workshop and deformation of billet to perform was carried out without dimensional distortion wrinkles and crack.