METALLURGICAL ENGINEERING
Year:2016 | Volume:19 | Issue:3 (63) |Papers Count:7

LaxSr1-xCoyFe1-yO3 (LSCF) perovskite oxides have been successfully synthesized by GNP method (Glycine Nitrate Process) to use as a cathode electrode in solid oxide fuel cells. X-ray diffraction (XRD) results showed formation of single phase LSCF powder without presence of any impurity. In this study, LSCF and LSCF/GDC inks were used as cathode material. The inks were analyzed with an in-situ sintering study where the in-plane conductivity was used to investigate the effect of different sintering temperatures on the conductivity of the electrodes. Compared to LSCF cathode, it was shown that LSCF/GDC has lower in-plane conductivity due to the present of GDC, which is not an electronic conductor at high temperature. Electrochemical analysis was performed at different temperatures to deeply understand the behavior of the cathode materials. A two-electrode configuration was used to measure the impedance of the cells. LSCF/GDC cathode manifest good performances with polarization resistance of 0.027 Wcm2 at 750°C in the air atmosphere.

Functionally graded material with aluminum matrix have many applications in the aerospace and automotive industry due to high strength and good wear resistance, as they can obtain optimum condition by centrifugal casting method. A390 hypereutectic alloy was cylindrically cast into a cylindrical steel mould as the base alloy with rotational speed of 1200, 1400, 1600 and 2000 rpm by vertical centrifugal casting method. Microstructure of samples, volume fraction of reinforcement particles and their hardness from inner wall to outer wall were investigated by optical microscope (OM). Results show that because of smaller density of primary Si particles than molten Al, these particles move to the inner wall of the samples due to centrifugal force and create a gradient distribution from inner layer to middle region. Moreover, the casting sample with rotational speed of 1400 rpm was chosen as the optimum sample. Possible consequences of characteristics of this sample are discussed.

Zn–Ni alloy coatings were electrodeposited from an acidic sulfate bath, while their microstructures, corrosion properties and wear behavior were investigated. To study their structures, X-ray diffraction (XRD) was used. To evaluate the wear behavior, wear tests via pin-on-disc were performed. Hardness measurements were carried out via Vickers micro hardness testing machine. Secondary and backscattered electron micrographs were taken from the worn surfaces and chemical compositions of the coatings were also investigated using Scanning Electron Microscope (SEM) equipped with Energy Dispersive Spectroscopy (EDS) analyzer. X-ray diffraction (XRD) technique was also used to determine the phase structures of the coatings. The results indicated that the amount of nickel in the coating had a strong impact on their properties so that by increasing the amount of nickel an increase in the coating hardness was obtained. Finally, Zn-14% Ni coating which contained a single phase γ-Ni5Zn21 face centered cubic had the lowest coefficient of friction as well as wear rate among all other coatings with different chemical compositions.

The effect of Fe addition (0.5، 1، 1.5 and 2 wt %) and Mn modification (Mn/Fe=0.5) on hot tearing behavior of F332 Al alloys was investigated. The results show that due to the formation of fine interdendritic b-Al5FeSi platelets، Fe addition up to 0.5 wt% improves high temperature tensile properties and promotes the formation of equiaxed grains thereby increases the hot tearing resistance of the alloy by about 25%. Further addition of Fe up to 2 wt%، however، increases the size and volume fraction of b-platelets، decreases the tensile properties، reduces the fluidity and interdendritic feeding and consequently substantially increases the hot tearing susceptibility (HTS). Mn addition، however، was shown that changes the morphology of b-platelets to less harmful Chinese script، polyhedral or star-like a-Al15(Fe،Mn)3Si2 whereby improves the tensile properties and interdendritic feeding characteristic of the alloy. Therefore، the HTS value is decreased to zero for 0.5 and 1 wt% Fe alloys، but increased by 50 and 40 %، respectively in the case of 1.5 and 2 wt% Fe containing alloys.

In this study, the sphericalurea granulates as space holder were used to manufacturing the steel foams by powder metallurgy technique. In this process, the urea granulates were coated by a mixture of iron, cupper, and carbon powders. After compacting the coated granulates up to 200 MPa through a hydraulic press in a metallic mold, the sintering process was carried out at 1120 ˚C in an especial powder metallurgy furnace. The performed studies on the manufactured specimens were included the measurement of the porosity fraction, microstructural evaluations by optical and scanning electron microscopies, and investigation of compression properties. The mean of the porosity fraction of manufactured specimens was measured 74.5 percent. The optical microscopic evaluations shown that the cells are exactly manufactured according to granulates geometry. In addition, no fracture was observed in the cell walls and in the urea granulates in compacting process. The SEM images shown that the all of cells walls connected to each other and sets of open and close cells were produced. In the compression stress vs. strain curves of manufactured steel foams, along plateau region was observed. The average of stress in the plateau region, maximum compression stress, and absorbed energy were 15 MPa, 25 MPa, and 14 Nm, respectively.

In this study, effect of sintering time used in the production of silver electrodes on the life of zinc - silver oxide batteries was investigated. For this purpose, initially four Ag electrodes (positive plate) with composition of 95 wt% silver oxide, 4.9 wt% carbon powder and 0.1 wt% resin prepared by powder metallurgy method. Then, four silver electrodes were sintered for 5, 10, 15 and 20 minutes at temperature 500°C. Electrical discharge method were used in the 1.4% KOH electrolyte to evaluate the effects of sintering time used in the production of silver electrodes on the life of zinc - silver oxide batteries. Scanning electron microscopy was used to examine the microstructures of electrodes and point analysis was accomplished by EDX method. Electrical discharge tests results showed that sintering time of 10 minute with discharge time of eight minutes and forty-seven seconds, is the most optimized sintering time for increase double of the life of zinc - silver oxide batteries. SEM images were showed that with increasing sintering time, the amount and size of apparent pores increased in the Ag electrodes. Also, point analysis results has implies on reduction of electrodes oxygen, with the increasing of sintering time.