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Showing 3 results for Vahedi
Optimization of Slip Casting Parameters of Alumina Yttria Nanocomposite Powder for Obtaining Transparent Yttrium Aluminum Garnet Ceramics
G. Kafili, B. Movahedi, M. Milani,
Volume 36, Issue 3 (Journal of Advanced Materials-Fall 2017)
Abstract

In this study, Spark Plasma Sintering (SPS)  of both slip casted and powder specimens of alumina/ yttria core-shell nanocomposite were utilized for fabricating transparent Yttrium Aluminum Garnet (YAG) ceramics. Phase evolution, optical transmittance and the microstructure of sintered samples were compared. In slip casting process, Dolapix CE64 was used as a dispersant for preparing the stable aqueous slurry of this nanocomposite powder. The effect of Dolapix concentration and pH value on the stability of the suspension was described, and the viscosity diagrams were investigated at different pH value and different weight percents of Dolapix. The rheological behavior of the nanocomposite powder slipped at 60-70 wt% solid loading was studied by measuring their viscosity and shear stress as a function of shear rate of the slurry. The results showed that, the suspension has a minimum viscosity at pH of 10 by addition of 2.5 wt% Dolapix. Also, the slurry with solid loading of 60 wt% showed the Newtonian behavior and this rheological behavior was preserved even above this solid loading values. Slip casting technique caused the uniform size and pores distribution as well as eliminating large pores in the green body. Consequently, transparent YAG ceramic with 60% optical transmittance was achieved after SPS process of slip casted green body which was much higher than that of nanocomposite powder, i.e. about 30% at the same sintering conditions.
 


The Effect of Tartrate Ion on the Separation Behavior of Zinc and Cadmium in the Sulfate Solution
A. Vahedi, H. Nadimi, D. Haghshenas Fatmesari, S. Firoozi,
Volume 37, Issue 3 (Journal of Advanced Materials-Fall 2018)
Abstract
The aim of this study was to investigate the effect of tartrate ion (C4H4O62-) on the extraction and separation of zinc and cadmium using D2EHPA extractant. The presence of tartrate ion in the solution caused the shift of  the  extraction curve of zinc and cadmium to the more alkaline pH; however, the shifting rate for the cadmium extraction curve was more significant. In the absence of tartrate ion, ΔpH50% value was equal to 0.65. If 0.2 M tartrate ion were added to the aqueous phase, ΔpH50% value would increase to 1.09. The FT-IR analysis of organic phase showed that tartrate ion absorbed the organic phase along with zinc and cadmium. "Slope analysis method" also showed that 0.25 M and 0.5 M tartrate ion participated in the zinc-tartrate and cadmium-tartrate complex formation, respectively; however, extraction number was changed with increasing the tartrate ion concentration.

Synthesis of Zinc/Zinc Oxide Nanoparticles by Electric Discharge Method in Distilled-Water and Argon-Gas Environments
T. Rajabi, M. Vahedi, S. K. Sadrnezhaad,
Volume 39, Issue 2 (Journal of Advanced Materials-Summer 2020)
Abstract
Zinc/zinc oxide nanoparticles are used in an increasing number of medical and industrial applications due to their attractive physical, chemical and antibacterial properties. Therefore, achieving a simple and beneficial way to produce them is an important aspect. In this study, zinc/zinc oxide nanopowders were synthesized by fast electric discharges between two electrodes of (a) a spark device in distilled water medium and (b) a handmade high-voltage ignition machine in argon gas medium. The resulting powders were characterized by x-ray diffraction (XRD), dynamic light scattering (DLS) and field emission electron microscopy (FESEM). Using the spark device in distilled water, a mixture of zinc crystals with an average diameter of 11.28 nm and zinc oxide crystals with an average diameter of 22.22 nm was produced. However, using the handmade device in argon, zinc crystals with an average diameter of 7.5 nm were obtained and subsequently oxidized due to their extremely high activity. The production rate of the high voltage discharge method was lower than other conventional methods. On the other hand, its ability in reducing the size and increasing the particle activity was higher than other methods.

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