Showing 5 results for Mirkazemi
Z. Ghiami, S. M. Mirkazemi, S. Alamolhoda,
Volume 12, Issue 2 (June 2015)
Abstract
trontium hexaferrite (SrFe
12
O
19
) nanosized powders were synthesized by sol-gel auto-combustion method
with and without cetyltrimethylammonium boromide (CTAB) addition in the sol with Fe/Sr ratio of 11 (using additional
Sr). The resultant powders were investigated by X-ray Diffraction (XRD), Transmission Electron Microscope (TEM),
Field Emission Scanning Electron Microscope (FESEM) and Vibration Sample Magnetometer (VSM) techniques.
Phase constituents of the synthesized samples which were heat treated at temperatures in the range of 700- 900 ◦C
were studied. XRD results revealed that CTAB addition facilitates the formation of single phase strontium hexaferrite
at 800 ◦C. Microstructural evaluations with FESEM represented that CTAB addition causes formation of larger
particles with a narrower size distribution. VSM results represented that the highest amount of intrinsic coercivity force
(
i
H
C
) was obtained in the sample without CTAB addition and with additional Sr, calcined at 800 ◦C for 1 h which was
equal to 5749.21 Oe, while the value of
i
H
C
was equal to 4950.89 Oe without additional Sr. The amount of maximum
magnetization (M
max
) was raised from 48.41 emu/g to 62.60 emu/g using CTAB and additional Sr. The microstructure
and magnetic properties of the samples have been explained
A. Mohammadpour, S. M. Mirkazemi, A. Beitollahi,
Volume 12, Issue 3 (September 2015)
Abstract
In the present study, the feasibility of α-Fe ferromagnetic phase formation in glass and glass-ceramic by
reduction in hydrogen atmosphere have been investigated. The glass with the composition of 35Na
2
O–24Fe2O3–20B
2O3
–
20SiO
2
–1ZnO (mol %) was melted and quenched by using a twin roller technique. As quenched glass flakes were heat
treated in the range of 400-675 °C for 1-2 h in hydrogen atmosphere, which resulted in reduction of iron cations to α-Fe
and FeO. The reduction of iron cations in glass was not completely occurred. Saturation magnetization of these samples
was 8-37 emu g -1
. For the formation of glass ceramic, As quenched glass flakes heat treated at 590 °C for 1 h. Heat
treatment of glass ceramic containing magnetite at 675°C in hydrogen atmosphere for 1 h led to reduction of almost all of
the iron cations to α-Fe. Saturation magnetization of this sample increased from 19.8 emu g
-1
for glass ceramic to 67 emu
g
-1
S. Alamolhoda, S. M. Mirkazemi, T. Shahjooyi, N. Benvidi,
Volume 13, Issue 1 (March 2016)
Abstract
Nano-sized NiFe2O4 powders were synthesized by sol–gel auto-combustion method using pH values from 7 to 9 in the sol. The effect of pH variations on complexing behavior of the species in the sol has been explained. Changes in phase constituents, microstructure and magnetic properties by changes in pH values were evaluated by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and vibration sample magnetometer (VSM) techniques. Changes in pH value from 7 to 9 changes the amounts of NiFe2O4, FeNi3 and α-Fe2O3 phases. Calculated mean crystallite sizes are in the range of 44 to 51nm. FESEM micrographs revealed that increasing the pH value to 9 causes formation of coarse particles with higher crystallinity. Saturation magnetization was increased from 36.96emu/g to 39.35emu/g by increasing pH value from 7 to 8 which is the result of increased FeNi3 content. Using higher pH values in the sol reduces the Ms value.
H. Mohebbi, S.m. Mirkazemi,
Volume 17, Issue 4 (December 2020)
Abstract
Flash sintering of 8 mol% yttria-stabilized zirconia (8YSZ) as solid oxide fuel cell (SOFC) electrolyte is studied. The relation between relative density, shrinkage, sample temperature during the flash, and incubation time, with the electric field strength, current density, as well as contact paste, are modeled by response surface methodology (RSM). The electric field strength and current density varied from 50 to 400V.cm-1 and 50 to 200mA.mm-2, respectively. Also, platinum (Pt) and lanthanum strontium manganite (LSM) used as contact paste. Results show that using LSM paste lead to higher density and more shrinkage compare with Pt paste. Contrary, the electric field strength has no significant effect on density and shrinkage. However, a minimum electric field strength equal to 80 V.cm-1 is necessary for flash onset. As the field increases, the incubation time decreases dramatically. Compare with samples with LSM paste, samples with Pt contact paste reach to a higher temperature during the flash. Flash sintered 8YSZ shows the mean grain size of 0.3μm, which is about half of the conventionally sintered 8YSZ. Electrochemical Impedance Spectroscopy reveals despite lower mean grain size, the resistivity of flash sintered 8YSZ is lower than conventionally sintered 8YSZ.
Farhood Heydari, Seyed Mohammad Mirkazemi, Bijan Eftekhari Yekta, Seyyed Salman Seyyed Afghahi,
Volume 21, Issue 0 (IN PRESS 2024)
Abstract
This study systematically investigates the crystallization behavior, phase evolution, and dielectric properties of a BaO-Al₂O₃-SiO₂ glass system modified with 10 wt% TiO₂. Thermal characterization revealed that TiO₂ addition notably reduced the glass transition temperature (from 781.6°C to 779.4°C) and softening point (from 838°C to 824.8°C) compared to the TiO₂-free glass, consequently decreasing the calculated nucleation temperature (from 810°C to 800°C). While differential thermal analysis indicated sluggish crystallization kinetics, isothermal heat treatments identified 1000°C as the optimal processing temperature, leading to the development of a multiphase crystalline assemblage that beneficially included the target monoclinic Ba3.75Al7.5Si8.5O32 phase, which was absent in the TiO₂-free glass. X-ray diffraction identified this phase, along with celsian (BaAl₂Si₂O8) polymorphs and barium titanate crystallites, as the dominant crystalline phases. SEM revealed anisotropic crystal growth (1.14-1.52 μm length). Dielectric characterization in the Ku-band (12.4-18 GHz) demonstrated significant property enhancements, with the relative permittivity decreasing from 10.40 to 6.38 and loss tangent improving from 0.3 to 0.2 after crystallization. These improvements, attributed to the specifically tailored crystalline phase assemblage facilitated by TiO₂, make this glass-ceramic system particularly suitable for advanced microwave applications requiring low dielectric loss and high-frequency stability. The effectiveness of TiO₂ as a crystallization modifier for achieving optimized dielectric properties through controlled devitrification and targeted phase formation is underscored.
