Showing 4 results for H. R. Rezaie
M. Ardestani,, H. Razavizadeh,, H. Arabi, H. R. Rezaie,
Volume 6, Issue 2 (Spring 2009 2009)
Abstract
Abstract:
materials can be fabricated by sintering of W-Cu composite powders. In this research W-20%wt Cu composite powders
was synthesized via a co-precipitation method. Precipitate obtained from a mixture of copper nitrate and ammonium
paratungstate (APT) in distilled water contained W-Cu compounds. This precipitate was washed, dried and calcined
at 550
of dried precipitate powder was determined by thermogravimetry (TG), differential thermal analysis (DTA) and X-ray
diffraction (XRD). The sintering of the reduced powders was investigated as a function of temperature. Relative density
of more than 98% obtained for the powders sintered at 1200
close to theoretical calculations. The hardness of the sintered powders was 320 Vickers.
W-Cu composites are widely used as contacts, heat sinks and electro discharge electrodes. These kinds of°C in air and then reduced in H2 atmosphere in order to convert to W-Cu powders. The calcination temperature°C . The corresponding electrical conductivity was too
F. Foroutan, J. Javadpou, A. Khavandi, M. Atai, H. R. Rezaie,
Volume 8, Issue 2 (spring 2011 2011)
Abstract
Abstract: Composite specimens were prepared by dispersion of various amounts of nano-sized Al2O3 fillers in a monomer system containing 60% Bis-GMA and 40% TEGDMA. For comparative purposes, composite samples containing micrometer size Al2O3 fillers were also prepared following the same procedure. The mechanical properties of the light- cured samples were assessed by three-point flexural strength, diametral tensile strength, and microhardness tests. The results indicated a more than hundred percent increase in the flexural strength and nearly an eighty percent increase in the diametral tensile strength values in the samples containing nano-size Al2O3 filler particles. It is interesting to note that, this improvement was observed at a much lower nano-size filler content. Fracture surfaces analyzed by scanning electron microscopy, indicated a brittle type of fracture in both sets of specimens.
A. Najafi, F. Golestani-Fard, H. R. Rezaie, N. Ehsani,
Volume 8, Issue 2 (spring 2011 2011)
Abstract
Abstract: SiC nano particles with mono dispersed distribution were synthesized by using of silicon alkoxides and phenolic resin as starting materials. After synthesis of sample, characterizations of the obtained powder were investigated via Fourier Transform Infrared Spectroscopy (FTIR) with 400-4000 cm-1, X-ray Diffractometry (XRD), Laser Particle Size Analyzing (LPSA), Si29 NMR analysis, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). FTIR and Si29 NMR results of the gel powder indicated that Si-O-C bonds were formed due to hydrolysis and condensation reactions . FTIR results showed a very strong peak for heat treated powder at 1500°C after carbon removal which is corresponded to Si-C bond. Obtained pattern from X-ray diffractometry showed that the final products contain -SiC phase with poly crystalline planes and little amounts of residual carbon. PSA results showed that the average particles size were 50.6 nm with monosized distribution. Also microstructural studies showed that the SiC nano powders have semi spherical morphology with mean particles size of 30-50 nm and also there are some agglomerates with irregular shape.
A. Najafi, F. Golestani-Fard, H. R. Rezaie,
Volume 11, Issue 1 (march 2014)
Abstract
Mono dispersed nano SiC particles with spherical morphology were synthesized in this project by hydrolysis and condensation mechanism during sol gel processing. pH, temperature and precursor’s ratio considered as the main parameters which could influence particles size. According to DLS test results, the smallest size of particles in the sol (<5nm) was obtained at pH<4. It can be observed from rheology test results optimum temperature for achieving nanometeric gel is about 60 ˚C. The optimum pH values for sol stabilization was (2-5) determined by zeta potentiometery. Si 29NMR analysis was used in order to get more details on final structure of gel powders resulted from initial sol. X-ray diffraction studies showed sythesized powder consists of β-SiC phase. Scanning electron microscopy indicated agglomerates size in β-SiC synthesis is less than 100 nm. Finally, TEM studies revealed morphology of β-SiC particles treated in 1500˚C and after 1hr aging is spherical with (20-30) nm size
