Showing 8 results for Growth
A. Hassani, R. Ravaee,
Volume 5, Issue 2 (6-2008)
Abstract
Abstract: To ensure the rail transportations safety, evaluation of fatigue behavior of the rail steel
is necessary. High cycle fatigue behaviour of a rail steel was the subject of investigation in this
research using fracture mechanics. Finite element method (FEM) was used for analyzing the
distribution of the stresses on the rail, exerted by the external load. FEM analysis showed that the
maximum longitudinal stresses occurred on the railhead. To find out about the relation of crack
growth with its critical size, and to estimate its lifetime, the behaviour of transverse cracks to rail
direction was studied using damage tolerance concept. It revealed that transverse crack growth
initially occurred slowly, but it accelerated once the crack size became larger. Residual service
life was calculated for defective segments of the rails. In addition, allowable crack size for
different non-destructive testing intervals was determined the allowable crack size decreased as
the NDT intervals increased.
M. J. Tafreshi1, M. Fazli2,
Volume 6, Issue 2 (6-2009)
Abstract
Abstract:
fabricated. Modifications carried out in different parts of the old system in order to control most
of the growth parameters with more accuracy. The fabricated system was used to grow sapphire
single crystals with almost 10 mm in diameter and 50 mm in length. The crystallinity and
structure of the grown crystals were characterized by computer aided single crystal X-ray
diffraction technique.
A Verneuil system, more sophisticated than a conventional one, has been designed and
P. Karimi, K. S. Hui, K. Komal,
Volume 7, Issue 3 (8-2010)
Abstract
Abstract:
(Y2O3) and ethyl acetate as a mineralizer by hydrothermal method at a low temperature (T=.230°C, and
P=100bars).The as-prepared powders were characterized by X-ray Diffraction (XRD), Fourier Transform Infrared
Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), UV-V Spectroscopy and Chemical Oxygen Demand
(COD) of the sewage water, respectively. The results show that hydrothermal method can greatly promote the
crystallization and growth of YVO4 phase. XRD pattern clearly indicates the tetragonal structure and crystallanity. An
FTIR spectrum of the YVO4 shows the presence of Y-O and V-O bond, respectively. The presence of these two peaks
indicates that yttrum vanadate has been formed. UV-V is absorption spectra suggesting that YVO4 particles have
stronger UV absorption than natural sunlight and subsequent photocatalytic degradation data also confirmed their
higher photocatalytic activity.
In this paper, YVO4 powder was successfully synthesized from Vanadium Pentaoxide (V2O5), Yttrium Oxide
M. J. Tafreshi, B. Dibaie, M. Fazli,
Volume 9, Issue 1 (3-2012)
Abstract
Abstract: A thermodynamic model was used to find out the optimum temperature for the growth of ZnS single crystals in closed ampoules by chemical vapor transport technique. Based on this model 1002 °C was found to be optimum temperature for 2 mg/cm3 concentration of transporting agent (iodine). ZnS Crystals were grown in optimum (1002 °C) and non-optimum (902 °C and 1102 °C) temperatures. The composition structure and microstructure of the grown crystals were studied by Atomic absorption spectroscopy, X-ray diffraction and Scanning electron microscopy measurements. Properties of the grown crystals were correlated to the growth conditions especially a stability in mass transport along the closed tube length.
R. Fazli, F. Golestani-Fard, Y. Safaei-Naeini, S. Zhang,
Volume 11, Issue 3 (9-2014)
Abstract
Well crystallized pure calcium zirconate (CaZrO3
) nanopowder was successfully synthesized using the
molten-salt method. CaCl2
, Na
2CO3, micro-ZrO
2and nano-ZrO
2
were used as starting materials. On heating, Na2CO3
reacted with CaCl
2to form NaCl and CaCO
3. Nano CaZrO
3
was formed by reacting equimolar amounts of in situformed CaCO
3 (or CaO) and ZrO
2
in molten Na
2CO3-NaCl eutectic mixture. CaZrO
3
particle size and synthesis
temparture was tailored as a function of ZrO
2particle size. Due to the usage of nano-ZrO
2
, the molten salt synthesis
(MSS) temperature was decreased and possible impurity phases in the final product were suppressed. The synthesis
temperature was lowered to 800°C and soaking time of the optimal synthesis condition was reduced to 3h. After
washing with hot-distilled water, the n-ZrO2sample heated at 800°C for 3h, was single phase CaZrO
3with 70-90 nm
in particle size, while the m-ZrO
2sample heated at 1000°C for 3h, was single phase CaZrO
3
with 250-400 nm in
particle size. Based on the TEM observation and thermodynamic analysis, the synthesized CaZrO
3
grains retained the
morphology of the ZrO2
nanopowders, which indicated that a template formation mechanism play a dominant role in
synthesis process
M. Soltanieh, M. Kiani, M. Hasheminiasari,
Volume 14, Issue 2 (6-2017)
Abstract
- The mechanism of diffusion layer growth in plasma nitrided coatings applied on a St52 steel using an active screen is investigated. The nitriding was performed at 450,500 and 550 ◦C temperature nitriding times of 5, 10 and 15 h, in a gas mixture containing 20 vol. % H2: 80 vol. % N2 and DC-pulsed plasma nitriding unit.
The surface, cross section and the thickness of diffusion of specimens was studied in terms of optical and scanning electron microscopy. According to the measurements of diffusion layer thickness, values of Q and D0 for nitrogen diffusion in substrate were calculated as 50585 (j/mol) and 4.11×10-10 (m2/s)respectively. The variations of depth of hardness during nitriding period was determined
M. Nouri, P. Alizadeh, M. Tavoosi,
Volume 14, Issue 3 (9-2017)
Abstract
In this study, the crystallization behavior of a 65GeO2-15PbO-10MgF2-10MgO glass (prepared by the conventional melt quenching technique) has been investigated. The microstructure and crystallization behaviors of this glass were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), non-isothermal differential thermal analysis (DTA) and Fourier transform infrared spectroscopy (FTIR). The results demonstrated that a fully glassy phase can successfully be prepared by the conventional melt quenching technique exhibiting one-stage crystallization on heating, i.e., the glassy phase transforms into crystalline MgGeO3 and Pb5GeO7 phases. The activation energy for the crystallization, evaluated from the Kissinger equation, was approximately 202±5 kJ/mole using the peak temperature of the exothermic reaction. The Avrami exponent or reaction order, n, indicates the nucleation rate in this glass to increase with time and the crystallization to be governed by a three-dimensional interface-controlled growth.
S. Manafi, S. Joughehdoust,
Volume 17, Issue 2 (6-2020)
Abstract
In this research, calcium titanate (CaTiO3) hollow crystals have been successfully prepared via hydrothermal method. Titanium tetrachloride, calcium chloride dihydrate and potassium hydroxide were used as Ti, Ca and precipitating agent, respectively. The hydrothermal synthesis was performed at different temperatures and time durations. The negative amount of the Gibbs free energy shows the reactivity of the reaction at room temperature. Characterization of CaTiO3 was carried out using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The optimum condition for preparing CaTiO3 is the sample kept in an autoclave at 300 ℃ for 3 h that requires less energy and time which consists of a high degree of crystallinity. In this research, tetragonal CaTiO3 hollow crystals have been successfully prepared via hydrothermal method. TiCl4, CaCl2.2H2O, and KOH were used as Ti, Ca and precipitating agent, respectively. The hydrothermal synthesis was performed at different temperatures and time durations. Characterization of CaTiO3 was carried out using SEM, HRTEM, and XRD. The sample kept in the autoclave at 300 ℃ for 3 h well crystallized and required less energy and time for synthesis. The powder has a homogenous dispersity of crystals with the range of nanometer to micrometer sizes which makes it a good candidate as a photocatalyst material
