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Showing 7 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.



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