روش جدید سنتز لایه های نازک ZnO: ریزساختار، خواص الکتریکی و اپتیکی

New process for synthesis of ZnO thin films: Microstructural, optical

and electrical characterization

روش جدید سنتز لایه های نازک ZnO: ریزساختار، خواص الکتریکی و اپتیکی

ABSTRACT

Zinc oxide (ZnO) is an interesting wide-band-gap semiconductor material with a direct band gap of 3.36 eV [1] at room temperature and exciton binding energy of 60 meV. It has crystalline structure of the wurtzite type and the unit cell with the constants a = 3.24 ˚A and c = 5.19A˚ . Thin films of ZnO are utilized for a wide variety of electronic and opto-electronic applications, such as surface acoustic wave devices [4], transparent conducting electrodes [2], heat mirrors [3]. Nanoscale porous structures of ZnO with a high surface area find their application in chemical sensors [5] and dye-sensitised solar cells [6]. Various techniques have been used to deposit undoped and doped ZnO films on different substrates, including spray pyrolysis [7], organometallic chemical vapor deposition [8], pulsed laser deposition [9], sputtering [10], and sol–gel process [11].

 

سنتز نانو ورقه های ZnO از طریق روش الکترورسوبی

Synthesis of ZnO nanosheets via electrodeposition method and

their optical properties, growth mechanism

سنتز نانو ورقه های ZnO از طریق روش الکترورسوبی ، خواص نوری و مکانیزم رشد

ABSTRACT

ZnO nanosheets were prepared by electrochemical deposition method at 80 C on seeded Indium Tin Oxide conducting glass substrates. The seed layer was coated on ITO by spin coating and annealed at 350 C for 30 min prior to electrochemical deposition growth. X-ray diffraction patterns (XRD) and field emission scanning electron microscope (FESEM) images confirmed that the ZnO nanosheets consist of polycrystalline structures. Room temperature photoluminescence spectra (PL) of the ZnO nanosheets exhibited band-edge ultraviolet (UV) and visible emission (blue) indicating the ZnO nanosheets had excellent optical properties. The UV–Vis absorption spectrum of ZnO nanosheets was shown a strong absorption at 300 nm. The ZnO nanosheets structure demonstrated higher photocatalytic activity during degradation of aqueous methylene blue under visible-light irradiation. Moreover, the growth mechanism of the ZnO nanosheets had been discussed.

 

جوشکاری آلیاژ Al–Cu–Mg–Mn به روش تیگ

Effect of welding parameters on the solidification microstructure

of autogenous TIG welds in an Al–Cu–Mg–Mn alloy

تاثیر پارامترهای جوشکاری بر میکروساختار انجمادی جوش های TIG

بدون ماده پر کننده در یک آلیاژ Al–Cu–Mg–Mn

ABSTRACT

The weld metal microstructures of autogenous TIG welds have been investigated for a range of welding conditions using an Al–Cu–Mg–Mn alloy. It was found that a combination of high welding speeds and low power densities provide the thermal conditions required for the nucleation and growth of equiaxed grains in the weld pool, providing heterogeneous nucleation sites are available. The most likely origin of the nucleants is from a combination of dendrite fragments and TiB2 particles that survive in the weld pool. The finest microstructure was observed in the centre of the weld and is attributed to the higher cooling rates which operate along the weld centreline. Composition profiles across the dendrite side arms were measured in the TEM and were found to follow a Scheil type segregation behaviour where there is negligible back diffusion in the solid. The measured core concentration of the dendrite side arms was found to rise with increasing welding speed and was attributed to the formation of significant undercoolings ahead of the primary dendrite tip, which enriched the liquid surrounding the dendrite side arms.

 

اثر ارتعاش مکانیکی روی ریزساختار ماده‎ی جوشکاری

Studies on the Effect of Mechanical Vibration on 

the Microstructure of the Weld Metal

تحقیقات در مورد اثر ارتعاش مکانیکی روی ریزساختار ماده‎ی جوشکاری

ABSTRACT

The solidification process in the weld metal produces solidification structure. The solidification process depends on the thermal gradient, solidification speed and the alloy content. These structures can be planar, cellular, columnar dendritic and equiaxed dendritic. The solidification process may change from planar to cellular, columnar dendritic and equiaxed dendritic across the weld metal zone as shown in fig.1. Three grains are shown to grow epitaxially from the fusion line. A short distance away from the fusion line, solidification changes to the cellular mode. Further away from the fusion line, the solidification changes to columnar dendritic mode. Near the weld centre line equiaxed dendrites nucleate and grow, blocking off the columnar dendrites. Each one of these structures would affect the hot cracking susceptibility in greater or smaller extent.

 

مشخصه یابی فولاد یاتاقان Characteristics of 100Cr6 bearing steel

Characteristics of 100Cr6 bearing steel after thixoforming process performed 

with prototype device

مشخصه یابی فولاد یاتاقان 100Cr6 بعد از فرایند thixoforming انجام شده با ابزار مدل اولیه

ABSTRACT

A device based on a high pressure die-casting(HPDC) machine was constructed, with a capacity to produce thixo-casts from steel. After inductive heating to the required semi-solid temperature range, the samples were transported in a protective argon atmosphere to a cylinder of modified HPDC and injected into a pre-heated die. Bearing steel 100Cr6 (after forging) was used as the feedstock material. The metallographic analysis of the steel showed a homogenous structure within a whole volume characterized by a grain size between 2 μm and 8 μm. Differential scanning calorimetry (DSC) analysis allowed to estimate the process temperature for thixoforming at 1 390 °C which was attributed to about 45% of a liquid phase.

 

آنالیز SEM و اشعه ایکس - SEM and X-ray Microanalysis

SEM and X-ray Microanalysis Image Formation and Interpretation

آنالیز اشعه ایکس و SEM - تفسیر و تشکیل تصویر

ABSTRACT

Scanning electron microscopy is a technique in which images form the major avenue of information to the user. A great measure of the enormous popularity of the SEM arises from the ease with which useful images can be obtained. Modern instruments incorporate many computer-controlled, automatic features that permit even a new user to rapidly obtain images that contain fine detail and features that are readily visible, even at scanning rates up to that of television (TV) display. Although such automatic “computer-aided” microscopy provides a powerful tool capable of solving many problems, there will always remain a class of problems for which the general optimized solution may not be sufficient.

اثر نرخ سرد شدن روی ساختار میکروسکوپی آلیاژ هایپر یوتکتیک Al-Ni

The influence of cooling rate on the microstructure of an Al–Ni hypereutectic alloy

اثر نرخ سرد شدن روی ساختار میکروسکوپی آلیاژ هایپر یوتکتیک Al-Ni

ABSTRACT

An Al–4 at.% Ni alloy was prepared by a melt spinning technique and characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and high resolution transmission electron microscopy. The resulting ribbon microstructure consists of intermetallic Al9Ni2 globular-like structures embedded within an aluminum matrix. Characteristic globules are nanometric (∼100 nm) and are mainly located at the grain boundaries. The resulting effect on the mechanical properties is the enhancement of the alloy hardness from 58 to 371 HV.

 

راهنمای عملیات حرارتی آلیاژهای غیرآهنی- آلومینیوم و آلیاژهای آن Heat Treaters Guide

Heat Treater's Guide Nonferrous Alloys Wrought Aluminum and Aluminum Alloys

راهنمای عملیات حرارتی آلیاژهای غیرآهنی- آلومینیوم و آلیاژهای آن

ABSTRACT

3003 Aluminum: Microstructures. (a) 3003-0 sheet, annealed. Longitudinal section shows recrystallized grains. Grain elongation indicates rolling direction, but not the crystallographic orientation within each grain. Polarized light. Barker's reagent. 100x. (b) 3003-0 sheet, annealed. Same as adjoining microstructure, but shown at a higher magnification. Dispersion of insoluble particles of (Fe,Mn)Als (large) and aluminum-manganese-silicon (both large and small) was not changed by annealing.

 

تنش‌های پسماند در جوش‌های لب به لب اتصالات لوله غیرمشابه

Effect of the welding heat input on residual stresses in butt-welds of dissimilar pipe joints

اثر ورودی حرارت جوشکاری بر تنش‌های پسماند در جوش‌های لب به لب اتصالات لوله غیرمشابه

ABSTRACT

This study used finite element techniques to analyse the thermo-mechanical behaviour and residual stresses in dissimilar butt-welded pipes. The residual stresses at the surface of some weld specimens were measured experimentally by using the hole-drilling method. The results of the finite element analysis were compared with experimentally measured data to evaluate the accuracy of the finite element modelling. Based on this study, a modelling procedure with reasonable accuracy was developed. The developed finite element modelling was used to study the effects of welding heat input on magnitude and distribution of welding residual stresses in butt-welded pipes made of ferritic and austenitic steels. The hoop and axial residual stresses in dissimilar pipe joints of 8 mm thick for V-groove shape were studied. It is shown that the welding heat input has a significant effect on magnitude and distribution of residual stresses in the stainless steel side of the studied joints.

 

تنش پسماند حرارتی در فرآیند جوشکاری لیزری هیبریدی-GMA welding process

Numerical and experimental study of thermally induced residual stress in the hybrid laser–GMA welding process

مطالعه عددی و تجربی تنش پسماند حرارتی در فرآیند جوشکاری لیزری هیبریدی-GMA

ABSTRACT

A model based on a double-ellipsoidal volume heat source to simulate the gas metal arc welding (GMAW) heat input and a cylindrical volume heat source to simulate the laser beam heat input was developed to predict the temperature field and thermally induced residual stress in the hybrid laser–gas metal arc (GMA) welding process. Numerical simulation shows that higher residual stress is distributed in the weld bead and surrounding heat-affected zone (HAZ). Effects of the welding speed on the isotherms and residual stress of the welded joint are also studied. It is found that an increase in welding speed can reduce the residual stress concentration in the as-weld specimen. A series of experiments has been performed to verify the developed thermo-mechanical finite element model (FEM), and a qualitative agreement of residual stress distribution and weld geometrical size is shown to exist.