3940

3718

كارشناسي ارشد

شناسايي و انتخاب مواد

اصفهان: دانشگاه صنعتي اصفهان، دانشكده مواد

1386

سيزده، 86، [II]ص.: مصور، جدول، نمودار

ص.ع. به: فارسي و انگليسي

مهندسي مواد

ID3718

به فارسي و انگليسي: قابل رؤيت در نسخه ديجيتال

AbstractMechanochemical reactions involving displacement reactions between a reactive metal and a metaloxide often led to the formation a nanocomposite structure The Mechanochemical reactions fall intotwo categories namely a those which occur during the mechanical activation process and there thereaction enthalpy is highly negative e g adiabatic temperature Tad 1300 1800 K and b thosewhich occur during subsequent thermal treatment and here the reaction enthalpy is only moderate e g Tad 1300 K The first type of reaction takes place in two distinct modes i e either combustionreaction or a progressive reaction Whenever a reaction is highly exothermic it can occur abruptly aftera certain time of milling and once started it proceeds in a self sustained way In this case the reactionrequires a given time to begin This time is called ignition time and due to the exothermic reaction canbe determined by an increase of temperature A number of studies have been focused on thedevelopment of A12O3 metal nanocomposites by different routes including synthesis of nanometer sized A12O3 M composite M Fe V Cr Mn Co Ni Cu Zn Nb Mo W Si Fe by ball milling ofan appropriate metal oxide and Al In this study fabrication and mechanical properties of alumina based ceramic matrix nanocomposite reinforced by Mo 15 and 26 6 vol was investigated Al2O3 Mo nanocomposite was synthesized by ball milling of aluminum and molybdenum oxide powdersmixtures in a SPEX8000 type ball mill The evaluation of powder particles after different milling timesand also after subsequent annealing was studied by x ray diffraction XRD scanning electronmicroscopy SEM transmission electron microscopy TEM and differential thermal analysis DTA The molybdenum oxide was found to be reacted with Al through a rapid self sustaining combustionreaction process forming an Al2O3 Mo nanocomposite powder After annealing at 800 C for 60min crystallite size of Mo and alumina remained constant In addition annealing caused formation ofdifferent polymorphic Al2O3 with a crystallite size of 50nm The powder particles were consolidatedby cold uniaxially pressing followed by sintering in vacuum atmosphere at 1300 C and 1400 C Results showed a significant improvement in flexural strength of Al2O3 Mo nanocomposites incomparison to alumina which increases by Mo content

فتح الله كريم زاده، محمد حسين عنايتي

احمد منشي

محمد حسن عباسي، پرويز كاملي