بررسي اثر اندازه ذرات و نرخ گرمايش بر مكانيزم اكسيداسيون پودر آلومينيوم

چكيده انگليسي :

83 The effects of particle size and heating rate on the oxidation mechanism of aluminum powder Mehnoosh Kalantari mn kalantari@ma iut ac ir Date of Submission 22 Augu 2015 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisors Masoud Panjepour panjepour@cc iut ac irMahdi Ahmadian ahmadian@cc iut ac irAbstractAluminum powder is a widely used material in industry due to owing unique properties In fact oxidation enthalpy and high combustion heat are the specifications of the oxidationprocess of aluminum powders In this research the effect of particle size on oxidationkinetics of aluminum powder its corresponding model and stress distribution in the oxidecrust under non isothermal conditions were comprehensively investigated For thispurpose the aluminum powders in different particle size 1 3 12 5 38 45 63 75 and 150micrometer went under TG DSC heat analysis tests under air atmosphere at differentheating rates 10 30 and 50 C min up to 1300 C The results obtained from these testsshow that the oxidation of aluminum powder particles in different sizes occurred inseveral stages In fact reducing particle size can lead to an increase oxidation rate and theeffect of heating rate would be reversed so that at the minimum heating rate the highestoxidation occurs Our findings were shown that the major part of the oxidation takes placeat non isothermal conditions up to 1000 C However the stress distribution in the oxidecrust at temperatures above 660 C is was considered In this temperature range theexpansion of the melt inside the film and also the shrinkage resulting from thetransformation of the oxide structure from to can impose a high rate of stress on thiscrust Although the rate of the stress resulting from expansion of the melt inside the oxidefilm was higher than the stress resulting its shrinkage from a quantitative perspective Thisshrinkage as an important factor in the direction of activating the defects presents in thestructure of the oxide film plays a determining role in the occurrence of its rupture Theresults were indicated that by reducing the particle size rupture of the oxide film occurrs ata lower temperature because of the stress concentration resulting from the microstructuredefects In addition due to the low volume of melt remaining in the oxide film the stressrelaxation of the particles is reduced By an increase in heating rate the crust rupture takesplace at higher temperatures Also non isothermal kinetic analysis using isoconversionalmethods and Coats Redfern method were illustrated that by changing the particle size theempirical kinetic triplets Ea A and g have been changed and on the basis of any size acomprehensive model was introduced Phase and structural were studied by X raydiffraction technique XRD and scanning electron microscopy SEM Particle sizeimposes an effect on the morphology of the oxide film so that in coarse particles the oxideblades due to higher volume of molten becomes larger and widerin shape but in smallerparticles needle blades were increased X ray diffraction patterns XRD support thepresence of residual aluminum with oxide In general one can conclude that by changingthe particle size and heating rates reaction kinetics its model stress distribution and eventhe morphology of the oxide crust has been changed KeywordsAluminum powder Oxidation mechanisms Non isothermal Tension analysis Kineticanalysis

كلانتري، مه نوش

بررسي اثر اندازه ذرات و نرخ گرمايش بر مكانيزم اكسيداسيون پودر آلومينيوم

غير همدما , آناليز تنش , آناليز سينتيكي