‎محمدحسين عنايتي، علي مالكي

1396/10/04

كتابنامه

مواد

مهندسي مواد

ID9656

به فارسي و انگليسي

92 Investigation of the effects of aluminum on self propagation and explosive combustion synthesis of MoSi2 Ali Naghi Alyari a alyari@ma iut ac ir 2015 08 02 Department of Materials Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisors Masoud Panjepour Associate Professor panjepour@cc iut ac irMahmoud Meratian Associate Professor meratian@cc iut ac irAbstractSilicides are a new promising group of materials which have gained a lot of interest forstructural applications in aerospace and energy industries due to their unique propertiesincluding high melting point relatively low density and good corrosion resistance In thisstudy effect of the oxidation of aluminum particles on the formation of MoSi2 throughcombustion synthesis process was investigated For this purpose samples with 0 4 7 and10 wt Al were prepared by pressing mixtures of molybdenum and silicon powders undera pressure of 175 kg cm 2 In order to evaluate the effect of aluminum addition on processprocedure and parameters self propagation hight temperature SHS and thermal explosive TE combustion synthesis tests were performed under air and argon atmospheres Phaseand structural characterization of process products were done using X ray diffraction XRD analysis and scanning electron microscopy SEM Optical microscope imagesalong with Clemex image analyzing software were used to determine percentage ofporosity in the synthesized samples Furthermore in order to study the reaction rate progress of combustion wave front in self propagating synthesized samples were recordedusing a Canon camcorder The results obtained reveals that aluminum dissolves in MoSi2by occupying Si sites via substitution mechanism causing the transformation of tetragonallattice to hexagonal structure In addition due to the endothermic nature oftetragonal hexagonal transformation temperature and velocity of combustion front arereduced In self propagating reaction aluminum acts as diluent and aluminum oxide has norole in SHS process In thermal explosive process aluminum and silicon form eutectic andnon eutectic melts which lead to a decrease in temperature and time of process initiation Also to investigate the influence of oxidation of aluminum powder on combustionsynthesized MoSi2 oxidation tests were performed on samples containing 0 and 10 wt aluminum for 12 hours with 2 hour cycles using a tube furnace It is observed thatoxidation of aluminum free samples occurs in the temperature range of 400 600 C thisoxidation often known as pest results in collapse of powder sample as well as changing ofits color from black to green However for sample containing 10 wt aluminum oxidation does not happen in this temperatures and no significant color change is observedfor sample in fact it can be concluded that aluminum prevents the oxidation of MoSi2 Also according to XRD analysis data at 850 C it can be concluded that aluminumincorporated in hexagonal structure forms a protective Al2O3 film which hinders oxidationof MoSi2 Therefore aluminum effectively improves the low temperature oxidation ofMoSi2 and prevents so called pest corrosion Keywords Combustion synthesis process MoSi2 Aluminum Oxidation

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‎محمدحسين عنايتي، علي مالكي