بررسي مكانيزم تشكيل MoSi2 در حضور آلومينيوم طي فرايند سنتز احتراقي

چكيده انگليسي :

A study on mechanism of MoSi2 formation in the present of aluminum during combustion synthesis Saeed Hasani s hasani@ma iut ac ir Department of Materials Engineering Isfahan University of Technology 84156 83111 Isfahan Iran Degree M Sc Language Farsi M Panjepour Assist Prof Supervisor E mail panjepour@cc iut ac ir M Shamanian Assoc Prof Supervisor E mail shamanian@cc iut ac ir Abstract The MoSi2 combustion synthesis process in the presence of aluminum was studied in this research Samples of a powder mixture of molybdenum and silicon by 1 2 Stoichiometric ratio were first prepared and a 5 wt aluminum powder by weight was added to them First with thermodynamic consideration the possibility of the performance of combustion synthesis process in the presence of aluminum due to adiabatic temperature calculation in inert gas atmospheres and air was studied Then to investigate the effect of the presence of aluminum on the trend of the performance of this process each of the samples went under self propagating high temperature synthesis SHS process in an air atmosphere In continuation in order to perform the phase and structural studies the products obtained from this process were examined by X ray diffraction and scanning electron microscope SEM Also simultaneous thermal analysis STA tests at different heating rates 10 15 20 C min and was carried out to study the mechanism of the performance of this process The results obtained from the X ray diffraction patterns along with electron microscope studies showed that all the aluminum particles were oxidized during SHS process Additionally the MoSi2 formation among the above particles took place in a more complete manner and the rate of the residual remaining reactants was significantly reduced On the other hand the thermodynamic calculations also showed that the adiabatic temperature of the combustion front is greatly increased because of the effect of the oxidation of the aluminum particles during the process of combustion synthesis which is definitely confirmed by the results obtained from the heat profiles and microscopic studies Accordingly the results obtained from the phase study of the thermal analysis products of the powder mixtures showed that in the presence of oxygen there is no possibility for the formation of MoSi2 due to the tendency of the molybdenum particles to violent oxidation and the peaks pointed in these curves are in fact resulted from the oxidation of these particles Also according to the role of aluminum during the performance of MoSi2 combustion synthesis process the process of the oxidation of the powder of aluminum particles was studied as well The results of the studies showed that with regard to the presence of an oxide layer non crystalline structure on the surface of aluminum particles the oxidation of these particles was done in a totally different manner under isothermal and non isothermal conditions In the isothermal conditions T 700 C due to its lack of high strength in the oxide layer cannot have a specific effect on the trend of oxidation While because of the effectiveness of this amorphous oxide layer this process is carried in a multi stage and in a complex manner in non isothermal conditions in other word the mechanism and rate of oxidation depend on the heating rate The results of the studies of thermal analysis the phase and structural studies performed on the products obtained from this test showed that in non isothermal conditions the rate of oxidation is very limited before reaching 1000 C due to the protection of the oxide layer of aluminum But by passing through this temperature and due to the great stress resulting from aluminum melt expansion the oxide layer is ruptured and because of the contact of this melt with oxide atmosphere a violent oxidation takes place This is done while the results of the X ray diffraction analysis obtained from the products resulted from these analysis showed that even after passing through this stage there

حسني، سعيد

بررسي مكانيزم تشكيل MoSi2 در حضور آلومينيوم طي فرايند سنتز احتراقي

دي سبليسيد موليبدن , اكسيداسيون