טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentNakibli Yifat
SubjectMorphologic Design of Nanoalloys by Means of Kinetic
Control
DepartmentDepartment of Chemical Engineering
Supervisor Ms. Rina Tannenbaum
Full Thesis textFull thesis text - English Version


Abstract

Alloys have always been an important class of materials due to the ability to tune properties as a function of composition. Designing alloys at the nanoscale provides additional degrees of freedom in material design due to the ability to control properties by variations in particle size and particle distribution. Moreover, the nanoscale may provide an opportunity to overcome limitations stemming from the phase diagram of the alloy in the bulk.

            The aim of this study is to determine the relationship between the kinetics of alloy formation and the morphology of the nanoalloys formed for the purpose of using formation kinetics as a tool to design alloy properties at the early stages of alloy formation. Hence, the synthesis method of choice in this study is the thermal decomposition of iron pentacarbonyl (Fe(CO)5) an dicobalt octacarbonyl (Co2(CO)8) which allows the tracking of the decomposition process and manipulation  of reaction conditions.

            The hypothesis in this work was that if one precursor decomposes faster that the other, core-shell morphology will form with the faster decomposing element at the core. Conversely, if both precursors decompose at the same rate, a mixed metal morphology will result. Experiments which precursors were added concurrently or consequently were performed. The assumption found in all recent works dealing with similar reactions, was that there was no mutual influence of the presence of one metal precursor on the reaction kinetics of the other. However, we found that at composition of 0.6-0.8 mol% Fe, both

TEM images revealed that all nanoparticles formed were spherical with an average size range of 2 - 6 nm. Electron diffraction measurement indicated the presence of g-Fe2O3 in the sample, and EDS measurements showed that all samples contained both Fe and Co. DTA measurements were performed in order to determine if the interaction between the surfactant used to stabilize the particles (NaAOT) and the nanoalloy surface this may reveal information regarding the nature of the metallic surface, and hence, the structure of the particle. The thermal profiles showed that all samples had a decomposition peak between 265-300°C which is attributed to the decomposition of the AOT molecules. As the molar ratio of Fe grew decomposition temperature enhanced, indicating that AOT has a better interaction with Fe. Moreover, similar thermal behavior was observed in systems in which the second component introduced in the consequent decomposition reactions was decomposed individually, implying core shell morphology.