Investigating Stainless Steel Particle Synthesis

This thesis focuses on the chemistry for stainless nanoparticle synthesis in order to develop corrosion resistant nanoparticles. Syntheses within the Maye lab have been successful, however at the large scale these processes have been hindered by low yields as a result of byproduct formation and oxidation loss. This study addresses these problems by introducing a new precursor to synthesize the Fe core of FeCr/Ni stainless core/shell particles. Traditionally iron pentacarbonyl (Fe(CO)5 is used, but this study uses iron acetylacetonate (Fe(acac)3) as a substitute. Although the degradation of Fe(CO)5 is more commonly used and is understood relatively well, Fe(acac)3 is safer and less costly. Properly synthesized particles show high crystallinity and have immense magnetic capabilities. A comparison between the two precursors is completed in this work. The ability for Fe0 particles to act as a core for stainless particles and the effects of shells on the cores is also analyzed. Analysis of the particles was done using thermogravimetric analysis (TGA), Laser Ablation Induced Coupled Plasma Mass Spectrometry (LA-ICPMS), Physical Property Measurement System (PPMS), and x-ray diffraction (XRD). These analysis methods allow for the approximate composition of the particles to be determined and the approximate extent of oxidation to be estimated. Results of the study show that Fe(acac)3 iron particles are less metallic than Fe(CO)5, suggesting that Fe(acac)3 is not an effective substitute for Fe(CO)5. This shows that further research needs to be completed in order to find a potential substitute or create a new route for the successful creation of stainless nanoparticles

Alloying and Phase Transformation of Fe/FeNi Core/Alloy Nanoparticles at High Temperatures

This work explores how to form and tailor the alloy composition of Fe/FexNi1-x core/alloy nanoparticles by annealing a pre-formed particle at elevated temperatures between 180 – 325 oC. This annealing allowed for a systematic FeNi alloying at a nanoparticle whose compositions and structure began as a alpha-Fe rich core, and a thin gamma-Ni rich shell, into mixed phases resembling gamma-FeNi3 and gamma-Fe3Ni2. This was possible in part by controlling surface diffusion via annealing temperature, and the enhanced diffusion at the many grain boundaries of the nanoparticle. Lattice expansion and phase change was characterized by powder X-ray diffraction (XRD), and composition was monitored by X-ray photoelectron spectroscopy (XPS). Of interest is that no phase precipitation was observed (i.e., heterostructure formation) in this system and the XRD results suggest that alloying composition or alloy gradient is uniform. This uniform alloying was considered using calculations of bulk diffusion and grain boundary diffusion for Fe and Ni self-diffusion, as well as Fe-Ni impurity diffusion is provided. In addition, alloying was further considered by calculations for Fe-Ni mixing enthalpy (Hmix) and phase segregation enthalpy (HSeg) using the Miedema model, which allowed for the consideration of alloying favorability or core-shell segregation in the alloying, respectively. Of particular interest is the formation of stable metal carbides compositions, which suggest that the typically inert organic self-assembled monolayer encapsulation can also be internalized