Preparation of nanoparticles of platinum, nickel, and copper and studies of film formation, oxidation, and carburization
Date
2020
Authors
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Publisher
University of Delaware
Abstract
The diffusive motion of atoms can lead to a variety of changes in the physical and chemical properties of solid materials over time. Though solid-state diffusion (SSD) and new phase formation (NPF) in bulk systems have been studied for more than 100 years, high quality 2-D diffusion couples and 0-D and 1-D diffusion couples have been much less extensively studied. This work focuses on the synthesis of samples for the study of diffusion: highly uniform films for two specific 0-D nanomaterial systems: platinum and nickel containing nanoparticles systems, including large-area uniform Pt nanoparticles film synthesis and film assembly mechanism study, and different structure Ni (fcc and hcp-Ni3C), Cu/Ni core/shell nano-structural material study. ☐ Large area, uniform films of 5-6 nm diameter Pt nanoparticles self-assembled into 30-40 nm diameter aggregates have been prepared at the interface of two immiscible liquid phases: an aqueous Pt colloidal solution and hexane. A possible film formation mechanism was proposed wherein three key aspects related to the film formation: the appropriate surface charges on the nanoparticle surface (ζ -potential of the colloidal Pt must be adjusted to about -30 mV), the driving-force for particles moving from water to water/hexane interface (addition of ethanol minimizes the interfacial energy), and the ability to assemble the film (creation of the gradient of the surface tension makes NPs migrate toward the area of higher tension with formation of a dense monolayer). ☐ In addition, XRD showed an unusual lattice parameter evolution of the Pt nanoparticles, which was not dependent on the inverse grain size with the monolayer film formation. Because the Pt NP surface was slowly oxidized overtime, which was shown by XPS, a reasonable explanation was proposed that the partially oxidation of the surface of Pt film reduced the compressive surface stress and lead to the lattice expansion (still small than the bulk value). ☐ In a separate study, different composition of nanoparticles of CuxNiy (Cu, Cu1Ni1, Cu1Ni2, Cu1Ni3, Cu2Ni1 and Ni) with a core/shell structure were synthesized by two reducing agents: sodium hypophosphite (NaH2PO2) and hydrazine (N2H4), via reduction of copper acetate tetrahydrate and nickel acetate tetrahydrate, respectively, in ethylene glycol. NaH2PO2 reduced Cu2+ at 100 ℃ and reduced Ni2+ at 175 ℃, while N2H4 with NaOH, which have a higher reducing power, can reduce Cu2+ at room temperature and reduce Ni2+ at 100 ℃. Both of these two processes form Cu/Ni core/shell structures. The Cu/Ni core/shell nanoparticles were successfully assembled into uniform films and this set of core/shell structure can be used as Cu/Ni diffusion couple.
Description
Keywords
Nanoparticles, Platinum, Nickel, Copper, Film formation, Oxidation, Carburization