This EAGER project is aimed at obtaining free standing quasicrystalline nanoparticles from properly annealed Zirconium-based amorphous alloys through chemical and electrochemical approaches. It is known that metastable quasicrystalline nanoparticles precipitate during the initial crystallization of some Zr-based amorphous alloys. These particles are embedded in the amorphous matrix and transform to stable crystalline phases upon further annealing. The size of the precipitated particles ranges from several to a 100 nanometers. The separation of these nanoparticles from the amorphous matrix will be carried out by chemical and electrochemical approaches. A Zr-based amorphous alloy, in which the precipitation of quasicrystalline nanoparticles has been confirmed, will be either etched chemically or electrochemically. The amorphous matrix will be removed preferentially, enabling the nanoparticles to fall into the solution, after which they will be recovered through filtering. The experimental conditions will be optimized. Due to their reduced sizes and unique atomic configurations, the Zr-rich particles are expected to exhibit novel properties.
NON-TECHNICAL SUMMARY: The particles synthesized in the present project represent a new class of material and are of interest for both fundamental studies and potential medicinal applications or as hydrogen storage materials. The properties of these nanoparticles are expected to differ from their normal crystalline and/or amorphous counterparts because of their nanometer size. The success of the present project could stimulate the demand for such particles for commercial exploitation or for the initiation of joint projects with researchers in other fields. The present project will have a significant impact on the teaching and research activities at Clarion University and will stimulate interest in nanotechnology in nearby institutions. Four undergraduate students will be involved in this project at different stages, providing valuable opportunities to work on real-world problems within the environment of a predominantly teaching university. In addition to publications in peer-reviewed journals and presentations at professional meetings, the results will be introduced in a nanotechnology course and in a campus-wide seminar series. Clarion University has a very close relationship with local middle and high schools. The results of this project will be introduced to teachers and students in these schools. The principal investigator of the present project is an active member of the National Science Foundation's Nanotechnology Application and Career Knowledge (NACK) Center at Pennsylvania State University. The results of this project will also be communicated to the NACK Center.
This EAGER project is to explore the feasibility of obtaining icosahedral quasicrystalline nanoparticles. The atomic configuration of icosahedral quasicrystalline structure is different from that of more commonly encountered crystalline and metallic glass structures. In crystalline structure, the arrangement of atoms has both translational and rotational symmetries while in metallic glass structures atoms are arranged in a random fashion. Quasicrystalline structure, in some sense, can be considered as a state between glassy and crystalline structures. It lacks translational symmetries but possesses rotational symmetries. Metallic glasses are metastable and transform to other stable phases upon annealing at elevated temperature, which is commonly referred to as crystallization process. It has been intensively reported that icosahedral quasicrystalline nanoparticles precipitate in the initial crystallization processes of Zirconium, Hafnium, and Titanium based metallic glasses. These particles are in metastable state, transforming to more stable crystalline phases upon further annealing. The particle size ranges from several to a hundred nanometers. The nanometer size, icosahedral quasicrystalline structure, and the metastable state set these particles aside from others. A variety of applications, such as in cancer treatment, are expected. It should be pointed out that, these particles are embedded in glassy matrix. Free standing particles must be prepared before any applications can be examined, which is the goal of the present project. We have focused on the separation of icosahedral quasicrystalline nanoparticles by mechanical approaches. Annealed metallic glasses of Zr65Al7.5Ni10Cu12.5Ir5, Zr70Al7.5Ni10Cu12.5, Zr70Cu27.5Rh2.5, Zr70Al8Cu13.5Ni8.5Nbx (x= 0, 2, 4,6,7, 8,10), Zr65Al7.5Ni10Cu17.5Ag10, and Hf69.5Al7.5Cu12Ni11 compositions have been used. The precipitation of icosahedral quasicrystalline nanoparticles in these samples has been confirmed by both X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) observation. Several mechanical approaches have been attempted, including (1) scraping with diamond pen in water and alcohol, (2) abrading with sand paper or diamond paper in alcohol or dry ice cooled alcohol. Here, the alcohol serves two purposes: to prevent the particles from bouncing around and to cool the sample during the scraping process. The usage of dry ice is to enhance the cooling effect. The crystal structure of the obtained particles has been analyzed by using TEM. Fig. 1(a) shows a TEM image, where the particles sit on the net-work shaped holey carbon film. In the same figure, Electron Diffraction Patterns corresponding to crystalline (d), glassy (c), and icosahedral quasicrystalline (b) phases, have been observed. The three fold symmetry and the 1.60 ratio of OB to OA distances of Electron Diffraction Pattern (b) are strong evidences that desired quasicrystalline nanoparticles have been fabricated. However, the ratio of different phases before and after separation by mechanical approach shows a significant change. It has been estimated that the volume ratio of icosahedral quasicrystalline nanoparticles to that of glassy matrix is in the order of 1:1 and there is no crystalline phase before scraping. Experiments have revealed that, for most of the samples, approximately 90% of the prepared particles are of crystalline structure and 10% of them are glassy phase. The icosahedral quasicrystalline phase is typically less than 1%. The best result was obtained with Hf69.5Al7.5Ni10Cu11 metallic glass, where approximately 30% of the particles examined are of icosahedral quasicrystalline structure while glassy and crystalline particles correspond to 30 and 40%, respectively. The discrepancy implies an undesired phase transformation in the particle separation processes and procedures to prevent this effect in the subsequent project are suggested. Local temperature increase is believed to be the reason. The fact that experiments on Hf69.5Al7.5Ni10Cu11 metallic glass experienced less undesired phase transformation supports this hypothesis because of its higher crystallization temperature and brittleness. Based on such analysis, improvements are suggested such as the usage of a dedicated cryo-microtome and preparation of relatively large particles followed by chemical etching. This project brought excitement to the Clarion community and enhanced students’ interest toward science. The background and partial results have been covered by local newspapers and also presented in the Faculty Author series at Clarion University (CU). The news and the partial results have also been introduced in several courses. A group of thirty students visited the PI’s laboratory and was exposed to the present project. Six Clarion students have been supported by this project, two for the whole project period while others for the fall or spring semesters. One student has been accepted to a Ph.D. program and the other to Master program to continue their graduate studies. Upon graduation, the other four students are planning to develop careers in engineering fields or to continue their graduate studies. This project has lead to one publication in peer-reviewed journal, one submitted, and one in preparation. Ten conference presentations have been made in places such as the annual meeting of 2012 Microscopy and Microanalysis. All these publications and presentations have students as co-author or leading author.
