Date of Award

2008

Publication Type

Doctoral Thesis

Degree Name

Ph.D.

Department

Mechanical, Automotive, and Materials Engineering

Keywords

Applied sciences, Aluminides, Magnides, Nanoparticles, Sodides

Supervisor

Derek O. Northwood

Rights

info:eu-repo/semantics/openAccess

Abstract

The hydrolysis phenomenon of transition metal (including Si and Ge) magnides, aluminides and sodides has been investigated in this study, and has been successfully developed to produce both transition metal and semiconductor element nanoparticles. Both in-situ synthesized Mg2Ni and as-cast Mg2Ni exhibited a close to zero discharge capacity due to hydrolysis of Mg 2Ni and Mg2NiH4. The hydrolysis characteristics of Mg2Ni and Mg2NiH4 suggest that they are not suitable for use as electrodes in rechargeable batteries. The hydrolysis byproduct of transition metal and semiconductor element magnides, Mg(OH)2, can be easily removed by a dilute acid. After removal of Mg(OH)2 from the hydrolysis product of Mg2Ni, Ni nanoparticles were obtained. Besides Ni nanoparticles, Cu, Au and Ag nanoparticles have been successfully prepared by this method. The hydrolysis byproduct of magnides, Mg(OH)2, has a very small solubility in water, and thus the newly-formed Mg(OH)2 precipitates from water in the vicinity of the Mg dissolution sites. The existence of the Mg(OH)2 particles, and the low mobility of transition metal atoms at room temperature, give rise to the formation of very fine transition metal nanoparticles. Therefore, the particle size of these transition metal nanoparticles prepared by this method was not sensitive to the concentration of the initial materials in aqueous solution. Al3Ni spontaneously undergoes hydrolysis in water at room temperature, and forms Al(OH)3, Ni nanoparticles and hydrogen in distilled water at room temperature. Due to chemical characteristics of Al(OH)3 including its low acidity, chemically active transition metal nanoparticles, such as Fe, Co, and Ni, can not be produced by using dilute hydrochloric acid to remove Al(OH)3. However, chemically inert transition metal nanoparticles such as Au and Ag could be prepared by this method. The transition metal-sodium intermetallic compounds, i.e. sodides, undergo severe hydrolysis in water at room temperature. The reaction byproduct, NaOH, has a high solubility and is easier to remove than Mg(OH)2, the hydrolysis byproduct of magnides. This method, therefore, offers a simpler method of preparing transition metal nanoparticles. The drawback of this method is the difficulty in controlling the reaction rate.

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