Spontaneous growth of one-dimensional nanostructures from films in ambient atmosphere at room temperature: ZnO and TiO2

One-dimensional oxide-based nanostructures have been intensively studied because of their excellent optoelectronic properties. Due to the drawbacks of vapor-phase or aqueous solution growth, including complex processes, high synthesis temperatures, expensive precursors, and also preceding patterned seeding or subsequent patterning processes, there is an urgent need to grow patterned nanostructures by a simple and direct process at low temperatures. In the present study, stress-induced growth of one-dimensional single-crystalline ZnO and TiO2 nanostructures directly from ZnO and TiO2 films, respectively, in an ambient atmosphere at room temperature were developed by indentation or scratching without the use of any reaction precursors. Under large applied stresses, oxide bonds were broken, assisted by hydrolysis in the presence of moisture, and subsequently were reconstructed (defined as a bond breaking-hydrolysis-reconstruction mechanism) leading to the spontaneous growth of one-dimensional nanocrystals. The direct growth at controlled locations provides an opportunity for the simple preparation of patterned nanostructures of oxide-based materials

Study of microporosity formation in nickel-base superalloys

peer reviewedThe susceptibility of nickel-base superalloys to microporosity formation is studied experimentally and theoretically. Analysis of a model introduced herein leads to formulation of a microporosity index, Ap*, which is expressed in terms of solidification parameters and alloy system properties. This index can be determined from information obtained by quantitative differential thermal analysis. The effect of composition on the formation of microporosity is evaluated. Thus, aluminum, titanium, and cobalt are found to increase, and chromium to decrease microporosity. The effect of carbon is beneficial or detrimental depending on the aluminum content in the alloy