IOWA STATE UNIVERSITY OF SCIENCE AND TECHNOLOGY

The objectives of this project are to 1) develop a novel laser-assisted non-contact technique to overcome the great challenges in thermal characterization of ceramic nanowires; and measure the porosity (F), thermal conductivity (k), and specific heat (volume based: C=?·cp) of TiO2 nanowires, and 2) investigate how and to what extent the SG-ES manufacturing conditions and the dimension and structures of TiO2 nanowires affect their thermophysical properties and porosity. This represents the first step toward establishing a comprehensive database for thermal property-synthesis condition-nanowire structure relations, which will provide the critical feedback for high-degree design and structure manipulation of TiO2 nanowires in manufacturing. Intellectual Merit. The outcomes of this project will feature a unique thermal characterization technique that will be fully developed, evaluated, and optimized to measure the thermophysical properties of TiO2 nanowires. This represents the very pioneering attempt to characterize the thermophysical properties of TiO2 nanowires to fill the knowledge gap about it. By using the proposed technique, an important knowledge base will be built about how and to what extent the synthesis conditions in the SG-ES technique, as well as the structure (e.g., grain size) of TiO2 nanowires, affect their thermophysical properties and porosity. This property-structure-synthesis condition relation will make it possible, for the first time, to achieve high degree of control of the thermophysical properties of TiO2 nanowires by adjusting the experimental parameters in the SG-ES technique and fine tailoring their structures, e.g., grain size and porosity. The impact of the proposed research can be visualized from two aspects. (1) Thermal Design. The temperature of TiO2 nanowires directly affects their mechanical, electrical, and optical properties, thereby having a profound impact on their engineering applications. For example, oxygen sensors based on TiO2 nanowires feature significantly improved sensitivity because of their super surface-to-volume ratio. In a thermally hostile environment, the sensor will change its bandgap because of the elevated/reduced temperature. Knowledge of the thermophysical properties of TiO2 nanowires provides the solid data needed to evaluate its thermal performance at elevated/reduced temperatures for oxygen sensing. The proposed research will also provide the information needed for evaluating the temperature response of TiO2 nanowire-based systems/devices under various thermal, electrical, mechanical, and optical loadings. (2) Process Optimization and Product Quality Monitor/Control. For ceramic nanowires made using the SG-ES technique, nanopores could form within wires when the solvent evaporates from the material. To date, no knowledge is available about the level of the nanopores and their concentration inside the wire. Nanowires with less porosity will have much better mechanical properties. For the first time, the measured volume-based specific heat (?·cp) can be used to directly evaluate the porosity level in ceramic nanowires and to guide the synthesis optimization. In addition, the proposed research will make it possible to control the thermal conductivity of TiO2 nanowires by using the measurement result as feedback to fine tune the SG-ES synthesis conditions.

Clarification of Codes