Browsing by Author "Lu, Kathy"

Now showing 1 - 4 of 4
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    Fundamental mechanisms of focused ion beam guided anodization
    Tian, Zhipeng; Lu, Kathy; Chen, Bo (American Institute of Physics, 2010-11-01)
    This paper is focused on understanding the fundamental mechanisms of focused ion beam guided anodization and the unique capabilities of generating new patterns based on such an understanding. By designing proper interpore distance, pore arrangement, and pore shape during focused ion beam patterning, nonspherical pore shape and nonhexagonal patterns can be obtained by further anodization. The electrical field and the mechanical stress field around each focused ion beam patterned concave dictate the pore formation and growth. The oxide barrier layer thickness and shape around the focused ion beam guided pores affect new pore formation and the meshing of different size pores. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3500513]
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    Network structure and thermal stability study of high temperature seal glass
    Lu, Kathy; Mahapatra, Manoj K. (American Institute of Physics, 2008-10-01)
    High temperature seal glass has stringent requirement on glass thermal stability, which is dictated by glass network structures. In this study, a SrO-La2O3-Al2O3-B2O3-SiO2 based glass system was studied using nuclear magnetic resonance, Raman spectroscopy, and x-ray diffraction for solid oxide cell application purpose. Glass structural unit neighboring environment and local ordering were evaluated. Glass network connectivity as well as silicon and boron glass former coordination were calculated for different B2O3:SiO2 ratios. Thermal stability of the borosilicate glasses was studied after thermal treatment at 850 degrees C. The study shows that high B2O3 content induces BO4 and SiO4 structural unit ordering, increases glass localized inhomogeneity, decreases glass network connectivity, and causes devitrification. Glass modifiers interact with either silicon- or boron-containing structural units and form different devitrified phases at different B2O3:SiO2 ratios. B2O3-free glass shows the best thermal stability among the studied compositions, remaining stable after thermal treatment for 200 h at 850 degrees C. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2979323]
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    New insight into SiOC atomic structure evolution during early stage of pyrolysis
    Lu, Kathy; Chaney, Harrison (Wiley, 2023-05)
    This study focuses on the early stage of polymer-derived SiOC ceramic conversion. We demonstrate that the perceived SiOC phase separation is nonexistent. Instead, SiO2 and free carbon clusters form first and then carbothermal reduction sets in to induce SiOC formation. Such fundamental understanding is supported by both synchrotron X-ray diffraction study and reactive force field simulation. This work for the first time unifies the understanding of atomic evolution process of polysiloxane-based polymer to ceramic conversion.
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    Thermal stability and electrical conductivity of carbon-enriched silicon oxycarbide
    Lu, Kathy; Erb, Donald; Liu, Mengying (Royal Society of Chemistry, 2016-01-28)
    Silicon oxycarbide (SiOC) is an interesting polymer-derived system that can be tailored to embody many different properties such as lightweight, electrochemical activity, and high temperature stability. One intriguing property that has not been fully explored is the electrical conductivity for the carbon-rich SiOC compositions. In this study, a carbon-rich SiOC system is created based on the crosslinking and pyrolysis of polyhydromethylsiloxane (PHMS) and divinylbenzene (DVB) mixed precursors. The carbon-rich nature can effectively delay SiOC phase separation and crystallization into SiO2 and SiC during pyrolysis. In an oxidizing air atmosphere, the SiOC materials are stable up to 1000 °C with <0.5 wt% weight loss. Before the onset of electrical conductivity drop at ∼400 °C, the material has electrical conductivity as high as 4.28 S cm−1. In an inert argon atmosphere, the conductivity is as high as 4.64 S cm−1. This new semi-conducting behavior with high thermal stability presents promising application potential for high temperature MEMS devices, protective coatings, and bulk semi-conducting components that must endure high temperature conditions.