Crystalline Gaq3Nanostructures: Preparation, Thermal Property and Spectroscopy Characterization

Crystalline Gaq31-D nanostructures and nanospheres could be fabricated by thermal evaporation under cold trap. The influences of the key process parameters on formation of the nanostructures were also investigated. It has been demonstrated that the morphology and dimension of the nanostructures were mainly controlled by working temperature and working pressure. One-dimensional nanostructures were fabricated at a lower working temperature, whereas nanospheres were formed at a higher working temperature. Larger nanospheres could be obtained when a higher working pressure was applied. The XRD, FTIR, and NMR analyses evidenced that the nanostructures mainly consisted of δ-phase Gaq3. Their DSC trace revealed two small exothermic peaks in addition to the melting endotherm. The one in lower temperature region was ascribed to a transition from δ to β phase, while another in higher temperature region could be identified as a transition from β to δ phase. All the crystalline nanostructures show similar PL spectra due to absence of quantum confinement effect. They also exhibited a spectral blue shift because of a looser interligand spacing and reduced orbital overlap in their δ-phase molecular structures

Hydrogen Transport and Hydrogen Embrittlement in Stainless Steels (Diffusion, Permeation, Solubility, Slow Crack Growth)

200 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1985.In order to understand the kinetics of gaseous hydrogen-induced slow crack growth (SCG) in metastable austenitic stainless steels, hydrogen permeation and/or cracking velocity were measured and compared for three types of stainless steels. These included austenitic, ferritic, and duplex ((gamma)/(alpha)) alloys. Deformation in AISI 301 resulted in various amounts of (alpha)' martensite, which enhanced the effective hydrogen diffusivity and permeability. No phase transformation was observed in deformed AISI 310. The effective hydrogen diffusivity in this alloy was slightly reduced after plastic deformation, presumably by dislocation trapping. In either the dynamic or static tensile test, AISI 301 exhibited the greatest hydrogen embrittlement and therefore the highest SCG velocity among all the alloys tested in this work. The SCG velocity was believed to be controlled by the rate of accumulation of hydrogen in the embrittlement region ahead of the crack tip and therefore could be explained with the hydrogen transport parameters measured from the permeation experiments. The relatively high SCG velocity in AISI 301 was probably due to the fast transport of hydrogen through the primarily stress-induced (alpha)' phase around the crack. No SCG was observed in AISI 310. The presence of H(,2)O vapor was found to reduce both the hydrogen permeation and SCG velocity. The reduction was possibly caused by surface interference or oxidation, or a combination of these two effects. The mechanism of hydrogen-induced SCG was discussed based upon hydrogen-enhanced plasticity proposed by Beachem and Birnbaum. This concept was consistent with the SCG behavior in hydrogen gas observed in this work.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD

Thermal Degradation of Vegetable Oils

Vegetable oils provide lipids and nutrition and provide foods with a desirable flavor, color, and crispy texture when used to prepare fried foods. However, the oil quality is degraded at elevated temperatures, and thus must be examined frequently because of the damage to human health. In this study, sunflower, soybean, olive, and canola oils were examined, and their properties were measured periodically at different elevated temperatures. The unsaturated triglyceride in oils reacted with the environmental oxygen or water vapor significantly changes in optical absorbance, viscosity, electrical impedance, and acid value. We used defect kinetics to analyze the evolution of these oil properties at elevated temperatures. The optical absorbance, viscosity, and electrical impedance follow the second-order, first-order, and zeroth-order kinetics, respectively. The rate constants of the above kinetics satisfy the Arrhenius equation. Olive oil has the lowest rate of color center and dynamic viscosity among the four oils, with the smallest pre-exponential factor and the largest activation energy, respectively. The rate constants of acid reaction also satisfy the Arrhenius equation. The activation energies of the polar compound and acid reaction are almost the same, respectively, implying that the rate constant is controlled by a pre-exponential factor if four oils are compared. Olive oil has the largest rate constant of acid reaction among the four oils, with the lowest pre-exponential factor

Preparation and Characterization of Molecularly Homogeneous Silica–Titania Film by Sol–Gel Process with Different Synthetic Strategies

Three silica–titania thin films with various degrees of molecular homogeneity were synthesized by the sol–gel process with the same precursor formula but different reaction paths. The dried films prepared by a single spin-coating process have a thickness of 500–700 nm and displayed no cracks or pin holes. The transmittances and refractive indices of the samples are >97.8% in the range of 350–1800 nm and 1.62–1.65 at 500 nm, respectively. The in-plane and out-of-plane chemical homogeneities of the films were analyzed by X-ray photoelectron spectroscopy and Auger electron spectroscopy, respectively. For the film with the highest degree of homogeneity, the deviations of O, Si, and Ti atomic contents in both in-plane and out-of-plane directions are less than 1.5%, indicating that the film is highly molecularly homogeneous. It also possesses the highest transparency and the lowest refractive index among the three samples

Fabrication of High-Activity Hybrid Pt@ZnO Catalyst on Carbon Cloth by Atomic Layer Deposition for Photoassisted Electro-Oxidation of Methanol

ZnO nanorods with a diameter of 25 nm have been synthesized on carbon cloth (CC) by combining atomic layer deposition (ALD) and hydrothermal methods. Platinum nanoparticles were then deposited on photoinduced hydrophilic surface of ZnO nanorods by ALD. Electrochemical performance of the nanocomposite catalyst (Pt@ZnO@CC) for methanol oxidation with or without UV irradiation was evaluated. According to the X-ray photoelectron spectroscopic (XPS) analysis, the surface of ZnO nanorods rich in hydroxide species was more favorable for removal of CO via the so-called bifunctional mechanism. Additionally, the XPS study indicates that the charge transfer occurs between the ZnO nanorods and the Pt nanoparticles. UV light irradiation on the catalyst surface increases the chronoamperometric response by 62%, which is attributed to a synergistic effect of large surface area and strong light absorption in the UV region by the presence of ZnO nanorod arrays

HNO₃‑Assisted Polyol Synthesis of Ultralarge Single-Crystalline Ag Microplates and Their Far Propagation Length of Surface Plasmon Polariton

We developed a HNO₃-assisted polyol reduction method to synthesize ultralarge single-crystalline Ag microplates routinely. The edge length of the synthesized Ag microplates reaches 50 μm, and their top facets are (111). The mechanism for dramatically enlarging single-crystalline Ag structure stems from a series of competitive anisotropic growths, primarily governed by carefully tuning the adsorption of Ag⁰ by ethylene glycol and the desorption of Ag⁰ by a cyanide ion on Ag(100). Finally, we measured the propagation length of surface plasmon polaritons along the air/Ag interface under 534 nm laser excitation. Our single-crystalline Ag microplate exhibited a propagation length (11.22 μm) considerably greater than that of the conventional E-gun deposited Ag thin film (5.27 μm)

Electronic Band Structure and Electrocatalytic Performance of Cu₃N Nanocrystals

High-density discrete Cu₃N nanocrystals were deposited on XC-72 carbon black by plasma-enhanced atomic layer deposition (PEALD). This heterostructured noble-metal-free catalyst served as a high-performance electrocatalyst for enhanced oxygen reduction reaction (ORR). The electronic band structure of Cu₃N was determined by ultraviolet photoelectron spectroscopy (UPS) and UV–vis spectrophotometry. The work function (Φ) of the Cu₃N nanocrystals was calculated to be 5.04 eV, which is lower than that of Pt (∼5.60 eV). With lower energy barrier, Cu₃N would exhibit stronger electron transfer to cause ORR than typical Pt catalyst. The UPS analysis also confirmed the synergistic coupling effect between the Cu₃N nanocrystals and the carbon support. Coupled with the XC-72, the Cu₃N200/C showed even smaller Φ (=4.34 eV) than pure Cu₃N nanocrystals. Thus, the Cu₃N200/C electrocatalyst prepared with 200 ALD cycles exhibited similar ORR catalytic activity, significantly improved mass activity, and potentially greater durability than its Pt/C counterpart in alkaline solution. The fabrication of Cu₃N by PEALD and its good performance in ORR suggest a promising alternative of non-noble-metal electrocatalyst for application in fuel cells