19 research outputs found
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
HNO<sub>3</sub>‑Assisted Polyol Synthesis of Ultralarge Single-Crystalline Ag Microplates and Their Far Propagation Length of Surface Plasmon Polariton
We
developed a HNO<sub>3</sub>-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 Ag<sup>0</sup> by ethylene glycol and the desorption of Ag<sup>0</sup> 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 Cu<sub>3</sub>N Nanocrystals
High-density
discrete Cu<sub>3</sub>N 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 Cu<sub>3</sub>N was determined by ultraviolet
photoelectron spectroscopy (UPS) and UV–vis spectrophotometry.
The work function (Φ) of the Cu<sub>3</sub>N nanocrystals was
calculated to be 5.04 eV, which is lower than that of Pt (∼5.60
eV). With lower energy barrier, Cu<sub>3</sub>N would exhibit stronger
electron transfer to cause ORR than typical Pt catalyst. The UPS analysis
also confirmed the synergistic coupling effect between the Cu<sub>3</sub>N nanocrystals and the carbon support. Coupled with the XC-72,
the Cu<sub>3</sub>N200/C showed even smaller Φ (=4.34 eV) than
pure Cu<sub>3</sub>N nanocrystals. Thus, the Cu<sub>3</sub>N200/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 Cu<sub>3</sub>N by PEALD and its good performance
in ORR suggest a promising alternative of non-noble-metal electrocatalyst
for application in fuel cells