Yakun Zhu

Sensitization Prediction and Validation for Al 5xxx Alloys Exposed to Long-Term Cyclical and Constant Heating at Low Temperatures

A number of Al 5xxx alloys were aged at constant temperatures (40, 50, 60, 70°C) and cyclic temperatures (40 to 45, 30 to 70, 50 to 70°C) for as long as 57.5 months. ASTM G67 nitric acid mass loss test (NAMLT) results of Al 5050-H32, 5052-H32, 5154-H32, 5083-H116, 5083-H131, and 5456-H116 alloys were obtained to evaluate the degree of sensitization. An intergranular β-phase growth model that considers nucleation, growth, and coarsening processes was developed to predict the formation and continuity of the β phase that leads to sensitization. Results obtained from scanning transmission electron microscopy were used to verify the model. A linear relationship between continuity and mass loss was adopted to predict the mass loss of Al 5083-H116 and -H131 aged at constant and cyclical temperature, and the modeling results agree well with experimental mass loss data.

Design, synthesis, and characterization of TPA-thiophene-based amide or imine functionalized molecule for potential optoelectronic devices

New sets of molecules containing tri-phenyl-amine (TPA) core and thiophene unit with amide and imine functional groups are designed, synthesized, characterized, and compared. These are solution processable small molecules with high mobility. The newly designed molecules have better solubility due to the C=N (imine) and CONH2 (amide) moiety as compared to the established molecules with CH=CH (methine) for optoelectronic applications. They have an optimal energy band gap, which indicates their potential utility in a variety of optoelectronic applications. These molecules also show efficient intermolecular charge transfer mechanisms similar to conventional organic semiconducting molecules as evidenced by optical measurements. Density functional theory simulation results show that the localization of the frontier highest occupied molecular orbital is around the TPA core for molecules coupled with imine and amide, and is reasonably stable.

Advanced selective non-invasive ketone body detection sensors based on new ionophores

New molecules and methods were examined that can be used to detect trace level ketone bodies. Diseases such as type 1 diabetes, childhood hypo-glycaemia-growth hormone deficiency, toxic inhalation, and body metabolism changes are linked with ketone bodies concentration. Here we introduce, selective ketone body detection sensors based on small, environmentally friendly organic molecules with Lewis acid additives. Density functional theory (DFT) simulation of the sensor molecules (Bromo-acetonaphthone tungstate (BANT) and acetonaphthophenyl ether propiono hydroxyl tungstate (APPHT)), indicated a fully relaxed geometry without symmetry attributes and specific coordination which enhances ketone bodies sensitivity. A portable sensing unit was made in which detection media containing ketone bodies at low concentration and new molecules show color change in visible light as well as unique irradiance during UV illumination. RGB analysis, electrochemical tests, SEM characterization, FTIR, absorbance and emission spectroscopy were also performed in order to validate the ketone sensitivity of these new molecules.

Precipitates in Long Term Aging Al 5083 Alloy

Al 5083 alloy aged at 343 K (70 °C) for 3–30 months was evaluated by high resolution transmission electron microscopy (HRTEM) results show that both thickness and continuity of β phase formed at grain boundaries increase with time. GP zones are observed in Al 5083 aged at 343 K for 3 months for the first time. TEM results reveal that GP zones can form homogeneously with the help of vacancies as well as heterogeneously at dislocations near grain boundaries, and the mechanism are explained in detail. Mg2Si precipitate was found to form at the grain boundary and energy-dispersive X-ray spectroscopy (EDS) results reveal that a Mg, Si (atomic ratio 1:1) rich phase nucleates at the interface of Mg2Si-matrix. β’ phase(Al3Mg2, hexagonal) is observed to form at grain boundaries of Al 5083 alloy aged at 343 K for 30 months. β phase was found at the grain boundary of Al 5083 aged at 343 K for 12 months using EDS.

Corrosion behaviour of stainless steel exposed to highly concentrated chloride solutions

ABSTRACT The characteristics of pitting corrosion of Type 304L stainless steel (SS) exposed to highly concentrated chloride solutions were studied through the evaluation of the corrosion potential, the pitting potential, the structure of the passive layer and the statistics of pitting depth and density. Both as-received and weld metal samples were studied. The weld metal sample was machined from the welding zone of a butt weld of Type 304L SS. The results showed an accelerated anodic dissolution and depressed film resistance at the welding zone, but no dramatic change on pitting corrosion was observed from the statistics of pitting during the test duration up to 720 h. The pitting corrosion resistance was significantly affected by the chloride concentration and slightly affected by the temperature under the investigated conditions.