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A set of bottom-gate Zinc Oxide (ZnO) thin film transistors (TFTs) with active layers containing 1, 4 and 8 layers of spin-coated ZnO were fabricated and their electrical characteristics such as transistor transfer and capacitance-voltage characteristics were analyzed. The transconductance of the single-layered ZnO transistor shows a single peak. On the other hand, multiple peaks and humps were observed in the transconductance and capacitance-voltage characteristics of multi-layered ZnO transistors. The multi-layers were grown by reiteration of the spin-coating process, producing ZnO − ZnO interlayer-interfaces. The surface of the ZnO layer in contact with the ambient contains active sites, resulting in chemisorption of ambient gases such as oxygen prior to the deposition of subsequent layers. The chemisorbed species become negatively-charged and form charge sheets, depleting the surface/interface region. It was proposed that the formation of depletion layers at ZnO − ZnO interlayer-interfaces is the main cause for the observed anomaly.

By correlating in-situ synchrotron X-ray diffraction measurements with electrochemical measurements using a rotating disc electrode, we demonstrate the critical dependence on the local supersaturation of the kinetics of formation of a protective crystalline scale on the surface of carbon steel during CO2 corrosion in brine at elevated temperature. We show that the total current is the sum of a current due to dissolution of iron and a current due to growth of a crystalline layer. We show that the dissolution current and the surface supersaturation are controlled by the thickness of an initially-formed amorphous layer. As in earlier work at room temperature, we infer that the amorphous layer dissolves as a carbonato-iron complex with surface concentration of the dissolving species determined by the electrode potential, and speculate on the importance of the chemistry of this dissolution reaction in determining the corrosion result. We construct a simple transport-reaction model, which shows that the supersaturation is determined by the precipitation rate constant of colloidal FeCO3 and by the product of the current for Fe dissolution and the diffusion boundary layer thickness. Using this model, we show crystal growth rate varying quadratically with supersaturation at pH 6.8 and linearly at pH 7.3. The effects of electrode potential, surface roughness, microstructure and flow are simply to change supersaturation by changing the current density per unit projected area flowing through the amorphous initially formed layer. Variation of brine concentration has no effect. We illustrate the sensitivity to solution flow of the crystallinity of the final scale. We show that siderite is the first crystalline product and that chukanovite follows, with a delay time that decreases with increasing pH. The ratio of chukanovite to siderite is low at sufficiently high pH and increases with decreasing pH, possibly through a maximum. From the results, we advance ideas concerning the importance of local microenvironments and local fluctuations in mass-transport rate. 2017 Elsevier Ltd Scopus

In this review, we discussed the current mechanistic understanding and effects of key parameters on corrosion of carbon and low alloy steel (CLAS) in CO2 environments. In particular, we emphasized on the current understanding related to the mechanism of early stage nucleation of siderite that has evolved from the outcomes of in-situ synchrotron-based X-ray studies under various modes. We also highlighted the effect of the most important environmental and metallurgical factors affecting the corrosion behavior of CLAS. Finally, we addressed the aspects of material chemistry and micro-alloying necessary for achieving the most effective and economic materials system for mitigating corrosion in CO2 environment. Scopus

Quantitative fractographic characteristics of 4340 steel is demonstrated for a grain size range of 10−100 µm and hardness range of 41–52 HRC. Double-notched tensile samples were electrochemically charged in-situ with hydrogen in 0.5 m H 2 SO 4 +5 mg/l As 2 O 3 solution for 0–40 min charging time. Hydrogen induced fracture initiations were analyzed by novel metallographic investigation of the “unbroken” notch while the overall fractographic behaviors were examined by the scanning electron microscopic imaging of the fracture surfaces of the actually broken notch. Effect of hydrogen was predominantly manifested as intergranular fracture for the harder samples and quasi-cleavage fracture for the softer counterparts. 10–40 µm samples showed the maximum intensity of the hydrogen induced fracture features (intergranular and/or quasi-cleavage) close to the notch which gradually reduced with increasing distance from the notch. The largest grained samples (100 µm) however showed brittle behavior even in absence of hydrogen with similar intensity of percent fracture features at all distance from the notch, while presence of hydrogen intensified the overall percent brittle fractures with their intensities being highest close to the notch. Finally, the brittle fracture characteristics of the hydrogen embrittled samples were shown to be distinguishably different from that of the liquid nitrogen treated samples of same grain sizes and hardnesses.

Hydrogen peroxide vapor has been proposed as a sterilant/decontaminant for usage in buildings and transportation vehicles including emergency vehicles, buses, trains and aircraft. Although the efficacy of the process has been demonstrated, questions regarding the compatibility of vaporized hydrogen peroxide treatments with the many diverse materials of construction have been raised. This paper presents results on the embrittlement of high strength AISI 4340 steel as a result of condensation of the vapor during exposure to vaporized hydrogen peroxide. Notched four point bending samples of AISI 4340 steel were tested using the standard test methods of ASTM F519-06 to quantify susceptibility to hydrogen embrittlement in this aggressive service environment. No embrittlement effects were observed for samples exposed to strictly vapor phase hydrogen peroxide for concentrations up to 1000 ppm H2O2 and exposure times of 4.8 h. Higher concentrations of 1300 and 1600 ppm H2O2 led to the condensation of the vapor throughout the process chamber and brittle fracture of samples. These results were confirmed by examination of the fracture surfaces of samples using scanning electron microscopy. Samples that were not considered embrittled possessed dimpled fracture surfaces consistent with ductile failure. Embrittled samples exhibited inter-granular fractures along prior austenitic grain boundaries near the root of the notch – a common characteristic of hydrogen embrittlement.