Hydrogen effects on the passive film formation and pitting susceptibility of nitrogen containing type 316L stainless steels

The effects of hydrogen on the passivity and pitting susceptibility of type 316L stainless steels have been investigated with alloys containing different nitrogen contents (0.015, 0.198 and 0.556 wt.% N). The study revealed that electrochemically pre-charged hydrogen significantly reduced the pitting resistance of alloys conatining 0.015 and 0.198 wt.% nitrogen contents. In alloy with highest nitrogen content (0.556 wt.% N), an increase in the passive film current density with hydrogen was observed without affecting breakdown potential. Auger electron spectroscopy (AES) analysis of the passive film indicated the presence of nitrogen in the passive film. On other hand, for hydrogen charged samples, nitrogen was found to be significantly less in the passive film. In Electrochemical impedance spectroscopy (EIS) measurement, the decrease in semi-circle radius of Nyquist plot, and the polarization resistance, R_P associated with the resistance of the passive film was observed with hydrogen, indicating that hydrogen decreased the stability of the passive film. The present investigation indicated that precharged hydrogen deteriorated the passive film stability and pitting corrosion resistance in these alloys, and the increase in nitrogen content of the alloy offsets the deleterious effect of precharged hydrogen.     

Prolonged sensitivity of immobilized thylakoid membranes in cross-linked matrix to atrazine

Freshly prepared pea thylakoid membranes were immobilized in bovine serum albumin-glutaraldehyde cross-linked matrix (BSA-GA matrix) and their stability under long term storage was analyzed by Pulse-Amplitude-Modulated (PAM) chlorophyll fluorescence and photosynthetic oxygen evolution measured by oxygen rate electrode. The thylakoid membranes stored at 4 °C showed prolonged stability in BSA-GA matrix and additional adsorption on nitrocellulose membrane filters gave them more stability. The sensitivity of the parameters of the oxygen evolution of thylakoid membranes to atrazine increased with immobilization. The half-inhibition time for oxygen evolution and quantum efficiency of photosynthesis could be prolonged to more than 15 days. These results suggest that the immobilized thylakoid membranes in BSA-GA matrix can be used as biological receptor in biosensors for a long period of time (up to 25 days) applying the proposed new method for atrazine detection by using polarographic oxygen rate electrode. This method is more sensitive, faster and easier to use than other methods for detection of herbicides based on determination of the photochemical activity of photosystem II.     

Why Intervals? Because If We Allow Other Sets,Tractable Problems Become Intractable

We show that if we add at least one non-interval set to the family of all intervals, then some reasonable interval computation problems that were previously computationally feasible become intractable. This result provides one more motivation for using the interval family: because if we increase this family, we lose computability.     

Enhanced calcium–magnesium–aluminosilicate (CMAS) resistance of GdAlO3 (GAP) for composite thermal barrier coatings

The impact of calcium–magnesium–alumino-silicate (CMAS) degradation is a critical factor for development of new thermal and environmental barrier coatings. Several methods of preventing damage have been explored in the literature, with formation of an infiltration inhibiting reaction layer generally given the most attention. Gd₂Zr₂O₇ (GZO) exemplifies this reaction with the rapid precipitation of apatite when in contact with CMAS. The present study compares the CMAS behavior of GZO to an alternative thermal barrier coating (TBC) material, GdAlO₃ (GAP), which possesses high temperature phase stability through its melting point as well as a significantly higher toughness compared with GZO. The UCSB laboratory CMAS (35CaO–10MgO–7Al₂O₃–48SiO₂) was utilized to explore equilibrium behavior with 50:50 mol% TBC:CMAS ratios at 1200, 1300, and 1400°C for various times. In addition, 8 and 35 mg/cm² CMAS surface exposures were performed at 1425°C on dense pellets of each material to evaluate the infiltration and reaction in a more dynamic test. In the equilibrium tests, it was found that GAP appears to dissolve slower than GZO while producing an equivalent or higher amount of pore blocking apatite. In addition, GAP induces the intrinsic crystallization of the CMAS into a gehlenite phase, due in part to the participation of the Al₂O₃ from GAP. In surface exposures, GAP experienced a substantially thinner reaction zone compared with GZO after 10 h (87 ± 10 vs. 138 ± 4 μm) and a lack of strong sensitivity to CMAS loading when tested at 35 mg/cm² after 10 h (85 ± 13 versus 246 ± 10 μm). The smaller reaction zone, loading agnostic behavior, and intrinsic crystallization of the glass suggest this material warrants further evaluation as a potential CMAS barrier and inclusion into composite TBCs.     

A study on the redistribution of ion-implanted nitrogen in Ti-modified austenitic steel

Titanium modified austenitic steel has been subjected to nitrogen implantation to different fluences. There is a considerable deviation of the experimental depth profile of nitrogen from the theoretical profile obtained using Monte-Carlo codes. Available literature ascribes such redistribution to sputtering; by following the implanted nitrogen and the vacancy-defects alongside using resonance nuclear reaction analysis and positron annihilation spectroscopy, clear experimental evidence for the formation of vacancy-nitrogen complexes is established. The possibility of role of complexes in redistributing the implanted nitrogen is explored here for the first time.     

The production of non linear damage under molecular ion implantation

Germanium atomic (Ge₁) and molecular ions (Ge₂) of equivalent energy are implanted in silicon at an elevated temperature. The ion induced damage has been characterized by RBS channeling (RBS/C) and positron annihilation spectroscopy. The RBS/C studies indicate that the molecular ion implantation has produced more defects in the near surface regions compared to the atomic ion implantation. This paper reports a first time observation of an enhanced production of vacancy related defects in silicon implanted with molecular ions.     

Effects of Ionic Liquid Additive Concentration on Scuffing and Wear in Oil-Starved EHL Contacts

Abstract

We show how various concentrations ranging from 0 to 5.0?wt% of the ionic liquid (IL) trihexyltetradecylphosphonium bis(2-ethylhexyl)phosphate added to a fully formulated aviation DOD-PRF-85734 gearbox lubricant affects the properties of the lubricant, including scuffing resistance under starved lubrication conditions, coefficient of friction (COF), wear rate, and lubricant chemical stability. Specimen surfaces were then characterized using scanning electron microscopy, energy-dispersive spectroscopy, and auger electron spectroscopy. Scuffing and wear properties were found to generally improve with IL concentration, which we hypothesize is due to the presence of a phosphorous-rich film observed on specimens exposed to IL.     

Mass transfer between solid and liquid in a gas-stirred vessel

Mass transfer between solid and bulk liquid in an axisymmetric gas-stirred water model of a metallurgical reactor has been investigated both experimentally and theoretically. To this end, mass transfer rates from benzoic acid compacts submerged in an aqueous gas bubble driven system were measured via a weight loss technique. In conjunction with the weight loss measurements, liquid velocity and turbulence kinetic energy distributions in the bath were also mapped via laser doppler velocimetry (LDV). From the detailed LDV measurements, relevant dimensionless groups such as $\operatorname{Re} _{loc,r} \left( { = \frac{{d\rho \sqrt {u^2 + v^2 } }}{\mu }} \right)$ and $\operatorname{Re} _t \left( { = \frac{{d\rho \hat u}}{\mu }} \right)$ were estimated. Experimental measurements indicated that flow parameters varied from one location to another within the system. The corresponding variation in dissolution rates was, however, less pronounced. Such a trend was observed for all three gas flow rates studied. It was found that experimentally measured dissolution rates can be correlated with the measured flow and turbulence parameters (viz., √u ²+v ² and û) in terms of a previously reported dimensionless correlation, viz., Sh=0.73 (Re_loc,r )^0.25 (Re _t )^0.32 (Sc)^0.33. Parallel to flow measurements, a two-phase turbulent flow model was also applied to numerically compute the distributions of mean and fluctuating velocity components in the vessel. Embodying the predicted velocity components in the aforementioned correlation, mass transfer rates were recalculated. A comparison between the two sets of Sherwood numbers (estimated on the basis of the experimentally measured and theoretically predicted flow fields) suggests that solid-liquid mass transfer rates in a gas-stirred vessel can be predicted reasonably well via an axisymmetric, steady-state, two-dimensional turbulent flow model.