Naval Surface Warfare Center

About: Naval Surface Warfare Center is a facility organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Radar & Sonar. The organization has 2855 authors who have published 3697 publications receiving 83518 citations. The organization is also known as: NSWC.

Solid-state activation of Li2O2 oxidation kinetics and implications for Li–O2 batteries

Abstract: As one of the most theoretically promising next-generation chemistries, Li–O2 batteries are the subject of intense research to address their stability, cycling, and efficiency issues. The recharge kinetics of Li–O2 are especially sluggish, prompting the use of metal nanoparticles as reaction promoters. In this work, we probe the underlying pathway of kinetics enhancement by transition metal and oxide particles using a combination of electrochemistry, X-ray absorption spectroscopy, and thermochemical analysis in carbon-free and carbon-containing electrodes. We highlight the high activity of the group VI transition metals Mo and Cr, which are comparable to noble metal Ru and coincide with XAS measured changes in surface oxidation state matched to the formation of Li2MoO4 and Li2CrO4. A strong correlation between conversion enthalpies of Li2O2 with the promoter surface (Li2O2 + MaOb ± O2 → LixMyOz) and electrochemical activity is found that unifies the behaviour of solid-state promoters. In the absence of soluble species on charge and the decomposition of Li2O2 proceeding through solid solution, enhancement of Li2O2 oxidation is mediated by chemical conversion of Li2O2 with slow oxidation kinetics to a lithium metal oxide. Our mechanistic findings provide new insights into the selection and/or employment of electrode chemistry in Li–O2 batteries.

Dislocation Mechanics of Shock-Induced Plasticity

Abstract: The constitutive deformation behavior of copper, Armco iron, and tantalum materials is described over a range of strain rates from conventional compressive/tensile testing, through split Hopkinson pressure bar (SHPB) test results, to shock-determined Hugoniot elastic limit (HEL) stresses and the follow-on shock-induced plasticity. A mismatch between the so-called Zerilli–Armstrong (Z-A) constitutive equation description of pioneering SHPB measurements for copper provided initial evidence of a transition from the plastic strain rate being controlled by movement of the resident dislocation population to the strain rate being controlled by dislocation generation at the shock front, not by a retarding effect of dislocation drag. The transition is experimentally confirmed by connection with Swegle–Grady-type shock vs plastic strain rate measurements reported for all three materials but with an important role for twinning in the case of Armco iron and tantalum. A model description of the shock-induced plasticity results leads to a pronounced linear dependence of effective stress on the logarithm of the plastic strain rate. Taking into account the Hall–Petch grain size dependence is important in specifying the slip vs twinning transition for Armco iron at increasing strain rates.

Hardness-assurance issues for lateral PNP bipolar junction transistors

Abstract: The dose-rate dependence of gain degradation in lateral PNP transistors is even stronger than the dependence previously reported for NPN BJTs. In this work, several hardness-assurance approaches are examined and compared to experimental results obtained at low dose rates. The approaches considered include irradiation at high dose rates while at elevated temperature and high-dose-rate irradiation followed by annealing. The lateral PNP transistors continue to degrade during post-irradiation annealing, in sharp contrast to NPN devices studied previously. High-temperature conditions significantly increase the degradation during high-dose-rate irradiation, with the amount of degradation continuing to increase with temperature throughout the range studied here (up to 125/spl deg/C). The high-temperature degradation is nearly as great as that observed at very low dose rates, and is even greater when differences between /sup 60/Co and X-ray irradiation are accounted for. Since high-temperature irradiation has previously been shown to enhance the degradation in NPN transistors, this appears to be a promising hardness-assurance approach for bipolar integrated circuits. Based on these results, preliminary testing recommendations are discussed.