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  1. Investigation of Sub‐Bandgap Emission and Unexpected n‐Type Behavior in Undoped Polycrystalline CdSe x Te 1‐x

    McGott, Deborah L. ; Johnston, Steven W. ; Jiang, Chun‐Sheng ; ... - Advanced Science
    Abstract Se alloying has enabled significantly higher carrier lifetimes and photocurrents in CdTe solar cells, but these benefits can be highly dependent on CdSe x Te 1‐x processing. This work evaluates the optoelectronic, chemical, and electronic properties of thick (3 µm) undoped CdSe x Te 1‐x of uniform composition and varied processing conditions (CdSe x Te 1‐x evaporation rate, CdCl 2 anneal, Se content) chosen to reflect various standard device processing conditions. Sub‐bandgap defect emission is observed, which increased as Se content increased and with “GrV‐optimized CdCl 2 ” (i.e., CdCl 2 anneal conditions used for group‐V‐doped devices). Low carrier lifetimemore » is found for GrV‐optimized CdCl 2 , slow CdSe x Te 1‐x deposition, and low‐Se films. Interestingly, all films (including CdTe control) exhibited n‐type behavior, where electron density increased with Se up to an estimated ≈10 17  cm −3 . This behavior appears to originate during the CdCl 2 anneal, possibly from Se diffusion leading to anion vacancy (e.g., V Se , V Te ) and Cl Te generation.« less

  2. Influence of Application Method on Disinfectant Byproduct Formation during Indoor Bleach Cleaning: A Case Study on Phenol Chlorination

    Jahn, Leif G. ; Bhattacharyya, Nirvan ; Blomdahl, Daniel ; ... - ACS ES&T Air
    Modern disinfection methods increasingly utilize droplet dispersal as a means of delivering disinfectant within an indoor space. Such an application produces droplets over wide size ranges, some of which may remain airborne for minutes to hours while serving as small reaction environments. We report here the formation of chlorophenolic disinfection byproducts (DBPs) during the injection of bleach microdroplets into an environmental chamber. These reactions within airborne microdroplets are driven by phenol dissolution and availability, and the observed DBPs span multiple generations of chlorination chemistry. DBPs representing successive chlorine addition to the phenol ring are initially observed (mono-, di-, and trichlorophenol),more » followed by DBPs that lack aromaticity (2,6-dichlorobenzoquinone and 2,4,4,6-tetrachloro-2,5-cyclohexadienone, among others). Chlorophenolic DBPs have not been reported during prior work examining indoor bleach cleaning and we attribute their observation in this work to the dispersal of disinfectant microdroplets rather than traditional mopping or wiping with a bulk aqueous solution on an indoor surface. Airborne microdroplets represent unique reaction and volatilization environments and unique exposure pathways to DBPs, via direct compound inhalation as well as the inhalation of DBP-containing microdroplets. The observed DBPs (particularly 2,6-dichlorobenzoquinone) have previously been linked to adverse health effects in humans through either direct toxicity or as precursors to other DBPs with adverse health effects. In conclusion, these measurements suggest that more work is needed to understand potential DBP formation and human exposure within a variety of indoor environments where disinfection techniques that generate airborne microdroplets are used.« less

  3. Adjusting the Chemical Reactivity of Oxygen for Propylene Epoxidation on Silver by Rational Design: The Use of an Oxyanion and Cl

    Carbonio, Emilia A. ; Sulzmann, Frederic ; Klyushin, Alexander Yu. ; ... - ACS Catalysis

  4. Evaluation of Potential Impacts of Free Chlorine during Washing of Fresh-Cut Leafy Greens on Escherichia coli O157:H7 Cross-Contamination and Risk of Illness

    Mokhtari, Amir ; Pang, Hao ; Santillana Farakos, Sofia ; ... - Risk Analysis
    Addition of chlorine-based antimicrobial substances to fresh-cut leafy green wash water is done to minimize microbial cross-contamination during processing. We developed the FDA Leafy Green Risk Assessment Model (FDA-LGRAM) to quantify the impact of free chlorine concentration in wash water during fresh-cut lettuce processing on the extent of water-mediated cross-contamination between shredded lettuce and the associated risk of illness due to exposure to Escherichia coli O157:H7. At different contamination prevalence and levels of E. coli O157:H7 on incoming lettuce heads, the model compared the predicted prevalence of contaminated fresh-cut lettuce packages and the risk of illness per serving between: (1)more » a scenario where fresh-cut lettuce was packaged without washing; and (2) scenarios involving washing fresh-cut lettuce with different levels of free chlorine (0 ppm, 5 ppm, 10 ppm, 15 ppm, and 20 ppm) prior to packaging. Our results indicate that the free chlorine level in wash water has a substantial impact on the predicted prevalence of contaminated fresh-cut lettuce packages and the risk of illness associated with E. coli O157:H7 in fresh-cut lettuce. Results showed that the required level of free chlorine that can minimize water-mediated cross-contamination and reduce the corresponding risk of illness depended on contamination prevalence and levels of E. coli O157:H7 on incoming lettuce heads. Our model also indicated that the pathogen inactivation rate in wash water via free chlorine was a key model parameter that had a significant impact on the extent of cross-contamination during washing and the predicted associated risk of illness.« less

  5. Impact of fuel-derived chlorine on CuO-based oxygen carriers for chemical looping with oxygen uncoupling

    Dai, Jinze ; Whitty, Kevin J. - Fuel
    During the chemical looping with oxygen uncoupling (CLOU) process for CO2 capture from solid fuels, CuO-based oxygen carriers are expected to efficiently transport oxygen from the air reactor and convert fuel in the fuel reactor by releasing gaseous oxygen. To maintain high fuel conversion and CO2 capture efficiency, it is important to understand the impact of the fuel-derived Cl, which is highly volatile and corrosive, on the CuO/Cu2O in a CLOU environment. In this work, thermodynamic modeling was carried out to predict the characteristics of Cu-Cl interaction and develop a Cu deactivation rate model. Combustion experiments were performed to examinemore » the impact of the Cl-containing flue gas on the CuO-based oxygen carrier. The oxygen transport capacities of the oxygen carriers exposed to the Cl-containing flue gas were measured by TGA. XRD and SEM-EDS were employed to characterize the ashes and oxygen carrier particles, respectively. The modeling results suggest that Cu-Cl interaction leads to the formation of CuCl and Cu3Cl3, causing the loss of effective Cu. The fraction of HCl converted to CuCl/Cu3Cl3 (XHCl) was predicted to be almost linearly correlated with the Cl content, while H2O could hinder the Cu-Cl interaction. The Cu deactivation rate model was successfully developed. For the fuels containing 0.2–0.4 wt% Cl, the Cu loss rate was estimated to be 0.0025–0.01%/cycle with XHCl = 0.12–0.24. The results of combustion experiments and material characterization were consistent with the modeling predictions, clearly demonstrating the Cl-induced deactivation. Given the modeling predictions and experimental findings, potential countermeasures were proposed.« less

  6. Mars Science Laboratory Observations of Chloride Salts in Gale Crater, Mars

    Thomas, N. H. ; Ehlmann, B. L. ; Meslin, P. ‐Y. ; ... - Geophysical Research Letters
    The Mars Science Laboratory Curiosity rover is traversing a sequence of stratified sedimentary rocks in Gale crater that contain varied eolian, fluviodeltaic, and lake deposits, with phyllosilicates, iron oxides, and sulfate salts. Here, we report the chloride salt distribution along the rover traverse. Chlorine is detected at low levels (<3 wt.%) in soil and rock targets with multiple MSL instruments. Isolated fine-scale observations of high chlorine (up to ≥15 wt.% Cl), detected using the ChemCam instrument, are associated with elevated Na2O and interpreted as halite grains or cements in bedrock. Halite is also interpreted at the margins of veins andmore » in nodular, altered textures. We have not detected halite in obvious evaporitic layers. Instead, its scattered distribution indicates that chlorides emplaced earlier in particular members of the Murray formation were remobilized and reprecipitated by later groundwaters within Murray formation mudstones and in diagenetic veins and nodules.« less

  7. Role of Manganese in Accelerating the Oxidation of Pb(II) Carbonate Solids to Pb(IV) Oxide at Drinking Water Conditions

    Pan, Weiyi ; Pan, Chao ; Bae, Yeunook ; ... - Environmental Science and Technology
    Pb(II) carbonate solids are corrosion products that form on the inner surfaces of lead service lines (LSLs) and can be oxidized by free chlorine to form Pb(IV) oxide (PbO2). The formation of PbO2 can maintain low dissolved lead concentrations in drinking water, but PbO2 can dissolve if a free chlorine residual is not maintained. Experiments demonstrated that the oxidation of Pb(II) carbonate by free chlorine was faster with manganese (Mn). Without Mn(II), the oxidation of Pb(II) carbonate was an autocatalytic process. With Mn(II), the overall oxidation rate was 2 orders of magnitude faster than without Mn(II). X-ray diffraction and freemore » chlorine consumption profiles indicated that δ-MnO2 was formed within several minutes of the reaction of Mn(II) with free chlorine, and δ-MnO2 catalyzed the oxidation of Pb(II) carbonate by free chlorine. Free chlorine consumption profiles for Pb(II) carbonate with and without Mn(II) were interpreted based on the kinetics and stoichiometry of the underlying chemical reactions. These findings highlight the importance of Mn in accelerating the formation of PbO2 in water with Pb(II) carbonate solids and free chlorine, and it may help explain why PbO2 is observed on LSLs of some but not all water systems that use free chlorine.« less

  8. Trace Element Mass Flow Rates from U.S. Coal Fired Power Plants

    Sun, Xiaodi ; Gingerich, Daniel B. ; Azevedo, Inês L. ; ... - Environmental Science and Technology
    Trace elements (TEs) exit coal-fired power plants (CFPPs) via solid, liquid, and gaseous waste streams. Estimating the TE concentrations of these waste streams is essential to selecting pollution controls and estimating emission reduction benefits. Our report presents a generalizable mass balance model for estimating TE mass flow rates in CFPP waste streams and evaluates model accuracy for the U.S. coal fleet given current data constraints. We stochastically estimate, using a bootstrapping approach, the 2015 plant-level mass flow rates of Hg, Se, As, and Cl to solid, liquid, and gas phase waste streams by combining publicly available data for combusted coalmore » TE concentrations with estimates of TE partitioning within installed air pollution control processes. When compared with measured and reported data on TE mass flow rates, this model generally overestimates masses by 30–50%, with larger errors for Hg. The partitioning estimates are consistent for Se, As, and Cl removal from flue gas, but tend to underestimate Hg removal. While our model is suitable for first-order estimates of TE mass flows, future work to enhance model performance should focus on collecting and using new data on TE concentrations in the coal blend, where data quality is the weakest.« less

  9. Effects of Chlorine in Ash on the Corrosion Performance of Ni-Based Alloys in a Simulated Oxy-Fuel Environment

    Zeng, Zuotao ; Natesan, Ken ; Cai, Zhonghou ; ... - Energy and Fuels
    Coal ash can severely attack alloy materials at high temperature. To understand coal ash corrosion, a critical study is needed to determine the effect of the elements in ash on corrosion and find an approach to reduce the corrosion rates in an ash environment at high temperature. Chlorine is a harmful element in coal. The role of chlorine in ash corrosion is investigated in simulated oxy-fuel environments. Long time tests up to 3000 hours were performed on various structural alloys at 750°C. Detailed results are presented on weight change, scale thickness, internal penetration, microstructural characteristics of corrosion products, and themore » cracking of scales for the alloys after exposure at 750°C for 3000h. In addition, we performed synchrotron nanobeam Furthermore X-ray analysis to study the phase and chemical composition of the oxide layers on the alloy surface. Results from these studies are used to address the role of chlorine in ash in the long-term corrosion performance of alloys. Nanobeam X-ray and SEM analyses indicate that chlorine can modify the diffusion mechanism near alloy surface, and increase corrosion rate.« less

  10. Nanometer-scale characterization of laser-driven compression, shocks, and phase transitions, by x-ray scattering using free electron lasers

    Kluge, T. ; Rödel, C. ; Rödel, M. ; ... - Physics of Plasmas
    In this paper, we study the feasibility of using small angle X-ray scattering (SAXS) as a new experimental diagnostic for intense laser-solid interactions. By using X-ray pulses from a hard X-ray free electron laser, we can simultaneously achieve nanometer and femtosecond resolution of laser-driven samples. This is an important new capability for the Helmholtz international beamline for extreme fields at the high energy density endstation currently built at the European X-ray free electron laser. We review the relevant SAXS theory and its application to transient processes in solid density plasmas and report on first experimental results that confirm the feasibilitymore » of the method. Finally, we present results of two test experiments where the first experiment employs ultra-short laser pulses for studying relativistic laser plasma interactions, and the second one focuses on shock compression studies with a nanosecond laser system.« less
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