Driving the sodium-oxygen battery chemistry towards the efficient formation of discharge products: The importance of sodium superoxide quantification

Sodium-oxygen batteries(SOBs) have the potential to provide energy densities higher than the state-ofthe-art Li-ion batteries. However, controlling the formation of sodium superoxide(NaO_(2)) as the sole discharge product on the cathode side is crucial to achieve durable and efficient SOBs. In this work, the discharge efficiency of two graphene-based cathodes was evaluated and compared with that of a commercial gas diffusion layer. The discharge products formed at the surface of these cathodes in a glyme-based electrolyte were carefully studied using a range of characterization techniques. NaO_(2) was detected as the main discharge product regardless of the specific cathode material while small amounts of Na_(2)O_(2).2H_(2)O and carbonate-like side-products were detected by X-ray diffraction as well as by Raman and infrared spectroscopies. This work leverages the use of X-ray diffraction to determine the actual yield of NaO_(2)which is usually overlooked in this type of batteries. Thus, the proper quantification of the superoxide formed on the cathode surface is widely underestimated;even though is crucial for determining the efficiency of the battery while eliminating the parasitic chemistry in SOBs. Here, we develop an ex-situ analysis method to determine the amount of NaO_(2) generated upon discharge in SOBs by transmission X-ray diffraction and quantitative Rietveld analysis. This work unveils that the yield of NaO_(2) depends on the depth of discharge where high capacities lead to very low discharge efficiency, regardless of the used cathode. We anticipate that the methodology developed herein will provide a convenient diagnosis tool in future efforts to optimize the performance of the different cell components in SOBs.

Modeling and Simulation of ΔH in Solid State Synthesis of Nanocomposites Al-Cu-Zr

Amorphous structure generated by high-energy ball miller(BM)is often used as a precursor for generating nanocomposites through controlled devitrification.The amorphous forming composition range of ternary Al-Cu-Zr system was calculated using the extended Miedema’s semiempirical model.Eleven compositions of Al-Cu-Zr system showed a wide range of negative enthalpy of mixing(-ΔH^(mix))and amorphization(-ΔH^(amor))among the constituent elements was selected for synthesis by BM.They yielded either nanocomposites of partial amorphous and crystalline structure or no amorphous phase at all in the as-milled condition.The Al_(88)Cu_(6)Zr_(6) alloy with relatively small negativeΔH^(mix)(-0.4 kJ/mol)andΔH^(amor)(-14.8 kJ/mol)became completely amorphous after 120 h of milling.

Temperature Dependence of Growth Mechanism forNanoscale High T_c Superconductors

The growth mechanisms of high temperature Yttrium- and Bismuth-based-superconductors were investigated at nanoscale. We started with studying the growth relationships among the three phases of Bi-2201, Bi-2212, and Bi-2233, and then extended to another growth mechanism of Bi-2223 and the growth of yttrium-based high-temperature nanosuperconductors （nano-YBCO）. A time dependence of growth experiment was performed. In this experiment, the Bi-based superconductors grew within different sintering periods, and its three phases were determined by X-ray diffraction. And then, a time dependence of growth model was suggested to explain the experimental facts. With this model, governing equations were derived to quantitatively describe the growth and decomposition mechanisms during sintering period. The results calculated from the derived equations were well in agreement with the experimental data. We also suggested an alternative growth mechanism for the Bi-2223 phase, which was supported by an observation of transmission electron microscopy （TEM）. The nano-YBCO also grew, and their orthorhombic crystal structures were determined by the TEM. The superconducting properties of Bi-2223 were investigated by the measurements of ac magnetic susceptibility. It is expected that the derived equations will fit the alternative experimental growth mechanism of the Bi-2223 phase and the nano-YBCO growth mechanism, too.

Quantification of flupirtine maleate polymorphs using X-ray powder diffraction

Flupirtine maleate, a pharmaceutical compound for treating psychotic disease in clinics, has seven polymorphs. Form A, with better crystal stability and bioavailability, has been widely used as the pharmaceutical crystal form. Unfortunately, it is usually found in a polymorphic mixture with form B. In this study, pure crystal forms of A and B were prepared and characterized by X-ray powder diffraction （XRPD）, Fourier transform infrared spectroscopy （FT-IR） and thermal analysis. An XRPD-based method for the quantitative determination of the amount of the flupirtine maleate polymorphs form A and form B was also established through a systematic optimization of instrumental parameters. The results of the analytical methodology validation showed that the XPRD method had a broad quantitative range of 0- 100% （w/w）, good linear relationship, with R2= 0.999, excellent repeatability and precision and low limits of detection （LoD） of 0.15% （w/w） and quantification （LoQ） of 0.5% （w/w）. The results also showed that the single-peak method was not as good as the whole pattern in reducing the influence of the preferred orientation, but this can be compensated for by a systematic optimization of instrumental parameters and validating the analytical methodology to reduce errors and obtain a good, repeatable, sensitive, and accurate method. This XRPD method can be used to analyze mixtures of flupirtine maleate polymorphs （forms A and B） quantitatively and control the quality of the bulk drug.

High-resolution characterization of the fretting corrosion of Alloy 690 in the simulated secondary water of pressurized water reactor

The worn scars on Alloy 690 after the fretting corrosion testing in simulated pressurized water reactor(PWR)secondary water have been comprehensively analyzed by scanning transmission electron microscopy(STEM)and transmission Kikuchi diffraction(TKD).The high-quality characterization results experimentally show that the fretting wear accelerates the corrosion of Alloy 690 in two approaches.The first one is to break the integrity of the oxide scale by introducing cavities at the oxide grain boundaries.The second one is to alter the microstructure of the underneath matrix,forming a nano-grained matrix layer.The increased grain boundary density in this layer can accelerate the consumption of Cr in the near-surface matrix.The loss of oxide scale integrity and the accelerated Cr consumption are believed to contribute to the deteriorated corrosion resistance of Alloy 690 during the fretting corrosion process.

Synthesis and Properties of Monodisperse Superparamagnetic Mg_(0.8)Mn_(0.2)Fe_2O_4 Nanoparticles Using Polyol Reflux Method

Superparamagnetic monodisperse Mg0.8Mn0.2Fe2O4 nanoparticles have been successfully synthesized in liquid polyol at elevated temperature of 200 °C. Diethylene glycol（DEG） used here plays dual role in synthesis as it acts as reducing agent and alternatively coats the surface of nanoparticles while synthesis and thereby maintaining uniform size and dispersibility. Powder X-ray diffraction（XRD） and magnetic measurements showed that the sample is cubic spinel and superparamagnetic at room temperature. Raman spectra confirmed the formation of the Mg0.8Mn0.2Fe2O4 nanoparticles.The nanoparticles exhibit very good stability in water due to in situ coating with DEG molecules.

Synthesis and characterization of Ca0.9Mg0.1TiO3：Pr3＋,Ag＋ phosphor

Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ phosphors were synthesized by solid-state reaction technique. The crystalline phase and luminescence performances of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ were observed by X-ray powder diffractometer（XRD）, transmission electron microscope（TEM）, photoluminescence spectrometer and brightness meter, respectively. The addition of Ag~＋ can diminish in the crystal particle sizes of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）. Because Ag＋ can reduce the concentration of the undesirable defects in the phosphor, luminescence intensity of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ is 2.3 times as high as that of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）at the same preparation condition. The effect of Ag＋ on the persistent afterglow properties is to deepen the energy storage traps and enhance the energy transfer efficiency from Ca_（0.9）Mg_（0.1）TiO_3 to Pr^（3＋）. The persistent afterglow properties of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ are better than those of Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋） at the same preparation condition. In conclusion,Ca_（0.9）Mg_（0.1）TiO_3：Pr^（3＋）,Ag~＋ phosphor with molar ratio of Ag~＋to Pr^（3＋） 3：1 obtained at 900 ℃ for 4 h exhibits the optimal photoluminescence performances.

Uncovering the hierarchical clusters in the heat-affected zone of an electron beam weldedα/βtitanium alloy joint

Using high-resolution transmission Kikuchi diffraction(TKD)and transmission electron microscopy(TEM),we examined the hierarchical clusters that form in situ in the heat-affected zone(HAZ),which are com-monly referred to as“ghost”structures,of bimodal titanium alloy Ti-5Al-2Sn-2Zr-4Mo-4Cr(wt%,TC17).The ghost structures are enriched with Al elements but poor in Mo and Cr compared to the surroundingβmatrix.TKD results show that the ghost structure in middle-HAZ mainly consists ofα_(L)laths with a high-angle grain boundary,which exhibits the classic Burgers orientation relationship(BOR)with the host matrix,while it encircles theα_(P)grains in far-HAZ.And the ghost structure is evidenced to form via in-complete martensitic transformation.TEM results further confirm that the ghost structure is composed ofαL and tinyβ_(L)laths with BOR,with the former being enriched with Al and poor with Cr and Mo,while the latter is the opposite.Interestingly,twoα_(L)variant clusters with a check-mark morphology are fre-quently observed viewed along[0001]_(αL)//[110]_(βL)directions,which are dominated by the crystallographic and geometrical relationships betweenαandβphases.Based on the microstructural characterization,it is hypothesized that the ghost structure is transformed from the initialα_(P)phase,due to the coupling ef-fect of high thermal stress(which induces the formation of a large number of dislocations)and element diffusion caused by sudden temperature increase and plunge cooling in the HAZ during the welding pro-cess.