Hf Trace Research Articles

In-situ observation of microstructure and orientation evolution of the Cu–Cr–Zr-Hf alloys

The roles of Hf element in the mechanical properties, deformation mode and orientation evolution of the Cu-0.4Cr-0.2Zr-0.2Hf (wt.%) alloys were investigated using both ex-situ and in-situ electron backscatter diffraction (EBSD). The results indicate that the trace Hf element (0.2 wt%) addition into the Cu–Cr–Zr alloys motivates the multiple slip activities. The activation of multiple slip systems indirectly or directly influences the tensile strength, strain distribution and lattice rotation. Firstly, it promotes the generation of dislocations, and thus enhances the work hardening rate, contributing to the improvement of the ultimate tensile strength. Secondly, it inhibits the movement of dislocations to the grain boundaries, and thus hinders the strain localization at the grain boundaries, promoting the homogeneous deformation. Thirdly, the interaction between dislocations on different slip systems restricts the intragranular lattice rotation, leading to the high stability of the grains with Goss orientation in the Cu–Cr–Zr-Hf alloys. The mutual transform between the R-CubeRD orientation and Goss orientation is also observed. This study deepens the understanding of deformation mechanisms and texture evolution of the Cu–Cr–Zr-Hf alloys.

Synthesis and Electrochemical Performances of Ni-Rich LiNixAl1 –XO2 (x=0.95, 0.92) Positive Electrode Materials for Li-Ion Batteries

Lithium-ion batteries (LIBs) have been put to practical use as power sources for portable devices and environmentally benign electric vehicles (EVs) because of their excellent electrochemical properties such as high specific energy, high power, and long cycle life. For the widespread use of these devices, it is necessary to improve energy density and reduce the cost. To realize high-energy density and low-cost positive electrode materials, we focused on Ni-rich (Ni content more than 80 at.%) layered positive electrode materials that do not contain Cobalt (Co), an expensive element. We have synthesized NA-based positive electrode material LiNixAl1–xO2 (x=0.92, 0.95, NA92, 95) under conditions where Ni and Al are atomically mixed. LiNiO2 (LNO), LiNi0.95Co0.05O2 (NC95) and LiNi0.95Co0.03Al0.02O2 (NCA95) with uniform particle sizes were also synthesized to clarify the effects of Al and Co substitution in Ni-rich layered positive electrode materials. Figure. 1 shows the cycle performances of the samples measured in the full cells. After 500 charge-discharge cycles in full cells under conditions of 45°C, 2 C rate, and 2.5-4.2 V, NA95 and NC95 with the same Ni ratio showed the similar capacity retention (54.1%, 56.5%), whereas NA92 showed excellent capacity retention of 75%. Compared to LNO and NC95 that do not contain Al, the increase of charge transfer resistance (R ct) with cycling was remarkably suppressed in LiNixAl1–xO2. The chemical state of Al before and after cycling was analyzed by Hard X-ray Photoelectron Spectroscopy (HAXPES). The results suggested that Al existed either as a part of the LiNixAl1–xO2 solid solution or Al oxides before cycling while it existed as the lithium aluminate and Al-F compounds. This indicates that the trace HF in the electrolyte reacted with the pristine Al compound on the topmost of electrode materials during cycling to form a Li-conductive coating layer, which suppressed the degradation during cycling. Furthermore, though the Co substitution has some effects of preventing particle cracking, the least particle cracking was observed in NA92 of all samples, indicating that both the surface degradation and the bulk degradation were suppressed with the Al substitution to produce the excellent cycle performance. The results of this study indicated that LiNixAl1–xO2 (x=0.92, 0.95) synthesized by the optimum conditions could be a promising Co-free Ni-rich layered positive electrode material. Figure 1

The roles of Hf element in optimizing strength, ductility and electrical conductivity of copper alloys

The trace Hf element (0.2 wt%) was added into the Cu-0.4Cr-0.2Zr (wt.%) alloy to achieve synchronous improvements in strength, ductility and electrical conductivity. The roles of the Hf element in the microstructural evolution and the mechanical and electrical properties were investigated via transmission electron microscopy (TEM), X-ray line broadening analysis and tensile tests. The results showed that the trace Hf element effectively decreased the stacking fault energy of copper alloys. The synergetic effect of the Hf element and the intermediate aging treatment contributed to the formation of high-density dislocations, profuse deformation twins and refined deformation bands in the Cu-0.4Cr-0.2Zr-0.2Hf alloy, thereby enhancing its tensile strength by ∼51 MPa. The addition of Hf also significantly improved the ductility of the copper alloys due to the presence of deformation twins. High strength (628 MPa), high ductility (∼5%) and high electrical conductivity (80.35% IACS) have been achieved simultaneously in the Cu-0.4Cr-0.2Zr-0.2Hf alloy subjected to the intermediate aging treatment.

Effect of trace hydrofluoric acid in a LiPF6 electrolyte on the performance of a Li–organic battery with an N-heterocycle based conjugated microporous polymer as the cathode

A novel electrochemical test confirms the acid-doping of trace HF into N-heterocycle based polymers in a LiPF6 electrolyte.

Multifunctional Manganese Ions Trapping and Hydrofluoric Acid Scavenging Separator for Lithium Ion Batteries Based on Poly(ethylene‐alternate‐maleic acid) Dilithium Salt

Manganese dissolution from positive electrodes seriously reduces the life of Li‐ion batteries, due to its detrimental impact on the passivation of negative electrodes. A novel multifunctional separator incorporating inexpensive mass‐produced polymeric materials may dramatically increases the durability of Li‐ion batteries. The separator is made by embedding the poly(ethylene‐alternate‐maleic acid) dilithium salt polymer into a poly(vinylidene fluoride‐hexafluoropropylene) copolymer matrix. LiMn2O4‐graphite cells comprising a 1 m LiPF6 solution in ethylene carbonate plus dimethyl carbonate (1:1 v/v) and the functional separator retain 31% and 100% more capacity than baseline cells with plain commercial separators after 100 cycles at C/5 rate, respectively, at 30 and 55 °C. Analyses of cycled cells indicate greatly reduced Mn contamination of the graphite negative electrodes and almost no irreversible structural change in the LiMn2O4 positive electrodes from cells containing the functional separator. The Mn amount in the graphite electrodes from cycled cells with functional separators is ≈80% lower than in the graphite electrodes from cycled baseline cells. Mn ions are found in the functional separators but not in baseline (plain) separators from cycled cells. Finally, it is shown that the reported performance improvements stem from the ability of the novel separator to chelate Mn ions and to scavenge trace HF.

The impact of psychiatric comorbidities on the length of hospital stay in patients with heart failure

BackgroundHeart failure (HF) is a major healthcare problem contributing significantly to hospital admission stays and National Health Service (NHS) spending. Reducing length of hospital stay (LoS) in HF is paramount in reducing this burden and is influenced by factors relating to the condition, sociodemographics and comorbidities. Psychiatric comorbidities are being increasingly identified amongst HF patients but their impact on LoS has not been studied in the UK. MethodsWe investigated the impact of psychiatric comorbidities on LoS amongst 31,760 HF patients admitted to hospitals in North England between 1st January 2000 and 31st March 2013 from the ACALM (Algorithm for Comorbidities, Associations, Length of stay and Mortality) study. The ACALM protocol uses ICD-10 and OPCS-4 coding to trace HF patients, psychiatric comorbidities and demographics including LoS. ResultsAmongst 31,760 HF patients mean LoS in the absence of psychiatric comorbidities was 11.2days. The presence of a psychiatric comorbidity increased LoS by 3.3days. Logistic regression accounting for age, gender and ethnicity showed that LoS was significantly longer in patients suffering from depression (3.4days, p<0.001), bipolar disorder (8.8days, p<0.001) and all types of dementia (4.2days, p<0.001). ConclusionsOur results demonstrate that psychiatric comorbidities have a significant and clinically important impact on LoS in HF patients in the UK. Clinicians should be actively aware of psychiatric conditions amongst HF patients and manage them to reduce LoS and ultimately the risk for patients and financial burden for the NHS.

Effects of electrolyte-volume-to-electrode-area ratio on redox behaviors of graphite anodes for lithium-ion batteries

This study reports on the crucial effects of the ratio of electrolyte volume to electrode area on redox reactions of graphite anodes for lithium-ion batteries (LIBs). It is found that a pyrolytic graphite edge plane electrode (PGE) exhibits reversible Li+ transport behavior in LiClO4 solution, but shows a suppressed redox reaction in LiPF6 electrolyte. The reversible Li+ transport in LiClO4 is hampered by the presence of trace HF, while the depressed activity in LiPF6 is improved by adding an HF scavenger, which points to the suppressive effects of HF on the redox behavior of PGE. In addition, the redox activity of PGE in LiPF6 solution is either enhanced by decreasing electrolyte volume or diminished by decreasing surface area. It is also revealed that graphite composite electrodes of practical LIBs are also subject to the influence of HF if an excessive amount of electrolyte is employed. These observations are attributed to the HF-induced formation of a passive LiF layer, which is facilitated at high ratio of electrolyte volume to electrode area. Our results clearly demonstrate that HF impurity significantly suppresses the redox activity of graphite anodes, and that the adverse HF influence becomes predominant at a high electrolyte-to-electrode ratio.

Effect of withdrawal rate on microstructure and mechanical properties of a directionally solidified NiAl-based hypoeutectic alloy doped with trace Hf and Ho

The hypoeutectic alloy, with nominal composition NiAl–31Cr–2.9Mo–0.1Hf–0.05Ho (at.%), was directionally solidified at three different withdrawal rates by liquid metal (Sn) cooling technique. Microstructural examination reveals that directional solidification gave rise to a shift in the coupled zone for the eutectic growth towards the Cr(Mo) phase. With the withdrawal rates increasing from 3 mm/min to 15 mm/min, the volume fraction of primary dendritic NiAl increases from 21.1% to 25.9%, while the size and the arm spacing of NiAl primary dendrite reduces simultaneously. The room temperature (RT) fracture toughness and the tensile strength at RT and elevated temperature (1373 K) present the valley value at intermediate rate (8 mm/min) among the withdrawal rate range which could be attributed to the decrease in volume fraction of eutectic NiAl/Cr(Mo) microstructure and the refinement of microstructure resulted from the increase of withdrawal rates. In terms of RT tensile elongation, the DS alloy grown at different withdrawal rates all break with no plastic flow.

Study on thermal decomposition of lithium hexafluorophosphate by TG–FT-IR coupling method

Using TG–FT-IR coupling method, direct evidences of the decomposition process of lithium hexafluorophosphate had been obtained. Studies showed that LiPF 6 is stable under normal temperature when the content of water is very low. When heated, LiPF 6 would react with the trace water in the air. HF and OPF 3 would be released in the same time which could be detected from the FT-IR spectra collected in situ. The peak temperature of the decomposition of LiPF 6 varied from 192.93 °C (average heating rate 2.0 °C min −1) to 223.83 °C (average heating rate 20.0 °C min −1). Based on the on-line FT-IR spectra, the characteristic absorption bands of PF 6 − in the decomposed substances were detected for the first time which might come from the reaction of trace HF with PF 5.

On the use of LiPF 3(CF 2CF 3) 3 (LiFAP) solutions for Li-ion batteries. Electrochemical and thermal studies

Electrolyte solutions comprising a mixture of LiPF 6 and LiPF 3(CF 2CF 3) 3 (LiFAP) in alkyl carbonates (ethylene, dimethyl and diethyl carbonate) were found to be superior to single salt LiFAP or LiPF 6 solutions for lithium–graphite anodes at elevated temperatures. Graphite electrodes could be cycled (Li insertion–deinsertion) more than hundred times at 80 °C with high and stable capacity in the two-salt solutions, while in the single-salt solutions this was impossible. Preliminary studies by voltammetry and impedance spectroscopy indicate that the combination of the two salts in solution has a unique influence on the electrodes surface (not yet defined). Thermal studies by accelerating rate and differential scanning calorimetry show that thermal decomposition of LiFAP solutions has a higher onset, but very high heat and pressure developing rates, compared to LiPF 6 solutions. The presence of LiPF 6 in LiFAP solutions decreased their self-heating and pressure-developing rates pronouncedly. From product analysis of the thermal reactions by NMR, FTIR and MS, we can suggest possible unique bulk reactions that occur in LiPF 6–LiFAP solutions. One of these is a nucleophilic reaction between F − and PF 3(CF 2CF 3) 3 −, which may neutralize the effect of trace HF in solutions (thus forming new P–F bonds and HCF 2CF 3). Such a reaction should have a positive effect on both the performance of the Li–graphite electrodes and the thermal behavior of the solutions.

The Study of Surface Phenomena Related to Electrochemical Lithium Intercalation into Lix MO y Host Materials (M = Ni, Mn)

We report herein on the comparative study of and electrodes in three salt solutions, namely, , , and in a mixture of the commonly used ethylene and dimethyl carbonates. The surface chemistry of the electrodes in these solutions was studied by surface‐sensitive Fourier transform infrared spectroscopy. X‐ray photoelectron spectroscopy, and energy‐dispersive X‐ray analysis, and their electrochemical behavior was studied by variable‐scan‐rate voltammetry and impedance spectroscopy. It was found that the electrochemical behavior of these electrodes is strongly dependent on their surface chemistry. Complicated reactions between the active mass and solution components, which include the solvents, the salt anions, and unavoidable contaminants such as HF and perhaps, , lead to the precipitation of surface films through which the Li ion has to migrate in order to reach the active mass. The impedance spectroscopy of these electrodes clearly reflects their surface chemistry. It demonstrates the serial nature of the Li insertion‐deinsertion processes, which includes, in addition to solid‐state diffusion and accumulation, Li‐ion migration through surface films and their charge transfer across the surface film/active mass interface, which strongly depends on the chemical composition of the surface films and hence, the solution chosen. is considerably more reactive with these solutions than , probably due to its stronger nucleophilic nature. In addition, in solutions, the electrodes' impedance is higher due to precipitation of films comprising LiF, which is highly resistive to Li ion transport (probably produced by reactions of the active mass with trace HF). © 2000 The Electrochemical Society. All rights reserved.

Construction of a novel generator for use in HF adsorption studies

An HF generator based on the dissociation pressure of an alkali bifluoride is described. Sodium bifluoride salt was found to yield HF pressures of the order of 0.001 to 0.3 mm in the temperature range 60 to 135 °C due to the equilibrium [Formula: see text]. The HF generator allows a dry carrier gas (typically N2) to pass through a thermoregulated chamber filled with the crystalline bifluoride and furnishes HF concentrations from 5 to 1000 ppm at flowrates up to 5 ℓ/min for periods up to one year. The HF concentrations thus generated were stable to within 1% after a 40 min warm up period. Described also is the associated control system which allows the operator to send alternately dry carrier gas with or without trace HF concentration to an external cell or analyser.