Dynamics of ethane and propane in zeolite ZSM-5 studied by quasi-elastic neutron scattering

Quasi-elastic neutron scattering has been used to study the dynamics of ethane and propane in zeolite ZSM-5. The experiments were performed at different loadings for the two alkanes and at different temperatures for propane. The long-range translational motion of the molecules has been observed and has been interpreted with a jump diffusion model, the mean jump lengths being of the order of 10 Å, slightly decreasing with increasing loading. The self-diffusion coefficients of ethane are about 2 × 10⁻⁹ m² s⁻¹ at 300 K, those of propane at the same temperature being smaller by a factor of two. An activation energy of 5 kJ mol⁻¹ is obtained for the self-diffusion of propane. These results are in good agreement with the pulsed-field gradient n.m.r. measurements. In addition to the translational motion, a rotational motion of the two molecules is also observed; it is described by an uniaxial rotational diffusion model and rotational diffusion constants are derived.     

Diffusive motion of hydrogen in mordenite studied by quasi-elastic neutron scattering

Neutron time-of-flight experiments have been done with hydrogen adsorbed in Na-mordenite at temperatures between 35 and 130 K and densities betweenn = 43 andn = 13 H₂ molecules in the unit cell of the zeolite lattice. The quasi-elastically scattered neutrons give rise to a peak that is not broadened at half-height with respect to the experimental energy resolution of 90 μeV (46 ns). A Lorentzian broadening at the bottom of the quasi-elastic peak has been interpreted in terms of a diffusion model yielding a rotational diffusion constantD_r = 2 · 10^{11rad s−1} and a translational diffusion constantD_t = 2 · 10⁻³cm² s⁻¹ atT = 130K andn = 35 H₂ molecules/unit cell.     

The project of ultracold neutron sources at the PIK reactor with superfluid helium as a moderator

The project of ultracold neutron sources at the PIK reactor with superfluid helium as a moderator is presented. The rate of producing ultracold neutrons in superfluid helium is 100 cm^?3 s^?1 at neutron flux density Φ(λ = 9 Å) = 10⁹ cm^?2 s^?1 Å^?1. At a moderator temperature of 1 K within the experimental volume of 351, the density of ultracold neutrons may be equal to 1.3 × 10³ cm^?3, which is two orders of magnitude exceeds that the currently existing ultracold neutron sources.     

Two Birds One Stone: Graphene Assisted Reaction Kinetics and Ionic Conductivity in Phthalocyanine-Based Covalent Organic Framework Anodes for Lithium-ion Batteries

This work reports a covalent organic framework composite structure (PMDA-NiPc-G), incorporating multiple-active carbonyls and graphene on the basis of the combination of phthalocyanine (NiPc(NH₂)₄) containing a large π-conjugated system and pyromellitic dianhydride (PMDA) as the anode of lithium-ion batteries. Meanwhile, graphene is used as a dispersion medium to reduce the accumulation of bulk covalent organic frameworks (COFs) to obtain COFs with small-volume and few-layers, shortening the ion migration path and improving the diffusion rate of lithium ions in the two dimensional (2D) grid layered structure. PMDA-NiPc-G showed a lithium-ion diffusion coefficient (D_Li⁺) of 3.04 × 10⁻¹⁰ cm² s⁻¹ which is 3.6 times to that of its bulk form (0.84 × 10⁻¹⁰ cm² s⁻¹). Remarkably, this enables a large reversible capacity of 1290 mAh g⁻¹ can be achieved after 300 cycles and almost no capacity fading in the next 300 cycles at 100 mA g⁻¹. At a high areal capacity loading of ≈3 mAh cm⁻², full batteries assembled with LiNi_0.8Co_0.1Mn_0.1O₂ (NCM-811) and LiFePO₄ (LFP) cathodes showed 60.2% and 74.7% capacity retention at 1 C for 200 cycles. Astonishingly, the PMDA-NiPc-G/NCM-811 full battery exhibits ≈100% capacity retention after cycling at 0.2 C. Aided by the analysis of kinetic behavior of lithium storage and theoretical calculations, the capacity-enhancing mechanism and lithium storage mechanism of covalent organic frameworks are revealed. This work may lead to more research on designable, multifunctional COFs for electrochemical energy storage.     

Neutron flux measurements with a Li2B4O7 crystal

The effect of neutron irradiation on a lithium tetraborate (Li₂B₄O₇, LBO) single crystal has been investigated. The crystals of high optical quality are found to be quite stable under high neutron fluence. This study shows that LBO crystals can be used as a proportional counter for neutron fluxes of the order 10⁹ cm⁻² s⁻¹ and higher. The detectors fabricated were found to have a sensitivity of ∼3×10⁻¹⁸ A (nv)⁻¹.     

Modifying the morphology and structure of graphene oxide provides high-performance LiFePO4/C/rGO composite cathode materials

In this study we synthesized LiFePO₄/carbon/reduced graphene oxide (LFP/C/rGO) composite cathode materials using a method involving sol–gel processing, spray-drying, and calcination. To improve the electrochemical performance of LFP/C, we tested graphene oxides (GOs) of various morphologies as conductive additives, including pristine GO, three-dimensional GO, and hydrothermal porous GO (HTGO). Among our samples, the cathode material prepared through spray-drying with the addition of 1 wt% of HTGO (denoted SP-LFP/C/1%rHTGO) displayed the best electrochemical performance; its discharge capacities at 0.1C, 1C, 5C, and 10C were 160.5, 151.8, 138.8, and 130.3 mA h g⁻¹, respectively. From measurements of its long-term cycling performance, the discharge capacity in the first cycle and the capacity retention after 30 cycles at 0.1C were 160.2 mA h g⁻¹ and 99.6%, respectively; at 10C, these values were 132.2 mA h g⁻¹ and 91.8%, respectively. The electronic conductivity of SP-LFP/C/1%rHTGO (6.58 × 10⁻⁵ S cm⁻¹) was higher than that of the pristine LFP/C (9.24 × 10⁻⁶ S cm⁻¹). The Li⁺ ion diffusivities (D_Li⁺) of the SP-LFP/C/1%HTGO cathode, measured using AC impedance (3.91 × 10⁻¹³ cm² s⁻¹) and cyclic voltammetry (6.66 × 10⁻¹⁰ cm² s⁻¹ for discharge), were superior to those of the LFP/C cathode (9.31 × 10⁻¹⁵ cm² s⁻¹ and 1.79 × 10⁻¹⁰ cm² s⁻¹ for discharge, respectively). Galvanostatic intermittent titration revealed that the value of D_Li⁺ was located in a reasonable range from 1 × 10⁻¹⁰ to 1 × 10⁻¹⁷ cm² s⁻¹; its value dropped to its lowest point when the state of charge was close to 50%. Thus, the use of spray-drying and the addition of conductive HTGO (having a 3D wrinkled morphology and interconnected pore structure) can enhance the electronic conductivity and Li⁺ ion diffusivity of LFP/C cathode materials, thereby improving the electrochemical performance significantly.     

7Li NMR study on the LiIAl2O3 composite electrolyte

Composite solid electrolyte of the LiIAl₂O₃ system was studied by means of the ⁷Li NMR relaxation time. Occurrence of a highly conductive phase in the composite was confirmed. Self diffusion constant of Li in this phase was 8.1×10⁻¹⁰ cm² s⁻¹ at 300 K. The value is 1600 times larger than that in the LiI matrix and of a reasonable order of magnitude to explain the enhanced conductivity quantitatively. Composition dependence of the enhancement could be explained by a change in thickness of the interfacial layer between an Al₂O₃ particle and the LiI matrix.     

Development of an inconel self powered neutron detector for in-core reactor monitoring

The paper describes the development and testing of an Inconel600 (2 mm diameter×21 cm long) self-powered neutron detector for in-core neutron monitoring. The detector has 3.5 mm overall diameter and 22 cm length and is integrally coupled to a 12 m long mineral insulated cable. The performance of the detector was compared with cobalt and platinum detectors of similar dimensions. Gamma sensitivity measurements performed at the ⁶⁰Co irradiation facility in 14 MR/h gamma field showed values of −4.4×10⁻¹⁸ A/R/h/cm (−9.3×10⁻²⁴ A/γ/cm²-s/cm), −5.2×10⁻¹⁸ A/R/h/cm (−1.133×10⁻²³ A/γ/cm²-s/cm) and 34×10⁻¹⁸ A/R/h/cm (7.14×10⁻²³ A/γ/cm²-s/cm) for the Inconel, Co and Pt detectors, respectively. The detectors together with a miniature gamma ion chamber and fission chamber were tested in the in-core Apsara Swimming Pool type reactor. The ion chambers were used to estimate the neutron and gamma fields. With an effective neutron cross-section of 4b, the Inconel detector has a total sensitivity of 6×10⁻²³ A/nv/cm while the corresponding sensitivities for the platinum and cobalt detectors were 1.69×10⁻²² and 2.64×10⁻²² A/nv/cm. The linearity of the detector responses at power levels ranging from 100 to 200 kW was within ±5%. The response of the detectors to reactor scram showed that the prompt response of the Inconel detector was 0.95 while it was 0.7 and 0.95 for the platinum and cobalt self-powered detectors, respectively. The detector was also installed in the horizontal flux unit of 540 MW Pressurised Heavy Water Reactor (PHWR). The neutron flux at the detector location was calculated by Triveni code. The detector response was measured from 0.02% to 0.07% of full power and showed good correlation between power level and detector signals. Long-term tests and the dynamic response of the detector to shut down in PHWR are in progress.     

Development of fast neutron profiling method

We discuss the effects of neutron scattering and γ-ray background in fast neutron imaging and the method to reduce them. As a profiling device, a combination of an imaging plate (IP) and a polypropylene film (CH₂) has been employed in this study. Good profiles were obtained by employing appropriate neutron energy, a CH₂ thickness and geometry for accelerator-based fast neutrons (5–14 MeV). The neutron flux was ∼3.5×10⁴ cm⁻² s⁻¹ in the CH₂–IP position. Furthermore, we are designing the device using a position-sensitive photomultiplier in order to improve the signal-to-noise ratio by obtaining the information of pulse height for particle selection together with position.     

Volume and dislocation diffusion of iron,chromium and cobalt in CVD β-SiC

Impurity tracer diffusion of ⁵⁹Fe, ⁵¹Cr and ⁵⁷Co in CVD β-SiC has been studied in the temperature range between 973 and 1873 K. The temperature dependence of the volume diffusion coefficients of iron and chromium can be expressed by linear Arrhenius equations. The preexponential factor and the activation energy are estimated to be 8.7×10⁻¹⁵ m² s⁻¹ and 111 kJ mol⁻¹ for iron, respectively, and 9.5×10⁻¹⁵ m² s⁻¹ and 81 kJ mol⁻¹ for chromium, respectively. The diffusion coefficients of iron and chromium are much higher than those of the self-diffusion in β-SiC. Furthermore, the activation energies for the diffusion of iron and chromium are about one-tenth of those for carbon and silicon in β-SiC. Therefore, it seems that an interstitial mechanism is predominant for the diffusion of iron and chromium in β-SiC. On the other hand, the diffusion coefficient of cobalt above 1673 K is higher than that of iron, while at lower temperatures it is much lower than that of iron. The difference in the diffusion coefficients at 1173 K is more than three orders of magnitude. Thus, the temperature dependence of the diffusion coefficients of cobalt shows a strongly curved Arrhenius relation. This suggests that cobalt atoms diffuse by an interstitial mechanism at higher temperatures and by a substitutional mechanism at lower temperatures. From the deeper regions of the penetration profiles of iron, chromium and cobalt the dislocation diffusion coefficients of them have been estimated.     

Preface

The diffusion of platinum and gold in nickel at relatively low temperatures (250–725 °C) was measured by Rutherford backscattering spectrometry (RBS). The diffusion profile of the noble metal in nickel was calculated from RBS spectra. This method takes fully into account the dependence of the energy losses of the backscattered particle along the inward and outward paths on the changing energy of the particle and the changing composition of the target. Diffusion coefficients are calculated from the measured diffusion profile. The dependence of the diffusion coefficient on temperature obeys the Arrhenius law. The activation enthalpies are 78.2 kJ mol^-1 and 119.6 kJ mol^-1 for the diffusion of platinum and gold respectively into nickel. The frequency factors are respectively 2.6 × 10^?9cm²s^?1 and 1.4 × 10^?7cm²s^?1. Experimental data suggest that diffusion along the grain boundaries is 2–3 times as fast as bulk diffusion.     

Electronic-Grade High-Quality Perovskite Single Crystals by a Steady Self-Supply Solution Growth for High-Performance X-ray Detectors

High-quality perovskite single crystals with large size are highly desirable for the fundamental research and high energy detection application. Here, a simple and convenient solution method, featuring continuous-mass transport process (CMTP) by a steady self-supply way, is shown to keep the growth of semiconductor single crystals continuously stable at a constant growth rate until an expected crystal size is achieved. A significantly reduced full width at half-maximum (36 arcsec) of the (400) plane from the X-ray rocking curve indicates a low angular dislocation of 6.8 × 10⁶ cm⁻² and hence a higher crystalline quality for the CH₃NH₃PbI₃(MAPbI₃) single crystals grown by CMTP as compared to the conventional inverse temperature crystallization (ITC) method. Furthermore, the CMTP-based single crystals have lower trap density, reduced by nearly 200% to 4.5 × 10⁹ cm⁻³, higher mobility increased by 187% to 150.2 cm² V⁻¹ s⁻¹, and higher mobility–lifetime product increased by around 450% to 1.6 × 10⁻³ cm² V⁻¹, as compared with the ITC-grown reference sample. The high performance of the CMTP-based MAPbI₃ X-ray detector is comparable to that of a traditional high-quality CdZnTe device, indicating the CMTP method as being a cost-efficient strategy for high-quality electronic-grade semiconductor single crystals.     

A Quasi-Elastic and Inelastic Neutron Scattering Study of H2 in Zeolite

The diffusion of molecular hydrogen adsorbed in zeolite 13X at high coverage's has been studied by quasi-elastic neutron scattering for temperatures ranging from 0 to 60 K. No diffusive motion was observed, within instrumental resolution, at temperatures below 20 K, well above the bulk melting point of H ₂ , in contrast to recent NMR studies. The diffusive motion of the adsorbed H ₂ could be described by a liquid like jump diffusion model above 35 K. The diffusion coefficient demonstrates an Arrhenius behavior: D = D₀ exp(E/kT), with D₀ = 1.2 × 10 ^–8 m ² /s and an activation energy of E = 62 K. The inelastic scattering spectrum has also been studied. The scattering consisted of several peaks superimposed on a broad background extending from 1 meV to above 100 meV and is consistent with rotational transitions for a hindered rotor in a strong orientational potential with a broad distribution of barrier heights.     

Molecular dynamics simulation of pressure effect on phase transition behaviour and dynamics in the isotropic and discotic nematic phases

Molecular dynamics simulation was performed at constant temperature and pressure to investigate the effect of pressure on molecular dynamics for disc-shaped molecules. The generic Gay-Berne model, GB(0.345, 5.0, 1, 3), was used to study the phase transition behaviour, and translational and rotational dynamics, under two different reduced pressures P^?, 10.0 and 20.0. Obvious shifts were detected in the transition temperatures. Both systems have the same phase sequence with different pressures: isotropic, discotic nematic and columnar phases. Translational motion is characterised by the parallel and perpendicular components of diffusion coefficients, with respect to the director in the orientational ordered phase. With regard to rotational dynamics, the correlation time of the first-rank orientational time autocorrelation function, which corresponds to end-over-end rotational motion of a molecule, has been investigated. A clear jump in the temperature dependence of the correlation time has been found at the isotropic-nematic phase transition point. The retardation factor g_|| as a function of the reduced temperature T^?/T_NI^? shows an apparent pressure effect on the rotational dynamics.     

Superplasticity of single-phase Ni–48Al intermetallics with large grains

Superplasticity was found in single-phase Ni–48Al alloy with initial grain size of 200 μm under an initial strain rate of 1.25×10⁻⁴ to 2×10⁻³ s⁻¹ at temperatures ranging from 1025 to 1100 °C. The maximum elongation of 188.2% was obtained under an initial strain rate of 1.125×10⁻³ s⁻¹ at 1100 °C. Optical metallography (OM) showed that the grains were refined during superplastic deformation from initial 200 to less than 20 μm. Transmission electron microcopy (TEM) observation showed that an unstable subgrain boundary network formed during superplastic deformation. The subgrain boundaries were transformed into low- and high-angle grain boundaries by absorbing gliding dislocations. The large-grained superplastic phenomenon could be explained by continuously dynamic recovery and recrystallization (CDRR).     

Flexible Porous Organic Polymer Membranes for Protonic Field-Effect Transistors

Artificial transistors represent an ideal means for meeting the requirements in interfacing with biological systems. It is pivotal to develop new proton-conductive materials for the transduction between biochemical events and electronic signals. Herein, the first demonstration of a porous organic polymer membrane (POPM) as a proton-conductive material for protonic field-effect transistors is presented. The POPM is readily prepared through a thiourea-formation condensation reaction. Under hydrated conditions and at room temperature, the POPM delivers a proton mobility of 5.7 × 10⁻³ cm² V⁻¹ s⁻¹; the charge carrier densities are successfully modulated from 4.3 × 10¹⁷ to 14.1 × 10¹⁷ cm⁻³ by the gate voltage. This study provides a type of promising modular proton-conductive materials for bioelectronics application.     

Trapped Pore Waters in the Open Proton Channel HV1

The voltage-gated proton channel, H_V1, is crucial for innate immune responses. According to alternative hypotheses, protons either hop on top of an uninterrupted water wire or bypass titratable amino acids, interrupting the water wire halfway across the membrane. To distinguish between both hypotheses, the water mobility for the putative case of an uninterrupted wire is estimated. The predicted single-channel water permeability 2.3 × 10⁻¹² cm³ s⁻¹ reflects the permeability-governing number of hydrogen bonds between water molecules in single-file configuration and pore residues. However, the measured unitary water permeability does not confirm the predicted value. Osmotic deflation of reconstituted lipid vesicles reveals negligible water permeability of the H_V1 wild-type channel and the D174A mutant open at 0 mV. The conductance of 1400 H⁺ s⁻¹ per wild-type channel agrees with the calculated diffusion limit for a ≈2 Å capture radius for protons. Removal of a charged amino acid (D174) at the pore mouth decreases H⁺ conductance by reducing the capture radius. At least one intervening amino acid contributes to H⁺ conductance while interrupting the water wire across the membrane.     

Measurement of the Diffusion Coefficient of Water in RP-3 and RP-5 Jet Fuels Using Digital Holography Interferometry

The diffusion coefficient of water in jet fuel was measured employing double-exposure digital holographic interferometry to clarify the diffusion process and make the aircraft fuel system safe. The experimental method and apparatus are introduced in detail, and the digital image processing program is coded in MATLAB according to the theory of the Fourier transform. At temperatures ranging from 278.15 K to 333.15 K in intervals of 5 K, the diffusion coefficient of water in RP-3 and RP-5 jet fuels ranges from 2.6967?×?10 ^?10 m²·s^?1 to 8.7332?×?10 ^?10 m²·s^?1 and from 2.3517?×?10 ^?10 m²·s^?1 to 8.0099?×?10^?10 m²·s^?1, respectively. The relationship between the measured diffusion coefficient and temperature can be well fitted by the Arrhenius law. The diffusion coefficient of water in RP-3 jet fuel is higher than that of water in RP-5 jet fuel at the same temperature. Furthermore, the viscosities of the two jet fuels were measured and found to be expressible in the form of the Arrhenius equation. The relationship among the diffusion coefficient, viscosity and temperature is analyzed according to the classic prediction model, namely the Stokes–Einstein correlation, and this correlation is further revised via experimental data to obtain a more accurate predication result.     

Characteristics of a mini Drift chamber

The characteristics of a drift chamber with 3 mm drift gap were investigated at a particle beam momentum of 10 GeV/c. The chamber has good linearity of the drift characteristics. It was tested and could reliably work in a particle flux of ∼ 3 × 10⁵ s⁻¹ cm⁻². A spatial resolution of ∼ 45 μm in the centre of the drift gap has been achieved.     

Kinetics of low-temperature discontinuous deformation of metals

Kinetic characteristics of discontinuous yielding at a temperature of 4 K as functions of a number of factors are obtained using numerical simulation and experimental data for austenitic steel and aluminum alloy. During the development of a strain jump, the deformation rate and acceleration are 19 s⁻¹ and 5000 s⁻², respectively, for steel specimens and are much lower for aluminum alloy. The jump duration is mainly determined by the characteristics of the loading system. An equation relating the strain jump and the critical stress for low-temperature ductile materials is derived. The energy balance and the mechanism of low-temperature discontinuous yielding of metals are discussed. Its dynamic and thermally activated components are estimated taking into account the strain hardening of the material.