Guangai Sun

Small-angle neutron scattering spectrometer Suanni equipped with ultra-thin biconcave focusing lenses

The small-angle neutron scattering (SANS) spectrometer Suanni at the liquid hydrogen cold neutron source of the 20 MW China Mianyang Research Reactor has recently been upgraded. Ultra-thin biconcave MgF2 lenses with a central thickness down to 0.2 mm have been installed between the collimator chamber and the sample stage. The lenses are able to improve the flux without too excessive an increase in the neutron beam size on the detector. A smaller minimum Q (Qmin) can be obtained by decreasing the beam size without changing the total length of the spectrometer. By testing the central beam profiles under different neutron wavelengths (∼0.56–1 nm) with both traditional pinhole SANS (PSANS) and focusing SANS (FSANS) geometries, the gain factor thanks to the neutron lenses is about one order of magnitude. Given the loss of intensity due to the absorption of neutrons by the lenses, the benefits of the focusing can only be realized if it is possible to increase the aperture size. With an identical source aperture, FSANS can minimize the nominal Qmin from 7.20 × 10−3 nm−1 (for PSANS) to 5.55 × 10−3 nm−1 at a neutron wavelength of 1 nm. The practical benefit provided by the lenses is verified with a solution of poly(methyl methacrylate) nanospheres, which yields a scattering intensity one order of magnitude higher and a better resolution with the FSANS geometry than with that of PSANS.

Chelating agents role on phase formation and surface morphology of single orthorhombic YMn 2 O 5 nanorods via modified polyacrylamide gel route

YMn2O5 nanorods were synthesized through a modified polyacrylamide gel route. The synthesis strategy in this work is based on a sol-gel process using a polyacrylamide gel method in which oxalic acid, citric acid or tartaric acid is employed as the chelating agent. In the gel routes, oxalic acid was used as a carboxyl chelating agent, while citric acid or tartaric acid was a carboxyl and hydroxyl chelating agent. The as-prepared samples were characterized by means of techniques such as X-ray powder diffraction (XRD) measurement, thermogravimetric analysis (TG), differential scanning calorimetry analysis (DSC), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), thermal expansion measurement and field-emission scanning electron microscopy (SEM) investigations. It was found that oxalic acid is the best chelating agent with Y(NO3)3·6H2O and Mn(CH3COO)2·4H2O as precursors to prepare a single orthorhombic YMn2O5 nanorods at 1000°C. Scanning electron microscope observation shows that the morphology of YMn2O5 powders is significantly dependent on the chelating agent. The peaks (single orthorhombic YMn2O5 nanorods) at 642, 600, 573, 546, 521, 493, 486, 468, 448 and 400 cm−1 were observed from FTIR spectra. The phase, surface morphology and chelation mechanisms of YMn2O5 samples have been discussed on the basis of the experimental results.

A novel method for the synthesize of nanostructured MgFe 2 O 4 photocatalysts

Nanostructured MgFe2O4 magnetic photocatalysts are facilely synthesized by 60Co γ-ray irradiation assisted polyacrylamide gel route. The influence of different irradiation doses on the morphologies, phase purity, energy bandgap, magnetic properties and photocatalytic activity of the as-prepared MgFe2O4 nanoparticles were studied. The experimental results demonstrate that the phase purity, particle size, morphology, energy bandgap, magnetic properties and photocatalytic activity of MgFe2O4 nanoparticles can be manipulated by the different irradiation doses. In particular, γ-ray irradiation improves the photocatalytic activity of MgFe2O4 nanoparticles significantly. These MgFe2O4 nanoparticles showed high efficiency for the degradation of methylene blue with simulated sunlight irradiation. These results bring up new ideas for the design of nanostructured MgFe2O4 magnetic photocatalysts with tuned magnetic properties and photocatalytic activity through a 60Co γ-ray irradiation assisted polyacrylamide gel route.Graphical AbstractSchematic representation of the polymerization reaction for MgFe2O4 nanoparticle synthesis, starting from acrylamide and bis-acrylamide (left). Mg-ferrite magnetic photocatalysts were synthesized by γ-ray irradiated assisted polyacrylamide gel route. Optimized utilization of irradiation dose, and sintering temperature allowed the formation of Mg-ferrite nanoparticles with a narrow size distribution. In particular, γ-ray irradiation improves the magnetic properties and photocatalytic activity of MgFe2O4 magnetic photocatalysts significantly. This MgFe2O4 nanoparticles showed high efficiency for the degradation of methylene blue (MB) with simulated sunlight irradiation.

Microstructure Changes in Polyester Polyurethane upon Thermal and Humid Aging

The microstructure of compression molded Estane 5703 films exposed to 11%, 45%, and 80% relative humidity and 70 °C for 1 and 2 months has been studied by small-angle neutron scattering (SANS), Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). Scattering data indicated increase of the interdomain distance and domain size with a higher humidity and longer aging time. GPC data showed a progressive shortening of polyurethane chains with increasing humidity and aging time. The shortening of the polyurethane chains caused a drop of the glass transition temperature of soft segments, and promoted crystallization of the soft segments during long-time storage of the aged samples at room temperature. FTIR showed a substantial increase in the number of inter-urethane H-bonds in the aged samples. This correlates with the increase of the hard domain size and the degree of phase separation as measured by SANS. The data collected reveals that the reduced steric hindrance caused by hydrolysis of ester links in polybutylene adipate residues promotes the organization of hard segments into domains, leading to the increase of domain size and distance, as well as phase segregation in aged Estane. These findings provide insight into the effects of humidity and thermal aging on the microstructure of aged polyester urethane from molecular to nanoscale level.

A New Operating Neutron Scattering Facility CMRR in China

Neutron News Volume 27 • Number 4 • 2016 21 The China Mianyang Research Reactor (CMRR) with the power of 20 MW is located in Mianyang City, Sichuan Province. It is a multifunctional pool research reactor and has a liquid hydrogen cold neutron source, which began to work from September 2013. The thermal and cold fl uxes for neutron scattering experiments are measured to be 2.4 × 1014 n·cm-2·s-1 and 109 n·cm-2·s-1, respectively. CMRR is devoted to both fundamental and applied research. In the fi rst phase, eight neuron scattering instruments have been installed and started operation from the middle of 2014, as shown in Figure 1. Four thermal neutron instruments have been installed in the reactor hall, which are a high resolution neutron diffractometer (HRND), a residual stress neutron diffractometer (RSND), a thermal neutron radiography station (TNR) and a high pressure neutron diffractometer (HPND), respectively. Four cold neutron instruments have been installed in the neutron guide hall (i.e., the cold neutron scattering hall), which are a small-angle neutron spectrometer (SANS), a time-of-fl ight and polarized neutron refl ectometer (TPNR), a cold neutron triple-axis spectrometer (CTAS) and a cold neutron radiography station (CNR), respectively.

Coordination mechanism, characterization, and photoluminescence properties of spinel ZnAl2O4 nanoparticles prepared by a modified polyacrylamide gel route

Single-phase ZnAl2O4 nanoparticles with the spinel structure were successfully synthesized using a modified polyacrylamide gel method according to the atomic ratio of Zn to Al = 1: 1.8. The as-prepared samples were characterized by means of X-ray powder diffraction (XRD), thermogravimetric analysis (TG), differential scanning calorimetry analysis (DSC), field-emission scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and photoluminescence (PL) spectra. XRD patterns show that the pure phase of ZnAl2O4 is obtained after heating the xerogel at 900°C for 5 h in air. The SEM images reveal that the ZnAl2O4 nanoparticles have a narrow particle size distribution and the average particle size is around 45 nm. Photoluminescence (PL) spectra demonstrate the single phase ZnAl2O4 nanoparticles have an emission peak located at 469 nm when excited by 350 nm light. The phase structure, coordination mechanism, and luminescence properties have been discussed on the basis of the experimental results.

Compression deformation behavior of Zircaloy-4 alloy changing with activated twinning type at ambient temperature: experiment and modeling

It is widely accepted that twinning is important for the plastic deformation of zirconium alloys, although the corresponding roles of different types of twinning are rarely discussed. Here, the deformation behavior of Zircaloy-4 alloy at ambient temperature under compression along the rolling, transverse and normal directions of the rolled plate is studied by examination of macroscopic stress–strain curves, texture evolution and in situ lattice strain, combined with elastic–plastic self-consistent simulation. It is concluded that tensile twinning {10\overline 12}〈10\overline 11〉, tensile twinning {11\overline 21}〈11\overline 26〉 and compressive twinning {11\overline 22}〈11\overline 2\overline 3〉 are the main deformation twinning types for compression along the three principal directions. A change in the activated twinning type induces differences in the plastic deformation mode and the stress/strain partitioning between parent and child grains. The work provides insight into the effects of deformation twinning on the plastic deformation behavior of Zircaloy-4 alloy.

Synthesis hexagonal ZrW2O8 and its thermal properties

ZrW2O8 as the typical negative thermal expansion (NTE) material has attracted much attention for the potential applications in various fields such as tailored coefficient of thermal expansion (CTE) composites. The hexagonal ZrW2O8 (h-ZrW2O8), with the combination of ZrO2 and WO3 in a composite, was synthesized at a pressure of 2 GPa and the temperature between 600°C and 700°C. We found h-ZrW2O8 decomposes to ZrO2+WO3 oxides that start from 500°C and end at 800°C, and determined the CTE of h-ZrW2O8 is−16.3×10−6°C−1 in the temperature range from 150°C to 450°C. The results show that ZrW2O8 with a hexagonal structure is metastable and exhibits high NTE property like its cubic structure.

Rotational Effects of Nanoparticles for Cooling down Ultracold Neutrons

Due to quantum coherence, nanoparticles have very large cross sections when scattering with very cold or Ultracold Neutrons (UCN). By calculating the scattering cross section quantum mechanically at first, then treating the nanoparticles as classical objects when including the rotational effects, we can derive the associated energy transfer. We find that rotational effects could play an important role in slowing down UCN. In consequence, the slowing down efficiency can be improved by as much as ~40%. Since thermalization of neutrons with the moderator requires typically hundreds of collisions between them, a ~40% increase of the efficiency per collision could have a significant effect. Other possible applications, such as neutrons scattering with nano shells and magnetic particles,and reducing the systematics induced by the geometric phase effect using nanoparticles in the neutron Electric Dipole Moment (nEDM), are also discussed in this paper.

Determination of deuteration level of K(H 1−x D x ) 2 PO 4 crystal

Neutron powder diffraction was applied to determine the deuteration level of K(H1−xDx)2PO4 (DKDP) crystals via Rietveld refinement method. Micro-Raman spectroscopy was employed using the neutron results to investigate the relation between deuteration level and PO4 vibration peak of DKDP crystal. The relative variation [Δν1 = ν1(KDP)−ν1(DKDP)] of the PO4 vibration peak was linearly well dependent on the deuteration level. Attenuated Total Reflectance-Infrared (ATR-IR) spectroscopy was also used to study the total relative variation [β(DKDP)-β(KDP) + ν1(DKDP)−ν1(KDP)] of β(O-H/D) and ν1(PO4) absorption band with the deuteration level of DKDP crystals. The IR results illustrate that two linear relationships existed between the deuteration level and the relative variations of the spectra. The two spectroscopic techniques can be combined and used to measure the degree of deuteration in the crystals of DKDP grown from solutions with deuteration level of less than 92%. ATR-IR spectroscopy is more suitable for measuring highly deuterated DKDP crystals.