General Purpose Powder Diffractometer Research Articles

Remote and automated high-throughput powder diffraction measurements enabled by a robotic sample changer at SSRL beamline 2-1.

The general-purpose powder diffractometer beamline (BL2-1) at the Stanford Synchrotron Radiation Lightsource (SSRL) is described. The evolution of design and performance of BL2-1 are presented, in addition to current operating specifications, applications and measurement capabilities. Recent developments involve a robotic sample changer enabling high-throughput X-ray diffraction measurements, applicable to mail-in and remote operations. In situ and operando capabilities to measure samples with different form factors (e.g. capillary, flat plate or thin film, and transmission) and under variable experimental conditions are discussed. Several example datasets and accompanying Rietveld refinements are presented.

Residual stress measurement system of the general purpose powder diffractometer at CSNS

Neutron diffraction has become a well-established technique for the determination of residual stresses in various structural materials and bulk industrial products because of the unique deep penetration, three-dimensional mapping capability, and volume averaged bulk measurements characteristic of the scattering neutron beam. To conduct experiments in this research area, a residual stress measurement system was established on the general purpose powder diffractometer (GPPD) at the China Spallation Neutron Source (CSNS), which diffractometer now combines both powder diffraction and residual stress measurement conditions. The best d-space resolution of the diffractometer of medium-angle detector bank is Δd/d ≈ 0.33%. The gauge volume is precisely controlled by the four-blade slits, neutron Kirkpatrick–Baez (KB) mirror and radial collimators, and the general gauge volume is φ2*2 mm 3. The intelligent scanning positioning system established by GPPD achieves high-precision sample positioning, with an accuracy of up to 100μm. Until now, it has completed measurements on standard cycle samples of VAMAS shrink fit rings and plugs with known residual stress distributions, the results confirming the diffractometer’s high sensitivity and high accuracy to stress/strain gradients in materials or components. A large number of beam times are dedicated to user researches including residual stress studies of superalloys, high-entropy alloys, engineering steels, welds, and more. This demonstrates that the GPPD’s residual stress test system and the established test methods are feasible and effective.

The performance of General Purpose Powder Diffractometer at CSNS

The first time of flight diffractometer at the China Spallation Neutron Source (CSNS), General Purpose Powder Diffractometer (GPPD), has entered the user program in 2018. GPPD is a flexible and versatile instrument to study the crystallographic and magnetic structures of polycrystalline materials. After more than 3 years of debugging and operation, the high performance of the diffractometer has been achieved for a good instrumental resolution 0.15% and a wide d-space detection range 0.05–50.48 Å together with the desirable signal-to-noise ratio characteristics, enabling a large number of user experiments and achievements. The typical scientific applications of GPPD demonstrate its outstanding potential for unraveling the precise structure of crystals.

The multifunctional neutron imaging system at GPPD: Design, principles and applications

A multifunctional neutron imaging system (MNIS) has been built recently on the day-one instrument general purpose powder diffractometer (GPPD) at the China Spallation Neutron Source (CSNS). The sample position of MNIS is located three meters downstream of the diffraction sample position to maintain good imaging performance without changing the existing layout. MNIS can accommodate several significant neutron imaging technologies, including two-dimensional neutron radiation, three-dimensional computer tomography, neutron Talbot–Lau grating interferometer, and Bragg edge neutron imaging. The system has a largest field of view (FOV) of 6 × 6 cm2 and a best spatial resolution of 25μm by changing the magnification of the optical lens. The wavelength resolution is better than 0.2%. Additionally, MNIS serves as an initial validation for Energy-Resolved Neutron Imaging instrument (ERNI), a dedicated neutron imaging instrument currently under construction at CSNS.

First neutron Bragg-edge imaging experimental results at CSNS* *Project supported by the National Key Research and Development Program of China (Grant Nos. 2017YFB0701903 and 2016YFA0401502), the National Natural Science Foundation of China (Grant No. 12041202), the Youth Innovation Promotion Association of Chinese Academy of Sciences (Grant No. 2017023), the Guangdong Natural Science Foundation, China (Grant No. 2016A030313129), and the Department

The neutron Bragg-edge imaging is expected to be a new non-destructive energy-resolved neutron imaging technique for quantitatively two-dimensional or three-dimensional visualizing crystallographic information in a bulk material, which could be benefited from pulsed neutron source. Here we build a Bragg-edge imaging system on the General Purpose Powder Diffractometer at the China Spallation Neutron Source. The residual strain mapping of a bent Q235 ferrite steel sample has been achieved with a spectral resolution of 0.15% by the time-of-flight neutron Bragg-edge imaging on this system. The results show its great potential applications in materials science and engineering.

A Nonlinear Optical Switchable Sulfate of Ultrawide Bandgap

Nonlinear optical (NLO) switchable materials have attracted intense attention because of their promising applications in optoelectronic devices. However, previous studies are mainly limited to mole...

The research of laser-based rapid measurement system for scintillator neutron detectors arrays

Scintillator Neutron Detectors Arrays (SNDA) were successfully installed at General Purpose Powder Diffractometer (GPPD) at the China Spallation Neutron Source (CSNS). The inhomogeneity of the detection efficiency in each detector module, which caused by the gain nonuniformity of the multi-anode photo-multiplier tubes (MA-PMTs) and the inconsistency of the wave-length shifting fibers in collecting scintillation photons, need to be mitigated before the installation. An automated rapid measurement system based on the blue laser and the two-dimensional mobile platform was developed to calibrate the light response of each channel in detector modules. According to the test results of this system, the electronics threshold of each channel of the SNDA is adjusted. Before the installation of the all 40 SNDA modules in GPPD, the electronics thresholds of each channel are adjusted according to the measurement results of this rapid measurement system. Compared with the unadjusted detector module, the adjusted one obtained a better uniformity of the neutron detection efficiency. The inhomogeneity of the detection efficiency is improved from 27.4% to 10.9%. The test result of the diffraction peak of the standard sample Si showed that the adjusted SNDA works well in GPPD.

First experimental results from the GPPD diffractometer at the CSNS

ABSTRACTThe general purpose powder diffractometer (GPPD) is the first powder diffractometer at the China Spallation Neutron Source (CSNS). Its aim is to provide a high-resolution, good-intensity instrument for users to study crystallographic and magnetic structures. The best resolution will be better than 0.2% at high-angle detector bank. The neutron flux at the sample position will be at the order of 107 n/s/cm2. The joint beam commissioning among accelerators, target station and instruments started in the CSNS on November 1, 2017. The neutron beam shutter for the general purpose powder diffractometer (GPPD) was opened for the first time. Initial measurements and standard sample diffraction experiments are reported, which are used to characterize the instrument performance. It is shown that the results agree well with the design goal. During the commissioning, a series of user experiments have been conducted. Two user experimental results have already been published.

The general purpose powder diffractometer at CSNS

The general purpose powder diffractometer (GPPD) at the China Spallation Neutron Source (CSNS) is designed to be a flexible and versatile instrument for a wide range study of crystallographic and magnetic structures. Decoupled poisoned hydrogen moderator is used as its neutron source. The distance between the sample and moderator is 30 m. Focusing neutron guide and an interchangeable neutron guide/collimator system are employed to transport neutron. The instrument can be optimally configured for individual experiments with desired resolution. There are three detector banks (high-angle, 90°, and low-angle), covering a wide d-spacing from 0.05 to 28.11 Å. The best resolution will be better than 0.2% at high angle detector bank. The neutron flux at the sample position will be at the order of 107 n/s/cm2. Now the construction of GPPD main building and fabrication of most key components have been done within 2016. The off-line integrated test with related system is going on well. The project will be completed in the end of March 2018, as one of the three day-one instruments for CSNS.

Preliminary shielding design of CSNS day-one neutron instruments

The China Spallation Neutron Source (CSNS), intended to operate in 2018, is designed with 1.6 GeV proton energy and 25 Hz repetition rates, with an initial proton beam power of 100 kW that can be upgradable to 500 kW. Twenty neutron beam lines are provided by the CSNS target station for neutron scattering and neutron science research. The three neutron scattering instruments to be operated on day-one are the general purpose powder diffractometer, the multi-purpose reflectometer and the small angle neutron scattering instrument. These instruments present dissimilar shielding issues and their shielding calculation methods are presented in this paper. The thermal, fast and high-energy neutron source terms with angular distribution are individually calculated using target-moderator-reflector geometry and surface tally at a 1 m distance to the moderator. The thermal neutron losses in the guide system are calculated using a ray-tracing simulation. Possible worse case scenarios are also considered in the shielding analyses. Variance reduction methods, such as source biasing, are employed to speed up the convergence of calculations. As an example, multi-purpose reflectometer shielding analysis is introduced in this paper. All calculations are normalized to 500 kW proton beam power and a 2.5 µSv/h dose limitation are applied in accessible locations.

Phase Transition and Texture Evolution in the Ni-Mn-Ga Ferromagnetic Shape-Memory Alloys Studied by a Neutron Diffraction Technique

The phase transition and influence of the applied stress on the texture evolution in the as-cast Ni-Mn-Ga ferromagnetic shape-memory alloys were studied by the time-of-flight (TOF) neutron diffraction technique. The neutron diffraction experiments were performed on the General Purpose Powder Diffractometer (Argonne National Laboratory). Inverse pole figures were determined from the neutron data for characterizing the orientation distributions and variant selections of polycrystalline Ni-Mn-Ga alloys subjected to different uniaxial compression deformations. Texture analyses reveal that the initial texture for the parent phase in the as-cast specimen was composed of \( {\left\{ {{\text{001}}} \right\}}{\left\langle {{\text{100}}} \right\rangle } \), \( {\left\{ {{\text{001}}} \right\}}{\left\langle {{\text{110}}} \right\rangle } \), \( {\left\{ {{\text{011}}} \right\}}{\left\langle {{\text{100}}} \right\rangle } \), and \( {\left\{ {{\text{011}}} \right\}}{\left\langle {{\text{110}}} \right\rangle } \), which was weakened after the compression deformation. Moreover, a strong preferred selection of martensitic-twin variants (\( {\left\{ {{\text{110}}} \right\}}{\left\langle {{\text{001}}} \right\rangle } \)and \( {\left\{ {{\text{100}}} \right\}}{\left\langle {{\text{001}}} \right\rangle } \)) was observed in the transformed martensite after a compression stress applied on the parent phase along the cyclindrical axis of the specimens. The preferred selection of variants can be well explained by considering the grain/variant-orientation-dependent Bain-distortion energy.

Time-of-flight Rietveld neutron structure refinement and quantum chemistry study of Y-α-sialon

A Y-α-sialon was prepared using a specially designed temperature regime supporting formation of α-sialon and the amount of non-crystalline phase was remarkably reduced by a chemical treatment. Chemical composition of the sample was determined by EDX analysis. Crystal structure of Y-α-sialon was refined using high quality time-of-flight neutron powder diffraction data taken with the General Purpose Powder Diffractometer (GPPD) at the IPNS, Argonne National Laboratory. Unrestrained structure refinement was done in the P31 c space group. The list of simultaneously refined parameters included profile parameters, atomic coordinates, individual isotropic temperature parameters and the occupancy parameter of Y. The contents of Y in the cell refined to 0.38(1) and calculated Si–N distances in tetrahedra varied from 1.716(3) to 1.773(3) Å, but their distributions in the respective tetrahedra differ as in the parent structure of α-Si 3N 4. Anisotropic temperature parameters refinement, as well as constrained refinements of the occupancy parameters of Si–Al and N–O pairs, were also attempted, but they all ended with unphysical values. Variation of the background was analyzed using RDF formalism. Three peaks centered around 1.7 Å (with a shoulder at 2.2 Å), 2.8 Å and 3.5 Å proved that the composition of amorphous phase was close to that of crystalline. Ab initio cluster calculations performed at the B3LYP/6-31G** level of theory excluded configuration with O atoms bonded to three Si atoms and proved that the most probable is the configuration where an O atom is shared by three Al atoms.

Neutron Diffraction Study of Highly Radioactive U3Si2 Reactor Fuel

AbstractNeutron diffraction data were collected from a highly radioactive, low-enrichment uraniumU3Si2/A1 fuel mini-plate that had been irradiated to 42% uranium burnup. The experiment was performed using the General Purpose Powder Diffractometer at IPNS. Most prominent in the diffraction pattern were the Bragg reflections from crystalline Al (fuel plate) and V (sample container). Rietveld refinement revealed a broad oscillatory signal from the U3Si2 typical of amorphous material. This “amorphous” scattering pattern has peaks at the same positions as the amorphous scattering components observed following room temperature neutron irradiation of U3Si2 powder. The irradiated U3Si2 is amorphous with a remote possibility that it consists of recrystallized nanocrystalline particles subject to the requirements that the crystallites: (i) are no larger than 100-200 Å in size, and (ii) possess a crystalline lattice which is distorted relative to the unirradiated material.

Defect Configurations in Neutron-Irradiated U3Si2

AbstractInvestigations of the nature of defects in neutron-irradiated intermetallic U3Si2 as a function of dose have been carried out. Defect categories of vacancies and interstitials, their clusters and dislocation loops have been considered. The effects of the displacement field from each on the neutron scattering intensity profiles are presented. The theoretical predictions are compared with experimentally determined intensity profiles from time-of-flight data using the General Purpose Powder Diffractometer at the Intense Pulse Neutron Source of Argonne National Laboratory. The results are illustrated for a particular peak at various doses and the physical implications discussed.

Application of neutron diffraction to the characterization of residual thermal strains in YBa2Cu3O7−δ/Ag

Additions of silver (Ag) have been reported to improve the mechanical properties of high-temperature superconductor by YBa2Cu3O7−δ (abbreviated YBCO). However, during fabrication of YBCO/Ag composites, differential thermal expansion upon cooling can lead to potentially troublesome residual stresses. The Intense Pulsed Neutron Source and General Purpose Powder Diffractometer at Argonne National Laboratory were used to show that neutron diffraction techniques can be applied to YBCO/Ag composites to measure bulk residual strains in the constituent parts, and to determine the effect of Ag on stoichiometry (and thus on the critical current density). We have observed residual tensile strains in Ag as a function of crystallographic direction; three strains range from as high as 0.085% in 15% Ag samples to as low as about 0.02% in a 30% Ag sample. Compressive strains in the YBCO (111) crystallographic direction were approximated by correcting for the diffraction peak shift due to changes in stoichiometry with varying Ag content. The estimated compressive-strain values vary from 0.04% (15% Ag) to 0.09% (20% Ag) to 0.01% (30% Ag), with an uncertainty of about 0.03%. The presence of significant average tensile strain in the Ag, particularly for 15% and 20% Ag samples, indicates good interface bonding between YBCO and Ag.

Powder diffraction facilities at Daresbury Laboratory

X-ray powder diffraction measurements using synchrotron radiation are currently being carried out on three experimental stations on the SRS at Daresbury Laboratory. Station 9.1 contains a general purpose powder diffractometer for angular dispersive measurements. The instrument is sited on the wiggler beamline, which provides radiation with a critical energy of 12 keV. A Si(111) water-cooled, channel-cut monochromator gives useful flux over an energy range from 6 to 30 keV. A cryostat and furnace are available for experiments requiring special environments, while a curved position sensitive detector can be used for time-resolved measurements. The wiggler white beam is employed on Station 9.7 for energy dispersive powder diffraction experiments. Various sample stages for kinetic experiments are in use on this station, and examples are shown of recent high-pressure work. A new high resolution powder diffractometer has been built and commissioned on Station 8.3, using bending magnet radiation. The diffractometer is based on the Parrish and Hart design, in which long, parallel foils are used to define the angular divergence accepted by the detector. In this way, large synchrotron beam cross sections can be employed while maintaining high angular resolution.

Use of Neutron Diffraction in Determining Strains in High-Temperature Superconducting Composites

ABSTRACTThe Argonne Intense Pulsed Neutron Source and General Purpose Powder Diffractometer have been used to study high Tc metal oxide composites composed of yttrium barium copper oxide and silver. Neutron diffraction techniques were applied to composites with 15, 20 and 30% silver content by volume. We have observed that after hot pressing, the 30% Ag specimens contained both orthorhombic high Tc and tetragonal, non-superconducting phases near the center of the specimens but only tetragonal near the surface. The relationship of shifts in Bragg peaks to strains of the constituents is discussed.

Neutron Powder Diffraction at a Pulsed Neutron Source: A study of Resolution Effects

AbstractThe General Purpose Powder Diffractometer (GPPD), a high resolution (∆d/d=0.002) time-of-flight instrument, exhibits a resolution function that is almost independent of d-spacing. Some of the special properties of time-of-flight scattering data obtained at a pulsed neutron source will be discussed. A method is described that transforms wavelength dependent data, obtained at a pulsed neutron source, so that standard structural least-squares analyses can be applied. Several criteria are given to show when these techniques are useful in time-of-flight data analysis.

The use of time-of-flight neutron diffraction to study grain interaction stresses

Time-of-flight neutron diffraction, using the General Purpose Powder Diffractometer at the IPNS (Intense Pulsed Neutron Source) at the Argonne National Laboratory, has been used to measure residual stresses in deformed, polycrystalline Zircaloy-2. It was found that a plastic tensile strain or 3% caused the ( 10 10 ) and ( 11 20 ) prism lines in the diffraction pattern to shift to higher d-spacings, while the (0002) basal line was shifted to a lower inter-planar spacing. Compressive deformation reversed the direction of the shifts, with the prism and basal planes being left in residual compression and tension respectively. The magnitude and sign of the residual stresses, which result from the interaction among the grains in the deforming polycrystalline specimen, are consistent with the texture and anisotropic yield surface of Zircaloy. For the specimen deformed to 424 MPa in tension, the principal residual stresses after unloading were −188 MPa in the 〈 c〉 direction and 173 MPa in the direction normal to the prism planes. The result is in good agreement with an analysis of the problem that considers an idealized texture that is representative of that found in Zircaloy-2 rod. The experiments demonstrate that time-of-flight neutron diffraction can be a sensitive and powerful tool for measuring residual stresses in bulk materials, where conventional X-ray techniques would be inapplicable.

Residual Stress Relaxation in Cemented Carbide Composites Studied Using the Argonne Intense Pulsed Neutron Source

AbstractCemented carbide composites with a WC hard phase and a Co-Ni alloy binder phase have been subjected to monotonic and cyclic deformation and studied using the high resolution General Purpose Powder Diffractometer at the Argonne Intense Pulsed Neutron Source. Upon deformation, relaxation of bulk differential thermal residual stresses, tensile in the binder and compressive in the carbide, is observed to occur as a function of loading mode and plastic strain via shifts in diffraction peak positions. In addition, peak breadth behavior indicates broadening. At low plastic strain this is due primarily to a range of residual stress and at high plastic strain it is attributable to the plastic deformation alone since relaxation is essentially complete. The appropriateness of neutrons is discussed.