Nanocrystalline magnesium hydride is considered to be one of the most promising alternatives for the reversible storage of hydrogen. In this work structural changes of high-energy ball-milled MgHx and MgH2/Cr2O3 with varying hydrogen content were investigated with small and ultra small-angle neutron scattering (SANS/USANS) using different milling parameters, e.g., milling time, vial and ball material, to obtain information about hydrogen sorption and desorption mechanisms. In a first attempt size distributions of spheres with radii from 1 nm up to 20 μm were calculated in order to characterize the influence of cycling history on the microstructure. Apparent changes of crystallite and particle structures due to hydrogen loading and unloading were found. The use of Cr2O3 nanoparticle additives result in distinct differences of the obtained scattering curves, which indicate that Cr2O3 not only has a catalytic function for the hydrogen sorption properties of MgH2 but also serves as an agent to breakup particles during the milling process. The results demonstrate the potential of the combination of SANS and USANS for structural characterization of nanocrystalline light-metal hydrides over the large size range of 1 nm up to 20 μm.

We report the results of ultra-small-angle neutron scattering (USANS) experiments from diblock copolymers A–B dissolved in a mixture of partially compatible solvents a and b. Solvent a is dimethylformamide, which is a good solvent for block A (polystyrene) and a bad solvent for block B poly(ethylene-co-propylene), and vice versa for solvent b, namely, cyclohexan. Such samples are microphase-segragated into a-rich and b-rich domains separated by interfaces covered with diblock copolymer. Our USANS measurements have shown that a long-range periodic structure of these segregations is limited in extend, it consists of grains with mean radius of several microns. Structural characteristics of these grains and kinetics of their formation depending on the temperature were studied by means of USANS for various chemical compositions of the samples.

An experimental procedure employing setups with standard resolution characteristics for multiple small-angle neutron scattering in fractal and nonfractal media is described. Specific features of the proposed method, which are related to a limited resolution of the spectrometer, are considered in the case of large-scale inhomogeneities with the characteristic size exceeding the inverse spatial resolution. A new approach to the extraction of information about the fractal dimension of the system studied is demonstrated, which takes into account the dependence of the attenuation and broadening of the transmitted neutron beam on the sample thickness.

Double-crystal diffractometers (DCD) of the Bonse–Hart type are used for small-angle neutron scattering (SANS) experiments with very high resolution. Scattering from inhomogeneities in the size range of typically 100 nm to 10 µm can be detected with a DCD. The evaluation of DCD scattering curves is more complicated than for conventional SANS instruments with point collimation for two reasons: first, a DCD operates with a long-slit geometry, and second, owing to the high scattering power of large inhomogeneities, multiple small-angle scattering is likely to play a significant role in many DCD experiments. A numerical procedure is proposed for the determination of particle size distributions from DCD scattering curves influenced by multiple scattering. This procedure is based on an n -fold convolution of single-scattering cross sections, where n depends on the degree of multiple scattering. It makes use of the indirect Fourier transformation method and thus, firstly, size distributions of arbitrary shape can be determined, and secondly, the calculation is fast, allowing an interactive analysis. The procedure is demonstrated with scattering from latex particles with different degrees of multiple scattering. The results show that the size and volume fraction of the latex spheres can be determined with a reasonable error even from scattering curves that are strongly influenced by multiple small-angle scattering.

Metallic foams are on the verge of being used in industrial applications. However, the mechanism of foam creation, especially the early stages, are still unexplored. Ultra small-angle neutron scattering (USANS), performed with the double-crystal diffractometer (DCD) at the Geesthacht Neutron Facility (GeNF), is a promising method for obtaining a three-dimensional average of a pore size distribution in a wide size range from about 100 nm to about 20 μm. Analysis of the neutron scattering curves yielded pore size distributions which conformed with the results obtained by microscopy.

Aluminium foils (99.99% purity) and single crystals (99.999% purity) were charged with hydrogen using a gas plasma method and electrochemical methods, resulting in the introduction of a large amount of hydrogen. X-ray diffraction measurements indicated that within experimental error there was a zero change in lattice parameter after plasma charging. This result is contradictory to almost all other face-centred cubic (f.c.c.) materials, which exhibit a lattice expansion when the hydrogen enters the lattice interstitially. It is hypothesized that the hydrogen does not enter the lattice as an interstitial solute, but instead forms an H–vacancy complex at the surface that diffuses into the volume and then clusters to form H 2 bubbles. Small- and ultra-small-angle neutron scattering (SANS, USANS) and small-angle X-ray scattering (SAXS) were primarily employed to study the nature and agglomeration of the H–vacancy complexes in the Al–H system. The SAXS results were ambiguous owing to double Bragg scattering, but the SANS and USANS investigation, coupled with results from inelastic neutron scattering, and transmission and scanning electron microscopy, revealed the existence of a large size distribution of hydrogen bubbles on the surface and in the bulk of the Al–H system. The relative change in lattice parameter is calculated from the pressure in a bubble of average volume and is compared with the experimentally determined value.

The double crystal diffractometer (DCD) at the Geesthacht Neutron Facility (GeNF) is equipped with triple-bounce channel-cut perfect Si(111) crystals. In this way the intrinsic background of DCD, i.e. given by the rocking-curve wings, has been decreased dramatically. Its former dependence on the scattering vector q of q−2 was changed to q−6. An observed deviation from the q−6 behaviour is possibly attributed to neutrons propagating and diffracting inside the walls of the channel-cut crystals. In order to reduce this parasitic intensity and for further improvement of DCD with respect to higher sensitivity to weak sample scattering quintuple-bounce side grooved channel-cut crystals have been used. The change in the rocking curves without and with inserting cadmium in the grooves of the walls is pointed out. The efficiency of DCD is shown in the case of neutron scattering from Latex spheres with radii of about 2200nm.

Aluminum foils of 99.99% purity were charged with hydrogen using a gas plasma method with a voltage in the range of 1.0–1.2 keV and current densities ranging from 0.66 to 0.81 mAcm−2, resulting in the introduction of a large amount of hydrogen. X-ray diffraction measurements indicated that within experimental error there was a zero change in lattice parameter after plasma charging. This result is contradictory to almost all other FCC materials, which exhibit a lattice expansion when the hydrogen enters the lattice interstitially. It is hypothesised that the hydrogen does not enter the lattice interstitially, but instead forms a H-vacancy complex at the surface which diffuses into the volume and then clusters to form H2 bubbles. The nature and agglomeration of the bubbles were studied with a variety of techniques, such as small angle, ultra small angle and inelastic neutron scattering (SANS, USANS and INS), transmission and scanning electron microscopy (TEM and SEM), precision density measurements (PDM) and X-ray diffraction. The USANS and SANS results indicated scattering from a wide range of bubble sizes from <10 Å up to micron size bubbles. Subsequent SEM and TEM measurements revealed the existence of bubbles on the surface, as well as in the bulk and INS experiments show that hydrogen is in the bulk in the form of H2 molecules. In this paper we calculate the radial distribution function of the bubbles from the SANS and USANS results using methods based on the models derived by Brill et al., Fedorova et al. and Mulato et al. The scattering is assumed to be from independent spherical bubbles. Mulato et al. model is modified by incorporating smearing effects, which consider the instrumental resolution of the 30 m SANS spectrometer at NIST. The distribution functions calculated from the two methods are compared, and these distributions are then compared with the range of particle sizes found from TEM and SEM techniques.

Failure of ceramic materials used in high-temperature applications is initiated by the formation of creep pores. Thus, investigating the kinetics of creep pore formation, especially the evolution of their size distribution, is of key importance in obtaining an understanding of the failure mechanisms. This investigation is concerned with recent progress in the characterization of creep pores in liquid-phase sintered alumina by means of small-angle neutron scattering (SANS) techniques. It is shown that creep pores ranging from about 40 nm to >1 μm are present even after the small amount of creep deformation at the end of primary creep. For the first time a strong correlation between the size of glass pockets and the creep pores has been determined. The results give new insights into pore formation in liquid-phase sintered ceramics.

The formation of pores during creep initiates the failure of ceramic materials used for high-temperature applications. Thus, the determination of pore sizes and their number densities is of key importance in obtaining an understanding of the failure mechanisms. In former investigations it was shown that small-angle neutron scattering (SANS) and beam broadening (BB) are powerful experimental techniques for the investigation of pore size distribution. In this paper it is noted that in addition to these methods complementary high resolution SANS experiments have to be performed in order to determine pore size distributions reliably in the size range from a few nanometers to several micrometers. The evolution of such pore size distributions have been observed during the creep of liquid-phase sintered alumina.

High resolution small-angle neutron scattering (HR-SANS) investigations have been performed by means of the double crystal diffractometer (DCD) at the Geesthacht Neutron Facility (GeNF). The two single perfect silicon crystals of the instrument have recently been replaced by channel-cut ones in the non-dispersive (1, −1) setting to reduce the intensity of the rocking curve in its wings by three-fold reflections. Thereby a very strong decrease of this intensity has been achieved, whereby its former dependence on the scattering vector q of q−2 has been changed to q−6. This improvement of the rocking curve leading to a reduction of the inherent background is presented, and a new perspective for future HR-SANS investigations is pointed out.

Small-angle neutron scattering (SANS) experiments generally provide the absolute SANS cross sections and this allows quantitative results to be obtained; however, data collected at double-crystal diffractometers are frequently not normalized to absolute cross sections and they are used only for qualitative analysis. In point-geometry diffractometers, the normalization is done by comparing the scattered intensities to those of samples of known cross sections or by measuring the direct-beam intensity; in the double-crystal diffractometer, the incident flux information is contained in the rocking curve measured without a sample and this feature can therefore be used to normalize the scattered intensities to the SANS cross sections. A sample of thickness 1 mm of the Ni-based superalloy UDIMET 520 was analyzed at a double-crystal diffractometer; the SANS cross section obtained by the proposed procedure compares well with the SANS cross section found for similar materials by using conventional point-geometry diffractometers and calibrated by light water.

Conventional SANS facilities cover scattering vectors q between about 0.01 and 3 nm−1 and are well suited for analyzing microstructures in materials with sizes from 1 to about 100 nm. At the Geesthacht neutron facility (GeNF), this range has been greatly extended. Larger values of q (up to 25 nm−1) are made accessible at the pin-hole facility SANS-2 by means of a second area detector, which can be rotated around the sample. Smaller q-values down to 10−3 nm−1 can be covered at the SANS-2 by means of the beam broadening (BB) technique. With the use of a double-crystal diffractometer (DCD) still smaller q-values down to 10−4 nm−1 become accessible. Investigations of extremely small structures (cluster with radii of only 0.3 nm), and extremely large ones (creep pores in ceramics with size up to some μm) are presented.

Failure of ceramic materials for high-temperature applications is initiated by the formation of creep pores. Thus, the determination of the sizes and number densities of pores induced during creep testing is one key to an understanding of their failure mechanisms. Small-angle neutron scattering (SANS) techniques are for this purpose one of the most potential tools as demonstrated by an analysis of creep pores in liquid-phase-sintered, hot isostatically pressed alumina. The exploration of creep induced pores requires the analysis of SANS intensity over an extremely extended region of scattering vectors, the scanning of which needs joint use of both conventional SANS and double crystal diffractometry (DCD), an ultra-small-angle scattering technique.

Failure of ceramic materials for high-temperature applications is initiated by the formation of creep pores. Thus, the determination of the sizes and number densities of pores induced during creep testing is one key to a understanding of their failure mechanisms and related life-time predictions. For this purpose small-angle neutron scattering (SANS) techniques are one of the most potential tools as demonstrated by an analysis of creep pores in liquid-phase-sintered, hot isostatically pressed alumina. The exploration of creep induced pores requires the analysis of SANS intensity over an extremely extended region of scattering vectors, the scanning of which needs joint use of both conventional SANS and double crystal diffractometry (DCD), an ultra small angle scattering technique.

Under German licensing rules, irradiation-induced embrittlement of a reactor pressure vessel (RPV) in the core belt region is taken into account basically by determining the shift of the 41-J transition temperature of the Charpy impact energy versus temperature curve and then adjusting either the exclusion line of the modified Porse diagram, or the KIR curve, by this 41-J shift. The accuracy limits of T 41 Jand Δ T 41 J determination are discussed and quantified. The transition temperature concept is shown to be conservative in the validity range of the respec-tive licensing rules because of the uncertainties in Δ T 41 J determination. Investigations with respect to irradiation effects on fracture toughness deserve high priority in current programs. Results from a A 533-B 2 steel (HSST03) are presented, and the shift of the KIC curve is evaluated for two fluence levels. Experiments related to the question of whether neutron flux density has an influence on embrittlement are briefly reported.

After a brief outline of the consideration of irradiation embrittlement of RPV steels in the pertinent German KTA licensing rules, the prerequisites of the licensing procedure are identified and addressed in the light of recent results, mainly from the Research Program Safety of Components.

Within the research program “Integrity of Components,” reactor pressure vessel steels are irradiated in capsules in the swimming-pool-type research reactor FRG-2 at 290°C to different fluences of fast neutrons. Steel heats both conforming and not conforming to specifications with respect to chemical composition as well as to tensile and deformation properties are included. So far, the results show that for the materials investigated the 41 J transition temperature shift from impact testing is always larger than the nil ductility transition (NDT) shift from drop-weight testing. This means that the mode of procedure of the regulatory rules leads to conservative values for the adjusted reference temperature even for material states near and beyond the specification limits. From instrumentated Charpy tests, the arrest load was determined. It was found that the irradiation-induced shift of the arrest load versus temperature curve corresponds closely to the NDT shift. By evaluating Charpy surveillance specimens along this line, one has a supplementary criterion for assessing irradiation embrittlement at hand. At low fluences, the 41 J transition temperature shifts are conservatively predicted by the trend curves of Regulatory Guide 1.99, whereas at high fluences—though a little beyond the validity limits—these shifts lie above the extrapolated trend curves.