Gas densities in helium bubbles in nickel measured by small angle neutron scattering

Neutron small angle scattering (SANS) combined with transmission electron microscopy (TEM) has been applied to obtain detailed information on the bubble structure in Ni, implanted with 1200 appm helium at room temperature and annealed at temperatures up to 1173 K. Besides conventional information such as size distributions of “small” bubbles in the bulk and “large” bubbles near grain boundaries, the density of helium in the bubbles could directly be determined by a contrast variation method of SANS. The most important result is the finding that even after the highest annealing temperature of 1173 K (≈ 70% of the melting temperature), the bubbles contain an overpressure which lies about 3 GPa above the value for thermodynamic equilibrium.     

Investigation of microstructural changes in INCONEL 706 at high temperatures by In-Situ small-angle neutron scattering

The Ni-Fe based superalloy INCONEL 706 (IN706) has a complex microstructure and many A₃B type phases, e.g., Ni₃Al γ′, Ni₃Nb γ″, Ni₃Nb δ, or Ni₃Ti η precipitates can form. The various precipitates can also have different morphologies, i.e., plate, needle, cube, or disc shape, and some of them exist as co-precipitates—γ′/γ″. In the present study, in-situ measurements by small-angle neutron scattering (SANS) were performed to monitor the microstructural evolution at elevated temperatures. The SANS measurements were complemented by microstructural observations at room temperature by scanning electron microscopy and transmission electron microscopy (SEM and TEM). It is demonstrated that η plates and γ″ needles form directly at high temperatures. Cooling from high temperature produces fine dispersions of γ′/γ″ precipitates, which coarsen on reheating to lower stabilization temperatures (893 and 993 K). The final morphology of the γ′/γ″ co-precipitates, i.e., compact/noncompact type very much depends on the stabilization temperature and the cooling rates from prior higher-temperature stabilization steps.     

Salt-dependent DNA superhelix diameter studied by small angle neutron scattering measurements and Monte Carlo simulations

Using small angle neutron scattering we have measured the static form factor of two different superhelical DNAs, p1868 (1868 bp) and pUC18 (2686 bp), in dilute aqueous solution at salt concentrations between 0 and 1.5 M Na+ in 10 mM Tris at 0% and 100% D2O. For both DNA molecules, the theoretical static form factor was also calculated from an ensemble of Monte Carlo configurations generated by a previously described model. Simulated and measured form factors of both DNAs showed the same behavior between 10 and 100 mM salt concentration: An undulation in the scattering curve at a momentum transfer q = 0.5 nm-1 present at lower concentration disappears above 100 mM. The position of the undulation corresponds to a distance of approximately 10-20 nm. This indicated a change in the DNA superhelix diameter, as the undulation is not present in the scattering curve of the relaxed DNA. From the measured scattering curves of superhelical DNA we estimated the superhelix diameter as a function of Na+ concentration by a quantitative comparison with the scattering curve of relaxed DNA. The ratio of the scattering curves of superhelical and relaxed DNA is very similar to the form factor of a pair of point scatterers. We concluded that the distance of this pair corresponds to the interstrand separation in the superhelix. The computed superhelix diameter of 16.0 +/- 0.9 nm at 10 mM decreased to 9.0 +/- 0.7 nm at 100 mM salt concentration. Measured and simulated scattering curves agreed almost quantitatively, therefore we also calculated the superhelix diameter from the simulated conformations. It decreased from 18.0 +/- 1.5 nm at 10 mM to 9.4 +/- 1.5 nm at 100 mM salt concentration. This value did not significantly change to lower values at higher Na+ concentration, in agreement with results obtained by electron microscopy, scanning force microscopy imaging in aqueous solution, and recent MC simulations, but in contrast to the observation of a lateral collapse of the DNA superhelix as indicated by cryo-electron microscopy studies.     

Double structural hardening in an AlLiCuMg alloy studied by anomalous small angle X-ray scattering

The sequence of precipitation at low temperatures (T < 150°C) in industrial AlLiCuMg alloys (2091 family) has been given as the superposition of the occurring in the binary AlLi (α → α + δ′ Al₃Li) and of that occurring in the pseudobinary AlCuMg (α → α + GPB → α + S′). Although the final state has been ascertained by TEM observations, no direct proof of the Guinier Preston Baragaskii (GPB) zones has been given. By small (medium) angle X-ray scattering and a comparison of the binary, ternary and quaternary alloys in the same aging conditions, the existence of GPB zones is proved and the superposition confirmed. Moreover anomalous scattering, by labeling Cu atoms, determines the nature of GPB zones and the sequence of (CuMg) precipitation.     

Microstructural characterization of a modified 706-type Ni-Fe superalloy by small-angle neutron scattering and electron microscopy

The new Ni-Fe-based superalloy DT706, derived from INCONEL 706, is the object of studies for potential uses in turbine-disk applications at temperatures above 973 K. This alloy aims at improving the microstructural stability while preserving the excellent machinability and good mechanical properties of the base material. This article is the first of a two-part study concentrating on the characterization of the microstructure of the DT706 precipitates, depending on the heat-treatment conditions. Analyses were performed by means of ex-situ small-angle neutron scattering (SANS) measurements, together with conventional scanning electron microscopy (SEM) and transmission electron microscopy (TEM) microscopy, on experimentally-heat-treated samples. The results, when compared to a similar analysis previously made on INCONEL 706, showed that the precipitation characteristics of DT706 reflect compositional changes, but are still remarkably dependent on the cooling stages between the different heat-treatment steps.     

Characterization of a diffusion-bonded Al-Mg alloy/SiC interface by high resolution and analytical electron microscopy

The interfacial structure of a diffusion-bonded Al-4.55 at. pct Mg/SiC interface was examined by conventional and high-resolution transmission electron microscopy. Formation of Mg₂Si, MgO, and Al₂MgO₄ was observed. The monoclinic Mg₂Si phase formed at the Al/SiC interface, while the oxides MgO and Al₂MgO₄ formed at the monoclinic Mg₂Si/Al interface. It is shown that the formation of these phases can be predicted using simple thermodynamic criteria such as the relative bond strengths between Al, Si, C, O, and Mg. In addition, precipitation of some equilibrium Al₈Mg₅ precipitate was also observed at the interface. The interfacial structure observed in the Al-Mg/SiC system is contrasted with that observed in the pure Al/SiC system.     

Evaluation of low-level asbestos exposure by transbronchial lung biopsy with analytical electron microscopy

To improve diagnostic sensitivity for detecting low-level asbestos exposure (AEx) in patients, a new method was developed using an analytical transmission electron microscope (ATEM) for specimens of transbronchial lung biopsy (TBLB). The TBLB specimens from 28 patients were examined and the results were: 1) In cases with long-term AEx, the present method detected a large amount of asbestos fibers (AF) as well as asbestos bodies (AB) showing a good agreement with the results of light microscope (LM) which detected definite amounts of ferruginous bodies (FB). 2) In cases with short-term or suspected AEx, the LM failed to detect FB in some cases, but an appreciable amount of AF was detected using the present method, and AEx was disclosed through a second close interview. 3) Neither AB nor AF were detected in most of the cases without any dust exposure. Although small amounts of chrysotile fibers were observed in some cases, this might simply reflect the exposure level of urban dwellers. These results show that the ATEM applied to the TBLB specimens promises to confirm low-level AEx in such small specimens even if the patients were unaware of their past AEx.     

X-射线小角散射法测定钢铁及合金中析出相的粒度

对钢铁及合金中各种不同粒度析出相的电解提取和化学分离方法、X-射线小角散射法测定析出相粉末的测定条件进行了研究,优选了各种测定参数,从而建立了钢铁及合金中多种析出相粒度分布分析方法。该方法被广泛应用于各种高温合金、中低合金钢、微合金化钢中碳化物、金属间化合物的粒度尺寸分布的测定。结果发现,随着回火温度的增加,低合金钢中的M3C相的数量增加,但粒度变化不大,当回火温度升至700℃时,M3C相分解而使平均粒度增加;在含铬的中低合金钢中,析出的M23C6相的粒度随时效温度的增加而增加,而MC相的粒度无明显变化;     

Composition changes during unmixing of ternary AlZnAg alloys studied by anomalous small angle scattering

By Anomalous Small Scattering (ASAXS) and Transmission Electron Microscopy (TEM), it is confirmed that unmixing of ternary AlZnAg alloys occurs initially by the formation of one type of Guinier-Preston zones. A further state consists of ϵ' hexagonal coherent transition platelets. We have performed several ASAXS experiments near the Zn absorption edge, with the following results. During growth and coarsening of GP zones in Al-9 at.% Zn-9 at.% Ag, it is shown that the particle composition is such that the ratio of Ag to Zn remains fairly constant of the order 1.10, while in Al-14 at.% Zn-4 at.% Ag, this ratio changes from 0.475 to 0.275 when particles transform from GP zones to ϵ' precipitates.     

Morphological observations on liposomes bearing covalently bound protein: studies with freeze-fracture and cryo electron microscopy and small angle X-ray scattering techniques

HT-29 cells, originating from a human colon carcinoma, can proliferate in standard culture conditions with an absolute requirement for polyamines. The major precursor provided in the culture medium for polyamine biosynthesis is L-arginine. L-Arginine conversion to L-ornithine by arginase is followed by stepwise conversion of this latter amino acid to putrescine, spermidine and spermine. The aim of the present work was to document the consequences of a total inhibition of L-arginine flux through arginase, resulting in a decreased L-ornithine availability, on HT-29 cell proliferation and polyamine metabolism. L-Valine, a known arginase inhibitor, when used at a high concentration, i.e., 100 mM, inhibits L-arginine flux through arginase almost totally. The addition in the culture medium of 100 mM L-valine or 50 mM NaCl used to mimic the L-valine induced increase in medium osmolality both reduced equally cellular growth. Cell viability, protein synthesis or oxidative metabolism measured in isolated cells were unaffected by the L-valine treatment, suggesting that decreased proliferation was not associated with an acute toxic effect of this aminoacid, but was rather due to the increase in the medium osmolality. L-Valine treated cells displayed an altered polyamine metabolism when compared with control cells grown in the absence of the amino acid. After 4 days of treatment with 100 mM L-valine, L-ornithine flux through ornithine decarboxylase was significantly higher as well as putrescine and spermidine cellular uptakes in treated cells. However, the changes in polyamine metabolism led to similar polyamine cell contents in untreated and L-valine treated cells. In conclusion, we propose that the observed alterations of polyamine metabolism may reflect an adaptative response of HT-29 cells to the presence of L-valine which contribute together with the low amount of L-ornithine present in the culture medium to polyamine homeostasis.     

Study of composition fluctuations in Fe0.56Cr0.21Ni0.23 by small angle neutron scattering with isotopic contrast

Small angle neutron scattering experiments have been performed with single crystals of Fe_0.56Cr_0.21Ni_0.23, using isotopic contrast variation. It is shown that annealing at 500°C produces a surface segregation layer, related to scattering at very low angle. The presence of chromium-rich or -poor bulk heterogeneities, with correlation radius of one of two lattice cells, can explain the slowly varying scattering cross section at higher angles. This result is compatible with previous measurements of the short-range order parameters with diffuse scattering experiments.     

Determination of carbide and matrix compositions in high-speed steels by analytical electron microscopy

Procedures for the analysis of the blocky (“primary”) carbides and of the matrix in high-speed tool steels with scanning transmission electron microscopy-energy dispersive X-ray (STEM-EDX) are described. Results for the alloys AISI Tl, M2, and M7 and for an experimental, Nballoyed material are reported and compared to determinations by quantitative metallography in scanning electron microscopy (SEM), combined with compositional analysis by SEM-EDX. With proper precautions, good accuracy can be obtained with either method, and the results obtained by the two routes are in good agreement. On leave of absence at Max-Planck-Institut für Metallforschung. formerly Research Assistant, Max-Planck-Institut für Metallforschung.     

Assessment of the aggregation state of integral membrane proteins in reconstituted phospholipid vesicles using small angle neutron scattering

The assessment of the physical size of integral membrane protein complexes has generally been limited to samples solubilized in non-ionic detergent, a process which may introduce artifacts of unknown scope and severity. A system has been developed that allows observation of the small angle scattering profile of an integral membrane protein while incorporated in small unilamellar phospholipid vesicles. Contrast matching of isotopically substituted phospholipid eliminates the contribution of the bilayer to the observed scattering, resulting in a profile dependent only on the structure of the individual membrane protein complexes and their spatial arrangement in the vesicle. After appropriate compensation for their spatial arrangement, information about the molecular mass and radius of gyration of the individual complexes can be obtained. The validity of the approach has been established using monomeric bacteriorhodopsin as a model system.     

An analytical electron microscopy study of the high temperature carbide formed in a V-5 Ti-C alloy

A finely dispersed high temperature carbide that precipitates at 1000°C in a V-5 pct Ti-C alloy has been studied using analytical electron microscopy. The crystal structure has been determined using electron diffraction as B1 (NaCl-type) with a lattice parameter of 4.29Å. The carbide develops a habit plane parallel to {001} of the matrix. The orientation relationship between the carbide and the matrix is [010] carbide ¦ | [ $$ \begin{gathered} [010] carbide || [0\bar 10] matrix \hfill \\ (001) carbide ||(101) matrix. \hfill \\ \end{gathered} $$ The elemental concentrations of the metal constituents of the carbide have been deduced using energy dispersive X-ray spectroscopy and electron energy loss spectroscopy, through examination of core electron excitations. The composition of the carbide is found to be V₁₁Ti₃gC₅₀, assuming a stoichiometric carbide.     

Cholesterol ester in corpus luteum of rat observed by analytical color fluorescence electron microscopy

We used an analytical color fluorescence electron microscope to observe cathodoluminescence (CL) in the corpus luteum of rat. CL was emitted from lipid droplets and has a typical spectrum of two peaks at wavelengths of 320 and 430 nm. The intensity of CL at 320 nm (CL320) in the corpus luteum showed a regular change during an estrous cycle: it was very weak at the newly formed stage, gradually increased, reached the maximum at diestrus 2, and then began to diminish at proestrus except in the patches of degenerated cells. CL320 decreased during early stages of pregnancy or after prolonged treatment with 4-aminopyrazolo-pyrimidine; CL at 430 nm (CL430) remained clearly visible. CL320 showed a strong emission from degenerated luteal cells 10 days after hypophysectomy, but was diminished in cells rescued by injection of 50 IU pregnant mare's serum gonadotropin. In the luteal cells of luteinized ovary 2 hr after intravenous injection of 10 IU luteinizing hormone, CL was barely detected. CL320 in interstitial cells was also weak in the rats hypophysectomized and then treated with pregnant mare's serum gonadotropin, and in the 4-aminopyrazolo-pyrimidine-treated rats, although it has little change through a natural estrous cycle. The results are consistent with the assumption that the content of cholesterol ester is reflected by the intensity of CL320 emitted from the lipid droplets of rat luteal cells. The possibility was shown that the condition of steroidogenesis can be monitored through CL analysis by microscopy.