Small-angle neutron scattering from samples of expanded carbon

The subatomic structure of expanded graphite has been investigated by small-angle neutron scattering. Samples were synthesized during quick thermal decomposition of intercalated compounds based on oxidized graphite. They had a low bulk density (up to 0.1 g/cm³) and were characterized by considerable small-angle scattering. It has been established that majority of the volume of expanded graphite samples is occupied by participles with characteristic sizes in two ranges: from 6 to 8 nm and from 20 to 30 nm. Small particles have properties of a surface fractal with the dimension D _s = 2.4–2.6, whereas the larger particles are mainly smooth and have the dimension D _s = 2.0–2.1. The specific surface of the samples studied was determined from the small-angle scattering data.     

Small-angle neutron scattering from non-crystalline materials on a pulsed neutron source

The small-angle neutron scattering technique is illustrated for a variety of amorphous materials by results obtained on the LOQ instrument at the ISIS pulsed neutron source. The simultaneous use of neutron wavelengths of 2–10 Å is a particular advantage of the pulsed source which gives good results over a wide Q range. Coupled with neutron contrast variation this gives a valuable insight into the structure of materials in the size range 10–1000 Å.     

Small-angle neutron scattering from polymer hydrogels with memory effect for medicine immobilization

Hydrogels synthesized based on cross-linked copolymers of 2-hydroxyethyl methacrylate and functional monomers (acrylic acid or dimethylaminoethyl methacrylate), having a memory effect with respect to target medicine (cefazolin), have been investigated by small-angle neutron scattering. The hydrogels are found to have a two-level structural organization: large (up to 100 nm) aggregates filled with network cells (4–7 nm in size). The structural differences in the anionic, cationic, and amphiphilic hydrogels and the relationship between their structure and the ability of hydrogels to absorb moisture are shown. A relationship between the memory effect during cefazolin immobilization and the internal structure of hydrogels, depending on their composition and type of functional groups, is established.     

Small-angle neutron scattering study of radiation-induced defects in synthetic quartz

The supraatomic structure of single crystals of synthetic quartz was studied by thermal neutron small-angle scattering in the initial state (dislocation densities 54 and 570 cm⁻²) and after irradiation in the WWR-M reactor (Petersburg Nuclear Physics Institute) by fast neutrons with energies E _n > 0.1 MeV at fluences F _n = 0.2 × 10¹⁷ −5 × 10¹⁸ neutrons/cm². It is established that fast neutrons form point, linear, and volume defects in the lattice throughout the entire volume of a sample. Large-volume structures—amorphous-phase nuclei—reach sizes of ∼100 nm in quartz, while occupying a small total volume of ∼0.3% even at the maximum fluence 5 × 10¹⁸ neutrons/cm². The main fraction of the damaged volume (up to 5%) corresponds to point (with a radius of gyration of 1–2 nm) and linear defects, giving a comparable contribution (∼1–4%). The extended linear structures with a radius of 2 nm, even at a moderate fluence of 7.7 × 10¹⁷ neutrons/cm², have a significant total length per volume unit (∼10¹¹ cm/cm³) and can form a connected network with a cell ∼30 nm in size in the sample. Foreign atoms and molecules can migrate through channels of this network.

     

The structure of rapidly solidified ribbons of Al-12 at. % Zn alloy

The structure of melt spun rapidly solidified ribbons of the Al-12 at.% Zn alloy has been investigated by scanning electron microscopy and by X-ray diffraction. Four solidification processes differing in the extent of associated segregation of zinc have been found to be operative during the solidification of the ribbon. These successive processes beginning from above the sites of good contact of the melt with the rotating plane of the copper substrate are as follows: massive planar growth of grains, arrayed dendritic growth, unaligned growth of dendrites, and star-like dendritic growth out from fragments of dendrites. Smaller grains resulting from the last two mentioned processes have been also found within the regions located above the sites of poor contact of the melt with the substrate (lift-off regions). All indicated successive growth modes starting with the epitaxial regrowth of grains have been also found to proceed during the solidification of the melt flowed over the already solidified alloy ribbon. Grain boundary precipitation of equilibrium β (≈︁ Zn) phase has been detected in all stages of solidification. High density of lattice defects built-up during solidification is leading to the immediate intragranular heterogeneous precipitation of β phase at elevated temperatures within the two-phase region without the formation of intermediate metastable precipitates.     

On the Size Distribution of Guinier-Preston Zones Grown in an Al-4.5 at.% Zn Alloy at Room Temperature

The size distribution SD of the Guinier-Preston (GP) zones grown in an Al-4.5 at.% Zn alloy were determined by analysis of the intensities of the small-angle X-ray scattering (SAXS) curves. Four different methods frequently used in the literature were applied and the obtained results were compared. In addition the SD's obtained by the SAXS methods were compared with that found by high-resolution electron microscopic investigations. – From these comparisons conclusions were drawn.     

Small-angle neutron scattering data on C60 clusters in weakly polar solutions of fullerenes

Solutions of fullerence C₆₀ in carbon disulfide CS₂ have been investigated by small-angle neutron scattering. Combination of solubility, contrast, and incoherent scattering make it possible to measure and analyze the relatively small scattering cross section of this system. Along with single fullerene molecules, a small amount of large fullerene clusters (more than 100 Å in size) is found in these solutions. The formation of these clusters depends on the procedure of solution preparation. The size distribution functions of clusters are compared with the results of the phenomenological cluster model of fullerene solubility.     

Structure and properties of potassium titanyl phosphate single crystals with 7 and 11 at. % Nb

This study is a continuation of research into the atomic structure and physical properties of niobium-doped potassium titanyl phosphate crystals, KTiOPO₄ (KTP: Nb). Crystals containing 7 and 11 at. % of niobium were grown and studied. With an increase in niobium content, the number of vacancies and additional potassium positions in the structure also increase. This fact accounts for an increase in both the intensities of relaxation peaks and the conductivity of KTP: Nb crystals.     

Study of the instability boundaries of plastic flow in Cu + 14 at.% Al single crystals at low temperatures

The authors experimentally revealed the existence of the temperature-strain rate region of jumplike deformation in Cu + 14 at.% Al single crystals between 4.2 and 25 K. For each particular temperature in this temperature range, there are a lower and an upper critical strain rates, between which deformation is jumplike. The character of transients occurring during strain rate variation was investigated by increasing the strain rate to the lower critical value. The experimental data are explained in terms of the thermomechanical instability concept and inertial effects of the sample-machine system.     

Algorithms for solving atomic structures of nanodimensional clusters in single crystals based on X-ray and neutron diffuse scattering data

New algorithms for solving the atomic structure of equivalent nanodimensional clusters of the same orientations randomly distributed over the initial single crystal (crystal matrix) have been suggested. A cluster is a compact group of substitutional, interstitial or other atoms displaced from their positions in the crystal matrix. The structure is solved based on X-ray or neutron diffuse scattering data obtained from such objects. The use of the mathematical apparatus of Fourier transformations of finite functions showed that the appropriate sampling of the intensities of continuous diffuse scattering allows one to synthesize multiperiodic difference Patterson functions that reveal the systems of the interatomic vectors of an individual cluster. The suggested algorithms are tested on a model one-dimensional structure.     

Information on the Operating Mode of Decomposition during the Cooling of an Al-10 at.% Zn Alloy to Various Tq

Information about the operating mode of decomposition during cooling to various T_q were gained by SAXS method. After reaching the T_q wanted the samples were quenched into water of RT and the SAXS intensity curves were measured at RT. Strong evidence was found that below about 175 °C the decomposition starts in this alloy with the nucleation and growth of Guinier-Preston zones. As proved by other authors, 175 °C is the upper limit temperature T_rhm for the onset of the rapid homogeneous nucleation of precipitates.     

Effect of neutron irradiation on stratigraphy in calcium fluoride single crystals

Natural single crystals of calcium fluoride have been cleaved along {111} planes and a number of matched pairs have been obtained. One piece from etch pairs have been irradiated with thermal and pile neutrons, the flux varying from 1.3 × 10⁴ to 3.0 × 10¹³ neutrons cm⁻². After irradiation, the irradiated and their non-irradiated counterparts have been matched. They were then etched simultaneously in 0.2 N hydrochlorid acid for the same period. The stratigraphical etch patterns produced have been studied optically. There is no exact correspondence of the stratigraphical etch patterns have been observed on the irradiated and non-irradiated matched pairs. The disappearing in the stratigraphical pattern of the irradiated crystals increases with increase in the dose of irradiation. The implications are dicussed.     

Structure Changes in an Al-4.5 at.% Zn-2.0 at.% Mg Alloy during Continuous Heating in Dependence on the Starting Conditions

Die in einer AlZn(4.5 at.-%) Mg(2.0 at.-%)-Legierung beim kontinuierlichen Aufheizen vonstatten gehenden Strukturumwandlungen wurden mit Hilfe von DSC und RKWS in Abhängigkeit vom Startradius, r_S = (0.7 … 2.7) nm, der metastabilen Phasen (GP-Zonen und/oder η'-Phase), die bei T_pre = R.T. oder 100°C gewachsen waren, untersucht. Die Stabilität der bei T_pre gebildeten metastabilen Phasen nimmt mit deren Größe zu, während eine Veränderung von T_pre keinen merklichen Einfluß zeigt. Startet man mit Partikeln von r_S > 1.6 nm, so erscheinen die Minima, die durch die Bildung von η'-Phase aus den aufgelösten GP-Zonen (1. Minimum) bzw. aus überkritischen Zonen entstanden sind (2. Minimum), mit Zunahme von r_S immer undeutlicher.