Small-angle Neutron Scattering Results Research Articles

Simulation and experimental analysis of nanoscale precipitation during ageing treatment of laser powder-bed fusion fabricated IN718 Ni-based superalloy

Temporal evolution of the nanoscale disc-shaped γ′′ (Ni 3 Nb) and spherical γ′ (Ni 3 (Al,Ti)) strengthening precipitates during double-stage ageing treatment of the laser powder-bed fusion (LPBF) fabricated IN718 Ni-based superalloy is studied by thermodynamic-based modeling, electron microscopy, and small-angle neutron scattering (SANS). The precipitation kinetics of both γ′′ and γ′ particles in the multi-component/multi-phase IN718 alloy system was successfully predicted by the Langer–Schwartz–Kampmann–Wagner approach. The simulated particle size and volume fraction during ageing was validated against electron microscopy and SANS results, respectively. The size and volume fraction of the γ′′ phase was monotonically increased during the first ageing stage up to about 100 nm and 14%, respectively, but interestingly unchanged during the second stage. On the other hand, the volume fraction of γ′ phase was sharply increased to about 15% after about 100 s and kept constant until the end of the first ageing stage, where it then decreased to about 7%. The γ′ particle size monotonically increased up to about 20 nm. According to the determined temporal evolution of the nanoscale precipitates, a shorter ageing treatment of the LPBF IN718 superalloy compared to the conventionally manufactured alloy could be suggested. • The precipitation kinetics during ageing of LPBF IN718 superalloy is simulated. • The γ′′ growth rate is faster in the wrought material than in the LPBF one. • The γ′′ volume fraction stagnated during the second stage of ageing. • The simulated concentrations of precipitates did not remain constant during ageing. • A shorter ageing for precipitation hardening of LPBF IN718 alloy can be suggested.

Stress driven creep deformation and cavitation damage in pure copper

The stress dependence of creep deformation and cavitation damage in pure copper at 250 °C under uniaxial loading is studied using a flat hourglass test specimen under uniaxial tensile load. In-situ digital image correlation (DIC) is used to monitor time dependent surface creep deformation, ex-situ small angle neutron scattering (SANS) applied to measure volumetric cavitation damage, and scanning electron microscopy used for surface characterisation. A self-consistent discolation model is successfully applied to explain the full field multi-stress creep deformation behaviour measured by DIC. Through approximating a range of shaped cavities with a model distribution of spherical voids, a minimum stable cavity nucleation diameter range of 600 to 1200 Å, depending on the applied stress level, is clearly observed in the SANS results. This finding supports the validity of the classical surface energy/work balance expression defining the minimum stable cavity size. All cavities observed in interrupted life samples were facetted in nature. The SANS data imply continuous cavity nucleation and growth throughout creep life, with a nucleation rate at stresses less than 100MPa linearly related to the creep rate. This is in accordance with the double ledge grain boundary sliding nucleation model of Sandström and Wu [1].

Water-accessibility of interfibrillar spaces in spruce wood cell walls

Water interactions and accessibility of the nanoscale components of plant cell walls influence their properties and processability in relation to many applications. We investigated the water-accessibility of nanoscale pores within the fibrillar structures of unmodified Norway spruce cell walls by small-angle neutron scattering (SANS) and Fourier-transform infra-red (FTIR) spectroscopy. The different sensitivity of SANS to hydrogenated (hbox {H}_2hbox {O}) and deuterated water (hbox {D}_2hbox {O}) was utilized to follow the exchange kinetics of water among cellulose microfibrils. FTIR spectroscopy was used to study the time-dependent re-exchange of OD groups to OH in wood samples transferred from liquid hbox {D}_2hbox {O} to hbox {H}_2hbox {O}. In addition, the effects of drying on the nanoscale structure and its water-accessibility were addressed by comparing SANS results and the kinetics of water exchange between never-dried and dried/rewetted wood samples. The results of the kinetic analyses allowed to identify two processes with different timescales. The diffusion-driven exchange of water in the spaces between microfibrils, which was observed with both SANS and FTIR, takes place within minutes and rather homogeneously. The second, slower process appeared only in the OD/OH re-exchange followed by FTIR, and it still continued after several weeks of immersion in hbox {H}_2hbox {O}. SANS could not detect any significant difference between the never-dried and dried/rewetted samples, whereas FTIR revealed a small portion of OD groups that resisted the re-exchange and this portion became larger with drying.Graphic abstract

Systematic Investigation of Solution-State Aggregation Effect on Electrical Conductivity in Doped Conjugated Polymers

Systematic Investigation of Solution-State Aggregation Effect on Electrical Conductivity in Doped Conjugated Polymers

Formation of Knots of Carbon Nanotubes in Isotactic Polypropylene Matrix due to the Results of Small-Angle Neutron Scattering and Lattice Numerical Simulation

Formation of Knots of Carbon Nanotubes in Isotactic Polypropylene Matrix due to the Results of Small-Angle Neutron Scattering and Lattice Numerical Simulation

Studies on the aggregation behavior of mineral acid and Zr(IV) loaded Tris(2-methylbutyl) phosphate and tri-n-alkyl phosphate systems using small angle neutron scattering

ABSTRACT The third-phase phenomenon has been observed during the extraction of certain metal ions and mineral acids by 30% (v/v) tri-n-butyl phosphate (TBP) in n-dodecane in the solvent extraction stage of spent nuclear fuel reprocessing. At molecular scale, it has been predicted that the self-organization of the extracted polar species to form reverse micelle-like structure is primarily responsible for third-phase formation. In this regard, the aggregation behavior of solutions of three different trialkyl phosphates in n-alkanes loaded with monoprotic mineral acids (HClO4, HCl and HNO3) as well as tetravalent Th and Zr has been evaluated using Small Angle Neutron Scattering (SANS). The aggregation of TBP has been compared with two of its five carbon analogues i.e. tri-n-amyl phosphate (TAP) and tris(2-methylbutyl) phosphate (T2MBP), which have gained its attention in the course of development of an alternate extractant for the reprocessing process. The effects of trialkyl phosphate structure, diluent chain length and extractant concentration on the aggregation have been emphasized. The contribution of the polar (anionic and cationic component) as well as the apolar part of the reverse micelle toward the phase splitting behavior has been analyzed. The SANS results are in agreement with the earlier reported solvent extraction data.

Study of hierarchical structure of fossil coals by small-angle scattering of thermal neutrons

The problem of safety and prevention of sudden gas and rock outbursts during coal mining remains relevant today. One of the factors characterizing the outburst hazard of a coal seam is the structure and petrographic composition of coal. Then we aimed to use small-angle neutron scattering (SANS) to characterize 27 coals to draw relationships between SANS results and seam outburst behavior and other characteristics of coals.Non-destructive method such as SANS of thermal neutrons makes it possible to study the structure in the volume of the samples. Fractal dimensions and their correlation with the specific surface of the pore space, the degree of coalification, the depth of coal-seam and the propensity of the seam to coal-gas-outbursts are determined for coals of the Donets Basin.The outburst hazardous coals were found to have the following characteristics: the surface fractal dimension Ds close to 2.9–3.0 or the mass fractal that are formed by conglomerates of various mineral inclusions containing iron and sulfur. Contrary to this case less outburst-prone coal structure is characterized by more “smooth” pore space surfaces at Ds < 2.9 and by a higher content of silicon and aluminum.

Tritium Aging Effects on Fracture Toughness of Stainless Steel Weldments

The long-term embrittlement effects of tritium and decay helium on the structural properties of stainless steels have been studied for years at Savannah River National Laboratory (Savannah River) to provide required data for establishing safe operating conditions and the lifetimes of the pressure vessels used to contain tritium gas. In this study, the fracture toughness properties of the longest-aged tritium-precharged stainless steel base metals and weldments tested at Savannah River were measured and compared to earlier results. The fracture toughness values were the lowest recorded here for tritium-exposed stainless steel. As-forged and as-welded specimens were thermally precharged with tritium gas at 34.5 MPa and 623 K, then aged for up to 17 years to build in decay helium prior to testing. American Society for Testing and Materials J-integral fracture mechanics analyses, transmission electron microscopy (TEM), and small-angle neutron scattering (SANS) examinations were conducted to characterize the effects of tritium and its radioactive decay product 3He. Results show that the fracture toughness values were reduced to less than 2% to 4% of the as-forged values for specimens with more than 1300 atomic parts per million helium from tritium decay. The trend of decreasing fracture toughness values with increasing helium content was consistent with earlier observations, and the data show that Type 304L stainless steel is more resistant to tritium-induced cracking than Type 21-6-9 stainless steel at similar decay helium levels. The fracture toughness properties of long-aged weldments were also affected, but the reductions were not as severe over time because the weldments did not retain as much tritium as did the base metals. TEM observations were used to characterize the effects of decay helium bubbles on the deformation substructures, but nanometer-sized helium bubbles were not easily resolved because of high dislocation densities within the forged microstructures. SANS results are presented that suggest the technique can provide information on decay helium bubble size, spacing, and distribution in these steels.

Interactions of alkyltriphenyl phosphonium based ionic liquids with block copolymer microstructures: A multitechnique study

Here we report comprehensive analysis on the influence of different alkyltriphenyl phosphonium (CnTPPBr) (with varying alkyl chain lengths) based cationic surfactants displaying analogical characteristics to ionic liquids (IL) on the physicochemical properties of an ethylene oxide–propylene oxide (EO–PO) triblock copolymer, Pluronic®, P103 (EO17-PO60-EO17; M. Wt-3250) using several techniques viz. cloud point (CP), viscosity, small angle neutron scattering (SANS), dynamic light scattering (DLS) and high sensitivity differential scanning calorimetry (HSDSC). The CP results indicate notable increase in values with the increase in alkyl chain length of IL. A significant decrease in the micelle size was witnessed from the DLS and SANS results. The presence of sodium bromide (NaBr), however, counteracted the disruptive effect of ILs and promoted micellar growth. The critical micelle temperature (CMT) results attained using HSDSC are also reported. The information acquired from the present study will be highly beneficial in understanding the behavior of Pluronic® micelles in the presence of CnTPPBr ILs and for their effective utilization in various industrial applications.

Effect of cosurfactant addition on phase behavior and microstructure of a water dilutable microemulsion

This study reports a detailed characterization of a nonionic microemulsion (μE) composed of n-butylacetate/α-tocopheryl polyethylene glycol succinate (TPGS)/alcohol/water. Two approaches of expanding the monophasic area were explored; (i) addition of Pluronic® 123 (P123) in aqueous phase, and (ii) use of short chain alcohol (CnHn+1OH; n = 2–4) as cosurfactant. Pseudo-ternary phase diagrams were constructed using water titration method. Characterizations were performed using dynamic light scattering (DLS), differential scanning calorimetry (DSC), small angle neutron scattering (SANS) and electron microscopic techniques. DSC and SANS results showed gradual structural transformation from water-in-oil to oil-in-water system. The optimized formulation (oil/Smix/water – 19/40/41) showed average hydrodynamic diameter of 22 nm, consistent with electron microscopic observations.Ethanol (EtOH), with its high fluidity and smaller headgroup area, offered maximum expansion in the phase boundary. Surfactant unimers, derived from EtOH-driven de-micellization, reinforced the interface and solubilized the incoming oil molecules. Oil incorporation was accompanied with improved loading of carbamazepine, a hydrophobic drug. Except marginal swelling, no significant microstructural changes were noticed during water dilution (≈90%) and salt addition (0.9% NaCl) in the optimized μE formulation. A linear increase in oil incorporation was noticed upon adding propylene glycol as a cosolvent.

Investigation of pre-existing particles in Al 5083 alloys

Pre-existing particles formed in Al 5083 alloys (H131 and H116) have been investigated using scanning transmission electron microscopy(STEM), energy-dispersive X-ray spectroscopy(EDS), atom probe tomography (APT), and small angle neutron scattering (SANS). Three types of pre-existing particles, Al6Mn, Mg2Si, and α-Al(Mn,Fe)Si, were observed in Al 5083 alloys, and their relative fraction was obtained from EDS results. The average size, number density, and interfacial area of pre-existing particle were calculated using STEM and SANS results. In addition, an extra layer rich in Mg and Si was found on a pre-existing Mg2Si particle, and an Al6Mn layer was identified on an α-Al(Mn,Fe)Si particle. Thermodynamic calculations were also applied to investigate the possible pre-existing particles formed in the alloys, which can be used to explain the extra layers formed on Mg2Si and α-Al(Mn,Fe)Si particles.

Microstructure and transitions in mixed micelles of cetyltrimethylammonium tosylate and bile salts

The effect of bile salts viz. sodium cholate (NaC) and sodium deoxycholate (NaDC) on the size and transition of cetyltrimethylammonium tosylate (CTAT) micelles is examined by viscosity, cryogenic transmission electron microscopy (Cryo-TEM), small angle neutron scattering (SANS), nuclear Overhauser enhancement spectroscopy (NOESY) and 1H NMR. The viscosity of worm-like micelles of CTAT solution strongly decreases as the temperature increases favoring the transformation to spheroidal micelles. At low NaC concentration (5–10mM), viscosity of 20mM CTAT solutions decreases, reaching a constant value close to that of water. However, for NaDC, a peak in viscosity is seen followed by a drop around 3mM concentration. The microstructure of CTAT micelles gets altered by bile salts as revealed by cryo-TEM. As manifested by SANS results, NaC transforms worm-like CTAT micelles into small spherical/ellipsoidal mixed micelles. However, there was no difference in SANS plot of worm-like CTAT micelles in D2O and in presence of NaDC; these clearly suggest the presence of worm-like micelles. NaDC behaves differently, showing a maximum in viscosity for 20mM CTAT at ∼3mM concentration and phase separation at equimolar ratio. The results are discussed in terms of location of bile salt in mixed micelles determined by NOESY and 1H NMR experiments.

Combination of acoustic levitation with small angle scattering techniques and synchrotron radiation circular dichroism. Application to the study of protein solutions

BackgroundThe acoustic levitation technique is a useful sample handling method for small solid and liquids samples, suspended in air by means of an ultrasonic field. This method was previously used at synchrotron sources for studying pharmaceutical liquids and protein solutions using x-ray diffraction and small angle x-ray scattering (SAXS). MethodsIn this work we combined for the first time this containerless method with small angle neutron scattering (SANS) and synchrotron radiation circular dichroism (SRCD) to study the structural behavior of proteins in solutions during the water evaporation. SANS results are also compared with SAXS experiments. ResultsThe aggregation behavior of 45μl droplets of lysozyme protein diluted in water was followed during the continuous increase of the sample concentration by evaporating the solvent. The evaporation kinetics was followed at different drying stage by SANS and SAXS with a good data quality. In a prospective work using SRCD, we also studied the evolution of the secondary structure of the myoglobin protein in water solution in the same evaporation conditions. ConclusionsAcoustic levitation was applied for the first time with SANS and the high performances of the used neutron instruments made it possible to monitor fast container-less reactions in situ. A preliminary work using SRCD shows the potentiality of its combination with acoustic levitation for studying the evolution of the protein structure with time. General significanceThis multi-techniques approach could give novel insights into crystallization and self-assembly phenomena of biological compound with promising potential applications in pharmaceutical, food and cosmetics industry. This article is part of a Special Issue entitled “Science for Life” Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo.

Growth Behavior, Geometrical Shape, and Second CMC of Micelles Formed by Cationic Gemini Esterquat Surfactants.

Micelles formed by novel gemini esterquat surfactants have been investigated with small-angle neutron scattering (SANS). The growth behavior of the micelles is found to differ conspicuously depending on the length of the gemini surfactant spacer group. The gemini surfactant with a long spacer form rather small triaxial ellipsoidal tablet-shaped micelles that grow weakly with surfactant concentration in the entire range of measured concentrations. Geminis with a short spacer, on the other hand, form weakly growing oblates or tablets at low concentrations that start to grow much more strongly into polydisperse rodlike or wormlike micelles at higher concentrations. The latter behavior is consistent with the presence of a second CMC that marks the transition from the weakly to the strongly growing regime. It is found that the growth behavior in terms of aggregation number as a function of surfactant concentration always appear concave in weakly growing regimes, while switching to convex behavior in strongly growing regimes. As a result, we are able to determine the second CMC of the geminis with short spacer by means of suggesting a rather precise definition of it, located at the point of inflection of the growth curve that corresponds to the transition from concave to convex growth behavior. Our SANS results are rationalized by comparison with the recently developed general micelle model. In particular, this theory is able to explain and reproduce the characteristic appearances of the experimental growth curves, including the presence of a second CMC and the convex strongly growing regime beyond. By means of optimizing the agreement between predictions from the general micelle model and results from SANS experiments, we are able to determine the three bending elasticity constants spontaneous curvature, bending rigidity, and saddle-splay constant for each surfactant.

Poly(ionic liquid)-derived nanoporous carbon analyzed by combination of gas physisorption and small-angle neutron scattering

The preparation of nanoporous carbon materials and their characterization combining small-angle neutron scattering (SANS) with gas physisorption is presented. Carbon with a porous structure and tunable form is obtained here by a salt-templating approach using poly(ionic liquid) as precursor. SANS in combination with contrast matching by deuterated p-xylene was used for a separation of the scattering component deriving from the density fluctuations of the carbon matrix and the inaccessible porosity. The resulting scattering curves could be used for an unambiguous characterization of the pore structure of the materials. SANS curves measured at different partial pressure of the matching agent p-xylene were used for a differential filling of the micro- and mesopores. The analysis using the chord length distribution (CLD) was employed to determine the specific surface area and the pore size at different adsorption steps. The SANS results were in good agreement with the quenched solid density functional theory (QSDFT) analysis of the nitrogen physisorption. By the comparison of both characterization methods the pore shape could be determined. The combination of both SANS and gas physisorption is thus shown to provide a comprehensive characterization of the pore structure of the carbon monoliths throughout the entire pertinent length scale.

Positron annihilation study of ageing precipitation in deformed Fe–Cu–B–N–C

The role of deformation-induced defects and carbon addition on copper precipitation during ageing at 550 °C is investigated in high-purity Fe–Cu–B–N–C alloy samples by positron annihilation spectroscopy. Complementary small-angle neutron scattering (SANS) and hardness tests are utilized to characterize the size distribution of the Cu precipitates formed and their influence on the mechanical properties. Samples with 0 and 8% cold pre-strain are utilized to study the influence of prior tensile deformation on the precipitation kinetics of copper. The time evolution of the coincidence Doppler-broadening spectra indicates that deformation-induced defects enhance the Cu precipitation kinetics, which is confirmed by the SANS results. In the S–W plot, a clear reduction in open volume defects is accompanied by a strong increase of Cu signature during the initial stage of ageing, implying that the open volume defects (mainly dislocations) act as nucleation sites for Cu precipitation. A comparison between the precipitation behaviour of Fe–Cu, Fe–Cu–B–N and Fe–Cu–B–N–C indicates that the addition of carbon does not alter the Cu precipitation mechanism but decelerates the kinetics. Hardness results confirm that carbon counteracts the acceleration of Cu precipitation caused by the addition of B and N.

SANS, Infrared, and 7Li and 23Na NMR Studies on Phase Separation of Alkali Halide–Acetonitrile–Water Mixtures by Cooling

Phase separation of alkali halide (MX) (M = Li+, Na+, and K+ and X = Cl– and Br–)–acetonitrile (AN)–water mixtures by cooling has been investigated at the molecular level. The phase diagram obtained for the MX–AN–H2O ternary systems showed that the temperatures of phase separation for the mixtures with MCl are higher than those with MBr. The phase-separation temperatures of the mixtures with MCl and MBr are higher in the sequence of NaX > KX > LiX, although the magnitude of the hydration enthalpies for the alkali metal ions is larger in the sequence of Li+ > Na+ > K+. To elucidate the reasons for the sequence of phase separation on the meso- and microscopic scales, small-angle neutron scattering (SANS), infrared (IR), and 7Li and 23Na NMR measurements have been conducted on MX–AN–water mixtures with lowering temperature. The results of SANS and IR experiments showed that the mechanism of phase separation of the mixtures by cooling is the same among all of the mixtures but did not clearly reveal the reasons for the phase separation sequence. In contrast, the spin–lattice relaxation rates and the chemical shifts of 7Li and 23Na NMR for the mixtures suggested the different solvation structure of Li+ and Na+ in the mixtures. In conclusion, the solvation of acetonitrile molecules for Li+ and the formation of Li+–X– contact ion pairs in the mixtures cause the weakest effect of LiX on phase separation of the mixtures by cooling among the alkali metal ions.

Small-Angle Neutron Scattering Study of Organic-Phase Aggregation in the TALSPEAK Process

The Trivalent Actinide-Lanthanide Separation by Phosphorus reagent Extraction from Aqueous Komplexes (TALSPEAK) process is a solvent extraction based method for separating trivalent lanthanides (Ln(3+)) from trivalent actinide cations in used nuclear fuel reprocessing. In conventional TALSPEAK, the extractant solution is di(2-ethylhexyl)phosphoric acid (HDEHP) in 1,4-diisopropylbenzene (DIPB). The aqueous medium is diethylenetriamine-N,N,N',N″,N″-pentaacetic acid (DTPA) in a concentrated lactic acid (HL) buffer. Lanthanides are extracted by HDEHP/DIPB, while the actinides remain in the aqueous phase as DTPA complexes. Lactic acid is extracted both independently of the lanthanides and as Ln/HL/HDEHP mixed complex(es). Previous results indicate that lanthanides are extracted both as the mixed complex and as a binary Ln(DEHP·HDEHP)(3) species. Small-angle neutron scattering (SANS) has been applied to study the self-organization properties of solute molecules in xylene solutions containing HDEHP, HL, selected lanthanide ions, and water. The scattering results demonstrate that the dominant HDEHP species is the hydrogen bonded dimer, (HDEHP)(2). Absent lanthanides, lactic acid is extracted as the 1:3 complex (HL·(HDEHP)(3)). Scattering in samples containing up to 0.005 M lanthanides (prepared by extracting lanthanides from aqueous media containing 1.0 M buffered lactic acid) indicates that the dominant metal complex is Ln(DEHP·HDEHP)(3). At 0.013 M extracted lanthanide, the scattering results indicate lower Ln:DEHP stoichiometry and larger scattering particles. At higher metal concentrations, the SANS results indicate large aggregates, the largest aggregates achieving a size equivalent to 20 HDEHP monomers as the primary scattering entity. Analysis of particle shapes indicates best fits with a uniform oblate spheroid particle. These results are discussed in connection with the results of a number of complementary observations that have been made on this system.

Small-Angle Neutron Scattering Study of Protein Crowding in Liquid and Solid Phases: Lysozyme in Aqueous Solution, Frozen Solution, and Carbohydrate Powders

The structure, interactions, and interprotein configurations of the protein lysozyme were studied in a variety of phases. These properties have been studied under a variety of solution conditions before, during, and after freezing and after freeze-drying in the presence of glucose and trehalose. Contrast variation experiments have also been performed to determine which features of the scattering in the frozen solutions are from the protein and which are from the ice structure. Data from lysozyme at concentrations ranging from 1 to 100 mg/mL in solution and water ice with NaCl concentrations ranging from 0 to 0.4 mol/L are fit to model small-angle neutron scattering (SANS) intensity functions consisting of an ellipsoidal form factor and either a screened-Coulomb or hard-sphere structure factor. Parameters such as protein volume fraction and long dimension are followed as a function of temperature and salt concentration. The SANS results are compared to real space models of concentrated lysozyme solutions at the same volume fractions obtained from Monte Carlo simulations. A cartoon representation of the frozen lysozyme solution in 0 mol/L NaCl is presented based on the SANS and Monte Carlo results, along with those obtained from other complementary methods.

In situ neutron scattering study of structural transitions in fibrin networks under shear deformation

Small angle neutron scattering (SANS) is used to decipher the origin of the strain hardening in biopolymer networks by directly measuring the structural response of a fibrin gel to simple shear deformation. A special Couette shear cell is used to systematically probe the structural properties of a fibrin clot over strain values in the range of γ = 1–170%. The SANS results indicate that the strain hardening response of coarse fibrin gels occurs in two distinct regions having different structural and mechanical signatures that are separated by an intermediate strain softening regime. At low strains (γ 30%), a second strain-hardening regime is directly correlated to significant fiber alignment. The mean diameter of the fibers determined directly from two-dimensional fits to the anisotropic scattering data is found to decrease monotonically in the high-strain regime. The results suggest that the non-linear mechanical properties of fibrin clots are the result of a reduction of lateral entropic fluctuations at low strains and a transition between bending and stretching at higher strain values.