Characterization of hollow silica–polyelectrolyte composite nanoparticles by small-angle X-ray scattering

Hollow silica–polyelectrolyte composite nanoparticles were prepared using templates of spherical polyelectrolyte brushes which consist of a polystyrene (PS) core and a densely grafted linear poly(acrylic acid) shell. The obtained hollow particles were systematically studied by small-angle X-ray scattering (SAXS) in combination with other characterization methods such as transmission electron microscopy and dynamic light scattering. The hollow structure formed by dissolving the PS core was confirmed by the reduction of electron density to zero in the cavity through fitting SAXS data. SAXS revealed both the inward and outward expansions of the hollow silica–polyelectrolyte composite particles upon increasing pH from 3 to 9, while further increasing pH led to the partial dissolution of silica layer and even destruction of the hollow structure. SAXS was confirmed to be a unique and powerful characterization method to observe hollow silica nanoparticles, which should be ideal candidates for controlled drug delivery.     

Influence of aggregate mineralogy on alkali–silica reaction studied by X-ray powder diffraction and imaging techniques

Reliable assessment of the potential alkali reactivity of aggregate to develop deleterious alkali–silica reaction is essential for construction of durable concrete structures. The potential alkali reactivity of silicified limestone and two limestones has been investigated. Preliminary characterisation of aggregate was performed by optical and environmental scanning electron microscopy. X-ray powder diffraction peak profile analysis was used to predict the aggregates’ potential alkali reactivity. Samples were aged in accordance to the RILEM AAR-2 procedure and further characterised by means of optical and environmental scanning electron microscopy as well as by synchrotron X-ray microtomography, where quantitative analysis relative to damage due to the alkali–silica reaction (ASR) was performed by morphometric analysis of volume data. Results highlight that (1) the microstructural domain size and microstrain values extracted form XRPD line profile analysis seem to be good parameters for predicting the potential alkali reactivity of quartz in aggregate, and (2) the mineralogy of the aggregate influences the weathering products (i.e. aggregate dissolution, ASR gel growth and microcracking) due to ASR in cement-based materials.     

Transient oxidation of alumina forming Ti–Al–Ag-based alloys and coatings studied by SEM,AFM, XPS and LRS

Abstract

γ-TiAl based intermetallics possess poor oxidation properties at temperatures above approximately 700°C. Previous studies showed that protective alumina scale formation on γ-TiAl can be obtained by small additions (around 2 at.%) of Ag. Recently, this type of materials has therefore been proposed as oxidation resistant coatings for high strength TiAl alloys. In the present study, a number of cast Ti–Al–Ag alloys and magnetron sputtered Ti–Al–Ag coatings were investigated in relation to transient oxide formation in air at 800°C. After various oxidation times the oxide composition, microstructure and morphology were studied by combining a number of analysis techniques, such as SEM, ESCA, AFM and LIOS-RS. The γ-TiAl–Ag alloys and coatings appear to form an α-Al₂O₃ oxide scale from the beginning of the oxidation process, in spite of the relatively low oxidation temperature of 800°C. The formation of metastable alumina oxides seems to be related to the presence of Ag-rich precipitates in the alloy matrix.     

Ultra-small angle neutron scattering and X-ray tomography studies of caseinate–hydroxyapatite microporous materials

Microporous hydroxyapatite–protein composite materials of bimodal pore size distribution, intended for utilization as bone regeneration scaffolds, have been prepared by means of milk caseinate emulsion droplet templating. Ultra-small angle neutron scattering (USANS) has been utilized in order to obtain information on the size distribution of the smaller pores (less than tens of micrometers), as compared to the emulsions that have been initially used as templates. The samples were subsequently visualized in 3 dimensions using synchrotron radiation X-ray tomography, where information concerning the larger pores has been obtained. The examination of the samples confirmed a strong correlation between the size of the templating droplets and the produced pores. In addition, 1 μm-sized pores appear to adhere to the surface of 20–70 μm pores, providing an irregular surface on the large pore walls, a desirable feature in bone-mimicking materials.     

Microstructure of organic–inorganic composite coatings studied by TEM and XANES

Chromate coatings on Zn or Zn alloy coated steel sheets often include silica for the aim to improve corrosion resistance. In the case of dry-in-place chromate coatings containing acrylic resin (hereafter referred to as an organic–inorganic composite coating), an addition of silica, however, did not show an improvement in corrosion resistance. The microstructures of the organic–inorganic composite coatings were observed by transmission electron microscopy (TEM) and the chemical states of Cr were investigated by the total electron yield X-ray absorption near edge structure (TEY-XANES) method. TEM samples were successfully prepared by dry ultramicrotomy preventing water-soluble components in the coatings fromdissolving out. TEY-XANES revealed the chemical states of components even in the organic matrix. Using these methods, it was found that the addition of silica changed just the morphology of the chromium compound in the organic–inorganic composite coating but not the chemical state of Cr. This is a reason for the addition of silica being not effective at improving corrosion resistance. The combination of dry ultramicrotomy-TEM and TEY-XANES spectroscopy was proven to be a powerful tool for characterizing organic–inorganic composite coatings.     

Microstructure and strength of AlN–SiC interface studied by synchrotron X-rays

Bulk AlN crystals grown by sublimation on SiC substrates exhibit relatively high dislocation densities. The kind of defect formation at early growth stages influences the structural quality of the grown crystals. In this work, the dislocation distribution near to the interface is understood through investigation of thin (≤1.5 mm) continuous (non-cracked) freestanding crystals obtained in one process with the evaporation of the substrates. The AlN specimens were characterized using synchrotron radiation imaging techniques. We revealed by triple-axis X-ray diffraction study that, near to the former interface, randomly distributed dislocations configured to form boundaries between \(\sim \)0.02\(^{\circ }\) misoriented sub-grains (from [0001] direction). Threading dislocation structure similar to that in epitaxial GaN films was not detected. To explain these observations, a theoretical model of misfit stress relaxation near the interface is suggested.     

Microstructure of organic–inorganic composite coatings studied by TEM and XANES

Chromate coatings on Zn or Zn alloy coated steel sheets often include silica for the aim to improve corrosion resistance. In the case of dry-in-place chromate coatings containing acrylic resin (hereafter referred to as an organic–inorganic composite coating), an addition of silica, however, did not show an improvement in corrosion resistance. The microstructures of the organic–inorganic composite coatings were observed by transmission electron microscopy (TEM) and the chemical states of Cr were investigated by the total electron yield X-ray absorption near edge structure (TEY-XANES) method. TEM samples were successfully prepared by dry ultramicrotomy preventing water-soluble components in the coatings from dissolving out. TEY-XANES revealed the chemical states of components even in the organic matrix. Using these methods, it was found that the addition of silica changed just the morphology of the chromium compound in the organic–inorganic composite coating but not the chemical state of Cr. This is a reason for the addition of silica being not effective at improving corrosion resistance. The combination of dry ultramicrotomy-TEM and TEY-XANES spectroscopy was proven to be a powerful tool for characterizing organic–inorganic composite coatings.     

Electrochemical behaviour of inorganic redox substances dispersed into Nafion® films

The voltammetric response of a Nafion^® film deposited on an indium tin oxide (ITO) electrode was studied. It was observed that the response is affected by the thickness of the Nafion^® layer. Also, the voltammograms show differences depending on the concentration and composition of the supporting electrolyte solution. The ITO–Nafion^® system can be stabilised by repetitive cyclic voltammetry, and then the inner hydrogen reduction is not detected by electrochemical impedance spectroscopy. Different substances were dispersed into the Nafion^® matrix in order to study their electrochemical response.     

Surface Yielding of Metals by X-ray Diffraction

Surface yielding of metallic material was measured with strain gage and X-ray diffraction methods.The results show that.when the residual stress in the transverse direction is involved,the surface yieldstrength should be evaluated with biaxial Mises criterion.For a medium carbon high strength steel,the yield strength of the bulk material is 581 MPa and the surface yield strengths for 0.05% and0.1%plastic strain are about 436 MPa and 463 MPa respectively.The 0.05% yield strength willapproximately increase to 788 MPa after shot peening.In the early stage of plastic deformation,strain hardening in the surface layer is quite different from that of the bulk sample.     

A study on the thermal expansion characteristics of Inconel-82® filler wire by high temperature X-ray diffraction

The lattice parameter (a) change with respect to temperature (T) has been measured by high temperature X-ray diffraction (HT-XRD) technique for Inconel-82®¹ filler wire used in the TIG welding of a dissimilar joint involving Inconel-600® and commercially pure iron. By taking proper precautions to minimise the temperature gradient across the sample thickness, and by suitably calibrating the shift in 2θ produced as a result of sample buckling at high temperatures, we could obtain fairly reliable estimates of lattice parameter in the temperature range 300–1200 K. The lattice parameter and the coefficient of mean linear thermal expansion at 300 K, have been found to be 3.546(2)×10⁻¹⁰ m and 11.03×10⁻⁶ K⁻¹, respectively.     

Methane in zeolites A and X studied by neutron scattering: a solid or a fluid phase at ambient temperature?

The motion of CH₄ molecules in the zeolites NaX and NaA has been studied by neutron time-of-flight experiments. Elastic peaks have been found, the intensity of which increases at decreasing scattering angle. The main features of the scattered neutron distributions are the same for different zeolite samples and various amounts of adsorbed methane. The observed neutron scattering law cannot satisfactorily be interpreted in terms of the current solid state models for the adsorbate dynamics. A computation of the neutron scattering law on the basis of a fluid phase model yields good agreement with the experiment.     

Transverse cracking of fibre bundle composites studied by acoustic emission and Weibull statistics—effects of postcuring and surface treatment

Transverse failure in composite materials is a mechanism in the ultimate failure of the engineering composite. It is controlled by the strength of the fibre/matrix interface and improvement in the strength of this interface will improve the overall transverse strength. Transverse fibre bundle composites (TFBC) have been tested to failure, where the condition of the composite and the fibre/matrix interface have been modified. Progression to failure has been monitored using acoustic emission with the AE data analysed in a novel way using Weibull statistics. Although Weibull statistics have previously been used to characterise fibre bundle failure, where the concept of weakest link applies, this work extends this approach in an empirical way using an acoustic emission form of Weibull equations. The AE profile, when compared to stress/strain data, showed a quiet-then-noisy profile for room cured resin, which changed to noisy-then-quiet when the resin was post cured. Kevlar reinforced TFBC showed regular AE from low strains. The pattern of AE changed when specimens had been post cured and when the Kevlar fibres had been subjected to ultrasound treatment. Although individual AE events were highly variable, Weibull analysis of the AE parameters derived from a glass reinforced composite proved highly robust, with the AE ringdown count distributions moving to higher values for the more brittle, stronger post-cured resin. Measuring interfacial failure stress via the onset of AE, suggested the interface was weakened, but in a selective way, which did not necessarily show in the final failure stress of the composite.     

Characterization of microshrinkage casting defects of Al–Si alloys by X-ray computed tomography and metallography

The statistical pore size characterization by metallography in the framework of Extreme Value Statistics (EVS) is presented and applied to different sets of cast AlSi7Mg specimens. Specimen production by separate casting or by extraction from automotive cast parts is found to result in different SDAS and porosity (i.e. pore morphology and size) but did not influence the fatigue strength. The application of two equivalent pore size definitions (i.e. maximum Feret diameter and (Area)^1/2) combined with the EVS approach is discussed in terms of predicted critical pore sizes and observed fatigue strengths. The role of casting pore morphology on stress concentration is investigated using the X-ray computed tomography and the finite element method.     

Production of Carbopol® 974P and Carbopol® 971P Pellets by Extrusion‐Spheronization: Optimization of the Processing Parameters and Water Content

Pellets obtained by extrusion‐spheronization represent multiparticulate dosage forms whose interest in intestinal drug delivery can be potentiated and targeted through bioadhesive properties. However, adhesion itself makes the process difficult or even impossible. The problem of tackiness encountered with bioadhesive wet masses was previously eliminated by the use of electrolytes such as CaCl₂. This approach is known to reduce the viscosity of polyacrylic acids by disturbing the interactions between carboxylate groups on adjacent polymer molecules, thereby decreasing their bioadhesive properties. The present study aimed at producing pellets containing carbomers without addition of electrolytes in order to maintain their bioadhesive potentiality at its maximum. Carbopol® 974P (10%, 15% and 20%) and Carbopol® 971P (10%) were used in combination with Avicel® PH101. The extrusion speed (30, 45, 60, 90, and 150 rpm), spheronizer speed (350, 700, 960, 1000, and 1300 rpm), spheronization time (5, 10, 15, and 20 minutes) and amount of water (45%, 50%, 54%, and 58%) were optimized in order to obtain the highest yield of spherical pellets ranging 710–1000 µm in diameter. For pellets containing 10%, 15% Carbopol® 974P or 10% Carbopol® 971P and 45% water content, 30 rpm extrusion speed, 960 rpm, and 10 minutes spheronization speed and time led to the highest yields and sphericities, respectively, 72% and 0.91, 67% and 0.78, and 76% and 0.80. Production of pellets with 20% Carbopol® 974P could be achieved through the increase of the water content up to 58% and implementation of 30 rpm extrusion speed, 1300 rpm, and 10 minutes spheronization speed and time. The yield and sphericity were 42% and 0.78 respectively.     

Growth Kinetics of Nanocrystals and Nanorods by Employing Small-angle X-ray Scattering （SAXS） and Other Techniques

In this article, we report the results of our detailed investigations of the growth kinetics of zero-dimensional nanocrystals as well as one-dimensional nanorods by the combined use of small angel X-ray scattering （SAXS）, transmission electron microscopy （TEM） along with other physical techniques. The study includes growth kinetics of gold nanocrystals formed by the reduction of HAuCl4 by tetrakis（hydroxymethyl） phosphonium chloride in aqueous solution, of CdSe nanocrystals formed by the reaction of cadmium stearate and selenium under solvothermal conditions, and of ZnO nanorods formed by the reaction of zinc acetate with sodium hydroxide under solvothermal conditions in the absence and presence of capping agents. The growth of gold nanocrystals does not follow the diffusion-limited Ostwald ripening, and instead follows a Sigmoidal rate curve. The heat change associated with the growth determined by isothermal titration calorimetry is about 10 kcal·mol^-1 per I nm increase in the diameter of the nanocrystals. In the case of CdSe nanocrystals also, the growth mechanism deviates from diffusion-limited growth and follows a combined model containing both diffusion and surface reaction terms. Our study of the growth kinetics of uncapped and poly（vinyl pyrollidone） （PVP）-capped ZnO nanorods has yielded interesting insights. We observe small nanocrystals next to the ZnO nanorods after a lapse of time in addition to periodic focusing and defocusing of the width of the length distribution. These observations lend support to the diffusion-limited growth model for the growth of uncapped ZnO nanorods. Accordingly, the time dependence on the length of uncapped nanorods follows the L3 law as required for diffusion-limited Ostwald ripening. The PVP-capped nanorods, however, show a time dependence, which is best described by a combination of diffusion （L^3） and surface reaction （L^2） terms.     

Investigation of properties of fluorogypsum-slag composite binders – Hydration,strength and microstructure

A composite binder of high strength and low water absorption has been developed using industrial by-products fluorogypsum, granulated blast furnace slag and Portland cement. The development of strength in the binder at an early age is attributed to the conversion of anhydrite into gypsum and at later age is due to the formation of ettringite and tobermorite, as a reaction of slag with lime produced during the hydration of cement. These cementitious phases fill in pores and voids of the hydrating gypsum crystals to form a dense and compact structure of low porosity and low pore volume. The reaction products formed during the hydration period were confirmed by scanning electron microscopy and X-ray diffraction. The reduction in porosity and low pore volume of binders, as studied by mercury intrusion porosimetry, are responsible for attainment of high strength and better stability towards water in composite binders than the conventional gypsum plaster.     

Study of the influence of TiB2 particles on the melt structure of the hypoeutectic Al–Cu alloy by small angle X-ray scattering

Small angle X-ray scattering (SAXS) studies were carried out in Shanghai Synchrotron Radiation Facility (SSRF) to study the effect of addition of TiB₂ particles on the melt structures of Al-15 wt% Cu. It was found that doping with TiB₂ particles could dramatically reduce the sizes of the melt aggregates at temperatures ranging from the melting point to 800 °C. The results show that the aggregates in the Al–Cu melt present mass fractal characteristics and distribution of incompact 3D flocs.