Nanostructure of potato starch. II. Structure of a highly crystalline gel obtained by retrogradation using X‐ray diffraction techniques

A highly crystalline gel (65% crystal portions) was prepared by retrogradation of injection‐molded potato starch in humid atmosphere. The different components of the nanostructure were identified by means of successive melting processes using “in situ” simultaneous wide and low angle X‐ray diffractions. At low temperatures, structural changes such as annealing phenomena or evaporation of water, giving rise to a thickening of the gel, are observed. In the range of 55–75°C, a first transition due to melting of a layered structure of concentric sphere‐like alternating crystalline and amorphous lamellar shells (amylopectine, AP, being the crystalline component) is detected. Analysis of results reveals that the AP crystallization contributes 25% to the overall crystal fraction. A spherulitic structure of alternating radial lamellae from amylose (AM) or AP melts in a higher temperature region between 75 and 86°C. This modification represents the major contribution to crystallinity of about 40%. Unexpectedly, the crystalline blocks of such a structure are abnormally anisometric; i.e., they are thicker than their width. This has been related to a contraction of the AMAP‐co‐spherulite due to an excessive growth of the AP‐shell crystals. The anisometry of the blocks of the AMAP lamellae vanishes at the beginning of the melting of the AP shell crystals, just when the total crystallinity decreases below 50% at 60°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 689–696, 2007     

Nanostructure of Potato Starch,Part I: Early Stages of Retrogradation of Amorphous Starch in Humid Atmosphere as Revealed by Simultaneous SAXS and WAXS

Crystallization experiments on amorphous, injection-molded starch in a humid atmosphere are reported. The crystallization mechanisms have been studied using simultaneous SAXS and WAXS during a temperature stepwise increase. In contrast to the crystallization of linear synthetic polymers, in starch the WAXS peaks are observed at low temperature before the appearance of the SAXS maximum. The initial state of crystallization is dominated by the amylose (AM) component of the potato starch alone. After the initial formation of large (16 nm) uncoordinated individual crystallites, stacks of lamellae and finally, an insertion of thinner lamellae within the stacks are observed. Results indicate that only if all AM is converted into a semicrystalline structure and if the secondary starch network of double helices of AM and amylopectin (AP) is molten by a temperature increase above 70°C, crystallization of AP also occurs. Because the AM crystals act as nuclei for the AP component, a common superstructure is developed. Within a spherulite, alternating AM and AP lamellae develop radially from the center of the AP molecule. Results suggest that the AM is distributed inhomogeneously with respect to the AP molecules, leaving approximately one half of the AP fraction free, which means not crystallized to a spherulitic structure together with AM.     

An X‐ray scattering study of water‐conditioned injection‐molded starch during isothermal heating

The in situ structure variation of injection‐molded starch (as processed and after water conditioning) during heat treatment was investigated by means of wide‐angle X‐ray scattering using synchrotron radiation. Results confirm that the crystal structure of potato starch is destroyed after injection molding, while as‐processed corn starch preserves some degree of crystallinity. This residual crystallinity in corn starch is related to the crystalline Vh‐form, made of complexes of amylose with lipids. Furthermore, it is shown that both starch types can develop crystallinity by water conditioning: potato starch yields the crystal B‐form, while corn starch yields the crystal A‐form coexisting with the persistent Vh‐form. Upon isothermal heating of samples under vacuum, a rapid decrease of crystallinity, which is a function of both time and treatment temperature, is detected. Crystallinity variations are discussed in terms of water evaporation, the leveling‐off values of crystallinity being dependent on the temperature of the isothermal treatment. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 17–21, 2003     

Recycled car bumpers' impact resistance investigated by wide‐angle X‐ray diffraction

The recycled polyolefinic product from discarded standard car bumpers collected from Rio de Janeiro suburb shops was characterized by mechanical and wide‐angle X‐ray scattering (WAXS) methods. We found that the recycled plastic mixture is composed mainly of polypropylene (PP), containing ethylene‐propylene‐diene (EPDM) terpolymers and a minor proportion of high‐density polyethylene (HDPE), and is highly resistant to impact. The results were compared with the corresponding data obtained from binary and ternary blends of virgin PP, EPDM, and HDPE. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 999–1004, 2000     

Small‐angle X‐ray scattering investigation of the deformation processes in the amorphous phase of high density polyethylene

In situ small‐angle X‐ray scattering of high density polyethylene under uni‐axial tensile test was used for investigating the deformation at the scale of the periodic crystalline–amorphous nano‐structure. The more or less uniform elastic straining of the rubbery amorphous layers is discussed in terms of mechanically active intercrystalline tie chains. Correlation is made with the long‐term use properties. It is concluded that this approach is a powerful means to assess the mechanical efficiency of tie molecules. Copyright © 2004 Society of Chemical Industry     

Blends of polypropylene with poly(cis‐butadiene) rubber. II. Small‐angle X‐ray scattering studies of the phase structure of immiscible blends of polypropylene with poly(cis‐butadiene) rubber

Pressed films of the blends of polypropylene (PP) with poly(cis‐butadiene) rubber (PcBR) were studied by IR spectra, small‐angle X‐ray scattering, and scanning electron microscopy. The problem of the interaction between different macromolecules in the blends of PP/PcBR is discussed by melt‐mixing at a temperature of 210°C using IR. X‐ray scattering from the relation of the phase was analyzed using Porod's law, and the interface layer thickness was calculated. The immiscibility of the blends of PP/PcBR was proved. The structure parameters, the correlation distance a_c, average chord lengths l?, and radius of gyration R?_g were obtained by the Debye–Buech statistical theory of scattering. Porod's index was calculated and the shape of the dispersed phase is discussed in relation to Porod's index in the blends. The morphology and structure of the blends were investigated by scanning electron microscopy. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2088–2094, 2002     

Method for Direct Determination of Glassy Phase Dissolution in Hydrating Fly Ash‐Cement System Using X‐ray Diffraction

A method for quantitative X‐ray diffraction analysis is developed for direct determination of the glassy phase content of fly ash in a hydrating binary blend of cement and low‐calcium, siliceous fly ash. The intensity contributions of the unhydrated glassy phase of fly ash and the amorphous reaction products to the intensity pattern of the total amorphous phase in the hydrating binary blend are obtained by decomposition of the total intensity signature as a sum of component pseudo Voigt (PV) peaks. An experimental program involving binary blends with three different low calcium siliceous fly ashes and two different curing temperatures is reported. The centers of the component PV peaks of the fly ash glassy phase fitted to the overall intensity pattern are found to be invariant. The glassy phase content of hydrating binary blends determined from the XRD method were found to agree well with the values obtained from a selective dissolution method.     

In situ Synchrotron X‐ray Radiography Investigations of Water Transport in PEM Fuel Cells

Water transport in an operating PEM fuel cell was investigated with synchrotron X‐ray radiography with a spatial resolution of 3 μm and a temporal resolution of 5 s. This method allows for the detection of water accumulations with less than 10 μm diameter. We demonstrate that synchrotron X‐ray imaging can dramatically expand the possibilities of imaging with high spatial and time resolution, especially as a complement to neutron radiography. Water transport processes from the first appearance of small water accumulations in the gas diffusion layer to their transport into the channel system were analysed in situ. Correlations between local effects such as water formation and operating conditions of the whole system, e.g. power variations, were found. A recently described eruptive water transport mechanism is analysed in detail.     

X‐ray photoelectron spectroscopy analysis of Ge–Sb–Se pulsed laser deposited thin films

Pulsed laser deposition was used to prepare amorphous thin films from (GeSe₂)_100?x(Sb₂Se₃)_x system (x = 0, 5, 10, 20, 30, 40, 50, and 60). From a wide variety of chalcogenide glass‐forming systems, Ge–Sb–Se one, especially in thin films form, already proved to offer a great potential for photonic devices such as chemical sensors. This system has a large glass‐forming region which gives the possibility to adjust the chemical composition of the glasses according to required physical characteristics. The chemical composition of fabricated thin films was analyzed via X‐ray photoelectron spectroscopy (XPS) and compared to energy dispersive spectroscopy (EDS) data. The results of both techniques agree well: a small deficiency in chalcogen element and an excess of antimony was found. The structure of as‐deposited thin films has been investigated by XPS. The presence of the two main structural units, [GeSe₄] and [SbSe₃] proposed by Raman scattering spectroscopy data analysis, was confirmed by XPS. Moreover, XPS core level spectra analysis revealed the presence of M–M bonds (M = Ge, Sb) in (Ge,Sb)–Ge–(Se)₃ and (Ge,Sb)–Sb–(Se)₂ entities that could correspond to Ge‐based tetrahedra and Sb‐based pyramids where one of its Se atoms at corners is substituted by Ge or Sb ones. The content of depicted M–M bonds tends to increase with introduction of antimony in the amorphous network of as‐deposited thin films from x = 0 to x = 40 and then it decreases. XPS analysis of as‐deposited thin films shows also the presence of the (Ge,Sb)–Se–(Ge,Sb) and Se–Se–(Ge,Sb) entities.     

Phase‐dependent radiation‐resistant behavior of BaTiO3: An in situ X‐ray diffraction study

The radiation‐resistant response of BaTiO₃ in the tetragonal and rhombohedral phases on exposure to 100 MeV Ag⁷⁺ ion irradiation was investigated by in situ X‐ray diffraction (XRD) at room temperature (300 K) and low temperature (25 K), respectively. This study revealed that the BaTiO₃ in rhombohedral phase retained crystallinity up to an ion fluence of 1×10¹⁴ ions/cm², whereas tetragonal phase amorphized at much lower fluence viz. 1×10¹³ ions/cm². The in situ XRD along with Raman spectroscopy studies revealed that BaTiO₃ in rhombohedral phase is more radiation resistant than that of tetragonal phase. The density functional theory (DFT) calculations confirmed higher bond strength of rhombohedral phase as compared to tetragonal phase, which supported the experimental result of higher radiation stability of rhombohedral phase. The theoretical predictions on high‐temperature phase will be of relevance to the nuclear waste applications.     

A Shielding Topology Stabilizes the Early Stage Protein–Mineral Complexes of Fetuin‐A and Calcium Phosphate: A Time‐Resolved Small‐Angle X‐ray Study

Biomineralization mechanisms : The serum protein α₂‐HS glycoprotein/fetuin‐A is an important inhibitor that prevents pathological mineralization of calcium phosphate in soft tissues and in the extracellular fluid. TR‐SAXS and stopped‐flow analysis were used to monitor the growth of protein mineral particles nucleating from supersaturated salt solutions in the presence of the protein. It was found that fetuin‐A did not influence the formation of mineral nuclei, but did prevent the aggregation of nuclei and thus mineral precipitation.

     

Sillimanite‐mullite transformation observed in synchrotron X‐ray diffraction experiments

High‐resolution synchrotron powder X‐ray diffraction (XRD) experiments were conducted to clarify the transformation of sillimanite to mullite (mullitization) and determine the mullitization temperature (T_c). We were able to distinguish sillimanite and mullite in the XRD patterns, despite their very similar crystallographic parameters, and to detect the appearance of small mullite peaks among sillimanite peaks. Analysis of the Johnson‐Mehl‐Avrami (JMA) equation for mullitization ratio (ζ) revealed that at temperatures T≥1240°C the mullitization had the same kinetics. The activation energy E at T≥1240°C obtained from the Arrhenius plot was 679.8 kJ mol^?1. In analysis using a time‐temperature‐transformation diagram for mullitization, a mullitization curve of ζ=1% can be described as where t is time, n is a reaction‐mechanism‐dependent parameter determined as 0.324 by JMA‐analysis, k₀ is the frequency factor, E_A is the activation energy for atomic diffusion, and represents the activation energy for nucleation. The results of fitting the data to this equation were T_c=1199°C, A=3.9×10⁶ kJ mol^?1 K^?2, E_A=605 kJ mol^?1, and k₀=3.65×10¹⁵. We conclude that the boundary between sillimanite and mullite+SiO₂ in the phase diagram is ~1200°C.     

The Change of X‐ray Diffraction Peak Width During in situ Conventional Sintering of Nanoscale Powders

Diffraction peaks of nanoscale particles of 3 mol% yttria‐stabilized zirconia become sharper as the powder sinters. The reduction in the peak width is correlated with the increase in density. The sharpening of the peak agrees reasonably well with the remaining free surface area as the sample sinters. Therefore, high curvature of the free surface of the pores is assumed to lead to peak broadening (the grain boundaries that grow at the expense of the free surfaces of the pores do not have this curvature). The change in the grain size during sintering does not make a significant contribution to peak width.     

Formation mechanism and growth of MNbO3, M=K,Na by in situ X‐ray diffraction

Hydrothermal synthesis is a well‐established method to produce complex oxides, and is a potential interesting approach to synthesize stoichiometric lead‐free piezoelectric K_0.5Na_0.5NbO₃. Due to challenges in obtaining the desired stoichiometry of this material, more knowledge is needed on how the end‐members, KNbO₃ and NaNbO₃, are nucleating and growing. Here, we report on the formation mechanisms and growth during hydrothermal synthesis of KNbO₃ and NaNbO₃ by in situ synchrotron powder X‐ray diffraction. We show that tetragonal KNbO₃ crystallites form from dissolved T‐Nb₂O₅ at 250°C‐300°C and 250 bar while orthorhombic NaNbO₃ forms via several crystalline intermediate phases at 225°C‐325°C and 250 bar. The crystallite size of KNbO₃ is decreasing while the crystallite size of NaNbO₃ is increasing with increasing temperature, demonstrating that the presence of intermediate phases is highly important for the nucleation and growth of the final product. The different crystallization schemes explain the challenge in obtaining stoichiometric K_0.5Na_0.5NbO₃ by hydrothermal synthesis.     

Non‐isothermal crystallization kinetics of Al2O3‐YAG amorphous ceramic coating deposited via plasma spraying

Crystallization kinetics of the newly developed Al₂O₃‐Y₃Al₅O₁₂ (YAG) amorphous ceramic coating fabricated by atmospheric plasma spraying (APS) were investigated via differential scanning calorimetry (DSC) under non‐isothermal conditions. The phase compositions and microstructure of the as‐sprayed coating were characterized by X‐ray diffraction (XRD) and Scanning electron microscopy (SEM). The glass transition temperature T_g, the onset temperature of crystallization T_c and the peak temperature of crystallization T_p presented heating rate dependence. The related kinetic parameters of activation energies (E_g, E_c, E_p) and Avrami exponents (n) were quantified using various methods including Kissinger, Augis–Bennett, Ozawa and Matusita–Sakka, etc., to understand the phase transition mechanism and crystallization process in depth. A series of parameters including devitrification interval ΔT, thermal stability (T_c, E_c), nucleation resistance E_c/RT_g and fragility index F were quantified in order to evaluate the nucleation mechanism, crystallization behavior and thermal stability of Al₂O₃‐YAG amorphous ceramic coating. Excellent thermal stability was witnessed in the studied coating. Furthermore, the YAG crystalline phases can be reasonably controlled and independently precipitated from the amorphous matrix via proper annealing.     

Bubbles in a fluidized bed: A fast X‐ray scanner

We present experiments on a bubble train in a 23‐cm‐diameter fluidized bed of a Geldart B powder. The bubbles are injected via a single capillary inserted in the bed. We use our double X‐ray tomographic scanner to measure the solids distribution in two parallel cross sections of the bed. We report data for four different heights of the measuring planes above the capillary outlet. The velocity of individual bubbles is found from the time of flight from the lower to the upper plane. We have done separate calibration experiments for the velocity. In this article, we present data for the size and velocity of individual bubbles. From the bubble velocity, we could obtain the vertical dimension of the bubbles. This makes it possible to measure the volume of each bubble. The results show that our scanner is capable of measuring properties of bubbles with a size of 2.5 cm and above. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Determination of crystal size distributions in alumina ceramics by a novel X‐ray diffraction procedure

A novel X‐ray diffraction based method is presented, capable of determining volume‐based crystal size distribution (CSD) of polycrystalline materials and crystalline powders with unprecedented sampling statistics; the method is named fast X‐ray diffraction crystal size distribution analysis (FXD‐CSD). FXD‐CSD can be performed with standard laboratory X‐ray diffractometers equipped with a position sensitive detector and uses a software package written in Python for the data analysis. FXD‐CSD is a destruction‐free and generally applicable method to establish CSDs of polycrystalline materials as well as powders for sizes well below 1 μm up to about 100 μm; it even allows for studies of samples enclosed in complex environments, e.g., for in situ measurements in a furnace or in a pressure cell. To show the capability of the method the microstructural evolution of four alumina substrates with different time‐spans of sintering (4, 8, 16, and 24 hour at 1600°C) is investigated via FXD‐CSD and SEM imaging. The corresponding CSDs and average grain sizes are determined, results obtained by FXD‐CSD and the line‐intersection methods are compared and clear evidence for the presence of abnormal grain growth (AGG) during sintering is shown. From three tested probability density functions (PDF) describing the CSDs a log‐normal PDF fits best to the volume based CSDs; the method provides size distributions with unprecedented precision opening the way to a systematic and meaningful comparison between theoretically predicted and observed CSDs.     

Bimodal X‐ray and Infrared Imaging of an Organometallic Derivative of Praziquantel in Schistosoma mansoni

An organometallic derivative of praziquantel was studied directly in worms by using inductively coupled plasma‐mass spectrometry (ICP‐MS) for quantification and synchrotron‐based imaging. X‐ray fluorescence (XRF) and IR absorption spectromicroscopy were used for the first time in combination to directly locate this organometallic drug candidate in schistosomes. The detection of both CO (IR) and Cr (XRF) signatures proved that the Cr(CO)₃ core remained intact in the worms. Images showed a preferential accumulation at the worm's tegument, consistent with a possible targeting of the calcium channel but not excluding other biological targets inside the worm.     

Pore structures in shungites as revealed by small-angle neutron scattering

The analysis of the small-angle neutron scattering data from shungites, one of the natural forms of carbon, is reported. Samples from different deposits are investigated. It is shown that shungites have a complex pore structure at a nanoscale of 1-100 nm depending on their origin. Along with it, common features, in particular, two-level organization at the given scale can be observed. The absorption of deuterated water by shungites is used to match the scattering from open pores and to separate the information about the open and closed porosity in the samples. The revealed structural units are compared with the previous experimental results obtained by the complementary techniques.     

Catalytic Mechanism of the Hotdog‐Fold Thioesterase PA1618 Revealed by X‐ray Structure Determination of a Substrate‐Bound Oxygen Ester Analogue Complex

Thioesterase activity accounts for the majority of the activities in the hotdog‐fold superfamily. The structures and mechanisms of catalysis for many hotdog enzymes have been elucidated by X‐ray crystallography and kinetics to probe the specific substrate usage and cellular functions. However, structures of hotdog thioesterases in complexes with substrate analogues reported to date utilize ligands that either represent truncations of the substrate or include additional atoms to prevent hydrolysis. Here we present the synthesis of an isosteric and isoelectronic substrate analogue—benzoyl‐OdCoA—and the X‐ray crystal structure of a complex of the analogue with Pseudomonas aeruginosa hotdog thioesterase PA1618 (at 1.72 Å resolution). The complex is compared with that of the “imperfect” substrate analogue phenacyl‐CoA, refined to a resolution of 1.62 Å. Kinetic and structural results are consistent with Glu64 as the catalytic residue and with the involvement of Gln49 in stabilization of the transition state. Structural comparison of the two ligand‐bound structures revealed a crucial ordered water molecule coordinated in the active site of the benzoyl‐OdCoA structure but not present in the phenacyl‐CoA‐bound structure. This suggests a general base mechanism of catalysis in which Glu64 activates the coordinated water nucleophile. Together, our findings reveal the importance of a closely similar substrate analogue to determine the true substrate binding and catalytic mechanism.