Structural changes at hydrophobic/hydrophilic interfaces induced by thermal changes and isotopic composition of the water

1979 ◽  
Vol 57 (5) ◽  
pp. 478-482 ◽  
Author(s):  
Fred Y. Fujiwara ◽  
Leonard W. Reeves
Keyword(s):  
Isotopic Composition ◽  
Structural Changes ◽  
Interface Structure ◽  
X Ray Diffraction ◽  
Chloride System ◽  
Structure Transition ◽  
Thermally Induced ◽  
Nmr Parameters ◽  
Thermal Changes ◽  
Remote Participation

A lyomesophase prepared from decylammorium tetrafluoroborate, ammonium tetrafluoroborate, and water, which orients in a magnetic field perpendicular to the directors (type II), has been investigated with respect to the isotopic composition, H2O/D2O of the aqueous compartment at constant overall chemical composition. An effect of the isotopic composition of the water has been discovered, which influences the packing of the water and tetrafluoroborate ions at the interface. An interface structure transition occurs at ∼ 14 mol% D2O in H2O. The ammonium ions, which do not form part of the first bound layer at the interface, are affected to a much smaller degree and the sudden changes in the direction of variation of nmr parameters are not observed for this ion. The interface structure at > 14 mol% D2O evidently does include more remote participation of NH4+ ions.Recent low angle X-ray diffraction studies, available to us, indicate that the mesophases which orient in magnetic fields have two levels of structure, the packing of amphiphiles in discrete anisotropic micelles and the super-packing of the micelles themselves. These studies now enable us to reinterpret other similar thermally induced structural changes in the interface, from results previously encountered, in the decylammonium chloride system. It is possible to have changes in the packing of water, amphiphiles, and ions at the interface without changes in the superstructure. Such changes in interface packing might well go undetected in a measurement of bulk properties but are revealed by measurement of nmr parameters for the oriented mesophase of different species involved in the interface structure. The isotope effect on structural packing at the interface is absent in two other mesophases investigated.

Multiple dielectric anomalies in xBiLaO3–(1 − x)PbTiO3 piezoelectrics

2008 ◽  
Vol 23 (2) ◽  
pp. 565-569 ◽  
Author(s):  
Runrun Duan ◽  
Michael S. Haluska ◽  
Robert F. Speyer
Keyword(s):  
Differential Scanning Calorimetry ◽  
Dielectric Constant ◽  
Excellent Agreement ◽  
Structural Changes ◽  
Dielectric Anomaly ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Thermally Induced ◽  
X Ray ◽  
Higher Temperature

Compositions of xBiLaO3–(1 − x) PbTiO3 over the range 0 ≤ x ≤ 0.225 were calcined and sintered. The dielectric constant with temperature and differential scanning calorimetry measurements were in excellent agreement with respect to Curie-like tetragonal to cubic transformations starting at 495 °C for pure PbTiO3, shifting to lower temperatures with increasing x. For compositions of x ≥ 0.05, a second higher-temperature (∼600 °C) endotherm, and matching dielectric anomaly, were consistently observed, for which there were no structural changes indicated by hot-stage x-ray diffraction. This transformation was speculated to be based on a thermally induced desegregation of B-site cations.

Effects of thermal processing on (SimGen)p superlattices

1991 ◽  
Vol 69 (3-4) ◽  
pp. 241-245 ◽  
Author(s):  
R. Pascual ◽  
S. Saimoto ◽  
J. M. Baribeau
Keyword(s):  
Structural Changes ◽  
Strain Relaxation ◽  
Buffer Layers ◽  
X Ray Diffraction ◽  
Thermally Induced ◽  
Exponential Decay Rate ◽  
Superlattice Peak ◽  
Short Period ◽  
Short Period Superlattices ◽  
Short Annealing

In this work we report an X-ray diffraction study of thermally induced interdiffusion and strain relaxation in molecular beam epitaxy grown (SimGen)p short-period superlattices. Both rapid and furnace thermal annealings in the range 500–700 °C were used to generate structural changes in the various samples. Strain relaxation was studied by measuring the shift of (400) superlattice peaks on annealing. About half of the strain was relieved in the first few minutes of annealing. The remaining strain was relieved at a much lower rate and residual strain persisted even after several hours of heating. Also, the decay of the first order (000) superlattice peak was monitored as a function of annealing time. An initial rapid nonexponential decrease in peak intensity was observed, coincident with the sudden strain relaxation found at short annealing times. A slower, exponential decay rate was observed at longer times, so that a wavelength-dependent interdiffusion coefficient Dλ could be calculated. The variation of Dλ with the superlattice period and the effect of different substrates and buffer layers was studied. Diffusion was faster in structures alternating thin Si and thick Ge layers suggesting that migration of Si into Ge is the dominant diffusion process.

scholarly journals Investigation of thermally induced phase transitions in uranium perovskites

2014 ◽  
Vol 70 (a1) ◽  
pp. C71-C71
Author(s):  
Emily Reynolds ◽  
Brendan Kennedy
Keyword(s):  
Phase Transitions ◽  
Structural Changes ◽  
Mode Analysis ◽  
X Ray Diffraction ◽  
Thermally Induced ◽  
X Ray ◽  
System A ◽  
Metastable Structures ◽  
Limited Temperature ◽  
Comprehensive Knowledge

The physical properties of inorganic solids are intimately related to their crystal structures and there is increasing awareness of the potential importance of metastable structures that exist over a limited temperature and/or pressure range. For the renaissance of nuclear energy to continue it is vital to improve the efficiency and safety of the nuclear fuel process. In order to do this, a comprehensive knowledge of the fundamental chemical, structural, and thermodynamic properties of uranium compounds is required. Compounds of the type A2BUO6 (A = Ba, Sr; B = Ba, Sr, Ca) have been prepared and characterised using neutron and X-Ray diffraction techniques as well as X-ray absorption spectroscopy. For the first time the high temperature behaviour of these complex oxides has been investigated, and as illustrated by Ba2SrUO6, heating such oxides can induce a sequence of phase transitions with the structure of Ba2SrUO6 changing from monoclinic in P21/n at room temperature to cubic in Fm-3m above 1200 K. [1] The compounds Ba2CaUO6 and BaSrCaUO6 were also found to undergo a series of thermally induced phase transitions from the P21/n monoclinic structure. In order to elucidate the structural changes involved in each system, a combination of diffraction techniques was required. We also utilised symmetry-mode analysis in which the structures are refined in terms of the fundamental tilting modes. This elegant way of tracking phase transitions provided vital insight when comparing and contrasting the thermal behaviour of these complex uranium oxides.

Tensile Stress-Induced Structural Changes Associated with Martensite Transformations in Fe-Mn-Si Based Shape Memory Alloys

2017 ◽  
Vol 907 ◽  
pp. 25-30 ◽  
Author(s):  
Mihai Mocanu ◽  
Elena Mihalache ◽  
Radu-Ioachim Comăneci ◽  
Bogdan Pricop ◽  
Burak Özkal ◽  
...  
Keyword(s):  
Structural Changes ◽  
Solution Treatment ◽  
Tensile Tests ◽  
Ingot Metallurgy ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Thermally Induced ◽  
Static Tensile Loading ◽  
Martensite Transformations ◽  
Static Tensile

Tensile specimens, with the chemical composition Fe-28Mn-6Si-5Cr (mass. %), were obtained by ingot metallurgy, hot rolling, solution treatment (1100°C/ 5 min/ water) and spark erosion cutting. Tensile tests were performed to failure and to prescribed strains, by loading-unloading. Ultimate strain and strength increased up to 80.8 % and 1033 MPa, respectively, with decreasing the cross section of specimens’ gauge down to 2 mm2. The specimens were pre-strained by static tensile loading-unloading tests, to permanent strains as high as 60 %. This procedure aimed to stress-induce martensite, which was further analyzed, on the gauges of pre-strained specimens, by optical and scanning electron microscopy (SEM) as well as X-ray diffraction (XRD). Thermally induced reversion to austenite, of stress-induced martensite, was emphasized, during heating, by differential scanning calorimetry (DSC).

Structural changes induced by cation ordering in ferrotapiolite

2006 ◽  
Vol 70 (3) ◽  
pp. 319-328 ◽  
Author(s):  
M. Zema ◽  
S.C. Tarantino ◽  
A. Giorgiani
Keyword(s):  
Structural Changes ◽  
Rapid Determination ◽  
Linear Increase ◽  
X Ray Diffraction ◽  
Ionic Radii ◽  
Structural Modifications ◽  
Lattice Constants ◽  
Structure Factors ◽  
Polyhedral Volumes ◽  
Degree Of Order

AbstractStructural modifications as a function of the degree of order (Q) in FeTa2O6 ferrotapiolite have been characterized by means of single-crystal X-ray diffraction (SC-XRD). A total of 26 datasets covering the range of Q between 0.154 and 1 have been obtained by thermal treatments followed by quenching of natural tapiolite crystals. Ordering of Fe2+ at the A sites and of Ta5+ at the B sites causes a linear increase in the a/c lattice constants ratio, as a consequence of a linear decrease of the c dimension and only slight modifications of the a parameter. Calibration of a/c vs. Q represents a very useful tool for a rapid determination of the degree of order of tapiolite samples. Polyhedral volumes of the two octahedral sites vary linearly with Q as a consequence of the different ionic radii of the two species. Both the sites remain almost regular at all Q values but the B site shows an increasing off-centre displacement of the cation with increasing Q. Observed structure factors of supercell reflections, characterized by l ≠ 3n, increase linearly as a function of Q, thus representing a further tool for a quick evaluation of the degree of order.

scholarly journals High temperature structural study of decagonal Al-Cu-Rh quasicrystal.

2014 ◽  
Vol 70 (a1) ◽  
pp. C94-C94
Author(s):  
Pawel Kuczera ◽  
Walter Steurer
Keyword(s):  
Structural Changes ◽  
Configurational Entropy ◽  
Lattice Vibrations ◽  
X Ray Diffraction ◽  
Stabilization Mechanism ◽  
X Ray ◽  
Comparative Structure ◽  
The Stability

The structure of d(ecagonal)-Al-Cu-Rh has been studied as a function of temperature by in-situ single-crystal X-ray diffraction in order to contribute to the discussion on energy or entropy stabilization of quasicrystals (QC) [1]. The experiments were performed at 293 K, 1223 K, 1153 K, 1083 K, and 1013 K. A common subset of 1460 unique reflections was used for the comparative structure refinements at each temperature. The results obtained for the HT structure refinements of d-Al-Cu-Rh QC seem to contradict a pure phasonic-entropy-based stabilization mechanism [2] for this QC. The trends observed for the ln func(I(T1 )/I(T2 )) vs.|k⊥ |^2 plots indicate that the best on-average quasiperiodic order exists between 1083 K and 1153 K, however, what that actually means is unclear. It could indicate towards a small phasonic contribution to entropy, but such contribution is not seen in the structure refinements. A rough estimation of the hypothetic phason instability temperature shows that it would be kinetically inaccessible and thus the phase transition to a 12 Å low T structure (at ~800 K) is most likely not phason-driven. Except for the obvious increase in the amplitude of the thermal motion, no other significant structural changes, in particular no sources of additional phason-related configurational entropy, were found. All structures are refined to very similar R-values, which proves that the quality of the refinement at each temperature is the same. This suggests, that concerning the stability factors, some QCs could be similar to other HT complex intermetallic phases. The experimental results clearly show that at least the ~4 Å structure of d-Al-Cu-Rh is a HT phase therefore entropy plays an important role in its stabilisation mechanism lowering the free energy. However, the main source of this entropy is probably not related to phason flips, but rather to lattice vibrations, occupational disorder unrelated to phason flips like split positions along the periodic axis.

Effect of Modified NanoSiO2 Agents on the Morphologies and Performances of UHMWPE Microporous Membrane via Thermally Induced Phase Separation

2016 ◽  
Vol 848 ◽  
pp. 726-732 ◽  
Author(s):  
Rong Liu ◽  
Yan Wang ◽  
Jing Zhu ◽  
Zu Ming Hu ◽  
Jun Rong Yu
Keyword(s):  
Phase Separation ◽  
Water Flux ◽  
Microporous Membranes ◽  
Thermally Induced Phase Separation ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Thermally Induced ◽  
And Performance ◽  
Surface Modified ◽  
Ultra High Molecular Weight

The effects of Modified NanoSiO2 Agents on the morphology and performance of ultra-high-molecular weight polyethylene (UHMWPE) microporous membranes via thermally induced phase separation were investigated in this work. The NanoSiO2 was surface modified by silane coupling agent KH570 (KH570-NanoSiO2). Differential scanning calorimetry (DSC) and X-Ray Diffraction (XRD) were performed to obtain crystallization of UHMWPE/white oil/ KH570-NanoSiO2 doped system. The morphology and performance of the prepared UHMWPE microporous membranes were characterized with scanning electron microscopy (SEM) and microfiltration experiments. The results showed that the morphology of UHMWPE membrane could be disturbed by KH570-NanoSiO2. Porosity and the rejection of Bovine serum albumin (BSA) of the blend membrane increased with increasing concentration of Modified NanoSiO2, while the water flux slightly decreased.

Investigations of Actinide Metals and Compounds under Pressure Provide Important Insights into Bonding and Chemistry

2003 ◽  
Vol 802 ◽  
Author(s):  
R. G. Haire ◽  
S. Heathman ◽  
T. Le Bihan ◽  
A. Lindbaum ◽  
M. Iridi
Keyword(s):  
Structural Changes ◽  
Chemical Properties ◽  
X Ray Diffraction ◽  
Interatomic Distances ◽  
X Ray ◽  
Effect Of Pressure ◽  
Electronic Configurations ◽  
5F Electrons ◽  
Actinide Series ◽  
Alloys And Compounds

ABSTRACTOne effect of pressure on elements and compounds is to decease their interatomic distances, which can bring about dramatic perturbations in their electronic nature and bonding, which can be reflected in changes in physical and/or chemical properties. One important issue in the actinide series of elements is the effect of pressure on the 5f-electrons. We have probed changes in electronic behavior with pressure by monitoring structure by X-ray diffraction, and have studied several actinide metals and compounds from thorium through einsteinium. These studies have employed angle dispersive diffraction using synchrotron radiation, and energy dispersive techniques via conventional X-ray sources. The 5f-electrons of actinide metals and their alloys are often affected significantly by pressure, while with compounds, the structural changes are often not linked to the involvement of 5 f-electron. We shall present some of our more recent findings from studies of selected actinide metals, alloys and compounds under pressure. A discussion of the results in terms of the changes in electronic configurations and bonding with regard to the element's position in the series is also addressed.

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