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Thermal Expansion (thermal + expansion)
Kinds of Thermal Expansion Terms modified by Thermal Expansion Selected AbstractsA Combined Process of In Situ Functionalization and Microwave Treatment to Achieve Ultrasmall Thermal Expansion of Aligned Carbon Nanotube,Polymer Nanocomposites: Toward Applications as Thermal Interface MaterialsADVANCED MATERIALS, Issue 23 2009Wei Lin Ultrasmall thermal expansion of aligned carbon nanotube,epoxy composites at temperatures below and above the glass transition is achieved by a novel combined process of in situ functionalization and microwave treatment. Carbon nanotube,polymer interfacial bonding is the key to the reduced thermal expansion, enhanced storage modulus, and improved thermal conductivity. [source] Isotropic "Islands" in a Cholesteric "Sea": Patterned Thermal Expansion for Responsive Surface Topologies,ADVANCED MATERIALS, Issue 14 2006E. Sousa A method to capture ordered and disordered regions in reactive mesogen films to take advantage of the anisotropic thermal properties and fabricate a thermally responsive patterned film is presented. The image shows white-light interferometer images of isotropic cylinders in cholesteric material. The underlying principle phenomenon observed here is well described by a finite-element simulation. [source] Negative Thermal Expansion and Correlated Magnetic and Electrical Properties of Si-Doped Mn3GaN CompoundsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2010Ying Sun The negative thermal expansion (NTE) and correlated magnetic and electrical transport properties of Mn3GaxSi1,xN were investigated. For pure Mn3GaN, there is a large NTE effect corresponding to the antiferromagnetic to paramagnetic transition. Very interestingly, when partial Ga was replaced by Si, the NTE properties around the magnetic transition were changed. The NTE temperature range was broadened to ,T=148 K for Mn3Ga0.75Si0.25N and the linear thermal expansion coefficient was estimated as ,=,1.4 × 10,5 K,1 (272,420 K). Accordingly, the resistivity also showed a decrease from 327 to 395 K with temperature. With a further increasing Si content to x=0.5, the magnetic transition still occured, but the NTE effect did not appear. After careful observation, an anomaly was found at around 350 K in a,T, ,,T, and DSC curves of Mn3Ga0.5Si0.5N, respectively. This phenomenon strongly implies the close correlation among lattice, spin, and charge in this series materials. [source] Negative Thermal Expansion in (HfMg)(WO4)3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2004Tomoko Suzuki A single-phase material (HfMg)(WO4)3 with an orthorhombic structure, A2 (WO4)3 -type tungstate, has been successfully prepared for the first time by the calcination of HfO2, MgO, and WO3, substituting Hf4+ and Mg2+ for A3+ cations in A2(WO4)3. The new material shows a negative thermal expansion coefficient of approximately ,2 ppm/°C from room temperature to 800°C. The mechanism of negative thermal expansion is assumed to be the same as that of Sc2(WO4)3. [source] Thermal Expansion of ,-Yttrium DisilicateJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2004Koichiro Fukuda Crystals of ,-Y2Si2O7 (space group P121/c1) were examined using high-temperature powder X-ray diffractometry to determine their unit-cell dimensions from 296 to 1473 K. The lattice deformation induced by thermal expansion was investigated using matrix algebra analysis to determine the directions and magnitudes of the principal distortions (,i, i= 1,2, and 3). The directions of ,1 and ,3 were defined by the acute angle ,1c, which linearly decreased from 5(2)° to ,5.5(3)° with increased temperature from 504 to 1473 K. The ,2 -axis invariably coincided with the crystallographic b -axis. The magnitudes of ,1 and ,2 steadily increased to, respectively, 1.0061(1) and 1.0068(1) during heating to 1473 K, while ,3 remained almost constant for the entire temperature range. The mean principal distortion, ,m (= (,1+,2+,3)/3), steadily increased to 1.0044(1) with increased temperature to 1473 K. The coefficient of mean linear thermal expansion (,) was derived from the mean principal strain (,m - 1) as ,= (,m - 1)/,T. The temperature dependence was determined to be ,= 2.03 times 103+ 1.36(T - 296) (10 -9 K -1). Provided that the rule-of-mixtures holds for the Y2Si2O7/Y2SiO5 composites as protective coating on SiC substrates, the volume fractions of 0.72-0.77 (70,75 mass%) would be necessary for the Y2Si2O7 component to match the ,-values of both materials. [source] EXAFS studies of lattice dynamics and thermal expansionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004P. Fornasini Abstract Accurate temperature-dependent EXAFS measurements can give original information on the correlation of thermal motion in crystals, not only along the bond direction (parallel Mean Square Relative Displacement, MSRD), but also within the perpendicular plane (perpendicular MSRD). This potential is demonstrated by the results obtained for copper and germanium, taken as model systems. Possible applications for investigating on the local origin of Negative Thermal Expansion are being supported by measurements on crystals with the cuprite structure. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Local Vibrational Mechanism for Negative Thermal Expansion: A Combined Neutron Scattering and First-Principles Study,ANGEWANDTE CHEMIE, Issue 3 2010Vanessa Lokale Ursache: Die dynamische Verformung der Dikupfertetracarboxylat-Schaufelradeinheit in einem Metall-organischen Gerüst von einer quadratisch-prismatischen (links) zu einer verzerrten Geometrie (rechts) findet bei sehr niedrigen Energien statt. Die Verformung, die stark zur negativen themischen Expansion des Systems beiträgt, ist eine lokale Schwingung, die durch eine Umverteilung der Elektronendichte in den Cu-O-Bindungen ausgelöst wird. [source] ChemInform Abstract: Low-Temperature Oxygen Migration and Negative Thermal Expansion in ZrW2-xMoxO8.CHEMINFORM, Issue 1 2001J. S. O. Evans Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Thermal expansion and atomic displacement parameters of cubic KMgF3 perovskite determined by high-resolution neutron powder diffractionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2002I. G. Wood The structure of KMgF3 has been determined by high-resolution neutron powder diffraction at 4.2,K, room temperature and at 10,K intervals from 373,K to 1223,K. The material remains cubic at all temperatures. The average volumetric coefficient of thermal expansion in the range 373,1223,K was found to be 7.11,(3) × 10,5,K,1. For temperatures between 4.2 and 1223,K, a second-order Grüneisen approximation to the zero-pressure equation of state, with the internal energy calculated via a Debye model, was found to fit well, with the following parameters: ,D = 536,(9),K, Vo = 62.876,(6),Å3, = 6.5,(1) and (VoKo/,,) = 3.40,(2) × 10,18,J, where ,D is the Debye temperature, Vo is the volume at T = 0, is the first derivative with respect to pressure of the incompressibility (Ko) and ,, is a Grüneisen parameter. The atomic displacement parameters were found to increase smoothly with T and could be fitted using Debye models with ,D in the range 305,581,K. At 1223,K, the displacement of the F ions was found to be much less anisotropic than that in NaMgF3 at this temperature. [source] Thermal expansion of organic crystals and precision of calculated crystal density: A survey of Cambridge Crystal DatabaseJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2007Changquan Calvin Sun Abstract True density is a physical property of both fundamental and practical importance to the study of pharmaceutical powders. True density may be calculated from crystal structure. However, precision of such calculated density is not well understood. Furthermore, thermal expansion properties of organic crystals have rarely been characterized. A survey of Cambridge Crystal Database is conducted to assess (1) precision of calculated crystal density from crystal structure; (2) thermal expansion properties of organic crystals. It is shown that calculated crystal density exhibits, on average, a relative standard deviation (RSD) of ,0.4%. It is found that crystal density generally increases linearly with decreasing temperature provided no phase change occurs. Slope of the line, termed thermal density gradient, of organic crystals ranges between 0.04 and 1.74 mg,cm,3,K,1 with an average of ,0.2 mg,cm,3,K,1. It is shown that majority polymorph pairs exhibit significantly different thermal expansion behavior and their density,temperature lines can cross. This likely contributes to the less than perfect prediction of relative stability of polymorphs at ambient temperature using the density rule. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96: 1043,1052, 2007 [source] Thermal expansion co-efficient of nanotube,metal compositesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11-12 2009Sheikh M. Uddin Abstract Thermal expansion exhibits considerable challenges developing residual stresses at the interfaces of different materials treated at high temperature. Electrical devices containing materials with different thermal expansion behaviour very often suffer this problem. Thermal expansion co-efficient (TEC) of different metals can be tuned by using carbon nanotube (CNT). Metal matrix composites (MMCs) using CNT are fabricated by hot-press sintering method and TEC of the composites are investigated throughout a wide range of temperature (,155 to 275,°C). Reduction of TEC of the composite materials was observed up to 20% compared to that of pure metals. The effect of CNTs in the matrix materials and the mechanism behind the improvement are explained from the microscopic investigation of the composites. [source] Analysis of phase transition and expansion behaviour of Al2(WO4)3 by temperature-regulated X-ray diffractionPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2008Takuya Hashimoto Abstract X-ray diffraction measurements of Al2(WO4)3 were carried out under various temperatures from 123 K to 373 K. Diffraction patterns above 273 K and below 253 K could be successfully explained as orthorhombic Pbcn (No. 60) and monoclinic P21/n (No. 14) with superstructure, respectively, which were in agreement with the results of convergent-beam electron diffraction. Thermal expansion of low-temperature monoclinic phase and slight shrinkage of high-temperature orthorhombic phase were observed from the temperature dependence of lattice constants and molar volume, showing agreement with the result of dilatometry. It is revealed that abrupt expansion of Al2(WO4)3 at the structural phase transition is attributed to an abrupt increase of the c -axis, which is parallel to the 21 screw axis and perpendicular to the n-glide plane. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Determination of lattice parameters and thermal expansion of CuGe2P3 + 0.2 Ge3P4 at elevated temperaturesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2006G. Bhikshamaiah Abstract CuGe2P3 is a p-type semiconductor with zincblende structure. Ge3P4 is soluble up to 35 mole% in CuGe2P3. Lattice parameters of CuGe2P3 + 0.2 Ge3P4 have been determined at elevated temperatures from room temperature to 873 K using the x-ray diffraction profiles (111), (200), (220), (311), (222), (400), (331), (420), (422) and (511) obtained from high temperature diffractometer. It is found that the lattice parameter increases linearly from 0.53856 nm at RT to 0.54025 nm at 873 K. The data on lattice parameter is used and coefficient of lattice thermal expansion of CuGe2P3 +0.2 Ge3P4 was determined at different temperatures. It is found that the coefficient of thermal expansion of CuGe2P3 +0.2 Ge3P4 is 5.48 x 10 -6 K -1 and is independent of temperature. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Crystal structure and thermal behaviour of (Rb,Cs)BSi2O6 solid solutionsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2006M. G. Krzhizhanovskaya Abstract The crystal chemistry of Rb-Cs boroleucites has been studied by means of X-ray powder diffraction at room and elevated temperatures. The cubic I-43d , cubic Ia3d phase transition was investigated using a series of samples prepared by solid-state reaction along the pseudobinary system RbBSi2O6 - CsBSi2O6. The Rietveld refinement of the structures of Rb1-xCsxBSi2O6 solid solutions (x = 0.2, 0.4, 0.6, 0.8) demonstrates that the solutions with a high Rb content crystallise in the cubic I-43d space group, and the boroleucites with a considerable Cs content have Ia3d symmetry. Rb can substitute Cs in a wide range of compositions. Within a narrow range of x = 0.5 - 0.6 immiscibility was revealed. Under Rb-Cs substitution the cubic lattice parameter, the (Rb,Cs)-O distances, and the angles between tetrahedra of the I-43d phase change clearly, while those of the Ia3d phase change slightly. The HTXRD data shows that the I-43d phase transforms into a Ia3d phase on heating analogously to a change of the composition. As the Cs content increases the transition temperature decreases. The low temperature I-43d phase shows a higher thermal expansion than the high temperature Ia3d phase. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim [source] Growth and characterization of La3Ga5.5Ta0.5O14 crystalCRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2004Haikuan Kong Abstract La3Ga5.5Ta0.5O14 (LGT) crystal was grown by using the Czochralski method. The as-grown crystal is transparent, free from inclusions and with no cracks. Specific heat, thermal expansion, dielectric constants, transmission spectrum and optical damage threshold of LGT have been measured, and the results show general properties of LGT are similar to that of La3Ga5SiO14 (LGS) crystal. The experiment to research the Q-switch properties of LGT has been performed and the results show LGT possesses smaller electrooptic coefficients than that of LGS and may not be an ideal material used as a Q-switch. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A Generalized System for Photoresponsive Membrane Rupture in PolymersomesADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Neha P. Kamat Abstract Polymersomes are vesicles whose membranes comprise self-assembled block copolymers. It has recently been shown that co-encapsulating conjugated multiporphyrin dyes in a polymersome membrane with ferritin protein in the aqueous lumen confers photolability to the polymersome. In the present study, the photolability is shown to be extendable to vesicles containing dextran, an inert and inexpensive polysaccharide, as the luminal solute. How structural features of the polymersome/porphyrin/dextran composite affect its photoresponse is explored. Increasing dextran molecular weight, decreasing block copolymer molecular weight, and altering fluorophore-membrane interactions results in increasing the photoresponsiveness of the polymersomes. Amphiphilic interactions of the luminal encapsulant with the membrane coupled with localized heat production in the hydrophobic bilayer likely cause differential thermal expansion in the membrane and the subsequent membrane rupture. This study suggests a general approach to impart photoresponsiveness to any biomimetic vesicle system without chemical modification, as well as a simple, bio-inert method for constructing photosensitive carriers for controlled release of encapsulants. [source] Boron Nanotube,Polymer Composites: Towards Thermoconductive, Electrically Insulating Polymeric Composites with Boron Nitride Nanotubes as Fillers (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Mater. Composites formed through embedding of high-concentration boron nitride nanotubes in polymers are reported by C. Y. Zhi et al. on page 1857. The composites possess high thermal conductivity, high break-over voltage, low coefficient of thermal expansion, and other favorable properties. These polymeric composites are promising highly thermoconductive electrically insulating materials for a range of applications. [source] Towards Thermoconductive, Electrically Insulating Polymeric Composites with Boron Nitride Nanotubes as FillersADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Chunyi Zhi Abstract Ultilizing boron nitride nanotubes (BNNTs) as fillers, composites are fabricated with poly(methyl methacrylate), polystyrene, poly(vinyl butyral), or poly(ethylene vinyl alcohol) as the matrix and their thermal, electrical, and mechanical properties are evaluated. More than 20-fold thermal conductivity improvement in BNNT-containing polymers is obtained, and such composites maintain good electrical insulation. The coefficient of thermal expansion (CTE) of the BNNT-loaded polymers is dramatically reduced because of interactions between the polymer chains and the nanotubes. Moreover, the composites possess good mechanical properties, as revealed by Vickers microhardness tests. This detailed study indicates that BNNTs are very promising nanofillers for polymeric composites, allowing the simultaneous achievement of high thermal conductivity, low CTE, and high electrical resistance, as required for novel and efficient heat-releasing materials. [source] Lithosphere structure of Europe and Northern Atlantic from regional three-dimensional gravity modellingGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2002T. P. Yegorova Summary Large-scale 3D gravity modelling using data averaged on a 1° grid has been performed for the whole European continent and part of the Northern Atlantic. The model consists of two regional layers of variable thickness,the sediments and the crystalline crust, bounded by reliable seismic horizons,the ,seismic' basement and the Moho surface. Inner heterogeneity of the model layers was taken into account in the form of lateral variation of average density depending on the type of geotectonic unit. Density parametrization of the layers was made using correlation functions between velocity and density. For sediments, sediment consolidation with depth was taken into account. Offshore a sea water layer was included in the model. As a result of the modelling, gravity effects of the whole model and its layers were calculated. Along with the gravity modelling an estimation of isostatic equilibrium state has been carried out for the whole model as well as for its separate units. Residual gravity anomalies, obtained by subtracting the gravity effect of the crust from the observed field, reach some hundred mGal (10,5 m s,2) in amplitude; they are mainly caused by density heterogeneities in the upper mantle. A mantle origin of the residual anomalies is substantiated by their correlation with the upper-mantle heterogeneities revealed by both seismological and geothermal studies. Regarding the character of the mantle gravity anomalies, type of isostatic compensation, crustal structure, age and supposed type of endogenic regime, a classification of main geotectonic units of the continent was made. As a result of the modelling a clear division of the continent into two large blocks,Precambrian East-European platform (EEP) and Variscan Western Europe,has been confirmed by their specific mantle gravity anomalies (0 ÷ 50 × 10,5 m s,2 and ,100 ÷,150 × 10,5 m s,2 correspondingly). This division coincides with the Tornquist,Teisseyre Zone (TTZ), marked by a gradient zone of mantle anomalies. In the central part of the EEP (over the Russian plate) an extensive positive mantle anomaly, probably indicating a core of ancient consolidation of the EEP, has been distinguished. To the west and to the east of this anomaly positive mantle anomalies occur, which coincide with a deep suture zone (TTZ) and an orogenic belt (the Urals). Positive mantle anomalies of the Alps, the Adriatic plate and the Calabrian Arc, correlating well with both high-velocity domains in the upper mantle and reduced temperatures at the subcrustal layer, are caused by thickened lithosphere below these structures. Negative mantle anomalies, revealed in the Western Mediterranean Basin and in the Pannonian Basin, are the result of thermal expansion of the asthenosphere shallowing to near-Moho depths below these basins. [source] Compositional constraints on the equation of state and thermal properties of the lower mantleGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2001Frank D. Stacey SUMMARY By extrapolating the lower mantle equation of state (EoS) to P=0, T=290 K, we determine the EoS parameters that are compatible with a mixture of (Mg, Fe)SiO3 perovskite (with a small admixture of Al2O3), (Mg, Fe)O magnesiowüstite and CaSiO3 perovskite in arbitrary proportions and with arbitrary Fe/(Fe+Mg) ratio. The parameters fitted are density, ,, adiabatic incompressibility, KS, and its pressure derivative, K,S,(,KS/,P)S. The first stage is adiabatic extrapolation to P=0, T=T0, that is, to the foot of the lower mantle adiabat, at which K,0(T0) is allowed to have any value between 3.8 and 4.6, and 1500 K,T0,2000 K. It is important to use an equation for which the lower mantle fitting does not prescribe K,0(T0) and this rules out the third-order Birch theory, which gives a seriously wrong value. The further extrapolation to 290 K at P=0 uses thermodynamic relationships with maximum generality, allowing all of the following thermoelastic parameters to be arbitrary functions of temperature: K;,; Grüneisen parameter, ,;q=(, ln ,/, ln V)T, where V is volume; volume coefficient of thermal expansion, ,; adiabatic Anderson,Grüneisen parameter, ,S=(1/,) (, ln KS/,T)P; and the mixed P, T derivative (,K,S/,T)P. The heat capacity at constant volume, CV, is assumed to follow the Debye function, so , is controlled by that. The temperature dependences of the dimensionless parameters ,, q and ,S at P=0 are slight. We find , to be precisely independent of T at constant V. The parameter dK,0/dT increases strongly with T, as well as with the assumed value of K,0(T0), where K,0 is K,S at P=0. The fitting disallows significant parameter ranges. In particular, we find solutions only if K,0(T0),4.2 and the 290 K value of K,0 for Mg perovskite is less than 3.8. Conclusions about composition are less secure, partly because of doubt about individual mineral properties. The volume of magnesiowüstite is found to be between 10 and 25 per cent for respective T0 values of 2000 and 1500 K, but the Ca-perovskite volume is no more than 6 per cent and has little influence on the other conclusions. The resulting overall Fe/(Fe+Mg) ratio is 0.12 to 0.15. Although this ratio is higher than expected for a pyrolite composition, the ratio depends critically on the assumed mineral densities; some adjustment of the mineral mix may need to be considered. [source] Large-Scale Fabrication of Boron Nitride Nanosheets and Their Utilization in Polymeric Composites with Improved Thermal and Mechanical PropertiesADVANCED MATERIALS, Issue 28 2009Chunyi Zhi Ultrathin boron nitride nanosheets are fabricated and detailed morphological and structural microscopic studies of are carried out. Polymeric composites containing BN nanosheets exhibit a remarkable reduction of the coefficient of thermal expansion (CTE) and possess enhanced elastic modulus and strength. [source] A Combined Process of In Situ Functionalization and Microwave Treatment to Achieve Ultrasmall Thermal Expansion of Aligned Carbon Nanotube,Polymer Nanocomposites: Toward Applications as Thermal Interface MaterialsADVANCED MATERIALS, Issue 23 2009Wei Lin Ultrasmall thermal expansion of aligned carbon nanotube,epoxy composites at temperatures below and above the glass transition is achieved by a novel combined process of in situ functionalization and microwave treatment. Carbon nanotube,polymer interfacial bonding is the key to the reduced thermal expansion, enhanced storage modulus, and improved thermal conductivity. [source] Thermal and mechanical numerical modelling of electric discharge machining processINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 12 2008Nizar Ben Salah Abstract In electric discharge machining (EDM), the heat gradients caused by the electric discharge create a non-uniform local thermal expansion on the level of the surface layers of machined materials from where genesis of thermal stresses takes place. These thermal stresses, if exceeding yield stress, can remain and become residual after the cooling of the part. The modelling of these phenomena, during the heating by the electric discharge and the cooling by the dielectric liquid, requires a heat transfer model, the material behaviour identification, a thermo-mechanical model for the thermal and the residual stress models. This paper presents numerical results concerning the temperature distribution, the thermal and residual stresses of a stable steel material (AISI316L) machined by EDM. Comparison of numerical results with experimental data and numerical results from the literature shows good agreement and is hence quite satisfactory. Copyright © 2008 John Wiley & Sons, Ltd. [source] Lanthanum Chromite-Based Interconnects as Key Materials for SOFC Stack DevelopmentINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2004Natsuko Sakai The historical investigations on the physicochemical and transport properties of lanthanum chromite-based perovskite oxides are reviewed to evaluate the compatibility as interconnects in solid oxide fuel cells. These materials improve sinterability in air. This has led to investigations on other physicochemical properties of these materials, such as thermal expansion, mechanical strength, and chemical stability. Lanthanum and chromium ion can be substituted by alkaline earths or transition metals, and this translates into a large flexibility in physicochemical properties. However, the formation of oxygen vacancies in a reducing atmosphere can result in an undesirable isothermal expansion or oxygen permeation. The chemical stability of these materials is governed by the fast cation diffusion at the grain boundary of the polycrystals. [source] Dependence of small-angle neutron scattering contrast on the difference in thermal expansions of phases in two-phase alloysJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2009Pavel Strunz Theoretical expressions describing small-angle neutron scattering (SANS) contrast dependence on temperature in the region where no phase-composition changes occur were derived for two-phase Ni superalloys. The theory is based on the difference in thermal expansion of the two primary phases, , and ,,. The simulations show that the scattering contrast temperature evolution is significant enough to be considered in in situ SANS experiments with superalloys at elevated temperatures. The simulations performed show that the magnitude of the scattering contrast at room temperature is firmly connected with the particular shape of the scattering contrast temperature dependence. This fact can be used for determination of the scattering contrast without a knowledge of the compositions of the individual phases. The theoretical expressions derived for scattering contrast were proven experimentally on an Ni,Fe-base alloy, DT706. The evolution of lattice parameters of both the matrix and the precipitate phases was obtained from an in situ wide-angle neutron diffraction experiment. The theoretical scattering contrast dependence was then successfully fitted to the measured SANS integral intensity. [source] Negative (and very low) thermal expansion in ReO3 from 5 to 300,KJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2009Monica Dapiaggi This paper reports the accurate measurement of the ReO3 cell parameter as a function of temperature. The thermal expansion is confirmed to be negative over most of the temperature range from 5 to 300,K. The main problems with the measurements are the very small variations (in the range of 10,5,Å) in the cell parameter at each temperature, requiring tight control of the stability and reliability of instrumental effects. In particular, achieving monochromator stability over time might be challenging with the high energy and high beam current variations of a third-generation synchrotron facility. On the other hand, such effects are usually checked by the addition of silicon as an internal standard, but the accuracy (and precision) of the published thermal expansion (which is not certified) might not be sufficient for its use when dealing with very small cell parameter variations. [source] A comparative in situ Rietveld refinement study: thermal decomposition and transformation of CoAl and CoZnAl layered double hydroxidesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2008Rune E. Johnsen Rietveld refinement based on in situ X-ray powder diffraction (XRPD) data was combined with thermogravimetric analysis (TGA) and mass spectrometry (MS) to study and compare the phase transformations, thermal stability, microstructural and structural changes of two cobalt-containing nitrate-based layered double hydroxides (LDHs) upon heating in a controlled inert atmosphere of nitrogen. The XRPD data were collected, using synchrotron X-ray radiation, with a time resolution of 107,s, which made it possible to carry out detailed structural studies of the initial layered double hydroxides as well as their decomposition products: spinel for a CoAl,NO3 LDH and spinel/zincite for a CoZnAl,NO3 LDH. Correlating these data with those from the TGA,MS analyses gives us information about the transformation mechanisms. Rietveld refinements of the two spinel phases reveal remarkable differences. The a axis of the spinel formed by decomposition of the CoAl,NO3 LDH increases almost linearly from approximately 598 to 1163,K, mainly due to the dominating thermal expansion, whereas the a axis of the spinel formed by decomposition of the CoZnAl,NO3 shows a more complex temperature dependency. Between approximately 698 and 1073,K, the a axis is almost constant due to pronounced chemical interaction with an additional amorphous phase and the zincite phase, whereas from 1073 up to 1163,K it increases linearly. Calculations, based on the results of the Rietveld refinements, of the size of the octahedral and tetrahedral coordination polyhedra in the spinel show that the octahedra shrink and the tetrahedra expand with increasing temperature. The unusual thermal behaviour of the octahedra is discussed and attributed to the low formation temperature of the cobalt aluminium spinel phase. Finally, the intensity of a low-angle scattering (LAS) signal observed in the XRPD patterns was correlated with the decomposition of the LDH, and determination of the specific surface areas gave the temperature-dependent BET surface areas. [source] A differential thermal expansion approach to crystal structure determination from powder diffraction dataJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2008P. Fernandes Differential thermal expansion over the range 90,210,K has been applied successfully to determine the crystal structure of chlorothiazide from synchrotron powder diffraction data using direct methods. Key to the success of the approach is the use of a multi-data-set Pawley refinement to extract a set of reflection intensities that is more `single-crystal-like' than those extracted from a single data set. The improvement in reflection intensity estimates is quantified by comparison with reference single-crystal intensities. [source] Structural redetermination, thermal expansion and refractive indices of KLu(WO4)2JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2006M. C. Pujol The crystal structure of monoclinic KLu(WO4)2 (KLuW) crystals was determined at room temperature by using single-crystal X-ray diffraction data. The unit-cell parameters were a = 10.576,(7), b = 10.214,(7), c = 7.487,(2),Å, , = 130.68,(4)°, with Z = 4, in space group C2/c. The unit-cell parameters of KLu1,xYbx(WO4)2 were determined in relation to Yb concentration. Vickers micro-indentations were used to study the microhardness of KLuW. The linear thermal expansion tensor was determined and the principal axis with maximum thermal expansion ( = 16.72 × 10,6,K,1), , was located 13.51° from the c axis. The room-temperature optical tensor was studied in the near-infrared (NIR) and visible range. The principal optical axis with maximum refractive index (ng = 2.113), Ng, was located 18.5° from the c axis at 632.8,nm. Undoped and ytterbium-doped KLuW crystals were grown by the TSSG (top-seeded-solution growth) slow-cooling method. The crystals show {110}, {}, {010} and {310} faces that basically constitue the habit of the KLuW crystals. [source] In situ high-temperature powder diffraction study of reversible phase transitions in decagonal Al71.2Co12.8Ni16JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2003Christian Soltmann This experimental work is aimed at confirming and broadening findings of former investigations into the type I,S1 phase transition in Al,Co,Ni quasicrystals. In situ high-temperature synchrotron radiation measurements were carried out on Al71.2Co12.8Ni16 powder samples. The cell parameters were precisely determined at various temperatures in the range 290,1110,K. The data provided a new extended insight into the thermal expansion of Al71.2Co12.8Ni16 and into fundamental properties of the phase transition. [source] | ||||||||||||||||||||||||||||||||||||||||