Thermal Expansion Studies Research Articles

What Nano-Confined Ionomers Can Tell Us about Fuel Cell Performance

Several emerging and growing applications like biosensors, gas separation membranes, protective coatings, photonics, nanocomposites and microelectronics depend on polymers of thicknesses under 100nm[1]. Ion conducting polymers (ionomers) of thickness <100nm have induced significant advances in the performance of polymer-electrolyte fuel cells (PEFCs) by serving as binder in the catalyst layers (CLs), aiding proton conduction and extending the reaction zone of the CL porous electrode.[2] Thin and ultra-thin polymer films provide ease of processing, application specific tunable properties and reduction in material cost. However, due to deviation of nano-confined polymers from bulk behavior, they pose a challenge of predictability. This is evident in PEFCs where thin-film ionomers are large contributors to mass-transport losses at low catalyst loadings required for commercialization. In-situ investigations over the past 10 years have provided a significant amount of insight into these losses in CLs.[3] As a result, it would be misleading to employ the same principles of understanding used for bulk polymers for nano-confined polymers without modification. In our study, we aim to understand nano-confined ionomers in two ways. First, looking at impact of interfaces by using ionomers supported on different substrates and tuning substrate-ionomer interaction via reducing and oxidizing environment. Second, by examining the impact of cooperative motion and chain dynamics using thermal expansion study of nano-confined ionomers. Combining these two studies we can gain new understanding of effect of confinement on performance. Understanding ionomer-catalyst surface interface and interaction can elucidate not only how ionomers impact catalyst performance but also how catalyst surface impacts ionomer performance. In our study we use water uptake and modulus to probe the effect of platinum surface on thin-film ionomers under oxidizing(Air) and reducing(H2) conditions. Several in-situ and ex-situ methods have demonstrated that oxide formation on the active platinum catalyst surface can reduce the catalytic activity, further hampering activity in the cathode catalyst layer[4]. Despite this, our studies show continued growth of oxides on platinum surface results in higher density of water maintained in the ionomer. This indicates that nano-confined ionomers have greater water stability in the cathode than on the anode catalyst layer, enhancing proton transport in the cathode catalyst layer. Using transition temperature as a proxy for material behavior, we also looked at relaxation behavior of nano-confined ionomers under slow heating conditions. For glass-forming polymers like perfluorinated sulfonic-acid (PFSA) ionomers (such as Nafion and 3M-ionomer) cooperative motion and dynamics of chains have been used to explain changes in modulus, thermal expansion, relaxation behavior, and gas transport. Thermal transition temperatures are often used as a broad physical description for these kinetically and thermodynamically-driven changes in polymer behavior[1]. In this study, we used heated cell ellipsometry to explore the presence of transition temperatures and their dependence on thickness and substrate in thin-film ionomers. We are able to see both α and β transition temperatures using ion exchanged nano-confined ionomers supported on silicon substrates. Our results demonstrate increased rate of expansion for thin films as compared to bulk and dramatic change of transition temperatures around 50-70nm indicating impact of ionomer-surface interaction and influence of electrostatic interaction on chain relaxation and gas transport. Acknowledgement We would like to thank Douglas Kushner for providing assistance and guidance in this study. This work made use of facilities at the Joint Center for Artificial Photosynthesis at Lawrence Berkeley National Laboratory. This work was funded in part by the University of California Chancellor's Graduate Fellowship, National Science Foundation Graduate Fellowship and the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U. S. Department of Energy under contract number DE-AC02-05CH11231.

Dimensionality of a Coordination Polymer as a Tool To Control Thermal Expansion in a Polymorphic Coordination Compound

Establishment of structure–property relationships is a subject of utmost importance in structural chemistry and materials science. The thermal expansion of strong bonds is known to be smaller than that of weaker bonds. Can this tendency be used to correlate the dimensionality of coordination polymers to their thermal expansion? In this study, we found that two 1D polymers of the polymorphic coordination complex of ZnCl2 and 4,4′‐bipyridine exhibit much higher thermal expansion than the corresponding 2D polymer. This finding suggests that higher dimensionality can induce lower thermal expansion in coordination compounds. The thermal expansion has also been used here to explain the solid‐state phase transformation between the 1D and 2D structures. We anticipate that the dimensionality would be considered as an effective tool in designing new coordination polymers with desired thermal expansion properties and thermal expansion studies would be used in explaining solid‐state phase transformations in many cases.

Thermal expansion anisotropy of β-TlInS2 crystals in the course of phase transitions

ABSTRACTBasing on the thermal expansion studies performed for β-TlInS2 crystals in the course of their phase transitions, we have found that the crystals aged for one year are composed from at least two polytypes, which undergo phase transitions at different temperatures. The detailed analysis of anisotropy of the thermal expansion demonstrates that all of the diagonal components of the thermal expansion tensor associated with the eigensystem have almost the same modules but differ by their signs. This leads to appearance of an elliptical conical surface of zero thermal expansion. The orientation of this surface does not depend on the temperature in the temperature interval under study. We have also found that the thermal expansion coefficients along the crystallographic a and b axes are close to zero.

Thermal Expansion in Organic Crystals

Though a large number of thermal expansion studies have been reported on inorganic systems, a considerably large number on metal–organic-based systems, but those on purely organic systems are too few. Moreover, owing to the complexity of the crystal structure of the organic systems, their thermal expansion behaviors are poorly understood. This review focuses on some interesting thermal expansion studies conducted on purely organic crystals and also on some important structure–property relationships of thermal expansion of organic crystals with intermolecular interactions, melting point of systems, guest molecules in inclusion compounds, and hydrogen bond dimensionality in the crystal structures. Most studies discussed here have been reported in recent years.

Structural, electrical and thermal expansion studies of tri-doped ceria electrolyte materials for IT-SOFCs

Nano crystalline tri-doped ceria Ce1–x(Pr1/3Sm1/3Gd1/3)xO2-δ (x = 0.00, 0.06, 0.12, 0.18, 0.24 and 0.30) solid electrolyte materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) were successfully synthesized by sol-gel auto-combustion method. The X-ray diffraction patterns of prepared compositions confirm the sample formation with a single-phase cubic fluorite structure. Reitveld refinement of all the samples carried out by using Fullprof software. The values of lattice parameter and average crystallite size values were calculated from the XRD patterns and were found to vary from 5.4107 Å to 5.4403 Å and from 18 to 32 nm respectively. Relative densities of all the samples were found above 95% after sintering at 1300 °C for 4 h. Microstructure and elemental composition were studied using scanning electron microscope (SEM) with energy dispersive spectrum (EDS). Evaluation of the concentration of oxygen vacancies of all the samples was carried out using Raman spectroscopy. The electrical properties of tri-doped ceria system were carried out by A.C. impedance spectroscopy in the temperature range from 250 to 600 °C. The investigation on total ionic conductivity was carried out with variation in microstructure and relative oxygen vacancies. It was found that among all the compositions, Ce0.76Pr0.08Sm0.08Gd0.08O2−δ exhibits highest total ionic conductivity and minimum activation energy. The linear thermal expansion measurements revealed moderate linear thermal expansion coefficient for this composition in the temperature range of 30 °C and 1000 °C. Therefore, it is concluded that tri-doped ceria material i.e. Ce0.76Pr0.08Sm0.08Gd0.08O2−δ may possible candidate for use as solid electrolyte in IT-SOFCs.

Studies of Microdefects, Thermal Expansion and Magnetic Properties of Fe-Ni-Co Invar Alloys

The microdefects, the thermal expansion coefficients and the magnetization -temperature curves of the Fe64Ni36-xCox (x=1~10) were characterized by means of positron lifetime, X-ray diffraction, Michelson's interferometer and VSM modular on PPMS, respectively. The Fe64Ni30Co6 alloy is a mixture of BCC and FCC structures. With the Co content increasing in Fe64Ni36-xCox alloys, the BCC phase increases, while the FCC phase decreases. In comparison with other Fe64Ni36-xCox alloys, the Fe64Ni31Co5 alloy has a rather high magnetization at temperature lower than Tc, a relatively large change of the magnetization with the temperature near Tc, and a rather low thermal expansion coefficient.

Photoluminescence and spectral performance of manganese ions in zinc phosphate and barium phosphate host glasses

Zinc and barium metaphosphate glasses containing dopants of MnO2 (2, 4, 8%) were prepared. Collective studies were carried out through optical, photoluminescence and Fourier transform infrared (FTIR) spectral measurements for the prepared glasses before and after gamma irradiation. Electron spin resonance (ESR), thermal expansion and crystallization studies were also investigated. Optical spectra for undoped and MnO2–glasses reveal strong ultraviolet (UV) absorption due to trace iron impurity in the materials used for preparation of glasses and Mn2+ ions are not identified due to spin–forbidden nature of their spectra. Upon gamma irradiation, the MnO2–doped glasses reveal extension of the UV absorption exhibiting two peaks together with the generation of an induced broad visible band centered at 570–580nm. Extra two glasses doped with 8% MnO2 were melted under reducing condition and they showed characteristic band at 410nm related to Mn2+ ions absorption. Photoluminescence (PL) spectra reveal two excitation peaks in MnO2–doped zinc phosphate glasses at 348 and a sharp peak at 410nm while the MnO2–doped barium phosphate glasses exhibit a sharp peak at 410nm and a curvature at 348nm. The emission spectra show a broad band centered at 620nm in both glasses but with a curvature at 605–610nm in zinc phosphate glasses which are correlated with the transition 4T1g→6A1g.The efficiency of the photoluminescence increases with the MnO2 content and the heat treatment. The values of the optical band gap (Eopt) and Urbach energy (∆E) were calculated. FTIR spectra reveal vibrational bands due to phosphate network mainly of metaphosphate groups but in zinc phosphate glasses, the mid spectra show compact network because of the ability of Zn2+ ions to participate partly as ZnO4 or P–O–Zn linkages. Thermal expansion data show different responses. Zinc phosphate glasses show anomalous behavior related to the change in the coordination of zinc cations while barium phosphate glasses exhibit normal expansion because Ba2+ ions exist only as modifiers. The crystallization behavior reflects also anomalous behavior. The zinc phosphate glass crystallizes in two crystalline species, mainly zinc metaphosphate phase and another zinc phosphate (3ZnO·P2O5) phase while the barium phosphate glass crystallizes only in barium metaphosphate phase.

Device for Compressibility and Thermal Expansion Study up to 3 GPa

Device for Compressibility and Thermal Expansion Study up to 3 GPa

Microstructure and thermal characteristics of SiC–Al2O3–Ni composite for high-temperature application

The development of the aviation industry is related to the production of new materials that can operate at high temperatures and corrosive atmospheres. The paper presents new material for application in high temperature obtained by pressing and sintering a composite made from SiC–Al2O3–Ni. Analysis of the microstructure showed high porosity, which is caused by used manufacturing technique. Studies of thermal expansion do not show any phase transition and keeps linearity in thermal expansion in wide range (from 550 to 1450 K). X-ray diffraction showed the presence of all components of phase with those used, the phase associated with the components and silicon oxide, which was formed during the sintering of the samples.

A simple, reliable and cost-effective, high temperature dilatometer for bulk thermal expansion studies on solids

Abstract A simplified, highly reliable, cost effective high temperature (RT-1373 K) vertical dilatometer system, based on linear variable differential transformer (LVDT) has been designed, fabricated and tested for measurement of linear thermal dilation of solid samples. Unique features of this fully automated PC-controlled system are: simple design, fabrication from locally available components, ease of operation and maintenance, good temperature resolution (1 K), wide measurement range (±1 mm, with 100 nm resolution), microcontroller-based data acquisition hardware and a simple windows-based software. The system has been tested for its performance using NIST sapphire reference and high purity metals including aluminum and nickel. Overall accuracy of the system for measurement of linear thermal dilation is within 3% of the reported values for NIST sapphire. The system is a good example of a simple experimental facility for routine thermal expansion characterization of solids. Combination of simplified design, automation and reliable performance without using sophisticated instrumentation/control systems makes it a novel cost effective thermo-analytical equipment, which can be put to widespread routine usage for researchers, academy and small/medium-scale industries.

Relaxor ferroelectricity and electric-field-driven structural transformation in the giant lead-free piezoelectric(Ba,Ca)(Ti,Zr)O3

There is great interest in lead-free (Ba0.85Ca0.15)(Ti0.90Zr0.10)O-3 (15/10BCTZ) because of its exceptionally large piezoelectric response Liu and Ren, Phys. Rev. Lett. 103, 257602 (2009)]. In this paper, we have analyzed the nature of: (i) crystallographic phase coexistence at room temperature, (ii) temperature-and field-induced phase transformation to throw light on the atomistic mechanisms associated with the large piezoelectric response of this system. A detailed temperature-dependent dielectric and lattice thermal expansion study proved that the system exhibits a weak dielectric relaxation, characteristic of a relaxor ferroelectric material on the verge of exhibiting a normal ferroelectric-paraelectric transformation. Careful structural analysis revealed that a ferroelectric state at room temperature is composed of three phase coexistences, tetragonal (P4mm)+ orthorhombic (Amm2) + rhombohedral (R3m). We also demonstrate that the giant piezoresponse is associated with a significant fraction of the tetragonal phase transforming to rhombohedral. It is argued that the polar nanoregions associated with relaxor ferroelectricity amplify the piezoresponse by providing an additional degree of intrinsic structural inhomogeneity to the system.

Does Higher-Dimensional Hydrogen Bonding Guarantee a Smaller Thermal Expansion? A Thermal Expansion Study of an Interdigitated 1D and Interpenetrated 3D Hydrogen-Bonded Colored Dimorphic System

The 1:1:1 complex of benzene-1,3,5-tricarboxylic acid (BTA), 4,4′-methylenebis(2,6-dimethylaniline) (MBDA), and methanol has two polymorphic forms that can be regarded as synthon polymorphs. The hydrogen bond dimensionalities in the crystal structure of the two forms are different, and the forms have their own unique colors. The polymorph, with a three-dimensional hydrogen bond topology (3D form), forms an interpenetrated network and is violet in color, whereas the other polymorph, which is bright yellow in color, forms an interdigitated one-dimensional hydrogen bond topology (1D form). The volumetric expansion of the 3D form is comparable to that of the 1D form, but the anisotropy of expansion is found to be significantly higher in the 3D form than in its 1D counterpart. A structure–property correlation study of the dimorphic complex is presented in the context of their thermal expansion behavior and color.

Thermal Expansion and Electrical Resistivity Studies of Nickel and ARMCO Iron at High Temperatures

The electrical resistance, \(\rho (T)\), and thermal expansion coefficient, \(\beta (T)\), of nickel and ARMCO iron have been simultaneously measured over a wide temperature range from (300 to 1100) K. The well-known standard four-probe potentiometric method was used for measurements of the electrical resistance. The thermal expansion coefficient was measured using the quartz dilatometer technique. Both techniques were combined in the same apparatus for simultaneous measurements of the electrical resistance and TEC for the same specimen. The combined expanded uncertainty of the electrical resistance and thermal expansion coefficient measurements at the 95 % confidence level with a coverage factor of \(k = 2\) is estimated to be 0.5 % and (1.5 to 4.0) %, respectively. The distinct \(\rho (T)\) scattering contribution (phonon \(\rho _{\mathrm{ph}}\), magnetic \(\rho _{\mathrm{m}}\), and residual \(\rho _{\mathrm{S}}\)) terms were separated and extracted from the measured total resistivity. The physical nature and details of the temperature dependence of the electrical resistance of solid materials and correct estimations of the contributions of various scattering mechanisms to the measured total resistivity were discussed in terms of the anharmonic effect. We experimentally found simple, universal, physically based, semiempirical linear correlations between the kinetic coefficient (electrical resistance) and a thermodynamic (equilibrium) property, the thermal expansion coefficient, of solid materials. The developed, physically based, correlation model has been successfully applied for nanoscale materials (ferromagnetic nickel nanowire). A new s-d-exchange interaction energy determination technique has been proposed.

Characterization and thermal expansion of Sr2Fe1-xInxMoO6 (x=0.0, 0.1 and 0.4 wt. %) double perovskites

Double perovskite oxides of Sr2Fe1-xInxMoO6 (x = 0.0, 0.1 and 0.4 wt. %.) were prepared by sol-gel growth followed by annealing under reducing atmosphere conditions of 10% H2/Ar flow. These samples were characterized by X-ray diffraction, Scanning Electron Microscopy and Electron Spin Resonance studies. High temperature thermal expansion studies were carried out using Netzsch 402PC dilatometer in the temperature range from 40 to 400°C. The coefficient of thermal expansion (α) was calculated at different temperature for all the samples. The value of α was found to increase with increase of temperature while average value of coefficient of thermal expansion found to decrease with indium composition in SFIMO materials.

PRODUCTION AND PROPERTIES OF GLASSES (GeS&lt;sub&gt;2&lt;/sub&gt;)&lt;sub&gt;X&lt;/sub&gt;(AsSBr)&lt;sub&gt;1-X&lt;/sub&gt;

The features of the synthesis, the results of studies of vibrational spectra and thermal expansion сhalkohalogenide glasses cut (GeS2)X(AsSBr)1-X are considered. Conclusions about structural features and structural relaxation of these materials are made on the basis of infrared spectra, Raman spectra, temperature dependence of the relative elongation of samples. Keywords: synthesis, glassy structure, oscillating spectra, Raman scattering, thermal expansion.

Phase transition and thermal expansion studies of alumina thin films prepared by reactive pulsed laser deposition.

Aluminium oxide (Al2O3) thin films were deposited on Si (100) substrates at an optimized oxygen partial pressure of 3 x 10(-3) mbar at room temperature by pulsed laser deposition (PLD). The films were characterized by high temperature X-ray diffraction (HTXRD), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The HTXRD pattern showed the cubic y-Al2O3 phase in the temperature range 300-973 K. At temperatures ≥ 1073 K, the δ and θ-phases of Al2O3 were observed. The mean linear thermal expansion coefficient and volume thermal expansion coefficient of γ-Al2O3 was found to be 12.66 x 10(-6) K(-1) and 38.87 x 10(-6) K(-1) in the temperature range 300 K-1073 K. The field emission scanning electron microscopy revealed a smooth and structureless morphology of the films deposited on Si (100). The atomic force microscopy study indicated the increased crystallinity and surface roughness of the films after annealing at high temperature.

Dielectric, thermal and ferroelectric properties of Na0.997Li0.003NbO3 ceramics

Na0.997Li0.003NbO3 ceramics of 93% density have been prepared by a solid-state chemical reaction of stoichiometric mixtures of the component oxides and carbonates. The dielectric, thermal expansion, heat capacity, Raman and ferroelectric studies of these ceramics have been performed. The electric permittivity peak shows rather a small dispersion and no change of the maximum position with increasing frequency can be observed. The results clearly show a first-order phase transition at about 375 °C on heating and near 310 °C on cooling and ambiguously indicated another phase transitions. The pyroelectric measurements show for the first time that the material has weak ferroelectric properties, which are rather metastable. The results show that the investigated ceramics are one of the promising lead-free materials for electronic applications.

Thermal expansion of beryllium oxide in the temperature interval 20–1550°C

The results of studies of thermal expansion of the sintered beryllium oxide in the temperature interval 20–1550°C are presented. Measurements were performed by a dilatometric method on a DIL-402C set-up manufactured by NETZSCH (Germany), with the accuracy of (1.5–2) × 10−7 K−1. Approximation dependences of coefficients of linear thermal expansion on temperature have been obtained and reference tables calculated. The data obtained are compared with data from the available literature.

Effect of nano/micro-mixed ceramic fillers on the dielectric and thermal properties of epoxy polymer composites

Nano/micro ceramic-filled epoxy composite materials have been processed with various percentage additions of SiO2, Al2O3 ceramic fillers as reinforcements selected from the nano and micro origin sources. Different types of filler combinations, viz. only nano, only micro, nano/micro, and micro/micro particles, were designed to investigate their influence on the thermal expansion, thermal conductivity, and dielectric properties of epoxy polymers. Thermal expansion studies were conducted using thermomechanical analysis that revealed a two-step expansion pattern consecutively before and after vitreous transition temperatures. The presence of micro fillers have shown vitreous transition temperature in the range 70–80°C compared with that of nano structured composites in which the same was observed as ~90°C. Similarly, the bulk thermal conductivity is found to increase with increasing percentage of micron-size Al2O3. It was established that the addition of micro fillers lead to epoxy composite materials that exhibited lower thermal expansion and higher thermal conductivity compared with nano fillers. Moreover, nano fillers have a significantly decisive role in having low bulk dielectric permittivity. In this study, epoxy composites with a thermal expansion coefficient of 2.5 × 10−5/K, thermal conductivity of 1.18 W/m · K and dielectric permittivity in the range 4–5 at 1 kHz have been obtained. The study confirms that although the micro fillers seem to exhibit good thermal conductivity and low expansion coefficient, the nano-size ceramic fillers are candidate as cofillers for low dielectric permittivity. However, a suitable proportion of nano/micro-mixed fillers is necessary for achieving epoxy composites with promising thermal conductivity, controlled coefficient of thermal expansion and dielectric permittivity. Copyright © 2013 John Wiley & Sons, Ltd.

Preparation and structure of BiCrTeO6: A new compound in Bi–Cr–Te–O system. Thermal expansion studies of Cr2TeO6, Bi2TeO6 and BiCrTeO6

A new compound BiCrTeO6 in Bi–Cr–Te–O system was prepared by solid state reaction of Bi2O3, Cr2O3 and H6TeO6 in oxygen and characterized by X-ray diffraction (XRD) method. It could be indexed on a trigonal lattice, with the space group P-31c, unit cell parameters a=5.16268(7)Å and c=9.91861(17)Å. The crystal structure of BiCrTeO6 was determined by Rietveld refinement method using the powder XRD data. Structure shows that there is one distinct site for bismuth (Bi) atom, one chromium rich (Cr/Te=68/32), and one tellurium rich (Te/Cr=68/32) sites, and one distinct site for oxygen (O) atom in the unit cell. All cations in this structure show an octahedral coordination with oxygen atoms at the corners. The thermogravimetric analysis (TGA) of the compound in air shows that it is stable up to 1103K and decomposes thereafter. The thermal expansion behavior of Cr2TeO6, Bi2TeO6 and BiCrTeO6 was studied using High Temperature X-ray diffraction (HTXRD) method from room temperature to 973, 873 and 923K respectively under vacuum of 10−8 atmospheres. All the compounds showed positive thermal expansion with the average volume thermal expansion coefficients of 14.38×10−6/K, 22.0×10−6/K and 16.0×10−6/K respectively.