Linear Thermal Expansion Behavior Research Articles

The atomistic study on the thermal expansion behaviors of nanowires

The thermal expansion coefficient of copper nanowire and bulk was investigated using molecular dynamics simulation in the temperature range up to 900 K. Both the size and crystal orientation effects on the thermal expansion coefficients of nanowires were studied. It is noticed that the linear thermal expansion is isotropic for single-crystalline bulk copper and the linear thermal expansion coefficient is exactly one third of the volumetric thermal expansion coefficient irrespective to the crystal orientations. The axial linear thermal expansion coefficient of an infinite long nanowire would be affected by both the surface and axial crystal orientation. Different temperature dependencies of lattice parameter and thermal expansion coefficient were found for nanowires with different width, and there is a transition from positive thermal expansion coefficient at low temperature to negative one at high temperature for the thinnest nanowires along [1 0 0] direction. However, the negative linear thermal expansion is not observed for nanowires along [1 1 0] and [1 1 1] direction. From the examination of the atomic configuration and radial distribution function for the thinnest [1 0 0] nanowires at various temperatures, it is concluded that the negative linear thermal expansion behavior is not caused by melting or the phase transformation.

Synthesis and properties of mullite-type (Bi 1− xSr x) 2(M 11− yM 2y) 4O 9− x (M = Al, Ga, Fe)

Mullite-type A 2M 4O 9 phases (M = Al, Ga, Fe), representing promising oxygen conducting materials for solid oxide fuel cells (SOFCs), were synthesized using the glycerine- and the EDTA/citric acid synthesis method. For strontium-doped material pure phases could be obtained only by washing the samples after the heating in both synthesis methods. Temperature dependent investigations were carried out to show the influence of the metal atoms on the structural stability and thermal expansion coefficients. Whereas the Sr-free phases show a quasi linear thermal expansion behavior in all three directions up to their incongruent melting points, a discontinuity in the measured range is observed for the investigated strontium doped dibismuth-nonaoxotetrametallate(III) caused by the decomposition into Bi 2M 4O 9, strontium metallates and bismuthoxide. Big single crystals were only observed for the Sr-free compound, of which the structure of Bi 2(Ga 0.45Fe 0.55) 4O 9 will be presented here in the Bärnighausen tree corresponding mullite-type setting.

Synthesis and Characterization of Nanocrystalline MnCo2O4-δ Spinel for Protective Coating Application in SOFC

Nanocrystalline (40-50 nm) powders of MnCo2O4-δ spinel have been synthesized through combustion technique at a relatively low temperature. The fuel to oxidant ratio has been optimized by carrying out the combustion reaction under various redox conditions (i.e. varying fuel : nitrate ratio) using different fuels viz., citric acid and glycine. A controlled combustion of the complex gel is achieved under a fuel lean condition using a mixed fuel of glycine and citric acid. Phase pure materials are obtained upon calcination of the ash at a temperature as low as 650degC and the powder can be consolidated to more than 95% of theoretical density at a temperature of only 1100degC. The bulk samples show a linear thermal expansion behaviour (CTE: 13.1 x 10-6 K-1) and a high electrical conductivity (>100 S/cm at 800degC). Crofer22APU interconnect plates are deposited with the synthesized powder using electrophoretic deposition (EPD) technique for protective coating application.

Synthesis and physicochemical characterization of nanocrystalline cobalt doped lanthanum strontium ferrite

Nanosized crystallites of La 0.6Sr 0.4Fe 0.8Co 0.2O 3− δ (LSCF), a promising cathode material for Intermediate Temperature-Solid Oxide Fuel Cells (IT-SOFCs) has been synthesized by alternative methods like ceramic route, polymerisable complex process and gel-combustion method and calcined at different temperatures. X-ray diffraction studies were used for the determination of phase purity, crystal structure and average crystallite size of the samples. Microstructure of LSCF samples was studied by SEM. Temperature-programmed reduction studies were done for evaluating the redox behavior of the samples prepared by alternative methods. The electrical conductivity measurements of sintered samples were carried out at elevated temperatures using four-probe method. The electrical conductivity of sample synthesized by gel-combustion method was more as compared to sample prepared by polymerisable complex process and ceramic route. The electrical conductivity decreased at high temperature due to loss of oxygen and the formation of oxygen vacancies. Thermo-dilatometry was used to study the linear thermal expansion behavior of the samples which shows that there is an observable increase in thermal expansion at high temperatures.

Thermal- and stress-induced lattice distortions in a single Kevlar49 fibre studied by microfocus X-ray diffraction

Understanding the macroscopic physical and mechanical properties of poly(p-phenylene terephthalamide) (PpTA) fibres as a function of temperature requires an understanding of how temperature influences its microscopic structure. This study investigates lattice distortions in single PpTA fibres using the high brilliance of a synchrotron radiation microbeam. Lattice distortions are studied over a temperature range of 110–350 K and the influence of tensile deformation is also considered. The results reveal linear thermal expansion behaviour for all unit cell axes, in general agreement with literature. Expansion/contraction is greatest along the [100] direction whilst being reduced along [010] by inter-chain hydrogen bonding. During macroscopic deformation, longitudinal crystal strain dominates with respect to axial lattice distortions induced by temperature changes. There is only a small change in the [100] coefficient of thermal expansion, with the [010] and [001] directions being largely unaffected.

Structure, electrical, and thermal expansion properties of (La0.8Ca0.2)(Cr0.9–xCo0.1Nix)O3–δinterconnect materials for intermediate temperature solid oxide fuel cells

The microstructure, lattice parameters, electrical conductivity, thermal expansion, and mechanical properties of (La0.8Ca0.2)(Cr0.9–xCo0.1Nix)O3–δ(x= 0.03, 0.06, 0.09, 0.12) were systematically investigated in this work. Nickel doping of (La0.8Ca0.2)(Cr0.9Co0.1)O3–δis an effective way of increasing the thermal expansion coefficient (TEC) and stabilizing the high-temperature phase transformation from rhombohedral to tetragonal. As the nickel-doped content increases, the TEC increases parabolically by TEC (x) (ppm/°C) = 10.575 + 63.3x−240x2(x= 0.03−0.12). The electrical conductivity of (La0.8Ca0.2)(Cr0.9–xCo0.1Nix)O3–δspecimens increases systematically with increasing nickel substitution in the range of 0.03 ≤x≤ 0.09 and reaches a maximum for the composition of (La0.8Ca0.2)(Cr0.81Co0.1Ni0.09)O3–δ(σ850 °C∼60.36 S/cm). There is a slight increase in the fracture toughness with increasing nickel doping content, and the fracture toughness is strongly affected by the grain size. It seems that there is an increase in the fracture toughness with decreasing grain size. However, the microhardness does not significantly depend on the grain size in this study. The (La0.8Ca0.2)(Cr0.81Co0.1Ni0.09)O3–δspecimen shows high electrical conductivity, a moderate thermal expansion coefficient, and nearly linear thermal expansion behavior from room temperature to 800 °C. It will be suitable for interconnect materials for intermediate temperature solid oxide fuel cells (IT-SOFCs).

Effect of the ratio of maleated polypropylene to organoclay on the structure and properties of TPO-based nanocomposites. Part II: Thermal expansion behavior

Significant reductions in linear thermal expansion coefficients in the flow and transverse directions of injection-molded specimens of thermoplastic polyolefin, or TPO, nanocomposites were achieved by controlling the maleated polypropylene (PP-g-MA)/organoclay ratio. Linear thermal expansion behavior was examined using a thermomechanical analyzer (TMA). The trends in thermal expansion for the nanocomposites are discussed in terms of the morphology of both dispersed clay and elastomer phases by means of transmission electron microscopic (TEM) and atomic force microscopic (AFM) observations and subsequent particle analyses. A higher PP-g-MA/organoclay ratio causes an increase in the aspect ratio of clay particles along the flow direction (FD) and transverse direction (TD) for the injection-molded specimens; however, the aspect ratio along the FD was higher than that along the TD. On the other hand, the aspect ratio of elastomer particles along the FD was much higher than that along the TD. Furthermore, highly elongated elastomer particles along the FD were observed. The combined effect of the mechanical constraint by organoclay and the highly elongated elastomer particles caused at high PP-g-MA contents was responsible for the significant reduction of thermal expansion for these materials.

Temperature-insensitive fiber Bragg grating tilt sensor

A temperature-insensitive optical fiber tilt sensor is presented. The sensor scheme uses a prestrained fiber Bragg grating to sense the strain, which depends on the tilt angle. To compensate for the temperature effect, materials that have different linear thermal expansion behaviors are used for implementation of the sensor body. The differentiation in the linear thermal expansion would then cause a counter effect to the original temperature effect. Experimental tests show an accuracy of +/-0.167 degrees in tilt angle measurement. A temperature stability better than +/-0.33 degrees over the temperature range from 27 degrees C to 75 degrees C is demonstrated. The resolution 0.0067 degrees in tilt angle measurement is achieved by using our preliminary sensor with a dimension of 1 6 x 5 x 5 cm(3).

High temperature thermal expansion and electrical conductivity of Ln 0.95MnO 3+ δ (Ln = La, Nd or Gd)

The rare earth deficient manganites Ln 0.95MnO 3+ δ (Ln = La, Nd or Gd) have been prepared by conventional ceramic method as well as by wet chemical methods like nitrate route and sol–gel route. Structural transformation, thermal expansion and electrical conductivity at elevated temperature were investigated on Ln 0.95MnO 3+ δ . The X-ray diffraction studies revealed that crystal symmetry of all the rare earth deficient manganites prepared either by sol–gel or solid-state route showed orthorhombic symmetry except lanthanum manganite prepared by solid-state route and the nitrate route. The thermal expansion behavior was studied using thermo-dilatometry and high temperature XRD techniques. The electrical conductivity studies of Ln 0.95MnO 3+ δ showed a clear phase transformation in case of La 0.95MnO 3+ δ synthesized by solid state route which was missing in all other rare earth manganites prepared by solid state and nitrate routes and wet chemical method. A comparative study on their linear thermal expansion behavior indicates that the value of coefficient of thermal expansion ( α) reduces to half as it goes from La to Gd. The electrical conductivity of sample synthesized by nitrate route was more as compared to sample prepared by other route like ceramic or sol–gel.

TPO based nanocomposites. Part 2. Thermal expansion behavior

The linear thermal expansion behavior of thermoplastic polyolefin, or TPO, nanocomposites based on a polypropylene/elastomer/masterbatch mixture was examined using a thermomechanical analyzer (TMA). For these experiments the masterbatch consisted of a mixture of organoclay and maleated polypropylene. The nanocomposites were prepared in a twin-screw extruder. The effects of both the elastomer domains and the filler particles on the thermal expansion behavior of the nanocomposites were investigated by means of transmission electron microscopy (TEM) and atomic force microscopy (AFM). The addition of elastomer tends to increase the linear coefficient of thermal expansion, CTE. On the other hand, the addition of clay significantly reduces the thermal expansion in both the flow (FD) and transverse directions (TD) of injection molded specimens; however, the extent of reduction of CTE in the FD is much greater than in the TD. The CTE in the normal direction (ND) increases when either the clay or elastomer content is increased. The trends in thermal expansion for the nanocomposites are discussed in terms of the morphology of both dispersed clay and elastomer phases based on TEM and AFM observations and subsequent particle analyses.

Effect of long-term heating and thermal cycling on thermal expansion, phase distribution, and microhardness of lithium aluminosilicate glass-ceramics

Lithium aluminosilicate glass-ceramics prepared by two different devitrification procedures were subjected to thermal cycling and heat treatment at 700 and 800 °C for up to 16 days in air. Changes in microstructure, phase distribution, microhardness, and thermal expansion behavior were monitored. Glass-ceramics prepared with a 950 °C nucleation step were observed to have various advantages over those prepared with a 1000 °C nucleation treatment. These advantages include finer microstructure, higher microhardness, and an almost linear thermal expansion behavior in the as-devitrified state. Additionally, no significant changes in physical properties were detected in the 950 °C-devitrified samples, while 1000 °C-devitrified glass-ceramics were found to be thermally unstable, causing important property changes, jeopardizing their reliability.

Ga-filled single-crystalline MgO nanotube: Wide-temperature range nanothermometer

A highly effective one-step approach was developed to synthesize single-crystalline MgO nanotubes and in situ fill nanotubes with Ga. The axes of nanotubes are in the [100] direction of cubic MgO. The prepared nanotube exhibits a square-like cross section both for its interior and exterior. The liquid metal-assisted route is suggested to be a general way to prepare oxide nanotubes. Linear thermal expansion behavior recorded for liquid gallium column confined in the MgO nanotube makes possible creation of a wide-temperature range nanothermometer with superior mechanical properties and environmental structural stability.

Thermal expansion behavior of nylon 6 nanocomposites

The linear thermal expansion behavior of nanocomposites was measured and compared with the theory by Chow. Nanocomposites were prepared by melt mixing organically modified montmorillonite with high and low molecular weight (LMW) grades of nylon 6 using a twin screw extruder. Thermal expansion measurements were made on samples taken from injection-molded Izod bars in the flow direction (FD), transverse direction (TD), and normal direction (ND). Addition of clay reduces the thermal expansion coefficient in both FD and TD while an increase is seen in ND; FD has a lower thermal expansion coefficient than TD. The latter suggests non-uniform orientation of exfoliated platelets about FD, since perfect alignment of disk-like platelets in an isotropic matrix must yield identical expansion coefficients for both FD and TD. High molecular weight (HMW) nylon 6 nanocomposites resulted in lower thermal expansion than LMW nylon 6 nanocomposites at the same organoclay content. This difference was attributed to the higher aspect ratio of particles (better exfoliation) in HMW nylon 6 nanocomposites. Thermal expansion coefficients predicted from a theoretical composite model were compared to the experimental data. Platelet aspect ratios deduced in this way were found to be dependent on the specimen direction, which further suggests imperfect orientation of particles about FD. Morphological analysis by transmission electron microscopy support the conclusions drawn above.

Control of the Thermal Expansion of Strontium‐Doped Lanthanum Chromite Perovskites by B‐site Doping for High‐Temperature Solid Oxide Fuel Cell Separators

The thermal expansion of La0.9Sr0.1Cr1‐xMxO3(M = Mg, Al, Ti, Mn, Fe, Co, Ni; 0 ≤x≤ 0.1) perovskites has been studied in oxidizing and reducing atmospheres in the temperature range from 50° to 1000°C. Cobalt doping of La0.9Sr0.1CrO3was an effective way of increasing the average linear thermal expansion coefficient (TEC), whereas titanium doping showed a negative effect. No effect on the TECs was observed for the B‐site dopants in perovskites with the remaining dopants. Linear thermal expansion behavior was observed in the La0.9Sr0.1Cr1‐xMxO3 perovskites with doping of ≥1 mol% aluminum or 10 mol% cobalt. TECs of La0.9Sr0.1Cr0.96Co0.02Al0.02O3 were 10.5 × 10−6/°C in air, 10.7 × 10−6/°C under He–H2 atmosphere (oxygen partial pressure of 4 × 10−15 atm at 1000°C), and 11.8 × 10−6/°C in H2 atmosphere.

Anisotropic thermal expansion of MgSiN2 from 10 to 300 K as measured by neutron diffraction

The lattice parameters of orthorhombic MgSiN2 as a function of the temperature have been determined from time-of-flight neutron powder diffraction. The results indicate that MgSiN2, just like several other adamantine-type crystals, exhibits a relatively small thermal expansion coefficient at low temperatures. This is ascribed to a strongly bonded 3D, relatively open, crystal structure which is characteristic of highly covalent bonded materials. The anisotropic linear thermal expansion behaviour could be qualitatively related to the characteristics of the crystal structure. The least dense packed crystallographic direction showed the smallest anisotropic linear expansion coefficient.

Thermomechanical behaviour of semicrystallinepolymers submitted to plane-strain compression

High-density polyethylene (HDPE) and poly(vinylidene fluoride) (PVF 2) were submitted to plane-straincompression at temperatures between the glass transition temperature ( T g) and the melting point ( T m) by using a deep channel die; this device allowed compression along the Z-axis, elongation along the X-axis and no dimensional change along the Y-axis. The thermomechanical and morphological changes occurring during the plastic deformation process and relaxation of the deformed materials were investigated by thermomechanical analysis, differential scanning calorimetry and density measurements. The results show that the deformation process affects the thermodynamic properties of polymers, introducing different characteristics into the material. An increase of amorphous phase was registered in both materials. The plastically deformed semicrystalline polymers showed non-regular linear thermal expansion behaviour in the deformation directions ( X and Z). The relaxation process, which is obtained by heating the deformed materials, is characterized by ‘shape and temperature memory’.

Thermal expansion, Debye temperature and Gr�neisen parameter of synthetic (Fe, Mg)SiO3 orthopyroxenes

Thermal expansion properties of synthetic orthopyroxenes (Fe0.20Mg0.80)SiO3, (Fe0.40Mg0.60)SiO3, (Fe0.50Mg0.50)SiO3, (Fe0.75Mg0.25)SiO3 and (Fe0.83Mg0.17)SiO3 were systematically studied by means of single-crystal x-ray diffraction in the temperature range from 296 to 1300 K. The measurements of unit cell dimensions as a function of temperature reveal that the a and c dimensions and the unit cell volume V increase nonlinearly with a positive curvature with rising temperature, whereas the b dimension behaves differently, depending on the total Fe content. For Mg-rich orthopyroxenes (Fe/(Fe+Mg) 30%. Together with the high temperature neutron diffraction data on enstatite (MgSiO3) (McMullan, Haga and Ghose, unpublished) and x-ray diffraction data on ferrosilite (FeSiO3) (Sueno et al. 1976), the measured unit cell dimensions were analyzed in terms of the Gruneisen theory of thermal expansion. The linear thermal expansion coefficients α a and α c both increase as temperature is elevated, with α c increasing faster, while α b changes gradually from increasing for Mg-rich orthopyroxenes to decreasing for Fe-rich orthopyroxenes. The relative magnitudes of linear thermal expansion coefficients are always in the order α b >α c >α a between 300 and 500 K, but at higher temperatures, the order changes to α c >α b >α a for Mg-rich orthopyroxenes and α c >α a >α b for Fe-rich ones. The linear thermal expansion behavior is interpreted on the basis of the structural mechanical model of Weidner and Vaughan (1982). The anomalous behavior of α b is mainly attributed to the changes in the Fe2+ population at the M2 site and the relative stiffness of the M2(Fe2+)-O bonds compared to the M2(Mg2+)-O bonds. The volume thermal expansion coefficients are nonlinear functions of temperature and lie between 23 and 49×10−6/K. The previously reported results of mean volume thermal expansion coefficients appear to represent the α V values characteristic of higher temperatures compared to our results. The thermal Debye temperatures are composition-dependent, decreasing linearly from 812 (MgSiO3) to 561 K (FeSiO3), and are systematically higher than the corresponding acoustic Debye temperatures. The Gruneisen parameters range from 0.85 to 0.89 and do not seem to vary with composition. The linear compressibilities derived from thermal expansion and elastic moduli data agree very well. The pressure derivatives of the isothermal bulk modulus (dK0/dP) are also composition-dependent and decrease from 11.2 (MgSiO3) to 8.77 (FeSiO3). Such large values indicate possible anomalous elastic behavior of orthopyroxenes at high pressures in the Earth's upper mantle.

Linear viscoelastic properties of epoxy resin polymers in dilatation and shear in the glass transition region: 2. Measurement of the glass transition temperature

Measurements of the 20 second creep compliances in dilatation and shear, over a range of temperature spanning the glass transition region, have been made for six epoxy resin polymers. The linear thermal expansion behaviour has been determined in the same temperature range. Shear and dilatational compliances, and the linear thermal expansion properties may all be measured on the same specimen. Values of the glass transition temperature derived from 20 sec shear and bulk compliance data agree well with values obtained from thermal expansion data. When T g was derived from creep data obtained at longer creep times (in part 1 of this paper), it was found that T g in dilatation exceeds T g in shear. It was shown that this is consistent with the difference in activation energies in dilatation and shear obtained in part 1 of this paper. An example is given of how systematic errors of the order of 1°C in temperature measurement may lead to maxima or minima when Poisson's ratio is calculated from measured values of shear and tensile compliances.

The magnetic susceptibility of niobium

The magnetic susceptibilities of several grades of niobium have been measured in the temperature range 78–400 K. For very-high-purity metal it is concluded that χ 300K = 214.1 ± 0.3 μ emu/mole. The susceptibility temperature dependence is not uniformly linear within 78–400 K but changes slope at 160 K, a temperature at which a change also seems to take place in the linear thermal expansion behavior. The susceptibility temperature dependences of high-purity niobium are: ∂χ ∂T (78–160 K) = −1.9 × 10 −2 μ emu/mole deg , and ∂χ ∂T (160–300 K) = −3.4 × 10 −2 μ emu/mole deg . Also considered are the influences of contamination by tantalum, and by oxygen.

The System ThO2‐P2O5

The existence of compounds with 1:1, 3:2, and 3:1 ThO2:P2O5 ratios in the system ThO2‐P2O5 was confirmed. A 1:2 compound found by previous workers was not investigated, and their 2:1 compound was not detected; however, extensive solid solution on either side of the 3:2 compound was established. The linear thermal expansion behavior of the compounds and solid solutions was determined.