Showing papers on "Thermal expansion published in 2006"

Fundamentals of Inorganic Glasses

Abstract: Introduction. Fundamentals of the Glassy State. Glass Formation Principles. Glass Microstructure: Phase Separation and Liquid Immiscibility. Glass Compositions and Structures. Composition-Structure-Property Relationship Principles. Density and Molar Volume. Elastic Properties and Microhardness of Glass. The Viscosity of Glass. Thermal Expansion of Glass. Heat Capacity of Glass. Thermal Conductivity and Heat Transfer in Glass. Glass Transition Range Behavior. Permeation, Diffusion and Ionic Conduction in Glass. Dielectric Properties. Electronic Conduction. Chemical Durability. Strength and Toughness. Optical Properties. Fundamentals of Inorganic Glassmaking. Appendix I: Elements of Linear Elasticity. Appendix II: Units and General Data Conversions. Subject Index.

Enhanced thermal conductivity of polymer composites filled with hybrid filler

Abstract: This study aims at investigating package materials based on polymer matrix for microelectronics. The next generation package materials are expected to possess high heat dissipation capability in addition to low coefficient of thermal expansion (CTE) as the accumulated heat from high performance electronic devices should be removed for proper operation. In this study, various inorganic fillers including aluminum nitride (AlN), wollastonite, silicon carbide whisker (SiC) and boron nitride (BN) with different shape and size were used alone or in combination to prepare thermally conductive polymer composites. In case of AlN, titanate coupling agent was used for the surface treatment of fillers. The use of hybrid filler was found to be effective in increasing thermal conductivity of the composite probably due to the enhanced connectivity offered by structuring filler with high aspect ratio in hybrid filler. For given filler loading, the use of larger particle and surface treated filler resulted in composite materials with enhanced thermal conductivity. The surface treatment of filler also allowed producing the composites with lower CTE.

Oxygen stoichiometry and chemical expansion of Ba0.5Sr0.5Co0.8Fe0.2O3- δ measured by in situ neutron diffraction

Abstract: The structure, oxygen stoichiometry, and chemical and thermal expansion of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) between 873 and 1173 K and oxygen partial pressures of 1 × 10-3 to 1 atm were determined by in situ neutron diffraction. BSCF has a cubic perovskite structure, space group Pm3m, across the whole T−pO2 region investigated. The material is highly oxygen deficient with a maximum oxygen stoichiometry (3 − δ) of 2.339(12) at 873 K and a pO2 of 1 atm and a minimum of 2.192(15) at 1173 K and a pO2 of 10-3 atm. Good agreement is obtained between oxygen stoichiometry data determined by neutron diffraction and thermogravimetry. In the range covered by the experiments, the thermal and chemical expansion coefficients are 19.0(5)−20.8(6) × 10-6 K-1 and 0.016(2)−0.026(4), respectively.

New double-ceramic-layer thermal barrier coatings based on zirconia–rare earth composite oxides

Abstract: A series of La 2 O 3 –ZrO 2 –CeO 2 composite oxides were synthesized by solid-state reaction The final product keeps fluorite structure when the molar ratio Ce/Zr ≥ 07/03, and below this ratio only mixtures of La 2 Zr 2 O 7 (pyrochlore) and La 2 O 3 –CeO 2 (fluorite) exist Averagely speaking, the increase of CeO 2 content gives rise to the increase of thermal expansion coefficient and the reduction of thermal conductivity, but La 2 (Zr 07 Ce 03 ) 2 O 7 has the lowest sintering ability and the lowest thermal conductivity which could be explained by the theory of phonon scattering Based on the large thermal expansion coefficient of La 2 Ce 325 O 95 , the low thermal conductivities and low sintering abilities of La 2 Zr 2 O 7 and La 2 (Zr 07 Ce 03 ) 2 O 7 , double-ceramic-layer thermal barrier coatings were prepared The thermal cycling tests indicate that such a design can largely improve the thermal cycling lives of the coatings Since no single material that has been studied so far satisfies all the requirements for high temperature thermal barrier coatings, double-ceramic-layer coating may be an important development direction of thermal barrier coatings

Crystal structure, thermal expansion and electrical conductivity of perovskite oxides BaxSr1-xCo0.8Fe0.2O3-δ (0.3 ≤ x ≤ 0.7)

Abstract: BaxSr1-xCo0.8Fe0.2O3-delta (0.3 0.5 compositions. Furthermore, conductivity relaxation behaviors were also investigated at temperature 400-550 degrees C. Generally, Ba0.4Sr0.6Co0.8Fe0.2O3-delta and Ba0.5Sr0.5Co0.8Fe0.2O3-delta are potential cathode materials. (c) 2005 Elsevier Ltd. All rights reserved.

Thermal behavior of single-walled carbon nanotube polymer–matrix composites

Abstract: Single-walled carbon nanotube (SWNT)–poly(vinylidene fluoride) (PVDF) composites were fabricated by dispersion of SWNT in an aqueous surfactant solution, followed by mixing with PVDF powder, filtration and hot pressing. The thermal properties of the composites at various SWNT volume fraction up to 49% were investigated. The coefficient of thermal expansion (CTE) was decreased with increase of the SWNT content. The thermal conductivity increased with temperature in the temperature range from 25 to 150 °C. The thermal conductivity was enhanced, but not up to the level required by heat sink applications. The melting point was not affected significantly by the addition of SWNT, but the degree of crystallinity was increased and the decomposition temperature of the matrix was decreased. The large number of junctions among SWNT largely offsets the benefit of the high thermal conductivity of SWNT. In addition, the impurity and defects in SWNT are believed to limit the thermal conductivity of the composites. Lastly, the reduced thermal stability of the composite compared to the matrix might result from the presence of the metal catalyst contained in the SWNT.

Yttria-stabilized zirconia thermal barrier coatings — a review

Abstract: Thermal barrier coatings (TBCs), which protect metallic components from high-temperature environments, have been widely applied to the fields of high-temperature and corrosion-resistant structural parts such as gas turbine engines, diesel engines, and power generation systems. Yttria-stabilized zirconia (YSZ) is one of the most widely used materials for TBCs owing to its excellent shock resistance, low-thermal conductivity, and relatively high coefficient of thermal expansion. In this paper the properties of YSZ and the recent developments of YSZ-TBCs are reviewed. The failure mechanism of YSZ-TBCs and corresponding methods for lengthening the lifetime of YSZ-TBCs are discussed. The advantages of graded thermal barrier coatings and the problems in processing are elucidated.

Fiber-content dependency of the optical transparency and thermal expansion of bacterial nanofiber reinforced composites

Abstract: We produced transparent nanocomposite reinforced with bacterial cellulose having a wide range of fiber contents, from 7.4to66.1wt%, by the combination of heat drying and organic solvent exchange methods. The addition of only 7.4wt% of bacterial cellulose nanofibers, which deteriorated light transmittance by only 2.4%, was able to reduce the coefficient of thermal expansion of acrylic resin from 86×10−6to38×10−6K−1. As such, the nanofiber network of bacterial cellulose has an extraordinary potential as a reinforcement to obtain optically transparent and low thermal expansion materials.

Temperature Dependence of Physical Properties of Ionic Liquid 1,3-Dimethylimidazolium Methyl Sulfate

Abstract: This paper reports on the synthesis of the ionic liquid 1,3-dimethylimidazolium methyl sulfate [MMIM][MeSO4]. Experimental densities, speed of sounds, and refractive indices were determined from (283.15 to 343.15) K. Dynamic viscosities were measured from (293.15 to 343.15) K. Surface tensions were measured from (288.15 to 313.15) K. The coefficient of thermal expansion and molecular volume of [MMIM][MeSO4] were calculated from experimental values of density.

Measurement of the Electronic Grüneisen Constant Using Femtosecond Electron Diffraction

Abstract: We report the first accurate measurement of the electronic Gruneisen constant gamma(e) using a novel method employing the new technique of femtosecond electron diffraction. The contributions of the conduction electrons and the lattice to thermal expansion are differentiated in the time domain through transiently heating the electronic temperature well above that of the lattice with femtosecond optical pulses. By directly probing the associated thermal expansion dynamics in real time using femtosecond electron diffraction, we are able to separate the contributions of hot electrons from that of lattice heating, and make an accurate measurement of gamma(e) of aluminum at room temperature. This new approach opens the possibility of distinguishing electronic from magnetic contributions to thermal expansion in magnetic materials at low temperature.

The thermal cycling behavior of Lanthanum–Cerium Oxide thermal barrier coating prepared by EB–PVD

Abstract: Bulk material and coatings of Lanthanum–Cerium Oxide (La2Ce2O7) with a fluorite structure were studied as a candidate material for thermal barrier coating (TBC). It has been showed that such material has the properties of low thermal conductivity about four times lower than YSZ, the difference in the thermal expansion coefficient between La2Ce2O7 and bond coat is smaller than that of YSZ in TBC systems, high phase stability between room temperature and 1673 K, about 300 K higher than that of the YSZ. The coating prepared by electron beam physical vapor deposition (EB–PVD) showed that it has good thermal cycling behavior, implying that such material can be a promising thermal barrier coating material. The deviation of coating composition from ingot can be overcome by the addition of excess La2O3 during ingot preparation and/or by adjusting the process parameters.

Structure and negative thermal expansion in the PbTiO3–BiFeO3 system

Abstract: The structures of (1−x)PbTiO3–xBiFeO3 (x=0.3 and 0.6) were investigated by means of the neutron powder diffraction. A splitting shift between Fe and Ti atoms was found along the c axis in 0.7PbTiO3–0.3BiFeO3; however, this splitting does not appear in 0.4PbTiO3–0.6BiFeO3. The tetragonal phase of PbTiO3–BiFeO3 exhibits a large spontaneous polarization. The negative thermal expansion of PbTiO3 is significantly enhanced in a wide temperature range by the BiFeO3 substitution. The average bulk thermal expansion coefficient of 0.4PbTiO3–0.6BiFeO3 is a¯v=−3.92×10−5°C−1, which is much strong in the known negative thermal expansion oxides.

Impulsive solvent heating probed by picosecond x-ray diffraction.

Abstract: The time-resolved diffraction signal from a laser-excited solution has three principal components: the solute-only term, the solute-solvent cross term, and the solvent-only term. The last term is very sensitive to the thermodynamic state of the bulk solvent, which may change during a chemical reaction due to energy transfer from light-absorbing solute molecules to the surrounding solvent molecules and the following relaxation to equilibrium with the environment around the scattering volume. The volume expansion coefficient alpha for a liquid is typically approximately 1 x 10(-3) K(-1), which is about 1000 times greater than for a solid. Hence solvent scattering is a very sensitive on-line thermometer. The decomposition of the scattered x-ray signal has so far been aided by molecular dynamics (MD) simulations, a method capable of simulating the solvent response as well as the solute term and solute/solvent cross terms for the data analysis. Here we present an experimental procedure, applicable to most hydrogen containing solvents, that directly measures the solvent response to a transient temperature rise. The overtone modes of OH stretching and CH3 asymmetric stretching in liquid methanol were excited by near-infrared femtosecond laser pulses at 1.5 and 1.7 microm and the ensuing hydrodynamics, induced by the transfer of heat from a subset of excited CH3OH* to the bulk and the subsequent thermal expansion, were probed by 100 ps x-ray pulses from a synchrotron. The time-resolved data allowed us to extract two key differentials: the change in the solvent diffraction from a temperature change at constant density, seen at a very short time delay approximately 100 ps, and a term from a change in density at constant temperature. The latter term becomes relevant at later times approximately 1 mus when the bulk of liquid expands to accommodate its new temperature at ambient pressure. These two terms are the principal building blocks in the hydrodynamic equation of state, and they are needed in a self-consistent reconstruction of the solvent response during a chemical reaction. We compare the experimental solvent terms with those from MD simulations. The use of experimentally determined solvent differentials greatly improved the quality of global fits when applied to the time-resolved data for C2H4I2 dissolved in methanol.

Rare‐Earth Zirconate Ceramics with Fluorite Structure for Thermal Barrier Coatings

Abstract: A series of rare-earth zirconate Ln2Zr2O7 ceramics (Ln=Dy, Er, and Yb) with a fluorite structure (F-Ln2Zr2O7) were prepared by pressureless sintering from zirconia and rare-earth oxide powders at 1600°C for 10 h in air. The microstructure experiments were performed by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The thermal conductivity and thermal expansion of these ceramics were evaluated using a steady-state laser heat-flux technique and high-temperature dilatometry, respectively. The XRD and SEM results demonstrate that Ln2Zr2O7 ceramics with a single fluorite phase are synthesized and no other phases are found. The results of thermal conductivity show that their thermal conductivities (1.3–1.9 W/(m·K), 20°–800°C) are as low as those of the referenced Ln2Zr2O7 ceramics (Ln=La, Nd, Sm, and Gd) with pyrochlore structure (P-Ln2Zr2O7). It is concluded that rare-earth zirconate ceramics with a fluorite structure can be considered as candidate materials for future thermal barrier coatings.

Thermal expansion anisotropy in extruded SiC particle reinforced 2080 aluminum alloy matrix composites

Abstract: Thermal expansion behavior is an important physical property of metal matrix composites (MMCs). For extruded Al/SiCp composites, both the particle volume percent and the orientation relative to the extrusion direction have significant effects on the coefficient of thermal expansion (CTE) of a composite. In this study, the coefficient of thermal expansion of extruded, SiC particle reinforced 2080 Al composites were measured using a thermal mechanical analyzer (TMA). It was found that the anisotropic distribution of SiC particles determines the anisotropic thermal behavior of Al/SiCp composites. For the same SiC content, the CTE in the short transverse direction (normal to the extrusion axis) is higher than that in the transverse direction, with the longitudinal direction (parallel to the extrusion axis) having the lowest CTE. Finite element modeling (FEM), based on the actual microstructure of Al/SiCp composites, was employed to simulate the thermal behavior. The experimental results for the CTE of the composite correlated very well with those predicted by two-dimensional (2D) numerical models. The FEM results showed that orientation of SiC particles changes the internal stress in the composite, which yields anisotropic thermal behavior. A comparison was made between the experimental results and the FEM model, and these were related to several analytical models.