Thermal Expansion Coefficient (thermal + expansion_coefficient)

Distribution by Scientific Domains


Selected Abstracts


MEASUREMENT OF THERMAL EXPANSION COEFFICIENT OF FLEXIBLE SUBSTRATE BY MOIR INTERFEROMETRY

EXPERIMENTAL TECHNIQUES, Issue 3 2001
B. Han
First page of article [source]


Zero Shrinkage of LTCC by Self-Constrained Sintering

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2005
Torsten Rabe
Low shrinkage in x and y direction and low tolerances of shrinkage are an indispensable precondition for high-density component configuration. Therefore, zero shrinkage sintering technologies as pressure-assisted sintering and sacrificial tapes have been introduced in the low-temperature co-fired ceramics (LTCC) production by different manufacturers. Disadvantages of these methods are high costs of sintering equipment and an additional process step to remove the sacrificial tapes. In this article, newly developed self-constrained sintering methods are presented. The new technology, HeraLock, delivers LTCC modules with a sintering shrinkage in x and y direction of less than 0.2% and with a shrinkage tolerance of 0.02% without sacrificial layers and external pressure. Each tape is self-constrained by integration of a layer showing no shrinkage in the sintering temperature range of the LTCC. Large area metallization, integration of channels, cavities and passive electronic components are possible without waviness and camber. Self-constrained laminates are an alternative way to produce zero shrinkage LTCC. They consist of tapes sintering at different temperature intervals. Precondition for a successful production of a self-constrained LTCC laminate is the development of well-adapted material and tapes, respectively. This task is very challenging, because sintering range, high-temperature reactivity and thermal expansion coefficient have to be matched and each tape has to fulfill specific functions in the final component, which requires the tailoring of many properties as permittivity, dielectric loss, mechanical strength, and roughness. A self-constrained laminate is introduced in this article. It consists of inner tapes sintering at especially low-temperature range between 650C and 720C and outer tapes with an as-fired surface suitable for thin-film processes. [source]


Volume-translated equations of state: Empirical approach and physical relevance

AICHE JOURNAL, Issue 6 2003
Leonid V. Yelash
The volume translation technique is widely applied in chemical engineering modeling of phase behavior and thermodynamic properties. This empirical correction of the molar volume improves the correlation of liquid densities when cubic equations of state are employed. Based on a recently proposed method of analyzing equations of state, the influence of the volume translation on the properties obtained from an equation of state, such as virial coefficients, as well as on the phase behavior, critical properties, the isobaric thermal expansion coefficient, and the heat capacities of pure substances is investigated. The influence of different kinds of temperature-dependent volume translations is investigated and compared to approaches that originate from theoretical considerations. The investigation shows that empirical as well as theoretical approaches for the development of equations of state can exhibit nonphysical behavior. However, the understanding of the reasons for such problems can help to develop reliable equations of state based on both kinds of method. [source]


Raman spectroscopic study on the structure, phase transition and restoration of zirconium tungstate blocks synthesized with a CO2 laser

JOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2007
E. J. Liang
Abstract Densely packed zirconium tungstate blocks were synthesized by rapid solidification with a CO2 laser. The structure and phase transition properties of the samples were studied by Raman spectroscopy and X-ray diffraction. Raman spectroscopic study reveals that zirconium tungstate solidifies with an orthorhombic structure. This is attributed to the pressure encountered by the samples during rapid solidification. Several Raman bands change discontinuously at about 390 K, indicating a phase transition from the ,- to the ,-phase occurring at this temperature. In the ,-phase, most of the Raman modes give rise to negative Grneisen parameters, suggesting contribution of the corresponding optical phonons to the negative thermal expansion coefficient of the material, at least for the ,-phase. A recovery of the ,-phase was observed when the samples were cooled to room temperature. This suggests that the cubic structure is metastable only at temperatures above 390 K, and at room temperature the ,-phase is preferred. Copyright 2007 John Wiley & Sons, Ltd. [source]


Diamond thermal expansion measurement using transmitted X-ray back-diffraction

JOURNAL OF SYNCHROTRON RADIATION, Issue 3 2005
Cris Adriano
The linear thermal expansion coefficient of diamond has been measured using forward-diffracted profiles in X-ray backscattering. This experimental technique is presented as an alternative way of measuring thermal expansion coefficients of solids in the high-resolution Bragg backscattering geometry without the intrinsic difficulty of detecting the reflected beam. The temperature dependence of the lattice parameter is obtained from the high sensitivity of the transmitted profiles to the Bragg angle variation with temperature. The large angular width of the backscattering profiles allows the application of this technique to mosaic crystals with high resolution. As an application of this technique the thermal expansion coefficient of a synthetic type-Ib diamond (110) single crystal was measured from 10 to 300,K. Extremely low values (of the order of 1 10,7 5 10,7) for the linear thermal expansion coefficient in the temperature range from 30 to 90,K are in good agreement with other reported measurements. [source]


Negative Thermal Expansion and Correlated Magnetic and Electrical Properties of Si-Doped Mn3GaN Compounds

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2010
Ying 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]


Optical and Mechanical Properties of Glasses and Glass,Ceramics Based on the Ge,Ga,Se System

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2008
Mathieu Roz
In this paper, the mechanical and thermo-mechanical properties of glasses and glass,ceramics belonging to the Ge,Ga,Se system are studied. Pure glasses slightly transparent in the visible range up to 16 ,m have been synthesized. Glass,ceramics were made using an appropriate heat-treatment time and temperature from the 80GeSe2,20Ga2Se3 base glass in order to improve the mechanical properties. The optical and mechanical properties of glasses and glass,ceramics such as hardness and toughness were investigated. X-ray diffraction (XRD) versus temperature experiments were performed to understand the crystallization evolution as a function of heat-treatment time. GeGa4Se8 and GeSe2 crystalline phases have been determined with XRD. As a result, glass,ceramics with 40% density of crystals present a very low thermal expansion coefficient (11.8 10,6 0.5 K,1) and an excellent infrared transmission in the 3,5 and 8,13 ,m regions. [source]


Thermophysical Properties of Complex Rare-Earth Zirconate Ceramic for Thermal Barrier Coatings

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2008
Liu Ling
Two complex rare-earth zirconates (La0.4Sm0.5Yb0.1)2(Zr0.7Ce0.4)2O7.4 and (Sr0.1La0.3Sm0.5Yb0.1)2(Zr0.7Ce0.4)2O7.3 for thermal barrier coatings (TBCs) were synthesized by the coprecipitation method. Their phase composition, microstructure, and thermophysical properties were investigated. X-ray diffractometry results revealed that single-phase (La0.4Sm0.5Yb0.1)2(Zr0.7Ce0.4)2O7.4 and (Sr0.1La0.3Sm0.5Yb0.1)2(Zr0.7Ce0.4)2O7.3 with pyrochlore structure were prepared, and the scanning electron microscopy results showed that the microstructures of the products were dense and no other phases existed among the grains. With the temperature increasing, the thermal expansion coefficient (CTE) of the ceramics increased, while the thermal conductivity decreased. The results indicated that the CTE of (Sr0.1La0.3Sm0.5Yb0.1)2(Zr0.7Ce0.4)2O7.3 was slightly higher than that of (La0.4Sm0.5Yb0.1)2(Zr0.7Ce0.4)2O7.4 and the thermal conductivity of (Sr0.1La0.3Sm0.5Yb0.1)2(Zr0.7Ce0.4)2O7.3 was lower than that of (La0.4Sm0.5Yb0.1)2(Zr0.7Ce0.4)2O7.4. These results imply that the thermophysical properties of (Sr0.1La0.3Sm0.5Yb0.1)2(Zr0.7Ce0.4)2O7.3 are better than that of (La0.4Sm0.5Yb0.1)2(Zr0.7Ce0.4)2O7.4 as the material for the ceramic layer in the TBC system. [source]


Preparation of Highly Dense PZN,PZT Thick Films by the Aerosol Deposition Method Using Excess-PbO Powder

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2007
Jong-Jin Choi
Lead zinc niobate,lead zirconate titanate thick films with a thickness of 50,100 ,m were deposited on silicon and alumina substrates using the aerosol deposition method. The effects of excess lead oxide (PbO) on stress relaxation during postannealing were studied. Excess PbO content was varied from 0 to 5 mol%. The as-deposited film had a fairly dense microstructure with nanosized grains. The films deposited on silicon were annealed at temperatures of 700C, and the films deposited on sapphire were annealed at 900C in an electrical furnace. The annealed film was detached and cracks were generated due to the high residual compressive stress and thermal stress induced by thermal expansion coefficient mismatch. However, the film deposited using powder containing 2% of excess PbO showed no cracking or detachment from the substrate after the postannealing process. The PbO evaporation at elevated temperature during the postannealing process seemed to have reduced the residual compressive stress. The remanent polarization and relative dielectric constant of the 50 ,m thick films annealed at 900C were 43.1 ,C/cm2 and 1400, respectively, which were comparable with the values of a bulk specimen prepared by a powder sintering process. [source]


Sintering Behavior of Gehlenite.

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2007
Macro-/Mesoporous Gehlenite, Mechanical, Microstructure, Part I: Self-Forming, Physical Properties, Pore-Forming Mechanism
A novel kind of pore self-forming macro-/mesoporous gehlenite (2CaOAl2O3SiO2) ceramic (abbreviated C2AS) having a highest porosity of 80% corresponding to a volume expansion of 134% during sintering has been developed. The pore self-forming ability, microstructure, mechanical, and thermal physical properties of the porous ceramic are related to the sintering temperature. The gehlenite ceramic shows a very good pore self-forming ability over a very wide range of temperature from 900 to 1450C. No vesicant is required and no hydrothermal treatment is needed, as is generally the case for other kinds of porous ceramics or glasses. The pore self-forming ability of the C2AS porous ceramic can be attributed to the escape of the adsorbed water vapor during the sintering process, due to automatic hydration of the fine, amorphous, flakey-shaped starting C2AS powder particles synthesized by the organic steric entrapment (PVA) method, as well as to their fine, porous microstructure. The pores of the ceramics can be either open or closed, and the average pore size ranges from 0.6 to 1.1 ,m, corresponding to a porosity of 75%,80%, respectively. The porous ceramic can preserve nanometer-sized (26,50 nm) crystallites up to 1000C. Sintered or thermally treated under different conditions, the porous ceramics exhibit relatively high flexural strengths ranging from 9.1 to 15.4 MPa, with a standard deviation of 0.3 and 4.2 MPa, respectively. Thermal properties of the porous ceramic up to 1000C, including thermal expansion coefficient, thermal diffusivity, specific heat, and thermal conductivity, were investigated, and the stability of the porous ceramic in boiling water was also studied. [source]


Use of CsCl to Enhance the Glass Stability Range of Tellurite Glasses for Er3+ -Doped Optical Fiber Drawing

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2007
Carmen Rosa Eyzaguirre
Tellurite glasses are important as a host of Er3+ ions because of their good solubility and because they present broadband optical gain compared with Er3+ -doped silica, with the potential to increase the bandwidth of communication systems. However, the small glass stability range (GSR) of tellurite glasses compromises the quality of the optical fibers. We show that the addition of CsCl to tellurite glasses can increase their GSR, making it easier to draw good-quality optical fibers. CsCl acts like a network modifier in glass systems, weakening the network by forming Te,Cl bonds. We show that the thermal expansion coefficient mismatch is in the right direction for optical fiber fabrication purposes and that the Bi2O3 content can be used to control the refractive index of clad and core glasses. Single-mode and multi-mode Er3+ -doped optical fibers were produced by the rod-in-tube method using highly homogeneous TeO2,ZnO,Li2O,Bi2O3,CsCl glasses. [source]


Spectroscopic and Thermal Properties of Ga2S3,Na2S,CsCl Glasses

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2006
Luiz C. Barbosa
The synthesis and properties of the vitreous system (0.75,x)Ga2S3,0.25Na2S,xCsCl, with x varying from 0.1 to 0.2, are presented. Thermal, optical, and structural properties such as density, viscosity, thermal expansion coefficient, glass transition temperature, softening point temperature, refractive index, and absorption coefficient were measured using several techniques: X-ray diffraction, Raman scattering, differential thermal analysis, thermal mechanical analysis, and absorption spectroscopy. This glass system presents a high third-order non-linear optical susceptibility that can be significantly increased by increasing the CsCl content without affecting the low phonon frequency. [source]


High-Intensity Discharge Lamp with Mo,SiO2 Functionally Graded Material

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2006
Ayumu Umemoto
We show the invention of the new type of hermetically sealed high-intensity discharge lamps, made of Mo,SiO2 functionally graded material (FGM) as an electrode and a sealing component. In the case of high-intensity discharge lamps with Mo,SiO2 FGM (FGM lamp), the thermal expansion coefficient between Mo and SiO2 is functionally graded so that it tolerates a large number of heating cycles, with no cooling system required. Furthermore, lamps survive without breakage. The W electrode is totally separated from the lamp envelope by the FGM, so that no leakage of the luminous elements or gases takes place, when a large gas pressure exists inside a lamp. [source]


Phase Relations and Thermal Expansion Studies in the Ceria,Yttria System

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2004
Sandeep V. Chavan
The synthesis, characterization, and bulk and lattice thermal expansions of a series of compounds with general composition Ce1,xYxO2,x/2 (0.0 ,x, 1.0) are reported. The XRD pattern of each product was refined to learn the solid solubility limit and the homogeneity range. The solid solubility limit of YO1.5 in CeO2 lattice, under the conditions of slow cooling from 1400C, is represented as Ce0.55Y0.45O1.775 (i.e., 45 mol% of YO1.5). The subsequent compositions were biphase. There was no solubility of CeO2 into the lattice of YO1.5. The bulk thermal expansion measurements from ambient to 1123 K, as investigated using a dilatometer, revealed that the ,l (293,1123 K) values, within the homogeneity range, decreased on increased Y3+ content. A similar trend was observed for average lattice thermal expansion coefficient, ,a (293,1473 K), as investigated using high-temperature XRD. No ordered phases were obtained in this system under the used conditions. These studies on Ce1,xYxO2,x/2 (0.0 ,x, 1.0) system can be used to simulate the phase relation and thermal expansion behavior of Pu1,xYxO2,x/2 (0.0 ,x, 1.0), because CeO2 is widely used as a surrogate material for PuO2. [source]


Negative Thermal Expansion in (HfMg)(WO4)3

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2004
Tomoko 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 800C. The mechanism of negative thermal expansion is assumed to be the same as that of Sc2(WO4)3. [source]


High-Temperature Resistant Composites in the AlN,SiC,MoSi2 System

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2003
Diletta Sciti
Two fully dense composites containing AlN, SiC, and MoSi2 in different amounts were produced by hot pressing. Young modulus, hardness, electrical conductivity, and thermal expansion coefficient were measured at room temperature. Strength and toughness were evaluated up to 1300C in air. According to statistical analysis, the temperature has little or no effect on high-temperature fracture behavior of the composites. These electroconductive materials are suitable for thermomechanical applications at high temperature, the strength being about 600 MPa at 1300C. [source]


Stepwise-Graded Si3N4,SiC Ceramics with Improved Wear Properties

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2002
Scott C. Thompson
The processing of stepwise graded Si3N4/SiC ceramics by pressureless co-sintering is described. Here, SiC (high elastic modulus, high thermal expansion coefficient) forms the substrate and Si3N4 (low elastic modulus, low thermal expansion coefficient) forms the top contact surface, with a stepwise gradient in composition existing between the two over a depth of ,1.7 mm. The resulting Si3N4 contact surface is fine-grained and dense, and it contains only 2 vol% yttrium aluminum garnet (YAG) additive. This graded ceramic shows resistance to cone-crack formation under Hertzian indentation, which is attributed to a combined effect of the elastic-modulus gradient and the compressive thermal-expansion-mismatch residual stress present at the contact surface. The presence of the residual stress is corroborated and quantified using Vickers indentation tests. The graded ceramic also possesses wear properties that are significantly improved compared with dense, monolithic Si3N4 containing 2 vol% YAG additive. The improved wear resistance is attributed solely to the large compressive stress present at the contact surface. A modification of the simple wear model by Lawn and co-workers is used to rationalize the wear results. Results from this work clearly show that the introduction of surface compressive residual stresses can significantly improve the wear resistance of polycrystalline ceramics, which may have important implications for the design of contact-damage-resistant ceramics. [source]


Roles of Ba/Ti Ratios in the Dielectric Properties of BaTiO3 Ceramics

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2001
Jung-Kun Lee
The effect of the Ba/Ti ratio on microstructure, dielectric/ferroelectric properties, and domain width was studied using optical microscopy, ,(T) curves, D,E hysteresis, and transmission electron microscopy. Although Ti-excess samples showed abnormal grain growth and a decrease of room-temperature permittivity due to a liquid phase at grain boundaries, its ferroelectric properties were similar to those of stoichiometric BaTiO3 ceramics. However, in Ba-excess samples, an increase of permittivity and ferroelectric properties different from those of stoichiometry were found. Changes in domain width and ferroelectric transition behavior indicated that the variation of dielectric properties was related to the internal stress. It is proposed that this internal stress originated from differences in the thermal expansion coefficient between the matrix and the second phase. [source]


Thermal Stability of Lanthanum Zirconate Plasma-Sprayed Coating

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2001
X. Q. Cao
Lanthanum zirconate (La2Zr2O7, LZ) is a newly proposed material for thermal barrier coatings (TBCs). The thermal stability of LZ coating was studied in this work by long-term annealing and thermal cycling. After long-term annealing at 1400C or thermal cycling, both LZ powder and plasma-sprayed coating still kept the pyrochlore structure, and a preferred crystal growth direction in the coating was observed by X-ray diffraction. A considerable amount of La2O3 in the powder was evaporated in the plasma flame, resulting in a nonstoichiometric coating. Additionally, compared with the standard TBC material yttria-stabilized zirconia (YSZ), LZ coating has a lower thermal expansion coefficient, which leads to higher stress levels in a TBC system. [source]


Effect of Nickel Oxide/Yttria-Stabilized Zirconia Anode Precursor Sintering Temperature on the Properties of Solid Oxide Fuel Cells

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2000
Sren Primdahl
An NiO/yttria-stabilized zirconia (YSZ) layer sintered at temperatures between 1100 and 1500C onto dense YSZ electrolyte foils forms the precursor structure for a porous Ni/YSZ cermet anode for solid oxide fuel cells. Conflicting requirements for the electrochemical performance and mechanical strength of such cells are investigated. A minimum polarization resistance of 0.09 ,.cm2at 1000C in moist hydrogen is obtained for sintering temperatures of 1300,1400C. The mechanical strength of the cells decreases with increased sintering temperature because of the formation of channel cracks in the electrode layers, originating in a thermal expansion coefficient mismatch between the layers. [source]


Vibrational properties of InP under pressure: a molecular-dynamics study

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2007
Paulo S. Brancio
Abstract Dynamical properties of InP in the zincblende (ZB) are investigated using isothermal,isobaric molecular-dynamics simulations based on a proposed interaction potential for InP consisting of two- and three-body terms. The two-body term represents steric repulsion, Coulomb interactions due to charge transfer, induced charge,dipole interaction, and van der Waals dipole,dipole interaction. The three-body term represents covalent bond bending and stretching. The model is fitted to reproduce crystalline lattice constant, cohesive energy, and the structural transition pressure from ZB to rocksalt. The effects of hydro- static pressure and temperature on the vibrational density-of-states, phonon anharmonicity, dynamic Debye,Waller factor, thermal expansion coefficient are described as well as the pressure induced structural phase transformation. Results are consistent with available experimental data, in particular the calculated equation of state and phonon density-of-states have very good agreement. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Temperature dependence of structural parameters in the perovskite Na0.74WO3

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2005
C. N. W. Darlington
Abstract NaxWO3 undergoes three phase transitions involving tilting of the oxygen octahedra about ,100, pseudocubic directions. We have measured the temperature dependence of the lattice parameters between 200 and 750 K , a temperature range that spans the three transitions , and determined the evolution of the structure within each phase as temperature changes. The experiments were performed on the high-resolution powder diffractometer HRPD, Rutherford Appleton Laboratory, UK, using time-of-flight neutron diffraction. The critical exponent that describes the temperature dependence of the total tilt angle has been evaluated. An unexpected change in the thermal expansion coefficient in the cubic phase is not understood: an argument based on Landau's theory of phase transitions is used to demonstrate that the change is not the result of co-existence of two phases. ( 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Realization of AlGaN/GaN HEMTs on 3C-SiC/Si(111) substrates

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008
Y. Cordier
Abstract Cubic SiC/Si (111) template is an interesting alternative for growing GaN on silicon. As compared with silicon, this substrate allows reducing the stress in GaN films due to both lower lattice and thermal expansion coefficient mismatch, and can provide better heat dissipation. In this work, we first developed the epitaxial growth of 3C-SiC films on 50 mm Si(111) substrates using chemical vapor deposition. AlGaN/GaN high electron mobility transistors were grown by molecular beam epitaxy on these films. Both the structural quality and the behavior of transistors realized on these structures show the feasibility of this approach. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Preparation and properties of nanoparticle and long-fiber-reinforced unsaturated polyester composites

POLYMER COMPOSITES, Issue 7 2009
Gang Zhou
In this study, a new approach was used to prepare polymer composites reinforced by both nanoparticles and continuous fibers. Carbon nanofibers were prebound onto glass fiber mats, and then unsaturated polyester composites were prepared by vacuum-assisted resin transfer molding. Mechanical and thermal properties of these composites were measured and compared with those of the composites synthesized by premixing carbon nanofibers with the polymer resin. Flexural strength and modulus of composites improved with the incorporation of nanoparticles. Specifically, the property improvement was higher in the case of the composites prepared by the new prebound method. It was also found that carbon nanofibers increased the glass transition temperature and reduced the thermal expansion coefficient of unsaturated polyester composites. POLYM. COMPOS., 2009. 2008 Society of Plastics Engineers [source]


The electrical behavior of thermosetting polymer composites containing metal plated ceramic filler

POLYMER COMPOSITES, Issue 1 2005
Hedva Bar
This paper describes the electrical behavior of a thermosetting system, based on epoxy resin, containing metal plated fillers. Ceramic fillers such as chopped glass fibers and mica flakes were coated with copper by electroless plating and incorporated into an epoxy resin based on di-glycidyl ether of bisphenol A (DGEBA) with tri-ethylenetetramine (TETA) curing agent. The percolation threshold in these systems is obtained at very low copper contents of 0.11,0.44 vol%. The epoxy/copper coated mica system is characterized by an extremely large positive temperature coefficient (PTC) effect, which is not followed by a negative temperature coefficient (NTC) effect. Increasing the copper coated mica concentration raises the PTC temperature of the first temperature cycle, and exposing the material to continuous heating-cooling cycles results in a decrease in the PTC temperature and an increase of its room temperature resistivity. Inverse relations were found between the coefficient of thermal expansion and the PTC temperature. Accordingly, the mechanism governing the PTC effect in the epoxy/copper coated mica composite is based on a larger thermal expansion coefficient of the matrix compared with the ceramic filler. POLYM. COMPOS., 26:12,19, 2005. 2004 Society of Plastics Engineers. [source]


Effect of resin compositions on microwave processing and thermophysical properties of benzoxazine-epoxy-phenolic ternary systems filled with silicon carbide (SiC) whisker

POLYMER ENGINEERING & SCIENCE, Issue 5 2009
Chanchira Jubsilp
Microwave processing of silicon carbide (SiC) whisker filled ternary systems based on benzoxazine, epoxy, and phenolic resins has been investigated using an industrial microwave apparatus at a fixed frequency of 2.45 GHz. The low viscosity molding compound and void-free cured specimens can easily be obtained from the resin mixtures. Increasing of epoxy mass fraction in the ternary systems provided a better microwave coupling, therefore, a faster curing time and higher conversion under microwave irradiation. However, the greater amount of epoxy resin in the mixture was observed to retard the traditional thermal cure process as seen in the shifting of the exothermic curing peaks to higher temperature. The higher dielectric constant of epoxy resin comparing with the benzoxazine resin can be attributed to the observed phenomenon. Additionally, benzoxazine fraction was found to render a reduction in linear thermal expansion coefficient of the ternary systems. The development of ternary systems yields the polymer systems with high flexibility in resin-curing agent mixing ratios with relatively high Tg in the broader range of mixing ratios i.e., BEP451-BEP811. Synergism in glass transition temperature of the ternary systems is also observed with the maximum Tg up to 160C in BEP721. POLYM. ENG. SCI., 2009. 2009 Society of Plastics Engineers [source]


Towards advanced circuit board materials: adhesion of copper foil to ultra-high molecular weight polyethylene composite

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 6 2002
Dmitry
Abstract Polyethylene based composites are attractive materials for advanced circuit board applications because of their unique combination of properties: low dielectric constant and loss factor, light weight, high flexural modulus and low thermal expansion coefficient controlled in all spatial directions. This investigation describes a process to consolidate chopped fibers of ultra-high molecular weight polyethylene concurrently with its bonding to a copper foil. Bonding is affected by a thin sheet of low-density polyethylene, incorporating a crosslinking agent with a concentration gradient across the sheets thickness. In this single step process, the composite material is formed and bonded to the metal foil, achieving good adhesion without the use of extraneous glue. Copyright 2002 John Wiley & Sons, Ltd. [source]


Cost-Efficient Metal,Ceramic Composites,Novel Foam-Preforms, Casting Processes and Characterisation,

ADVANCED ENGINEERING MATERIALS, Issue 3 2010
Gisela Standke
Because of their dissatisfactory cost-performance ratio metal matrix composites (MMCs) are still not established in industry, although they show improved properties compared to pure metals in some application fields. The present paper describes the development of enhanced MMCs based on silicon carbide (SiC) foams made by the Schwartzwalder process. Therefore, foams with cell sizes of 30, 45 and 60,ppi based on pressure less sintered SiC (SSiC) were developed. They were coated with layers of coarse SiC particles, which form a rough strut surface. The ceramic content of the foams could be increased to values of 20,30,mass%. Additionally, foam preforms based on clay-bonded SiC (as they are known from molten metal infiltration) were tested. The preforms were infiltrated with aluminium alloys AlSi9Cu3 and AlSi7Mg0.6 and cast iron EN-GJSA-XNiCr35-5-2 and EN-GJL-250. For aluminium alloys high pressure die casting (HPC) as well as gravity casting was applied, whereas iron was only infiltrated by gravity casting. For HPC an excellent interlocking of metal and preform was observed because of the microporosity of the rough surface of the SSiC foam struts. By the use of gravity casting preform cells up to 45,ppi could be well infiltrated. Microporosity in the ceramic coating and the typical hollow struts of the foams did not show metal infiltration. Even by use of moderate ceramic volume fractions pressure-infiltrated aluminium matrix composites showed a high specific stiffness of up to E/,,=,42,GPa,cm3,g,1 compared to conventional Al or Mg alloys (E/,,=,25,27,GPa,cm3,g,1). Ceramic foam based MMCs produced by pressure less casting showed no advantages in mechanical properties compared to pure metals. Nevertheless it can be expected that they can provide improved wear resistance and lower thermal expansion coefficients. [source]


Strength estimation of ceramic,metal joints with various interlayer thickness

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 5 2003
M. TAKAHASHI
ABSTRACT Residual stresses generated by the mismatch of thermal expansion coefficients of ceramics and metals affect the strength of ceramic,metal joints. An interlayer metal can be inserted between the ceramic and metal in order to relax this stress. An analysis was carried out of the residual stresses produced during joint-cooling and in 4-point bending tests. The effects of interlayer thickness on ceramic,metal joint strength were then studied by considering a superimposed stress distribution of the residual stress and the bending stress. Finally, joint strength was estimated from fracture mechanics and strength probability analysis by considering the residual stress distribution, defect size and position of pre-existing defects in the ceramic parts. As a result of this study, we suggest an optimum material selection and interlayer thickness for ceramic,metal joint structures. This approach is generally suitable for the design of electrical and mechanical structures. [source]


Diamond thermal expansion measurement using transmitted X-ray back-diffraction

JOURNAL OF SYNCHROTRON RADIATION, Issue 3 2005
Cris Adriano
The linear thermal expansion coefficient of diamond has been measured using forward-diffracted profiles in X-ray backscattering. This experimental technique is presented as an alternative way of measuring thermal expansion coefficients of solids in the high-resolution Bragg backscattering geometry without the intrinsic difficulty of detecting the reflected beam. The temperature dependence of the lattice parameter is obtained from the high sensitivity of the transmitted profiles to the Bragg angle variation with temperature. The large angular width of the backscattering profiles allows the application of this technique to mosaic crystals with high resolution. As an application of this technique the thermal expansion coefficient of a synthetic type-Ib diamond (110) single crystal was measured from 10 to 300,K. Extremely low values (of the order of 1 10,7 5 10,7) for the linear thermal expansion coefficient in the temperature range from 30 to 90,K are in good agreement with other reported measurements. [source]