Linear Coefficient of Thermal Expansion

GaAs, GaAs:Si and GaAs:C films were deposited on GaAs substrates by Metal Organic Chemical Vapor Deposition( MOCVD) technique. The vibrational study of the heterostructures was performed by mu-Raman technique, and measurements were made at different temperatures using a sample holder with a micro-heater included within it. The spectral information was used to determine the strain caused in GaAs heterostructure because

This paper deals with the properties of the glasses and thin films from multi-component chalcogenide prepared by co-evaporation technique. The thin chalcogenide layers from the Ge30Se70-xInx system were deposited by thermal co-evaporation of bulk glasses from Ge-Se system and In2Se3. Using X-ray microanalysis it was found that the film compositions are close to the expected ones. The refractive index, n, and the optical band gap, E-g(opt), were determined by spectral ellipsometric measurements. The thin film's structure was investigated by Raman spectroscopy.

The temperature coefficients of the linear thermal expansion, alpha 1 and the band gap, beta(Eg) were determined. Decrease of the values of at from 2.49 x 10(-4) K-1 to 4.55 x 10(-5) K-1 and beta(Eg) from -1.3 x 10(-3) eV.K-1 to -0.7 x 10(-3) eV.K-1 was observed when indium content in the thin films was increased from 0 to 17 at.%.

Nano-crystalline Sr0.5Ba0.5Nb2O6 was synthesized by a one-pot method using PEG400 and citric acid. Calcination of the (Sr,Ba,Nb)-gel at 600 °C leads to Sr 0.5 Ba 0.5 Nb 2 O 6 with a crystallite size of 24(2) nm and a specific surface area of 38.5(10) m2 g-1. Sintering up to 1325 °C leads to ceramics with globular or irregular-shaped grains and average grain sizes between 1.3 and 2.4 µm, whereas higher temperatures lead to a rod-like microstructure. The indirect allowed optical band gap varies between 3.70(5) and 3.29(5) eV. Dielectric measurements show a diffuse phase transition and weak relaxor properties. The maximum of the permittivity occurs between 116 and 147 °C. The frequency dependence of the impedance can be well described by one or two RC-circuits depending on sintering temperature. The  melting temperature is determined as 1506(7) °C with dH f = 140(20) kJ mol -1. The average linear thermal expansion coefficient is found to be 10.5(5)*10-6 K-1 .

The 2019 ITCC-ITES Conference is less than a month away. The Conference will be held in Wilmington, Delaware (USA) beginning at 6pm on June 16 (Sunday) and ending at Noon on June 20, 2019 (Thursday).

It will be a great conference – in addition to the Workshop on Thermal Conductivity Reference Materials, we have 80 talks in the conference schedule. Plus, we’ve added a Poster session & Social on Sunday before the Conference officially starts.

Thermal conductivity and coefficient of thermal expansion (CTE) of silicon particulates reinforced highdensity polyethylene (HDPE) composites are reported. Composite samples were fabricated by mixing
the components in proper volumetric ratio, molding and hot pressing. Incorporation of Si powder in
HDPE enhances both the thermal stability and the effective thermal conductivity of the composites.
CTE of the composites display substantial reduction with increasing Si content in HDPE, while with
increasing temperature CTE increases linearly. Effective thermal conductivity for HDPE containing 20-volume fraction (%) Si becomes double than that for unfilled HDPE. Results on both the effective thermal
conductivity and CTE of the composites have been discussed in light of various theoretical models. Our
analysis confirms that the effective thermal conductivity of HDPE/Si composites is predicted extremely
well by the model proposed by Agari et al. and conductive channels are not easily formed in HDPE/Si
composites. We also show that CTE data could be successfully explained taking into account the role of
the interphase volume and the strength of the polymer–filler interactions.

The preparation of a nano-sized LaFeO3 powder by a soft-chemistry method using starch as complexing agent is described herein. Phase evolution and development of the specific surface area during the decomposition process of (LaFe)-gels were monitored up to 1000 °C. A phase-pure nano-sized LaFeO3 powder with high specific surface area of 25.7 m2/g and a crystallite size of 37 nm was obtained after calcining at 570 °C. TEM investigations reveal a porous powder with particles in the range of 20 to 60 nm. Calcinations to 1000 °C result in crystallite sizes up to 166 nm. The dilatometric measurements of the sintering behaviour show that the beginning of shrinkage of pellets from the nano-sized powder is downshifted by more than 300 °C compared to the coarse-grained mixed-oxide powder. The orthorhombic ⇆ rhombohedral phase transition was observed at 980 °C in DTA measurements for the coarse-grained ceramic bodies. The enthalpy change (ΔH) during the phase transition and the thermal expansion coefficient (αdil) for the ceramics were determined as 410 J/mol and 11.8·10− 6 K− 1, respectively. Whereas the enthalpy changes during the phase transition of the nano-sized LaFeO3 powders are ≤ 200 J/mol.

High-density microelectronics require packaging materials and systems that provide superior thermal management and highly functional interconnection schemes for component performance and reliability. Aluminum Silicon Carbide (AlSiC) metal matrix composite (MMC) packages have a unique set of material properties that are ideally suited to thermal management performance, and a functionality that supports high density interconnection microelectronic packaging applications. Furthermore, the AlSiC fabrication and processing technology provides these high performance attributes cost-effectively. The AlSiC coefficient of thermal expansion (CTE) value is compatible with direct IC device attachment allowing for the maximum thermal dissipation into the high thermal conductivity (170 – 200 W/mK) AlSiC package. Additionally, the low material density of AlSiC (3 g/cm 3 ) makes it ideal for weight sensitive applications such as airborne, spaceborne, or portable devices. The AlSiC material and func...

A facile method to prepare nanoscaled BaFe 0.5 Nb 0.5 O 3 via synthesis in boiling NaOH solution is described herein. The nano-crystalline powder has a high specific surface area of 55 m 2 g −1 and a crystallite size of 15 nm. The as-prepared powder does not show any significant crystallite growth up to 700 °C. The activation energy of the crystallite growth process was calculated as 590 kJ mol −1. Dense ceramics can be obtained either after sintering at 1200 °C for 1 h or after two-step sintering at 1000 °C for 10 h. The average grain sizes of ceramic bodies can be tuned between 0.23 µm and 12 µm. The thermal expansion coefficient was determined as 11.4(3)⋅10 −6 K −1. The optical band gap varies between 2.90(5) and 2.63(3) eV. Magnetic measurements gave a Néel temperature of 20 K. Depending on the sintering regime, the ceramic samples reach permittivity values between 2800 and 137000 at RT and 1 kHz.

The authors examine the stability of an outwardly propagating spherical flame accounting for both hydrodynamic and thermodiffusive effects. For Lewis numbers less than a critical value Le* <1, disturbances of the flame front grow during the initial phase of propagation, i.e. when the radius is comparable to the flame thickness. However, for Le > Le*, the flame, which is stable to thermodiffusive effects, becomes unstable only after a critical size is reached. This instability is hydrodynamic in nature and is caused by the thermal expansion of the gas. In this study the authors provide an expression for the determination of the critical size, or a critical Peclet number, which depends on the thermal expansion coefficient and on the Lewis number. The explicit dependence on all the relevant physiochemical parameters enables comparison of results with experimental data.

Ionic liquids are a class of fluids that requires the attentions of experimentalist and theoreticians. In a new project on synthesis and characterization of new and not-so-new ionic liquids, the study of several thermophysical properties of these liquids was started, namely binary diffusion, electrical conductivity, heat capacity, surface tension, viscosity and thermal conductivity. Among others we will study 1-n-butyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide,

The residual stress induced in assembly is a common concern in electronic packaging. The mismatch in coefficient of thermal expansion between borosilicate glass and silicon, upon temperature variation, generates an internal stress state. This affects important characteristics of microelectromechanical devices or constituent elements. Such as self frequence or stiffness. Stresses caused by thermal expansion coefficients mismatch of anodically bonded glass and silicon samples are studied in this paper. Stress calculation based on lamination theory is presented. Usage examples of such calculations are described. For bonded silicon and LK-5 glass several results of calculations are presented. Stress distribution in bonded silicon and glass of several thicknesses is evaluated. Stress distribution in bonded glass-silicon-glass structure is evaluated. Bonded silicon surface stress dependence of glass to silicon wafer thickness ratio is evaluated. Experimental study of thermal mismatch stress in glass based on birefringence phenomenon was conducted. It's results are presented in this paper.

This paper presents the modeling of a polyimide diaphragm for an optical pulse pressure sensor. Polyimide is a type of polymer materials that possessed low linear coefficient of thermal expansion and has good thermal stability. The polyimide diaphragm has been designed and its performance is analyzed in terms of diaphragm deflection, diaphragm pressure sensitivity and diaphragm resonance frequency. Two design parameters namely diaphragm radius and diaphragm thickness are varied to study the diaphragm performance. It can be concluded that the modeled micro-diaphragm with a diaphragm radius of 90μm and diaphragm thickness of 4μm respectively has satisfied the maximum allowable deflection and operated in optimum frequency response.

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5412059

Finite difference formulations for variable thickness thermal analysis and variable thickness plane stress analysis are presented. In heat transfer analysis, radiation effects and temperature-dependent thermal conductivity are taken into account. While in thermal stress analysis, the thermal expansion coefficient is considered as temperature dependent. An application of the variable thickness window for a synchrotron radiation beamline under very strong X-rays is provided.