The Experts below are selected from a list of 174 Experts worldwide ranked by ideXlab platform
H L Tam - One of the best experts on this subject based on the ideXlab platform.
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Low Thermal Diffusivity measurements of thin films using mirage technique
Journal of Applied Physics, 1998Co-Authors: P K Wong, P C W Fung, H L TamAbstract:Mirage technique is proved to be powerful in measurements of Thermal Diffusivity. Its contactless nature makes it suitable for delicate samples such as thin films and single crystals. However, as the damping of the Thermal wave profile increases progressively upon the decrease in Thermal Diffusivity of the medium, mirage technique becomes more difficult to be applied to Low Thermal Diffusivity measurements. Moreover influences from substrate signals make analysis difficult when the samples are Thermally thin. Recently a Thermal-wave-coupling method for mirage signal analysis [P. K. Wong, P. C. W. Fung, H. L. Tam, and J. Gao, Phys. Rev. B 51, 523 (1995)] was reported for Thermal Diffusivity measurements of thin film down to 60 nm thick. In this article we apply the Thermal-wave-coupling method to thin films of Low Thermal Diffusivity, especially polymer films. A new Lower limit of Thermal Diffusivity measurable by mirage technique has been reached.
Tamer Sinmazcelik - One of the best experts on this subject based on the ideXlab platform.
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characterization of the drilling alumina ceramic using nd yag pulsed laser
Journal of Materials Processing Technology, 2009Co-Authors: E Kacar, M Mutlu, E Akman, A Demir, Levent Candan, Timur Canel, Volkan Gunay, Tamer SinmazcelikAbstract:Laser micromachining can replace mechanical removal methods in many industrial applications, particularly in the processing of difficult-to-machine materials such as hardened metals, ceramics, and composites. It is being applied across many industries like semiconductor, electronics, medical, automotive, aerospace, instrumentation and communications. Laser machining is a Thermal process. The effectiveness of this process depends on Thermal and optical properties of the material. Therefore, laser machining is suitable for materials that exhibit a high degree of brittleness, or hardness, and have favourable Thermal properties, such as Low Thermal Diffusivity and conductivity. Ceramics which have the mentioned properties are used extensively in the microelectronics industry for scribing and hole drilling. Rapid improvement of laser technology in recent years gave us facility to control laser parameters such as wavelength, pulse duration, energy and frequency of laser. In this study, Nd:YAG pulsed laser (with minimum pulse duration of 0.5 ms) is used in order to determine the effects of the peak power and the pulse duration on the holes of the alumina ceramic plates. The thicknesses of the alumina ceramic plates drilled by laser are 10 mm. Average hole diameters are measured between 500m and 1000m at different drilling parameters. The morphologies of the drilled materials are analyzed using optical microscope. Effects of the laser pulse duration and the peak power on the average taper angles of the holes are investigated.
Markus Retsch - One of the best experts on this subject based on the ideXlab platform.
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photoacoustic Thermal characterization of Low Thermal Diffusivity thin films
Photoacoustics, 2021Co-Authors: Kai Herrmann, N W Pechmay, Markus RetschAbstract:Abstract The photoacoustic measurement technique is a powerful yet underrepresented method to characterize the Thermal transport properties of thin films. For the case of isotropic Low Thermal Diffusivity samples, such as glasses or polymers, we demonstrate a general approach to extract the Thermal conductivity with a high degree of significance. We discuss in particular the influence of Thermal effusivity, Thermal Diffusivity, and sample layer thickness on the significance and accuracy of this measurement technique. These fundamental Thermal properties guide sample and substrate selection to alLow for a feasible Thermal transport characterization. Furthermore, our data evaluation alLows us to directly extract the Thermal conductivity from this transient technique, without separate determination of the volumetric heat capacity, when appropriate boundary conditions are fulfilled. Using silica, poly(methyl methacrylate) (PMMA) thin films, and various substrates (quartz, steel, and silicon), we verify the quantitative correctness of our analytical approach.
Anne M Hofmeister - One of the best experts on this subject based on the ideXlab platform.
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heat transfer in plagioclase feldspars
American Mineralogist, 2012Co-Authors: Joy M Branlund, Anne M HofmeisterAbstract:Laser-flash analyses (LFA) of oriented sections of six natural plagioclase crystals provide Thermal Diffusivity ( D ) as function of temperature (to ~1300–1500 K) and composition (An5–95). Plagioclase has Low-Thermal Diffusivity; our measurements indicate that plagioclase is more insulating than other major igneous rock-forming minerals. Over much of the solid solution, room-temperature D ranges from 0.751 to 0.979 mm2/s along c , 0.722 to 0.919 mm2/s along b , and 0.632 to 0.868 mm2/s perpendicular to b and c . The directionally averaged D is 30–45% Lower than D of Amelia albite. Thermal conductivities calculated using measured D values are almost the same for all samples with 18 ≤ An ≤ 65, ranging from 1.5 to 1.9 W/m/K and changing little with temperature. Increasing Al-Si disorder causes D to decrease with increased An content, although sample structure causes more ordered samples to have higher D than more disordered samples. Anorthite is a special case. Although ordered, the larger unit cell provides many lattice modes, leading to Low Diffusivity. Structure dictates whether D along the b -axis is greater or less than that along the c -axis, possibly because ordering in An-like domains increases D more along c relative to b . Inflections in 1/ D ( T ) are connected with lattice distortion during heating, and occur near temperatures expected for phase transitions; for example, the lattice stretch occurring at the temperature of the transition to C 1 structure Lowers Diffusivity. Likewise, lattice distortion during heating decreases D in albite along c but has little impact on D in the other directions. The anharmonic lattice effects that dictate both Thermal expansivity and D are masked by effects of disorder; the latter plays a major role in heat transport in plagioclase.
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the influence of temperature dependent Thermal Diffusivity on the conductive cooling rates of plutons and temperature time paths in contact aureoles
Earth and Planetary Science Letters, 2012Co-Authors: Peter I Nabelek, Anne M Hofmeister, Alan G WhittingtonAbstract:Abstract We explore the conductive cooling rates of plutons and temperature-time paths of their wall rocks using numerical methods that explicitly account for the temperature dependence of Thermal Diffusivity ( α ) and heat capacity (C P ). We focus on α because it has the strongest influence on the temperature-dependence of Thermal conductivity (k = ρ·C P · α ) at high temperatures. Latent heats of crystallization are incorporated into the models as apparent C P 's. Two sets of models are presented, one for a 50 m thick basalt sill emplaced into rocks with Diffusivity of the average crust, and one for a 5 km wide and 2 km thick granite pluton emplaced into dolostones. The sill's liquidus is 1230 °C, the solidus 980 °C, and the sill is emplaced into wall rocks that are at 150 °C. The pluton's liquidus is 900 °C, the solidus 680 °C, and the pluton is emplaced into wall rocks with initial geoThermal gradient of 30 °C/km. The top of the pluton is at 3 km depth. Incorporating appropriate α = f(T) into calculations can more than double the solidification times of intrusions in comparison with incorporating constant α of 1 mm 2 ·s − 1 that is used in most petrologic heat transport models. The instantaneously emplaced basalt sill takes ~ 51 a to completely solidify, whereas the granite pluton takes ~ 52 ka to completely solidify. The solidification time is longer because of Low Thermal Diffusivity of magma and because wall rocks become more insulating as temperature rises. In contact aureoles, maximum temperatures reached with α = f(T) are somewhat Lower in comparison with α = 1 mm 2 ·s − 1 ; however, temperatures in inner aureoles stay elevated significantly longer with α = f(T), and consequently promote approach to mineralogical and textural equilibrium. The elevated temperature regime in inner aureoles enhances temperature gradients that may promote greater fluid fluxes if fluid pore pressures are controlled by temperatures. The results demonstrate the need to incorporate temperature-dependent transport properties of magmas and wall rocks into models of metamorphism and fluid fLow in contact aureoles.
F P Incropera - One of the best experts on this subject based on the ideXlab platform.
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Design of operating conditions for crackfree laser-assisted machining of mullite
International Journal of Machine Tools & Manufacture, 2004Co-Authors: Patrick A Rebro, Yung C Shin, F P IncroperaAbstract:Abstract The present study focuses on the evaluation of the laser-assisted machining (LAM) of pressureless sintered mullite ceramics. Due to mullite’s Low Thermal Diffusivity and inferior tensile strength, a new method for applying laser power is devised to eliminate cracking and fracture of the workpiece during laser heating by controlling the development of temperature gradients. Numerical modeling of workpiece temperature along with experimental measurement by a pyrometer is performed to determine the temperature at the material removal zone during LAM and to analyze the temperature gradient information to delineate the occurrence of cracking. With a designed gradual heating method, LAM of mullite is successfully performed without inducing any surface or subsurface cracks. Under the designed heating cycle, LAM of mullite is shown to be successful with a relative long tool life of carbide tools and good surface integrity.
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laser assisted machining of reaction sintered mullite ceramics
Journal of Manufacturing Science and Engineering-transactions of The Asme, 2002Co-Authors: Patrick A Rebro, Yung C Shin, F P IncroperaAbstract:The present study focuses on the evaluation of the laser-assisted machining (LAM) of pressureless sintered mullite ceramics. Due to mullite's Low Thermal Diffusivity and tensile strength, a new method for applying laser power is devised to eliminate cracking and fracture of the workpiece during laser heating. The LAM process is characterized in terms of cutting force, surface temperature, chip morphology, tool wear, surface roughness and subsurface damage for a variety of operating conditions. Estimated material removal temperatures and the ratio of the feed force to the main cutting force are used to determine material removal mechanisms and regimes for brittle fracture and semi-continuous and continuous chip formation. Surface roughness and subsurface damage are compared between typical parts produced by LAM and grinding. Tool wear characteristics are investigated for variations in laser power, and hence material removal temperature, during LAM of mullite with carbide tools.
