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May 2012

Volume 83, Issue 5, Articles (05xxxx)

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Rev. Sci. Instrum. 83, 051101 (2012); http://dx.doi.org/10.1063/1.4709621 (18 pages)

Igor Lubomirsky and Oscar Stafsudd

The periodic pulsed heating technique for measuring pyroelectricity (the Chynoweth method) is one of several measurement techniques that have been significantly enhanced through advances in instrumentation such as fast digital averaging oscilloscopes and modulated light sources.

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back to top Thermometry; Thermal Diffusivity; Acoustics; Photothermal and Photoacoustic

Development of a continuous testing apparatus for temperature reduction performance of cool coatings

Zhongnan Song, Yunxing Shi, Weidong Zhang, Jianrong Song, Jian Qu, Yanwen Li, and Zhongde Wang

Rev. Sci. Instrum. 83, 054901 (2012); http://dx.doi.org/10.1063/1.4709494 (5 pages) | Cited 2 times

Online Publication Date: 2 May 2012

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The working principle of a continuous testing apparatus for the temperature reduction performance of cool coatings is presented in this work. The apparatus consists of infrared reflector type lamps, an adiabatic box, and a data acquisition system. It was calibrated with the different conventional reference panels. The tests for dynamic and steady state temperature reduction performances were illustrated with two cool coatings. Results obtained directly from the simultaneous measurement are in good agreement with those calculated from separate measurements, thus confirming this apparatus as a valuable experimental tool for research and development of cool coatings.
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07.05.Hd Data acquisition: hardware and software
07.20.Dt Thermometers

Highly sensitive thermal conductivity measurements of suspended membranes (SiN and diamond) using a 3ω-Völklein method

A. Sikora, H. Ftouni, J. Richard, C. Hébert, D. Eon, F. Omnès, and O. Bourgeois

Rev. Sci. Instrum. 83, 054902 (2012); http://dx.doi.org/10.1063/1.4704086 (7 pages) | Cited 3 times

Online Publication Date: 8 May 2012

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A suspended system for measuring the thermal properties of membranes is presented. The sensitive thermal measurement is based on the 3ω dynamic method coupled to a Völklein geometry. The device obtained using micro-machining processes allows the measurement of the in-plane thermal conductivity of a membrane with a sensitivity of less than 10 nW/K (+/−5 × 10−3 Wm−1 K−1 at room temperature) and a very high resolution (ΔK/K = 10−3). A transducer (heater/thermometer) centered on the membrane is used to create an oscillation of the heat flux and to measure the temperature oscillation at the third harmonic using a Wheatstone bridge set-up. Power as low as 0.1 nW has been measured at room temperature. The method has been applied to measure thermal properties of low stress silicon nitride and polycrystalline diamond membranes with thickness ranging from 100 nm to 400 nm. The thermal conductivity measured on the polycrystalline diamond membrane support a significant grain size effect on the thermal transport.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Cm Micromechanical devices and systems
07.20.-n Thermal instruments and apparatus

A thermal porosimetry method to estimate pore size distribution in highly porous insulating materials

V. Félix, Y. Jannot, and A. Degiovanni

Rev. Sci. Instrum. 83, 054903 (2012); http://dx.doi.org/10.1063/1.4704842 (8 pages) | Cited 1 time

Online Publication Date: 11 May 2012

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Standard pore size determination methods such as mercury porosimetry, nitrogen sorption, microscopy, or x-ray tomography are not always applicable to highly porous, low density, and thus very fragile materials. For this kind of materials, a method based on thermal characterization is proposed. Indeed, the thermal conductivity of a highly porous and insulating medium is significantly dependent on the thermal conductivity of the interstitial gas that depends on both gas pressure and size of the considered pore (Knudsen effect). It is also possible to link the pore size with the thermal conductivity of the medium. Thermal conductivity measurements are realized on specimens placed in an enclosure where the air pressure is successively set to different values varying from 10−1 to 105 Pa. Knowing the global porosity ratio, an effective thermal conductivity model for a two-phase air-solid material based on a combined serial-parallel model is established. Pore size distribution can be identified by minimizing the sum of the quadratic differences between measured values and modeled ones. The results of the estimation process are the volume fractions of the chosen ranges of pore size. In order to validate the method, measurements done on insulating materials are presented. The results are discussed and show that pore size distribution estimated by the proposed method is coherent.
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07.20.-n Thermal instruments and apparatus
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials

The thermal flash technique: The inconsequential effect of contact resistance and the characterization of carbon nanotube clusters

Nayandeep K. Mahanta and Alexis R. Abramson

Rev. Sci. Instrum. 83, 054904 (2012); http://dx.doi.org/10.1063/1.4717733 (5 pages)

Online Publication Date: 29 May 2012

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This article presents a comprehensive mathematical treatment of the theory behind the thermal flash technique used to measure the thermal diffusivity of nanostructures. Analytical expressions predicting the temperature and its rate of change for various combinations of sample length and diffusivity confirmed that the presence of contact resistance between the heat sink/source or within a cluster of materials does not influence the measurement. Measurements on multi-walled carbon nanotube clusters provide further experimental evidence supporting the claim that contact resistance is inconsequential to this technique and yield a thermal conductivity of 2665 W/m K, which corresponds to an isolated nanotube and not the overall cluster.
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65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
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