Finite pulse-time and heat-loss effects in pulse thermal diffusivity measurements

Heckman, Richard C.

doi:10.1063/1.1662393

Cited by 159 publications

(47 citation statements)

References 7 publications

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“…The software supplied with the apparatus uses 5 different analysis methods to compute the thermal diffusivity. These methods are the Parker 20 , Heckman 21 , Cowan 22 , Clark and Taylor 23 , and Degiovanni 24 methods. Each analysis method, except for the Parker method, uses a different approach to correct for deviations from the ideal caused by factors such as radiative cooling, 2-D heat flow, and others.…”

Section: Microstructuresmentioning

confidence: 99%

Ultra high temperature ceramics for hypersonic vehicle applications.

Tandon¹,

Dumm²,

Corral³

et al. 2006

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HfB 2 and ZrB 2 are of interest for thermal protection materials because of favorable thermal stability, mechanical properties, and oxidation resistance. We have made dense diboride ceramics with 2 to 20 % SiC by hot pressing at 2000°C and 5000 psi. High-resolution transmission electron microscopy (TEM) shows very thin grain boundary phases that suggest liquid phase sintering. Fracture toughness measurements give RT values of 4 to 6 MPam 1/2 . Four-pt flexure strengths measured in air up to 1450°C were as high as 450 -500 MPa. Thermal diffusivities were measured to 2000°C for ZrB 2 and HfB 2 ceramics with SiC contents from 2 to 20%. Thermal conductivities were calculated from thermal diffusivities and measured heat capacities. Thermal diffusivities were modeled using different two-phase composite models. These materials exhibit excellent high temperature properties and are attractive for further development for thermal protection systems. 4 ACKNOWLEDGMENTS

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Section: Microstructuresmentioning

confidence: 99%

Ultra high temperature ceramics for hypersonic vehicle applications.

Tandon¹,

Dumm²,

Corral³

et al. 2006

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“…Two different models were then applied to fit the experimental data. The first model is the two-layers adiabatic model [25], whereas the second model takes into account the heat loss of the sample [31], and the contact resistance at the interface between the coatings and the substrate [32]. In addition, due to the measurement processing, estimated thickness values of the coatings were used to perform the experiments, and the values obtained were corrected to account for the true thicknesses of the coatings.…”

Section: Thermal Diffusivity Of the Coatingsmentioning

confidence: 99%

Thermal and mechanical properties of crack-designed thick lanthanum zirconate coatings

Weber

Lein

Grande

et al. 2014

Journal of the European Ceramic Society

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Vertical cracks are beneficial in thermal barrier coatings due to enhanced thermomechanical compliance. Accordingly, an aqueous nitrate based precursor solution was atomized on stainless steel substrates by spray pyrolysis to deposit thick crack-designed lanthanum zirconate coatings. Coatings with designed crack patterns were deposited and characterized by electron microscopy, tribology, Vickers indentation, and thermal diffusivity. The crystallization of the coatings was investigated by in situ high temperature X-ray diffraction. The green coatings crystallized from 600 °C and the pyrochlore structure was formed after heat treatment at 1000 °C. Crystalline lanthanum zirconate multilayered coatings with small crack spacing and crack opening exhibited a higher density, a higher hardness, lower thermal diffusivities, and higher thermal conductivities compared to crystalline monolayered coatings of similar thickness with large crack spacing and crack opening. The thermal diffusivity of the coatings, ~28 mm 2 /s at room temperature, was similar to the values reported for yttria-stabilized zirconia plasma sprayed coatings.

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“…: T m ϭ1 000 K, Dϭ0.001 m, kϭ1 W/m K), the order of L m is less than one (L m Ϲ1) in Eq. (9). As the heat loss in DHTT will be large at the detection thermocouple (CH-2) and the difference of heat loss between the radiation and the conduction is quite large, the characteristic two cases of heat loss are assumed as L 1 ϭ L 2 ϭ1 and L 1 ϭL 2 ϭ1 000 (triangular pulse; tϭ0.2 (pulse duration), t c ϭ20.736 and bϭ0.1: Appendix I).…”

Section: Effect Of Heat Lossmentioning

confidence: 99%

Factors on the Measurement of Effective Thermal Diffusivity of Molten Slag Using Double Hot Thermocouple Technique.

Kashiwaya

Ishii

2002

ISIJ International

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The molten slags that are used not only in the continuous caster but also in every metal industry play an important role and affect the quality of products. The authors initially developed the double hot thermocouple technique (DHTT) for in situ observation of mold slag crystallization.In this study, the DHTT was further developed to allow the measurement of the overall thermal diffusivity of molten slag applying the principle of the laser flash method. The affecting factors (finite pulse time, shape of pulse and heat loss from sample surface) on the measurement of thermal diffusivity using the DHTT were discussed theoretically using both the analytical and the numerical methods. New relationship between the thermal diffusivity a and the time at half-maximum temperature t 0.5 was obtained as follows:a(ϫ10 4 m 2 /s)ϭ0.000707(t 0.5 /t p ) Ϫ1.8946 The thermal diffusivity obtained from the experimental half-maximum time t 0.5 /t p (t p is the time of peak on the heat pulse) was in good agreement with the one from literature.KEY WORDS: thermal diffusivity; thermal conductivity; slag melt; laser flash; hot thermocouple; DHTT.DHTT and the laser flash method. The laser flash method is an excellent method and can predict a relatively suitable value of thermal diffusivity using Parker's method 4) (Eq. (3)). However, it will need a special alignment for the measurement of liquid and/or transparent material. Furthermore, a direct observation during measurement is almost impossible. On the other hand, the DHTT can observe the molten sample in situ. As shown in the previous study, 1,2) the solidification of mold slag is complicate phenomena including the bubble formation/breaking and the crystallization. It would be very important to know the sample image during measurement. The thermal diffusivity obtained from DHTT, however, is not yet established and it is not reported what kinds of factors affected on the measurement until now.For the preliminary approach to the application of the DHTT to the measurement of thermal diffusivity, the affecting factors on the measurement were elucidated from both the theoretical and the experimental method. In the case of laser flash method, an instantaneous laser pulse was used as a heat source and the temperature increase at the rear surface was measured by an infrared pyrometer (IR detector). In the case of DHTT, the temperature of one side thermocouple (CH-1, in Fig. 1) increased in a pulse shape and the other side of thermocouple (CH-2) was used as a detector. The typical temperature profiles of both CH-1 and CH-2 are shown in Fig. 2. The time t 0.5 at the half-maximum temperature (1/2 DT max ) was defined as shown in Fig. 2 and used for the calculation of thermal diffusivity according to the laser flash method (the details will be shown in below). The large differences between the laser flash method and DHTT are as follows: (1) Heat source is the order of several seconds (millisecond order in laser flash method). (2) Shape of pulse is not square. This factor might be decisive in bo...

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Finite pulse-time and heat-loss effects in pulse thermal diffusivity measurements

Cited by 159 publications

References 7 publications

Ultra high temperature ceramics for hypersonic vehicle applications.

Ultra high temperature ceramics for hypersonic vehicle applications.

Thermal and mechanical properties of crack-designed thick lanthanum zirconate coatings

Factors on the Measurement of Effective Thermal Diffusivity of Molten Slag Using Double Hot Thermocouple Technique.

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