The Thermal Conductivity of Several Fluoride Glasses

1985 ◽  
Vol 61 ◽  
Author(s):  
K. A. McCarthy ◽  
H. H. Sample ◽  
M. B. Koss
Keyword(s):  
Thermal Conductivity ◽  
Strong Correlation ◽  
Preliminary Analysis ◽  
Fluoride Glass ◽  
Plateau Region ◽  
Fluoride Glasses ◽  
Fluorozirconate Glasses ◽  
Temperature Range ◽  
Beryllium Fluoride ◽  
Thermal Conductivities

ABSTRACTThe thermal conductivities of beryllium fluoride glass and a fluoroberyllate glass have been measured in the 2–100K temperature range. These results are compared with earlier results on fluorozirconate glasses. The “plateau” region is well-defined for both materials. The plateau-center conductivity for BeF2 glass is the lowest yet recorded for any glass; it is some three times lower than the fluoroberyllate glass and four times lower than the fluorozirconates. A preliminary analysis of the data show a strong correlation between plateau-center conductivity and average cation mass of the material.

Effects of Nb doping on thermoelectric properties of Zn4Sb3 at high temperatures

2009 ◽  
Vol 24 (2) ◽  
pp. 430-435 ◽  
Author(s):  
D. Li ◽  
H.H. Hng ◽  
J. Ma ◽  
X.Y. Qin
Keyword(s):  
Thermal Conductivity ◽  
Electrical Resistivity ◽  
High Temperatures ◽  
Thermoelectric Properties ◽  
Figure Of Merit ◽  
Thermoelectric Performance ◽  
Temperature Range ◽  
A Value ◽  
Nb Doping ◽  
Thermal Conductivities

The thermoelectric properties of Nb-doped Zn4Sb3 compounds, (Zn1–xNbx)4Sb3 (x = 0, 0.005, and 0.01), were investigated at temperatures ranging from 300 to 685 K. The results showed that by substituting Zn with Nb, the thermal conductivities of all the Nb-doped compounds were lower than that of the pristine β-Zn4Sb3. Among the compounds studied, the lightly substituted (Zn0.995Nb0.005)4Sb3 compound exhibited the best thermoelectric performance due to the improvement in both its electrical resistivity and thermal conductivity. Its figure of merit, ZT, was greater than the undoped Zn4Sb3 compound for the temperature range investigated. In particular, the ZT of (Zn0.995Nb0.005)4Sb3 reached a value of 1.1 at 680 K, which was 69% greater than that of the undoped Zn4Sb3 obtained in this study.

Thermal Expansion and Isotopic Composition Effects on Lattice Thermal Conductivities of Crystalline Silicon

2006 ◽  
Author(s):  
Yunfei Chen ◽  
Guodong Wang ◽  
Deyu Li ◽  
Jennifer R. Lukes
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Md Simulation ◽  
Lattice Thermal Conductivity ◽  
Mass Difference ◽  
Dynamics Simulation ◽  
Temperature Range ◽  
Simulation Results ◽  
Callaway Model ◽  
Thermal Conductivities

Equilibrium molecular dynamics simulation is used to calculate lattice thermal conductivities of crystal silicon in the temperature range from 400K to 1600K. Simulation results confirmed that thermal expansion, which resulted in the increase of the lattice parameter, caused the decrease of the lattice thermal conductivity. The simulated results proved that thermal expansion imposed another type resistance on phonon transport in crystal materials. Isotopic and vacancy effects on lattice thermal conductivity are also investigated and compared with the prediction from the modified Debye Callaway model. It is demonstrated in the MD simulation results that the isotopic effect on lattice thermal conductivity is little in the temperature range from 400K to 1600K for isotopic concentration below 1%, which implies the isotopic scattering on phonon due to mass difference can be neglected over the room temperature. The remove of atoms from the crystal matrix caused mass difference and elastic strain between the void and the neighbor atoms, which resulted in vacancy scattering on phonons. Simulation results demonstrated this mechanism is stronger than that caused by isotopic scattering on phonons due to mass difference. A good agreement is obtained between the MD simulation results of silicon crystal with vacancy defects and the data predicted from the modified Debye Callaway model. This conclusion is helpful to demonstrate the validity of Klemens' Rayleigh model for impurity scattering on phonons.

THERMAL CONDUCTIVITY OF METALS AT HIGH TEMPERATURES: I. DESCRIPTION OF THE APPARATUS AND MEASUREMENTS ON IRON

1947 ◽  
Vol 25a (6) ◽  
pp. 357-374 ◽  
Author(s):  
L. D. Armstrong ◽  
T. M. Dauphinee
Keyword(s):  
Thermal Conductivity ◽  
Heat Flow ◽  
High Temperatures ◽  
Armco Iron ◽  
Absolute Error ◽  
Cylindrical Sample ◽  
Comprehensive Analysis ◽  
Temperature Curve ◽  
Temperature Range ◽  
Thermal Conductivities

An apparatus for measuring the thermal conductivity of metals in the temperature range 0° to 800 °C. is described. The method utilizes unidirectional heat flow in a cylindrical sample in a vacuum. The advantages of the method are outlined and a comprehensive analysis of possible errors in the measurements is included. Measurements on Armco iron indicate that results with an absolute error of less than 2% may be obtained. The results of measurements on a sample of Armco iron gave thermal conductivities of 0.1819 c.g.s units at 0 °C. and 0.0698 c.g.s. units at 800 °C. A change in slope of the thermal conductivity–temperature curve was found at a temperature of approximately 375 °C., and is tentatively attributed to the presence of 0.03% nickel impurity.

Anisotropy of thermal conductance in near-ideal graphite

1965 ◽  
Vol 284 (1396) ◽  
pp. 17-31 ◽  
Keyword(s):  
Thermal Conductivity ◽  
Basal Plane ◽  
Thermal Conduction ◽  
Theoretical Estimate ◽  
Thermal Conductance ◽  
Temperature Range ◽  
Neutron Damage ◽  
Plane Direction ◽  
Umklapp Scattering ◽  
Thermal Conductivities

Measurements of thermal conductivities of a number of pyrolytic graphites are reported in­cluding values for annealed, hot pressed graphite (IFPA 57). Thermal conductivities of IFPA 57 in both basal plane and c -axis directions approach the values for ideal graphite at higher tem­peratures. A theoretical estimate of the anisotropy of thermal conduction in ideal graphite in the temperature range where umklapp scattering predominates shows fair agreement with the present experimental value. Such defects as are normally present in well-oriented graphite produce comparatively little effect on the c -axis thermal conductivity and exposure to neutron damage has a much smaller effect in the direction of the c axis, than in the basal plane direction.

scholarly journals The variation with temperature of the thermal con­ductivity and the X-ray structure of some micas I—The thermal conductivity up to 600° C

1937 ◽  
Vol 163 (913) ◽  
pp. 189-198 ◽  
Keyword(s):  
Thermal Conductivity ◽  
High Temperatures ◽  
Temperature Curve ◽  
X Ray ◽  
Temperature Range ◽  
Conductivity Change ◽  
Initial Values ◽  
Thermal Conductivities

The authors recently had occasion to measure the thermal conductivities of several varieties of mica up to a temperature of 600° C. In the course of this work it has been observed that whereas the thermal conductivities of the muscovite varieties of mica alter but little over this temperature range, the thermal conductivities of certain phlogopite micas decrease to about one-third of their initial values when the micas are heated to about 200° C. In such cases there is incomplete reversibility in the thermal conductivity temperature curve on cooling. Subsequent examination of these micas by means of X-ray crystal analysis has revealed the fact that in those samples which suffered appre­ciable change in conductivity, the arrangement of the elementary crystals composing the mica laminae becomes displaced from their ordered setting at approximately the same temperature as the thermal conductivity change. The present paper describes the thermal conductivity experiments, which are believed to be the first determinations carried out on mica to high temperatures. In the paper which follows, Mr. W. A. Wood describes the X-ray experiments on some of these samples of mica.

Detailed Theoretical Investigation and Comparison of the Thermal Conductivities of n- and p-type Bi2Te3 Based Alloys

2013 ◽  
Vol 1543 ◽  
Author(s):  
Ö. Ceyda Yelgel ◽  
Gyaneshwar P. Srivastava
Keyword(s):  
Thermal Conductivity ◽  
Theoretical Investigation ◽  
Total Thermal Conductivity ◽  
Type Alloy ◽  
Electron Hole ◽  
Temperature Range ◽  
Image Position ◽  
P Type ◽  
Type 3 ◽  
Thermal Conductivities

ABSTRACTIn this work we present a detailed theoretical investigation of the thermal conductivities of n-type 0.1 wt.% CuBr doped 85% Bi2Te3 - 15% Bi2Se3 and p-type 3 wt% Te doped 20% Bi2Te3 - %80 Sb2Te3 single crystals. The thermal conductivity contributions arising from carriers, electron-hole pairs and phonons are computed rigorously in the temperature range $300\,{\rm{K}}\, \le \,T\, \le \,500\,{\rm{K}}$. In agreement with available experimental measurements we theoretically find that the lowest total thermal conductivity is 3.15 W K−1 m−1 at 380 K for the n-type alloy and 1.145 W K−1 m−1 at 400 K for the p-type alloy. Stronger mass-defect scattering is found to be responsible for the lower thermal conductivity of the p-type alloy throughout the temperature range of the study.

Study on Comparison of Thermal Conductivities of Thermal Insulations Using Different Measurement Methods in Wide Range of Temperature

2007 ◽  
Author(s):  
Takahiro Ohmura
Keyword(s):  
Thermal Conductivity ◽  
Measurement Methods ◽  
Transient Hot Wire ◽  
Hot Wire ◽  
Standard Material ◽  
Temperature Range ◽  
Hot Disk ◽  
Cyclic Heat ◽  
Thermal Insulations ◽  
Thermal Conductivities

Guarded hot plate method (GHP method) is the most popular way of measuring thermal conductivity of thermal insulation. However, there are large differences among the thermal conductivities measured by different apparatuses which are made in different institutions in the temperature range above 100 °C. It is considered the reason that we have no standard material for measurement of thermal conductivity. The standard material is only glass wool which are produced by NIST (National Institute of Standards and Technology) in a temperature range from about 7 to 67 °C. Then, I have researched how far the influence of the difference in measurement methods and apparatuses extends. Furthermore, I have investigated how to measure accurately thermal conductivity in the temperature range which there are few reference materials. In this study, I proposed to increase the accuracy of thermal conductivity of thermal insulation by comparing with values obtained using different methods. I investigated the practicality of the comparison of the results obtained by different methods, which are the GHP, cyclic heat, transient hot wire, and Hot Disk methods, for the accurate measurement at the temperature range from −170 to 1300 °C. First, I developed the three types of measurement apparatuses; one can measure thermal conductivity by using both the GHP and cyclic heat methods in the temperature range from 100 to 1300 °C, the second can measure using both the cyclic heat and transient hot wire methods in the temperature range from 100 to 1000 °C, and the third can measure using both the cyclic heat, transient hot wire, and Hot Disk methods in the temperature range from −170 to 25 °C. Next, I measured thermal conductivities of various thermal insulations using these apparatuses. In the temperature range above 100 °C, the results obtained by using the GHP and cyclic heat methods agree with each other within ± 10% deviations. In like manner, the results obtained by using the cyclic heat and transient hot wire methods agree with each other within ± 10% deviations. Furthermore, in the temperature range from −120 °C to 25°C, the results obtained by using the cyclic heat, transient hot wire, and Hot Disk methods agree with each other within ± 10% deviations. Therefore, it is thought that to compare the thermal conductivities obtained by the different measurement methods will be practical for improvement of the accuracy measurement at the temperature range in the absence of reference materials.

Thermal Characteristics of Damp Hydrophobic, Microfibrous Batt

1988 ◽  
Vol 110 (1) ◽  
pp. 19-22
Author(s):  
K. A. Steele
Keyword(s):  
Thermal Conductivity ◽  
Mathematical Model ◽  
Thermal Characteristics ◽  
Region Of Interest ◽  
Experimental Results ◽  
Preliminary Design ◽  
Insulating Material ◽  
Temperature Range ◽  
Higher Temperature ◽  
Thermal Conductivities

The thermal characteristics of damp, hydrophobic insulating material used primarily in underwater dry suit applications were investigated. Testing was performed in a Rapid-K Thermal Conductivity Instrument manufactured by Dynatech, Inc. A mathematical model of the process was proposed, and the results obtained using this model were compared to experimental results. The two agreed well except in the higher temperature range, where the model predicts higher thermal conductivities than those observed. However, for the region of interest agreement was good, and the model should be considered valid for the preliminary design of dry suits using hydrophobic batting as an insulator.

Thermal Conductivity of the New Candidate Materials for Thermal Barrier Coatings

2007 ◽  
Vol 280-283 ◽  
pp. 1503-1506 ◽  
Author(s):  
Jing Dong Wang ◽  
Wei Pan ◽  
Qiang Xu ◽  
Kazutaka Mori ◽  
Taiji Torigoe
Keyword(s):  
Thermal Conductivity ◽  
Rare Earth ◽  
Thermal Barrier Coatings ◽  
Thermal Barrier ◽  
Pressureless Sintering ◽  
Barrier Coatings ◽  
Temperature Range ◽  
Thermal Conductivities

Rare-earth zirconate ceramics (Gd2Zr2O7, Sm2Zr2O7, Nd2Zr2O7, Dy2Zr2O7, Er2Zr2O7 and Yb2Zr2O7) were successfully prepared by pressureless sintering at 1550oC for 10 hours. The thermal conductivities of these ceramics were measured and the results indicated that the thermal conductivities of rare-earth zirconates were much lower than that of YSZ in the temperature range 20-800oC.

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