Thermal conductivity of polycrystalline graphite
โ Scribed by R. Taylor; K.E. Gilchrist; L.J. Poston
- Publisher
- Elsevier Science
- Year
- 1968
- Tongue
- English
- Weight
- 630 KB
- Volume
- 6
- Category
- Article
- ISSN
- 0008-6223
No coin nor oath required. For personal study only.
โฆ Synopsis
Measurements of thermal conductivity from 100 to 900ยฐK and electrical resistivity at 80ยฐK have been made on two mutually perpendicular directions of two types of anisotropic polycrystalline graphites and of two isotropic graphites of different densities. The thermal conductivity curves can be fitted using expressions calculated for thermal resistance due to boundary and isotope scattering and a relationship for Umklapp scattering derived from pyrolytic graphite. By invoking a factor to account for the reduction in conductivity due to porosity and irregular arrangement of crystallites in polycrystalline graphite, crystallite sizes values are obtained from thermal conductivity analysis. Crystallite sizes obtained from electrical resistivity measurements using the simple two band model are about Z/3 those derived from thermal conductivity and various reasons are suggested to explain the difference.
๐ SIMILAR VOLUMES
El Segundo, California). Graphite samples which have been heated resistively or by a laser to produce chaoite have been studied by an Ion Microprobe Mass Analyzer (IMMA). The yield of secondary negative ions from the starting material is typically C,-, C2-, and with lesser amounts of C3-and C\*-but
Experimental data are presented on the changes of thermal conductivity of a number of polycrystalline graphites due to doping with boron and bromine, which respectively represent a substitutional and interstitial acceptor type defect. The results are compared with changes in thermal conductivity due
An effective conductivity (thermal or electrical) is derived for polycrystaltine graphite using a very simple approach. The material is modeled as a series of links and junctions, the former representing the crystallies and the latter the intercrystallite region. The large anisotropy of the principa
The length of polycrystalli~e graphite samples was measured as a function of temperature while cycling from 1000" to 24OO'C. A sample oriented perpendicular to the extrusion direction exhibited thermai expansion hysteresis for cycling to 2400" and 2200ยฐC but little or no hysteresis for cycling to 20