Heat spreaders can be made from natural graphite sheet materials. These spreaders take advantage of the anisotropic thermal properties of natural graphite. Natural graphite exhibits a high thermal conductivity in the plane of the sheet combined with a much lower thermal conductivity through the thickness of the sheet. As a result, a natural graphite sheet can function as both a heat spreader and an insulator and can be used to eliminate localized hot spots in electronic components. In some cases, a natural graphite heat spreader can replace a conventional thermal management system consisting of a heat sink and cooling fan. This paper examines the properties of natural graphite heat spreaders and the application of these spreaders to thermal management problems in laptop computers. The thermal and mechanical properties of natural graphite heat spreaders are presented along with a discussion of how those properties are measured. The use of a natural graphite heat spreader to reduce the touch temperature in a laptop computer is presented. Both experimental techniques and numerical models are used to examine performance of the heat spreader in this application.
The deformation characteristics of Ti-6AI-4 V have been established by torsion testing in the temperature range 800-1150°C. Constitutive equations are proposed for both the f3-region and the (J. +{3-region which, it is suggested, may have some practical applications. Extensive optical and electron microscopy have established that dynamic recovery is the operative deformation mode in the {3-region, while dynamic recrystallisation predominates in the ex + f3-region. MST/806
Expanded flexible graphite sheet materials have become attractive as Thermal Interface Materials (TIM’s). Flexible graphite sheet materials were originally developed as gaskets for fluid sealing applications. Properties that make flexible graphite sheets of interest as TIM’s include their relatively high thermal conductivities and their ability to conform well to surfaces. Specific grades of flexible graphite have been developed for TIM applications. Because flexible graphite sheets are porous, with open interconnected pores, it is possible to impregnate these sheets with various materials to improve properties. In particular, various polymers, such as mineral oils, synthetic oils, etc can be added to flexible graphite to improve its performance in thermal interface applications. This paper will review the thermal properties of TIM’s made by adding two different polymeric materials to a grade of flexible graphite specifically developed as a thermal interface material.
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