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Ceramic principle

  • Author:naky
  • Source:www.diecastingpartsupplier.com
  • Release on:2015-01-16
Ceramic principle

Thermal radiation

The basic approach for heat exchange : conduction, convection and radiation. In order to effectively heat,
people often approach by reducing the thermal resistance of the heat flow and enhanced convection coefficient to
achieve, often overlooked thermal radiation. LED lamps generally use natural convection , the heat sink of the
LED is quickly transmitted to the heat sink surface , due to the lower coefficient of convection , heat can not
be dissipated to the surrounding air , resulting in the surface temperature, the deterioration of the working
environment LED . Emissivity can effectively improve the heat radiator surface of the heat radiation of the form
away , typically aluminum radiator to increase the emissivity of the surface by anodic oxidation , the ceramic
material itself may have a high emissivity characteristic , the need for intricate subsequent processing .

Radiation Mechanism

Radiation mechanism of ceramic materials are produced by random vibration of non-resonant two- phonon effects
and multi- phonon . High radiation ceramic material such as silicon carbide , metal oxides , borides etc. exist
strong infrared activation polar vibrations , these vibrations due to the extremely polar anharmonic effects ,
the absorption coefficient of the dual- frequency region and , in general with 100 ~ 100cm-1 order of magnitude
, corresponds to the absorption zone of moderate intensity reflectance is low in the remaining region of the
reflection band , therefore , is conducive to the formation of a relatively flat with strong radiation。

In general , with high thermal radiation efficiency of the radiation belts , roughly extending from the strong
resonance wavelength to shortwave throughout the two -phonon combinations and frequency region , including some
combination of multi- phonon region , which is a common feature of most ceramic materials with high radiation
radiation belts It can be said , mainly due to strong radiation with radiation combination of the two phonon
band. With few exceptions , the general radiation ceramic radiation belts focused than 5m of two phonons , three
phonon region . Thus , for the purposes of the infrared radiation ceramics , 1 ~ 5m band radiation mainly from
the direct transition transition of free carriers from the impurity band or electron to the conduction band
energy level , greater than 5m band radiation attributable to two main phonon combination radiation。

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