Vacuum electronic devices operate with very high voltage differences between their sub-assemblies which are separated by very small distances. These devices also emit large amounts of heat that needs to be dissipated. Hence, there exists a requirement for high-voltage insulators with good thermal conductivity for voltage isolation and efficient heat dissipation. However, these voltage insulators are generally poor conductors of heat. In the present work, an effort has been made to obtain good high-voltage insulation materials with substantial improvement in their thermal conductivity. New mixtures of composites were formed by blending varying percentages (by volumes) of aluminum nitride powders with that of neat room-temperature vulcanizing (RTV) silicone elastomer compound. In this work, a thermal conductivity test setup has been devised for the quantification of the thermal conductivity of the insulators. The thermal conductivities and high-voltage isolation capabilities of various blended composites were quantified and were compared with that of neat RTV to evaluate the relative improvement.
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Abbreviations
- W :
-
Width of the sample (m)
- B :
-
Breadth of the sample (m)
- A = W × B :
-
Area of heat conduction (m2)
- L :
-
Thickness of the sample (m)
- T max :
-
Maximum temperature at steady state (°C)
- T min :
-
Minimum temperature at steady state (°C)
- ΔT = T max − T min :
-
Difference in temperature (°C)
- V :
-
Voltage applied to heater (V)
- I :
-
Current measured at heater (A)
- Q = V × I :
-
Heat supplied (W)
- R th = ΔT/Q :
-
Thermal resistance (°C/W)
- m :
-
Mass of the sample (kg)
- ρ :
-
Density (kg/m3)
- M :
-
Mass of the copper plate (kg)
- C p :
-
Specific heat capacity of copper (J/kg/K)
- dT:
-
Change in temperature around T min (°C)
- t s :
-
Time at T min + 1°C (s)
- t f :
-
Time at T min − 1°C (s)
- dt = t f − t s :
-
Time taken for dT cooling (s)
- dT/dt :
-
Rate of change of temperature (°C/s)
- k exp :
-
Thermal conductivity experiment (W/m/°C)
- k ds :
-
Thermal conductivity data sheet (W/m/°C)
- V RTV :
-
Volume of RTV (m3)
- V AlN :
-
Volume of AlN (m3)
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Suresh, C., Srikrishna, P. Experimental Evaluation and Comparison of Thermal Conductivity of High-Voltage Insulation Materials for Vacuum Electronic Devices. J. Electron. Mater. 46, 4414–4419 (2017). https://doi.org/10.1007/s11664-017-5372-5
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DOI: https://doi.org/10.1007/s11664-017-5372-5