Question
Asked 12th Dec, 2014
Deleted profile

Is it possible to electrically insulate an aluminum block by fabrication?

Their is an aluminum block that is internally hollow. It has to be electrically insulated but thermally active.
Is it to possible to electrically insulate it by depositing a layer of Aluminum Nitride or Silicon carbide or magnesium oxide.
If yes, what should be the fabrication process and what should be the thickness of deposition.
Any information or experience with regards to the subject is welcomed.

Most recent answer

26th Feb, 2018
Liang Tian
University of Michigan
Diamond coating is an alternative solution due to the fact that most diamonds are electrical insulators but extremely efficient thermal conductors. The Al2O3 layer on Al surface may not be fully insulating when the layer thickness is thin. It also reduce thermal conductivity at the same time.

Popular Answers (1)

13th Dec, 2014
Gerard Macias
University of Glasgow
Anodization of the aluminum block may be the most appropriate solution for insulation.  However take into account that there will be some volume expansion. In most applications it shouldn't be a problem but if you have tight tolerances you may need to take that into account. Besides, thermal conductivity and thermal expansion of aluminum oxide are diferent from that of  aluminum. Take this into account for your application.
With regard to the procedure, in industry it is quite common to perform anodization in sulfuric acid due to its high transparency. The quality standards in industry specify a thickness of aluminum oxide of 20 microns (which could take around 4 h under mild anodization conditions) but for electrical insulation you would need much much less (a few nanometers might do the work but I would recomment some microns if the block may be subject to scratching).
Typical parameters for sulfuric acid anodization are 0.3M sulfuric acid in water, 20V as the applied potential and a cold bath at 5 ºC.
Hope that works for you!
3 Recommendations

All Answers (11)

13th Dec, 2014
Satish Wani
Delphi
You can anodized the aluminum block surface. Check its process at http://en.wikipedia.org/wiki/Anodizing
2 Recommendations
13th Dec, 2014
Bhupendra Desai
Indian Institute of Technology Roorkee
Al2O3, the aluminum oxide is a bad conductor electricity, hence let the block get rusted, thicker the layer better will be the electricity insulation, paint it with aluminum oxide . Thickness of which depends on the voltage to be applied......
2 Recommendations
13th Dec, 2014
Gerard Macias
University of Glasgow
Anodization of the aluminum block may be the most appropriate solution for insulation.  However take into account that there will be some volume expansion. In most applications it shouldn't be a problem but if you have tight tolerances you may need to take that into account. Besides, thermal conductivity and thermal expansion of aluminum oxide are diferent from that of  aluminum. Take this into account for your application.
With regard to the procedure, in industry it is quite common to perform anodization in sulfuric acid due to its high transparency. The quality standards in industry specify a thickness of aluminum oxide of 20 microns (which could take around 4 h under mild anodization conditions) but for electrical insulation you would need much much less (a few nanometers might do the work but I would recomment some microns if the block may be subject to scratching).
Typical parameters for sulfuric acid anodization are 0.3M sulfuric acid in water, 20V as the applied potential and a cold bath at 5 ºC.
Hope that works for you!
3 Recommendations
Deleted profile
@ Gerard Macias
Thank you for detailed explanation.
Is the same concept applicable for Aluminum nitride?
 According to my information it has more conductivity(thermally) than aluminum but acts as electrical insulator.  I want to use it as a body for the heater i want to design which will be subjected to 750w above condition. 
Any information will be of great help
regards
Abhishek Pathak
14th Dec, 2014
Gerard Macias
University of Glasgow
Well, I haven't worked with AlN but certainly it should work better for heater applications than alumina thanks to its higher thermal conductivity. However, you should check if this AlN layer has good adhesion with the Al beneath since peeling off would destroy the insulation. But I guess that if you use direct nitridation on the aluminum block you will have no problem as it would grow from the Al present in your block. Also, I would expect some volume expansion using this method.
Since I haven't work with this material I can't really help with the process, but I would advice you also to have some microns of AlN on your Al block to provide scratch-resistant electrical insulation.
Deleted profile
@ Gerard Macias
Thanks for the info
17th Dec, 2014
R. Brian Peters
US ITER Project Office
An alternative if you have access to the technology and your  design is primarily driven by the thermal conductivity of the insulating layer would be to  apply a CVD diamond coating to the block.  Best available thermal conductor, Electrical Insulator, High scratch resistance,  but a more expensive process than anodization, or nitriding    As with other coating systems you will need to do some research on bond strength to the aluminum and relative thermal expansion of the aluminum and coating materials.  These two considerations may be the downside  for this solution.
Regards,
Brian
Deleted profile
@ R.Brian Peters
Thanks for the info
I hope by CVD you mean chemical vapor deposition. my system is subjected to water based experiment i.e water will be in contact, If i am not wrong CVD loses it strength over a time on action of water.
Any information again will be of great help.
19th Dec, 2014
R. Brian Peters
US ITER Project Office
I do not know specifics regarding CVD diamond and exposure to water.  You might consult with a company that specializes in the process such as:
 or
Good luck with your project.
Deleted profile
@ R.Brian Peters
Thank you 

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