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Electrical resistance of Type III Hardcoat Anodize

I know Hard anodize is an excellent electrical resistor. Is there a specification, or guideline to describe how much electrical resistance in Ohm/sq?

Is this a function of the sealing process (dichromate, teflon, hot water, etc.)?

I would imagine there is a general range for electrical resistivity and I am trying to find info on this.

Thank you.

Sr. Mechanical Engineer

Robert Will
design engineer - Waialua, HI, USA
July 30, 2008

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The latest edition of Sheasby and Pinner show some dielectric strength tables. contact me via email furnish fax number and I will send some of the data to you.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

August 1, 2008

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As you say, anodized aluminium has good electrical resistance. There are two distinctly separate features.

One, to which Robert Probert refers concerns electrical breakdown resistance. This depends mainly on anodic film thickness. Before the use of eddy-current instruments for determining film thickness, instruments were available which applied an increasing AC voltage until electrical breakdown occurred. A thickness of one mil would require a potential in excess of 1000 volts.

The other concerns electrical conductivity of the film. This involves measuring resistance using an electrolyte to make the contact. An AC current is used so more correctly impedance is measured. It is usual to express the result as admittance (1/impedance). The admittance is a measure of sealing quality: the lower, the better the sealing. The ISO standards for anodizing include methods of testing.

Harry Parkes
- Birmingham, UK
August 2, 2008