I have heard aluminium forms a thin layer of AL2O3 on its surface. Is it electrically conductive? How much? For example if I put a sheet of aluminium under ground can it transfer the electricity to the earth? Can the oxide be considered as an obstacle?
Aluminium is a highly reducing metal, and because of this,it spontaneously oxidises in air. Fortunately, the alumina barrier which is formed is almost totallly impervious, so oxidation is nearly completely stopped. Fortunately, otherwise aluminium would burn spontaneously in air. Moreover, Al powder is pyrophoric, i.e. can be very dangerous when exposed abruptly to air. But bulk Al is just covered by a very thin Al2O3 layer, and this is the reason why pure Al is never shiny. Alumina is an electronic insulator, but becomes ionic conductor at high temperature. Because it is very thin over its metal, alumina doesn't prevent electric conduction, but just add a contact resistance. Conduction takes place throughout alumina by tunnelling effect.
Alain
As far as I know, Al2O3 takes usually the form of a ceramic powder (at room temperature and 1 Atm). Just as CO2, it is the product of combustion, and is quite stable. It is commonly utlised as insulator in the Dens ePlasma Focus experiments, as it provides insulation between the anode and the cathode of the Dense Plasma Focus.
thanks Andea
any information about the thin layer of Al2O3 on Aluminium metal. Does it insulate the metal. how much?
I can speak about Dense Plasma Focus application only, where Al2O3 is mandatory. Al2O3 provides coating of copper in a 2 Torr atmosphere of deuterium at troom temperature, and Dense Plasma Focus works with 2-microseconds, 20 kV, 20 kA discharges . Thickness of Al2O3 is about 1 mm, but this is a rough estimate indeed. For more details, see e.g. H. Herold, A. Jerzykiewicz, M. Sadowski and H. Schmidt "Comparative analysis of large plasma focus experiments performed at IPF, Stuttgart, and IPJ, Świerk", Nucl. Fusion 29 1255 (1989).
Al2O3 is a bad conductor of electricity, and also offering high resistance to conduction of electricity. Aluminium forms oxide when comes in contact of air(oxygen) in humid atmosphere like other metals( Fe,Cu etc). As it is economical to( reduce wire thept), to use aluminium as transmission line wire, compare to copper, now a days, is used by many electricity boards, utilities and companies. Drawback is more maintanence needed to remove oxide and to make perfect connection to reduce the voltage drop and power losses at junction/joints to increase distribution efficiency and voltage regulation of system.
Dear Bhupendra Desai, thanks
What is you idea about using aluminium as earth plate, will it work or not.
We have to consider that the Al2O3 layer is so thin, 4nm and lower conductivity may be compensated by using larger plate to keep the resistance constant.
please consult your professor and others having deep understanding about earth, resistance aluminum ...
Best Regards
With its dielectric dielectric constant and dissipation factor ranging in between 9.7-9.1 and 0.0007-0.0002SI/ Metric[ depending upon whether the Al2O3 cotains 99.5%- 94%Al] makes PURE Al2O3 high temperature electrical insulator*
As regards to second part of your query, I submit as:
It is a well reported phenomenon that when exposed to air[or heated] ,Al forms a protective Al2O3 layer to make it nonconducting but when scratched[ there are every chance of its being scratched while driving[ wear and tear], the NONCONDUCTING Al2O3 OXIDE LAYER MAY BE PEALED OFF. BELOW THIS OXIDE LAYER, THERE COMES THE UNOXIDIZED [Al ]METAL WHICH CAN CONDUCT THE ELECTRICITY to creat problems intermitantly.
*Of course, its thermal conductivity lies in between 30-22.4 W/m degreeK
Aluminium is a highly reducing metal, and because of this,it spontaneously oxidises in air. Fortunately, the alumina barrier which is formed is almost totallly impervious, so oxidation is nearly completely stopped. Fortunately, otherwise aluminium would burn spontaneously in air. Moreover, Al powder is pyrophoric, i.e. can be very dangerous when exposed abruptly to air. But bulk Al is just covered by a very thin Al2O3 layer, and this is the reason why pure Al is never shiny. Alumina is an electronic insulator, but becomes ionic conductor at high temperature. Because it is very thin over its metal, alumina doesn't prevent electric conduction, but just add a contact resistance. Conduction takes place throughout alumina by tunnelling effect.
Alain
I have done some rough resistivity experiments with AL powder using a glass tube, metal electrodes and a DC power supply. To my surprise the powder was conducted NO current at all. Other powder like grafene and carbon conducted quite well. I assume the AL powder oxidized
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