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scott <sco### [at] scott com> wrote:
> It's just the dull grey of aluminium oxide you are seeing on the outer
> surface. If you looked close and polished them a bit you'd see nice shiny
> aluminium :-)
What stops the aluminum from oxidizing all the way through?
--
- Warp
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"scott" <sco### [at] scottcom> wrote:
> > And isn't alumina pretty much transparent at the thicknesses it's likely
> > to
> > reach in ambient conditions?
>
> Having had a car with bare aluminium panels, I can tell you that it quickly
> goes dull grey if you don't polish it :-) I have no idea what the thickness
> is, but it certainly is visibly very different.
Ah, fair enough, I must be thinking of something else.
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On Thu, 03 Sep 2009 10:13:50 +0100, Invisible <voi### [at] devnull> wrote:
>You're aware that those cables are carrying several *million* volts?
No.
--
Regards
Stephen
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On 3 Sep 2009 05:39:36 -0400, Warp <war### [at] tagpovrayorg> wrote:
>scott <sco### [at] scottcom> wrote:
>> It's just the dull grey of aluminium oxide you are seeing on the outer
>> surface. If you looked close and polished them a bit you'd see nice shiny
>> aluminium :-)
>
> What stops the aluminum from oxidizing all the way through?
Aluminium oxide. Aluminium is so reactive that it almost instantly forms a skin
of aluminium oxide which insulates it from the surrounding air stopping it from
oxidising further.
--
Regards
Stephen
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Warp <war### [at] tagpovrayorg> wrote:
> scott <sco### [at] scottcom> wrote:
> > It's just the dull grey of aluminium oxide you are seeing on the outer
> > surface. If you looked close and polished them a bit you'd see nice shiny
> > aluminium :-)
>
> What stops the aluminum from oxidizing all the way through?
The initial oxide layer. It slows further oxygen access to the bulk beneath.
Aluminium oxide is particularly effective at this - many high-temperature
alloys are designed with this phenomenon in mind.
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Invisible wrote:
>
> You're aware that those cables are carrying several *million* volts?
>
Where is that kind of voltage used?
The biggest powerlines in Finland are carrying 400kV.
-Aero
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Invisible wrote:
>>> Why do overhead cables never flap around in the wind? Come to think
>>> of it, why doesn't rain short out power cables?
>>
>> Those cables are pulled rather tight, also take a close look at high
>> tension wires, they'll have some funny looking thing hanging off of
>> them that looks like some sort of paddle, This also helps with the
>> wind. And they're too far apart to short out in the rain. Fresh water
>> is actually not a great conductor, and air is even a worse conductor.
>> Submerge them in salt water, and they'll short for sure.
>
> Rain water isn't chemically pure. (Depending on pollution levels.) Once
> the pylon gets wet, it's entire surface is covered in a continuous sheet
> of water, which also covers all of the cables. So why don't they short out?
>
Right, but think of the impedance and the distances the electricity
needs to travel. It's not chemically pure, and may be mildly conductive,
but the layer is thin, and not continuous. There's enough resistance to
current that it doesn't flow.
>
> [Actually, apparently peppers are hot due to an antifungal toxin...]
Hmm, and I thought it was to discourage mammals from eating them, since
some mammals can actually destroy the seeds before they're "deposited"
> Seems plausible, I guess...
--
~Mike
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Invisible wrote:
>
> You're aware that those cables are carrying several *million* volts?
>
At most about 500kV. Typically 250kV. ;) Not millions.
>
> Well, this stuff clearly works - it's just a mystery to me *why* it
> works. ;-)
Physics is why it works ;)
--
~Mike
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Bill Pragnell wrote:
> The initial oxide layer. It slows further oxygen access to the bulk beneath.
> Aluminium oxide is particularly effective at this - many high-temperature
> alloys are designed with this phenomenon in mind.
The oxide layer also doesn't flake off like, say, iron oxide. So no
fresh metal is exposed.
--
~Mike
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scott schrieb:
>> Why do overhead cables never flap around in the wind?
>
> Actually they do, it's just it's usually very fast and very low
> amplitude flapping. Imagine holding out a stretched violin string in
> the wind, it's not really going to flap is it?
Indeed, in strong wind you can actually hear such cables "sing".
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