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| BobBob Member Since: 28 Nov 2020 Location: Harrogate Posts: 6   
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I've been pondering this a lot. And it turns out that that this is what i think happens, (though I really don't have a proper grasp of chemistry and have lots of questions unanswered - I might ask my son's gcse chemistry teachers! or some guys at work with chemistry degrees).
Alu connected to steel (in the body rivets, screws etc) with exposed metal in salt water: The Alu loses electrons to the saltwater, the electrons are "pulled off" by the galvanic potential between steel and alu with steel being the anode - gaining the electrons, and alu loosing them - the anode. The cations of Alu (positively charged atoms as they have lost electron) then join with the Sodium ion (sodium chloride (salt) breaks apart in water) to form the white stuff - sodium aluminate. the electrons the steel have received actually create a 'reduction' and can prevent rusting getting rid of oxygen atoms. I even  have two jars with salty water. One where the aluminium is connect to the steel bolt (above water if that matters?) and the other jar has them apart. The one where they are connected, the steel is fine, not rusting!, I'm still waiting for the Alu foil to do some noticeable. the one where they are not touching, the bolt is degrading fast into a rusty mess.
If you charge up the steel in difference to the aluminium you could potentially advance this process, perhaps I'll give this a try in a third jar! Reverse the charge and you'd lose steel really quickly. On red arc, most of the forum chat seem say you need to immerse the vehicle to get these electronic system to work. we are dealing with a different problem that just steel rusting. So in theory if you raise the potential of the steel it might prevent rusting, but I'm not sure about this still, and it's practically difficult. In a defender the aluminium is connected too the steel in too many places and will be at the same potential anyway and you can't do much electronically. Sacraficial anodes - the ones loosing electrons and allowing it's atoms to combine with the salt - need to be isolated and have a lowered potential, either by virtue of the galvanic scale or the electronics. So for a sacfafial anode for the aluminium then we might need to have something that is pretty more negative than the steel-alu voltage, and be isolated from the steel/Alu and in every drop of salt water where there is a exposed alu-steel junction. Totally impractical. And because the galvanic scale I presume it would probably just protect the steel still anyway. So I conclude we just stop the bare alu touching the bare steel. Salt can't do much to bare alu and there is not much you can do to protect bare steel with electronics, so all steel needs proper coating, obviously. Happy to be corrected on my basic chemistry lesson. |
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10th Feb 2021 10:13pm |
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| donmacn Member Since: 06 Nov 2017 Location: Nth Scotland Posts: 1841 
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I'm not the one to correct anyone's chemistry. I stopped doing that in my 4th year at school, and get lost when the ions and cations come out to play....
But you said: "we stop the bare alu touching the bare steel" - and that is, 100% my simple approach. It's not even the 'bare' stuff - even if they were coated when assembled, 10/20/30 years later that coating will be just a memory. If you're in a country where the roads are salted during winter, then the further north you are, the more salty things will be, and that just adds to the problem. I had an experience a few years ago: in a queue for a ferry, an older Australian guy got off the tour bus in front of me to take some pics. He walked back past my car, had a look at my then tailgate and asked; "Jeez - what do you do with that? Wash it in salt water??" It occurred to me that, in winter, that's exactly what's happening with a 'daily driver' - the gunk that gets deposited on the back of the car will have a very high salt content. Unless you wash it off every single time the car is used - which is just impractical - then that salt will do its worst. In every single place on my car, where alu. and steel meet, and where I've had the time and opportunity to fix it, then I've put in a physical barrier - either a plastic/pvc gasket or duralac. On the electronic thing, I'm near 100% convinced that I spoke to a guy with a stand at a Game Fair in the Highlands, several years ago, who was selling some sort of system. I'm a sucker for impulse buys when I've had a pint or two, but either I didn't have the Defender then, or the price was still beyond the 'impulse' level. I still see Defenders around here these days with the branding on the back. I'm going to try and track that down - but it could well be that he was importing something from Aus. Donald 1994 Defender 300Tdi 110 SW - owned since 2002 - 230k miles and going strong (The 'rolling restoration' or tinkering thread: http://www.defender2.net/forum/topic58538.html ) 2000 Range Rover P38 4.0L V8 in the past.. RR classic - fitted with 200Tdi 1984 RR classic - V8 with ZF auto box 1993 Discovery 300Tdi not to mention the minis and the Type 2 VW camper... |
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11th Feb 2021 9:55am |
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| s55shh Member Since: 30 Dec 2019 Location: staffs Posts: 193
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My elise was done at the factory and in the afternoon we did a trackday. I wish LR did the same/similar |
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11th Feb 2021 4:04pm |
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| Supacat Member Since: 16 Oct 2012 Location: West Yorkshire Posts: 11018 
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Engineering integrity and professional ethics ~ Lotus has them both. 🤐
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11th Feb 2021 4:08pm |
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