vyv_cox
Well-Known Member
Its the lovely triangular phase diagrams on p43 that Nigel should study
Ah, three-component phase diagrams. I remember answering exam questions on them. Couldn't do it now, though
One for the chemists: Zinc or Magnesium?
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Ah, three-component phase diagrams. I remember answering exam questions on them. Couldn't do it now, though
Leonidas
Well-Known Member
In shipping, we normally use two types of anodes: Zinc which yieds 780 Ah and Aluminium which yields 2700Ah. There several specialist firms that manufacture and market these. One of them is Wilson Walton up in the North who have their own foundries and smelting facilities (www.wilsonwalton.com) They might be able to help out with your research.
Leonidas
Well-Known Member
Correction : Zn: 780Ah/kg, Al: 2700Ah/kg
VicS
Well-Known Member
No not specifically. They are called aluminium anodes because they are an aluminium alloy.
They are recommended for use in brackish water, when Zn is not suitable, but can be used in salt water
The electrode potential makes then as effective, even a bit more so perhaps, as zinc.
The RAM is much lower , and Al is trivalent, so for the same "activity" less mass of metal is lost
OTH aluminium is less dense so for the same mass the anode is larger
Depending on metal prices aluminium may or may not the an attractive alternative to zinc in salt water.
.
nigelmercier
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A lot of my bits of scrap are attached to bits of steel, so I was looking for a simple test that would positively identify the zinc without having to melt each piece individually, I can then junk the rest.
Perhaps an acid that would produce a certain coloured salt?
Hoolie
Well-Known Member
Try a flame test, broadly described in Wikipaedia here.
VicS
Well-Known Member
A cannot think of any coloured salts of Zn, Mg or Al.
None of the elements in question produces a coloured flame.
The slightest contamination with sea water will led to the familiar orange/yellow sodium flame
Last edited:
Carduelis
Well-Known Member
Is it safe?
Very slightly off topic, but how do you intend to melt them? When this idea was raised a while ago, someone pointed out that heating zinc gives off a toxic gas.
I'm not a chemist, so personally I've no idea if this is correct, but maybe somebody could advise?
Very slightly off topic, but how do you intend to melt them? When this idea was raised a while ago, someone pointed out that heating zinc gives off a toxic gas.
I'm not a chemist, so personally I've no idea if this is correct, but maybe somebody could advise?
nigelmercier
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Thanks Vic.
Looks like I will have to try igniting small slivers to rule out Mg, and assume that there will be no Al.
VicS
Well-Known Member
What i suggested earlier ,#7, will distinguish the Mg from Zn but Al will behave similarly to Zn.
ZnO is distinctly yellow when heated strongly. That should identify the Zn.
When I did A level chemistry distinguishing Zn Al and Mg would have been a doddle with the equipment and materials available in a school chem lab.
They dont do that sort of analysis now but would still not be difficult to do with what's avaialble
ZnO is distinctly yellow when heated strongly. That should identify the Zn.
When I did A level chemistry distinguishing Zn Al and Mg would have been a doddle with the equipment and materials available in a school chem lab.
They dont do that sort of analysis now but would still not be difficult to do with what's avaialble
AntarcticPilot
Well-Known Member
Ah, three-component phase diagrams. I remember answering exam questions on them. Couldn't do it now, though
Me too - but in my case, it was minerals like Feldspar.
winsbury
Well-Known Member
slightly off topic - is an anode needed at all if no shore power is used and no electrical connection exists between any of the metal hull fittings ?
VicS
Well-Known Member
Fitting anodes has nothing to do with shorepower. If a shorepower system is isnatlled it may cause rapid anode depletion unless certain precautions (viz fitting a galvanic isolator) are taken.
Interconnecting metal fittings may lead to galvanic corrosion. Cathodic protection may help to prevent this but the better solution would be to not interconnect the fittings if there was no reason to do so.
Some metals will naturally corrode at an unacceptable rate, steel for example and cathodic protection can be used to prevent this.
They may be times when a mix of metals cannot easily be avoided. Folding props are a typical example. Anodes can prevent corrosion of the vulnerable components.
In some cases there is no sound reason to fit anodes.
I used to crew a Westerly Berwick. It had no anodes and it still does not. There is no significant corrosion. It has all the original skin fittings and seacocks and the original (fixed 3 bladed) prop on the original shaft.
Perhaps the engine cooling water intake strainer has been replaced. If so its only because the perforated element inside it fell apart due to dezincification.
winsbury
Well-Known Member
Thanks, that was pretty much what I thought but keep getting worried by the fact my boat has none - there are a couple of bronze skin fittings and the prop from the outboard but non of these are interconnected internally, no shore power and its going on a swinging mooring. The boat currently has no fittings for an anode but its been in freshwater until now so was just checking as its about to start a new chapter of life on the sea.
VicS
Well-Known Member
Ah not quite the "if its been Ok until now dont go fixing things that aren't broken" scenario
Keep a close watch on things that might have been OK in freshwater but wont fare to well in salt water.
The possibility of ordinary brass skin fittings etc comes to mind.
Keep an eye open for dezincification but they won't fail in 5 minutes. Some builders now fit brass ( allowed under all the European nonsense) on the basis that they will last for 5 years . But if they are bronze or even DZR there should be no worries
Keep an eye on the prop as well.
Sail drive? If so that will have anodes which will become even more important to maintain.
winsbury
Well-Known Member
99.999% certain the fittings are bronze, the skeg is definitely aluminum-bronze, there is no inboard motor although the outboard sits in a well in the cockpit so is in essence the saildrive but theres no electrical connection to the motor although it does have an alternator this isnt used.
VicS
Well-Known Member
The outboard will almost certainly have an anode. Often set underneath the cavitation plate.
Keep an eye on it and replace when necessary esp if your outboard is permanently mounted with its LU in the water
Of you cannot undo the screw(s) holding it you can through bolt a small one to the underside of the cavitation plate
winsbury
Well-Known Member
The manual says there is one but damned if I can find any trace of an old one or anyone selling one that fits; its a 8hp Mariner Saildrive 2-stroke.
VicS
Well-Known Member
You dont say what the serial number is.
Different types of anode have been fitted at different times/to different versions.
Find the relevant diagram of the gearcase at http://www.boats.net/parts/search/Merc2/Mariner/parts.html and you will see the anode .
It should be mentioned in the owners manual which you should be able to find at
http://download.brunswick-marine.com/download/main;jsessionid=105vjo07c1lcd?type=corp if you have mislaid your copy
winsbury
Well-Known Member
found it - basically not much left of it, it nothing like whats in the manual and what there was was caked in white salty stuff hence had trouble indentifying it, new one now ordered. I love WD40, it uncovers all kinds of mysteries !