tumadre
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lead compound in my radiator corroded
My rebuilt radiator is soldered together with what appears to be normal lead solder, what is interesting is that the solder is slowly being converted
into a light brown oxide.
The joint that broke is an overlaping flange with a 2mm spacing that is 6mm wide. Over approximatly 6 years the cooling fluid has eaten through 3 to
6mm of that solder.
question: the solder used seems to be mostly lead, in my experience from working with lead it is exactly like lead but a little harder. So what could
be alloyed with lead that would allow is to corrode like it did? and any ideas on how can I analize the small amount that I have left?
The solder has the hardness of 15%zinc--85%lead
I would think that if it was pb-zn then it would corrode on the surface only.
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AllanD
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Typical solder mixes for brass radiators do not contain Zn, but Sn.
And the corrosion of the solder joints can be interestingly complex.
the water antifreeze mixes and the typical presence of
several different metals can result in a weak electrolytic
reaction that can increase over time as the anti-freeze
degrades.
Iron engine blocks
aluminum cylinder heads, timing covers (through which water flows) water pumps manifolds and the brass radiator and a coolant solution that becomes
increasingly alkaline as time
and temperature cycles pass is an invitation for degradation of the weakest link, the solder joints which are in direct contact
with the most noble metal (the copper) in the system.
And in cars with soldered brass radiators that is the Pb/Sn soldered brass radiators.
Which is yet another reason why most manufacturers have switched to either specially brazed aluminum radiators
or mechanically joined radiators selaed with an epoxy compound
and at a stroke eliminating both the less "noble metals" (the lead and tin of the solder joints) and the most noble metal
(the copper/Zinc alloy of the radiator tank and tubes.
And grealy reduced the liklihood of corrosion failure within the system.
Then when the auto manufacturer's material engineers solved that problem they created a new one by replacing various components made of aluminum for
new components made of magnesium-aluminum alloys, primarily for the weight reduction...
AD
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futurenobellaureate
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Who manufactured your radiator?
Sciguy
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tumadre
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I have no manufacturer
sorry.
I am more concerned about how AllanD gets an alkaline solution
I was thinking acidic but that doesn't explain anything considering the iron involved being more active than the lead,
although the electrolytic reaction would be uneven if that were the case, because the radiator is floating electrically relative to the engine block.
and the corrosion was very even.
I am interested in finding some epoxy that would be thermally conductive, stick to aluminum, and have some malibility, unlike most epoxys, which have
no malibility
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AllanD
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I'll admit right off I don't understand it, but I know from measurement that under some circumstances (over time) the glycol/water mix becomes
Alkaline.
Under uther (equally unknown) it becomes acidic.
In either case the coolant starts to act as an electrolyte
and with the variety of metals involved there are a host of possibilities....
You have
Iron in engine blocks and/or cylinder heads
Aluminum in the Cylinder heads, water pump housing manifolds and timing covers.
Copper/Zinc (Red Brass) in the radiator
Lead/Tin (solder) in the joints of the radiator
Plus you have the high likelihood of Combustion gasses (HC, CO, CO2, H2O and NOx) seeping past the gaskets and reacting with the coolant as well as
Silicon which is a component of most automotive castings, Both Ferrous and aluminum based...
So you could potentially have several different acids, silicates
metal oxides
So how about you explain it?
And BTW, why assume that the radiator is "floating"
both are usually grounded to the chassis, though I'll point out that most modern radiators are made of brazed or expoied radiators with glas
reinforced thermoplastic side tanks and the radiators are invariably mounted by said tanks, and so ARE isolated as you say, but lder brass radiators
are usually attached metal-to-metal to the body structure and are thus grounded to the engine block like most other metal parts of the car.
AllanD
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tumadre
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The radiator was not connected via metal-to-metal,
metal to several molded rubber shock absorbers with plastic mounting clips.
I can't explain the chemistry, I was really asking why the lead/tin/sn/zn would not stop corroding past the surface.
does it not take a relativly strong acid/hydroxide to attack lead/tin/sn ?
red brass doesn't get corroded because the zinc does, and is there by removed, thus changing the color to a straight copper color.
I did find that the brass was very brittle.
I think we are looking for a lead/tin/sn/zn ion attatched to a decomposed glycol,
and one that would disolve in water.
what really matters is how to stop overheating in stop and go traffic.
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Heisenberg
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If you are using a soldered radiator you can't use the orange antifreeze, it attacks the solder. If you are using green coolant, you should check for
electrolysis by inserting 1 probe from a voltmeter into the radiator neck and the other to battery ground.
3. VERIFY THAT NO ELECTROLYSIS IS PRESENT IN THE COOLING SYSTEM.
THIS ELECTROLYSIS TEST CAN BE PERFORMED BEFORE OR AFTER THE SYSTEM HAS BEEN REPAIRED. USE A DIGITAL VOLT METER SET TO 12 VOLTS. ATTACH ONE TEST LEAD
TO THE NEGATIVE BATTERY POST AND INSERT THE OTHER TEST LEAD INTO THE RADIATOR COOLANT, MAKING SURE THE LEAD DOES NOT TOUCH THE FILLER NECK OR CORE.
ANY VOLTAGE READING OVER 0.3 VOLTS INDICATES THAT STRAY CURRENT IS FINDING ITS WAY INTO THE COOLANT. ELECTROLYSIS IS OFTEN AN INTERMITTENT CONDITION
THAT OCCURS WHEN A DEVICE OR ACCESSORY THAT IS MOUNTED TO THE RADIATOR IS ENERGIZED. THIS TYPE OF CURRENT COULD BE CAUSED FROM A POORLY GROUNDED
COOLING FAN OR SOME OTHER ACCESSORY AND CAN BE CHECKED BY WATCHING THE VOLT METER AND TURNING ON AND OFF VARIOUS ACCESSORIES OR ENGAGE THE STARTER
MOTOR.
quoted from GM manual, I'm not shouting, just too lazy to paraphrase tonite. 
I am just starting out with chemistry, but I have 20 years with cars.
[Edited on 9/8/2006 by Heisenberg]
[Edited on 9/8/2006 by Heisenberg]
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tumadre
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cool, chemistry is more fun than cars, no matter what happens you can always reduce it.
i would recommend that anyone who has an older car put a block of zinc in the radiator.
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Mr. Wizard
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| Quote: | Originally posted by tumadre
cool, chemistry is more fun than cars, no matter what happens you can always reduce it.
i would recommend that anyone who has an older car put a block of zinc in the radiator. |
Lead, Zinc, and Aluminum in contact through an electrolyte, should make an interesting mess. I'll vote the Aluminum goes first. I've seen the white
chunks of crap that form when Zinc or die cast alloy corrode when in contact with an Aluminum engine part. It looks like plaster and takes a chisel to
get it off. I'd vote for using anticorrosion additives and keeping your antifreeze new or clean. If you were to use a sacrificial anode, I'd use a
Magnesium one. I don't know exactly where it would be placed, except it should have electrical contact with whatever is is going to protect.
I've had personal experience with not have a good engine to frame ground on the alternator circuit, which caused some serious corrosion around the
Aluminum water pump housing. I speculate some of the current tried to return via the coolant since I didn't have a heavy ground on the alternator
bracket to the car body. Putting a heavy cable from the alternator case to the frame solved that problem.
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