Battery freezing?

[MarcJ]

Yes which comes back to what I said in #2 and #5. I just dont remember any spell of cold weather this winter when it might have happened. Perhaps there was briefly early on.

Even if nearly pure water when it froze its now worth checking for any acid remaining in the bilges or wherever it would have gone and give everywhere likely to have been contaminated a rinse with a solution of washing soda. Although with luck its all been retained by the glass mat

Thanks Vic, good point about the giving the area a rinse down...

 

[JumbleDuck]

That freezing point graph is really strange, if I am reading it right. The way the freezing point changes both up and down as the concentration increases doesn't compute in my head. At 77% it freezes at -10°C, at 91% it freezes at -10°C but at 83% it freezes at +7°C. Is that right?

It reflects the rather complicated phases diagram of sulfuric acid - lots of diffferent structures form at different concentrations. Here's a picture

(Oops, VicS has already done this)

taken from http://www.homepages.ucl.ac.uk/~ucfbanf/research/sulfuric_acid_hydrates.htm

 

[JumbleDuck]

I cannot compete with VicS' brilliant work in tracking down the sulphuric acid phase diagram but you may be interested in similar low melting points resulting from eutectics in metals. Perhaps the best known is Woods Metal with a melting temperature of 70C, despite being composed of elements that all have melting points well into the hundreds. There is a good page on it, and similar eutectics, at http://en.wikipedia.org/wiki/Wood's_metal

I'd have thought the best known, if not quite so extreme, would be standard 60-40 solder ...

PS I found the same diagram as VicS by doing a GIS on "sulfuric acid phase diagram". Using the correct spelling of "sulfuric" matters!