Microwaves for dehydrating magnesium chloride
Susan Hill
product it hydrolyses to the hydroxy chloride MgOHCl (although the PDF
files on the XRD are a little out of date and I suspect that this formula
is, at best, an approximation). Has anyone any experience at dehydrating
any Group II deliquescent salts to an anhydrous product using microwave
energy rather than conventional heat ?
Brook Hill
Uncle Al
Potent oxophiles (small highly-charged cations) cannot be physically
dehydrated without forming oxo-species. Cook it up in SOCl2 (reflux,
in a hood, CAREFULLY).
--
Uncle Al Schwartz
http://www.mazepath.com/uncleal/
http://www.ultra.net.au/~wisby/uncleal/
http://www.guyy.demon.co.uk/uncleal/
http://uncleal.within.net/
(Toxic URLs! Unsafe for children and most mammals)
"Quis custodiet ipsos custodes?" The Net!
Boaz Ben-David
>
> When I microwave MgCl2.6H2O crystals - instead of converting to an anhydrous
> product it hydrolyses to the hydroxy chloride MgOHCl (although the PDF
> files on the XRD are a little out of date and I suspect that this formula
> is, at best, an approximation). Has anyone any experience at dehydrating
> any Group II deliquescent salts to an anhydrous product using microwave
> energy rather than conventional heat ?
>
When I was going over the Merck Index, it looks that many hydrated salts,
behave deferent at slow heating then at rapid heating.
Though I never tested that phenomenon, I tend to agree with it.
That is: at rapid heating, the decomposition procceed, deferently then at slow heating.
Some times, melting is observed at other T then as in slow T.
It looks that high T grad. force different energy transformation in such salts.
[any one know on other kind of materials that undergo such phenomenon?]
Any coments on the above are welcome.
[It may be that the general and schematic scenario relates to "sudden" change vs.
gradual change and is much broader then just for salts.
I wonder if any one knows how to quantify that into solid figures, which will
allow predictions?]
Hence, what you observed is likely to be due to rapid heating.
[MW is less T gradient stimulator then heating from the outside. I would expect
that if you heat it conventionaly, but rapidly, the phenomenon will be stronger]
If I recall correctly, Merck Index (11th ed) mention the evolution of HCl at rapid heating.]
Boaz
Susan Hill
is corroding away. However the use of microwaves is going to produce some
radical new chemistry I feel sure. If I could find a way to absorb the H2O
before it hydrolyses the MgCl2 it may work - how about if I dissolve it in
some higher boiling point alcohols. I've hear that ethylene glycol works
at removing the water before you reach the BP of the glycol - but I've also
heard that some other nasties are evolved besides water. Anyone heard
anything about this ??
Gavin Whittaker
: When I microwave MgCl2.6H2O crystals - instead of converting to an anhydrous
: product it hydrolyses to the hydroxy chloride MgOHCl (although the PDF
: files on the XRD are a little out of date and I suspect that this formula
: is, at best, an approximation). Has anyone any experience at dehydrating
: any Group II deliquescent salts to an anhydrous product using microwave
: energy rather than conventional heat ?
It looks to me as though you've had no temperature control on there
for starters. If you simply stuck it in an oven and heated, then the
result isn't surprising.
Gavin
Microwave chemistry web pages at http://www.ed.ac.uk/~ah05/microwave.html
Gerry Harbison
Susan Hill wrote:
>
> Yes - there was HCl evolved at higher temperatures which is why my microwave
> is corroding away. However the use of microwaves is going to produce some
> radical new chemistry I feel sure. If I could find a way to absorb the H2O
> before it hydrolyses the MgCl2 it may work - how about if I dissolve it in
> some higher boiling point alcohols. I've hear that ethylene glycol works
> at removing the water before you reach the BP of the glycol - but I've also
> heard that some other nasties are evolved besides water. Anyone heard
> anything about this ??
The fact that MgCl2.6H2O gives MgOHCl on heating has been known for a
long time. I don't think it has anything to do with the rate of dehydration.
Bill
Try lowering the power on the mike to only zap it every so often instead
of a continual irradiation.
Can't you simply put it in the oven or fuse it over a flame?
Stirring and vacuum may help remove the water of crystallization as it
is released so that it doesn't hydrolyze the dehydrating salt. Only one
way to find out.
Bill
Susan Hill wrote:
>
> When I microwave MgCl2.6H2O crystals - instead of converting to an anhydrous
> product it hydrolyses to the hydroxy chloride MgOHCl (although the PDF
> files on the XRD are a little out of date and I suspect that this formula
> is, at best, an approximation). Has anyone any experience at dehydrating
> any Group II deliquescent salts to an anhydrous product using microwave
> energy rather than conventional heat ?
>
> Brook Hill
JJ
mine during her summer job under contract with Noranda Technologies. Yes,
you do need a high boiling point alcohol-- I can't remember which one.
There are actually two components required. I can't say anything more than
this as the work is being patented as we speak. She did give a presentation
on it at the Quebec Canadian Mining Conference in late August, but even that
just referred to the components as "reagent X and reagent Y".
Just know it can be done.
Yonek Hleba
Queen's University
Kingston, Ontario, Canada
6y...@qlink.queensu.ca
(please reply to the above email address)
Susan Hill wrote in message <37f74...@news.esc.net.au>...
>Yes - there was HCl evolved at higher temperatures which is why my
microwave
>is corroding away. However the use of microwaves is going to produce some
>radical new chemistry I feel sure. If I could find a way to absorb the H2O
>before it hydrolyses the MgCl2 it may work - how about if I dissolve it in
>some higher boiling point alcohols. I've hear that ethylene glycol works
>at removing the water before you reach the BP of the glycol - but I've also
>heard that some other nasties are evolved besides water. Anyone heard
>anything about this ??
>