Expert: Reza Foudazi - 12/5/2007

Question
I am a student at Brigham Young University, Provo, UT

Thank you for your previous answer about this ice pack blanket...maybe you can help me with what I have learned since then:

Here's my idea so far:

As you know, I am trying to come up with the concept of an automatic ice pack in the form of a blanket.
However, I want to avoid using water, and I want it to look like a normal blanket.
I've decided that I'll need to find two powders that cause an endothermic reaction.
The two I came up with are:
1) barium hydroxide octahydrate and ammonium nitrate: [Ba(OH)2. 8H2O(s)   2 NH4NO3 (s) ?Ba(NO3)2(s)   2NH3(aq)   10H2O (1).]  

or

2) thionyl chloride (SOCl2) and cobalt(II) sulfate heptahydrate.

I would put each (in its free flowing powder form) into little pockets in a big cellophane sheet (like a quilt), alternating the powders (like a checkerboard).

Each pocket has small openings (or slots) on all four "walls" of the pocket. This pocketed cellophane sheet would be sown into underneath blanket material (wool or cotton) so that it looks and has the texture of a normal blanket.

The blanket is folded carefully so the powders stay in their respective pockets.
However, when unfolded and wrapped around a person, the cellophane would be moved so much that the powders would come out of the openings and mix, thus creating their endothermic reaction and turning the blanket into an instant, giant ice pack.

So, the initial question I have is, for each reaction, how much of a temperature drop from room temperature could each of these reactions go, and how long would each reaction last?

I know that with the normal ammonium nitrate and water mixture, it goes down to about 34 deg. F. and
lasts about 15-30 mins before it goes back to room temp.  

I have also decided to put a time-release mechanism so that the reactions would take a lot longer than normal. Because there are no body fluids involved, I have to come up with some kind of medium.
The ideas I have so far are:

1) put a certain polymer/gum thing in all the openings between the pockets as a "door-type barrier.) Then the powders from both sides would stick against the polymer, or be absorbed, and slowly be combined through the "door" (time release polymer medium.)

Or

2) put the powders in capsules that go through the slots between the pockets, but I would need to figure out how to get these to dissolve without water. The reason is, is that I want the blanket to be as light as possible.

I know that most time release related things work with the ph in the body, but I wonder how it could work in this blanket?  

What do you think, and do you have any alternate suggestions, especially regarding the time release mechanism? Thanks!

~Brooke Doud

Answer
Hi,
Your idea is good, but you should think about practicality and also possibility.
I'm not sure about the reactions you mentioned, but I think that these reactions take place in an aqueous media and if you mix the powders with each other nothing will happen!!
So at least you should be sure about the reactions, you can check it in general chemistry books like Mortimer's one.
The next thing that you should consider is the reactants (products of reaction) should easily de-react (it means that if you warm or cool your blanket, the primary chemicals will be produced again). I don't think that you want this blanket for single use...
These above points and their consideration affect your idea very much, so it does not seem necessary to write about the release and other things you asked.
Regards,
Reza