Should I have learned this in high-school Chemistry?

November 6, 2007 10:05 AM

Chemistryfilter: I'm looking for a solution (colliod? emulsion? gel? resin?) of a few inexpensive and non-dangerous ingredients whose composition can be adjusted to create a melting point near to room temperature (and moderate pressures).

Ideally, I'd like a solution for which melting and freezing would be repeatable, reversible, and the substance relatively dense, and not have a great change in volume between the liquid and the solid phase.

My notion was to create a kind of thermal mass for insulating a home, such that it might cause the internal temperature of the home to remain closer to room temperature, while outside temperature is fluctuating.

I guess in a location where the outside temperature were always to one side of room temperature, Death Valley say, this might not be helpful. A larger question - would such a scheme actually work (somewhere)? How might one determine whether this notion actually has any merit, presuming a suitable substance could be identified, and without building an actual prototype?

posted by newdaddy to science & nature (21 comments total)

I don't see how you're going to create anything like that without relying on hydrocarbons, which would be a dreadful fire hazard.
posted by Steven C. Den Beste at 10:35 AM on November 6, 2007

Gallium is the standard if you want something that's easy to freeze or melt around room temperature. I don't know about inexpensive, though.

You've got bigger problems, though. Most things I can think of along these lines conduct heat fairly well -- so you use a little heat to melt/freeze them, but the temperature inside is the same as the temperature outside pretty quickly. Add to that the fact that half the time your material will be in liquid phase, sloshing around in the walls, and on the whole, I'd still rather have fiberglass.
posted by rossmik at 10:36 AM on November 6, 2007

BASF is working on this - see Micronal. I believe the general keyword is "phase change insulation".
posted by pocams at 10:39 AM on November 6, 2007 [1 favorite has favorites]

the only substances i can think of which melt at or near room temperature are fats (think: butter). that, or metals like gallium. both seem pretty implausible as home insulation though. what you need is something like an icewater bath that is at the melting point such that hot days melt the ice and cool days freeze it.

as to your second question, i think it sounds plausible. the latent heat of fusion of most things is on the order of ~200 kJ/kg. a metric ton of such a substance melting completely would soak up about 200 MJ which is about 55 kW-hr.

does it need to be solid -> liquid transition? lots of things go from liquid -> gas at room temperatures under pressure, like CO₂ for instance. bonus that the heat of vaporization is generally a lot higher. but you would need some very sturdy construction, as you'd be basically living inside a bomb.

you should look into geothermal exchange heat pumps which operate on a similar (and cheaper) principle.
posted by sergeant sandwich at 10:42 AM on November 6, 2007

I do not understand how your system is supposed to work. How is the substance contained, how is it applied to the house, and what are the benefits its properties are supposed to provide?

I also wonder if such a system is really likely to create benefits beyond well established technologies like passive design and conventional insulation.

I don't think (I've got a bachelor's degree in chemistry that's over a decade old, so consider that as an endorsement/grain of salt on my opinion as you like) that just applying basic chemistry principles is going to get you to this substance. There are a lot of parameters here - a specific and presumably tunable melting point, non-toxicity, suitability to building applications (and keep in mind that building materials are subject to regulation), and low expense. You'd probably need to get a real materials scientist involved and have them plugged into parameter-searchable databases of materials for a start, and you might end up having to make it from scratch. Here's an article that might provoke some thought on materials candidates, in any event.
posted by nanojath at 10:44 AM on November 6, 2007

This is not exactly what you're asking for, but according to this episode of Quirks and Quarks, pine resin has properties similar to what you're looking for, and a company in North Carolina is making energy efficient homes by using pine or other woods treated with pine resin.
posted by dreadpiratesully at 10:49 AM on November 6, 2007

Nanojath, the OP is trying to take advantage of heat of crystalization and use it as a passive temperature regulation system. It's an interesting idea, but I'm not sure it's practical, for several reasons.
posted by Steven C. Den Beste at 11:07 AM on November 6, 2007

By the way, I'm not sure that an amorphous solid making a phase change to liquid actually has a very large heat of crystallization.
posted by Steven C. Den Beste at 11:09 AM on November 6, 2007

SCDB, did you read pocams BASF link? I think that pretty much covers what the OP was after.
posted by kuujjuarapik at 11:11 AM on November 6, 2007

To address the feasibility question, you want to look at (1) the "heat of phase change" - the amount of energy per mol or kg that is adsorbed/released during the phase change, (2) the density of the material you are considering (kg/m³) and its thickness (m), and (3) the heat flux incident on the material (W/m²). This third value is how much energy per second passes through the insulation and existing walls when the house and environment are at different temperatures (this number itself is temperature dependent).

With this information, you can calculate how long the material can effectively buffer a temperature excursion before the phase change is complete. You may find, for example, that you need meter-thick walls to contain the amount of material you need.
posted by Mapes at 11:23 AM on November 6, 2007

Wow, never heard of Micronal. One inch of a 30% mixture is the same as six inches of brick. Pretty cool, but I guess the cost is the reason it's not positioned as a replacement for insulation. Neat stuff, pocams.
posted by Tacodog at 11:30 AM on November 6, 2007

kuujjuarapik: "Microcapsules" are not made "of a few inexpensive and non-dangerous ingredients".

In terms of what the OP was thinking of, my biggest concern is mechanical loading on the building structure. Because the proposed material can become liquid, it means all the walls have to be sealed tanks -- and the shape is just about the worst imaginable for that. On hot days, the walls would bulge at the bottom. The stuff will also weigh a lot, and all that weight has to be supported by the building structure.

At the very least, the proposed material could not be retroinstalled into existing structures; the walls wouldn't be correct. To make it work, the stuff would probably have to be provided in the form of premade sealed panels which would be inserted into walls between studs during construction before the cladding was put on. But they would be heavy (compared, for instance, to glass wool), so the building structure would have to take that into account when it was designed.

And I'm still very concerned about the fire hazard, because there's no way anything like this is going to be done cheaply without relying on hydrocarbons.

The BASF material isn't quite the same as what the OP proposes, and I do believe that BASF can make it work. But that's because they're experts on microcapsulation, a very sophisticated and esoteric technology.

(BASF is mixing their microcapsules in with gypsum used for wallboard, which largely ameliorates the fire hazard.)
posted by Steven C. Den Beste at 11:43 AM on November 6, 2007

I think pocam's link is on the right track, if not exactly what the poster envisions. Also related, although not what the poster is looking for is this stuff for insulating homes against temps in the 1000 degree range; interestingly enough it is similar to the absorbent gel in diapers.
posted by TedW at 11:54 AM on November 6, 2007

How about Glauber's salt? That's an old-school thermal storage solution for solar heating systems. It's apparently non-toxic and non-flammable.
posted by srt19170 at 12:29 PM on November 6, 2007

I'd have to agree that pocam's link is, if not exactly what I was hoping for, a realistic means to attain the effect I was aiming for. But one would have to ask, if tiny plastic nodules filled with this wax are good, wouldn't larger volumes of this wax built into the structure of the house be better?

I know that building a metric ton of wax (with the potential of it liquifying at any moment) into a building would not be easy - SCDB does point out the several very real difficulties with what I was imagining.
posted by newdaddy at 12:35 PM on November 6, 2007

For the purposes the OP has in mind, Glauber's salt's phase change temperature (90 degrees F) is too high.
posted by Steven C. Den Beste at 12:36 PM on November 6, 2007

I disagree Steven: microcapsule technology really isn't a big deal, nor is it super high-tech. It takes some care to make, but it's not a bleeding edge technology by any means. It's been used in the food and drug industries for decades, for example. The reason it was used in this application is precicely to counter all of the objections your raise concerning bulk material handling and fire hazard. It's actually a rather elegant solution: here's an insulator that you can add to the gypsum aggregate that buffers temperatures at 78.5F. No extra manufacturing, no extra costs to installers, no retraining necessary. Micronal is a clever engineering application of some prosaic sythetic polymer chemistry.

Sometimes the best answer to an engineering problem is to go a simple as possible, but no simpler. To me, Micronal looks like one of those applications. I'll bet someone could gene engineer a quick-growing conifer wood to do something similar, but it probably wouldn't be cost effective.
posted by bonehead at 1:27 PM on November 6, 2007

Well, OK, let me pursue this half-baked notion just a bit further then. What if I said "Sure, I'm stepping up. I'm interested in embedding Micronal in a structural concrete that I'll be casting for part of my new, 2-and-a-half story building (in Baltimore)." How do I take the next step? Is it possible for a retail builder to get this stuff on the open market? How do I find out if it will "work"?

This is kind of fun - I ask questions, and people answer them. I could get used to this -
posted by newdaddy at 7:33 AM on November 7, 2007

I take it back. Skip the concrete idea. BASF has a gypsum board product already - a "smartboard" - with Micronal in it. Here is their "story" webpage for the product, and there's a nifty little animation link from there.
posted by newdaddy at 7:40 AM on November 7, 2007

Contact BASF (via the sales page on their site) and request a sales call back. BASF doesn't sell to the public really, but if you can come up with a reasonable pitch as a business customer, they'll give you the benefit of the doubt. You'll want to talk to one of their application specialists for certain. You could probably sweet talk them into giving you engineering samples, then take it from there.
posted by bonehead at 5:39 PM on November 7, 2007

Well, I have an architect and am looking to make a custom home. It would be hard to make a business pitch, other than that if the house were "successful" in the design sense, they may score some good press somewhere (it's a little to early to write that byline for ARCHITECTURAL RECORD, but we might hope for MARYLAND HOME initially, or aspire to DWELL.) We'll see. First I have to get my architect in sync with my intentions.
posted by newdaddy at 6:41 AM on November 8, 2007