Iain and I are to find/extract some zeolite for use in a vacuum pump. The idea is for the Team to build a vacuum-driven water-cooling system that can be used to cool down a spacesuit. At low pressures, water will “boil” at a lower temperature than it does at atmospheric pressure.
The process of boiling/evaporation should be able to cool a water supply that can be circulated round the spacesuit. The role of the zeolite is to lower the pressure in the vacuum system even more by adsorbing the evaporated (boiled) water.
Zeolites are microporous materials containing lots of little cavities and channels (much like the activated charcoal and pumice in Programme 1). This porosity provides a huge surface area onto which small molecules like water can adhere.
Iain and I have two sources of zeolite – mine will be the packet of washing powder that Kate has provided in the chest. Iain will go and look for a more natural zeolite source.
It should be easy enough for me to extract the zeolite from the washing powder; it is, after all, the only component of the powder that is insoluble in water.
The problem is that the zeolite is so finely powdered, it won’t simply be a matter of dissolving everything else in water and filtering off what doesn’t dissolve – I’d need especially fine filter papers to do that, and I don’t have them.
One potential way round the problem would be to thoroughly shake the washing powder up in water and let what doesn’t dissolve (the zeolite) settle out overnight under the effect of gravity.
Tomorrow morning I could then decant off the water above the settled solid and dry the solid outside in the heat of the day. That’s what I decide to do. Tomorrow's going to be quite an easy day … or so I think!
I suspected it would be more difficult that I’d imagined. Although some of the zeolite settles out overnight, it’s so finely powdered that much of it stays suspended in the water. Separating the zeolite out this way won’t produce as much as I need. I'll have to find an alternative method.
Out here in California it gets pretty hot during the day. The temperature inside the workshop can top 38 degrees Celsius at times. We’ve thoughtfully been provided with a couple of large electric fans to keep us cool, and over an early lunch, I entertain the idea of converting one of them into a centrifuge.
That would be a much more effective way of getting the undissolved zeolite to settle out from a ‘solution’ of the detergent. Because of the size of the fan, I’d only be able to process smallish quantities of detergent at a time, but at least I’d be able to get a much more efficient separation this way.
The problem, of course, is that I’m depriving colleagues of 50% of their cooling system for a while. I only need the fan for a few hours though – surely they won’t mind. As it turns out, no-one notices the fan has gone missing.
By early afternoon I’ve dismantled one of the fans, and knocked together a centrifuge of sorts. It’s taken a while to get the balance right, and I’ve soaked myself in the process, but at last I can get on with separating out the zeolite from the washing powder more efficiently now.
Well the idea’s worked – by lunchtime on day three I’ve retrieved enough zeolite from the washing powder to go into the vacuum pump that Kathy and Jonathan have designed. What’s more, Iain’s managed to locate a good source of natural zeolite, and he’s brought back enough to make sure the pump will work effectively even without my ‘artificial’ material.
Yesterday wasn’t just spent separating out zeolite though. The thought occurred to me that we might be able to cool the water circulating around our spacesuit down even more effectively by using a bit of chemistry.
Dissolving certain inorganic salts in water can bring about a cooling effect – the temperature of the water will actually drop. Only a few inorganic salts are capable of producing this effect, and ammonium chloride is one of them. But where can I get some from?
In the chest on day one was a bag of ammonium sulphate fertilizer. By boiling this ammonium sulphate in water for 30 minutes or so with an equivalent amount of sodium chloride (table salt) I could actually make some ammonium chloride.
OK, it would be contaminated with sodium sulphate (a by-product of the reaction), and I’d have no way of separating the two products, but it might just work.
And it did! From the boiled ammonium sulphate/sodium chloride solution that I’d left to cool overnight last night, beautiful white crystals of (albeit contaminated) ammonium chloride had formed.
All I had to do was filter off the solid, dry it in air and then test it to see if dissolving it in water did actually produce a cooling effect. Lo and behold, when I added some of the dried ammonium chloride crystals to water, the temperature of the water dropped by six degrees Celsius. Amazing!
By 2 pm we were headed off to Death Valley to test out our spacesuit and vacuum pump. By the time we'd arrived, it was hot; 37 degrees Celsius.
When we came to film, I decided to add just a third of the ammonium chloride that I’d made over the last couple of days. I wish I’d added it all now, because it turned out that we’d only have one shot at filming it. It would have been much better to have used the lot in one go.
Nevertheless, adding even this amount of ammonium chloride to the system did actually give us a small temperature drop.