Mike, Yes, we are saturating the filters, drying them, then firing. Aside from the tiny amount of CS we use, the filters are made entirely from local, red clay, combined with a very fine grained combustible, which burns out, thus aiding permeability. In this case the combustible is wheat flour, which is inexpensive in Bangladesh. Keeping the materials simple will help keep the purifiers very cheap.
My primary challenge in developing this purifier has been to achieve good flow, and get control over the amount of flow. To do this we first prepare a 'grog,' a pre-fired material comprising 37% flour and 63% earthenware clay. We do not use a lot of water in the mix, as potters do, but keep it 'dry,' about 15 to 20% water. We then press this material into disks using a car jack. The disks are then dried, fired and crushed to the powder we call 'permeable grog.' Permeable grog is mixed with un-fired red clay powder, in some ratio that achieves the amount of flow we want. Aside from the micro-porosity of the grog, the mechanism of flow is what appears under the microscope as a network of elongated pores, appearing to be an average of 100 microns diameter by perhaps 0.05mm. in length. These pores (or planar shapes) occur because the un-fired clay shrinks away from the grog during the processes of drying and firing. As a result our purifiers, 6cms. dia. by 17cms height, with wall thickness 1.2cms., give a flow ranging from 0.5 to 1.5 liters per hour, depending on the mix of materials, the column height and several other variables. By contrast a convnetional earthenware container filled with water will be merely damp on the outside. The reason for this is that while there are lots of pores within the earthenware these are only very poorly inter-connected. The idea of mixing the clay materials with the CS solution would appear to be a good one, and I'm anxious to try it. But right now we are simply doing the things which we know will work. For one thing, if mixing CS in with the clay did not work I'm afraid we would not immediately know the reason for this, as there are so many variables, and our 'lab' is a collection of very primitive devices. It is one thing to do appropriate technology in the field and quite another to do it in the lab. Still, by patience, trial and error and appropriate evaluation, over time we hope to greatly improve our purifier. Reid Mike D. said: Reid, You're talking about saturating the filter elements in CS then drying and firing them, correct? Are the filter elements themselve produced locally? From what kind of clay medium are they made? If it's a powdered or crushed dry clay that is re-hydrated before forming or slip casting, would it make sense to use water with silver in it to wet the clay? Then the bisque firing will incorporate the silver right in the substrate, in a fashion that will keep the silver bound but available, I'd bet. There's no way I can think of to avoid blackening in a reducing atmosphere, but then I've got *no* experience there. On the other hand, are you sure that the oxide is not an acceptable form for the silver? Interesting project. Thanks for sharing it with us. Be well, Mike D. -- The silver-list is a moderated forum for discussion of colloidal silver. To join or quit silver-list or silver-digest send an e-mail message to: [email protected] -or- [email protected] with the word subscribe or unsubscribe in the SUBJECT line. To post, address your message to: [email protected] Silver-list archive: http://escribe.com/health/thesilverlist/index.html List maintainer: Mike Devour <[email protected]>
