One of the problems with concrete - AKA portland cement, or lime - is that
it slowly, for weeks and months, recrystallizes. This is the "cure" you
have to wait for when you pour a floor or wall, the reason you put plastic
or wet sacks over newly poured concrete and/or water it down. It doesn't
acheive full strength for months, though it gains most of it in the first
coupla weeks. The crystals form in the spaces between particles as the
water slowly leaves.
Most porous concrete is made with additives or fillers that go away after
the stuff has set, or by using a mix with no fines - e.g., pebbles but no
sand, as for cinder block.
Concrete technology is getting pretty upscale, you might get a pleasant
surprise if you contact one of the concrete specialty Co.s like Burke.
Take care, Malcolm
At 08:43 AM 10/18/03 -0400, you wrote:
Reid
There's probably no danger of vaporizing the silver.
The boiling point of silver is 2210 deg Centigrade.
I "think" that's higher than the firing temperature of pottery. You would
know better than I about that.
Cinder block is pretty porous, however, you're right..not much flow.
Porousity is probably linked to strength where the concrete that's porous
enough won't be strong enough.
The cement part is what gives the strength of the bond to the aggregates
and takes up the spaces that water would seep through.
It might be possible to smear the inside of a pottery container with a
thin and very weak concrete mix. [Morter really, as gravel would get in
the way.]
Essentially, a stabilized sand filter. [mix charcoal dust in too?]
If that's too weak, then two pots...one inside the other with a layer of
very very weak morter in between...or maybe just charcoal dust mixed wet
with CS? It may set up a little like a briquette.
More difficult to make but maybe more porous...a concrete foam, aka,
lightweight concrete made with an airflow as used to level floor systems.
Nowadays, they make something called "Hable block". It's a foam concrete
block that's so light that it floats till it soaks up enough water to
sink. It can be cut with a hand saw.
But it takes a day or two to sink a big block.
Ode
At 02:55 AM 10/18/2003 +0530, you wrote:
>Friends,
>To let you know, several years ago I did try making water filters out of
>concrete. I used a very dry mix, like that of a concrete block, and
>even less water, in hopes there would be some interconnectedness of the
>pores/ voids/ fissures. However I just wasn't getting the flow. I'm
>guessing there's something about the concrete bond that prevents the
>flow. It is apparent, at the very least that it's not possible to fine
>tune the flow rate (average), as is the case with pottery. For the
>pottery, using about half, pre-fired particles, and half unfired, normal
>clay, there's a pulling away of particles during drying and firing,
>that's caused by shrinkage of the normal clay. That brings about an
>ideal, and adjustable, permeable medium that's very responsive to
>alteration of flow rate, per composition. So givine the idiosyncracies
>of pottery clays, almost any of these can be rendered into a purifier.
>Maybe some more clever person than I am can make concrete work, but I
>just don't see it.
>
>As to the two liter flask, in the double boiler, my new plan of action
>is that next time I'll simply leave the starter out, using the bigger
>electrodes. The reaction rate may be slowish but with time I may still
>get viable concentrations. But I'm also proceeding to a back up
>methodology. Now we're saturating candles with AgNO3. I cannot think
>of another silver compound that's so easy to make, with such implicit
>likelihood of small partiucle size. We're mixing this in with the clay
>materials, then forming purifiers, drying and firng. Firing will lose
>the nitrate and should leave the metal, with a bond to the pottery.
>Even using lab made, reagent grade should prove very inexpensive.
>Making ones own, under proper conditions of course, should make silver
>nitrate far less expensive, giving a purifier that's still within the
>reach of the poor.
>Reid
>
>
>
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