I was thinking that he ran salty water through the filter to convert the
silver nitrate to silver chloride, which is barely soluble so it would
get "stuck" in the matrix. I may be wrong though.
I remember we went back and forth here on several possible methods and
protocols before he settled on his final solution.
Marshall
Ode Coyote wrote:
Then there is Harvey Reid [?] [a silverlister]
That impregnated saw dust with silver [nitrate?] and mixed it with
clay to fire, making activated carbon/silver ceramic pot water
filters [in Africa?]
" Barefoot Native tech".....on a shoe without even a string from WalMart.
Now, to hook it up to a solar panel and pass a few microamps through
it all......
ode
At 07:11 PM 8/31/2010 -0500, you wrote:
Some extracts from the article are below.
- Steve N
<http://www.rdmag.com/News/2010/08/Materials-Nanotechnology-High-speed-filter-uses-electrified-nanostructures-to-purify-water-at-low-cost/>http://www.rdmag.com/News/2010/08/Materials-Nanotechnology-High-speed-filter-uses-electrified-nanostructures-to-purify-water-at-low-cost/
High-speed filter uses electrified nanostructures to purify water at low
cost
By dipping plain cotton cloth in a high-tech broth full of silver
nanowires and carbon nanotubes, Stanford researchers have developed a
new high-speed, low-cost filter that could easily be implemented to
purify water in the developing world.
Instead of physically trapping bacteria as most existing filters do,
the new filter lets them flow on through with the water. But by the
time the pathogens have passed through, they have also passed on,
because the device kills them with an electrical field that runs
through the highly conductive "nano-coated" cotton.
Silver has long been known to have chemical properties that kill
bacteria. "In the days before pasteurization and refrigeration,
people would sometimes drop silver dollars into milk bottles to
combat bacteria, or even swallow it," Heilshorn said.
Cui's group knew from previous projects that carbon nanotubes were
good electrical conductors, so the researchers reasoned the two
materials in concert would be effective against bacteria. "This
approach really takes silver out of the folk remedy realm and into a
high-tech setting, where it is much more effective," Heilshorn said.
Using the commonplace keeps costs down
But the scientists also wanted to design the filters to be as
inexpensive as possible. The amount of silver used for the nanowires
was so small the cost was negligible, Cui said. Still, they needed a
foundation material that was "cheap, widely available and chemically
and mechanically robust." So they went with ordinary woven cotton
fabric.
"We got it at Wal-mart," Cui said.
To turn their discount store cotton into a filter, they dipped it
into a solution of carbon nanotubes, let it dry, then dipped it into
the silver nanowire solution. They also tried mixing both
nanomaterials together and doing a single dunk, which also worked.
They let the cotton soak for at least a few minutes, sometimes up to
20, but that was all it took.
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