Ceramic pot filters are crucial for accessing clean water in third-world countries and underdeveloped regions of emerging nations. For a variety of reasons, much of the research regarding the manufacturing and effectiveness of these filters has occurred in Guatemala.

The attractiveness of these filters in countries like Guatemala is that almost all of the raw materials are easily available from abundant indigenous sources, with one exception: colloidal silver (silver nitrate). Levels of E. coli and coloform bacteria are typically used as representative indicators to measure general water quality, and while the ceramic material filters out most of the E. coli and coloform in the water, silver is added to as an additional anti-bacterial agent to kill what is not caught in the filters. In a story that appeared in our Bulletin magazine last year, a researcher reported that untreated filters caught 97% of the bacteria, while filters painted with the colloidal silver stopped 99%.

Everyone agrees that the amount of colloidal silver required per pot is very small. But, even though the per-pot cost is minimal, this additive must be imported and moved to remote regions. Ceramic filter technology is also competing, in a sense, with other indigenous filtering approaches, such as biosand filter applications.

Heinley exams E. coli growing from water samples.

Now, new research suggests that the use of the silver additive may not be all that important and the benefits may not justify the effort to obtain the material. According to a press release, Missouri S&T graduate student Nicole Heinley traveled to Guatemala to conduct research on the ceramic pot filters used to remove bacteria from water.

Heinley collected contaminated water samples from a river in the city of Antigua and studied the structure of the ceramic pot filters available locally. She found that the filters not lined with silver removed a higher than expected rate of E. coli — an average of 99.499 % — high enough that she calls into question whether the benefits of silver justify the logistical and expense problems involved.

“[Colloidal silver] is the only material that has to be imported to manufacture the filters,” Heinley says. “The remaining materials - sawdust and clay - are available locally.”

A paper on these findings written by Heinley and Curt Elmore, associate professor of geological engineering at Missouri S&T, will soon be published in the Journal of Water Science and Technology.

“Perhaps the greatest drawback to using the silver is maintaining the imported supply,” notes Elmore.  He said that developing a household water treatment that does not rely on imported components would be appealing even in a developed area, let alone a developing one.

Moving from lab-based conclusions to real manufacturing often leads to unexpected problems and Heinley warns that, “additional, long-term studies of filters without silver should be undertaken in order to further investigate the issue.”

Below is a two-part video explaining the making and function of ceramic/colloidal filters:

A 5 nm silicon nanowire can be repeatedly broken and reconnected by applying a pulse of varying voltage through the silicon oxide, creating a two-terminal resistive switch. A chip with 1000 of these silicon-oxide/silicon nanowire memory elements has been assembled as a proof-of-concept.(Credit: Jun Yao/Rice.)

It’s not often that “plain vanilla” silicon oxide makes the front page of a paper like the New York Times, but it happened when Rice University scientists announced that they have created the first two-terminal memory chips based on silicon oxide in a way that they say should be easily adaptable to nanoelectronic manufacturing techniques, and promises to extend the limits of miniaturization subject to Moore’s Law.

Their technique creates nanocrystal wires that are as small as 5 nanometers wide, far smaller than circuitry in even the most advanced computers and electronic devices. The Rice group believes its nanocrystal conductors could lead to massive, robust 3-D storage.

“The beauty of it is its simplicity,” says James Tour, Rice’s T.T. and W.F. Chao chair in chemistry as well as a professor of mechanical engineering and materials science and of computer science. That, he said, will be key to the technology’s scalability. Silicon-oxide switches or memory locations require only two terminals, not three (as in flash memory), because the physical process doesn’t require the device to hold a charge.

According to the Rice press release:

“[Graduate student] Jun Yao sandwiched a layer of silicon oxide, an insulator, between semiconducting sheets of polycrystalline silicon that served as the top and bottom electrodes.

“Applying a charge to the electrodes created a conductive pathway by stripping oxygen atoms from the silicon oxide and forming a chain of nano-sized silicon crystals. Once formed, the chain can be repeatedly broken and reconnected by applying a pulse of varying voltage.”

Layers of silicon-oxide memory can be stacked in three-dimensional arrays. “I’ve been told by industry that if you’re not in the 3-D memory business in four years, you’re not going to be in the memory business. This is perfectly suited for that,” Tour says.

Silicon-oxide memories are compatible with conventional transistor manufacturing technology, says Tour, who recently attended a workshop by the National Science Foundation and IBM on breaking the barriers to Moore’s Law, which states the number of devices on a circuit doubles every 18 to 24 months.

Austin tech design company PrivaTran is already bench testing a silicon-oxide chip with 1,000 memory elements built in collaboration with the Tour lab.

The findings were published in Nano Letters.

ORNL’s James Klett holds an LED streetlamp. The lamp will use heat sinks of graphite foam
(samples in his left hand) to extend the life of the LEDs and cut operating costs.

Around 1997, Oak Ridge National Lab’s James Klett and Timothy Burchell discovered how to make graphite foam, a material that had at least one amazing property: It transfers heat like crazy.

If this property of the foam seems a little counterintuitive, that’s because foam materials are often associated with with heat insulation properties. But in this case, the foam acts as a super heat radiator. A story in an ORNL newsletter said the stuff worked so well that if you put an ice cube on a hockey puck-sized chunk of the graphite foam, and put the foam on you hand, “the cube melts from your body heat as if it were on a hot griddle.”

At the time, Klett, a researcher in the lab’s Metals and Ceramics Division, noted that, “Graphite foam is as thermally conductive as aluminum at one-fifth the weight. It has a very high surface-area-to-weight ratio and a high heat transfer coefficient. This interests engineers and designers because products that use energy wage an ongoing battle with heat,” he says.

He said the key to the foam’s conductivity is its unusual graphite crystal structure that is full of air pockets, making it only 25% dense and lightweight. A network of graphite “ligaments” in the foam wicks heat away from its source.

Klett shows that ice held against the graphite foam will melt quickly because the heat from the hand holding the foam is transferred rapidly through the foam. As a result, this hand feels the cold fast.

When they made their discovery, Klett and Burchell were building on a legacy of carbon innovations that go back to at least the 1960s when Johhn Googin developed the first method to produce carbon foams was used as high-temperature furnace insulation. Klett and Burchell also developed a commercial carbon-carbon disk brakes system.

Over the past decade, Klett, Burchell and ORNL have licensed the special foam for numerous applications – especially with mechanical and electronic heat-transfer applications – and the material garnered an R&D 100 award.

Now, the foam’s ability to act as an efficient heat sink is being put to new uses in the world of energy-efficient lighting. On Friday, ORNL announced that it has licensed the foam to LED North America for use in commercial LED lighting systems such as in the large arrays now being manufactured for street lamps and parking garages.

The lab says passive cooling materials, such as the foam, are needed to increase LED efficiency and lifetime. ORNL reports that each 10° decrease in temperature can double the life of the lighting components. “While this technology will reduce temperatures and increase the life of the LED lighting systems, what it will really do is save municipalities millions of dollars every year in replacement fixture costs as well as maintenance,” Klett said.

Besides being lightweight, Klett says the foam is easy to machine and use in manufacturing. These advantages give it a growing edge compared to traditional heat transfer materials, such as copper or aluminum.

LED North America president Andrew Wilhelm predicts that the foam will double the life of the LED units. He also says the first lamps using the foam will be installed later this year in an ORNL parking lot.