spheres of influence

Minuscule balls of nickel may well help power cars and usher in the hydrogen economy.

By Joseph Romano

The sphere is a wonderful shape: It has the smallest surface area encompassing a given volume. That's great if you want to limit the amount of material exposed to an environment or build the largest enclosure with a given amount of material. Geodesic domes, for instance, are really efficient, even if they lack aesthetic appeal.

But not every application needs this kind of efficiency. Often, it is surface area that is needed—maximizing surface is vital to making catalysts work. To get a large surface, some manufacturers create tortured, distended, difficult-to-make shapes. Surprisingly, a sphere can work, too. If you shrink the volume of a sphere by a factor of 1,000 and the surface goes down by only a factor of 100. Make the spheres small enough, and even quotidian metals can do amazing things.

That's one of the promises of nanoparticles, minuscule bits of material that have properties the same material in larger sizes does not. Nanoparticles, the first real commercial breakthrough in nanotechnology, are now found in everything from paint to tennis balls.

But it is as catalysts and reactants that nanoparticles may have their biggest impact. These nanoscale metals have already made their way into rocket fuel and explosives. And they may well be able to cheaply replace platinum in fuel cell applications.

Catalysts help foster chemical reactions without being consumed themselves. For many applications, the best catalyst is platinum, which is found in catalytic converters in automobiles and in oil refineries. Platinum is so prized and so rare that pound for pound it's worth more than gold.

That puts a crimp in many plans to use catalysts more widely. One major challenge in bringing down the costs of some fuel cells, for example, has been the need for platinum catalysts. Spread thinly across a membrane, the platinum in these cells separates protons from electrons in hydrogen atoms.

Platinum is the best catalyst by far, but other materials can do much the same work, if at slower intrinsic reaction rates. Lithium, nickel, and copper can be used to catalyze many of the same reactions.

One way to increase the catalytic power of a material is to increase the overall surface area exposed to the reactants. A quick look at the relationship between the volume and surface area of a sphere points to a solution: make powdered catalysts of exceedingly small diameter—the smaller, the better. It was only a matter of time before the particles desired were on the scale of nanometers.

As early as the 1930s, Kodak researchers were experimenting with particles a dozen or so nanometers across for use in photographic film. Other researchers created nanoscale materials in the 1970s, using the gas phase condensation method. Today, there are dozens of processes for producing nanomaterials worldwide. These processes include chemical vapor deposition, physical vapor deposition, reactive sputtering, laser pyrolysis, plasma gun spray conversion, mechanical alloying, grinding, and sol gel.

Many observers feel that nanoparticles have become the first breakout nanotechnology. But in 2002, the founders of QuantumSphere, a technology company based in Costa Mesa, Calif., saw an opening in the field. Most of the processes that are used by other companies to make nanoparticles were too expensive or required sophisticated equipment, intensive labor, and frequent maintenance. In addition, the size and shape of particles created through these methods could be inconsistent at best.

QuantumSphere, now a leading manufacturer of metallic nanopowders for material applications, including high-quality nickel nanoparticles, found a way to adapt gas phase condensation, one of the original nano- particle technologies, into a continuous, fully automated manufacturing process. Metal wire is fed into the vacuum chamber and melted on intermetallic composite boats heated by electricity to a very high temperature.

The metal vaporizes, and the vapor is cooled by inert gas and condenses into droplets of liquid metal that further cool to solid nanospheres. Oxygen is then added to the gas stream containing the spheres to develop an oxide shell.

QuantumSphere's nanonickel products can come as compressed disks (top) or in powder form (bottom). The material is fabricated in bulk inside a two-part machine (middle): The nanoparticles created in the upper cylinder are collected in the lower one.

The nanopowder is collected and conveyed into metal containers for packaging in inert gas. Tweaking the metal flux, chamber pressure, temperature, and gas flow changes the characteristics of the particles. For example, technicians can manipulate the size of the nanoparticles by controlling the laminar flow region around the chaotic metal vapor zone. This bottom-up process allows the technicians to grow the nanoparticles to the desired diameter prior to gas quenching. The result is a uniform distribution of controlled particle sizes. And by multiplying the number of controlled laminar quench zones around the heating elements within the vacuum chamber, the process can be scaled to meet the output demand.

The process can produce spheres of metal that are incredibly small. For certain applications, we have made particles that are a mere two nanometers across and consisting of just a few hundred atoms.

Nanoparticles have been used for years in tires, cosmetics, and specialty coatings. But mass producing very small, very uniform metal spheres opens up some new frontiers.

Even at the micron scale, most metals can react with oxygen. Ships made from an aluminum alloy burned in the water during the Falklands War of the 1980s. When milled to smaller and smaller diameters, individual particles of metal expose enough surface to become extraordinarily reactive. The nanoparticles created through QuantumSphere's process are small enough that virtually every atom in the particle can react. Nanonickel and other nanoparticles made by the company must be specially treated and stored in airtight containers lest they spontaneously combust.

Let it loose in a controlled environment and nanoaluminum can be dynamite—and rocket fuel. Because it can increase combustion rates so dramatically, nanoaluminum is being incorporated into munitions for the U.S. Department of Defense. The result is more explosive force per ton, which means that bombers can fly longer routes to deliver the same wallop. NASA has also investigated nanoaluminum particles for use as a high-tech, high-energy propellant ingredient.

Destroying tanks or launching rockets with aluminum nanoparticles is certainly attention-grabbing, but on a day-to-day basis, the most important nanomaterial may be simple nickel.

Nickel is an inexpensive catalyst, used to hydrogenate vegetable oil. Aerospace researchers have proposed using nickel-based reactors to help turn Martian carbon dioxide and water into rocket fuel.

Even so, nickel's power pales in comparison to platinum's. But nickel has the advantage of being more than 10,000 times more abundant and more than 500 times cheaper. Find a way to swap in nickel for platinum, and you potentially could help turn hydrogen fuel cells, which rely on platinum, into a cost-competitive technology.

It turns out nanoparticles of nickel have much greater catalytic power than ordinary plate nickel. So much so that nanoparticles of nickel can be used in the conductive electrolytic membranes of various fuel cells, replacing platinum as a catalyst. Such a shift would result in a reduction in the cost of fuel cell catalysts by more than 50 percent, based on current prices.

Replacing platinum with nickel nanoparticles would also have an impact on the cost of internal combustion engines. Platinum is found in lean-burn diesel engine catalytic materials and in catalytic emissions controls—applications where nanoparticles of nickel can be used.

By developing nanonickel, QuantumSphere plans to significantly reduce the amount of platinum and related metals required in conventional catalytic processes. And its use in new sources of power will go a long way to help alleviate the portion of the U.S. trade deficit due to petroleum imports. According to the National Energy Foundation, oil imports drain $1 billion from the U.S. economy every week.

The changes in the nature of common metals when they are in spheres a few atoms wide is a testament to the most profound insight of nanotechnology. At the nanoscale, almost everything is different. Finding ways to harness these differences can give us great power.

Joseph Romano is an executive with QuantumSphere Inc., a technology company in Costa Mesa, Calif.



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