ESSENTIAL MINERALS
“ Workhorse pigment titanium dioxide is also the stuff that dreams are made of”
T itanium dioxide is an opaque white pigment. One coat of paint often does the trick because titanium dioxide is there. Manufacturers also use this inert, stable filler and colorant to make products as diverse as paper, plastics, lipstick, toothpaste, and pharmaceutical tablets.
But there is more to TiO 2 when it goes unseen. Nanosized particles in the 10- to 50-nm range take on unusual properties that chemists and chemical engineers are trying to exploit, with varying degrees of success.
They have imagined and produced self-cleaning window glass, air and water purification systems, and antibacterial coatings by tapping the photocatalytic properties of these particles. Engineers have adapted them to remove nitrogen oxides from power plant exhausts, and they are looking at ways to harness these environmental catalysts to treat diesel vehicle emissions.
These tiny minerals have semi conducting properties, too. And researchers are looking at them as substitutes for silicon to make solar power cells, as well as battery storage media.
But there may be more hoopla about nanosized TiO 2 than it deserves. "Nanosized TiO 2 is a nanosized market," says Jim Fisher, president of consultants International Business Management Associates (IBMA). "There is a lot of interest in it. Even at prices of $10 per lb and up, sales will pale compared with high-volume TiO 2 pigment that sells for about 90 cents, he says.
Among the largest TiO 2 makers, Du Pont and Millennium Chemicals have shown interest in these small-volume specialties. Because they are such big players, Fisher wonders why they would even attempt to go after such small and esoteric markets. It may make more sense for smaller players such as MG Technologies affiliate Sachtleben, Kemira, and Japan's Tayca.
IN A MARKET where global TiO 2 sales annually exceed 8 billion lb per year, 60% of which goes into paints and coatings, Fisher does not even have a number for the fine particles sold for photocatalytic uses. Photovoltaics may just be about a 1 million lb per year market, he figures. Catalytic applications, including those where TiO 2 only functions as an inert support media, he sets at about 20 million lb per year.
New production methods allow TiO 2 makers to provide coated ultrafine TiO 2 in the 10- to 20-nm range. Because of the particles' small size, they scatter and reflect ultraviolet light but allow visible light to pass through. Many personal care product makers incorporate these fine particles in the latest generation sunscreens. At $2.00 to $5.00 a lb, they are more profitable than the commodity pigments, which are in the 200-nm range. Fisher figures the sunscreen crystals have a potential market size of 25 million lb per year.
With the level of control over particle size available today, chemical engineers are taking a closer look at how they might manipulate the versatile mineral. Adam Heller, a research professor in the department of engineering at the University of Texas, Austin, successfully developed and sold a process to coat expensive kitchen and bathroom fixtures with fine particles of TiO 2 to Japanese appliance maker Toto. UV light passed over the coated surfaces activates the titanium dioxide and oxidizes organic molecules, thus breaking down dirt and destroying bacteria.
But Heller is a realist. "It is extremely important to distinguish between what exists and what people dream about," he says. When researchers at the University of Tokyo discovered the photocatalytic properties of TiO 2 about 30 years ago, many scientists hoped to harness the pigment to make devices to clean air, sanitize operating rooms, and disinfect bathrooms.
"Their work generated several thousand papers on the environmental cleanup possibilities of TiO 2 ," Heller says. "But test-tube successes are irrelevant to real life. Very few understand the marketing and engineering realities." Heller devised a way to clean up oil spills in waterways by covering the spills with coal fly ash coated with titanium dioxide. But the oxidation of the spill was too slow. "Customers want something that acts fast--before the government and press can see the spill."
Heller also developed an indoor air cleaner. The cost of the TiO 2 to treat the air is not nearly as great as the investments in UV lamps, ballasts, fans, and the mechanical housing for such a unit. Few are willing to pay the $1,000 necessary to produce a module to treat the air in a typical-sized room, he says.
About 10 years ago, the Texas scientist also did some work on methods to coat glass with titanium dioxide to make a self-cleaning glass. Drawing in part on the inspiration he provided, enterprising glassmakers Pilkington and PPG Industries developed their own processes to coat window glass with transparent TiO 2 . About two years ago, first Pilkington, then PPG began to sell the first self-cleaning glass.
Caroline Harris, a senior research associate at PPG, says she and her colleagues learned how to apply a transparent functional coating on glass by chemical vapor deposition. Using TiO 2 precursors deposited during float glass manufacturing at temperatures between 800 and 1,300 °F, PPG creates a coating less than 1,000 Å thick. Even indirect UV light activates the TiO 2 and erases fingerprints and dirt, she points out. And because the coating makes the glass hydrophilic, rain sheets on its surface, further helping to wash dirt away.
PPG and Pilkington are among the first to target a significant market to commercialize the photocatalytic properties of TiO 2 , says Tommy Böök, a product manager at Kemira. Other markets such as water, air, and self-cleaning hard surfaces are much smaller and hardly off the ground. While the Finnish pigments maker is interested in these emerging markets, it is pursuing more immediate specialty applications in environmental catalysts.
Kemira supplies TiO 2 that when mixed with tungsten oxide and vanadium oxide removes nitrous oxide from power plant emissions. Ammonia injected into the waste stream combines with the catalyst, allowing recovery of nitrogen and water.
A variation Kemira is betting on is a diesel engine catalyst. Beginning in 2005, Böök explains, European regulations will require removal of NO x and particulates from diesel emissions. The U.S. is likely to follow soon after. "Intensive efforts are under way to develop this catalyst," he says.
Millennium Chemicals is similarly interested in developing the catalytic properties of TiO 2 and has, according to Robert E. Lee, executive vice president, developed a $30 million business to supply catalysts to remove NO x from power plant exhaust. At an investment conference last year, Lee said, "As clean air legislation becomes the norm globally, we believe that we are well positioned to continue to grow this business as well as leverage it into
other environmental improvement applications like coating highway sound barriers to neutralize certain auto emissions--an application currently being tested in Japan."
A Millennium spokesman adds that besides the sound-barrier coatings, the company is interested in other photocatalytic applications. "We have products with surface areas and particle sizes that work better for air treatment, and others that will work in water," he says.
Perhaps no company has higher hopes for nanosized TiO 2 than Altair. Ken Lyon, president of the nanomaterials subsidiary of the company, jokingly looks for the day "when we can coat ourselves in TiO 2 and take air baths." For now, though, he is hoping to leverage new solution-process manufacturing technology to make nanoparticles that range in size from 10 mm to 10 nm, depending on manufacturing conditions.
IT'S A PROCESS, he says, that is uniquely suited to making the smallest particles. While the firm operates only a pilot plant today, in Reno, Nev., Lyon thinks he could supply customers at $1.00 per lb if annual demand ramps up to 55 million lb or more. The day when that happens may be a long way off. The company had just $650 in nanosized TiO 2 sales last year for photocatalytic purposes.
Altair sold $18,200 worth of lithium titanate, a titanium derivative, to nine battery makers looking to make a fast charging, high-capacity storage cell. It "could be the basis for a new electrolyte," Lyon says, making fast-charging electric car batteries a reality.
As Altair's sales show, there just is not a very large market for the most unusual types of TiO 2 today. But Bernd R. Proft, senior scientist at Germany's Sachtleben, says his firm still provides customers with a number of nanosized particles for research. Sachtleben's TiO 2 output goes mostly to textile fiber markets, but also to paints, coatings, and plastics.
But Sachtleben has an eye on photo catalytic uses for TiO 2 . It is working with one researcher to oxidize colored wastewater from textile dye plants. The team is looking into using solar reactors as an economical source of UV light to make the reaction work. For the near term, the company expects to boost sales with less rarified specialty TiO 2 such as nanoparticles to confer UV protection to cosmetic sunscreens and clear plastics, and for emissions catalysts.
People are spending a lot of time trying to find markets for the most specialized TiO 2 , IBMA's Fisher says. But though it is an interesting material, Fisher says nanosized TiO 2 "is not a business that producers should spend a lot of time with unless they are small and can use it to augment their other activities."
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