Although ceramic substrates still dominate in the production of catalytic converters, according to Göran Nyström, vice president and sales and marketing manager of Sandvik Steel (Sandviken, Sweden), metal substrates are being more widely used. Metal now accounts for 25% of the world market, with further growth of 5% during the next two years anticipated. Presently, European catalyst manufacturers—especially those in Germany—lead in the demand for steel from Sandvik, although the company is finding an increased number of customers in the U.S. and Asia.
Why metal rather than ceramic? A key reason is the ability to produce thin-walled materials. For example, Sandvik's steel grade OC404, a ferritic chromium steel (20% chromium, 0.2% rare earth elements, 5% aluminum) is available in standard foil thicknesses of 0.03, 0.04 and 0.05 mm.
Typically, metallic catalysts are based on a metal honeycomb monolith that's produced by coiling flat and corrugated metal strip into a cylinder with longitudinal channels. The monolith is coated first with oxides (e.g., zirconium, cerium), then a layer of metals such as platinum, rhodium, and palladium is added. The monolith is finally inserted in a stainless, chromium steel housing and is ready to purify >95% of exhaust gasses.
The benefit of the thin steel is that it permits the creation of greater cell density, which results in a greater surface area for purification, a greater catalytic capacity.
It is sort of a Catch-22 situation. People have long talked about carbon fiber-based composite materials as being as beneficial to automotive components as they are to skis and tennis rackets and even stealthy aircraft. In fact, in some ways, they could be even more beneficial in automotive, when you take into account the facts that there isn't a corrosion issue and compared to steel, the composite component can be as little as one-fifth the mass but without reductions in strength or stiffness. But there has always been a bit of a snag with regard to automotive. OK: not a bit of a snag, but a big snag. Cost.
With the exceptions of a handful of specialty applications, carbon-fiber is seen in greater abundance on the F1 circuit than on Woodward Avenue. Which is part of the Catch-22 nature: As long as few people use it, it will remain expensive. The cost won't come down until more people use it. But since it costs so much (20X steel—or more), only a few people will use it.
A large factor in this cost equation is capacity to produce the material in automotive quantities. And the production facilities needed to produce the materials are capital intensive.
John W. Powers, automotive development manager for the Carbon Fibers business of Conoco Inc. (Houston, TX), says that the energy company, which has developed proprietary carbon fiber technology that allows it to produce comparatively lower-cost carbon fibers (they use mesophase pitch rather than the more common PAN—or polyacrylonitrile—material), wants to show the auto industry (as well as other interested parties) that they are serious about providing carbon fibers by building a new plant in Ponca City, OK, that is scheduled to come on line early in 2002. This plant will have the capacity to produce eight million pounds of carbon fiber per year. While Powers admits that when the material comes into its own that capacity will be small, that single plant will be a measurable boost in the world's overall production of carbon fibers. Applications range from body panels to carbon-to-carbon brakes.
Alternative aluminum alloy.
Speaking of light-weight materials, according to Hsien-Yang Yeh, a professor in the Department of Mechanical Engineering, California State University, Long Beach, some of his colleagues at that school as well as a professor from East China University and he have developed a process that permits the casting of aluminum silicon alloys for applications including pistons, cylinder heads, blocks, and wear-parts. The process, for which a patent is pending, causes the silicon particles that are used in the alloying to become nodulized and to have an average size of not more than 40 microns. The professor says that ordinarily, when silicon is alloyed in aluminum there is a tendency for it to form in the shape of needles, which can lead to crack propagation.
Because of the new process, the ends are blunt. Although he acknowledges that there is a price premium, the wear resistance is said to be greatly enhanced (by as much as 100% compared with traditional Al-Si alloys, he says), so the cost differential could be offset.