Issue: Dec 2006

Silicon Carbide filter technology

by Rob White

“We are experiencing a growing responsiveness to our technology” - Lars Tinggaard Johannesen, NoTox sales director

Automotive Industries (AI) spoke to Lars Tinggaard Johannesen, NoTox’s Sales Director and asked him what he felt about the company’s participation at the IAA fair in Hanover

Danish company NoTox A/S was one of the most innovative participants at the IAA fair in Hanover this September. The company, which manufactures diesel particulate filters, is part of Scandinavian Brake Systems (SBS).

NoTox’s Diesel Particulate Filter, is made using silicon carbide which the company claims, combined, offers the best durability. The company is expected to play an important role in the Manufacturers of Emission Controls Association or MECA. MECA is a non-profit association headquartered in Washington DC. Formed in 1976, it provides the latest technical information on emission control technology for motor vehicles. MECA members manufacture include catalytic converters catalysts, substrates, mounting sleeves, and converter housings for all fuels, diesel particulate filters, oxygen, NOx, and temperature sensors, thermal management strategies, engine/fuel management technologies, crankcase emission control technologies, evaporative emission controls, enhanced combustion technologies, plasma/corona technologies and components for fuel cell technology. Stationary products include selective catalytic reduction (SCR) systems, non-selective catalytic reduction (NSCR) systems, diesel particulate filters and catalytic oxidation systems.

NoTox is in the business of retrofitting diesel vehicles with filters to cut emissions.

In a demonstration in 1998, NoTox fitted a city bus with a filter system based on NoTox XD-90 filter substrate. The bus was in service until 2003, with the same filter substrate in place. The filter reached more than 700,000 km, without any deterioration. The NoTox ceramic technology comprises a thorough understanding of the chemical and physical reactions involved in creating a highly porous structure of recrystallized silicon carbide. NoTox offers silicon carbide wall flow filters (WFF), primarily used for soot filtration in engine exhaust. The honeycomb design is also suitable as catalyst support, bed material for chemical reactors and other applications.

NoTox manufactures its filters in two different versions, each targeted at different applications. According to the company, the filtration efficiency is above 97% in all the filter versions. NoTox’s MD filters are often used for applications where active regeneration is employed. For this type of applications, where regeneration takes place under controlled conditions, a filter with less durability is required. This enables a filter design with more attention on reducing the pressure drop as much as possible.

NoTox was the first to patent the technology that extrudes and fires coarse grained silicon carbide. This enabled NoTox to produce porous structures with pore sizes from a few microns up to more than 100 microns. Such a porous structure, constituted of particles, bonded together in the contact points, has a 100% open porosity, and no dead-end pores.

Automotive Industries asked Lars Johannesen about the growth prospects for its products.

Johannesen: We are experiencing a growing responsiveness to our technology. We have entered into crucial dialogue with a number of OEMs and we anticipate these discussions to result in the selection of our technology for both heavy duty vehicles as well as light vehicles.

AI: How successful have your displays been at fairs?

Johannesen: Our displays have been tremendously successful and exceeded our most optimistic expectations. This reception in the market place endorses our belief in the growth strategy we have set in motion for our product and technology.

AI: Are you planning to participate in future OE shows in 2007?

Johannesen: We will most definitely be present at the most important OE shows in 2007. The focus on emissions from all OEMs and Tier 1s is so strong that we expect a huge interest in our products. We also expect to strengthen the dialogue which we are engaged in with a number of significant OEMs.

AI: Any plans to become a member of MECA?

Johannesen: MECA is an important association for promoting an understanding of its member’s emission control technologies and we therefore consider it central to participate in their efforts.

Facts about Silicon Carbide

• Silicon Carbide is produced artificially by heating a blend of pure silica and petroleum to 3000°C in an electrical heated furnace. This creates large crystals which after crushing and sieving is separated into different size fractions often employed as grinding powder.

• Silicon Carbide features exceptional thermal stability and easily exhibits a 10.000 hours use in an oxidizing atmosphere of 1500°C.

• It has a high material strength (NoTox type 25-40 mPa) but also a high thermal expansion (~4 x10-6 mm/°K).

• The thermal conductivity is high compared to other ceramics (higher than 15 W/mK for NoTox type SiC).

• Silicon Carbide does not melt, but decompose at temperature >1800°C in oxidizing atmosphere.

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