Developed originally for the UK nuclear industry, a
zirconia-basedcoating is finding increasing uses in the automotive industry and
Rather than being painted on, the ceramic is ionized
in a high-powered electric arc so that fine, molten particles can be sprayed
onto a surface.
enthusiasm for nuclear power has waned, the spark of creativity that its
development fostered still glows. Originally developed for nuclear
applications, a durable, heat-resistant ceramic coating* has found increasing
uses in the automotive industry, the medical sector and beyond.
Since the internal combustion engine is a thermodynamic system rendered in
metal, thermal management is fundamental to automotive engine design. Ceramic
coatings have been used in the automotive field before, to retain heat within
specific sub-systems or to protect components and operators from excessive
temperatures. More durable and simpler to package than wrap, today’s road
vehicles require more efficient methods of heat management-and ceramic coatings
are the answer.
available from Zircotec, Oxfordshire,
of the original customers for these coatings were in the motorsport sector. “We
were approached by Prodrive [which runs the Subaru World Rally Team] back in
1994,” says Andy McCabe, technical director of Zircotec, a ceramic coating
manufacturer headquartered in Oxfordshire. “Their drivers were getting hot. We
found that putting our coating on the exhaust pipe-not only under the bonnet,
but running under the entire length of the car-helped lower cabin temperature
by between 6 and 8ºC.”
From this initial application, word spread about the benefits of using ceramic
coatings, and positive word-of-mouth led to the use of the system in touring
cars and, subsequently, Formula One. In addition to driver comfort, coating hot
components offers other advantages. For Formula One teams, one of the major
benefits comes about because of the formula’s extensive use of carbon fiber
composites. These composite components are very light but can be susceptible to
delamination when exposed to high temperatures.
To solve this problem, a new technique has been developed to plasma spray coat
composites and laser sintered nylon. Formula One teams have found that by
coating the exhaust components of their cars, carbon fiber composites can be
reliably used much closer to the exhaust than would otherwise be possible,
allowing a greater number of components to be made from carbon fiber and
reducing the need for heat shielding. This also gives designers greater
flexibility to design vehicles that are as aerodynamic as possible, with the
bodywork following the underlying structures much more closely.
heat can also improve reliability. Reducing the amount of heat escaping around
the powertrain can increase the durability and effectiveness of engine and
transmission oils, improve
engine cooling, and
help to protect ancillaries such as regulators, wiring
and ignition systems from the degrading affects of excessive heat. The effect
of coating the exhausts extends beyond simply protecting heat-sensitive
components-ensuring that thermal energy stays where it is supposed to can help
engines perform as they were designed. Retaining heat energy in the exhaust
system means that the gases within the exhaust move faster, reducing
backpressure on cylinders and helping to increase engine efficiency.
Protecting air intakes from locally generated heat also means the engine
receives denser, more oxygen-rich air, which helps boost performance further. A
in air intake temperature tends to boost power output by around 1%. The 30ºC reductions
seen by customers mean that 6% rises in horsepower are possible.
When Litchfield, an importer and tuner of Japanese performance cars, decided to
create its own version of the Subaru Impreza, performance and an OEM appearance
were its two main goals. Litchfield found that coating the up- and down-pipes
to and from the turbocharger helped keep the entire engine bay cool. An added
benefit was that more of the energy in the hot exhaust gases leaving the engine
reaches the turbo rather than being radiated away from the up-pipe.
“The more heat you can keep in the system, the faster the turbo will spool up,
making the car more responsive,” says Managing Director Iain Litchfield. “We’re
finding that it’s bringing the turbo up to speed 300 or 400 rpm sooner, which
you can really feel in the crispness of the throttle response.”
Type 25 Impreza enjoys improved responsiveness thanks to the zirconia-based
use of the coating has not been restricted to the futuristic technology of
cutting-edge motorsports, however. The cream finish that the coating exhibits
is becoming popular with restorers of the classic racing cars of the 1950s and
60s, which would have originally featured asbestos-based paints as a safety
feature on their exposed exhaust pipes. Users have found that the coating
offers a superior level of heat shielding and greatly improved durability
without impacting the original appearance of the vehicle.
A variety of finishes have been developed for the coating, including black,
dark grey and silver. The silver, for instance, has been used to coat the
manifolds of a classic Aston Martin DB4 to protect the rest of the engine bay.
Modern fuels tend to generate much higher temperatures than the blends used in
the 1960s, meaning that classic components are being subjected to much greater
thermal loads than would have been anticipated at the time of their design. The
coating helps ensure that the finish of a carefully restored engine bay is retained
for many years to come.
Cut the Wrap
of the benefits derive not just from the thermal insulation properties of the
zirconia-based coating, but also from the application method. Rather than being
painted on, the ceramic is ionized in a high-powered electric arc so that fine,
molten particles can be sprayed onto a surface. The result is a coating that
adheres much more effectively to the parts being sprayed than the wraps and
paints used in the past.
In order to create a highly resilient coating, all parts are first degreased
and shot-blasted to provide a clean and predictable surface to spray on. A
nickel-based coat is plasma-sprayed to give a rough surface so that the ceramic
coating can adhere as firmly as possible. In addition, this bond coat also
minimizes the thermal mismatch between the substrate and the ceramic coating.
The final result is a highly uniform coating of between 300 and 350 microns in
thickness, with around a third of that made up by the undercoat. The effect on
the component’s weight is an additional 1.6 kg per square meter.
The current spraying process is labor intensive and requires complex
extraction, as well as strict health and safety controls for the operators.
Huge growth in the medical market (a similar coating is used for coating
medical implants like replacement hip and knee joints), has led to robotized
spraying. With the expansion into OEM road car and commercial vehicle markets,
a new robotized spray booth has been commissioned that will come on stream
later this year.
Not Just Automotive
spraying method was developed that enables the production of free-standing
ceramic components in complex shapes, including components used in the
manufacture of optical fibers. The fibers are created by drawing glass through
an electromagnetic induction furnace at high temperatures. The ceramics are
used to create the susceptors that conduct the furnace’s heat through to the
glass. This requires the ability to withstand thermal shock, since the
components are heated to around 2000ºC and allowed to cool again.
The technology’s first use outside the nuclear industry was for medical
implants. Starting with the same coating technology, it was discovered that
orthopedic implants formed a more reliable join to re-growing bone if they were
given a rough, textured coating first. The durability of the biocompatible
titanium coating gives reassurance when using it over such long periods in such
a sensitive environment.
Another coating was developed that incorporates hydroxyapatite, a substance
similar to human bone. A textured layer of hydroxyapatite creates a structure
that bone can grow into, creating an even stronger bond between the implant and
the damaged bone.
Spray Technician Alec Samler with finished components for a classic Mercedes
Road Car Applications
in the vehicle market have been varied. Several high-performance car
manufacturers are adopting the technology to prevent heat from the exhaust pipe
from damaging surrounding materials. The high-performance Koenigsegg from Sweden is the latest
example (see sidebar).
For the diesel engine market (both road car and commercial vehicles), the
ceramic coating can offer more precise temperature control, helping particulate
filters reach optimum operating temperature more quickly and improving system
performance. By significantly reducing heat loss from the exhaust system, the
coating retains high exhaust gas temperatures, reducing warm-up times for
after-treatment systems and the need for close coupling. This allows for more
consistent control of exhaust gas temperatures. The technology is expected to
be particularly useful for keeping particulate filters at their operating
“Maintaining sufficient heat in the after-treatment system is an
increasing challenge, especially as catalysts and filtration stack up, allowing
efficient working temperatures to be maintained,” says McCabe.
Keeping the thermal energy in the exhaust stream can also significantly improve
turbo response, which makes the coating ideal for selective catalytic reduction
(SCR) diesel exhaust systems. The coating protects surrounding components from
the high temperatures reached in the catalyst converter and removes the need
for separate heat shields.
New derivatives (including different surface finishes and colors) are under
development with auto manufacturers clearly in mind. With several concept cars
using the ceramic coating as an alternative to some traditional brightwork, the
technology may well find additional uses in the near future.
For additional information regarding
high-temperature ceramic coatings, contact Zircotec at 528 10 Unit 2,
Rutherford Ave., Harwell Science and Innovation Campus, Didcot, Oxfordshire
OX11 0QJ, UK; (44) 01235-434326; fax (44) 01235-434329; e-mail email@example.com; or visit www.zircotec.org.
SIDEBAR: Keeping the Swedes Cool
Koenigsegg’s £540,000 (~ $1.1 million) CCX (Competition
Coupe X) supercar is the latest vehicle to benefit from using the ceramic
coating for its exhaust manifold. The CCX delivers incredible performance,
dispatching 0-60mph in 3.2 seconds with an 806 bhp engine helping the car
achieve over 395 km/h.
Installing the 4.7 liter engine in a sleek, aerodynamic carbon fiber body means
package space is at a premium. The result is a very restricted engine bay with
sensitive components and the painted composite parts close to the exhaust. The
CCX also incorporates a new exhaust system with catalysts moving nearer to the
engine (to improve light-off time), further increasing temperatures under the
Koenigsegg needed a solution that would dramatically reduce temperatures to
safeguard electrical components and the composite bodywork. Limited space meant
exhaust wrap was not feasible, and it would be unsightly for such a highly
aesthetic engine bay. The engineers turned to spray coatings in order to
achieve a robust and effective solution that would satisfy rigorous OEM quality
“The Zircotec coating offered us an immediate solution and a substantial
improvement over the coating we were already using,” says Koenigsegg Chief
Operating Officer Jeff Stokes. “Plus, it has more significantly reduced
under-bonnet temperatures.” As a niche performance car manufacturer, the
adoption of the ceramic coating provided other benefits to Koenigsegg. “There
was no tooling investment for ordinary heat shields, it is low weight and it
needs minimal package space,” adds Stokes.