Catalytic Converter

Case Study: Lightweight & High‑Temperature Resistant Catalytic Substrates for Aircraft

A few years ago, a company that makes environmental control systems for business jets called us. They had a problem. Their ECS – the system that manages cabin air pressure and temperature – needed a catalytic converter to clean up bleed air from the engine. But the space was tiny. The heat was brutal. And weight was critical.

They'd tried a few suppliers. The parts were too heavy. Or they couldn't handle the temperature. Or they cracked on the test rig.

They asked if we could do something lighter and tougher.

The Problem

The ECS sits in the belly of the aircraft. Not much room. The converter had to fit in a can that was barely 100mm in diameter and 150mm long. But it had to process a lot of air flow.

Standard 400 cpsi substrates were too restrictive. Backpressure would be too high. So they needed lower cell density – around 200 cpsi – to keep the air moving.

But here's the kicker. The bleed air coming off the engine could hit 750 degrees Celsius. That's way hotter than a car converter ever sees. Most metal honeycomb would soften and sag at that temp. Aluminum is out of the question. Even standard stainless can struggle.

And the whole assembly had to be light. Every gram matters on an airplane.

What We Proposed

We went back and forth with their engineers for a few weeks. They sent us a drawing of the can. We sent back substrate specs.

We settled on 200 cpsi – bigger cells, less backpressure. Foil material: 347 stainless steel. Not the common 304 or 316. 347 has better high‑temperature creep resistance. It doesn't sag as much when it's hot for a long time.

Foil thickness: 0.04 mm. That's thinner than our standard automotive foil. Lighter, and less metal to heat up. But thin foil is fragile. We had to be careful with handling and brazing.

We also used a special high‑temperature brazing filler. Normal filler would melt at 750 degrees. This one had a higher melting point, so it wouldn't soften during operation.

The substrate was round, small – just 95mm diameter, 140mm long. We made a few samples and sent them over.

The Testing

They put our substrates through a rig that simulated real ECS conditions. Hot air at 750 degrees, flowing through for hours. Then cooling down. Then heating up again. Dozens of cycles.

First test: The substrate didn't sag. Cells stayed round. Good.

Second test: They measured backpressure before and after cycling. No change. That meant the foil hadn't deformed.

Third test: Vibration. They shook it at frequencies typical for the aircraft belly. Our substrate held together. The brazing didn't crack.

Then they coated it with their own catalyst formula and ran an emissions test. Passed with margin.

The weight? Our 0.04 mm foil cut about 30% of the mass compared to a standard 0.05 mm substrate. Not huge, but for aerospace, every gram counts. They were happy.

What Made It Work

The 347 stainless was the key. Most people think 304 is fine for high heat. It's not. Not at 750 degrees continuous. 347 has columbium and tantalum added. Those elements prevent chromium carbide precipitation – basically, it stays strong and doesn't crack.

The thin foil was a risk. 0.04 mm is delicate. We had to adjust our stacking fixtures to avoid denting the edges. And the brazing cycle had to be dialed in perfectly – too hot and the thin foil would warp, too cold and the braze wouldn't flow.

We also had to be careful with the mounting mat. Standard mats start to break down above 600 degrees. We used a high‑temperature mat rated for 800 degrees. It cost more, but it wouldn't turn to dust.

The Result

The customer ordered a small batch first – 50 pieces. Then 200. Then they put our substrate into production for that ECS model.

We've been shipping to them for three years now. No field failures that I know of. Their buyer told me once, "You're the only supplier who got the thermal stability right."

We also learned a few things. Thin foil is doable, but you have to handle it like glass. And 347 stainless is worth the extra cost for extreme heat.

What We'd Do Different Next Time

If another aerospace customer came with a similar request, we'd do a few things faster.

We'd test the brazing filler at temperature before committing to production. That first batch, we had to re‑braze a few samples because the filler didn't flow right. Now we have a qualified process.

We'd also recommend a thermal barrier coating on the outside of the can. We didn't do that – the customer handled it themselves. But it helps keep the substrate from seeing the full peak temperature.

And we'd quote a longer lead time for the first batch. Tooling and process development always takes more time than you think.

Aircraft environmental control systems are not cars. The temperatures are higher. The space is tighter. The weight limit is stricter.

But a metal honeycomb substrate can still work – if you pick the right alloy, the right thickness, the right brazing, and the right mat.

We did it for one ECS supplier. We can do it for others.

If you need a lightweight, high‑temperature catalytic substrate for aviation or any other extreme application, give us a call. Bring your drawings. We'll figure it out.