Metal Substrate

Why Metal Substrates Are Preferred for High-Temperature Oxidation Applications

In high-temperature exhaust systems, every component inside the can has a hard life, but few parts take more punishment than the substrate sitting directly in the exhaust stream. Whether we’re talking about DOCs, catalytic burners, VOC reactors, or auxiliary oxidation units on industrial engines, the substrate is the first structure exposed to rapid heat swings, vibration, pulsation, and corrosive gas chemistry. Over the years, one trend has become very clear: when the job involves high heat and frequent thermal cycling, metal substrates outperform ceramic units in most real-world applications.

What makes metal substrates more suitable isn’t just one advantage—it’s a combination of how they react to heat, how they handle stress, and how well they hold a coating after thousands of hours in harsh service.

The biggest factor is thermal response. Metal heats up fast, much faster than ceramic. If the goal is to push CO and HC oxidation as early as possible, a fast light-off temperature makes a noticeable difference. Diesel equipment, especially in off-road or variable-load conditions, doesn’t stay at a stable temperature. Exhaust temperatures surge, drop, surge again. Metal substrates adapt quickly to these swings without cracking or losing structural integrity. That quick heat-up also shortens the time needed for the catalyst to reach operating temperature, which helps with compliance during cold start and low-load operation—where most emissions spikes happen.

Durability under high thermal stress is another area where metal substrates prove their worth. Ceramics handle heat well, but they don’t enjoy rapid heat cycling. A DOC on a construction machine can jump from 180°C to 600°C in minutes. Metal foils, especially FeCrAl alloys, tolerate these conditions far better. The alloy forms a stable oxide layer that stays bonded to the surface, giving the washcoat something consistent to adhere to. That oxide layer also improves corrosion resistance, which matters in marine, mining, and industrial settings where moisture and chemical contaminants are common.

Then there’s vibration. High-temperature oxidation systems are rarely installed on gentle equipment. They’re bolted to diesel engines on graders, excavators, drilling rigs, generators—machines that shake constantly. Ceramic substrates can crack under this type of mechanical stress. Metal substrates handle vibration much better because the foil structure flexes instead of fracturing. The combination of corrugated and flat foil layers acts almost like a mechanical spring system, absorbing a surprising amount of movement without deforming permanently.

Coating adhesion plays a big part in long-term catalyst stability, and here again metal substrates offer practical advantages. FeCrAl, once thermally conditioned, forms an alumina layer that bonds well with the washcoat. The adhesion remains stable even after extended high-temperature endurance tests. Ceramics can hold a coating well too, but once a crack forms or a chunk breaks out, the loss is permanent. Metal substrates tend to maintain structural continuity, which helps the coating stay intact for longer periods.

Another often overlooked reason for their preference is design flexibility. Metal substrates can be wound in a variety of geometries—round, oval, racetrack, even custom shapes—without compromising mechanical strength. OEMs designing tight engine compartments or retrofitting existing engine platforms often rely on this flexibility. The assembly process, from brazing to mounting, also gives engineers more control over durability features like anti-vibration reinforcement, spot welding patterns, and flange integration.

Flow characteristics are another advantage. A metal substrate allows engineers to fine-tune channel density, foil thickness, and corrugation to get the right balance between pressure drop and catalytic surface area. When high-temperature oxidation requires high gas throughput—burners, thermal reactors, or large-displacement engines—this tunability becomes essential. The gas needs enough residence time to react, but not so much restriction that it increases backpressure or affects engine performance.

Long-term stability is where the difference becomes most obvious. After thousands of hours, high-temperature oxidation systems start showing their weaknesses. Ceramics can develop hairline cracks that slowly expand. Metal, especially FeCrAl-based substrates, holds its geometry longer. Even if minor deformation occurs, it usually doesn’t result in total failure. As long as the foil stack stays intact and the coating bond remains strong, oxidation performance stays within expected limits.

For industries under tightening emission regulations—construction, marine, stationary power, mining—the reliability of the DOC or burner directly affects certification and operational costs. A metal substrate gives engineers more breathing room when designing systems that must withstand extreme heat cycles without losing catalytic efficiency.

In short, metal substrates have earned their place in high-temperature oxidation applications because they simply survive conditions that strain other materials. Quick heat response, vibration tolerance, coating stability, and long-term durability make them the practical choice when engines or reactors operate in environments where heat comes fast and often. For engineers building the next generation of emission systems, metal substrates aren’t just an option—they’re the baseline for making a system that works reliably from day one to the last hour of its service life.