Thursday, January 16, 2014
Metallic Catalysts Vs Ceramic
As the key component in a vehicles emissions control system (and some machinery as well), catalytic converters are responsible for turning tons of potentially harmful exhaust emissions into harmless carbon dioxide. Until the early 1990s, the catalyst supports in these systems were almost entirely ceramic. Recently, however, metal supports are slowly beginning to replace ceramic as the material of choice. There are a number of reasons for this continuing shift in the industry, many of which have to do with the elemental properties of metal vs. ceramic.
How the Catalytic Process Works
To better understand the differences in metal and ceramic catalyst supports, it is necessary to first appreciate how catalysts and the catalytic converters they are housed in function. As carbon monoxide and other harmful gases are passed through an exhaust system, heat produces a chemical reaction with "catalysts" housed in the converter. The result of this reaction is the dangerous gases are cleaned and converted to harmless carbon dioxide before being admitted into the atmosphere.
Thermal Properties
One of the most significant differences in metal and ceramic catalysts are the superior thermal properties of metal. Because harmful gases like carbon monoxide are converted only when high temperatures are reached, the more quickly the engine warms, the more efficient is the conversion of gases. Also, metals improved heat conductivity does not take as long as a ceramic catalyst to reach high temperatures, which allows for a more uniform transfer of heat through the system.
Mounting Placement
Metal catalysts allow the converter to be mounted closer to the engine, increasing heat flow. This is particularly important in cold conditions, when the engine, and subsequently the catalytic converter, take longer to warm up. This closer placement also results in less vibration, backflow of gases and pressure drop (as much as 15 to 30 percent less) than comparable ceramic catalysts.
Manufacturing Process
Metal catalysts are made via a production process prior to the assembly of the converter, so they can be easily changed or adapted if needed. The manufacturer simply needs to change the shape of the "cell" support. Ceramic, on the other hand, is much less flexible to change dimensions. From a manufacturing perspective, both metal and ceramic catalysts are priced about the same. The distinction is in the performance and enhanced efficiencies that metal provides.
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