Emissivity is the ability to absorb energy and subsequently release that energy by reradiating or transferring it to a cooler thermal load. Emissivity is also a function of temperature with the reradiation potential increasing as temperatures rise.

Dynacote with Emisshield is applied as an even coating 3 - 5 thousandths of an inch thick. Once the coating has dried, some of the ceramic material migrates to the surface, enclosing the emissivity agent. As radiant heat waves bombard the surface of the coating, the waves bounce around the ceramic molecules and are then absorbed by the emissivity agent. The energy imparted on these molecules causes them to vibrate. The higher the temperature, the faster the vibration of the molecules developing a more effective thermal barrier because more heat is transferred to the cooler thermal load thus protecting the underlying material. And because the coating was originally developed for extreme speeds (up to 14,000 miles per hour) in space applications, it is extremely resistant to wear and abrasion.

NASA developed Protective Ceramic Coatings (PCC) for the X-33; NASA’s re-usable Space Vehicle Program. Wessex Incorporated was able to license the patent for PCC for the purpose of its commercialization into unique products for the ceramic, refractory, metal textile and other markets.

The NASA developed PCC, and therefore Emisshield™ Products, is based upon the important concept of emissivity for substrate protection and increased performance. Emissivity is defined as a substrates ability to absorb energy and subsequently re-radiate that energy to a cooler place.

Any substrate: metal, ceramic, refractory, paint, wood, etc., has an emissivity rating between 0.0 and 1.0. However, most of these emissivity ratings are based upon ambient temperatures. When temperatures increase most substrates are destroyed or see their emissivity reduce significantly. If a substrate has an emissivity of 0.01, it would not absorb and therefore release energy as well as a substrate with an emissivity if 0.98. The graph below demonstrates this with three different types of metal versus steel coated with an Emisshield™ Coating.

This equation determines the amount of potential energy that is re-radiated from a substrates surface: Where: qre-rad. is measured in units of Btu/hour-ft² ew= emissivity s = Stefan-Boltzmann Constant Ts = surface temperature Tsur= surrounding temperature This formula shows that emissivity is a function of temperature in that as the temperatures rise, the reradiation potential increases. Emisshield™ Coatings have a high emissivity rating of 0.8 to 0.9 at low and high temperatures.

Substrate Protection and Re-Radiation

The key components of Emisshield™ Products are based on patented NASA technology. These components are blended in optimal proportions, sintered if necessary, to produce a surface with high emissivity characteristics for refractories, metals, fabrics and other substrates. The coatings retain and improve their emissivity characteristics during and after exposure to elevated temperatures.

Thermal Energy (heat) is transferred through convection, radiation, or conduction. As the 2nd Law of Thermal Dynamics dictates, energy will always flow from hot to cold using the path of least resistance. Therefore, Emisshield™ Coatings will reradiate absorbed energy to a cooler place; in many cases, away from its surface. This is because the surrounding atmosphere is cooler than the substrate and easily accepts the radiated energy. Emisshield™ Coatings reduce the amount of thermal energy that would be normally conducted through the substrate, by re-radiating it at the surface. Cross sections of substrates with and without a coating are shown below to illustrate the advantage of Emisshield™ Coatings.

To learn more about how Emisshield™ Coatings could help improve your fireplace, chimney, stove, barbeque and accessory products, contact a Dynacote LLC Representative at 207.439.0311 or toll free at 866.439.6226.