How does sandblasting a smooth, shiny metal surface affect the emissivity of that surface?

How does sandblasting a smooth, shiny metal surface affect the emissivity of that surface?

• A. Reduces it
• B. Has no effect
• C. Raises it
• D. Makes it zero

Answer: (C)

Emissivity describes how efficiently a surface radiates infrared energy compared to a perfect blackbody. A smooth, shiny metal reflects most of the IR, so its absorptivity—and thus emissivity—are low. Sandblasting roughens the surface, creating microfacets and pits that trap light and reduce specular reflection. With more of the incident IR energy absorbed, the surface behaves more like a blackbody, so emissivity increases. It won’t become zero, and the texturing does have an effect, so raising emissivity is the best description.

Emissivity describes how efficiently a surface radiates infrared energy compared to a perfect blackbody. A smooth, shiny metal reflects most of the IR, so its absorptivity—and thus emissivity—are low. Sandblasting roughens the surface, creating microfacets and pits that trap light and reduce specular reflection. With more of the incident IR energy absorbed, the surface behaves more like a blackbody, so emissivity increases. It won’t become zero, and the texturing does have an effect, so raising emissivity is the best description.