Chapter 2.9.5 - Carbon Dioxide (Dry-Ice) Blasting

Dry-ice particle blasting is similar to sand blasting, plastic bead blasting, or soda blasting where a media is accelerated in a pressurized air stream (or other inert gas) to impact the surface to be cleaned or prepared. With dry-ice blasting, the media that impacts the surface is solid carbon dioxide (CO2) particles. One unique aspect of using dry-ice particles as a blast media is that the particles sublimate (vaporize) upon impact with the surface. The combined impact energy dissipation and extremely rapid heat transfer between the pellet and the surface cause instantaneous sublimation of the solid CO2 into a gas. The gas expands to nearly eight hundred times the volume of the particle in a few milliseconds in what is effectively a “microexplosion” at the point of impact that aids the coating removal process. Because of the CO2 vaporizing, the dry-ice blasting process does not generate any secondary waste. All that remains to be collected is the removed coating. As with other blast media, the kinetic energy associated with dry-ice blasting is a function of the particle mass density and impact velocity. Since CO2 particles have a relatively low density, the process relies on high particle velocities to achieve the needed impact energy. The high particle velocities are the result of supersonic propellant or air-stream velocities. Unlike other blast media, the CO2 particles have a very low temperature of –109°F (–78.5°C). This inherent low temperature gives the dry-ice blasting process unique thermodynamically induced surface mechanisms that affect the coating or contaminate in greater or lesser degrees, depending on coating type. Because of the temperature differential between the dryice particles and the surface being treated, a phenomenon known as fracking, or thermal shock, can occur. As a material’s temperature decreases, it becomes embrittled, enabling the particle impact to break-up the coating and sever the chemical bond that is weakened by the lower temperature. The thermal gradient or differential between two dissimilar materials with different thermal expansion coefficients can serve to break the bond between the two materials. This thermal shock is most evident when blasting a nonmetallic coating or contaminate bonded to a metallic substrate.