*3.3. Motivation for CO2 Coolants*

Whilst LN2 can be shown to outperform conventional MWF's across a broad range of performance indices (i.e., demonstrated improvements to tool life, surface integrity, etc.), the current research landscape has largely made strides to transition away from LN2, and instead focus upon CO2; this is likely a consequence of the following factors:


**Figure 1.** Adapted CO2 pressure–temperature phase diagram. Reprinted from reference [8].
