Sintered porous ceramic experiences a condition known as Thermal Shock that results in structural degradation. It happens when the ceramic is heated unevenly. This structural degradation is further compounded when a heating coil is sintered inside of the host ceramic.
Basically, the metal coil expands and contracts with temperature change at a much higher rate than ceramic (which hardly expands and contracts at those same temperatures by comparison). So the heated and cooled coil (during
vaping conditions) is constantly destroying the surrounding ceramic at a microscopic level, breaking the structural bonds that contain the negative space of it's porous structure. When that happens, filamentous crystalline shards become presently free-floating in the ceramic. This condition increases the deeper the heating coil is sintered inside the ceramic wick.
Now add the hydrodynamics of
eliquid through the porous ceramic wick. The liquid passes from the outside of the ceramic wick, through the negative space pores, "washing" the free-floating ceramic particulate directly to the hollow core of the coil head, where it is exhausted with the vapor into the lungs of the user.
Of course none of this can be "seen" happening on a macroscopic level, giving the illusion that the ceramic is still in pristine condition and appears to be "safe". There are also no rock solid lab results on this exact use of these materials (especially considering the new-ness of such a creation), but the physics of these conditions are definitely real and provable, and have been studied and documented.
A simple test can be performed to check for this condition:
Determine the pressure required to crush a new (unused) ceramic coil.
Then determine the pressure required to crush a well used ceramic coil.
If there is any difference in required pressure, then the structural integrity has been vastly compromised and it's unsafe for use.
Here's a simple thought experiment that correlates to ceramic wicks with embedded heating coils.
1. Take a raw egg in it's shell.
2. Microwave it.
3. Clean up the mess
The egg shell represents the ceramic wicking material. The egg yolk represents the metal heating coil and
ejuice. The yolk expands at a far greater rate when quickly heated in comparison to the shell. The shell is brittle and doesn't expand at the same rate as the yolk.
Regardless of the ceramic formulation used in these coils, thermal shock and material expansion are conditions that cannot be denied, and are huge causes for concern in regards to the safe use of ceramic coils.