Yesterday, I went to see my fluid mechanics professor, Dr. Placek, for help with some coursework. During the time I spent in his office hours he showed me some of his research on pottery glazes. Some of the glazes were created from multiple materials and had different fluid behaviors. One behavior that interested me the most was that some of the materials in the glaze diffused throughout the glaze when heated in a kiln. Other materials remained in relatively the same shape as they began. This is due to different diffusivity coefficients. I was interested in how to quantitatively describe this behavior. I googled the topic and this is selected information from what I found:
Diffusivity is recorded as a coefficient. The higher the coefficient the faster the two
materials diffuse into each other. Generally, the diffusion coefficient is 10,000 times
higher in air than in a liquid medium. The equation to quantitatively define diffusivity is
D = D0e-E/RT
where D is the diffusion coefficient, D0 is the maximum diffusion that occurs at an infinite temperature, E is the activation energy for diffusion, R is the universal gas constant and T is the absolute temperature.
In the above photo, you can see the dye look like they "bleed through" and run down the surface of the vase.
In this photo, you can see that the spots of dye have not "bled" or moved on the surface of the vase at all.
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