VII. Shear thinning and Thixotropy

I think I am jumping a bit here. The words shear thinning are familier enough but not thixotropy.

What is the meaning of thixotropy? Googling it I found a few sites give the defination; a thixotropy material is a material that appears or feels like a gel but flows when forced. Wait a minute, isn't that the same as shear thinning? Yes, you are about right. No, you are just almost right, means you are wrong. Thixotropic materials will thin even the shear rate remains but the shear thinning materials do not become thinner at a fixed shear rate. If you shear the thixotropic materials, the viscosity depends on how long you shear it; the longer, the lower. So, time is an important factor when describing thixotropic materials. And, it is the time dependent behavior that distingushes the shear thinning and thixotropic materials.

Example for thixotropic materials? Er...ok found one: thixotropic clay. URL it by clicking below:

http://www.potters.org/subject18056.htm

The clay mentioned here should be a high concentration clay slurry that you can shape it into a pot. The material, if I am not mistaken, should appear like gel. It will flow only when certain amount of force applied to it (not gravity though). The spinning pot and your hand (also with the air) will create shearing to the clay, so shear thinning will occur. The constant rotating speed will provide the constant shear rate provided your hand didn't move much. Under this circumstances, the clay will thin (but I guess it would not thin very quickly and would not thin a lot) and make the shaping easier.