Question

The correct expression for Thixotropy B where U1 & U2 are plastic viscosity of two down curves after shearing at constant rate for t1 and t2 seconds, respectively:

• A. $B=1-(U2-U1)/(Ln(t2/t1))$
• B. $B=(U1-U2)/(Ln(t2/t1))$
• C. $B=(U1-U2)/(Ln(t1/t2))$
• D. $B=(U1-U2)/(1-Ln(t2/t1))$

Hint:

Thixotropy B deals with "Time" ($t$). Formula involves the difference in viscosity over the log of the time ratio.

Answer 1

The Correct Option is B

Step 1: Concept
Thixotropy is a time-dependent shear-thinning property. The rate of breakdown of a thixotropic system can be measured quantitatively.

Step 2: Meaning
$B$ represents the coefficient of thixotropic breakdown with time at a constant shear rate.

Step 3: Analysis
When a material is sheared at a constant rate for different durations ($t1$ and $t2$), the plastic viscosities measured from the resulting down-curves ($U1$ and $U2$) decrease. The relationship is logarithmic.

Step 4: Conclusion
The standard formula derived for this time-dependent breakdown is $B = \frac{U1 - U2}{\ln(t2/t1)}$.

Final Answer: (B)