[Viscosity changes of zinc phosphate cements in setting process (author's transl)]

A better understanding of setting process of zinc phosphate cements is important to obtain optimum conditions of manipulation. Viscosity changes of zinc phosphate cements in setting process were investigated using a rotational viscometer in various conditions. The results obtained were as follows. 1) The viscosity of the cement mixture increased exponentially as a function of time. 2) The setting process of the cements was characterized by two parameters, the coefficient of setting speed and the setting time. The coefficient of setting speed was defined as the slope of the linear portion of log viscosity versus time curve, and the setting as the time required to reach a certain level of viscosity after the start of the mixing. 3) Shear rate was observed to affect on the time-related changes of viscosity. As the shear rate increased, the coefficient decreased and the setting time increased. These changes were more remarkable in the lower range of shear rate. 4) The coefficient of setting speed was found to be dependent on environmental temperature in accordance with Arrhenius' low. 5) Apparent activation energy calculated 16.41 kcal/mol by Arrhenius' equation. The coefficient increased by a factor of 2.6, when the temperature was raised from 20 degrees to 30 degrees C. 6) A decrease of the P/L ratio caused the logarithm of the coefficient to increase linearly and the setting time to decrease. 7) All the four commerical zinc phosphate cements tested showed different values of both the coefficient and the setting time.