Method and apparatus for measuring deposit forming capacity of fluids using an electrochemically controlled pH change in the fluid proximate to a piezoelectric microbalance

A method of measuring the effectiveness of inorganic scale inhibitors comprising

• a) measuring the inorganic scale forming propensity of a continuously flowing solution having a bulk pH of about 1 to about 12 comprising measuring the rate at which deposit forms on a quartz crystal microbalance having a top side comprising a working electrode in contact with the solution and a bottom side isolated from the solution, wherein the pH of the solution proximate to the microbalance is controlled electrochemically at about 1 to about 14 by applying to the working electrode a cathodic current of about −0.001 to about −100 mA/cm2 or an anodic current of from about 0.001 to about 100 mA/cm2 and wherein the working electrode is coated with or made of a conductive material on which the rate of hydrogen gas evolution is at least 10 times lower than on a gold cathode under acidic conditions;
• b) adding a deposit inhibitor to the solution;
• and
• c) re-measuring the rate of deposition on to the quartz crystal microbalance.

A measurement cell for measuring the deposit forming propensity of a continuously flowing solution having a pH of about 1 to about 12 comprising

• a) a quartz crystal microbalance assembly having a top side comprising a working electrode for exposure to the fluid and a bottom side isolated from the fluid;
• b) a counter electrode in contact with the fluid for providing a uniform electric field to the microbalance;
• and
• c) means for stirring the fluid, wherein the pH of the solution proximate to the microbalance is controlled electrochemically at about 1 to about 14 by applying to the working electrode a cathodic current of about −0.001 to about −100 mA/cm2 or an anodic current of from about 0.001 to about 100 mA/cm2 and wherein the working electrode is coated with or made of a conductive material on which the rate of hydrogen gas evolution is at least 10 times lower than on a gold cathode under acidic conditions.