In School Suspensions
Flocculation in ceramics
Objective:
The objective of this demonstration is to show the effect the pH on the flocculation of suspensions.
Review of Scientific Principles:
The process of forming a ceramic object usually involves filling a form (mold) with a ceramic suspension (such as clay). The suspension will gradually settle out due to gravity. It is important in ceramic processing to have the particles settle out individually to achieve the closest packing of the particles because the strength of a ceramic is partially determined by its density.
The rate of settling depends on the size of the particle (big particles or particle clusters settle faster) and the charge that may be on the particles in solution. The charge on each particle may repel the other particles and keep the material in suspension, or it may cause the particles to be attracted to each other and form clusters (or Flocs) which settle faster. By adjusting the pH of the solution, ceramic processors can control the degree of flocculation (settling out) of the ceramic particles and thus control the properties of the product. The chemicals that control flocculation are called deflocculating agents. This demonstration shows the effect of pH on the flocculation of a clay suspension.
Applications:
Understanding how chemistry influences suspension structure is important in numerous fields, such as ceramics, paint industry, even food products.
Time:
Fifteen minutes to set up and run.
Materials and Supplies:
Slip
distilled water
acidic, neutral and basic solutions
100 ml. graduated cylinders (3)
General Safety Guidelines:
*The acidic and basic solutions are corrosive and should be handled with care. Use a dump bucket for ceramic materials.
Procedure:
1. Measure out the slip to equal a 10% volume of the graduated cylinder.
2. Fill each graduated cylinder with a different pH solution.
3. Shake well. Take measurements of volume of settled material over a period of time.