Electrostatic Microencapsulation Technique for Producing Composite Particles

Abstract

The electrostatic microencapsulation process and the various means of achieving such encapsulation for developing composite particles with two or more powders is briefly reviewed, with a particular focus on the dual-function sorbent/scintillation particles for use in radionuclide selective sensing. In preparing the composite particles, two different types of particles, an ion-exchange resin and scintillating microbeads, were used. The sorbent particles capture and preconcentrate the radionuclide of interest (e.g., 99 Tc) from solution. The scintillating microbeads are used to convert the energy of radioactive decay into that detectable light that can be deducted by a photomultiplier tube arrangement. To simulate the electrostatic microencapsulation of resin and scintillators, several surrogate materials such as acrylic powder (mean particle diameter, d 50 =23 µm), red toner (d 50 =16 µm), resin (d 50 =134 µm), and fluorescent latex spheres (d 50 =2 µm) were used. A microencapsulation tower was constructed to use corona guns operating at high voltages of opposite polarity to charge the "host" and "guest" particles. Experimental arrangements and test results are presented. The results show that if polymer particles are used and if one of the two powders is smaller than 10 µm in diameter, the electrostatic and van der Waals forces provide enough interparticle adhesion to bond the guest and host particles through plastic deformation. Interparticles adhesion between resin (d 50 =133 µm) and toner (d 50 =15 µm) showed that the composite particles were stable in water suspension. For larger particles, such as resin and scintillators, the use of a binding agent is necessary to form stable composite particles. electrostatic microencapsulation particle coating groundwater monitoring composite particles radionuclide detection