An electron microscopic study of Na-attapulgite particles showed their lath-like habit with aspect ratios of approximately 100:3:1 (length:width:thickness). The average length of the particles is 0.951 μm. The nature and density of titratable surface charge was studied using an automatic potentiometric and titration apparatus. The results revealed that both positive and negative charges develop at the edges of the particles. The point of zero net proton charge (PZNPC) of the edges is at pH 6~7 depending on the electrolyte (NaCl) concentration (<I>c</I>). Electrophoretic mobility determined (using a Malvern Zeta Sizer II) over a range of pH and electrolyte concentrations showed a significant influence of the edge titratable charges on the electrokinetic properties. Particle size analysis (in suspension) using the technique of photon correlation spectroscopy (PCS) suggested that measurements of mobility reflect the electrokinetics motion of single laths at pH<6 and c<10<SUP>-3</SUP> NaCl. However small aggregates form the electrokinetic units at pH<6 and/or high electrolyte concentrations. Conversion of mobility to zeta potentials proved difficult due to the lack of a suitable theory for the electrophoresis of lath-like and non-uniformly charged particles. An approximate method (Williams & Williams, 1978) was applied for resolving zeta potentials into separate face and edge components. The linear viscoelastic behaviour of concentrated Na-attapulgite suspensions was investigated using the techniques of shear wave propagation and forced non-resonant dynamic oscillation.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:636203 |
| Date | January 1995 |
| Creators | Cao, E. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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