X-RAY-DIFFRACTION AND RHEOLOGY STUDY OF HIGHLY ORDERED CLAY PLATELET ALIGNMENT IN AQUEOUS-SOLUTIONS OF SODIUM TRIPOLYPHOSPHATE

Highly ordered parallel alignment of a synthetic clay, referred to her ein as an expandable mica (ME) but similar in behavior and physical ch aracteristics to montmorillonite, in sodium tripolyphosphate (STP) sol utions has been observed by an X-ray diffraction method. The weight ra tio of the clay was 7%, and the ME/STP by weight ratio was varied from 0.1 to0.4. The X-ray diffraction patterns of the suspensions at high STP concentrations were very sharp, and the basal reflections of the c lay gave up to fifth order reflections in some samples. The basal spac ing of the clay in the suspensions decreased from 8.70 to 4.82 nm with increasing STP concentrations. The rheological properties of the same suspensions showed non-Newtonian behavior at zero STP addition. The s teady shear viscosity of the suspensions decreased dramatically with i ncreasing STP addition at a given shear rate. The total potential ener gy for particle-particle interaction calculated using classical DLVO t heory indicates that the clay particles fall into a secondary minimum and that phosphate anions play an important role in controlling the al ignment of the platelets.