Microstructure determination of IQ-WB clays: a direct procedure by small-angle X-ray scattering

An accurate characterization of the microstructure of raw and pure homoionic clays from Wadi Bashira in Iraq (IQ-WB) has been carried out experimentally, using small-angle X-ray scattering (SAXS) and dynamic light scattering. The structures of lamellar IQ-WB dispersions were identified by these techniques and by complementary free swelling and dialysis experiments. SAXS measurements were used to resolve the characteristic distance, h_s, between individual platelets in Na IQ-WB and between platelets inside tactoids formed in Ca clays. The tactoids in raw and Ca IQ-WB have well formed lamellar structures where h_s = 1.9 nm. The average lateral size, 〈D〉, of a platelet is determined to be a few hundred nanometres. Analysis of the SAXS peaks, based on the Scherrer relation, revealed a small difference in the average number of platelets per tactoid, 〈N〉 = 6–9, depending on platelet size and the concentrations of divalent counter-ions. It was also found that the average tactoid size can be estimated from an empirical relation as follows: 〈N〉 ≃ δ + α〈D〉, where δ is a constant and α the slope.