Dispersion of H−Magadiite and H−Kenyaite Particles by Ion Exchange of H⁺ with Alkali Ions

Abstract

Synthetic magadiite and kenyaite and their silicic acids were obtained as spherical and loosely packed aggregates composed of platelike crystals. Particle dispersion of the silicic acids was investigated by scanning electron microscope (SEM) observation, electrokinetic characterization, and particle size distribution analysis. SEM observation indicated that the particles of these compounds were dispersed into individual platelets by treatment with KOH, LiOH, and NH 4OH solutions, but this phenomenon did not occur in NaOH solution. The effectiveness of alkaline solutions for dispersion followed the order LiOH > KOH > NH4OH. H-kenyaite particles were also found to be more easily delaminated than H-magadiite particles. Measurement of relative acoustophoretic mobility of the particles and solution specific conductivity indicates that the dispersion is due to the increase in electrical double-layer repulsion between particles surrounded by OHanions in solution.

One-Step Synthesis of Alkyltrimethylammonium-Intercalated Magadiite

“…In contrast, the tetradecyltrimethylammonium-intercalated magadiite (Figure 4b) is more disaggregated and more exfoliated than magadiite. This result also supports the partial replacement of Na + ions by H + since this procedure is known to cause exfoliation (Kosuge and Tsunashima, 1996). Unexchanged-magadiite aggregates, with a morphology similar to samples prepared by other methods (Kosuge and Tsunashima, 1996;Crone et al, 1995), are also larger than alkyltrimethylammonium-intercalated magadiite: aggregates from 3.8 to 16,9 p~m in size were found.…”

“…The three bands in the "quartz" gap (-620, 580, and 540 cm -1) are present in all samples and correspond to double-ring vibrations (Flanigen et al, 1976) which are characteristic of magadiite among the other silicic acids of this family (Kosuge and Tsunashima, 1996). Figure 3 shows the 298i-MAS NMR spectra of magadiite (Figure 3, trace a) and CTA-intercalated magadiite (Figure 3, trace b).…”

“…This result is probably related to the exchange of Na + ions by H +. In H-rich magadiite, only one peak is observed in powder X-ray diffraction patterns, at --0.342 nm (--26 ~ (Kosuge and Tsunashima, 1996). This peak (-0.343 nm) is more evident in samples where the organic molecules have been extracted (Figure 1, trace i) because an acid solution is used that probably promotes exchange of CTA + and/or Na + by H § The interlayer spacing observed for these samples also indicates that the samples are at least partially acidic.…”

Performance of natural and modified smectite: kinetic and thermodynamics involving arsenic (V) adsorption

“…The adsorption-desorption isotherms of gaseous nitrogen on natural and modified smectite fitted the type IV curve behavior, as illustrated in Fig. 3b, indicating that the pores are formed by open cylinders on the two extremes [13]. Through the BJH method the pore diameters obtained for unmodified and modified smectite were 26.0 ± 1 and 79.0 ± 1 nm, respectively.…”

Influence of magadiite dispersion states on the flammability of polystyrene and polyphenylene ether-polystyrene alloy nanocomposites

“…7,19 This tendency can be applied to polymer/clay systems; in other words, clays with better dispersion and higher aspect ratios should exhibit greater flame retardance. Therefore, magadiite with a relatively high aspect ratio 20,21 must be a great potent candidate for high flame-retardant material only if magadiite can be successfully delaminated into polymer matrices.…”