Hectorite Synthetic

Polyimide-clay nanocomposites constitute another example of the synthesis of nanocomposite from polymer solution [70-76]. Polyimide-clay nanocomposite films were produced via polymerization of 4,4 -diaminodiphenyl ether and pyromellitic dianhydride in dimethylacetamide (DMAC) solvent, followed by mixing of the poly(amic acid) solution with organoclay dispersed in DMAC. Synthetic mica and MMT produced primarily exfoliated nanocomposites, while saponite and hectorite led to only monolayer intercalation in the clay galleries [71]. Dramatic improvements in barrier properties, thermal stability, and modulus were observed for these nanocomposites. Polyimide-clay nanocomposites containing only a small fraction of clay exhibited a several-fold reduction in the... 

FIG. 13 Reduction of the relative permeability coefficient is dependent on the clay platelet aspect ratio in the system of polyimide-clay hybrid with water vapor as the permeate. Each hybrid contains 2 wt% clay. The aspect ratios for hectorite, saponite, montmorillonite, and synthetic mica are 46, 165, 218, and 1230, respectively. (From Ref. 71.)... 

R. B. Carpenter, J. B. Bloys, and D. L. Johnson. Cement composition containing synthetic hectorite clay. Patent WO 9902464,1999. 

Smectites are 2 1 charged layered silicates from natural (montmorillonite, hectorite, beidellite, saponite etc.) or synthetic (synthetic fluorohectorites, such as... 

There are many other forms of clay including synthetic clays such as laponite, a synthetic hectorite. Suitable tuning of the properties of these systems can produce similar structures. These systems have the advantage of small particle size and a relatively improved level of particle monodispersity over their naturally occurring counterparts and are being increasingly used as rheology modifiers. 

In the presence of Na" " ions, the Gd(HI)-exchanged natural hectorite and the Gd(IH)-exchanged synthetic hectorite showed a different behavior. At lower Na" "-concentration (0.13 M), none of the samples showed Gd(HI)-release, whereas at higher Na-concentration (0.25 M), the natural sample released 24 % Gd(IH) and the synthetic sample did not show any exchange ofNa+ for Gd(HI). 

Calculated based on the precursory synthetic hectorite. Calculated from MB adsorbed, Calculated from thermogravimetric data. 

These results indicate that the mesoporous material OH-02-600 having exceptionally large pores was produced from the synthetic silicate-bearing hectorite H-02 by the intercalation of AMC3A cation and the removal of organic materials. 

Fig. 1. Nitrogen adsorption-desorption isotherms at -196 C for the mesoporous material OH-02-600 and its precursory synthetic hectorite H-02-300. Open symbols adsorption. Solid symbols desorption.

Pore volumes of heat-treated mesoporous material OH-02 and its precursory synthetic hectorite H-02 as a function of temperature are shown in Fig. 3. The material OH-02 was stable after being heat-treated to 600°C, at which temperature the volume started to decrease. On the other hand, the pore volume of the precursory hectorite H-02 started to decrease gradually at 400°C. As shown in Fig. 3, the pore volume increased with increasing temperature in the range of... 

Last three figures designate the heat-treatment temperature for th, Calculated by BET equation for the samples unless otherwise specified, and by Langmuir equation for the samples designated with, Pore volume ratio of the mesoporous material to its precursory synthetic hectorites. 

K. J. D. MacKenzie and R. H. Meinhold, The thermal reactions of synthetic hectorite studied by Si, Mg and Li magic angle spinning nuclear magnetic resonance. Thermochim. Acta, 1994, 232, 85-94. 

The presence of an organophilic clay increases the catalyst activity (10). Suitable clays include montmorillonite, hectorite, mica, etc. For example, Lucentite is a trioctylmonomethylammonium salt-treated synthetic hectorite. The clays are modified with quaternary ammonium compounds. The clays are heat treated prior to their use in the polymerization process. Further, the incorporated clay can improve the performance of the UHMWPE or function as filler. 

Figure 1. SAXS high-q data for 30 wt% synthetic PVP-hectorites (prior to calcination).

The use of clays as supports for hydroprocessing has been reported and summarized [9-11], Dibenzothiophene (DBT) diluted with hexadecane (0.75 wt% S) was the liquid feed for HDS tests. The pore diameter of the MSC catalysts is seen to have a strong effect on both the HDS activity and selectivity (Figure 4). A commercial catalyst (Crosfield 465, Co/Mo alumina) was also measured under these conditions where it gave 77% DBT conversion and 61% BP selectivity. In a previous study [12], other synthetic hectorites were compared using these conditions except that a 1 wt% S feed was utilized. One sample was a control made without template that consisted of only micropores. The DBT conversion and BP selectivity were very low for this microporous material. The Crosfield material has significant macroporosity (42% of the pore volume) in addition to a broad distribution of mesoporosity, and has clearly been optimized to perform well under these HDS conditions. 

Hectorite - [SILICON COMPOUNDS - SYNTHETIC INORGANIC SILICATES] (Vol 22)... 

Typical spectra of the p-xylene/synthetic hectorite intercalate are shown in Fig. 78. Although the proton peaks are rather broad, they are much narrower than would be obtained from solid p-xylene, indicating that the intercalated species has considerable freedom of motion. The two proton peaks for the xylene intercalate have relative intensities of 2 3 and the chemical shifts are very similar to the aromatic and methyl resonances in the high-resolution solution spectrum. 

Al3+-exchanged synthetic hectorite is a good catalyst for these conversions, and the 13C NMR spectrum obtained in the interlamellar, proton-catalyzed addition of water to 2-methylpropene is indistinguishable (Fig. 79) from that of f-butanol. Doubtless studies of this kind, where natural-abundance, 3C NMR signals are used to probe the chemical identity and motional freedom of reactant and product species situated in the interlamellar spaces of clays or pillared clays (see below), will become increasingly popular. Using l3C NMR linewidths and spin-lattice relaxation studies, Matsumoto et al. (466) have succeeded in discriminating between the internal and external surfaces of pillared montmorillonites. 

Fig. 79. I3C NMR spectra showing that when 2-methylpropene (isobutene) is intercalated in a synthetic hectorite r-butanol is formed when the guest species reacts with the interlamellar water. The peaks labeled 1 and 2 refer to the two distinct types of carbon atom in r-butanol (453).

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