Saponite thermal stability

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. 4 shows the 001 line evolution of sample la with regard to the thermal treatment. Pillared clays of process 1 (Table 5) still exhibit thermal stability at 750°C. These thermal stabilities up to 750°C may be related to (i) the nature of the phyllosilicate (magnesian octahedral sheet, Si/Al substitutions) and (ii) the thermal stabilization of the intercalated saponite. 

Complementary results on thermal stabilities of Al-pillared saponites are presented elsewhere (22). 

It is possible to prepare saponites with specific surface areas between 100 and 750 nfilg and pore volumes of 0.03-0.32 ml/g, all displaying a house-of-cards structure. The thermal stability of the synthetic saponites is high, which enables us to dehydrate the clay minerals efficiently, prior to the catalytic reaction. 

The use of bifunctional protonated titanium-containing aminopropylisobutyl POSS (Ti-NH3POSS) to intercalate synthetic sodium saponite leads to significant thermal stabilization of PS nanocomposites [30] (Table 3.1). The catalytic activity of the Ti centers leads to the formation of stable charring products by secondary reactions. This causes significant improvement of the thermal stability and flame retardancy of the nanocomposite. 

The acidities of cliys and pillared clays are between those of amorphous aluminosilicates and zeolites. Pillared clays can provide large-pore two-dimensional networks. Hectorite, montmorillonite, saponite and beidellite are the clays most often used to make pillared clays. Most pillared clays coke and deactivate st. This, and low thermal and hydrothermal stabilities have so far limited catalytic applications. Al, Ti, Zr, Cr, Si, and Fe and their mixtures give more stable pillars than those tried in the past. Occelli and Robson reviewed pillrued clays [52]. 

The A1 content fixed by the pillared clay increases with the pH and with the Al/clay ratio. According to the preparation process, the whole amount of the pillaring Al-species is not always completely fixed in the interlayer space. For some samples, it may be suspected that another Al-species is precipitated to a greater or lesser extent on the layer surface. The best stability of Al-pillared saponite is obtained under the following experimental conditions clay concentration < 5 g.l Al/clay < 5 mmol.g and pH values between 4.8 and 6.0. A very carefull thermal treatment is required up to SOOX (36 /h heating rate) to transform the intercalated species into oxide pillars. At 750 C, the surface areas are about 150- 250 m. g and the basal spacings dpoi about 17.3 A. According to these values, Al-pillared saponites may be used as catalysts of 7-8 A pore space. 

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