Hectorite 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... 

Pillared montmorillonite (and hectorites) have thermal stability in air that does not exceed 800°C. In contrast, the ACH-rectorites under study after calcination at 800°C, retain their pillared structure (Fig. 3) and more than 902 of their initial surface area. As a result, after calcining at 800°C/5h, only minor changes in the cracking properties of the two ACH-rectorites are observed. Table 2. 

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]. 

Pillared rectorites have thermal and hydrothermal stability much superior to that of similarly prepared montmorilIonites and hectorite catalysts. In fact, ACH-rectorites retain their pillared structure even after calcination in air at 800°C/5h or after steam-aging with 100% steam at 760°C/5h, Fig. 3. High temperature (800°C) calcination or steaming has little effect on the shape and intensity of the clay 001 and 002 reflections. Fig. 3. At 800°C the d(OOl)... 

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