Sepiolite thermal stability

Figure 43. Phase diagram of phyllosilicates found above the thermal stabilities of sepiolite and palygorskite in the system Si-R -R. ...

As a parenthesis, Figure 42 shows the system Si-R -R as it appears above the thermal stability limits of sepiolite and palygorskite. This is based upon the experiments of Velde (1973) in the Mg-Al-Si-H20 system at 2Kb pressure and temperatures above 200°C, and the experiments at high pressure of Frank-Kameneckiji and Klockova (1969) on natural sepiolite. 

The incorporation of 5 % organically modified sepiolite, which is a microcrystalline-hydrated magnesium silicate, in a bisphenol A-based epoxy resin has no significant effect over the thermal stability of the epoxy resin, due to the poor dispersion of the clay and poor diffusion of the resin between fibres [69]. The effect of attapulgite (magnesium aluminium phyllosilicate) over the thermal properties of hyperbranched polyimides was studied. The presence of this silicate in the nanocomposites significantly improved the thermal stability of the neat polyimide [70]. 

Huang N, Chen Z, Liu H, Wang J (2012) Thermal stability and degradation kinetics of poly (methyl methacrylate)/sepiolite nanocomposites by direct melt compoimding. J Macromol Sci Part B 52 521-529... 

The hydrothermal stability of the SA1 sample has been compared with that of the original SMg in Figure 6. The X-Ray diffraction pattern of an A1 sepiolite before (a) and after (b) steaming at 700aC, 100% steam and a natural sepiolite (SMg) also steamed at 7000C (c). The results indicate that after this thermal treatment an important fraction of the aluminic sepiolite remains unalterated, while the natural sample is completely folded. The folding of the sepiolite is shown by the disappearance of the (1,10) reflexion at 7.2, 20, and the appearance of a new reflexion at 8.9, 20 (16). Moreover, the adsorption of pyridine shows the presence of a residual Bronsted acidity in the SA1 after the hydrothermal treatment which is approximately 30% of the untreated sample. 

The selection of the more suitable nature for a porous support was based in the criteria of thermal and thermo dynamical stability (AG 0, chemically inert support) in the sulfurization step. The melting temperatures of 1000 C or higher, are required because zinc ferrite phase is prepared about 950 C. One representative material from each of the aforementioned categories has been selected for the preparation of every supported sorbent Coimnereial sepiolite (Tolsa, S.A., Spain), USY zeolite (Zeolyst Ine., U.K.), and Zr02, m.p. 2500°C,... 

Tartaglione et al. [62] have recently studied the thermal behavior of melt-compounded PP/sepiolite composites (3 wt% loading) and the effect of the clay surface modification. In inert atmosphere, the catalytic activity of sepiolite on PP pyrolysis was confirmed, except for the begiiming of the degradation process (less than 20% of mass loss) where the presence of the clay improved the polymer stability (Figure 12.21a). This was explained by the adsorption of PP volatile products by the sepiolite external surface and internal zeolitic channels. 

The inductive effect of alkyl groups in alkyl isocyanates, such as -butyl isocyanate, stabilizes the silylurethane bonds. This improves thermal and hydrolytic resistance over aryl isocyanates. In this context, phenyl isocyanate reacts with sepiolite, giving large amounts of diphenyl urea, wha-eas butyl isocyanate gives stable grafted compounds, producing low amounts of secondary products (dibutyl urea) (101). Because diisocyanates (e.g., hexamethylene diisocyanate and 2,4-... 

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