Precursors thermal ageing

The reduced precursors were characterized by CO (H2) adsorption measurements performed in a small reactor attached to a quadrupole mass spectrometer and UHV system. The reduced samples were saturated with CO (H2) at 298 K (1.33 kPa CO), the reactor was then evacuated (10 Pa) and the next thermal desorption test was applied. The experimental setup was also used to follow hydrogen and hydrocarbon desorption from aged catalysts. 

Synthesis and Characterization of Layered Precursors. Hydrotalcite-like materials of Mg-Al, Zn-Cr, Ca-Al, and Ni-Al were prepared from the nitrate salts. A mixed solution of the appropriate divalent and the trivalent cation salts in the required molar ratios was co-precipitated with a base, typically NaOH, at room temperature. The pH of the suspension was maintained between -8 and 10 during the addition, which required approximately 1 hour. After complete addition, the precipitate was allowed to age for 16 hours and later washed with deionized water. The purity and crystallinity of the material was verified by X-ray diffraction. DTA/TGA analysis was used to study the thermal stability as well as the accompanying weight loss of the materials. 

Woignier T, Phalippou J (1988) Mechanical strength of silica aerogels. J Non-Cryst Sohds 100 404-408 Haereid S, Anderson J, Einarsrud M A, Hua D W, Smith D M (1995) Thermal and temporal aging of TMOS-based aerogel precursors in water. J Non-Cryst Solids 185 221-226... 

Even if supercritical drying permits to obtain perfectly monolithic and transparent sihca-based thermal insulators, the process to obtain such crack-free large plates remains stUl too far from industrial large-scale commercialization. This was the initial reason why different processes have been studied to develop subcritical routes to access rapid massive commercialization. Among the various studies, aging of the gels in silica precursor containing solution has permitted to reach room temperature thermal conductivities as low as... 

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