Thermal gels, main steps

The main steps in the thermal crystallization of gels are the following (a) preparation of the sol, (b) progress of the network formation leading to the gelation of the reaction mixture, (c) drying of the gel monoliths, and (d) thermal treatment. 

Kim et al.32 reported the preparation, characterization, and catalytic performance of a finely dispersed and thermally stable nickel catalyst incorporated into mesopo-rous alumina. Mesoporous alumina catalysts that incorporate Ni (Ni-alumina) with different Ni/Al molar ratios were synthesized by a one-step sol-gel method using lauric acid as a template. The prepared Ni-alumina catalysts showed a relatively high surface area with a narrow pore size distribution after calcination at 700 °C these effects were independent of the Ni/Al molar ratio. The Ni-alumina catalysts were found to be highly active in the POX of methane. The deactivation of catalysts examined in this work was not due to catalyst sintering, but mainly to carbon deposition. 

Whatever the technique used (thermal or ionotropic gelation), gel particles are generally formulated in a two-step procedure involving a droplet formation and hardening. The droplet formation step determines the mean size and the size distribution of the resulting gel particles. In the following, the main procedures used for droplet formation—droplet extrusion, nebulization (spray), and emulsification—are described. 

Novel types of synthesis of modem electrocatalysts revealed that the properties of electrode materials can be affected by the controlled formation of nano-sized, finely dispersed, electrocatalyst particles. In the case of DSA, already the traditional preparation procedure involves the thermal decompositiOTi of the corresponding chlorides after dissolution in an appropriate solvent (usually a solvent of low viscosity, e.g., 2-propanol) [3], Recently, sol-gel synthesis was introduced for DSA preparatirMi, with the main effect being related to the increase in the real surface area of the anode [9,10], The effect is recognized as the geometric factor of increased electrocatalytic ability in addition to an electronic factor related to the chemical structure of electrocatalyst [2,4], which is essential for step (6). The geometric factor is important since the measure for the reaction rate is the current density, i.e., the current per surface area of the electrode available for the reaction. Thus, the reaction rate can be considerably increased by the application of nano-3D electrodes, which are porous systems with an extended real surface area. The polarization curves for the CER on... 

Several factors influence the grade of mechanical protection afforded by the sol-gel ceramic layer (1) composition and structure of the coating, (2) inherent mechanical properties of the substrate and coating, (3) residual stresses in the coating mainly formed during its thermal consolidation step [39], and (4) coating thickness and adhesion strength to the substrate. 

---