Graphite chemical regime

In the E/C synthesis, the first step in which metal nanocrystals are deposited on the substrate is critical. The semiconductor particles grow from the metal particles on a particle-by-particle basis (i.e. each metal particle is chemically transformed to the corresponding semiconductor). The size and size distribution, therefore, in the first step determine the final size of the semiconductor particles. For that reason, it is important to achieve an understanding of the growth mechanism of the metal nanocrystal deposition. Penner and associates studied the electrodeposition of various metal nanoparticles (Ag, Pt, Zn, Cu, Cd) mainly onto basal plane-oriented graphite and also onto Si electrodes [6-11]. The depositions were carried out from dilute aqueous solutions of metal ions using a potentiostatic pulse regime. A short (typically tens of ms) potential pulse was applied followed by open[Pg.174]

As follows from the model, high activation energy of the chemical reaction is an important prerequisite for intensive regime of the electrolysis. Thus, the developed theoretical approach was checked in experiments on the electrolysis of KF-KBF4 melts with graphite anode [32]. The ability of boron to increase the activation energy of thermal destmction of carbon compounds was taken into consideration when choosing the molten system. 

Mode B—In-pore diffusion regime The second regime can be considered an intermediate regime between modes A and C, where in-pore diffusion becomes more restrictive with increasing temperature. This occurs because at elevated temperatures the chemical reaction occurs more quickly than in mode A, such that the rate at which oxygen can be transported to the internal pore surface and the rate at which the products can diffuse back out of the graphite are slow enough to inhibit the natural intrinsic rate of reaction. This can also occur in a material with a particularly restrictive stracture. 

The discovery of presolar grains was made possible by the development of chemical procedures in which carbonaceous meteorites were subjected to a stringent acid digestion regime. Carbon compounds such as diamonds, SiC and graphite were isolated in this manner and identified through their distinctive pattern and anomalous noble gas component. These carbonaceous phases are samples of interstellar matter which provide a window into the prehistory of the Solar System. 

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