Nickel formate, decomposition nucleation

There have been many instances of examination of the effect of additive product on the initiation of nucleation and growth processes. In early work on the dehydration of crystalline hydrates, reaction was initiated on all surfaces by rubbing with the anhydrous material [400]. An interesting application of the opposite effect was used by Franklin and Flanagan [62] to inhibit reaction at selected crystal faces of uranyl nitrate hexa-hydrate by coating with an impermeable material. In other reactions, the product does not so readily interact with reactant surfaces, e.g. nickel metal (having oxidized boundaries) does not detectably catalyze the decomposition of nickel formate [222],... 

The kinetics of decomposition of nickel formate [6,7] are sensitive both to the experimental conditions [8] and the reactant structure, ar-time curves for the isothermal decomposition (about 450 K) are usually [8], though not invariably [9], sigmoid and there is microscopic evidence [6] that reaction proceeds through nucleation and growth. The induction period [6] and the shape of the subsequent acceleratory process [8] are influenced by the rapidity with which product water vapour is removed from the vicinity of the reactant. Data fit the Prout-Tompkins equation with , about 100 kJ mol". ... 

Since the rate of formation of cementite is determined by nucleation, and therefore proceeds more rapidly in fine-grained steels, it follows that the T-T-T diagram will show a more rapid onset of austenite decomposition than in steels of the same composition, but a coarser grain size. The shape of the T-T-T curve is also a function of the steel composition, and is altered by the presence of alloying elements at a low concenuation. This is because the common alloying elements such as manganese, nickel and clrromium decrease... 

Carbon Formation. Steam reforming involves the risk of carbon formation by the decomposition of methane and other hydrocarbons or by the Boudouard reaction (reactions (7) -(10)). Reactions (7) - (8) are catalyzed by nickel (Rostrup-Nielsen, 1984a). The carbon grows as a fibre (whisker) with a nickel crystal at the tip. The methane or carbon monoxide is adsorbed dissociatively on the nickel surface (Alstrup, 1988). Carbon atoms not reacting to gaseous molecules are dissolved in the nickel crystal, and solid carbon nucleates at the non-exposed side of the nickel crystal, preferably from Ae dense (111) surface planes. Reaction (10) results in pyrolytic carbon encapsulating the catalyst. 

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