Pack aluminising

Mukherjee studied the gas phase equilibria and the kinetics of the possible chemical reactions in the pack-chromising of iron by the iodide process. One conclusion was that iodine-etching of the iron preceded chromis-ing also, not unexpectedly, the initial rate of chromising was controlled by transport of chromium iodide. Neiri and Vandenbulcke calculated, for the Al-Ni-Cr-Fe system, the partial pressures of chlorides and mixed chlorides in equilibrium with various alloys and phases, and so developed for pack aluminising a model of gaseous transport, solid-state transport, and equilibria at interfaces. 

Chromium powder is often included in the aluminising mixture. Chromium and aluminium may diffuse together (chromaluminising ) or by balancing the activities of chromium in the alloy and the pack, de-chromising may be prevented. Alloying of the chromium and aluminium powders may be used to control aluminising. 

CVD can be performed in a so-called closed or open system. In closed CVD, both reactants and products are recycled for reuse within an enclosure [11], The closed reactor CVD method is primarily used for metal purification and protection coating for aero-engine blades (e.g. pack cementation for aluminising, chromising, etc.). In most cases, CVD happens in an open state which is described in Chapter 1 and Figure 1.1. 

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