Mobility lattice

Ni3C decomposition is included in this class on the basis of Doremieux s conclusion [669] that the slow step is the combination of carbon atoms on reactant surfaces. The reaction (543—613 K) obeyed first-order [eqn. (15)] kinetics. The rate was not significantly different in nitrogen and, unlike the hydrides and nitrides, the mobile lattice constituent was not volatilized but deposited as amorphous carbon. The mechanism suggested is that carbon diffuses from within the structure to a surface where combination occurs. When carbon concentration within the crystal has been decreased sufficiently, nuclei of nickel metal are formed and thereafter reaction proceeds through boundary displacement. 

Figure 8 Schematic illustration for the formation of SAMs of alkanethiolates on gold [73], (A) Alkanethiols adopt the highly mobile lattice-gas phase (B) above a critical value of coverage, striped-phase islands are formed (C) surface reaches saturation coverage of striped phase (D) surface undergoes lateral-pressure-induced solid phase transition high-density islands nucleate and grow at domain boundaries (E) high-density islands grow at the expense of the striped phase until the surface reaches saturation...

Another feature of catalyst A is when it was poisoned at 200°C, 30 minutes was too short, or 200°C was too low to remove the adsorbed S02. But when some of its active sites were set free from the adsorbed SO2 at 280°C, it could react according to the redox mechanism by its mobile lattice oxygen when the temperature was lowered to 200°C again. 

Recently, Diamond (1990) has published a theoretical analysis of vibrations in crystals of BPTI (bovine pancreatic trypsin inhibitor). In this study (see figures 8.9(a)-(c)) he is able to separate contributions of intra- and intermolecular mobility (lattice vibrations and disorder) to... 

Equation (53) describes Debye relaxation. Magnesium and calcium-doped lithium fluorides have a characteristic Debye relaxation diagram from vhich the dopant concentration and the relaxation time can be deduced. Many others crystals containing mobile lattice defects have similar Debye s relaxation processes. Major understanding of the structure of color centers results from dielectric relaxation spectra. Nuclear magnetic resonance, optical and Raman spectroscopy can be used efficiently in conjunction vith dielectric spectroscopy. 

In other systems, new polymorphs can originate in the migration of atoms within a lattice in which the lattice particles have a relatively high mobility because the lattice can be regarded as one with unoccupied positions. This can also take the form of a change from a rigid lattice to one with mobile lattice particles. For instance, in the a and... 

Vacancy clusters Aggregation of vacancies in a mobile lattice the onset of melting 0-2.5... 

---