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The formation of the crystalline Ag50Pd50 solid solution during mechanical alloying under shock interaction of Ag and Pd metallic powders has been studied using electron microscopy and X-ray diffraction. The process involved for impact interaction occurs via the incorporation of the small Pd particles into the Ag matrix in which, under the action of mechanical strain, the mutual diffusion of Ag and Pd leads to the formation of two solid solutions, one rich in Ag and the other rich in Pd. Further grinding allows the homogenization of the two Ag and Pd solid solutions whose composition changes to finally reach the initial Ag50Pd50 composition. The defects as dislocations generated by the impact conditions may be responsible for the reaction mechanism.

Replacement of nickel by aluminium in the brucite-type Ni(OH)2 layers leads to layered double hydroxides (LDH), which can be used as active materials for nickel hydroxide electrodes. Ni/Al LDH compounds [0 < Al/(Ni + Al)⩽ 0.25] were synthesized by precipitation with ammonia from mixed Ni/Al nitrate solutions and characterized by X-ray powder diffraction, infrared spectroscopy, chemical analysis and transmission electron microscopy. X-Ray powder diffractograms of fresh precipitates are characteristic of turbostratic layered double hydroxides. A structural model describing the turbostratic layered double hydroxides is proposed on the basis of the experimental results. The brucite-type layers are non-stoichiometric and present hydroxide vacancies: their chemical composition can be written as [Ni1–x2+ Alx3+(OH–)2–(y+2z–x)] and the interlamellar layers as [(NO3–)y(CO32–)z·nH2O] with x⩽ 0.25. The interlamellar anions (NO3– or CO32–) play two roles: those in D3h symmetry, compensate for the positive-charge excess of Al3+ ions, while those in C2v, symmetry, compensate for that of hydroxide vacancies. When aged, mixed turbostratic Ni/Al hydroxides with the higher aluminium content (x 0, 18) change into synthetic takovites (crystallized Ni–Al–CO3 double hydroxides) through a dissolution–recrystallization process.