Intercalation alloying reaction

The synthesis of M Cgo (M = Na, n = 2, 3 M = K, n = 3) has been achieved by the reaction of solid Cjq with solid MH or MBH4 [116]. The advantage of these reactions is the easier handling of small quantities of MH or MBH4 compared with alkali metals. As a source for alkali metals, binary alloys of the type CsM (M = Hg, Tl, Bi) can also be used [109]. However, the heavy metals partly co-intercalate into the Cgo lattice [115, 117]. 

Two types of transformations can be very broadly distinguished. The first is the formation of a solid solution, in which solute atoms are inserted into vacancies (lattice sites or interstitial sites) or substitute for a solvent atom on a particular sublattice. Many types of synthetic processes can result in this type of transformation, including ion-exchange reactions, intercalation reactions, alloy solidification processes, and the high-temperature ceramic method. Of these, ion exchange, intercalation, and other so-called soft chemical (chimie douce) reactions produce no stmctural changes except, perhaps, an expansion or contraction of the lattice to accommodate the new species. They are said to be under topotactic, or topochemical, control. 

Intercalation compounds containing two metals can be prepared by reaction of binary alloys of K, Rb, and Cs and also with alloys of metals that intercalate easily combined with those that do not. For example, Billaud and Herold prepared a compound Na2BaCg by reaction with a NaBa alloy. The interlayer separation implies a sandwich stracture... 

Direct reaction of Cs and C o has not resulted in superconductivity or the formation of an intercalated f.c.c. phase in our experiments. A recent report of superconductivity at 30 K in CS ,C6o synthesized by reaction of C, with CSM2 alloys (where M is Hg,TI or Bi) indicates a lower than we would predict for f.c.c. CsjCio. These materials probably adopt a different structure or contain a ternary intercalant. ... 

The time needed for thin films of CaGc2 to form this intercalation compound is of the order of several hours at ambient conditions. In contrast, Ca(Sii.xGe c)2 alloys react significantly faster, with thin films of CaSiGe being decomposed in less than 60 s. In the reaction of Ca(Sii. cGe c)2 with H2O, the formation of (GeH) layers competes with the formation of Si02. Indeed, crystalline layered polygermanosilyne calcium dihydroxide intercalation compounds have been found only for 0.7 < x < 1. " At lower Ge contents x, the reaction products become amorphous. 

A semiquantitative analysis carried out by integrating the silicon-related peak intensities revealed that at the beginning of the first lithiation Li preferentially saturated the graphite phase (intercalation), and later, silicon became involved in the reaction (alloying). However, due to the milder alloying conditions, in the presence of the carbonaceous phase, the formation of lithium-silicon alloys with high lithium content on the surface of the alloying silicon particles has been suppressed. Therefore, the carbonaceous media led to a more uniform distribution of Li within the bulk of the active silicon particles. 

Besides hydrogen adsorption and evolution, hydrogen absorption into metals might occur. It is observed in Pd and certain alloys of the type AB5 (e.g., LaNis) or AB2 and is used in metal hydride batteries. The theory developed here is also applicable to other reactions, e.g., Li intercalation in Li-ion batteries. Let us consider first the simplest adsorption-absorption reaction [272]. 

Electrochemical Lithium Intercalation Reaction of Anodic Vanadium Oxide Film. J. Alloys Compounds 217, 52—58. 

I = 7/2-1—> 5/2-F). The materials that can be studied, thanks to the Mossbauer effect of the above-mentioned nuclei, are also varied. Both cathode and anode materials can be examined. Moreover, the electrochemical reactions in which they are involved may vary from intercalation to conversion and/or alloying. Table 28.1 shows some examples. Fe MS provides useful information in the study of insertion cathodes, such as olivine LiFeP04, as well as layered solids structurally related to LiCo02. Fe MS is also useful to analyze anodes consisting of binary or ternary oxides for conversion reactions, or tin intermetallics that react with lithium by alloying processes. In the latter case, a multiisotope approach can be developed, due to the Mossbauer effect of both Fe and Sn nuclei. 

The potential of rapid reaction is generally higher with primary cells of high loadability than with low rate types or secondary cells with alloy or intercalation anode. Primary reaction products can also initiate additional undesired reactions if they possess suitable reactivity. The sulfur which is released during the discharge of thionyl chloride cells belongs to this category. 

A recent publication [904] reports on the reaction of Na—Ba alloys with graphite, that leads to blue, airstable second-stage phases of compositions Nai-xBaxC- 7.5 with x = 0.2 0.4. The separation of the carbon layers increases from 3.35 A to 7.38 A since the metal atoms are inserted in the form of triple layers Na—Ba—Na. The intercalated metal sublattice is hexagonal with a = 6.36 A and parallel to the graphite lattice. Similar intercalated sandwiches have been observed with FeCb, CrCls and alkali metals + hydrogen [904]. 

---