Beevers alumina

The disposition of the atoms in the conduction plane itself is identical to that in (3-alumina (Fig. 6.10b). However, the local environment of the conduction planes is different in the two phases because the oxygen ions on both sides of the conduction plane are superimposed in (3-alumina and staggered in (3"-alumina (Fig. 6.KM). This means that Beevers-Ross and anti-Beevers-Ross sites are not present. Instead the sodium sites, which have a tetrahedral geometry, are called Beevers-Ross-type (BR-type). The mid-oxygen (mO) sites, located midway between the BR-type sites, also have a different geometry in the two phases. 

The )5-aluminas are described in some detail in Chapter 2, only a few specific features are noted here. In the "-aluminas, the spinel blocks are stacked in such a way that the energetically equivalent sites occupied by Na" ions are ideally just half-filled in the -aluminas the spinel blocks are stacked so as to distinguish two types of Na" -ion sites of different potential energy, the Beevers-Ross (BR) and anti-Beevers-Ross (aBR) sites. In the Na-O planes, the shortest bottleneck distance 2.7 A is just a little greater than the sum of the ionic radii, 2.4 A, at room temperature, so a small value of AH can be anticipated. The discovery of fast Na -ion conductivity in the Na j5-aluminas (Yao and Kummer, 1967 Kummer and Weber, 1967) led to the invention of the Na/S battery that triggered extensive interest in the solid-electrolyte problem. 

FIG. 13.6. (a) The relation of the structure of 0-alumina, NaAli 1O17, to that of spinel (after Beevers and Ross). Large circles represent Na, small ones O, and black circles Al. (b) The relation of the structure of magneto-plumbite, PbFei jOij, to that of magnetite Fe304 (after Adelskold). Large circles represent Pb, small ones O, and black circles Fe. 

Beevers, C.A., and M.A.S. Ross. 1937. The crystal structure of beta alumina Na20-1 IAI2O3. Zeitschrift fur Kristallogr hie 97 59-66. Bertsch, P.M. 1989. Aqueous polynuclear aluminum species. Pp. 88-111 in The Environmental Chemistry of Aluminum, G. Sposito (ed.). 

A related issue is whether roughening a surface increases the strength of an adhesive joint. Harris and Beevers [82] found no difference in adhesion to mild steel and aluminium alloy blasted with alumina grits of different particle sizes. Shahid and Hashim [83] used a structural epoxide adhesive with mild steel adherends in cleavage joints. The surfaces had been grit-blasted or diamond-polished, and surface profiled. The results are shown in Table 15, where all differences in strength seem to be the same, within experimental scatter. 

---