Aluminium fluoride structure

The structure of T12A1F5 exhibits an infinite chain of octa-hedra, each with two opposite common corners. With four common corners sheets are produced T1A1F4 is an example of this. With the complex aluminium fluorides there are also other possibilities thus sheets are formed in Na5Al3 Fu with octahedra in which one third part have four corners in common, the remainder, however, only two (Brosset). 

Fig. 8.19. Clinographic projection of the unit cell of the (idealized) cubic structure of aluminium fluoride, A1F3. Two co-ordinating [A1FQ] octahedra are indicated to show their linkage by sharing corners.

Fireclay bricks (alumina silica bricks, alumina calcium oxide silica bricks, and other silicate bricks) are not optimal barrier materials for A1 reductirMi cells. As we have mentioned, cryolite-based electrolyte for A1 reduction is a substance that dissolves alumina better than anything else. Certainly, it will dissolve all alumina-based refractory compositions and almost all other oxides similar in chemical structure to alumina. From a chemical point of view, the effective refractory barriers against the penetration of cryolite might be tin oxide, nickel oxide, compounds of nickel oxide, iron oxide, or zinc oxide (such as spinel Fe NiOs). These oxides almost do not react with NaF and aluminium fluoride [175]. Yet the cost of these materials, which is 50-100 times higher than that of firebrick, provides the impetus to find less costly variants of alumina silica materials. 

E. Kemnitz, U. GroB, St. Rudiger, G. Scholz, D. Heidemann, S. I. Troyanov, I. V. Morosov and M.-H. Lemee-CaiUeau, Comparative structural investigation of aluminium fluoride solvates. Solid State Sci., 8,1443 1452 (2006). 

R. Konig, G. Scholz, A. PawUk, C. Jager, B. v. Rossum, H. Oschkinat and E. Kemnitz, Crystalline aluminium hydroxy fluorides structural insights obtained by high-field solid state NMR and trend analyses, J. Phys. Chem. C, 112, 15708-15720 (2008). 

R. Chandross, Tbe structure of a new phase of aluminum trifluoride monohydrate, Acta Cryst. 17,1477 (1964). (It should be noted that the synthesis of a cubic form of an aluminium fluoride monohydrate proposed by Chandross could not be satisfactorily reproduced.). 

K. Scheurell, G. Scholz and E. Kemnitz, Structural study of VOx doped aluminium fluoride and aluminium oxide catalysts, J. Solid State Chem., 180, 749-758 (2007). 

We apply ab initio atomistic thermodynamic modelling techniques to the study of aluminium fluorides. We predict the atomistic structure and composition of crystalline a- and /3-AIF3 under realistic conditions. We then extend this work to make predictions of the true nature of the synthesized HS-AIF3 materials. An understanding of how the two differ may lead to improved synthesis methods that allow the production of materials with preferred characteristics. 

The melting and boiling points of the aluminium halides, in contrast to the boron compounds, are irregular. It might reasonably be expected that aluminium, being a more metallic element than boron, would form an ionic fluoride and indeed the fact that it remains solid until 1564 K. when it sublimes, would tend to confirm this, although it should not be concluded that the fluoride is, therefore, wholly ionic. The crystal structure is such that each aluminium has a coordination number of six, being surrounded by six fluoride ions. 

In the gold(lll) halides (except the fluoride) there is evidence for the formation of double molecules, AujXg (cf. chlorides of iron(III) and aluminium) so that the coordination is brought up to four, but with a planar structure ... 

About structures of lithium compounds LisMeFs we have but rare knowledge. Klemm, Brandt and Hoppe (193) report in accordance with Meyers and Cotton (225) that the x-ray-diagrams of the cobalt compound LisCoFe were of a poor quality. The polymorphism that Carton and Wanklyn (108) report of the aluminium compound LisAlFe points to a more complicated situation in this ternary fluoride. The sizes given of the unit cells do not show any simple relation to the cryolite cell. The same may be true of compounds LisMeFa of the transition metals. 

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