Calcium fluoroaluminate

Many other systems have subsequently been found to display anion conductivity. The electrical conductivity of lead fluoroborate and fluorogermanate glasses is similar to that of the lead fluorosilicate glasses. Calcium fluoroaluminate glasses also conduct by fluorine migration. Fluorophosphate glasses have also proven to be good anionic conductors. All of these systems are free of alkali ions. 

A staining procedure for calcium fluoroaluminate (rare in normal clinker) was developed by microsco-pists in the 1960s at the PC A laboratories. It is based on the slightly different activities of C A and CjjA CaF. A polished surface of clinker, etched for 3 seconds in distilled water with a pH of 6.5 to 7.0, reveals C A as a bluish color. The surface is then given a second polish and a 30-second etch with a 0.1-molar potassium hydroxide solution that reveals CjjA CaF as a deep brownish-purple hue. Comments on each of these etches follow. 

The phases dodecacalcium heptaaluminate (12Ca0.7Al203 or Caj2Alj4033, abbreviation C. A ) and calcium fluoroaluminate (llCaO.7ALO3.CaF2 or... 

The main product of hydration at shorter hydration times is ettringite (AFt phase), which is formed in a reaction between calcium fluoroaluminate and anhydrite. At the same time aluminum hydroxide is also formed. The fluorine in the fluoroaluminate phase enters the stmctuie of aluminum hydroxide, yielding aluminum hydroxide fluoride. The process can be expressed by the following equation ... 

Belite fluoro-sulfo-aluminate cement contains simultaneously the phases calcium fluoroaluminate (CjjAy.CaF2) and caldum sulfoaluminate (C4A3S), together with belite and calcium sulfate. It also may contain limited amounts of the ferrite phase. 

CALCIUM ACUMINATE AND CALCIUM FLUOROALUMINATE MODIFIED PORTLAND CEMENTS... 

M. Body, G. Silly, C. Legein, J.-Y. Buzare, Correlation between environment and isotropic chemical shift in barium and calcium fluoroaluminates, Inorg. Chem., 43, 2474—2485 (2004). 

Similarly influence the soluble fluorides for example the F ions released from NaF to the solution form the insoluble CaFj which covers the cement grains. The complex fluorosilicates Na2SiFg and NajAlFg can additionally result in the precipitation of siUcate or aluminate gel on the surface of cement grain poor in calcium. Phosphogypsum, soluble calcium phosphates and sodium fluoroaluminates containing by-products exhibits the retarding effect too [96]. 

Tricalcium sihcate hydrates to yield the C-S-H phase and calcium hydroxide, which in due course may participate in the hydration of the fluoroaluminate phase and the formation of ettringite ... 

Alite-fluoroaluminate cements do not exhibit expansive properties, unless the amount of interground calcium sulfate is excessively high. This absence of expansion is explained by the formation of the ettringite phase in a through-solution process, rather than in a topochemical reaction (Chvatal, 1993). 

In blended alite-fluoroaluminate cements the alite-fluoroaluminate clinker is interground with granulated blast furnace slag and/or limestone, in addition to calcium sulfate (KnOfel and Wang, 1994). Such binders have similarities with blended cements on the basis of ordinary Portland clinker, but still exhibit a short setting time and a distinct short-term strength. 

Calcium aluminate modified Portland cement is essentially a Portland cement with added dodecacalcium heptaaluminate (Cj2Ay), produced separately, and with an elevated calcium sulfate content (Chvatal, 1973 Kondo et al., 1997). The phase composition of the binder differs from that of a conventional alite-fluoroaluminate cement by the presence of tricalcium aluminate, and of instead of C,A,.CaF,. The cement... 

Kohler and Muller (1991) obtained a divalent samarium fluoroaluminate, LiSm-AlFg, by heating a confined mixture of the appropriate fluorides two days at < 700°C. In contrast to the structure of the closely related strontium and calcium analogues in which the divalent cation is coordinated octahedrally, the Sm ion coordination is trigonal prismatic. Magnetic-susceptibility measurements show temperature dependence typical of divalent samarium. 

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