Friedel's salt

Friedel's salt
IUPAC name Calcium chloroaluminate
Other names Friedel's salt Calcium aluminium chlorohydrate Calcium aluminium chlorohydroxide Calcium aluminium oxychloride
Properties
Molecular formula	Ca₂Al(OH)₆(Cl, OH) · 2 H₂O
Appearance	White solid
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Friedel's salt is an anion exchanger mineral belonging to the family of the layered double hydroxides (LDHs). It has affinity for anions as chloride and iodide and is capable to retain them to a certain extent in its crystallographical structure.

1 Composition
2 Discovery
3 Formation
4 Role in cement
5 Anion getter
6 See also
7 References
8 External links

Composition

Friedel's salt general formula is:

Ca₂Al(OH)₆(Cl, OH) · 2 H₂O.

In the cement chemist notation, considering that

2 OH^– ↔ O^2– + H₂O,

and doubling all the stoichiometry, it can also be written as follows:

3CaO·Al₂O₃·CaCl₂ · 10 H₂O

Friedel's salt can also be considered as an AF_m phase in which chloride ions have replaced sulfate ions and is formed in cements initially rich in tri-calcium aluminate (C₃A).

2 Cl^- + 3CaO·Al₂O₃·CaSO₄ · 10 H₂O → 3CaO·Al₂O₃·CaCl₂ · 10 H₂O + SO₄^2-

It plays a main role in the retention of chloride anions in cement and concrete. However, Friedel's salt remains a poorly understood phase in the CaO-Al₂O₃-CaCl₂-H₂O system, and is critical for the stability of salt-saturated Portland cement-based grouts.

Discovery

Nowadays, Friedel's salt discovery is relatively difficult to trace back from the recent literature, simply because it is an ancient finding of a poorly known and non-natural product. It has been synthesised and identified in 1897 by Georges Friedel, mineralogist and crystallographer, son of the famous French chemist Charles Friedel.^[1] Georges Friedel also synthesised Calcium aluminate (1903) in the framework of his work on the Macles theory (twin crystals). This point requires further verification.^[2]

Formation

Relation with Tricalcium aluminate.
Incorporation of chloride.
Solid solutions.

Role in cement

Importance for the reactive transport of chloride in cement in relation with corrosion of steel reinforcement.

Anion getter

Trap toxic anions in cement such as, e.g., ¹²⁹I^-, SeO₃^2-, SeO₄^2-

References

^ Friedel, Georges (1897). "Sur un chloro-aluminate de calcium hydrate´ se maclant par compression". Bulletin de la Société française de minéralogie et de cristallographie 19: 122–136. http://www.archive.org/stream/bulletindelasoc16mingoog/bulletindelasoc16mingoog_djvu.txt.
^ Biography of Georges Friedel by F. Greandjean on annales.org., in French.

Bai, J.; S. Wild, B. B. Sabir (2003). "Chloride ingress and strength loss in concrete with different PC–PFA–MK binder compositions exposed to synthetic seawater". Cement and Concrete Research 33 (3): 353–362. doi:10.1016/S0008-8846(02)00961-4.

Barberon, F.; V. Baroghel-Bouny, H. Zanni, B. Bresson, J. B. d'Espinose de la Caillerie, L. Malosse, Z. Gan (2005). "Interactions between chloride and cement-paste materials". Magnetic Resonance Imaging 23 (2): 267–272. doi:10.1016/j.mri.2004.11.021. PMID 15833625.

Birnin-Yauri, U. A.; F. P. Glasser (1998). "Friedel's salt, Ca₂ Al(OH)₆ (Cl, OH) · 2H₂O: its solid solutions and their role in chloride binding". Cement and Concrete Research 28 (12): 1713–1723. doi:10.1016/S0008-8846(98)00162-8.

Bothe, James V.; Paul W. Brown (2004-06). "PhreeqC modeling of Friedel's salt equilibria at 23 ± 1 °C". Cement and Concrete Research 34 (6): 1057–1063. doi:10.1016/j.cemconres.2003.11.016. http://www.sciencedirect.com/science/article/B6TWG-4B94K0R-1/2/2182af1335b6bdcd0a4cecc34f70d7f7. Retrieved 2008-10-04.

Brown, P. W.; S. Badger (2000). "The distributions of bound sulfates and chlorides in concrete subjected to mixed NaCl, MgSO₄, Na₂SO₄ attack". Cement and Concrete Research 30 (10): 1535–1542. doi:10.1016/S0008-8846(00)00386-0.

Brown, P. W.; A. Doerr (2000). "Chemical changes in concrete due to the ingress of aggressive species". Cement and Concrete Research 30 (3): 411–418. doi:10.1016/S0008-8846(99)00266-5.

Chatterji, S. (1995). "On the applicability of Fick's second law to chloride ion migration through portland cement concrete". Cement and Concrete Research 25 (2): 299–303. doi:10.1016/0008-8846(95)00013-5.

Csizmadia, J.; G. Balázs, F. D. Tamás (2001). "Chloride ion binding capacity of aluminoferrites". Cement and Concrete Research 31 (4): 577–588. doi:10.1016/S0008-8846(01)00458-6.

Mohammed, T. U.; H. Hamada (2003). "Relationship between free chloride and total chloride contents in concrete". Cement and Concrete Research 33 (9): 1487–1490. doi:10.1016/S0008-8846(03)00065-6.

Nakamura, A.; E. Sakai, K. Nishizawa, Y. Ohba, M. Daimon (1999). "Sorption of chloride-ion, sulfate-ion and phosphate-ion in calcium silicate hydrates". Journal of the Chemical Society: 415–420.

Nielsen, E. P.; M. R. Geiker (2003). "Chloride diffusion in partially saturated cementitious material". Cement and Concrete Research 33 (1): 133–138. doi:10.1016/S0008-8846(02)00939-0.

Pitt, J. M.; M. C. Schluter, D. Y. Lee, W. Dubberke (1987). Sulfate impurities from deicing salt and durability of Portland cement mortar. Transportation Research Board.

Reddy, B.; G. K. Glass, P. J. Lim, N. R. Buenfeld (2002). "On the corrosion risk presented by chloride bound in concrete". Cement and Concrete Composites 24 (1): 1–5. doi:10.1016/S0958-9465(01)00021-X.

Suryavanshi, AK; RN Swamy (1998). "Influence of penetrating chlorides on the pore structure of structural concrete". Cement, concrete and aggregates 20 (1): 169–179. doi:10.1520/CCA10451J.

Suryavanshi, A. K.; J. D. Scantlebury, S. B. Lyon (1996). "Mechanism of Friedel's salt formation in cements rich in tri-calcium aluminate". Cement and Concrete Research 26 (5): 717–727. doi:10.1016/S0008-8846(96)85009-5.