Friedel's salt

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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.

Composition

Friedel's salt general formula is:

Ca₂Al(OH)₆(Cl, OH) · 2 H₂O.

In the cement chemistry notation, considering that

2 OH^– ↔ O^2– + H₂O,

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

3CaO·Al₂O₃·CaCl₂ · 10 H₂O

Friedel's salt forms in cements rich in tri-calcium aluminate (C3A).

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

Its synthesis or identification is difficult to trace back, but it could have been discovered/synthesised by the famous French chemist Charles Friedel, or identified later by his own son Georges Friedel, mineralogist and crystallographer. This point is unclear and requires further verification. ^{[citation needed]}.

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

Bai, J. (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. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

Barberon, F. (2005). "Interactions between chloride and cement-paste materials". Magnetic Resonance Imaging. 23 (2): 267–272. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

Birnin-Yauri, U. A. (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. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

Bothe, James V. (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. Retrieved 2008-10-04. {{cite journal}}: Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)

Brown, P. W. (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. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

Brown, P. W. (2000). "Chemical changes in concrete due to the ingress of aggressive species". Cement and Concrete Research. 30 (3): 411–418. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

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.

Csizmadia, J. (2001). "Chloride ion binding capacity of aluminoferrites". Cement and Concrete Research. 31 (4): 577–588. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

Mohammed, T. U. (2003). "Relationship between free chloride and total chloride contents in concrete". Cement and Concrete Research. 33 (9): 1487–1490. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

Nakamura, A. (1999). "Sorption of chloride-ion, sulfate-ion and phosphate-ion in calcium silicate hydrates". Journal of the Chemical Society: 415–420. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

Nielsen, E. P. (2003). "Chloride diffusion in partially saturated cementitious material". Cement and Concrete Research. 33 (1): 133–138. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

Pitt, J. M. (1987). Sulfate impurities from deicing salt and durability of Portland cement mortar. Transportation Research Board. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

Reddy, B. (2002). "On the corrosion risk presented by chloride bound in concrete". Cement and Concrete Composites. 24 (1): 1–5. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

Suryavanshi, AK (1998). "Influence of penetrating chlorides on the pore structure of structural concrete". Cement, concrete and aggregates. 20 (1): 169–179. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

Suryavanshi, A. K. (1996). "Mechanism of Friedel's salt formation in cements rich in tri-calcium aluminate". Cement and Concrete Research. 26 (5): 717–727. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)

External links