Infrared spectra of AFm-phases with univalent anions

Infrared spectra of AFm-phases with univalent anions

Citation for published version (APA):

Stein, H. N. (1977). Infrared spectra of AFm-phases with univalent anions. In Reaction of aluminates during the setting of cements : summaries of contributions to a seminar at the University of Technology, Eindhoven, The Netherlands, April 13-14, 1977 (pp. 50-52). Cembureau.

Document status and date: Published: 01/01/1977

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Infrared Spectra of AFm-Phases with Univalent Anions.

H. N. Stein, Laboratory of General Chemistry, Eindhoven University of Technology, Eindhoven, The Netherlands.

IR spectroscopy is used for characterizing the state of binding of interlayer water molecules in AFm-phases Ca 2Al (OH) 6X. m H 2 0 ( = 3 CaO.Alz03.CaX₂.n HzO ), with X= Cl-, Br-,

r,

Cl04 , N03, Cl03, Br03 , J03.

The IR spectra of the hydrates, both withand without interlayer water, are analyzed and the bands corresponding with interlayer water are indicated.

By means of the isotope dilution technique 1) it is possible to establish the properties of the hydrogen bond of the interlayer

water. Replacement of part of the interlayer water by D 2 0 uncouples the stretching frequencies of an OH group, if HOD is present amidst large amounts of D 2 0 ; or of an OD group, if HOD is pre sent amidst

large amounts of H

20. In practice, this can be accomplished easily

by rehydrating the dehydrated compound through the gas phase, exposingit toa mixture of HzO and D₂0 vapours.

If we assume q. linear relation between the stretching vibration frequency of an OH group and the enthalpy of the hydrogen bond this OH group is envolved in, we can calculate the enthalpy of the hydrogen bond by means of a Badger-Bauer relation 2)3) :

11

OH, g -11oH, X YoH,g -VoH,ice

x = _{- {l HH bond}

Here, A H~G = the enthalpy of vapourization of ice,

VoH,

g = the stretching vibration frequency of a free water molecule in the gas phase,

V

oH, X= the stretching vibration frequency of an OH group

in the compound Ca_{2Al(OH) 6}

x.

m HzO, belonging to interlayer water,

y OH, ice = the stretching vibration frequency of an OH group in ice.

The values found thus can be compared with the enthalpies

A

HO/Z of forming hydrates X. Z Hz 0 in the gas phase 4), and wi th the

enthalpies of dehydration of the compounds Ca₂Al(OH)

6. m Hz 0 (see table I, columns 3 and 4, respectively).

It is seen that the hydragen honds as formed in the interlayers are les s stable than those in the gas pha se (4 hydragen honds are formed in the latter case per mol anion X), presumably by reason of sterical restrictions in the interlayers. The enthalpies of

dehydration of the crystalline compounds (column 4) show a certain correlation with the enthalpies of the hydragen honds (column 2) indicating that hydragen bond formation is a major factor in the uptake of interlayer water ; the differences remaining can be accounted for, at least partially, by

Table I

Comparison of various enthalpies for different anions X. 1 Anion J Br Cl Br03 2

-AH

H bond,X Kcal/H bond 1.8 3. 1

3.6

3.7

3. 7

3.8

4

.

2

5.5 3 - A.H0/2, g Kcal/ mol X 20. 0

24. 5

24.

9 25. 8 4 AHdehydr, X

Kcal/ mol compound 10.7 15. 5 15. 3

12. 9

18.6

1

9

.9

22.9 38.2

The electrical work required for separating themainlayers Ca₂Al(OH)6 from the interlayer anions X during the introduetion of interlayer water 6).

Only one OH absorption band and one OD absorption band are found in all cases. Thus, at room temperature all hydragen bands are equal, and the interlayer water is bound symmetrically.

a larger influence on the frequencies of the OH groups of neighbouring water molecules, than cationsin the comparable case of c1ay minerals.

More details on this investigation can be found in ref. 7).

Reference s.

1. J. Schiffer and D.F.Hornig, J.Chem.Phys. 49, 4150 (1968). 2. R.M.BadgerandS.H.Bauer, J.Chem.Phys. 5, 839 (1937). 3. G.Brink and M.Falk, Can. J.Chem. 48, 2096 (1970).

4. J. D. Payzant, R. Yamdagni and P. Kebarle, Can. J. Chem. 49; 3 3 08 ( 1 9 71) .

5. C. J. M. Houtepen and H. N. Stein, Cement and Concrete Research

.§_,

651 (1976).

6. C. J. M. Houtepen and H. N. Stein, J. Coll. int. Sci., ~. 370 (1976).

7. C.J.M.Houtepen and H.N.Stein, Spectrochim.Acta 32 A, 1409 (1976).