International
Tables for
Crystallography
Volume H
Powder diffraction
Edited by C. J. Gilmore, J. A. Kaduk and H. Schenk

International Tables for Crystallography (2018). Vol. H, ch. 2.9, pp. 193-194

Section 2.9.3.3.2. Cells with humidity control

W. van Beeka* and P. Pattisona,b

aSwiss–Norwegian Beamlines at ESRF, CS 40220, 38043 Grenoble CEDEX 9, France, and bLaboratory for Quantum Magnetism, Institute of Physics, Ecole Polytechnique Federale de Lausanne, CH-1015 Lausanne, Switzerland
Correspondence e-mail:  wouter@esrf.fr

2.9.3.3.2. Cells with humidity control

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Humidity is a relevant parameter in many areas of research. For instance, the interlayer spacing in clays, corrosion, pharmaceutical processes, cement hardening, phase transitions in minerals or proton conductors and crystal growth of salts are all dependent on relative humidity, often in combination with high temperatures.

Most work so far has been carried out in home laboratories with flat-plate commercial chambers connected to a manifold with a gas mass-flow controller and liquid mass-flow controllers, thus providing an air flow with controlled humidity (Chipera et al., 1997[link]; Kühnel & van der Gaast, 1993[link]; Watanabe & Sato, 1988[link]). In addition, capillary cells have also successfully been used (Walspurger et al., 2010[link]) on synchrotrons. It is imperative to have very good thermal stability and to avoid temperature gradients throughout the system. The dew point of water is strongly affected by temperature, and unwanted condensation of water can easily occur on colder parts of the system. Fig. 2.9.6[link] shows a schematic of a humidity-control system developed by Linnow et al. (2006[link]). The thermal management in this design has been optimized to avoid condensation.

[Figure 2.9.6]

Figure 2.9.6 | top | pdf |

Schematic drawing of the humidity-control system: (1) mass-flow controller, (2) adsorption dryer, (3) pressure regulator, (4) heated bubbler, (5) peristaltic pump, (6) water reservoir, (7) thermostat, (8) condensation trap, (9) mixing chamber and (10) thermostat. Adapted with permission from Linnow et al. (2006[link]). Copyright (2006) American Chemical Society.

Linnow et al. (2006[link]) and Steiger et al. (2008[link]) have used the system in Fig. 2.9.6[link] to investigate the crystal growth of various salts, which is considered to be the cause of many failures in building materials (stone, brick, concrete). In order to do so, they scanned through the relative humidity (RH) versus temperature phase diagrams of these salts in various porous materials used in the building industry. Diffraction experiments revealed differences in reaction pathways and stress in both host and guest materials.

The NASA Phoenix Mars Lander has discovered perchlorate anions on Mars. This is important, since they could possibly be used as indicators for hydrological cycles. Robertson & Bish (2010[link]) studied a magnesium perchlorate hydrate system, Mg(ClO4)2·nH2O, with the aim of solving the various unknown crystal structures as a function of water content n. Fig. 2.9.7[link] shows in situ diffraction data collected during dehydration in a commercial Anton Paar flat-plate heating stage connected to an automated RH control system similar to that shown in Fig. 2.9.6[link]. The rapidly collected in situ data (30 s per scan, with a position-sensitive detector) were crucial to define at what temperatures longer data collections had to be taken in order to acquire single-phase, high-quality powder patterns suitable for crystal structure solution. Robertson & Bish (2010[link]) managed to index and solve the dihydrate and tetrahydrate phases by charge flipping. Although the tetrahydrate structure was later revised by Solovyov (2012[link]) using the exact same data, this example clearly indicates the level of complexity that can be studied in local laboratories under in situ conditions. In this case, this task included understanding the dehydration pathway, solving the structure of Cl2H4MgO10 with two molecules in the unit cell and refining anisotropic displacement parameters using Rietveld refinement.

[Figure 2.9.7]

Figure 2.9.7 | top | pdf |

Sequence of XRD measurements between 21 and 27° 2θ. On heating at a rate of 2° min−1 at <1% RH, sequential dehydration was observed, with the anhydrate observed at the highest temperature. The vertical axis represents intensity. The `time' (scan number) axis represents temperature from 298 to 498 K in 2° min−1 increments. Adapted from Robertson & Bish (2010[link]).

References

Chipera, S. J., Carey, J. W. & Bish, D. L. (1997). Controlled-humidity XRD analyses: application to the study of smectite expension/contraction. Adv. X-ray Anal. 39, 713–722.Google Scholar
Kühnel, R. & van der Gaast, S. J. (1993). Humidity controlled diffractometry and its application. Adv. X-ray Anal. 36, 439–449.Google Scholar
Linnow, K., Zeunert, A. & Steiger, M. (2006). Investigation of sodium sulfate phase transitions in a porous material using humidity- and temperature-controlled X-ray diffraction. Anal. Chem. 78, 4683–4689.Google Scholar
Robertson, K. & Bish, D. (2010). Determination of the crystal structure of magnesium perchlorate hydrates by X-ray powder diffraction and the charge-flipping method. Acta Cryst. B66, 579–584.Google Scholar
Solovyov, L. A. (2012). Revision of the Mg(ClO4)2·4H2O crystal structure. Acta Cryst. B68, 89–90.Google Scholar
Steiger, M., Linnow, K., Juling, H., Gülker, G., Jarad, A. E., Brüggerhoff, S. & Kirchner, D. (2008). Hydration of MgSO4·H2O and generation of stress in porous materials. Cryst. Growth Des. 8, 336–343.Google Scholar
Walspurger, S., Cobden, P. D., Haije, W. G., Westerwaal, R., Elzinga, G. D. & Safonova, O. V. (2010). In situ XRD detection of reversible dawsonite formation on alkali promoted alumina: a cheap sorbent for CO2 capture. Eur. J. Inorg. Chem. 2010, 2461–2464.Google Scholar
Watanabe, T. & Sato, T. (1988). Expansion characteristics of montmorillonite and saponite under various relative humidity conditions. Clay Sci. 7, 129–138.Google Scholar








































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