Andreas Hallbrucker

The Preparation and Structures of Hydrogen Ordered Phases of Ice

Two hydrogen ordered phases of ice were prepared by cooling the hydrogen disordered ices V and XII under pressure. Previous attempts to unlock the geometrical frustration in hydrogen-bonded structures have focused on doping with potassium hydroxide and have had success in partially increasing the hydrogen ordering in hexagonal ice I (ice Ih). By doping ices V and XII with hydrochloric acid, we have prepared ice XIII and ice XIV, and we analyzed their structures by powder neutron diffraction. The use of hydrogen chloride to release geometrical frustration opens up the possibility of completing the phase diagram of ice.

A second distinct structural “state” of high-density amorphous ice at 77 K and 1 bar

High-density amorphous ice (HDA), further densified on isobaric heating from 77 K to 165 (177) K at 1.1 (1.9) GPa, relaxes at 77 K and 1 bar to the same structural “state” with a density of 1.25 ± 0.01 g cm−3. Its density is higher by ≈9% than that of HDA, and thus it is called very-high-density amorphous ice (VHDA). X-ray diffractogram and Raman spectrum of VHDA clearly differs from that of HDA, and the hydrogen-bonded O–O distance increases from 2.82 A in HDA to 2.85 A in VHDA. Implications for the polyamorphism of the amorphous forms of water are discussed.

Two Calorimetrically Distinct States of Liquid Water Below 150 Kelvin

Vapor-deposited amorphous solid and hyperquenched glassy water were found to irreversibly transform, on compression at 77 kelvin, to a high-density amorphous solid. On heating at atmospheric pressure, this solid became viscous water (water B), with a reversible glass-liquid transition onset at 129 ± 2 kelvin. A different form of viscous water (water A) was formed by heating the uncompressed vapor-deposited amorphous solid and hyperquenched liquid water. On thermal cycling up to 148 kelvin, water B remained kinetically and thermodynamically distinct from water A. The occurrence of these two states, which do not interconvert, helps explain both the configurational relaxation of water and stress-induced amorphization.

The heat capacity and glass transition of hyperquenched glassy water

Abstract The glass transition and heat capacity of hyperquenched glassy water have been studied by differential scanning calorimetry and by isothermal measurements from 103 K to a temperature where its crystallization to cubic ice is complete. Glassy water shows a thermally reversible glass-liquid transition and has a Tg, of 136 ± 1 K. The activation energy of structural relaxation in the transition range is ∼55kjmol−1 and is a reflection of the energy required to break two hydrogen bonds before a rotational-translational diffusion of a water molecule in the H-bonded network can occur. The temperature width of the transition is ∼12°, and the increase in the heat capacity is 1.6±0.1JK−1 mol−1. Liquid water formed on heating the glassy water to 146 K is more stable against crystallization than that which exists near 232 K. The hyperquenched glassy form of water can be thermodynamically continuous with liquid water, but whether or not it has the same structure as water above 273 K or supercooled water near t...

The local and intermediate range structures of the five amorphous ices at 80 K and ambient pressure: A Faber-Ziman and Bhatia-Thornton analysis

Using isotope substitution neutron scattering data, we present a detailed structural analysis of the short and intermediate range structures of the five known forms of amorphous ice. Two of the lower density forms--amorphous solid water and hyperquenched glassy water--have a structure very similar to each other and to low density amorphous ice, a structure which closely resembles a disordered, tetrahedrally coordinated, fully hydrogen bonded network. High density and very high density amorphous ices retain this tetrahedral organization at short range, but show significant differences beyond about 3.1 A from a typical water oxygen. The first diffraction peak in all structures is seen to be solely a function of the intermolecular organization. The short range connectivity in the two higher density forms is more homogeneous, while the hydrogen site disorder in these forms is greater. The low Q behavior of the structure factors indicates no significant density or concentration fluctuations over the length scale probed. We conclude that these three latter forms of ice are structurally distinct. Finally, the x-ray structure factors for all five amorphous systems are calculated for comparison with other studies.

Crystallization kinetics of water below 150 K

Metastable liquid water, obtained by heating its hyperquenched glassy state above its glass→liquid transition temperature, crystallizes to cubic ice. Kinetics of this crystallization has been studied by Fourier transform infrared spectroscopy by determining the change in the spectra of stretching vibrations of the decoupled OD oscillator in 3.6 mole % HOD in H2O. The crystallization kinetics follows the equation x=[1−exp(−ktn)] and is diffusion controlled. Annealing at a temperature below its glass→liquid transition temperature alters this kinetics as the grain–growth process begins to control the early stages of crystallization.

Towards the Experimental Decomposition Rate of Carbonic Acid (H2CO3) in Aqueous Solution

Dry carbonic acid has recently been shown to be kinetically stable even at room temperature. Addition of water molecules reduces this stability significantly, and the decomposition (H2CO3 + nH2O --> (n+1)H2O + CO2) is extremely accelerated for n = 1, 2, 3. By including two water molecules, a reaction rate that is a factor of 3000 below the experimental one (10 s(-1)) at room temperature was found. In order to further remove the gap between experiment and theory, we increased the number of water molecules involved to 3 and took into consideration different mechanisms for thorough elucidation of the reaction. A mechanism whereby the reaction proceedes via a six-membered transition state turns out to be the most efficient one over the whole examined temperature range. The determined reaction rates approach experimental values in aqueous solution reasonably well; most especially, a significant increase in the rates in comparison to the decomposition reaction with fewer water molecules is found. Further agreement with experiment is found in the kinetic isotope effects (KIE) for the deuterated species. For water-free carbonic acid, the KIE (i.e., kH2CO3/kD2CO3) for the decomposition reaction is predicted to be 220 at 300 K, whereas it amounts to 2.2-3.0 for the investigated mechanisms including three water molecules. This result is therefore reasonably close to the experimental value of 2 (at 300 K). These KIEs are in much better accordance with the experiment than the KIE for decomposition with fewer water entities.

X-ray and neutron scattering studies of the structure of hyperquenched glassy water

X‐ray and neutron diffraction measurements were performed on glassy water prepared by rapid cooling of water droplets on a cryoplate. Structure factors and radial distribution functions were found to be nearly identical to those obtained from amorphous ice formed either by vapor deposition onto substrates cooled at 77 K or after heating the high‐density amorphous ice.

The glassy water–cubic ice system: a comparative study by X-ray diffraction and differential scanning calorimetry

Mixtures of various ratios of cubic ice and glassy water were obtained by so-called hyperquenching of micrometer-sized water droplets at cooling rates of ≈106–107 K s−1 on a substrate held at selected temperatures between 130 and 190 K. These samples were characterized by differential scanning calorimetry (DSC) and X-ray diffraction. The minimum deposition temperature to obtain almost entirely vitrified samples is ≈140 K. Glassy water prepared at this temperature exhibits on heating an endothermic step assignable to a glass→liquid transition, without the requirement for previous annealing. Cubic ice samples obtained by deposition at 160 and 170 K undergo on heating two distinct exothermic processes of comparable intensity. One centered at ≈230 K is caused by the phase transition to hexagonal ice. The other is centered at ≈201 K in a sample deposited at 170 K, and it shifts to ≈193 K on deposition at 160 K. The latter process is attributed to the increase in particle size, relief of non-uniform strain and/or healing of different kinds of defects. Since the temperature of this second exotherm depends on the deposition temperature of the sample, it merges on sample deposition at 190 K with the exotherm from the cubic→hexagonal ice phase transition. Therefore, this can lead to an overestimation of the heat of the cubic→hexagonal phase transition. For samples deposited at ⩽150 K, the low temperature exotherm merges with the intense exotherm due to glassy water→cubic ice phase transition. X-ray diffractograms and DSC scans of cubic ice samples of different thermal history show, after annealing at the same temperature of 183 K for 5 min, essentially identical patterns. Likewise, X-ray diffractograms of cubic ice made on heating hyperquenched glassy water or vapor-deposited amorphous solid water up to 183 K are indistinguishable. Cubic ice deposited at 190 K, or annealed at 183 K, contains at most 20% amorphous component which persists up to the cubic to hexagonal ice phase transition. This is in contrast to recent claims of Jenniskens et al. (J. Chem. Phys. 1997, 107, 1232) that cubic ice obtained by heating thin films of vapor-deposited amorphous water contains more than 50% of amorphous, or even liquid, water.

Isotope effect on the glass transition and crystallization of hyperquenched glassy water

The thermal behavior of hyperquenched glassy D2O was investigated by differential scanning calorimetry from 103 to 250 K, in order to investigate the isotope effect on the glass→liquid transition and on the liquid to cubic, and cubic to hexagonal ice. For a heating rate of 30 K min−1 the temperatures of the thermal effects are: 137 K for the onset of the reversible glass→liquid transition (Tg), 154 and 173 K for the beginning and the peak minimum of the crystallization exotherm, and ≊229 K for the peak minimum of the transformation cubic→hexagonal ice. Increase in heat capacity at Tg and the width of the glass transition are similar to those reported for glassy H2O. Tg of D2O is higher than that of H2O by an amount that is expected for isorelaxational and/or isoviscous states assuming that the functional form of the molecular reorientation rates with temperature is unaffected by the isotopic substitution. The increase in the temperature of crystallization of ‘‘fluid’’ D2O is ≊three times greater than the ...