Amorphous ice

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Amorphous ice is a form of solid water , which is characterized by the fact that the water molecules are arranged irregularly like in a glass , so there is no long-range order . This is how amorphous ice differs from the 15 known crystalline ice forms.

The predominant solid form on earth is ice (I h ), which has a regular hexagonal crystal structure. In interstellar space, however, the amorphous forms are considered to be dominant.

As with crystalline ice, there are different forms of amorphous ice, this fact is called polyamorphism. The various amorphous forms are distinguished based on their density:

  • low density amorphous ice (LDA)
  • high density amorphous ice (HDA) and
  • very high density amorphous ice (VHDA).

to form

Low density amorphous ice (LDA)

Low-density amorphous ice or low-density amorphous ice (LDA) is the longest known form of amorphous ice.

One way of producing amorphous materials is to cool them down so quickly that the material cannot form a crystalline structure (see vitrification ). By condensing water vapor on a cooled copper rod and using the Debye-Scherrer method, it was possible to show as early as 1935 that below the glass transition temperature of water (about 130  K at 1  bar ) a solid without a crystalline structure forms. This form was initially called amorphous solid water (ASW).

Further manufacturing options were developed in 1980, in which an n-heptane water emulsion is sprayed into a cryogenic liquid or a water aerosol is sprayed onto a cryogenic copper plate with a supersonic flow. Cooling rates of 10 6 to 10 7 K / s are achieved. This form is called hyperquenched glassy water (HGW) due to its manufacture .

A third option is to warm up HDA (see below) at ambient pressure. This shape transforms into low-density amorphous ice at around 120 K.

These three types of generation, all of which result in a density of around 0.94 g / cm 3 , were initially considered to be different forms. Johari et al. a. published in 1996 that ASW and HGW have a glass transition temperature of 135 K at ambient pressure, while it is 129 K for LDA. According to recent findings, however, all three types of generation are likely to lead to the same form of amorphous ice, which is known as LDA.

High density amorphous ice (HDA)

In 1984, physicists working with Osamu Mishima discovered another form of amorphous ice that can be produced by compression instead of a change in temperature. They showed that at a temperature of 77 Kelvin and a pressure of 10  k bar, hexagonal ice, so to speak, "melts" and changes into a glass-like, amorphous state. This form of amorphous ice has a higher density of 1.17 g / cm 3 and is therefore also called high-density amorphous ice (HDA). HDA and LDA can be converted into one another by changing the pressure or temperature. A sharp transition was observed here.

Very high density amorphous ice (VHDA)

This form was also discovered by Mishima in 1996 when he heated HDA to 160 K at pressures between 1 and 2 GPa. The mold obtained has a density of 1.26 g / cm 3 - very-high density amorphous ice (VHDA).

Initially, VHDA was not seen as a separate form until 2001 Lörting u. a. suggested this.

Application of amorphous ice

In cryo-electron microscopy , water-containing biogenic samples are vitrified by cryogenic liquids such as liquid nitrogen or liquid helium . In this way, the native structures of the samples can be retained without being changed by ice crystals.

Individual evidence

  1. ↑ Jenniskens , Peter; Blake , David F .: Structural Transitions in Amorphous Water Ice and Astrophysical Implications'. In: Science 65 (1994), pp. 753-755
  2. ↑ Burton , EF; Oliver , WF: The crystal structure of ice at low temperatures. In: Proc. R. Soc. London Ser. A 153 (1935), pp. 166-172
  3. ↑ Brüggeler , Peter; Mayer , Erwin: Complete Vitrification in Pure Liquid Water and Dilute Aqueous Solutions. In: Nature 288 (1980) pp. 569-571
  4. ↑ a b Mishima , Osamu; Calvert , LD; Whalley , Edward: An apparently first-order transition between two amorphous phases of ice induced by pressure. In: Nature 314 : 76-78 (1985)
  5. ↑ Johari , Gyan P .; Hallbrucker , Andreas; Mayer , Erwin: Two calorimetrically Distinct States of Liquid Water Below 150 Kelvin. In: Science 273 (1996), pp. 90-92
  6. ^ Bowron , Daniel T .; Finney , John L .; Kohl , Ingrid; u. a .: The local and intermediate range structures of the five amorphous ices at 80 K and ambient pressure. In: J. Chem. Phys. 125 (2006), pp. 194502-1-194502-14 PDF
  7. ↑ Elsäßer , Michael S .; Winkel , K .; Mayer , Erwin; Lörting , Thomas: Reversibility and isotope effect of the calorimetric glass → liquid transition of low-density amorphous ice. In: Phys. Chem. Chem. Phys 12 (2010) 708-712 PDF
  8. ↑ Mishima , Osamu; Calvert LD; Whalley , Edward: "Melting ice" I at 77 K and 10 kbar: a new method of making amorphous solid. Nature 310 (1984), pp. 393-395
  9. ↑ Lörting , Thomas; Salzmann , Christoph G .; Kohl , Ingrid; u. a .: A second distinct structural "state" of high-density amorphous ice at 77 K and 1 bar. Phys. Chem. Chem. Phys. 3 (2001) pp. 2810-2818 PDF

literature

Angell , C. Austen: Amorphous Water. In: Annu. Rev. Phys. Chem. 55 (2004), pp. 559-583

Mishima , Osamu; Stanley , H. Eugene: The relationship between liquid, supercooled and glassy water. Nature 396 (1998), pp. 329-335 PDF

Mishima , Osamu: Polyamorphism in water. In Proc. Jpn. Acad., Ser. B. 86 (2010), pp. 165-175 PDF