Baixe Phase properties and type of Earth's water ice and soace ices e outras Notas de estudo em PDF para Química, somente na Docsity! PHASE PROPERTIES AND TYPE OF EARTH'S WATER ICE AND SPACE ICES Thakur K. Praveen1 and A. Velumurgan1, 1Indian Institute of Remote Sensing, Dehradun, Uttarakhand, India Corresponding author: praveen@iirs.gov.in Introduction: Ice is the name given to any one of the 15 known crystalline solid phases of water. In non-scientific contexts, it usually describes ice Ih, which is the most abundant of these phases. It can appear transparent or an opaque bluish-white color depending on the presence of impurities such as air. The addition of other materials such as soil may further alter appearance [1]. The most common phase transition to ice Ih occurs when liquid water is cooled below 0 °C (273.15 K, 32 °F) at standard atmospheric pressure. It can also deposit from a vapor with no intervening liquid phase, such as in the formation of frost. Ice appears in nature in varied forms such as hail and glaciers. Amorphous ice is more common in outer space whereas hexagonal crystalline ice is extremely rare, which is predominant on Earth [6]. Phase properties of Earth's Water Ice: The main physical nature and phases of water ice are given in the table 1. The figure 1 a) and b) shows the phase diagram of water and different ice types. Table 1: Phases and characteristics of Water Ice [6] Space Ice: The solid-vapor curve becomes very low (fig. 1a) [3] as pressures and temperatures decreases and by -90oC the vapor pressure of ice is about 10-4 mb. At the temperatures of the outer solar system, the vapor pressure of ice is so low that ice remains for geologically long times even in a vacuum. In Space, instead of pure water Phase Characteristics Amorphous ice Amorphous ice as an ice which does not have crystal structure. This ice occurs in three forms; low density (LDA) formed at atmospheric pressure, or below, high density (HDA) and very high density amorphous ice (VHDA), forming at higher pressures. LDA forms by extremely quick cooling of liquid water ("hyperquenched glassy water", HGW), by depositing water vapour on very cold substrates ("amorphous solid water", ASW) or by heating high density forms of ice at ambient pressure. Ice Ih Normal hexagonal crystalline ice. Almost all ice in the Earth's biosphere is ice Ih with small amount of Ic Ice Ic Metastable cubic crystalline variant of ice. The oxygen atoms are arranged in a diamond structure, made at 130-150 K, and is stable upto 200K, when it transform to ice Ih. It is sometimes present in the upper atmosphere. Ice 2 A rhombohedral crystalline form with highly ordered structure. Formed from ice Ih by compressing it at temperature of 190-210 K. When heated it undergoes transformation to ice 3. Ice 3 A tetragonal crystalline ice, formed by cooling water down to 250 K a 300 MPa, least dense of the high pressure phases and denser than the water. Ice 4 Metastable rhombohedral phase. Does not easily form without a nucleating agent. Ice 5 A monoclinic crystalline phase, formed by cooling water to 253 K at 500 MPa. Most complicated structure of all. Ice 6 A tetragonal crystalline phase, formed by cooling water to 270 K at 1.1 GPa, shows Debye relaxation. Ice 7 A cubic phase. The hydrogen atom's position is disordered, the material shows Debye relaxation. The hydrogen bonds from two interpenetrating lattices. Ice 8 A more ordered version of Ice 7, where the hydrogen atoms assume fixed positions, formed from ice 7 by cooling it beyond 5oC. Ice 9 A tetragonal metastable phase, formed gradually from ice 3 by cooling it from 208 K to 165 K, stable below 140 K and pressures between 200 and 400 MPa. It has density of 1.16 g/cm³, slightly higher than ordinary ice. Ice 10 Proton ordered symmetric ice, forms at about 70 GPa. Ice 11 An orthorhombic low temperature equilibrium form of hexagonal ice, which is ferroelectric. Ice 12 A tetragonal metastable dense crystalline phase. it is observed in the phase space of ice V and ice VI. It can be prepared by heating high-density amorphous ice from 77 K to about 183 K at 810 MPa Ice 13 A monoclinic crystalline phase, formed by cooling water below 130 K at 500 MPa. The proton-ordered from of ice 5. Ice 14 An orthorhombic crystalline phase, formed below 118 K at 1.2 GPa. The proton-ordered from of ice 12. Ice 15 The predicted but no proven proton ordered form of ice 6, thought to be formed by cooling water to around 108-80 K at 1.1 Gpa Science of Solar System Ices (2008) 9014.pdf