Abstract
Thermal processes in amorphous solid water (ASW), including those relevant to cryogenic and astrophysical environments, depend sensitively on its thermal conductivity, κ. However, κ is not a unique material constant for amorphous water; rather, it is governed by preparation and thermal history, which determine whether the structure is predominantly low-density or high-density. Amorphous water can be produced by hyperquenching micrometer-sized droplets to form hyperquenched glassy water (HGW), by low-temperature vapor deposition to form ASW, by pressure-induced amorphization of hexagonal ice to form high-density amorphous ice (HDA), and by transformation of HDA to low-density amorphous ice (LDA). Guided by reported structural correspondences linking HGW and ASW formed or annealed at higher temperatures to LDA-like structures and some very-low-temperature ASW deposits to structures with HDA-like characteristics, we analyze κ data across liquid, crystalline, and amorphous forms of water to estimate limiting κ values for nonporous amorphous water. We find κ = (1.5 ± 0.1) W m−1 K−1 for LDA-like amorphous water in the 70–100 K range and κ = (0.2 ± 0.1) W m−1 K−1 for HDA-like amorphous water in the 10–30 K range. These results define limiting intrinsic κ values for nonporous amorphous water and provide reference points for future treatments of porous ASW in vapor-deposited and astrophysical ice environments.