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A laboratory study of the ice nucleating properties of some mineral particulates
Author(s) -
Roberts P.,
Hallett J.
Publication year - 1968
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49709439904
Subject(s) - ice nucleus , supersaturation , nucleation , supercooling , ice crystals , saturation (graph theory) , relative humidity , materials science , efflorescence , particulates , mineralogy , humidity , thermodynamics , chemistry , composite material , meteorology , physics , mathematics , combinatorics , organic chemistry
Laboratory studies using a microscope cold stage with controlled humidity environment have been carried out on the ice nucleation and preactivation properties of several naturally occurring particulate substances. For initial nucleation water saturation was necessary, but below a critical temperature a constant ice supersaturation (water subsaturation), was sufficient. The values of both temperature and supersaturation depended on the substance. In preactivation the behaviour was similar but with a higher initial and critical temperature. Typical values are : for kaolinite, initial nucleation − 10·5, − 19°C, 20 per cent; preactivation − 6, − 11·5°C, 12 per cent: montmorillonite, − 25, below − 27°C; preactivation − 4, − 13·5°C, 14 per cent. The first temperature gives one ice crystal in 10 4 particles; the second is critical for nucleation at water subsaturation. The low values of supersaturation required for nucleation suggest that preactivation is caused by the freezing of a supercooled, adsorbed, liquid‐like layer, rather than by the retention of ice embryos in cavities. A necessary condition for the measurement of the ice nucleating ability of particles from an air sample is that they must not be heated to a temperature above at least − 5°C or subjected to a relative humidity over ice of less than about 35 per cent before the measurement is made.