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Ultra‐rapid freezing by spraying/plunging: pre‐cooling in the cold gaseous layer
Author(s) -
Chang Zhaohua,
Baust John G.
Publication year - 1991
Publication title -
journal of microscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0022-2720
DOI - 10.1111/j.1365-2818.1991.tb03101.x
Subject(s) - freon , materials science , cryogenics , helium , liquid helium , water cooling , thermodynamics , nuclear engineering , mechanics , chemistry , physics , organic chemistry , engineering
SUMMARY A thermophysical model is established to analyse the influence of pre‐cooling of a biological specimen in the cold gas layer associated with spray‐freezing techniques. The basic principles governing the process of pre‐cooling are provided. It is concluded that pre‐cooling is one of the major limiting steps in attaining an overall ultra‐rapid cooling rate. Pre‐cooling has a substantial influence on the nature of the final frozen specimens. In order completely to avoid crystallization before entry into the liquid cryogen and maximize the overall cooling rate of the specimen, precautions should be taken to control the height of the gaseous layer and the size of the specimen. The probability of the specimen being frozen in the cold gaseous layer is reduced by increasing the entry speed. The effectiveness, however, becomes less marked at speeds greater than 10 m/s. In order to minimize the risk of misinterpreting the measured cooling rate, it is necessary to specify the pre‐cooling conditions. The pre‐cooling effect is much more evident in liquid helium than in cryogens such as propane, ethane, Freon 12, 13 and 22.