A practical method of realizing the triple point of water using totally frozen cells

ISSN： 0026-1394

Source： Metrologia, Vol.34, Iss.2, 1997-05, pp. : 177-179

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Abstract

Abstract. A simple, economical and time-saving procedure is described for maintaining water triple point cells (WTPCs) ready for use for indefinite periods, based on storing the WTPCs totally frozen. The uncertainty of reproducibility of the triple point temperature does not exceed 0,1 mK. The WTPC is kept in direct contact with crushed ice in a Dewar flask. Under such conditions the natural tendency of the cell is to solidify completely over a period of several weeks, but it will not break as long as the crushed ice is made of deionized water. The procedure for inducing the initial appearance of the ice phase seems irrelevant within the stated uncertainty. This may indicate that the impurities in the cell attain a stationary quasi-two-dimensional distribution in the ice phase, having migrated to the interfaces between the individual crystals, some of which can be observed with the naked eye (linear dimensions 1 cm to 3 cm). This final state is only slightly perturbed during use, since a very small fraction of ice is melted when forming the inner and outer ice/water interfaces. The triple point temperature is mainly determined by the bulk properties of the pure crystals. Reduced lixiviation and unattended shipping of the WTPCs are possible by-products of the method.