Standard Reference Materials: Tin Freezing-Point Standard - SRM 741a

Published

June 1, 1999

Author(s)

Gregory F. Strouse, N P. Moiseeva

Abstract

The freezing point of tin (231.928 degrees C) is a defining fixed point of the International Temperature Scale of 1990 (ITS-90). Realization of this freezing point is performed using a fixed-point cell containing high-purity ({> or =} 99.9999 % pure) tin. A 24 kg single lot of tin (99.999 97 % pure) constituting Standard Reference Material (SRM ) 741a has been evaluated, and certified as suitable for use in the realization of the freezing-point temperature of tin for the ITS-90. Based on results obtained with three fixed-point cells containing random samples of SRM 741a, the expanded uncertainty (k = 2) assigned to the freezing point temperature of the metal is 0.52 m degrees C. SRM 741a has a higher purity and a smaller expanded uncertainty (k = 2) than that of SRM 741 (originally supplied as a 350 g ingot) of 99.9999 % purity and 1 m degrees C, respectively. In this document, the methods used for the fabrication of the tin freezing-point cells and for the evaluation of SRM 741a are described.

Citation

Special Publication (NIST SP) - 260-138

Report Number

260-138

NIST Pub Series

Special Publication (NIST SP)

Pub Type

NIST Pubs

Download Paper

Local Download

Keywords

ITS-90, SPRT, SRM, Standard Reference Material, thermometric fixed point, tin freezing-point

Citation

Strouse, G. and Moiseeva, N. (1999), Standard Reference Materials: Tin Freezing-Point Standard - SRM 741a, Special Publication (NIST SP), National Institute of Standards and Technology, Gaithersburg, MD, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=830607 (Accessed October 16, 2025)