High-temperature platinum resistance thermometry: the problem with silver and the case for gold

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DOIResolve DOI: http://doi.org/10.1088/0026-1394/52/4/478
AuthorSearch for:
TypeArticle
Journal titleMetrologia
ISSN0026-1394
1681-7575
Volume52
Issue4
Pages478485; # of pages: 8
Subjectplatinum resistance thermometer; silver fixed point; gold fixed point; contamination
AbstractThe diffusion of silver through quartz at high temperatures leads to contamination of the platinum sensing element of high temperature platinum resistance thermometers. While some protection of the PRT element may be afforded by the application of appropriate electric fields, the contamination of the quartz elements of silver fixed points causes their premature failure. Contamination is evidenced by the yellowish colour imparted to the glass by the silver particles growing within the quartz glass matrix. The presence of silver as the contaminating element has been confirmed unambiguously through energy dispersive x-ray analysis and secondary ion mass spectrometry. To mitigate the risk of silver contamination , the gold point is proposed as an alternative calibration point. PRT resistance ratios measured at the freezing points of silver and gold in different laboratories at different times are highly correlated. This suggests that the ITS-90 reference function might be extrapolated to 1064.18 °C (the gold fixed point). However, it remains unclear from the gold and silver PRT resistance ratios from the literature whether extrapolation of the reference function leads to the correct value at the gold point. A direct comparison of gold fixed points may be required to resolve the inconsistencies. Additional PRT data may help resolve the discrepancy.
Publication date
PublisherIOP Publishing
LanguageEnglish
AffiliationNational Research Council Canada; Measurement Science and Standards
Peer reviewedYes
NPARC number21275087
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Record identifier5009fce3-2cca-463a-8b49-76b6b9d17165
Record created2015-05-07
Record modified2016-05-09
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