Isotech 17401 Gallium Fixed Point Cell

The Sostmann–Isotech Gallium Cell is recognised worldwide as one of the most reliable and reproducible fixed‑point standards within the ITS‑90. With a melting point of 29.7646 °C, gallium provides a highly accessible and practical reference temperature: easy to realise, extremely stable and free from many of the complications associated with other fixed points. Developed in the 1970s by Henry Sostmann, the cell has built a reputation for exceptional robustness and accuracy. With more than thirty years of proven use in national and primary laboratories, it is a standard that users can trust without hesitation.

Total confidence and global recognition

Confidence is essential in a primary standard. Isotech gallium cells have been used in international comparisons, long‑term stability studies and primary laboratories worldwide. A comparison between an Isotech reference cell and the NIST standard showed agreement within 4 µK (0.000004 °C) — a remarkable demonstration of quality. Each cell contains 7N‑purity gallium (99.99999%), producing a flat, stable melt plateau with day‑to‑day reproducibility of only ±0.000025 °C.

High‑quality construction

The Sostmann design uses a dual‑structure approach:

• > A resilient inner housing that prevents any reaction between the gallium and the container.
• > A metal outer sleeve that ensures longitudinal temperature uniformity and mechanical strength.

Hundreds of cells have been shipped worldwide without damage, demonstrating the robustness of the design.

Sealed and Open models

Sealed Gallium Cell

The sealed model is recommended for most users. It offers maximum convenience, protection and sub‑millikelvin performance with no need for pressure control.

Open (Resealable) Gallium Cell

For advanced metrology, the open model includes a valve and Klein flange, allowing connection to vacuum and gas systems. This enables pressure adjustment to exactly 1 bar at the melt point or measurement according to CCT/2000‑13. With the open cell, uncertainties as low as ±100 µK are achievable.

Why the gallium point stands out

Comparisons between the gallium point and the water triple point show that gallium offers several practical advantages:

• > no isotope variation
• > no peritectics
• > excellent robustness
• > no detectable drift
• > plateau achieved in 1–2 hours
• > simple warm‑water realisation instead of ice–CO₂ baths

This makes gallium one of the most user‑friendly and reliable fixed points in the ITS‑90. The Sostmann–Isotech Gallium Fixed‑Point Cell is one of the most accurate, stable and robust fixed‑point standards available. With 7N‑purity metal, exceptional reproducibility and decades of proven performance in national laboratories, it is an essential reference for any organisation requiring absolute precision in low‑temperature metrology.