ISOTECH Gallium Fixed-Point Cell
| Brand | ISOTECH |
|---|---|
| Origin | United Kingdom |
| Type | Sealed or Open-Style Fixed-Point Cell |
| Certified Uncertainty | ±0.000070 °C (k = 1) |
| Purity | ≥99.99999% Ga (7N) |
| Compliance | Traceable to NPL and CIPM MRA |
Overview
The ISOTECH Gallium Fixed-Point Cell is a primary temperature reference standard engineered for high-accuracy calibration and validation of precision thermometers, including standard platinum resistance thermometers (SPRTs), industrial platinum resistance thermometers (IPRTs), and radiation thermometers. It realizes the gallium melting point—defined by the International Temperature Scale of 1990 (ITS-90) at 302.9146 °C—with exceptional reproducibility and long-term stability. Unlike water triple-point cells, gallium fixed-point cells operate in the mid-temperature range and eliminate the need for complex phase-change apparatus or vacuum-jacketed handling. The cell employs ultra-high-purity gallium (≥99.99999%, 7N grade), purified via zone refining and verified by mass spectrometry and residual resistivity ratio (RRR) analysis, ensuring compliance with ISO/IEC 17025 requirements for reference material certification.
Key Features
- Calibration-grade uncertainty of ±0.000070 °C (k = 1) at the gallium melting plateau, validated through interlaboratory comparisons coordinated by the UK’s National Physical Laboratory (NPL)
- Two structural configurations: hermetically sealed cells for long-term archival stability and open-style cells enabling direct thermometer immersion and real-time thermal equilibration monitoring
- Quartz or fused-silica ampoule construction with low thermal expansion coefficient (α ≈ 0.5 × 10−6 K−1) and high chemical inertness toward molten gallium
- Integrated freeze/melt cycle protocol support—designed for repeatable, hysteresis-minimized phase transitions under controlled furnace ramp rates (≤0.1 K/h)
- No internal nucleation aids or seeding agents; relies on spontaneous nucleation to preserve thermodynamic purity and avoid metastable supercooling artifacts
Sample Compatibility & Compliance
The ISOTECH Gallium Fixed-Point Cell is compatible with standard SPRT probe diameters (3–6 mm), miniature thermocouple sensors (Type S, R, or B), and infrared radiometer apertures (≥8 mm field-of-view). Each cell is supplied with a full metrological dossier including purity assay reports, impurity profile (Fe, Cu, Zn, Pb, Mg, Al, Si ≤ 10 ng/g each), furnace compatibility guidance, and ITS-90 deviation correction tables. All units are certified traceable to the International Bureau of Weights and Measures (BIPM) through the CIPM Mutual Recognition Arrangement (MRA) and conform to ASTM E220, ISO 5725, and EURAMET cg-18 guidelines for fixed-point cell characterization. Documentation supports GLP/GMP audit trails and FDA 21 CFR Part 11-compliant data integrity when integrated with validated calibration software platforms.
Software & Data Management
While the cell itself is a passive physical standard, its integration into automated calibration workflows is supported via ISOTECH’s optional ThermCal Suite—a Windows-based application compliant with ISO/IEC 17025 Clause 7.7 and NIST SP 800-53 controls. The software enables automated plateau detection using first-derivative thresholding, uncertainty propagation per GUM Supplement 1, and generation of calibration certificates aligned with ISO 17025 Annex A3. Raw temperature-time datasets are stored in vendor-neutral CSV and HDF5 formats, with embedded metadata (cell ID, melt date, operator ID, furnace model) to satisfy ALCOA+ data governance principles. Audit logs record all user actions, parameter changes, and certificate revisions with time-stamped digital signatures.
Applications
- Primary calibration of SPRTs used in national metrology institutes (NMIs) and accredited calibration laboratories
- Validation of high-temperature blackbody sources and cavity radiometers in radiometry labs
- Intercomparison campaigns between regional standards laboratories under COOMET or APMP frameworks
- Uncertainty budget refinement for industrial furnace qualification (e.g., aerospace heat-treatment ovens per AMS2750E)
- Reference anchor point for in-house development of custom ITS-90 interpolation equations beyond the silver point (961.78 °C)
FAQ
What is the defined ITS-90 temperature of the gallium fixed point?
The gallium melting point is defined as 302.9146 °C on the International Temperature Scale of 1990 (ITS-90).
How often should a gallium fixed-point cell be recalibrated?
Recalibration is recommended every 2–3 years for sealed cells operated under ISO/IEC 17025 conditions; open-style cells require annual verification due to potential oxidation exposure.
Can this cell be used for both freezing and melting plateaus?
Yes—the cell is characterized for both gallium freeze (solidification onset) and melt (liquidus onset); however, the ITS-90 defining fixed point is the melt temperature.
Is furnace uniformity critical during realization?
Yes—axial temperature gradients must be maintained below ±5 mK over the sensing zone length, per ISO/IEC 17025 Clause 6.4.3 and EURAMET cg-18 Section 5.2.
Does ISOTECH provide on-site training for fixed-point cell operation?
Yes—certified metrology engineers deliver hands-on workshops covering freeze/melt protocol execution, plateau evaluation per CCT-WG3 guidelines, and uncertainty contribution analysis.
