Tantalum-Hafnium: Optical Hydrogen Sensing Materials for High-Temperature Applications.

Area of Science:

• Materials Science
• Nanotechnology
• Chemical Engineering

Background:

• Thin film metal hydrides, particularly tantalum-based sensors, offer excellent hydrogen sensing capabilities.
• However, pure tantalum sensors exhibit reduced sensitivity to low hydrogen concentrations at temperatures above 200 °C.
• This limits their application in high-temperature environments.

Purpose of the Study:

• To investigate the effect of hafnium alloying on tantalum-based metal hydride optical sensors.
• To enhance the performance of these sensors for detecting low hydrogen concentrations at elevated temperatures.
• To maintain the desirable properties of tantalum sensors, such as a large, hysteresis-free sensing range and stability.

Main Methods:

• Optical transmission measurements.
• Ex situ and in situ X-ray diffraction (XRD).
• X-ray and neutron reflectometry.

Main Results:

• Tantalum-hafnium alloys form a stable solid solution up to 21% hafnium.
• Alloying expands the unit cell, altering hydrogenation enthalpy and shifting the sensing range.
• Hafnium alloying approximately doubles sensitivity for low hydrogen concentrations (<10^3 ppm) above 200 °C.

Conclusions:

• Hafnium alloying effectively tailors tantalum's properties for improved high-temperature hydrogen sensing.
• Ta-Hf alloys maintain the large, hysteresis-free sensing range and stability of pure tantalum.
• This development expands the potential applications of metal hydride optical sensors in demanding environments.