Complex hydrides, such as sodium alanate, can reversibly accept and release hydrogen, making them viable materials for hydrogen storage systems. However, before such systems can be designed and optimized, the engineering properties and physical behavior of the materials must be characterized. This enables optimization of gravimetric and volumetric storage densities and accurate thermal modeling. Parameters, such as thermal conductivity, will dramatically influence the sodium alanate hydrogen-storage bed design and its performance.

Figure 1. Engineering properties hydrogen manifold.

Sandia researchers have developed the capability to investigate the following engineering properties, using custom-developed hardware:

• Thermal properties as a function of phase, cycle, and pressure
  • Thermal conductivity
  • Heat capacity
  • Wall resistance
  
  
• Mechanical properties as a function of cycle and phase
  • Pressure exerted on a vessel wall
  • Densification effects
  
  
• Electrical properties
  • DC resistivity as a function of phase

A custom sorption manifold was built and is available specifically for the material properties work (Figure 1).

A thermal properties test cell (Figure 2) was the first capability developed for the properties lab. The test cell utilizes the thermal probe method to measure low-conductivity materials with conductivity values between 0.001 and 3 W/m-K. Thermal conductivity can be measured as a function of cycle, phase, pressure, and temperature.

Figure 2. Thermal properties test cell.

To expand the capabilities of the lab, a mechanical properties test cell (Figure 3) was designed and built to measure the pressure exerted on a vessel wall by volumetric expansion during phase change. The material can be compacted into the vessel at various densities. The expansion pressure is measured using a strain gauge affixed to a membrane.

Additionally, the lab contains an electrical properties test cell that was designed and built to measure the DC properties of the sodium alanate. The method utilizes a three-electrode system for accurate measurement of the material at various densities.

Figure 3. Mechanical properties test cell.

Contact:
Daniel Dedrick
dededri@sandia.gov
(925) 294-1552