Electrical conductivity is the ability of a material to conduct an electric current. For metals in their solid forms, this conductivity is generally high. However, when materials are in powder form, the conductivity is often significantly lower and cannot be predicted from the conductivity of the solid form. Therefore, it is necessary to measure conductivity in powder form.

Why measuring powder conductivity

The conductivity of a powder is of huge interest in many fields of application. Indeed, it is highly dependent on both the chemical properties of grain surfaces and the arrangement of these grains. Therefore, a change in conductivity can evidence a change in the powder properties. For example, in metal additive manufacturing, the oxidation of the powder material is detrimental to the quality of the printed part and can be monitored by a change in conductivity. In Pharmaceutics, moisture uptake is a common issue encountered with lactose or active material, which also influences conductivity, and can be monitored by it.

The electric conductivity of powders is particularly useful in the framework of battery manufacturing. Indeed, the electrode needs to have good conductivity to transfer electrons during charge or discharge of the battery. This directly depends on the conductivity of the raw powder material. The problem is that the active material is generally a poor conductor. Consequently, a conductive additive is added to increase conductivity. Nevertheless, this decreases at the same time the quantity of active material in the electrode. Therefore, the optimal proportion between this active material and the conductive additive needs to be found. In addition, this blend is more and more used in dry processes and compacted into a calendar gap to form an electrode.

This highly changes the structure and the packing of the grains and consequently the conductivity of the material. Therefore, evaluating the evolution of conductivity with the packing fraction of the powder is needed.

Conclusion

Measuring powder conductivity is of huge interest in many fields. It is necessary for quality control of the material (moisture uptake, oxidation, coating…) and for improving powder formulation to optimize the conductivity of the final product. In this context, the GranuPack Conductivity provides a useful tool. With its excellent repeatability and the user-friendly protocol, this new instrument allows for measuring the conductivity of a powder at different packing fractions in an accurate and user-independent way.

The tapped density measurement is coupled with the conductivity measurement to give a complete view of the evolution of conductivity during densification. With this approach, effects such as moisture uptake and oxidation, optimal powder formulation and conductivity prediction can be investigated to improve the quality of the final product.