Creating Structural Material From Martian Regolith Using Spark Plasma Sintering

Abstract

In order to establish a sustained extra-terrestrial presence, habitats need to be built on the Moon and Mars using novel materials made from local resources. Several material processing methods can be applied to transform the locally abundant regolith into materials suitable for structural purposes. One promising method is sintering. This process can be used to create strong material using little to no Earth-imported additives. However, sintering still requires a large amount of energy to heat the material. A possible method to lower the energy requirement is by introducing small amounts of sintering aids. However, little is known about the effect of aids on the properties of sintered regolith. This research aims to investigate the effect of sintering aids on the densification and mechanical properties of sintered Martian regolith simulant.

In this study, the chosen Martian regolith simulant, Martian Global Simulant - 1 (MGS-1), was first investigated using a variety of powder characterisation techniques to assess the similarity with actual Martian material. Using the Spark Plasma Sintering (SPS) technique, disk shaped samples were sintered at temperatures between 700 °C and 1060 °C and pressures of 30 MPa to 50 MPa. Several powder mixtures were used. Two different additives, aluminium and bismuth oxide, were used in two weight percentages, 2.5wt% and 5wt%, and mixed with baseline material. Samples sintered from this enriched material were compared to those made using baseline MGS-1 material. In order to assess the mechanical properties, the Ball-on-Ring (BoR) compression test was used to determine the biaxial flexure strength of the samples. Since the BoR compression test is a semi-standardised method, an effort was made to validate the testing procedure and obtained results using soda-lime glass samples. Additionally, mortar disks were created and tested to provide a reference for terrestrial material properties. After compression testing, some samples were ground back into a powder and examined using X-ray Diffraction (XRD) to assess any bulk composition changes induced by the additive and/or sintering process.

The results from the powder characterisation techniques show that the chemical composition of MGS-1 is close to that of actual Martian material. In order to achieve strengths comparable to terrestrial mortar, a relative density of at least 70 % needs to be achieved. For the baseline material, the sintering temperature needs to exceed 1000 °C in order to obtain these results. This value is 950 °C for 2.5wt% aluminium additive material, and 900 °C for 5wt% aluminium, 2.5wt% and 5wt% bismuth oxide additive material. For equal sintering temperatures, the biaxial strength of enriched powders exceeds that of baseline material. Hence, the sintering temperature can be lowered for enriched materials to achieve similar strengths. Samples made from bismuth oxide enriched material exhibited superior properties compared to aluminium enriched material. For aluminium enriched material, no clear increase in properties is observed with increasing additive fraction. For bismuth oxide enriched material, there appears to be an increase in properties with increasing additive fraction. A material behaviour transition from brittle to tough appears to be linked to biaxial strengths exceeding 12 MPa. Compared to literature on Martian regolith-based materials, the results for sintered enriched MGS-1 perform well in terms of required additive fraction and mechanical properties. Using additives could potentially be a way to lower the energy requirement for regolith sintering on Mars. This work opens up areas of further research into the optimal additive, additive amount and sintering parameters for on-site application.