Sintering and 3D printing of lunar regolith to make building materials on the Moon

Establishing infrastructure on other planetary bodies will require building materials that cannot be imported from Earth. Therefore, it will be crucial to develop techniques for precision material fabrication at low cost and with minimal equipment requirement. The most abundant material on the immediate surface of the Moon and Mars – two potential infrastructure targets – is the regolith; a lunar or Martian soil comprising dusts of variable mixtures of glass and crystalline rock fragments. Here, this project aims to test the hypothesis that the regolith can be transformed into building materials at extremely low cost, reproducibly, and rapidly. The technique to be tested is sintering and is used widely on Earth to produce ceramics and glasses with bespoke engineering properties. Sintering will have to involve partial or complete melting of the regolith at controlled temperatures. This project therefore combines geology, engineering, and physical materials science, in order to solve a key problem for the coming century.

To date, so-called simulants of regoliths have been devised and mass produced by NASA, the ESA, and various universities worldwide. These simulants are for the scientific community to explore the properties and behaviour of regolith at a range of conditions. A successful student would join this international community of scientists exploring the utility of regolith at a range of conditions. Alongside this, the supervisory team are the world experts in sintering of geological materials, and have developed fundamental models for sintering behaviour, with which the physical characteristics of the resultant sintered materials can be controlled accurately [1,2]. In this project, the successful candidate will perform precise, small-scale sintering tests using an optical dilatometer and packed compacts of the lunar and Martian regolith simulants. The data collected will be the first of its kind, and will represent the basis for high-impact work that directly addresses the question: what temperatures held for what times are required to convert regolith to useful materials? Coupled with material constraints of the phase diagram of these regoliths, these data can be used to develop a predictive model for lunar and Martian sintering.

Towards the second half of this project, the student will work directly with external collaborators at the National Glass Centre in Sunderland to upscale these experimental results and produce a proof-of-concept that lunar sintered materials can be produced in-bulk. These bulk materials will then be subjected to mechanical tests in order to constrain their elastic, thermal, hydraulic, and strength properties, all required for effective extra-terrestrial engineering projects. Alongside these upscaling experiments, the student will engage directly with collaborators at German Aerospace and the European Space Agency, in order to explore the specific techniques of fabrication that may be feasible on the Moon, including high-temperature 3D printing.

[ref 1] Wadsworth, F.B., Vasseur, J., Llewellin, E.W., Schauroth, J., Dobson, K.J., Scheu, B. and Dingwell, D.B., 2016. Sintering of viscous droplets under surface tension. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 472(2188), p.20150780.

[ref 2] Wadsworth, F.B., Vasseur, J., Llewellin, E.W. and Dingwell, D.B., 2022. Hot sintering of melts, glasses and magmas. Reviews in Mineralogy and Geochemistry, 87(1), pp.801-840.

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The core method of this project is termed ‘optical dilatometry’ and involves the direct in situ optical observation of the behaviour of a material inside a furnace using a lamp-and-camera array in series. This allows us to collect continuous data of the evolution of the volume of materials as they are heated to temperatures up to 1600 degrees celcius. This method will be applied to all available lunar and Martial regolith simulants. Primarily the dependent variables include: temperature, rate of heating, grainsize of the regolith powder, and time held at a given temperature. By varying these parameters, the student will be able to explore all the variations that may be applicable to the real case of sintering on the Moon or Mars. Additional methodologies include differential scanning calorimetry in order to determine the solidus, liquidus, and glass transition temperatures. And viscometry, in order to determine the shear viscosity of the molten materials using Durham University’s flagship geological rheometry suite. Finally, the student will be trained in a range of material testing techniques that include permeametry, porosimetry, and both uniaxial and triaxial mechanical testing. There is an opportunity to apply for beamtime at the national Diamond Light Source synchrotron, in order to perform some of the sintering tests in situ and capture 3D structural data using X-ray tomography. In all of these techniques, the supervisory team have extensive experience and can guide the student.

Project Timeline

Year 1

Year 1 will involve two guided literature reviews in parallel: (1) on the material science of sintering with a focus on viscous sintering of partially molten systems; and (2) on the planetary science of the Moon and Mars, with a focus on regolith production and compositions. Year 1 will also include pilot experiments using the regolith simulants, and materials characterisation in order to find the fundamental properties that will be required to design the sintering experiments.

Year 2

Year 2 will be primarily lab-based and will involve the campaign of sintering experiments at Durham and at LMU, Munich. During this year, the student will also make collaborative research visits to DLR (German Aerospace) in Berlin and the ESA, in order to compile existing additional materials characterisation data on the regolith samples. Toward the end of Year 2, the student will analyse the data in full, and work toward a high-impact piece of work that lays out the fundamental feasibility test of lunar and Martian sintering as a fabrication technique.

Year 3

Year 3 will focus on the upscaling of the lab work from Year 2 by materials testing of larger brick-shaped products of the sintering technique. This will involve a research secondment at the University of Strasbourg and work in the Durham Rock Physics laboratory. The goal of these tests is to prove that the materials produced by sintering regolith can be designed in a bespoke manner with predetermined mechanical building properties.

Year 3.5

In the final 6 months, the student will receive support in thesis preparation and writing of work for publication (this will also be provided throughout all 3 years as the student finishes components of the work).

& Skills

The student will be trained in: (1) laboratory skills and how to perform scaled and well-posed experimental investigations into viscous sintering; (2) dimensional analysis and mathematical modelling; (3) rock physics testing; (4) materials science techniques across a range of materials tests; and (5) scientific writing, communication, and presentation skills for publications and conference contributions.

References & further reading

The following resources are recommended ahead of application:
 Meurisse, A., Beltzung, J.C., Kolbe, M., Cowley, A. and Sperl, M., 2017. Influence of mineral composition on sintering lunar regolith. Journal of Aerospace Engineering, 30(4), p.04017014.
 Wadsworth, F.B., Vasseur, J., Llewellin, E.W. and Dingwell, D.B., 2022. Hot sintering of melts, glasses and magmas. Reviews in Mineralogy and Geochemistry, 87(1), pp.801-840.
 Zanotto, E.D. and Prado, M.O., 2001. Isothermal sintering with concurrent crystallisation of monodispersed and polydispersed glass particles. Part 1. Physics and chemistry of glasses, 42(3), pp.191-198.
 Meurisse, A., Makaya, A., Willsch, C. and Sperl, M., 2018. Solar 3D printing of lunar regolith. Acta Astronautica, 152, pp.800-810.

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