Offworld Life Science Hardware: Autoclave Design for Microgravity Hydrothermal Synthesis
Microgravity offers an enticing synthetic knob for materials scientists to explore—however, this environment creates major challenges in hardware development that can turn a simple 3-day experiment into a 3-year long nightmare.
This paper provides an overview of engineering an autoclave, compatible with NASA’s Solidification Using a Baffle in Sealed Ampoules (SUBSA) furnace, to enable microgravity hydrothermal synthesis—an acceleration-sensitive technique that processes aqueous samples above the boiling point of water. Hydrothermal synthesis is a universal chemical transformation technique that is used to produce a range of advanced materials with applications in alternative energy, healthcare, and the food industry.
In this work, we use the synthesis of graphene hydrogel as a case study to verify our hardware design on Earth before launching to the International Space Station for microgravity testing. The design addresses pertinent challenges which include enabling thermal expansion while preventing air bubble formation in solution and implementing a pressure fail-safe above the maximum operating temperature. Our goal in presenting this autoclave design is to provide a step forward towards commercial-of-the-shelf microgravity hardware.
Summary of the hydrothermal synthesis of graphene hydrogel we plan to use as a case study for our microgravity autoclave. The starting material consists of an aqueous dispersion of graphene oxide flakes, which is then heated to 180 °C for 3 h for hydrothermal reduction to graphene hydrogel. When this transformation occurs on Earth, buoyancy induced effects can lead to sedimentation of the graphene flakes and subsequently a non-uniform microstructure of the resulting hydrogel. Conversely, in microgravity we anticipate Brownian motion driven effects, allowing for a homogeneous distribution of graphene flakes and a more uniform microstructure of the hydrogel sample. — Microgravity Science and Technology
Overview of the SUBSA furnace, sample ampoule assembly (SAA), and autoclave relationship. (a) Image of the SUBSA furnace and (b) SAA with the stainless-steel autoclave on the tailored end. (c) Drawing of the SAA close-up of the autoclave showing the position of the four thermocouples (TC1, TC2, TC3, and TC4) with respect to the position of Reaction Volumes A and B, shown in light blue. (d) The TC temperature profiles of a test run in the ground SUBSA unit (heater setpoint = 184 °C), heating GO dispersion in both reaction volumes for 3 h — Microgravity Science and Technology
Autoclave Design for Microgravity Hydrothermal Synthesis, Microgravity Science and Technology (open access)
Astrobiology
