experiments

getting my hands dirty

most of my experiments involve ice, or icy materials, so i spend a lot of time in the ice physics lab in earth sciences at ucl. here i can prepare samples to my heart’s content, without worrying about accidental melting, although this does invariably mean wearing a big green balaclava most of the day.

i’m interested in planetary ices, so this involves ice at low temperatures (and high pressures for icy moon interiors), and hydrated and hydrous minerals. i’m particularly interested in hydrated sulfate minerals, both on mars and in the icy moons. my experiments can be split onto two main categories: mechanical properties and diffusion.

the results of these experiments feed directly back into the modelling, and are constrained by observations.

mechanical properties

the goal of these experiments is to better understand the mechanical properties of materials that occur on mars and the icy moons. i use three main ways of conducting these experiments, by using equipment here at ucl, and also at the rutherford appleton laboratory. most of my time at the moment is spent preparing samples and setting up the uniaxial and triaxial rigs for running low-temperature experiments.

the main aim of using the triaxial deformation cells is to better understand the roles that different parameters such as temperature, pressure, grain size and growth and strain rate have on the rheology of ice and other condensed volatile materials. have a look at the paper by durham and stern (2001) for a nice introduction to the complexities of ice rheology.

the uniaxial cell is our workhorse, and with the environmental chamber fitted, is capable of very low temperatures. the main advantage of this equipment is the ability to perform cyclic loading tests in order to quantify the evolution of the elastic moduli, while also monitoring the acoustic emission.

diffusion

the goal of these experiments is to determine the rate of diffusive exchange between the surface and atmosphere of mars. i’m particularly interested in understanding the exchange of water vapour, and how the rate of diffusion has changed over time. it is the rate of diffusion that controls whether the martian surface and atmosphere are in equilibrium at timescales ranging from tens of thousands, to hundreds of millions of years.

during my current fellowship i have designed and built the vacuum system and the monitoring set-up, so that i can measure the mass, temperature, and humidity of four different samples at the same time. this method means that i can carry out four simultaneous experiemnts for a single pump-down, which comes in handy. the kit is working well and has been calibrated at room temperature, and i’m currently running tests looking at the low-pressure-driven precipitation of sulfates, and whether it (1) causes significant rock damage, and (2) causes a significant changes in the diffusion coefficient.
[image_frame style=”framed_shadow” title=”ice and hydrate diffusion” align=”left” height=”179″ width=”one_half”]http://petergrindrod.net/wp-content/uploads/2011/11/exp_timescales.jpg[/image_frame]

have a look at my publications page for details of experiments, there should be more there in the future.