CoPhyLab Cryogenic Granular Sample Production, Storage and Quantification

One of the most important analogue materials for comet simulation experiments are micrometer-sized water ice particles. In the framework of the CoPhyLab project we developed a system to produce and to securely store this material in large amounts for laboratory experiments. First, the ice is produced by spraying micrometer-sized water ice droplets into liquid nitrogen. This is achieved by using a piezo nebulizer placed in distilled water. The vibration of the piezo leads to the formation of a cloud of micrometer-sized water droplet. A gas stream is used to push the droplets into a dewar, filled with liquid nitrogen, where the particles freeze. This procedure leads to the formation of the micrometer-sized ice particles. The filling height inside the dewar is controlled by a valve system and hence the machine can run automatically. The production rate of the ice producer is ~200 g of ice per hour. Second, the liquid nitrogen must be removed while the ice remains cold to avoid sintering. Therefore, the mixture is placed in a cooled stainless-steel tube, which is placed in a cryogenic desiccator. The desiccator is a cylindrical vacuum chamber with a cooling system inside, which keeps the stainless-steel tube below 110 K. The nitrogen is removed by evacuating the chamber to a pressure of 10-6 mbar while constantly stirring the mixture. The result is a dry water ice powder composed of the individual micrometer-sized particles. The consistency of this ice can be described as powdered sugar. After the ice is dried it can be stored inside the desiccator or in cryogenic transport canes, which enables the transport even by plane to other laboratories. The ice particles were investigated with a cryogenically cooled scanning electron microscope at the Christian-Albrechts-University in Kiel. The results are showing that the ice is not altered at any point of the production process or during storage. The mean radius of the particles is 2.4 micrometer and 80 % of the particles are between 1.5 micrometer and 3.5 micrometer.