Investigation of nucleation processes during dynamic recrystallization of ice using cryo-EBSD.

Nucleation mechanisms occurring during dynamic recrystallization play a crucial role in the evolution of microstructures and textures during high temperature deformation. In polycrystalline ice, the strong viscoplastic anisotropy induces high strain heterogeneities between grains which control the recrystallization mechanisms. Here, we study the nucleation mechanisms occurring during creep tests performed on polycrystalline columnar ice at high temperature and stress (T=-5°C;σ=0.5 MPa) by post-mortem analyses of deformation microstructures using cryogenic electron backscatter diffraction. The columnar geometry of the samples enables discrimination of the nuclei from the initial grains. Various nucleation mechanisms are deduced from the analysis of the nuclei relations with the dislocation sub-structures within grains and at grain boundaries. Tilt sub-grain boundaries and kink bands are the main structures responsible for development of polygonization and mosaic sub-structures. Nucleation by bulging at serrated grain boundaries is also an efficient nucleation mechanism near the grain boundaries where strain incompatibilities are high. Observation of nuclei with orientations not related to the 'parent' ones suggests the possibility of 'spontaneous' nucleation driven by the relaxation of the dislocation-related internal stress field. The complexity of the nucleation mechanisms observed here emphasizes the impact of stress and strain heterogeneities on dynamic recrystallization mechanisms.This article is part of the themed issue 'Microdynamics of ice'.

Swelling of hydrocolloid dressings.

Wound healing is promoted by dressings that maintain a moist environment. Specifically, hydrocolloid dressings allow excess fluid to escape without permitting wound desiccation. However, the fluid handling capacity of hydrocolloid dressings depends on many factors such as the physicochemical properties of the gel formulation, and the design of the dressing. We measured the moisture uptake kinetics of different hydrocolloid dressings by placing the gel side of a sample in contact with water. The time evolution of the thickness was measured by means of a video camera linked to a computer. The theory of Tanaka and Fillmore (1979) was used to predict the kinetics of uniaxial swelling of a cylindrical gel sample. The model allows to associate to an experimental curve a total thickness increase hf-h0 (where hf and h0 are respectively the final and initial thickness) and a characteristic time tau. The model also relates hf-h0 and tau to the physiochemical composition of the dressing, and to the initial thickness h0. The influence of h0 is discussed by means of experiments performed on dressings with different initial thickness.