Jacob Bastacky

The process of freezing and the mechanism of damage during hepatic cryosurgery

Experiments were performed to correlate the structures of liver tissue frozen during cryosurgery, liver frozen at various constant cooling rates, and unfrozen, dried normal liver. The results show that during freezing of tissue ice forms and propagates along the vascular system, expanding during freezing at low cooling rates. This expansion occurs over most of the region frozen during cryosurgery and may be one of the mechanisms of damage to tissue during cryosurgery.

OBSERVATIONS OF ICE LENS FORMATION AND FROST HEAVE IN YOUNG PORTLAND CEMENT PASTE

Abstract As part of a research program to image frozen cement past specimens, abnormal microstructural formations are seen in specimens frozen after 10-h hydration. The formations are areas of loose microstructure with aspect ratios of 6–10, which appear perpendicular to the direction of cooling in the specimen. After sublimation of the water in the specimens during the imaging process, these formations collapse, indicating that ice is instrumental to their structure. These formations coincide with longitudinal cracks in the specimen, which do not appear to be due to specimen preparation and are consistent with an internal tensile strain. The authors have hypothesized that ice lens formation and frost heave, or a similar freezing mechanism, is responsible for these microstructural features, which are seen in 10-h specimens and are absent in all other cement paste specimens. Triaxial permeability tests have also shown that the cement paste mix used in this study has a permeability at 10-h age of ∼10−6 cm/s. This permeability is similar to that of silty soil, some of the most susceptible to frost heave.

Ice in cement paste as analyzed in the low-temperature scanning electron microscope

Abstract The low-temperature scanning electron microscope (LTSEM) allows the study of ice in cement paste. Ice formed inside the large voids was studied in the LTSEM successfully during sessions of eight hours or more. The change in the void morphology due to ice sublimation was examined by allowing the specimen to warm up in a controlled fashion while the specimen was being observed in the LTSEM. In the freeze-dried state, a complex system of cracks was observed on the surface of the air void. Three main morphologies of ice in the frozen paste were observed: large single crystals partially filling the large voids, small crystals intergrown with the hydration products inside air-voids, and spheres of ice on the cement paste produced by the frozen mist collected in the Dewar preparation flask and attracted to the sample surface