Studies on Whisker of Ice Crystals

Purpose of this study is to investigate an origin of ice whisker and a mechanism of growth of its tip surface((0001))。The following results were obtained.1)We made an experimental apparatus for growth of ice whisker from the vapor phase at-80℃at lowest and for in-situ observation of grawing whisker using a refrigerator LAUDA-SK80D which was bought by this Grant.2)We succeded in growing ice whisker on(0001)substrate of PBI_2 crystal at-50[[-70°C.Its growth diction is c-axis and tip is surface is composed of 0001]A necessary condition of ice whisker growth is that screw dislocations intersect only(0001)faces of ice crystals nucleated on PbI_2substrate.4)The Growth rates R_&lt；Exp&gt；of tip surface were measured as functions of supersaturation&lt；sigma&gt；_&lt；&lt；infinite&gt；&gt；5)The experimental results were analyzed by taking into account the diffusion process of water molecules and the surface kinetic process for incorporating the molecules into crystal lattice，and it was found that the dependences on surface supersaturation of condensation coefficient and condensation as functions of disendences on surface supersaturation of tip surface supersaturation of condensation.

Purpose of this study is to investigate an origin of ice whisker and a mechanism of growth of its tip surface ((0001)). The following results were obtained.1) We made an experimental apparatus for growth of ice whisker from the vapor phase at -80゜C at lowest and for in-situ observation of grawing whisker using a refrigerator LAUDA-SK80D which was bought by this Grant.2) We succeded in growing ice whisker on (0001)substrate of PBI_2 crystal at -50[[ -70゜C. Its growth direction is c-axis and tip surface is composed of (0001) face.3) Since a probablity of growth of ice whisker was less than 1%, a necessary condition of ice whisker growth is that screw dislocations intersect only (0001) faces of ice crystals nucleated on PbI_2 substrate.4) The Growth rates R_<exp> of tip surface were measured as functions of supersaturation<sigma>_<<infinite>> 5) The experimental results were analyzed by taking into account the diffusion process of water molecules and the surface kinetic process for incorporating the molecules into crystal lattice, and it was found that the dependences on surface supersaturation of kinetic coefficient and condensation coefficient were interpreted by spiral growth with the aid of screw dislocations.