TY - JOUR
T1 - Neutron diffraction and NMR relaxation studies of structural variation and phase transformations for water/ice in SBA-15 silica
T2 - I. the over-filled case
AU - Liu, E.
AU - Dore, J. C.
AU - Webber, Beau
AU - Khushalani, D.
AU - Jähnert, S.
AU - Findenegg, G. H.
AU - Hansen, T.
PY - 2006/11/8
Y1 - 2006/11/8
N2 - Neutron diffraction and NMR relaxation measurements have been made of water/ice in SBA-15, a mesoporous silica constituting an ordered array of cylindrical mesopores of pore diameter ~86, over the temperature range 180-300K in a cooling and heating cycle. The over-filled sample shows the initial formation of hexagonal ice on the outside of the silica grains, followed by the nucleation of cubic ice inside the pores at a lower temperature. Neutron scattering profiles for the cubic ice peaks are significantly broadened and indicate a defective structure, as observed in previous experiments on ice formation in sol-gel and MCM-type silicas. Below the pore freezing temperature the intensity of the cubic ice peaks exhibit a significant increase, down to the lowest experimental temperature, indicating a reversible conversion of defective ice to ordered ice crystals. The peak profile analysis for the two ice patterns indicates a systematic variation in the position as a function of temperature, giving values of the expansion coefficients that are slightly lower than other measurements for the bulk phase. NMR results on proton relaxation as a function of temperature indicate the presence of a mobile phase for temperatures below pore freezing that supports the view that there is interconversion between brittle and plastic phases of ice. © IOP Publishing Ltd.
AB - Neutron diffraction and NMR relaxation measurements have been made of water/ice in SBA-15, a mesoporous silica constituting an ordered array of cylindrical mesopores of pore diameter ~86, over the temperature range 180-300K in a cooling and heating cycle. The over-filled sample shows the initial formation of hexagonal ice on the outside of the silica grains, followed by the nucleation of cubic ice inside the pores at a lower temperature. Neutron scattering profiles for the cubic ice peaks are significantly broadened and indicate a defective structure, as observed in previous experiments on ice formation in sol-gel and MCM-type silicas. Below the pore freezing temperature the intensity of the cubic ice peaks exhibit a significant increase, down to the lowest experimental temperature, indicating a reversible conversion of defective ice to ordered ice crystals. The peak profile analysis for the two ice patterns indicates a systematic variation in the position as a function of temperature, giving values of the expansion coefficients that are slightly lower than other measurements for the bulk phase. NMR results on proton relaxation as a function of temperature indicate the presence of a mobile phase for temperatures below pore freezing that supports the view that there is interconversion between brittle and plastic phases of ice. © IOP Publishing Ltd.
U2 - 10.1088/0953-8984/18/44/003
DO - 10.1088/0953-8984/18/44/003
M3 - Article
SN - 0953-8984
VL - 18
SP - 10009
EP - 10028
JO - Journal of Physics: Condensed Matter
JF - Journal of Physics: Condensed Matter
IS - 44
M1 - 003
ER -