Dielectric response of ice grown from dilute sulfate solutions
and ATM 89-21289 to New Mexico Institute of Mining and Technology.
Legrand, M., C. Feniet-Saigne, E.S. Saltzman, C. Germain, N.I. Barkov, and V.N. Petrov. 1991. Ice-core record of oceanic emissions of dimethylsulphide during the last climate cycle. Nature, 350(63 14),
References
Mulvaney, R., E.W. Wolff, and K. Oates. 1988. Sulphuric acid at grain boundaries in antarctic ice. Nature, 33 1(6153), 247-249. Whung, P.-Y., E.S. Saltzman, M.J. Spencer, P.A. Mayewski, and N. Gundestrup. 1994. A two hundred year record of biogenic sulfur in a south Greenland ice core (20D). Journal of Geophysical Research,
144-146.
Gross, G.W., P.M. Wong, and K. Humes. 1977. Concentration dependent solute redistribution at the ice-water phase boundary. III. Spontaneous convection. Chloride solutions. Journal of Chemical Physics, 67(11), 5264-5274.
99(D1), 1147-1156.
Dielectric response of ice grown from dilute sulfate solutions and ROBERT K. SvEC, Department of Geoscience, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801 PAI-YEI WHUNG, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida 33149-1098 GERARDO W. GROSS
ulfate (H2SO4) in polar ice reflects atmospheric circulation S patterns at the time of deposition; if related to specific volcanic events, it can date ice layers. Electrical conductivity measurement (ECM) and dielectric profiling (DEP) techniques provide a rapid means for logging the distribution of sulfate (and other aerosols) in ice cores (Moore, Paren, and Oerter 1992). The present work aims at obtaining baseline data on dielectric response of sulfate in ice columns (=20-25 centimeters (cm), 4=3.8 cm] grown in the laboratory under quasiequilibrium conditions. Trapping of solute in grain boundaries is minimized by continuous stirring of the melt. For sulfate concentration and electrical measurements, the columns were sliced in approximately 1.5-cm increments. On selected [10-13-millimeter (mm) thick] slices dielectric relaxation is measured at 31 frequencies in the range 1 hertz to 100 kilohertz at 13 temperatures between -1°C and -85°C. A linear blocking layer, that is, a 0.13-mm thick foil of a dielectric low-loss material (Teflon) is inserted between each electrode and the sample. With linear blocking layers, electrode reaction effects are suppressed and replaced with a constant series capacitance (Gross and McGehee 1988). Inversion of the data yields ice parameters uncontaminated by electrode effects. In the figures, three dielectric relaxation parameters (principal relaxation time, high-frequency conductivity, and static or direct-current conductivity), measured on six ice samples of different sulfate concentrations, are plotted against reciprocal absolute temperature (Arrhenius plots).
5
4
[C] 0 U)
C) 0 -J
2
The principal relaxation time the principal relaxation time (figure 1), is the characteristic response time of ice molecules reorienting themselves in an electric field. t2 is dependent on both temperature and solute concentration. For pure ice, it falls on the solid line, but it is depressed when, with decreasing temperature, "extrinsic" interactions of solute molecules with the ice dipoles become dominant. Three such extrinsic effects are observed in figure 1:
3.54 4.5 5 5.5 6 Figure 1. Arrhenius plot of the principal relaxation time, t2. Ice samples (starting with sample number 187010) grown, respectively, from 10-1 N (approximately 4,900 ppm sulfate), 10-2 N, 10- N, and 10- 4 N H 2 SO 4; 2 and 400-2 N (NH 4 ) 2SO4 solutions. Concentrations are expressed in units of gram-equivalent weight per liter of solution (N) or in parts per million (ppm) of melted ice.
ANTARCTIC JOURNAL - REVIEW 1994 75
• A gradual departure from the pure ice locus at temperatures below -40°C characterizes samples grown from the three more dilute H2SO4 solutions. • Sample 187010, grown from the most highly concentrated solution [10- 1 normal (M], exhibits an abrupt slope reversal around -24°C, followed by a renewed more gradual rise of the relaxation time; this pattern could be indicative of solute trapped in grain boundaries. In crystal growth from the liquid, solute trapping commonly occurs with a transition from a smooth to a rough interface. Scanning electron microscopy of a sample grown from a similar concentration has, indeed, shown prominent grain-boundary segregation of solute. • The two ammonium sulfate samples show a much higher sulfate content and a strong extrinsic response throughout the whole temperature range. We attribute these findings to the ease with which the polar ammonium ion (in contrast with other common cations) forms hydrogen bonds binding sulfate (and other anions) to the ice-crystal lattice. As seen in these examples, dielectric response is not only determined by solute concentration: just as important is the distribution pattern of solute molecules in the ice matrix, and their structural relationships to the crystal lattice.
-5
0C-30 -50 -80 Sulfate in ice [ppm] H2SO4 # 187010 • 0.129 0.192 #187014 0.014 # 187022 # 187026 ® 0.018 A
-6
Im
(NH4)2SO4 # 187046 18 #186092 8.16 [7
-8
'A
-ic
3.5 4 4.5 5 5.5 1 000IT [1(1]
Figure 2. Arrhenius plot of the high-frequency conductivity, oc,, for the sulfate samples of figure 1. -6
The high -frequency conductivity the high-frequency (hO conductivity (figure 2), represents dielectric losses associated with dipole relaxation, plus a contribution, generally minor, from the static, or direct current, conductivity (see below). The three extrinsic effects discussed above find their expression in an increase of the hf conductivity as compared to pure ice. (In figure 2, the pure ice values are well represented by curves 187022 /026).
-7
-8
Static conductivity he static, or direct-current, conductivity (figure 3), 00, is a T true conductivity, that is, it represents losses associated with the transport of net charge (protons) through the ice. Figure 3 shows that only in sample 187010, H2SO4 has contributed appreciably to the proton population; in all others, the static conductivity is comparable with or even lower than that which would have been measured in pure ice. By comparing figure 2 with figure 3, it can be seen that the hf conductivity of sample 187010 contains an appreciable ao component (from 16 to 27 percent depending on temperature), perhaps representing conduction through grain boundaries. By contrast, the large hf conductivity of the ammonium sulfate samples is paired with a reduced direct current conductivity. This reduction bears resemblance to the sharp decrease of ° observed in preHolocene ice cores where it is due to their increased (calcium and magnesium) alkalinity. The ECM method, used in ice-core logging, yields a qualitative index of (Jo. Ice grown from methanesulfonic acid solutions of similar concentrations and from their ammonium salt showed only slight departures from pure ice response because uptake into the ice matrix was much lower than that of sulfate. Important contributions to this work are electronmicrographs of sulfate-doped ice samples by Joan Fitzpatrick (U.S. Geological Survey, Denver) and Michael Lilly (U.S. Geological
-10
-11
3.5 4 4.5 5 5.5 1000/T (1(1
Figure 3. Arrhenius plot of the static (direct current) conductivity, 00, for the sulfate samples of figure 1. Survey, Fairbanks). Richard B. Alley (Pennsylvania State University) performed grain-size analysis. These results will be discussed in future papers. This research was supported by National Science Foundation grant ATM 89-21289.
References Gross, G.W., and R.M. McGehee. 1988. The layered-capacitor method for bridge measurements of conductive dielectrics. IEEE Transactions on Electrical Insulation, 23(3), 387-396.
Moore, J., J. Paren, and H. Oerter. 1992. Sea salt dependent electrical conduction in polar ice. Journal of Geophysical Research, 97(B13), 19803-19812.
ANTARCTIC JOURNAL - REVIEW 1994 76
Legrand, M., C. Feniet-Saigne, E.S. Saltzman, C. Germain, N.I. Barkov, and V.N. Petrov. 1991. Ice-core record of oceanic emissions of dimethylsulphide during the last climate cycle. Nature, 350(63 14),
References
Mulvaney, R., E.W. Wolff, and K. Oates. 1988. Sulphuric acid at grain boundaries in antarctic ice. Nature, 33 1(6153), 247-249. Whung, P.-Y., E.S. Saltzman, M.J. Spencer, P.A. Mayewski, and N. Gundestrup. 1994. A two hundred year record of biogenic sulfur in a south Greenland ice core (20D). Journal of Geophysical Research,
144-146.
Gross, G.W., P.M. Wong, and K. Humes. 1977. Concentration dependent solute redistribution at the ice-water phase boundary. III. Spontaneous convection. Chloride solutions. Journal of Chemical Physics, 67(11), 5264-5274.
99(D1), 1147-1156.
Dielectric response of ice grown from dilute sulfate solutions and ROBERT K. SvEC, Department of Geoscience, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801 PAI-YEI WHUNG, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida 33149-1098 GERARDO W. GROSS
ulfate (H2SO4) in polar ice reflects atmospheric circulation S patterns at the time of deposition; if related to specific volcanic events, it can date ice layers. Electrical conductivity measurement (ECM) and dielectric profiling (DEP) techniques provide a rapid means for logging the distribution of sulfate (and other aerosols) in ice cores (Moore, Paren, and Oerter 1992). The present work aims at obtaining baseline data on dielectric response of sulfate in ice columns (=20-25 centimeters (cm), 4=3.8 cm] grown in the laboratory under quasiequilibrium conditions. Trapping of solute in grain boundaries is minimized by continuous stirring of the melt. For sulfate concentration and electrical measurements, the columns were sliced in approximately 1.5-cm increments. On selected [10-13-millimeter (mm) thick] slices dielectric relaxation is measured at 31 frequencies in the range 1 hertz to 100 kilohertz at 13 temperatures between -1°C and -85°C. A linear blocking layer, that is, a 0.13-mm thick foil of a dielectric low-loss material (Teflon) is inserted between each electrode and the sample. With linear blocking layers, electrode reaction effects are suppressed and replaced with a constant series capacitance (Gross and McGehee 1988). Inversion of the data yields ice parameters uncontaminated by electrode effects. In the figures, three dielectric relaxation parameters (principal relaxation time, high-frequency conductivity, and static or direct-current conductivity), measured on six ice samples of different sulfate concentrations, are plotted against reciprocal absolute temperature (Arrhenius plots).
5
4
[C] 0 U)
C) 0 -J
2
The principal relaxation time the principal relaxation time (figure 1), is the characteristic response time of ice molecules reorienting themselves in an electric field. t2 is dependent on both temperature and solute concentration. For pure ice, it falls on the solid line, but it is depressed when, with decreasing temperature, "extrinsic" interactions of solute molecules with the ice dipoles become dominant. Three such extrinsic effects are observed in figure 1:
3.54 4.5 5 5.5 6 Figure 1. Arrhenius plot of the principal relaxation time, t2. Ice samples (starting with sample number 187010) grown, respectively, from 10-1 N (approximately 4,900 ppm sulfate), 10-2 N, 10- N, and 10- 4 N H 2 SO 4; 2 and 400-2 N (NH 4 ) 2SO4 solutions. Concentrations are expressed in units of gram-equivalent weight per liter of solution (N) or in parts per million (ppm) of melted ice.
ANTARCTIC JOURNAL - REVIEW 1994 75
• A gradual departure from the pure ice locus at temperatures below -40°C characterizes samples grown from the three more dilute H2SO4 solutions. • Sample 187010, grown from the most highly concentrated solution [10- 1 normal (M], exhibits an abrupt slope reversal around -24°C, followed by a renewed more gradual rise of the relaxation time; this pattern could be indicative of solute trapped in grain boundaries. In crystal growth from the liquid, solute trapping commonly occurs with a transition from a smooth to a rough interface. Scanning electron microscopy of a sample grown from a similar concentration has, indeed, shown prominent grain-boundary segregation of solute. • The two ammonium sulfate samples show a much higher sulfate content and a strong extrinsic response throughout the whole temperature range. We attribute these findings to the ease with which the polar ammonium ion (in contrast with other common cations) forms hydrogen bonds binding sulfate (and other anions) to the ice-crystal lattice. As seen in these examples, dielectric response is not only determined by solute concentration: just as important is the distribution pattern of solute molecules in the ice matrix, and their structural relationships to the crystal lattice.
-5
0C-30 -50 -80 Sulfate in ice [ppm] H2SO4 # 187010 • 0.129 0.192 #187014 0.014 # 187022 # 187026 ® 0.018 A
-6
Im
(NH4)2SO4 # 187046 18 #186092 8.16 [7
-8
'A
-ic
3.5 4 4.5 5 5.5 1 000IT [1(1]
Figure 2. Arrhenius plot of the high-frequency conductivity, oc,, for the sulfate samples of figure 1. -6
The high -frequency conductivity the high-frequency (hO conductivity (figure 2), represents dielectric losses associated with dipole relaxation, plus a contribution, generally minor, from the static, or direct current, conductivity (see below). The three extrinsic effects discussed above find their expression in an increase of the hf conductivity as compared to pure ice. (In figure 2, the pure ice values are well represented by curves 187022 /026).
-7
-8
Static conductivity he static, or direct-current, conductivity (figure 3), 00, is a T true conductivity, that is, it represents losses associated with the transport of net charge (protons) through the ice. Figure 3 shows that only in sample 187010, H2SO4 has contributed appreciably to the proton population; in all others, the static conductivity is comparable with or even lower than that which would have been measured in pure ice. By comparing figure 2 with figure 3, it can be seen that the hf conductivity of sample 187010 contains an appreciable ao component (from 16 to 27 percent depending on temperature), perhaps representing conduction through grain boundaries. By contrast, the large hf conductivity of the ammonium sulfate samples is paired with a reduced direct current conductivity. This reduction bears resemblance to the sharp decrease of ° observed in preHolocene ice cores where it is due to their increased (calcium and magnesium) alkalinity. The ECM method, used in ice-core logging, yields a qualitative index of (Jo. Ice grown from methanesulfonic acid solutions of similar concentrations and from their ammonium salt showed only slight departures from pure ice response because uptake into the ice matrix was much lower than that of sulfate. Important contributions to this work are electronmicrographs of sulfate-doped ice samples by Joan Fitzpatrick (U.S. Geological Survey, Denver) and Michael Lilly (U.S. Geological
-10
-11
3.5 4 4.5 5 5.5 1000/T (1(1
Figure 3. Arrhenius plot of the static (direct current) conductivity, 00, for the sulfate samples of figure 1. Survey, Fairbanks). Richard B. Alley (Pennsylvania State University) performed grain-size analysis. These results will be discussed in future papers. This research was supported by National Science Foundation grant ATM 89-21289.
References Gross, G.W., and R.M. McGehee. 1988. The layered-capacitor method for bridge measurements of conductive dielectrics. IEEE Transactions on Electrical Insulation, 23(3), 387-396.
Moore, J., J. Paren, and H. Oerter. 1992. Sea salt dependent electrical conduction in polar ice. Journal of Geophysical Research, 97(B13), 19803-19812.
ANTARCTIC JOURNAL - REVIEW 1994 76
