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Electro-osmotic core cutting
Marine Geology - Elsevier Publishing Company, Amsterdam - Printed in The Netherlands
ELECTRO-OSMOTIC CORE C U T T I N G FRANK B. CHMELIK Department of Oceanography, Texas A & M University, College Station, Texas ( U.S.A.)I
(Received February 7, 1967)
SUMMARY The application of the principlc of electro-osmosisfor cutting unconsolidated or poorly consolidated peliticsedimentary samples offersa simple means of reducing distortionduring handling in the laboratory.
INTRODUCTION By using the principle of electro-osmosis, soft pelitic samples can be cut into required shapes for various tests without the usual mechanical distortion. The time required for sample preparation is therefore significantly reduced and the validity of test data is enhanced. The necessary equipment is readily available or easily manufactured at a minimum of expense. The electro-osmotic effect should prove most helpful to anyone involved in the study of unconsolidated or poorly consolidated fine-grained sediments.
DESCRIPTION The electro-osmotic effect found in clays is by no means new, but its application in the marine geological laboratory has apparently been neglected. The theoretical aspect of electro-osmosis involves: (1) negative electrical charge on clay particles; (2) existance of an electrical double layer; (3) small-diameter interconnecting pores which act as capillary tubes throughout the clay mass; and (4) electrical potential applied across the sample. The reader is referred to VAN OLPHEN (1965) for an excellent review of electro-osmosis. In a clay mass, the interstatial fluid is forced to migrate from the positive to the negative electrodes. This effect can be used to continuously lubricate the blade of a cutting knife and thereby greatly facilitate the slicing of clay.
1
Present address: Lockheed Marine Laboratory, San Diego, Calif. ( U . S . A . ) . Marine Geol., 5 (1967) 321-325
322
~:. B. CItMELIK
It was found that the cutting characteristic of even air-dry samples was greatly improved by this method. Two types of power sources were tested. The first consisted of a wmable potential device, a transformer, and a rectifier. This combination allows a wide range of potentials but involves some expense. The second power source tested consisted of a pair of 24 V lead storage batteries. The electrodes of the individual cells were tapped so that a range of potentials could be used. This system has the advantage of being less expensive and not requiring a l I 0 V outlet for field operation. Experimentally it was found that for work in the laboratory with most clay samples (including 10 ft. long deep-sea cores) a source of 50 V at 4 A was sufficient. If the amperage was allowed to rise much above this figure, excessive heating was noted at the positive electrode resulting in some sample damage.
Fig.l. Cutting a sagital section of a soft core sample. Without using the electro-osmotic effect, the frictional drag of the knife blade causes significant shortening of the slice (A). A thinner section cut from the same core sample using the electro-osmotic effect (B) shows no shortening. The handle of the spatula, which acts as the positive electrode, can be seen extending to the right of the core sample. Marine Geol., 5 (1967) 321-325
ELECTRO-OSMOTICCORE CUTTING
323
)
;~;ii ¸II
i
............... ¸'¸'¸~¸¸¸¸'
Fig.2. The smooth blade mounted horizontally in the hacksaw frame draws a sheet of aluminum foil with it as the blade is passed through the sample. The 2 cm aluminum strip on top of the sample is the positive electrode. The sbeet of aluminum foil attached to the blade is the negative electrode. The thickness of the finished slice is regulated bythe height of the sides of the plexiglas tray containing the sample.
A n u m b e r of types of cutting devices were tried during this study. The wellknown cheese cutter operated even better when the electro-osmotic effect was applied. The difficulty with this cutter was that the two sides of the slice stuck together again as soon as the wire had passed. Most satisfactory was a 12 inch butcher knife of chrome v a n a d i u m steel. The blade was connected via a long insulated copper wire to the negative terminal of the power source. A simple spring loaded on-off electrical button was m o u n t e d on the handle (Fig. 1A, B). The positive terminal was connected to a stainless steel spatula which served as the positive electrode. The spatula, acting as the positive electrode, was placed in contact with one end of the core. The knife (negative electrode) was applied to the other end of the core. The o p t i m u m speed at which the knife could be moved was determined by "feel". The frictional drag on the knife blade increased noticeably if the knife was drawn too fast. The cut was made vertically along the centerline of the core with the knife blade inclined at 45 ° Marine Geol., 5 (1967) 321-325
324
J,. B. CHMELIK
toward the direction of travel. With this knife it was found that marine cores could be easily and cleanly cut longitudinally. Cores of even the most unconsolidated material could be sectioned into 1 mm slices with no appreciable distortion (Fig.lA, B). However, care had to be taken that the electrical circuit remained complete between the thin sediment slice and the knife, otherwise distortion occurred when the knife was withdrawn. A specific knife was designed and developed for cutting longitudinal sections suitable for radiographic studies. These sections, 1 cm or less thick, were prepared in the folllowing manner. After the core was cut in half longitudinally an appropriate length was separated (15 cm in this particular study). One half core piece was placed fiat side down in a 1 cm deep plexiglas tray. A strip of aluminum foil, 2 cm wide, was placed along the length of the top of the core to act as the positive electrode. The negative electrode was an 8 cm × 20 cm strip of aluminum foil folded along the leading edge of a flat hacksaw blade (teeth ground off and blade mounted horizontally in the frame). The electrical wire from the negative terminal was connected to the rear of the foil with a clip. Current was applied and the blade with the foil was drawn longitudinally through the core. The flat blade was kept in contact with the side of the plexiglas tray thereby governing the thickness of the slice. The blade could be drawn completely through the core leaving the foil strip separating the two portions (Fig.2). The current was turned off, the blade extracted and the top portion of the core removed by gently lifting the foil. The result was a uniformly thick, undistorted, not compressed, longitudinal section of core which required no other preparation prior to being radiographed. It was convenient to retain the undisturbed top portion of the core for reference, additional testing, and as a "replacement" in case of future damage to the prepared sample. Both of the above-mentioned methods were also used in the preparation of samples for photography. In both cases the resulting cut surface was clean and displayed a maximum amount of detail without additional "touch up." The time required for sample preparation was appreciably reduced. Additional applications of the electro-osmotic effect are currently being tested. Among these are a thin-walled cylinder for the cutting of sediment plugs for consolidometer tests, and a coring device with an electrically charged barrel (CHMELm, in preparation a, b).
ACKNOWLEDGEMENTS The author wishes to thank Dr. A. H. Bouma, Department of Oceanography, Texas A &M University, for his help and encouragement in this study.
Marine Geol., 5 (1967) 321-325
ELECTRO-OSMOTIC CORE CUTTING
325
REFERENCES
CHMELIK,F. B., in preparation a. Sample preparation for consolidometer tests. CrIMELIK,F. B., in preparation b. Electro-osmotic corer. VAN OLPt-mN, H., 1965. An Introduction to Clay Colloid Chemistry. Interscience, New York, N.Y., 301 pp.
Marine GeoL, 5 (1967) 321-325
ELECTRO-OSMOTIC CORE C U T T I N G FRANK B. CHMELIK Department of Oceanography, Texas A & M University, College Station, Texas ( U.S.A.)I
(Received February 7, 1967)
SUMMARY The application of the principlc of electro-osmosisfor cutting unconsolidated or poorly consolidated peliticsedimentary samples offersa simple means of reducing distortionduring handling in the laboratory.
INTRODUCTION By using the principle of electro-osmosis, soft pelitic samples can be cut into required shapes for various tests without the usual mechanical distortion. The time required for sample preparation is therefore significantly reduced and the validity of test data is enhanced. The necessary equipment is readily available or easily manufactured at a minimum of expense. The electro-osmotic effect should prove most helpful to anyone involved in the study of unconsolidated or poorly consolidated fine-grained sediments.
DESCRIPTION The electro-osmotic effect found in clays is by no means new, but its application in the marine geological laboratory has apparently been neglected. The theoretical aspect of electro-osmosis involves: (1) negative electrical charge on clay particles; (2) existance of an electrical double layer; (3) small-diameter interconnecting pores which act as capillary tubes throughout the clay mass; and (4) electrical potential applied across the sample. The reader is referred to VAN OLPHEN (1965) for an excellent review of electro-osmosis. In a clay mass, the interstatial fluid is forced to migrate from the positive to the negative electrodes. This effect can be used to continuously lubricate the blade of a cutting knife and thereby greatly facilitate the slicing of clay.
1
Present address: Lockheed Marine Laboratory, San Diego, Calif. ( U . S . A . ) . Marine Geol., 5 (1967) 321-325
322
~:. B. CItMELIK
It was found that the cutting characteristic of even air-dry samples was greatly improved by this method. Two types of power sources were tested. The first consisted of a wmable potential device, a transformer, and a rectifier. This combination allows a wide range of potentials but involves some expense. The second power source tested consisted of a pair of 24 V lead storage batteries. The electrodes of the individual cells were tapped so that a range of potentials could be used. This system has the advantage of being less expensive and not requiring a l I 0 V outlet for field operation. Experimentally it was found that for work in the laboratory with most clay samples (including 10 ft. long deep-sea cores) a source of 50 V at 4 A was sufficient. If the amperage was allowed to rise much above this figure, excessive heating was noted at the positive electrode resulting in some sample damage.
Fig.l. Cutting a sagital section of a soft core sample. Without using the electro-osmotic effect, the frictional drag of the knife blade causes significant shortening of the slice (A). A thinner section cut from the same core sample using the electro-osmotic effect (B) shows no shortening. The handle of the spatula, which acts as the positive electrode, can be seen extending to the right of the core sample. Marine Geol., 5 (1967) 321-325
ELECTRO-OSMOTICCORE CUTTING
323
)
;~;ii ¸II
i
............... ¸'¸'¸~¸¸¸¸'
Fig.2. The smooth blade mounted horizontally in the hacksaw frame draws a sheet of aluminum foil with it as the blade is passed through the sample. The 2 cm aluminum strip on top of the sample is the positive electrode. The sbeet of aluminum foil attached to the blade is the negative electrode. The thickness of the finished slice is regulated bythe height of the sides of the plexiglas tray containing the sample.
A n u m b e r of types of cutting devices were tried during this study. The wellknown cheese cutter operated even better when the electro-osmotic effect was applied. The difficulty with this cutter was that the two sides of the slice stuck together again as soon as the wire had passed. Most satisfactory was a 12 inch butcher knife of chrome v a n a d i u m steel. The blade was connected via a long insulated copper wire to the negative terminal of the power source. A simple spring loaded on-off electrical button was m o u n t e d on the handle (Fig. 1A, B). The positive terminal was connected to a stainless steel spatula which served as the positive electrode. The spatula, acting as the positive electrode, was placed in contact with one end of the core. The knife (negative electrode) was applied to the other end of the core. The o p t i m u m speed at which the knife could be moved was determined by "feel". The frictional drag on the knife blade increased noticeably if the knife was drawn too fast. The cut was made vertically along the centerline of the core with the knife blade inclined at 45 ° Marine Geol., 5 (1967) 321-325
324
J,. B. CHMELIK
toward the direction of travel. With this knife it was found that marine cores could be easily and cleanly cut longitudinally. Cores of even the most unconsolidated material could be sectioned into 1 mm slices with no appreciable distortion (Fig.lA, B). However, care had to be taken that the electrical circuit remained complete between the thin sediment slice and the knife, otherwise distortion occurred when the knife was withdrawn. A specific knife was designed and developed for cutting longitudinal sections suitable for radiographic studies. These sections, 1 cm or less thick, were prepared in the folllowing manner. After the core was cut in half longitudinally an appropriate length was separated (15 cm in this particular study). One half core piece was placed fiat side down in a 1 cm deep plexiglas tray. A strip of aluminum foil, 2 cm wide, was placed along the length of the top of the core to act as the positive electrode. The negative electrode was an 8 cm × 20 cm strip of aluminum foil folded along the leading edge of a flat hacksaw blade (teeth ground off and blade mounted horizontally in the frame). The electrical wire from the negative terminal was connected to the rear of the foil with a clip. Current was applied and the blade with the foil was drawn longitudinally through the core. The flat blade was kept in contact with the side of the plexiglas tray thereby governing the thickness of the slice. The blade could be drawn completely through the core leaving the foil strip separating the two portions (Fig.2). The current was turned off, the blade extracted and the top portion of the core removed by gently lifting the foil. The result was a uniformly thick, undistorted, not compressed, longitudinal section of core which required no other preparation prior to being radiographed. It was convenient to retain the undisturbed top portion of the core for reference, additional testing, and as a "replacement" in case of future damage to the prepared sample. Both of the above-mentioned methods were also used in the preparation of samples for photography. In both cases the resulting cut surface was clean and displayed a maximum amount of detail without additional "touch up." The time required for sample preparation was appreciably reduced. Additional applications of the electro-osmotic effect are currently being tested. Among these are a thin-walled cylinder for the cutting of sediment plugs for consolidometer tests, and a coring device with an electrically charged barrel (CHMELm, in preparation a, b).
ACKNOWLEDGEMENTS The author wishes to thank Dr. A. H. Bouma, Department of Oceanography, Texas A &M University, for his help and encouragement in this study.
Marine Geol., 5 (1967) 321-325
ELECTRO-OSMOTIC CORE CUTTING
325
REFERENCES
CHMELIK,F. B., in preparation a. Sample preparation for consolidometer tests. CrIMELIK,F. B., in preparation b. Electro-osmotic corer. VAN OLPt-mN, H., 1965. An Introduction to Clay Colloid Chemistry. Interscience, New York, N.Y., 301 pp.
Marine GeoL, 5 (1967) 321-325