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Some unusual ice nucleating materials
Some Unusual Ice Nucleating Materials Following work which was carried out earlier in the Soviet Union (1), Ramachandra Murty and Ramana Murty recently examined bulk nucleation thresholds of freshly prepared cement (2) and confirmed its excellent properties. They elaborated on that subject at a later date (3) when they reported on the nucleation activities of fresh quicklime, brick powder, and C a S O 4 " 1/2H~O; they suggested that hydration of those materials influence their thresholds of nucleation. This observation appears to be of considerable interest since it was also recently found that the well-known activity of phloroglucinol (4-7) considerably decreases with hydration (8). Ramachandra Murty and Ramana Murty also suggested (3) that the activity of A12S3 whose ice-forming properties (threshold of about -3.5°C) were long ago discovered in our laboratory (9) and which, together with some other materials, was used for purposes of a hail-suppression experiment (10), was also due to hydration effects. Some of the above work appears to gain practical importance because of earlier studies by Ludlam which indicated that an enrichment, at the cloud level, of a giant condensation nuclei population, could lead to a decrease of both hail occurrences and surface damage per hailstrike (11, 12). Also, Hallett and Mossop (13, 14) recently discovered that a copious production of ice splinters occurs at relatively low undercoolings (-5°C) by riming on falling graupel particles. This phenomenon appears to account for the high ratio between ice crystals within and ice nuclei around a cloud which occurs when the diameter of the cloud drops is of about 20 /z. Clearly, the ice splinters thus formed act in turn within the cloud as further centers for the freezing of supercooled water. Apart from the well known attributes which giant condensation nuclei may thus bear in precipitation phenomena, this mechanism would evidently call some more for the use of those giant nuclei in weather modification studies in order to increase populations of those 20-/z drops. These nuclei should obviusly be both efficient and inexpensive and, in case they also were ice-forming, their lifetimes should be long enough in order to enable them to act readily On a cloud system, but also sufficiently short in order to inhibit undesirable effects downwind from the target area. Hence, unlike in the case of silver iodide, after a suitable period of time has elapsed the ice-forming activity of those nuclei should be permanently destroyed. Both, AIzS3 and some of the materials mentioned by Ramachandra Murty and Ramana Murty obviously do meet those prerequisites. 383 Journal of Colloid and Interface Science, Vol. 64, No. 2, April 1978
S o m e Experiments on the Bulk-Contact Nucleation o f Ice Unless otherwise stated distilled water which by itself froze below -15°C, and Merck's reagent-purity chemicals were used "as received" and the experimental assembly and related techniques were as previously described (15-16). (i) Aluminum sulfide. This compound was prepared from "sublimed and washed" sulfur powder and powdered aluminum metal -270 mesh ASTM, both of which were made by the "Carlo E R B A " Co., Milan. Twenty-gram aliquots of mixtures, containing a 10% excess of metal with respect to stoichiometry, were made to react in porcelain or quartz crucibles which, in turn, were imbedded in sand. These mixtures were ignited using freely burning magnesium ribbons. They reacted according to the well-known process: 2 A1 + 3 S~AI~S3;
AHf =
-121.6 kcal/mole.
[1]
The resulting slag was allowed to cool and was ground under dry nitrogen in an agate mortar. The - 1 5 0 mesh fraction was stored in closed vials until used since aluminum sulfide is known to hydrolyze slowly, spontaneously, and exothermally in moist air according to: A12S3 + 6 H 2 0 ~ 2
AI(OH)3 + 3 H2S; A H - - -100 kcal.
[2]
The drops were seeded at - I ° C ; experiments on ice nucleation were carried out under both tungsten and UV illumination. No statistically significant differences were found between the results of these two series. On the basis of twelve cumulative experiments, thresholds of - 3 . 8 __+0.2°C were obtained for this material. We have found, however, that the use of "freshly prepared" sulfide yielded a significantly more active product: six " a d hoc" preparations gave, in fact, glaciation thresholds of -3.1 -+ 0.2°C. Blank tests using hydrolyzed material failed to show nucleation at above -10°C; the nucleation events obeyed patterns outlined in our earlier work, as substantiated by the example shown in Fig. 1 and also by a rms linear correlation coefficient between the Y-X parameters of those 18 lines, of 0.95. Those results are in agreement with earlier work from our laboratory (9) where nucleation thresholds of -3.5°C were obtained by a less precise method using the same material. Solid, insoluble A12S3 is known to react spontaneously but slowly with water 0021-9797/78/0642-0383502.00/0 Copyright © 1978 by Academic Press, Inc. All rights of reproduction in any form reserved.
384
NOTES oct"+ O , 10-2 e\ I
3.
4.
-1..
-2.
For practical purposes zinc, and not magnesium, possesses the attributes of a good ice-forming substance as long as the inevitable oxide coating of its surface is suitably removed. Zinc also is another example of a material which nucleates ice while a chemical reaction occurs on it surface. ACKNOWLEDGMENTS The technical assistance of Messrs. C. Luttazzi and E. Evangelisti is hereby gratefully acknowledged.
FIG. l. Typical plot of freezing events according to Eq. [5], Ref. (15) at cooling parameters of Eq. [2], Ref. (15): A = 100.22; n = 1.61. Bars indicate spans of practically contemporaneous events of number indicated; dots stand for single occurrences. Line was fitted to single experimental values.
Whereby substantial amounts of energy are released and whereby overcoming of the energy barrier to nucleation on a metallic sulfide may be favored (16). Because of its high heat of formation it also is easy to disperse in the atmosphere as giant nuclei. A point of interest consists of the fact that, in the case of AlaSz, ice nucleation thus occurs in a chemically reacting system whereby fresh surface sites are regenerated until the sulfide particulates are " s p e n t . " A test, on whether glaciation could have merely been due to the evolution of gas from surfaces of these reacting solids, was separately carried out using the same experimental method. Droplets were seeded with powdered calcium carbonate or with calcium sulfite which was obtained from solutions of chloride by precipitation with aqueous Na2SO3. Careful addition, at temperatures of -5°C, of small amounts of either 10-~ N H2SO4 or HC1, followed by cooling to -10°C, yielded no freezing events despite detectable gas evolution from these solids, (ii) Zinc metal. As an attempt to apply to metallic zinc some of the lines of thought which were put forth by Fukuta (17), we have tested qualitatively this finely powdered substance on both, a greased copper cold stage and a greased glass stage. No ice nucleation occurred above -10°C. However, when 10-2 N sulfuric, hydrochloric, or acetic acid was used instead of distilled water, the drops nucleated readily with onset temperatures of -4.8°C. No nucleation occurred above -10°C in alkaline solutions of the same concentration where the formation of hydroxides and zincates could have been expected to contaminate the surface. Also, no nucleation occurred at these experimental conditions when using magnesium metal.
Journal of Colloid and Interface Science, Vol. 64, No. 2, April 1978
REFERENCES 1. Battan, L. J., Bull. Amer. Meteorol. Soc. 50, 924 (1969). 2. Ramachandra Murty, A. S. and Ramana Murty, Bh.V., Tellus 24, 581 (1972). 3. Ramachandra Murty, A. S. and Ramana Murty, Bh. V., Riv. Ital. Geofis. 22, 287 (1973). 4. Bashkirova, G. M. and Krasikow, P. N., T. GI. Geofiz. Observ. 72, 118 (1957). 5. Langer, G., Rosinski, J. and Bernsen, S., J. Atmos. Sci. 20, 557 (1963). 6. Braham, R. R., Jr., J. Atmos. Sci. 20, 563 (1963). 7. Fukuta, N., J. Atmos. Sci. 23, 191 (1966). 8. Piotrovich, V. V., Meterol. Gidrol. 6, 111 (1975). 9. Montefinale, A. C., Zawidzki, T. W., Petriconi, G. L. and Papee, H. M.,Ric. Sci. (Rome) 39, 843 (1969). 10. Gori, E. G., Petriconi, G. L., Montefinale, A. C. and Papee, H. M., Pure Appl. Geophys. 99, 230 (1972). 11. Ludlam, F. H., Nubila 1, 12 (1958). 12. Ludlam, F. H., Nubila 2, 7 (1959). 13. Hallett, J. and Mossop, S. C., Nature 249, 26 (1974). t4. Mossop, S. C. and Hallett, J., Science 186, 632 (1974). 15. Montefinale, T., Montefinale, A. C. and Papee, H. M., J. Colloid Interface Sci. 54, 409(1976). 16. Montefinale, T. and Pape¢, H. M., J. Colloid Interface Sci. 59, 337 (1977). 17. Fukuta, N., J. Meteorol. 15, !7 (1958). Z. MONTEFINALE
H. M. PAPEE
Laboratorio Nucleazione Aerosoli, CNR Via Vettore 4 (Monte Sacro) 00141 Roma, Italy Received June 25, 1977; accepted September 15, 1977
S o m e Experiments on the Bulk-Contact Nucleation o f Ice Unless otherwise stated distilled water which by itself froze below -15°C, and Merck's reagent-purity chemicals were used "as received" and the experimental assembly and related techniques were as previously described (15-16). (i) Aluminum sulfide. This compound was prepared from "sublimed and washed" sulfur powder and powdered aluminum metal -270 mesh ASTM, both of which were made by the "Carlo E R B A " Co., Milan. Twenty-gram aliquots of mixtures, containing a 10% excess of metal with respect to stoichiometry, were made to react in porcelain or quartz crucibles which, in turn, were imbedded in sand. These mixtures were ignited using freely burning magnesium ribbons. They reacted according to the well-known process: 2 A1 + 3 S~AI~S3;
AHf =
-121.6 kcal/mole.
[1]
The resulting slag was allowed to cool and was ground under dry nitrogen in an agate mortar. The - 1 5 0 mesh fraction was stored in closed vials until used since aluminum sulfide is known to hydrolyze slowly, spontaneously, and exothermally in moist air according to: A12S3 + 6 H 2 0 ~ 2
AI(OH)3 + 3 H2S; A H - - -100 kcal.
[2]
The drops were seeded at - I ° C ; experiments on ice nucleation were carried out under both tungsten and UV illumination. No statistically significant differences were found between the results of these two series. On the basis of twelve cumulative experiments, thresholds of - 3 . 8 __+0.2°C were obtained for this material. We have found, however, that the use of "freshly prepared" sulfide yielded a significantly more active product: six " a d hoc" preparations gave, in fact, glaciation thresholds of -3.1 -+ 0.2°C. Blank tests using hydrolyzed material failed to show nucleation at above -10°C; the nucleation events obeyed patterns outlined in our earlier work, as substantiated by the example shown in Fig. 1 and also by a rms linear correlation coefficient between the Y-X parameters of those 18 lines, of 0.95. Those results are in agreement with earlier work from our laboratory (9) where nucleation thresholds of -3.5°C were obtained by a less precise method using the same material. Solid, insoluble A12S3 is known to react spontaneously but slowly with water 0021-9797/78/0642-0383502.00/0 Copyright © 1978 by Academic Press, Inc. All rights of reproduction in any form reserved.
384
NOTES oct"+ O , 10-2 e\ I
3.
4.
-1..
-2.
For practical purposes zinc, and not magnesium, possesses the attributes of a good ice-forming substance as long as the inevitable oxide coating of its surface is suitably removed. Zinc also is another example of a material which nucleates ice while a chemical reaction occurs on it surface. ACKNOWLEDGMENTS The technical assistance of Messrs. C. Luttazzi and E. Evangelisti is hereby gratefully acknowledged.
FIG. l. Typical plot of freezing events according to Eq. [5], Ref. (15) at cooling parameters of Eq. [2], Ref. (15): A = 100.22; n = 1.61. Bars indicate spans of practically contemporaneous events of number indicated; dots stand for single occurrences. Line was fitted to single experimental values.
Whereby substantial amounts of energy are released and whereby overcoming of the energy barrier to nucleation on a metallic sulfide may be favored (16). Because of its high heat of formation it also is easy to disperse in the atmosphere as giant nuclei. A point of interest consists of the fact that, in the case of AlaSz, ice nucleation thus occurs in a chemically reacting system whereby fresh surface sites are regenerated until the sulfide particulates are " s p e n t . " A test, on whether glaciation could have merely been due to the evolution of gas from surfaces of these reacting solids, was separately carried out using the same experimental method. Droplets were seeded with powdered calcium carbonate or with calcium sulfite which was obtained from solutions of chloride by precipitation with aqueous Na2SO3. Careful addition, at temperatures of -5°C, of small amounts of either 10-~ N H2SO4 or HC1, followed by cooling to -10°C, yielded no freezing events despite detectable gas evolution from these solids, (ii) Zinc metal. As an attempt to apply to metallic zinc some of the lines of thought which were put forth by Fukuta (17), we have tested qualitatively this finely powdered substance on both, a greased copper cold stage and a greased glass stage. No ice nucleation occurred above -10°C. However, when 10-2 N sulfuric, hydrochloric, or acetic acid was used instead of distilled water, the drops nucleated readily with onset temperatures of -4.8°C. No nucleation occurred above -10°C in alkaline solutions of the same concentration where the formation of hydroxides and zincates could have been expected to contaminate the surface. Also, no nucleation occurred at these experimental conditions when using magnesium metal.
Journal of Colloid and Interface Science, Vol. 64, No. 2, April 1978
REFERENCES 1. Battan, L. J., Bull. Amer. Meteorol. Soc. 50, 924 (1969). 2. Ramachandra Murty, A. S. and Ramana Murty, Bh.V., Tellus 24, 581 (1972). 3. Ramachandra Murty, A. S. and Ramana Murty, Bh. V., Riv. Ital. Geofis. 22, 287 (1973). 4. Bashkirova, G. M. and Krasikow, P. N., T. GI. Geofiz. Observ. 72, 118 (1957). 5. Langer, G., Rosinski, J. and Bernsen, S., J. Atmos. Sci. 20, 557 (1963). 6. Braham, R. R., Jr., J. Atmos. Sci. 20, 563 (1963). 7. Fukuta, N., J. Atmos. Sci. 23, 191 (1966). 8. Piotrovich, V. V., Meterol. Gidrol. 6, 111 (1975). 9. Montefinale, A. C., Zawidzki, T. W., Petriconi, G. L. and Papee, H. M.,Ric. Sci. (Rome) 39, 843 (1969). 10. Gori, E. G., Petriconi, G. L., Montefinale, A. C. and Papee, H. M., Pure Appl. Geophys. 99, 230 (1972). 11. Ludlam, F. H., Nubila 1, 12 (1958). 12. Ludlam, F. H., Nubila 2, 7 (1959). 13. Hallett, J. and Mossop, S. C., Nature 249, 26 (1974). t4. Mossop, S. C. and Hallett, J., Science 186, 632 (1974). 15. Montefinale, T., Montefinale, A. C. and Papee, H. M., J. Colloid Interface Sci. 54, 409(1976). 16. Montefinale, T. and Pape¢, H. M., J. Colloid Interface Sci. 59, 337 (1977). 17. Fukuta, N., J. Meteorol. 15, !7 (1958). Z. MONTEFINALE
H. M. PAPEE
Laboratorio Nucleazione Aerosoli, CNR Via Vettore 4 (Monte Sacro) 00141 Roma, Italy Received June 25, 1977; accepted September 15, 1977