On the Preparation and Sintering of Cloud Precipitating Agents. Lead Di-Iodide Microcrystals

Papée, Henry M.

doi:10.1139/v58-213

Cited by 5 publications

(3 citation statements)

References 7 publications

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“…refs. 1, 2, 3, 4, 5) must invariably result in partial alteration of the salt (8). I t is thought therefore that a brief discussioil of the results obtained in this series is justified, since it might be helpful towards further studies of the subject.…”

Section: Pi (S-s)mentioning

confidence: 75%

“…The decrease of lead iodide surface with time upon hydration has been show11 previously (8) to follow a first-order pattern according to the equation…”

Section: Time (Hours)mentioning

confidence: 99%

“…Pure lead di-iodide of large specific surface areas was prepared by a method previously described, and the specific areas of the product were changed, when required, by heating (8).…”

Section: Reagentsmentioning

confidence: 99%

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Microcalorimetry of Adsorption of Water Vapor on Lead Di-Iodide

Papée¹

1959

Can. J. Chem.

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Using a microcalorimeter of the Calvet type, measurements of the total heat of adsorption of water vapor on microcrystals of lead di-iodide have been made. By comparing the results obtained with those relating to the kinetic process of surface sintering by water vapor, heats for the process of sintering were calculated. The same sintering characteristics were found for preheated and unheated samples, but it was found that the heated product adsorbs more water than the original salt. Qualitative esperi~nents on lead mono-iodide show a different pattern of heat evolution \vitIi time, and the over-all process requires more water to reach completion than in the case of di-iodide. The heats evolved are n1~1ch greater, probably partly due to the reaction of water with the surface. INTRODUCTIONThe activity of lead iodide crystals towards ice nucleation and cloud precipitation (1, 2, 3, 4, 5) has recently resulted in studies with the object of gaining insight illto the mechanism of the process. Much information was obtained by Birstein (6), who studied the process using conventional adsorption techniques and established that a considerable number of layers of water molecules can be formed on lead iodide particles. A study of the phenomenon by use of microcalorimetry was attempted in this laboratory under a U.S.A.F. contract, with the object of directly measuring the energies of the steps involved. EXPERIMENTAL ApparatusA microcalorimeter of the Tian-Calvet type was used, and the general pattern of the experimentation followed closely t h a t used recently in this laboratory for the study of the process of adsorption of water vapor on sodium chloride microcrystals (7). ReagentsPure lead di-iodide of large specific surface areas was prepared by a method previously described, and the specific areas of the product were changed, when required, by heating (8). ProcedureThree series of experiments* were carried out as follows: Series 1.-In this series of measurements, the microcalorimetry was carried out using different amounts of salt originating from a batch product of an initial surface area of 2.05 m2/g. The original material was never heated above 25' C.Series 2.-The work was done on samples of different specific surface areas. These were obtained by heating the original product under vacuum.Series %-Two measurements were carried out on samples of lead tnono-iodide. This product was obtained from the di-iodide by thermal decompositio~l a t 240' C under dry nitrogen and a t atmospheric pressure. The product obtained in this way had been outgassed by pumping it t o a high vacuum for several days a t 25' C.

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Section: Pi (S-s)mentioning

confidence: 75%

“…The decrease of lead iodide surface with time upon hydration has been show11 previously (8) to follow a first-order pattern according to the equation…”

Section: Time (Hours)mentioning

confidence: 99%