On a New Method for Producing Aerosols

All the fundamental properties of aerosols depend on the conditions under which they are formed, and for this reason much attention is devoted to them. Nevertheless, despite the abundance of methods described in the literature for producing aerosols, until now there has existed no method that would be applicable to a wide range of substances and would yield homogeneous, highly dispersed, and stable aerosols of high concentration. Therefore the discovery of any new method is extremely important for the development of the doctrine of the aerosol state of matter.

Walton and Toms have proposed a new method for producing aerosols[^1]. Its essence consists in spraying a solution of a high-melting substance in a solvent that is at a temperature above the critical one. This is carried out as follows. A solution of the high-melting substance that it is desired to convert into the aerosol state is poured into a capillary made of thick glass (diameter 1 mm), the solution filling only part of the capillary volume. The solvent is chosen with a low critical temperature. The capillary is sealed and slowly heated until it ruptures. The temperature at which rupture of the capillary occurs must be above the critical temperature of the solvent. The vapors of the high-melting substance rapidly condense, as a result of which an aerosol is formed.

An indispensable condition for obtaining an aerosol by the method described is the homogeneity of the solution at the critical temperature of the solvent. Far from all solutions satisfy this condition; many of them, at a temperature close to the critical temperature of the solvent, partially separate into their constituent components[^2], and therefore this method is not universal.

The authors described only one case of obtaining an aerosol from an aqueous solution of potassium dichromate. The capillary ruptured at a temperature of 500° C, and the vapors of potassium dichromate condensed into smoke particles. The authors indicate that the sizes of the greater part of the aerosol particles were about 1 μ, but some reached 10 μ.

Thus the method described, although it does not solve the main difficulties in obtaining homogeneous, highly dispersed, and stable aerosols, is nevertheless very important in that it makes it possible to obtain aerosols of such high-melting substances as potassium dichromate (melting point about 1000° C), which is scarcely possible by other existing methods.

N. Smirnov

References Cited

1. W. H. Walton, B. A. Toms, Nature 159, 232—233 (1947).
2. C. H. Holder, O. Maass, Canad. J. Res. 18, 293 (1940).