HAL Id: jpa-00217086
https://hal.archives-ouvertes.fr/jpa-00217086
Submitted on 1 Jan 1977
HAL is a multi-disciplinary open access
archive for the deposit and dissemination of
sci-entific research documents, whether they are
pub-lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d’enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.
FINELY DISPERSED ULTRAFINE PARTICLES
N. Wada
To cite this version:
JOURNAL DE PHYSIQUE Colloque C 2 , supplkment au no 7 , Tome 38, Juillet 1977, page C2-219
FINELY DISPERSED ULTRAF'INE PARTICLES
N. WADA
Department of Physics, Faculty of Science, Nagoya University, Nagoya 464, Japan
Rksum6. - Une mkthode a Ct6 d&velopp&e pour prCparer de trks petites particules finement disperskes au moyen d'une &vaporation, sous vide ou dans un gaz, sur la surface refroidie de differents solvants liquides.
Abstract.
-
A method was developed for preparation of finaly dispersed ultrafine particles bymeans of gas or vacuum evaporation on to the frozen surface of various liquid solvent.
A method of gas evaporation is a versatile technique of subdividing various materials into ultrafine particles such as metals [I], alloys [2-31, oxide and many other compounds [4]. It is expect- ed as a technique of providing particles of pure with clean surfaces.
The particles collected by the technique (brushing the wall) are often sticking each other making chains which are entangled. It is difficult or practically impossible to separate the chains of particles once stuck each other. If the surfaces of the particles are so clean, the smaller particles can be sintered at the lower temperature than the melting point of the material. This means there must consider the smallest limit for the obtainable particle size. Thus, the actual ultrafine particle that we can use should always be coated by protection layer and/or kept at low temperature as possible. This would be accomplished by taking the following method for collecting the ultrafine particles condensed by gas evaporation.
The schematic arrangement of the apparatus is shown in figure 1. It is conventional vacuum evaporation unit except the chamber is designed to keep liquid solvents in it and to refrigerate them from outside of the chamber with liquid nitrogen (Fig. 2). After the chamber is evacuated up to
-
torr. and the valve to the evacuation system is closed. The solvent liquid is introduced into the chamber through the feeder pipe, which is frozen into solid by dipping the chamber bottom into liquid nitrogen. A certain amount of helium(1
-
100 torr.) is introduced into the chamber and the specimen material in the heater is evaporated. The ultrafine particles of the materials is deposited on the surface of the frozen solvent. After the evaporation is stopped, the liquid nitrogen is removed off the chamber. The frozen solvent is melted and the fine particles deposited on the surface dispersed into the liquid solvent. Repeatingsoivent(vapor) ~ p e c i m e n feeder vacuum
.
. .-.
...
4 svstem Pyrex glass,
t rogen foamthe same process, a desired amount of fine particles is collected in the solvent (Fig. 2a).
If the solvent is volatile such as ethylether, it is possible to introduce the solvent in the vapour phase through the feeder pipe. In that case, by freezing the whole chamber with liquid nitrogen, a sold film of the solvent is deposited inside wall of the chamber. The evaporated ultrafine particles are deposited on this film. Rasing the temperature of the chamber wall, the film is melted and flows down to the bottom of the chamber with deposited ultrafine particle (Fig. 2 b).
Various modifications of the method are possible to be considered but the essential part of this method is that the condensed ultrafine particles is to be collected on the frozen liquid surface. Many sorts of liquid solvents become possible to set in
C2-220 N. WADA
the vacuum chamber by freezing as their vapour pressure is low enough at the temperature. At low temperature, also sinterring or coalescence of the deposited particles is to be suppressed.
The solution of ultrafine particles of metals shows various colors, depending on metals, particle size and solvent. A few examples are tabulated in table I. The colors of the solutions were disappear- ed in two or three days and fine particles with black color like the ones collected in ordinal gas evapora- tion. It is noted here that the deposited fine particles were dispersed again in the solvent by stirring the solution and showed the same colors.
The particles solution with volatile solvent such as ethylether were possible to be condensed by evaporating the solvent. By evaporating the solvent completely, only dried particles could be left in the vessel. Such dried particles are never dispersed again even the same solvent was filled in the vessel. The facts are suggesting that each particle was actually protected by the solvent molecules on the surface from sticking each other and each particle in the solution WERE ISOLATED.
FINELY DISPERSED ULTRAFINE PARTICLES References
[I] KIMOTO, K., KAMIYA, Y., NONOYAMA, M. and UYEDA, R., [3] KATO, M., SAWAMOTO, H., KUMASAWA, M. and WADA, N . ,
Japan J. appl. Phys. 2 (1963) 702. Japan J. appl. Phys. 14 (1975) 181.
[4] KASHU, S., NAGASE, M., HAYASHI, C., UYEDA, R . , WADA,
[2] KUSAKA, K., WADA, N . and TASAKI, A., Japan J. appl. Phys. N. and TASAKI, A., Japan J. appl. Phys. Suppl. 2 (1974)
