. Electron microscopy; proceedings of the Stockholm Conference, September, 1956. Electron microscopy. Freeze-drying Technique in Investigating Sodiiim-Montinorillonitc 335 In the first place it is impossible under these circumstances to maintain the proper dispersion and concentration of the montmorillonite particles. The latter are frequently present in the suspension in the form of very thin sheets. When the drop dries, these sheets tend to be fiattened or distorted. Further, the actual distribution of the particles tends to be obscured. In air-dried preparations the particles are sometimes
. Electron microscopy; proceedings of the Stockholm Conference, September, 1956. Electron microscopy. Freeze-drying Technique in Investigating Sodiiim-Montinorillonitc 335 In the first place it is impossible under these circumstances to maintain the proper dispersion and concentration of the montmorillonite particles. The latter are frequently present in the suspension in the form of very thin sheets. When the drop dries, these sheets tend to be fiattened or distorted. Further, the actual distribution of the particles tends to be obscured. In air-dried preparations the particles are sometimes observed as separate units, but sometimes also as sheets of considerable dimen- sions. The latter might have been composed of a number of smaller particles, but it is impossible to distinguish these clearly. If, moreover, we are interested in the structure of the clay skeleton in the suspension, the investiga- tion by electron microscopy becomes extremely diffi- cult. The above considerations induced us to try and find a new technique of preparation that would obviate these objections. Application of the principle of freeze-drying has turned out to lead to good results. In this technique the specimen is rapidly frozen, after which the water is removed by evaporation of the ice formed. Any change in the cohesion of the clay particles is minimized by freezing as quickly as possible. By pumping the water vapour from the solid phase a slow and even removal is ensured. Consequently, here again a good retention of the cohesion of the clay particles may be expected. For the application of this technique there are several possibilities. For instance, the drop of suspen- sion may be either placed on a specimen carrier covered with a supporting film or dried on a narrow slit, without supporting film. The cohesion of the particles has proved to be such that a 200 /< slit can be bridged by the clay skeleton, if the concentra- tion is not too low. Freezing, too, can be effected in differ
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