Vertical dilatometers

Changes in the dimensions of a sample are detected by a mechanical, optical or electrical transducer although the transducer is usually a linear variable differential transformer (LVDT). The sample may be positioned either vertically or horizontally. The latter usually introduces friction between the sample and the support tube, which may be reduced to acceptable levels but never totally eliminated (l). Vertical dilatometers overcome the prob-... 

A dilatometer consists essentially of a glass tube (the body ), containing the reaction mixture, to which a straight capillary tube is attached (usually, but not always, vertical). The movement of the meniscus of the reaction mixture in the capillary amplifies changes in the volume of the reaction mixture and is measured, as a function of time, with a cathetometer or by some automatic device. Dilatometry has been used for a very long time because it is simple, cheap, convenient and can be made very accurate. 

Figure 7.6 Two example LVDT stages offered by Theta Industries. Top constant force system, used for vertically mounted dilatometers and parallel plate viscometers. Bottom horizontally mounted dual pushrod system with leaf springs.

As soon as the solution has come to a thermal equilibrium, the volume of solution will decrease. The change in height of the liquid in the capillary is measured periodically with a cathetometer (a rigidly mounted, vertically sliding telescope) or from the scale on the dilatometer. The rate of poly-... 

In this technique, commonly known as TMA, a vertical probe (flat, 0.140" diameter) is placed on the sample and thermal expansion measured as the sample is heated or cooled. The vertical probe is balanced in oil suspension and a certain weight is added to the probe to arrive at a net zero weight on the sample. Additional weight may be placed on the probe to improve the signal/noise ratio, but this affects the results as does spring loading in the horizontal dilatometer. Strain gauge techniques were also examined by us and were found to be less useful.(4)... 

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