TMA parallel-plate viscometry

When a sample of glass is pressed between two parallel plates and heated to above 7, the sample will exhibit viscous flow. The patterns of flow can be complex so in order to calculate the rate of flow, a simple geometry must be considered. The case for a glass sample in the form of a disc with the height less than the diameter and for the sample sticking to the plates such that the glass melt must flow and not slide has been considered by Gent [38] and an expression for the viscosity was derived  

Sample preparation will depend on the glass to be measured and the TMA to be used. In typical TMA equipment, the sample space is of about 10 mm diameter. In order to allow for the sample to be pressed out during the measurement, the maximum sample diameter at the start will be about 5 mm. Sample height is not critical but should be less than the 

Agreement is excellent between 10 - and 10 Pas. The verified range was extended to 10 Pa s by using a smaller load and smaller sample height. 

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Figure 10.22 The viscosity-temperature data set measured using thermomechanical analysis (TMA) parallel-plate viscometry of the National Bureau of Standards (NBS), USA, 710 glass is compared to the Vogel-Fulcher-Tammann [9] model issued by the NBS.

Figure 10.23 Thermomechanical analysis (TMA) parallel-plate viscometry is used to investigate the behaviour of the oxyfluoride glass 32Si02-9AIOi.5-31.5CdF2-18.5PbF2-5.5ZnF2-3.5ErF3 (mol %) in which nanocrystals are homogeneously nucleated above Tg [39]. Description of the viscosity-temperature curves may be found in Section 10.5.6.

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