Viscometry indentation

High viscosities, more than 10 Pa s,canbesatisfactorilymeasuredinthecommercialTMA and it is in this region that the glass-forming liquid is typically shaped. Table 10.2 summarises the way in which TMA has been used for beam bending, indentation and parallel-plate viscometers to cover the viscosity range 10 - 10 Pa s. The TMA indentation and parallel-plate viscometry are described in detail below (Section 10.5.5 and 10.5.6, respectively). 

Figure 10.16 Photograph of the experimental arrangement for thermomechanical analysis (TMA) indentation viscometry using a cylindrical indenter (32).

Figure 10.17 The viscosity-temperature data set measured using thermomechanical analysis (TMA) indentation viscometry of the National Bureau of Standards (NBS), USA, 711 glass is compared to that obtained using the Vogei-Fuicher-Tammann [9] model issued by the NBS [32].

Figure 10.18 Photograph of a sample of the fluoroaluminate glass 37AIF3-12BaF2-15CaF2-12MgF2-9SrF2-15Yp3 (molar %) that has undergone thermomechanical analysis (TMA) indentation viscometry with a cylindrical probe. The sample has devitrified during the indentation [35].

Figure 10.19 Viscosity-temperature curves for [Geo.sSo./lioo-xlx glasses in the range 0 < x < 30 were measured using indentation viscometry with a cylindrical probe [36 (a) isoviscous points are found to shift to a lower temperature as the iodine content is increased (b) addition of iodine tends to break down the connectivity of the network in the supercooled melt producing an increasingly fragile liquid [8, 36 and 37). , 0at% I A, 5at% I , 10at% I A, 15at% I o, 20at% I.

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