Shrinkage measurement

HDT, heat distortion temperature. b Approximate composition, 45/45/10. c Approximate composition, 80/20. d Shrinkage measured with the flow . e Shrinkage measured across the flow ... 

Network formation by photopolymerization has been studied for tetraethyleneglycol diacrylate (TEGDA) using isothermal calorimetry (DSC), isothermal shrinkage measurement and dynamic mechanical thermal analysis (DMTA). Due to vitrification the polymerization does not go to completion at room temperature. The ultimate conversion as measured by DSC seems to depend on light intensity. This can be explained by the observed delay of shrinkage with respect to conversion. 

Stainless steel powder with a mean particle diameter of 50 mm has been compacted to a green density of 58% and sintered in pure H2. The resulting shrinkage measurements are given below. Published diffusion data for this stainless steel show that the activation energies are 225 kJ/mol for surface diffusion, 200 kJ/mol for grain boundary diffusion, and 290 kJ/mol for volume diffusion. Use the data below to determine the mechanism. 

Tariq, A.U.R. and Durnford, D.S. (1993) Soil volume shrinkage measurements A simple method. Soil Sci. 155, 325-330... 

Specific volume Cure shrinkage measurement (Dilatometry, etc.) A—>C 35,36... 

Much more detailed procedures are described in Prime (1997a). Ramis et al, (2003) use shrinkage measurements on a TMA to determine the gelation point of polyester-based thermoset coatings. As shown in Figure 3.55, the gel point is defined as the point at which the rate of change of shrinkage abruptly slows down. 

The results of the shrinkage measurements, shown in Figures 4 and 5, also show the retardation of sintering in oxygen. Up to 300°C there is an apparent expansion of the samples due to the thermal expansion difference between Ba2YCu307.x and alumina. The... 

For determination of T from shrinkage measurements, fibers were allowed to shrink at tfie specified temperature, and length measurements were made manually. 

Time for exposure of boards to boiling water (min) Shrinkage measured after 24 h of cooling and conditioning (%) Moisture of the boards after 24 h Moisture of the boards after 48 h... 

Fitzer, Frohs and Heine (1986) [209] used TMA and DSC to study the optimum heating rate for a 6% MA/1% ITA PAN copolymer. Shrinkage measurements indicated the start and end of the stabilization reaction. The optimum heating rate was 5°Cmin reducing to l°Cmin when the reaction started, in order to avoid overheating by the exothermic reaction and stopping at 270°C to avoid over-oxidation. 

Table 3. Shrinkage Measurements on Epon 828 Cured with Different Curing Agents, TETAandDTA ...

Figure 4.32. Schematic of a DMA quartz sample chamber used for shrinkage measurements at 23°C.The DMA is operated in aTMA-like static mode. Typically, polymerizable samples were 0.5 mm thick and the 3.5-mm-diameter probe carried a load of 5 mN (equivalent to a pressure of 520Pa). [From Bair et al. (1998) reprinted with permission from the American Chemical Society.]...

These TMA shrinkage measurements were carried out without the instrument furnace in place, that is, at ambient temperature. During a typical 60-min run an estimate of the ambient thermal fluctuations of the surroundings was made and found to be of the order of +0.2 °C. For a 0.6-mm-thick photopolymer, these temperature changes would result in only a 0.004% change in sample height and would be a negligible source of error in the experiments. 

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