Induction time measurement

In addition to induction time measurements, several other methods have been proposed for determination of bulk crystallization kinetics since they are often considered appropriate for design purposes, either growth and nucleation separately or simultaneously, from both batch and continuous crystallization. Additionally, Mullin (2001) also describes methods for single crystal growth rate determination. 

S.M. Marcus and R.L. Baine, Estimation of bias in the oxidative induction time measurement by pressure DSC, Application note TA-228, TA Instruments, Inc., New Castle, DE, USA. 

Induction time measurement on cassiterite particles further explained the difficulties to establish particle/bubble contact with coarse cassiterite. This is not the case with other cassiterite collectors. 

The above studies support the notion that nucleation is a very stochastic phenomenon when the sample is held at constant temperature, compared to when the sample was cooled at a constant cooling rate. As suggested previously, the magnitude of the driving force can affect the degree of stochastic or random behavior of nucleation. For example, on the basis of extensive induction time measurements of gas hydrates, Natarajan (1993) reported that hydrate induction times are far more reproducible at high pressures (>3.5 MPa) than at lower pressures. Natarajan formulated empirical expressions showing that the induction time was a function of the supersaturation ratio. 

Figure 12.16 Isothermal induction time measured in 6 experiments with a first heating period at 390°C with a variable duration, followed by a 10 minute cooling period and again heated at 390°C.

The measurement of SFC by pNMR is commonly used to monitor fat crystallization. It is, however, generally less sensitive than absorbance spectrophotometry (see below) in the early stages of crystallization, as crystals can be visible before solid fat is detectable by pNMR (Wright et al., 2001a). Notwithstanding this, Wright et al. (2000) found a strong correlation between the induction time measured by pNMR and that measured by absorbance spectrophotometry for three milk fat systems. The principles of NMR are described in Chapter 20. 

Schott and Kinsey in 1958 [102] were the first to use induction time measurements in shocked H2 02 Ar mixtures in order to derive kinetic... 

Induction times for nucleation of a tripalmitin melt at different temperatures are shown in Figure 12 (36). The tripalmitin melt was cooled quickly from 80°C to the different crystallization temperatures indicated on the figure and induction time measured as the first point of detection of crystals on a polarized light microscope. The relative time scales for the onset of nucleation are clearly shown, with the less-stable ot form taking significantly less time to nucleate than the (3 polymorph. The induction time for the most stable (3 polymorph was substantially longer than for either of the less-stable polymorphs. 

Figure 4. Loss of effective stabilization in low-density polyethylene. Induction time measured by differential scanning calorimetry.

HPDSC Induction Times Measured on Samples from Thermal Diffusion Containing Amine Antioxidant... 

A series of high pressure oxidative induction time measurements (HPOIT) were conducted on a PE geomembrane sheet in order to investigate the interaction of the pressure and temperature variables on the induction time. The experiments consisted of determining the EffOIT at constant cell volume employing a wide operational range of pressure and temperature values. The HPOIT test results were found to be inversely related to both variables, with temperature being the predominant factor (Tikuisis et al. 1985). 

Unfortunately, any attempt to predict the long-term stability of polyethylene based on an Arrhenius plot of high-temperature oxidative induction times measured above the melting point fails when projected to lower temperatures where polyethylene is a semicrystalline solid (Bair 1973 Chan et al. 1978). The reasons for this nonlinear behavior appear to be associated with complex chemical and physical interactions that behave differently in the solid state than in the melt. 

Using an alternative approach to determine kinetics, induction time measurements were made in a recent study of the well-mixed batch precipitation of... 

Table 9.3 ASTM international oxidative induction time measurements...

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