Stepped isothermal method

Figure 8.7 First stage of the stepped isothermal method (SIM) for oriented polyester fibres. Creep strain is measured under a single load while the temperature is increased...

GSIO Accelerated Tensile Creep Rupture of Geosynthetic Materials Based on Time—Temperature Superposition Using Stepped Isothermal Method D6992... 

A special case of time temperature shifting the stepped isothermal method... 

There are two possibilities for performing a frontal chromatography experiment for the purpose of the determination of equilibrium isotherms. The step-series method uses a series of steps starting from C = 0 to C +i. After each experiment, the column has to be reequilibrated and a new step injection with a different end concentration C +i can be performed. In the staircase method, a series of steps is performed in a single run with concentration steps from 0 to Q, Q to C2,.. ., C to C +i. The column does not have to be reequilibrated after each step and, therefore, the staircase method is faster than the step-series method. Both modes of frontal analysis give very accurate isotherm results. 

FIGURE 6.7 Free-volume frozen fraction versus pressure for three PS samples differently vitrified 1, the standard isothermal method of dilatometric tests 2, isobaricaUy cooling from about Tg + 30°C to ambient, then reheating, increasing P, and so on 3, isobaricaUy heating from 30 to 240°C in 170 temperature-steps at each level of pressure. (From Utracki... 

Table 5.3 lists the principal experimental methods used in dynamic mechanical testing. Of the experiments considered below, the thermal scan mode (method 1) is the technique most commonly used by thermal analysts. Here typical applications in quality control or processing look for differences in material batches, thermal history, different grades, reactivity, and other characteristics. The stepped isotherm (or step isothermal) experiment (method 2) is used mainly in studies involving detailed mechanical property determination for structural analysis, vibration damping applications, and for determining time-temperature superposition master curves. Method 3 (fast scan or single isotherm) is application specific. 

Figure 1.23 A diagram of the temperature profiie used in step-based methods and the heat flow signal that results. Heat capacity is calculated either from peak height as in the cl lssical method, or peak area of the heat flow trace. The kinetic response is obtained from the isothermal portion.

The BET method for calculation of specific surface A involves two steps evaluation of the monolayer capacity n from the isotherm, and conversion of n into A by means of the molecular area a . 

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