Ramp rate modulation

The compositions of the composites were determined simply by weighing the tared solid sample. Melting endotherms and glass transition temperatures were determined using a TA Instruments 2910 modulated differential scanning calorimeter (DSC) operated with a 3°C/min ramp rate, a 0.75 °C oscillation amplitude, and a 60-s oscillation period. 

Modulation amplitude Modulation period Underlying or average ramp rate. 

The ramp rate and heat flow modulation should be considered. It is important to establish whether the peaks are spiky or well formed and uniform. Well-formed sine-wave shaped peaks are necessary for achieving a proper modulation with no distortion showing a uniform wave pattern. Figure 2.95 shows differences between modulations with no distortion and those that are highly distorted. 

This new technique introduced in 1993 has been thoroughly examined and discussed. Main advantages are the separation of overlapping events in the DSC scans. In conventional DSC, a constant linear heating or cooling rate is applied. In modulated DSC (MDSC), the normally linear heating ramp is overlaid... 

The TS-BR does not require modules 1, 2 or 5 shown in Figure 13.1. The reactor is filled off-line and introduced into the heater assembly. Appropriate probes are inserted to monitor temperature and composition and the ramping proceeds at any desired rate, in fact along any random or desired trajectory. The requirement of TS-BR operation is simply that the several runs constituting an experiment use different temperature trajectories. 

This provides one way of measuring heat capacity in a linear rising temperature experiment one simply divides the heatflow by the heating rate. If the temperature programme is replaced by one comprising a linear temperature ramp modulated by a sine wave, this can be expressed as... 

Modulated DSC (MDSC ) is a patented technique from TA Instruments, New Castle, DE. In MDSC, a controlled, single-frequency sinusoidal temperature oscillation is overlaid on the linear temperature ramp. This produces a corresponding oscillatory heat flow (i.e., rate of heat transfer) proportional to physical properties of the sample. Deconvolution of the oscillatory temperature and heat flow lead to the separation of the overall heat flow into heat capacity and kinetic components. 

To further characterize the products released upon thermochemolysis, comprehensive GC x GC-TOFMS was utilized. Thermochemolysis was performed at 280°C under conditions as described above. GC x GC-TOFMS analysis was performed using an Agilent 6890 GC with a GC X GC modulator (Leco) coupled to a Pegasus IV TOF mass spectrometer (Leco). The GC injector was operated in split mode (20 1) with a column flow rate of 1 mL/min and held at 250°C. GC x GC separation utilized a nonpolar column and a polar column a BPX5 (30 m X 0.25 mm x 0.25 pm SGE) and a BPX50 (1.8 m X 0.1 mm x 0.1 pm SGE), respectively. The GC oven temperature was held for 10 min at 35°C and ramped to 300°C at a rate of 5°C/min and then held for 5 min the second column was ramped at +15°C relative to the first column with a modulation time was 4 s. Mass spectra were acquired in electron ionization mode from 33 to 500 amu with an acquisition rate of 135 Hz. 

Originally (in the technique introduced by Barker [89] in 1952) the square-wave potential was applied to the DME with constant modulation frequency (225 Hz) and slow scan rate of the voltage ramp (about 2 mV s" ). The current response was recorded at the end of each drop life in a short period of time ( 2 ms). This method could be treated by the steady-state theory in an analogous way to the derivative and differential pulse polarography. It has attained considerable attention for reversible electrode processes due to its applicability especially in trace analysis [90]. 

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