Dynamic heating rate

As shown by Eq. (8), the kineties governing a thermal decomposition event depend on time, temperature, and rate of decomposition. TG experiments performed at a constant heating rate allow temperature and time to be interehanged in the ease of first order kinetics and one-step decompositions. ] Hi-Res TGA allows the determination of kinetic parameters such as activation energy and reaction order for each step in multiple component materials using four different TG approaches I constant heating rate, constant reaction rate, dynamic heating rate, and stepwise isothermal. 

In a dynamic heating rate approach, the activation energy value, E, can be calculated from a plot of In (Hr/T ) versus l/T, where at least three experiments with different maximiun heating rates have been used. The calculation of E is independent of reaction rate and mechanism... 

In the analysis of polymers, temperatures from ambient to 1000°C can be used in either oxidising (e.g. oxygen or air) or non-oxidising (e.g. nitrogen or hehum) atmospheres, and either isothermal or dynamic heating rates can be employed. 

Measurement of dynamic mechanical properties was carried out under tension mode using a viscoelasto-meter, (Rheovibron DDV-III-EP, M/s, Orientec Corp., Tokyo, Japan). Sample size was 3.5 cm x 6.5 mm x 2 mm. Testing was carried out at a low amplitude, 0.025 mm, over a temperature range of - 100°C to +200°C. Heating rate was TC/min and frequency of oscillation was 3.5 Hz or 110 Hz. 

Liquid is fed continuously to a stirred tank, which is heated by internal steam coils (Fig. 1.21). The tank operates at constant volume conditions. The system is therefore modelled by means of a dynamic heat balance equation, combined with an expression for the rate of heat transfer from the coils to the tank liquid. 

Characterization Methods. Stress-strain experiments were carried out with an Instron model 1122. Dogbone samples of 10mm in length were used, and the initial strain rate was 2 mm/min. Dynamic mechanical data were obtained utilizing a DDV-IIC Rheovibron Dynamic Viscoelastometer. Most samples were tested within the temperature range of -100°C to 220°C with a heating rate of 2-3°C/min. A frequency of 11 Hz was selected for all the dynamic mechanical experiments. 

Thermolysis was carried out under quasi-isothermal conditions (in other cases under dynamic conditions with a heating rate of 10°C/min). 

It must be also considered that the reaction rates of different thermal processes which can occur simultaneously are influenced by the treatment conditions (temperature, heating rate, pressure, static or dynamic atmosphere). This will affect the relative quantities of the products formed and in some cases also their nature, when recombination reactions give rise to secondary degradation products. On account of its sensitivity and resolution power Py-GC/MS will also provide useful information on minor components present in a material, including low molecular weight additives and pigments. 

Dynamic Mechanical and Thermomechanical Analysis. A DuPont Model 981 DMA was used to determine the dynamic modulus and damping characteristics of baseline and irradiated specimens. Transverse composite samples 1.27 cm x 2.5 cm were used so that the modulus and damping data were primarily sensitive to matrix effects. Data were generally determined from -120°C through the glass transition temperature (Tg) of each material using a heating rate of 5°C/min. 

The most widely recommended calibration method for dynamic DSC operation involves the determination of the extrapolated onset temperature for the fusion of several standard substances, using various heating rates [255,256],... 

Molecular mixing via dynamic mechanical spectroscopy. While electron microscopy yields the phase size, shape, etc., as delineated above, dynamic mechanical spectroscopy (DMS) yields the composition within each phase. The DMS measurements employed a Rheovibron direct reading viscoelastometer model DDV-II (manufactured by Toyo Measuring Instruments Co., Ltd., Tokyo, Japan). The measurements were taken over a temperature range from -120°C to 140°C using a frequency of 110 Hz and a heating rate of about 1°C/ min. Sample dimensions were about 0.03 x 0.15 x 2 cms. 

It is impractical to attempt to explore conventional TPD dynamics for NO/Pt(l 11) at values of Tg > 400 K since this would require extreme heating rates. Two techniques have been utilized to extend state-resolved dynamics to higher Tg. These include trapping/desorbing beam scattering and surface reactions (i.e. as observed for the NO-NHj coadsorption system). 

Cured Olixomer Properties. The T, of the cured specimen ms not obvious by DSC, however the T was observed at 383°C (Q maac) by dynamic mechanical testing of a torsion bar. The T obtained by this method has been driven up in temperature by the slow heating rate of 2°C/minute used in the test, the actual T is somewhat lower... 

In the nonisothermal or dynamic mode, a sample is set into a calorimeter and the temperature is raised at a certain constant heating rate up to the operational temperature. The total heat of reaction is independent of the heating rate (recommended range is 2-20°C/min [1,140]). Three methods are possible ... 

The glass transition temperature can be measured in a variety of ways (DSC, dynamic mechanical analysis, thermal mechanical analysis), not all of which yield the same value [3,8,9,24,29], This results from the kinetic, rather than thermodynamic, nature of the transition [40,41], Tg depends on the heating rate of the experiment and the thermal history of the specimen [3,8,9], Also, any molecular parameter affecting chain mobility effects the T% [3,8], Table 16.2 provides a summary of molecular parameters that influence the T. From the point of view of DSC measurements, an increase in heat capacity occurs at Tg due to the onset of these additional molecular motions, which shows up as an endothermic response with a shift in the baseline [9,24]. 

Dynamic Mechanical Measurements. Films were prepared by casting the acetone solution of sample No. 2 onto a Teflon sheet after adding curing agents. The sample was allowed to stand at room temperature for one day, and then cured at 130°C for 2 hours. The dynamic mechanical spectroscopic data were measured in tension with a Rheovibron DDV-II (Toyo Baldwin Co. Ltd.) at a frequency of 110 Hz with a heating rate of about l°C/min. 

The variation of the damping factor (tan 5) with temperature was measured using a Polymer Laboratories Dynamic Mechanical Thermal Analyzer (DMTA). The measurements were performed on the siloxanfe-modified epoxies over a temperature range of — 150° to 200 °C at a heating rate of 5 °C per minute and a frequency of 1 Hz. The sample dimensions were the same as those used for flexural modulus test specimens. 

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