Differential thermal analysis temperature-time curve

Many different test methods can be used to study polymers and their physical changes with temperature. These studies are called thermal analysis. Two important types of thermal analysis are called differential scanning calorimetry (DSC) and differential thermal analysis (DTA). DSC is a technique in which heat flow away from a polymer is measured as a function of temperature or time. In DTA the temperature difference between a reference and a sample is measured as a function of temperature or time. A typical DTA curve easily shows both Tg and T . 

Heat activated reactions show a variation of the position of the peak in the cure rate curves with varying heating rate. If the temperature rises during reaction, the reaction rate, dc/dt, will rise to a maximum value and then returns to zero as reaction completes. The temperature at which the reaction rate reaches its maximum is also the temperature of maximum deflection in differential thermal analysis. Dynamic DSC measurements at different heating rates are used to determine the activation energy of the material, because they show the effects both time and temperature have on the reaction. 

Frey s variant of the silvered vessel test has been in use in the Germany. In its variant, different amounts of heat are supplied to the electric heating elements mounted inside the Dewar flask, and the temperature differences between the interior of the Dewar vessel and the furnace are measured by thermocouples. A calibration curve is plotted from the values thus obtained, and the heat of decomposition of the propellant is read off the curve. In this way, the decomposition temperature at a constant storage temperature can be determined as a function of the storage time, and the heat of decomposition of the propellants can thus be compared with each other. If the measurements are performed at different storage temperatures, the temperature coefficient of the decomposition rate can be calculated. (-< also Differential Thermal Analysis.)... 

X-ray diffraction patterns were recorded on a Siemens D5000 diffractometer using CuKa radiation. Thermogravimetric and differential thermal analysis curves were recorded on a Setaram Setsys 12 thermal analysis station by heating in an argon atmosphere from 25 to 1200 -C at a rate of 5 min". Samples were used untreated. The Pt content was determined by the Service Central d Analyse, CNRS (Vernaison, France) and the microanalyses (C, H) were performed at Complutense University (Madrid, Spain). Na isotherms were determined on a Micromeritics ASAP 2000 analyzer. H MAS NMR, Si MAS NMR and C CP MAS NMR spectra were recorded at 400.13, 79.49 and 100.61 MHz, respectively, on a Broker ACP-400 spectrometer at room temperature. An overall 1000 free induction decays were accumulated. The excitation pulse and recycle time for H MAS NMR spectra were 5 ps and 3 s, respectively, those for Si MAS NMR spectra 6 ps and 60 s and those for C CP MAS NMR spectra 6 ps and 2 s. Chemical shifts were measured relative to a tetramethylsilane standard. Prior to measurement, if necessary, samples were dehydrated in a stove at 423 K for 24 h. 

Derivative Differential Thermal Analysis. A technique yielding the first derivative of the differential thermal curve with respect to either time or temperature. 

Differential thermal analysis, DTA, was also carried out to determine the optimum nucleation temperature according to the method reported by Marotta et al. who concluded that, if samples are held for the same time tn, at each heat-treatment temperature Tn, then In 1 (kinetic rate constant for nucleation) is proportional to (1/Tp) - (1/Tp ), where Tp and Tp are, respectively the crystallization exotherm temperatures obtained with and without a nucleation hold. Plotting (1/Tp) - (1/Tp ) against nucleation hold temperature gives a bell shaped curve, with the optimum nucleation... 

Filled PVC compounds can be flame-retarded by alumina trihydrate. Figure 5.9 shows the burning time of flame-retarded PVC plasticized by 50 phr. of di-isooctyl phthalate. Extinction time after the ignition of a horizontal rod specimen at environmental temperature of 100 or 120 °C is plotted against the additive content. In Figure 5.10, differential thermal analysis (DTA) curves of the same PVC compounds are presented. 

Differential thermal analysis curve Graphical representation of data collected by a differential thermal analyser, where the difference temperature is plotted as a function of temperature (scanning mode) or time (isothermal mode). 

High pressure DTA measurements. Differential Thermal Analysis (DTA) is a version of the method of parameter -property curves in which the thermal effect is a measured property of a system and temperature or time are the parameters ( Therm.anal. in Table 1.1). 

Altunbas and Harris (1980) studied the cerium-praseodymium alloy system using electrical resistivity. X-ray diffraction and differential thermal analysis (DTA) techniques. In most of the research they used standard commercial material but some relatively pure praseodymium (purified by solid state electrolysis) was used in the DTA measurements. Appropriate amounts of the component metals were arc-melted in purified argon, turned and remelted several times. This was followed by a seven day vacuum anneal at 600°C with slow cooling to room temperature. Their electrical resistivity curves for the praseodymium sample indicated only one solid phase transformation (dhep bcc) whereas the curves for cerium and the Ce-Pr alloys exhibited two transitions, dhep fee (below 61°C for pure cerium) and fee bcc. 

Heating and cooling curves are used in determining phase diagrams, since all (first-order) phase changes give rise to thermal arrests (the temperature remains constant for a period of time). Differential thermal analysis (DTA) is a refinement of the time-temperature method. In a DTA experiment, the sample is heated simultaneously with a standard sample, usually an inert material... 

Differential Scanning Calorimetry. A sample and an inert reference sample are heated separately so that they are thermally balanced, and the difference in energy input to the samples to keep them at the same temperature is recorded. Similarly to DTA analysis, DSC experiments can also be carried out isothermally. Data on heat generation rates within a short period of time are obtained. Experimental curves from DSC runs are similar in shape to DTA curves. The results are more accurate than those from DTA as far as the TMRbaiherm is concerned. 

The relationship between observed enthalpy-volume relaxations and thermal treatment of slightly oriented industrial PVC films was investigated. Differential scanning calorimetry at 20 -C per minute and specific volume analysis (density gradient column) were used to study the effects of annealing near and below Tg. Nonlinear effects in the volume relaxation at relatively long times and temperatures close to the glass transition produce deviations in the specific heat curves at temperatures far above Tg in addition to the normal overshoot effects. 

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