Dynamic differential calorimeter

Another dynamic differential calorimeter has been described by O Neill (1964). This instrument is also available commercially. It differs from the differential calorimeters above by keeping identical temperatures in sample and reference by automatic control. The differential heat input per second necessary to achieve this, d/iQldt, is monitored. Its value during heating with rate g = dTjdt is proportional to the differential specific heats ... 

A calorimeter is usually regarded as an object that can be described by one differential equation or a system of linear differential equations with constant coefficients. These equations are treated as the mathematical models of calorimeters. If there are many output functions, then the dynamic object (calorimeter) is described by a system of n differential equations. Assuming linearity and applying the superposition rule, one... 

From the dynamic properties of differential calorimeters, it is clear that the disturbances can be eliminated only if the transmittances of calorimeters I and II are the same. It is very difficult to fulfill this condition. Hence, for a given differential calorimeter it is useful to determine an acceptable range of difference of the time constants for which, for a given disturbance and required accuracy of T(t) measurements, the assumption of a differential character of the calorimetric system is satisfied [207]. The application of the dynamic equations discussed in Chapter 4 can be very helpful in this type of investigations. 

An other type of calorimeters used is the group of devices called twin calorimeters. In such calorimetric systems, it is necessary to obtain equal temperatures of the inner parts of calorimeters I and II in such a way that in calorimeter II a the heat power has the same magnitude and course as that in calorimeter I. It is obvious that, for twin calorimetric systems, similarly as for differential calorimeters, the dynamic properties of the two calorimeters should be the same. 

Let us consider a system composed of two calorimeters (I and II), characterized by the dynamic properties of inertial objects of the first order, placed in a common shield. The sample is situated in one of them, and the reference substance in the other. The forcing input function is the ramp function generated in the thermostat. Let us assume that this function is at the same time the input function of both calorimeters. The influence of the forcing function on a differential calorimeter is shown... 

Differential Scanning Calorimeter (DSC) thermograms were obtained on a Perkin Elmer DSC-2 run at 10°C per minutes. Dynamic Mechanical Thermal Analysis (DMTA) spectra were obtained on a Polymer Labs DMTA at a frequency of 1Hz with a temperature range from -150°C to +150°C at a scan rate of 5°C per minute. 

Dough Moulding Compound Dynamic Mechanical Thermal Analysis Direct Resin Injection and Venting Differential Scanning Calorimeter Differential Thermal Analysis Elongation at Break... 

Other thermal techniques are Thermogravimetric Analysis (TGA) [55,68], High Pressure Calorimeter (HPC) [1], Thermomechanical Analysis (TMA) [1,141], and Differential (or Dynamic) Thermal Analysis (DTA) [74]. These are rarely used and will not be discussed here. 

The glass transition (Ta) and melting (Tm) temperature of the pure component polymers and their blends were determined on a Perkin-Elmer (DSC-4) differential scanning calorimeter and Thermal Analysis Data Station (TADS). All materials were analyzed at a heating and cooling rate of 20°C min-1 under a purge of dry nitrogen. Dynamic mechanical properties were determined with a Polymer Laboratories, Inc. dynamic mechanical thermal analyzer interfaced to a Hewlett-Packard microcomputer. The... 

In this category of calorimeters, we find the isothermal calorimeters and the dynamic calorimeters where the temperature is scanned using a constant temperature scan rate. The instrument must be designed in such a way that any departure from the set temperature is avoided and the heat of reaction must flow to the heat exchange system where it can be measured. The instrument acts as a heat sink. In this family we find the reaction calorimeters, the Calvet calorimeters [7], and the Differential scanning calorimeter (DSC) [8],... 

In order to obtain the degree of cure and rate of curing, we must first measure the reaction. This is typically done using a differential scanning calorimeter (DSC) as explained in Chapter 2. Typically, several dynamic tests are performed, where the temperature is increased at a constant rate and heat release rate (Q) is measured until the conversion is finished. To obtain Qt we must calculate the area under the curve Q versus t. Figure 7.17 shows four dynamic tests for a liquid silicone rubber at heating rates of 10, 5, 2.5 and 1 K/min. The trapezoidal rule was used to integrate the four curves. As expected, the total heat Qt is the same (more or less) for all four tests. This is to be expected, since each curve was represented with approximately 400 data points. 

DIFFERENTIAL SCANNING CALORIMETER REACTION KINETICS, 1 DYNAMIC SCAN... 

Figure 3. Differential scanning calorimeter traces of 73-series Halthanes show the soft and hard segment glass transitions and a melting endotherm. The temperatures of these transitions are consistent with the dynamic mechanical measurements.

A differential scanning calorimeter (DSC) (Du Pont 910) was used to monitor the Tg s of the epoxies. The heating rate was 10°C/min. The dynamic mechanical properties of the epoxies were monitored by a Rheometrics mechanical spectrometer (Model RMS-7200). Epoxy specimens with dimensions of 6.4x1.3x0.3 cm were torqued at an oscillating frequency of 2.0 Hz. The shear storage (G ) and loss (G") moduli and tan 5 were determined from -160°C to +140 C. The densities of the epoxies were performed on 1x1x0.3 cm epoxy specimens that were immersed in methyl ethyl ketone for seven days. The weights (w) and volumes (v) of the specimens were measured prior to (wj and V ) and after (wf.and Vf) immersion and the swelling ratio v /v determined. 

Batch testing is carried out to verify prepreg properties, such as resin content, volatile level, and flow. The resin advancement (chemical reaction) is monitored via a Differential Scanning Calorimeter (DSC) and the formulation consistency by testing the Tg via DSC or Dynamic Mechanical Analyzer (DMA). The laminate properties are also determined. All are documented and quoted on a Release Certificate. 

DMTA dynamic mechanical thermal analysis DSC differential scanning calorimeter... 

The specific heat of polystyrene is in addition sufficiently large that the dynamic gradients across samples of this material are equal to or larger than the pseudosteady state gradients across these at standard heating rates. The total temperature differentials across polystyrene samples are thus in the same range, and commonly greater than, the total temperature drop across the calorimeter cup. 

DTA as well as power compensation DSC instruments, and is called temperature modulated DSC, or TMDSC. The following trade marks are used by different TA instrument manufacturers for their temperature modulated differential scanning calorimeters Modulated DSC (MDSC ) of TA Instruments Inc., Oscillating DSC (ODSC ) of Seiko Instruments Inc., Alternating DSC (ADSC ) of Mettler-Toledo Inc. and Dynamic DSC (DDSC ) of Perkin-Elmer Corp. 

See differential thermal analysis, differential scanning calorimeter, dynamic mechanical analyzer, and thermogravimetric analysis. 

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