Temperature and Enthalpy Calibration

Mercury = 234.4 K) and gallium = 303.0 K) are sometimes used as standard reference 

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A change in the flow rate of the gas used to purge the DSC can have several effects. First, it is possible that it will change the temperature and enthalpy calibration. The magnitude of this variation will vary from one type of DSC design to another as some instruments preheat the purge gas prior to its entering the DSC cell. Second, for experiments where a volatile substance is evolved from the sample when it is heated, the DSC peak shape will be affected by the speed at which the volatile substance is removed. 

DSC measurements were performed on a TA Instruments 2190 DSC with temperature and enthalpy calibrations performed using an indium reference. Experiments were performed under a nitrogen atmosphere with a flow rate of 50ml/min. Extruded granules of nanocomposites were heated at 2°C/min to 250°C, held isothermally for 5mins, then cooled to room temperature at 2°C/min. All samples were heated twice, first to examine the properties post extrusion and secondly to examine the preferred crystal structures with slow cooling. 

Temperature modulated DSC requires the same baseline, temperature and enthalpy calibration as conventional DSC (see Sections 3.1 and 3.2). Measuring the heat capacity is a necessary First step in calculating the reversing and nonreversing heat flows, so a heat capacity calibration must be performed for TMDSC. Calibration parameters such as sample vessel type, purge gas, heating rate, modulation amplitude and period must be identical to those used in subsequent experiments. 

Temperature and enthalpy calibration of DSC curve. Calibration is carried out using the DSC curve determined under the same conditions as in step 2 for high-purity indium (purity >99.99%), and the leading slope of the indium is used to determine the instantaneous sample temperature during melting taking into account the heat-resistance correction and the heat of fusion of indium (28.41 J g ) used to calibrate the enthalpy of the DSC curve (mjcm" ). 

Today s calorimeters have a furnace calibration routine that is separate from the temperature and enthalpy calibration routines. Follow the manu-... 

Instrumental. The Mettler TA2000B thermal analysis system is equipped with an interface system, and Hewlett-Packard 9815 desk top calculator and 7225 plotter. Samples, weighing 5-10 mg, sealed in aluminum pans and under a nitrogen blanket, were heated in the calorimeter at a rate of 10 deg/min from -35 or 10 deg C to 180 deg C respectively, for specific heat and kinetic scans. Specific heat measurements were calibrated with alumina to an accuracy of 3%. Temperatures and enthalpies were calibrated with an Indium sample. The accuracies were .02 deg C and 2% (Indium 28.5 J/g), respectively. 

The underlying heat flow signal is calibrated by the use of standards with known melting temperatures and enthalpies of fusion. A series of such samples is run over the operating temperature range of the instrument. The sample thermocouple has a nominally known relationship between its output and temperature. Any observed differences between measured (by the sample thermocouple) and expected melting... 

With computer equipped DSC instrviments it is possible to measure temperatures and enthalpies with one and the same run. For the practical application of this possibility, standards are needed which allow the simultaneous calibration for both types of measurements. Based on numerous T and AH measurements a set of 12 standards is proposed in this paper. 

A disadvantage to the method is that calibration is required for temperature, enthalpy, and the heat capacity, as opposed to temperature and enthalpy only for standard DSC. 

The temperature and enthalpy of DSC should be calibrated following standard procedures. The temperature of the hot stage is calibrated by using a pure crystal with known melting temperatures. 

A general overview of temperature calibration and enthalpy calibration (heat of fusion) is best if DSC operational basics are understood before calibration is begun. 

Calibration of DTA and DSC instruments is usually carried out using standards with well-characterized and tested transition temperatures and enthalpies of reaction for example, the melting of indium occurs at 156.6°C and absorbs 28.7 J g while zinc melts at 419.4°C and absorbs 111.2 J g". ... 

DSC measurements were carried out using a DSC 820 Mettler-Toledo apparatus. Calibrations for temperature and enthalpy were performed using the melting point... 

Isothermal crystallization characterization was performed using a Perkin - Elmer Pyris 1 system, which was calibrated using the melting temperature and enthalpy of indium. The samples with a weight around 12 mg were put into an aluminum pan and hermetically sealed. An empty pan was used as a reference. For crystallization characterization, a sample was heated from 20 to 200°C at 20°C/min and maintained at 200°C for 2 min. Subsequently, it was rapidly quenched (-80°C/min) to the isothermal crystallization temperature and held there until completion of crystallization. Once crystallized, the samples were then reheated to 200°C at a rate of 20°C/min in order to investigate the melting behavior. 

Proper calibration of the DSC instruments is crucial. The basis of the enthalpy calibration is generally the enthalpy of fusion of a standard material [21,22], but electrical calibration is an alternative. A resistor is placed in or attached to the calorimeter cell and heat peaks are produced by electrical means just before and after a comparable effect caused by the sample. The different heat transfer conditions during calibration and measurement put limits on the improvement. DSCs are usually limited to temperatures from liquid nitrogen to 873 K, but recent instrumentation with maximum temperatures close to 1800 K is now commercially available. The accuracy of these instruments depends heavily on the instrumentation, on the calibration procedures, on the type of measurements to be performed, on the temperature regime and on the... 

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