Differential thermal analysis calibration

R.L. Bohon, AnalChem 35 (12), 1845-52 (1963) CA 60,1527 (1964) Approx heats of expin, Qv were detd on mg amounts of propints and expls by differential thermal analysis (DTA). Small-screw-cap metal cupsi sealed with a Cu washer served as constant vol sample containers the initial cup pressure could be controlled from 0 to approximately lOOOpsia. The calibration constant was calcd for each run from the total heat capacity of the cup and the relaxation curve, thereby compensating for equipment variations. 

A variety of techniques have been used to determine the extent of crystallinity in a polymer, including X-ray diffraction, density, IR, NMR, and heat of fusion [Sperling, 2001 Wunderlich, 1973], X-ray diffraction is the most direct method but requires the somewhat difficult separation of the crystalline and amorphous scattering envelops. The other methods are indirect methods but are easier to use since one need not be an expert in the field as with X-ray diffraction. Heat of fusion is probably the most often used method since reliable thermal analysis instruments are commercially available and easy to use [Bershtein and Egorov, 1994 Wendlandt, 1986], The difficulty in using thermal analysis (differential scanning calorimetry and differential thermal analysis) or any of the indirect methods is the uncertainty in the values of the quantity measured (e.g., the heat of fusion per gram of sample or density) for 0 and 100% crystalline samples since such samples seldom exist. The best technique is to calibrate the method with samples whose crystallinites have been determined by X-ray diffraction. 

The thermal properties of benzoic acid were evaluated using simultaneous differential thermal analysis (DTA) and thermogravimetric analysis (TGA). This work was performed on a Shimadzu DT-30 Thermal Analyzer system, which was calibrated using indium standard. Using a heating rate of 10°C/min, the thermograms presented in Figure 3 were obtained. 

Differential Thermal Analysis. High temperature differential thermal analyses were obtained with a Dupont Model 1200 instrument. Samples were heated from room temperature to 950° C at a rate of 20°C/min in a slow stream of hydrogen. Molybdenum cups were used to hold the sample and alumina reference. The instrument was calibrated with sodium chloride (mp 800° C). 

Differential thermal analysis was performed with the DuPont 900 differential thermal analyzer the heating rate was usually 10°C. per minute. To determine heats of reaction, the calorimeter attachment to the Du Pont instrument was employed. Planimeter determinations of peak areas were converted to heat values by using standard calibration curves. For the infrared spectra either a Beckman IR5A instrument or a Perkin Elmer 521 spectrophotometer with a Barnes Engineering temperature-controlled chamber, maintained dry, was used. Specimens for infrared were examined, respectively, as Nujol mulls on a NaCl prism or as finely divided powders, sandwiched between two AgCl plates. For x-ray diffraction studies, the acid-soap samples were enclosed in a fine capillary. Exposures were 1.5 hours in standard Norelco equipment with Cu Ko radiation. For powder patterns the specimen-to-film distance was 57.3 mm. and, for long-spacing determinations, 156 mm. 

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.)... 

Using differential scanning calorimetry (DSC) (or, less directly, differential thermal analysis (DTA)) (see Section 2.8.5., above) it is possible to measure several of the thermodynamic properties of solids and of solid state reactions. The DSC response is directly proportional to the heat capacity, Cp, of the sample, so that by use of a calibrant it is possible to obtain values of this fundamental thermodynamic property, at a particular temperature, or as an average over a specified temperature range. Other thermodynamic properties are readily derived from such measurements ... 

The decomposition temperatures of hydrates were measured by means of differential thermal analysis (DTA) under the conditions of excess gas in a stainless steel flask that was developed specially for the investigation of hydrate formation with a gaseous guest at high hydrostatic pressure. The hydrate decomposition temperature was measured with a chromel-alumel thermocouple to the accuracy of 0.3 K. The thermocouple was calibrated with the use of temperature standards. Pressure was measured with a Bourdon-tube pressure gauge. The error of the pressure measurements did not exceed 0.5 %. This procedure was described in more detail previously.The gases used in the investigation... 

There are several different types of instrument covered under the term DSC, which have evolved from differential thermal analysis (DTA) and measure the temperature difference between sample and reference pans located in the same furnace. This is then converted to heat flow using a calibration factor. A detailed analysis of DSC requires consideration of the various sources of heat loss, and these are generally captured in the calibration routine for the instrument. Absolute temperature calibration is achieved through the use of pure indium (156.6 °C) and tin (231.9 °C) melting-point standards. A comprehensive analysis of the theory of DSC contrasted with DTA may be found in several reference works (Richardson, 1989, Gallagher, 1997). 

In many of the methods of quantitative differential thermal analysis, the calibration coefficient can be mathematically deiermined and no experimental procedures are necessary. For example, Kronig and Snoodjik ((04) calculated K for a cylindrical sample holder as... 

As with many other analytical techniques, the temperature axis used in differential thermal analysis (and DSC) must be calibrated with materials having known transition temperatures. The International Confederation of Thermal Analysis (ICTA) has been very active in developing a set of standard materials for this purpose (19) and has worked with the U.S. National Bureau of Standards to have these materials made commercially available (20). The U.S. National Bureau of Standards GM 754-GM 760 DTA temperature standards are listed in Table 6.2. They cover the temperature range from —83 to 925 C. The results of an ICTA round-robin study with 24 cooperating laboratories have been reported by Menis and Sterling (20). 

Thermal gravimetric analysis and differential thermal analysis (TGA/DTA) can be performed by using a SDT 2960 Simultaneous Differential Thermal Analyzer (TA Instruments, Inc., New Castle, DE). The instrument was calibrated with gold supplied by Perkin-Ehner. Samples (70 mg) of as-prepared powders were hand-pressed in a 3 mm dual action die and placed inside Pt sample cups and heated at the rates of 10 K/ min from ambient temperature to 1400°C. The reference material was used as a pellet of a-alumina. A flow of synthetic air at 50mL/min was maintained during the experiments. 

Test method for glass transition temperatures by differential scanning calorimetry or differential thermal analysis Standard practice for calibration of temperature scale for thermogravimetry... 

Differential Scanning Calorimetry. Differential scanning calorimetry is in some respects a modification of differential thermal analysis, and the schematic diagram of a differential scanning calorimeter (dsc) is similar to that of the dta device shown in Figure 12. The essential difference, however, is that the measured quantity here is the differential power supplied to the two wells, rather than the temperature difference. In other words, the dsc device maintains the same programmed temperature in each well and records the power required to achieve this. If a transition takes place in the sample, a characteristic excursion in the measured differential power is observed. The nature of these excursions can be related to the transitional properties of the sample. Furthermore, by proper calibration with a reference material of known thermal properties, the specific heat capacity of the sample may be obtained. 

Standard Test Method for Assessing the Thermal Stability of Chemicals by Method of Differential Thermal analysis. (Specimens weight varies from 20 to 30 mg. The reference was an empty pan. The Heat Rate used was 10 °C/min) Standard Test Method for Temperature Calibration of Differential scanning Calorimeters and Differential Thermal Analyzers... 

If much well-ordered kaolinite is present, the assymmetric peaks are not prominent in the patterns from random samples, and the basal reflections are sharper and much enhanced in intensities in patterns from oriented samples. If much disordered kaolinite is present, the assymmetric peaks are prominent in the first patterns, and the basal reflections are much enhanced in the second. Chemical pretreatments prior to X-ray diffraction, such as those proposed by Wada [1965] and Alexiades and Jackson [1965], are sometimes useful in determining amounts of kaolinite and halloysite. Where the halloysite is tubular, it is easily detected in electron micrographs, although the amount can seldom be determined. Amounts of hydrated halloysite can be determined if allophane is not present in differential thermal analysis by calibrating and measuring the low-temperature endothermic peak. 

Barshad, L, 1952. Temperature and heat of reaction calibration of the differential thermal analysis apparatus. Am, Mineral 37 667-694. 

The deactivated catalysts were also burned in a calorimeter under compressed air flowing at 40 ml/min. (Thermal Analysis Station TAS 100 - Rigaku - TG 8110). Analysis were performed by differential scanning calorimetry (TPO/DSC) and combustion heats were obtained by integration of the profiles and using appropriate calibration samples. 

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