Differential thermal analysis instrumentation

Measurements of differential scanning calorimetry (DSC) were obtained on a TA Instruments 2910 thermal analysis system (Fig. 2). Samples of approximately 1-2 mg were accurately weighed into an aluminum DSC pan, and covered with an aluminum lid that was crimped in place. The samples were then heated over the range of 20-140 °C, at a heating rate of 10 °C/min. Valproic acid was found to boil at 227 °C. 

This instrument was originally proposed for quantitative differential thermal analysis (DTA) (34) and it has proved indeed to be very suitable... 

Differential. thermal analysis can also be used to construct binary phase diagrams on the basis of observed melting points. This information is of importance since the nature of the phase diagram as would exist for an enantiomeric pair can be instrumental in choosing a resolution strategy [23,24]. When a drug candidate contains one or more chiral centers, it is frequently... 

ARC = Accelerating Rate Calorimeter (Columbia Scientific Instrument Corp.) DSC = Differential Scanning Calorimeter DTA = Differential Thermal Analysis RC1 = Reactor Calorimeter (Mettler-Toledo Inc.) RSST = Reactive System Screening Tool (Fauske and Associates) VSP = Vent Size Package (Fauske and Associates) ... 

Major instrumentation involved with the generation of thermal property behavior of materials includes thermogravimetric analysis (TG, TGA), DSC, differential thermal analysis (DTA), torsional braid analysis (TBA), thermomechanical analysis (TMA), thermogravimetric-mass spectrometry (TG-MS) analysis, and pyrolysis gas chromatography (PGQ. Most of these analysis techniques measure the polymer response as a function of time, atmosphere, and temperature. 

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. 

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. 

DSC and related methods (differential thermal analysis, DTA) are of great practical importance. Therefore, one finds highly sophisticated commercial instruments for a variety of applications. DTA has been combined with in-situ emf and Knudsencell measurements. The interested reader is referred to the special literature on this subject [M.E. Brown (1988)]. 

Interest in the use of calorimetry as a routine diagnostic or analysis tool has gained significant momentum only in the last 50 years. This interest has lead to the development of popular procedures such as differential thermal analysis (DTA) and differential scanning calorimetry (DSC). A wide variety of solution calorimetric techniques exist today. These techniques include thermometric titration, injection and flow emhalpimetry. The major growth of commercial instrumentation for calorimetry has occurred to address applications in routine analysis and the rapid characLerizaiion of materials. 

All manufacturers offer computer software in various degrees of sophistication, most of which are at present in a state of development. The instruments are microprocessor controlled, provide differentiation, integration, disc storage of data and data analysis 6.4.1 Differential Thermal Analysis... 

An other method to study structures during cooling and warming is differential thermal analysis (DTA) (Figure 1.25). It measures the different course of temperature between the sample and a probe, which changes its thermal behavior uniformly but does not have a phase transition in the measured temperature range. Such an instrument is illustrated in Figure 1.26. 

Figure 18.13. Differential thermal analysis of titanium. Reproduced from TA Instruments, Inc. (1995b), by permission of TA Instruments, Inc.

Practical methods also have been reported for semicon-tinuous measurement of nitrate and carbon in particles from ambient air. For example, an instrument for nitrate monitoring uses collection of particles on an impactor surface, followed by flash volatilization and determination of the nitrate present using a chemiluminescence technique. Ion chromatographs also have been adopted for semicontinuous determination of gaseous and particulate nitrate. Real-time carbon analyzers also are available, one of which uses differential thermal analysis of impactor-collected material. 

Figure 2. Service drops in instrumental laboratory, (a) Gas and electrical supply for differential thermal analysis and (b) cooling water and electrical connections to a mass spectrometer.

The compositions of the products were determined by inductively coupled plasma (ICP) with a Perkin-Elmer plasma 40 emission spectrometer. Simultaneous differential thermal analysis and thermogravimetric (DTA-TG) curves were carried out by using Perkin-Elmer DTA-7000, TGA-7 PC series thermal analysis instrument in air with a heating rate of 10 °C /min. The infrared (IR) spectra were recorded on an Impact 410 IR spectrometer on samples pelletized with KBr powder. Valence states were determined by X-ray photoelectron spectroscopy (XPS). The XPS for powder samples fixed on double sided tapes was measured on an ESCA-LAB MKII X-ray photoelectron spectrometer. The Cis signal was used to correct the charge effects. 

Our processing is much better now, and we can get the properties right so they re reproducible. We know enough about the process and the conditions, and so we can always get to reasonable quality with 95 K materials. We have a lot more instrumentation now to do things that we had done by just pure happenstance. We ve put eyes into the ceramists methods. We put a resistor, say, into it so that as you go up and down the temperature scale, you monitor the differences as you see them, and that s called differential thermal analysis. Once the ceramists make the stuff, we go to an electron microscope and see what that little glitch means insofar as the microstructure is concerned. We go to the data acquisition system, the computer, and find out where the atoms are, what the crystal structure is, and we ask, Did the electrons go the wrong way ... 

Preliminary TGA and differential thermal analysis (DTA) curves were obtained on individual oxides and on the mixed transition metal-uranium oxides to ascertain the reaction characteristics of the individual systems. The TGA data were obtained on an Ainsworth BR balance equipped with an AU recorder. Samples of 1 gram each were heated to 1100°G. at 10°G. per minute. DTA information was obtained on a Tempres Research Model DT-4A instrument. Samples weighing approximately 50 mg. were heated at 5°G. per minute to 1250°G. Differential temperatures were measured with a platinum-platinum 10% rhodium thermocouple at a recorder sensitivity of 20 microvolts per inch. 

Fig. 1 Schematic diagrams of the (A) differential thermal analysis (DTA) (B) power-compensated DSC and (C) heat-flux DSC cells. (From Ref adapted from DuPont Instruments Systems Brochure.)...

An instrument performing measurements of D2 (viz. the ratio of the resistivity of ice to that of a product at a given temperature) and implementing DTA (differential thermal analysis) was developed to control freeze-drying processes the principal components are a test chamber, a cooling and heating unit, a digital computer system and a printer. It was used to evaluate the thermal features of a 20% sucrose solution [12]. 

Thermal analysis involves observation of the usually very delicate response of a sample to controlled heat stimuli. The elements of thermal-analysis techniques have been known since 1887 when Le Chatelier used an elementary form of differential thermal analysis to study clays (4), but wide application did not come until the introduction of convenient instrumentation by du Pont, Perkin-Elmer, Mettler and other sources in the 1960 s. Currently, instrumentation and procedures are commercially available for DTA, DSC, TGA, TMA, and a number of so-called hyphenated methods. Several methods are currently under study by ASTM committees for consideration as to their suitability for adoption as ASTM standards. 

Dynamic methods of thermal analysis such as "thcrmogravimetric analysis," differential thermal analysis and dynamic calorimetry" have resulted from more recently achieved technical and instrumental refinements. 

Anonymous Differential Scanning Calorimetry, A Quantitative Technique for Differential Thermal Analysis. MPL-6632, Perkin-Elmer Instrument Division, Norwalk, Conn. (1964). 

Figure 10.2 Differential thermal analysis (DTA) instrumentation. VTs and VTr are the thermocouple voltages for measuring sample and reference temperatures, respectively. (Reproduced with permission from R.F. Speyer, Thermal Analysis of Materials, Marcel Dekker, New York. 1993 Taylor Francis Group Ltd.)...

---