High-pressure DTA

Raemy, A. and Ottaway, M. (1991) The use of high pressure DTA, heat flow and adiabatic calorimetry to study exothermic reactions. Journal of Thermal Analysis, 37, 1965-71. 

A high-pressure DTA or high-pressure DSC apparatus may be used. 

Despite the theoretical advantages of the power compensated approach, the associated instrumentation is much more complex and, therefore, there are circumstances where the simpUcity of DTA has much to recommend it. DTA requires just two thermocouples and can, therefore, be used under demanding conditions. For example, high-pressure DTA experiments have been used extensively to generate phase diagrams of polyethylene and related low molar mass compounds— high-pressure DSC is rather more complex. 

Fig. 4.43 A schematic drawing of a high-pressure DTA apparatus (1) high-pressure pipe, (2) copper tube, (3) sheathed heater, (4) sheathed Alumel-Chromel thermocouple, (5) high-pressure vessel, (6) copper seal, (7) sample, and (8) reference. (Reprinted with permission from Polymer J. 1992, 24, 422.)...

High-pressure DTA has been reviewed briefly by Locke (72). The previous studies have been concerned mainly with the effect of pressure on solid - liquid and solid - solid, equilibria. The equipment used in high-pressure studies employs piston-cylinder pressure-generating systems in the 60-80-kbar range, while lower-pressure equipmem involves external pressurization by gases. 

DTA instruments for high-pressure hydrogenation reactions have been described by various Japanese investigators (76, 77). Bousquet et al, (78) described a high-pressure DTA furnace and sample holder which could be... 

Figure 6.21. Three-wire thermocouple assembly for high-pressure DTA apparatus 74).

Figure 6 22. High-pressure DTA apparatus of KubaMa and Schneider (75). (u) a. r = coolers. b, n = pyrophillite insulating disk c = heating block d = high-pressure vessel e. m — copper seals f, I = Zr02 blocks g = copper shield h = calorimeter block i = thermocouple k = corundum capillary o = fastening screw p = support c] = in- and outlet of refrigerant. (/ )(i) Open Pt/Ir well In) closed teflon well with brass holder lh = steel-sheathed thermocouple).

Figure 6.23. High-pressure DTA system described by Williams and Wendlandt (131. l ) Schematic diagram of apparatus. A. high-pressure DTA cell B. T T Controls Company Model No. TPC-2000 temperature programmer C Du Pont Model 900 recording module D, relief valve E, valve F. pressure gauge G. gas pressure regulator H. gas cylinder, b) Schematic diagram of DTA cell. A. furnace chamber B. high-pressure connectors for furnace wires and thermocouples. C. furnace D. DTA sample and reference holders E. gas outlet tube F, Buna-N O-ring G. base plate H. Conax connector for thermocouple wires 1. gas inlet-outlet connector.

High-pressure DTA and DSC systems have been described by Wurflinger et al. (132-135). These instruments can be used in the temperature range —200-150CC at up to 3 kbar pressure. The DTA cell is a cylindrical pressure vessel made of copper-beryllium, closed al the top by a Bridgman piston. From the bottom, two steel-sheathed thermocouples were introduced into the inner volume of the vessel where identical DTA wells were fastened onto the two thermocouple junctions and inserted into a symmetrical calorimeter block. 

The boiling point of benzoic acid is shifted to higher temperatures by use of high-pressure DTA. Levy et al. (38) obtained the DTA curves of pure benzoic acid at ambient pressure and at a pressure of 2000 psig, as shown in Figure... 

The diagram in Fig. A.10.2 displays an instrument based on the classical design of a heat flux DTA (see Appendix 9). With a related design, differential calorimetry and thermogravimetry can be carried out simultaneously. Figure A. 10.3 illustrates a typical high-pressure DTA setup which is usable up to 500 MPa of pressure, 5,000 times atmospheric pressure. The pressure is transmitted by a gas, such as nitrogen. 

A high-pressure DTA assembled by the user is illustrated schematically in Figure 2.15 [27, 28). The pressure in the sample holder unit is increased by an electrical or mechanical pump, using either dimethylsilicone (maximum pressure 600 MPa) or kerosene (maximum pressure 1000 MPa) as the pressure medium. The temperature range of this instrument is 230-670 K at a heating rate of 1-5 K min" . The phase transiton behavior of various polymers is measured using the above type of high-pressure DTA [29-31]. 

Figure 2.14 Schematic diagram of a commercial high-pressure DTA apparatus (reproduced by permission of TA Instruments)...

Commercial high-pressure DTA instruments use an inert purge gas to attain a maximum operating pressure of 10 MPa. The DTA heating curves of polyethylene measured over a range of pressures are presented in Figure 2.16. 

Custom high-pressure DTA was used (15]. Sample mass 8-10 mg heating rate 10 °C min. ... 

Figure 7.15 High-pressure DTA curves of poly(ethylene terephthalate)(PET) [14]...

Sample mass, 5 mg apparatus, Rigakudenki R-1 high-pressure DTA crucible, hermetically sealed aluminum crucible with a pinhole in the center of the cover (diameter 5 mm, height 2.5 mm) heating rate, 10 "C min". ... 

Stability [37] (nitroglycerine begins to decompose at 223 K (50 °C), to decompose more rapidly at 333-343 K (60-70 °C), to decompose very quickly at 408 K (135 C), boils at 418 K (145 "C) and detonates at 488-491 K (215-218 Clin a nitrogen atmosphere at different pressures (high-pressure DTA, sample mass 5.0 mg, 5 C min ), data obtained are as follows when the pressure is >7.8 MPa, nitroglycerine ignites, whereas at normal pressure there is only a vaporization endothermic peak (Tp ca 463 K ca 190 °C)... 

Figure 15. Summary of glass transition temperatures of HDA P < 0.4 GPa) and VHDA (P>0.8 GPa) deduced in the literature as measured by Andersson et al. (squares) [80-84], Mishima (circle and grey bar) [41], Seidl et al. (triangles) [123], and Handle et al. (stars) [124]. Open squares from dielectric relaxation measurements [80-83] filled square from high-pressure Cp and thermal conductivity data [84] circle from high-pressure DTA [41] open triangle by DSC at Ibar [123] filled triangles by high-pressure dilatometry [123] stars from high-pressure structural relaxation times [124],...

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). 

FIG. 16 DTA curves of cellulose heated and burned under 25 bars of oxygen. High-pressure DTA 404 H instrument from Netzsch. (From Ref. 112.)... 

It should become clear from this review that calorimetry, (high pressure) DTA, and DSC give relevant, reproducible data that are of great importance in many fields of food technology, because this information characterizes the food globally. From the basics of food technology it is easy to understand that calorimetric techniques help in quality control, improvement of food characteristics, development of new operations, and process safety [127-134]. 

The first differential scanning calorimeter was introduced by Watson et al. (1964) (Fig. 10.2(a)). A number of new developments in the instrumentation have since been made. The temperature scan is controlled, and data are collected and analysed by computers in today s instruments. Simultaneous measurements of differential temperature (AT) and sample weight, i.e. combined DTA and TG as well as combined DTA and TO A, are now commercially available. High-pressure DTA instruments have been in use since the early 1970s. In 1966, Cohen and co-workers constructed a DTA cell which could be... 

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