DTA Technique

Methodology appropriate for the measuring of DTA profiles has been extensively reviewed [12,13]. A schematic diagram illustrating the essential aspects of the DTA technique is shown in Fig. 3. Both the sample and reference materials are contained within the same furnace, whose temperature program is externally controlled. The outputs of the sensing thermocouples are amplified, electronically subtracted, and finally shown on a suitable display device. 

The crystallinity of the so formed intermediate phases was checked by various physical methods. No XRD crystallinity was detected after the first 45 hours of heating, while other techniques such as Infrared (20,66,67), TG-DTA 01,32,67) or 13C NMR (32,33), which are sensitive to the presence of very small amounts of Pr N+ species occluded in ZSM-5 crystallites, confirm that very small size ZSM-5 particles are present in the early beginning of the synthesis process (Table III). Further IR studies of the ZSM-5 skeleton vibration bands (20,66) or catalytic tests (66) have confirmed their presence in B-type procedures. By contrast, and as expected, XRD and DTA techniques give identical crystallinity values in the case of synthesis A (Table III). 

Fig. 4.4. Schematic diagram illustrating the essential aspects of the DTA technique.

Differential thermal analysis (DTA) Chemical testing technique that produces similar data to DSC. DTA uses temperature differences to generate test results DSC has largely replaced the DTA technique as a screening tool for obtaining chemical hazard test data... 

Some scientists describe DSC techniques as a subset of DTA. DTA can be considered a more global term, covering all differential thermal techniques, while DSC is a DTA technique that gives calorimetric (heat transfer) information. This is the reason that DSC has calorimetry as part of its name. Most thermal analysis work is DSC, and Sections 15.3.3 and 15.3.4 provide information about the instrumentation and applications of this technique. 

More advanced techniques are now available and section 4.2.1.2 described differential scanning calorimetry (DSC) and differential thermal analysis (DTA). DTA, in particular, is widely used for determination of liquidus and solidus points and an excellent case of its application is in the In-Pb system studied by Evans and Prince (1978) who used a DTA technique after Smith (1940). In this method the rate of heat transfer between specimen and furnace is maintained at a constant value and cooling curves determined during solidification. During the solidification process itself cooling rates of the order of 1.25°C min" were used. This particular paper is of great interest in that it shows a very precise determination of the liquidus, but clearly demonstrates the problems associated widi determining solidus temperatures. 

Harris (Ref 91), using a differential thermal analysis (DTA) technique, gives an activation energy of 34000cal/mole for RDX and an autoignition temp (apparently the ignition temp at the minimum rate of heating) of 197°C. 

The DTA technique is used to precisely determine the temperature at which the water is released. 

Matsumoto, S., Sherman, P. 1970. A DTA technique for identifying the phase inversion... 

Kurosawa et al. (6), using differential thermal analysis (DTA) techniques, determined = 4.7 kcal mol , an average of... 

We adopt 652 3 k as the transition temperature of stoichiometric NiS from rhombohedral (B) to hexagonal (a) form base on the phase diagram of Kullerud and Yund (8). The temperature of this transition is very dependent on the exact stoichiometry of the material (8 ). The transition enthalpy has been measured via a DTA technique by Conard et al. (7) and we adopt their value of 1.54 0.1 kcal mol". This is considerably higher than an older value of 0.63 kcal mol measured by Biltz et al. (9, 5) but should be much more accurate due to the calibration technique used. Mah and Pankrantz ( 4) estimated 0.7 kcal mol. This transition enthalpy cannot be measured by drop calorimetry since the a form does not revert to the B form on cooling. 

Probably the most important characteristic of military and commercial explosives and solid rocket propellants is performance as related to end use and safety. Performance can be described by a variety of conventional properties such as thermal stability, shock sensitivity, friction sensitivity, explosive power, burning, or detonation rate, and so on. Thermal analysis methods, according to Maycock (51), show great promise for providing information on both these conventional properties and other parameters of explosive and propellant systems. The thermal properties have been determined mainly by TG and DTA techniques and isothermal or adiabatic constant-volume decomposition. Physical processes in pseudostable ma-... 

Catalytic oscillations were detected for various catalysts using DTA techniques by Gallagher and Johnson (287). The rapid response and high sensitivity of DTA make it suitable for the study of these oscillations which may be more difficult to detect by other techniques. 

Rajeshwar et al. (180) used DSC to determine the enthalpy of crystal structure transformations of MC104 salts, where M — Na, K, Rb, Cs, and NH4. As illustrated in Table 7.15, inconsistencies in the literature data are striking, especially with M = Na, K, Rb, and Cs. Most of the earlier studies used DTA techniques to determine the enthalpy changes. However, the literature values for NH4CI04 are in good agreement with the author s results. 

Using sealed-tube sample holders, Santoro and co-workers (32-35) investigated a wide variety of organic reactions. Examples are the cis - trans isomerization of stilbene and oleic acid, polymerization of styrene, Diels-Alder reactions, and others. Unstable intermediates in an organic reaction have been detected using DTA techniques by Koch (36). If a solution of an unstable compound is heated, temperature changes characteristic of reactions of the intermediate can be detected. Conversely, the absence of thermal effects indicates that no unstable product is present. 

Over a decade, Bandi and co-workers have employed EGA-DTA techniques to determine second-phase compounds isolated from steels by selective chemical or anodic dissolution of the matrix. This method has been used qualitatively to identify and quantitatively to determine approximately 35 carbides, carbonitrides, and nitrides, some of which could not be identified... 

---