DTA diagram

Upon heating in air the TGA-DTA measurement showed that the spent catalyst sample lost 5% weight and two exothermal peaks (at 300°C and 400°C) were observed. Similar measurements with spent alumina (without CuO) showed only one peak in the DTA diagram (405°C). A fresh and spent Cu0/A1203 sample were characterized with EDAX. The analysis showed that chlorine was present on the spent catalyst, whereas it was totally absent in the fresh sample. The origin of chlorine was from a chlorine containing impurity in the hydroxy ketone I which irreversibly adsorbed on the catalyst. Adsorbed chlorine is known to increase the acidity of the alumina support and thereby may enhance cracking or polymerisation processes which finally lead to catalyst deactivation. The dark-yellow colour of the initially white supports after use in the reaction indicated that residues were retained on the catalyst. The yellow colour disappeared after calcination in air at 500°C,... 

Thermo-gravimetric analyses (TGA) were carried out to show that there was no difference between the curves of intermediate products and the one after calcinations. The results showed that there was no notable loss of weight in the TGA curves, proving the existence of CuO, which does not decompose at this temperature range. Further, the similarity of the TG curves of two samples shows the direct synthesis of CuO. fig 17a shows the TGA diagrams of the sample No. 2, and copper acetate and the compoxmd before calcinations, fig 17b shows the DTA diagrams of the sample No. 2, copper acetate and the compound before calcinations. 

The enthalpy and temperature data in Table 3.13 is intended to identify the main groups of minerals from an available TGA or DTA diagram from coal pyrolysis or low-temperature ash (ashing below 380 °C). If, for example, in a pyrolysis curve from TGA, the mass change per time peaks at 670 °C, it can be concluded that MgCOs is part of the coal and a part of the measured ultimate carbon content will require heat to be gasified. To quantify the effect, the carbonate CO2 should be determined for that sample. 

In this diagram, the arrangement of the sample, S, and the reference, R, across the differential TC is shown, and a typical DTA analysis is also given. Note that at low temperatures, the DTA peaks are endothermic. That is, heat is absorbed. Such peaks are similar to those obtained when water-of-hydratlon is lost, or when the solid state reaction undergoes a loss of water. 

One can quantify the heat flow involved within the system in terms of the DTA peak produced. Consider the following, given as 7.1.17. on the next page. In this diagram, the sample, S, is within the furnace which is at a temperature, Tg. The heat flow is dQ/dt emd r is the thermal resistance. The sample undergoes an enthalpy ehange, AH, at its solid state reaction temperature. 

We can thus "interpret" a DSC peak in terms of this equation, as we did for the DTA peak, as shown in the following diagram ... 

DTA is especially suited in the construction of unknown phase diagrams of binary compounds. A hypothetical phase die am and the DTA curves which would be used to construct it are shown in the followii diagram, given as 7.2.1. on the next p e. 

Construction of a Phase Diagram ly Use of Several DTA Thermograms (DTA Runs 1 through 7)... 

Phase diagrams give valuable information about the compounds that can form in a system of components. These compounds can then be prepared and studied. For the experimental determination of phase diagrams the following methods are used. In differential thermal analysis (DTA) a sample of a given composition is heated or cooled slowly... 

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. 

Proceeding along a parallel track, Guillory and coworkers used DTA analysis to study complexation phenomena [2]. Through the performance of carefully designed studies, they were able to prove the existence of association complexes and deduced the stoichiometries of these. In this particular work, phase diagrams were developed for 2 1 deoxycholic acid-menadione, 1 1 quinine-phenobarbital, 2 1 theophylline-phenobarbital, 1 1 caffeine-phenobar-bital, and 1 1 atropine-phenobarbital. The method was also used to prove that no complexes were formed between phenobarbital and aspirin, phenacetin, diphenylhydantoin, and acetaminophen. 

Two types of DSC measurement are possible, which are usually identified as power-compensation DSC and heat-flux DSC, and the details of each configuration have been fully described [1,14]. In power-compensated DSC, the sample and reference materials are kept at the same temperature by the use of individualized heating elements, and the observable parameter recorded is the difference in power inputs to the two heaters. In heat-flux DSC, one simply monitors the heat differential between the sample and reference materials, with the methodology not being terribly different from that used for DTA. Schematic diagrams of the two modes of DSC measurement are illustrated in Fig. 9. 

From DTA measurements phase diagrams can be constructed as shown for ethyleneglycol in Fig. 1.34. A solution of 40 % ethyleneglycol is only stabile in the glass phase below = -135 °C, at = -120 °C unfrozen water starts to crystallize, at = -65 °C a recrystallization is found, and at = —45 °C melting will start. As recrystallization is the growing of existing crystals, and not the nucleation of new ones, this event cannot be detected by DTA, but can be observed in a microscope when a transparent area becomes opaque. 

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

The following diagram (Fig. 11) shows the original DTA melting curve of indium and the inserted calibration rectangle which is required for the manual evaluation. The experimental parameters which were used for the calculation of AH are given below, and also the evaluation of /uV sec for the peak area. 

Figure 2.40. Phase diagram of the Mg-Cu alloy system. For the alloys marked (1) (at 5 at.% Cu) and (2) (at 20 at.% Cu), the DTA curves are shown on the right. Notice that, on cooling, a sharp thermal effect due to the invariant eutectic transformation is observed. At higher temperature the crossing of the liquidus curves is detected. (The coordinates of the eutectic point are 485°C and 14.5 at.% Cu.)...

Possible determinations from DSC or DTA measurements include (1) heat of transition, (2) heat of reaction, (3) sample purity, (4) phase diagram, (5) specific heat, (6) sample identification, (7) percentage incorporation of a substance, (8) reaction rate, (9) rate of crystallization or melting, (10) solvent retention, and (11) activation energy. Thus, thermo-calorimetric analysis can be a useful tool in describing the chemical and physical relationship of a polymer with respect to temperature. 

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