TG/DTA

Accurate temperature calibration was necessary for the example above, and this leads on to another advantage of TG-DTA instruments the temperature calibration can be properly carried out as the sample temperature is measured directly, which is not so in conventional thermobalances in which the temperature sensor is not in contact with the sample. A TG-DTA instrument was used to provide accurate transition temperatures for the ICTAC Curie point standards for TG calibration. 

The fact that the sample mass is continuously monitored means that DTA peak measurements can be referred back to a true sample weight, after allowing for prior lower temperature weight losses such as drying. Confidence in the quality of peak area measurements, especially at high temperatures, is increased when the TG data show that no sublimation or decomposition is taking place. Glass transition measurements can be markedly influenced by the moisture content in the case of many important polymers. With STA, the moisture content at the time of measurement is known exactly. 

DTA data can help to explain unusual features of the TG curve. Abrupt changes in the rate of weight loss can occur when the sample melts, or at 

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HPLC-PDA-MS) are already being used. Although HPLC-NMR-MS provides a very powerful approach for compositional and structural analysis, it by no means represents the limit of what is possible in terms of hyphenation. On-line extraction and the attachment of multiple detectors (e.g. IR, F) make the technique even more powerful. Other analytical laboratories such as TG-DTA-DSC-FTIR, TD-CT/Py/GC-MS/FTIR and HPLC-UV/NMR/IR/MS have been put to work, but do not represent practical solutions for routine polymer/additive analysis. 

Fujii and coworkers reported the synthesis and detailed structural analyses of alkylammonium/magnesium phyllosilicate hybrids [88], which were prepared by hydrothermal reaction from a mixture ofoctadecyldimethyl(3-trimethoxysilylpropyl)-ammonium chloride, silica sol, and magnesium hydroxide Mg(OH)2. The structure of the hybrid compound was studied by XRD, TEM, electron diffraction, high-resolution solid-state NMR, TG-DTA/MS, and elemental analysis. The resulting analytical information confirmed the unit structure, which consists of a 2 1... 

Simultaneous TG/DTA studies of zinc hydroxystannate (Figure 6), indicate that dehydration of this compound occurs during the temperature range 190°-285°C, with a loss of 19.1% of its initial weight, this corresponding to the loss of 3 moles of water ... 

Figure 7. Simultaneous TG/DTA traces of brominated polyester resin containing 2% ZnSnO in air and in argon.

Figure 9.1. TG-DTA curves for Bisphenol A-derived poly(formal) (A) and Bisphenol AF-derived poly(formal) (AF).

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). 

Cone. This type of crucible shape (Fig. 8 c) provides an increased contact area between crucible and its counterpart on the crucible holder. Especially in the combination TG-DTA this decreases the thermal resistance and allows a better resolution of the measured DTA-effect. 

In the combination TG-DTA normally two crucibles of identical shape and size are used, one for the sample and the other one for the inert reference material. The crucibles may be e.g. cylindrical, conical, plate-type or any other form which favors a good contact between the sample, thermocouple and sample holder (Fig. 8 j). The thermocouples are placed either on the bottom of the crucible or in the center of a cylindrical crucible. The latter type allows the element to be brought protected or unprotected into the center of the substance. 

Another type of Micro TG/DTA sample holder is shown in (Fig. 13 e). It can be equipped with Al, Ni, or Pt crucibles with a miximum volume of 0.15 cm3. For use with the low-temperature furnace, or for sensitive DTA in the middle-range temperature furnace up to a maximum of 600 °C. 

For very high temperatures up to 2400 °C a different Micro TG/DTA sample holder (Fig. 13 f) must be used which usually is equipped with tungsten crucibles. The thermocouple in this case is a combination of W — W 26% Re. This type can be applied for thermoanalytical measurements in high vacuum and in inert atmosphere (noble gases). 

Figure 16 shows a schematic sketch of a thermobalance for TG, DTA and mass spectrometer measurements. - In the center is the thermobalance, enclosed in a vacuum-tight tank, with a thermostatically controlled water jacket. The reaction chamber (R) is surrounded by the furnace and is clearly separated from the balance housing by a diffusion baffle. Diffusion pumps (K) evacuate the balance housing and the reaction chamber. 

In all thermoanalytical investigations it is very important how the substance is placed and positioned on the sample holder. This was illustrated in simultaneous TG-DTA measurements in connection with gas analytical investigations by Wiedemann42. The three profiles shown in Fig. 37 correspond to the water vapor pressures recorded with a mass spectrometer during thermal dehydration of fine-grained calcium... 

The number of experimental factors which influence the results increases considerably when thermogravimetry is combined with other techniques such as DTA, gas chromatography46, mass spectrometry, X-ray etc. A systematic discussion of all these additional factors would lead too far, therefore only a representative example will be discussed here. One of the often-applied multiple techniques is the combination TG-DTA. Besides the actual thermal reactions of the sample, the important factors in DTA are the heat capacity and the thermal conductivity of the sample. Optimum heat transfer is required for such thermoanalytical measurements therefore the shape of the sample and its contact with the crucible is of special importance. 

Fig. 65. Simultaneous TG-DTA curves of o-acetophenetitide measured at various pressures. A start of vaporization, B boiling point, C end of vaporization...

The XPS data were acquired on a Physical Electronics model 5400 XPS system using a Mg anode. For survey spectra, the pass energy was 44.75 eV with a step size of 0.5 eV. The time per step was 50 msec. High resolution spectra were acquired with a pass energy of 35.75 eV and step size of 0.1 eV, The time per step was 50 msec. Thermogravimetric data were obtained on a Perkin-Elmer, Diamond Thermogravimetric/ Differential Thermal Analyzer (TG/DTA) with Pyris software, version 7.0-0.0110. 

Multiple techniques are also possible such as TG-DTA whereby the mass loss of a sample and the DTA curve may be obtained simultaneously. 

The identification of the solid phases and the evaluation of their crystallinity were performed by X-ray powder diffraction while the pore volume of the ZSM-48 materials was evaluated by isothermal (90 °C) sorption of n-hexane, followed in the thermobalance (Stanton Redcroft ST-780 combined TG-DTA-DTG thermoanalyser). 

It was experimentally shown in ref.[3] that the conformation could be confirmed by the pleochromic profile in the IR spectra of the phenyl group. Also, the TG-DTA studies showed that the dyes were confined to keeping such conformations between the interlayers over the melting temperature of the dye (e.g. 300°C). 

Based on those propositions mentioned above, we tried to design a mesoporous material having micro crystalline wall by controlling the ratio of Q4 silicate species formed around TPA and Q2,3 silicate species interact with the micelles. To synthesize micro-mesoporous composite material through the control of Q2-3 and Q4 groups, two different templates were used and nucleation step of microporous material was introduced prior to the crystallization. And also we have attempted to monitor microenvironment of micro-mesoporous composite materials during the nucleation and crystallization steps using TG-DTA and photoluminescence with pyrene probe. 

This study demonstrated that the micro-mesoporous composite materials could be synthesized with two-step treatment by microwave using two different templates system with TPABr and MTAB. This formation was controlled by the self-assembly formation of supramolecular templates between MTA micelles and SiO /TPA gels. As varying microwave irradiation time of micro-mesoporous materials, gradually transition from the mesophase to micro-mesophase was occurred. These materials have higher dm spacing of mesoporous materials and lead to transition from mesophase to micro-microphase by an increment of synthetic time, while the calcined products is formed with bimodal and trimodal pore size distribution under microwave irradiation within 3 h. From TG-DTA and PL analysis, the self-assembly formation of supramolecular templates between MTA+ micelles and SiO /TPA+ gels were monitored. 

Metal content was determined by a LABTAM 8401 inductively coupled plasma spectrometer. X-ray powder diffraction was carried out on a Rigaku 2304 diffractometer with CuK radition(Ni filtered). IR and UV-vis spectra of the solid samples were recorded on a PE FTIR 1760 spectrometer and a PE Lambda Bio 40 instrument respectively. TG-DTA was performed on a CN8076E(Rigaku) thermal analysis instrument. 

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