Micro-DTA

Takemura and co-workers31 have shown by optical measurements, X-ray diffraction and micro-DTA measurements that the high-pressure phase is liquid-crystalline, and that... 

A special type of micro DTA-holder (Fig. 13 c) uses large-surface, vapor-deposited thermopiles as the AT sensor which assure excellent heat contact with the crucibles. No undesirable heat exchange occurs at the sensor leads which are also vapor-deposited. This results in high sensitivity and precision. 

Audiere et al. (122) described a thin-film micro-DTA apparatus that permitted the study in situ of thin-film materials. The samples are deposited by evaporation, cathodic sputtering, and so on, on to a substrate bearing metallic films, which constitute the thermocouples of the DTA. The sample... 

The determination of DTA curves from microgram quantities of sample has previously been described by Mazieres (4) (Section 2). A more comprehensive review of micro-DTA instrumentation is that by Sommer and Jochens (84). In this review, the entire area of high-temperature microscopy, coupled with DTA measurements, is discussed in detail. In most of the instruments described, the thermocouple junction acts as a heater and temperature detector, as well as the sample holder. 

The micro-DTA apparatus developed by Miller and Sommer (85) is shown in Figure 6.26. The circuit used a motor-driven variable voltage regulator and was capable of heating rates from 5r C/min to lOOOQsec. Recordings... 

Figure 6.26. Micro DTA apparatus (2). [a) sample holder (6 electrical circuit l85. 86. ...

There are several forms of /i-TA. Micro-DTA involves comparison of the temperature difference of the sample with respect to a thermally inert reference material, as in normal DTA. If the probe is loaded with a small force, microthermomechanical analysis results. The u-TA configuration can be used for rapid pyrolysis of a small area of the sample and the evolved gases can be analyzed online by a GC-MS system. This mode is particularly valuable for the compositional analysis of synthetic polymers. Sinusoidal temperature programs have also been applied in -TA leading to temperature modulated /t-TA. 

Figure 7.10. Micro-TMA (sensor deflection) and micro-DTA (derivative power) curves for quenched poly (ethylene terephthalate).

It should be noted that the use of the L-TA power signal was previously termed micro-DTA and not micro-DSC. This is because, as discussed above, the volume and hence the mass of the heated sample is unknown and its calculation at present does not seem possible. Hence it is argued that micro/nano-TA cannot be described as a form of calorimetry, because it cannot measure the heat capacity of a material or the enthalpies associated with particular transitions. This is a major limitation of thermal probing. However, the ability of this technique to detect transitions occurring in a sample at the micrometer and submicrometer levels and to measure the temperature range over which those transitions occur is a major advantage. 

The crucibles of DTA-holders are chosen according to the sample weight. That means that for small samples or large samples one has to decide between macro and micro holders. 

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). 

Fig. 13. Special types of DTA micro- and macro-sample holders (a - h)...

Although a number of secondary minerals have been predicted to form in weathered CCB materials, few have been positively identified by physical characterization methods. Secondary phases in CCB materials may be difficult or impossible to characterize due to their low abundance and small particle size. Conventional mineral identification methods such as X-ray diffraction (XRD) analysis fail to identify secondary phases that are less than 1-5% by weight of the CCB or are X-ray amorphous. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM), coupled with energy dispersive spectroscopy (EDS), can often identify phases not seen by XRD. Additional analytical methods used to characterize trace secondary phases include infrared (IR) spectroscopy, electron microprobe (EMP) analysis, differential thermal analysis (DTA), and various synchrotron radiation techniques (e.g., micro-XRD, X-ray absorption near-eidge spectroscopy [XANES], X-ray absorption fine-structure [XAFSJ). 

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. 

Early devices fbr thermogravimetric analysis were limited in precision and convenience when compared with DTA or DSC equipment. Now devices for simultaneous DSC and TG are on the market which can operate at high temps in reactive atms permitting the simulation of high temp reactions on a micro scale. The use of TG for the study of reaction kinetics was described in Sect 5.3.3. An exptl study of the sublimation of ammonium perchlorate was published by Jacobs and Jones (Ref 25). Similar techniques should find application in the study of other propint systems. The product gases have been collected for further analysis using gas chromatography and mass spectrometry... 

For the determination of reaction parameters, as well as for the assessment of thermal safety, several thermokinetic methods have been developed such as differential scanning calorimetry (DSC), differential thermal analysis (DTA), accelerating rate calorimetry (ARC) and reaction calorimetry. Here, the discussion will be restricted to reaction calorimeters which resemble the later production-scale reactors of the corresponding industrial processes (batch or semi-batch reactors). We shall not discuss thermal analysis devices such as DSC or other micro-calorimetric devices which differ significantly from the production-scale reactor. 

The differential thermal analysis (DTA) curve of meperidine hydrochloride run from room temperature to the melting point exhibits no endotherms or exotherms other than that associated with the melt. The DTA curveof meperidine hydrochloride, U.S.P. (Vforeth Lot No. F-665901) run on a Dupont 900 DTA using a micro cell and a heating rate of f>°C./min. is shown in Figure 5. 

In the present paper, the main objectives are (i) to prepare reactive peroxocomplexes in situ at the material s surface starting from a precursor material, and (ii) to control the catalytic properties (activity, selectivity, oxidant efficiency) via modification of the micro-environment of the catalytic center through variation of the anion population. The catalyst precursors and the in situ formed peroxocomplexes are characterized by means of XRD, IR, TGA/DTA and UV-Vis reflectance spectroscopy. 

With the controlled atmosphere heated sample holder, it was a simple matter to connect a thermistor-type thermal conductivity cell to the system and, by means of an external multichannel recorder, record the DRS and the evolved gas detection lEGD) curves simultaneously (17). This modification of the apparatus is shown in Figure 9.4. The cell was connected to a Carle Model 1000 Micro-Detector system by means of metal and rubber tubing. The thermal conductivity cell was enclosed by an aluminum block which was heated to 100 C bv means of a cartridge heater. The block was connected to a preheat chamber, also operated at 100 C, which was used to preheat the helium gas stream before it entered the detector. The output from the detector bridge was led into one channel of a four-channel 0-5 mV Leeds and Northrup multipoint strip-chart potentiometric recorder. The temperature programmer from a Deltatherm III DTA instrument was used to control the temperature rise of the DRS cell. Output from the Beckman Model DK-2A... 

New methods of micro heterogeneous super loaded ZnO/FAU systems synthesis were developed which allow to control oxide phases state. Their formation and properties were studied by TG-DTA, XRD and IR spectroscopy. High ZnO dispersion, which is provided by a decomposition of Zn salts on ion exchanged FAU, is favorable for catalytic conversion of CH3OH to water-free CH2O over these systems. Suggested methods can be used for a preparation of systems containing oxide phases of one or several transition metals which, due to their unusual properties, may find various applications in adsorption and catalysis. 

Besides the commercially available DTA / DSC equipment there are quite a variety of micro calorimetric measuring techniques, which are suitable to characterize the thermal stress capacity of substances and mixtures using only small amounts of sample material. Some of these are also commercially available, others are self-made. 

Thermal decomposition studies of TNPDU and its mixtures were carried out using a micro differential thermal analyzer (m-DTA) fabricated in our laboratory. Details of the apparatus are given elsewhere The mixtures of the TNPDU with 3-amino-5-nitro-1,2,4-triazole (ANTA),... 

The aim here is simply to present an overview of the various features on offer. The range of instruments extends from differential scanning calorimeters in a suitcase for on-site use to spatially resolved micro-thermal analysis equipment for samples as minute as 2 x 2 fim. Between these rather extreme examples there is a wide choice of commercial DTA and DSC equipment which allows samples to be studied at temperatures ranging from — 150°C to about 1600°C. For higher temperature measurements (above 1600°C) the equipment becomes increasingly more specialised. The detailed specification of equipment is often difficult (sometimes impossible ) to decipher - there appears to be no common practice between manufacturers. Information can best be obtained by raising questions directly with the manufacturers. Even so, hands-on experience is to be recommended when choosing equipment. 

Analytical services include optical microscopy, scanning electron microscopy, transmission electron microscopy, electron probe microanalysis, scanning auger microanalysis, electron spectroscopy for chemical analysis, x-ray fluorescence, x-ray diffraction, thermal analysis (DSC, DTA, TGA, TMA) and Micro-Fourier transform infrared spectroscopy. 

Mctikr-ToJctlo TMA DTA 134 inr(ice itwdulaied loive) 7 Micro Themutl Analysii 91,99-10QJ29... 

For this summary, forms of thermal analyses under extreme conditions are described for the measurement of heat and temperature, as dealt within Sects. 4.1-4. The distinction between DTA and DSC seen in these methods is described in Appendix 9. In Appendix 10, DTA or DSC at very low and high temperatures and DTA at very high pressures are mentioned. This is followed by a discussion of high-speed thermal analysis which, in some cases, may simply be thermometry. Finally, micro-calorimetry is treated. One might expect that these techniques will develop in this century [1]. The numbers in brackets link to references at the end of this appendix. 

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