Thermal analysis coupled

Positron annihilation Thermal analysis coupled with mass spectroscopy... 

The reaction processes of substances cannot be analyzed by simple DTA/DSC or TG when thermal transition and the mass change due to reaction overlap. If DTA/DSC or TG is coupled with an evolved gas detector (EGD) and/or evolved gas analyzer (EGA), the reaction process can clearly be detected. Among various thermal analysis coupled simultaneous techniques [56], DTA/DSC or TG coupled with EGD and/or EGA is extensively used. TA-EGD-EGA coupled... 

A common feature in the models reviewed above was to calculate pressure and temperature distributions in a sequential procedure so that the interactions between temperature and other variables were ignored. It is therefore desirable to develop a numerical model that couples the solutions of pressure and temperature. The absence of such a model is mainly due to the excessive work required by the coupling computations and the difficulties in handling the numerical convergence problem. Wang et al. [27] combined the isothermal model proposed by Hu and Zhu [16,17] with the method proposed by Lai et al. for thermal analysis and presented a transient thermal mixed lubrication model. Pressure and temperature distributions are solved iteratively in a iterative loop so that the interactions between pressure and temperature can be examined. 

Notice that two thermocouples can be differentially connected, for instance in a differential thermal analysis apparatus (see Fig. 2.39), in order to be able to measure at the same time the specimen temperature and the temperature difference in comparison to a reference sample. Several thermocouples, moreover, may be connected in series to form a thermopile, which is a device with an increased sensitivity relative to a simple couple. 

Characterization. Differential scanning calorimetry and thermal mechanical analysis data were obtained on a DuPont 990 thermal analyzer coupled with a DuPont DSC or TMA cell. Isothermal aging studies were carried out with an automatic multisample apparatus. 

Nasraoui, M., Bilal, E. Gibert, R. 1999. Fresh and weathered pyrochlore studies by Fourier transform infrared spectroscopy coupled with thermal analysis. Mineralogical Magazine, 63, 567-578. 

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). 

The research papers which originated in the last couple of years in different countries in this field indicate that ED and Er are not generally reported and there is an emphasis on the study of comprehensive thermal behavior of explosives as a function of temperature or time by means of different thermal analytical techniques. Most commonly used methods of thermal analysis are differential thermal analysis (DTA), thermogravimetric analysis (TGA) or thermogravimetry and differential scanning calorimetry (DSC). 

Differential scanning calorimetry is primarily used to determine changes in proteins as a function of temperature. The instrument used is a thermal analysis system, for example a Mettler DSC model 821e. The instrument coupled with a computer can quickly provide a thermal analysis of the protein solution and a control solution (no protein). The instrument contains two pans with separate heaters underneath each pan, one for the protein solution and one for the control solution that contains no protein. Each pan is heated at a predetermined equal rate. The pan with the protein will take more heat to keep the temperature of this pan increasing at the same rate of the control pan. The DSC instrument determines the amount of heat (energy) the sample pan heater has to put out to keep the rates equal. The computer graphs the temperature as a function of the difference in heat output from both pans. Through a series of equations, the heat capacity (Cp) can be determined (Freire 1995). 

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. 

Thermal analysis probes the enthalpy change of a reacting solid as a function of time, which is time-resolved calorimetry. In order to enhance the low solid state reaction rates of the reaction couples, the calorimeter has to operate at elevated tempera-... 

Photo-DSC on the other hand, is a much more recent technique which has been developed thanks to technological developments in thermal analysis and coupled techniques. Until very recently, it has been used mainly to study photopolymerization or photocuring reactions by measuring the heat of reaction. We proposed the use of this powerful technique to study polymer photo-aging, using the photo-DSC as an accelerated aging device and coupled in situ analysis of the modification of the morphology of the materials. In this case, the crystallizability of the polymer is used as an indicator of the structural modifications. 

Whereas Redfern [57] has pointed out the advantages of simultaneous thermal analysis techniques (particularly TG-DSC and TG-DTA) over techniques conducted singly, an even more complete thermal profile is provided when a thermal analyser is coupled to some form of gas analyser (MS or FTIR). Mohler and co-workers [51] have reported TG-DSC-MS of the thermal decomposition of the vulcanisation accelerator tetramethyl thiuram disulphide (TMTD) in rubber degradation of TMTD starts at about 155 °C, as evidenced by m/z 76 (CS2) and 44 (radical of the secondary dimethylamine). 

The changes occurring during the initial activation stage of chromia are illustrated in Fig. 1 on the basis of coupled thermal analysis mass spectrometry measurements for the dismutation reactions of CHC1F2 and CHC12F, Eqns (2) and (3). 

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