Modulated temperature methods

In many DSC traces, there is evidence of a kinetic signal being present in addition to the usual changes in heat capacity such as those due to the glass transition and melting. This is 

The heat flow into the sample = C x scanning rate, where C is a generalised heat capacity 

Ta can be chosen such that the effect of modulation on the reaction is small and so a linear approximation to the effect of the temperature profile on the reaction can be used. 

If the modulation amplitude is higher, such that Ta cannot be neglected or it causes the reaction to behave non-linearly, i.e. requires higher terms in the expansion for a(T), then a simple separation can no longer be made. Further, if the signal is delayed in time from the stimulus, in this case the temperature rate, then the treatment of the data cannot be analysed in the previous way and needs to be treated in a linear-response framework along the lines of rheology and dielectric data to obtain in-phase and out-of-phase components. Interpretation of data can then become very complex and difficult to relate to events in the material. 

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ASTM E1952, 2001. Standard test method for thermal conductivity and thermal diffusivity by modulated temperature differential scanning calorimetry. 

Hydrothermal routes Under ambient conditions, the low reaction temperature and fast precipitation rate have deleterious effect on the crystallization and optical performance of rare earth vanadate nanomaterials. Referring to traditional solid-state reactions, bulk YV04 Eu phosphors require a calcinations temperature above 1300 K, but it is too high for the preparation of nanomaterials. Alternatively, hydrothermal routes could provide the adequate energy for solution phase reactions, which have been widely described in preparation of ceramic powders. The high pressure and temperature largely promote the dissolution-reprecipitation process, so as to decrease the lattice defects of NCs. With fine modulation, this method is also efficient to produce nano-sized crystals. 

In the modulated beam method the specimen is in the form of a disc, which is maintained at a constant temperature, whilst the front face is subjected to a laser beam which produces a periodic variation in temperature of constant frequency. The phase shift between this input and the signal from a temperature sensor in contact with the back face is determined. By carrying out measurements at two or more frequencies, Schatz and Simmons were able to derive values of both eff extinction coefficient. If this method were applied to... 

Simmons - (modulated beam method) for temperatures up to 1300 C there is excellent agreement between the values obtained by the latter two groups of workers. Schatz and Simmons — reported that the extinction coefficient of 2MgO.SiO increases from 5 cm at 270 to 25 cm at 1300 °C. 

The book opens with the first three chapters devoted to differential scanning calorimetry (DSC), the most commonly used thermal method. These chapters cover the principles, optimal use, and pharmaceutical applications of the method. Subsequent chapters explore modulated temperature DSC, thermogravimetric analysis, thermal microscopy, microcalorimetry, high sensitivity DSC, dynamic mechanical analysis, and thermally stimulated current, all of which have attracted great interest within the pharmaceutical field. Each chapter includes theoretical background, measurement optimization, and pharmaceutical applications. 

Figure 22. Two different methods of two setup excitation TG methods [143]. Temperature distributions of a sample for the (left) TSETG-I and (right) TSETG-II method are shown, (left) (1) After the prepulse, the temperature rises uniformly by the nonradiative transition from the excited states. (2) The transient absorption by the grating pulses creates the spatially modulated temperature distribution and it produces the TG signal. (3) The stimulated emission decreases the concentration of the excited state and temperature, (right) (1) After the grating pulse, sinusoidally modulated temperature is created. (2) The transient absorption by the boosting laser with a spatially uniform intensity enhances the temperature modulation. (3) The stimulated emission suppresses the modulation.

Knowledge of vapor pressure helps in estimating the volatility of the plasticizer. It is therefore important to find a method of determination which is precise, easy to handle, and uses commonly available equipment, for example, thermobalance. A quick and simple method was developed to determine vapor pressure at different temperatures using thermobalance.Figure 15.2 shows the data measured by the method and data from other studies. It is evident that the results are obtained with high precision. Details of method and the use of modulated temperature programs is described. ... 

Modulated temperature x-ray powder diffraction (XRPD) is being used increasingly in the pharmaceutical industry both at preformulation and at formulation stages. Airaksinen et al. (11) studied polymorphic transitions during drying using two methods a multichamber microscale fluid-bed dryer or a variable temperature powder x-ray diffractometer. Relative amounts of different polymorphic... 

Traditionally, simple combinations of linear heating or cooling rates and isothermal segments have been employed. Modern methods, however, frequently impose cyclic temperature programs coupled with Fourier analyses to achieve particular advantages and added information. These approaches are referred to as modulated techniques, and temperature is the most commonly modulated parameter. Note that in DMA, stress or strain is the modulated parameter and that in DEA, the electric field is modulated, but in modulated temperature DSC and modulated temperature TMA, it is the temperature that is modulated. 

El 142, Standard Terminology Relating to Thermophysical Properties E1952, Standard Test Method for Thermal Conductivity and Thermal Dif-fusivity by Modulated Temperature Differential Scanning Calorimeter E2069, Standard Test Method for Temperature Calibration on Cooling for Differential Scanning Calorimeters... 

Apart from combined TA techniques (on-line or not) the actual trends in thermal analysis are the introduction of modulated and high-resolution techniques, hyphenated thermal analysis methods e.g. TG-FTIR, TG-MS, DSC-XRD, etc.), alternative heating modes, microthermal analysis methods, industrial standardisation and quality control. Modulation means a periodic perturbation of a temperature program. Temperature modulation finds application in DSC, TG, DETA, TMA and uTA. Temperature-modulated techniques, such as Modulated DSC (MDSC ) and Modulated TGA (MTGATM), broaden the insight into the material properties. The use of modulated temperature programs in thermal methods has been reviewed [37,37a]. 

Calculated using the module temperature and RH and kinetics 2nd order in RH from the Miami TMY3 dataset and the method for effective temperature described in [13]. 

Reports on the detailed thermal behaviour of PEEK/HAp composites [as well as other polymer/HAp (nano)composites] are scarce in the literature. Advanced thermal analysis methods, e.g., modulated temperature differential scanning calorimetry (MTDSC) or hyphenated thermoanalytical methods such as thermogravimetry coupled with Fourier transform infrared spectroscopy (TG-FTIR) or mass spectrometry... 

The thermal and thermomechanical properties of the polymer/HAp composites (glass transition temperature, melting and crystallization behaviour, thermal stability, crosslinking effects, phase composition, modulus, etc.) can be evaluated by thermal analysis methods, like TG, DSC and DMA. Recently, a modulated temperature DSC (MTDSC) technique has been developed that offers extended temperature profile capabilities by, for example, a sinusoidal wave superimposed on the normal linear temperature ramp [326]. The new capabilities of the MTDSC method in comparison with conventional DSC include separation of reversible and non-reversible thermal events, improved resolution of closely occurring and overlapping transitions, and increased sensitivity ofheat capacity measurements [92,327]. 

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