Laser flash technique

This technique has been used to determine the specific heat of poly vinylidene fluoride [59,79]. 

Ranade et al. [80] showed that polyamide-imide-montmorillonite nanocomposites had a distinctly reduced specific heat when compared to the clay-free polymer. 

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Second, these proteins are particularly stable and because of the particularly rich spectroscopy of their heme porphyrin active sites, a wide variety of physical methods are available to monitor the thermodynamics and kinetics of binding, and subsequent electron transfer reactions, ranging from 2D NMR to laser flash techniques. 

A laser flash technique can be used to generate radical-cations and follow the kinetics of their reaction with nucleophiles [68, 69]. The experimental technique... 

More detailed studies have been made where the thermal conductivity in the different crystal directions have been determined for SiC (see Table 1.1 [5]). As can be seen, there is a dependence on the purity of the crystal as well as on the crystal direction. At the time of this study, the material was not of the high quality we see today, and more sophisticated techniques have been developed to measure thermal conductivity. Thus, as higher-quality material has been grown, values close to the theoretical values have been measured using the laser flash technique [10]. 

Recent studies by Schuster and collaborators67,54, based on nanosecond laser flash techniques, revealed important conclusions, including (a). The enone excited state responsible for the photocycloaddition is the jt-Tt which possesses different polarization than the n-7T state, considered in rationalizing the effect of the oriented jr-complex. (b) Direct measurement of the reactivity scale of alkenes measured by nanosecond flash photolysis provided different results from those obtained with no consideration of the diradical fragmentation to starting materials. 

A laser flash technique can be used for determining the thermal conductivity of fibers (Whittaker et al., 1990). The laser flash technique provides us the dilfusivity, a, which, in turn, is a function of the thermal conductivity, specific heat, and density of the material. Thus,... 

Using fluorescence and laser flash techniques one can show that the lipophilic substituted iodonium hexafluoroantimonates react efflcently with singlet and triplet states of several sensitizers. Furthermore, one observes the decay of the electron donor, which was investigated with 9,10-diphenylanthracene (DPA) and 9,10-dimethylanthracene as sensitizers, which act as electron donor. Using the CIDNP-technique and laser flash photolysis one can prove that electron transfer takes place to the iodonium salts [9], which results in formation of a proton (see Scheme 3). 

The phase composition of the resulted specimens was identified by X-ray diffraction (XRD). Rod-like pieces (3x3xl5mm) and disk-shaped pieces (2mm thickness and 10mm diameter) were cut out for the electrical conductivity measurement and the thermal conductivity measurement, respectively. Microstmcture and phase distribution were observed by a scanning electron microscopy equipped with EPMA (JEOL JXA-8621MX). Electrical conductivity was measured using a D.C. four-probe method. Thermal conductivity was measured using a laser-flash technique. All the measurements were performed in the temperature range of 300 to 1200 K. 

Hydrogen abstraction from lipids by triplet states of benzophenone derivatives followed directly by the use of laser flash techniques allows the separation of physical quenching processes from chemical reactions of the excited state. 98 xhe production of 2 by the photochemical decomposition of aromatic endoperoxides has also been studied by ps kinetic procedures. 99 mechanistic study has also been reported on the phototransformation of 3-nitrophenol in aqueous solution. 99 There is a strong wavelength dependence of the low quantum yield for the phototransformation in this system. 

Several techniques are used to measure A,h- One method that has gained popularity recently is the laser flash technique. In principle the technique attempts to measure the time evolution of the temperature on one side of the sample as the other side is very rapidly heated by a laser pulse. As it passes through the solid, the signal will be altered in two ways There will be a time lag between the time at which the solid was pulsed and the maximum in the response. This time lag is directly proportional to the thermal diffusivity, of the material. The second effect will be a reduction... 

The heat capacity measurements of Wallace [1960WAL] from 298.15 to 1273 K merge smoothly with the low temperature data of [1953GRI/SKO]. However, Nakamura et al. [1980NAK/TAK] measured the heat capacity of thorium containing 0.05 mass% impurities using a laser-flash technique. This a valuable study, as not only... 

Electron transfer between molecules is the most essential process in biological systems [1,2]. Electron transfer in biological substances such as enzymes is very rapid, so that it is in many cases investigated by utilizing electron transfer in a photoexcited state with a laser flash technique. By this method one single step of an electron transfer can be measured. For this purpose a specific position of an enzyme is modified with a redox-center molecule such as a metal complex, and electron transfer is studied with laser flash photolysis. 

Kim] DC four probe and laser flash techniques Thermoelectric power, electrical and thermal conductivity... 

Surface oxidation behaviour of uranium carbide (UC) in air was studied. It is seen that formation of uranium oxide/hydroxide and free carbon can happen as a consequence of the reaction between UC and oxygen/moisture. It is noted that the sutl ce of the oxidised UC consists of a top contamination layer of adsorbed oxygen/moisture, followed by a layer containing uranium oxide, uranium hydroxide and free carbon and then grain boundary oxide and finally bulk UC. The bahaviour of sintered and arc-melted samples is found to be similar. Thermal conductivity of mixed oxide fuel (45%U - 55%Pu) was measured using laser flash technique covering a temperature range from 700 to 1550 K. 

The laser flash technique has been used to measure the specific heat of fibre-reinforced phenol-formaldehyde resins [31]. This technique has also been used to determine the specific heat of PVDF [45, 52]. 

Figure 5 Schematic diagram of the laser flash technique. (Courtesy of Holometrix Corp.)...

A laser flash technique has been used to determine the diffusivity of pyroelectric polymers such as polyvinylidene fluoride [83], whereas hot-wire techniques have been used to determine the thermal diffusivity of high-density polyethylene, low-density polyethylene propylene, and polystyrene [83], Dos Santos and coworkers [84] utilized the laser flash technique to study the effect of recycling on the thermal properties of selected polymers. Thermal diffusivity expresses how fast heat propagates across a bulk material, and thermal conductivity determines the woiking temperature levels of a material. Hence, it is possible to assert that those properties are important if a polymer is used as an insulator, and also if it is used in applications in which heat transfer is desirable. Five sets of virgin and recycled commercial polymers widely used in many applications (including food wrapping) were selected for this study. 

Since thiyi radicals and disulfide radical anions are one-electron redox intermediates between thiols and disulfides, electrochemistry or other classical radical chemistry methods are, in principle, also suitable for initiating reactions based on these intermediates. For direct observation of radicals and their kinetics, these methods are, however, generally inferior to time resolved pulse radiolysis and laser flash techniques which have provided most of the available information. 

The generation of sulfuranyl radicals by laser flash techniques allows their monitoring as transients by UV/vis spectroscopy. Alkyl and aryl groups as substituents on the S radical center—as compared to hydrogen—shift the absorption maximum to longer wavelengths, as illustrated in Table 2 for 1,2-dithiolan-1-yl radicals (4) [17]. 

W. N. dos Santosa, P. Mummery, A. Wallwork. Thermal Diffusivity of Polymers by The Laser Flash Technique. Polymer Testing 2005 24 628-634. 

The thermal properties of ZnO doped with A1 and Mg were also studied by a number of groups [149-153] for the evaluation of the thermoelectric performance. Tsubota et al. [152] investigated the thermal conductivity of sintered (Zni yMgy)i xAlj 0 (x O-Q. , y = 0-0.1) samples determined from thermal diffusivity and specific heat capacity measured by the laser flash technique and differential scanning calorimetry (DSC), respectively. The temperature dependences of the thermal conductivities of (Zni yMgy)o.9gAlo.o20 (y = 0.0-02,0.1) are shown in Figure 1.29 in comparison with that of ZnO. The reduction of k from... 

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