Fast pulse-heating technique

Obendrauf et al. have measured the thermophysical properties of nickel by a fast pulse heating technique using a newly developed highly sensitive pyrometer. The values obtained for A 77°(Ni) are slightly greater than, and the values for C" (Ni, 1) are significantly greater than the calorimetrically determined values on which the quantities in this review are based. 

All the macrostructures mentioned further above, i.e. thin film and screen printed structures, ITO electrodes and paste electrodes can be heated using all the described techniques of AC distortion compensation and also the methods of temperature determination. Till now, macrostructures throughout were subject to permanent heating only, since fast pulsed heating-up is less useful due to the much higher thermal inertia of the electrodes which are carried by isolating supports. 

The isobaric heat capacity is obtained mathematically by differentiation of the specific enthalpy. Graphically, Cp is given by the slope of the enthalpy versus temperature trace leading to an individually constant number for isobaric heat capacity in the liquid state and also for the solid state, if no phase transitions occur. This result for the solid state is in contradiction with measurement data obtained by techniques such as differential scanning calorimetry (DSC) but has been proved to be correct for the liquid state. Dynamic pulse-heating rates are usually too fast and small phase transitions, which are detectable by DSC or similar instruments, become undetectable. As a result, pulse-heating data for Cp... 

Temperature is undeniably the most important property for all calorimetric measurements, because it is the common denominator. Two different techniques for temperature measurements are used for pulse calorimetry contact thermometry (e.g. thermocouples) and radiation thermometry or pyrometry. Because pulse calorimetry is often used to handle and measure liquid materials, non-contact radiation thermometry is far more common in pulse-heating than contact thermometry. Other reasons for non-contact temperature measurement methods include the fast heating rates and temperature gradients (inertia of the thermocouples), difficulties mounting the contact thermometers (good thermal contact needed), and stray pick-up in the thermocouple signal because the sample is electrically self-heated. 

Solutions of dicyclohexyl-18 crown 6 in DMSO have been used to prepare pale yellow 0.15 mol P solutions of KO2 which contain the O2 anion in approximately the same concentration. The specificity of the superoxide dismutase enzyme was used to show that the solution did indeed contain the superoxide ion in solution. I hc redox potentials of the superoxide and hydroperoxy free radicals, O2 and HO2, have been measured by the fast reaction technique of pulse radiolysis and kinetic absorption spectrophotometry. A d.t.a. study has shown that, during the heating of LiC104-K02 mixtures containing <30% KO2, a eutectic melt occurred at 100—250 C with the loss of superoxide oxygen. At 250—300 °C the mixture melted with loss of peroxide oxygen and at 360— 500 °C the perchlorate decomposed with the loss of all the perchlorate oxygen. 

P-jump techniques can achieve fast heating of the reaction system by pulsed radiation, for example with a microwave source or an IR laser. In the latter case one often adds an efficient inert absorber, such as SF. The heating of the reaction system then results from fast collisional relaxation of the initially-excited absorber molecules [48, 49]. 

PAS is a technique based on the so-called optoacoustic effect When a short pulse of electromagnetic radiation interacts with condensed matter, the absorbed energy is converted into heat by fast nonradiative relaxation processes. Subsequently, the thermal expansion of the instantaneously heated medium causes an acoustic pulse, which is detected. 

Raman spectra can be recorded in times as short as several nanoseconds using pulsed laser excitation/gated array detection techniques. This capability is important for the identification of transient species during fast chemical reactions or for characterizing structural failure modes in thin films exposed to heat or intense electromagnetic fields. An existing system... 

A secmid popular soft ionization method is MALDI. In this technique, analytes are co-crystallized with a matrix (typically a small, acidic, organic molecule), with an absorption maximum close to the wavelength of a laser used to irradiate the substrate. This process is typically performed in vacuum (although it has been shown to be feasible at atmospheric pressure) after the analytes have been desorbed and ionized (in MALDI, it is believed that fast heating caused by the laser pulse desorbs analytes into gas phase however, the process by which... 

Shock tubes are of limited utility. A more general approach to the study of reactions which are complete in the range 1 msec-1 nsec is to use fast reaction methods. An equilibrium system is perturbed by an external stimulus applied for a very short time (always less than the half-time for reestablishing equilibrium). A common approach is to effect a temperature jump in the system by a brief burst of heating. If the equilibrium is temperature sensitive the concentration of reactants must readjust by synchronizing an automatic recording technique with the onset or termination of the heating pulse the relaxation to the new equilibrium state can be followed. There are many other stimuli that can be used to perturb the system. These include dilation (pressure jump), electric field (Wien effect), etc. Any method that can perturb the system very rapidly is potentially useful for such an experiment. 

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