Temperature measurement resonance

A. G. Webb 2001, (Temperature measurement using nuclear magnetic resonance), Annu. Rep. N. M. R. Spectrosc. 45,... 

Dynamic mechanical testers apply a small sinusoidal stress or strain to a small sample of the polymer to be examined and measure resonant frequency and damping versus temperature and forced frequency. Instrument software computes dynamic storage modulus (G ), dynamic loss modulus (G") and tan delta or damping factor. Measurements over a wide range of frequency and temperature provide a fingerprint of the polymer with sensitivity highly superior to DSC. 

Figure 12. Variable-temperature measurement of y-carbon resonance of sample from Figure 11a + 50 to — 50°C.

Evidence for such stable free radicals has been obtained from electron spin resonance measurements. A sample of the 77-23 PVC-styrene, which had been exposed to 0.8 megarad of gamma-radiation at room temperature, displayed resonance peaks comparable to 3 X 10 8 mole per gram of free radicals (compared with a diphenyl picrylhydrazyl standard). When an identical sample was heated for 10 minutes at 75°C. following irradiation, the free radical population had fallen below detection limits. Heating evidently destroyed or decreased the free radical content by reaction or termination. 

The temperature dependence of the spectral spin diffusion and crossrelaxation was examined by Mueller et a/.287,288 with spin- and spin-1 systems. They showed that the diffusion rate can be strongly temperature dependent if it is motionally driven. It is therefore, unreliable to discriminate spin diffusion and chemical exchange by variable-temperature measurement of 2D exchange spectra. Mueller et al. suggested that the dependence of the polarization transfer rate on the spectral difference of the relevant resonances should be measured in a single crystal to safely distinguish the two different polarization transfer processes (see also ref. 289). They also explained satisfactorily why the relaxation of the quadrupolar order is much faster than the Zeeman order. This... 

Apart from high applied field measurements, another powerful technique for the determination of the interaction fields is antiferromagnetic resonance (AFMR)253 255). Below the ordering temperature, the resonance frequency depends strongly on both HE and Ha according to the relation oily — (2HE HA)1/2 for HE > HA m is the applied frequency and y = ge/2mc is the magnetochemical ratio. 

In principle, a resonance frequency or difference in frequencies can be employed to perform NMR thermometry. The accuracy of temperature measurement depends on the accuracy of the thermocouple (0.2°C) in the NMR spectrometer. Generally, a precision of better than 0.2°C has been reported with these NMR thermometry measurements. Individual calibration plots may not be required when using aqueous buffers. Proper calibration procedures should be adopted with nonaqueous buffers and in the presence of organic modifiers. 

The number of resonant peaks that can be measured is dependent on the loss factor of the material, but, typically, there are three to five peaks. As expected, the resonant peaks appear at higher frequencies in the glassy state than in the rubbery state. From the amplitude and frequency of each measured resonant peak. Young s modulus and loss factor are determined at the corresponding frequency and temperature. By assuming Poisson s ratio of 0.5, Young s modulus is converted to shear modulus. The loss factor in extension is assumed to equal the loss factor in shear. 

Temperature Measurements using Nuclear Magnetic Resonance... 

P NMR spectra were registered on a Broker MSL-400 spectrometer at room temperature. The resonance frequency of 161.98 MHz and accumulation frequency of 0.05 Hz were used, chemical shifts (5) were measured with respect to an external aqueous solution of 85% H3PO4. 0.1 M solution of Na7PWn039 has been used to estimate the concentration of heteropolytungstate. 

The temperature dependence of the isotropic shift in uranocene was measured on two independent samples from -80°C to 100°C. At the same nominal temperature slight differences in the shift between the two samples are undoubtedly due to slight differences in the true temperature of the samples and provide an estimate of the error in temperature measurement or measurement of the resonance frequency in this study. 

The pseudo-first-order rate constant for the reaction of atomic chlorine with Br2 has been determined by means of measurements of the Cl resonance fluorescence. Yellowish-orange M Cl (M = Li, Na, K, Rb, Cs, or Ba) species have been produced in low-temperature matrixes. Resonance Raman spectra of... 

Another approach the authors have found to work well is to have the ratio of the nitrogen concentration to the non-resonant susceptibility as an additional fit parameter in the CARS signal analysis. This does not interfere with the CARS signal strength and gives accurate temperature measurements however, the fitted non-resonant susceptibility is incorrect and the technique is not recommended for simultaneous measurements of concentration [13]. 

One inch immersion transducers (Panametrics) are used with resonance frequencies of respectively 0.48 MHz., 0.70 MHz., 0.90 MHz. and 4.0 MHz. These transducers can be used for measurements between -50°C and 80°C. The two transducers shown in Figure 4.9 are special high temperature transducers (resonance frequency 1.0 MHz.) which can be used up to 200°C. 

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