tailieunhanh - Volume 10 - Materials Characterization Part 7

Tham khảo tài liệu 'volume 10 - materials characterization part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Fig. 12 Observed ESR spectrum of chromia alumina catalyst. The sample contained mol Cr 2O3. Example 3 Turquoise and Metatorbernite. Turquoise CuAj PQi 4 OH 82 l-bO is triclinic and the cupric ions êí are easily detected using ESR. The spectrum shown in Fig. 13 is a typical powder pattern arising from a completely anisotj f aDior. The arrows show the magnetic-field positions corresponding to the three prinqgffabtorsg g2 andg3. Some turquoise samples exhibit an additional isotropic line arising from êthat decreased in intensity as the temperature was lowered below ambiei suggesting the onset of antiferromagnetic ordering. Fig. 13 ESR spectrum of turquoise. Left to right locations in gauss of the three principal and that of the free-radical marker DPPH ợ-values of Cu 2 ions The mineral metatorbernite Cu Ụ 3 PQí 2 l-bO also contains divalent copper and its ESR spectrum was a single lin whose position and width depend on the orientation of the crystal in the magnetic field. The linewidth anisotropy explained in terms of the layered structure associated with the cupric ions. Example 4 Electrolytically Generated Radical Ions. When the voltage is varied across a polarographic cell containing polycyclic hydrocarbons the compounds bet ionized and a plot of the current through the cell versus the applied voltage exhibits flat regions termed plateaus a from the presence of particular ionic species. Measuring the ESR spectrum of a polycyclic hydrocarbon sue anthracene or benzpyrene in the plateau region yields a spectrum containing many narrow lines each perhaps Í wide. Obtaining such a spectrum necessitates scrupulous removal of oxygen by alternately freezing the sample pu on it to remove the oxygen then melting it. The number spacings and intensity ratios of the various lines in the spe permit deduction of the amount of time the unpaired electron spends at each carbon atom in the molecule. Example 5 Kinetics of Radical Production and Subsequent Decay. Free radicals are .