NNR IN RAPIDLY ROTATED METALS By - Nottingham eTheses ...

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- 114 - very weak signals from the reference solution. The resonance freq- uencies of the CdC12 solutions were found to vary considerably with the amount of paramagnetic doping. For example, compared to a saturated solution of CdC12 in 0.2% molar MnC12 the chemical shift of the reference solution used in the above measurements was about +15 ppm. Nevertheless the values quoted above illustrate that any isotopic dependence of the Knight shift is less than 2x 10 3. A second set of measurements were made against diluted undoped solutions of Cd(N03)2. The signal intensity was again poor, but, by pulsing rapidly and transforming the transient signal to the frequency domain, the resonance frequency could be assessed quite accurately. Choosing a solution concentration for which the chemical shift is known should in principle enable the measured Knight shift to be related to the cadmium ion in a vanishingly small dilut- ion of the salt, i. e. to a single ion in water. Against a concentration of solution corresponding to 0.06 moles of Cd in 1 mole of water the measured Knight shifts at a temperature of 285 ±2K were 4321 ±6 ppm and 4324 ±8 ppm for 111Cd and 113Cd respectively. <strong>By</strong> employing the experimentally determined value for the fractional change in Knight shift with pressure(135), acalculation of the rotat- ionally induced stresses in the metal gives a maximum possible contrib- ution to the Knight shift of 2 ppm, well within the experimental error. The effect of the sample bulk susceptibility is negligible in comparison. The results of . Kruger et a1. (135) indicate that a correction factor of -46 ppm could normally be applied to relate the Knight shift values recorded above to the free ion in solution. How- ever, this value of the chemical shift was measured at a temperature of 306 K, so the magnitude of this correction may well be inaccurate at the somewhat lower temperature of our measurements.
- 115 - 8.4.3 SP<strong>IN</strong>-LATTICE RELAXATION TIMES The spin-lattice relaxation times of 111 Cd and 113 Cd were measured in the spinning and static samples. The results of 1.65 ± 0.15 ms for 111Cd and 1.40 ± 0.10 ms for 113Cd at a room temperature of 298 K were independent of rotation rate as expected. The measured T1 for 113Cd is considerably higher than Masuda's reported room temperature value of 0.5 ms(137), but it is in better agreement with the figure of approximately 1.2 ms recorded by Dickson(138) No measurements of the 111Cd T1 have apparently been reported in the literature. However the relaxation time measured here is consist- ent with the lower gyromagnetic ratio of this isotope. It is of interest to compare the product T1K2T found by experi- ment with the theoretical value derived from the Korringa relation given by equation (2.23). In cadmium the direct contact mechanism arising from the s-type conduction electrons is assumed to dominate the Knight shift and the spin-lattice interactions. In this event the scalar R defined thus RT1KZT = 4'rk (Y 2 Bn is a measure of electron enhancement of both K and l/T1. At room temperature the results of Seymour and Styles(133) indicate that the experimental Knight shift increases by about 4 ppm/°K. The temperature correction acts in the opposite direction to the chemical shift coxrection, so it is not unreasonable to take the Knight shift of cadmium at 298 K as 0.43% to a first approximation. Substituting our experimental values for the illCd and 113Cd relaxation times at
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NNR IN RAPIDLY ROTATED METALS By R.
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I wish to express my thanks to: ACK
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quadrupole relaxation. However theo
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2.3.5 Quadrupole Relaxation 26 (i)
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5.9 Sample Preparation 71 5.9.1 Cup
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1.1 BASIC THEORY -i- CHAPTER 1 INTR
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-3- Transforming to the rotating fr
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-5- lattice and T2 is the spin-spin
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and -7- Vd(t) f(w1)cos w't dw Sao -
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-9- where the terms represent the Z
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- 11 - If rii = nrij = (Xli + X2j +
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- 13 - In powdered samples a weak i
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- 15 - This contact term manifests
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- 17 - where 0 is the angle between
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- 19 - termed pseudo-dipolar. It is
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- 21 - the non-secular terms of the
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- 23 - to the lattice directly via
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- 25 - (2.25), can then be assumed
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- 27 - quadrupole moments to produc
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- 29 - where En are the Zeeman ener
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3.1 INTRODUCTION - 31 - CHAPTER 3 N
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Aý T. B a A"T"B " - 33 - It is a g
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(-Ur Ho FIGURE 3.1. : Co-ordinate s
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D, (t) = 331 2 + 3YI2 sin 2a 4 - 36
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- 38 - X (t) = cos a cos ßp + sin
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- 40 - 3.7 THE EFFECT OF ROTATION O
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- 42 - observations are inconsisten
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- 44 - that it apparently offered n
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- 46 - bearings suffer from instabi
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SI FIGURE 4.1 SCALE il cm : The con
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N to 9 . ýC 8 Ü7 Z w D 06 w ax U.
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- 50 - The rotors used in this work
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Ip IJýi O 1 t - 1 - 1 p OI ý I ý
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- 52 - at rotation speeds around 4
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- 53 - the manufacture of which was
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PTFE Tape_ FIGURE 4.7 rotors SCALE
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4.4.4 COMMENTS - 55 - For completen
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Clamp Pf-£-- SECTION II SECTION 11
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5.1 EQUIPMENT - 58 - CHAPTER 5 EXPE
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- 59 - the range ±1 V are digitise
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SCALE 3 cm j Cooling Gas ; tainiess
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Trensmitter EXL, FIGURE 5.3 : The s
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FIGURE $. 4 s The spectrometer prob
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Gas Tuning ransmi tter Input Receiv
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- 64 - phase can then be set so tha
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-66- The transient nuclear signals
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- 68 - 5.7.1 THE SOLID ECHO PULSE S
Page 95 and 96: - 70 - sequence may be repeated. In
Page 97 and 98: a° P/'rvu - 72 - p is the resistiv
Page 99 and 100: - 74 - combined with a low viscosit
Page 101 and 102: 6.2 RESULTS AND DISCUSSION - 76 - A
Page 103 and 104: IC 1 I. FIGURE 6.2 : Measured T1 va
Page 105 and 106: - 78 - TABLE 6.1. DEBYE TEMPERATURE
Page 107 and 108: - 80 - TABLE 6.2. RATIO OF TI VALUE
Page 109 and 110: - 82 - TABLE 6.3. DEPENDENCE OF T1
Page 111 and 112: - 84 - provides further evidence th
Page 113 and 114: - 86 - CHAPTER 7 EXPERIMENTAL RESUL
Page 115 and 116: - 88 - Lorentzian NMR lineshape of
Page 117 and 118: - 90 - at the top with epoxy glue.
Page 119 and 120: - 92 - (c) Bulk Susceptibility Effe
Page 121 and 122: - 94 - aluminium nuclei in the meta
Page 123 and 124: FIGURE 7.1 : 27A1 F. I. Ds and corr
Page 125 and 126: - 97 - TABLE 7.1. COMPUTED SECOND A
Page 127 and 128: - 99 - and Slichter(104) reported t
Page 129 and 130: - 101 - of this value would be requ
Page 131 and 132: N JL I F- 0 z J I0 0123456789 ROTAT
Page 133 and 134: -103- results obtained at a tempera
Page 135 and 136: T10 ms 3. O 2.5 2'C H 1"C o.. v 234
Page 137 and 138: 0 - 106 - CHAPTER 8 MEASUREMENTS ON
Page 139 and 140: - 108 - process for vanadium the me
Page 141 and 142: - 109 - in the same way to the prec
Page 143 and 144: Qv == , 2 28 kHz -111- which is sli
Page 145: - 113 - from Cerac Inc. (USA). The
Page 149 and 150: tv D Xm =o N O Ul- X- z N O FIGURE
Page 151 and 152: which gives K=0.048 an ± 0.002 - 1
Page 153 and 154: - 118 - Lifetime broadening alone g
Page 155 and 156: - 120 - cannot be spun at low tempe
Page 157 and 158: - 122 - 11. L. E. Orgel, J. Phys. C
Page 159 and 160: - 124 - 59. P. J. Randall, Ph. D. T
Page 161 and 162: - 126 - 101. H. R. Khan, J. M. Reyn
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NNR IN RAPIDLY ROTATED METALS By - Nottingham eTheses ...

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