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

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- 95 - annealed aluminium powder was placed in the standard Bruker probe system. The measurements were recorded at temperatures in the range 290-300 K using resonant frequencies of 15 and 16 MHz, but the results obtained were insensitive to these variations. Powders (a) and (b) were sieved so as to separate the specimen particle sizes so: 37 um, 37-44 um, and 44-76 pin. A few drops of pure acetone were added to the largest grain specimens in order to reduce distortion of the detected signals by mechanical vibrations set up in individual crystallites. The problem could not be cured by the powders being encapsulated in resin because the widths of the resonance spectra of the cured slugs were found to be increased by this treatment. (That this broadening was due to a quadrupole interaction rather than any stress induced distribution of Knight shifts was made evident by its partial removal upon rapid rotation of the specimens about the magic angle. ) Owing to the small skin depth (ti 20 um) the signal intensities obtained from the coarsest powders were less than those from the finer powders. However, with- in the limits of experimental error, the transformed lineshapes were found to be unaffected by particle size. The observed characteristic decay shapes from powder samples, (a) and (c), were quite distinguishable from each other. (Powder (c) was filtered to a particle size of less than 44 pm. ) Typical FIDs obtained from these two samples are shown in Figure 7.1 together with the corresponding lineshapes in the frequency domain. The FID and absorption spectrum of powder (b) were very similar in appear- ance to those obtained for (c), and are therefore not illustrated separately. The tails of nuclear spectra in the frequency domain are deter- mined largely by the supposition made about the behaviour of the FID
FIGURE 7.1 : 27A1 F. I. Ds and corresponding spectra in tho frequency domain for annealed powder prepared by the metal spraying gun (full line) and filing (broken line) 41 kHz
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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
Page 71 and 72: PTFE Tape_ FIGURE 4.7 rotors SCALE
Page 73 and 74: 4.4.4 COMMENTS - 55 - For completen
Page 75 and 76: Clamp Pf-£-- SECTION II SECTION 11
Page 77 and 78: 5.1 EQUIPMENT - 58 - CHAPTER 5 EXPE
Page 79 and 80: - 59 - the range ±1 V are digitise
Page 81 and 82: SCALE 3 cm j Cooling Gas ; tainiess
Page 83 and 84: Trensmitter EXL, FIGURE 5.3 : The s
Page 85 and 86: FIGURE $. 4 s The spectrometer prob
Page 87 and 88: Gas Tuning ransmi tter Input Receiv
Page 89 and 90: - 64 - phase can then be set so tha
Page 91 and 92: -66- The transient nuclear signals
Page 93 and 94: - 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: - 94 - aluminium nuclei in the meta
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 and 146: - 113 - from Cerac Inc. (USA). The
Page 147 and 148: - 115 - 8.4.3 SPIN-LATTICE RELAXATI
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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