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

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ABSTRACT Although this thesis is concerned solely with nuclear magnetic resonance, it may be divided into two parts. One part deals with a series of measurements on the NMR parameters of several pure metal powders, namely aluminium, cadmium, niobium and vanadium, and in particular the effect on their resonance spectra of rapid macro- scopic sample rotation at the 'magic angle'. The other part relates measurements of spin-lattice relaxation time as a function of temperature for the three solid cuprous halides. <strong>By</strong> spinning at high speeds a significant narrowing of the resonance lineshape has been achieved in the case of cadium and aluminium. This has enabled precise determinations of their iso- tropic Knight shifts to be made. For cadmium the width of the residual symmetric central spectrum has been used to obtain an estimate of the magnitude of the indirect electron coupled exchange interaction. Complete narrowing of the aluminium resonance line requires rotation rates in excess of 8 kHz. To this end it has been necessary to develop a new rotor system capable of carrying small metal samples at extremely high spinning rates. In connect- ion with the work on aluminium, pure powder specimens have been prepared which exhibit values of second moment and dipolar relaxation time that agree well with theory. This is in contradiction to the results obtained from filed powders and those recorded by all other workers. Below room temperature the form of the T1 results obtained from the cuprous halides is in accord with the theory of Raman
quadrupole relaxation. However theoretical T1 values, as derived from the simple Raman two-phonon mechanism in an ionic crystal lattice, fail to give quantitative agreement with experiment.
Page 1 and 2: NNR IN RAPIDLY ROTATED METALS By R.
Page 3: I wish to express my thanks to: ACK
Page 7 and 8: 2.3.5 Quadrupole Relaxation 26 (i)
Page 9 and 10: 5.9 Sample Preparation 71 5.9.1 Cup
Page 11 and 12: 1.1 BASIC THEORY -i- CHAPTER 1 INTR
Page 13 and 14: -3- Transforming to the rotating fr
Page 15 and 16: -5- lattice and T2 is the spin-spin
Page 17 and 18: and -7- Vd(t) f(w1)cos w't dw Sao -
Page 19 and 20: -9- where the terms represent the Z
Page 21 and 22: - 11 - If rii = nrij = (Xli + X2j +
Page 23 and 24: - 13 - In powdered samples a weak i
Page 25 and 26: - 15 - This contact term manifests
Page 27 and 28: - 17 - where 0 is the angle between
Page 29 and 30: - 19 - termed pseudo-dipolar. It is
Page 31 and 32: - 21 - the non-secular terms of the
Page 33 and 34: - 23 - to the lattice directly via
Page 35 and 36: - 25 - (2.25), can then be assumed
Page 37 and 38: - 27 - quadrupole moments to produc
Page 39 and 40: - 29 - where En are the Zeeman ener
Page 41 and 42: 3.1 INTRODUCTION - 31 - CHAPTER 3 N
Page 43 and 44: Aý T. B a A"T"B " - 33 - It is a g
Page 45 and 46: (-Ur Ho FIGURE 3.1. : Co-ordinate s
Page 47 and 48: D, (t) = 331 2 + 3YI2 sin 2a 4 - 36
Page 49 and 50: - 38 - X (t) = cos a cos ßp + sin
Page 51 and 52: - 40 - 3.7 THE EFFECT OF ROTATION O
Page 53 and 54: - 42 - observations are inconsisten
Page 55 and 56:
- 44 - that it apparently offered n
Page 57 and 58:
- 46 - bearings suffer from instabi
Page 59 and 60:
SI FIGURE 4.1 SCALE il cm : The con
Page 61 and 62:
N to 9 . ýC 8 Ü7 Z w D 06 w ax U.
Page 63 and 64:
- 50 - The rotors used in this work
Page 65 and 66:
Ip IJýi O 1 t - 1 - 1 p OI ý I ý
Page 67 and 68:
- 52 - at rotation speeds around 4
Page 69 and 70:
- 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 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 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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