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

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4.3.2 - 48 - EXPERIMENTAL DETAILS At a spinning frequency of 5 kHz the velocity of the rotor flutes is close to the velocity of sound in air. Both hydrogen and helium are capable of propelling rotors to considerably greater speeds, but because sparks are often produced when a spinning rotor touches the metal stator, helium is the gas used on the grounds of safety. <strong>By</strong> using a compressor it would have been possible to (59) collect and recycle helium after use. However, in practice such an arrangement was not found to be very satisfactory because the gas soon became 'dirty'. With the pulse spectrometer used in this work it was only necessary to maintain rotation frequencies for relatively short periods - particularly for metals with their short spin-lattice relaxation times. Helium could then reason- ably be taken directly from a cylinder and vented to the atmos- phere. Unfortunately it proved extremely difficult to start the rotors spinning with helium as the driving gas. The reason for this was unclear, but attributed to the low gas density, the large masses of the metallic, specimens and the lack of dynamic balancing. Figure 4.2 shows the rotation rates that have been achieved by a solid nylon rotor when propelled by compressed air and helium. The conical rotors start more easily with their axes of rotation vertical, but will rotate about any direction - even upside down. Consequently a normal electromagnet was employed in this work and the rotors spun about an axis inclined at 540 44' to the horizontal magnetic field. The single radiofrequency coils were wound on nylon formers and held in position about the rotor superstructure by screws 1
N to 9 . ýC 8 Ü7 Z w D 06 w ax U. 5 z 0 Q4 oC d FIGURE 4.2. t Rotation rates attained by a solid nylon conical rotor when driven by air and helium 10 20 30 40 50 60 70 PRESSURE p. s. i.
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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)
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: SI FIGURE 4.1 SCALE il cm : The con
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
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- 84 - provides further evidence th
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- 86 - CHAPTER 7 EXPERIMENTAL RESUL
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- 88 - Lorentzian NMR lineshape of
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- 90 - at the top with epoxy glue.
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- 92 - (c) Bulk Susceptibility Effe
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- 94 - aluminium nuclei in the meta
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FIGURE 7.1 : 27A1 F. I. Ds and corr
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- 97 - TABLE 7.1. COMPUTED SECOND A
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- 99 - and Slichter(104) reported t
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- 101 - of this value would be requ
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N JL I F- 0 z J I0 0123456789 ROTAT
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-103- results obtained at a tempera
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T10 ms 3. O 2.5 2'C H 1"C o.. v 234
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0 - 106 - CHAPTER 8 MEASUREMENTS ON
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- 108 - process for vanadium the me
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- 109 - in the same way to the prec
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Qv == , 2 28 kHz -111- which is sli
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- 113 - from Cerac Inc. (USA). The
Page 147 and 148:
- 115 - 8.4.3 SPIN-LATTICE RELAXATI
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tv D Xm =o N O Ul- X- z N O FIGURE
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which gives K=0.048 an ± 0.002 - 1
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- 118 - Lifetime broadening alone g
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- 120 - cannot be spun at low tempe
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- 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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