Nmr Studies of Compressed Supercritical Water and Proton Exchange in Compressed Liquid Water

Lamb, Walter James

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Description

Title

Nmr Studies of Compressed Supercritical Water and Proton Exchange in Compressed Liquid Water

Author(s)

Lamb, Walter James

Issue Date

1981

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Chemistry, Physical

Abstract

• Pulsed NMR techniques are used to study spin-lattice relaxation of compressed water in the region 150-700(DEGREES)C, self-diffusion of compressed supercritical water in the region 400-700(DEGREES)C, and proton exchange of compressed liquid water in the region 0-100(DEGREES)C. For the proton relaxation study from 150-350(DEGREES)C, the spin-rotation and dipolar mechanisms which contribute to the observed relaxation rate are separated. Above the critical temperature (t(,c) = 374(DEGREES)C), the spin-rotation relaxation data (T(,1)('SR)) are analyzed in terms of a dilute gas model assuming a single correlation function which is an exponential function of time. The T(,1)('SR) data exhibit a stronger temperature dependence than found for other gases revealing that cross sections for angular momentum transfer are large. Mean angles of rotation between successive collisions are in the range from 50(DEGREES) to 800(DEGREES). The rate, 1/T(,1)('SR), is a linear function of the Enskog relaxation time, (tau)(,E). Angular momentum correlation times, (tau)(,J)'s, are calculated from 1/T(,1)('SR). The experimental ratio of (tau)(,E)/(tau)(,J) reflecting the efficiency of angular momentum transfer shows density and temperature dependence in agreement with expectation.
• The experimental self-diffusion data were compared to theoretical predictions based on a dilute polar gas model using a Stockmayer potential for the evaluation of collision integrals and a temperarture dependent hard sphere diameter. The empirical expression (rho)D = 2.24 x 10('-6)T('0.763) fits the experimental data to within (+OR-) 10%. The value of the temperature exponent agrees favorably with values found for diffusion of other gases. The product (rho)D is density independent which indicates that two-body collisions dominate the diffusion behavior. The hydrodynamic Stokes-Einstein equation appears to hold above the critical density. A fit to a hard sphere model failed but the data could be fit to an equation of the form ln(rho)D = A/T + B where A and B are constants. The self-diffusion results are in agreement with the proton relaxation results.
• The temperature and density dependence of the average time a proton resides on a water molecule, (tau)(,e), is determined. The slow ((TURNEQ)10 kHz) proton exchange process results in a difference in the relaxation rates of spin-lattice (T(,1)) and spin-lattice in the rotating frame (T(,1(rho))). The T(,1(rho)) technique is developed and compared to other methods used to study proton exchange. The density dependence of (tau)(,e) exhibits trends observed for other dynamic properties of liquid water. The values of (tau)(,e) in bulk neutral water are compared to (tau)(,e) values in porous clays and cation-exchanged chabazites.
• In the appendices are details of two design projects. The first concerns a design for loading high pressure NMR probes into superconducting magnets. The second is the design of a variable temperature (-50 to 1000(DEGREES)C) NMR probe. The relaxation times of Na('+) in NaCl(l) are also reported in this appendix.

Graduation Semester

1981

Type of Resource

text

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