Compact and portable low-field pulsed NMR dispersion analyzer

Abstract

A compact and integrated portable device is provided for the analysis of dispersions by low-field pulsed NMR including: an NMR probe module, a means for generating radio frequency and magnetic field gradient pulses, a signal processor, and a master controller. Also provided are methods for using the device to measure one or more characteristics of phases or particles comprising a dispersion such as surface area, solid/liquid ratio, particle size, and elemental analysis.

Description

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic view of the NMR device showing the key modules.

FIG. 2A is perspective view of the magnet and yoke assembly.

FIG. 2B is a side exploded view of the magnet and yoke assembly.

FIG. 3 illustrates a simple single pulse and collect pulse sequence.

FIG. 4 illustrates a simple spin echo pulse sequence.

FIG. 5 illustrates a simple spin-lattice relaxation T₁ pulse sequence.

FIG. 6 illustrates emulsion sizing pulse sequence.

FIG. 7 is an example of a R₂ simulation for three silica dispersions in water: 30 nm, 60 and 90 nm particle sizes.

FIG. 8 is an example of R₂ simulation using results from FIG. 7 as a function of Area/Liquid ratio.

FIG. 9 is a graph of experimental results of measurement of R_2sp for a silica dispersion in water.

FIG. 10 is a graph of R_2sp experimental data for surfactant adsorption at two different solids concentrations in water.

FIG. 11 is a graph of R_2spexperimental data for three different particles in water: alumina (triangles), silica (diamonds), and polystyrene latex (circles).

Claims

1. A compact and portable device for the analysis of dispersions by low-field pulsed NMR comprising: an NMR probe module, a means for generating radio frequency and magnetic field gradient pulses, a signal processor, and a master controller; wherein the device measures one or more characteristics of the phases or particles comprising the dispersion selected from the group consisting of surface area, solid/liquid ratio, particle size by diffusion, and elemental analysis; and wherein the device has a total footprint area less than about 0.25 m2, an elevation less than about 0.45 m, a weight less than 20 kg, and an operating power demand less than 500 W.

2. The device according to claim 1 wherein the characteristic of the phases or particles being measured is the total surface area.

3. The device according to claim 1 wherein the total footprint area is less than 0.2 m2, the maximum elevation is less than 0.3 m, and the operating power demand is no more than 150 W.

4. The device according to claim 1 wherein the NMR probe module, the means for generating radio frequency and magnetic field gradient pulses, the signal processor and the master controller are integrated into a single cabinet having a total footprint area less than about 0.25 m2, an elevation less than about 0.45 m, a weight less than 20 kg, and an operating power demand less than 500 W.

5. The device according to claim 4 wherein the cabinet has a total footprint area is less than about 0.2 m2, the maximum elevation is less than about 0.3 m, and the operating power demand is no more than about 150 W.

6. The device according to claim 1 wherein the NMR probe module comprises a magnet and yoke assembly having adjustable faces, said magnet maintaining a magnetic field directed across the chamber having a field strength between 0.2 and 0.5 Tesla and a magnetic field inhomogeniety of less than 1 part in 103 over a sample volume of 1.0 cm3; a means for transmitting radio frequency pulses and detecting magnetic response from the dispersion; and a means for transmitting magnetic field gradient pulses.

7. The device according to claim 6 wherein the yoke assembly has 3-fold symmetry and is comprised of three arms fitted with adjustable alignment screws

8. The device according to claim 6 wherein the magnet comprises samarium cobalt or neodymium-iron-boron.

9. The device according to claim 6 wherein the magnet is an electromagnet.

10. The device according to claim 1 wherein the pulse generator comprises a selectable means for generating a radio frequency pulse of about 10 W up to about 200 W to a sample volume of 1.0 cm3 at frequencies between about 1 and about 20 MHz over a duration of about 5 to about 20 μs; and a selectable means for generating a magnetic field gradient pulse that generates a magnetic field gradient across a sample volume of up to 1.0 cm3 of up to about 1 Tm−1.

11. The device according to claim 1 wherein the master controller comprises a field programmable logic array capable of timings accurate to better than +/−1 microsecond and providing RF pulses of about 1 μs to about 1000 μs with rise and fall times less than 1 μs, and sequence pulsing having a step size less than 0.1 μs with 0, 90, 180, and 270 degree phase shifts.

12. The device according to claim 1 wherein the radio frequency pulses are generated by the discharge of one or more capacitors.

13. The device according to claim 1 wherein magnetic response detecting means is sensitive to 10−6 Tesla over a length of 5 mm.

14. A method of using the portable device according to claim 1 to measure the surface area and/or particle size and/or volume fraction of liquid of a dispersion comprising finely divided liquid, gas, or solid particles dispersed in a fluid phase.

15. The device according to claim 1 that further provides a user with a series of predetermined actions or steps through hard-wired or software algorithms whereby the measurement of one or more characteristics of the phases or particles comprising the dispersion selected from the group consisting of surface area, solid/liquid ratio, particle size, and elemental analysis is accomplished according to a set protocol.

16. A method for determining the in-situ surface area of particles dispersed in a liquid using low field NMR relaxation times, said method comprising the steps of: i) determining an average NMR relaxation rate constants, R1ave,ref or R2ave,ref, of one or more reference dispersions having known total particle surface area per unit volume of liquid, ArefT;ii) computing the proportionality constant, kAL, for the reference dispersion from the equation, Rnave,ref=kALref ATref; where n=1 or 2;iii) determining an average NMR relaxation rate constants R1ave,sample or R2ave, sample of a sample dispersion whose surface area is to be determined; andiv) computing the total surface area of the sample dispersion, ATsample from the equation, Rnave, sample=kALref ATsample, where n=1 or 2.

17. The method according to claim 16, wherein the relaxation times are measured with the device of claim 1.

18. A method for determining the atomic concentration of Lithium, Fluorine, or Phosphorus from the signal intensity of the device of claim 1.

19. A method for determining surfactant adsorption isotherms from the measured NMR relaxation rate constants using the device of claim 1.