Continuous wave NMR imaging in the solid state
The development of a continuous wave NMR imaging system and its application to the study of materials in the solid state is described. The three dimensional, multi-nuclear imaging capability of the system, together with its ability to image materials with extremely short T2* relaxation values, was demonstrated on materials of real scientific and industrial interest such as cements, polymers, rocks, clay minerals, wood, and fuel cells. Hardware and software modifications that were made to a prototype system are described. These included the installation of a new PC and multifunction in/out board, which allowed for the replacement of several hardware components with equivalent software routines, and the development of a new sequence control and data acquisition program, together with a suite of data and image processing routines. Experiments carried out on a range of cement, rock, polymer, confectionary and wood samples demonstrated the broad versatility of the system and its ability to obtain quantitative information from materials which have proved difficult or impossible to image using other NMR techniques. The upgrading of the system to include multi-nuclear and 3-D imaging is also described. A range of rf resonators (1H, 13C, 7Li, and 23Na/27Al) were developed for specific imaging applications, and a new gradient and ramp coil assembly with improved gradient and field strength and uniformity was tested and installed. The new system was used to measure water diffusion coefficients in a clay mineral, as well as to image solid phases of 13C, 27Al, 23Na and 7Li in cements and fuel cells. Finally, the 3-D imaging capability of the system was demonstrated by acquiring a high resolution 3-D image of a perspex phantom.