NMR imaging has been applied to some elastomeric materials of industrial interest. The T2s of common elastomers, Particularly after filling and curing, are sufficiently short That spin-echo sequences at submillisecond echo times cannot Produce T2 independent images. The sensitivity to T2 Potentially makes spin echo imaging a good probe of elastomer Blend composition, as demonstrated for a series of filled and Cured cis-polybutadiene, styrene-butadiene rubber blends. The Technique can be used to distinguish good and bad carbon black Dispersion in actual tire tread samples. The configuration of Polyester tire cord, voids, rubber layer boundaries, differences of molecular mobility and composition, and other inhomogeneities can be detected in end-product tire samples. The value of isotropic voxels at 80–100 um and the effect of resolution Relative to pore size are demonstrated on a model, H2O-saturated Porous glass disk of 200-um average pore size. The feasibility of multinuclear NMR imaging for fluid-specific characterization of porous materials such as oil cores is demonstrated for 7Li and 19F

The possibilities of acquiring NMR images of solids with conventional imaging apparatuses are explored. To this end a multiple-pulse line-narrowing sequence is introduced which averages both homonuclear dipolar couplings and time independent linear lz, interactions such as chemical shifts and susceplibility shifts. For imaging the multiple-pulse cycle is accompanied by an oscillating magnetic field gradient which phase encodes the spatial location o each spin. The period of the gradient oscillation is matched to the period of effective field toggling such that the multiple-pulse cycle does not average to zero the gradient induced spin evolution. A small radio frequency coil of 3.0 mm i.d. is used since then only modest radio frequency (RF) power is sufficient to generate a strong RF field, and the RF homogeneity is quite good over the sample volume. The resolution of the image is not spatially uniform, but near the center the resolution is better than 100 μm and the resolution at the edges of the image is degraded by only a factor of 3 to 5. Images of solids with acceptable resolution and sensitivity can be collected by this method- with minimal setup time and difficulties.

A three dimensional (3D) Electron Paramagnetic Resonance Imaging (EPRI) method has been developed to probe the structure and size of pores in ceramic materials. A computer control current source and magnetic field gradient coil assembly were added on the conventional EPR instrument as imaging devices. This added-on facility was tested using a phantom sample having cavities filled with DPPH (2,2-diphenyl-1-picrylhydrazyl) particles. Pumice was then used to demonstrate the feasibility of the technique. Porous pumice stone was immersed in a 0.5mM 15N-PDT-water solution to introduce the spin labels into the open volume of the sample. A two-dimensional image was reconstructed from a set of 1-D projections using a filtered back-projection technique. A three-dimensional image was derived from 22 2-D images each constructed by 22 1-D projections. At present, the facility allows a resolution of 69 and 46 μm for 2-D and 3-D imaging.

Polymeric beads are valuable tools for a variety of applications in chemistry, e.g. separation and synthesis support. A common property of all applications is, that diffusion processes and mass transport balances play an important part and are heavily dependent upon matrix parameters such as crosslinking. We have applied 1H and 19F-microscopy to monitor diffusion processes in differently crosslinked polystyrene beads (CL-PS). MRI is used primarily as a medical diagnostic method, but has begun to find increasing application in material science, including studies of fluids in polymers [1,2].

Aging of polymers and elastomers is a time dependent alteration of the chemical composition and physical properties depending on the aging conditions. Chemical reactions and hence changes in the chemical composition result in many cases from influence by oxygen or solvents and treatment of the bulk material at high temperatures. Aging of the materials by mechanical strain as well as in an oxidative manner can alter the ratio of amorphous to crystalline portions in the polymer, break chemical bondings and hence can alter the physical behavior of the materials.

Fast NMR imaging techniques for the study of objects with circular or spherical symmetry are introduced. Quantitative, radially-resolved information for an object with circular symmetry is obtained by Abel inversion of a single one-dimensional (1D) NMR image or equivalently by Hankel transformation of the 1D time domain NMR signal. With adequate sensitivity, the entire image information is obtained in a single experimental iteration, providing snapshot temporal resolution. Thus these techniques are useful for the study of transport phenomena. Spherical objects can also be radially resolved from a 1D projection image by applying two sequential Abel inversions, or in one simple differentiation step. These radial imaging techniques are easy to implement and the computational and data storage requirements are nominal. These procedures are also applicable to microscopic and solids NMR imaging, as well as to X-ray CAT and other projective imaging techniques. Noise effects, and the detection and handling of distortions from circular symmetry are also considered.

Silicone based biomaterials are characterized with NMR. Bulk spin-lattice (T1) and spin-spin (T2) relaxation times are measured in polydimethylsiloxane (PDMS) model networks and various types of implants. The T2 results seem to indicate that crosslink densities of these biomaterials are lower than those of the PDMS model networks studied. 1H chemical shift NMR imaging techniques are developed to investigate the aging (e.g., migration of free polymer, rupture due to mechanical stress, etc.) of biomaterials in vivo.

The understanding of the adsorption of solvents into materials is of great interest in different fields of material science. NMR imaging techniques can be used to follow the process of solvent adsorption by obtaining spatial and chemical information in a nondestructive way. We report here a study of the uptake of methanol (a non-solvent) into poly(methyl methacrylate) beads produced by suspension polymerization and into compression mouldings. In both cases, the uptake is far faster than the rate of diffusion measured elsewhere. We also illustrate the nonreversible nature of this uptake with respect to temperature cycling.

Preliminary results of two applications of 17O/lH NMR microimaging (MRμI) are described. In the first case, it is shown that oxygen-17 MRμI presents a unique advantage in situations where a strong proton background hinders the analysis of water ingress in polymeric materials. This is illustrated with 17O-enriched water diffusion into an agar gel from a central well. While proton imaging cannot readily distinguish between exogenous and endogenous water, 17O imaging makes a clear differentiation, due to the fact that the natural abundance gel has virtually no 17O background. In the second case, proton MRμI was used to analyze the structure and performance of commercial time-release pellets (ProMacR) containing an active ingredient (surfactant) dispersed into an inert matrix. This was done after leaching the detergent with natural abundance water or after drying the leached sample and refilling the pores with water. Pores ranging in size from 25 to 325 μm diameter are clearly visualized. The 1H images have been quantitated with commercial image analysis software in terms of the total porosity and the individual pore characteristics. Two types of water can be separately imaged: “bound” water with restricted mobility (interacting with the polymer matrix), and “free” water (in large pools). The majority of water is in the bound state. It is possible to evaluate the control-release performance of the product from the size of the pores, the uniformity of dispersion and the time course of detergent-water exchange.

Nuclei with a spin, 1 > 1/2, possess a nuclear quadrupole moment which can couple to the electric field gradients in a material. They can be static, leading to NMR frequency shifts, or dynamic, which can influence relaxation times. In either case, an NMR image can be made which is sensitized to changes in the electric quadrupole interaction to provide a sensitive measure of the macroscopic spatial dependence of the microscopic changes in the material. Several examples are presented. Special considerations need to be given in the case when the strength of the Zeeman interaction between the nucleus and the magnetic field and/or the rf field is small compared to the electric quadrupole interaction.

The application of nuclear magnetic resonance flow imaging to the study of Poiseuille flows of solid/liquid suspensions is described. The basic imaging method is presented along with results on suspensions with solid particle loading levels up to 52 vol. % and viscosities up to 7kPoise. The most concentrated suspensions are non-Newtonian, and the NMR flow data show evidence for deviations from a simple parabolic velocity profile in straight pipes. Cross-sectional intensity images derived from the flow image data on concentrated suspensions are non-uniform. Possible explanations for these results are discussed in terms of current rheological understanding of suspension flow and relaxation weighting phenomena in the NMR imaging experiments.

A technique for nondestructively imaging microstructures of materials in situ, especially a technique capable of delineating the time evolution of chemical changes or damage, will greatly benefit studies of materials processing and failure. X-ray tomographic microscopy (XTM) is a high resolution, three-dimensional inspection method which is capable of imaging composite materials microstructures with a resolution of a few micrometers. Because XTM is nondestructive, it will be possible to examine materials under load or during processing, and obtain three-dimensional images of fiber positions, microcracks, and pores. This will allow direct imaging of microstructural evolution, and will provide time-dependent data for comparison to fracture mechanics and processing models.

We have developed several x-ray microtomography systems which function as quantitative three dimensional x-ray microscopes. In this paper we describe the evolutionary path followed from making the first high resolution experimental microscopes to later generations which can be routinely used for investigating materials. Developing the instrumentation for reliable quantitative x-ray microscopy using synchrotron and laboratory based x-ray sources has led to other imaging modalities for obtaining temporal and spatial two dimensional information.

Acceptance criteria for disposal of radioactive waste drums require that the cement-solidified material in the drum contain minimal free liquid after the cement has hardened. Free liquid is to be avoided because it may corrode the drum, escape and cause environmental contamination. The DOE has requested that a nondestructive evaluation method be developed to detect free liquid in quantities in excess of 0.5% by volume. This corresponds to about 1 liter in a standard 208 liter (55 gallon) drum. In this study, the detection of volumes of free liquid in a 57 cm (2′) diameter cement-solidified drum is demonstrated using high-energy X-ray computed tomography (CT). It is shown that liquid concentrations of simulated radioactive waste inside glass tubes imbedded in cement can easily be detected, even for tubes with inner diameters less than 2 mm (0.08″). Furthermore, it is demonstrated that tubes containing water and liquid concentrations of simulated radioactive waste can be distinguished from tubes of the same size containing air. The CT images were obtained at a rate of about 6 minutes per slice on a commercially available CT system using a 9 MeV linear accelerator source.

In X-ray cone-beam tomography, the only planar source trajectory that does not produce incomplete data is the infinite line. Such a source trajectory is not experimentally possible. To ensure complete data acquisition with cone-beam radiographs, a set of nonplanar trajectories has been studied. Among the trajectories proposed in the literature, a simple one is a set of two circular trajectories with intersection of the two trajectory axes. The angle between the two axes is related to the maximum aperture of the cone beam. We propose here an exact method for performing this reconstruction using the 3-D Radon transform of the object. The modulation transfer function of this algorithm remains identical to that for the central slice of reconstruction in a single circular trajectory. The relative mean square error for density stays within 2% for an aperture of ±30°. With a single circular trajectory, the relative mean square error may reach 20% at the same aperture. With a double circular trajectory, horizontal artifacts are nearly suppressed.

Structural information provided by computed tomography (CT) can be used for quality control and optimization of processes for manufacturing better materials. The squeeze casting method for producing metal matrix composites involves infiltrating a preform of ceramic fibers with molten metal under high pressure. Part quality can be improved if CT is used before infiltration to determine if the preforms have the desired distribution of fibers and are free of defects. Measurements do not require uniform shapes, and CT systems can even be used to obtain accurate densities on complicated part shapes that are not amenable to bulk density measurements based on weight and size. With this quantitative distribution information as a guide, preform production can be modified to produce either a more uniform fiber distribution or to selectively increase the fiber concentration in critical areas. Problems occurring during later stages of processing can be detected in CT images of the completed part. For example. CT can be used to detect unreinforced regions in metal matrix composites caused by cracking of the preform during the squeeze casting process. CT scans of completed parts can also detect and distinguish variations in structure such as microporosity.

The paper describes our 3D X-ray CT algorithm “RADON” using attenuation measurements acquired with a bidimensional detector. Our inversion diagram uses the first derivative of the Radon transform synthesis then its inversion. The potentiality of that new method, particularly for the large aperture, prompted us to develop an optimized software offering convenience and high performances on a modem scientific computer. After a brief recall of the basic principle of X-ray imaging processing, we will introduce the theoretical developments resulting in the present inversion diagram. A general algorithm structure will be proposed afterwards. As a conclusion we will present the performances and the results obtained with ceramic rotors examination.

Damage in a continuous, aligned-fiber SiC/Al metal matrix composite (MMC), e.g. fiber fracture, fiber-matrix interphase microcracking, intra-ply matrix voids and cracks, is examined with synchrotron x-ray tomographic microscopy (XTM). Quantitative three-dimensional measurements of damage are reported in as-fabricated and monotonically loaded SiC/Al. The XTM results indicate that increases in observed macroscopic structural stiffness during the first few fatigue cycles of an MMC coupon correspond to elimination of processing-related matrix porosity and to displacement of the fibers from a somewhat irregular arrangement into a more nearly hexagonal array. The XTM data also show that the carbon cores of the SiC fibers begin to fail at or below 828 MPa, that is, at loads far less than those for fracture of the entire fiber. The implications of these results and of the use of in situ loading for fatigue damage quantification are also discussed for mechanical/thermal modelling.

In Ion Microtomography (IMT), material densities are determined from the energy lost by ions as they pass through a specimen. For fine-scale measurements with micron-size beams, mechanical stability and precision of motion can impact the quality of the reconstruction. We describe several preprocessing procedures used to minimize imperfect specimen manipulation, including adjustment of the center of mass motion in sinograms and correction for vertical translations. In addition, the amount of noise in the reconstruction is reduced by utilizing median (as opposed to mean) ion energy loss values for density determinations. Furthermore, particular portions of the sampled image can be enhanced with minimal degradation of spatial resolution by a judicial choice of spatial filter in the reconstruction algorithm. The benefits and limitations of these preprocessing techniques are discussed.

The utility of cone-beam tomography in the analysis of material has been demonstrated by Feldkamp et al [1]. Recent advances in cone-beam tomography will enhance its usefulness in the analysis of material.