Publikationsserver der RWTH Aachen University
Non-destructive characterization of materials by single-sided NMR
Abstract
dc:descriptionNMR is a proved powerful method for the characterization of structure and motion in materials. Compared to other physical investigation methods, NMR provides unique information from a large variety of experiments, showing up in its different shapes as a unique tool for characterization of a large variety of materials in an ever broadening field of applications. In particular, single-sided NMR exhibits important advantages like non-invasiveness and non-destructiveness, portability, simplicity and not least, low costs. The experiments conducted in this work demonstrate the efficiency and sensitivity of single-sided NMR for investigating macromolecular materials on large time and length scales. Elastomers can readily be characterized by unilateral NMR of protons in terms of a variety of parameters, which correlate with the overall molecular mobility. In this way information about the cross-link density, state of cure and strain, the effects of aging and product heterogeneity can obtained. For these purposes, the NMR-MOUSE was used to optimize product development and to monitor product and production quality on-line. The sensor is also suitable for nondestructive probing of the mechanical deformation in cross-linked elastomers. A special magnet design that fits a stress-strain device has been used for complementary investigation of a series of different rubber stripes during mechanical testing. Such a setup promises to be of great use for predicting the time of failure based on NMR relaxation measurements in cyclic loading tests. The main reasons why NMR is considered sticky by many non-NMR scientists is the fact that the information expressed in terms of NMR parameters, such as the relaxation times, is apparently difficult to understand or handle. In this context, NMR specialists often meet the request of characterizing the material in terms of well-known parameters. In these conditions, the establishment of correlation maps between NMR parameters and material properties exhibits special importance. Moreover, the use of such maps makes possible the macroscopic characterization of objects which do not fit the specific test devices, since open NMR sensors do not impose limitations concerning the sample size. As a type of multi-dimensional NMR in low-fields, the development of imaging techniques on single-sided sensors has opened a broad field of new applications in medicine and materials science. Besides being a non-destructive technique, single-sided NMR allows in situ characterization of large immobile objects. Several strategies have been developed to incorporate 2D and 3D spatial resolution and enhance contrast on single-sided sensors with a large number of applications that illustrate the performance of the technique in fields like quality control, medicine and material science. In the cases where no multi-dimensional information but rather high resolution along a single spatial direction is needed, the generation of uniform static gradients provides a simple method to resolve layered structures. A high-resolution profiling technique can be exploited to resolve multi-layer structures and to follow dynamic processes like the absorption of oil in high pressure rubber hoses or the UV aging of cross-linked elastomers. In a related study, the profile NMR-MOUSE was found to be a unique tool for the characterization of changes induced by the UV irradiation in natural rubber. The aging profiles were interpreted for the first time based on a novel model in which the radiation absorption coefficient depends on the depth in the sample. The method can be applied to investigate the effect of other aging agents on the surfaces of elastomers.
Degree
thesis:*- Grantor dc:publisher
- Publikationsserver der RWTH Aachen University
- Year dc:date
- 2007
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Goga, Nicolae-Octavian
- Contributors dc:contributor
-
- Blümich, Bernhard
Subjects
dc:subject × 9Rights
dc:rights- Statement dc:rights
-
- info:eu-repo/semantics/openAccess
- Language dc:language
- eng