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Three-Dimensional Nuclear Magnetic Resonance Imaging of Green-State Ceramics

Description: Objective is the development of nuclear magnetic resonance imaging techniques and technology applicable to the nondestructive characterization of green-state ceramics. To this end, a three-dimensional (3-D) NMR imaging technique has been developed, based on a back-projection acquisition protocol in combination with image reconstruction techniques that are based on 3-D Radon transform inversion. The method incorporates the experimental flexibility to overcome many of the difficulties associated with imaging of solid and semisolid broad-line materials, and also provides contiguously sampled data in three dimensions. This technique has been evaluated as a nondestructive characterization method for determining the spatial distribution of organic additives in green-state injection-molded cylindrical Si₃N₄ tensile specimens. The technique has been evaluated on the basis of providing moderate image resolution over large sample volumes, high resolution over smaller specimen volumes, and sensitivity to variations in the concentration of organics. Resolution of 200 micrometers has been obtained with excellent sensitivity to concentration. A detailed account of the 3-D imaging results obtained from the study, a discussion of the difficulties and limitations of the imaging technique, and suggestions for technique and system improvements are included.
Date: September 1991
Creator: Dieckman, S. L.
Partner: UNT Libraries Government Documents Department

Development of a magnetic resonance sensor for on-line monitoring of {sup 99}Tc and {sup 23}Na in tank waste cleanup processes: Final report and implementation plan

Description: In response to US Department of Energy (DOE) requirements for advanced cross-cutting technologies, Argonne National Laboratory is developing an on-line sensor system for the real-time monitoring of {sup 99}Tc and {sup 23}Na in various locations throughout radioactive-waste processing facilities. Based on nuclear magnetic resonance spectroscopy, the highly automated sensor system can provide near-real-time response with minimal sampling. The technology, in the form of a flow-through nuclear-magnetic-resonance-based on-line process sensing and control system, can rapidly monitor {sup 99}Tc speciation and concentration (from 0.1 molar to 10 micro molar) in the feedstocks and eluents of radioactive-waste treatment processes. The system is nonintrusive, capable of withstanding harsh plant environments, and reasonably immune to contaminants. Furthermore, the system is capable of operating over large variations in pH, conductivity, and salinity. This document describes design parameters, results from sensitivity studies, and initial results obtained from oxidation-reduction studies that were conducted on technetium standards and waste specimens obtained from DOE's Hanford site. A cursory investigation of the system's capabilities to monitor {sup 23}Na at high concentrations are also reported, as are descriptions of site requirements, implementation recommendations, and testing techniques.
Date: February 24, 2000
Creator: Dieckman, S. L.; Jendrzejczyk, J. A. & Raptis, A. C.
Partner: UNT Libraries Government Documents Department

Application of NMR spectroscopy and multidimensional imaging to the gelcasting process and in-situ real-time monitoring of cross-linking polyacrylamide gels

Description: In the gelcasting process, a slurry of ceramic powder in a solution of organic monomers is cast in a mold. The process is different from injection molding in that it separates mold-filling from setting during conversion of the ceramic slurry to a formed green part. In this work, NMR spectroscopy and imaging have been conducted for in-situ monitoring of the gelation process and for mapping the polymerization. {sup 1}H nuclear magnetic resonance spectra have been obtained during polymerization of a premix of soluble reactive methacrylamide (monomer) and N, N`-methylene bisacrylamide (cross-linking molecules). The premix was polymerized by adding ammonium persulfate (initiator) and tetramethyl-ethylene-diamine (accelerator) to form long-chain, cross-linked polymers. The time-varying spin-lattice relaxation times T{sub 1} during polymerization have been studied at 25 and 35{degrees}C, and the variation of spectra and T{sub 1} with respect to extent of polymerization has been determined. To verify homogeneous polymerization, multidimensional NMR imaging was utilized for in-situ monitoring of the process. The intensities from the images are modeled and the correspondence shows a direct extraction of T{sub 1} data from the images.
Date: April 1, 1995
Creator: Ahuja, S.; Dieckman, S.L. & Gopalsami, N.
Partner: UNT Libraries Government Documents Department

An on-line NMR technique with a programmable processor

Description: Nuclear magnetic resonance (NMR) spectroscopy is used to determine molecular content of materials, mainly in laboratory measurements. The reduced cost of fast computer processors, together with recent break throughs in digital signal processor technology, has facilitated the on-line use of NMR by allowing modifications of the available technology. This paper describes a system and an algorithm for improving the on-line operations. It is base on the time-domain NMR signal detected by the controller and some prior knowledge of chemical signal patterns. The desired signal can be separated from a composite signal by using an adaptive line enhancer (ALE) filter. This technique would be useful for upgrading process procedures in on-line manufacturing.
Date: July 1, 1995
Creator: Razazian, K.; Dieckman, S.L. & Raptis, A.C.
Partner: UNT Libraries Government Documents Department

DSP-based on-line NMR spectroscopy using an anti-Hebbian learning algorithm

Description: This paper describes a nuclear magnetic resonance (NMR) system that uses an adaptive algorithm to carry out real-time NMR spectroscopy. The system employs a digital signal processor (DSP) chip to regulate the transmitted and received signal together with spectral analysis of the received signal to determine free induction decay (FID). To implement such a signal-processing routine for detection of the desired signal, an adaptive line enhancer filter that uses an anti-Hebbian learning algorithm is applied to the FID spectra. The results indicate that the adaptive filter can be a reliable technique for on-line spectroscopy study.
Date: July 1, 1995
Creator: Razazian, K.; Dieckman, S.L.; Raptis, A.C. & Bobis, J.P.
Partner: UNT Libraries Government Documents Department

NMR imaging: A chemical' microscope for coal analysis

Description: This paper presents a new three-dimensional (3-D) nuclear magnetic resonance (NMR) imaging technique for spatially mapping proton distributions in whole coals and solvent-swollen coal samples. The technique is based on a 3-D back-projection protocol for data acquisition, and a reconstruction technique based on 3-D Radon transform inversion. In principle, the 3-D methodology provides higher spatial resolution of solid materials than is possible with conventional slice-selection protocols. The applicability of 3-D NMR imaging has been demonstrated by mapping the maceral phases in Utah Blind Canyon (APCS {number sign}6) coal and the distribution of mobile phases in Utah coal swollen with deuterated and protic pyridine. 7 refs., 5 figs.
Date: January 1, 1991
Creator: French, D.C.; Dieckman, S.L.; Gopalsami, N. & Botto, R.E.
Partner: UNT Libraries Government Documents Department

Solid-state NMR imaging system

Description: An accessory for use with a solid-state NMR spectrometer includes a special imaging probe with linear, high-field strength gradient fields and high-power broadband RF coils using a back projection method for data acquisition and image reconstruction, and a real-time pulse programmer adaptable for use by a conventional computer for complex high speed pulse sequences.
Date: January 1, 1990
Creator: Gopalsami, N.; Dieckman, S.L. & Ellingson, W.A.
Partner: UNT Libraries Government Documents Department

Solid-state NMR imaging system

Description: An accessory for use with a solid-state NMR spectrometer includes a special imaging probe with linear, high-field strength gradient fields and high-power broadband RF coils using a back projection method for data acquisition and image reconstruction, and a real-time pulse programmer adaptable for use by a conventional computer for complex high speed pulse sequences.
Date: December 31, 1990
Creator: Gopalsami, N.; Dieckman, S. L. & Ellingson, W. A.
Partner: UNT Libraries Government Documents Department

Real time simulator with Ti floating point digital signal processor

Description: This paper describes the design and operation of a Real Time Simulator using Texas Instruments TMS320C30 digital signal processor. This system operates with two banks of memory which provide the input data to digital signal processor chip. This feature enables the TMS320C30 to be utilized in variety of applications for which external connections to acquire input data is not needed. In addition, some practical applications of this Real Time Simulator are discussed.
Date: August 1, 1994
Creator: Razazian, K.; Bobis, J. P.; Dieckman, S. L. & Raptis, A. C.
Partner: UNT Libraries Government Documents Department

Development of a hand-portable photoionization time-of-flight mass spectrometer

Description: ANL is currently developing a portable chemical sensor system based on laser desorption photoionization time-of-flight mass spectrometry. It will incorporate direct sampling, a cryocooler base sample adsorption and concentration, and direct surface multiphoton ionization. All components will be in a package 9 x 11 x 4 in., weighing 15-18 lbs. A sample spectrum is given for a NaCl sample.
Date: June 1996
Creator: Dieckman, S. L.; Bostrom, G. A.; Waterfield, L. G.; Jendrzejczyk, J. A. & Raptis, A. C.
Partner: UNT Libraries Government Documents Department

Magnetic resonance imaging of gel-cast ceramic composites

Description: Magnetic resonance imaging (MRI) techniques are being employed to aid in the development of advanced near-net-shape gel-cast ceramic composites. MRI is a unique nondestructive evaluation tool that provides information on both the chemical and physical properties of materials. In this effort, MRI imaging was performed to monitor the drying of porous green-state alumina - methacrylamide-N.N`-methylene bisacrylamide (MAM-MBAM) polymerized composite specimens. Studies were performed on several specimens as a function of humidity and time. The mass and shrinkage of the specimens were also monitored and correlated with the water content.
Date: April 1, 1997
Creator: Dieckman, S.L.; Balss, K.M. & Waterfield, L.G.
Partner: UNT Libraries Government Documents Department

Alternative catalyst and exhaust gas sensor work at Argonne National Laboratory

Description: Research programs at Argonne National Laboratory in the areas of automobile emissions monitoring and control are described. The mandate to improve automobile efficiency while reducing Pollution requires the development of new catalysts for exhaust emissions control that are capable of functioning efficiently under lean-burn engine operating conditions. It is also desirable that the use of expensive noble metal catalysts be avoided. NO{sub x} emissions will not be efficiently controlled by the current three-way, supported noble metal catalysts under lean-burn conditions. New catalysts are being sought that could effect the selective catalytic reduction (SCR) of NO{sub x} by exhaust hydrocarbons in the presence of oxygen. Molecular sieve zeolites of the ZSM-5 and ferrierite types, ion-exchanged with copper ions, are the best of the catalysts known to effect this chemistry, but the mechanism of the SCR is still not understood. In this project the authors will first undertake the investigation of the SCR of NO using model reactions to test postulated mechanistic pathways. Initial experiments have been devised to investigate the possible participation of metal alkyl complexes, metal oxime complexes, N-alkyl-N-nitroso-alkylaminato-metal complexes, and metal nitrile complexes in the zeolites. ANL will also develop microsensors, based on surface acoustic wave (SAW) chemical sensing techniques, and a micro mass-spectrometer (MS) for tailpipe or engine-out emission monitoring. The sensor configurations and sensing techniques of the proposed SAW and micro-MS are described.
Date: December 31, 1994
Creator: Iton, L.E.; Maroni, V.A.; Dieckman, S.L.; Sheen, S.H. & Raptis, A.C.
Partner: UNT Libraries Government Documents Department

Millimeter-wave imaging of composite materials

Description: This work addresses the application and evaluates the potential of mm-wave imaging in the W-band (75-110 GHz) using samples of low-loss dielectric and composite materials with artificial defects. The initial focus is on the measurement of amplitude changes in the back scattered and forward-scattered fields. The c-scan system employs a focused beam antenna to provide spatial resolution of about one wavelength. A plane-wave model is used to calculate the effective reflection (or transmission) coefficient of multilayer test sample geometry. Theoretical analysis is used to optimize the measurement frequency for higher image contrast and to interpret the experimental results. Both reflection and transmission images, based on back scattered and forward-scattered powers, were made with Plexiglas and Kevlar/epoxy samples containing artificially introduced defects such as subsurface voids and disbonds. The results clearly indicate that mm-wave imaging has high potential for non-contact interrogation of low-loss materials.
Date: September 1, 1993
Creator: Gopalsami, N.; Bakhtiari, S.; Dieckman, S. L.; Raptis, A. C. & Lepper, M. J.
Partner: UNT Libraries Government Documents Department

Intelligent hand-portable proliferation sensing system

Description: Argonne National Laboratory, with support from DOE`s Office of Nonproliferation and National Security, is currently developing an intelligent hand-portable sensor system. This system is designed specifically to support the intelligence community with the task of in-field sensing of nuclear proliferation and related activities. Based upon pulsed laser photo-ionization time-of-flight mass spectrometry technology, this novel sensing system is capable of quickly providing a molecular or atomic analysis of specimens. The system is capable of analyzing virtually any gas phase molecule, or molecule that can be induced into the gas phase by (for example) sample heating. This system has the unique advantages of providing unprecedented portability, excellent sensitivity, tremendous fieldability, and a high performance/cost ratio. The system will be capable of operating in a highly automated manner for on-site inspections, and easily modified for other applications such as perimeter monitoring aboard a plane or drone. The paper describes the sensing system.
Date: August 1, 1997
Creator: Dieckman, S.L.; Bostrom, G.A.; Waterfield, L.G.; Jendrzejczyk, J.A.; Ahuja, S. & Raptis, A.C.
Partner: UNT Libraries Government Documents Department

In-situ real time monitoring of the polymerization in gel-cast ceramic processes

Description: Gelcasting requires making a mixture of a slurry of ceramic powder in a solution of organic monomers and casting it in a mold. Gelcasting is different from injection molding in that it separates mold filling from setting during conversion of the ceramic slurry to a formed green part. In this work, NMR spectroscopy and imaging were used for in-situ monitoring of the gelation process and gelcasting of alumina. {sup 1}H NMR spectra and images are obtained during polymerization of a mixture of soluble reactive acrylamide monomers. Polymerization was initiated by adding an initiator and an accelerator to form long- chain, crosslinked polymers. Multidimensional NMR imaging was used for in-situ monitoring of the process and for verification of homogeneous polymerization. Comparison of the modeled intensities with acquired images shows a direction extraction of T{sub 1} data from the images.
Date: August 1, 1996
Creator: Ahuja, S.; Dieckman, S.L.; Bostrom, G.A.; Waterfield, L.G.; Raptis, A.C. & Omatete, O.O.
Partner: UNT Libraries Government Documents Department

Nuclear Magnetic Resonance Imaging of Green-State Ceramics

Description: Proton (¹H) nuclear magnetic resonance (NMR) imaging techniques are investigated as a means to nondestructively characterize green-state (unfired) Si{sub 3}N{sub 4} ceramic components. Spectroscopic results indicate that the organic additives used in the injection molding of ceramics behave as soft solids, with broad spectral peak widths (T₂ <0.5 ms) and moderate multicomponent spin-lattice relaxation rates (T{sub 1} ranging from 11 ms to 1 s). Because of the intrinsically different spectral characteristics of the organic additives, conventional-solution NMR imaging techniques cannot be applied to these materials. Hence, the authors developed specialized NMR imaging accessories capable of applying high magnetic field gradients in a back-projection protocol. NMR images were acquired of injection-molded test bars that had been fabricated with different mixing and molding parameters. Organic concentrations determined from the NMR images were correlated with results obtained through destructive testing. The correlation suggests that NMR imaging is a viable technique for quantifying organics in injection-molded green-state ceramics.
Date: August 1990
Creator: Gopalsami, Nachappa; Dieckman, S. L.; Ellingson, W. A.; Botto, Robert E.; Wong, P. S.; Yeh, H. C. et al.
Partner: UNT Libraries Government Documents Department

Development of nondestructive evaluation methods and prediction of effects of flaws on the fracture behavior of structural ceramics

Description: Characterization of ceramic matrix composites (continuous and whisker-type) by nondestructive evaluation (NDE) methods and an understanding of fracture behavior, together with correlation of fracture and NDE data, may provide insight into the prediction of component performance and the development of process technology. Knowledge of the degradation extent of fiber tows or monofilament degradation after processing, extent of open porosity before densification, and filament/fiber alignments before and after processing are also examples of important variables to be measured. Work in this program has emphasized continuous fiber ceramic matrix composites (CFCCs) that use chemical vapor infiltration (CVI)-infiltrated SiC/SiC materials, primarily those made of Nicalon satin or plain weave with 16 {times} 16 tows/in. in 2-D layups. All studied samples were provided by Oak Ridge National Laboratory and were made using 100 layers per inch. CVI specimens with 0/30/60, 0/90, and 0/45 were examined by 3-D X-ray microtomography to characterize in-plane fiber orientations. Current information suggests that for Nicalon-type fiber architecture, a {plus minus}2--1/2{degrees} misalignment may not affect mechanical properties. Thus the near-term goal has been to establish a detection capability for angular orientation. By using 512 {times} 512 images from 3-D X-ray CT data with pixel sizes of < 140 {mu}m and a special 2-D fast-Fourier transform image processing analysis, we have shown that fiber orientations to {plus minus}2--1/2{degrees} with SiC/SiC CVI type 2-D weave architecture can be measured.
Date: May 1, 1992
Creator: Ellingson, W.A.; Singh, J.P.; Holloway, D.L.; Dieckman, S.L.; Singh, D.; Sivers, E.A. et al.
Partner: UNT Libraries Government Documents Department

NMR spectroscopy and imaging of macerals in Argonne premium coals

Description: Macerals that have been separated from two high-volatile bituminous coals from the Argonne Premium Coal Sample Program are surveyed using chemical and NMR spectroscopic techniques. Quantitative aspects of the method are discussed. Alkylation using {sup 13}C enriched methyl iodide followed by solid {sup 13}C NMR analysis was used to determine the concentrations of acidic OH and CH sites in these macerals. Also, the first successful application of nuclear magnetic resonance imaging (MRI) for spatially mapping chemically distinct regions within a Utah coal has been demonstrated. 15 refs., 5 figs., 2 tabs.
Date: January 1, 1990
Creator: Botto, R.E.; Choi, C.Y.; Dieckman, S.L.; Gopalsami, N.; Thompson, A.R. & Tsiao, C.J.
Partner: UNT Libraries Government Documents Department

Development of nondestructive evaluation methods and prediction of effects of flaws on the fracture behavior of structural ceramics

Description: Work emphasized continuous-fiber ceramic matrix composites (CFCCs) with 2-D lay-ups composed of chemical-vapor-infiltrated (CVI) SiC/SiC materials, mostly made of Nicalon plain weave with 16 [times] 16 tows/in. One sample examined comprised a 3-D SiC/SiC braid made by Techniweave. Using a new 1024[times]1024[times]14 bit detector, images from 3-D X-ray CT data with pixel sizes of <140 [mu]m and 2-D fast-Fourier transform (FFT) image processing, we have shown that fiber orientations can be measured to [plus minus]2-1/2[degree]. 3-D FFT analysis was used to determine 3-D braid/weave fiber spacing. Multinuclear ([sup l]H, [sup 13]C, and [sup 29]Si) NMR spectroscopy, is being studied. Surface chemistry of fibers and chemistry of interfacial regions in composites are being studied. We are also conducting initial studies to investigate the bulk composition of matrix materials ([alpha], [beta], amorphous phase, silica, and oxynitride concentration) and surface chemistry of Si[sub 3]N[sub 4] and SiC fibers. Fracture mechanics work to correlate with NDE data focused on strength distribution of as-fabricated Nicalon fibers obtained from bundle tests. Strength distribution of fractured Nicalon fibers in composites was assessed from fracture mirror radii. SEM was used to determine distribution of fiber pullout length distribution for fibers in composites, for their strength distribution. From the strength distribution plots, scale parameters were determined to be 3.45 GPa for as-fabricated fibers and 1.31 GPa for fibers in processed composites. However, the Weibull moduli for the two distributions were similar. Reduction in strength of the fibers in processed composites is believed to be due to surface flaws and defects. Effects of fiber misorientation on mechanical properties of NDE-tested CVI continuous-fiber composites are currently being investigated. 8 figs, 11 refs.
Date: March 1, 1993
Creator: Ellingson, W.A.; Singh, J.P.; Holloway, D.L.; Dieckman, S.L.; Singh, D. & Sivers, E.A.
Partner: UNT Libraries Government Documents Department

Development of nondestructive evaluation methods and prediction of effects of flaws on the fracture behavior of structural ceramics

Description: In the NDE area, specimens with different cloth lay-up orientations were examined by a 3-D X-ray microtomography device and image processing to measure and map in-plane fiber orientations. Results show detection sensitivity to better than {plus_minus}3{degrees}. We establish detection of 3-D braid/weave fiber orientation and spacing. Another NDE method, multinuclear ({sup 13}C,{sup 29}Si, and {sup 11B} NMR spectroscopy, is being developed to determine the chemical state of the fiber surface and its potential impact on fiber pullout. We have conducted initial studies to investigate sensitivity to bulk composition of the matrix materials (a,b, amorphous phase, silica, and oxynitride concentration). The first {sup 29}Si NMR experiments focused on methods to enhance the signal from the surface by selectively reducing surface relaxation. Additionally, we have determined that there is sufficient sensitivity of {sup 11}B NMR for monitoring fiber coatings.
Date: May 1, 1994
Creator: Ellingson, W. A.; Singh, J. P.; Sivers, E. A.; Holloway, D. L.; Jacobs, T. D.; Dieckman, S. L. et al.
Partner: UNT Libraries Government Documents Department

Development of Nondestructive Evaluation Methods and Prediction of Effects of Flaws on the Fracture Behavior of Structural Ceramics

Description: Work emphasized continuous-fiber ceramic matrix composites (CFCCs) with 2-D lay-ups composed of chemical-vapor-infiltrated (CVI) SiC/SiC materials, mostly made of Nicalon plain weave with 16 {times} 16 tows/in. One sample examined comprised a 3-D SiC/SiC braid made by Techniweave. Using a new 1024{times}1024{times}14 bit detector, images from 3-D X-ray CT data with pixel sizes of <140 {mu}m and 2-D fast-Fourier transform (FFT) image processing, we have shown that fiber orientations can be measured to {plus_minus}2-1/2{degree}. 3-D FFT analysis was used to determine 3-D braid/weave fiber spacing. Multinuclear ({sup l}H, {sup 13}C, and {sup 29}Si) NMR spectroscopy, is being studied. Surface chemistry of fibers and chemistry of interfacial regions in composites are being studied. We are also conducting initial studies to investigate the bulk composition of matrix materials ({alpha}, {beta}, amorphous phase, silica, and oxynitride concentration) and surface chemistry of Si{sub 3}N{sub 4} and SiC fibers. Fracture mechanics work to correlate with NDE data focused on strength distribution of as-fabricated Nicalon fibers obtained from bundle tests. Strength distribution of fractured Nicalon fibers in composites was assessed from fracture mirror radii. SEM was used to determine distribution of fiber pullout length distribution for fibers in composites, for their strength distribution. From the strength distribution plots, scale parameters were determined to be 3.45 GPa for as-fabricated fibers and 1.31 GPa for fibers in processed composites. However, the Weibull moduli for the two distributions were similar. Reduction in strength of the fibers in processed composites is believed to be due to surface flaws and defects. Effects of fiber misorientation on mechanical properties of NDE-tested CVI continuous-fiber composites are currently being investigated. 8 figs, 11 refs.
Date: March 1993
Creator: Ellingson, W. A.; Singh, J. P.; Holloway, D. L.; Dieckman, S. L.; Singh, D. & Sivers, E. A.
Partner: UNT Libraries Government Documents Department

Development of nondestructive evaluation methods and prediction of effects of flaws on the fracture behavior of structural ceramics

Description: Characterization of ceramic matrix composites (continuous and whisker-type) by nondestructive evaluation (NDE) methods and an understanding of fracture behavior, together with correlation of fracture and NDE data, may provide insight into the prediction of component performance and the development of process technology. Knowledge of the degradation extent of fiber tows or monofilament degradation after processing, extent of open porosity before densification, and filament/fiber alignments before and after processing are also examples of important variables to be measured. Work in this program has emphasized continuous fiber ceramic matrix composites (CFCCs) that use chemical vapor infiltration (CVI)-infiltrated SiC/SiC materials, primarily those made of Nicalon satin or plain weave with 16 {times} 16 tows/in. in 2-D layups. All studied samples were provided by Oak Ridge National Laboratory and were made using 100 layers per inch. CVI specimens with 0/30/60, 0/90, and 0/45 were examined by 3-D X-ray microtomography to characterize in-plane fiber orientations. Current information suggests that for Nicalon-type fiber architecture, a {plus_minus}2--1/2{degrees} misalignment may not affect mechanical properties. Thus the near-term goal has been to establish a detection capability for angular orientation. By using 512 {times} 512 images from 3-D X-ray CT data with pixel sizes of < 140 {mu}m and a special 2-D fast-Fourier transform image processing analysis, we have shown that fiber orientations to {plus_minus}2--1/2{degrees} with SiC/SiC CVI type 2-D weave architecture can be measured.
Date: May 1, 1992
Creator: Ellingson, W. A.; Singh, J. P.; Holloway, D. L.; Dieckman, S. L.; Singh, D.; Sivers, E. A. et al.
Partner: UNT Libraries Government Documents Department

Three-dimensional nuclear magnetic resonance imaging of green-state ceramics

Description: Objective is the development of nuclear magnetic resonance imaging techniques and technology applicable to the nondestructive characterization of green-state ceramics. To this end, a three-dimensional (3-D) NMR imaging technique has been developed, based on a back-projection acquisition protocol in combination with image reconstruction techniques that are based on 3-D Radon transform inversion. The method incorporates the experimental flexibility to overcome many of the difficulties associated with imaging of solid and semisolid broad-line materials, and also provides contiguously sampled data in three dimensions. This technique has been evaluated as a nondestructive characterizauon method for determining the spatial distribution of organic additves in green-state injection-molded cylindrical Si{sub 3}N{sup 4} tensile specimens. The technique has been evaluated on the basis of providing moderate image resolution over large sample volumes, high resolution over smaller specimen volumes, and sensitivity to variations in the concentration of organics. Resolution of 200{mu}m has been obtained with excellent sensitivity to concentration. A detailed account of the 3-D imaging results obtained from the study, a discussion of the difficulties and limitations of the imaging technique, and suggestions for technique and system improvements are included.
Date: September 1, 1991
Creator: Dieckman, S. L.; Gopalsami, N.; Ford, J. M.; Raptis, A. C.; Ellingson, W. A.; Rizo, P. et al.
Partner: UNT Libraries Government Documents Department

Application of NMR Spectroscopy and Multidimensional Imaging to the Gelcasting Process and in-situ Real-Time Monitoring of Cross-Linking Polyacrylamide Gels

Description: In the gelcasting process, a slurry of ceramic powder in a solution of organic monomers is cast in a mold. The process is different from injection molding in that it separates mold-filling from setting during conversion of the ceramic slurry to a formed green part. In this work, NMR spectroscopy and imaging have been conducted for in-situ monitoring of the gelation process and for mapping the polymerization. ¹H nuclear magnetic resonance spectra have been obtained during polymerization of a premix of soluble reactive methacrylamide (monomer) and N, N'-methylene bisacrylamide (cross-linking molecules). The premix was polymerized by adding ammonium persulfate (initiator) and tetramethyl-ethylene-diamine (accelerator) to form long-chain, cross-linked polymers. The time-varying spin-lattice relaxation times T₁ during polymerization have been studied at 25 and 35 C, and the variation of spectra and T₁ with respect to extent of polymerization has been determined. To verify homogeneous polymerization, multidimensional NMR imaging was utilized for in-situ monitoring of the process. The intensities from the images are modeled and the correspondence shows a direct extraction of T₁ data from the images.
Date: April 1995
Creator: Ahuja, S.; Dieckman, S. L.; Gopalsami, Nachappa; Raptis, A. C. & Omatete, Oritsegbemi O.
Partner: UNT Libraries Government Documents Department