William A. Ellingson

Polymeric binder distribution maps in green ceramics by 1H NMR imaging

Abstract Polymeric binder maps in green ceramics are obtained by 1H NMR imaging techniques. Two- and three-dimensional Fourier transform techniques are compared to determine the trade-off between contrast/ noise and imaging time. The influence of particle size of the ceramic powder and the sample length/diameter ( L D ) ratio upon the polymer distribution are examined. Heterogeneous distributions of binder are found at small L D ratios. Computerized image analysis can provide a means to assess the uniformity of green ceramic parts.

The Science and Technology of Coal and Coal Utilization

Coal is a complex yet abundantly available energy source. This complexity largely determines coal acceptability and convenience in use, and creates a need for high-quality applied research. The primary problem in using coal is the necessity to minimize pollution. This requirement leads to the use of indirect or elaborate means for extracting the energy content of coal. For example, the high sulfur content of much coal in the eastern United States points to the need for advanced combustion processes, gasification or liquefaction processes, or reasonably expensive cleanup systems on conventional combustion processes, to overcome this environmental liability.

Die swell measurements of second-order fluids : numerical experiments.

An analysis of the flow of a second-order fluid is presented. Reference values for some variables are defined, and with these a non-dimensional formulation of the governing equations. From this formulation, three dimensionless numbers appear; one is the Reynolds number, and two numbers that are called the first- and second-dimensionless normal stress (NSD) coefficients. The equations of motion are solved by a finite element method using a commercially available program (Fidap), and the steady state converged solution was used to measure the die swell. The factors that influence die swell and that are studied in this work include: the die geometry for circular cross sectional dies, including tubular, converging, diverging, half-converging/half-tubular shapes; fluid characteristics such as Reynolds number and first- and second-DNS coefficients (both positive and negative values); and flow rates, as determined by the maximum velocity in a parabolic velocity profile at the entrance to the die. The results suggest that shear and deformation histories of the fluid directly influence not only swell characteristics, but also convergence characteristics of the numerical simulation

Development of nuclear magnetic resonance imaging techniques for characterizing green-state ceramic materials

Nuclear magnetic resonance (NMR) imaging holds great potential for aiding ceramics processing development. NMR is a nondestructive method of analysis which has been in routine use in chemistry, physics, and biology for over 35 years. In these areas, its main applications are in determining chemical composition, molecular or crystal structure, and molecular dynamics.1,2 In 1973, the use of NMR in producing tomographic images of objects was reported.3 The development of NMR imaging (NMRI or MRI) for medical diagnosis is now proceeding at a furious pace.4 However, applications of NMR imaging in the materials sciences are only recently being explored. Our overall objective is to develop NMR methods for nondestructive evaluation in ceramics processing. The present report describes preliminary research directed toward the use of NMR for nondestructively mapping porosity and internal voids in green-state bodies. Some future extensions of this work include the imaging of pore size distribution, and the imaging of binders, plasticizers and other components of the test sample.

Rapid Infrared Characterization of Thermal Diffusivity in Continuous Fiber Ceramic Composite Components

Continuous fiber ceramic composites (CFCCs) are currently being developed for a variety of high-temperature applications, including use in advanced heat engines due to their relatively high strength and toughness at high temperatures and their relatively low density. In the development of these material systems, quantification of the mechanical and thermal properties is necessary. Furthermore, it is necessary to detect flaws and defects that may result in subsequent failure of the part. The need for this inspection is critical in evaluating material system performance and reliability. In most instances, due to the high cost associated with material manufacturing, the testing must be nondestructive.

A PORTABLE MICROWAVE INTERFERENCE SCANNING SYSTEM FOR NONDESTRUCTIVE TESTING OF MULTI-LAYERED DIELECTRIC MATERIALS

The projected microwave energy pattern, wave guide geometry, positioning methods and process variables have been optimized for use of a portable, non‐contact, lap‐top computer‐controlled microwave interference scanning system on multi‐layered dielectric materials. The system can be used in situ with one‐sided access and has demonstrated capability of damage detection on composite ceramic armor. Specimens used for validation included specially fabricated surrogates, and ballistic impact‐damaged specimens. Microwave data results were corroborated with high resolution direct‐digital x‐ray imaging. Microwave interference scanning detects cracks, laminar features and material properties variations. This paper presents the details of the system, the optimization steps and discusses results obtained.

NDE Technology for Ceramic Composites

Installation of gas turbine components made of ceramic matrix composite (CMC) materials, which have limited test bed data bases, can put test engines at risk. Further, changes in properties of the materials of these components have been shown to occur with exposure. Risks to the engine can be mitigated through the application of proper nondestructive inspection methods. Further, while still under development, proper application of certain nondestructive evaluation (NDE) technologies seem likely to be able to provide data that can be correlated to retained strength or other properties of these composite materials. If sufficient data were available informed decisions could be made regarding reuse, repair or replace with appropriate NDE. Over the past fourteen years, Argonne National Laboratory (ANL), has been developing various NDE methods specifically for CMC materials. These NDE technologies include: infrared based thermal imaging, air-coupled ultrasonic approaches, high spatial resolution x-ray computed tomography and more recently optical coherence tomography and guided plate waves. This paper will review the developments of these NDE technologies and will provide results with collaboration from engine and laboratory materials tests.Copyright

Development of nondestructive evaluation methods for hot gas filters

AbstractRigid ceramic hot gas candle filters are currently under development for high-temperature hot gas particulate cleanup in advanced coal-based power systems. The ceramic materials for these filters include monolithics (usually non-oxides), oxide and non-oxide fiber-reinforced composites, and recrystallized silicon carbide. A concern of end users in using these types of filters, where over 3000 may be used in a single installation, is the lack of a data base on which to base decisions for reusing, replacing or predicting remaining life during plant shutdowns. One method to improve confidence of usage is to develop nondestructive evaluation (NDE) technology to provide surveillance methods for determination of the extent of damage or of life-limiting characteristics such as thermal fatigue, oxidation, damage from ash bridging such as localized cracking, damage from local burning, and elongation at elevated temperatures. Although in situ NDE methods would be desirable in order to avoid disassembly of th...

Determining thermal diffusivity and defect attributes in ceramic matrix composites by infrared imaging

Ceramic matrix composites are being developed for numerous high temperature applications, including rotors and combustors for advanced turbine engines, heat exchanger and hot-gas filters for coal gasification plants. Among the materials of interest are silicon-carbide-fiber- reinforced-silicon-carbide (SiC(f)/SiC), silicon-carbide-fiber-reinforced-silicon-nitride (SiC(f)/Si3N4), aluminum-oxide-reinforced-alumina (Al2O3(f)/Al2O3, etc. In the manufacturing of these ceramic composites, the conditions of the fiber/matrix interface are critical to the mechanical and thermal behavior of the component. Defects such as delaminations and non-uniform porosity can directly affect the performance. A nondestructive evaluation (NDE) method, developed at Argonne National Laboratory has proved beneficial in analyzing as-processed conditions and defect detection created during manufacturing. This NDE method uses infrared thermal imaging for full-field quantitative measurement of the distribution of thermal diffusivity in large components. Intensity transform algorithms have been used for contrast enhancement of the output image. Nonuniformity correction and automatic gain control are used to dynamically optimize video contrast and brightness, providing additional resolution in the acquired images. Digital filtering, interpolation, and least-squares-estimation techniques have been incorporated for noise reduction and data acquisition. The Argonne NDE system has been utilized to determine thermal shock damage, density variations, and variations in fiber coating in a full array of test specimens.

Defect detection in multilayered, plasma-sprayed zirconia by time-resolved infrared radiometry: a comparison between analytical and experimental methods

Analytical and experimental methods were used to study a series of test specimens consisting of plasma sprayed layers of NiCrA1Y/ZrO{sub 2} of various compositions.The coatings were seeded with artificial defects and were sprayed on steel disks. Two types of defects were used: flat bottomed holes drilled in the steel substrate and patches of room temperature vulcanizing silicone within the coatings. Defect sizes ranged from 0.1 to 10 mm and were at depths below the coating surface from 0.6 to 3.6 min. The method of time resolved infrared radiometry was used with two different heat sources, an acetylene torch and a high intensity lamp, to inspect the coatings. The torch allowed excellent sensitivity at depths of less than 2 mm and the lamp revealed flaws through the full coating thickness. Two analytical models were developed to study beat flow in the test specimens: a finite element model and an electrical analog model. Results from the two models were compared to check consistency and the finite element model results were compared with experimental results. The finite element code was chosen for further development due to its greater flexibility and ease of use.