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Role of Intergranular Films in Toughened Ceramics

Description: Self-reinforced silicon nitride ceramics rely the generation of elongated grains that act as reinforcing elements to gain increases in fracture toughness. However, the size and number of the reinforcing grains must be controlled, along with the matrix grain size, to optimize the fracture toughness and strength. Furthermore, the toughening processes of crack bridging are dependent upon retention of these reinforcing grains during crack extension by an interfacial debonding process. Both the debonding process and the resultant toughening effects are found to be influenced by the composition of the sintering aids which typical are incorporated into the amorphous intergranular films found in these ceramics. Specifically, it is shown that the interface between the intergranular glass and the reinforcing grains is strengthened in the presence of an epitaxial SiAlON layer. In addition, the interface strength increases with the Al and 0 content of the SiAlON layer. Micromechanics modeling indicates that stresses associated with thermal expansion mismatch are a secondary factor in interfacial debonding in these specific systems. On the other hand, first principles atomic cluster calculations reveal that the debonding behavior is consistent with the formation of strong Si-0 and Al-O bonds across the glass-crystalline interface.
Date: May 10, 1999
Creator: Becher, P.F.; Hsueh, C.H.; More, K.L.; Painter, G.S. & Sun, E.Y.
Partner: UNT Libraries Government Documents Department

Electrolytic In-process Dressing (ELID) for high-efficiency, precision grinding of ceramic parts: An experiment study

Description: This report describes Electrolytic In-process Dressing (ELID) as applied to the efficient, high-precision grinding of structural ceramics, and describes work performed jointly by Dr. B.P. Bandyopadhyay, University of North Dakota, and Dr. R. Ohmori, of the Institute of Physical and Chemical Research (RINEN), Tokyo, Japan, from June through August, 1994. Dr. Ohmori pioneered the novel ELID grinding technology which incorporates electrolytically enhanced, in-process dressing of metal bonded superabrasive wheels. The principle of ELID grinding technology is discussed in the report as will its application for rough grinding and precision grinding. Two types of silicon nitride based ceramics (Kyocerals Si{sub 3}N{sub 4}, and Eaton`s SRBSN) were ground under various conditions with ELID methods. Mirror surface finishes were obtained with {number_sign} 4000 mesh size wheel (average grain size = 4 {mu}m). Results of these investigations are presented in this report. These include the effects of wheel bond type, type of power supply, abrasive grit friability, and cooling fluid composition. The effects of various parameters are discussed in terms of the mechanisms of ELID grinding, and in particular, the manner of boundary layer formation on the wheels and abrasive grit protrusion.
Date: August 1, 1995
Creator: Bandyopadhyay, B.P.
Partner: UNT Libraries Government Documents Department

Single Nanopores in Silicon Nitride Membranes with Applications to Viral Sensing

Description: While current viral sensing methods are extremely sensitive, there is still a need for platforms capable of detecting engineered viruses and being integrated into device architectures for point-of-care assessments. Nanopores could provide a single pathway to achieve these goals.
Date: March 29, 2012
Creator: Davenport, M W; Healy, K; Teslich, N; Letant, S E & Siwy, Z S
Partner: UNT Libraries Government Documents Department

Wire Electrical Discharge Truing of Metal Bond Diamond Grinding Wheels

Description: Cylindrical wire EDM profile truing of the metal bond diamond wheel for precision form grinding of ceramics is presented in this report. First a corrosion-resistant, precise spindle with the high-electrical current capability for wire EDM truing of grinding wheel was fabricated. An arc profile was adopted in order to determine form tolerances capabilities of this process. Results show the wire EDM process can generate {micro}m-scale precision form on the diamond wheel efficiently. The wheel, after truing, was used to grind silicon nitride. Grinding forces, surface finish of ground components, and wheel wear were measured. The EDM trued wheel showed a reduction in grinding force from that of the stick dressed wheel. Surface finishes between the two truing methods were similar. In the beginning of the grinding, significant wheel wear rate was identified. The subsequent wheel wear rate stabilized and became considerably lower.
Date: January 24, 2002
Creator: McSpadden, SB
Partner: UNT Libraries Government Documents Department

Tailoring the intergranular phases in silicon nitride for improved toughness

Description: Intergranular glass phases can have a significant influence on fracture resistance (R-curve behavior) of Si nitride ceramics and appears to be related to debonding of the {beta}-Si{sub 3}N{sub 4}/oxynitride-glass interfaces. Applying the results from {beta}- Si{sub 3}N{sub 4}-whisker/oxynitride-glass model systems, self- reinforced Si nitrides with different sintering additive ratios were investigated. Si nitrides sintered with a lower Al{sub 2}O{sub 3}: Y{sub 2}O{sub 3} additive ratio exhibited higher stead-state fracture toughness together with a steeply rising R-curve. Analytical electron microscopy suggested that the different fracture behavior is related to the Al content in the SiAlON growth band on the elongated grains, which could result in differences in interfacial bonding structures between the grains and the intergranular glass.
Date: December 31, 1996
Creator: Sun, E. Y.; Becher, P. F.; Plucknett, K. P.; Waters, S. B.; Hirao, K. & Brito, M. E.
Partner: UNT Libraries Government Documents Department

Tensile creep performance of a developmental in-situ reinforced silicon nitride

Description: The evaluation was done between 1300 and 1425 C in ambient air. Minimum creep rate was evaluated vs tensile stress and temperature, and measured tensile creep performances of two different specimen geometries (buttonhead and dogbone - machined from same billet) were compared. This Si nitride exhibited comparable or better creep resistance than other Si nitrides described in the literature. Measured creep response of the material and lifetime were observed to be geometry dependent; the smaller cross-sectioned dogbone samples exhibited faster creep rates and shorter lives, presumably due to faster oxidation-induced damage in this geometry. The tensile creep rates and lifetimes were found to be well represented by the Monkman- Grant relation between 1350 and 1425 C, with some evidence suggesting stratification of the data for the 1300 C tests and a change in dominant failure mode between 1300 and 1350 C. Lastly, values of the temperature-compensated stress exponent and activation energy for tensile creep were found to decrease by 80 and 75% in compression, respectively, illustrating anisotropic creep behavior in this Si nitride.
Date: February 1, 1997
Creator: Wereszczak, A.A.; Kirkland, T.P.; Lin, H.T.; Ferber, M.K.; Li, C.W. & Goldacker, J.A.
Partner: UNT Libraries Government Documents Department

Interfacial composition analysis of silicon nitride whisker reinforced oxynitride glass systems

Description: Scanning transmission electron microscopy combined with energy-dispersive x-ray spectroscopy and parallel-detection electron energy-loss spectroscopy was used to analyze the composition at interfaces in {beta}-Si{sub 3}N{sub 4} whisker reinforced oxynitride glass systems.
Date: June 1, 1995
Creator: Sun, E. Y.; Alexander, K. B.; Becher, P. F. & Hwang, S. L.
Partner: UNT Libraries Government Documents Department

Crystal phases and lattice dynamics of slip-cast {beta}{prime}-sialons

Description: The crystal structures and phonon densities of states (DOS) of {beta}{prime}-Sialon ceramics, Si{sub 6-z}Al{sub z}O{sub z}N{sub 8-z} (O {le} z {le} 6), prepared by a novel slip-cast method were studied by neutron scattering techniques. A Rietveld analysis of the diffraction patterns shows that samples of z < 4 form a single-phase solid solution of Si-Al-O-N isostructural to {beta}-Si{sub 3}N{sub 4} (space group P6{sub 3}/m). Within this structure there is a consistent preferred occupation of O on the 2c sites and N on the 6h sites. For z > 4 the materials exhibit multiple-phase structure. The observed phonon DOS of the O {le} z {le} 4 ceramics displays phonon bands at about 50 and 115 meV. These features are considerably broader than the corresponding ones in {beta}-Si{sub 3}N{sub 4} powder. As z increases, effects due to atomic disorder lead to an overlap of the two phonon bands and a complete fill up of the phonon gap at {approximately} 100 meV observed in Si{sub 3}N{sub 4}.
Date: December 31, 1995
Creator: Loong, C.K.; Richardson, J.W. Jr.; Suzuki, S. & Ozawa, M.
Partner: UNT Libraries Government Documents Department

High Temperature Alkali Corrosion of Dense SN4 Coated with CMZP and Mg-Doped A21TiO5 in Coal Gas

Description: Si3N4 heat exchangers used in industrial systems are usually operating in harsh environments. Not only is this structural material experiencing high temperatures, but it is also subjected to corrosive gases and condensed phases. Past studies have demonstrated that condensed phases severely attack Si3N4 and as a consequence, dramatically reduce its lifetime in industrial operating systems.1,2 Previous research conducted at Virginia Tech on low thermal expansion coefficient oxide ceramics,3,4,5 (Ca1-X,MgX)Zr4(PO4)6 (CMZP), and Mg-doped Al2TiO5, for structural application have shown that these two materials exhibited better resistance to alkaline corrosion than Si3N4. Thus, they were envisioned as good candidates for a protective coating on Si3N4 heat exchangers. As a result, the goal of the present work is to develop CMZP and Mg-doped Al2TiO5 protective thin films using the sol-gel process and the dip coating technique and to test their effectiveness in an alkali-containing atmosphere.
Date: October 1, 1997
Creator: Brown, J. J. & Thierry, Nguyen
Partner: UNT Libraries Government Documents Department

Transient and steady-state erosion of in-situ reinforced silicon nitride

Description: Relative to most other materials silicon nitride is very erosion resistant. However, the resulting surface flaws degrade strength - a serious concern for component designers. AlliedSignal Ceramic Components GS-44 in-situ reinforced silicon nitride was eroded in a slinger apparatus. Both transient (extremely low level) and steady-state erosion regimes were investigated. Alumina particles with effective average diameters of 140 Jim and 63 {mu}m were used at velocities of 50 m/s, 100 m/s, and 138 m/s. Biaxial tensile strength was measured. Strength decreased by about 15% after a very small erodent dosage and then remained virtually constant with further erosion. In-situ reinforcement produces R-curve behavior in which the fracture toughness increases with crack size. The effect of this is quite dramatic with strength loss being significantly less than expected for a normal silicon nitride with constant fracture toughness.
Date: October 1, 1994
Creator: Karasek, K.R.; Whalen, P.J.; Rateick, R.G. Jr.; Hamilton, A.C. & Routbort, J.L.
Partner: UNT Libraries Government Documents Department

THE STRUCTURE OF GRAIN BOUNDARIES IN SILICON NITRIDE BASED ALLOYS

Description: Grain boundaries in silicon-based ceramics have been characterized by high resolution electron microscopy including the technique of lattice fringe imaging, and this work is illustrated with examples from both hot-pressed silicon nitrides (MgO and Y{sub 2}O{sub 3} fluxed) and a magnesium-sialon (Mg{sub 1.86} Si{sub 1.67} Al{sub 2.47} O{sub 3.19} N{sub 3.81}). Room temperature observations of the glassy phase are consistent with it being only a partially wetting phase, indicating that it cannot form a continuous film. The atomic configuration of the grain boundaries in both materials is presented together with lattice fringe observations of segregation at grain boundaries in the magnesium-sialon.
Date: December 1, 1977
Creator: Clarke, David R. & Thomas, G.
Partner: UNT Libraries Government Documents Department

Heavy-Ion Irradiation of Thulium(III) Oxide Targets Prepared by Polymer-Assisted Deposition

Description: Thulium(III) oxide (Tm{sub 2}O{sub 3}) targets prepared by the polymer-assisted deposition (PAD) method were irradiated by heavy-ion beams to test the method's feasibility for nuclear science applications. Targets were prepared on silicon nitride backings (thickness of 1000 nm, 344 {micro}g/cm{sup 2}) and were irradiated with an {sup 40}Ar beam at laboratory frame energy of {approx}210 MeV (50 particle nA). The root mean squared (RMS) roughness prior to irradiation is 1.1 nm for a {approx}250 nm ({approx}220 {micro}g/cm{sup 2}) Tm{sub 2}O{sub 3} target, and an RMS roughness of 2.0 nm after irradiation was measured by atomic force microscopy (AFM). Scanning electron microscopy of the irradiated target reveals no significant differences in surface homogeneity when compared to imaging prior to irradiation. Target flaking was not observed from monitoring Rutherford scattered particles as a function of time.
Date: September 15, 2008
Creator: Garcia, Mitch A.; Ali, Mazhar N.; Chang, Noel N.; Parsons-Moss, Tashi; Ashby, Paul D.; Gates, Jacklyn M. et al.
Partner: UNT Libraries Government Documents Department

Rolling Contact Fatigue of Ceramics

Description: High hardness, low coefficient of thermal expansion and high temperature capability are properties also suited to rolling element materials. Silicon nitride (Si{sub 3}N{sub 4}) has been found to have a good combination of properties suitable for these applications. However, much is still not known about rolling contact fatigue (RCF) behavior, which is fundamental information to assess the lifetime of the material. Additionally, there are several test techniques that are employed internationally whose measured RCF performances are often irreconcilable. Due to the lack of such information, some concern for the reliability of ceramic bearings still remains. This report surveys a variety of topics pertaining to RCF. Surface defects (cracks) in Si{sub 3}N{sub 4} and their propagation during RCF are discussed. Five methods to measure RCF are then briefly overviewed. Spalling, delamination, and rolling contact wear are discussed. Lastly, methods to destructively (e.g., C-sphere flexure strength testing) and non-destructively identify potential RCF-limiting flaws in Si{sub 3}N{sub 4} balls are described.
Date: September 1, 2006
Creator: Wereszczak, Andrew A; Wang, W.; Wang, Y.; Hadfield, M.; Kanematsu, W.; Kirkland, Timothy Philip et al.
Partner: UNT Libraries Government Documents Department

Noise Properties of Rectifying Nanopores

Description: Ion currents through three types of rectifying nanoporous structures are studied and compared for the first time: conically shaped polymer nanopores, glass nanopipettes, and silicon nitride nanopores. Time signals of ion currents are analyzed by power spectrum. We focus on the low-frequency range where the power spectrum magnitude scales with frequency, f, as 1/f. Glass nanopipettes and polymer nanopores exhibit non-equilibrium 1/f noise, thus the normalized power spectrum depends on the voltage polarity and magnitude. In contrast, 1/f noise in rectifying silicon nitride nanopores is of equilibrium character. Various mechanisms underlying the voltage-dependent 1/f noise are explored and discussed, including intrinsic pore wall dynamics, and formation of vortices and non-linear flow patterns in the pore. Experimental data are supported by modeling of ion currents based on the coupled Poisson-Nernst-Planck and Navier Stokes equations. We conclude that the voltage-dependent 1/f noise observed in polymer and glass asymmetric nanopores might result from high and asymmetric electric fields inducing secondary effects in the pore such as enhanced water dissociation.
Date: February 18, 2011
Creator: Powell, M R; Sa, N; Davenport, M; Healy, K; Vlassiouk, I; Letant, S E et al.
Partner: UNT Libraries Government Documents Department

DoE Advanced Ceramic Microturbine

Description: In July 2001, Ingersoll-Rand began work on this program. Its objective was to introduce ceramic hot section components into the IR family of microturbines to permit higher operating temperatures and hence improved efficiency. The IR microturbine product line combines a novel application of industrial turbocharger equipment, our commercially successful recuperator, and proven industrial gas turbine design practices. The objective of the joint development program is to combine the high production success of the Si{sub 3}N{sub 4} turbocharger rotors, largely from Japan, with the IR turbocharger-based microturbines. The IR 'Ceramic Microturbine' (CMT) program has been configured to use the most practical ceramic rotor, considering size, geometry, proven manufacturing methods, and physical material limitations Performance predictions indicate that 36% LHV electric conversion efficiency could be attained at a Turbine Inlet Temperature (TIT) of nominally 1000 C. The initial 72kW engine is being designed to have comparable life and costs to our current product The package power rating is expandable to 100kW with this equipment by slightly increasing pressure ratio flow and TIT. This program was initially planned as five major tasks In Task 1 a comprehensive analysis of the state of the art ceramics and their applicability to microturbines was performed Milestone I was achieved with the joint DoE/IR decision to concentrate on our 70kW microturbine, with elevated turbine inlet temperature and pressure ratio,. This preserved the ability of the engine to utilize the standard IR recuperator and the majority of the microturbine subassemblies, A commercialization report, projecting the market size, was also completed as part of this task. Task 2's detailed design of the special hot-section components has been completed,. The two critical milestones, No.3 and No.4, associated with the detailed design of the monolithic silicon nitride turbine rotor and the release of the purchase order for this critical component were ...
Date: May 31, 2004
Creator: Systems, IR Energy
Partner: UNT Libraries Government Documents Department

Nanograting-based compact VUV spectrometer and beam profiler for in-situ characterization of high-order harmonic generation light sources

Description: A compact, versatile device for VUV beam characterization is presented. It combines the functionalities of a VUV spectrometer and a VUV beam profiler in one unit and is entirely supported by a standard DN200 CF flange. The spectrometer employs a silicon nitride transmission nanograting in combination with a micro-channel plate based imaging detector. This enables the simultaneous recording of wavelengths ranging from 10 nm to 80 nm with a resolution of 0.25 nm to 0.13 nm. Spatial beam profiles with diameters up to 10 mm are imaged with 0.1 mm resolution. The setup is equipped with an in-vacuum translation stage that allows for in situ switching between the spectrometer and beam profiler modes and for moving the setup out of the beam. The simple, robust design of the device is well suited for non-intrusive routine characterization of emerging laboratory- and accelerator-based VUV light sources. Operation of the device is demonstrated by characterizing the output of a femtosecond high-order harmonic generation light source.
Date: July 9, 2010
Creator: Kornilov, Oleg; Wilcox, Russell & Gessner, Oliver
Partner: UNT Libraries Government Documents Department

High sensitivity resonance frequency measurements of individualmicro-cantilevers using fiber optical interferometry

Description: We describe a setup for the resonance frequency measurement of individual microcantilevers. The setup displays both high spatial selectivity and sensitivity to specimen vibrations by utilizing a tapered uncoated fiber tip. The high sensitivity to specimen vibrations is achieved by the combination of optical Fabry-Perot interferometry and narrow band RF detection. Wave fronts reflected on the specimen and on the fiber tip end face interfere, thus no reference plane on the specimen is needed, as demonstrated with the example of freestanding silicon nitride micro-cantilevers. The resulting system is integrated in a DB-235 dual beam FIB system, thereby allowing the measurement of micro-cantilever responses during observation in SEM mode. The FIB was used to modify the optical fiber tip. At this point of our RF system development, the microcantilevers used to characterize the detector were not modified in situ.
Date: March 4, 2009
Creator: Duden, Thomas & Radmilovic, Velimir
Partner: UNT Libraries Government Documents Department

The synthesis, characterization and formation chemistry of Si-C-N-O-M ceramic and composite powders. Final technical report

Description: Brief summaries are given for the work in each of the following areas: (1) general pattern of behavior in the conversion processes of SiNC precursors; (2) thermal and oxidative stability of SiNC ceramics; and (3) modification of PMVSEDA(poly(methylvinyl)silylethylenediamine) with borane-dimethyl sulfide.
Date: August 1, 1998
Creator: Mariam, Y.H.
Partner: UNT Libraries Government Documents Department

Effects of the amorphous oxide intergranular layer structure and bonding on the fracture toughness of a high purity silicon nitride

Description: The microstructural evolution and structural characteristics and transitions in the thin grain-boundary oxide films in a silicon nitride ceramic, specifically between two adjacent grains and not the triple junctions, are investigated to find their effect on the macroscopic fracture properties. It is found that by heat treating a model Si3N4-2wt percent Y2O3 ceramic for {approx}200 hr at 1400 degrees C in air, the fracture toughness can be increased by {approx}100 percent, coincident with a change in fracture mechanism from transgranular to intergranular.
Date: November 18, 2002
Creator: Ziegler, A.; Kisielowski, C.; Hoffmann, M.J. & Ritchie, R.O.
Partner: UNT Libraries Government Documents Department

Gelcasting of silicon preforms for the production of sintered reaction-bonded silicon nitride

Description: Gelcasting of silicon metal for the production of sintered reaction-bonded silicon nitride (SRBSN) was investigated in order to identify associated advantages over conventional forming techniques, i.e., die and isostatic pressing. Compacts were formed from identical powder mixtures by both gelcasting and pressing, and were nitrided and sintered to produce SRBSN ceramics using both conventional and microwave heating. Characterization of the samples included measurement of green density, green and nitrided pore structure, weight gain during nitridation, final density, microstructure, toughness, and flexural strength. It was found that a more uniform pore structure existed in the green gelcast samples. It is believed that this pore configuration aided in nitridation, and manifested itself in a more uniform final microstructure. In addition, improved mechanical properties were achieved in the gelcast samples. This improvement can be attributed to green microstructure homogeneity. An additional finding of this study was that microwave hearing combined with gelcast forming resulted in SRBSN materials with improved mechanical properties.
Date: December 1995
Creator: Kiggans, J. O., Jr.; Nunn, S. D.; Tiegs, T. N.; Davisson, C. C.; Coffey, D. W. & Maria, J.P.
Partner: UNT Libraries Government Documents Department

Studies on the scale-up of the microwave-assisted nitridation and sintering of reaction-bonded silicon nitride

Description: Studies using laboratory test samples have shown that microwave heating produces sintered reaction-bonded silicon nitride materials with improved properties. The final challenge for processing this material by microwave heating is the development of a technology for processing larger batch-size quantities of these materials. Initial microwave scale-up experiments were performed using powder compacts of a bucket tappet geometry. In experiments using microwave-transparent boron nitride sample crucibles, temperature gradients within some crucibles led to larger variations in the sample densities than were obtained with the conventionally processed samples. The use of a microwave-suscepter type crucible made of silicon carbide and boron nitride resulted in an improved temperature uniformity and in density variations comparable to those obtained for the control groups.
Date: May 1, 1996
Creator: Kiggans, J.O.: Tiegs, T.N. & Kimrey, H.D.
Partner: UNT Libraries Government Documents Department

Non-destructive inter-level dielectric via in-line process monitoring by atomic force microscopy

Description: A new application using atomic force microscopy (AFM) for in-line process control monitoring (PCM) of an interlevel dielectric via etching step is reported. The AFM with its near atomic-level resolution is capable of nondestructively measuring whether micron-sized vias have been etched to completion. Etch completion is determined by comparing the AFM measured etch depth of adjacent via holes through {approximately}4000 {Angstrom} thick Si{sub 3}N{sub 4} over Au-based ohmic and W gate metallizations. Due to etch selectivity, of the SF{sub 6}/0{sub 2} reactive ion etch (RIIE) generated plasma, the ohmic metal acts as an etch stop whereas the W-based refractory gate continues to etch. For etch times beyond endpoint in the range of 20 to 50%, the AFM measured via etch depth differences is 250 to 400 {Angstrom} when comparing via depths over ohmic metal and W gate metal. This etch depth difference is a specific marker for etch completion and it is measured nondestructively at a point in the process where rework is still a feasible option.
Date: December 31, 1994
Creator: Howard, A.J.; Baca, A.G. & Shul, R.J.
Partner: UNT Libraries Government Documents Department

Indentation and oxidation studies on silicon nitride joints

Description: Si nitride ceramics have been joined with a Y oxide-SiO{sub 2} interlayer. A 1:2 molar ratio of Y{sub 2}O{sub 3} to SiO{sub 2} was chosen to obtain the desired Y{sub 2}Si{sub 2}O{sub 7} stoichiometry, which should give the interlayer better oxidation resistance compared to other interlayer materials. Mechanical characterization of the joints performed by indentation shows it to have good room temperature strength.
Date: May 1, 1996
Creator: Gopal, M.; De Jonghe, L.C. & Thomas, G.
Partner: UNT Libraries Government Documents Department