bluuebunny/crossref_metadata_2025 huggingface dataset:
The Long Term Effect on Cement Mortar by Admixture of Spray Drying Absorption Products
Authors: Jeppesen K. G.
Published: March 2011

Preliminary investigations have shown that the substitutions of up to 10% fly ash (FA), with spray drying absorption products (SDA), in cement mortars (cement: 80% rapid portland cement (RPC), 10–20% FA, 0–10% SDA) results in low early strength of the same magnitude as in mortar with 80% RPC + 20% FA. After storing for 3 months under wet or moist conditions the strengths of some of the SDA-containing mortars had surpassed the strength of the (80% RPC + 20% FA) mortar. Dry stored SDA-containing mortars showed a higher tendency to desiccate. Determination of SO32− showed quick oxidation to SO42− and XRD revealed the formation of ettringite. After a year the strengths of mortars made of 100% RPC, (80% RPC + 20% FA) and (80% RPC + 10% FA + 10% SDA) stored wet or moist were equal. Attempts to use synthetic CaSO3 · ½H2O (CS·½H) as a retarding agent for cement hydration failed, but conductivity measurements of tricalcium aluminate (C3 A)-CS · ½H mixes showed reaction. SEM and XRD investigations identified calcium aluminate sulphite hydrate (C4ASH8). DTA–DTG examinations of synthetic C4ASH8 showed the formula to be C4ASH11. A modification of the instructions for preparation of mortar prisms resulted in the desired retarding reaction between the C3A from portland cement (PC)-clinker and synthetic CS · ½H and SDA-products as well. The resulting C4ASH11 proved to be very unstable and changed to ettringite within a very short time. Use of the modified instructions for preparation of mortar prisms containing SDA resulted in satisfactory early strengths. A series of mortar prisms with increasing content of SDA (x% RPC, (100-x)% SDA in cements; 0<x<80) were prepared and stored under wet, moist and dry conditions. These mortars, now one year old, show a gradual development of properties. Mortars with a SDA content in cement >80% cannot be stored wet. The effects on mortars of the individual constituents of the SDA-products are studied by XRD, development in strength and density. Fragments of 2 year old SDA containing cement mortars and SDA containing concrete from a parking place have been studied.
Characterization of North American Lignite Fly Ashes II. XRD Mineralogy
Authors: McCarthy G. J. , Johansen D. M. , Thedchanamoorthy A. , Steinwand S. J. , Swanson K. D.
Published: March 2011

X-ray powder diffraction has been used to determine the crystalline phase mineralogy in samples of fly ash from each of the lignite mining areas of North America. The characteristic phases of North Dakota lignite fly ashes were periclase, lime, merwinite and the sulfate phases anhydrite, thenardite and a sodalite-structure phase. Mullite was absent in these low-Al2O3 ashes. Montana lignite ash mineralogy had characteristics of ND lignite and MT subbituminous coal fly ashes; mullite and C3A were present and the alkali sulfates were absent. Texas and Louisiana lignite fly ashes had the characteristic mineralogy of bituminous coal fly ash: quartz, mullite, ferrite-spinel (magnetite) and minor hematite. Even though their analytical CaO contents were 7–14%, all but one lacked crystalline CaO-containing phases. Lignite fly ashes from Saskatchewan were generally the least crystalline of those studied and had a mineralogy consisting of quartz, mullite, ferrite spinel and periclase. Quantitative XRD data were obtained. The position of the diffuse scattering maximum in the x-ray diffractograms was indicative of the glass composition of the lignite fly ash.
The Use of Glass Slides for Preparing Cross-Section TEM Samples of Discrete Transistors
Authors: Cowden William G. , Datye Abhaya K.
Published: March 2011

A procedure for preparing cross-section samples of specific regions on an integrated circuit die is outlined. The procedure involves the use of glass slabs to prepare the sample stack used for cross-sectioning. The transparent glass slabs on the top surface of the die enable monitoring of the region of interest during the thinning process. This ensures that the region of interest will be located in the electron-transparent section used for TEM imaging. Samples prepared using this technique are sturdy enough to survive successive thinning and observation in a TEM. The glass slides do not give any charging problems and generally thin much slower than the silicon so as to provide added stability to the sample. An additional advantage is that the sample thickness can be accurately measured using the vernier attachment on an optical microscope during the sample thinning process. The imaging of specific NMOS transistors fabricated on buried oxide layers is illustrated.
Equipment for Preparing Electropolished TEM Specimens at Controlled and Low Temperatures
Authors: Franetovic Vjekoslav
Published: March 2011

A cooling device for use with the Fishione twin-jet electropolisher Model 110 has been developed for electropolishing TEM specimens at controlled and low temperatures necessary for some materials. This consists of an explosion-proof pump circulating methanol through a specially designed stainless steel bath, and a copper coil immersed in a mixture of methanol and dry ice in a dewar. A thermocouple with a temperature control unit provides precise temperature control.

With this device, electropolishing can be conducted at temperatures as low as −55°C. This allows electropolishing of certain materials which cannot be polished with conventional equipment. The precisely controlled temperature also improves the performance of the electropolishing equipment at all temperatures because the success of electropolishing depends on maintaining constant conditions during the process. The unit further allows the use of aggressive electrolytes and preparation of solutions which could otherwise become hazardous due to heat buildup during electropolishing or preparation.
A New Method of Preparing Tilt Boundaries for High Resolution Electron Microscopy
Authors: Krakow William , Castańo Victor
Published: March 2011

A new method of preparing bicrystal substrates of NaCl with a common tilt zone axis has been developed. Upon a lateral overgrowth of NaCl, bridging the two mechanically polished and oriented crystals, very thin films can then be vapor deposited. Au bicrystals of ∼ 75Å thickness and b.c.c. Cr films of similar thickness with grain boundaries have been fabricated.
A Polishless Method For Preparation Of Cross-Sectional Tem Samples
Authors: Wetzel J. T. , Danner D. A.
Published: March 2011

Cross-sectional samples for Transmission Electron Microscopy (TEM) have been made without the use of mechanical polishing and ion beam milling. Instead of traditional methods, we have used a combination of electron beam (e-beam) lithography for metal lift-off and reactive ion etching (RIE) to produce TEM samples of selected areas. The sample integrity for handling, dropping and ease of use is excellent, and the large amount of transparent area available for study is nearly 2 orders of magnitude larger than that given by traditional methods. The thickness of the samples is somewhat extreme, on the order of 0.50–1.0μm, but efforts are being made to reduce this dimension in order to make the method applicable to the whole range of materials used in silicon technology.
Cross-Sectioning Specific Devices and Regions in I.C. Wafers
Authors: Brown J. N. , Sheng T. T.
Published: March 2011

Line widths of less than a micron and junction depths within devices of the order of a thousand angstroms are common practice In today's electronic components. Transmission electron microscopy (TEM) is fast becoming a very valuable and often essential tool in many areas of semiconductor manufacture. The characterization of a given device structure is often required to fully understand its electrical behavior. This paper will review the methods that can be used to prepare cross-sectional samples from specific regions within an integrated circuit device for examination in the TEM.
Ion Milling of Compound Semiconductors for Transmission Electron Microscopy
Authors: Cullis A G , Chew N G
Published: March 2011

Serious artefactual structures can be introduced into transmission electron microscope specimens of compound semiconductors when the latter are prepared by ion milling under non-optimum conditions. In the present investigations, the nature of these artefacts is characterised and results obtained using conventional argon ion milling are compared with those obtained using alternative ion species, including iodine ions. This work demonstrates the large improvement in specimen structural quality which can be achieved by combining a logical selection of ion species with a careful choice of milling conditions.
Six-Inch Diameter GaAs on Si Wafers
Authors: Salerno Jack P. , Hill D. S. , Lee J. W. , McCullough R. E. , Fan John C. C.
Published: March 2011

The growth of high-quality single crystal GaAs on Si wafers up to six inches in diameter by organometallic chemical vapor deposition (OMCVD) is reported. These wafers have specular surfaces, excellent thickness uniformity, and are shown to have properties comparable to those of smaller diameter GaAs on Si wafers. The mechanical and electrical properties of the six inch GaAs on Si wafers are shown to be suitable for GaAs device fabrication.
Omvpe Growth and Characterization of GaAs on Si for Device Applications
Authors: Shastry S. K. , Zemon S. , Armiento C. , Stern M. B. , Levinson M. , Lehman L. , Rothman M. , Dugger D. , Hefter J.
Published: March 2011

Significant progress has been made in the OMVPE growth of GaAs directly on Si by the previously reported low-temperature growth technique. These films have been characterized by low-temperature PL, SIMS, TEM, and DLTS. The epitaxial layers, whose quality has been determined by PL measurements (4.2 K PL spectral width of heavy-hole exciton ≈ 3 meV), were implanted with 29Si+ for fabrication of MESFET channels. Background concentrations of ≈ 1014 cm−3 have been achieved for the first time after rapid thermal annealing without the need to use oxygen implantation or vanadium doping. SIMS measurements do not show Si pileup on the surface or much Si diffusion at the GaAs-Si interface, a significant improvement over earlier results. DLTS measurements and electrical characterization of the GaAs-Si heterojunction diode indicate the presence of only two trap levels (< 1014 cm−3 in concentration) in the GaAs ≥ 2.5 μm away from the interface.
Principles and Applications of Metalorganic Chemical Vapor Deposition for the Growth of ih-V Compounds on Si Substrates
Authors: Dupuis Russell D.
Published: March 2011

The use of the metalorganic chemical vapor deposition thin film materials technology in the heteroepitaxial growth of GaAs on Si substrates is of increasing interest for a wide variety of applications. This paper will describe the principles and applications of this materials technology and discuss possible future approaches to the growth of high-quality HI-V heteroepitaxial layers on Si substrates.
Growth and Characterization of Lpe GaAs on GaAs-Coated Si Prepared By Mbe
Authors: Sakai Shiro , Chang S.S. , Matyi R.J. , Shichijo H.
Published: March 2011

GaAs has been successfully grown by LPE on partly covered (windowed) GaAs-on-Si substrates prepared by MBE. Almost dislocation-free layers were obtained in narrow stripe windows. The grown layers were characterized by photoluminescence and Hall effect measurement. The photoluminescence polarization indicated that a uniaxial tensile stress along the stripe direction is applied in the mesa stripe LPE layer while it is biaxial in the wide GaAs layer on Si. The stress relaxation in the direction perpendicular to the stripe is discussed.
Capacitance Transient Analysis of Mbe Grown Gaas on Silicon Substrates
Authors: Burns G. F. , Chong T. C. , Fonstad C. G.
Published: March 2011

Capacitance transient spectroscopy has been applied to identify deep levels associated with heteroepitaxial GaAs grown on silicon. Results from p+n diode test structures reveal creation of the electron trap EL2 and a high density of hole states in the bandgap. This is the first reported observation of hole traps in MBE GaAs on Si. The activation behavior of the electron and hole signal peaks fits the signature of two different charge states associated with EL2, a native point defect complex seen in MOCVD, VPE, and bulk-grown GaAs, but not usually observed in MBE grown GaAs. Interstingly, the spectra seen show many similarities with earlier deep level transient spectroscopy (DLTS) observations on plastically deformed GaAs.
Resonant Photoluminescence Excitation in GaAs Grown Directly on Si
Authors: Zemon S. , Jagannath C. , Shastry S. K. , Miniscalco W. J. , Lambert G.
Published: March 2011

We describe new results observed during resonant excitation in the excitonic region of GaAs grown directly on Si by organometallic vapor phase epitaxy. Two resolved features were found in the light hole photoluminescence (PL) region, one identified with a free exciton process and the other with donor-related transitions. Features which track the laser excitation line were observed and identified with a process in which a donor is excited from the n=l ground state to an n=2 excited state. The PL excitation spectra associated with these features have spectral widths as narrow as 1.5 meV. PL spectral widths of ~3 meV have been attained for the heavy hole exciton band, representing the narrowest value obtained for OMVPE material and an improvement of about 30% over our best previous results.
The Stimulated Crystallization of Amorphous SiO2Films on Si Substrates Induced By Laser and Thermal Treatments
Authors: Edelman Felix
Published: March 2011

The transformation of amorphous to crystal (a-c) structure of Si02layers, thermally grown on both (100) and (111) Si substrates, was carried out by CO2laser, flash-lamp, and furnace heat: treatments. All the treatments resulted in S102crystallization according to two different mechanisms: normal and self-sustained growth processes. The kinetic characteristics of the S102crystallization process such as incubation time, rates of nucleation and growth, and the microstructure of the Si-Si02interface were investigated and are discussed from the point of view of growth theory. The a-c transformation in Si3N4and SixOyNzfilms on Si substrates is also discussed.
Nucleation and Growth of CrSi2 on Si(111)
Authors: Fathauer R.W. , Grunthaner P.J. , Lin T.L. , Chang K.T. , Mazur J.H.
Published: March 2011

Chromium disilicide layers have been grown on Si(111) in a commercial molecular beam epitaxy machine. Islands are found to nucleate with more than one epitaxial orientation, and three different orientations have been identified: CrSi2(0001)//Si(111) with CrSi2 [1010]//Si[110]. CrSi2(0001)//Si(111) with CrSi2[ll20]//Si[1l0], and CrSi2(1100)//Si(111) with CrSi2[000l]//Si[112]. Very thin (2 nm) layers have been studied under a variety of growth conditions to determine factors controlling the orientation of nuclei. The degree and direction of substrate misorientation, the growth technique, and the use of a CoSi2 buffer layer are all factors affecting the morphology of CrSi2 islands.
Epitaxial Gold in Au/Si Eutectic Reaction and Epitaxial Aluminum Spikes in Al-1%Si/Ti-W/Si System
Authors: Chang Peng-Heng
Published: March 2011

Epitaxial regrowth of gold film on Si as a result of Au/Si eutectic reaction and epitaxial aluminum spikes forming at IC contacts during sintering have been investigated by transmission electron microscopy (TEM). For gold film on Si, three types of epitaxy were observed: (1) the crystal structures of the two lattices are exactly the same, (2) the two structures have the orientation relationship of Au(111)//Si(111) and Au[132]//Si[231] and (3) 20° misorientation from the relationship in (2). Two orientation relationships were observed in the case of Al spike in Si: (1) Al[011]//Si[123] and Al(200)//Si(11), (2) Al[001]//Si[112] and 2° misorientation between Al(200) and Si(111). Possible mechanisms are proposed to explained the observed epitaxial growth.
Heteroepitaxial Nucleation and Growth of Ge ON Si(100) Surfaces Using Remote Plasma Enhanced Chemical Vapor Deposition
Authors: Rudder R.A. , Hattangady S.V. , Vitkavage D.J. , Markunas R.J.
Published: March 2011

Heteroepitaxial growth of Ge on Si(100) has been accomplished using remote plasma enhanced chemical vapor deposition at 300*#x00B0;C. Reconstructed surfaces with diffraction patterns showing non-uniform intensity variations along the lengths of the integral order streaks are observed during the first 100 Å of deposit. This observation of an atomically rough surface during the initial stages of growth is an indication of three-dimensional growth. As the epitaxial growth proceeds, the diffraction patterns become uniform with extensive streaking on both the integral and fractional order streaks. Subsequent growth, therefore, takes place in a layer-by-layer, two-dimensional mode. X-ray photoelectron spectroscopy of the early nucleation stages, less than 80 Å, show that there is uniform coverage with no evidence of island formation.
Model for Heteroepitaxy on Patterned Substrates
Authors: Kao Y. C. , Wang K. L.
Published: March 2011

In this work, a new model based on energy balance for heteroepitaxial growth on a patterned substrate and an additional thin buffer layer on top of it has been developed. The structure used in our model is assumed to be GeSi/buffer-Si/patterned-Si and comparisons are made with simple crystalline GeSi/Si. However, the model described here is quite general and can be adopted for any other material systems. Using this model, coupled with experimentally known material constants, the critical layer thickness (hc) of a lattice mismatched heterolayer can be determined for a patterned substrate, having a characteristic “seed pads” size (l), and a buffer layer thickness (hb). The dislocation-free condition under this case is also established.
An Artificial Intelligence Approach to Real Time control of carbonization
Authors: Pardee William J. , Chung Kwang , Lan Ming Shong
Published: March 2011

Carbonization of carbon-carbon composites is presently a slow, costly process. The failure rate and the variation in final material properties are both excessive. The complex physical and chemical changes require new control methods. Real time sensing of material properties can, in combination with a priori expert knowledge, be used to improve real time model estimates of process outcome and to revise the process. The basic elements of the control strategy for real time control of carbonization based on thermal, acoustic, conductivity, and gas chemistry sensors are described. Preliminary results relate real time gas analysis to physical changes.
Studies of Flow Fields in Low-Pressure Spraying Plasmas Using Laser Diagnostics
Authors: Hidaka R. , Ohki T. , Takeda J. , Kondo K. , Kanda H. , Muraoka K. , Akazaki M. , Maeda M. , Teshima K.
Published: March 2011

In order to make desirable surface layers by low pressure plasma spraying (LPPS), optimum operating conditions and plasma torch gun designs must be decided upon for understanding LPPS plasma and powder behavior. As the first step of this approach, LPPS plasmas without powders were measured by the Thomson scattering, the Michelson interferometry and a Pitot tube. These diagnostics revealed that LPPS plasma jets may be treated as supersonic neutral gas flows as the first approximation. In addition, the neutral particle temperature Tn and ion temperature Ti were found to be the same as the electron temperature Te, which is 1 eV at an oblique shock wave heating point and 0.2 eV at the sugsequent cooling point. LPPS plasmas and flows were modeled by a computer Simulation of a supersonic nozzle flow, 2nd yielded reasonable understanding of the thermodynamic and fluid-mechanical conditions.
Cars Diagnostics for Combustion and Plasma Processes
Authors: Eckbreth Alan C. , Stufflebeam John H.
Published: March 2011

Coherent anti-Stokes Raman spectroscopy (CARS) is a powerful analysis approach for nonintrusive temperature and species measurements in hostile environments. Widely utilized in combustion, it may be able to significantly impact materials processing research. CARS is described and its applications to combustion and plasma process environments are reviewed and contrasted.
High-Speed Photography of Energetic Materials and Components with a Copper Vapor Laser
Authors: Dosser Larry R. , Reed John W. , Stark Margaret A.
Published: March 2011

The evaluation of the properties of energetic materials, such as burn rate and ignition energy, is of primary importance in understanding their reactions and the functioning of devices containing them. One method for recording such information is high-speed photography at rates of up to 20,000 images per second. When a copper vapor laser is synchronized with the camera, laser-illuminated images can be recorded that detail the performance of a material and/or component in a manner never before possible. The laser can also be used for ignition of the energetic material, thus eliminating the need for bridgewires or electric squibs that can interfere with photography. Details of such ignitions are readily observable, and the burn rate of a material can be determined directly from the film. There are indications that information useful for the modeling of pyrotechnic reactions will become available as well. Recent results from high-speed photography of several pyrotechnic materials and devices will be presented.
Development of Laser Diagnostics for Studies of High Temperature Plasmas and Plasma-Surface Interactions
Authors: Muraoka K. , Uchino K. , Kajiwara T. , Matsuo K. , Matsuda Y. , Kim H. , Maeda M. , Okada T. , Honda C. , Akazaki M.
Published: March 2011

The developments of the laser diagnostics at Kyushu University for studies of high temperature plasmas and plasma-surface interactions are reviewed, followed by the recent results and future plans.
Ion Current, Energy Distribution, and Radical Species Detection in RF Plasmas by Cylindrical Mirror Analyzer Quadrupole Mass Spectroscopy
Authors: Greene Wayne M. , Hartney Mark A. , Hess Dennis W. , Oldham William G.
Published: March 2011

Mass spectroscopy has been used to diagnose plasma processing atmospheres by detailing the flux of neutral and ion species and the energy distribution of ions impinging upon a substrate immersed in a glow discharge. The institution of a diagnostic tool to investigate the chemical (reactive neutral) and physical (ion) aspects involved in plasma processing is necessary to improve control and reliability in thin film materials processing. Research has focussed on ion-enhanced etching of tungsten thin films in NF3/O2 and the deposition of tungsten by the reaction of WF6 and H2 in rf glow discharge reactions.
Diagnostic Techniques for PACVD Systems for Depositing Protective Coatings
Authors: Roman Ward C. , Stufflebeam John H. , Eckbreth Alan C.
Published: March 2011

PACVD techniques for depositing protective coatings are an emerging field in plasma processing technology. Technology transfer is limited by a lack of understanding of the basic mechanisms involved in the gas phase plasma chemistry. The aspects of plasma species concentration and distribution and plasma gas temperature are fragmentary and unclear. Laser diagnostic techniques represent a critical starting point for providing some of this needed information. The techniques are in-situ, nonintrusive, and give excellent spatial and temporal resolution. Numerous diagnostic techniques for detailed coating characterization are available, but a correlation of the PACVD parameters with some of the key coating properties is required. Thus, a predictive capability that is lacking in the present science base can be established together with important phenomenological aspects needed for efficient deposition of high quality protective coatings. As the mechanisms become better understood, use of remote sensors and A.I may then be introduced. This paper will review selected diagnostic techniques available for characterizing these nonequilibrium reactive plasmas and the coatings.
Thin Film Adhesion to Ion Bombarded Surfaces
Authors: Ingemarsson P. Anders , Tombrello T. A.
Published: March 2011

We report on the use of 20 MeV C14+ ion beams for pre-irradiation of Si, SiO2 and Al2O3 surfaces with resulting alterations in the adhesion of subsequently deposited Au and Ag thin films. The effect does not follow the same pattern for Au and Ag films, nor is there a simple correlation to the previously observed adhesion effect induced by ion irradiation after film deposition. Possible mechanisms, both for pre-irradiation and post-irradiation effects, are discussed, as is the importance of chemical structures with respect to interfacial bond strength.
Photo-Chemical Changes of Aluminium Films on Silicon
Authors: Kellock A. J. , Williams J. S. , Nyberg G. L. , Liesegang J.
Published: March 2011

X-ray Photoelectron Spectroscopy and Rutherford Backscattering Spectroscopy with channeling are employed to study surface and interface changes resulting from irradiation of thin Al films on Si-SiO2 substrates using < 6eV visible photons. Results indicati that surface oxidation and bonding rearrangements at the Al-SiO2-Si interface can take place at room temperature under photon bombardment. These changes are correlated with enhanced adhesion and modification of film etch properties which are also a result of photon irradiation.
Gallium Arsenide and Silicon Optical Assemblies: An Advanced Glass-Polymer-Semiconductor Adhesion Process
Authors: Vendura George J.
Published: March 2011

A simple adhesion process has been developed for applying glass lenses to the active surfaces of Si and GaAs optical devices such as detectors and solar cells [1]. The method, which uses a film of fluorinated ethylene propylene (FEP) offers reliability, cost and throughput advantages over the conventional dimethyl silicone adhesive. Critical to the process is the ion bombardment of individual surfaces before assembly. The resulting enhanced adhesion suggests some modification of surface properties. Four possible mechanisms are briefly discussed. The technique is believed to have broad applicability to amorphous and crystalline semiconductor systems and devices other than those under test.
The Influence of Alloy Chemistry on Controlling Fiber Volume Fraction in Ni-Base Mc Aligned Eutectics
Authors: Jackson M. R. , Walter J. L.
Published: March 2011

For the Ni-base TaC eutectics, it has been shown previously that carbide volume fraction is a strong function of Ta/C ratio. Now in a number of Ni,Cr-TaC and Ni,Cr,Al-TaC alloys, Cr has been observed to have only a small influence on volume fraction of carbide, while Al has a major influence acting to decrease the volume fraction. The Al present in the matrix causes the phase equilibrium to approach that of a much greater Ta/C ratio. This analysis has been extended to more complex NiTaC alloys as well. For the simple Ni-Cr-Ta-C alloys, creep behavior has been studied as a function of volume fraction of carbide.

Other carbide systems have been evaluated as well, including TiC and NbC. A general understanding of volume fraction differences between these systems and TaC can be reached by consideration of ideal solution behavior and the appropriate phase diagrams.
Feasibility Of Directional Solidification Of Lanthanum Hexaboride In a Boron Matrix
Authors: Logan Kathryn V.
Published: March 2011

Attempts were made to directionally solidify lanthanum hexaboride as uniformly spaced rods, less than one micron in diameter, in a boron matrix. Lanthanum hexaboride and boron powders were combined in a near eutectic mixture, formed into right circular cylinders and melted by RF induction heating in a pure hydrogen atmosphere using a modified internal zone melting technique.

Ball milling, uniaxial cold pressing, isostatic pressing and hot pressing were investigated as possible means of increasing the sample density before melting in the RF induction furnace. RF coupling was achieved directly in the hot pressed pellet, and indirectly through the use of a molybdenum preheater in the uniaxially cold pressed pellets. Internal zone melting and conventional crucible melting in various materials were tried.

Directional growth was observed in the pellets that were uniaxially cold pressed and preheated with a molybdenum tube sleeve. Lanthanum hexaboride fibers with an ℓ/d ratio of about ten to one and other forms of aligned microstructures were observed in selected areas of the pellet.
Transverse Mechanical Behavior of High-Strength Monocarbide Eutectics
Authors: Gigliotti M.F.X. , Jackson M. R. , Yang S. W. , Henry M. F. , Woodford D. A.
Published: March 2011

Superalloy eutectics strengthened with monocarbide whiskers are highly anisotropic in strength. Mechanical behavior transverse to the growth axis is governed largely by the fracture resistance of the matrix grain boundaries. While the matrices of these eutectics are essentially columnar grained superalloys, there are significant differences between d.s. superalloys and superalloy-monocarbide eutectics. These differences arise, in part from different solidification processes and from the alloying limitations in eutectic systems.
Directionally Crystallized Potassium Silicate Glass-Ceramic
Authors: Lu Grant , Klein L. C.
Published: March 2011

Glasses in the potassium silicate system were directionally crystallized in a temperature gradient furnace. A composition of approximately 40 wt % K2O and 60 wt % SiO2 was used. Quenched glass samples were placed in alumina crucibles with K2O·2SiO2 seed crystals on the bottom surface. The crucible was translated from the hot zone to the cold zone of the furnace. A thermal gradient of 14°C/mm was maintained. Sample height was about 6 mm and translation rates were about 5 mm/h, 1.33 mm/h and 0.83 mm/h. Well-aligned crystals were observed to grow from the bottom of the crucible. Individual crystals were about 0.07 mm wide and extended the length of the crucible parallel to the thermal gradient. The degree of alignment was found to depend on initial temperature and translation rate. The samples have been studied using primarily optical microscopy.
The Long Term Structural Stability of the Eutectic Composites Cd-Zn and Pb-Cd
Authors: Delamore G.D. , Van De Merwe R.W. , Dunne D.P. , Smith R.W.
Published: March 2011

It is shown that marked microstructural coarsening can occur when eutectic composites are exposed for relatively short periods to temperatures approaching 0.9 TM (where TM is the eutectic melting temperature in °K). Less well known and, perhaps, of more practical importance, are the microstructural changes and consequent changes in properties which result from prolonged exposure at 'safe' operating temperatures, e.g. 0.5 Tm.

Cd-Zn and Pb-Cd eutectic specimens of various thermal histories were examined immediately on preparation and subsequently re-examined after storage at ambient laboratory temperatures for up to 1000 days. In general, microstructural changes from the as-grown and heat-treated conditions were observed. In some cases for the Pb-Cd alloy this consisted of only slight thickening of the already coarse larnellae terminations. However, in the more rapidly frozen, and therefore microstructurally finer, specimens marked discontinuous coarsening was observed, but confined to eutectic-cell-wall regions. There the coarse precipitates grew at many angles, including being perpendicular to the eutectic habit plane but were not separated by any well-defined large angle grain boundaries.

It was concluded that high temperature degradation occurs mainly by continuous coarsening, whereas at lowtemperatures, microstructural changes are effected mainly by discontinuous coarsening.
Off-Axis Tensile Properties of γ/γ'-αMo Ds Eutectic
Authors: Hu Z. Q. , Zhang J. H. , Xu Y. B. , Zhang Z. Y. , Zhang Y. S. , Tang Y. J.
Published: March 2011

This paper reports a study of off-axis tensile properties of γ/γ'-αMo Ds eutectic and the dynamic fracture process directly observed with a scanning electron microscope. If the loading direction deviates from the Mo fiber growth direction, the tensile strength and ductility decrease gradually. During the loading process, two types of cracking are observed: one is cracking of the fiber, and the other is delamination along the fiber-matrix interface. In plastic deformation, slip can pass through both the matrix and the fiber. As a rule, the thicker fibers are cracked earlier than the thinner ones, because they have less defects and better ductility. Delamination is the main source of final fracture.
The low Cycle Fatigue Behavior of Three advanced
Nickel-Base Eutectic Composites
Authors: Ishii T. , Duquette D. J. , Stoloff N. S.
Published: March 2011

The low cycle fatigue behavior at 25°C and 825°C of three advanced nickel-base eutectics is described. Fatigue lives are shown to obey a linear relation with plastic strain range (Coffin-Manson relation) but lives are much lower than are observed for conventional metals and alloys. Cyclic hardening and softening were observed in each alloy at 25 °C; however, this behavior differs from the classical saturation behavior observed with isotropic materials.
Internal Friction of Cast Graphite-Magnesium Composites
Authors: Armstrong J. H. , Rawal S. P. , Misra M. S.
Published: March 2011

Internal friction behavior in cast 8-ply [0°1 P55Gr/Mg-0.6%Zr alloy and P55Gr/Mg-1%Mn composites as a function of vibratory strain amplitude was measured at 80 kHz using a Marxtype piezoelectric composite oscillator. Both the matrix and composite exhibited strain amplitude independent internal friction below ε ≈ 10−6, while significant strain amplitude dependence was noted at higher strain levels. A maxima in damping was observed for most of the specimens tested. Heat treatment to enlarge grain size was found to increase both the strain amplitude independent and dependent internal friction of the composite. Strain amplitude dependence of the internal friction, including the existence of the maxima, was explained by the Granato-Lucke (G-L) dislocation internal friction model. Dislocation densities obtained from various TEM images from the fiber-matrix interface were compared to values predicted by G-L theory.
High-Energy High-Rate Processing of High-Temperature Metal-Matrix Composites
Authors: Persad C. , Raghunathan S. , Lee B.-H. , Bourell D. L. , Eliezer Z. , Marcus H. L.
Published: March 2011

Advances in kinetic energy storage devices have opened up a new approach to powder processing of High Temperature Composites. The processing consists of internal heating of a customized powder blend by a fast electrical discharge of a homopolar generator. The high-energy high-rate “lMJ in 1s” pulse permits rapid heating of a conducting powder in a cold wall die. This short time at temperature approach offers the opportunity to control phase transformations and the degree of microstructural coarsening not readily possible using standard powder processing approaches. This paper will describe the consolidation results of two high temperature composite materials, (W-Ni-Fe)/B4C and (Ti3Al+Nb)/SiC. The focus of this study was the identification of the reaction products formed at the matrix/reinforcement interface as a function of input energy and applied stress. Input energies beyond a threshold value for each system were required to produce detectable reaction products. In the (W-Ni-Fe)/B4C system, the reaction products formed at 4000 kJ/kg input energy under 420 MPa applied stress were a series of complex carbides and borides including W2C, FeWB, Fe3C, Fe6W6C and Ni4B3. The intermetallic Fe7W6was also observed. In the (Ti3Al+Nb)/SiC system, the reaction products observed at 3400 kJ/kg and 210 MPa were TiC and TiSi2.
Role of Fiber-Matrix Interfacial Shear Stress on the Toughness of Reinforced Oxide Matrix Composites
Authors: Singh Raj N.
Published: March 2011

Mullite and zircon ceramic matrix composites uniaxially reinforced with as-supplied and BN-coated silicon carbide filaments were fabricated. The filament-matrix interfacial shear stresses were measured by a modified indentation technique and mechanical properties were determined in flexure mode. Significant improvements in strength and toughness were observed for the composites in comparison to monolithic mullite and zircon ceramics. Lower filament-matrix interfacial shear stresses were measured in composites with BN-coated filaments than in composites containing as-supplied filaments. The influence of filament-matrix interfacial shear stress on the critical stress for first matrix cracking, maximum composite strength, and toughness of the composites were studied.
New Pathways to Processing Composites
Authors: Mehrabian Robert
Published: March 2011

Compositing routes are reviewed for the fabricaiton of metal and metalceramic matrices combined with ceramic reinforcements and/or ductilizing phases. The important role of micromechanics in elucidating microstructural design principles to guide the processing “pathways” is emphasized. Specific processing techniques are described including incorporation of particles and fibers into melts, melt infiltration into preforms, powder metallurgy and melt oxidation.
Phase Stability and Interface Reactions in the Al-SiC System
Authors: Lee Doh-Jae , Vaudin Mark D. , Handwerker Carol A. , Kattner Ursula R.
Published: March 2011

The Al-SiC system has been used as a model system in an examination of phase stability in the presence of a liquid phase and microstructure development in metal-matrix composites. The Al-Si-C phase diagram has been calculated for temperatures between 500°C and 1500°C. The phases formed between Al(liquid) and SiC at 920°C have been determined experimentally, using analytical electron microscopy, in both fiber and particulate composites and compared with what is predicted from the equilibrium phase diagram. The morphologies and the spatial distributions of phases have also been examined in addition to the phase analysis. The only phases found were Al, Al4C3, SiC, and Si. Although Al4SiC4 is calculated to be stable at 920°C, it was not found. The SiC grain structure was found to influence strongly the morphology of the Al4C3-SiC and Al-SiC interfaces.
Elevated Temperature Slow Plastic Deformation of NiAl/TiB2 Particulate Composites
Authors: Viswanadham R. K. , Whittenberger J. Daniel , Mannan S. K. , Sprissler B.
Published: March 2011

To enhance the high temperature strength of aluminides, NiAl–iB2 composites with particulate contents up to 30 vol. pct. were made by XDTM synthesis and hot pressed to full density. Microstructures of these composites were characterized by optical, scanning and transmission electron microscopy (TEM). The average size of the TiB2 particles was about 1 μm, and the average grain size of the NiAl matrix was on the order of 10 μm. Elevated temperature compression testing was conducted on these composites in air at 1200 and 1300 K with strain rates varying from −10−4 to −10−7 s−1. Flow strengths were found to increase with increasing TiB2 content; for example, the 20 vol. pct. TiB2 composite was three times stronger than unreinforced NiAl. Post test TEM analysis showed that the primary feature of the dislocation substructure of deformed NiAl was well defined subgrain boundaries, whereas the structure of the higher volume fraction composites consisted of a very high density of tangled dislocations, loops and subgrain boundaries connecting particles. These observations suggest that TiB2 particles can stabilize a completely different dislocation structure than that normally found in NiAl.
The Gel Route to Yttrium Oxide
Authors: Ribot F. , Sanchez C. , Livage J.
Published: March 2011

Synthesis of pure Y2O3 Powders have been performed through the sol-gel process. Stable colloids in the range of 500 Å to 2000 Å have been obtained by hydroxylation of yttrium-aquo ions performed through an anion exchange resin.

The chemical nature of these sols and gels investigated by GTA, DTA and EXAFS is in close agreement with Y(OH)3nH2O. Scattering experiments (S.A.N.S, S.A.X.S, light scattering) show that these colloids are made of anisotropie particles, that can be described as platelets 30 Å thick, 500 Å large and a few thousand Angstroms long.

This synthesis can be extended to other rare earth colloids.
Structural Characterization of Polysilicate Intermediates Formed During Sol-Gel Polymerization
Authors: Klemperer W. G. , Mainz V. V. , Ramamurthi S. D. , Rosenberg F. S.
Published: March 2011

Identification of polysilicate intermediates formed during sol-gel processing of silica gels and glasses is an important step toward understanding the nature of this process on a molecular level. Although capillary gas chromatography using mass spectrometric detection gives the molecular formulas for low molecular weight intermediates [1], this approach is only semi-quantitative and provides no structural information. An improved protocol has been developed that allows structural assignment and quantitative determination of the principal mono- through hexasilicate structural isamers formed by hydrolysis of methanolic tetramethylorthosilicate in the presence of HC1. This protocol combines quenching by diazomethane, fractionation using spinning band column distillation, identification by capillary gas chromatography, and structural characterization using 29Si{1H} NMR techniques (l-pulse, ID-INADEQUATE, and 2D-INADEQUATE) to provide structural assignments and response factors for the components separated by gas chromatography.
Structural Organization of Early Gels and Precipitates of Chemically Bonded Ceramics
Authors: White William B. , Vesper Dorothy J. , Kraus Julia
Published: March 2011

Ceramic precursor materials in the silica-alumina-phosphous pentoxide system can be retained as solutions under suitably high or low pH conditions. Molecular species in these solutions have been characterized by their sharp, well-defined Raman spectra. Changes in pH or reduced water activity by addition of miscible organic solvents takes the system across sharp precipitation boundaries. Precipitates can take the form of colloidal gels, polymerized gels, or crystallites depending on chemical composition and rate of precipitation. Raman spectra of precipitates immersed in their parent solutions have much less structure and broader bands. Information of the structural characteristics of the precipitates are deduced from band widths and the amount of fine structures related to the coherence length for Raman scattering. Phosphate-rich compositions tend to be more highly ordered with more detailed spectra than the silicate rich compositions.
Multi-Phasic Nanocomposite Sol-Gel Processing of Cordierite
Authors: Kazakos-Kijowski Ann , Komarneni Sridhar , Roy Rustum
Published: March 2011

Cordierite (Mg2Al4Si5O18) powders prepared from compositionally triphasic nanocomposite gels led to enhanced densification when compared to powders made by the conventional SSG route. The densification of the sintered cordierite pellets was determined by utilizing the Archimedes method and the microstructure of the pellets was examined with a scanning electron microscope (SEM). Bulk densities of monophasic, triphasic nanocomposite (two sols and one solution) and truly triphasic nanocomposite (three sols) pellets sintered at 1300°C for 2 hours were 2.01 g/cm3 (80% relative density), 2.42 g/cm3 (96% relative density) and 2.51 g/cm3 (100% relative density) respectively. The enhanced densification of α-cordierite utilizing triphasic nanocomposite sol-gel processing is, at least in part, due to the contribution of the heat of reaction from the three components.
Effekts of Temperature and Reactant Concentration on Properties of Fine TiO2 Particles Prepared by Vapor-Phase Hydrolysis of Titanium Teiraisopropoxide
Authors: Kirkbir Fikret , Komiyama Hiroshi
Published: March 2011

Submicrometer-size TiO2 powders were continuously produced by vapor-phase hydrolysis of titanium tetraisopropoxide, TTIP, in a tubular-flow reactor. Particle size increased with increasing inlet TTIP concentration, and with decreasing inlet water concentration and temperature. At high water concentrations, primary particles form by instantaneous chemical reactions and particle growth occur by collision and coalescence of the particles. Brownian collision and coalescence theory could predict the experimental effect of inlet TTIP concentration on particle size. The experimental deviations occurred from the theory with increasing temperature were attributed to the changing particle properties with temperature.
Sol-Gel Syntheses and Characterization of BaTi4O9 and BaTiO3-Powders
Authors: Phule Pradeep P. , Rkbud Subhash H.
Published: March 2011

Sol-gel processes for the synthesis of high purity, ultrafine BaTi4O9 and BaTiO3 powders are described. Hydrolysis of an alkoxide precursor derived from barium metal and titanium (IV) isopropoxide resulted in formation of powders consisting of ultrafine (0.2 to 1.0 μm) spherical particles. These amorphous precursor powders were converted to crystalline BaTi4O9 powders (particle size 2–3 μm) by heat treatment at 1100 C. The sol-gel process for the synthesis of BaTiOj powders utilized chemical polymerization between moisture insensitive and relatively inexpensive barium acetate and titanium (IV) isopropoxide in the presence of acetic acid. The gel to ceramic conversion was achieved by firing the gels at 1000 °C to obtain high purity, stoichiometric BaTiO3 powders. The powders were sintered to obtain relatively dense (90 % relative density) ceramic bodies.
Growth and Structure of Pyrogenic Silica
Authors: Schaefer D. W. , Hurd A. J. , Christen D. K. , Spooner S. , Lin J. S.
Published: March 2011

Fractal analysis is used to interpret small-angle X-ray and neutron scattering data on commercial fumed silica powders. Rough primary particles are found in high surface area powders. A model based on ballistic polymerization, sintering, and diffusion-limited aggregation is proposed to explain the observed powder structure.
Kinetics Study of the Acidic Catalyzed Polymerization of Tetraethoxysilane by 29Si NMR.
Authors: Pouxviel Jean-Claude , Boilot J. P.
Published: March 2011

TEOS has been hydrolysed under acidic condition with stoichiome-tric or excess amount of water. Evolution of the silicon species is followed by 29Si NMR. The data are analyzed at different levels of detail; first, analysis of the by products of polymerization reactions, second determination of the extents and overall rate constants of hydrolysis and condensation reactions and finally kinetics simulations of the evolution taking into account all the present silicon species. We have shown that the hydrolysis rate increases with the number of hydroxyl groups, and the reesterification reactions have a significant contribution. We also found that condensation reactions preferentially occur with loss of water between the more hydrolyzed monomers; their rates rapidly decrease with the degree of condensation. We compare the two compositions as a function of their water content and pH.
Chemical Preparation of Powders and Films for High Temperature Superconductors
Authors: Bunker B. C. , Voigt J. A. , Lamppa D. L. , Doughty D. H. , Venturini E. L. , Kwak J. F. , Ginley D. S. , Headley T. J. , Harrington M. S. , Eatough M. O. , Tissot R. G. , Hammetter W. F.
Published: March 2011

A precipitation process has been developed to prepare precursor powders which can be calcined and sintered to form high critical temperature superconductors such as YBa2Cu3O7−x. Precursor powders are prepared using a continuous precipitation system in which a solution containing highly soluble salts of the desired metal cations is rapidly and completely mixed with a solution containing precipitating anions such as hydroxide and carbonate ions. The resulting amorphous powder can be calcined to form sub-micron particles of desired superconducting phases which are useful in preparing inks for the ink-jet printing of superconducting interconnects. The powders can be redissolved in organic solvents to form solutions which can be used in spin or dip coating substrates with thin superconducting films. Finally, the powders have been used to prepare bulk ceramics which exhibit the highest reported critical currents of any chem-prep ceramics. Bulk samples prepared from chloride doped precursors exhibit large, oriented grains and extensive flux pinning.