bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation and Sintering Behavior of Fine‐Grained A12O3‐SiO2 Composite
Authors: Debély Pierre E. , Barringer Eric A. , Bowen H. Kent
Published: June 2006

A fine, uniform A12O3‐SiO2 powder was prepared by heterocoagulation of narrow Al2O3 and SiO2 powders. This composite powder was dispersed, compacted, and fired in air at 900° to 1580°C for 1 to 13 h. Full density was achieved at 1550°C with the formation of a mullite phase. Relative densities of 83% and 98% (0.3 μm grain size) were measured for samples sintered at 1200°C for 13 h and at 1400°C for 1 h, respectively.
Ion‐Exchange Treatment of Silicon‐Yttria Dispersions
Authors: Crosbie Gary M.
Published: June 2006

Improved rheological stability in silicon‐yttria slurries for sinterable reaction‐bonded silicon nitride was obtained by treating casting slips with NH4+‐ion‐exchange resin. The substitution of NH4+ ions for flocculating ions (Ca2+ or Y3+) appears to be the principal factor leading to more time‐stable pseudoplastic yield stress and viscosities.
Environmentally Enhanced Crack Growth in Soda‐Lime Glass
Authors: FREIMAN S. W. , WHITE G. S. , FULLER E. R.
Published: June 2006

Crack growth data are presented for soda‐lime glass in various chemical environments. It is shown that the same environments which govern crack growth rates in vitreous silica also do so in soda‐lime glass. The slopes and positions of the crack growth curves in soda‐lime glass are shown to differ from those in vitreous silica. It is hypothesized that the differences between the behavior of soda‐lime glass and silica result from the effects of the modifier ions, Na+ and Ca2+, on the reactivity of the Si‐O bond or through changes in the elastic properties of the bridging network. It is shown that sodium ion exchange and silica dissolution may also be important to crack growth, particularly at low crack velocities.
Stresses in Dumet‐Glass Seals
Authors: VARSHNEYA A. K. , MARRA J. E.
Published: June 2006

Hull and Burger's calculations of stresses in the Dumet‐glass bead seals, which were based on Poritsky's erroneous analysis, are corrected. Copper yielding is properly introduced. Calculated anisotropic thermal expansion of two types of Dumet alloy, as well as stresses in Dumet wire‐soft lead glass bead seals are in good agreement with those measured experimentally. Metal composites suitable for glass sealing can be formulated by using the analysis presented.
Electrical Resistivity and Microwave Transmission of Hexagonal Boron Nitride
Authors: FREDERIKSE H. P. R. , KAHN A. H. , DRAGOO A. L. , HOSLER W. R.
Published: June 2006

The dc conductivity of hexagonal boron nitride (BN) and BN‐containing composites was measured as a function of temperature up to 2400°C. The results confirm that at high temperatures BN is an intrinsic semiconductor with an energy gap of 0.99 ± 0.06 aJ (6.2 ± 0.4 eV) at T= 0 K. Extrapolated values for the resistivity of BN in the range 2600° to 3000°C are used to analyze the absorption, reflectivity, and transmissivity of a BN window when subjected to microwave radiation under atmospheric reentry conditions. It appears that the transmissivity is of the order of 1 to 10% at these temperatures due mainly to the high conductivity in a very thin, very hot surface layer. The transmissivity can be improved by using a composite made of boron nitride and silica.
Metastability of Tetragonal Zirconia Powders
Authors: OSENDI MARIA ISABEL , MOYA JOSE S. , SERNA CARLOS J. , SORIA JAVIER
Published: June 2006

The formation of metastable t‐ZrO2 by thermal treatment was studied in a systematic way on two different samples: a gel (G) and zirconyl acetate (A). The results show that initially nucle‐ation of t‐ZrO2 is favored by creation of anionic vacancies with trapped electrons. At higher temperatures the electronic defects disappear, the crystallites grow, and the m‐phase can nucleate. This evolution is observed perfectly on sample A because of its special morphological characteristics.
Comparison of 80‐keV D+ Ion Implantation with Thermal D2 Doping in Silica by FTIR and ESR Spectroscopy
Authors: SAEKI MASAKATSU , OHNO SHIN‐ICHI , TACHIKAWA ENZO , AZUMA NAOTO , MIYAZAKI TETSUO , FUEKI KENJI
Published: June 2006

Behavior of deuterium atoms in fused silica, which were implanted by 80‐keV D+ (D2+, D3+) ions or doped thermally by D2 (or D2O), was studied by infrared Fourier transform spectroscopy (FTIR) and by ESR spectroscopy. When 80‐keV deuteron ions are implanted into fused silica, OD bonds are formed. The OD bonds are also formed by thermal doping with D2 or D2O. When the deuterated silica is γ‐ray irradiated at 77 K, D atoms are formed by rupture of the OD bonds. The efficiency of the OD bond rupture in the deuteron‐implanted silica is much less than that in the D2‐doped silica. It is concluded from the results of thermal annealing that the low efficiency of the OD bond rupture in the deuteron‐implanted silica is due to the radiation damage accompanying the implantation process. However, the decay rate and detrapping energy of deuterium atoms, once formed in the silica, are similar in both cases.
Formation and Properties of Calcium Aluminosilicate Glasses
Authors: SHELBY J. E.
Published: June 2006

The glass‐forming region for calcium aluminosilicate glasses has been determined. A number of properties of these glasses (thermal expansion coefficient, glass transformation and dilatometric softening temperature, and refractive index) have been studied. The results of these measurements suggeq that the structures of these glasses may not as closely resemble those of alkali aluminosilicate glasses as is commonly assumed. Evidence is presented which suggests that the binary calcium aluminate glasses may be phase separated.
Crystalline‐Phase Formation in Hot Isostatic Pressing of Nuclear Waste Ceramics with High Zirconia Content
Authors: HARKER ALAN B. , FLINTOFF JOHN F.
Published: June 2006

Ceramic forms with a significant glass phase have been prepared from Zr‐rich simulated Idaho Chemical Processing Plant high‐level nuclear waste by hot isostatic pressing of redox‐controlled waste and chemical additive calcines. Crystalline‐phase formation in the ceramics is a function of the waste loading, additives, and consolidation temperature. Actinide host phases are controlled by silica‐zirconia crystal chemistry; the composition of the amorphous phase dominates the leaching behavior. Two phase assemblages—one consisting of CaF2, ZrO2, ZrSiO4, and glass, the second of CaF2, ZrO2, YNaSiO4, ZrSiO4, and glass—showed leach resistance superior to melter‐processed borosilicate glass forms for uranium and, at waste loadings >80 wt%, offer a factor of up to 3.2 times greater volume reduction. The presence of the designed glass phase in the waste forms makes them more flexible to variations in waste composition and lowers the required hot isostatic pressing temperature for consolidation as compared with polycrystalline waste ceramics, while maintaining the actinide leach resistance of the crystalline phases.
Effect of R3+ Ions on the Structure and Properties of Lanthanum Borate Glasses
Authors: CHAKRABORTY INDRA N. , DAY DELBERT E.
Published: June 2006

Glass formation in the systems (mole percent) 25La2O3· xR2O3· (75 ‐ X)B2O3 (R = Al, Ga) and (25 ‐ x)La2O3· xLn2O3· 75B2O3 (Ln = Gd, Er, Y) was investigated. Up to 25 mol% Al2O3 or Ga2O3 can be substituted for B2O3, but more than ∼ 5 mol% Ln2O3 substituted for La2O3 caused macro phase separation. X‐ray diffraction and infrared analysis of these glasses and their devitrified products indicate that the basic structural units are similar to (B3O6)∞ chains found in binary 25La2O3* 75B2O3 glass. However, the BO4 units in the (B3O6)∞ chains are replaced by AlO4 or GaO4, units when Al2O3 or GaZO3 is substituted for B2O3. In these systems, Al2O3, Ga2O3, and B2O3 act as glass formers, whereas Ln2O3 and La2O3 act as network modifiers. The substitution of either R2O3 or Ln2O3 in the lanthanum borate system changes the separation distance between adjacent (B3O6)∞ chains. The effect of this structural change on the molar volume, transformation temperature, thermal expansion coefficient, and transformation‐range viscosity is discussed.
Defects and Charge Transport in β‐Ta2O5: II, Analysis of the Conductivity of Nb2O5‐doped β‐Ta2O5
Authors: McHale A.E. , Tuller H.L.
Published: June 2006

The model proposed to explain the defect behavior of nominally pure β‐Ta2O5 was extended to the case of defect equilibria and charge transport in β‐Ta2O5 doped with a multivalent cation, i.e., Nb2O5‐doped P‐Ta2O5. This case is of practical interest in the electronics industry, where Nb2O5, is a dominant impurity in capacitor‐grade β‐Ta2O5.
Oxygen Sensors Based on the Electrical Conductivity of the Solid Solutions (Mg1–xFex)O and(Mg1–xCox)O
Authors: VALVERDE NILO
Published: June 2006

Solid solutions of general compositions (Mg1‐ xFex)O and (Mg1‐xCox)O (0.05 ≤ x ≤ 0.25) were investigated with regard to the dependence of their specific electrical conductivity on the oxygen partial pressure (10−17≤ po2≤ 105 Pa) at 900c and 800°C. The experimental results, especially the slopes of plots of log σ vs log po2 and the stability of the solid solutions studied, indicate that some of these compositions could be used as oxygen sensors at high temperatures.
Characterization of the Near‐Surface Region of Single‐Crystal Alumina Diffusion Samples Using Rutherford Backscattering and Channeling
Authors: CAWLEY JAMES D. , L'HOIR ALAIN , SCHMAUS DIDIER
Published: June 2006

Rutherford backscattering was used to characterize the near‐surface region of single‐crystal Al2O3 diffusion samples. Both structural and chemical information was obtained. Results indicate that mechanical polishing produces significant structural damage, but that this damage may be removed through annealing. Glass droplets containing impurities condensed onto the sample surface. The Rutherford backscattering and channeling results indicate that these droplets served as a source for impurities which diffused into the sample during the diffusion anneal.
Saturation Factors for Calcium Hydroxide and Calcium Sulfates in Fresh Portland Cement Pastes
Authors: GARTNER ELLIS M. , TANG FULVIO J. , WEISS STUART J.
Published: June 2006

Aqueous extracts from five cement pastes at w/c = 0.5 were analyzed for Ca2+, SO2–4, Na+, and K+. Degrees of saturation with respect to portlandite, gypsum, and syngenite were determined at ages from 6 min to 3 h, taking into account ionic association effects. Portlandite saturation is usually attained within a few minutes of mixing, but rates of saturation vary. The maximum degree of saturation is 2 to 3 times the equilibrium value and is attained within 2 h. Initial super‐saturation with respect to gypsum, and in some cases syngenite, occurs at very early ages and declines to the saturation level within 12 min. Results are interpreted by use of a solution‐precipitation model for cement hydration. The calculated critical size of portlandite nuclei at early ages is ∼0.1 μm. Slow growth of portlandite nuclei suggests a surface poisoning phenomenon.
Analytical Study of Pure and Extended Portland Cement Pastes: II, Fly Ash‐ and Slag‐Cement Pastes
Authors: TAYLOR H. F. W. , MOHAN K. , MOIR G. K.
Published: June 2006

A range of pastes of portland cement interground with low‐calcium fly ash or granulated blast furnace slag was studied by X‐ray diffraction, analytical electron microscopy, thermo‐gravimetry, and determinations of CO2 and of unreacted fly ash or slag. Partial replacement of clinker by fly ash results in increased reaction of the alite from at least as early as 3 d. The amount of Ca(OH)2 formed from a given weight of clinker increases at 3 d due to the enhanced reaction, but from 28 d onward, it decreases due to the pozzolanic reaction. The mean Ca/SI ratio of the C‐S‐H decreases with time or fly ash content, toward a lower limit of ∼1.4. Partial replacement of clinker by slag also decreases both the amount of Ca(OH)2 formed from a given weight of clinker and the mean Ca/Si ratio of the C‐S‐H, but to a lesser extent. Using the methods described in Part I of this paper, the results of the experimental methods were tested for mutual consistency, and volume percents of phases, porosities, and related quantities were calculated.
Ferrous/Ferric Mössbauer Analysis of Simulated Nuclear Waste Glass with and without Computer Fitting
Authors: GOLDMAN DON S. , BEWLEY DEBORAH E.
Published: June 2006

Wet‐chemical and 57Fe Mössbauer analyses of ferrous/ferric ratios in complex borosilicate and simple silicate glasses were compared. The results support the validity of the colorimetric wet–chemical procedure and establish a linear calibration for the Mössbauer data. The resulting correlation indicates that using area ratios from Mössbauer spectra will overestimate the proportion of ferrous iron by a factor of 1.2. The linear calibration was achieved only after statistically optimizing the peak line shape for each Mössbauer spectrum. Samples with a greater proportion of ferrous iron tended to have a greater Gaussian contribution to the peak line shape. A procedure to determine ferrous/ferric ratios from measured intensity data at three velocity locations was developed. With instrument modification, this result will lead to a substantial reduction in data collection time and the elimination of complex spectral fitting.
Elastic Properties and Sound Wave Velocity of PZT Transducers Doped with Ta and La
Authors: Tawfik A.
Published: June 2006

Lead zirconate‐titanate (Pb(Zr0.54Ti0.46)O3) was doped with varied concentrations of Ta5+ and La3+ and sintered at 1200°C for 2 h. Dense ceramic materials were obtained when the cation stoichiometry was adjusted to allow for charge compensation of the donor ions by Pb vacancies. Bulk density, capacitance at 1 KHz, grain size, piezoelectric charge, and elastic compliance were determined experimentally. Sound wave velocity, inductance, and capacitance near resonance were calculated.
Compatibility of AIN with Group VIII Transition Metals
Authors: Schuster Julius C.
Published: June 2006

The stability of aluminum nitride coexisting with group VIII transition metals was investigated. Although Fe and Co do not react to form intermetallic compounds, formation of Ni3Al, RuAl, RhAl, and Pd2Al was observed. These results were rationalized by calculating the equilibrium nitrogen pressures for the reaction of AlN with Fe, Co, and Ni.
Glass Inhomogeneity Measurement Using the Shelyubskii Method
Authors: VARSHNEYA ARUN K. , LOO MIKE C. , SOULES THOMAS F.
Published: June 2006

Inhomogeneity in glass can be measured in terms of the variance of the refractive index distribution by using the Shelyubskii method. In the method, the transmission of an optical cell containing glass particles immersed in a nearly matching refractive index liquid is measured. Transmission can be measured accurately and reproducibly as a function of wavelength with a conventional spectrophotometer. The primary source of errors, hitherto, has been the Raman‐Shelyubskii theory to relate the transmission to the refractive index variance by using interference optics principles. It is shown that a common Shelyubskii experiment can be described more cogently by a theory based on the principles of geometric optics. A Monte Carlo simulation of light ray tracing through the optical cell containing glass particles with a random distribution of refractive index was conducted. The fraction of intensity collected within the acceptance angle of the spectrophotometer, identified as the transmission, agrees well with the measured data. A glass inhomogeneity meter based on the simulation experiments is described.
Mechanical Behavior of Lightweight Ceramics Based on Sintered Hollow Spheres
Authors: GREEN D.J. , HOAGLAND R. G.
Published: June 2006

A simple micromechanical model, describing the Young's modulus, fracture toughness, and density of a lightweight ceramic structure produced by the sintering of hollow spheres and based on shell theory, was developed. The approach combined an analysis of the elastic deformation using shell theory and a simple analysis of the densification in terms of the micro‐structural parameters. The results were compared with experimental data for materials produced by the sintering of hollow glass spheres and gave reasonable to good agreement, especially in the prediction of the nonlinear variation of Young's modulus and fracture toughness with density. The model should provide a useful basis for rationalizing the relation between mechanical properties and fabrication procedure for such materials.
Measurement of Small Concentrations of Cr and Fe in α‐Al2O3 Using Electron Spin Resonance
Authors: de BIASI R. S. , RODRIGUES D. C. S.
Published: June 2006

Electron spin resonance line widths for Cr3+ and Fe3+ were measured in α‐Al2O3 samples doped with <1.2 mol% of Cr and Fe. Line width increased with increasing Cr and Fe concentration and decreased with increasing grain size. The experimental results show that this technique can be used to determine, rapidly and nondestructively, small concentrations of Cr and Fe in commercial Al2O3. Nomograms are provided to facilitate interpretation of the results.
Influence of Externally Applied Stresses on Kinetics of Ion Exchange in Glass
Authors: VARSHNEYA A. K. , DUMAIS GLENN A.
Published: June 2006

Soda‐lime‐silica glass canes were ion‐exchanged in a bent mode in a molten KNO3 salt bath. After ion exchange and cooling, the specimens showed asymmetry of residual stresses. Measured penetration profiles of potassium showed that the maximum diffusion occurred from the tension side, the minimum from the compression side, with the neutral side being in between. These observations support the notion that externally applied stresses can alter the average site size for cation diffusion in glass.
Effects of Mechanical Processing on Semiconducting Properties of Barium Titanate
Authors: AMIN AHMED , SHUKLA VISHWA
Published: June 2006

Semiconducting barium titanate elements with positive temperature coefficient of resistance (PTCR) are usually subjected to different degrees of stress levels during processing operations like grinding, ultrasonic drilling, and slicing, etc. In this work we have examined the influence of these operations on the semiconducting properties of PTCR barium titanate using X‐ray diffraction and electrical resistivity measurements.
Suppression of Frothing by Silicon Addition During Oxynitride Glass Synthesis
Authors: BAIK SUNCCL , RAJ RISHI
Published: June 2006

Several oxynitride glasses were synthesized with and without the addition of a few weight percent of free silicon. For Mg‐Si‐0‐N and Si‐Al‐0‐N glass compositions, the severe frothing (or “bubbling”) which was observed during melting could be eliminated completely by the addition of silicon. In a Y‐Si‐Al‐0‐N composition, frothing was not observed, even when no silicon was added. The results are used to explain why A1N is superior to Si3N4 for synthesizing transparent oxynitride glasses.
Electrical Conductivity of Alkali‐Doped Zr‐Ba‐La‐Al Fluoride Glasses
Authors: SHELBY JAMES E.
Published: June 2006

The effect of alkali ion identity on the dc electrical conductivity of alkali‐doped Zr‐Ba‐La‐Al fluoride glasses containing 5 mol% MF, where M is Li, K, or Cs, was measured. The electrical conductivity increases in the order Li < K < Cs. This trend is the reverse of that found for typical oxide glasses. Results support the contention that these glasses are anion conductors.
Sodium Diffusion in Sodium Aluminophosphate Glasses
Authors: RAJARAM MOHAN , DAY DELBERT E.
Published: June 2006

The self‐diffusion of sodium ions in xAl2O3‐(100‐x)Na,P2O6 glasses (2.44 < × <25.92 mol%) was measured from ∼ 170°C to near the glass transition temperature. The sodium diffusion coefficient decreased only by a factor of 2 to 3 with increasing Al2O3 concentration.
Stress in Leached Phase‐Separated Glass
Authors: SCHERER GEORGE W. , DREXHAGE MARTIN G.
Published: June 2006

When a phase‐separated glass is leached, stresses develop because of release of thermal stresses, creation of surface area, ion exchange, and hydration. Analyses are presented for the thermal stresses, including the portion that develops on cooling from the heat‐treatment temperature to the setting temperature of the less viscous phase. During leaching, the interfacial energy of the residual phase increases, so that phase tends to contract. A more important effect is the contraction caused by removal of alkali and B2O3 from the residual phase during leaching. The extent of removal of B2O2 decreases with heat‐treatment time, tH, because the scale of the microstructure increases as t1/3H. The change in residual B2O2 content with tH is shown to be consistent with diffusion‐controlled ion exchange. The dependence of stress on tH in partially leached glasses, measured by Drexhage and Gupta, results principally from the change in extent of ion exchange; the reduction in surface area with increasing tH also has a significant effect on the stresses.
Preparation and Properties of Silver Borate Glasses
Authors: PIGUET JOYCE L. , SHELBY JAMES E.
Published: June 2006

Silver borate Basses containing 0 to 30 mol% Ag2O were formed. Properties measured include density, thermal expansion coefficient, glass transformation and dilatometric softening temperatures, transformation‐range viscosity, dc electrical conductivity, and helium permeability and diffusivity. Optical spectroscopy revealed that the color of these glasses results from absorption bands at ∼407, ∼310, and ∼250 nm. Each band increased in intensity as the silver oxide content of the glass was increased. The properties of these glasses were consistent with the structural model currently used to describe the structure of alkali borate glasses. No evidence for the existence of phase separation was found for the conditions of the present study.
Stability of Metal Oxide Doped ZnO in Molten Alkali Carbonates
Authors: BAUMGARTNER CHARLES E.
Published: June 2006

The decomposition of Cr‐doped ZnO and Zr‐doped ZnO in Li2CO3/K2CO3 melts at 923 K under a humidified 30% CO2/air atmosphere was found to occur by different routes, with the relevant equilibrium solubilities in the carbonate melt mitigating the decomposition path. Chromium–doped ZnO undergoes Cr depletion resulting from dissolution of the doped material followed by reprecipitation of a Cr‐depleted ZnO; the Cr remains dissolved as highly soluble chromate. This reaction progresses until Cr equilibrium solubility is met. Zirconium‐doped ZnO shows preferential ZnO solubility, with reprecipitation of ZrO2 and Li2ZrO3.
Electrostriction in Lead Lanthanum Zirconate‐Titanate Ceramics
Authors: MENG Z.Y. , KUMAR U. , CROSS L.E.
Published: June 2006

Electric polarizations and elastic strain were measured simultaneously for several lead lanthanum zirconate‐titanate (PLZT) compositions cycled around their high‐field electric hysteresis loops. Using the accepted symbolism for compositions, where the first number gives the mole percent of La2O3 and the second two numbers give the ratio of PbZrO3 to PbTiO3 in the composition, data were taken for (7,7.5,8,8.8,9.5)/65/35 and 8/70/30 compositions. The results show that for all compositions in which the base state is macroscopically nonpolar, the strains are dominantly electro‐strictive in nature. Both of the polarization‐related constants, Q11 and Q12, are almost independent of temperature and of the same order as in other perovskites but decrease slightly in magnitude with increasing La2O3 content.
Hot‐Pressing of Sic with Additions of BaO and C
Authors: SAKAI TOSIKAZU , HIROSAKI NAOTO
Published: June 2006

Barium oxide and carbon were added to β‐Sic powder as sintering aids. When only BaO or C was added, the Sic powder did not densify. However, densification was promoted by adding both additives together. Transmission electron microscopy of the compact revealed a boundary phase, which was deduced to result from reaction between Sic and barium carbide, the latter being produced by reaction between BaO and C. It is suggested that this reaction product promotes sintering.
Effect of Atmosphere and Temperature on the Equilibrium between Molten Tin and Soda‐Lime Glass
Authors: LIANG ZHI HONG , COOPER ALFRED R.
Published: June 2006

The interaction of soda‐lime glass with molten tin is of practical and scientific interest. Here the observation that the interfacial tin content of glass in contact with molten tin decreases with increasing temperature and increases with increasing oxygen pressure is confirmed and discussed.
Cathodoluminescence: A Microstructural Technique for Exploring Phase Distributions and Deformation Structures in Zirconia Ceramics
Authors: CZEKNUSZKA J.T. , PAGE T. F.
Published: June 2006

The scanning electron microscope cathodoluminescence behavior of two partially stabilized zirconias is presented. Monoclinic material, either occurring on grain boundaries or produced by deformation, appears strongly luminescent, whereas in cubic‐plus‐tetragonal material grain boundaries appear dark, as do deformed regions associated with hardness indentations and wear tracks. These preliminary observations suggest that cathodoluminescence may be a valuable microstructural technique for characterizing the microstructure and deformation behavior of zirconia‐based ceramics.
Eigensolution of the Spinodal Equation
Authors: BARRON LAWRENCE M.
Published: June 2006

Spinodal calculations are a very effective and thorough means of studying the geometry of n‐component immiscibility. An efficient technique is presented for solving the spinodal constraint IGI=0, where matrix elements G, = d2G/(dX,ax,). The constraint is recast into temperature‐dependent and ‐independent portions as G=H‐TS; then it follows that the eigensolution for S'H must contain the spinodal temperature and spinodal ray. Thus, spinodal calculations can be performed using standard eigensolution software instead of existing polynomial techniques.
High‐Temperature Electrical Conductivity of Aluminum Oxynitride Spinel
Authors: KIM IL‐UNG , RICHARDS VON L.
Published: June 2006

The electrical conductivity of pure aluminum oxynitride spinel was measured at 1300° to 1500°C under flowing nitrogen gas. The re sults for two nonstoichiometric spinel compositions can be fitted by exponential expressions with an activation energy of 116± I Wlmol. The mobilities calculated from aluminum vacancy concentrations and conductivities, 8.07x cm'/V‐s, are reasonable for ionic conduction. The complex impedance plot suggests electrode double‐layer effects being damped out at higher frequencies in the range 10’to lo4 Hz.
Determination of v‐K1 Curves by a Modified Evaluation of Lifetime Measurements in Static Bending Tests
Authors: FETT T. , MUNZ D.
Published: June 2006

A method is presented to evaluate complete v‐KI curves from static bending tests, whereby no special assumptions for the type of v‐KI relation are necessary. The method permits determination of crack growth rates of <10−12m/s.
Liquid‐Phase Sintering in Thick‐Film Resistor Processing
Authors: PALANISAMY PONNUSAMY , SARMA DWADASI H. R. , VEST ROBERT W.
Published: June 2006

Equations are derived to express the initial‐stage neck growth in liquid‐phase sintering of particles completely immersed in a liquid. Sintering kinetics are calculated for RuOl neck growth in a lead borosilicate glass, taking into account the effect of the dissolved alumina content of the glass phase. Sintered contacts are shown to be possible under favorable processing conditions and materials and reaction parameters during thick‐film resistor processing.
Relation between Chemical, Mechanical, and Electrical Properties of Nb2O5‐Modified 95 Mol% PbZrO3‐5 Mol% PbTiO3
Authors: DUNGAN R.H. , STORZ L.J.
Published: June 2006

The use of an Nb2O5‐modified PZT (containing ∼95 mol% zirconate and ∼5 mol% titanate) in explosively driven electrical power supplies is described. A small but significant number of test specimens exhibit dielectric breakdown during explosive testing. A failure mechanism is proposed in which the electromechanically induced stresses result in fracture. Charged particles released during the fracture process initiate dielectric failure. The fracture toughness and mechanical strength of a given material are about the same for unpoled and poled material, but after pressure depoling, a given material typically exhibits a nominal 50% increase in toughness and strength. Varying the lead concentration from ∼5 at.% deficiency to ∼2 at.% excess results in a degradation in toughness and strength. An optimum niobium concentration is observed at ∼1.8 at.% in terms of mechanical properties and functional performance.
PTCR Effect in BaTiO3
Authors: LEWIS G. V. , CATLOW C. R. A. , CASSELTON R. E. W.
Published: June 2006

Calculations of bulk and surface defect energies were used to develop a model of the grain structure of doped BaTiO3, Segregation processes are expected as a consequence of thermo‐dynamic and kinetic factors and result in the development of n‐i‐n junctions at intergranular contacts, thus leading to the observed PTCR behavior of polycrystalline materials.
Fracture Toughness of High‐Pressure‐Sintered Diamond/Silicon Nitride Composites
Authors: Noma Tatsuo , Sawaoka Akira
Published: June 2006

Diamond particles were dispersed in silicon nitride, sintered at 6 GPa and 1600°C for 30 min, and heat‐treated under vacuum at 1300°C to induce graphitization of the diamond. Improved fracture toughness values up to 7.5 MN/m312 were achieved for these composites. Stress‐induced microcrack toughening is considered to be a plausible toughening mechanism. Comparisons with diamondlalumina ceramics were made.
Crystallization and Transformation of Distorted Tetragonal YNbO4
Authors: YAMAGUCHI OSAMU , MATSUI KAZUHIRO , KAWABE TAKASHI , SHIMIZU KIYOSHI
Published: June 2006

Distorted tetragonal YNbO4 crystallizes from an amorphous material prepared by the simultaneous hydrolysis of yttrium and niobium alkoxides. It can be preserved at room temperature by quenching and has a unit cell with α=0.5164 nm and c= I,0864 nm. The structure contains tetrahedral NbO4 groups.
Fast Firing of a Lead‐Iron Niobate Dielectric Ceramic
Authors: Kassarjian Michael P. , Fox Bradley H. , Biggers James V.
Published: June 2006

A Pb(Fe, Nb)O3−Pb(Fe, W)O3−Pb(Zn, Nb)O3 dielectric ceramic fires at temperatures low enough for 100% silver electrodes to be used in multilayer capacitors made with the ceramic. Good dense Pb(Fe, Nb)O3, ceramics were obtained by fast, firing, i.e. by using rapid ramp rates and very short firing times. The densified ceramic was characterized by determination of its dielectric properties, X‐ray diffraction, and scanning electron microscopy.
Effect of Impurities on Sic Whisker Morphology
Authors: Mazdiyasni K. S. , Zangvil Avigdor
Published: June 2006

Thermal decomposition of polymeric organosilicon, as precursor to Sic whiskers, in the presence of impurities such as alkali and alkaline‐earth metals and aluminum resulted in glass beads or droplets on the β‐Sic whiskers. Semiquantitative analysis of typical whiskers and whiskers with glass beads were performed using a transmission electron microscope equipped with an energy‐dispersive X‐ray spectrometer and a scanning transmission electron microscope equipped with an electron energy loss spectrometer. The major impurities identified were correlated with the processing method employed
Creep Deformation of an Alumina Matrix Composite Reinforced with Silicon Carbide Whiskers
Authors: Chokshi Atul H. , Porter John R.
Published: June 2006

Whisker‐reinforced ceramic composites with enhanced fracture toughness properties are being developed. The creep behavior of such a composite was studied. The introduction of silicon carbide whiskers significantly improves the creep resistance of polycrystaline alumina.
Effect of Additives on the Formation of Ti02 Particles by Vapor Phase Reaction
Authors: Suyama Yoko , Kato Akio
Published: June 2006

The effect of additives on the formation of fine Ti02 particles by vapor phase reaction was studied. The oxygenolysis of TiC14 was enhanced by the addition of Fecl3, and AlBr3, and suppressed by SiCl4, and ZrCl4. Particles formed in the presence of additives were 1/2 to 1/5 the size of those formed without additives, and particle size distributions became very narrow. Particle shape was also influenced by the additives.
Phase Studies Concerning Sintering in Aluminas Doped with Ti4+
Authors: Morgan Peter E. D. , Koutsoutis Michael S.
Published: June 2006

Previous solid state analyses of sintering in Ti4+‐doped‐commercial alumina are shown to be in error because a liquid phase exists in the appropriate region of the Al2O3−TiO3−Na2Ophase diagram at least by 1350°C, a temperature lower than that at which “solid state” studies were conducted. It is suggested that liquid‐phase sintering is a much more common occurrence than was realized formerly.
Sintering Behavior of Ceramic Films Constrained by a Rigid Substrate
Authors: BORDIA R.K. , RAJ R.
Published: June 2006

A model is presented in which the sintering behavior of a ceramic film which is constrained by a rigid substrate is contrasted with the sintering behavior of a free film. The problem is made simple by the assumption that the stress field developed in the film is uniform. This simplification allows several closed form solutions to be obtained. The solutions give new insights into the sintering behavior of films supported on a substrate. It is found (1) that the shear rate of the film is more important in the sintering process than its densification rate when the film is constrained by a substrate, (2) that the incompatibility stress is time dependent and reaches its maximum value during the initial stages of sintering, (3) that the magnitude of that maximum stress may be tensile or it may be compressive depending on the shear response of the material, and (4) that if the incompatibility stress is tensile it can lead to the formation of cracks or defects in the ceramic film.
Experimental Procedure for Determining Transport Properties of Oxide Scales
Authors: BEN ABDERRAZIK G. , MILLOT F. , MOULIN G. , HUNTZ A. M.
Published: June 2006

To determine the transport properties of oxide scales growing on an alloy, a laboratory apparatus was developed which allows plotting of characteristic V = f (i) curves and oxidation with an applied electric field. The apparatus and formalism used are described; it appears that such experimental procedures allow determination of the mean ionic transport number, ti; the conductivity values σ, σi, and σ,e; and the effective charge, Z*, of the moving species in the oxide scale (A12O3 in the present case).
Determination of Transport Properties of Alumina Oxide Scale
Authors: BEN ABDERRAZIK G. , MILLOT F. , MOULIN G. , HUNTZ A. M.
Published: June 2006

By measuring the potential difference between the two interfaces of an alumina scale developed on a FeCrAl alloy, or by applying an electric field during its growth, values of ti, σi, and σe along with their temperature dependence were determined. A residual potential, V0, which was measured between the two oxide interfaces, is related to the oxygen chemical potential gradient on the scale. Alumina growth is controlled by oxygenion diffusion (by either V″ or O″i), and the transport properties are modified by the amount and distribution of impurities.
Transformation of Yttria‐Doped Tetragonal ZrO2 Polycrystals by Annealing in Water
Authors: SATO TSUGIO , SHIMADA MASAHIKO
Published: June 2006

Phase changes and the microstructure resulting from low‐temperature annealing of yttria‐doped tetragonal ZrO2 polycrystals in water were investigated at 65° to 120°C. Tetragonal ZrO2 on the surface of the sintered body transformed to the monoclinic phase, accompanied by microcracking. The transformation rate in water, which was much greater than that in air, was first order with respect to surface concentration of tetragonal ZrO2. Nonaqueous solvents with a molecular structure containing a lone‐pair electron orbital opposite a proton donor site also greatly enhanced the transformation.
Thermodynamic Stability and Incorporation of Phosphorus into Germanium‐Doped Silica Glass
Authors: McAFEE KENNETH B. , GAY DAVID M. , WALKER KENNETH L. , HOZACK ROBERT S.
Published: June 2006

A thermodynamic calculation of the incorporation of phosphorus into germanium‐doped silica glass is presented. The calculation predicts that, quite like germanium, the phosphorus concentration has a maximum as a function of temperature near 1800 K. In the five‐component system (CI, Ge, 0, P, Si) under typical strongly oxidizing conditions, phosphorus is lost as PO2 at equilibrium above 1800 K. A new way to minimize the Gibbs energy of the complex system is described briefly; no initial estimate of the solution components is required. This method should be widely applicable to chemical problems that involve multiple components and phases.
Reaction‐Rate‐Limiting Steps in Carbothermal Reduction Processes
Authors: VAN DIJEN F. K. , METSELAAR R. , SISKENS C. A. M.
Published: June 2006

The production of β‐sialon (Si3A1303N5) and nonoxidic powders by carbothermal reduction of oxides is discussed. Special attention is paid to the rate‐determining steps in the conversion process performed in a packed‐bed reactor. It is shown that powders with specific surface area >10 m2/g can be produced by the correct choice of pellet size, gas flow rate, temperature, and raw material.
Reactions and Bonding of Sodium Disilicate Glass with Chromium
Authors: TOMSIA ANTONI P. , FEIPENG ZHANG , PASK JOSEPH A.
Published: June 2006

Reactions and reaction mechanisms occurring at sessile drop interfacial regions of sodium disilicate glass on chromium were identified at 1000°C and an ambient atmosphere of 2.7 × 10−4Pa with a p(O2) of 1 × 10−15 and 1 × 10−5 Pa. Depending on the experimental conditions, the principal reactions were redox reactions of Cr0 with Na+ to form Cr2+ and Na0, Cr2+ with Na+ to form Cr3+ and Na+, Cr0 with Si4+ to form CrSix, alloy dendrites and Cr2+, and Cr2+ with Si4+ to form Cr3+ and SiO(gas). Adherence was developed when the interfacial region was saturated with Cr3+, i.e., Cr2O3.
Influence of Shear Bands on Creep Rupture in Ceramics
Authors: EVANS A. G. , DALGLEISH B. J.
Published: June 2006

Observations of damage during the creep rupture of poly‐crystalline alumina have revealed an important influence of shear bands on the failure process. The shear bands are regions of appreciable damage, consisting of high densities of facet‐sized cavities. The cavities within the bands become crack nuclei at shear band intersections and crack coalescence sites during the final stage of failure. Further understanding of shear bands and shear band damage is needed to permit the development of quantitative expressions for the rupture times measured for this material.
Strength and Fracture Toughness of Isostatically Hot‐Pressed Composites of Al2O3 and Y2O3‐Partially‐Stabilized ZrO2
Authors: Tsukuma Koji , Ueda Kuniyoshi , Shimada Masahiko
Published: June 2006

Composites of Al2O3 and Y2O3 partially‐stabilized ZrO2 were isostatically hot‐pressed using submicrometer powders as the starting material. The addition of Al2O3 resulted in a large increase in bending strength. The average bending strength for a composite containing 20 wt% Al2O3 was 2400 MPa, and its fracture toughness was 17 MN·w−3/2
Auger Analysis of Hot‐Pressed and Sintered Silicon Carbide
Authors: Sherman Robert
Published: June 2006

Intergranular and transgranular chemistries of hot‐pressed and sintered silicon carbides were investigated by Auger electron spectroscopy. Results indicated major differences in grain‐boundary compositions between the two. Hot‐pressed silicon carbide displayed a complex intergranular chemistry. Sintered silicon carbide displayed grain facets that were free of impurities and additives. The observed intergranular chemistries for both silicon carbides are discussed in terms of their relation to the processing methods.
Kinetics of Precipitation from a Dilute Solid Solution
Authors: Virkar Anil V.
Published: June 2006

Kinetics of precipitation in a binary or a pseudobinary system, where diffusion and interface transfer are comparable, were examined along lines similar to those proposed by Wert and Zener. An equation which explicitly relates annealing time to the fraction transformed is derived. The possibility of change‐over from diffusion to interface control of the kinetics in ceramics through appropriate doping is suggested.
Comparison of Data for Thermal Diffusivity Obtained by Laser‐Flash Method Using Thermocouple and Photodetector
Authors: Lee Honc Lim , Hasselman D.P.H.
Published: June 2006

Thermal diffusivities of cordierite glass and glass‐ceramics measured by the laser‐flash method using remote optical sensing to monitor the transient temperature of the specimen were higher than those obtained with a thermocouple. The latter data were thought to be lower because of thermal contact resistance, the heat capacity of the cement used to adhere the thermocouple, and heat loss along the thermocouple wire. It is concluded that remote optical sensing yields more reliable data.
The Stability of Pore Channels: Experimental Observations
Authors: Drory Michael D. , Glaeser Andreas M.
Published: June 2006

Micrographic evidence is presented suggesting that perturbation phenomena of the type described by Rayleigh and others may play a role in the development of closed pores in powder compacts undergoing densification. Several difficulties in applying the thermodynamic and kinetic analyses based on cylindrical pore geometries are discussed.
Grain‐Growth Kinetics for Alumina in the Absence of a Liquid Phase
Authors: Bennison Stephen J. , Harmer Martin P.
Published: June 2006

The kinetics of grain growth in fully dense Al2O3 with and without MgO solute additions were measured for high‐purity samples containing no liquid phases. The MgO was found to suppress the grain‐boundary migration rate by a factor of 50. Compensating lattice defects are suggested to play a role in grain‐growth inhibition. Implications of these results to the sintering of Al2O3 are discussed.
Room‐Temperature Mechanical Behavior of Fiber‐Reinforced Ceramic‐Matrix Composites
Authors: Mah T. , Mendiratta M. G. , Katz A. P. , Ruh R. , Mazdiyasni K. S.
Published: June 2006

Ceramic‐matrix composites reinforced with SiC fibers were tested at room temperature both in, flexural and tensile configurations. The stress‐strain behavior for composites tested in tension was correlated with progressive microcracking and failure processes. Significant differences between failure modes in tension and flexure were observed.
Interaction of Silicon Nitride and Metal Surfaces
Authors: Tennenhouse Gerald J. , Ezis Andre , Runkle Frankling D.
Published: June 2006

An Mn‐Fe‐rich slag forms near the tips of Si3N4‐based indexible cutting tools during the machining of cast iron. Manganese and iron were found to react chemically with Si3N4 to form a liquid phase in the presence of air, but not in the absence of air, at temperatures comparable to those reached during machining operations. Thus, chemical reactions between Fe, Mn, Si3N4, and O2 may be a factor in the wear of Si3N4 tools against cast iron.
Tracer Diffusion and Electrical Conductivity in Sodium‐Rubidium Silicon Sulfide Glasses
Authors: THOMAS M. P. , PETERSON N. L. , HUTCHINSON E.
Published: June 2006

The tracer diffusion coefficients of 22Na and 86Rb and electrical conductivity were measured in a series of 0.56(Na, Rb)2S.0.44SiS2 glasses as a function of the Rb/Na ratio and temperature. The data were used to calculate the Haven ratio as a function of the Rb/Na ratio. The Haven ratio at 149.6°C increases from ∼0.3 in single‐alkali glasses to ∼0.80 for intermediate compositions. The results are consistent with a single jump mechanism involving jumps of alkali ions between unoccupied sites. The observed correlation effects arise through interactions between alkali ions and charge‐compensating centers in the glass network. The charge‐compensating centers are thought to correspond to non‐bridging oxygen ions in some oxide glasses and to nonbridging sulfur ions in sodium‐rubidium silicon sulfide glasses.
Mechanical Properties of Hot‐Pressed TiB2‐ZrO2 Composites
Authors: Watanahe Tadahiko , Shoubu Kazuhisa
Published: June 2006

The use of monoclinic ZrO2 as an additive improves the mechanical properties of TiB2‐based composites without the use of stabilizers. In particular, TiB2‐30% ZrO2 compacts exhibited a transverse rupture strength of 800 MN/m2, few pores, and a KIc of 5 MPa·m1/2. The high strength and toughness are thought to result mainly from the presence of partially stabilized tetragonal ZrO2 and from solid solution of (TiZr)B2 formed in sintering.
Effect of Heat Treatment on Fracture Toughness of Alumina‐Diamond Composites Sintered at High Pressures
Authors: Noma Tatsuo , Sawaoka Akira
Published: June 2006

Alumina composites containing dispersed diamond particles were fabricated under very high pressure at a temperature where diamond is stable. Subsequent heat treatment in vacuum improves the toughness of the 5 vol% composite but not that of the 10 vol% composite. The heat treatment time was varied for both composites, and the influence of graphitization and morphology of the second‐phase particles on toughness were studied.
Phase Equilibrium in the System LiAlSiO4‐NaAlSiO4‐SiO2
Authors: Badger William B. , Hummel Floyd A.
Published: June 2006

The existence of eucryptite, spodumene, carnegieite, nepheline, and albite is very well known. To establish the phase diagram of the system LiAlSiO4‐NaAlSiO4‐SiO2, high‐SiO2 equilibria and the sections LiAlSi2O6‐NaAlSi3O8, LiAlSi2O6‐NaAlSiO4, LiAlSiO4‐NaAlSiO4, and LiAlSiO4‐NaAlSi3O8were examined. The joins LiAlSi2O6‐NaAlSi3O8, LiAlSi2O6‐NaAlSiO4, and LiAlSiO4‐NaAlSiO4 were established down to 800°C at atmospheric pressure.
Palmqvist Crack Extension and the Center‐Loaded Penny Crack Analogy
Authors: Laugier Michael T.
Published: June 2006

Palmqvist crack extension in WC‐Co can be described using the center‐loaded penny crack analogy. When Palmqvist cracks are represented by semicircles of diameter l (l=crack length measured from an impression corner), the stress intensity factor which controls crack extension differs from that of a half‐penny crack of radius l+a (2a = impression size) by only a slowly varying factor m=21/2 (l/a)1/2; m≅1.0 to 2.4 for WC‐Co and m≅0.8 to 1.4 for ceramics.
Oxygen Self‐Diffusion in Single‐Crystal Mn‐Zn Ferrite
Authors: Haneda Hajime , Yamamura Hiroshi , Watanabe Akio , Shirasaki Shin‐Ichi
Published: June 2006

Self‐diffusion coefficients for the oxygen ion in single‐crystal Mn‐Zn ferrite were determined by the gas‐solid isotope exchange technique. The oxygen volume diffusion coefficients can be expressed as D =6.70 × 10−4 exp (‐330 (kJ /mol) /RT)m2/s (>1350°C), D=3.94 × 10−10 exp (−137 (kJ/mol)/RT)m2/s (1100° to 1350°C), and D=7.82 × 104 exp (−507 (kJ/mol)/RT)m2/s (<1100°C).
Stress Rate and Proof‐Testing of Silicon Wafers
Authors: Chen C. P. , Leipold M. H.
Published: June 2006

Fracture mechanics test methods were applied to evaluate the proof‐test characteristics of single‐crystal silicon wafers. The results indicate that the strength distribution of silicon wafers is truncated by proof‐testing. No subcritical crack growth occurred during proof‐loading, as inferred from the lack of a stress‐rate effect on strength. Mechanical proof‐testing appears to be an effective method for eliminating weak samples before cell processing.
High‐Temperature Strength and Fracture Toughness of Y2O3‐Partially‐Stabilized ZrO2/Al2O3 Composites
Authors: Tsukuma Koji , Ueda Kuniyoshi , Matsushita Kenichi , Shimada Masahiko
Published: June 2006

The temperature dependence of bending strength, fracture toughness, and Young's modulus of composite materials fabricated in the ZrO2 (Y2O3)‐Al2O3 system were examined. The addition of A1203 enhanced the high‐temperature strength. Isostatically hot‐pressed, 60 wt% ZrO2 (2 mol% Y2O3)/40 wt% Al2O3 exhibited an extremely high strength, 1000 MPa, at 1000°C.