bluuebunny/crossref_metadata_2025 huggingface dataset:
Noble Metal and Spinel Deposition on the Floor of the Joule‐Heated Ceramic Melter
Authors: Jain Vijay , Barnes Steven M. , Vethanayagam Thirukumar K. , Pye L. David
Published: March 2005

At the West Valley Demonstration Project (WVDP), the slurry‐fed ceramic melter (SFCM) was in test operation from December 1984 to December 1989 to vitrify simulated nuclear waste slurries. In this study, deposition of insolubles and crystallized species on the SFCM floor during the vitrification process were analyzed. The results indicate that the thickness of the sludge layer on the floor of the SFCM was not more than 6 cm deep and consisted mostly of Fe‐Cr spinels, and RuO2 dispersed in a glassy borosilicate matrix. Also, crystalline Ce2O3 and undissolved phases consisting primarily of alumina and chromia were present in trace amounts but were inhomogeneously distributed in the glassy matrix on the SFCM floor. Greater than 87% of the RuO2 fed to the melter was flushed out with normal glass pouring.
Creep‐Crack Growth by Damage Accumulation in a Glass‐Ceramic
Authors: Chan Kwai S. , Page Richard A.
Published: March 2005

The growth rate, near‐tip creep response, and damage processes of creep cracks in a pyroceram glass‐ceramic were studied under tensile loading at elevated temperatures. The rates of crack extension were characterized as a function of the applied stress intensity factor. The damage processes which occurred near the crack tip and led to creep crack extension were identified using a replica technique and by direct observations in a scanning electron microscope equipped with a high‐temperature loading stage. The accumulated creep strains near the crack tip were measured via the stereoimaging technique. The results indicate that creep‐crack growth in the pyroceram glass‐ceramic occurs in both continuous and discontinuous manners, with the damage processes manifested as the nucleation, growth, and coalescence of inhomogeneously distributed cavities and microcracks. Measurements of the total accumulated creep strain near the crack tip suggest that crack extension follows a critical strain criterion. Both the microcrack density and the total accumulated creep strain show similar dependence with distance from the crack tip. These observations suggest that damage accumulation and crack extension in the glass‐ceramic are controlled by the near‐tip creep rates.
Microstructural Characterization of Ferroelectric Thin Films in Transverse Section
Authors: Reaney Ian M. , Barber David J.
Published: March 2005

A technique has been developed for the TEM examination of ferroelectric thin films in transverse section. Some preliminary results are reported for three different thin‐film/substrate systems. The microstructures of thin films of lead scandium tantalate deposited onto sapphire and MgO, and lead titanate deposited onto AIN, have been examined, with particular attention being paid to the quality of the thin‐film/substrate interfaces and to the changes in the nature of the microstructures of the thin films as a function of distance from their substrates. It is demonstrated that the technique successfully produces adequate electron transparent regions for the characterization of the thin‐film/substrate interface of all the samples examined and that it is possible to prepare transverse sections of ferroelectric thin films routinely.
Effect of Annealing on the Surface Microstructure of Y‐Ba‐Cu‐O Superconducting Ceramics
Authors: Sinn Dong‐Sook , Kim Moon G.
Published: March 2005

Precusors to the YBa2Cu3O7‐δ material were prepared by both the oxalate precipitation method and conventional ceramic processing. Second‐phase grains were observed to develop on the exposed fracture surface during annealing at 500° to 600°C in an ambient atmosphere. The second‐phase grains were identified to be BaCO3 using EDX and XRD. The liquid phase, which was formed because of local chemical inhomogeneity in the Y‐Ba‐Cu‐O system, contributed to the formation of second‐phase grains as a source of Ba.
Thermooptic Coefficients of Some Standard Reference Material Glasses
Authors: Jewell John M.
Published: March 2005

The thermooptic coefficients, i.e., the change in refractive index with temperature (dn/dT), of four National Institute of Standards and Technology standard reference material (SRM) glasses have been measured over the range of 25° to 125°C. The thermooptic coefficients of all four glasses, NBS‐710 (a soda‐lime silicate), SRM‐711 (a lead silicate), SRM‐717 (a borosilicate), and SRM‐739 (silica) are positive and range in value from 2 × 10−6/K to 9.8 × 10−6/K. The differences in the dn/dT of these glasses arise from differences in the coefficient of thermal expansion and the temperature coefficient of the electronic polarizability.
Charge‐Up Scanning Electron Microscopy Images of Intergranular Phases in Semiconducting BaTiO3 Positive Temperature Coefficient of Resistivity Ceramics
Authors: Nemoto Hiroshi
Published: March 2005

A charge‐up image was observed in the intergranular phases of semiconducting BaTiO3 positive temperature coefficient of resistivity (PTCR) ceramics when the ceramic specimens were heated to the Curie temperature in a scanning electron microscope. Experiments showed that this image was caused by intense secondary electron emission localized in the phases. This charge‐up state seemed to be closely related to the PTCR mechanism.
Grain Growth in Superplastically Deformed Zinc Sulfide/Diamond Composites
Authors: Xue Liang A. , Raj Rishi
Published: March 2005

Grain growth in superplastically deformed ZnS/diamond composites was much greater than in undeformed specimens exposed to the same time and temperature. The extent of grain growth depended on the volume fraction of diamond particles. Grain growth was suppressed by the addition of 10 wt% diamond particles in superplastically deformed specimens. In static annealing, however, only 1 wt% diamond particles were enough to supress grain growth, which is a factor of 10 smaller than estimated by the Zener condition.
Thermal Shock Behavior of Duplex Ceramics
Authors: Lutz Ekkehard H. , Swain Michael V. , Claussen Nils
Published: March 2005

The thermal‐stress fracture behavior of duplex ceramics is investigated by quenching in water and in oil. Comparison with the matrix materials shows that the critical quenching temperature difference, ΔTc, is not or is only slightly reduced, even for duplex ceramics of significantly reduced strength. In sintered composites, thermal‐stress‐induced microcracking within pressure zones and crack initiation at pressure zone–matrix interfacial defects develop before ΔTc is reached. The effects are accompanied by a gradual reduction in strength. At ΔTc, critical crack propagation occurs. The retained strength after thermal shock of duplex ceramics is significantly improved compared with the respective matrix materials. This behavior can be related reasonably well with the KR‐curve behavior.
Ionic Double Layers at the Surface of Magnesium‐Doped Aluminum Oxide: Effect on Segregation Properties
Authors: Mukhopadhyay Sharmila M. , Blakely Jack M.
Published: March 2005

A model involving ionic double layers at the surface has been constructed for magnesia‐doped sapphire based on earlier models which were developed for cubic halides. The model takes into account the presence of electrostatic potentials, isolated point defects, defect complexes, and special surface sites which can act as sources and sinks for ions. Equations have been set up for the various defect concentrations, and Poisson's equation has been solved numerically to give depth profiles for defects and corresponding electric fields. The calculations suggest that Mg2+ ions can segregate both to the free surface and to the space charge region. The effective (or Langmuir) enthalpy of segregation depends not only on the actual binding energies of the dopant ion, but also on other parameters such as the density of special surface sites. Over the temperature range studied, the variation of the calculated surface magnesium concentration with temperature is found to be approximately Arrhenius in nature, as was observed in segregation experiments.
Synthesis of Potassium Niobate from Metal Alkoxides
Authors: Amini Mostafa M. , Sacks Michael D.
Published: March 2005

Preparation of potassium niobate from metal alkoxides was investigated. Potassium‐niobium ethoxide, KNb(OC2H5)6, and potassium‐niobium propoxide, KNb(OC3H7)6, were synthesized and subsequently hydrolyzed using several water concentrations (0.75 to 6.0 mol of water/(mol of alkoxide)). Rapid precipitation of potassium‐deficient particles occurred when higher concentrations of water were used. This resulted in the formation of a multiphase material after calcination, as X‐ray diffraction showed the presence of both KNbO3 and potassium‐deficient oxide phases(s). Single‐phase KNbO3 could be prepared by two methods: (1) hydrolysis of KNb(OC3H7)6/propanol solutions using 1 mol of water (per mole of propoxide) added as a water/propanol solution and (2) hydrolysis of KNb(OC2H5)6/ethanol solutions using 1 mol of water (per mole of ethoxide) added as a water/methanol solution. The latter method provided advantages of low calcination temperature for the formation of single‐phase KNbO3 and low weight loss after calcination.
Preparation of PbZrO3–PbTiO3 Ferroelectric Thin Films by the Sol–Gel Process
Authors: Tohge Noboru , Takahashi Satoshi , Minami Tsutomu
Published: March 2005

Ferroelectric films, PbZrxTi1−xO3 (x= 0 to 0.6), have been prepared from corresponding metal alkoxides partially stabilized with acetylacetone through the sol‐gel process. The films dip‐coated in an ambient atmosphere were heat‐treated at 400°C for decomposition of residual organics and then at temperatures between 500° and 700°C for crystallization of the films. The perovskite phase precipitated at temperatures above 560°C, accompanied by an increase in dielectric constant. The dielectric constant of the films, which was comparable with that of sintered bodies, showed a maximum (∼620) at around x= 0.52 in PbZrxTi1−xO3. These films showed D–E hysteresis, with slightly higher values of coercive field, compared with those of sintered bodies.
Effect of Interparticle Potentials and Sedimentation on Particle Packing Density of Bimodal Particle Distributions During Pressure Filtration
Authors: Velamakanni Bhaskar V. , Lange Fred F.
Published: March 2005

Effect of interparticle forces, bimodal particle size distribution, and slurry viscosity on particle packing in alumina bodies consolidated by pressure filtration is presented. The requirements for packing colloidal particles to their highest density are strong repulsive interparticle forces and optimum particle size distribution. Even though these conditions are met, the high packing density in consolidated bodies may be adversely affected by particle segregation resulting from sedimentation. Therefore, the slurry during consolidation must have a sufficiently high viscosity to prevent sedimentation.
High‐Toughness Ce‐TZP/Al2O3 Ceramics with Improved Hardness and Strength
Authors: Cutler Raymond A. , Mayhew Robert J. , Prettyman Kevin M. , Virkar Anil V.
Published: March 2005

Simulataneous additions of SrO and Al2O3 to ZrO2 (12 mol% CeO2) lead to the in situ formation of strontium aluminate (SrO · 6Al2O3) platelets (∼0.5 μm in width and 5 to 10 μm in length) within the Ce‐TZP matrix. These platelet‐containing Ce‐TZP ceramics have the strength (500 to 700 MPa) and hardness (13 to 14 GPa) of Ce‐TZP/Al2O3 while maintaining the high toughness (14 to 15 MPa ± m1/2) of Ce‐TZP. Optimum room‐temperature properties are obtained at SrO/Al2O3 molar ratios between 0.025 and 0.1 for ZrO2 (12 mol% CeO2) with starting Al2O3 contents ranging between 15 and 60 vol%. The role of various toughening mechanisms is discussed for these composite ceramics.
Crack‐Bridging Analysis for Alumina Ceramics under Monotonic and Cyclic Loading
Authors: Hu Xiaozhi , Mai Yiu‐Wing
Published: March 2005

Frictional degradation of grain‐localized bridges behind a crack tip has been recognized as the major cyclic fatigue mechanism in alumina ceramics. Such a fatigue mechanism implies that the crack growth resistance (R) curve behavior during cyclic fatigue is different from that of monotonic loading due to the reduction in crack‐tip shielding. A recent crack‐bridging theory based on crack compliances is used to study the bridging stresses under monotonic loading and during cyclic fatigue. The bridging‐stress distributions of two coarse‐grained aluminas under monotonic loading are determined using compliance measurements. Because the interlocking grain bridges at the crack wake are subject to frictional damage from cyclic loading, the bridging‐stress distribution evaluated during cyclic fatigue is distinct from that for monotonic loading. These results indicate that it is incorrect to incorporate the R‐curve behavior from monotonic loading to the analysis of cyclic fatigue of alumina ceramics.
TEM of Dislocations in AIN
Authors: Seifert Andreas , Berger Axel , Müller Wolfgang Friedrich
Published: March 2005

Sintered AIN specimens were deformed by Vickers hardness (HV) indentations. Compared with Al2O3 the HV hardness values indicate a much higher plasticity of AIN at room temperature, but above 600°C a higher ductility for Al2O3. Deformed AIN specimens were examined by transmission electron microscopy. Basal and prismatic glide with the slip systems (0001) 〈1120〉 and {1100}〈1120〉 were frequently observed. This results in four linearly independent slip systems. The critical resolved shear stress for single prismatic slip seems to be even smaller than for basal slip. However, thermally activated dislocation reactions are frozen up to at least 1000°C. Thus, prismatic slip is suppressed as soon as more than one slip direction is activated.
Edge‐Crack Resistance Curves in Supercritical Ceramics
Authors: Stump David M.
Published: March 2005

The growth of edge cracks in zirconia‐reinforced ceramics is analyzed theoretically with the „supercritical” transformation model. The injection of an initial edge crack by a damage process is modeled in an approximate manner. Subsequent crack growth under the application of a remote tensiles stress models the evolution of the transformed region as the crack advances. For the range of initial crack sizes considered, „nominal” resistance curves depend strongly on a transformation‐toughening parameter. The analysis may have a bearing on the indentation/bend method of testing fracture toughnesses.
Combustion Synthesis of Metal Chromite Powders
Authors: Manoharan S. Sundar , Patil Kashinath C.
Published: March 2005

Fine‐particle metal chromites (MCr2O4, where M = Mg, Ca, Mn, Fe, Co, Ni, Cu, and Zn) have been prepared by the combustion of aqueous solutions containing the respective metal nitrate, chromium(III) nitrate, and urea in stoichiometric amounts. The mixtures, when rapidly heated to 350°C, ignite and yield voluminous chromites with surface areas ranging from 5 to 25 m2/g. MgCr2O4, sintered in air at 1500°C for 5 h, has a density of 4.0 g/cm3.
Stability of CaNiSi2O6 (“Niopside”) and Activity–Composition Relations of CaMgSi2O6– CaNiSi2O6 Solid Solutions at 1350°C
Authors: Pretorius Eugene B. , Muan Arnulf
Published: March 2005

A complete solid‐solution series exists between diopside (CaMgSi2O6) and its nickel analogue, “niopside”(CaNiSi2O6). Activity–composition relations within this solid solution, and the stability of the end member CaNiSi2O6, have been determined by equilibrating CaNiSi2O6 with SiO2, CaSiO3, and metallic Ni in atmospheres of known oxygen pressures. Within limits of accuracy of the experiments, the solution is ideal at 1350°C. From the experimental data obtained in the present investigation, the standard free energy (ΔG°) of formation of CaNiSi2O6 according to the equation CaO + NiO + 2SiO2= CaNiSi2O6 is calculated to be ΔG°=−165862 + 42.40T J. Experiments in the system CaO–NiO–SiO2 have shown that the nickel analogue of the phase pseudo‐enstatite (MgSiO3) is unstable with respect to SiO2 and nickel olivine (Ni2SiO4), and the nickel analogues of the phases akermanite (Ca2MgSi2O7) and monticellite (CaMgSiO4) are unstable relative to the phase assemblage pseudo‐wollastonite (CaSiO3) plus NiO. In the system CaO–MgO–NiO–SiO2, however, substitution of Ni for Mg in these phases was observed. The percentage substitution of Ni for Mg in the phases is given in parentheses: diopside (100%), olivine (100%), enstatite (18%), akermanite (20%), and monticellite (57%).
Estimation of Crack Closure Stresses for In Situ Toughened Silicon Nitride with 8 wt% Scandia
Authors: Choi Sung R. , Salem Jonathan A. , Sanders William A.
Published: March 2005

An 8‐wt%‐scandia silicon nitride with an elongated grain structure was fabricated. The material exhibited high fracture toughness (∼ 7 MPa · m1/2) and a rising R‐curve as measured by the indentation strength technique. The “toughening” exponent m was found to be m∼ 0.1. The high fracture toughness and R ‐curve behavior was attributed mainly to bridging of the crack faces by the elongated grains. The crack closure (bridging) stress distribution in the wake region of the crack tip was estimated as afunction of crack size from the R‐curve data, with an arbitrarily assumed distribution function.
Fatigue of Ferroelectric Polarization and the Electric Field Induced Strain in Lead Lanthanum Zirconate Titanate Ceramics
Authors: Pan Wuyi , Yue Cheng‐Feng , Tosyali Ogus
Published: March 2005

Fatigue of ferroelectric polarization and the electric field induced strain is investigated in lead lanthanum zirconate titanate ceramics. Fatigue rate increases as the coercive field or the hysteretic nature of the electric field induced polarization of the ferroelectric ceramics increases. The ferroelectric polarization lost during fatigue can be partly restored by decreasing the frequency and increasing the amplitude of the applied ac electric field. The ferroelectric fatigue is modeled phenomenologically by an increase of the energy barrier for the ferroelectric switching and atomistically by a coupling of the spontaneous polarization with defects and/or space charge in the orientation of ferroelectric fatigue.
Foaming in Glass Melts Produced by Sodium Sulfate Decomposition under Ramp Heating Conditions
Authors: Kim Dong‐Sang , Hrma Pavel
Published: March 2005

Ramp heating a glass batch with sulfate permits determination of the foaming temperature and maximum foam height as a function of sulfate addition. Experiments revealed that, in the soda–lime glass studied, foam was produced when the mass fraction of SO3 in the glass was higher than 0.0027. With increasing sulfate content, the foaming temperature decreased and the maximum foam height increased until the mass fraction of SO3 was 0.01. Further additions of sulfate had little effect on foaming temperature and decreased maximum foam height. The results are discussed in terms of sulfate solubility and nonequilibrium effects.
Flow Mechanics on Extrusion through a Square‐Entry Die
Authors: Zheng Jingmin , Carlson William B. , Reed James S.
Published: March 2005

The relationships between the constants of the Herschel‐Bulkley (H‐B) equation describing plastic flow and the Benbow equation for extrusion through a square‐entry die were studied via computer simultions. These relationships are fundamental for characterizing the rheology of ceramic extrudates using the square‐entry rheometer and are difficult to obtain from experiments. Results showed that the apparent shear rate should be used instead of extrudate velocity in the Benbow equation, and the Benbow equation was modified accordingly. The exponent in the H‐B equation was exactly the same as the shear thinning exponent for the extrudate body in the modified Benbow equation. The die‐entry velocity factor was a function not only of the shear rate factor but also of the shear thinning exponent in the H‐B equation. The yield strength of the modified Benbow equation was zero when the yield strength in the H‐B equation was zero.
Thermodynamic Calculation of the Zirconia–Calcia System
Authors: Du Yong , Jin Zhanpeng , Huang Peiyun
Published: March 2005

An optimal thermodynamic data set for the zirconia–calcia system is evaluated by the CALPHAD (CALculation of PHAse Diagrams) method applied to experimental phase diagram and thermodynamic data. The liquid and Css (cubic ZrO2 solid solution) are described by a subregular solution model. Three compounds, CaZr4O9, Ca6Zr19O44, and CaZrO3, are modeled as stoichiometric compounds. A regular solution model is applied to the other phases. Comparisons between calculated and measured phase diagrams and thermodynamic quantities show that most of experimental information is satisfactorily accounted for by thermodynamic calculations. The calculations also reasonably predict the measured electromotive force concerning the metastable Css.
Wetting and Interfacial Bonding of Metals with Ionocovalent Oxides
Authors: Li Jian‐Guo
Published: March 2005

The adhesion and interfacial bonding between nonreactive liquid metals and solid inocovalent oxides are studied on the basis of the experimental work of adhesion W data. An analysis of the experimental W values of different liquid metals on various solid oxides is first performed to put into evidence the dependences of the work of adhesion of a metal/oxide system on the electron density of the metal and on the thermodynamic stability of the oxide. An electronic model is then proposed to describe the microscopic mechanism of metal–oxide interactions. Based on the model, the work of adhesion and the contact angle of different liquid metals on various solid oxides can be interpreted and estimated, and their correlations to the various physical properties of the oxides can be easily deduced. The basic consideration of the model is that the adhesion between a metal and an oxide is assured by the electron transfer from the metal into the oxide valence band which is not completely filled with electrons at high temperatures, and is enhanced when this electron transfer at the metal/oxide interface is increased. The extension and application of the model to solid metal/solid oxide systems is also presented.
Study of Electrical Conduction Behavior of the System La1−xNaxCo1−xNbxO3 (x 0.50)
Authors: Parkash Om , Tewari Hari S. , Tare Vasudeo B. , Kumar Devendra , Pandey Lakshman
Published: March 2005

Electrical behavior of a few compositions with x 0.50 in the system La1−xNaxCo1−xNbxO3 has been studied by complex‐plane‐impedance analysis in the temperature range 300–525 K. Three depressed semicircular arcs have been observed in the complex impedance plot of the composition with x= 0.50. These arcs represent the contributions of bulk, grain boundaries, and electrode polarization to the total observed resistance. Two semicircular arcs have been observed in the complex‐impedance plot of the compositions with x= 0.70 and 0.80. They represent the bulk and the grain boundaries contribution to the total observed resistance. The values of the resistance for the bulk and grain boundaries in each sample indicate the formation of barrier layers in these materials.
Cyclic Compaction of Ceramic Powders
Authors: Kim Kitae T. , Son Geonseog
Published: March 2005

Cyclic compaction is shown to be more efficient than single‐stroke and static compaction. The application of a bias pressure during cyclic compaction decreases the degree of powder compaction. A densification equation, based on the Cooper and Eaton compaction equation, is proposed to describe the cycle‐dependent pressure–volume fraction relation for ceramic powder compaction. Data from cyclic compaction of alumina powder are well represented by the proposed equation.
Activation of Ground Blast‐Furnace Slag by Alkali‐Metal and Alkaline‐Earth Hydroxides
Authors: Roy Amitava , Schilling Paul J. , Eaton Harvill C. , Malone Philip G. , Brabston W. Newell , Wakeley Lillian D.
Published: March 2005

The effects of pH, time, valence, and radius of the activator cation on the reaction products and microstructure of ground granulated iron blast‐furnace slag were studied by thermogravimetry and derivative thermogravimetry, X‐ray diffractometry, scanning electron microscopy, and energy dispersive X‐ray microanalysis. Blast‐furnace slag was activated by alkali‐metal hydroxides of Li, Na, and K (12.34 pH 14.71) and alkaline‐earth hydroxides of Ca, Sr, and Ba(12.47 pH 13.53) using a water/slag ratio of 0.4 and curing for 1 day to 26 months. Reactivity of the slag was more strongly dependent on pH than on time. The reaction products were mainly varieties of C─S─H, (C,M)4AH13, and minor amounts of Ca(OH)2 and C2ASH8 (strätlingite). The nature of C─S─H was dependent on pH. A 1.2‐nm peak appeared in X‐ray diffractograms only when the activation pH was ⌣14.7. Water was present in the C─S─H in a way similar to water in tobermorite and synthetic C─S─H. Leached Ca from unreacted blast‐furnace slag was present around the glass particles as an amorphous layer which crystallized into Ca(OH)2 with time; Mg behaved similarly. The effect of the charge or ionic radius of the activator cation was insignificant.
{0001}<1010> Slip and Basal Twinning in Sapphire Single Crystals Shock‐Loaded at Room Temperature
Authors: Wang Yucong , Mikkola Donald E.
Published: March 2005

The microstructures of sapphire single crystals explosively shocked at pressures of 5, 12, and 23 GPa, with the basal plane perpendicular to the shock wave direction, have been studied using transmission electron microscopy. There was no evidence of microplastic deformation, dislocations or twins, for crystals shocked at 5 GPa. Perfect dislocations with 1010 and ⅓1120 Burgers vectors on the basal planes were observed at the higher pressures. The gliding of 1010 dislocations on the basal plane established the activation of {0001}1010 slip, which has not been experimentally verified previously. In addition to dislocation generation and motion, a significant number of basal twins were observed.
Thermally Induced Failure of Copper‐Bonded Alumina Substrates for Electronic Packaging
Authors: Yoshino Yuichi , Ohtsu Hidehiko , Shibata Takashi
Published: March 2005

Although copper‐bonded alumina substrate has been used for some power electronic devices, its use has been rather limited because of lack of information on the thermally induced failure of the substrate. The phenomenology of thermal cracking was experimentally studied in this work. Interface debonding occurred at the side edge of copper chips and grew inwardly along the interface. Subsequently, the interface crack deviated into the alumina after propagating up to approximately 200 μm. The curving of the interface crack was caused by a mixed Mode I and Mode II loading near the edge. The cracking was widespread, whereby small cracks coalesced with one another to form a long, shallow crack along the perimeter of the copper chips. The cracking sensitivity was influenced by such design factors as edge sharpness, nickel plating, and copper backing. Annealing the substrate above 700 K before testing promoted the cracking considerably. The substrate cracking is discussed in terms of stress conditions near the edge.
Influence of Fiber Roughness on the Sliding Behavior of Sapphire Fibers in TiAl and Glass Matrices
Authors: Mackin Thomas J. , Yang Jingyu , Warren Paul D.
Published: March 2005

Push‐out experiments on sapphire fibers in both glass and γ‐TiAl matrices show a sinusoidal modulation in the load–displacement trace that is identical in wavelength to the surface roughness of the sapphire fibers. A model, presented in a previous paper, is used to describe the push‐out behavior, and is shown to agree with experiment. The results quantitatively validate the key role of fiber surface roughness during fiber sliding.
Effect of Copper Additive on the Microstructure and Electrical Properties of Polycrystalline Zinc Oxide
Authors: Chiou Bi‐Shiou , Chung Ming‐Chih
Published: March 2005

Nonohmic behavior is obtained for polycrystalline ZnO with copper as the only additive in the range 0.3 x 1 wt%. The effect of copper on the microstructure and electrical behavior of ZnO:Cu ceramics is investigated. The leakage current decreases and the breakdown electric field increases as the copper concentration increases. The large apparent dielectric constant of ZnO:Cu ceramic (k > > kZnO, kZnO is the dielectric constant of pure ZnO) is attributed to the grain boundary barrier layer effect. A Schottky barrier height of 0.27–0.46 eV is obtained for various copper‐added samples, depending on sintering temperatures.
Gas Pressure and Temperature Dependences of Thermal Conductivity of Porous Ceramic Materials: Part 1, Refractories and Ceramics with Porosity below 30%
Authors: Litovsky Efim Ya. , Shapiro Michael
Published: March 2005

A review of experimental results and theoretical models for thermal conductivities of ceramic materials with porosity less than 30% is given. It is shown that the abnormal non‐monotonic pressure and temperature dependences of thermal conductivity arise from the effects of microcracks and porous grain boundaries, characterizing many industrial refractories, and from the competitive influences of classical and novel mechanisms of heat transfer in composite multiphase materials. The latter mechanisms include segregation and surface diffusion of impurities and defects in crystal structure, and the mechanism arising from chemical conversion and gas emission, occurring within pores of ceramic materials. A fractal model of porous materials' structure is proposed and used for analysis, explanation, and classification of thermophysical properties of ceramic materials measured in various thermodynamic conditions.
Preparation of KTaO3 and KNbO3 Solid Solutions through Sol–Gel Processing
Authors: Nazeri Azar , Kahn Manfred
Published: March 2005

Potassium tantalate–niobate solid‐solution (KTN) powders and thin films were prepared from metallo–organic compounds through sol–gel processing. The KTN precursors were chemically modified and then prehydrolyzed with various concentrations of water. The stability of the modified solutions and the effects of prehydrolysis on the crystallization are discussed. Powder gels were obtained by exposing the solution to the atmospheric water, hydrolyzing the solutions. Alternatively, thin films were deposited on fused silica, silicon, sapphire, MgO, and SrTiO3, using the spinning technique. The pyrolysis and crystallization of KTN powders and films were investigated by differential thermal analysis, theromogravimetric analysis, and X‐ray diffraction. The effects of substrate and other processing parameteres on the crystal structure of the KTN phases were also investigated. KTN powders crystallized into a perovskite phase regardless of the processing conditions. The crystal structure of the KTN thin films had a strong dependency on the crystal structure of the substrates, while other processing parameters played smaller roles. Pyrochlore KTN was the major phase that crystallized on fused silica and silicon, whereas oriented perovskite KTN was obtained on single‐crystal MgO and SrTiO3.
Thermal Expansion of Homogeneous and Gradient Solid Solutions in the System KZr2(PO4)3─KTi2(PO4)3
Authors: Yamai Iwao , Ota Toshitaka
Published: March 2005

Low‐thermal‐expansion ceramics having arbitrary thermal expansion coefficients were synthesized from homogeneous solid solutions in the system KZr2(PO4)3─KTi2(PO4)3 (KZP–KTP). Dense and strong ceramics were fabricated by sintering at 1100° to 1200°C with 2 wt% MgO. The thermal expansion coefficient increased from 0 to +3 × 10−6/°C with increasing x in KZr2 − xTix (PO4)3 (KZTP). In addition, a functionally gradient material with respect to thermal expansion was prepared by forming a series of KZTP solid solutions in a single ceramic body. By heating a pile of KZP and KTP ceramics in contact with each other, KZP and KTP bonded together to form a KZTP gradient solid solution near the interface.
X‐RAY DETERMINATION OF THE STRUCTURE OF GLASS *
Authors: Warren B. E.
Published: March 2005

A method has been developed for analyzing the X‐ray diffraction patterns of amorphous solids, and the atomic arrangement in two simple glasses has been completely worked out. In SiO2, for example, each silicon is tetrahedrally surrounded by 4 oxygens at a distance 1.60 Å, and each oxygen is shared between two such tetrahedral groups. The mutual orientation of the two groups about their common direction of bonding is random, and hence it is a random three‐dimensional network which is built up. The configuration does not repeat at regular intervals and hence is noncrystalline; it is this feature which distinguishes the glassy state from the crystalline.
Joining of Silicon Carbide/Silicon Carbide Composites and Dense Silicon Carbide Using Combustion Reactions in the Titanium–Carbon–Nickel System
Authors: Rabin Barry H.
Published: March 2005

A new ceramic joining technique has been developed that utilizes an exothermic combustion reaction to simultaneously synthesize the joint interlayer material and to bond together the ceramic workpieces. The method has been used to join SiC/SiC composites and dense SiC ceramics using TiC‐Ni powder mixtures that ignite below 1200°C to form a TiC‐Ni joining material. Thin layers of the powder reactants were prepared by tape casting, and joining was accomplished by heating in a hot‐press to ignite the combustion reaction. During this process, localized exothermic heating of the joint region resulted in chemical interaction at the interface between the TiC‐Ni and the SiC ceramic that contributed to bonding. Room‐temperature four‐point bending strengths of joints produced by this method have exceeded 100 MPa.
Temperature Profile Analysis in Combustion Synthesis: I, Theory and Background
Authors: Dunmead Stephen D. , Munir Zuhair A. , Holt J. Birch
Published: March 2005

An analysis of the use of temperature profiles in the determination of the kinetic parameters of self‐sustaining combustion synthesis is provided. Two mathematical approaches are discussed. In the first approach, the analysis focuses on the initial portion of the temperature profile and thus emphasizes the kinetics of the initial stages (η≲ 1.0) of this process. The second approach emphasizes both the initial and final stages of the process (η∼ 1.0). With the simultaneous measurements of the velocity of the combustion wave, temperature profile analysis provides values for the effective thermal diffusivity of the reactants.
Temperature Profile Analysis in Combustion Synthesis: II, Experimental Observations
Authors: Dunmead Stephen D. , Munir Zuhair A. , Holt J. Birch
Published: March 2005

The temperature profiles associated with the passing of a self‐propagating wave in the combustion synthesis of zirconium boride were investigated. The use of these profiles in the determination of the kinetics of the associated synthesis reaction was investigated. From profile analysis an activation energy of 144.5 ± 15 kJ · mol−1 was calculated and was found to agree very well with the corresponding value obtained from wave velocity measurements, 148.6 ± 12 kJ · mol−1. From these analyses, the thermal diffusivity of the reactants was also calculated. The thermal diffusivity decreased slightly with increasing combustion temperature, with the values ranging from 2.10 × 10−3 to 1.79 × 10−3 over the range of 2609 to 2909 K, respectively.
Controlled Crack Growth Specimen for Brittle Systems
Authors: Calomino Anthony M. , Brewer David N.
Published: March 2005

A pure Mode I fracture specimen and test procedure has been developed which provides extended, stable, through‐thickness crack growth in ceramics and other brittle, nonmetallic materials. Fixed displacement loading, applied at the crack mouth, promotes stable crack extension by reducing the stored elastic strain energy. Extremely fine control of applied displacements is achieved by utilizing the Poisson expansion of a compressively loaded cylindrical pin. Stable cracks have been successfully grown in soda‐lime glass and monolithic Al2O3 for lengths in excess of 20 mm without uncontrollable catastrophic failure.
Hall Effect and Charge Carrier Generation in Y1Ba2Cu3Ox
Authors: Yoo Han‐Ill , Choi Hyun‐Suk
Published: March 2005

The Hall coefficient, and hence the charge carrier density, of the system of Y1Ba2Cu3Ox was measured at room temperature as a function of oxygen content, x, in its entire homogeneity range (6 < x < 7). The cuprate is essentially of the p‐type (σp/σn > 70) and of extrinsic origin for x > ∼6.37, below which the electron contribution grows appreciably, and hole generation mechanisms differ depending on crystal structure: one hole is generated for every oxygen atom added in the orthorhombic structure (x > ∼6.5) and for every two oxygen atoms added in the tetragonal structure (x < ∼6.5). The redox reactions, 1/2O2(g) = Oi′+ h. and O2(g) = (Oi,Oi)′+ h., respectively, are proposed as responsible for the hole generation, and their equilibrium constants are evaluated with the reaction enthalpies of 0.75 ± 0.05 and 2.7 ± 0.2 eV, respectively. Based on these data, predictions about such properties as the oxygen potential dependences of isothermal conductivity are compared with reported results, and the numerical values for hole mobility are extracted. Other proposed redox reactions are discussed in light of the present findings.
Damage and Failure in Unidirectional Ceramic–Matrix Composites
Authors: Beyerle Douglas S. , Spearing S. M. , Zok Frank W. , Evans Anthony G.
Published: March 2005

A study of the mechanical characteristics of a unidirectional fiber–reinforced calcium aluminosilicate matrix composite has been conducted. The properties have been related to the individual properties of the matrix, the fibers, and the interfaces, as well as the residual stress, using available models of matrix cracking and fiber fracture. Comparisons have been made with lithium aluminosilicate matrix composites. Predictions of initial matrix cracking and of ultimate strength using the models are found to correlate well with the measured values. However, deficiencies have been noted in the ability of the models to predict the evolution of matrix cracks, plus associated changes in the modulus.
Ceramic Grinding Temperatures
Authors: Hebber Rajadasa R. , Chandrasekaar Srinivasan , Farris Thomas N.
Published: March 2005

Workpiece and abrasive‐tip temperatures are measured during the grinding of silicon nitride, zirconia, sapphire, and Ni‐Zn ferrite with diamond abrasives. The measurements are carried out using a multiple‐element infrared sensor having a time constant of ∼7 μs and a spot size as small as 30 μm in diameter; the temperature measurements were made for both single‐point and full‐wheel grinding. A simple analytical model is used to predict the abrasive‐tip and work‐surface temperatures, the subsurface temperature of the workpiece, and the cooling of the abrasive grains between cutting. The predictions of the model agree reasonably well with experiments. The model requires as inputs only the grinding forces, grinding process variables, and the physical properties of the abrasive and workpiece materials. It is shown that, in view of the excellent thermal properties of the diamond abrasive, the surface temperature of the ceramic workpieces is essentially independent of the thermal properties of the ceramics.
Low‐Pressure Chemical Vapor Deposition of α‐Si3N4 from SiF4 and NH3: Nucleation and Growth Characteristics
Authors: Lee Woo Y. , Strife James R. , Veltri Richard D.
Published: March 2005

The crystal structure and surface morphology of Si3N4 prepared by LPCVD were characterized as a function of processing conditions. Temperature was the most dominant variable which affected the coating microstructure. Strongly faceted crystalline Si3N4 was deposited at temperatures above ∼ 1410°C. In the temperature range of 1300° to 1410°C, crystalline and amorphous phases were codeposited. The content of the crystalline phase rapidly decreased with decreased temperature. In this temperature range, the coating crystallinity was also influenced by kinetic factors such as deposition rate and reagent depletion. For example, Si3N4 became more crystalline as the deposition rate was decreased by either decreasing the flow rate or increasing the NH3/SiF4 molar ratio. At ∼ 1300°C, the coating surface appeared fully botryoidal, and the coatings were mostly amorphous. Changes in the orientation and size of Si3N4 crystallites were parametrically documented. As the temperature was increased, the Si3N4 grains generally became more preferentially oriented to the (102) and/or (l0l) where l= 1,2,3,., directions. The average facet size increased with coating thickness.
Phase Relations in the Ternary Systems Nd─B─N, Sm─B─N, and Gd─B─N
Authors: Klesnar Helmuth , Rogl Peter
Published: March 2005

Phase relations and phase stabilities have been derived for the ternary systems RE─B─N (RE = Nd, Sm, or Gd) at elevated temperatures (1400°C and above) by means of X‐ray powder analysis. Under the experimental conditions selected, various ternary compounds are found to be stable: Nd3B2N4 with the Ce3B2N4 type and (Nd,Sm,Gd)BN2 with the PrBN2 type. Phase equilibria at 1400°C and under 105 Pa of argon are mainly characterized by the incompatibility of the RE metals Nd, Sm, and Gd with BN due to the competing equilibria between the RE tetraborides and the RE mononitrides. Each of the ternary compounds, however, is found to be in a two‐phase equilibrium with hex‐BN. Because of the different thermodynamic stabilities within the various structure series of ternary rare‐earth boron nitrides RE3B2N4 and REBN2, the compound Nd3B2N4 is observed only at temperatures below 1800°C and under 105 Pa of Ar, whereas GdBN2 is found to be stable only at temperatures above 1400°C under a partial pressure of 105 Pa of N2.
Thermodynamics and Phase Equilibria in the Sr─Cu─O System
Authors: Suzuki Ryosuke O. , Bohac Petr , Gauckler Ludwig J.
Published: March 2005

Phase equilibria in the SrO─CuO─Cu system were determined at 1173 K from the results of X‐ray diffraction measurements using specimens annealed under low oxygen partial pressure (po2= 0.21–10−8 atm). Electromotive force (EMF) measurements using ZrO2 solid electrolyte cells were carried out in the ternary phase equilibria. Gibbs free energies for five reactions in the cell electrodes were summarized by equations with linear temperature dependence. The standard free energies of formation for Sr2CuO3, SrCuO2, Sr14Cu24O41, and SrCu2O2 were derived. The stability conditions of all oxides are displayed in the p‐T‐x diagram using the new data.
Porous Glass‐Ceramics with a Skeleton of the Fast‐Lithium‐Conducting Crystal Li1+xTi2−xAlx(PO4)3
Authors: Hosono Hideo , Abe Yoshihiro
Published: March 2005

Porous glass‐ceramics with a skeleton of the fast‐lithium‐conducting crystal Li1+xTi2−xAlx(PO4)3 (where x= 0.3–0.5) were prepared by crystallization of glasses in the Li2O─CaO─TiO2─Al2O3–P2O5 system and subsequent acid leaching of the resulting dense glass‐ceramics composed of the interlocking of Li1+xTi2−xAlx(PO4)3 and β‐Ca3(PO4)2 phases. The median pore diameter and surface area of the resulting porous Li1+xTi2−xAlx(PO4)3 glass‐ceramics were approximately 0.2 μm and 50 m2/g, respectively. The electrical conductivity of the porous glass‐ceramics after heating in LiNO3 aqueous solution was 8 × 10−5 S/cm at 300 K or 2 × 10−2 S/cm at 600 K.
Depletion Effects of Silicon Carbide Deposition from Methyltrichlorosilane
Authors: Besmann Theodore M. , Sheldon Brian W. , Moss Thomas S. , Kaster Michael D.
Published: March 2005

The deposition rate of SiC on carbon‐coated Nicalon fibers from methyltrichlorosilane in hydrogen was measured as a function of temperature, pressure, total flow rate, and simulated reactant depletion. The results, together with kinetic information on the stability of methyltrichlorosilane, led to two conclusions: (1) two different mechanisms of deposition can occur depending on whether the methyltrichlorosilane has an opportunity to dissociate into separate silicon‐ and carbon‐containing precursors, and (2) the deposition rate is strongly reduced by the generation of byproduct HCl. The data were fitted to a simple etch model to obtain a kinetic expression that accounts for the significant effect of HCl.
Transformation Plasticity and Toughening in CeO2‐Partially‐Stabilized Zirconia–Alumina (Ce‐TZP/Al2O3) Composites Doped with MnO
Authors: Tsai Jing‐Fong , Chon Uong , Ramachandran N. , Shetty Dinesh K.
Published: March 2005

Microstructure, phase stability, and mechanical properties of CeO2‐partially‐stabilized zirconia (12 mol% Ce‐TZP) containing 10 wt% Al2O3 and 1.5 wt% MnO were studied in relation to the base Ce‐TZP and the Ce‐TZP/Al2O3 composite without MnO. The MnO reacted with both CeO2 and Al2O3 to form a new phase of approximate composition CeMnAl11O19. The reacted phase had a magnetoplumbite structure and formed elongated, needlelike crystals. The MnO‐doped Ce‐TZP/Al2O3 composites sintered at an optimum temperature of 1550°C exhibited high strength (650 MPa in four‐point bending) and rising crack‐growth‐resistance behavior, with fracture toughness increasing from 7.6 to 10.3 MPa.In12 in compact tension tests. These improved mechanical properties were associated with relatively high tetragonal‐to‐monoclinic transformation temperature (Ms=−42°C) at small grain size (2.5 μm), significant transformation plasticity in mechanical tests (bending, uniaxial tension, and uniaxial compression) and transformation zones at crack tips in compact tension specimens. The transformation yield stress, zone size, and fracture toughness were sensitive to the sintering temperature varied in the range 1500° to 1600°C. Analysis of the transformation zones using Raman microprobe spectroscopy and calculation of zone shielding for the observed zones indicated that a large fraction of the fracture toughness (∼70%) was derived from transformation toughening.
Thermochemical Etching Method for Ceramics
Authors: Owate Israel O. , Freer Robert
Published: March 2005

A thermochemical etching procedure, comprising a short chemical etch followed by a low‐temperature thermal anneal (typically 10 min at ≲70% of the sintering temperature), has proved successful for the preparation of alumina, aluminum nitride, and nickel zinc ferrite ceramics for micro‐structural studies. Good‐quality results have been achieved in times much shorter than those normally associated with chemical etching and at temperatures lower than those usually used for thermal etching. Under such conditions, grain growth and surface modification are believed to be minimal.
In‐Situ Alumina/Aluminate Platelet Composites
Authors: Chen Pei‐Lin , Chen I‐Wei
Published: March 2005

Alumina composites containing in‐situ‐formed hexaluminate (LaAl11O18, LaMgAl11O19, SrAl12O19, and Mg2NaAl15O25) platelets can be pressureless‐sintered to high density. The grain morphology of the aluminates can be controlled by composition. A peak toughness 50% higher than that of alumina is obtained at 30 vol% aluminates, with a modest reduction (10%) in hardness and Young's modulus. Although crack‐bridging by aluminate platelets is apparently operating, the maximum toughness is intrinsically limited by the low cohesive strength of these layer compounds.
India as a Hot Corrosion‐Resistant Stabilizer for Zirconia
Authors: Jones Robert L. , Mess Derek
Published: March 2005

After showing that india (In2O3) resisted high‐temperature reaction with SO3/Na2SO4 and vanadate melts, we prepared india‐stabilized zirconia (ISZ) by a proprietary sol–gel process, and tested the material for corrosion resistance to 700–900°C molten vanadates. ISZ was superior to yttria‐stabilized zirconia (YSZ) in vanadate resistance at 700°C, and essentially equivalent at 900°C. Certain differences were observed between the vanadate‐induced corrosion/destabilization of ISZ and that of YSZ.