bluuebunny/crossref_metadata_2025 huggingface dataset:
Smart Electroceramics
Authors: Newnham Robert E. , Ruschau Gregory R.
Published: March 2005

“Smart” materials have the ability to perform both sensing and actuating functions. Passively smart materials respond to external change in a useful manner without assistance, whereas actively smart materials have a feedback loop which allows them to both recognize the change and initiate an appropriate response through an actuator circuit. Many smart materials are analogous to biological systems: piezoelectric hydrophones are similar in mechanism to the “ears” by which a fish senses vibrations. Piezoelectrics with electromechanical coupling, shape‐memory materials that can “remember” their original shape, electrorheological fluids with adjustable viscosities, and chemical sensors which act as synthetic equivalents to the human nose are examples of smart electroceramics. “Very smart” materials, in addition to sensing and actuating, have the ability to “learn” by altering their property coefficients in response to the environment. Integration of these different technologies into compact, multifunction packages is the ultimate goal of research in the area of smart materials.
Role of Autocatalytic Transformation in Zone Shape and Toughening of Ceria–Tetragonal‐Zirconia–Alumina (Ce‐TZP/Al2O3) Composites
Authors: Tsai Jing‐Fong , Yu Cheng‐Sheng , Shetty Dinesh K.
Published: March 2005

Stress–strain behaviors in three‐point bending, transformation zones in single‐edge‐notch‐bend specimens, and transformation toughening were studied in two types of Ce‐TZP/Al2O3 composites. A commercial grade exhibited yield‐point behavior triggered by autocatalytic transformation and elongated zones. A new grade of Ce‐TZP/Al2O3 composite showed monotonic stress–strain behavior and a zone shape close to theoretical prediction based on a shear–dilatation yield criterion. The effects of zone sizes and shapes on fracture toughness of the two ceramic composites are shown to be qualitatively consistent with the predictions of transformation‐zone shielding theories.
Fatigue of Yttria‐Stabilized Zirconia: II, Crack Propagation, Fatigue Striations, and Short‐Crack Behavior
Authors: Liu Shih‐Yu , Chen I‐Wei
Published: March 2005

Fatigue crack propagation in 3Y‐TZP was investigated using controlled surface flaws. A unique growth law strongly dependent on the maximum stress intensity factor and quadratically dependent on the amplitude of the range of stress intensity factor was established. This growth law was found to apply for both surface flaws and internal flaws and could be used to predict fatigue lifetime. The presence of residual stress altered the growth mechanics so that an inverse growth rate dependence on the applied stress, reminiscent of the so‐called “short‐crack behavior,” was manifested. Fatigue striations resulting from alternate overload fracture and fatigue fracture during stress cycling were observed. The appearance of striations varied with theRratio and was very sensitive to the loading condition and crack geometry.
Grain Growth of Zinc Oxide During the Sintering of Zinc Oxide—Antimony Oxide Ceramics
Authors: Senda Tetsuya , Bradt Richard C.
Published: March 2005

Grain growth in a high‐purity ZnO with systematic additions of Sb2O3 from 0.29 to 2.38 wt% was studied for sintering in air from 1106° to 1400°C. The results are discussed and compared with previous studies of pure ZnO and ZnO with Bi2O3 additions in terms of the kinetic grain growth expression: Gn–Gn0=K0t exp(—Q/RT). Additions of Sb2O3 inhibited the grain growth of ZnO and increased the grain growth exponent (n‐value) to 6 from 3 for pure ZnO and 5 for the ZnO—Bi2O3 ceramic. The apparent activation energy for the grain growth of ZnO also increased to about 600 kJ/mol from 220 kJ/mol for pure ZnO and 150 kJ/mol for the ZnO—Bi2O3 ceramics. Both the grain growth exponent and the activation energy were independent of the Sb2O3 content. Particles of the Zn7Sb2O12 spinel were observed on the grain boundaries and at the grain triple point junctions. It was also observed that the Sb2O3 additions caused twin formation in each ZnO grain. It is concluded that both the Zn7Sb2O12 particles and the twins are responsible for the ZnO grain growth inhibition by Sb2O3.
Chemical Processing and Microwave Characteristics of (Zr,Sn)TiO4 Microwave Dielectrics
Authors: Hirano Shin‐ichi , Hayashi Takashi , Hattori Akiyoshi
Published: March 2005

Monosized spherical particles of (Zr, Sn)TiO4 with an average diameter of about 0.3 μm were synthesized by the controlled hydrolysis of metal alkoxides. The as‐prepared, amorphous, particles were compacted without any sintering aid, crystallized, and then sintered at 1600°C for 3 h into bodies with >96.0% of theoretical density. The dense sintered bodies of (Zr0.80Sn0.20)TiO4 showed good microwave characteristics; ɛr= 40.0, Q= 5000, and τt= 3 ppm/°C at 10 GHz. The dielectric constant was remarkably dependent upon the relative densities of the sintered bodies and the change of the lattice parameters, while Q value was mainly affected by the oxygen deficiency. An increase of the dielectric constant with the substitution of Sn4+ in ZrTiO4 was attributable to the enhancement of ionic polarization with the increase of the c‐axis length.
Local Structure of Alkaline‐Earth Boroaluminate Crystals and Glasses: II, 11B and 27Al MAS NMR Spectroscopy of Alkaline‐Earth Boroaluminate Glasses
Authors: Bunker Bruce C. , Kirkpatrick R. James , Brow Richard K. , Turner Gary L. , Nelson Carolyn
Published: March 2005

11B and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectra of alkaline‐earth boroaluminate glasses show that the structure of these glasses are far more complicated than previously thought. The relative concentrations of 3‐ and 4‐coordinated boron vary as found by previous investigators using continuous‐wave NMR methods, but the 27Al NMR spectra indicate the presence of Al in 4‐, 5‐, and 6‐fold coordination, in contrast to previous assignments. Analysis of the data based on local charge balance considerations provides a qualitative model that correctly predicts compositional variations of the NMR peak intensities and 27Al chemical shifts for a wide range of boroaluminate glass compositions.
Synthesis of Yttrium Aluminum Garnet by the Glycothermal Method
Authors: Inoue Masashi , Otsu Hiroyuki , Kominami Hiroshi , Inui Tomoyuki
Published: March 2005

The reaction of a stoichiometric mixture of aluminum isopropoxide and yttrium acetate in 1,4‐butanediol at 300°C yielded crystalline yttrium aluminum garnet having an approximate particle size of 30 nm. No other phases were detected. The use of ethylene glycol in place of 1,4‐butanediol afforded an amorphous product.
Effects of Noncompositional Inhomogeneity ont→mPhase Transformation During Grinding of Various Rare‐Earth‐Doped Zirconias
Authors: Yashima Masatomo , Noma Tatsuo , Ishizawa Nobuo , Yoshimura Masahiro
Published: March 2005

The phase transformation from metastable tetragonal (t) into monoclinic (m) phase must be studied using samples that are homogeneous in their compositions and microstructures. The present study investigated the transformability by grinding for compositionally homogeneous samples prepared by rapid quenching of melts in the system ZrO2–RO1.5(R: Nd, Sm, Y, Er, Yb). The volume fraction ofm‐phaseVm(tg) against grinding timetgwas investigated using powder X‐ray diffraction for the rapidly quenched sample. TheVm(tg) value increased with grinding timetg, then saturated to a certain valueVm(∞) of between 1 and 0 when it was ground and crushed for a long time. Both the transformation rate (dVm/dtg)tg = 0and the saturated valueVm(∞) decreased with dopant contentX.The species of dopants had less influence on the transformability. The experimentalVm(∞) andVm(0) data could be explained using a model which has a normal distribution of effective free energy change betweentandmphases, ΔGt‐m, among hypothetical parts of the sample. This distribution occurred because of nonchemical energies such as strain, interfacial, and surface energies, which associated with the nucleation ofmphase. The average effective free energy change ΔG¯t‐m/σ was found to be a linear function of ErO1.5contentXas 0.65X+ 3.00, where σ is a standard deviation of the normal distribution. The transformation rate dVm/dtgattg= 0 decreased with RO1.5content. The axial ratioc/aof thetphase was an important factor in the transformability, theVm(0),Vm(∞), and the dVm/dtg. The validity and limitation that thec/ais a factor of the transformability were discussed.
Preparation and Electrical Properties of Lanthanum‐Doped Lead Titanate Thin Films by Sol–Gel Processing
Authors: Shimizu Yasuhiro , Udayakumar K. R. , Cross L. Eric
Published: March 2005

Lanthanum‐doped lead titanate thin films have been prepared by sol–gel processing. These studies reveal the structural and electrical properties of 18 mol% La‐doped PbTiO3 thin films to be dependent on the annealing conditions. With appropriate annealing conditions, a relative dielectric constant of about 900 was obtained, comparable to the bulk composition.
Oxidation–Reduction Equilibrium in Copper Phosphate Glass Melted in Air
Authors: Bae Byeong‐Soo , Weinberg Michael C.
Published: March 2005

Copper phosphate glasses with 40, 50, and 60 mol% CuO in batch were melted in air at 1000°, 1100°, and 1200°C using quartz or alumina crucibles, and the [Cu2+]/[Cutotal] ratio variations with melting time were measured. Glasses were oxidized during melting and reached equilibrium [Cu2+]/[Cutotal] ratios which were independent of melting temperature and identical for the 40 and 50 mol% CuO content glasses. Structural considerations seemed to have determined oxidation‐reduction equilibrium rather than an equilibrium redox reaction. Also, the effects of crucible type on the oxidation‐reduction balance were examined. It was found that a quartz crucible is more inert and has less effect on the oxidation‐reduction equilibrium of glass than an alumina crucible. Crucible contamination and phosphorus vaporization were found to diminish as the CuO content in the batch was increased.
Boron Nitride Powders Formed by Aerosol Decomposition of Poly(borazinylamine) Solutions
Authors: Lindquist David A. , Kodas Toivo T. , Smith Douglas M. , Xiu Xiaomei , Hietala Susan L. , Paine Robert T.
Published: March 2005

Micrometer‐sized aerosol droplets of a liquid ammonia solution of poly(borazinylamine) were formed in a nitrogen carrier gas by using an aerosol generator. The resulting droplets were thermally decomposed in a flow reactor at 1000°C. The white powder obtained was amorphous to X‐rays and spherical with particle sizes on the order of 0.5 μm. The particles at this stage were porous, and some appeared to exhibit a hollow‐shell morphology. Subsequent calcining at 1600°C yielded dense, crystalline boron nitride powder with partial sintering.
BxO: Phases Present at High Pressure and Temperature
Authors: Srikanth Varanasi , Roy Rustum , Graham Earl K. , Voigt Donald E.
Published: March 2005

Boron suboxide compounds are of interest because of their low densities coupled with high hardness. In the present study, we have attempted to determine the nature of the BxO phases that occur in the field defined by pressures of zero to 1.5 GPa, temperature between 1200° and 1700°C, and the compositional range 2/3 x 24. Amorphous boron powder and boric acid B2O3 were the starting reactants for all the runs. The processing of the specimens was carried out in a controlled atmosphere furnace, a hot‐pressing assembly, and in a piston—cylinder high‐pressure apparatus within quasi‐hydrostatic and inductively heated cell assemblies. After processing at elevated temperature and pressure, for compositions over the range 2/3 x 6, B2O3 (identical to the hexagonal starting material) and B6O (R3¯m) were the dominant phases present. For the compositions 6 x 24, B6O and rhombohedral B were the primary phases identified. In general, the hardness of the processed composites was dominated by the occurrence of B6O (approximately equivalent to B4C). However, there is some suggestion of particularly high values of hardness on a very localized scale in specimens near the B22O composition.
Fracture Toughness of Chemically Vapor‐Deposited Diamond
Authors: Drory Michael D. , Gardinier Clayton F. , Speck James S.
Published: March 2005

The fracture toughness of chemically vapor‐deposited diamond is estimated by a Vickers indentation method. Freestanding diamond films of 400‐μm thickness are produced with plasma‐enhanced chemical vapor deposition and highly polished for indentation testing. Indentation testing was performed with a microhardness tester using a load range of 5 to 8 N. The average fracture toughness is estimated as 5.3 ± 1.3 MPA · m1/2.
Simple and Inexpensive Flash Technique for Determining Thermal Diffusivity of Ceramics
Authors: Log Torgrim , Jackson T. Barrett
Published: March 2005

A simple technique for determining the thermal diffusivity of ceramics at room temperature is presented. The technique is a variant of the well‐known flash technique, but uses an inexpensive photo flash as the energy source, a fast‐response paste‐on thermocouple, and a precision digital voltmeter to measure the temperature rise. A data analysis technique, which does not need any knowledge of either the initial or the maximum sample temperature, is presented. Good agreement with the laser‐flash technique for ceramics with thermal diffusivities in the range 0.5 × 10−6 to 75 × 10−6 m2· s−1 is obtained. Measurements of thermal diffusivity of stainless steel and graphite (standard reference materials) indicate that the method is accurate to within 3%.
Sintering Behavior of Fully Agglomerated Zirconia Compacts
Authors: Shi Jian‐Lin , Gao Jian‐Hua , Lin Zu‐Xiang , Yen Tung‐Sheng
Published: March 2005

Fully agglomerated superfine zirconia powders were prepared with the coprecipitation and spray‐drying method. The compaction of such powders shows no fragmentation of the agglomerates. The sintering behavior of the compacts was studied and two sintering stages were identified: densification within agglomerates at temperatures not higher than 1250°C and the removal of interagglomerate pores at temperatures above 1600°C. The interagglomerate pores are difficult to remove, and sintering between agglomerates even at 1600°C is still insignificant. Heating of the compacts at temperatures above 1600°C leads only to grain growth and the entrapping of pores in large grains.
Microindentation‐Induced Transformation in 3.5‐mol%‐Yttria‐Partially‐Stabilized Zirconia Single Crystals
Authors: Martinez‐Fernandez J. , Jimenez‐Melendo M. , Dominguez‐Rodriguez A. , Heuer Arthur H.
Published: March 2005

The temperature dependence of the Vickers microhardness was studied in 3.4‐mol%‐Y2O3‐partially‐stabilized ZrO2 (Y‐PSZ) single crystals up to 1000°C; the samples had previously been annealed at 1600°C for 150 h to develop “colony” precipitates of tetragonal ZrO2 in the cubic ZrO2 matrix. Indentation caused extensive stress‐induced martensitic transformation of the colony precipitates to monoclinic symmetry in zones which extended in extreme cases up to several hundred micrometers from the indent. For indents made at 500°C and above, the Md and Mf temperatures are 450° and 310°C, respectively; As is ∼600°C (Md is the temperature of initial transformation (the “martensite start temperature”) in deformed samples; Mf is the temperature at which the final transformation occurs; As is the temperature at which the reverse (monoclinic → tetragonal) transformation begins). However, extensive transformation zones are also found for indents made at 200°, 300°, and 400°C. The dislocation density introduced during indentation is responsible for nucleating the transformation in a zone adjacent to the indent. However, the transformation zone extends further than the plastic zone around the indent, indicating extensive autocatalytic transformation. Transformation within the zone appeared to occur in individual plates with {110} habit planes. The plate dimensions (∼100 μm ×∼175 μm ×∼10 μm) are large compared to the size of the colony precipitates (∼2 μm in maximum dimension).
Hydrolytic Condensation of Tin(IV) Alkoxide Compounds to Form Particles with Well‐Defined Morphology
Authors: Gulliver Eric A. , Garvey John W. , Wark Teresa A. , Hampden‐Smith Mark J. , Datye Abhaya
Published: March 2005

The sol‐gel‐type condensation of tin(IV) ethoxide [Sn(OEt)4]n (where OEt is ethoxide) under basic conditions produced spherical, submicrometer‐sized tin(IV) oxide (cassiterite) particles. Transmission electron microscopy and powder X‐ray diffraction data indicated that the grain size was approximately 20 to 30 Å (2 to 3 nm). The mixed‐metal alkoxide compound [ZnSn(OEt)6] was hydrolyzed under analogous conditions to give either spherical or octahedral submicrometer‐sized crystalline particles of ZnSn(OH)6 depending on the solvents used. These data demonstrated that the stoichiometry of the mixed‐metal alkoxide precursor was retained during condensation. Thermal treatment of ZnSn(OH)6 resulted in crystallization of ZnSnO3 at approximately 676°C. At neutral pH, hydrolysis of [ZnSn(OEt)6] resulted in formation of a high surface area (261 m2/g) amorphous powder.
Inversion Domains in Aluminum Nitride
Authors: Berger Axel
Published: March 2005

Flat and curved, basal and nonbasal planar defects are frequently observed in sintered AIN ceramics. To prove the existence of inversion domains, TEM techniques sensitive to crystal polarity were used. Dark‐field imaging in certain multiple‐beam situations with g= (0002) (where g is operating reflection) yielded strong domain contrast giving clear evidence of an inverted crystal structure within the domains. This was confirmed by the dynamic contrast in the disks of convergent‐beam electron diffraction. All planar defects observed were found to be associated with inversion domains. The formation of inversion twins may be nucleated by accidental growth or by nucleation and growth within the bulk of a preexisting AIN grain. Both mechanisms are supposed to be associated with the accommodation of impurities.
Mullite Formation from Nonstoichiometric Diphasic Precursors
Authors: Li Dong X. , Thomson William J.
Published: March 2005

Diphasic gels with Al/Si atomic ratios of 6/1, 3.1/1, 3/1, 2/1, and 1/1 were used to study the effect of precursor composition on mullite formation process and the resulting microstructure. Mullite formation initiated at about 1300°C for all samples, with only some slight differences in temperatures. The mullite formation temperature was a minimum for an Al/Si ratio of 3.1/1 and increased as the Al/Si ratio of the gels increased or decreased. For the 6/1 gel, dissolution of alumina into mullite solid solution was observed after the initial mullite formation. The dissolution process was reversed above 1450°C with the formation of θ‐Al2O3 and then α‐Al2O3. Change of microstructures from equiaxed to elongated mullite grain structures was found within a narrow range of composition near the nominal Al/Si ratio of 3/1.
High‐Temperature Active Oxidation of Chemically Vapor‐Deposited Silicon Carbide in an Ar─O2 Atmosphere
Authors: Narushima Takayuki , Goto Takashi , Iguchi Yasutaka , Hirai Toshio
Published: March 2005

Active oxidation behavior of chemically vapor‐deposited silicon carbide in an Ar─O2 atmosphere at 0.1 MPa was examined in the temperature range between 1840 and 1923 K. The transition from active oxidation (mass loss) to passive oxidation (mass gain) was observed at certain distinct oxygen partial pressures (PO2t). The values of PO2t increased with increasing temperature and with decreasing total gas flow rates. This behavior was well explained by Wagner's model and thermodynamic calculations. Active oxidation rates (ka) increased with increasing O2 partial pressures and total gas flow rates. The rate‐controlling step of the active oxidation was concluded to be O2 diffusion through the gaseous boundary layer.
Kinetic Analysis of Chemical Vapor Deposition of Boron Nitride
Authors: Lee Woo Y. , Lackey W. J. , Agrawal Pradeep K.
Published: March 2005

BN was deposited on Al2O3 substrates from the BCl3─NH3─Ar reagent system. An impinging jet reactor configuration was used to obtain kinetic data in the temperature range of 800° to 1000°C and in the pressure range of 4 to 20 kPa. The BN deposition could be described by a simple kinetic rate expression with an activation energy of about 39 kcal/mol and a first‐order dependency on BCl3 concentration. The BN deposition rate increased with temperature, pressure, and BCl3 concentration. The microstructure of the BN coatings was not strongly influenced by the process parameters.
Mechanical Behavior of Fiber‐Reinforced Cement‐Based Composites
Authors: Shah Surendra P. , Ouyang Chengsheng
Published: March 2005

The use of fibers in a cement‐based matrix can fundamentally improve its mechanical properties. Such improvement may lead to a new class of cement‐based materials. Further developments depend on an understanding of the interaction between different fibers and cement‐based matrices. The current knowledge on the mechanical behavior of fiber‐reinforced cement‐based composites is summarized. Toughening mechanisms, interface properties, and tensile response of fiber‐reinforced cement‐based composites are presented. Various theoretical approaches used to describe the mechanical behavior of fiber‐reinforced composites are reviewed.
Preparation of Tetragonal Barium Titanate Thin Film on Titanium Metal Substrate by Hydrothermal Method
Authors: Kajiyoshi Koji , Ishizawa Nobuo , Yoshimura Masahiro
Published: March 2005

Tetragonal BaTiO3 thin films were prepared directly on Ti metal substrates in Ba(OH)2 solutions by a hydrothermal method at temperatures 400° to 800°C for 5 to 240 min. The film thickness estimated from weight gain of Ti plate was in the range from 0.5 to 2.5 μm, and it increased with increasing treatment temperature, treatment time, and Ba(OH)2 concentration. Rectangular crystals having {100} and {001} faces grew idiomorphically with approximate crystal size of 0.3 to 2.0 μm. The tetragonality of the BaTiO3 films became apparent when the average crystal size exceeded about 1 μm. Lattice parameters of the films were a= 3.994 Å, c= 4.035 Å, and c/a= 1.010. The films formed above 600°C had preferred orientation showing stronger XRD peaks of h00 and 00l than the other peaks.
Preparation of La2Zr2O7 by Sol—Gel Route
Authors: Kido Hiroyasu , Komarneni Sridhar , Roy Rustum
Published: March 2005

The La2Zr2O7 phase was prepared from metal acetylacetonates by a sol—gel route without any intermediate phase formation. X‐ray peaks appeared at a temperature as low as 500°C at the positions expected for La2Zr2O7, although they were broad. The crystal structure of La2Zr2O7 was found to be of the fluorite type below 900°C and of thepyrochlore type above 1000°C. The substitution of a small amount of Eu for La was carried out to investigate the crystal structure from the viewpoint of fluorescence, and these results confirmed the formation of fluorite type La2Zr2O7 below 900°C.
Effect of Alumina Addition on the Tetragonal‐to‐Monoclinic Phase Transformation in Zirconia–3 mol% Yttria
Authors: Tsubakino Harushige , Nozato Ryoichi , Hamamoto Mitsuharu
Published: March 2005

The tetragonal‐to‐monoclinic martensitic phase transformation in ZrO–3 mol% Y2O3 (PSZ) containing 0 to 12 wt% Al2O3 was investigated by dilatometry, XRD, and SEM‐EDS methods. The propagation of the transformation into the specimen interiors was suppressed by the addition of Al2O3. The grain size was independent of the addition of Al2O3. Both Y2O3 and Al2O3 segregated at grain boundaries. From this segregation behavior, it was suggested that a certain compound or phase of Y2O3–Al2O3 could be formed at grain boundaries, which would presumably prevent the propagation of the transformation into interiors of PSZ‐containing Al2O3.
Alkali Durability of Oxynitride Glass Fibers
Authors: Wusirika Raja
Published: March 2005

Oxynitride glass fibers were drawn from the melt in N2 atmospheres. The fibers were tested for their alkali durability in 10% NaOH at 96°C for 6 h. The durability is reported as weight loss in mg/cm2. The photomicrographs of the fibers before and after testing are presented. Calcium silicate oxynitride fibers have good durability because of a protective surface layer of Ca(OH)2. Yttria‐containing glasses have the best durability among the compositions reported here.
Transmission Electron Microscope Study of Antimony‐Doped Zinc Oxide Ceramics
Authors: Kraševec Viktor , Trontelj Marija , Golič Ljubo
Published: March 2005

A transmission electron microscope investigation of a ZnO powder and low‐temperature air‐sintered pellets with small additions of Sb2O3 was conducted in order to study the thin Sb‐rich film on the surfaces of ZnO particles. This film was found to be noncrystalline at temperatures below 700°C, and partially crystalline or completely crystalline above this temperature. An oriented overgrowth of the spinel Zn7Sb2O12 was observed on the prismatic planes as well as on the basal planes of ZnO crystallites. It is shown that these coherently overgrown spinel films are responsible for the inhibition of grain growth at high temperatures.
Alignment of YBa2Cu3O7‐xand Ag─YBa2Cu3O7‐xComposites at ∼930°C by Eutectic Formation
Authors: Zhou Ji‐Ping , Sorrell Charles C. , Dou Shi‐Xue , Apperley Miles H.
Published: March 2005

The present work describes a new technique to synthesize aligned YBa2Cu3O7‐xand Ag─YBa2Cu3O7‐xsuperconducting composites from Ba‐ and Cu‐deficient compositions (relative to YBa2Cu3O7‐x) plus BaCuO2. For YBa2Cu3O7‐x, high transition temperature midpointTc(91 K), temperature of zero resistivityT0(90 K), and critical current densityJc(>3000 A°Cm−2at 77 K) were achieved by using this technique. This procedure provides the potential for using a reliable and reproducible densification and alignment technique alternative to partial or full melting. The composite is highly aligned, with an average grain size of ∼1 to 2 mm and domains of width greater than 5 mm. The initial phase assemblage consists of YBa2Cu3O7‐x(123) as the major phase plus YBa2CuO5(211) CuO as minor phases. The BaCuO2is added to the Ba‐ and Cu‐deficient starting composition in order to assist in the formation of a CuO‐rich liquid as well as to compensate for the Ba and Cu deficiences in 123. Since the liquid forms at ∼900°C and is compatible with 123, it can be used to facilitate alignment of 123 at ∼930°C. The addition of Ag to the system results in eutectic formation with the (solidified) liquid, substantial filling of the pores during sintering, and improved alignment.
Effects of Wet Oxidation on the Properties of Sub‐10‐nm‐Thick Silicon Nitride Films
Authors: Lee Eun Gu , Im Ho Bin , Roh Jae Sung
Published: March 2005

Capacitors were prepared by wet oxidation of 8 nm (80 Å) thick silicon nitride films which had been deposited on polysilicon substrates. The capacitance and breakdown field of these capacitors were measured as a function of the wet oxidation conditions. The properties of the polysilicon films were also investigated by varying the preparation conditions to find a better substrate for the deposition of the ultrathin silicon nitride films. These polysilicon films were prepared using low‐pressure chemical vapor deposition at 560° and 625°C on silicon wafers. The films were then annealed at 900°C for 30 min after As doping by implantation with a dose of more than 2 × 1015/cm2. The films deposited at 560°C have a smooth surface and a low electrical resistivity and are thus suitable substrates for the ultrathin silicon nitride films as well as suitable contact electrodes. For the capacitors with an oxide nitride composite layer, the capacitance decreases sharply, but the breakdown field increases with an increase in the wet oxidation time at 900°C. This is due to an increase in the thickness of the oxide—nitride layer. For the capacitors with silicon oxynitride layers created by removing the top oxide of the silicon nitride wet‐oxidized at 900°C for more than 35 min, however, the values of both the capacitance and the breakdown field are higher than those of capacitors with an unoxidized silicon nitride layer.
Aqueous Dispersion and Slip Casting of Boron Carbide Powder: Effect of pH and Oxygen Content
Authors: Williams P. Douglas , Hawn David D.
Published: March 2005

The effect of pH and oxygen content on the zeta potential, viscosity, and casting performance of fine (>3 μm) boron carbide powder is presented. X‐ray photoelectron spectroscopy of the powder revealed a surface layer of adsorbed water and oxides of boron and carbon. The soluble boric acid impurity was removed by washing the powder with water or alcohols. Electrophoresis indicated that the B4C surface was negatively charged in water above pH 1, but the presence of dissolved boric acid suppressed the zeta potential at high pH. Stable, low‐viscosity dispersions of >30 vol% solids were prepared and slip cast at pH >6, but boric acid was destabilizing for dispersions prepared above pH 7. The green density of slip‐cast parts was more reproducible and about 3% to 5% higher for washed powders than for high‐oxygen‐content powders.
KR‐Curve Behavior of Duplex Ceramics
Authors: Lutz Ekkehard H. , Claussen Nils , Swain Michael V.
Published: March 2005

The fracture toughness behavior during crack growth (KR‐curve behavior) of duplex ceramics is investigated. Different types of KR‐curves can be distinguished depending on the microstructural designs of these materials which are characterized by the volume fraction and size of the dispersed pressure zones, and by their effective volume expansion. According to their KR‐curve behavior, duplex ceramics can be subdivided into two groups consisting of “short‐range” and “long‐range” toughened materials. The experimental results are discussed regarding the appearance of different toughening mechanisms which are documented by crack path micrographs. An unusual toughening effect, a “crackbranching chain reaction,” is documented by in situ observations. The critical stress to nucleate the observed process zone development is calculated and compared with the internal stress intensity factor Ki which has been previously proposed for these materials and with the material strength.
Effect of Heat‐Treatment Temperature on the Properties of a Lithium Aluminosilicate Glass
Authors: Jewell John M. , Spess Marie S. , Ortolano Renee L. , Shelby James E.
Published: March 2005

The effects of isochronal heat treatments on the properties of a lithium aluminosilicate glass have been measured. Heat treatment of the base glass at temperatures between 700° and 1100°C initially results in phase separation of the glass, followed by the formation of β‐quartz solid solution (ss) at about 850°C. The β‐quartz(ss) converts to β‐spodumene in the temperature range between 950°C and 1000°C. The dependence of the properties of the material on the heat‐treatment temperature is controlled by phase separation below 850°C, by the rapid crystallization of β‐quartz(ss) between 850°C and 900°C, and by the lack of change in morphology with heat treatment above 900°C. The effects of heat treatment on the properties of this material are explained on the basis of the changes in the composition and morphology of the residual amorphous and crystalline phases.
Phase Separation in the SiC–AlN Pseudobinary System: The Role of Coherency Strain Energy
Authors: Chen Jong , Tian Qiang , Virkar Anil V.
Published: March 2005

SiC–AlN polycrystalline samples of equimolar composition were fabricated by hot‐pressing. Single‐phase samples were annealed over a range of temperatures between 1600° and 2000°C for up to 1145 h to effect the formation of modulated structures. Electron diffraction from the [2110] zone axis showed four distinct satellite spots around every main diffraction spot with modulations occurring orthogonal to {0112} planes. The direction of modulation experimentally observed is consistent with that determined by the minimization of the coherency strain energy. Computer simulation was conducted to generate the morphology of modulated structures. The simulated microstructure was found to be very similar to that observed experimentally.
Processing Effects on Microstructural Charcteristics and Properties of Reactively Ion‐Plated Titanium Nitride Coatings
Authors: Komvopoulos K.
Published: March 2005

The effects of key processing parameters on the resulting microstructure and mechanical properties of thin TiN coatings, reactively ion‐plated on polished aluminum and steel substrates, were investigated experimentally. A deposition procedure was established and a processing scheme for reactive ion plating was developed. Optimization of processing conditions was achieved by means of controlling the principal ion‐plating parameters to prevent the growth of species different from TiN, evaporant poisoning, and variations in the coating thickness. Emphasis was placed on identifying the effects of critical independent and dependent processing parameters, such as the rf power density, the deposition rate, and the coating thickness, on the TiN microscopic morphology, crystal structure, surface roughness, microhardness, and deformation behavior arising under static and sliding contact loads. Results from various testing and characterization methods revealed that deposition of hard, strongly adherent, and relatively smooth TiN coatings possessing dense microstructures of fine equiaxed grains with a preferential (200) texture can be accomplished under certain ionplating conditions.
Sintering of Confined Silica in Oxidized Silicon Particles
Authors: Ajayan Pulickel M. , Iijima Sumio
Published: March 2005

We observed electron‐beam‐induced sintering of amorphous silica in oxidized submicrometer silicon particles and analyzed the nature of mass transport in linear and triangular particle assemblies. The movement of silica around the rigid crystalline cores occurs rapidly and fills the necks, but the relative core positions in the sintered product depends on the initial geometry of the confined oxide. However, a thin layer of silica remains stable against the flow.
Rapid and Continuous Hydrothermal Crystallization of Metal Oxide Particles in Supercritical Water
Authors: Adschiri Tadafumi , Kanazawa Katsuhito , Arai Kunio
Published: March 2005

Hydrolysis of 10 metal salt aqueous solutions of 6 metal oxides was conducted in supercritical water. Continuous and rapid production of metal oxide fine particles was achieved by mixing a metal salt aqueous solution with preheated water fed from another line. The reaction time required was less than 2 min. Particle size, morphology, and crystal structure of the obtained metal (hydrous) oxides were examined. Particle size (20 to 600 nm) was different among the systems but the size range was relatively narrow in all the cases.
Oxidation State of Chromium in CaO–Al2O3–CrOx–SiO2 Melts under Strongly Reducing Conditions at 1500°C
Authors: Pretorius Eugene B. , Snellgrove R. , Muan Arnulf
Published: March 2005

Equilibrium ratios Cr2+/Cr3+ of chromium oxide dissolved in CaO–chromium oxide–Al2O3–SiO2 melts have been determined by analysis of samples equilibrated at 1500°C under strongly reducing conditions (po2= 10−9.56 to 10−12.50 atm). The majority of the chromium is divalent (Cr2+) under these conditions and Cr2+/Cr3+ ratios at given constant oxygen pressures decrease with increasing basicity of the melts, expressed as CaO/SiO2 ratios. In addition, Cr2+/Cr3+ ratios, at a given CaO/SiO2 ratio, are relatively unaffected by the amount of Al2O3 present.
Activity–Composition Relations in NiAl2O4─MnAl2O4 Solid Solutions and Stabilities of NiAl2O4 and MnAl2O4 at 1300° and 1400°C
Authors: Timuçin Muharrem , Muan Arnulf
Published: March 2005

Activities of NiO were measured in the oxide and spinel solutions of the system MnO–NiO–Al2O3 at 1300° and 1400° C with the aim of deriving information on the thermodynamic properties of the spinel phases. Synthetic samples in selected phase assemblages of the system were equilibrated with metallic nickel and a gas phase of known oxygen partial pressures at a total pressure of 1 atm. The data on NiO activities and directions of conjugation lines between coexisting oxide and spinel phases were used to establish the activity–composition relations in spinel solid solutions at 1300° and 1400°C. The MnAl2O4–NiAl2O4 solid solutions exhibit considerable negative deviations from ideality at these temperatures. The free energy of formation of MnAl2O4 from its oxide components (MnO + Al2O3) at 1300° and 1400°C is calculated to be −24.97 and −26.56 kJ. mol−1, respectively. The activities determined in the stoichiometric spinel solid solutions are more negative as compared with those predicted from cation distribution models.
Enthalpy of Formation of Zircon
Authors: Ellison Adam J. G. , Navrotsky Alexandra
Published: March 2005

Using high‐temperature solution calorimetry in molten 2PbO. B2O3, the enthalpy of reaction of the formation of zircon, ZrSiO4, from its constituent oxides has been determined: ΔrH977(ZrSiO4) =−27.9 (± 1.9) kJ/mol. With previously reported data for the heat contents of ZrO2, SiO2, and ZrSiO4 and standard‐state enthalpies of formation of ZrO2 and SiO2, we obtain ΔfH°298· (ZrSiO4) =−2034.2 (±3.1) kJ/mol and ΔfG°298 (ZrSiO4) =−1919.8 kJ/ mol. The free energy value is in excellent agreement with a range previously estimated from solid‐state reaction equilibria. At higher temperature also the data are in close agreement with existing data, though the data sets diverge somewhat with increasing T. The limitations of the data for predicting the breakdown temperature of zircon into its constituent oxides are discussed.
The System CaO–“CaCr2O4”–CaAl2O4 in Air and under Mildly Reducing Conditions
Authors: Kaiser Arno , Sommer Burkhard , Woermann Eduard
Published: March 2005

The system CaO–chromium oxide in air is reinvestigated and the existence of intermediate phases with chromium in oxidation states >3+ (Ca5Cr3O12, Ca3(CrO4)2, and Ca5(CrO4)3) confirmed. Under reducing conditions these phases are unstable. A metastable, polymorphic form of calcium chromite, δ‐CaCr2O4, is observed. In the CaO‐rich section of the CaO–Al2O3–Cr2O3 system a ternary intermediate phase, chrome‐haüyne, Ca4[(Al,Cr3+)6O12](Cr6+O4), coexists with calcium chromate and calcium aluminate phases. In air, low melting temperatures are preserved in all assemblages containing calcium chromate phases. Under reducing conditions a new ternary phase, Ca6Al4Cr2O15, coexists with CaO, CaCr2O4, chrome‐haüyne, and calcium aluminate phases. The influence of chromium oxide additions on the solidus temperatures of the CaO–Al2O3 system is insignificant.
Coarsening Kinetics in Mg(Ca,Ti,Y)‐Partially‐Stabilized Zirconias
Authors: Bateman Charles A. , Notis Michael R.
Published: March 2005

The coarsening kinetics of a magnesia‐partially‐stabilized zirconia with and without ternary additions of calcia, titania, or yttria at the 2 mol% level have been studied as a function of aging time at 1420°C. Addition of titania was found to markedly increase the coarsening rate and it is thought that this is due to a higher precipitate volume fraction in this system. Both calcia and yttria decreased the coarsening kinetics by a similar amount, probably due to both lower precipitate volume fractions and lower interdiffusion coefficients. The precipitate “transformability” was found to vary among the four systems examined, with calcia and yttria acting to stabilize tetragonal precipitates to larger sizes; titania was found to act as a destabilizer. Coherency stresses are important in determining the precipitate morphology and distribution in these alloys but we were unable to ascertain what effect these stresses had on the coarsening rates of the different alloys.
Piezoelectric Lead Zirconate Titanate Ceramic Fiber/Polymer Composites
Authors: Waller David J. , Safari Ahmad
Published: March 2005

Piezoelectric lead zirconate titanate (PZT) ceramic fiber/polymer composites were fabricated by a novel technique referred to as “relic” processing. Basically, this involved impregnating a woven carbon‐fiber template material with PZT precursor by soaking the template in a PZT stock solution. Careful heat treatment pyrolized the carbon, resulting in a PZT ceramic relic that retained the fibrous template form. After sintering, the densified relic was backfilled with polymer to form a composite. Optimized relic processing consisted of soaking activated carbon‐fiber fabric twice in an intermediate concentration (405‐mg PZT/(1‐g solution)) alkoxide PZT solution and sintering at 1285°C for 2 h. A series of piezoelectric composites encompassing a wide range of dielectric and piezoelectric properties was prepared by varying the PZT‐fiber orientation and polymer‐matrix material. In PZT/Eccogel polymer composites with PZT fibers orientated parallel to the electrodes,K= 75,d33= 145 pC/N,dh= 45 ± 5 pC/N, anddhgh= 3150 × 10−15m2/N were measured. Furthermore, in composites with a number of PZT fibers arranged perpendicular to the electroded surfaces,K= 190,d33= 250 pC/N,dh= 65 ± 2 pC/N, anddhgh= 2600 × 10−15m2/N.
Nitridation of Silicon Containing MgO and CeO2 Powders and SiC Whiskers
Authors: Huang Jow‐Lay , Simms Frederick E.
Published: March 2005

Processing and nitridation of MgO/CeO2‐doped silicon containing SiC whiskers was studied. The reaction time was dramatically reduced by incorporating MgO/CeO2 dopants and SiC whiskers in silicon powders prior to nitridation. The decomposition of SiC whiskers depends on the nitriding temperature, sintering aids, and whisker surface composition.
Hole Mobility in Acceptor‐Doped, Monocrystalline SrTiO3
Authors: Fleischer Maximilian , Meixner Hans , Tragut Christian
Published: March 2005

The oxidation reaction equilibrium constant and the holes mobility in p‐type‐semiconducting SrTiO3 single crystals were determined directly by simultaneous Hall and conductivity measurements between 500° and 1000°C. This information and the SrTiO3 defect model were used to interpret the electrical measurements taken on this substance which represents a model substance for semiconducting perovskites. Measurements with varying oxygen partial pressures showed that shifts of the crystal defect equilibrium give rise to changes in the carrier concentration with unchanged carrier mobility.
Effect of Chlorine Atmosphere on the Anatase‐Rutile Transformation
Authors: Gamboa Julio Andrade , Pasquevich Daniel M.
Published: March 2005

The anatase‐rutile phase transformation in Ar–Cl2 atmosphere has been investigated by X‐ray powder diffraction, thermogravimetry, and scanning electron microscopy. At 950°C the phase transformation in Ar–Cl2 atmosphere is about 300 times faster than in air. The growth of crystals of rutile from the vapor phase has been observed. We also determined that anatase powders with adsorbed chlorine rapidly rapidly transformed to rutile and underwent a color change from white to gray when they were heated in Ar atmosphere.
Sol–Gel Processing and Microwave Characteristics of Ba(Mg⅓Ta⅔)O3Dielectrics
Authors: Renoult Olivier , Boilot Jean‐Pierre , Chaput Frédéric , Papiernik Renée , Hubert‐Pfalzgraf Liliane G. , Lejeune Martine
Published: March 2005

The sol–gel method has been developed for the preparation of pure Ba(Mg1/3Ta2/3)O3ceramics. This involves the reaction of the heterometallic alkoxide Ta2Mg(OEt)12with hydrated barium hydroxide Ba(OH)2·8H2O. Complete crystallization of the sol–gel‐derived powder is achieved at 600°C, leading to a cubic perovskite type phase. After sintering at 1400°C (2–5 h), a trigonal cell arises from Mg–Ta ordering (the degree of order is greater than 0.9), and about 98.5% of the theoretical density is obtained. Preliminary microwave dielectric measurements show that the dielectric constant and the unloadedQuof the ceramics are 24.2 and 6750, respectively, at 7.7 GHz.
Interpretation of the Parabolic and Nonparabolic Oxidation Behavior of Silicon Oxynitride
Authors: Persson Jeanette , Käll Per‐Olov , Nygren Mats
Published: March 2005

The oxidation process of Si2N2O, prepared by a hot isostatic pressing technique, has been studied by the thermogravimetric method. The oxidation has been performed in oxygen for 20 h in the temperature range 1300° to 1600°C, producing oxide scales of amorphous SiO2 and α‐cristobalite. The weight gain for T 1350°C does not begin to follow a parabolic rate law, until a certain time, t0. The A0 parameter in the parabolic rate law, (Δw/A0)2=Kpt+B, represents the cross section area, A, through which the oxygen diffuses; in the derivation of this law A is assumed to be constant during the experiment. If crystallization occurs during the oxidation process, A will decrease with time. A function, A(t), describing the time dependence, has been developed and incorporated into the parabolic rate law, yielding a new rate law, which reads ΔW/A0=a arctan √bt+c√t. This new rate law is valid in the time interval t < t0, whereas, for t > t0, the oxidation process follows the equation (Δw/A0)2=K°pt+B0. The relation of the latter equation to the common parabolic rate law is described. All of the oxidation curves are described by these equations. The activation energy of the oxygen diffusion (and of the oxidation (Kp)) is found to be 245 ± 25 kJ/mol, which is consistent with literature values reported for oxygen diffusion.
Design of a Laminated Ceramic Composite for Improved Strength and Toughness
Authors: Russo Charles J. , Harmer Martin P. , Chan Helen M. , Miller Gary A.
Published: March 2005

Adding aluminum titanate to alumina can result in dramatic improvements in toughness and R‐curve properties. However, the improved toughness is offset by a significant reduction in strength at small flaw sizes. This problem can be overcome through the use of a laminated composite construction. By placing a thin layer of high‐strength material on the surface of a high‐toughness body, the toughness and flaw tolerance of the body material can be maintained without sacrificing small flaw strength. In this study, alumina + 20 vol% aluminum titanate (AAT20) was used for both the surface layer and the bulk material. The surface material was a homogeneous, fine‐grained mixture of the two phases, while the bulk was an inhomogeneous mixture having a bimodal grain structure. In monolithic form, the homogeneous AAT20 displays a nearly P−1/3 indentation strength response, and the inhomogeneous material displays a flat strength response, indicative of R‐curve behavior. The trilayer material shows a composite indentation strength response, with high strength throughout the entire range of starting flaw sizes. A method for predetermining the optimum surface layer thickness is presented. The processing and mechanical properties of these materials will be discussed.
Aerogels
Authors: Fricke Jochen , Emmerling Andreas
Published: March 2005

The first aerogels were made by S. S. Kistler in 1931. Aerogels are produced by a sol–gel process followed by supercritical drying of the wet gel in an autoclave. Their porosity extends from about 1 to 100 nm, which is the reason why properly made aerogels are highly transparent. Aerogels have a spongelike, open‐pore structure with a large inner surface. Monolithic aerogels are used in Cerenkov detectors in high‐energy physics; several houses have been insulated with layers of translucent granular aerogels for the purpose of passive solar energy usage; opacified aerogel powders are being tested as substitutes for chlorofluoro‐carbon‐blown polyurethane foams and as thermal superinsulations in heat‐storage systems; experiments have been performed with aerogels as catalytic substrates, acoustic impedance matching layers, precursors for high‐quality glasses, containment for fusion fuels, and gas filters; and aerogels are used in radioluminescent light and energy sources. The attraction that these low‐density materials exert on physicists, chemists, and material scientists is recognized from the upsurge of publications on aerogels: about 200 papers are currently published per year. Recently, the periodical Science has rated aerogels as one of the top ten scientific and technological developments.