bluuebunny/crossref_metadata_2025 huggingface dataset:
Interactions between Ruthenia‐Based Resistors and Cordierite–Glass Substrates in Low‐Temperature Co‐fired Ceramics
Authors: Ting Ching‐Jui , Hsi Chi‐Shiung , Lu Hong‐Yang
Published: July 2009

Low‐temperature co‐fired ceramics (LTCCs) that are composed of a RuO2‐based resistor and a cordierite–glass substrate have been sintered at temperatures of 850° and 900°C. The microstructure of the resistor/substrate interface has been investigated using scanning and transmission electron microscopy, and its correlation to the overall resistance has been discussed. X‐ray diffractometry has revealed that lead ruthenate pyrochlore (Pb2Ru2O6.5) in peak‐fired thick‐film resistors (TFRs) disappears and the co‐fired samples contain only RuO2 in the resistor film when sintered at 900°C. The overall resistance of the LTCC resistors is increased by a factor of ∼3 when temperature is increased from 850°C to 900°C. The cordierite–glass composition of the initial substrate reacts with glass in the resistor film. The greatly extended layer of the resistor/substrate interface that contains the conductor particles is either broad or diffuse, which contrasts the abrupt interface that often is observed in conventional TFRs. This layer contains predominantly faceted platelike crystals of anorthite, in addition to other phases (such as diopside, sapphirine, and cristobalite) that apparently crystallize during co‐firing as vitrification and chemical reactions between glass compositions of the substrate and the resistor occur. The increase in the resistance of the LTCC resistors is attributed to the interruption of the conducting path by platelike anorthite crystals that are produced in the resistor/substrate interface when subjected to co‐firing.
Chemical Preparation of Pure and Strontium‐ and/or Magnesium‐Doped Lanthanum Gallate Powders
Authors: Taş A. Cüneyt , Majewski Peter J. , Aldinger Fritz
Published: July 2009

Powder compositions of LaGaO3, La0.9Sr0.1GaO2.95, and La0.8Sr0.2Ga0.83Mg0.17O2.815 were prepared via a Pechini‐type process that uses citric acid and ethylene glycol. The calcination behavior of the precursor powders of the above‐mentioned phases was studied in the temperature range of 200°–1400°C in an air atmosphere. Characterization of the powder samples were performed using several processes, including X‐ray diffractometry, thermogravimetry/differential thermal analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, inductively coupled plasma–atomic emission spectroscopy, and carbon and nitrogen analyses.
Effect of Nitrate Salts as Sintering Additives during the Ball‐Milling Process of Silicon Nitride Powders
Authors: Park Dae‐Chul , Yano Toyohiko , Iseki Takayoshi , Urabe Kazuyori
Published: July 2009

A chemical adsorption method in a Si3N4 slurry that contained a nitrate solution was studied during ball milling, with particular interest in increasing the oxide layer in the Si3N4 powder and improving the distribution homogeneity of the sintering additives. The nitrate salts Al(NO3)3·9H2O and Y(NO3)3·6H2O were selected as sintering additives. The following characterization techniques were used: oxygen–nitrogen analysis, X‐ray photoelectron spectroscopy, high‐resolution electron microscopy (coupled with energy‐dispersive X‐ray spectroscopy), and X‐ray imaging (using wavelength‐dispersive X‐ray spectroscopy). The thickness of the amorphous layer and the oxygen content of the Si3N4 powder were greater for samples that were milled with nitrate additives, which were heat‐treated at 600°C, than those of powders that were milled with oxide additives. The chemical composition of the oxygen‐containing layer—that is, the amorphous layer that formed and/or changed on the Si3N4 surface—was similar to Si2N2O in heat‐treated Si3N4 powder with nitrate additives, whereas the composition of heat‐treated Si3N4 powder with oxide additives was similar to SiO2. Furthermore, a homogeneous distribution of the additives was achieved via the incorporation of aluminum and yttrium into the amorphous layer on the Si3N4 surface. The metal ratio (Y:Al) of the adsorbates was somewhat higher than that of the additives.
Preparation of Stabilized Nanosized Tin Oxide Particles by Hydrothermal Treatment
Authors: Baik Nam seok. , Sakai Go , Miura Norio , Yamazoe Noboru
Published: July 2009

Stable colloidal suspensions of tin oxide (content 0.9–6.1 wt%) were synthesized by subjecting conventionally prepared tin oxide gels to hydrothermal treatment with an ammonia solution (pH 10.5) at 200°C for 3 h in an autoclave. Based on X‐ray diffractometry analyses, the tin oxide crystallites after hydrothermal treatment were resistant to thermal growth at elevated temperatures, and this feature became more conspicuous as the tin oxide content of the colloidal suspension decreased. For the powder derived from a 1.8 wt% colloidal suspension, for example, the mean sizes of the tin oxide crystallites were 7.5 and 13 nm after calcination at 600° and 900°C, respectively, in comparison with corresponding values of 13.5 and 29 nm for the untreated gel‐derived powder. Thin film spin‐coated from the same suspension had good uniformity, packed with tin oxide grains (crystallites) of a mean size of 6 nm after calcination at 600°C. Optical determination of the tin oxide sol particle size, as well as gravimetric analysis of the dehydration from the powder samples, were conducted to determine effects of hydrothermal treatment.
Preparation and Proton Conductivity of Surfactant‐Templated Mesoporous Silica Gels Impregnated with Protonic Acids
Authors: Nishiwaki Shogo , Tadanaga Kiyoharu , Tatsumisago Masahiro , Minami Tsutomu
Published: July 2009

Surfactant‐templated mesoporous silica gel that was impregnated with various protonic acids has been prepared, and we propose this material as a new type of proton conductor. The conductivity of the mesoporous silica gel that was impregnated with 5.0M H2SO4 was ∼1 × 10−4 S/cm at room temperature in a dry nitrogen‐gas atmosphere after drying in vacuo at room temperature; this value was four orders of magnitude greater than that of silica gel that was prepared via the conventional sol–gel method and impregnated with H2SO4. The amount of impregnated H2SO4 in the mesoporous silica gel was ∼2.5 times larger than that of impregnated H2SO4 in the conventional silica gel. The H2O molecules in the mesoporous silica gel that was impregnated with H2SO4 remained in the pores of the gel, even after drying in vacuo at room temperature.
Ceramic Composites with Multilayer Interface Coatings
Authors: Besmann Theodore M. , Kupp Elizabeth R. , Lara‐Curzio Edgar , More Karren L.
Published: July 2009

Silicon carbide matrix composites have been fabricated from either ceramic‐grade NicalonTM or Hi‐NicalonTM fibers coated with an interface material consisting of six alternating carbon and silicon carbide layers. Initial efforts involved the use of chemical vapor infiltration to produce minicomposites (single tows of fibers). In subsequent work, forced‐flow thermal‐gradient chemical vapor infiltration was used to produce a single composite plate with a multilayer interface from ceramic‐grade Nicalon fabric and two plates from Hi‐Nicalon fabric, one with a single carbon layer and one with a multilayer interface. Tensile testing of the minicomposites and of specimens cut from the plates revealed typical composite behavior and strengths for the as‐processed samples. Exposure of tensile specimens to 950°C air for 100 h resulted in large losses in strength and strain tolerance regardless of the interface coating. The results demonstrate that forced‐flow thermal‐gradient chemical vapor infiltration can be used to prepare multilayer interface material. The results also verified that relatively thick (>100 nm) single or multiple carbon layers are susceptible to oxidation that causes the loss of composite properties.
A Layered Alumina Composite Tested at High Temperature in Air
Authors: O'Brien Michael J. , Capaldi Franco M. , Sheldon Brian W.
Published: July 2009

An oxidation‐resistant interphase for layered alumina composites was prepared by aerosol spray deposition of submicrometer alumina powder. A model composite specimen was made by placing the interphase between thin layers of monolithic alumina. The composite sandwich was hot‐pressed to control the interphase fracture resistance for successful crack deflection. Specimens were tested under four‐point bending in air at two crosshead speeds at ambient temperature, 1000°C, and 1200°C. The fracture behavior was temperature dependent, with a higher work of fracture at higher temperatures. Interphase delamination and composite toughening behavior were very pronounced at all temperatures. At the highest temperature, the transition to multiple widely distributed cracks and increased crack deflection may be related to inelastic deformation in the alumina.
Oxidation Behavior of Si‐C‐O Fibers (Nicalon) under Oxygen Partial Pressures from 102 to 105 Pa at 1773 k
Authors: Shimoo Toshio , Morisada Yoshiaki , Okamura Kiyohito
Published: July 2009

Polycarbosilane‐derived SiC fibers (Nicalon) were oxidized at 1773 K under oxygen partial pressures from 102 to 105 Pa. The effect of oxygen partial pressure on the oxidation behavior of the Nicalon fibers was investigated by examining mass change, surface composition, crystal phase, morphology, and tensile strength. The Nicalon fibers were passively oxidized under oxygen partial pressures of >2.5 ×102 Pa and actively oxidized under an oxygen partial pressure of 102 Pa. Under oxygen partial pressures from 2.5 × 102 to 103 Pa, active oxidation occurred at the earliest stage of oxidation, resulting in the formation of both a silica film and a carbon intermediate layer. Although the unoxidized core retained considerable levels of strength under the passive‐oxidation condition, fiber strength was lost under the active‐oxidation condition.
Comparison of Methods to Determine the Fracture Toughness of Three Glass‐Ceramics at Elevated Temperatures
Authors: Quinn Janet B. , Lloyd Isabel K.
Published: July 2009

Two standardized methods for measuring kIc in ceramics are compared for use at high temperatures (precracked beam and surface crack in flexure). Results from a third technique involving the measurement of cracks around Vickers indentations are also presented. Three dental glass‐ceramics, differing primarily in microstructure, were used as model materials in this study. They emphasized the importance of microstructure in determining high‐temperature kIc values and the challenges in measuring them. The measured fracture toughnesses decreased with temperature and increased with imbedded grain size for all three methods.
Thermodynamic Assessment of the Lithium‐Borate System
Authors: Yu Hao , Jin Zhanpeng , Chen Qing , Hillert Mats
Published: July 2009

The Li2O–B2O3 quasi‐binary system is assessed. A two‐sublattice ionic solution model, (Li1+)P(O2−, BO33−, B4O72−, B3O4.5)Q, is adopted to describe the liquid phase. All solid phases are treated as stoichiometric compounds. A set of parameters consistent with most of the available experimental data on phase diagram and thermodynamic properties is obtained by using the CALPHAD technique.
Alumina Agglomerate Effects on Toughness‐Curve Behavior of Alumina–Mullite Composites
Authors: Khan Ajmal , Chan Helen M. , Harmer Martin P. , Cook Robert F.
Published: July 2009

Toughness‐curve (T‐curve) behavior of composites of spherical, polycrystalline, coarse‐grained, alumina agglomerates dispersed throughout a constant‐toughness, fine‐grained, 50–50 vol% alumina–mullite matrix has been evaluated as a function of agglomerate content for the range 15 to 45 vol%. T‐curve behavior was evaluated using the indentation‐strength method. Increasing alumina agglomerate content resulted in a progressive increase of large indentation load strengths with negligible change of plateau strength levels at small indentation loads. This behavior is consistent with underlying T‐curves that rise to greater values and are shifted toward longer crack lengths with increasing agglomerate content, suggesting that both bridge spacing and bridge potency increase with increasing agglomerate content over the range tested. The proposed relationships between bridge spacing and agglomerate content, and bridge potency and agglomerate content, are rationalized in terms of residual stress considerations. The indentation‐strength data also demonstrated that the composite containing the greatest alumina agglomerate content, 45 vol%, exhibited the greatest flaw tolerance.
High‐Temperature Tensile Deformation of Glass‐Doped 3Y‐TZP
Authors: Imamura Philip H. , Evans Neal D. , Sakuma Taketo , Mecartney Martha L.
Published: July 2009

Amorphous grain boundary phases in 3‐mol%‐yttria‐stabilized zirconia ceramics (3Y‐TZP) were studied to determine the influence of intergranular amorphous silicate phases on tensile superplasticity at temperatures of 1300–1500°C. Controlled additions (1 wt%) of compositionally distinct barium silicate and borosilicate phases were used. The initial grain sizes of the pure, barium silicate added, and borosilicate‐added samples were 0.45, 0.55, and 0.55 μm, respectively. Systems with added barium silicate and borosilicate glass both exhibited a 60% reduction in flow stress as compared with pure 3Y‐TZP, with the lower‐viscosity barium silicate system exhibiting a slightly greater reduction in flow stress. The higher‐viscosity borosilicate glass/3Y‐TZP materials exhibited the greatest elongation to failure, while the barium silicate/3Y‐TZP materials had the least elongation. Yttrium was found to segregate to grain boundaries in the pure and borosilicate‐containing samples, and both yttrium and barium were found to segregate to grain boundaries in the barium silicate containing samples. No silicon was observed along two‐grain boundaries in any of the samples, even those containing pockets of glass. The difference in deformation behavior may be due to a combination of viscosity of the glass addition, grain boundary segregation, and grain boundary bond character.
Shape Dependence of the Coarsening Behavior of Niobium Carbide Grains Dispersed in a Liquid Iron Matrix
Authors: Oh Kyung‐Sik , Jun Jae‐Yong , Kim Doh‐Yeon , Hwang Nong M.
Published: July 2009

In niobium carbide–iron (NbC‐Fe) specimens where the grains were faceted, abnormally large grains appeared during coarsening. Normal and uniform grain growth occurred when the grain shape was changed to a spherical morphology by the addition of a small amount of boron. The results have been discussed, in terms of a coarsening mechanism, depending on the atomic structure of the interface. For faceted grains with an atomically smooth interface structure, the coarsening was suggested to occur via two‐dimensional nucleation and a lateral‐growth mechanism. For spherical grains with an atomically rough interfacial structure, diffusion was suggested to control the coarsening process.
Densification Behaviors of Fine‐Alumina and Coarse‐Alumina Compacts during Liquid‐Phase Sintering with the Addition of Talc
Authors: Kim Ho‐Yang , Lee Jung‐A , Kim Jeong‐Joo
Published: July 2009

The densification behavior of fine alumina (mean particle size of ∼0.31 μm) and coarse alumina (mean particle size of ∼4.49 μm) during liquid‐phase sintering with additions of talc have been studied, as well as the microstructural evolution. Small amounts (0, 5, and 10 wt%) of talc were added to the fine alumina and coarse alumina, which were sintered at various temperatures for 2 h. When 5 wt% of talc was added to the coarse alumina, densification proceeded rapidly above the liquid‐formation temperature in alumina–talc compacts, because of the promotion of a rearrangement process of the solid grains by the liquid phase. The addition of 10 wt% of talc greatly accelerated densification by increasing the volume fraction of liquid. On the other hand, in the fine alumina, which has a higher activity and a greater driving force for sintering, appreciable densification started below the liquid‐formation temperature, which prevented further densification after liquid formation. Moreover, the densification was suppressed as the talc content increased. The rigid skeleton of solid grains that was formed by densification below the liquid‐formation temperature is believed to have suppressed the rearrangement process of the solid grains, and further densification of the compacts was retarded, even after the formation of a liquid phase above the liquid‐formation temperature.
Texture Development in Silicon Nitride–Silicon Oxynitride In Situ Composites via Superplastic Deformation
Authors: Xie Rong‐Jun , Mitomo Mamoru , Kim Wonjoong , Kim Young‐Wook
Published: July 2009

Silicon nitride–silicon oxynitride (Si3N4–Si2N2O) in situ composites have been fabricated via either the annealing or the superplastic deformation of sintered Si3N4 that has been doped with a silica‐containing additive. In this study, quantitative texture measurements, including pole figures and X‐ray diffraction patterns, are used in conjunction with scanning electron microscopy and transmission electron microscopy techniques to examine the degree of preferred orientation and texture‐development mechanisms in these materials. The results indicate that (i) only superplastic deformation can produce strong textures in the β‐Si3N4 matrix, as well as Si2N2O grains that are formed in situ; (ii) texture development in the β‐Si3N4 matrix mainly results from grain rotation via grain‐boundary sliding; and (iii) for Si2N2O, a very strong strain‐dependent texture occurs in two stages, namely, preferred nucleation and anisotropic grain growth.
Sintering Behavior, Microstructure, and Phase Composition of Sr(Fe,Co)O3−δ Ceramics
Authors: Kleveland Kjersti , Einarsrud Mari‐Ann , Grande Tor
Published: July 2009

SrFe1−xCoxO3−δ (x= 0, 0.33) ceramics have been prepared in the temperature interval 900–1350°C in air, nitrogen, and oxygen atmosphere. The effect of cation nonstoichiometry on densification behavior, microstructure, and phase composition has been investigated. Densification of Sr‐deficient SrFeO3−δ initiates at a lower temperature than near stoichiometric SrFeO3−δ probably due to enhanced diffusion of Sr. However, for Sr‐deficient samples Sr4Fe6O13 is formed above ∼775°C, causing a significant decrease in the sintering rate. It is therefore necessary to avoid Sr deficiency to obtain dense SrFeO3−δ ceramics. The densification rate was significantly increased by Co substitution. Dense ceramics (>95% of theoretical density) of Sr‐excess and Co‐substituted SrFeO3−δ were obtained by sintering in the temperature region 1000–1200°C. The grain size increases by increasing temperature, decreasing partial pressure of oxygen and Co substitution. Exaggerated grain growth in the Co‐substituted material occurred at high temperatures. Sintering above 1200°C caused all materials, apart from Co‐substituted SrFeO3−δ in oxygen, to swell and develop a porous microstructure. The swelling mechanism was related to heterogeneous phase equilibria, which is reductive in nature and leads to evolution of oxygen gas. The phase equilibria are governed by the cation nonstoichiometry of the materials. The present findings demonstrate the importance of controlling the cation stoichiometry of ternary transition‐metal oxides to achieve ceramics with the desired homogeneous microstructure. The mixed valence state of the transition metal may lead to both swelling during sintering and cracking during cooling due to reduction/oxidation during heating/cooling.
Microstructural Development in SnO2‐Doped ZnO–Bi2O3 Ceramics
Authors: Daneu Nina , Rečnik Aleksander , Bernik Slavko , Kolar Drago
Published: July 2009

The effects of adding small quantities of SnO2 to the basic ZnO–Bi2O3 varistor composition were studied in terms of phase reactions, microstructural development, and the formation of inversion boundaries. Scanning and transmission electron microscopy studies showed that the inversion boundaries, triggered by the addition of SnO2, cause anisotropic grain growth in the early stages of sintering. ZnO grains that include inversion boundaries grow exaggeratedly, at the expense of normal grains, until they dominate the microstructure. Higher additions of SnO2 lead to an increase in number of grains with inversion boundaries and to a more fine‐grained microstructure. The increasing amount of secondary phases is also related to a higher level of SnO2 addition; however, the influence of these phases on ZnO grain growth is subordinate to the role of inversion boundaries.
Temperature Dependence of the Coarsening Behavior of Barium Titanate Grains
Authors: Kang Myung‐Goo , Kim Doh‐Yeon , Lee Ho‐Yong , Hwang Nong M.
Published: July 2009

The coarsening behavior of large seed particles during the sintering of BaTiO3 ceramics has been investigated. At 1350°C, the grains are faceted, and the seed particles grow extensively. At 1380°C, however, the grains are spherical, and coarsening of the seed particles is limited. The observed difference is discussed in terms of the growth mechanism and the atomic structure of the interfaces.
Hydrothermal Corrosion and Strength Degradation of Aluminum Nitride Ceramics
Authors: Tamai Hiroyasu , Hamauzu Takashi , Ryumon Akihito , Aoki Kaoru , Oda Kohei , Yoshio Tetsuo
Published: July 2009

The hydrothermal corrosion and strength degradation of aluminum nitride (AlN) ceramics were investigated. The weight gain in AlN ceramics after corrosion occurred because of the formation of boehmite. The reaction kinetics of AlN with water were diffusion controlled through the boehmite product layer. At 180°C, immersion in water caused no strength degradation, and water vapor caused a 20% strength degradation. At 300°C, immersion in water caused a 20% strength degradation, and water vapor caused a 30% strength degradation.
Conversion from β‐Ce2O3·11Al2O3 to α‐Al2O3 in Tetragonal ZrO2 Matrix
Authors: Tsukuma Koji
Published: July 2009

Composites of β‐Ce2O3·11Al2O3 and tetragonal ZrO2 were fabricated by a reductive atmosphere sintering of mixed powders of CeO2, ZrO2 (2 mol% Y2O3), and Al2O3. The composites had microstructures composed of elongated grains of β‐Ce2O3·11Al2O3 in a Y‐TZP matrix. The β‐Ce2O3·11Al2O3 decomposed to α‐Al2O3 and CeO2 by annealing at 1500°C for 1 h in oxygen. The elongated single grain of β‐Ce2O3·11Al2O3 divided into several grains of α‐Al2O3 and ZrO2 doped with Y2O3 and CeO2. High‐temperature bending strength of the oxygen‐annealed α‐Al2O3 composite was comparable to the β‐Ce2O3·11Al2O3 composite before annealing.
Structure Determination in Colloidal Crystal Photonic Bandgap Structures
Authors: Ballato John , DiMaio Jeffrey , Taylor Theodore D. , Gulliver Eric , Han Dae‐Gon , Riman Richard E. , Carroll David L.
Published: July 2009

Structure/optical property relationships in photonic bandgap structures are evaluated by a novel combination of sample sectioning, microscopy, and image analysis. Disordered colloidal crystals of solution‐derived, monosized SiO2 particles were sectioned by focused ion beam (FIB) milling and then imaged using field emission scanning electron microscopy (FE‐SEM). Pair correlation and radial distribution functions of the particulate arrangement were generated directly from a binary color scale rendering of the FE‐SEM images, therein defining the level of order or disorder in the structure. These experimentally obtained spatial correlation functions were used to compute the scattering spectral properties in an analogous, although inverse (i.e., solving the inverse scattering problem), method to that used in X‐ray diffraction for structure determination. Using a first‐order approximation to the scattering from a disordered structure, the bandwidth and midgap values for the colloidal crystal photonic bandgap materials were within 15% of those measured. This new methodology promises to provide a simple and direct approach for quantifying the structure/optical property relationships in ordered and disordered photonic crystals directly from standard microstructural imaging techniques.
Processing and Characterization of Bulk Chalcogenide Glasses Used for Waveguide Applications
Authors: Lopez Cedric , Richardson Kathleen A. , de Castro Michelle , Seal Sudipta , Verma Dharmendra K. , Shulte Alfons , Rivero Clara , Villeneuve Alain , Gastian Tigran V. , Turcotte Karine , Saliminia Ali , Laniel Jacques
Published: July 2009

Chalcogenide glasses (ChG) are of interest due to their optical and electronic properties for use in waveguide applications. To assess expected uniformity in films deposited from bulk glass starting materials, the extent of parent bulk glass property variation was evaluated. Resulting structural and optical properties of melt‐derived ChG's were investigated using X‐ray diffraction (XRD), Raman spectroscopy, differential thermal analysis and spectrophotometric analysis. The influence of melt size, purification, and other melting conditions on sample homogeneity were quantified and within‐melt property variation of bulk glass samples was found to be less than 5% for all parameters examined.
Spectroscopic Study of Neodymium(III) in Sodium Tellurite Glass
Authors: Li Hong , Sundaram S. Kamakshi , Blanc‐Pattison P. A. , Li Liyu
Published: July 2009

The local environment of Nd‐O in a sodium tellurite glass was elucidated as a function of Nd2O3 concentration, from 0.1 to 2.5 mol%, using optical spectroscopy. The Judd‐Ofelt (J‐O) theory was used to determine the oscillator strength parameters (J‐O parameters) of the glasses. According to the J‐O parameters, a significant change in the local environment of Nd‐O was suggested for the glass containing 1 mol% Nd2O3; the asymmetry of the Nd‐O crystal field was shown to be at a maximum and the bond covalency at a minimum. The results were further supported by a significant shift of the structural hypersensitive band of the glass with 1 mol% Nd2O3, as compared with those of the other glasses.
Visible Frequency Thin Film Photonic Crystals from Colloidal Systems of Nanocrystalline Titania and Polystyrene Microspheres
Authors: Subramania Ganapathi , Constant Kristen , Biswas Rana , Sigalas Mihail M. , Ho Kai‐ming
Published: July 2009

This work describes a simple and novel ceramic processing technique to form periodic ordered structures in ceramic materials with a uniform pore size distribution. This material shows photonic gaps at visible/near‐IR wavelengths. Monodisperse colloidal polystyrene microspheres are self‐organized into a crystalline structure of close‐packed spheres in a suspension of nanocrystalline titania. The nanoparticle titania fills the intersphere region simultaneously during colloidal crystallization. Removal of the polystyrene microspheres by calcination at a temperature of 520°C results in a periodic porous structure with a high refractive index background material. Crystals having ordered regions, a few millimeters across with typical grain sizes of 50–70 μm, are grown as thin films on substrates including glass and silicon. Optical reflectivity measurements indicate peaks at the stop band wavelengths that scale with the pore size. Visual inspection and optical microscopy reveal uniform colored regions for crystals with periodicity comparable to visible wavelengths. Despite the presence of cracks resulting from drying and heat treatment as well as numerous grain boundaries, optical characterization clearly demonstrates a photonic band gap. Reflectance peaks due to a pseudogap can be shifted by application of high pressure. In the following sections we will describe the experimental procedure and discuss optical reflectance and transmission measurements that can reveal information about the crystals, namely, the lattice constant, the refractive index, and the filling fraction of the background material.
Vibrational Spectra of Water‐ and Ammonium‐Chloride‐Related Residues and Upconversion Fluorescence of Er3+ in ZnCl2‐Based Glasses
Authors: Wada Noriyuki , Tsuneoka Takashi , Kojima Kazuo
Published: July 2009

Chloride glasses of the ZnCl2 and 20KCl‐20BaCl2‐60ZnCl2‐0.5ErCl3 systems were prepared using NH4Cl as a dehydrating and chlorinating agent, under the melt‐quenching method. Water‐ and ammonium‐chloride‐related residues in ZnCl2 glasses were investigated by infrared and near‐infrared absorption spectra. Water, Zn—OH, ClO, ClO2−, Zn2+‐coordinated water, free NH3, NH4+, and Zn2+‐coordinated NH3 were identified in ZnCl2 glasses. 20KCl‐20BaCl2‐60ZnCl2‐0.5ErCl3 glasses prepared by melting at 500°C for 20 min, under reduced pressure, contained the smallest amounts of water, Zn—OH, and Zn2+‐coordinated NH3 and showed strong Er3+ upconversion fluorescence.
Aqueous Degradation and Chemical Passivation of Yttria‐Tetragonally‐Stabilized Zirconia at 25°C
Authors: Kimel R. Allen , Adair James H.
Published: July 2009

The objective of this study was to establish the mechanism(s) controlling degradation of yttria‐tetragonally‐stabilized zirconia (Y‐TZP) powder in aqueous suspensions and determine the significance of this degradation to the aqueous physical chemistry of Y‐TZP. Experiments were performed on commercially available Y‐TZP powder placed in aqueous suspensions at 25°C. Experimental investigations included analysis of the aqueous chemistry of Y‐TZP in water via ICP‐MS, determination of the surface and bulk structure of the powder via XRD and solid‐state NMR, and observation of changes in surface charges via zeta potential determinations. The goal of this study was to control the surface chemistry of Y‐TZP in aqueous suspension to promote dispersion and permit aqueous processing of Y‐TZP powders.
Phase‐Pure Mullite from Kaolinite
Authors: Yamuna Ammini , Devanarayanan Sankaranarayana , Lalithambika Malathi
Published: July 2009

Sintering of kaolinite in the presence of certain carbonate mineralizers, viz., CaCO3, Na2CO3, and K2CO3, has been conducted at 950°–1350°C. The influence of these mineralizers at the above temperatures is evaluated using XRD and SEM techniques. A comparative study of phase formation of the above compositions shows that the sodium‐ and calcium‐fluxed samples give rise to multiphase systems, while K2CO3‐incorporated samples give phase‐pure mullite. The observation that kaolinite in the presence of K2CO3 can act as a precursor material for phase‐pure mullite is of great industrial significance.
Synthesis of Gallium Oxide Hydroxide Crystals in Aqueous Solutions with or without Urea and Their Calcination Behavior
Authors: Taş A. Cüneyt , Majewski Peter J. , Aldinger Fritz
Published: July 2009

Gallium oxide hydroxide (GaOOH·xH2O) single crystals were synthesized in aqueous solutions by using two different precipitation techniques: homogeneous decomposition of urea and forced hydrolysis in pure water. Precipitation of crystals started at exactly the same pH value (i.e., 2.05 at 85°C) in both cases. The morphology of crystals turned out to be quite different (zeppelin‐like with urea, rodlike without urea) in each of the above methods. Calcination of these gallium oxide hydroxide crystals in air at temperatures ≥500°C transformed them into Ga2O3. Characterization of the samples was performed by X‐ray diffractometry, scanning electron microscopy, thermogravimetry/differential thermal analysis, Fourier transform infrared spectroscopy, and ICP, carbon, and nitrogen analyses.
Fabrication and Characterization of Cordierite/Zircon Composites by Reaction Sintering: Formation Mechanism of Zircon
Authors: Sun En‐Hai , Kusunose Takafumi , Sekino Tohru , Niihara Koichi
Published: July 2009

The formation mechanism of ZrSiO4 in the cordierite‐ZrO2 system was studied in the temperature range of 1250° to 1400°C by X‐ray diffraction analysis and discussed by analyzing experimental data using some reported reaction models. Nuclei growth models were found to describe the reaction well, and a satisfactory fit was obtained by applying the Avrami equation to estimate the reaction rate constant κ. Different values of the time exponent m were obtained at different temperatures: 0.32 at 1250°C, 0.34 at 1300°C, 0.39 at 1350°C, and 0.49 at 1400°C. The results indicate that there is a progressive change in reaction mechanism.
Development of a Self‐Forming Ytterbium Silicate Skin on Silicon Nitride by Controlled Oxidation
Authors: Lee Seung Kun , Readey Michael J.
Published: July 2009

A dense and uniform polycrystalline ytterbium silicate skin on silicon nitride ceramics was developed by a controlled oxidation process to improve the hot corrosion resistance of silicon nitride. The process consists of purposely oxidizing the silicon nitride by heating it at high temperatures. It was found that the ytterbium silicate phase was formed as an oxidation product on the surface of the silicon nitride when it was exposed to air at temperatures above 1250°C. The volume fraction of ytterbium silicate compared with that of SiO2 on the silicon nitride surface increased with increasing oxidation time and temperature. The formation and growth of ytterbium silicate on the surface of silicon nitride is attributed to a nucleation and growth mechanism. Ultimately, a dense and uniform ytterbium silicate skin with 3–4 μm of skin thickness was obtained by oxidation at 1450°C for 24 h. The ytterbium silicate layer, formed by oxidation of the silicon nitride, is associated with the reaction of SiO2 on the surface of silicon nitride with Yb2O3 introduced in the silicon nitride as a sintering additive. Preliminary tests showed that the ytterbium silicate skin appears to protect silicon nitride from hot corrosion. No observable evidence of a reaction between the skin and molten Na2SO4 was found when it was exposed to molten Na2SO4 at 1000°C for 30 min.
Measuring Permeability of Rigid Materials by a Beam‐Bending Method: III, Cement Paste
Authors: Vichit‐Vadakan Wilasa , Scherer George W.
Published: July 2009

The evolution of permeability and elastic modulus for Type III portland cement pastes with water/cement ratios varying from 0.4 to 0.6 were measured using a beam‐bending method. Young's modulus was independently verified by measuring the ultrasonic pulse velocity. The permeability ranged over 2 orders of magnitude, depending on the water/cement ratio and the age of the samples. The advantage of the beam‐bending method is that the permeability results are obtained in a few minutes to a few hours, whereas conventional techniques take hours or days to measure permeability of this order of magnitude. More importantly, there is no need to maintain high pressure during the measurement period, so leaks are not a problem.
Hardness, Toughness, and Scratchability of Germanium–Selenium Chalcogenide Glasses
Authors: Guin Jean‐Pierre , Rouxel Tanguy , Sanglebœuf Jean‐Christophe , Melscoët Isabelle , Lucas Jacques
Published: July 2009

Ge–Se chalcogenide glasses are characterized by relatively low hardness (0.39–2.35 GPa) and low fracture toughness (0.1–0.28 MPa·m1/2). Actually, the hardness of chalcogen‐rich glasses is low enough so that the brittleness parameter, B=H/Kc, is lower than that of silicate glasses. Whereas hardness and Young's modulus increase with increasing germanium contents, fracture toughness follows a trend similar to that of the density and exhibits a maximum for the Ge20Se80 composition, which corresponds to the rigidity percolation threshold. Optical microscopy and atomic force microscopy observations suggest that the indentation deformation proceeds by a localized shear deformation phenomenon. Glasses in the chalcogen‐rich region behave viscoelastically at room temperature. As a consequence, an increase of the loading time results in a decrease of hardness and toughness.
Failure of Crossply Ceramic‐Matrix Composites
Authors: O'Day Michael P. , Curtin William A.
Published: July 2009

The fast‐fracture and stress‐rupture of a crossply ceramic‐matrix composite with a matrix through‐crack are examined numerically to assess the importance of fiber architecture and the associated stress concentrations at the 0/90 ply interface on failure. Fiber bridging in the cracked 0 ply is modeled using a line‐spring bridging model that incorporates stochastic and time‐dependent fiber fracture. A finite‐element model is used to determine the stresses throughout the crossply in the presence of the bridged crack. For both SiC/SiC and a typical oxide/oxide, the fast‐fracture simulations show that as global failure is approached, a significant fraction of fibers near the 0/90 interface are broken, greatly reducing the stress concentration. For fibers with low Weibull moduli (m < 10), the tensile strength is thus nearly identical to that of a unidirectional composite scaled by the appropriate fiber volume fraction, while for fibers with larger Weibull moduli (m≥ 10), there are modest (10−17%) reductions in tensile strength. Stress‐rupture simulations show that initially high stress concentrations are relieved as fibers fail with evolving time near the 0/90 interface and shed load away from the interface. For a wide range of fiber properties, efficient load redistribution occurs such that the crossply rupture lifetime is generally within an order of magnitude of the unidirectional lifetime, when the applied stress is normalized by the relevant fast‐fracture strength. Overall, stress concentrations at the 0/90 interface are largely relieved with increasing load or time due to the nonlinear bridging response and preferential fiber failure near the interface, resulting in crossplies that respond very similarly to unidirectional composites.
Morphological Evolution and Weak Interface Development within Chemical‐Vapor‐Deposited Zirconia Coating Deposited on Hi‐Nicalon™ Fiber
Authors: Li Hao , Lee Jinil , Libera Matthew R. , Lee Woo Y. , Kebbede Anteneh , Lance Michael J. , Wang Hongyu , Morscher Gregory N.
Published: July 2009

The phase contents and morphology of a ZrO2 fiber coating deposited at 1050°C on Hi‐NicalonTM by chemical vapor deposition (CVD) were examined as a function of deposition time from 5–120 min. The morphological evolution in the ZrO2 coating was correlated to the development of delamination within the ZrO2 coating. The delamination appears to occur as a result of: (i) continuous formation of tetragonal ZrO2 nuclei on the deposition surface; (ii) martensitic transformation of the tetragonal phase to a monoclinic phase on reaching a critical grain size; and (iii) development of significant compressive hoop stresses because of the volume dilation associated with the transformation. Our observations suggest that it will be of critical importance to further understand and eventually control the nucleation and grain growth behavior of CVD ZrO2 and its phase transformation behavior for its potential applications for composites.
Incorporation of Er3+ into BaTiO3
Authors: Buscaglia Maria Teresa , Viviani Massimo , Buscaglia Vincenzo , Bottino Carlo , Nanni Paolo
Published: July 2009

The incorporation of Er3+ into BaTiO3 ceramics was investigated on samples containing 0.25, 0.5, 1, 2, 8, and 10 at.% of dopant, after sintering at 1350–1550°C in air. For Er3+ concentrations ≤1 at.%, dense and large‐grained ceramics with low room‐temperature resistivity (102–103Ω·cm) were obtained. The observed properties are largely independent of stoichiometry. Simultaneous substitution of Er3+ at both cation sites, with higher preference for the Ba site, is proposed. The behavior of heavily doped ceramics depends on stoichiometry. When Ba/Ti < 1, the electrical properties change from slightly semiconducting to insulating as Er concentration increases from 2 to 8 at.%. The ceramics have tetragonal perovskite structure and contain a large amount of Er2Ti2O7 pyrochlore phase. On the other hand, when Ba/Ti > 1, the ceramics are insulating, fine‐grained, and single phase. In this case, incorporation of Er3+ predominantly occurs at the Ti site, with oxygen vacancy compensation. Incorporation is accompanied by a significant reduction of tetragonality and by expansion of the unit cell. The different results indicate that Er3+ solubility at the Ba site does not exceed 1 at.%, whereas solubility at the Ti site is at least 10 at.%. However, the incorporation of Er3+ and the resulting properties are also strongly affected by sintering conditions.
Grain Growth and Twin Formation in 0.74PMN·0.26PT
Authors: Wallace Jay S. , Huh Jong‐Moo , Blendell John E. , Handwerker Carol A.
Published: July 2009

The mechanisms controlling normal and exaggerated grain growth in lead magnesium niobate–lead titanate (PMN–PT) ceramics have been investigated by varying the PbO‐based liquid‐phase volume fraction from 0.03 to 0.6 and sintering temperature from 900° to 1100°C. There is a transition in matrix grain growth rate and matrix grain shape with liquid fraction; samples with liquid volume fractions less than ∼0.15 show relatively small equiaxed grains resulting from grain‐to‐grain impingement. Samples with higher liquid fractions show significantly larger, facetted, cube‐shaped grains, whose size is independent of liquid fraction, indicating that a surface nucleation rate mechanism controls growth in this regime. Exaggerated grains were found in the high liquid fraction samples. Electron backscatter diffraction showed that all of the exaggerated grains contained 60°〈111〉 twins but none of the normal matrix grains contained twins. The reentrant angles in the twinned grains give them a growth advantage over untwinned grains, resulting in a population of exaggerated grains.
Iron as an Oxygen Tracer at the Aluminum‐Alumina Interface
Authors: Levi George , Kaplan Wayne D.
Published: July 2009

During wetting experiments of pure aluminum on the (0001) plane of sapphire, an aluminum sample was unintentionally contaminated with 31 atoms/parts per million of iron. Transmission electron microscopy investigations of the sample after cooling showed the formation of FeAlO3 at the aluminum‐Al2O3 interface. Formation of FeAlO3 confirms the existence of a high oxygen activity at the liquid aluminum‐sapphire interface, which is considered to be the reason for the strong adhesion between aluminum and Al2O3. A low indexed orientation relationship between FeAlO3 and Al2O3 was determined, where [22¯1]FeAlO3‖ [11¯00]Al2O3 and (110)FeAlO3‖ (0001)Al2O3.
Methods of Purification of Zirconium Tetrafluoride for Fluorozirconate Glass
Authors: MacFarlane Douglas R. , Newman Peter J. , Voelkel Alice
Published: July 2009

High‐purity zirconium tetrafluoride (ZrF4) has been produced using sublimation and distillation techniques. The transition‐metal impurities have been determined in these purified samples, and it has been found that distillation is the preferred method of purification using a number of criteria. A detailed description of the apparatus used to produce this material is also given.
Synthesis of Two‐Phase SiAlONs in the Yttrium–Silicon–Aluminum–Oxygen–Nitrogen System
Authors: Bandyopadhyay Siddhartha , Maiti Himadri Sekhar
Published: July 2009

The reaction sequences of formation of different SiAlON phases along the Si3N4–Y2O3·9AlN–AlN·Al2O3 concentration plane in the Y‐Si‐Al‐O‐N system have been studied through dilatometric investigations. The presence and stability of some crystalline phases greatly influence the nature of the liquid, which ultimately governs the sintering process. Detailed knowledge of the sintering of different phases is useful to highlight a useful compositional zone where good densification of the multiphase SiAlON ceramics may be achieved.
Reaction Sintering and Mechanical Properties of Hydroxyapatite–Zirconia Composites with Calcium Fluoride Additions
Authors: Kim Hae‐Won , Koh Young‐Hag , Yoon Byung‐Ho , Kim Hyoun‐Ee
Published: July 2009

The effects of calcium fluoride (CaF2) additions on the densification and mechanical properties of hydroxyapatite–zirconia composites (HA–ZrO2) were investigated. When small amount of CaF2 was added, the density of the composites was markedly enhanced. The reactions of HA with CaF2, which led to the formation of fluorapatite (FA), were attributed to the observed improvements in densification. When HA–20‐vol%‐ZrO2 composites were sintered, with the addition of 5 vol% of CaF2, in air at 1300°C, the density of the specimen approached 98% of the theoretical value. The flexural strength and fracture toughness of the composites were also improved, as a result of the enhanced densification.
Alkoxide Sol‐Gel‐Processed Cordierite Fiber
Authors: Tsai Mu‐Tsun
Published: July 2009

An alkoxide sol‐gel route was developed to prepare stoichometric cordierite fibers. The influences of the aging treatment and heating rate on the sinterability of the gel fibers were also examined. X‐ray diffraction analysis revealed that the unaged and aged fibrous gels all remained amorphous <800&, but began crystallization into μ‐cordierite and α‐cordierite at ∼900°C and 1050°C, respectively; single‐phase α‐cordierite fibers were obtained at 1300°C. Heating the unaged fibers yielded denser microstructures, with fine grain sizes of ∼0.2–0.4 μm, whereas the aged fibers exhibited porous microstructures following heating at 1300°C. A higher heating rate and aging treatment resulted in a higher open porosity of the fired fiber.
Effect of Polyelectrolyte Dispersants on the Preparation of Silica‐Coated Zinc Oxide Particles in Aqueous Media
Authors: Wang Hongzhi , Nakamura Hiroyuki , Yao Ken , Uehara Masato , Nishimura Satoshi , Maeda Hideaki , Abe Eiichi
Published: July 2009

Sodium silicate was utilized to obtain a SiO2 coating on ZnO particles to prevent a photocatalytic reaction between ZnO and phenol. During the coating process, pH control is important to avoid dissolution of the ZnO as well as to obtain a good dispersion. Two kinds of polyelectrolyte dispersants were used to control the surface charge of the ZnO particles in aqueous media. As a result, poly(ethylenimine) (PEI) shifted the isoelectric point of ZnO from pH 9 to pH 10, whereas poly(ammonium acrylate) (PAA) made the surface charge of ZnO negative between pH 6 and pH 11. The change in the ZnO surface charge produced by adding polyelectrolyte dispersants makes it possible to obtain uniform silica–coated ZnO particle in aqueous media. UV–irradiation experiments showed that PEI, which can make the surface charge opposite to that of SiO2, is more effective in obtaining a thick silica coating on ZnO.
Synthesis and Hydration Characteristics of Alinite Cement
Authors: Kim Young‐Min , Hong Seong‐Hyeon , Kim Hwan
Published: July 2009

A chlorine‐bearing alinite cement was synthesized using reagent‐grade chemicals, and the phase evolution and hydration behavior of the alinite clinker were examined. The effects of the MgO content on alinite formation and hydration also were investigated. Alinite began to appear at 1000°C from β‐C2S, C11A7CaCl2, and unreacted raw materials, and an almost single‐phase alinite was obtained at 1300°C. The alinite phase also was produced without MgO addition. However, CaO, β‐C2S, and C11A7CaCl2 phases were present. Alinite cements hydrated rapidly after a short incubation period, and the hydration products were C‐S‐H gels, Ca(OH)2, and a Fridel's saltlike phase. The local environmental changes of silicon and aluminum during the formation and hydration of alinite were determined using magic‐angle‐spinning nuclear magnetic resonance spectroscopy. The Cl−‐ion exsolution from the alinite paste during hydration was measured using ion chromatography.
In Situ Coagulation of High‐Alumina Zero‐Cement Refractory Castables
Authors: Studart André R. , Pandolfelli Victor C. , Tervoort Elena , Gauckler Ludwig J.
Published: July 2009

Coagulation methods originally developed for colloidal processing were investigated in this paper as alternative approaches to consolidate high‐alumina refractory castables free of hydraulic binders (zero‐cement). Three in situ reactions based on the direct coagulation casting (DCC) technique were evaluated to promote castable coagulation: (1) the autocatalytic hydrolysis of gluconic acid lactone, (2) the gradual dissolution of hydroxyaluminum diacetate particles in water, and (3) the enzyme‐catalyzed hydrolysis of urea. The coagulating behavior of castables and matrix‐representative suspensions was investigated with the help of zeta potential analysis, pH measurements, castable free‐flow evaluation, and oscillatory rheological tests. The enzyme‐catalyzed hydrolysis of urea seemed to be the most appropriate mechanism to promote the coagulation of initially self‐flow zero‐cement refractory compositions.