bluuebunny/crossref_metadata_2025 huggingface dataset:
Dense, Shaped Ceramic/Metal Composites at lessthan equal to1000°C by the Displacive Compensation of Porosity (DCP) Method
Authors: Rogers Kirk A. , Kumar Pragati , Citak Ramazan , Sandhage Ken H.
Published: July 2010

The Displacive Compensation of Porosity method for fabricating dense, shaped ceramic/metal composites at modest temperatures is demonstrated. In this process, liquid‐metal/solid‐ceramic displacement reactions are used to generate more ceramic (by volume) than is consumed, so that pores within a ceramic preform can be filled with the new ceramic phase (i.e., densification without sintering). Dense, lightweight MgO/Mg‐Al composites (74–86 vol% oxide) and higher‐melting, co‐continuous MgAl2O4/Fe‐Ni‐Al‐bearing composites (42–59 vol% oxide) have been produced via the pressureless infiltration and reaction of magnesium‐bearing liquids with porous preforms of Al2O3 and NiAl2O4+Fe, respectively, at temperatures of 900°−1000°C. The composites are relatively tough and retain the shapes and dimensions (to within a few percent) of the starting preforms.
Titanium Phosphate Glass‐Ceramics with Silver Ion Exchangeability
Authors: Kasuga Toshihiro , Nogami Masayuki , Abe Yoshihiro
Published: July 2010

Na2O‐CaO‐TiO2‐P2O5 glass‐ceramics containing Nasicon‐type crystals were found to have silver‐ion exchangeability. The Nasicon‐type phase contains Ca2+ and Na+ ions which are located in two different sites of the conduction channels: the Na+ ions with high mobility can be exchanged easily with Ag+ ions in aqueous solution. The Ag+‐ion‐exchanged glass‐ceramics showed excellent bacteriostatic activity and a relatively high strength of 160 MPa in bending.
Effect of Impurity Cations on the Growth and Habits of SnO2 Crystals in the SnO2‐Cu2O Flux System
Authors: Kawamura Fumio , Kamei Masayuki , Yasui Itaru , Sunagawa Ichiro
Published: July 2010

The effects of a small amount of cations with valence states ranging from mono‐ to hexavalent on the growth and habits of SnO2 crystals growing in the SnO2‐Cu2O flux system were systematically investigated. Trivalent cations having ionic radii closer to that of Sn4+ had a conspicuous effect upon the size and habits of SnO2. Pentavalent cations with ionic radii similar to those of Sn4+ had some effect, whereas cations of other valence states showed no effect at all.
Anisotropy of Silicon Nitride with Aligned Silicon Nitride Whiskers
Authors: Park Dong‐Soo , Kim Chang‐Won
Published: July 2010

A model based on anisotropic sintering shrinkage of silicon nitride with aligned silicon nitride whisker seeds was built in order to provide an easy way to obtain information on how the large elongated grains were aligned. The method requires a simple measuring device for the information. XRD analysis showed a good correlation with predictions of the model. Both predictions of the model and experimental results indicated that the fraction of aligned large elongated grains increased as the whisker content increased.
Low‐Temperature Fabrication of Cordierite Ceramics from Kaolinite and Magnesium Hydroxide Mixtures with Boron Oxide Additions
Authors: Sumi Katsuhiro , Kobayashi Yuichi , Kato Etsuro
Published: July 2010

Thermal reactions of mixtures of ultrafine particles of magnesium hydroxide (Mg(OH)2) and kaolinite in a composition of MgO:Al2O3:2SiO2 were investigated to obtain dense cordierite ceramics at temperatures <1000°C. While heating the mixture of kaolinite and Mg(OH)2 with the equivalent of 2 mass% of boron oxide (B2O3) (in the form of magnesium borate, 2MgOB2O3), an amorphous phase formed at a temperature of ∼850°C after thermal decomposition. Firing the mixture at a temperature of 900°C yielded dense ceramics with an apparent porosity of almost zero. The addition of B2O3 promoted the densification at 850°‐900°C and accelerated the crystallization of alpha‐cordierite. The specimen with 3 mass% of B2O3 that was fired at a temperature of 950°C showed a linear thermal expansion coefficient of ∼3 × 10−6 K−1, a bending strength of >200 MPa, and a relative dielectric constant of 5.5 at 1 MHz. These cordierite ceramics may be used as substrate materials for semiconductor interconnection applications.
Surface Chemistry and Rheology of Electrostatically (Ionically) Stabilized Alumina Suspensions in Polar Organic Media
Authors: Wang Gonghou , Sarkar Partho , Nicholson Patrick S.
Published: July 2010

Alumina particles were dispersed in ethanol (EtOH) and dimethyl sulfoxide (DMSO). The surface chemistry and interparticle forces were manipulated by controlling the ionic strength of the suspensions without dispersants. The effects of the chemical nature of the solvents and the concentration of dispersed particles on the suspension rheology were evaluated. It was observed that the viscosity of suspensions decreased with increasing salt concentration. Solvent type also had a marked influence on the suspension rheology. Interparticle interactions were calculated and used to describe the rheological behavior.
Rapid and Sensitive Radioscopy for Fine Ceramics Using an Image‐Subtraction Method
Authors: Ikeda Yasushi , Mizuta Yasutoshi , Onda Katsuhiro
Published: July 2010

A new microfocus X‐ray testing method has been developed to detect very small defects in ceramic products with high speed and reliability. By using image subtraction, enhanced X‐ray images of defects were extracted from the background noise. Much‐better sensitivity (e.g., 0.1% in Si3N4 that was 20 mm thick) was obtained within a few minutes. This method is considerably superior to the conventional film method. In this study, Si3N4 test pieces (penetrameters) that had very small artificial defects (such as slits and pores) were prepared and examined by using the new method.
Origin of Solid‐State Activated Sintering in Bi2O3‐Doped ZnO
Authors: Luo Jian , Wang Haifeng , Chiang Yet‐Ming
Published: July 2010

Activated sintering in Bi2O3‐doped ZnO has been studied with emphasis on the mechanistic role of intergranular amorphous films. The atomic‐level microstructures and bismuth solute distributions in doped powders have been investigated using high‐resolution electron microscopy and scanning transmission electron microscopy. Densification is observed to be significant below the bulk eutectic temperature in the presence of Bi2O3 concentrations as low as 0.58 mol%. Transmission electron microscopy of as‐calcined and sintered powders shows that significant neck growth and particle coarsening occur in the solid state. Intergranular amorphous films of ∼1 nm thickness, terminating in wetting menisci at sinter‐necks, are observed to form concurrently with the onset of activated sintering. In a few instances, amorphous films are also observed at surfaces of the ZnO particles. These films appear to be the free‐surface counterpart to equilibrium‐thickness intergranular films. Activated sintering in this binary system is attributed to rapid mass transport through subeutectic, equilibrium‐thickness intergranular films, with the amorphous phase also providing capillary pressure.
Homogeneous Precipitation of TiO2 Ultrafine Powders from Aqueous TiOCl2 Solution
Authors: Kim Sun‐Jae , Park Soon‐Dong , Jeong Yong Hwan , Park Sung
Published: July 2010

Crystalline TiO2 powders were prepared by the homogeneous precipitation method simply by heating and stirring an aqueous TiOCl2 solution with a Ti4+ concentration of 0.5M at room temperature to 100°C under a pressure of 1 atm. TiO2 precipitates with pure rutile phase having spherical shapes 200‐400 nm in diameter formed between room temperature and 65°C, whereas TiO2 precipitates with anatase phase started to form at temperatures >65°C. Precipitates with pure anatase phase having irregular shapes 2‐5 µm in size formed at 100°C. Possibly because of the crystallization of an unstable intermediate product, TiO(OH)2, to TiO2xH2O during precipitation, crystalline and ultrafine TiO2 precipitates were formed in aqueous TiOCl2 solution without hydrolyzing directly to Ti(OH)4. Also, formation of a stable TiO2 rutile phase between room temperature and 65°C was likely to occur slowly under these conditions, although TiO2 with rutile phase formed thermodynamically at higher temperatures.
Determining Residual Stresses in Thin‐Walled Ceramic/Ceramic Composite Pipes
Authors: Seif Mohamed A. , Kishawy Hossam A.
Published: July 2010

Fiber‐reinforced ceramic materials exhibit excellent strength, toughness, and resistance to high temperatures and thermal shocks. To determine the service stress limit of a material, it is very important to determine residual stresses that are developed during the manufacturing processes. This work uses the laser speckle technique as a sensitive, noncontact, quantitative tool to determine residual stresses in thin‐walled pipes made of ceramic/ceramic composite. The laser measurement is combined with an elastic solution to obtain both the radial and the tangential stress distributions along the thickness of the pipe. The proposed approach, suitable only for thin‐walled cylinders, possesses different advantages with respect to simplicity and sensitivity. The results obtained show that this approach is more reliable and accurate than the strain gauge method.
High‐Temperature Strength and Microstructural Analysis in Si3N4/20‐vol%‐SiC Nanocomposites
Authors: Cheong Deock‐Soo , Hwang Kwang‐Taek , Kim Chang‐Sam
Published: July 2010

Si3N4/20‐vol%‐SiC nanocomposites with Al2O3 and Y2O3 as sintering additives have demonstrated very high strength at room temperature; however, the high‐temperature strength was drastically decreased, because of the low softening temperature of the grain‐boundary phase. To improve the high‐temperature strength, only Y2O3 was used as a sintering additive. Results showed that the fracture strength of this nanocomposite at temperatures >1200°C was increased by adding Y2O3 without Al2O3; however, a distinct decrease in the high‐temperature strength still was observed for higher Y2O3 contents. The fracture strength at room temperature (∼1 GPa) was maintained up to 1400°C in the sample that contained SiC particles (30 nm in size) and 4 wt% of Y2O3. Remarkably, the SiC particles at the grain boundaries were bonded directly to Si3N4 grains without a glassy phase. This sample fractured in an elastic manner without exhibiting plastic deformation up to 1400°C and showed no evidence of subcritical crack growth on the fracture surface. The significant improvement of the high‐temperature strength in this nanocomposite can be attributed to inhibition of grain‐boundary sliding and cavity formation, primarily by intergranular SiC particles that are bonded directly to the matrix grains, as well as crystallization of the grain‐boundary phase. Rietveld analysis of the X‐ray diffraction data revealed the presence of a secondary phase‐10Y2O39SiO2Si3N4 (h‐phase)‐in samples with Y2O3, whereas YSiO2N was present in the samples that contained both Y2O3 and Al2O3.
Formation and Transformation of Cubic Lead Niobate Pyrochlore Solid Solutions
Authors: Sreedhar Krishnan , Mitra Anjana
Published: July 2010

Formation of lead niobate pyrochlores by the reaction of PbO with Nb2O5 in various molar ratios and at various temperatures has been investigated. It has been shown that for a PbO/Nb2O5 molar ratio between 1.5 and 3.0, a pyrochlore solid solution having cubic symmetry is formed at low temperatures (∼500‐600°C). X‐ray diffraction data show evidence for the existence of compositional inhomogeneity for this phase which contains part of the Pb in the Nb site leading to the formula Pb1.5+x(Nb2‐yPby)O7‐delta (0.0 < x < 0.5; 0.0 < y < 0.5). A phase‐pure Pb‐deficient pyrochlore (Pb1.5Nb2O6.5) and Pb‐excess pyrochlores (Pb2.5Nb2‐O8, Pb3Nb2O8) are formed by the decomposition of this cubic solid solution and subsequent reaction at high temperatures. These results indicate that the mechanism of the structural transformation from the low‐temperature (LT) cubic solid solution to the corresponding high‐temperature (HT) phases is reconstructive.
Diamond‐Coated Silicon Carbide Whiskers
Authors: Demkowicz Paul A. , Bell Nelson S. , Gilbert Don R. , Singh Rajiv , Drawl William R. , Adair James H.
Published: July 2010

Colloidal techniques have been used to seed SiC whiskers with submicrometer‐sized diamond particles. The diamond and SiC particulates are co‐suspended in an aqueous medium and cast to form highly porous bodies. Electron cyclotron resonance chemical vapor deposition is used to grow dense, polycrystalline diamond coatings on the seeded whiskers. The low packing density of the cast green bodies allows for infiltration of the growth zone beneath the exposed surface. Electron microscopy is used to estimate the coating thickness and depth of growth infiltration.
Formation of Core‐Shell Structure in the BaTiO3‐SrTiO3 System
Authors: Kim Joo‐Sun , Kang Suk‐Joong L.
Published: July 2010

When a 1‐mol%‐Fe2O3‐added 0.67BaTiO3‐0.33SrTiO3 (mole ratio) powder compact was sintered at 1380°C, a core‐shell structure was developed. The core phase formed via solid‐state interdiffusion of barium and strontium ions between BaTiO3 and SrTiO3 particles. In contrast, the shell phase formed via a solution‐precipitation process in the presence of an Fe2O3‐containing liquid phase. Energy‐dispersive X‐ray analysis showed that the core was a strontium‐rich paraelectric phase and the shell was a barium‐rich ferroelectric phase at room temperature. The core‐shell structure developed in the BaTiO3‐SrTiO3 system suggests the possibility of obtaining a variety of phase distributions with different Curie temperatures.
Compression and Reswelling of Nanometric Zirconia Dispersions: Effect of Surface Complexants
Authors: Peyre Véronique , Spalla Olivier , Belloni Luc
Published: July 2010

Dispersions of bare zirconia nanoparticles are not redispersable after a strong osmotic compression. In order to obtain a spontaneous redispersion from concentrated pastes, the surfaces of particles have been complexed by organic molecules (acetylacetone, acetic acid, citric acid, and diethanolamine) prior to compression. Controlled cycles of deswelling‐reswelling have been performed using the osmotic stress method in order to test the reversibility of the compression. Osmotic pressure and small‐angle X‐ray scattering measurements indicate that the chemical nature of a complexant is of the highest importance to control the interaction potential between particles.
Peroxo‐oxalate Preparation of Doped Barium Titanate
Authors: Van der Gijp Sven , Winnubst Louis , Verweij Henk
Published: July 2010

The peroxo‐oxalate complexation method is a method that can be used for the preparation of doped barium titanate. In this paper we focus on BaTi0.91Zr0.09O3, which can be used for discharge capacitors in lamp starters. The preparation method described here is based on the complexation and subsequent precipitation in basic environment of Ba, Ti, and Zr ions with hydrogen peroxide and oxalate. The influence of several process parameters, like precipitation temperature and pH, on powder properties is described. A single‐phase perovskite crystal structure is obtained after calcination starting from a chloride precursor solution using a precipitation temperature of 40°C and a pH of 9. Because the peroxo‐oxalate process starts with inexpensive chlorides and is performed in air, the peroxo‐oxalate process is suitable for the commercial production of doped barium titanate.
Extended X‐ray Absorption Fine Structure Investigation of Calcium Silicate Hydrates
Authors: Lequeux Nicolas , Morau Alain , Philippot Samuel , Boch Philippe
Published: July 2010

29Si MAS‐NMR, and Ca‐EXAFS experiments have been conducted on calcium silicate hydrates (C‐S‐Hs) with structure derived from wollastonite. Crystalline compounds (wollastonite, xonotlite, hillebrandite, foshagite, 1.1 nm and 1.4 nm tobermorites, and jennite) and C‐S‐H were synthesized and characterized. 29Si NMR provides information on silicate chains and EXAFS on calcium environment. The refined EXAFS values are in agreement with XRD data, except for tobermorite. The calcium order in C‐S‐H (C/S molar ratio from 0.7 to 1.4) is similar to that of tobermorite but different from that of jennite. Structural models of C‐S‐H are discussed.
Preparation of Tubular Silica‐Glass Membranes with Thin Silica Layers by Sputtering, Using the Novel Sputtering Apparatus for Tubular Supports
Authors: Kuraoka Koji , Yazawa Tetsuo
Published: July 2010

Tubular SiO2‐glass membranes with thin, dense SiO2layers on porous glass supports were prepared via sputtering, using the novel sputtering apparatus for tubular supports. This apparatus had a holder for tubular supports and a rotation mechanism. The sputtering conditions of the membranes were investigated. A support temperature of 573 K was determined to be the best among the temperatures that were selected in our experiments. Scanning electron microscopy observations showed that the membrane surfaces became smooth as the sputtering time increased and had no cracks. The permeances of helium, nitrogen, and CO2were measured at a temperature of 373 K. The permeances for the membranes were on the order of 10‐9 molm‐2s‐1Pa‐1 (10‐5 cm3(STP)cm‐2s‐1(cm Hg)‐1). The ratio of the permeances of helium to nitrogen was similar to the theoretical Knudsen value. These values were much lower than the values that were expected from the dense SiO2glass. This phenomenon was considered to be attributable to the presence of microcracks during the sputtering deposition.
Rapid Nondiffusional Penetration of Oxide Melts along Grain Boundaries of Oxide Ceramics
Authors: Belousov Valery V.
Published: July 2010

Interaction of the liquid phase with the grain boundaries of solids and a rapid mass transport in solids were studied in the present work with a CuO ceramic melt of the Bi2O3system as an example. Anomalously rapid penetration of the liquid phase along the grain boundaries of a solid ceramic material was observed. The velocity and activation energy of the process were each determined. A mechanism for the development of a grain‐boundary liquid channel in the kinetic mode, when the channel growth rate is reaction‐limited, was proposed. This mechanism leads to the formation of a liquid‐channel grain‐boundary structure (LGBS) in solids. It was demonstrated that liquid can interact with one‐dimensional as well as two‐dimensional defects in solids.
Incorporation of Yttrium in Barium Titanate Ceramics
Authors: Zhi Jing , Chen Ang , Zhi Yu , Vilarinho Paula M. , Baptista João L.
Published: July 2010

In this work, X‐ray diffractometry and scanning electron microscopy techniques were used to study the incorporation of yttrium in BaTiO3, with the following nominal compositions: (Ba1‐xYx)TiO3(0.015 ≤ to x≤ to 0.08), (Ba1‐xYx)Ti1‐x/4‐(□Ti)x/4O3(0.005 ≤ to x≤ to 0.1), and Ba(Ti1‐yYy)O3‐delta(0.028 ≤ to y≤ to 0.258). The phase assemblage and the lattice parameters indicated a slight solubility (∼1.5 at.%) of yttrium at the Ba sites at 1440°C but a high solubility (∼12.2 at.%) of yttrium at the Ti sites at 1515°C. When BaTiO3was heavily doped with yttrium at the Ti sites (a yttrium concentration (y) of <0.059), the crystallographic structure was tetragonal, whereas for y greater than equal to 0.059, the crystallographic structure was cubic.
Mechanochemical Synthesis of New Amorphous Materials of 60Li2S·40SiS2 with High Lithium Ion Conductivity
Authors: Morimoto Hideyuki , Yamashita Hideki , Tatsumisago Masahiro , Minami Tsutomu
Published: July 2010

New amorphous materials were mechanochemically synthesized by use of crystalline starting materials of Li2S and SiS2. The conductivity of a mechanochemically prepared sample of 60Li2S40SiS2(mol%) after a milling for 20 h was around 10‐4 Scm‐1 at room temperature. This conductivity was comparable to that of the corresponding glassy powders prepared by twin‐roller rapid quenching of melt and then pulverizing. The transport number of lithium ions in the mechanochemically prepared sample was nearly unity. Mechanochemical synthesis is a promising way to produce new solid electrolytes for solid‐state lithium secondary batteries.
Barium Rare‐Earth Hafnates: Synthesis, Characterization, and Potential Use as Substrates for YBa2Cu3O7‐delta Superconductor
Authors: John Asha Mary , Jose Rajan , Kurian Jose , Sajith Poo Koodan , Koshy Jacob
Published: July 2010

A new group of complex perovskites Ba2REHfO5.5 (where RE = La, Pr, Nd, and Eu) has been synthesized and sintered as single‐phase materials with high sintered density and stability using a solid‐state reaction method for the first time. The structure of Ba2REHfO5.5 has been studied by X‐ray diffactometry (XRD) and all of the perovskites are isostructural and have a cubic structure. The dielectric constant and loss factor values of these materials are in a range suitable for their use as substrates for YBa2Cu3O7‐delta superconductors. XRD and resistivity measurements show that there is no detectable reaction between YBa2Cu3O7‐delta and Ba2REHfO5.5, even when the two substances are mixed thoroughly and sintered at 950°C for 15 h. The addition of Ba2REHfO5.5 up to 20 vol% in YBa2Cu3O7‐delta‐Ba2REHfO5.5 composite shows no detrimental effect on the superconducting transition temperature of YBa2Cu3O7‐delta. Thick films of YBa2Cu3O7‐delta fabricated on polycrystalline Ba2REHfO5.5 substrate have a superconducting zero resistivity transition of 92 K, indicating the suitability of these new materials as substrates for YBa2Cu3O7‐delta films.
Localized Surface Modification of Low‐Thermal‐Conductivity Brittle Solids
Authors: Umezu Yuya , Lehman Richard L. , Wagner Jeff , Biswas Prasenjit , Murnick Daniel E.
Published: July 2010

A new method utilizing temporal and spatial control of a CO2 laser beam to generate temperatures sufficient to melt and fuse a vitreous material without concomitant development of crack‐inducing thermal gradients has been developed for the localized surface modification and repair of small manufacturing defects in brittle and low‐thermal‐conductivity solids. Heat transfer and mechanical modeling of the process have allowed development of specialized heating algorithms. Low‐positive‐expansion frits with low glass transition temperature also have been developed that enable rapid treatment of small areas without the generation of parasitic critical stresses.
Preparation of Tungsten Cobalt Carbides and Oxide via an Organometallic Heterobimetallic Complex as a Single‐Source Precursor
Authors: Shyu Shin‐Guang , Wu Chun‐Seng , Sung Yung‐Sheng , Chi Kai‐Ming
Published: July 2010

Tungsten cobalt carbides and oxides can be obtained via a single‐step pyrolysis of an organometallic single‐source precursor (eta5‐C5H5)(CO)3WCo(CO)4 (1). Pyrolysis of 1 in an oxygen atmosphere produced WCoO4 at 600°C. In a nitrogen atmosphere W6Co6C was obtained when 1 was heated at 700°C. However, under vacuum, the pyrolysis of 1 produced the other phase‐W3Co3C‐at 700°C. Both carbides were contaminated with graphitic carbon, as indicated by their ESCA spectra. Powders that were obtained by using these procedures had particle sizes of up to 100 µm. Micrography showed that the particles were porous, which indicated outgassing during pyrolysis.
Controlled Oxygen Partial Pressure Sintering of (Pb,La)(Zr,Ti)O3 Ceramics
Authors: Sun Ping , Xu Chao‐Nan , Akiyama Morito , Watanabe Tadahiko
Published: July 2010

Transparent PLZT(7/60/40) ceramics with large piezoelectric coefficients were obtained using a two‐step sintering process with controlled oxygen partial pressure. Specifically, low‐oxygen‐pressure and low‐temperature sintering were used in the first step, followed by a high‐oxygen‐pressure, high‐temperature sintering cycle. High‐density ceramics with small grain sizes of about 3 µm were prepared. As a result, kp= 0.71, k33= 0.78, d33= 850 × 10‐12 C/N, and a transparency of 15% (λ= 610 nm, thickness of 1 mm) have been achieved; 20% improvement of d33 was gained compared to conventional processed PLZT ceramics (d33= 710 × 10‐12 C/N).
Transmission Electron Microscopy Study of a 3Y‐TZP Worn under Dry and Water‐Lubricated Sliding Conditions
Authors: Barceinas‐Sánchez J. D. Oscar , Rainforth W. Mark
Published: July 2010

A fine‐grained 3‐mol%‐Y2O3‐stabilized t‐ZrO2 (3Y‐TZP) was worn under dry and water‐lubricated sliding conditions against a magnesia‐partially‐stabilized zirconia (Mg‐PSZ) counterface. Detailed transmission electron microscopy of cross sections of the worn surface indicated dramatic microstructural changes. The outer region of both test specimens consisted of randomly oriented, fine (6‐8 nm) tetragonal zirconia crystals. Below this, the tetragonal grains had become elongated, corresponding to a 95% reduction in thickness from the starting material for the dry test. Transformation of tetragonal to monoclinic zirconia was first found at a depth of 1.0‐2.2 µm (water‐lubricated) and 2.2‐3.5 µm (dry) and extended up to a maximum depth of ∼6 µm. Evidence of dislocation flow was found in all phases. The mechanisms of the microstructural change are discussed.
Codoping of Alumina to Enhance Creep Resistance
Authors: Li Yan‐Zun , Wang Chongmin , Chan Helen M. , Rickman Jeffrey M. , Harmer Martin P. , Chabala Jan M. , Gavrilov Konstantin L. , Levi‐Setti Riccardo
Published: July 2010

The tensile creep behavior of both singly and multiply doped alumina samples has been investigated in order to understand better the impact of dopant segregation to grain boundaries on observed creep resistance. Previous studies have suggested that the segregation of the oversized dopant ions reduces the grain boundary diffusivity and thus the creep rate. The aims of the present work are to examine the possibly beneficial effects of selective codoping in enhancing creep resistance, and to elucidate the role (if any) of precipitates in creep inhibition. The specific singly and codoped systems considered in this work were as follows: hot‐pressed alumina samples containing nominally (i) 100 ppm zirconium, (ii) 100 ppm neodymium, (iii) 100 ppm zirconium codoped with either 100, 350, or 1000 ppm neodymium, (iv) 100 ppm zirconium codoped with 1000 ppm scandium. Microchemical mapping using secondary ion mass spectrometry revealed direct evidence of cosegregation of the dopant ions to grain boundaries. Tensile creep tests were carried out in the temperature range of 1200‐1350°C, utilizing stresses ranging from 20 to 100 MPa. In the case of the Nd/Zr codoped alumina, it was found that the creep rate decreased by 2 to 3 orders of magnitude relative to undoped alumina. This improvement was greater than that achieved by doping with either Nd or Zr alone, and demonstrates that the incorporation of ions of differing sizes may be beneficial. The observed enhancement in creep resistance was obtained for compositions both above and below the solubility limit of Nd in alumina; hence the phenomenon is primarily a solid solution effect.
ZrO2/ZrO2 Layered Composites for Crack Bifurcation
Authors: Sánchez‐Herencia Antonio J. , Pascual C. , He Ju , Lange Fred F.
Published: July 2010

Laminates containing a thin layer (5 to 200 µm thick) sandwiched between two thick layers (2 mm thick) were fabricated by sequential slip casting in order to study crack bifurcation. The thin layer was formed with a mixture of a pure ZrO2 powder (MZ) and a Zr(Y)O2 powder containing 3 mol% Y2O3 (TZ). The thick layers were formed with TZ powder containing 0.05 volume fraction of Al2O3 powder to distinguish the interfaces between the different layers in the scanning electron microscope. Dilatometry data for monolithic specimens formed with the mixed MZ and TZ powders (0.30 to 1.00 volume fraction MZ) showed that the monoclinic‐to‐tetragonal transformation temperature and strain varied with the MZ content, suggesting the yttria in the TZ powder diffused into the MZ powder during processing at 1500°C/2 h. These data also showed that large compressive stresses developed in the thin layer due to the transformation. Conditions (thin layer composition and thickness) for observing edge cracks produced along the center line of the thin layer and for observing crack bifurcation during flexural failure were determined. Delamination occurred during cooling for layers fabricated with greaterthan equal to0.40 volume fraction of the MZ powder when the thin layers were 200 µm thick. Edge cracking, which occurred during cooling, and crack bifurcation, which occurred during flexural loading, occurred for thin layer compositions containing greaterthan equal to0.40 volume fraction MZ powder, when the thickness of the thin layer was between similar/congruent50 and 150 µm. Crack bifurcation was not observed in thinner layers. With decreasing layer thickness, thin layers fabricated with >0.60 volume fraction of the MZ powder contained multiple microcracks, parallel to the center line, on the surface, instead of a single edge crack. The flexural strength of all specimens depended on the strength of the thicker Zr(Y)O2 layers, regardless of whether bifurcation occurred.
Interfacial Reaction between Titanium Thin Films and Aluminum Nitride Substrates
Authors: Imanaka Yoshihiko , Notis Michael R.
Published: July 2010

Interdiffusion and reaction at the interface between titanium thin films and AlN have been studied by using Rutherford backscattering spectrometry and transmission electron microscopy. Ti2AlN is formed as a result of reaction with titanium and AlN at temperatures of 800°‐950°C. The activation energy for Ti2AlN formation in the temperature range of 800°‐850°C is 224 kJ/mol, which is similar to that of nitrogen diffusion in titanium. Therefore, the formation of Ti2AlN is believed to be controlled by the diffusion of nitrogen in titanium.
Strength of a Hi‐Nicalon™/Silicon‐Carbide‐Matrix Composite Fabricated by the Multiple Polymer Infiltration‐Pyrolysis Process
Authors: Takeda Michio , Kagawa Yutaka , Mitsuno Shiro , Imai Yoshikazu , Ichikawa Hiroshi
Published: July 2010

A woven‐fabric Hi‐Nicalon™‐fiber reinforced SiC‐matrix composite has been fabricated by using a multiple polymer infiltration‐pyrolysis (PIP) process. The three‐point bend strength, at room temperature, of the composite is examined as a function of total porosity of the composite. The porosity of the composite decreases as the number of PIP cycles (N) increases. Both the proportional‐limit load and the maximum load in the three‐point bend test increase as N increases. A compressive fracture mode is observed for N < 10 (total porosity of >10%), and a tensile fracture mode is observed for N greaterthan equal to 10 (total porosity of lessthan equal to10%). For the composite with N= 14, with a total porosity of 8 vol%, a proportional‐limit stress of 410 MPa and a maximum stress of 600 MPa are achieved.
High‐Temperature Phase Relations in the Sc2O3‐Ta2O5 System
Authors: Yokogawa Yoshiyuki , Yoshimura Masahiro
Published: July 2010

The phase relations for the Sc2O3‐Ta2O5 system in the composition range of 50‐100 mol% Sc2O3 have been studied by using solid‐state reactions at 1350°, 1500°, or 1700°C and by using thermal analyses up to the melting temperatures. The Sc5.5Ta1.5O12 phase, defect‐fluorite‐type cubic phase (F‐phase, space group Fm3m), ScTaO4, and Sc2O3 were found in the system. The Sc5.5Ta1.5O12 phase formed in 78 mol% Sc2O3 at <1700°C and seemed to melt incongruently. The F‐phase formed in ∼75 mol% Sc2O3 and decomposed to Sc5.5Ta1.5O12 and ScTaO4 at <1700°C. The F‐phase melted congruently at 2344°± 2°C in 80 mol% Sc2O3. The eutectic point seemed to exist at ∼2300°C in 90 mol% Sc2O3. A phase diagram that includes the four above‐described phases has been proposed, instead of the previous diagram in which those phases were not identified.
Effect of Oxidation on the Room‐Temperature Flexural Strength of Reaction‐Bonded Silicon Carbides
Authors: Kim Hae‐Won , Kim Hyoun‐Ee , Song Huesup , Ha Jowoong
Published: July 2010

The oxidation behavior of reaction‐bonded silicon carbide (RBSC) and the effect of oxidation on the room‐temperature flexural strength of RBSC were investigated. Four different types of RBSC, each having various SiC particle‐size distributions and free silicon contents, were exposed to air at 1300°C for up to 200 h. Parabolic weight gains, with respect to oxidation time, were observed in all the specimens. The strength of the RBSC increased after oxidation for up to 50 h, because of the blunting of cracks by the silica layer that was formed on the surface. However, with further oxidation, the beneficial role of the oxide layer was negated by the cracks that were newly generated on the surface because of the thermal mismatch between the substrate and the silica layer. The amount of free silicon had a negligible effect on the strength retention of the specimens after the oxidation processes.
Conversion Efficiency of Alkoxide Precursor to Oxide Films Grown by an Ultrasonic‐Assisted, Pulsed Liquid Injection, Metalorganic Chemical Vapor Deposition (Pulsed‐CVD) Process
Authors: Krumdieck Susan , Raj Rishi
Published: July 2010

Polycrystalline coatings of an oxide, with a columnar grain morphology, were grown on metal substrates from metalorganic precursors using the pulsed‐CVD process. In a model study, films of the rutile phase of titanium dioxide were grown on nickel by thermal decomposition of titanium isopropoxide. Growth rates of up to 0.3 µm/min were obtained with conversion efficiencies (mole oxide per mole precursor) approaching 100%. The high growth rates and conversion efficiencies portend the application of this method for the manufacture of films and coatings on large surface areas, as, for example, required in the deposition of zirconium dioxide on nickel‐based superalloys to serve as thermal barrier coatings on turbine blades.
In Situ Synthesis of Yttria‐Stabilized Tetragonal Zirconia Polycrystal Powder Containing Dispersed Titanium Carbide by Selective Carbonization
Authors: Liu Jifu , Li Jianbao , Wang Houliang , Huang Yong
Published: July 2010

Reaction thermodynamics was utilized to analyze the selective carbonization conditions of ZrO2‐TiO2‐Y2O3 ultrafine powder and to define the temperature range of the selective carbonization. The ZrO2‐TiO2‐Y2O3 powder was prepared by coprecipitation from a solution containing Zr4+, Ti4+, and Y3+. The powder was selectively carbonized at 1350°, 1450°, 1550°, and 1650°C, respectively, for 2 h under argon atmosphere with sucrose as the carbon source. The resulting product was analyzed by X‐ray diffraction. The experimental results indicated that the ZrO2‐TiO2‐Y2O3 powder could be selectively carbonized in situ at 1450°C to form a carbonized powder which was composed of TiC and t‐ZrO2. It was also found that zirconium carbide could be formed at 1550°C, which is much lower than the carbonization temperature of ZrO2 defined by thermodynamics.
Evaluation of Crack Growth in Glass by Using Stress‐Wave Fractography
Authors: Yoshida Satoshi , Matsuoka Jun , Soga Naohiro
Published: July 2010

Subcritical crack growth in glass shows three characteristic regions, depending on crack velocity. Among three regions, in region III, where water does not affect crack‐growth behavior, the slope of the crack‐growth curve can be correlated with the intrinsic nature of glass fracture. In this study, to measure the crack velocity in region III, a periodic stress wave was applied to produce fracture‐surface markings in the double‐cleavage‐drilled compression specimen. The crack‐growth data obtained were compared with results obtained via direct observation of the crack front. As a result, this method, by using stress‐wave fractography, was found to be effective to obtain the crack‐growth curve in region III.
Mechanical Properties of Al2O3‐NiAl Composites
Authors: Tuan Wei‐Hsing , Pai Yu‐Pan
Published: July 2010

The mechanical properties of the Al2O3‐NiAl system are investigated in the present study. Specimens containing 0 to 100 vol% NiAl in Al2O3 were prepared by hot pressing. Both the strength and toughness of the Al2O3‐NiAl composites are higher than the values predicted by the rule of mixtures. The grain growth of Al2O3 and NiAl in the composites is constrained by each component. The increase in strength is thus partly attributed to microstructural refinement. The toughness enhancement is contributed by a combination of crack deflection and crack bridging.
Fabrication and Mechanical Properties of Titanium Boride Ceramics
Authors: Nakane Shingo , Takano Yoshihiko , Yoshinaka Masaru , Hirota Ken , Yamaguchi Osamu
Published: July 2010

Dense TiB ceramics (99.6% of theoretical) with a grain size of ∼5 µm have been fabricated by reaction hot pressing of TiB2 and titanium for 2 h at 1900°C and 28.5 MPa. The TiB ceramics exhibit a fracture toughness (KIC) of 4.5 MPa·m1/2 and a bending strength (sigmab) of 360 MPa. Electrical resistivity (rho) is 3.4 × 10‐7 Omega·m at room temperature.
Inducing Crystallization in an Amorphous Lead Zirconate Titanate Precursor by Mechanical Activation
Authors: Xue Junmin , Wan Dongmei , Lee See Ee , Wang John
Published: July 2010

For the first time, crystallization of perovskite lead zirconate titanate (PZT) phase in an amorphous hydroxide precursor is realized by mechanical activation, instead of calcination at an intermediate temperature. The resulting PZT powder exhibits well‐established crystalline perovskite structure with a crystallite size of ∼20 nm, as indicated from the peak broadening of X‐ray diffraction. An average particle size of 30 to 50 nm is observed using transmission electron microscopy for the mechanical‐activation‐derived PZT powder.
Low‐Temperature Pressureless Sintering of alpha‐SiC with Al4C3‐B4C‐C Additions
Authors: Zhou You , Tanaka Hidehiko , Otani Shigeki , Bando Yoshio
Published: July 2010

Various combinations of Al4C3, B4C, and carbon were used as sintering aids for pressureless sintering of alpha‐SiC (94% 6H+ 6% 15R) powders. Densification behavior, polytypic transformation, microstructural development, and mechanical properties were studied. Appropriate amounts of Al4C3‐B4C‐C additions could facilitate alpha‐SiC powders being pressureless sintered to high densities (>95% TD) at temperatures greaterthan equal to1850°C. Even using an alpha‐SiC as a starting powder, many elongated grains developed in the microstructures during sintering at low temperature that might contribute to toughening. Anisotropic grain growth was found to be associated with the faulted structures and the 6H→ 4H phase transformation.
Preparation of TiO2‐Coated Al2O3 Particles by Chemical Vapor Deposition in a Rotary Reactor
Authors: Li Chunzhong , Han Jinyi , Zhang Zongtao , Gu Hongchen
Published: July 2010

A process of coating Al2O3 particles with TiO2 by hydrolysis of Ti(OC4H9)4 using chemical vapor deposition in a rotary reactor has been developed. The process resulted in (1) a coating film of TiO2 which was compact and uniform with the fraction of TiO2 being 0.1%–10.0% and (2) an amorphous TiO2 coating at a low reaction temperature converted to anatase at a reaction temperature higher than 673 K.
Processing of Homogeneous Zirconia‐Toughened Alumina Ceramics with High Dry‐Sliding Wear Resistance
Authors: Kerkwijk Bas , Winnubst Louis , Mulder Elmer J. , Verweij Henk
Published: July 2010

The preparation of dense homogeneous zirconia‐toughened alumina (ZTA) with high dry‐sliding wear resistance is described. These ZTA ceramics are obtained by sintering green compacts, made by colloidal filtration of well‐defined ZrO2‐Al2O3 particle suspensions, for 2 h at 1400°C. The optimum solid and stabilizer concentrations for the filtration process were determined. The sintered ZTA microstructure consists of a homogeneous distribution of zirconia grains in an alumina matrix with grain sizes of 0.2 and 0.5 µm, respectively. In pin‐on‐disk tribological measurements at relatively high initial contact pressures (1130 MPa) and sliding speeds (0.5 m/s) a very low specific wear rate (about 5 × 10‐8 mm3/(N·m)) and a coefficient of friction of 0.45–0.55 were found. It is shown that, in this case, wear is dominated by abrasion and polishing.
A New Metastable Thin‐Film Strontium Tantalate Perovskite
Authors: Rodriguez Mark A. , Boyle Timothy J. , Hernandez Bernadette A. , Tallant David R. , Vanheusden Karel
Published: July 2010

A novel Sr‐Ta‐O perovskite phase has been synthesized by a chemical preparation route and crystallized on Pt‐coated SiO2/Si substrates at ∼800°C. The phase was isolated as a thin film only (not as a polycrystalline powder) and is likely metastable. SEM, EDS, XRD, EPR, and Raman analyses suggest this phase is cation‐deficient, having the formula SrxTaxO3 (x∼ 0.85). X‐ray Rietveld analysis indicates the structure to be a simple‐cubic perovskite‐type lattice; Pm3m space group, a= 3.955(2) Å, V= 61.86 Å3, Z= 1. Electrical property measurements recorded a dielectric constant k of ∼16 with a tan delta of 0.04.
Synthesis of Silicon Carbide Ceramics Using Chemically Modified Polycarbosilanes as a Compaction Binder
Authors: Sawai Yuichi , Iwamoto Yuji , Okuzaki Sachiko , Yasutomi Yoshiyuki , Kikuta Koichi , Hirano Shin‐ichi
Published: July 2010

A chemically modified polycarbosilane (PC) containing organofluoric groups (PCOCF) has been synthesized from PC and fluoroalkylmethyldimethoxysilane. PCOCF acts as an efficient compaction binder for SiC powders and as a coating material with excellent oxidation resistance in wet air. PCOCF‐coated SiC powders also show excellent packing properties because of the organofluoric side chains, which give highly dense green compacts. PCOCF provides a high ceramic yield of 75% and highly dense SiC ceramics. Four‐point bending strength increases and the scatter in strength values decreases significantly by PCOCF coating.
Electrochemical Study of the Localized Corrosion of Vacuum‐Furnace‐Fused Cermet Coatings
Authors: Neville Anne , Hodgkiess Trevor
Published: July 2010

The corrosion behavior of two thermal‐spray‐fused cermet coatings has been investigated using electrochemical techniques. It has been demonstrated that, without any influence of the substrate, the coatings that are based on cobalt‐chromium‐tungsten‐boron and nickel‐chromium‐silicon‐boron are susceptible to localized corrosion attack in seawater. Mechanisms of corrosion occur that resemble those observed on passive alloys. Galvanic effects between the components of the coating and between the coating and the substrate can have an important role in the corrosion of thermal‐spray coatings. The susceptibility of both coatings have been demonstrated to be severely affected as the seawater temperature increases.
Effect of Porosity on the Erosive Wear of Liquid‐Phase‐Sintered Alumina Ceramics
Authors: Latella Bruno A. , O'Connor Brian H.
Published: July 2010

The erosive wear susceptibility of porous and near‐fully‐dense liquid‐phase‐sintered (LPS) alumina ceramics has been studied from dry particle impact testing. Results show that the wear rates remained relatively constant with increasing porosity to a level above which the wear degradation was accelerated markedly. Microscopic observations indicate evidence of scratching and inelastic deformation in the erosion sites of the most porous structures, while brittle fracture and grain dislodgment dominated the material removal processes in the dense material. Implications of the erosion response in the LPS aluminas are discussed.
Granularity and Surface Structure of Ground Granulated Blast‐Furnace Slags
Authors: Tsuyuki Naomitsu , Koizumi Koshiro
Published: July 2010

Ground granulated blast‐furnace slags (GGBS) show improved hydration reactivity when granularity fineness increases, but the reason for the improvement in reactivity is still unknown. GGBS specimens with Blaine surface areas of 4680, 6470, and 8050 are analyzed, but the conventional reactivity criteria, such as degree of vitrification, basicity, and mineralogical composition, of the GGBS show no significant differences. X‐ray photoelectron spectroscopic analysis, however, successfully distinguishes and identifies SiO2 gels as well as glassy phases of CaO‐SiO2 and Al2O3‐SiO2 in the slag surfaces, where, with an increase in the Blaine surface area of the slag, CaO‐SiO2‐type glass becomes dominant and contributes to the evolution of hydration, determined in terms of silicate anion morphology by the trimethylsilylation (TMS) method.
Ternary System Al2O3‐MgO‐CaO: I, Primary Phase Field of Crystallization of Spinel in the Subsystem MgAl2O4‐CaAl4O7‐CaO‐MgO
Authors: de Aza Antonio H. , Pena Pilar , de Aza Salvador
Published: July 2010

Using a novel experimental procedure in the field of ceramics/materials science that is based on the precise microanalysis (scanning electron microscopy, coupled with wavelength‐dispersive spectroscopy) of the phases that are present in equilibrated specimens, the solid‐state compatibility relations in the subsystem MgAl2O4‐CaAl4O7‐CaO‐MgO and the melting relationships in the subsystems MgAl2O4‐CaAl2O4‐MgO and MgAl2O4‐CaAl2O4‐CaAl4O7 were established. The primary phase field of crystallization of spinel in the above‐mentioned subsystem, MgAl2O4‐CaAl4O7‐CaO‐MgO, was determined subsequently. The temperature, composition, and character of the ternary invariant points of the subsystem were established, and the ranges of the solid solutions in periclase, spinel, monocalcium aluminate, and dicalcium aluminate also were studied and determined, up to 1725°C.
Activation‐Induced Pyrochlore‐to‐Perovskite Conversion for a Lead Magnesium Niobate Precursor
Authors: Junmin Xue , Wang John , Weibeng Ng , Dongmei Wan
Published: July 2010

One or more pyrochlore phases are often involved as transitional phases prior to the formation of the perovskite phase in lead magnesium niobate (PMN) precursors. The elimination of these pyrochlore phases requires careful control of the calcination temperature and therefore is often difficult to complete. We report on the pyrochlore‐to‐perovskite conversion triggered by mechanical activation in a freeze‐dried PMN precursor. The resulting PMN powder exhibits a well‐established crystalline perovskite structure which is stable for calcination temperatures ranging from 400° to 800°C. A refined particle size in the range of 30‐50 nm was obtained.
Continuous Coating of Oxide Fiber Tows Using Liquid Precursors: Monazite Coatings on Nextel 720™
Authors: Boakye Emmanuel , Hay Randall S. , Petry M. Dennis
Published: July 2010

Seven different aqueous or ethanolic precursors were used to continuously coat monazite (LaPO4) on Nextel 720™ fiber tows. Immiscible liquid displacement was used to minimize bridging of coating between filaments. Precursor viscosities, densities, and concentrations were measured, and solids were characterized by DTA/TGA and X‐ray. Coatings were cured in‐line at 1200°‐1400°C and characterized for thickness, microstructure, and composition by optical microscopy, SEM, and TEM. Tensile strengths of the coated fibers varied with the precursor used and were 25% to >50% lower than those of the as‐received fiber. The coating stoichiometry and coating thickness of a particular precursor did not correlate with tensile strength. Median coating thicknesses were typically ∼50–100 nm for precursors with 40–80 g/L monazite, much larger than thicknesses predicted by theory for 12 mm diameter monofilaments. There were significant thickness variations from filament to filament, but usually little variation in composition or microstructure. Amorphous AlPO4 layers formed from phosphate‐rich precursors. Factors that could affect coating characteristics and tensile strength reduction were discussed.
Ambient‐Temperature Mechanochemical Formation of Titanium Nitride‐Alumina Composites from TiO2 and FeTiO3
Authors: Welham Nicholas J. , Kerr Tony , Willis Paul E.
Published: July 2010

The fabrication of a homogeneous submicrometer‐sized powder composed of nanocrystalline (<10 nm) alumina and titanium nitride during high‐energy ball‐milling is reported in this paper. The starting materials were rutile (TiO2) and aluminum powder. A similar composite with iron was also produced using the mineral ilmenite (FeTiO3) as the starting material. The powders were ball‐milled together under a nitrogen atmosphere for 100 h in a laboratory‐scale mill and subjected to thermal analysis and isothermal annealing at up to 1200°C. X‐ray diffraction showed that all of the phases formed within the milling step and underwent grain growth on annealing. Differential thermal analysis indicated no residual elemental aluminum, confirming that the reaction was completed during the milling operation.