bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Grain Size on the Thermal Conductivity of Si3N4
Authors: Watari Koji , Hirao Kiyoshi , Toriyama Motohiro , Ishizaki Kozo
Published: July 2010

Polycrystalline Si3N4 samples with different grain‐size distributions and a nearly constant volume content of grain‐boundary phase (6.3 vol%) were fabricated by hot‐pressing at 1800°C and subsequent HIP sintering at 2400°C. The HIP treatment of hot‐pressed Si3N4 resulted in the formation of a large amount of ß‐Si3N4 grains ∼10 µm in diameter and ∼50 µm long, and the elimination of smaller matrix grains. The room‐temperature thermal conductivities of the HIPed Si3N4 materials were 80 and 102 Wm−1K−1, respectively, in the directions parallel and perpendicular to the hot‐pressing axis. These values are slightly higher than those obtained for hot‐pressed samples (78 and 93 Wm−1K−1). The calculated phonon mean free path of sintered Si3N4 was ∼20 nm at room temperature, which is very small as compared to the grain size. Experimental observations and theoretical calculations showed that the thermal conductivity of Si3N4 at room temperature is independent of grain size, but is controlled by the internal defect structure of the grains such as point defects and dislocations.
Hydrothermal Synthesis of Nanocrystalline Cerium(IV) Oxide Powders
Authors: Hirano Masanori , Kato Etsuro
Published: July 2010

Nanocrystalline cerium(IV) oxide (CeO2) powders were prepared by heating solutions of cerium(IV) salts in the presence of urea under hydrothermal conditions at 120° to 180°C. The effects of the concentration of urea and hydrothermal treatment temperature on the morphology and crystallite size of the synthesized particles were investigated. The synthesized particles were angular, ultrafine CeO2, with a cubic fluorite structure. Their crystallite size decreased from 20 to 10 nm with increasing urea concentration from 2 times to 8 times that of the Ce4+ ion. The size only slightly changed by calcining at temperatures below 600°C.
Development of Textured Mullite by Templated Grain Growth
Authors: Hong Seong‐Hyeon , Messing Gary L.
Published: July 2010

Highly textured mullite was obtained by enhancing anisotropic grain growth by TiO2 doping and by templating grain growth on oriented acicular mullite seed particles in a mullite precursor. Upon heating, the mullite precursor crystallized and densified to an equiaxed microstructure of 1‐2 µm mullite grains at which time the mullite seed particles grew rapidly in the length direction (c‐axis) to produce a highly textured microstructure. By changing the seed (template) particle concentration, a range of oriented microstructures and anisotropic grains could be produced.
Controlled Firing of Reaction‐Bonded Aluminum Oxide (RBAO) Ceramics: Part I, Continuum‐Model Predictions
Authors: Gaus Shaun P. , Harmer Martin P. , Chan Helen M. , Caram Hugo S.
Published: July 2010

The reaction‐bonded aluminum oxide (RBAO) process is a novel, reaction‐forming technique for producing monolithic, alumina‐based ceramics. Although there has been extensive work on the RBAO process, it is often difficult to reproduce the process and avoid sample cracking. To solve the problems that are associated with the RBAO process, it is necessary to have a fundamental understanding of the reaction‐bonding process and the effects of various processing parameters on the reaction behavior. To gain some insight into the process, a continuum model has been developed. The model, which considers the interaction between the macroscopic material and energy balances, is used to predict conditions under which RBAO bodies may be fired in a controlled manner, i.e., avoiding the runaway reaction. In particular, the effects of the oxygen content of the atmosphere, the heat loss by convection and radiation, the heating cycle, and scale (sample size) have been investigated. For small sample sizes, model predictions indicate that the reaction may be controlled by reducing the oxygen content of the atmosphere, increasing the heat loss, and/or incorporating an isothermal hold into the heating cycle at a temperature just below the ignition temperature. For larger sample sizes, model predictions indicate the need for multiple low‐temperature holds at increasing temperatures. It is believed that firing RBAO bodies in a controlled manner will allow one to avoid sample cracking. Part II of this work presents a complementary experimental study that investigates the reaction behavior and structural integrity of samples that have been fired under the predicted conditions.
Creep and Creep‐Recovery Behavior in Silicon‐Carbide‐Particle‐Reinforced Alumina
Authors: Deng Zhen‐Yan , Shi Jian‐Lin , Zhang Yu‐Feng , Lai Ting‐Rong , Guo Jing‐Kun
Published: July 2010

Flexure creep and creep‐recovery behavior were investigated for monolithic Al2O3 and 10‐vol%‐SiC‐particle‐reinforced Al2O3‐matrix composites in an air atmosphere at temperatures of 1160°‐1400°C. Two types of SiC particles were used: one has an average size of 2.7 µm and has an amount of SiO2 impurities per unit surface area that is one order of magnitude higher than the other, which has an average size of 0.6 µm. Compared to the creep behavior of monolithic Al2O3, the strain rate of the composites with the 0.6 µm SiC particles (denoted here as S‐10) did not decrease; the composites with the 2.7 µm SiC particles (denoted here as L‐10) exhibited excellent creep resistance. This difference was related to the microstructural features and the oxidation behavior of the composites: the Al2O3 grains in S‐10 were mainly equiaxed, only ∼10% of the Al2O3 grains were elongated, and most of the SiC particles that resided at the grain boundaries or at triple‐grain junctions were oxidized during creep, whereas the Al2O3 grains in L‐10 were mostly irregularly shaped and elongated and most of the SiC particles were entrapped in the Al2O3 matrix grains, which prevented the oxidation of the SiC particles. These different microstructural features were associated with different amounts of SiO2 impurity content per unit surface area on the SiC particle surfaces. In addition, the monolithic Al2O3 showed no anelastic recovery when the load was removed; however, the composites exhibited significant anelastic recovery, especially for L‐10. This phenomenon was attributed to the elongated grain morphology.
Phase Relationships and Stability of α′‐SiAlON
Authors: Rosenflanz Anatoly , Chen I‐Wei
Published: July 2010

Phase diagrams on the α′‐SiAlON plane have been investigated for ytterbium‐, yttrium‐, and neodymium‐containing systems at different temperatures. Phase relationships between α′‐SiAlON, β′‐SiAlON, AlN polytypoids, and liquid/grain‐boundary phases have been determined. The stability region of the α′‐SiAlON phase increases as the temperature increases and the ionic size of the rare‐earth cation decreases. Meanwhile, the solubility of aluminum and oxygen in β′‐SiAlON varies with the solubility of aluminum and oxygen in α′‐SiAlON, which causes migration of all the phase lines on the α′‐plane toward the nitrogen‐rich side at lower temperatures and with larger modifying cations. These systematic variations of the phase relationships fully explain the occurrence of α′→β′ reverse transformations that are sometimes observed in this system.
Fabrication and Mechanical Properties of Silicon Carbide‐Silicon Nitride Composites with Oxynitride Glass
Authors: Kim Young‐Wook , Lee Young‐Il , Mitomo Mamoru , Choi Heon‐Jin , Lee June‐Gunn
Published: July 2010

A microstructure that consisted of uniformly distributed, elongated β‐Si3N4 grains, equiaxed β‐SiC grains, and an amorphous grain‐boundary phase was developed by using β‐SiC and alpha‐Si3N4 powders. By hot pressing, elongated β‐Si3N4 grains were grown via alpha right arrow β phase transformation and equiaxed β‐SiC grains were formed because of inhibited grain growth. The strength and fracture toughness of SiC have been improved by adding Si3N4 particles, because of the reduced defect size and the enhanced bridging and crack deflection by the elongated β‐Si3N4 grains. Typical flexural‐strength and fracture‐toughness values of SiC‐35‐wt%‐Si3N4 composites were 1020 MPa and 5.1 MPam1/2, respectively.
Mechanization of Glass Manufacture
Authors: Cable Michael
Published: July 2010

Mechanization of glass manufacture had just begun in 1898 but was accelerating. Notable advances were soon to be made in all branches of the industry, many of them in the United States, and have continued to the present day. M. J. Owens occupies a unique position as the inventor of the first successful fully automatic container machine in 1903; he was also involved in several other important developments. However, within 20 years, machines fed with gobs supplied by the Peiler forehearth and gob feeder, also American inventions, became successful competitors. From about 1930 to 1960, a wide variety of machines was used to make containers, but these have been superseded nearly everywhere by the individual section machine, another American invention. The Lubbers process for sheet glass cylinders was an early success in 1903. About 12 years later the direct drawing of flat sheet was developed almost simultaneously by Fourcault in Belgium and Colburn in the United States. The Pittsburgh process followed a few years later. Ford was the first to succeed in making continuously cast plate, but Pilkington in the United Kingdom soon exploited that process to make much wider cast plate. At that time Pilkington also developed the simultaneous grinding of both faces of the continuous ribbon. The invention and development of float glass by Pilkington in the 1950s has made all other flat glass processes obsolete for most purposes. Owens‐Corning has played a major role in the glass‐fiber industry since its beginnings in the 1930s. The most important advance in manufacture of optical glass was the small continuous tank with vigorous stirring developed by Corning Glass Works. Corning also made other notable advances, such as the ribbon machine for lamp bulbs and the lamination process used for Corelle ware.
Effect of Dispersants on the Rheological Behavior of Zirconia‐Wax Suspensions
Authors: Liu Dean‐Mo
Published: July 2010

Three types of fatty acids‐namely, stearic acid, oleic acid, and 12‐hydroxystearic acid‐were used as dispersants for stabilization of highly concentrated zirconia‐wax suspensions. Rheological properties such as viscosity and yield stress of the suspensions were determined over a temperature range of 65°‐85°C. Experimental results indicated that better suspension stabilization was achieved when the 12‐hydroxystearic acid was used. Adsorption behavior revealed a greater affinity at the solid/liquid interface that occurred for the 12‐hydroxystearic acid than for stearic acid or oleic acid. This observation suggests that the adsorption of 12‐hydroxystearic acid may lead to a better packing (or surface concentration) of the acid molecules onto the solid surface than others and also results in a better suspension fluidity and processability. Attractive interparticle interaction was estimated quantitatively by using the Vold model and resulting analysis showed a linear correlation between the yield stress and the attractive potential for the suspensions.
Tensile Creep and Rupture of Silicon Nitride
Authors: Jr. Krause Ralph F. , Luecke William E. , French Jonathan D. , Hockey Bernard J. , Wiederhorn Sheldon M.
Published: July 2010

We have characterized the tensile creep, rupture lifetime, and cavitation behavior of a commercial, gas‐pressure‐sintered silicon nitride in the temperature range 1150° to 1400°C and stress range 70 to 400 MPa. Individual creep curves generally show primary, secondary, and tertiary creep. The majority of the primary creep is not recoverable. The best representation of the data is one where the creep rate depends exponentially on stress, rather than on the traditional power law. This representation also removes the need to break the data into high and low stress regimes. Cavitation of the interstitial silicate phase accompanies creep under all conditions, and accounts for nearly all of the measured strain. These observations are consistent with a model where creep proceeds by the redistribution of silicate phase from cavitating interstitial pockets, accommodated by grain‐boundary sliding of silicon nitride.
Measurement of Microscopic Bridging Stresses in an Alumina/Molybdenum Composite by In Situ Fluorescence Spectroscopy
Authors: Pezzotti Giuseppe , Suenobu Hiroyuki , Nishida Toshihiko , Sbaizero Orfeo
Published: July 2010

The R‐curve behavior of an Al2O3 ceramic with 25 vol% of molybdenum‐metal particles added was studied by using fracture‐mechanics experiments and in situ piezospectroscopic measurements of microscopic bridging tractions. Cracks were propagated by using a crack stabilizer, which allowed stable crack growth in a bending geometry. Microscopic bridging stresses were measured in situ during fracture propagation by detecting the shift of the Cr3+ fluorescence lines of Al2O3. Laser spots ∼1 µm in diameter and ∼10 µm deep were focused at the ceramic/metal interface of the bridging sites, and the closure stresses that acted on the crack faces were recorded as a function of external load. The maximum stress that was experienced by the stretched metal particles prior to final failure was ∼0.4 GPa. The maximum stress magnitude was not markedly different in relatively small (i.e., <5 µm) metal particles, failing with large ductility, as compared with larger particles which, instead, fractured in semibrittle fashion. A map of bridging tractions along the crack wake was constructed under a constant stress intensity factor, almost equal to that which is critical for crack propagation. Using this map to theoretically predict the rising R‐curve behavior of the composite led to results that were consistent with the fracture‐mechanics experiments, thus enabling us to explain the observed toughening, primarily in terms of a crack‐bridging mechanism.
Surface and Bulk Crystallization of Glass‐Ceramic in the Na2O‐CaO‐ZnO‐PbO‐Fe2O3‐Al2O3‐SiO2 System Derived from a Goethite Waste
Authors: Romero Maximina , Rincón Jesús Ma.
Published: July 2010

A goethite waste from zinc hydrometallurgical processes has been used to produce a glass‐ceramic in the Na2O‐CaO‐ZnO‐PbO‐Fe2O3‐Al2O3‐SiO2system. The surface and bulk microstructure of this glass‐ceramic have been studied by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The surface was comprised of crystalline and glassy areas. Two different types of crystalline growth and two morphologies were observed in the crystallized and glassy zones, respectively. The bulk microstructure was composed of a homogeneously distributed dendritic network comprised of small crystallites of magnetite. A glassy matrix was observed surrounding the magnetite network. Further heat treatment produced the precipitation of a nonstoichiometric zinc ferrite with magnetite crystals, being the nucleating agents of the secondary phase.
Synthesis of Nanocrystalline Lithium Zinc Ferrites Using Polyacrylic Acid, and Their Initial Densification
Authors: Cho Yong S. , Burdick Vernon L. , Amarakoon Vasantha R. W.
Published: July 2010

A chemical synthesis technique that uses polyacrylic acid (PAA) to prepare nanocrystalline Li0.3Zn0.4Fe2.3O4 was investigated. Phase‐pure spinel that had an average particle size of ∼13 nm was synthesized at a low temperature (450°C) for 30 min. The average particle size was dependent on the firing temperature and amounts of PAA and Bi2O3. The combustion reaction of PAA was believed to be the main reason for the low‐temperature synthesis of nanocrystalline lithium zinc (LiZn) ferrites. In addition, a chelating tendency was observed, via infrared (IR) spectroscopy, in the dried gel precipitates that were prepared at a low pH (∼2). The initial densification behavior of the nanopowder compacts was studied using linear‐shrinkage data. Densification of the nanopowder without Bi2O3 started at low temperatures (∼400°C). The addition of Bi2O3 to the nanopowder noticeably did not contribute to reducing the initial densification temperature. This result was supported by the activation‐energy calculation for the initial densification. Compared to an activation energy of 280 kJ/mol for grain‐boundary diffusion of the nanopowder without Bi2O3, a higher value (430 kJ/mol) was obtained in the case of the 3 wt% Bi2O3‐containing nanopowder.
Early Stages of Diamond‐Film Formation on Cobalt‐Cemented Tungsten Carbide
Authors: Polini Riccardo , Le Normand François , Marcheselli Giancarlo , Traversa Enrico
Published: July 2010

The surface composition of cemented tungsten carbide (WC‐5.8 wt% Co) was studied by X‐ray photoelectron spectroscopy (XPS), during the early stages of diamond‐film deposition, by hot‐filament chemical vapor deposition (HFCVD). The nucleated diamond films were analyzed by scanning electron microscopy (SEM), energy‐dispersive spectroscopy (EDS), and automatic image analysis (AIA). The evolution of the surface composition of cemented tungsten carbide during the early stages of diamond‐film deposition was strongly dependent on the substrate temperature. At relatively low temperature (750°C), cobalt‐rich particles started to segregate at the substrate surface after a few minutes of diamond deposition. The conspicuous segregation of the binder partly inhibited the formation of stable diamond nuclei, through intense carbon dissolution or carbon segregation at the binder surface, but did not affect nucleic growth. At higher temperatures (940°C), no cobalt‐rich particles formed at the substrate surface, even after 2 h of deposition. However, XPS results demonstrated the presence of cobalt in a surface layer, although in a lower amount than at 750°C. Nevertheless, the nucleation density of diamond at 940°C was much lower than at 750°C. Gaps between WC grains formed within 10 mins. Therefore, intergranular cobalt was removed at 940°C, a finding attributed to the etching performed by monohydrogen, rather than to binder evaporation. The time evolution of the substrate area fraction covered by diamond islands, S(t), was well described by Avrami kinetics for two‐dimensional phase transformations, suggesting that diamond formation took place via a heterogeneous nucleation process. The S(t) functions exhibited a similar trend at 750° and 940°C, because the higher growth rate of diamond crystallites at higher temperature counteracted the slower nucleation rate at the higher temperature.
Behavior of Electric‐Field‐Induced Strain in PT‐PZ‐PMN Ceramics
Authors: Yamaguchi Hirofumi
Published: July 2010

In this study, the electric‐field‐induced strain of PT‐PZ‐PMN ceramics was investigated in view of actuator applications under relatively high electric fields. The electric‐field‐induced strain was maximum at the composition x= 39.5, where x denotes the PbTiO3 (PT) content in the formula xPbTiO3·25PbZrO3·(75 ‐ x)Pb(Mg1/3Nb2/3)O3. This composition was 2 mol% richer in PT than the composition at which the piezoelectric constant was maximum. The mechanism of electric‐field‐induced strain at the composition x= 39.5 was analyzed using in situ X‐ray diffraction (XRD) under various electric fields. No change in c/a (tetragonality) was observed. On the other hand, the diffraction intensity ratio of the (200) to (002) planes varied with the electric field. The strain value calculated from changes in the intensity ratio showed good agreement with the measured value, indicating that 90° domain switching dominated in electric‐field‐induced strain for 39.5PbTiO3· 25.0PbZrO3·35.5Pb(Mg1/3Nb2/3)O3.
Fracture Strength and Microstructure of β‐SiAlON with Hafnia Addition
Authors: Goto Yasuhiro , Komatsu Michiyasu
Published: July 2010

The influence of HfO2 addition on the fracture strength and microstructure of ß‐SiAlON ceramics sintered from Si3N4 and Al2O3 powders was investigated. The strength was increased by the addition of HfO2, from ∼500 MPa to 700 MPa, and was almost constant from ambient temperature to 1300°C. Monoclinic HfO2 grains that were distributed in the SiAlON grain boundaries had a flat shape (∼20 nm thick) and were surrounded by an amorphous phase. The aluminum concentration in ß‐SiAlON in the samples with an Al2O3 starting composition of 15 wt% was decreased by the addition of HfO2. The amount of secondary phases was very small at grain boundaries between the SiAlON grains; amorphous phases were observed infrequently at the triple points but were very small (∼20 nm). The effects of HfO2 addition on the mechanism of the microstructure development and fracture strength are discussed.
High‐Resolution Electron Microscopy Investigation of Viscous Flow Creep in a High‐Purity Silicon Nitride
Authors: Jin Qiang , Wilkinson David S. , Weatherly George C.
Published: July 2010

The redistribution of intergranular amorphous films during creep deformation of Si3N4 has been studied by high‐resolution transmission electron microscopy. The film thickness distribution of a high‐purity Si3N4 material before and after creep was measured. A narrow range of film widths in the uncrept material and a bimodal distribution after creep were observed. These observations provided convincing evidence of the occurrence of viscous flow of intergranular amorphous films during creep deformation of Si3N4. Moreover, the creep response predicted by a viscous flow model was in good agreement with experimental data.
In Situ TEM Heating of Nanosized ZrO2
Authors: Rankin Janet
Published: July 2010

In situ TEM heating experiments at temperatures between 820° and 860°C provide significant insights into the atomistics of neck formation during the sintering of nanoscale faceted, single‐crystal particles of ZrO2. High‐resolution TEM was used to observe the crystallography and the relative orientation in a variety of original particle‐pairs and the relative orientation of their evolving necks. Previous studies have determined that unconstrained particles can rotate during neck growth. When there is a significant amount of misalignment, the particles are not able to align completely. In these instances, the neck that forms is epitaxial with one of the particles. Additionally, in particle‐pairs with significant misalignment, the neck stops growing when it forms a crystallographic facet which is continuous with the preexisting facet of the template particle. When the two particles have close to the same orientation, the particles rotate into complete alignment and the neck that forms is consequently epitaxial with both particles. When the neck‐particle system is in complete registry, the growing neck is rounded: there is an aperiodic arrangement of steps, even on the atomic resolution scale. The experimental results are discussed in terms of the random starting state of the two particles, the equilibrium crystal shape of the particle‐neck system, and the operative kinetic mechanisms.
Photoreaction of Titanium‐Based Metal‐organic Compounds for Ceramic Fine Patterning
Authors: Kikuta Koichi , Takagi Katsuhiko , Hirano Shin‐ichi
Published: July 2010

The photoreaction of metal‐organic compounds prepared by the chemical modification of metal alkoxides was investigated for the patterning of ceramic films. The chemical stability and photoreactivity of these compounds were found to be greatly influenced by the kind of chemical additive applied during the syntheses of the precursor solutions. In this study, the photoreaction of the precursor thin films prepared by the addition of alkanolamines was achieved by tuning the wavelength of the incident UV light. The decomposition of the organic moieties of the percursors was clearly observed in IR spectra during UV irradiation. Furthermore, the spectrum of the titania precursor film in the visible and ultraviolet regions (UV‐vis) changed in accordance with the irradiation time. The photolithography of the titanium precursor pattern was successfully achieved by means of these techniques.
Improved Strength Recovery of a Titanium Carbide/Silicon Nitride Composite from Thermal Shock Damage via Microwave Heating
Authors: Li Jianbao , Kong Xiangyang , Xie Zhipeng , Huang Yong
Published: July 2010

Microwave processing has been used to heat treat a TiC/Si3N4 ceramic composite. The strength degradation from thermal shock was substantially recovered. The recovery rate was much greater with microwave heating than with conventional heat treatment at equivalent average temperature. The mechanism of strength recovery was hypothesized to be microwave radiation, which caused selective heating of TiC particles, enhanced the reaction of grain boundaries, and resulted in the sintering of microcracks around TiC particles.
A Simple Way to Synthesize Yttrium Aluminum Garnet by Dissolving Yttria Powder in Alumina Sol
Authors: Han Kyoung R. , Koo Hee Jin , Lim Chang Sup
Published: July 2010

A precursor for Y3Al5O12 was synthesized as a YAG sol by simply dissolving Y2O3 powder in an alumina sol. Phase‐pure Y3Al5O12 powder was obtained by precipitating the YAG sol with an aqueous dilute ammonia solution followed by calcination at 1100°C. TG/DTA analysis showed an exotherm at 938°C attributed to formation of YAG phase and weight loss of 44% at 1000°C. XRD and FT‐IR analysis showed that phase‐pure YAG can be formed through noncrystalline and metastable hexagonal YAlO3 without forming either yttrium or aluminum formate intermediate.
Use of Ozone to Prepare Silver Oxides
Authors: Suzuki Ryosuke O. , Ogawa Takamichi , Ono Katsutoshi
Published: July 2010

The possible use of ozone to produce higher oxides was analyzed thermodynamically. Because the activity of oxygen in ozone is ∼1018 at room temperature and ∼108 at 773 K, ozone may react with metals to yield higher‐oxidation‐state products than does an ambient pressure of pure oxygen. In agreement with this thermodynamic prediction, silver oxides (AgO and Ag2O) were synthesized experimentally by blowing a gas mixture of 6 vol% ozone and oxygen through a water‐cooled lance. Neither Ag3O4 nor Ag2O3 was detected. Slow oxygen diffusion into a metal and/or reaction products and decomposition of unstable oxides that are formed successively are obstacles to practical applications of syntheses via ozone oxidation.
Processing of Functionally Gradient Ceramic Membrane Substrates for Enhanced Porosity
Authors: Darcovich Ken , Cloutier Caroline R.
Published: July 2010

A method to cast functionally gradient porous ceramics was conceived and established. A previous initial study had established viability of the technique: samples were shown to have a functionally gradient cross section with a continuously increasing mean particle size from top to bottom. This article reports on a modified two‐level factorial experimental design that was undertaken to determine the interdependent effects of pH, polyelectrolyte additive concentration, sintering temperature, and powder blend on the sintered microstructure. Ceramic disks ∼45 mm in diameter and 3.3 mm thick were cast by sedimentation. The green bodies were dried prior to sintering. For each point in the experimental space, mercury porosimetry was used to obtain the porosity and pore‐size distribution in the solid sample. From metastable suspensions, it was possible to form functionally gradient porous structures. Porosimetric data obtained in this study corroborated previous observations. Structures were produced with a wide pore‐size range and high porosity (up to 0.68). These structures, formed from a one‐step process, could be used as‐is for ultrafiltration applications, but they also had a sufficiently fine top layer for facilitating subsequent thin‐coating operations.
Aetiology of Defects in Large Ceramic Moldings
Authors: Krug Steffen , Evans Julian R. G. , ter Maat Johan H. H.
Published: July 2010

This study is an attempt to identify the causes of defects that appear in large ceramic injection molded bodies after sintering. It asks the question: are such defects established at the injection molding stage or are they caused by the debinding process or by sintering? Moldings with ascending thickness were prepared using a mold cavity with replaceable tool faceplates. Control over pressure during solidification was compared by using conventional molding and a novel molding technique that uses an insulated sprue. The organic vehicle is polyoxymethylene, which can be displaced by catalytic degradation in the solid state. This is a shrinking unreacted core process with a clearly defined reaction boundary in which there is no provision for particle movement in the liquid state. This study tracks the development of defects at each stage and concludes that the defects apparent after sintering have their origin in injection molding, even though they do not mature until a later stage.
Effects of Heating Profiles on the Orientation and Dielectric Properties of 0.5Pb(Mg1/3Nb2/3)O3‐0.5PbTiO3 Thin Films by Chemical Solution Deposition
Authors: Park Jeong Hwan , Kang Dong Heon , Yoon Ki Hyun
Published: July 2010

0.5Pb(Mg1/3Nb2/3)O3‐0.5PbTiO3 thin films were prepared on Pt(111)/Ti/SiO2/Si(100) substrates by varying the film formation procedures and heating processes. Depending on the multilayer film formation and appropriate heating process, the films were grown with a preferential orientation. The films showed a (100)‐preferred orientation and large grain‐size distribution when they were directly heat‐treated after deposition of amorphous layers. The films showed a (111)‐preferred orientation and small grain‐size distribution when formed layer‐by‐layer or directly heating amorphous thin films with a perovskite seed layer. These results were explained by the effect of a seed layer. Saturation polarization of the (111)‐preferred films was ∼35 µC/cm2, which was somewhat higher than that of the (100)‐preferred film. In contrast, the dielectric constant of the (100)‐preferred film was ∼1600, which was larger than that of the (111)‐preferred film.
Mechanism of Apatite Formation on a Sodium Silicate Glass in a Simulated Body Fluid
Authors: Hayakawa Satoshi , Tsuru Kanji , Ohtsuki Chikara , Osaka Akiyoshi
Published: July 2010

29Si and 31P magic‐angle‐spinning nuclear magnetic resonance (MAS‐NMR) spectra were used to analyze 20Na2O·80SiO2 glass particles before and after soaking in a simulated body fluid (SBF; Kokubo solution, pH 7.4) for various periods (up to 14 d). The structure of the bulk glass and the glass surface, as well as the chemical states of the calcium phosphates adsorbed on the glass surface, were examined. The bulk glass before soaking in the SBF showed two 29Si MAS‐NMR resonances, at −100 and −110 ppm, which were attributable to Si(OSi)3ONa and Si(OSi)4 units, respectively. A new ‐105 ppm peak, which was due to Si(OSi)3OH units, appeared after soaking in the SBF and grew as the soaking period increased. Thus, in the SBF, the glass network was degraded and hydrolyzed; that is, dissolution of the Na+ ions from the glass network and the formation of Si‐O‐ groups occurred. After soaking for 1 d, a 31P MAS‐NMR resonance peak of orthophosphate (PO43‐) ions that were deposited on the glass surface appeared at ∼3.0 ppm and grew as the soaking period increased. The chemical shift shows that the local structural environment of phosphorus atoms and ions was very similar to that of hydroxyapatite or rabbit cortical bone. Inductively coupled plasma atomic emission spectroscopic analysis confirmed the adsorption of calcium phosphates on the glasses and the close relationship between the dissolution of the Na+ ions and the precipitation of the calcium phosphates. It was concluded that the layer of hydrated silica gel, which was composed of Si(OSi)3O‐ units, provided the negatively charged sites that induced or promoted the precipitation of calcium phosphates, which led to apatite nucleation and crystallization.
A Study of Thermal Cutting of Glass
Authors: Muralidhar Seshadri , Pal Sanjeeb , Jagota Anand , Kale Sunil R. , Mittal Ramesh K.
Published: July 2010

Thermal stresses due to a hot‐air jet impinging on a glass sheet can be used to stably initiate and attract a crack toward the jet axis. Relative motion between the jet and glass sheet then can be used to cut the glass sheet. This paper presents a theoretical and experimental study of this process for straight cuts. The model consists of sequentially coupled thermal and stress analyses for different cutting velocities. The stress field is used to compute stress‐intensity factors for different assumed positions of a crack behind the moving air jet. The minimum air temperature for cutting and the stand‐off distance of the crack behind the nozzle increase as the cutting velocity increases. The various process and material parameters that control the process‐including cutting speed, air temperature, and sheet thickness‐are reduced to dimensionless numbers. Theoretical results, presented as a map in the space of these dimensionless numbers, describe the conditions under which cutting is possible. An experimental cutting apparatus has been constructed and used to validate the heat‐transfer analyses. Cutting experiments on this apparatus are in good agreement with the model.
Correlation of Fracture Toughness and Strength
Authors: Munro Ronald G. , Freiman Stephen W.
Published: July 2010

An extensive collection of data on the fracture toughness (KIc) and strength (sigmaf) of brittle materials has been used to examine the relationship between the mean measured values of KIc and sigmaf. Within this collection of data, it has been observed empirically that KIc frequently is linearly related to sigmaf when values are compared under conditions of either constant grain size (g) or constant density (rho). Assuming that the most‐significant material parameters are g and rho, the general fracture‐mechanics relationship among KIc, sigmaf, and the critical flaw size (c0) has been used to derive a general expression for (partial lowercaseKIc/partial lowercase sigmaf)x in which the subscript x indicates a condition of constant grain size (x=g) or constant density (x= rho). In general, (partial lowercaseKIc/partial lowercase sigmaf)g is not the same as (partial lowercaseKIc/partial lowercase sigmaf)rho. Imposing the empirical condition (partial lowercaseKIc/partial lowercase sigmaf)x= lambdax, where lambdax is a constant, a relationship between sigmaf and flaw size has been derived. For the observed conditions, the analysis indicates that the square root of the flaw size should vary as the reciprocal of the observed fracture strength.
Friction Coefficient of (α+β)‐SiAlON Composite against a Steel and Dense Silicon Nitride Tribopair
Authors: Prakash Brahm , Bandyopadhyay Siddhartha , Mukerji Joydeb
Published: July 2010

The friction characteristics of hot‐pressed (α+β)‐SiAlON, versus those of bearing steel and dense Si3N4 under dry sliding conditions, are reported. The coefficient of friction decreases as the alpha‐SiAlON content increases and is double that of a metal‐ceramic pair, in comparison to that of a ceramic‐ceramic pair.
Patterning of Tin Oxide Film from Photoreactive Precursor Solutions Prepared via the Addition of N‐Phenyldiethanolamine
Authors: Kikuta Koichi , Suzumori Kiichiro , Takagi Katsuhiko , Hirano Shin‐ichi
Published: July 2010

Metallo‐organic compounds were synthesized for the preparation of tin oxide fine patterning via the addition of alkanolamines. Tin(IV) isopropoxide was chemically modified with diethanolamine (DEA) and/or N‐phenyl‐diethanolamine (PhDEA). Then, the chemical stability and photoreactivity of the prepared metallo‐organic compounds were compared. A tin precursor solution that was formed via the stepwise additions of both DEA and PhDEA showed good chemical stability in air and efficient photoreactivities under ultraviolet irradiation. The fine patterning of tin oxide was achieved successfully on a substrate, using the precursor solution.
Fracture Statistics Based on Pore/Grain‐Size Interaction
Authors: Zimmermann André , Rödel Jürgen
Published: July 2010

The statistics of fracture in ceramics are discussed based on a model that describes crack instability that occurs at a configuration of a microcrack positioned in the stress‐concentrating effect of a large pore. The interaction of pore size and grain‐size distribution is considered, and the effect of a locally varying stress field is included. Results are presented as predictions of the critical pore size and microcrack size that cause fracture for the two assumed average grain sizes of 1 and 5 µm.
Electronic Structure of Pristine and Solute‐Incorporated SrTiO3: II, Grain‐Boundary Geometry and Acceptor Doping
Authors: Rodrigues Richard P. , Chang Hyunju , Ellis Donald E. , Dravid Vinayak P.
Published: July 2010

Grain boundaries in ceramics have a major influence on various mechanical and electrical properties of the material system. Nonlinear electronic properties of electroceramics are directly linked with the grain‐boundary phenomena caused by the variations in the crystallography and the chemical environment, and consequent variations in the electronic structure of the grain boundaries. In this Part II of the three‐part report, the electronic structure of pristine and acceptor‐impurity‐incorporated 36.8° symmetric tilt σ5 grain boundary in SrTiO3 is investigated. A relaxed model of the atomic structure of this grain boundary derived by Ravikumar et al. using lattice statics simulations based on pair‐potential calculations has been used for electronic structure calculations. This model is a very good approximation to the true relaxed structure, because it accurately reveals some of the structural features observed experimentally. The methodology of one‐electron first‐principle cluster calculations discussed in Part I has been used to study the pristine titanium‐ and strontium‐centered grain‐boundary clusters. Clusters with a single acceptor impurity at the central titanium site also have been considered in order to investigate the effects of impurities at the grain boundaries. As in Part I, no additional local lattice relaxations have been considered for the impurity‐incorporated clusters. Calculations involve determination of the aspects of the electronic structure outlined in Part I. The influence of grain‐boundary crystallography on local electronic structure is evaluated in terms of variations in densities of states and spatial charge densities. The influence of the grain boundary on local charge transfer and on impurity‐induced changes in charge populations also is investigated. The role of impurity incorporation at the grain boundaries is discussed in comparison with impurity incorporation in the bulk. The calculations reveal an increased covalence in the nature of the Ti‐O and Sr‐O bonds at the SrTiO3 grain boundary. The optical bandgap at the grain boundary is reduced because of the broadening of the O 2p valence and Ti 3d conduction states toward the Fermi level. An enhancement in the acceptor nature of transition‐metal impurities is observed at the grain boundary with an increase in the degree of association between the impurity ions and the oxygen neighbors. The variations in the electronic structure resulting from the variations in the crystallography at the grain boundary have implications on grain‐boundary segregation, space‐charge, and conductivity phenomena associated with the impurities.
High‐Resolution Transmission Electron Microscopy of Ti4AlN3, or Ti3Al2N2 Revisited
Authors: Barsoum Michel W. , Farber Leonid , Levin Igor , Procopio Adam , El‐Raghy Tamer , Berner Alex
Published: July 2010

The structure and chemistry of what initially was proposed to be Ti3Al2N2 are incorrect. Using high‐resolution transmission electron microscopy, together with chemical analysis, the stoichiometry of this compound is concluded to be Ti4AlN3‐delta (where delta = 0.1). The structure is layered, wherein every four layers of almost‐close‐packed Ti atoms are separated by a layer of Al atoms. The N atoms occupy ∼97.5% of the octahedral sites between the Ti atoms. The unit cell is comprised of eight layers of Ti atoms and two layers of Al atoms; the unit cell is hexagonal with P63/mmc symmetry (lattice parameters of a= 0.3 nm and c= 2.33 nm). This compound is machinable and closely related to other layered, ternary, machinable, hexagonal nitrides and carbides, namely M2AX and M3AX2 (where M is an early transition metal, A is an A‐group element, and X is carbon and/or nitrogen).
Corrosion Behavior of Single‐Crystal Alumina in Argon, Air, and Water Vapor Atmospheres at 1700‐2000°C
Authors: Yue Xue‐Mei , Zhang Guo‐Jun , Watanabe Tadahiko , Tai Weon‐Pil
Published: July 2010

The results for the corrosion of alumina single crystals at 1700‐2000°C in argon, argon/water vapor, air, and air/water vapor for 10 h are reported. There were no obvious weight and volume changes after corrosion. White spots were observed on the surfaces of the specimens after corrosion tests. The initial temperature for the appearance of these white spots was 1800°C for argon and air, 1900°C for argon/water vapor, and 2000°C for air/water vapor. These white spots were likely formed by internal impurities, which diffused outward to the surface and coalesced at high temperatures. There was no evidence of corrosion damage inside the specimens. The flexural strength of the specimens was clearly enhanced after the corrosion tests and showed no evident relation to the corrosion conditions. This increase in strength after corrosion was likely due to the healing of surface machining flaws. The surface flaw healing temperature for alumina crystals was higher than 1400°C.
Processing and Mechanical Properties of Ti3SiC2: I, Reaction Path and Microstructure Evolution
Authors: El‐Raghy Tamer , Barsoum Michel W.
Published: July 2010

In this article, the first part of a two‐part study, we report the reaction path and microstructure evolution during the reactive hot isostatic pressing of Ti3SiC2, starting with titanium, SiC, and graphite powders. A series of interrupted hot isostatic press runs have been conducted as a function of temperature (1200°–1600°C) and time (0–24 h). Based on X‐ray diffractometry and scanning electron microscopy, at 1200°C, the intermediate phases are TiCx and Ti5Si3Cx. Fully dense, essentially single‐phase samples are fabricated in the 1450°–1700°C temperature range. The time‐temperature processing envelope for fabricating microstructures with small (3–5 μm), large (∼200 μm), and duplex grains, in which large (100–200 μm) Ti3SiC2 grains are embedded in a much finer matrix, is delineated. The microstructure evolution is, to a large extent, determined by (i) the presence of unreacted phases, mainly TiCx, which inhibits grain growth; (ii) a large anisotropy in growth rates along the c and a directions (at 1450°C, growth normal to the basal planes is about an order of magnitude smaller than that parallel to these planes; at 1600°C, the ratio is 4); and (iii) the impingement of grains. Ti3SiC2 is thermally stable under vacuum and argon atmosphere at temperatures as high as 1600°C for as long as 24 h. The influence of grain size on the mechanical properties is discussed in the second part of this study.
Decomposition Mechanisms in Aluminum Oxide–Apatite Systems
Authors: Adolfsson Erik , Nygren Mats , Hermansson Leif
Published: July 2010

Aluminum oxide was mixed with solid solutions of hydroxyapatite and fluorapatite, prepared by solid‐state reactions, for a study of the relation between composites of apatite and of their phase stability in the presence of aluminum oxide. The amount of water released from the apatite was quantified from thermogravimetric measurements, and the fraction of vacancies present at the onset temperature of its decomposition in the presence of aluminum oxide was estimated. The results show that the decomposition takes place when a certain fraction of vacancies has been formed. By incorporation of F− in the structure, the fraction of vacancies was reduced and the thermal stability of apatite was improved. Based on these findings, a modified mechanism describing the thermal decomposition of hydroxyapatite in the aluminum oxide–hydroxyapatite system is formulated.
Prediction of a Critical Temperature for Aluminate Formation in Alumina/Copper–Oxygen Eutectic Bonding
Authors: Trumble Kevin P.
Published: July 2010

A pseudobinary thermodynamic analysis of the alumina/copper–oxygen eutectic bonding process yields a value of approximately 1076°C for the invariant temperature of the {Cu(ss), Cu(L1), CuAlO2, Al2O3} equilibrium. This temperature, which is 11°C above the eutectic, corresponds to a critical temperature for stability of the copper aluminate CuAlO2 in eutectic bonding. Implications for controlling interface microstructure are highlighted.
Surface Relief Associated with Isothermal Martensite in Zirconia–3‐mol%‐Yttria Ceramics Observed by Atomic Force Microscopy
Authors: Tsubakino Harushige , Kuroda Yoshihide , Niibe Masahito
Published: July 2010

Surface relief associated with martensitic transformation—tetragonal‐to‐monoclinic phase transformation—that occurred during isothermal aging at temperatures of 400 and 473 K was observed via atomic force microscopy, using prepolished and thermally etched surfaces of zirconia–3 mol% yttria that was sintered at a temperature of 1923 K for 5 h. The isothermal martensitic transformation occurred first at grain boundaries and advanced into grain interiors as the aging time increased and then spread successively into the surrounding grains. The transformation area, which had an approximately round shape, increased as the aging time increased. The fine structure of the surface relief was composed of many tent shapes that were several nanometers high with an angle of ∼165°.
Reinforcement of Hydroxyapatite Bioceramic by Addition of ZrO2 Coated with Al2O3
Authors: Kong Young‐Min , Kim Sona , Kim Hyoun‐Ee , Lee In‐Seop
Published: July 2010

The mechanical properties of hydroxyapatite (HAp) bioceramic material were improved significantly by adding tetragonal‐zirconia‐polycrystalline (TZP) powder coated with Al2O3. The coating was done by dispersing the TZP powder in a boehmite suspension and adjusting the pH to cause heterocoagulation. The coating effectively reduced the deleterious reaction between the HAp and the TZP that tended to form tricalcium phosphate (TCP) and fully stabilized cubic zirconia. When 15 vol% zirconia and 30 vol% alumina were added to the HAp by the coating method, the strength and the fracture toughness of the composite were 300 MPa and 3 MPa·m1/2, respectively, which are about 3 times higher than those of pure HAp.
Phase Transformation of Hydrous‐Zirconia Fine Particles Containing Cerium Hydroxide
Authors: Matsui Koji , Ohgai Michiharu
Published: July 2010

Monoclinic hydrous‐zirconia fine particles that contained cerium(IV) hydroxide (Ce(OH)4) were heated from 200°C to 600°C, to investigate the phase transformation to CeO2‐doped tetragonal ZrO2. Both ZrOCl2·8H2O and CeCl3·7H2O were dissolved in aqueous solutions and then boiled to prepare the hydrous‐zirconia particles. The Ce(OH)4‐containing hydrous‐zirconia particles were prepared by adding aqueous ammonia into the boiled solutions. The monoclinic‐to‐tetragonal (m right arrow t) phase transformation of the Ce(OH)4‐containing hydrous zirconias was observed at 300°C using X‐ray diffraction (XRD). XRD and Brunauer‐Emmett‐Teller (BET) specific surface area measurements revealed that the Ce(OH)4‐containing hydrous zirconias had a tendency to transform from the monoclinic phase to the tetragonal phase at lower temperatures as the primary particle size of the hydrous zirconia decreased and the Ce(OH)4 content increased. These tendencies for the m right arrow t phase transformation agree with the conclusions that have been derived from thermodynamic and kinetic considerations.