bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanism of Reaction between Lanthanum Manganite and Yttria‐Stabilized Zirconia
Authors: Taimatsu Hitoshi , Wada Keiji , Kaneko Hiroyuki , Yamamura Hiroshi
Published: July 2005

The reaction of La1‐xCaxMnO3 (x= 0, 0.1, 0.2) with ZrO2‐8 mol% Y2O3 (YSZ) has been investigated at temperatures ranging from 1300° to 1425°C in air. Substitution of Ca for La in LaMnO3 depresses the reactivity with YSZ. A layer of La2Zr2O7 is formed at the La1‐xCaxMnO3/YSZ interface after an induction period, and its formation is accelerated when the La1‐xCaxMnO3 phase is porous. The reaction proceeds by unidirectional diffusion of La, Mn, and/or Ca ions, mainly Mn ions, into YSZ. The diffusion coefficients of La and Mn ions in YSZ, which are estimated using a LaMnO3/single‐crystal YSZ couple, are much lower than that of oxygen ion. From the experimental data, a reaction mechanism is proposed.
Indentation Method for Determining the Macroscopic Fracture Energy of Brittle Bimaterial Interfaces
Authors: Bhattacharya Arun K. , Petrovic John J. , Danforth Stephen C.
Published: July 2005

Based on the mechanics analysis of crack‐interface interaction, a simple and direct micro‐indentation technique has been developed to evaluate the fracture energy of a bimaterial interface. The technique, when applied to a pristine planar SiC‐Si3N4 interface at various angles of attack, is shown to provide a reasonable estimate of the interfacial fracture resistance. The experimentally obtained fracture energy has been compared favorably with a proposed atomic model of bond breaking between SiC and Si3N4.
Mechanical Properties of Interpenetrating Microstructures: The Al2O3/c‐ZrO2 System
Authors: French Jonathan D. , Chan Helcn M. , Harmer Martin P. , Miller Gary A.
Published: July 2005

Composites of Al2O3 (A) and cubic ZrO2 (Z) (8 mol% Y2O3) (with c‐ZrO2 volume fractions ranging from O to 1) were fabricated by pressureless sintering of mechanically mixed powders. The microstructures of the AZ composites were duplex, with the grains of both phases exhibiting similar size. Room‐temperature mechanical properties including Young's modulus (determined from elastic wave velocity measurements), strength and toughness (by indentation‐strength‐in‐bending), and Vickers microhardness were evaluated for the full range of compositions. All properties exhibited a linear decrease with increasing c‐ZrO2 content, and no R‐curve behavior was seen in any of the composite compositions. Fracture morphology, observed from cracks emanating from microhardness indentations, changed from essentially intergranular for the tougher Al2O3 to transgranular for c‐ZrO2, with AZ composites exhibiting mixed morphology.
Lifetime Prediction of Internally Pressurized Siliconized SiC Tubes Subjected to Creep Rupture Loading
Authors: Jadaan Osama M. , Shelleman David L. , Tressler Richard E.
Published: July 2005

The main objective of this research was to develop an experimental and analytical methodology to predict the lifetime of internally pressurized SiC tubes from the lifetimes of simple specimens subjected to similar delayed failure modes. Finite element analysis was used to determine the strain rate distribution in a thick‐wall tube subjected to sustained internal pressure. This analysis was used along with the Monkman‐Grant creep rupture criterion (obtained from creep testing of tensile specimens) to predict the lifetime of SCRB210 tubes. Results showed a large difference between experimental and predicted lifetimes. This difference was due to the existence of severe defects in the SCRB210 tubes which failed at low stresses. These tubes failed in crack growth mode rather than creep mode. This result leads to the conclusion that creep rupture criteria obtained from testing simple specimens cannot be projected to predict the lifetimes of large and more complex components.
Yttrium α‐Sialon Ceramics by Hot Isostatic Pressing and Post‐Hot Isostatic Pressing
Authors: Bartek Alena , Ekström Thommy , Herbertsson Harald , Johansson Thomas
Published: July 2005

Dense α‐sialon materials were produced by hot isostatic pressing (HIP) and post‐hot isostatic pressing (post‐HIP) using compositions with the formula Yx(Si12–4.5x, Al4.5x)‐(O1.5x,N16–1.5x) with 0.1 ≤x≤ 0.9 and with the same compositions with extra additions of yttria and aluminum nitride. X‐ray diffraction analyses show how the phase content changes from large amounts of β‐sialon (x= 0.1) to large amounts of α‐sialon (x= 0.4) and increasing amounts of mellilite and sialon polytypoids (x= 0.8). Samples HIPed at 1600°C for 2 h contained unreacted α‐silicon nitride, while those HIPed at 1750°C for 1 h did not. This could be due to the fact that the time is to short to achieve equilibrium or that the high pressure (200 MPa) prohibits α‐sialon formation. Sintering at atmospheric pressure leads to open porosity for all compositions except those with excess yttria. Therefore, only samples with excess yttria were post‐HIPed. Microstructrual analyses showed that the post‐HIPed samples had the highest α‐sialon content. A higher amount of α‐sialon and subsequently a lower amount of intergranular phase were detected at x= 0.3 and x= 0.4 in the post‐HIPed samples in comparison to the HIPed. The hardness (HV10) and fracture toughness (KIC) did not differ significantly between HIPed and post‐HIPed materials but vary with different x values due to different phase contents. Measurements of cell parameters for all compositions show a continuous increase with increasing x value which is enhanced by high pressure at high x values.
Studies of the Crystallization of Antimony‐Containing Slag Glass‐Ceramic
Authors: Shaoqiu Tang , Zhongjun Liang , Guorong Chen
Published: July 2005

The paper explains the necessity and basic principles of fabricating slag glass‐ceramic based on special local antimony‐containing slag. A CaO‐Al2O3‐SiO2 three‐component phase diagram was used to plan a base glass composition, to which four selected nucleating agents, Cr2O3, ZrO2, P2O5, and TiO2, were added separately. Studies focused on their roles in the crystallization of the present slag glass system with the aid of differential thermal analysis, X‐ray diffractometery, and scanning electron microscopy. Comparisons showed that the four nucleating agents behaved differently and therefore exerted different influences on crystallization. TiO2 proved to be the best one, and its optimal concentration was 10 wt%.
Formation of Al2O3/Metal Composites by the Directed Oxidation of Molten Aluminum‐Magnesium‐Silicon Alloys: Part I, Microstructural Development
Authors: Antolin Stanislav , Nagelberg Alan S. , Creber David K.
Published: July 2005

The growth of α‐Al2O3/metal composites by the directed oxidation of molten Al‐Mg‐Si alloys proceeds through four distinct stages. The first stage encompasses the early heating of the alloy ingot, melting, and continued heating to between 1123 and 1173 K. In this latter temperature range, the molten alloy surface rapidly oxidizes to form a MgO‐covered MgAl2O4 layer. During further heating and initial soak at the composite growth temperature (1373 to 1573 K), the duplex layer slowly thickens (second stage). The start of the third stage, growth initiation, is marked by the spread of a metal‐rich zone over the duplex layer; this metal‐rich zone is believed to be connected to the molten alloy through microcracks in the thickened MgO/MgAl2O4 layer. Small nodules of the oxide/metal composite nucleate from the metal‐rich layer. During the final rapid growth stage, the small composite nodules grow and coalesce to form a macroscopically planar growth front, which persists until growth is complete. Throughout the growth process, the external surface of the α‐Al2O3/metal composite is covered by a thin MgO layer. Immediately under this external layer and separating it from the α‐Al2O3 is a thin layer of molten metal.
Formation of Al2O3/Metal Composites by the Directed Oxidation of Molten Aluminum‐Magnesium‐Silicon Alloys: Part II, Growth Kinetics
Authors: Nagelberg Alan S. , Antolin Stanislav , Urquhart Andrew W.
Published: July 2005

The growth kinetics of an Al2O3/metal composite by the directed oxidation of an aluminum alloy (10 wt% Si, 3 wt% Mg, balance Al) have been measured as a function of temperature (1398 to 1548 K) and oxygen partial pressure in O2/Ar gas mixtures. The growth rate exhibited an activation energy of ∼370 kJ/mol and a dependence on oxygen partial pressure consistent with a Po1/42 relationship. A dissolution‐precipitation growth mechanism is proposed in which the growth rate is controlled by the electronic conductivity of an external Al2O3‐doped MgO surface layer in conjunction with grain boundary diffusion of magnesium.
Pro‐ and Subeutectoid Behavior of the Tetragonal Phase in Magnesia‐Partially‐Stabilized Zirconia
Authors: Montross Charles S.
Published: July 2005

Magnesia‐partially‐stabilized zirconia (Mg‐PSZ) is industrially important because of transformable metastable tetragonal precipitates which interact with and arrest cracks. This work addresses the precipitation of tetragonal phases at one composition, 9.5 mol% MgO, throughout a range of temperatures. High‐purity zirconia samples were sintered at 1700°C and rapidly quenched to heat‐treatment temperatures ranging from 1600° to 1100°C, then quenched to room temperature. Cooling rates through the tetragonal + MgO and the monoclinic + MgO two‐phase regions were found to affect the phase content. The kinetics of nonequilibrium phase transformation for high‐purity Mg‐PSZ are presented in terms of time‐temperature‐transformation diagrams.
Preparation of High‐Strength and Translucent Alumina by Hot Isostatic Pressing
Authors: Mizuta Hiroyuki , Oda Kiichi , Shibasaki Yasuo , Maeda Masaki , Machida Michihide , Ohshima Kazuyuki
Published: July 2005

A vacuum‐pressure slip‐casting technique and hot isostatic pressing (HIPing) were used to prepare high‐strength and translucent alumina ceramics. A low‐viscosity and high‐solids‐content slurry (46 vol% solids) was prepared, and a dense green compact was formed. The samples were sintered and subjected to capsule‐free HIPing. Extremely high‐density (99.9%) and fine‐grained (0.7 to 15 μm in diameter) alumina ceramics were obtained. The HIPed samples showed high bend strength and translucency with in‐line transmittance of 30% to 46% (1 mm thick).
Extended X‐ray Absorption Fine Structure (EXAFS) Study on the local Environment around Copper in Low Thermal Expansion Copper Aluminosilicate Glasses
Authors: Kamiya Kanichi , Okasaka Kensuke , Wada Masanori , Nasu Hiroyuki , Yoko Toshinobu
Published: July 2005

The local environment around copper in the Cu2O·Al2O3·4SiO3 and CuO·Al2O3·4SiO2 glasses was investigated using the extended X‐ray absorption fine structure (EXAFS) technique. It has been found that each Cu(I) in the former glass is coordinated to two oxygens through covalent Cu(I)‐O bonds. This is the primary reason for its low thermal expansion coefficient (∼10 × 10−7 K−1). In the latter glass, which was made by heating the former glass at 600°C in air, each Cu(II) is coordinated to four oxygens and the bonds are ionic in character, contributing to the increase in the thermal expansion coefficient to ∼30 × 10−7 K−1.
Effect of Mismatched Sintering Kinetics on Camber in a Low‐Temperature Cofired Ceramic Package
Authors: Lu Guo‐Quan , Sutterlin Robert C. , Gupta Tapan K.
Published: July 2005

Linear shrinkage profiles of an unconstrained gold thick film material and a low ‐tempearture cofireable glass‐ceramic (LTCC) green tape were measured using a noncontact optical technique. A laser beam scans across a sample, at various times during the sintering process. The unconstrained sintering kinetics of the gold film were found to differ significantly from those of the LTCC tape. The densification of the gold film was nearly completed before the LTCC began to densify. The development of camber (warpage) during consintering of a gold/LTCC composite structure was monitored and recorded with a video camera. This camber development is analysed based on the viscous constitutive relations for porous based on the viscous constitutive relations for porous sintering bodies. The mismatched sintering kinetics of the two materials lead to the development of in‐plane stresses in the two constituents of the composite structure as one material being constrained from composite structure as one material being constrained of the composite structure as one material being constrained from sintering by the other. The resulting camber during the consintering process is explained by the development of these stresses.
Calculation of Temperatures in Microwave‐Heated Two‐Dimensional Ceramic Bodies
Authors: Evans Deepak , Evans James W.
Published: July 2005

Tempertures are calculated in a ceramic material exposed to microwaves. The method entails calculation of electromagnetic fields by integral formulation and subsequent solution of the heat conduction equation for temperature in a ceramic piece. The solution of the equation is numerical and the parameters used are estimates for properties of SiC. The results include a case where the complex dielectric constant is varied with temperature The computed results demonstrate that SiC can be heated to high temperatures (1000‐1500 K) and that both the temperature and the temperature gradient can be controlled by varying the power density of the micro waves and the external cooling. The results also exhibit high sensitivity of temperatures to the dimensions of the material and the orientation in which microwaves impinge on the ceramic body.
Mathematical Model for Chemical Vapor Infiltration in a Microwave‐Heated Preform
Authors: Deepak  , Evans James W.
Published: July 2005

A mathematical model, in which mass fluxes are expressed according to the “dusty gas” model, is proposed to described densification of a ceramic perform by chemical vapor infiltration (CVI) Local temperatures previously computed for a perform subjected to microwaves are input to the mass transport model. The model is solved numerically for deposition of SiC from trichloromethylsilane in a porous SiC perform. The computed results clearly demonstrate an advantage in employing, microwaves heating in CVI, Also, greater infilatration is achieved in a perform of greater pore size and at lower temperature. However for successful infiltration, diffusion/chemical‐reaction‐controlled CVI is shown to impose limits on the preform size.
Kinetics of Silicon Nitride Chemical Vapor Deposition from Silicon Tetrafluoride and Ammonia
Authors: Larson Richard S.
Published: July 2005

Rate laws for the chemical vapor deposition of Si3N4 from SiF4and NH3 are obtained by fitting the results of pareametric reactor experiments with a one‐dimensional steady‐state model for the reactor. The model includes axial mass transport by both convection and multicomponent diffusion, and allowance is made for the use of an expressions with adjustable constants are used to account for deposition on both crystalline and amorphous surfaces, as well as the heterogeneous decomposition of NH3. In addition, there are mechanisms that determine the actual degree of surface crystallinity at any location. Optimum values for the rate constants are found by searching for the best overall fit to the experimental deposition rate and crystallinity data. It is shown that the model, with simple second‐order expressions for the deposition rates, is quite successful in reproducing the experimentally observed effects of temperature, flow rate, reactant mole ratio, and axial position.
Ceramic Wear Maps: Zirconia
Authors: Lee Soo W. , Hsu Stephen M. , Shen Ming C.
Published: July 2005

The wear characteristics of an yttria‐stabilized zirconia (Y‐TZP) are represented by a set of three‐dimensional wear maps under dry and lubricated conditions. Water, paraffin oil, and a formulated oil were used as lubricants. Different wear regions were identified as function of load, speed, and lubricants environment. Sudden increases in wear, identified as wear transitions, were found at certain loads and speeds. The onset of wear transitions was moderated by the presence of a lubricant. Below the wear transitions, the wear was mild and the wear mechanism was predominantly plastic deformation and microfracture. Above the wear transisitons, the wear was severe, dominated by brittle fracuture and third‐body abrasion. Diferent fluids had different effects on wear. Water had a deleterious effect on wear of this material. The presence of oil lubricants effectively reduced friction and moderated wear. Under high load andd high speed, additional stress induced by a thermal gradient within a small area contributed significantly to wear. A critical velocity model was found to describe the locations of the wear transition zones successfully.
Effect of Praseodymium on Superconductivity and Magnetism in Y1–xPrxBa2Cu4O8 Prepared by Nitrite Pyrolysis Method
Authors: Meen Teen‐Hang , Chen Ying‐Chung , Liaw Ken‐Whie , Yang Hung‐Duen
Published: July 2005

X‐ray diffraction patterns show that most samples of Y1‐x PrxBa2Cu4O8 examined in the present study contained a single YBa2 Cu4O8 (1‐2‐4) superconductive phase for x<0.7.Lattice parameters a and b increased with Pr concentration, suggesting that most of the Pr is trivalent in Y1‐x Prx‐Ba2Cu4O8. The zero‐resistance temperature, T co, decreases monotonically from 80 K at x=0 to 12 K at x=0.65, and superconducting transition widths tend to broaden for x>0. The room‐temperature resistivity changes linearly until x=0.7 and increases abruptly at x=‐0.75. The critical concentration, xcr, thus was estimated to be 0.7. The effective magnetic moments of Pr in Y 1‐x PrxBa2Cu4O8 were 3.63., 3.35, and 3.23, μB for x=0.2, 0.4 and 0.6, respectively. In the R0.8 Pr0.2Ba2Cu4O8 system, the depression of Tcweakly depends on the ionic radius of rare‐earth elements. Similarities and differences between Y 1‐x PrxBa2Cu4O8 and Y1‐xPrx‐Ba2Cu3O7‐y also were noted and are discussed in this paper.
Micromechanisms of Creep–Fatigue Crack Growth in a Silicide‐Matrix Composite with SiC Particles
Authors: Ramamurty U. , Kim A. S. , Suresh S. , Petrovic J. J.
Published: July 2005

An experimental study has been conducted to examine the cyclic fatigue crack growth characteristics in 1200oC air of a MoSi2‐50 mol% Wsi2 alloy the unreinforced condition and with 30 vol% SiC particles. For comparison purposes, crack growth experiments under sustained loads were also carried out in the silicide‐matrix composite. Particular attention is devoted to developing an understanding of the micromechanisms of subcritical crack‐tip damage. The results indicate that enhanced viscous flow of glass films along interfaces and grain boundaries imparts pronounced levels of subcritical crack growth in the composite material; the composite exhibits a higher fatigue fracture threshold and a more extended range of stable fracture than the unreinforced alloy. The effects of glass phase in influencing fatigue crack growth in the silicide‐based material are compared to the influence of in situ‐formed and preexisting glass films on high‐temperature cyclic fatigue crack growth in ceramics and ceramic composites. The paper concludes with a comparison of present results with the high‐temperature damage tolerance of a variety of intermetallic alloys and ceramic materials.
Determination of Young's Modulus in Chemically Vapor‐Deposited SiC Coatings
Authors: Watkins Thomas R. , Green David J. , Ryba Earle R.
Published: July 2005

Young's modulus of CVD and SiC coatings was measured in situ(on the substrate) using strain gage/flexure and dynamic resonance techniques. The average Young's moduli of CVD SiC from these techniques were 446 and 415 Gpa, respectively, and were considered to be in good agreement. The determination of a representative coating thickness and cross section is critical in order to accurately estimate Young's modulus of coatings.
Elastic Effect on Domain Morphology and Kinetics of Spinodal Decomposition in the Tetragonal System
Authors: Nambu Shinji , Sato Akinori
Published: July 2005

A method was proposed for calculation of the effect of elastic strain on spinodal decomposition in the tetragonal system. An effective free energy for the composition field was derived by eliminating elastic fields which are coherently induced by composition inhomogeneities It was shown that anisotropic long‐range interactions between composition fields play a major role in determining both the domainmorphology and domain growth law of spinodal decomposition with the coherence of the lattice. Computers simulations were performed on the basis of a two‐dimensional model by taking into account those long‐range interactions. The results demonstrated the appearance of lamella structure and its coarsening in the late stage of the phase separation The calculation for the TiO2‐SnO2 system showed slow coarsening due to the anisotropic elastic long ‐range interactions The asymptotic growth of the lamella size was described by λα tn, where n is 0.18.
Silicon Carbide Platelet/Alumina Composites: III, Toughening Mechanisms
Authors: Chou Yeong‐Shyung , Green David J.
Published: July 2005

This is the last part of a series of papers on the processing and fracture behavior of SiC‐platelet/Al2O3 composites. The objective of this paper was to identify the mechanisms involved in the toughening process. A hot‐pressed composite with a SiC volume fraction of 0.3 was chosen as the model system for study. Based on microstructural observations, crack deflection and grain bridging were both identified as possible toughening mechanisms and were further investigated. A Modified two‐dimensional crack deflection model is presented to account for the anisotropic microstructure in hot‐pressed platelet composites, in which preferred platelet orientation was present. Relative toughness values were predicted for two crack propagation directions assuming crack deflection is the toughening mechanism. Fracture toughness measurements for specific crack directions were made using a bridge indentation technique. The correlation of experimental results with theoretical predictions is discussed. To distinguish the effect of grain bridging from crack deflection, an in situ observation of crack growth was conducted. The results showed no distinct rising T‐curve behavior for cracks in the size range 80 to 500 μ m. Measurement of fracture surface roughness was also made and the implications are discussed. The results indicate that crack deflection is the dominant toughening mechanism in the SiC‐platelet/ Al2O3 composites studied herein.
Comparison of Bulk Properties of Mg‐PSZ with Temperature–Time Contour Diagrams
Authors: Montross Charles S.
Published: July 2005

The relationships of the precipitated metastable and stable phases with respect to the bulk properties of Mg‐PSZ were analyzed versus time and temperature. An application of the temparature‐time‐transformation diagram method detailed in a previous study was used to analyze the data. A new methodology is presented to compare the complex property relationships between the bulk properties and precipitated phases. Fracture toughness (KIC), Vickers hardness, as well as area fractions of unreacted secondary precipitate zones and grain boundary phase, were measured and plotted. For example, a maximum in fracture toughness was found to correlate with the disappearance of the unreacted secondary precipitate zones.
MAS NMR Studies of Partially Carbonated Portland Cement and Tricalcium Silicate Pastes
Authors: Thomas Sabine , Meise‐Gresch Karin , Müller‐Warmuth Werner , Odler Ivan
Published: July 2005

29Si, 27Al, and 1H MAS NMR studies of partially carbonated mature ordinary Portland cement (OPC) and tricalcium silicate (C3S) pastes have been carried out. The water‐to‐solid ratios (W/S) have been varied between 0 and 1 at hydration temperatures of 23o and 90oC. Various Q ni units with n=0, 1,2,3, and 4, and a Q3 (1Al) group have been identified using 29Si NMR. Cross‐polarization experiments, in addition, have made it possible to assign the OH groups. Two types of fourfold‐ and one type sixfold‐coordinated aluminum have been distinguished using 27Al NMR. In C3S pastes for w/s>0.7, progressive carbonation leads to a nearly perfect three‐dimensional network consisting of Q3 and Q4only. In contrast, in OPC pasted only about 40% of the highly polymerized silicate units are formed, partially copolymerized with AlO4 tetrahedra.
Chemical Reactions in the Processing of MoSi2 Carbon Compacts
Authors: Jacobson Nathan S. , Lee Kang N. , Maloy Stuart A. , Heuer Arthur H.
Published: July 2005

Hot‐pressing of MoSi2 powders with carbon at high temperatures reduces the siliceous grain boundary phase in the resultant compact. The chemical reactions in this process were examined using the Knudsen cell technique. A 2.3 wt% oxygen MoSi2 powder and a 0.59 wt% oxygen MoSi2 powder, both with additions of 2 wt% carbon, were examined. The reduction of the siliceous grain boundary phase was examined at 1350 K and the resultant P(SiO)/P(CO) rations interpreted in terms of the SiO(g) and CO(g) isobars on the Si‐C‐O predominance diagram. The MoSi2+ carbon mixtures were then heated at the hot‐pressing temperature of 2100 K. Large weigh losses were observed and could be correlated with the formation of a low‐melting eutectic and the formation and vaporization of SiC.
Phase Diagram of Na2O‐B2O3‐SiO2 System
Authors: Ghanbari‐Ahari Kazem , Cameron Andrew M.
Published: July 2005

The binary isopleth Na2O.B2O3‐SiO2 of the Na2O‐B2O3 SiO2 ternary system has been investigated. A phase diagram is presented based upon data from differential thermal analysis studies of prepared glasses and direct observation of the melting behavior using solid‐state video imaging. Phase equilibria relations in the Na2O‐B2O3‐SiO2 ternary system have been reassessed by combining information from this study with existing data from the literature. A revised liquidus surface for the ternary is presented in which the form of the isotherms is updated.
Microstructure and Properties of Cr2O3‐Doped Ternary Lead Zirconate Titanate Ceramics
Authors: Liang Chich‐Kwo , Wu Long
Published: July 2005

The effects of Cr2O3 doping (0 to 0.6 wt%) on the microstructure and electrical properties of ternary Pb0.97Sr0.03‐ [Zr0.458Ti0.452 (Mn1/3Nb2/3) 0.09]O3 piezoelectric ceramics have been studied. Abnormal grain growth (grain sizes of 2.8 to 28.5 μm) and densification (porosities of 2% to 12%) are found, and the tetragonality c/a nearly keeps constant wherease c and a slightly decrease in the doping range. The results for the temperature dependence of electric conductivity and the dielectric constant show that electric conductivity increase continuously over 0.1 wt% content, activation energies are all close to 0.92 eV in the paraelectric state, and the Curie temperature Tc decreases with increasing doping content. Minor additives of ≤0.1 wt% improve the dielectric and piezoelectric properties, but with more additives of ≥0.4 wt% electrical properties appear to deteriorate. Thus, these phenomena can be ascribed mainly to anomalous developed microstructure.
Microchemical Analysis of the SCS‐6 Silicon Carbide Fiber
Authors: Ning Xian‐Jie , Pirouz Pirouz , Farmer Serene C.
Published: July 2005

A detailed quantitative study of the microstructural variation of chemical composition of chemically vapor‐deposited commercial SiC SCS‐6 fiber is presented. Chemical etching and various electron‐optical techniques including scanning electron microscopy, transmission electron microscopy, transmission electron microscopy, scanning Auget microscopy, Auger electron spectroscopy, and parallel electron energy loss spectroscopy are used to analyze the chemical composition of the as‐received fiber. In addition, some results on stereology of the high‐temperature annealed fiber are presented. The results show that the carbon‐to silicon atom ratio in the SiC layers decreases in a stepwise fashion from ∼ 3:2 to ∼ 1:1 in going from the inner‐most layer to outermost layer.
Temperature Dependence of Anelastic Deformation in Polycrystalline Silicon Nitride
Authors: Sato Kazunori , Tanaka Kohichi , Nakano Yoshinori , Mori Tsutomu
Published: July 2005

The influence of grain‐boundary sliding on the evaluation of the apparent Young's modulus and plastic‐deformation (flow) stress was investigated by bending tests for two types of silicon nitrides sintered with Y2O3‐based additives The apparent Young's moduli measured at high temperatures are consistent with those predicated from a theory based on polycrystalline anelasticity due to grain‐boundary sliding. The temperature dependence of the critical bending stress for the onset of plastic deformation shows viscoplastic properties of the interglanular glass. The ductile‐to‐brittle transition of fracture is discussed by the bending strengths normalized by the measured Young's modulus.
Microstructural Evolution during the Sintering of TiC–Mo–Ni Cermets
Authors: Chun Dong‐Il , Kim Doh‐Yeon , Eun Kwang‐Yong
Published: July 2005

TiC‐Ni‐Mo cermet specimens were prepared by using a mixture of fine (1.5 μm) and coarse (30 μm) TiC powders. When the fraction of fine TiC particles was 80%, a (Ti,Mo,Ni)C complex carbide phase was observed deposited on the coarse TiC particles and resulted in a typical cored structure. As the fraction of fine TiC particles decreased, the coarse TiC particles exhibited a unique microstructural evolution with the development of a concave interface. This microstructural change of the coarse TiC grains can be explained in terms of the coherency strain energy.
Positive Temperature Coefficient of Resistivity in Ba1‐xSrxPb1+yO3‐8 Ceramics
Authors: Nagamoto Hidetoshi , Kagotani Hiroshi , Okubo Tatsuya , Koya Toshiyuki
Published: July 2005

The positive temperature coefficient of resistivity (PTCR) effect in Ba1‐xSrxPb1+yO3‐s ceramics is systematically studied. The influence of the preparation conditions on the PTCR properties is experimentally tested. The PTCR effect in metallic‐conducting BaPb1+yO3 is confirmed around 700°C. The temperature where the PTCR effect starts can be shifted to a higher temperature range by substituting strontium for the A‐site barium. By the enhancement of the sintering, the magnitude of the PTCR effect was increased and the resisitivity was reduced. In addition to Pb(IV) in the perovskite structure, Pb(II) is detected at the grain boundary in the sintered body.
Optimization of the Thermodynamic Properties and Phase Diagrams of the Na2O–SiO2 and K2O–SiO2 Systems
Authors: Wu Ping , Eriksson Gunnar , Pelton Arthur D.
Published: July 2005

Available thermodynamic and phase diagram data have been evaluated for all phases in the Na2O‐SiO2 and K2O‐SiO2 systems at 1 bar pressure from 298 K to above the liq‐uidus temperatures. All reliable thermodynamic and phase diagram data have been simultaneously optimized in order to obtain one set of model equations for the Gibbs energies of all phases as functions of temperature and composition. The thermodynamic properties and phase diagrams calculated from these parameters are self‐consistent. The modified quasi‐chemical model was used to represent the Gibbs energies of the molten slag phases.
Critical Evaluation and Optimization of the Thermodynamic Properties and Phase Diagrams of the CaO–FeO, CaO–MgO, CaO–MnO, FeO–MgO, FeO–MnO, and MgO–MnO Systems
Authors: Wu Ping , Eriksson Gunnar , Pelton Arthur D.
Published: July 2005

All available thermodynamic and phase diagram data at 1 bar pressure have been critically assessed for the liquid and solid (rock salt structure) phases of the six binary systems formed among the components CaO, FeO, MgO, and MnO. In the case of FeO‐containing systems, data were evaluated at Fe saturation. All reliable data for each system were optimized simultaneously to give one set of model equations for the liquid and solid solutions. In systems for which the liq‐uidus or solidus curves have not been measured, they were calculated. The thermodynamic properties and phase diagrams calculated from these equations are self‐consistent and are the most reliable currently available estimates of the true values.
Xenon Emission Accompanying Fracture of Xenon‐Implanted Cubic Zirconia
Authors: Norton M. Grant , Jiang Wenbiao , Dickinson J. Thomas , Jensen Leslie C. , Langford Stephen C. , Fleischer Elizabeth L. , Mayer James W.
Published: July 2005

The emission of xenon following the fracture of xenon‐implanted cubic zirconia has been studied using mass spec‐trometry. All samples showed intense Xe bursts at failure. Order of magnitude estimates of the amount of Xe released suggest that micrometer‐scale regions of the tensile surface on either side of the fracture surface of these samples do not show sufficient damage to account for this emission. However, SEM micrographs of the fracture surface show evidence for extensive microcracking immediately adjacent to the tensile surface. It is believed that these microcracks are formed when the advancing crack encounters the tensile stresses immediately below the Xe‐implanted surface layer and disrupts the Xe inclusions produced by implantation. Some samples also show Xe bursts prior to failure; SEM observations of these samples show shallow conchoidal cracks on the tensile surface, which apparently form during loading and would account for the release of Xe prior to failure.
Journal Spherical Mullite Particles Prepared by Hydrolysis of Aerosols
Authors: Ocaña Manuel , Sanz Jesús , Gonzalez‐Carreño Teresita , Serna Carlos J.
Published: July 2005

Nonhollow spherical particles were prepared by hydrolysis of liquid aerosols consisting of mixtures of silicon methoxide and aluminum sec‐butoxide. In order to obtain particles with mullite composition, some chloroform had to be added to the alkoxides mixture. TEM microanalyses carried out in single particles revealed a rather narrow distribution in composition around the mullite nominal value. The particles, as prepared, were amorphous. Their thermal evolution was studied by thermal analyses, X‐ray diffraction, and infrared and 27A1, 29Si NMR spectroscopies. Crystallization of pseudo‐tetragonal mullite was detected at 950°C, suggesting a high degree of Al‐Si mixing in the original particles. At the same time, some silica segregation was also observed. Between 1200°‐1400°C, the pseudo‐tetragonal/ orthorhombic mullite transformation took place, accompanied by the incorporation of segregated silica into the originally formed mullite.
Sol–Gel Route to Synthesis of Microporous Ceramic Membranes: Thermal Stability of TiO2–ZrO2Mixed Oxides
Authors: Xu Qunyin , Anderson Marc A.
Published: July 2005

In this paper concerning the synthesis of microporous ceramic membranes, we focus on the preparation and ther‐ mal stability of unsupported microporous TiO2‐ZrO2, mixed‐oxide membranes. It has been observed that, by add‐ ing up to 20% ZrO2, into TiO2, or up to 10% TiO2, into ZrO2, these microporous membranes display improved thermal stability. They can be fired up to 500°C for 0.5 h without closing micropores. However, membranes containing almost equal percentages of each component have lost microporous features and have low surface areas and low porosities. A phase diagram of a two‐component TiO2‐ ZrO2, mixed‐oxide membrane has been prepared based on DTA and X‐ray diffraction data in order to better under‐ stand the microstructure changes upon firing.
Compositional Effects on the Liquid‐Phase Sintering of Praseodymium Oxide‐Based Zinc Oxide Varistors
Authors: Alles Aldo B. , Puskas Robert , Callahan Gregory , Burdick Vernon L.
Published: July 2005

The influence of the formation of eutectic liquid phases during sintering of the ternary varistor system ZnO‐Pr6O11‐Co3O4 was studied. The temperature at which the samples were observed to be liquid‐phase sintered was found to depend on the nominal batch composition. The appearance of the liquid phase had a significant effect on the final microstructure as well as on the electrical properties of the varistors. Small additions of ZrO2, purposely added or resulting from ball‐mill contamination, were found to affect moderately the properties of the liquid phases observed in this system.
Crystallization and Properties of a Si‐Y‐Al‐O‐N Glass‐Ceramic
Authors: Besson Jean‐Louis , Billieres Dominique , Rouxel Tanguy , Goursat Paul , Flynn Robert , Hampshire Stuart
Published: July 2005

Glasses have been prepared in the Si ‐Y‐Al O‐N system by melting mixtures of silica, alumina, yttria, and silicon nitride. One particular glass containing 17 equiv% N has been investigated to Observe the crystallization at temperatures in the range 1050o‐1300oC. The major crystalline phase observed is Y2Si2O7, existing as the α form below 1200oC and the β form above this temperature. Properties of the glass‐ceramic, including thermal expansion coefficient, hardness, electrical resistivity, and creep have been assessed.
Raman Spectroscopy of Tetragonal Zirconia Solid Solutions
Authors: Kim Dae‐Joon , Jung Hyung‐Jin , Yang In‐Sang
Published: July 2005

Raman spectra of tetragonal zirconia were studied for the systems ZrO2‐Y2O3, ZrO2‐CeO2, ZrO2‐Y2O3‐Nb2O5, and ZrO2‐Y2O3‐Ta2O5 There was no change in the Raman bands for tetragonal ziraconia in the ZrO2‐Y2O3 system as a function of Y2O3 content . On the other hand, in the ternary systems, the Raman lines corresponding to the stretching modes of two sets of cation‐oxygen bonds shifted to greater wave numbers as either Nb2O5 Contents increased in Y2O3‐stabilized tetragonal zirconia. This difference was interpreted by local bonding environments of the pentavalent cations, which were supposed to occupy tetrahedral sites in teteragonal zirconia solid solutions.
1H Nuclear Magnetic Resonance Imaging of Water Diffusion in Hardened Cement Pastes
Authors: Papavassiliou George , Milia Fanny , Fardis Michael , Rumm Ron , Laganas Edward , Jarh Orest , Sepe Anna , Blinc Robert , Pintar Mik Milan
Published: July 2005

The diffusion of water into hardened cement samples containing different kinds of additives has been studied for the first time using nuclear magnetic resonance imaging (NMRI). The results indicate that NMRI can be used as a research and industrial method to evaluate the properties (permeability, durability, etc.) of the final cement product.
Solid Solubility of Aluminum in O'‐SiAlON
Authors: Ohashi Masayoshi , Hirao Kiyoshi , Brito Manuel E. , Takaaki Nagaoka , Yasuoka Masaki , Kanzaki Shuzo
Published: July 2005

Energy ‐dispersive X‐ray spectroscopy(EDXS) analysis was used to investigate the solid solubility of aluminum (X value) in O ‐SiAlONs (Si2‐xAlxO1+xN2‐x)using transmission electron microscopy in the scanning transmission electron microscopy mode. Lattice parameter a of the O ‐SiAlONs increased with increased X value =0.16. The X value of 0.16 was the maximum of the X value in SiAlONs precipitated from a Si‐Al O‐N melt which was sasturated with aluminum and nitrogen at 1700oC.The X value of O ‐SiAlONs measured by EDXS were smaller than those calculated on the assumption that the Si2N2O structure accommodated the total amount of the doped Al2O3 . This result suggested that a considerable amount of Al2O3 remained in grain boundaries as secondary phases.
Sintering of Sol—Gel‐Prepared Submicrometer Particles Studied by Transmission Electron Microscopy
Authors: Chu Xi , Chung Won‐il , Schmidt Lanny D.
Published: July 2005

We studied the sintering process of sol‐gel‐prepared monodisperse submicrometer CeO2 spheres by examining the microstructural changes of single spherical particles after successive heat treatment in oxygen up to 850°C using transmission electron microscopy. Steps of organic phase removal, CeO2 crystallization, grain growth, and particle condensation were clearly illustrated. Grain‐size and sphere‐diameter changes were measured quantitatively using this technique. CeO2 particles were found to be highly porous until collapse, which occurred at~850°C.
Determination of the Oxygen Self‐Diffusion Coefficients in Y2O3‐Containing Tetragonal Zirconia Polycrystals by Raman Spectrometric Monitoring of the 16O‐18O Exchange Reaction
Authors: Kim Byung‐Kook , Park Soon‐Ja , Hamaguchi Hiro‐o
Published: July 2005

A new method of determining the oxygen self‐diffusion coefficients (D) in oxides has been developed. The method is based on Raman spectroscopy combined with the 16O–18O exchange technique. By using the time dependent 18O2 concentration measured in a quasi in situ manner by Raman spectroscopy, the oxygen self‐diffusion coefficients are calculated. The calculation takes into account the influence of the surface exchange reaction and the limited gas volume. The result obtained in 2.8 mo1% Y2O3‐containing tetragonal zirconia polycrystals is D = 1.55 (+0.07‐0.07) x 10‐2 exp[(‐120.0 0.4) (kJ/mol) /RT] cm2/sec. It was demonstrated that Raman spectroscopy is useful tool for determining the oxygen self‐diffusion coefficients in oxides.
A Controlled Flaw Technique for Lifetime Characterization
Authors: Liniger Eric G. , Cook Robert E.
Published: July 2005

A new technique for studying the lifetime characterstics of brittle materials is presented. The technique involves the use of controlled identification flawa and treats time‐to‐failure as an experimentally fixed parameter rather than a dependent variable. Experimental advantages include specimen economy and unambiguous data analysis (for example, no specimens or results are lost due to test “run‐out”). The technique is applied to a borosilicate glass and the data compared with indentation fracture mechanics predicitions from a previous study. The data show the significant effects of reactive environment, in this case water, to reduce the failure stress of components.
Influence of Metal Ions on the Order‐Disorder Transition Temperature of the Ba‐M‐O (M: La, Y, In, or Ga) System
Authors: Mitamura Takashi , Ogino Hiroyuki , Kobayashi Hidehiko , Mori Toshiyuki , Yamamura Hiroshi
Published: July 2005

Preparation of BaLa2O4, Ba3,Y4O9, Ba,In2O5, and Ba3Ga2O6 powders and their sintering were investigated in Ar or air. These sintered bodies with perovskite‐related structure were synthesized by reaction sintering, using mixed powders in the atomic ratios of Ba/La = 1, Ba/Y = 0.75, Ba/In = 1, and Ba/Ga = 1.5. The order‐disorder transition temperatures of the BaLa2O4, Ba3Y4O9, Ba2In2O5, and Ba3Ga2O6 sintered bodies were 270°, 350°, 880°, and 123OoC, respectively. It was found that the temperatures were influenced by the ionic radius of cations in B sites, and the transition temperatures decreased with increasing ionic radius.
Phase Structure and Dielectric Properties of Bi2O3‐ZnO‐Nb2O5‐Based Dielectric Ceramics
Authors: Liu Donhang , Liu Yi , Huang Shui‐Q. , Yao Xi
Published: July 2005

Phase structures and dielectric properties of the compounds with formulas BixZn2/3Nb4/3O4+3x/2 (group M), BixZn8/3‐x Nb4/3O6+x/2 (group V), and BixZn2‐2x/3Nb2‐x/3O7 (group W) have been investigated. Initial results indicate that a cubic pyrochlore structure is the predominant phase of these compound. Most of the measured ceramic specimens exhibit dielectric properties suitable as temperatures‐stable and temperature‐compensating dielectrics in the capacitor industry. The values of the dielectric constant K are 80‐160, while those of the temperature coefficient are–500 to + 160 ppm/°C. The composition limits of the single pyrochlore phase are determined mainly by Bi2O3 additives.
Assessment of Residual Strain in Zirconia‐Toughened Alumina Using Neutron Diffraction
Authors: van Riessen Arie , O'Connor Brian H.
Published: July 2005

Neutron powder diffractometry has been used to examine bulk, volume‐averaged, microstrain character for each of the ctystalline phases in a suite of zirconia‐toughened alumina ceramics. Line‐broadening estimates and cell parameter shifts, determined by the Rietveld method, have provided microstrain assessments of the nonuniform and uniform types, respectively.
Dislocation Loops in a‐Silicon Nitride
Authors: Wang Chong‐Min , Riley Frank L. , Castro Francisco , Iturriza Iñigo
Published: July 2005

Thin foils of fully dense, but only partially transformed, hot pressed silicon nitride materials have been examined by high‐resolution transmisson electron microscopy. Large untransformed grains are seen to contain high densities of nanometer dimension, round or oval, textural features. Examination at high magnification shows thest to be clusters of dislocation loops, which are concentrated towards grain centers. The loops occur most commonly in grains of materials with a high proportion (70%) of unconverted α‐Si3N4as shown by quantitative x‐ray diffraction analysis. They are seen less ofte in material more fully converted to the β‐Si3 N4 phase (5%α‐Si3N4). The loops are believed to form by condensation form supersaturated concentrations of vacancies during rapid cooling from densification temperature. The loops are confined exclusively to the grain interiors, and in consequence an estimate of the nitrogen vacancy diffusion coefficient can be made
Enhanced Formation of Calcia‐Gallia Glass by Containerless Processing
Authors: Weber J. K. Richard , Merkley Dennis R. , Anderson Collin D. , Nordine Paul C. , Ray Chandra S. , Day Delbert E.
Published: July 2005

Glass formation from melts of 44 CaO 56Ga2O3(mol%) was investigated under containerless conditions obtained by acoustically stabilized aerodynamic levitation in combination with laser beam heating. The critical cooling rate for glass formation was Rc<100°C/s, much less than values reported in the literature (Rc=550o±120o C/s and ca 350oC/s) for pendant drops of this composition attached to Pt‐Rh thermocouples. High values of Rc in pendant drop experiments were confirmed for the specimens used in this work.
Surface Strengthening of Alumina‐Zirconia Composite by Addition of Molybdenum Dioxide
Authors: Shin Yu‐Seon , Kang Suk‐Joong L.
Published: July 2005

MoO2 is found to stabilize m‐ZrO2 Because of the addition of MoO2 into ZrO2 at the surface region of an Al2O3‐15 vol% ZrO2composite, the volume fraction of m‐ZrO2 at the surface increases from 0.3 to 0.5–0.6 without changing the size of the ZrO2grains. This enhanced transfomation results in an increase in flexural strength of up to 30% because of compressive stresses built in at the surface. The increase in flexural strength is proportional to the difference in volume fraction of m‐ZrO2 between the surface layer and the bulk matrix, in agreement with a previous analysis.
Phase Regions and Kinetics of Formation of (Bi,Pb)2Sr2Ca2Cu3Ox in Ag‐Sheathed Tape
Authors: Sung Yeon Soo , Hellstrom Eric E.
Published: July 2005

Ag‐sheathed (Bi,Pb)2Sr2Ca2Cu3O, (2223) tapes were made by the oxide‐powder‐in‐tube method. Tapes were heat‐treated isothermally at several different temperatures in 7.5% O2/Ar, then quenched into oil to retain the phase assemblages at the reaction temperatures. 2223 formed between ∼810° and ∼837°C. The Avrami equation was applied to describe the kinetics of 2223 formation from a mixture of Bi2Sr2CaCu2Ox and nonsuperconducting phases, mainly Ca2PbO4 and CuO. The calculated Avrami exponent, n∼ 1, indicated that the kinetics in this system could be described as a diffusion‐controlled, two‐dimensional nucleation and growth process. The apparent activation energy for forming 2223 was ∼2900 kJ/mol from ∼817° to ∼825°C and ∼890 kj/mol from ∼825° to ∼837°C. A temperature‐time‐transformation diagram was constructed based on the kinetic data; it describes the transformational behavior of this particular system.