bluuebunny/crossref_metadata_2025 huggingface dataset:
THE EFFECTIVENESS OF CHILD SAFETY SEAT LAWS IN THE FIFTY STATES
Authors: Houston David J. , Richardson Lilliard E. , Neeley Grant W.
Published: June 2005

This study evaluates the effectiveness of state child safety seat laws in the United States. Data for all fifty states for the period 1975 to 1994 are used. Pooled time series analysis is employed to estimate a model of the rate of fatalities suffered by children ages 0–5 years as occupants in automobile crashes. The occupant fatality rate for children 6–11 years of age is used as a comparison group to control for other trends not introduced in the estimated models. The results show that child safety seat policies have significantly reduced fatality rates among children 0–5 years of age. For each additional year of age covered by a state statute, this fatality rate drops 4.8%. A similar reduction in the fatality rate of the older age cohort (6–11 years old) was not observed.
MAPPING ECONOMIC DEVELOPMENT POLICY CHANGE IN THE AMERICAN STATES1
Authors: Brace Paul
Published: June 2005

This article explores an interesting question. Why, despite compelling evidence arguing against their effectiveness, do ever‐larger incentive packages continue to be offered by the states to attract firms?
Liquid Phase Sintering of Alumina, I. Microstructure Evolution and Densification
Authors: Dong Weimin , Jain Himanshu , Harmer Martin P.
Published: June 2005

The microstructure evolution and densification of alumina containing 10 vol% calcium aluminosilicate glass and 0.5 wt% magnesium oxide sintered at 1600°C were quantified by measuring the evolution of pore‐size distribution, the redistribution of liquid phase, and the fraction of closed and open pores. The densification stopped at a limiting relative density during the final stage of sintering, and the small and large pores were filled simultaneously by glass during sintering. In addition, the results indicate that the pressure build‐up of the trapped gases in pores causes a significantly negative contribution to the driving force, and consequently the observed reduction in densification during the final stage of liquid phase sintering.
Liquid Phase Sintering of Alumina, II. Penetration of Liquid Phase into Model Microstructures
Authors: Dong Weimin , Jain Himanshu , Harmer Martin P.
Published: June 2005

Alumina preforms containing artificial pores were sintered at 1630°C in air and vacuum. Glass penetration into the alumina preforms was conducted at 1600°C in air. It was found that the trapped gases in alumina preforms sintered in air caused the random and incomplete filling of the smaller and larger artificial pores. In contrast, the pores in the alumina preform sintered in vacuum were completely filled during glass penetration.
Liquid Phase Sintering of Alumina, III. Effect of Trapped Gases in Pores on Densification
Authors: Dong Weimin , Jain Himanshu , Harmer Martin P.
Published: June 2005

The microstructure evolution and densification kinetics of alumina containing 10 and 20 vol% calcium aluminosilicate glass were studied, for sintering under vacuum and air at 1600°C. Residual porosity was always present in the air‐fired samples. The kinetic analysis lent strong support to the notion that trapped gases inhibited the densification and limited the attainment of full density. The samples containing 20 vol% glass were able to reach full density during vacuum sintering. However, the samples containing 10 vol% glass contained some residual porosity even after vacuum sintering, which was attributed to the preferential volatalization of liquid phase.
Surface Potential of Poly(lactic acid) Composites Containing Calcium Carbonates in Simulated Body Fluid
Authors: Maeda Hirotaka , Kasuga Toshihiro , Nogami Masayuki
Published: June 2005

The surface of a poly(lactic acid) composite (CCPC) containing calcium carbonate was reported to show apatite formation in simulated body fluid (SBF) within 24 h at 37°C. In the present work, ζ potentials of CCPC were examined to determine the rapid apatite formation mechanism at an early stage after soaking in SBF. The ζ potentials of CCPC showed negatively charged values in SBF. The potential decreased immediately after soaking, and subsequently increased during 1–6 h of soaking. After 6–9 h of soaking, no change in ζ potentials was observed. Laser Raman spectroscopy results suggested that the change in the ζ potential is closely related to the amount of Ca2+‐coordinated carboxy groups on the CCPC surface. The concentration of phosphate ion in SBF decreased after 6 h. Apatite formation was suggested to begin after 6–9 h of soaking via Ca2+ coordination to carboxy groups and the subsequent adsorption of phosphate ions.
Advantages of SiC Hi‐Nicalon or NLM 202 Fibers in SiCf–SiBC Composites
Authors: Darzens Séverine , Chermant Jean‐Louis , Sangleboeuf Jean‐Christophe
Published: June 2005

SiCf–SiBC composites were produced using NLM 202 and Hi‐Nicalon SiCf fibers. Tensile creep tests were performed under a reduced pressure of argon. These composites show a good creep resistance at 1473 K with a strain rate ranging from 10−9 to 10−7 s−1, depending on the stress level. The creep strength was improved by using Hi‐Nicalon instead of NLM 202 SiCf fibers, to the extent of increasing the loadability by 50 MPa at the same operating temperature or increasing the temperature by 50 K for the same load. The damage observed in SEM micrographs and the use of the damage mechanics provide evidence that creep is governed by a damage‐creep mechanism in two steps.
Spark Plasma Sintering of LiTi2(PO4)3‐Based Solid Electrolytes
Authors: Chang Chae‐Myung , Lee Young Il , Hong Seong‐Hyeon , Park Hyun‐Min
Published: June 2005

Solid electrolytes, LiTi2(PO4)3 (LTP), Li1.3Al0.3Ti1.7(PO4)3 (LATP), and Li1.3Al0.3Ti1.7(PO4)2.9(VO4)0.1 (LATPV), were prepared by conventional sintering (CS) and spark plasma sintering (SPS) methods, and the Li+ ion conductivity of the sintered pellets was examined using an impedance analyzer. SPS remarkably improved the densification compared to CS and resulted in dense ceramics (95–97% of theoretical density) irrespective of the substituted ions. The highest conductivity of 2.6 × 10−4 S/cm was found for the LATPV specimen sintered by spark plasma at 1100°C. LATP and LATPV exhibited an order of magnitude higher ionic conductivity than LTP in the specimens of similar densities. The results demonstrated that the enhanced conductivity in substituted LTP is not due to the enhanced densification alone. The other possible explanations are discussed in terms of bottleneck size, lithium content, and grain boundary characteristics.
Low Temperature Chemical Vapor Deposition of Aluminosilicate Thin Films on Carbon Fibers
Authors: Richards Vernal N. , Vohs Jason K. , Fahlman Bradley D. , Williams Geoffrey L.
Published: June 2005

We report the deposition of aluminum oxide and aluminosilicate thin films onto carbon fiber substrates, at temperatures of 200° and 250°C, respectively. For aluminosilicate films, the Al/Si ratio of the resultant film varied concomitantly with the composition of the liquid precursor mixture. The growth rate for the oxide films was 15–17 Å/min, comparable with other methods carried out at higher temperatures. Cross‐section SEM images indicate that the deposited films are conformal, following the complex topography of the carbon fiber substrate. Preliminary gas‐phase IR analysis suggests that the coatings decompose the nerve agent simulant dimethyl methylphosphonate at temperatures as low as 35°C, suggesting the utility of the reported methodology for the design/fabrication of actively protective fabrics and clothing.
Aluminum Nitride Thin Films on an LTCC Substrate
Authors: Lee Jung W. , Cuomo Jerome J. , Cho Yong S. , Keusseyan Roupen L.
Published: June 2005

Aluminum nitride thin films deposited on a low‐temperature co‐fired ceramics substrate by reactive magnetron sputtering were investigated with regard to their crystal orientation and microstructural characteristics. Strong c‐axis orientations of AlN thin films were observed when either a higher deposition temperature or an RF bias was adopted. This orientation was believed to be responsible for the high thermal conductivity of 26 W/mK for the AlN films deposited at 700°C under 25‐W bias. Photoluminescence spectrum in the wavelength range of 350–650 nm was analyzed to prove the involvement of potential oxygen‐related defects in the thin films.
Synthesis and Characterization of Nano‐Hetero‐Structured Dy Doped CeO2 Solid Electrolytes Using a Combination of Spark Plasma Sintering and Conventional Sintering
Authors: Mori Toshiyuki , Kobayashi Tomoaki , Wang Yarong , Drennan John , Nishimura Toshiyuki , Li Ji‐Guang , Kobayashi Hidehiko
Published: June 2005

Doped ceria (CeO2) compounds are fluorite‐type oxides that show oxide ionic conductivity higher than yttria‐stabilized zirconia in oxidizing atmosphere. As a consequence of this, considerable interest has been shown in application of these materials for “low” (500°–650°C) temperature operation of solid oxide fuel cells (SOFCs). To improve the conductivity in dysprosium (Dy) doped CeO2, nano‐size round shape particles were prepared using a coprecipitation method. The dense sintered bodies with small grain sizes (<300 nm) were fabricated using a combined process of spark plasma sintering (SPS) and conventional sintering (CS). Dy‐doped CeO2 sintered body with large grains (1.1 μm) had large micro‐domains. The conductivity in the sintered body was low (−3.2 S/cm at 500°C). On the other hand, the conductivity in the specimens obtained by the combined process was considerably improved. The micro‐domain size in the grain was minimized using the present process. It is concluded that the enhancement of conductivity in dense specimens produced by the combined process (SPS+CS) is attributable to the microstructural changes within the grains.
Synthesis of Li4SiO4 by a Modified Combustion Method
Authors: Cruz Daniel , Bulbulian Silvia
Published: June 2005

We report for the first time the synthesis of Li4SiO4 by the modified combustion method, a rapid chemical process that takes 5 min for completion. This method uses nonoxidizer compounds instead of nitrate mixtures, which are not always commercially available.

The effects of the following parameters on the production of Li4SiO4 were studied: (1) different lithium hydroxide:silicic acid:urea (LiOH:H2SiO3:CH4N2O) molar ratios; (2) the presence of air flow in the furnace chamber; and (3) the furnace heating temperature. It was found that LiOH:H2SiO3:CH4N2O molar ratios 6:1:3 heated at 1100°C in the presence of additional air in the muffle chamber formed the best precursors to produce Li4SiO4.
Crystallographic Orientation in Pure and Aluminum‐Doped Zinc Oxide Thin Films Prepared by Sol–Gel Technique
Authors: Bel Hadj Tahar Radhouane , Bel Hadj Tahar Noureddine
Published: June 2005

Novel sol–gel processes for the preparation of grain‐oriented thin films of pure and aluminum‐doped zinc oxide (AZO) are reported. Using various stabilizing ligands, oxide films with different degree of c‐axis orientation could be prepared on amorphous substrates. The origin of orientation in sol–gel‐derived ZnO and AZO films is investigated. The texture selection of ZnO films is independent of the heat‐treatment schedule but sensitive to the precursor system. The electrical properties of the films do not depend significantly on the crystallographic orientation. The film visible transmittance remained higher than 90% even after vacuum annealing.
Hydrothermal Synthesis of Anisotropic Monoclinic Zirconia Particles in the Presence of 1,12‐Diaminododecane
Authors: Chen Fengxi , Zhong Ziyi , Gan Geok Joo , Xu Xiao‐Jun
Published: June 2005

Anisotropic monoclinic zirconia particles (aspect ratio of 4–10) have been prepared upon hydrothermal processing of 1,12‐diaminododecane (DADD)‐hydrous zirconia gels at pH of 14 and at 230°C for 3 days. A biphasic growth model comprising melted DADD and the water/ethanol mixture is proposed to account for the generation of rod‐like morphology.
Thermochemistry of Framework Titanosilicate A2TiSi6O15 (A=K, Rb, Cs)
Authors: Xu Hongwu , Navrotsky Alexandra , Nyman May , Nenoff Tina M.
Published: June 2005

A new family of framework titanosilicates, A2TiSi6O15 (A=K, Rb, Cs) (space group Cc), has recently been synthesized using the hydrothermal method. This group of phases can potentially be utilized for storage of radioactive elements, particularly 137Cs, due to its high stability under electron radiation and chemical leaching. Here, we report the syntheses and structures of two intermediate members in the series: KRbTiSi6O15 and RbCsTiSi6O15. Rietveld analysis of powder synchrotron X‐ray diffraction data reveals that they adopt the same framework topology as the end‐members, with no apparent Rb/K or Rb/Cs ordering. To study energetics of the solid solution series, high‐temperature drop‐solution calorimetry using molten 2PbO·B2O3 as the solvent at 975 K has been performed for the end‐members and intermediate phases. As the size of the alkali cation increases, the measured enthalpies of formation from the constituent oxides () and from the elements () become more exothermic, suggesting that this framework structure favors the cation in the sequence Cs+, Rb+, and K+. This trend is consistent with the higher melting temperatures of A2TiSi6O15 phases with increase in the alkali cation size.
Highly Porous Vitrified Bonded Abrasives by the Selective Extraction of Butyl Carbamate from Green Grinding Wheels with Supercritical CO2
Authors: Davis Timothy D. , Sheldon D. , Erkey Can
Published: June 2005

Highly porous vitrified bonded grinding wheels were produced by selective extraction of butyl carbamate pore inducer using supercritical (sc) CO2. Butyl carbamate was found to be an excellent pore inducer, as the extraction was fast and the desired pore structure was obtained. The investigation revealed that the extraction was controlled by the solubility of butyl carbamate in scCO2 and the flow direction had a large effect on extraction times. The solubility of butyl carbamate determined from cloud point measurements was found to be high at moderate conditions. Grinding tests demonstrated that scCO2 pore‐induced wheels performed slightly better then conventionally produced wheels at the conditions investigated. The power required for grinding, wheel wear, and part quality were comparable with those of conventionally produced wheels at low metal removal rates. However, the extracted wheels outperformed the conventional wheel at high metal removal rates, indicating the scCO2 processing produces a slightly superior product than that made by conventional means. Liquefaction of the pore inducer during extraction had a minor effect on the final properties of the wheel.
De‐Agglomeration Kinetics of Feedstocks with Granule Tetragonal Zirconia Polycrystalline Powder
Authors: Wu Rong‐Yuan , Wei Wen‐Cheng J.
Published: June 2005

This study establishes the relationship between homogeneity of tetragonal zirconia polycrystalline (TZP) feedstocks and the kneading time in order to understand the kneading energy adsorption during the de‐agglomeration period of pre‐existing ceramic granules. Two spray‐dried Y‐TZP powders with different compress strengths were investigated using torque rheometer and transmission optical microscopy. Several properties, kneading torque (T), Casson viscosity (μ), Reynolds number (Re), and dispersive index (Ds) of the feedstocks were introduced, and monitored as a function of kneading time. Optimal processing windows were identified from the dependence of dispersive index with a power number (Np). The best shear‐kneading procedure was proposed in consideration of best feedstock homogeneity and shortest kneading time. One homogenous feedstock and two comparable cases were prepared for subsequent injection molding, debinding, sintering, and mechanical testing. The fracture strength of sintering parts by a partially homogeneous feedstock can be improved from 520 to 680 MPa by a homogeneous feedstock.
Sintering Kinetics of Porous Ceramics from Natural Diatomite
Authors: Zhang Xuebin , Liu Xingqin , Meng Guangyao
Published: June 2005

The sintering kinetics of the porous ceramics from natural diatomite is investigated by means of stepwise isothermal dilatometry (SID) accompanied with XRD, scanning electron microscope (SEM), and porosity measurement. We find that the isothermal shrinkage data from SID could be well analyzed to get kinetic parameters according to the empirical rate equation developed by Makipirtti–Meng,
image

where Y is the fractional volume shrinkage during sintering process and n a dimensionless exponent. The apparent activation energy ΔE values obtained for 850°–1000°C and 1050°–1150°C are 911.8 and 610.5 kJ/mol, respectively. Correspondingly, the exponent n values for the two temperature ranges are also much different and can be served to reveal the morphology changing during the sintering process, which is well consistent with the SEM observation.
Synthesis and Structural Characterization of a Metastable Mullite‐Like Alumina Phase
Authors: Subasri Raghavan , Roy Sukumar , Matusch Dirk , Näfe Helfried , Aldinger Fritz
Published: June 2005

A solution combustion technique for the synthesis of different β‐alumina compositions in the Na2O·xAl2O3 system (where x=5, 6, or 7) is described along with the structural characterization of the materials prepared. The amorphous powder obtained after a combustion reaction between the nitrate salts of the cations and aminoacetic acid was calcined in air at different temperatures in the range from 600°C up to 1300°C. The phases were investigated by powder X‐ray diffraction (XRD) and infrared spectroscopic measurements. A metastable mullite‐like alumina phase was found to form as an intermediate at a minimum calcination temperature of 750°C and stable up to 1000°C, which transformed completely into β/β″‐alumina phases beyond a temperature of 1100°C. The crystal structure of the mullite‐like alumina phase was deduced by rietveld refinement of slow scan powder XRD data. A better understanding of the crystal structure of the mullite‐like alumina was possible using other supplementary experimental evidences.
Mechanical Properties of Rough TiN Coating Deposited on Steel by Cathodic Arc Evaporation Technique
Authors: Gunda R. , Biswas S. K. , Bhowmick S. , Jayaram V.
Published: June 2005

We investigate here the axial and transverse mechanical properties of thin (1.5–7 μm) titanium nitride films deposited on high‐speed steel by cathodic arc evaporation. The deposited films are rough, the roughness varying with film thickness. Mechanical properties deconvoluted from nanoindentation data show variations with penetration depth and scatter. We explore the effect of film surface roughness on these variations and comment on the possible effects of material heterogeneity and crystal structure on the estimated properties.
Anisotropic Fracture Behavior in Ferroelectric Relaxor PZN–4.5%PT Single Crystals
Authors: Oates William S. , Lynch Christopher S. , Kounga Njiwa Alain B. , Lupascu Doru C.
Published: June 2005

The anisotropic fracture behavior in unpoled and poled (1−x)Pb(Zn2/3Nb1/3)−xPbTiO3 (x=0.045) (PZN–4.5%PT) single‐crystal relaxor ferroelectrics cut along the crystal planes, [010] and [001], was characterized. The crack tip toughness (Ktip) determined from Vickers indentations was compared with the R‐curve behavior measured using the single‐edge V‐notch beam (SEVNB) method. Several of the SEVNB fracture experiments resulted in cracks forming and propagating under mixed mode loading (KI and KII) along the [110] crystal plane. Other specimens formed cracks at 0° along the [010] plane. To assess the anisotropic fracture behavior, the local and global critical energy release rates were determined using Stroh's formalism.
Thermodynamic Modeling of the MgO–Al2O3–CrO–Cr2O3 System
Authors: Jung In‐Ho , Decterov Sergei , Pelton Arthur D.
Published: June 2005

A complete critical evaluation and thermodynamic modeling of the phase diagrams and thermodynamic properties of the MgO–Al2O3–CrO–Cr2O3 system at 1 bar total pressure are presented. Optimized equations for the thermodynamic properties of all phases are obtained which reproduce all available thermodynamic and phase equilibrium data within experimental error limits from 25°C to above the liquidus temperatures at all compositions and oxygen partial pressures. The optimized thermodynamic properties and phase diagrams are believed to be the best estimates presently available. The database of the model parameters can be used along with software for Gibbs energy minimization in order to calculate any type of phase diagram section.
Effect of Powder Coating on Stabilizer Distribution in CeO2‐Stabilized ZrO2 Ceramics
Authors: Fang Ping‐an , Gu Hui , Wang Pei‐ling , Van Landuyt Jef , Vleugels Jef , Van der Biest Omer
Published: June 2005

The phase and microstructure relationship of 12 mol% CeO2‐stabilized ZrO2 ceramics prepared from coated powder was investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy‐dispersed X‐ray spectroscopy (EDS). As compared with the sample prepared with co‐precipitated method, which exhibited a similar grain size distribution, the EDS analysis revealed that the powder coating induced a wide distribution of CeO2 solubility, which decreases monotonically with the increase of grain size. This variation of stabilizer content from grain to grain rendered many large grains in the monoclinic phase. Stronger cerium segregation to grain boundaries was observed between large grains, which often form thin amorphous films there. The inhomogeneous CeO2 distribution keeps more tetragonal ZrO2 grains close to the phase boundary to facilitate the transforming toughness. Addition of an Al2O3 precursor in coated powders effectively raises the overall CeO2 stabilizer content in the grains and preserves more transformable tetragonal phase in the microstructure, which further enhanced the fracture toughness. The dependence of CeO2 solubility on grain size may be explained in a simple coating‐controlled diffusion and growth process that deserves further investigation.
Microstructure and Mechanical Performance of Belite Cements from High Calcium Coal Fly Ash
Authors: Guerrero A. , Goñi S. , Moragues A. , Dolado J. S.
Published: June 2005

The microstructure and mechanical performance of two low energy fly ash belite cements (FABC‐1‐W and FABC‐1‐N) obtained from high calcium‐coal fly ash as raw material is studied in this work. The FABC were obtained after a previous hydrothermal treatment of the fly ash in demineralized water and NaOH 1M solution. The hydration of both FABC‐1‐W and FABC‐1‐N during 180 days was followed by thermal analysis, X‐ray diffraction, FT infrared spectroscopy, scanning electron microscopy and Brunauer‐Emmett and Teller‐N2 surface area measurements. The mechanical properties were studied under different curing conditions: normal (21°C and <95% RH) and accelerated (40°C and <95% RH). Porosity and pore‐size distribution were also studied. The results showed a better mechanical performance for FABC‐1‐N when the curing was normal and a better mechanical performance for FABC‐1‐W when the curing was accelerated.
Processing of Composite Thin Film Solid Oxide Fuel Cell Structures
Authors: Gorman Brian P. , Anderson Harlan U.
Published: June 2005

A solid oxide fuel cell (SOFC) structure is proposed in which a composite thin film cathode substrate supports a dense thin film electrolyte with a thickness of less than 1 μm. The cathode substrate has a graded porosity achieved through the partial sintering of a spin‐coated CeO2 colloidal suspension. The resulting surface has a pore size and surface roughness which allowed a fully dense ZrO2:16%Y (YSZ) electrolyte to be spin‐coated directly from a polymeric precursor without capillary forces removing the precursor from the surface of the porous substrate. Using this process, fuel cell structures were constructed with temperatures not exceeding 800°C. The porous CeO2 interlayer should allow for decreased ohmic losses, as well as decreased reactions between the YSZ and the cathode substrate. In addition, the nanocrystalline grain sizes should allow for increased catalytic activity on the cathode. Calculated ohmic losses indicated the resistance of the CeO2 interlayer limited the power of the structure, which was minimized by impregnating the porous layer with a mixed‐conducting perovskite. The final structure shows significantly reduced ohmic losses as calculated at 400°C.
Microstructural Characterization of Commercial Hot‐Pressed Boron Carbide Ceramics
Authors: Chen M. W. , McCauley J. W. , LaSalvia J. C. , Hemker K. J.
Published: June 2005

Two commercial hot‐pressed boron carbide ceramics were investigated by transmission electron microscopy. Atomic‐scale observations suggest that the grain boundaries of the two materials are free of grain‐boundary films. Two triple‐junction phases were found and characterized to be rhombohedral Fe2B103 and orthorhombic Ti3B4. In addition, intra‐granular precipitates, AlN, Mo2(C, B) and graphite, were identified and found to have coherent relationships with the boron carbide matrix. Micron‐scale inclusions were also observed and most of them were determined to be graphite. The formation mechanisms of the secondary phases and their possible influence on mechanical properties are also discussed.
Preparation and Characterization of KNbO3 Ceramics
Authors: Birol Hansu , Damjanovic Dragan , Setter Nava
Published: June 2005

The processing and characterization of electrical properties of potassium niobate ceramic, KNbO3 (KN) have been studied. The difficulty of obtaining dense samples by conventional methods limits the knowledge on electrical properties of this material. In this paper, a complete route for processing of KN with density over 94% is described. Piezoelectric and dielectric data are presented. It is observed that the major problem concerning the density is related to incorrect stoichiometry, which is believed to be a more critical issue for this system compared with other electro‐ceramics.
Gibbs Free Energy of Formation of Zircon from Measurement of Solubility in H2O
Authors: Newton Robert C. , Manning Craig E. , Hanchar John M. , Finch Robert J.
Published: June 2005

We exploited the large difference in the solubility of SiO2 and ZrO2 in H2O to constrain precisely the Gibbs energy of formation of zircon (ZrSiO4). Solubility in H2O was determined at 800°C, 1.2 GPa, by weight loss of synthetic zircon crystals. The experiments yielded fine‐grained monoclinic ZrO2 as an incongruent solution product uniformly coating zircon crystals. Experiments on the ZrO2‐coated zircon crystals were also carried out with an initially slightly SiO2‐oversaturated fluid, causing weight gain by zircon regrowth. The mean SiO2 concentration for forward and reverse experiments was 0.069±0.010 mol/kg H2O (2σ). When combined with precise activity–composition measurements for aqueous SiO2, the data constrain the Gibbs free energy of zircon from its oxides at 298 K, 105 Pa, to be −19.30±1.16 kJ/mol (2σ). This determination is comparable in precision to the best measurements obtainable by more conventional methods, which suggests that determination of the thermochemical properties of other important ceramic materials may also be amenable to this method.
Synthesis of Titanium Carbonitride Phases by Reactive Milling of the Elemental Mixed Powders
Authors: Córdoba José M. , Sayagués María J. , Alcalá María D. , Gotor Francisco J.
Published: June 2005

Titanium carbonitride (TiCxN1−x) powders were obtained by high‐energy ball milling of elemental titanium and carbon (activated carbon or graphite) in a nitrogen atmosphere. The formation of the carbonitride phase was controlled by adequately choosing the experimental conditions of the milling process. The stoichiometry of TiCxN1−x powders was modified by adjusting the titanium‐to‐carbon molar ratio. The composition and cell parameters of the carbonitride phases were determined. Microstructural characterization of these phases showed a nanocrystalline nature.
Non‐Isothermal Crystallization Kinetics of a Blast Furnace Slag Glass
Authors: Francis A. A.
Published: June 2005

The capability of the blast furnace slag to be vitrified was investigated by means of differential thermal analysis (DTA), scanning electron microscopy, and X‐ray diffraction (XRD) in samples prepared by melting without the addition of any other ingredients. Differential thermal analysis revealed the presence of two major exothermic peaks. XRD indicates the presence of more than one crystalline phase: gehlenite Ca2Al2SiO7, BaAl2Si2O8, and pyroxene Ca(Mg,Al)(Si,Al)2O6. The activation energy of crystallization was estimated on the basis of DTA carried out on particle size 312–500 μm at different heating rates. Analysis of non‐isothermal DTA data yielded values of 457.5 KJ/mol and 2.21 for the activation energy of crystallization and the Avrami exponent, respectively. A value for the activation energy corresponding to structural relaxation at temperatures around the glass transition has also been determined for this glass.
Improved Artificial Neural Network for Data Analysis and Property Prediction in Slag Glass–Ceramic
Authors: Qiye Wen , Huaiwu Zhang , Peixin Zhang , Xiangdong Jiang
Published: June 2005

The development of slag glass–ceramics has environmental and commercial value. However, new types of these materials are usually developed using the “trial and error” method because of little understanding of the relationship between the composition, processing, microstructure, and properties. In this paper, artificial neural network (ANN) technology was applied to investigate the relationship between the composition content and the properties of slag glass–ceramic. The investigation showed that the ANN model had an outstanding learning ability and was effective in complex data analysis. If the data set reflects the relationship of the composition and property, the trained network will learn the relationship and then give relatively accurate and stable prediction. A new “virtual sample” technology has also been created which improves the prediction performance of the network by providing greater accuracy and reliability. With this virtual sample technology, the ANN model can establish the exact relationship from a small‐size‐data set, and gives accurate predictions. This improved ANN model is a powerful and reliable tool for data analysis and property prediction, and will facilitate the material design and development of slag glass–ceramics.
Phase Relations In The Pseudo‐Ternary System La2O3–SrO–Fe2O3
Authors: Fossdal Anita , Einarsrud Mari‐Ann , Grande Tor
Published: June 2005

The phase relations in the pseudo‐ternary system La2O3–SrO–Fe2O3 have been investigated in air. Isothermal sections at 1100° and 1300°C are presented based on X‐ray diffraction and thermal analysis of annealed samples. Extended solid solubility was observed for the compounds Srn+1−vLavFenO3n+1−δ (n=1, 2, 3, and ∞) and Sr1−xLaxFe12O19, while only limited solubility of La in Sr4−zLazFe6O13±δ was observed. At high Fe2O3 content, a liquid with low La2O3 content was stable at 1300°C.
Effects of Low‐Pressure Oxidation on the Surface Composition of Single Crystal Silicon Carbide
Authors: Song Yongwei , Smith Frederick W.
Published: June 2005

We report on thermodynamic modeling and experimental studies of the reaction of oxygen with the 4H‐ and 6H‐SiC surfaces at high temperatures T. It is observed that this reaction leads to the growth of passivating SiO2 layers at high pressures P(O2), etching of the surface at lower P(O2), and enhancement of the surface segregation of carbon at still lower P(O2). A unified P(O2)–T phase diagram for the reaction of O2 with SiC is presented and a thermodynamic model predicting these three distinct reaction regions is described. Evidence for the thermal decomposition of the SiO2 layer due to its reaction with the SiC substrate is also presented.
Spark Plasma Sintering Effect on the Decomposition of MgH2
Authors: Schmidt Jürgen , Niewa Rainer , Schmidt Marcus , Grin Yuri
Published: June 2005

Spark plasma sintering (SPS) is one of the advanced consolidation techniques developed in the last few decades. We have studied the decomposition behavior of MgH2 and MgH2/graphite 1:1 mixtures in the SPS process. The standard SPS setup chosen was modified by including the temperature measurement inside the sample, so that the data can be compared with findings from thermal analysis. The results show clearly the reduction of the decomposition temperature measured in the SPS process if the necessary conditions (sufficient current density by applying the insulation) are realized.
Synthesis of Nanocrystalline Enstatite Fiber Via Alkoxide Sol–Gel Process
Authors: Tsai Mu‐Tsun
Published: June 2005

An alkoxide sol–gel route to precursors to transparent enstatite fibers is described. The fibrous gels were drawn from acetic acid‐modified viscous solutions. The amount of acetic acid was found to be the crucial factor in the spinnability. Infrared studies indicated that the acetate anion behaved as a ligand and modified the molecular structure of the enstatite gel. The fibrous gel was amorphous after drying by X‐ray, and began to convert to enstatite at temperature as low as ∼600°C. The enstatite fibers were nanocrystalline up to 1100°C. At 1300°C, transparent and dense enstatite fibers were produced, with the room temperature dielectric constants of around 5.2–5.8 (at 1 MHz).
Polarization of High‐Permittivity Dielectric NiO‐Based Ceramics
Authors: Lin Yuanhua , Zhao Rongjuan , Wang Jianfei , Cai Jingnan , Nan Ce‐Wen , Wang Yutian , Wei Long
Published: June 2005

Polarization and dielectric behavior of Li and Ti co‐doped NiO (LTNO) ceramics was investigated. Analysis of the ceramic microstructure and composition indicate that an obvious grain boundary was formed and surrounded the grains, and Ti ions distributed in grains and grain boundaries. The concentration of Ti had a remarkable effect on the dielectric properties of the LTNO ceramics. Positron annihilation spectra measurements implied that a large amount of defects exist in the LTNO ceramic samples. Anomaly polarization–electric field hysteresis loops were observed in the high‐permittivity dielectric LTNO ceramics, which are totally different from those for ferroelectric materials and are due to defect‐dipoles induced, and electrical conduction effects of samples could also have an influence on the hysteresis loops. The high dielectric constant response of the LTNO ceramics is enhanced partially by the boundary layer capacitor mechanism, and partially by the huge polarization of a large amount of defect dipoles.
Fabrication and Performance of Impregnated Ni Anodes of Solid Oxide Fuel Cells
Authors: Jiang San Ping , Zhang Sam , Zhen Yong Da , Wang Wei
Published: June 2005

Y2O3‐stabilized ZrO2 (YSZ) and Gd‐doped CeO2 (GDC) oxide impregnated Ni was investigated and developed as anodes of solid oxide fuel cells. Performance of the Ni anodes for the H2 oxidation reaction was substantially enhanced after the impregnation of submicrometer (100–300 nm) YSZ and GDC oxide particles. After impregnation of 1.7 mg/cm2 GDC (∼8.5 vol% GDC), the electrode polarization resistance dropped to 0.71 Ω·cm2 at 800°C, close to 0.24 Ω·cm2 reported on good Ni (50 vol%)/YSZ (50 vol%) cermet anodes at the same temperature. The results demonstrated that ion or wet impregnation is an effective process to introduce ionic conducting and catalytic active nano‐sized YSZ and GDC phases into stable and porous Ni electronic network structure without the high temperature sintering process.
Effect of SiO2 and TiO2 Addition on the Morphology of Abnormally Grown Large Pb(Mg1/3Nb2/3)O3–35 mol% PbTiO3 Grains
Authors: Jo Wook , Chung Ui‐Jin , Hwang Nong‐Moon , Kim Doh‐Yeon
Published: June 2005

Abnormal grain growth (AGG) during the sintering of Pb(Mg1/3Nb2/3)O3–35 mol% PbTiO3 was investigated. When a small amount of SiO2 was added, large abnormal grains with the penetration twin characteristic were observed to appear. AGG, in this case, is because of the twin plane re‐entrant edges that provide coarsening advantage. When TiO2 was added, on the other hand, the abnormal grains were simple cubic in morphology with well‐developed {100} planes. In this case, the coarsening advantage is suggested to be because of grain boundary re‐entrant edges.
Wear‐Resistant Titanium Carbonitride Coatings onto WC–Co Cutting Tools by Pulsed High‐Energy Density Plasma
Authors: Peng Zhijian , Miao Hezhuo , Qi Longhao , Yang Size , Liu Chizi
Published: June 2005

Nanometer grain superhard ternary Ti(C,N) coatings with Vicker's nanohardness more than 50 GPa were deposited onto WC–Co cutting tools at ambient temperature using pulsed high‐energy density plasma coaxial gun. Young's modulus of the coated tools was about 550 GPa. Because of the continuously graded interfaces between the coatings and substrates, the coatings are well adherent to the tool substrates with very high critical load up to more than 100 mN measured by nanoscratch tester. The coefficients of friction were lower than 0.1. In contrast with the uncoated tools, the coated tools could be applied in turning hardened CrWMn steel at high speed under industrial conditions without lubricants, and the cutting performances were greatly improved with rather low flank wear and long tool life.
Reactive Melt Infiltration Processing of Biomorphic Si–Mo–C Ceramics from Wood
Authors: Chakrabarti Omprakash , Weisensel Lars , Sieber Heino
Published: June 2005

Different kinds of natural wood specimens (beech, pine, and rattan) were converted to biomorphic, microcellular Si–Mo–C ceramics by reactive melt infiltration processing. During processing at 1500°C under vacuum the carbon of the pyrolyzed native preforms reacted with Si of the infiltrating Si–Mo eutectic melt (90.4 wt% Si). The resulting materials have fractional densities of >90%, and contained silicon carbide (SiC), MoSi2, in addition to unreacted Si and carbon. The residual carbon remains covered by SiC. The conversion process retains the microcellular morphology of the parent wood tissue. Depending on the initial morphology of the different kinds of wood, reactive melt infiltration processing of Si–Mo–C ceramics can be used to manufacture light weight materials with low density but adequate strength for wide ranging applications where anisotropic behavior is required.
Thermodynamic Modeling of the Binary Barium–Oxygen System
Authors: Zhou Shihuai , Arroyave Raymundo , Randall Clive A. , Liu Zi‐Kui
Published: June 2005

The phase equilibria and thermodynamic properties of the binary Ba–O system were analyzed. The Gibbs energy functions of individual phases were modeled, and the model parameters were obtained by means of the CALculation of PHAse Diagram (CALPHAD) technique, based on available experimental data in the literature. The liquid phase was described with a two‐sublattice ionic model. For the non‐stoichiometric BaO and BaO2 phases, a two‐sublattice ionic model was applied, and two sets of Gibbs energy functions were obtained by treating them either as separate phases or as a common solution phase with a miscibility gap. The ionic sublattice models used in the present work provide an approach to better describe the physical behavior of the Ba–O binary system such as defect chemistry and doping effects, which will be studied in multicomponent systems.
Adsorption of n‐Alkanes on Silicon Nitride Nanopowder
Authors: Čerović Ljiljana S. , Milonjić Slobodan K. , Hourlier‐Bahloul Djamila
Published: June 2005

Adsorption properties of silicon nitride beads were investigated by the inverse gas chromatography (IGC) method. Silicon nitride beads were obtained from a commercial nanopowder. Retentions of n‐pentane, n‐hexane, n‐heptane, and n‐octane were measured in the temperature range from 343 to 383 K, at zero surface coverage. Surface partition coefficients and the related thermodynamic functions (standard free energy changes, standard state enthalpy, and entropy changes) of the adsorption process were determined. The dispersive component of the surface free energy of silicon nitride, at investigated temperatures, was also calculated.
Quaternary System Al2O3–CaO–MgO–SiO2: II Study of the Crystallization Volume of MgAl2O4
Authors: Alicia Vázquez Bertha , Caballero Ángel , Pena Pilar
Published: June 2005

Solid‐state compatibility and melting relations of MgAl2O4 in the quaternary system Al2O3–CaO–MgO–SiO2 were studied by firing and quenching selected samples located in the 65 wt% MgAl2O4, plane followed by microstructural and energy dispersive X‐ray analysis. A projection of the liquidus surface of the primary crystallization volume of MgAl2O4 was constructed from CaO, SiO2 and exceeding Al2O3, not involved in stoichiometric MgAl2O4 formation; those three amounts were recalculated to 100 wt%. The temperature and character of six invariant points, where four solids co‐exist with a liquid phase, were defined. One maximum point was localized and the positions of the isotherms were tentatively established. The effect of CaO, SiO2, and Al2O3 impurities on the high temperature behavior of spinel materials was also discussed.
Microstructural Coarsening of Zirconia‐Toughened Alumina Composites
Authors: Casellas D. , Nagl M. M. , Llanes L. , Anglada M.
Published: June 2005

In this work, the microstructural coarsening induced by heat treatment at temperatures between 1450° and 1750°C, for different zirconia‐toughened alumina (ZTA) materials has been studied. In doing so, grain growth kinetics and fracture toughness have been documented and analyzed. Obtained results are discussed and rationalized in terms of microstructural effects on zirconia clustering and transformability (content and size) and operative toughening mechanisms. Based on the relatively broad microstructural and toughness ranges exhibited by the ZTA composites developed and characterized, it is concluded that fracture toughness tailoring through microstructure control may be effectively implemented for these materials.
Vibrational Spectra of Ca3SiO5: Ultraviolet Laser Raman Spectroscopy at High Temperatures
Authors: Fujimori Hirotaka , Komatsu Hiroshi , Ioku Koji , Goto Seishi , Watanabe Tomoaki
Published: June 2005

The Raman spectra of Ca3SiO5 have been successfully obtained at temperatures up to 1353 K by a continuous‐wave ultraviolet Raman spectroscopic system. The Raman spectra do not change significantly with an increase in temperature, despite triclinic (T)→monoclinic (M)→rhombohedral (R) transitions. The present result is described in terms of the parameter related to temperature variation at constant pressure, defined in a manner similar to the Gruneisen parameter. Raman bands located above 350 cm−1 show smaller values of the parameter than lower frequency modes, suggesting that these higher frequency modes are assigned to SiO4 internal modes.
Synthesis of Al2O3–CeO2 Mixed Oxide Nano‐Powders
Authors: Bose Susmita , Wu Yujie
Published: June 2005

Ceria (CeO2)‐doped alumina (Al2O3) composite nano‐particles were synthesized using sucrose as a chelating agent and template material. As‐synthesized powders were characterized using X‐ray diffraction technique for their phase analysis, BET surface area analyzer for specific average surface area, and transmission electron microscope for particle size and morphology. Both CeO2 and Al2O3 delayed the amorphous to crystalline phase transformation for each other. These composite nano‐powders had particle size in the range of 20–50 nm with an aspect ratio of 1.5 with platelet morphology and surface area between 100 and 300 m2/g. Synthesis parameters were optimized varying the sucrose to metal ion ratio, calcinations time and temperature. This method can be applied to synthesize various monolithic and mixed metal oxide based ceramic nano‐particles.
Sintered Glass–Ceramics and Glass–Ceramic Matrix Composites from CRT Panel Glass
Authors: Bernardo E. , Andreola F. , Barbieri L. , Lancellotti I.
Published: June 2005

Sintering with simultaneous crystallization of powdered glass represents an interesting processing route for glass–ceramics, especially originating from wastes. Highly dense glass–ceramic samples may be obtained from a simple and short treatment at a relatively low temperature. In addition, glass–ceramic matrix composites may be obtained by mixing glass with suitable reinforcements. In this work sintered nepheline glass–ceramics, based on panel glass from cathode ray tubes, are illustrated. A limited addition of Al2O3 platelets caused a significant improvement in the mechanical properties (elastic modulus, bending strength, microhardness, fracture toughness), already remarkable for the un‐reinforced glass–ceramic, compared with traditional nepheline glass–ceramics.
Flexural Strength and Shear Strength of Silicon Carbide to Silicon Carbide Joints Fabricated by a Molybdenum Diffusion Bonding Technique
Authors: Cockeram B.V.
Published: June 2005

The capability to form robust SiC‐to‐SiC joints is needed to enable the fabrication of complex SiC‐based structures. In this work, molybdenum foils are used to develop a diffusion bond with SiC during a vacuum heat treatment at 1500°C for 10 h. The bond consists of a central region of Mo2C with Mo5Si3+carbon and/or Mo5Si3C phases at the SiC interface. Flexure strength determined using a standard 4‐point flexural test method (ASTM C1161) over the temperature range from room temperature to 1100°C showed that the molybdenum foil joined SiC failed at a somewhat lower value (263–50 MPa) than similarly tested monolithic chemically vapor deposited (CVD) SiC without any bond (443–197 MPa). Differences in elastic properties and coefficient of thermal expansion between SiC and the phases produced in the molybdenum foil joint region likely result in the formation of slightly larger flaws in the SiC near the joint, which are fracture initiation sites that result in lower flexural strength values for molybdenum‐joined SiC. Shear strength results obtained using a double‐notched specimen are also compared for the joined and monolithic specimens, which provides fracture strength data that can be used for comparisons. The shear strength values for the molybdenum‐joined SiC (264–61 MPa) are found to be within the data scatter of the monolithic material (397–31 MPa). These results indicate that a molybdenum foil diffusion bonding technique can be used to produce joints that are as strong as continuous bars of monolithic SiC in shear‐type loading, but they have lower flexural strength values than monolithic SiC. However, the flexure strength values for molybdenum foil‐joined SiC are within the range of values or higher than values reported in literature for the joining of SiC using reaction forming, reaction‐bonding, polymer precursors, and niobium diffusion bonding.
Synthesis of Nanocrystalline Alumina Using Egg White
Authors: Dhara Santanu
Published: June 2005

A new simplified route to prepare nanocrystalline alumina powders is proposed. The method involved the use of freshly extracted egg white (ovalbumin) and aluminum nitrate in an aqueous medium. Changes in ionic strength upon addition of aluminum nitrate resulted in gelation of ovalbumin. The added metal ions were dispersed in the gelled ovalbumin matrix. Heat treatment of the gelled mass resulted in nanosized γ alumina at as low a temperature as 330°C. TEM analysis showed that the particle size ranged from 15 to 80 nm.
Three‐Dimensional Magnesia‐Based Nanocrystal Assemblies Via Low‐Temperature Magnesiothermic Reaction of Diatom Microshells
Authors: Cai Ye , Allan Shawn M. , Sandhage Kenneth H. , Zalar Frank M.
Published: June 2005

A low‐temperature (≤700°C) magnesiothermic reaction has been used for the first time to convert three‐dimensional (3‐D) silica‐based diatom microshells into nanocrystalline magnesia‐based replicas. Exposure of diatom microshells to Mg(g) at only 650°–700°C resulted in the initial (direct) formation of MgO and Si nanocrystals (≤5 nm), that is, no intermediate magnesium silicate compounds were detected. Further reaction of Si with Mg(g) led to the formation of Mg2Si, and then a Mg–Si liquid that sweated away to yield free‐standing, nanocrystalline MgO‐based replicas. Such direct low‐temperature magnesiothermic conversion of diatom microshells enables the synthesis of large numbers of 3‐D nanocrystal assemblies with well‐controlled morphologies for catalytic/chemical, biological, optical, and other applications.