bluuebunny/crossref_metadata_2025 huggingface dataset:
The adaptation of water law to climate change
Authors: Hurlbert Margot
Published: July 2009

Purpose

The purpose of this paper is to focus on the adaptive capacity of the institution of water law in two provinces of Canada, Alberta, and Saskatchewan, through the examination of several water conflict case studies in the last decade. By examining outcomes in cases of water shortage, legal mechanisms promoting adaptation can be identified and suggestions made for improving those which potentially increase vulnerability.

Design/methodology/approach

This paper explores several case studies situated in Western Canada, identified during interviews relating to a broader theme of water governance adaptation as part of the Institutional Adaptation to Climate Change (IACC) Project as well as other case studies carried out in the larger IACC project relating to the institutional adaptation to climate change in Canada and Chile. The outcomes of these case studies are examined in relation to their effect on vulnerability and their inter‐relationship to established principles of water law.

Findings

This examination provides insight into the actual workings of water law in resolving water conflicts and important modifications in the institution of water law which will increase adaptive capacity. These cases illustrate that legal provisions which facilitate timely engagement of civil society to water shortages in an all inclusive participatory process provides optimal conflict resolution.

Originality/value

These case studies provide important insights for the development of law and policy which reduces vulnerability and assists people in adapting to climate change in a resilient, effective manner.
Observing novel soil conditioners for carbon emissions mitigation
Authors: Coles A.J.C. , Lewis K.A. , Sims R.E.
Published: July 2009

Purpose

The New Zealand (NZ) Government's commitment to a sustainable, low emissions energy future may be met, in part, by expanding bioenergy systems fuelled by short rotation forestry through utilising lower quality land affecting soil organic matter content and soil CO2 flux. The purpose of this paper is to investigate the carbon sequestration potential of a range of soil conditioners in order to minimise or offset carbon emissions due to ground disturbance.

Design/methodology/approach

Seven soil conditioners are evaluated using incubation chambers to measure the affect of their incorporation within three NZ soil types on soil respiration.

Findings

Charcoal is found to produce a distinct and significant carbon sequestering trend, as do newspaper and whey. Conversely, vegetable oil, paper mill pulp, biodiesel and methanol showed overall carbon emitting trends.

Research limitations/implications

The research is limited as only CO2 is monitored within the incubation chambers rather than the whole gaseous carbon profile. No microbial observations are conducted.

Practical implications

The investigation concluded that of the conditioners observed, charcoal, newspaper and whey warrant further observation as carbon sequestration soil conditioners.

Originality/value

The paper forms part of the foundations within the development of soil conditioners specifically designed for carbon sequestration.
Pulsed Electric Current Sintering of Silicon Nitride
Authors: Suganuma Motohiro , Kitagawa Yasunori , Wada Shigetaka , Murayama Norimitsu
Published: July 2009

Pulsed electric current sintering (PECS) has been used to densify α‐Si3N4powder doped with oxide additives of Y2O3and Al2O3. A full density (>99%) was achieved with virtually no transformation to β‐phase, resulting in a microstructure with fine equiaxed grains. With further holding at the sintering temperature, the α‐to‐β phase transformation took place, concurrent with an exaggerated grain growth of a limited number of elongated β‐grains in a fine‐grained matrix, leading to a distinct bimodal grain size distribution. The average grain size was found to obey a cubic growth law, indicating that the growth is diffusion‐controlled. In contrast, the densification by hot pressing was accompanied by a significant degree of the phase transformation, and the subsequent grain growth gave a broad normal size distribution. The apparent activation energy for the phase transformation was as high as 1000 kJ/mol for PECS, almost twice the value for hot pressing (∼500 kJ/mol), thereby causing the retention of α‐phase during the densification by PECS.
Development of Solid Oxide Fuel Cell Anodes Using Metal‐Coated Pore‐Forming Agents
Authors: Corbin Stephen F. , Qiao Xin
Published: July 2009

Adding Ni‐coated graphite particulates to a tape casting colloidal suspension is capable of creating a sintered solid oxide fuel cell anode with a critical percolation threshold for conductivity significantly lower than conventional anode materials. For example, conductivity at 800°C reached over 1200 Ω−1·cm−1 in these anodes at a Ni volume below the percolation threshold reported for conventional anode materials. This behavior was explained based on an “effective” Ni content, VNieff, which includes the graphite portion of the particle. In the green tape, VNieff controls the creation of a percolating network of Ni. However, when the graphite burns away, it leaves a percolated Ni network at a much lower volume fraction than would otherwise be required.
Low‐Temperature Synthesis and Properties of LaMnO3±d and La0.67R0.33MnO3±d (R = Ca, Sr, Ba) from Citrate Precursors
Authors: Licci Francesca , Turilli Giuseppe , Ferro Patrizia , Ciccarone Antonio
Published: July 2009

LaMn1−y3+Mny4+O3±d and La0.67R0.33Mn1−y3+Mny4+O3±d (R = Ca, Sr, Ba) phases were synthesized at 350°C by using very reactive, amorphous precursors obtained from the stoichiometric citrate solutions. The chemical process was optimized with respect to the solution concentration, pH, and additives. The precursor reactions were investigated as a function of the cation stoichiometry and the additive by simultaneous thermal and thermogravimetric analysis and X‐ray diffraction. The reaction pathway was found to be independent of the cation stoichiometry, but related to the acid or base additive. The annealing temperature was systematically increased in the 350–1200°C interval and the La0.67Sr0.33MnO3±d properties (i.e., crystal sizes, Mn average valence, Curie temperature, magnetization, magnetic susceptibility) were measured and found to vary consistently as a function of it.
Nanosize Powders of Aluminum Nitride Synthesized by Pulsed Wire Discharge
Authors: Kinemuchi Yoshiaki , Murai Keiichi , Sangurai Channalong , Cho Chu‐Hyun , Suematsu Hisayuki , Jiang Weihua , Yatsui Kiyoshi
Published: July 2009

Nanosize particles of aluminum nitride have been successfully synthesized by a pulsed wire discharge (PWD). Intense pulsed current through an aluminum wire evaporated the wire to produce a high‐density plasma. The plasma was then cooled by an ambient gas mixture of NH3/N2, resulting in nitridation. As a result, nanosize particles of aluminum nitride were formed. The average particle diameter was found to be ∼28 nm with a geometric standard deviation of 1.29. The maximum AlN content of 97% in the powders was achieved by optimizing various parameters: the gas pressure, the ratio of NH3 and N2, the wire diameter, the pulse width, and the input electrical energy. The ratio of the AlN powder production to the electrical energy consumption was evaluated as ∼40 g/(kW·h). Thus, PWD is a very efficient and promising method to synthesize nanosize powders of AlN.
Cracking and the Indentation Size Effect for Knoop Hardness of Glasses
Authors: Quinn George D. , Green Patrice , Xu Kang
Published: July 2009

The Knoop hardnesses of five glasses decreased with increasing load in accordance with the classic indentation size effect (ISE). At moderate loads, cracking dramatically altered the indentation sizes and the ISE trends in three of the five glasses. Cracked indentations were as much as 10 μm longer than uncracked indentations made under identical conditions. Diagonal length readings must be corrected for optical resolution limitations if low power lenses are used.
Independent Effects of Nitrogen Substitution for Oxygen and Yttrium Substitution for Magnesium on the Properties of Mg‐Y‐Si‐Al‐O‐N Glasses
Authors: Pomeroy Michael J. , Mulcahy C. , Hampshire Stuart
Published: July 2009

Glasses of composition (in equivalent percent) (28 −x)Mg:xY:56Si:16Al:(100 −y)O:yN, with x= 0, 14, or 28 for y= 0 and 15 and with x= 0, 7, 14, 21, or 28 for y= 10, were prepared by melting and casting. For glasses where the nitrogen content was varied for a constant cationic ratio, the glass molar volume (MV), compactness (C), Young's modulus (E), glass‐transition temperature (Tg), and dilatometric‐softening temperature (Tds) varied linearly as the nitrogen content increased, with MV decreasing and the other properties increasing. From the incremental changes in these properties with nitrogen content, for glasses with x= 0, 14, and 28, good linear fits (R2 > 0.99) were obtained, and best‐fit slopes are reported here. The property changes and their linearity were consistent with the increased cross‐linking of the glass network by tricoordinated nitrogen. The replacement of magnesium by yttrium led to a nonlinear decrease in glass compactness and to nonlinear increases in MV, Tg, and Tds. However, linear correlations were found for MV and ionic volume and for Tg, Tds, and the coordination of (Si,Al)(O,N) tetrahedra of the glass structural units to the modifier cations not involved in charge compensating aluminum ions in fourfold coordination. The replacement of magnesium by yttrium had little effect on Young's modulus, and this result was related to similar changes in the compactness, C. The present results showed that the effects of substituting nitrogen for oxygen and yttrium for magnesium are independent and additive; thus, no synergistic effects of anion and cation substitutions were observed.
Transparent Alumina: A Light‐Scattering Model
Authors: Apetz Rolf , van Bruggen Michel P. B.
Published: July 2009

A model based on Rayleigh–Gans–Debye light‐scattering theory has been developed to describe the light transmission properties of fine‐grained, fully dense, polycrystalline ceramics consisting of birefringent crystals. This model extends light transmission models based on geometrical optics, which are valid only for coarse‐grained microstructures, to smaller crystal sizes. We verify our model by measuring the light transmission properties of fully dense (>99.99%), polycrystalline α‐Al2O3 (PCA) with mean crystal sizes ranging from 60 to 0.3 μm. The remarkable transparency exhibited by PCA samples with small crystal sizes (<2 μm) is well explained by this model.
Internal Reduction of an Iron‐Doped Magnesium Aluminosilicate Melt
Authors: Everman Rebecca L. A. , Cooper Reid F.
Published: July 2009

Optical and electron microscopies are used to analyze the mechanism and kinetics of internal reduction of an Fe2+‐doped magnesium aluminosilicate melt. Melt samples are heated to temperatures in the range of 1300°–1400°C under a flowing gas mixture of CO/CO2, which corresponds to a pO2 range of 1 × 10−13–4 × 10−13 atm. The melt experiences an internal reaction in which a dispersion of nanometer‐scale iron‐metal precipitates forms at an internal interface. The metal precipitates show no signs of coarsening within the samples; however, the crystals at the surface (which formed in the initial part of the reaction) do grow via vapor phase transport. The overall reaction is characterized by parabolic kinetics, which is indicative of chemical diffusion being the rate‐limiting step. The diffusion of network‐modifier divalent cations—particularly Mg2+ cations—is demonstrated to be the rate‐limiting factor, and its diffusion coefficient is calculated to be ∼1 × 10−6 cm2/s within the temperature range of the experiments.
Fluorine as a Donor Dopant in Barium Titanate Ceramics
Authors: Makovec Darko , Drofenik Miha , Baker Judith
Published: July 2009

We have studied the electrical properties and microstructure of fluorine‐doped BaTiO3 ceramics. The samples were prepared using a classical ceramic technology that involved the calcination of intimately mixed powders of BaCO3, TiO2, and BaF2. When the samples were sintered in untreated ambient air, the fluorine from the sample reacted with water vapor and formed gaseous HF. To prevent this hydrolysis of the fluorine, we sintered the samples in dried air. The fluorine‐doped BaTiO3 ceramics sintered in a dry atmosphere showed microstructures and electrical properties typical of donor‐doped BaTiO3. The samples containing up to 0.3 mol% of fluorine were coarse‐grained, semiconducting, and displayed a remarkable PTCR effect. In contrast, the samples with a higher fluorine concentration were fine grained and insulating. A SIMS elemental mapping of the samples showed that the fluorine was distributed throughout the microstructure of the semiconducting samples; however, the fluorine concentration was enriched at grain boundaries and in the BaTi2O5 intergranular phase.
Microwave Dielectric Properties of Gallium‐Doped Hexagonal Barium Titanate Ceramics
Authors: Feteira Antonio , Sarma Kumaravinothan , Alford Neil McN. , Reaney Ian M. , Sinclair Derek C.
Published: July 2009

High‐permittivity and low‐loss ceramics with composition BaTi0.92Ga0.08O2.96 have been prepared in the BaO–Ga2O3–TiO2 system using the mixed‐oxide route. This compound forms as the hexagonal polymorph (6H) of BaTiO3 with the space group P63/mmc. The dielectric properties of dense ceramics have been studied, at microwave frequencies, with the ceramics fired at 1450°C under flowing oxygen gas; the results are a relative permittivity, ɛr, of ∼74 and a quality factor, Q·fr, of ∼7815 at 5.5 GHz. The quality factor is strongly influenced by the sintering conditions (temperature and atmosphere), whereas the relative permittivity is not influenced significantly by ceramic processing for pellets ≥93% of the theoretical X‐ray density. To our knowledge, this is the first report of microwave dielectric resonance in a perovskite‐type BaTiO3‐based ceramic.
Sintered Hydroxyapatite Latticework for Bone Substitute
Authors: de Sousa F. Cristina Gomes , Evans Julian R. G.
Published: July 2009

Hydroxyapatite suspensions were extruded through a range of nozzles from 100 to 330 μm diameter from a stepper‐driven syringe. Regular latticework scaffolds were built by fused deposition modeling (FDM), a solid freeforming method, on a three‐axis table using 330 μm diameter filament. The scaffolds were sintered at 1250°C to 97% density retaining the hydroxyapatite crystal structure. The scaffolds were introduced to cultured human osteoblast cells and, after 48 h, the surfaces were thoroughly covered with active cells.
Transformation Mechanism of the Dehydration of Diaspore
Authors: Löffler Lars , Mader Werner
Published: July 2009

The dehydration of diaspore to corundum was investigated by means of X‐ray powder diffraction at reaction temperatures (400° and 600°C) as well as by transmission electron microscopy (TEM). The TEM studies were performed at the reaction interface of partially dehydrated natural diaspore crystals. The corundum produced consisted of thin dense regions which were separated by nanometer‐sized pores forming lamellae with a periodicity of 3.7 nm. At the reaction front a transition phase (D′) could be detected in electron diffraction patterns. The phase D′ is isotypic to diaspore, but with a larger spacing of the close‐packed (100) oxygen planes (aD′ from 0.475 to 0.480 nm). The expansion with respect to diaspore is explained by breaking of the hydrogen bonds of diaspore, considered to be the initial step of the transformation. The spacing of the lamellar pore system in corundum is explained by the misfit of the (100) planes of D′ and the (0003) planes of corundum. We conclude that at well‐fitting regions of the closed‐packed planes at the D′/C interface, dense corundum is formed, while at misfitting regions, the formation of corundum is not favored and the pores are produced. Hence, the transformation of the solid phases takes place as a two‐step process, i.e., D → D′→ C.
Effect of Yttrium and Erbium Ions on Epitaxial Phase Transformations in Alumina
Authors: Ragan Deirdre D. , Mates Thomas , Clarke David R.
Published: July 2009

The effect of low concentrations of Y, Er, and Cr solutes on the amorphous‐to‐γ transformation and on the γ‐to‐α transformation in aluminum oxide has been studiedin situby time‐resolved reflectivity. The activation energies of the two transformations with these dopants are the same as in undoped alumina, being 4.1 ± 0.1 and 5.2 ± eV, respectively. Although not affecting the activation energies, Y, Er, and Cr do affect the transformation kinetics. Y and Cr ions decrease the γ‐to‐α transformation velocity and, over the limited range studied, do so in proportion to their concentration. Concentrations of Er as low as ∼6 ppm retard the γ‐to‐α transformation and concentrations of 32 ppm essentially stop the transformation occurring within the times and temperatures accessible within the present experiment, thereby preventing quantification of the effect of Er on the α‐phase transformation. Erbium also retards the amorphous‐to‐γ transformation relative to undoped alumina whereas yttrium and chromium accelerate it.
Experiment and Theory of Diffusion in Alumina
Authors: Harding John H. , Atkinson Kurt J. W. , Grimes Robin W.
Published: July 2009

Despite all the work conducted over many decades, there remains a major problem in understanding diffusion in alumina. It is certain that all measurements of diffusion in alumina refer to extrinsic diffusion. However, the experimental activation energy is larger than any theoretical prediction by a factor of 2. The problem with grain boundary diffusion is, if anything, worse. The most complete set of experimental data suggests that the activation energy for boundary diffusion is 50% larger than for bulk diffusion. We discuss the problems involved in understanding the experimental data and in producing theoretical models and propose a strategy for resolving the problems.
Atomic Structures and Energies of Σ7 Symmetrical Tilt Grain Boundaries in Alumina Bicrystals
Authors: Nishimura Hitoshi , Matsunaga Katsuyuki , Saito Tomohiro , Yamamoto Takahisa , Ikuhara Yuichi
Published: July 2009

Symmetrical Σ7 tilt grain boundaries of alumina (Al2O3) were studied using bicrystals. Three types of Σ7 boundaries were successfully fabricated, that is, rhombohedral twin (Σ7{1[Onemacr]02}) and two types of [0001] symmetrical tilt grain boundaries with grain‐boundary planes {4[Fivemacr]10} and {2[Threemacr]10} (Σ7{4[Fivemacr]10} and Σ7{2[Threemacr]10}). Their atomic structures and grain‐boundary energies were investigated using high‐resolution transmission electron microscopy (HRTEM) and a thermal grooving technique, respectively. HRTEM observations showed that the Σ7{1[Onemacr]02} boundary had a completely symmetrical atomic arrangement with respect to the grain‐boundary plane. In contrast, Σ7{2[Threemacr]10} and Σ7{4[Fivemacr]10} boundaries exhibited asymmetrical atomic structures, which were confirmed by analyzing the atomic configurations using static lattice calculations. Thermal grooving experiments showed that the grain‐boundary energies strongly depended on the properties of the grain‐boundary planes.
Structure and Chemistry of Symmetrical Tilt Grain Boundaries in α‐Al2O3: I, Bicrystals with “Clean” Interface
Authors: Gemming Thomas , Nufer Stefan , Kurtz Wolfgang , Rühle Manfred
Published: July 2009

Several low‐index symmetrical tilt grain boundaries in α‐Al2O3 were investigated by combining high‐resolution transmission electron microscopy and spatially resolved energy dispersive X‐ray analysis. Bicrystals with a well‐defined orientation relation and interface plane were produced by diffusion bonding under ultrahigh vacuum. Grain boundaries like the prismatic and rhombohedral twin develop an atomically sharp and clean interface, whereas higher index grain boundary (GB) planes show a more complex structure and are able to accommodate both Si and Ca in the interface. Additionally, it was found that asymmetric GB planes which occur as facets at rhombohedral and prismatic twins also accommodate impurity atoms.
Microstructural Evolution of Calcium‐Doped α‐Alumina
Authors: Altay Arzu , Gülgün Mehmet Ali
Published: July 2009

Effect of different calcium doping levels on the microstructure of high‐purity α‐alumina was studied as a function of sintering time and temperature using scanning electron microscopy (SEM). Microstructural evolution was related to hypothetical calcium excess at the grain boundaries (ΓCa) that was calculated assuming zero solubility of calcium in bulk α‐alumina. Under all sintering conditions, grains were uniform in size and equiaxed for low calcium concentrations (<3 Ca atoms/nm2). The grain morphology became elongated when the calcium concentration at the grain boundaries reached calcium excess of ΓCa= 3–3.5 Ca atoms/nm2 in all samples. The average grain sizes of undoped samples were ∼10% larger than the average grain sizes of low‐calcium‐doped samples. This decrease is believed to be due to solute drag effect of segregated Ca impurities on the grain boundary mobility. For the samples that were sintered at 1500° and 1600°C, slablike abnormally grown grains appeared for critical calcium excess concentrations of ΓCa= 4.5–8 Ca atoms/nm2. With abnormally grown grains a dramatic increase in average grain size was observed. However, when the calcium concentration was increased further, above certain calcium excess concentration depending on sintering temperature, a significant decrease in grain size was observed. In contrast to samples sintered at 1500° and 1600°C, when the samples sintered at 1400°C, although the hypothetical calcium coverage exceeded ΓCa= 11 Ca atoms/nm2, only few grains grew abnormally without significantly affecting the average grain size. Observations clearly indicated that calcium impurities caused elongated (slablike) grain morphology when their excess concentrations reached a critical level at the grain boundaries.
Effect of Magnesium Oxide Addition on Surface Roughening of Alumina Grains in Anorthite Liquid
Authors: Kim Mi Jin , Yoon Duk Yong
Published: July 2009

Alumina sintered with 5 wt% anorthite at 1620°C for 48 h has grains with flat boundaries and a size distribution representing abnormal grain growth. TEM observations of the grain triple junctions show flat grain surfaces, some of which are the (0001), ([Onemacr]012), and (1[Onemacr]01) planes. HRTEM observations confirm these surfaces to be atomically flat and hence singular. When sintered further after embedding in MgO powder, the {0001} and { 01[Onemacr]2} planes remain flat, but curved surface segments also appear. These curved surface segments are confirmed to be atomically rough by HRTEM. They are connected to the flat segments with discontinuously changing slopes. Thus, when MgO is added, the singular and rough surface phases coexist.
Abnormal Grain Growth in Alumina: Synergistic Effects of Yttria and Silica
Authors: MacLaren Ian , Cannon Rowland M. , Gülgün Mehmet A. , Voytovych Rayisa , Popescu‐Pogrion Nicoletta , Scheu Christina , Täffner Ulrike , Rühle Manfred
Published: July 2009

Abnormal grain growth without strong anisotropy or faceting of the grains has been observed in high‐purity yttria‐doped alumina specimens, often starting at the surface and spreading right through the bulk at higher sintering temperatures. This appears to occur because of an interaction between Si contamination from sintering and the yttria doping; no such effect is seen for undoped samples. Similar microstructures were observed after deliberate Y/Si codoping. Analytical STEM showed that some grain boundaries bordering on large grains contained more Si than Y. HRTEM and diffuse dark‐field imaging revealed thin (0.5–0.9 nm) disordered layers at some boundaries bordering large grains. It appears that Si impurities are accumulating at some boundaries and together with the Y inducing a grain boundary structural transformation that accounts for the dramatically increased mobility of these boundaries.
Impurity Effects on Alumina Scale Growth
Authors: Hou Peggy Y.
Published: July 2009

Most high‐temperature‐resistant alloys oxidize to form an external alumina layer, or scale, whose slow growth protects the underlying alloy from continued aggressive oxidation. The growth of the Al2O3 scale is controlled by the transport of oxygen inward and aluminum outward through it, with the rate dominated by the fastest diffusing species down the fastest path. Components in the alloy can be incorporated into the growing Al2O3 layer, hence affect the transport rates of oxygen and/or aluminum. This paper summarizes existing experimental data to assess the possible effect of these incorporated impurities on the growth rate and transport properties of Al2O3 scales formed on Fe‐, Ni‐, and Pt‐based alloys. The amount and distribution of the alloy base metal, sulfur impurity, and reactive elements, such as Hf, Y, Zr, and Ce, in the alumina scale are evaluated. Their effect on the oxidation and transport rates through the scale are discussed and compared with Al and O diffusion rates deduced from creep studies.
Initial Stages of Growth of Alumina on NiAl(001) at 1025 K
Authors: Frémy Nicolas , Maurice Vincent , Marcus Philippe
Published: July 2009

The initial stages of growth of ordered layers of Al2O3 on NiAl(001) single‐crystal surfaces at 1025 K and 10−7 mbar (10−5 Pa) in O2 have been studied using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). The STM results evidence the formation of elongated strips (26 Å wide and 11 Å high) of Al2O3 oriented along the [100] and [010] directions of the substrate. With longer oxidation, the substrate is increasingly covered by rectangular and striped islands resulting from the vicinal and parallel growth of the strips. On the ultrathin oxide film formed after 500 L (1 L = 10−6 torr·s (∼1.33 × 10−4 Pa·s)) of exposure, STM atomic resolution images have been obtained for the first time. They evidence the [001] orientation of the oxygen sublattice in Bain epitaxy on the substrate. The observation of one‐dimensional atomic trenches together with the strips observed on the nanometer scale is consistent with the growth of θ‐Al2O3. The STS local measurements evidence the insulating behavior of the oxide layer formed with a gap value ranging from 7 and 8 eV for amorphous and ordered domains, respectively.
Optimization of Reactive‐Element Additions to Improve Oxidation Performance of Alumina‐Forming Alloys
Authors: Pint Bruce A.
Published: July 2009

It is well‐known that the addition of reactive elements (including yttrium, zirconium, lanthanum, cerium, and hafnium) improve the high‐temperature oxidation performance of alumina‐forming alloys. Less studied are strategies for optimizing these additions for developing a high‐performance, wrought FeCrAl alloy with maximum oxidation‐limited component life. Results from the literature are summarized regarding potential improvements. One promising strategy is the addition of two reactive elements, such as yttrium and hafnium, which has been effective in commercial and laboratory nickel‐based alloys and appears to impart the expected benefits, such as reducing the scale growth rate while minimizing detrimental effects, such as the formation of reactive element‐rich oxides in the scale and internal oxidation. Although there are promising data, the long‐term studies are not yet complete, and it is difficult to predict if “co‐doped” FeCrAl alloys will produce superior oxidation‐limited lifetimes in high‐temperature environments.
Fabrication of TiN/Si3N4 Ceramics by Spark Plasma Sintering of Si3N4 Particles Coated with Nanosized TiN Prepared by Controlled Hydrolysis of Ti(O‐i‐C3H7)4
Authors: Kawano Shuichi , Takahashi Junichi , Shimada Shiro
Published: July 2009

TiN‐coated Si3N4 particles were prepared by depositing TiO2 on the Si3N4 surfaces from Ti(O‐i‐C3H7)4 solution, the TiO2 being formed by controlled hydrolysis, then subsequently nitrided with NH3 gas. A homogeneous TiO2 coating was achieved by heating a Si3N4 suspension containing 1.0 vol% H2O with the precursor at 40°C. Nitridation successfully produced Si3N4 particles coated with 10–20 nm TiN particles. Spark plasma sintering of these TiN/Si3N4 particles at 1600°C yielded composite ceramics with a relative density of 96% at 25 vol% TiN and an electrical resistivity of 10−3Ω·cm in compositions of 17.5 and 25 vol% TiN/Si3N4, making these ceramics suitable for electric discharge machining.
Water‐Induced Degradation of Barium Titanate Ceramics Studied by Electrochemical Hydrogen Charging
Authors: Chen Wan Ping , Jiang Xiang Ping , Wang Yu , Peng Zhi , Chan Helen Lai Wah
Published: July 2009

Water‐induced degradation of barium titanate (BTO) ceramics has been investigated using electrochemical hydrogen charging, in which the silver electrodes of BTO ceramic specimens are made cathodes in a 0.01M NaOH solution to evolve hydrogen by electrolysis of water. After 80 h of treatment, the resistance of BTO decreases by ∼3 orders of magnitude, and the dielectric loss obviously increases. The degradation can be explained by the reduction reaction of atomic hydrogen with BTO. Hydrogen acts as a donor in BTO, and electrons are formed by the reduction. It is proposed that the reduction reaction of atomic hydrogen at ambient temperature by electrolysis of water is an important origin for degradation of BTO‐based ceramic devices.
Thermal Shock Behavior of Isotropic and Anisotropic Porous Silicon Nitride
Authors: She Jihong , Yang Jian‐Feng , Jayaseelan Daniel Doni , Kondo Naoki , Ohji Tatsuki , Kanzaki Shuzo , Inagaki Yoshiaki
Published: July 2009

The thermal shock behavior of isotropic and anisotropic porous Si3N4 was evaluated using the water‐quenching technique. The critical temperature difference for crack initiation was found to be strongly dependent on the ratio of fracture strength to elastic modulus. Because of a very high strain‐to‐failure, anisotropic porous Si3N4 showed no macroscopic cracks and was able to retain its strength even at a quenching‐temperature difference of ∼1400°C.
Surface Pretreatments of Silicon Nitride for CVD Diamond Deposition
Authors: Belmonte Manuel , Silva Vitor A. , Fernandes Antonio José , Costa Florinda , Silva Rui
Published: July 2009

The efficiency of different surface pretreatments (four standard chemical etchings and four diamond powder abrasive procedures) on silicon nitride (Si3N4) substrates for chemical vapor deposition (CVD) of diamond has been systematically investigated. Blank Si3N4 samples were polished with colloidal silica (∼0.25 μm). Diamond nucleation and growth runs were conducted in a microwave plasma chemical vapor deposition apparatus for 10 min and 6 h, respectively. Superior results concerning nucleation density (Nd∼ 1010 cm−2 after 10 min), film uniformity, and grain size (below 2 μm after 6 h) were obtained for the mechanically microflawed samples, revealing that chemical etchings (hot and cold strong acids, molten base or CF4 plasma) are not crucial for good CVD diamond quality on Si3N4.
Fine Patterning of Hybrid Titania Films by Ultraviolet Irradiation
Authors: Segawa Hiyoro , Adachi Shinichi , Arai Yasuhiko , Yoshida Kazuaki
Published: July 2009

Photosensitive hybrid titania films have been prepared from titanium butoxide modified with β‐diketone and methacrylic acid. When this film is exposed to UV light, the β‐diketonato chelate from the alkoxide and β‐diketone is dissociated, and the unsaturated hydrocarbon of methacrylic acid is polymerized. These structural changes in the gel film have led to a difference between the solubility of irradiated and unirradiated parts in the film; therefore, a fine patternable hybrid titania film has been fabricated.
Microstructure Development in Reactive‐Templated Grain Growth of Bi1/2Na1/2TiO3‐Based Ceramics: Template and Formulation Effects
Authors: West David L. , Payne David A.
Published: July 2009

“Reactive‐templated grain growth” (RTGG) processing of Bi1/2Na1/2TiO3 (BNT)‐based ceramics is reported. Molten salt synthesis was used to prepare platelike (∼0.2 μm × 5 μm × 5 μm) Ruddlesden–Popper (Sr3Ti2O7 (ST)) and Aurivillius (BaBi2Nb2O9 (BBN)) phases which were used as “templates” in studies of RTGG with BNT‐based matrixes. A “citrate‐gel” route was designed to produce intimately mixed, fine‐grain matrixes for these studies. The analytical techniques used were powder X‐ray diffraction and microstructural examination of dry‐pressed and fired compacts. For mixtures templated with BBN, single‐phase perovskite readily formed, and an initially heterogeneous microstructure evolved toward a dense assemblage of anisometric, micrometer‐scale grains. Perovskite formation was more sluggish in the mixtures templated with ST, and the final sintered microstructure featured larger, porous grains in an equiaxed, micrometer‐scale matrix. A qualitative model, which examined the excess constituents in the matrix after formation of stoichiometric ABO3 perovskite, is proposed to explain the observations. The model predicted an excess of Na2O and TiO2 in the matrix in the case of BBN templates and only excess TiO2 in the case of ST templates. The results indicate that careful examination of matrix and template chemistry could be important in the selection of systems for RTGG processing.
Nanoindentation Method for Measuring Residual Stress in Brittle Materials
Authors: Kese Kwadwo , Rowcliffe David J.
Published: July 2009

The lowered threshold load for cracking with the cube‐corner indenter has been used in developing a method that can be used to measure residual stresses in small volume brittle materials. By studying a series of orthogonal cracks generated at loads not exceeding 10 mN with the cube‐corner indenter, a variation of crack length with position around a large Vickers impression in soda–lime glass was observed. Using an indentation fracture mechanics approach residual stresses were evaluated at the positions where the cube‐corner indents had been made. The stress values thus evaluated were generally higher than those reported in the literature where micro‐Vickers indents had been used to measure the stresses. Possible reasons for the disparity are discussed.
Influence of a Dispersion of Aluminum Titanate Particles of Controlled Size on the Thermal Shock Resistance of Alumina
Authors: Uribe Rafael , Baudín Carmen
Published: July 2009

The possibility of developing fine‐grained (∼0.5–3 μm) and dense (≥0.98ρth) alumina (90 vol%)–aluminum titanate (10 vol%) composites with improved thermal shock resistance and maintained strength is investigated. One alumina material and one composite with similar microstructures (porosity and grain‐size distribution) were fabricated to investigate the effect of Al2TiO5 on thermal shock behavior. The size of the Al2TiO5 particles was kept under 2.2 μm to avoid spontaneous microcracking. The mechanical and thermal properties of the materials involved in their response to thermal shock and the results for the evolution of indentation cracks of equal initial crack length with increasing ΔT in samples quenched in glycerine are described. The combination of thermal and mechanical properties—thermal conductivity, thermal expansion coefficient, Young's modulus, and toughness—improve the thermal shock resistance of the alumina–aluminum titanate composite in terms of critical temperature increment (>30%). The suitable structural properties of alumina—hardness and strength—are maintained.
Synthesis of (Pb,La)(Zr,Ti)O3 Inverse Opal Photonic Crystals
Authors: Li Bo , Zhou Ji , Li Qi , Li Longtu , Gui Zhilun
Published: July 2009

(Pb,La)(Zr,Ti)O3 (PLZT) inverse opal photonic crystals were synthesized by a sol‐gel process with synthetic opal templates of monodisperse submicrometer polystyrene spheres. This process involves infiltration of precursors into the interstices of the opal template, followed by hydrolytic condensation of the precursors and removal of the polystyrene opal combined with crystallization of PLZT perovskite by calcination at a final temperature of 750°C. By this method, PLZT inverse opal photonic crystals with a periodical structure of 280 nm center‐to‐center distance between the air spheres are prepared from opal templates of polystyrene microspheres with a mean diameter of 400 nm. The PLZT inverse opals reflect yellow‐green light strongly.
Morphology of Oxide Particles Made by the Emulsion Combustion Method
Authors: Tani Takao , Watanabe Naoyoshi , Takatori Kazumasa , Pratsinis Sotiris E.
Published: July 2009

Various oxide powders were prepared by the emulsion combustion method (ECM) using metal precursors, kerosene, and a surfactant. The product particles were characterized by transmission electron microscopy (TEM), nitrogen adsorption, and X‐ray diffraction. Hollow γ‐Al2O3 particles were produced from aluminum nitrate or chloride precursors dispersed in air, whereas dispersion of the precursor emulsion in oxygen resulted in solid α‐Al2O3 particles. Hollow spheres were obtained also for TiO2, ZrO2, and Y2O3 by ECM of TiCl4, zirconium oxynitrate, and yttrium nitrate in aqueous solution. A simple method was developed to predict the thickness and diameter of hollow particles using the nitrogen adsorption data and initial droplet concentration of the ECM spray. The TEM diameter and shell thickness of hollow particles were consistent with those predicted. In contrast, solid particles were formed by ECM for ZnO, Fe2O3, CeO2, and MgO from aqueous solutions of their corresponding nitrates.
10‐mol%‐Gd2O3‐Doped CeO2 Solid Solutions via Carbonate Coprecipitation: A Comparative Study
Authors: Li Ji‐Guang , Ikegami Takayasu , Wang Yarong , Mori Toshiyuki
Published: July 2009

10mol% Gd2O3‐doped CeO2 solid solutions (20GDC) have been synthesized via carbonate coprecipitation using ammonium bicarbonate (AHC) and urea as the precipitants. The precursors and the resultant oxide powders were characterized via chemical analysis, X‐ray diffractometry (XRD), Brunauer–Emmett–Teller (BET) analysis, and high‐resolution scanning electron microscopy (HRSEM). Sinterabilities of the 20GDC oxides in air were studied by constant‐rate‐of‐heating (CRH) sintering and the conventional ramp‐and‐holding sintering methods. The precursor processed by both methods is hydroxyl carbonate but shows quite different particle morphologies in the two cases. Highly sinterable 20GDC oxides that can be densified to >99% of the theoretical at 1050°C within 4 h have been obtained via the AHC method.
Perovskite Formation and Dielectric Characteristics of Pb(Zn1/3Ta2/3)O3 with PbTiO3 Substitution
Authors: Kim Jee‐Su , Kim Nam‐Kyoung , Kim Hwan
Published: July 2009

Perovskite developments in the Pb(Zn1/3Ta2/3)O3–PbTiO3 system were explored. Formation yields and lattice parameters of the perovskite were determined from X‐ray diffractometry results. Weak‐field low‐frequency dielectric properties of the system ceramics were investigated, followed by microstructure examination. Perovskite started to develop in Pb(Zn1/3Ta2/3)O3 after the introduction of 30 mol% PbTiO3, whereas complete stabilization was accomplished at 60% substitution. Dielectric relaxation behavior was not substantial across the entire composition range, whereas phase transition modes changed from diffuse to sharp with increased PbTiO3 fraction.
Characterization and High‐Temperature Mechanical Behavior of an Oxide/Oxide Composite
Authors: Zawada Larry P. , Hay Randall S. , Lee Shin S. , Staehler James
Published: July 2009

An oxide/oxide ceramic fiber‐matrix composite (CMC) has been extensively characterized for high‐temperature aerospace structural applications. This CMC is called GEN‐IV™, and it has a porous and cracked aluminosilicate matrix reinforced by 3M Nextel 610™ alumina fibers woven in a balanced eight harness weave (8HSW). This CMC has been specifically designed without an interphase between the fiber and matrix, and it relies on the porous matrix for flaw tolerance. Stress‐strain response is nearly linear to failure and without a well‐defined proportional limit in tension and compression. In‐plane shear and interlaminar strength increases with increasing temperature. The 1000°C fatigue limit in air at 105 cycles is 160 MPa, and the residual tensile strength of run‐out specimens is not affected by the fatigue loading. The creep‐rupture resistance above 1000°C is relatively poor, but it can be improved with a more‐creep‐resistant fiber.
Novel Compressive Mica Seals with Metallic Interlayers for Solid Oxide Fuel Cell Applications
Authors: Chou Yeong‐shyung , Stevenson Jeffry W. , Chick Lawrence A.
Published: July 2009

A novel hybrid compressive mica seal was developed that showed an exceptionally low leak rate of ∼8.9 × 10−4 sccm/cm (standard cubic centimeters per minute per unit leak length of seal) at 800°C and a compressive stress of 100 psi, about 740 times lower than that of the conventional compressive mica seals (6.6 × 10−1 sccm/cm), at a pressure gradient of 2 psi. The hybrid compressive mica seals were composed of two compliant metallic layers and a mica layer. Three commercially available micas were tested in this study. All showed substantial improvements in reducing the leak rates by using the hybrid design. The best results were obtained using muscovite single‐crystal mica and 125 μm silver layers. Using the paper form of muscovite and phlogopite mica, the leak rates were still far superior (∼1 × 10−1 sccm/cm) compared with mica without the compliant silver layer (about 6–9 sccm/cm). The microstructure of the mica was examined before and after the 800°C leak tests. These results are compared with results for hybrid seals using glass interlayers. In addition, an explanation for the substantial reduction of the leak rates is proposed, and the application of the hybrid compressive mica seals in planar SOFC stacks is briefly addressed.
Texture in Silicon Nitride Seeded with Silicon Nitride Whiskers of Different Sizes
Authors: Bae Byoung‐Chan , Park Dong‐Soo , Kim Young‐Wook , Kim Wonjoong , Han Byoung‐Dong , Kim Hai‐Doo , Park Chan
Published: July 2009

Silicon nitride ceramics seeded with 3 wt%β‐Si3N4whiskers of two different sizes were prepared by a modified tape casting and gas pressure sintering. The fine whiskers had a higher aspect ratio than the coarse whiskers. Quantitative texture analysis including calculation of the orientation distribution function (ODF) was used for obtaining the degrees of preferred orientation of sintered samples. The maximum multiples of random distribution (mrd) values of samples seeded with the fine and coarse whiskers were large, greater than 15 and 9, respectively. Meanwhile, the mrd value of a sample seeded with fine whiskers was only 9 when it was prepared by conventional tape casting. The microstructures and the XRD data revealed that the well‐aligned whiskers grew significantly after sintering and dominated the texture. Differences among the degrees of preferred orientation of the samples were explained using Jeffrey's model on rotation of elliptical particles carried by a viscous fluid.
Ceramic Microtubes from Preceramic Polymers
Authors: Colombo Paolo , Perini Katia , Bernardo Enrico , Capelletti Tiziano , Maccagnan Giorgio
Published: July 2009

A novel process for the production of ceramic microtubes involving the microextrusion of preceramic polymers was studied. Microtubes with a wide range of inner and outer diameters and several centimeters long were produced from two silicone resins. A coextrusion approach was also used to extend the forming capability of the technique. The addition of carbon black resulted in electrically conductive silicon oxycarbide (SiOC) ceramic microtubes. SiOC microtubes possessed a high bending strength, ranging from ∼30–1100 MPa.
Synthesis of Al4SiC4
Authors: Inoue Koji , Yamaguchi Akira
Published: July 2009

The conditions necessary for synthesizing Al4SiC4 from mixtures of aluminum, silicon, and carbon and kaolin, aluminum, and carbon, as starting materials, were examined in the present study. The standard Gibbs energy of formation for the thermodynamic reaction SiC(s) + Al4C3(s) = Al4SiC4(s) changed from positive to negative at 1106°C. SiC and Al4C3 formed as intermediate products when the mixture of aluminum, silicon, and carbon was heated in argon gas, and Al4SiC4 then formed by reaction of the SiC and Al4C3 at >1200°C. Al4C3, SiO2, Al2O3, SiC, and Al4O4C formed as intermediate products when the mixture of kaolin, aluminum, and carbon was heated under vacuum, and Al4SiC4 formed from a reaction of those intermediate products at >1600°C.
Nucleation Sites of Calcium Phosphate Crystals during Collagen Mineralization
Authors: Zhang Wei , Huang Zhao‐Long , Liao Su‐San , Cui Fu‐Zhai
Published: July 2009

The nucleation sites of calcium phosphate crystals during collagen mineralization were studied by Fourier transform infrared spectrometry and transmission electron microscopy. It was found for the first time that there is another nucleation site, i.e., carbonyl (>C=O) on collagen, besides the previous reported nucleation site of carboxyl (–COOH). By comparing the IR spectra of collagen not only with collagen/calcium phosphate but also with collagen/Ca2+, it was observed that the peak intensities of amides I, II, and III of collagen decreased significantly after mineralization. The decrease of the amide I peak intensity was mainly due to blockage of the C=O stretch. Furthermore, the peak for amide I gradually shifted to a lower wavenumber during collagen mineralization. This shift indicated that chemical interaction between carboxyl groups and Ca2+ ions formed in the mineralization.
Synthesis of Hydroxyapatite Nanopowders via Sucrose‐Templated Sol–Gel Method
Authors: Bose Susmita , Saha Susanta Kumar
Published: July 2009

The present research describes synthesis of hydroxyapatite (HAp) nanopowders using a sol–gel route with calcium nitrate and ammonium hydrogen phosphate as calcium and phosphorous precursors, respectively. Sucrose is used as template material, and alumina is added as a dopant to study its effects on particle size and surface area. Synthesized powders are characterized using X‐ray diffractometry, BET surface‐area analysis, and transmission electron microscopy. Results show that alumina stabilizes the HAp crystalline phase. Average particle size of mesoporous HAp samples is between 30 and 50 nm with surface area of 51–60 m2/g.
Paralinear Oxidation of Silicon Nitride in a Water‐Vapor/Oxygen Environment
Authors: Fox Dennis S. , Opila Elizabeth J. , Nguyen QuynhGiao N. , Humphrey Donald L. , Lewton Susan M.
Published: July 2009

Three Si3N4 materials were exposed to dry oxygen flowing at 0.44 cm/s at temperatures between 1200° and 1400°C. Weight change was measured using a continuously recording microbalance. Parabolic kinetics were observed. When the same materials were exposed to a 50% H2O–50% O2 gas mixture flowing at 4.4 cm/s, all three types exhibited paralinear kinetics. The material was oxidized by water vapor to form solid SiO2. The protective SiO2 was in turn volatilized by water vapor to form primarily gaseous Si(OH)4. Nonlinear least‐squares analysis and a paralinear kinetic model were used to determine parabolic and linear rate constants from the kinetic data. Volatilization of the protective SiO2 scale could result in accelerated consumption of Si3N4. Recession rates under conditions more representative of actual combustors were compared with the furnace data.