bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of functional and phenotypic changes in anti-Gag vaccine-induced T cell responses and their role in protection after HIV-1 infection
Authors: Betts Michael R. , Exley Barbara , Price David A. , Bansal Anju , Camacho Zenaido Tres , Teaberry Vanessa , West Sadie M. , Ambrozak David R. , Tomaras Georgia , Roederer Mario , Kilby J. Michael , Tartaglia Jim , Belshe Robert , Gao Feng , Douek Daniel C. , Weinhold Kent J. , Koup Richard A. , Goepfert Paul , Ferrari Guido
Published: March 2005

Worldwide HIV-1 vaccine efforts are guided by the principle that HIV-specific T cell responses may provide protection from infection or delay overt disease. However, no clear correlates of T cell-mediated immune protection have been identified. Here, we examine in a HLA-B27
+
HIV seronegative vaccinee persistent HIV-specific vaccine-induced anti-Gag CD4
+
and CD8
+
T cell responses. Although these responses exhibited those characteristics (multifunctionality, appropriate memory phenotype, and targeting of epitopes associated with long-term nonprogression) predicted to correlate with protection from infection, the subject became HIV infected. After HIV infection, the vaccine-induced CD8
+
T cells expanded, but both CD4
+
and CD8
+
T cell responses acquired the functional and phenotypic patterns characteristic of chronic HIV infection. The virus quickly escaped the vaccine-induced T cell response, and the subject progressed more rapidly than expected for someone expressing the HLA-B27 allele. These data suggest that control of HIV by vaccine-elicited HIV-specific T cell responses may be difficult, even when the T cell response has those characteristics predicted to provide optimal protection.
Nitroaspirin corrects immune dysfunction in tumor-bearing hosts and promotes tumor eradication by cancer vaccination
Authors: De Santo Carmela , Serafini Paolo , Marigo Ilaria , Dolcetti Luigi , Bolla Manlio , Del Soldato Piero , Melani Cecilia , Guiducci Cristiana , Colombo Mario P. , Iezzi Manuela , Musiani Piero , Zanovello Paola , Bronte Vincenzo
Published: March 2005

Active suppression of tumor-specific T lymphocytes can limit the immune-mediated destruction of cancer cells. Of the various strategies used by tumors to counteract immune attacks, myeloid suppressors recruited by growing cancers are particularly efficient, often resulting in the induction of systemic T lymphocyte dysfunction. We have previously shown that the mechanism by which myeloid cells from tumor-bearing hosts block immune defense strategies involves two enzymes that metabolizel-arginine: arginase and nitric oxide (NO) synthase. NO-releasing aspirin is a classic aspirin molecule covalently linked to a NO donor group. NO aspirin does not possess direct antitumor activity. However, by interfering with the inhibitory enzymatic activities of myeloid cells, orally administered NO aspirin normalized the immune status of tumor-bearing hosts, increased the number and function of tumor-antigen-specific T lymphocytes, and enhanced the preventive and therapeutic effectiveness of the antitumor immunity elicited by cancer vaccination. Because cancer vaccines and NO aspirin are currently being investigated in independent phase I/II clinical trials, these findings offer a rationale to combine these treatments in subjects with advanced neoplastic diseases.
Simulation of dynamical properties of normal and superfluid helium
Authors: Nakayama Akira , Makri Nancy
Published: March 2005

The formation of a superfluid when4He is cooled below the characteristic lambda transition temperature is accompanied by intricate quantum mechanical phenomena, including the emergence of a Bose condensate. A combination of path integral and semiclassical techniques is used to calculate the single-particle velocity autocorrelation function across the normal-to-superfluid transition. We find that the inclusion of particle exchange alters qualitatively the shape of the correlation function below the characteristic transition temperature but has no noticeable effect on the dynamics in the normal phase. The incoherent structure factor extracted from the velocity autocorrelation function is in very good agreement with neutron scattering data, reproducing the width, height, frequency shift, and asymmetry of the curves, as well as the observed increase in peak height characteristic of the superfluid phase. Our simulation demonstrates that the peak enhancement observed in the neutron scattering experiments below the transition temperature arises exclusively from particle exchange, illuminating the role of Bose-statistical effects on the dynamics of the quantum liquid.
Agendas, past & future
Authors: Bujra Janet , Cliffe Lionel , Szeftel Morris , Abrahamsen Rita , Zack-Williams Tunde
Published: March 2005

This issue marks the 30th anniversary of the birth of The Review of African Political Economy in 1974. At the time, its founders were unsure if it would get off the ground and they certainly never thought it would last thirty years! Apart from debate about what its role would be, there were doubts about their own stamina, and about whether successor generations would emerge to take it on. The challenge was set out by Anderson in relation to another Left Review:

…political journals have no choice: to be true to themselves, they must aim to extend their real life beyond the conditions or generations that gave rise to them (Anderson, New Left Review, 2000).
Beyond Bush: The future of popular movements & US Africa policy
Authors: Martin William G.
Published: March 2005

This article reviews US policy towards Africa, arguing that continuity over the past four administrations far outweighs differences between presidential candidate Senator Kerry and President George Bush. If Kerry were to win the Presidential elections in November, this would not lead to any radical change in US-Africa relations. What is new over the longer term, and is posed so starkly by Bush's unilateralist and militarised actions, is the relentless development of a post-liberal world order and policy agenda. Opposition to this agenda by progressive movements and organisations focused upon such issues as debt cancellation, privatisation, and public health has already born fruit in Africa and elsewhere. The successes, failures, and contradictions of these new campaigns and organisations reflect the post-liberal conditions they work under, and are thus significantly different from the solidarity struggles of the past.

The assistance of Jim Cason was invaluable in constructing this essay, for which the author is very grateful.
Solidarity & Africa in the new century
Authors: Sachikonye Lloyd M.
Published: March 2005

Solidarity is an awareness of a common humanity and global citizenship and the voluntary acceptance of the responsibilities that go with it. It is the conscious commitment to redress inequalities both within and between countries. It is based on recognition that in an interdependent world, poverty or oppression anywhere is a threat to prosperity and stability everywhere…

1

The second half of the 20th century witnessed the most sustained upsurge in the process of national liberation and independence in the developing or ‘Third’ world. This upsurge reached a climax in the attainment of national liberation in such diverse countries as Vietnam in 1975, the Lusophone states also in the 1970s, in Africa, and in Zimbabwe in 1980. The transition to independence and democracy in Namibia and South Africa in the 1990s represented a fitting climax of this liberation and de-colonisation process. The last quarter of the century was similarly momentous in that it witnessed the flowering of the international solidarity movement. The struggles against United States imperialism in Vietnam and elsewhere in the world, and against apartheid in Southern Africa and Portuguese fascism took on a special resonance during this period.
Among- and within-patch components of genetic diversity respond at different rates to habitat fragmentation: an empirical demonstration
Authors: Keyghobadi Nusha , Roland Jens , Matter Stephen F , Strobeck Curtis
Published: March 2005

Habitat fragmentation is a ubiquitous by-product of human activities that can alter the genetic structure of natural populations, with potentially deleterious effects on population persistence and evolutionary potential. When habitat fragmentation results in the subdivision of a population, random genetic drift then leads to the erosion of genetic diversity from within the resulting subpopulations and greater genetic divergence among them. Theoretical and simulation analyses predict that these two main genetic effects of fragmentation, greater differentiation among resulting subpopulations and reduced genetic diversity within them, will proceed at very different rates. Despite important implications for the interpretation of genetic data from fragmented populations, empirical evidence for this phenomenon has been lacking. In this analysis, we carry out an empirical study in populations of an alpine meadow-dwelling butterfly, which have become fragmented by increasing forest cover over five decades. We show that genetic differentiation among subpopulations (
G
ST
) is most highly correlated with contemporary forest cover, while genetic diversity within subpopulations (expected heterozygosity) is better correlated with the spatial pattern of forest cover 40 years in the past. Thus, where habitat fragmentation has occurred in recent decades, genetic differentiation among subpopulations can be near equilibrium while contemporary measures of within subpopulation diversity may substantially overestimate the equilibrium values that will eventually be attained.
Granular cell atypical fibroxanthoma
Authors: Rudisaile Sarah N. , Hurt Mark A. , Santa Cruz Daniel J.
Published: March 2005

Abstract:  We report on two patients with granular cell atypical fibroxanthoma. Both neoplasms were solitary, light‐tan, dome‐shaped papules on sun‐exposed areas of the head in two elderly white men. Microscopically, these neoplasms showed a dermal proliferation of pleomorphic granular cells with irregular hyperchromatic nuclei, multinucleated cells, and scattered mitoses. Immunohistochemical stains were positive for CD68 and vimentin and negative for Melan‐A or human melanoma black (HMB)‐45, S‐100 protein, pancytokeratin, and actin, consistent with atypical fibroxanthoma. The differential diagnosis of granular cells in neoplasms containing cytological pleomorphism is challenging in view of the many different neoplasms that may present with granular cytoplasm. These include the conventional granular cell tumor and its malignant form, leiomyoma, leiomyosarcoma, dermatofibroma, dermatofibrosarcoma protuberans, and angiosarcoma.
Selective O–H Bond Cleavage in the Radiolysis of Quartz
Authors: AZUMA NAOTO , MIYAZAKI TETSUO , FUEKI KENJI , SAKAGUCHI ISAO , HIRANO SHIN‐ICHI
Published: March 2005

Cleavage of the O–H bond in quartz was studied by Fourier transform infrared spectroscopy and ESR spectroscopy. When quartz single crystals and fused silica glass are γ‐irradiated at 77 K, hydrogen atoms are produced by rupture of O–H bonds. The initial efficiency of O–H bond cleavage in quartz single crystals, i.e. the initial yield of H atoms, was three times as great as that in fused silica glass, although the concentration of O–H bonds in quartz single crystals (70 ppm) is much lower than that in fused silica glass (4000 ppm). The efficiency of O–H bond cleavage in quartz single crystals indicates that energy transfer from the irradiated single crystal to the O–H bonds takes place effectively at 77 K. The efficiency of O–H bond cleavage decreases with increasing γ‐ray dose, i.e. with increasing amounts of radiation‐induced defects in quartz single crystals. When the radiation‐induced defects are removed by annealing the irradiated quartz single crystal at 773 K, the O–H bonds are ruptured again as effectively as for a fresh quartz single crystal. The distance of the energy transfer, estimated by a target model, is ∼15 nm.
Grain Growth During Sintering of Donor‐Doped BaTiO3
Authors: Drofenik Miha H.
Published: March 2005

Grain growth of donor‐doped BaTiO3 in the presence of KF b'quid phase was studied. The results showed that the composition of the liquid phase present during sintering had a pronounced influence on grain growth and on the formation of semiconducting donor‐doped BaTiO3.
Behavior of Multicomponent Gas Bubbles in Glass Melts
Authors: RAMOS J. I.
Published: March 2005

A mathematical model is proposed to study the behavior of multicomponent gas bubbles in glass melts. The effects of the melt temperature on bubble radius, trajectory, and composition were studied as a function of time, both accounting for and disregarding bubble boundary motion. It is shown that accounting for the boundary motion results in shorter refining times, smaller bubbles, and larger concentrations of the gaseous species than if this motion is disregarded. It is also shown that the bubble trajectory is almost a linear function of time and that mass transfer has a very small effect on bubble trajectory and refining times; however, it has a strong influence on the bubble radius, which, in the absence of mass transfeir, increases linearly with the temperature.
Phase Changes in a Leucite‐Containing Dental Porcelain Frit
Authors: Mackert J. Rodway , Butts Michael B. , Morena Robert , Fairhurst Carl W.
Published: March 2005

The high average thermal expansion required for thermal compatibility of dental porcelains with their substrate alloys is supplied by the mineral leucite (K2O Al2O3 4SiO2). Since leucite is not an equilibrium phase at the composition of component No. 1 of the Weinstein et al. patent, phase changes in this leucitecontaining frit could be responsible for the observed thermally induced changes in dental porcelain expansion behavior. This study sought to explore such phase changes.
Toughening of Dental Porcelain by Tetragonal ZrO2 Additions
Authors: Morena R. , Lockwood P. E. , Evans L. , Fairhurst C. W.
Published: March 2005

The effect on mechanical behavior of ZrO2 additions to a dental porcelain was investigated. The ZrO2 was introduced into the glassy matrix phase of the porcelain by refritting the all‐glass porcelain constituent. X‐ray diffraction indicated that a sizeable fraction of the ZrO2 was retained in the tetragonal form after the porcelain was fired. Zirconia additions to the porcelain produced substantial improvements in fracture toughness, strength, and thermal shock resistance.
Volume Relaxation Far from Equilibrium
Authors: SCHERER GEORGE W.
Published: March 2005

Narayanaswamy's model of structural relaxation is applied to the data of Hara and Suetoshi on volume relaxation in plate glass. Both the Adam‐Gibbs and Arrhenius equations are used to represent the relaxation time. Equally good fits are obtained with both equations, but only the Adam‐Gibbs model gives Physically meaningful fitting parameters. The exponent b describing the shape of the relaxation time spectrum decreases at small values of reduced time, as it does for stress relaxation Discrepancies between calculated and measured densities at 350°C are not resolved by allowing for a nonlinear driving force or thermorheological complexity.
Thermochemistry of MgAl2O4‐Al8/3O4 Defect Spinels
Authors: NAVROTSKY ALEXANDRA , WECHSLER BARRY A. , GEISINGER KAREN , SEIFERT FRIEDRICH
Published: March 2005

Solution calorimetry of MgAl2O4‐Al8/3O4 solid solutions was performed in a molten 2PbO · B2O3 solvent at 975 K. The results indicate small negative heats of mixing, relative to spinel standard states for both end‐members. These data were combined with information on the energetics of the α‐γ transition in Al2O3 and on the MgAl2O4‐Al8/3O4 (MgO‐Al2O3) subsolidus phase relations to estimate the partial molar entropy of mixing of γ‐Al8/3O4 in the solid solution. This entropy is much less positive than that calculated from several models for the configurational entropy of mixing of magnesium, aluminum, and vacancies on octahedral and/or tetrahedral sites. The data suggest a good deal of local order to be present in the solid solutions, consistent with negative enthalpies of mixing and entropies of mixing far less than ideal configurational values.
Syntheses and Unit‐Cell Determination of Ba3V4O13 and Low‐and High‐Temperature Ba3P4O13
Authors: Millet J.M. , Parker H.S. , Roth R.S.
Published: March 2005

The syntheses and the results of unit‐cell determinations ofBa3V4O13 and the two forms (low‐ and high‐temperature) of Ba3P4O13 are presented. Ba3V4O13 crystallizes in the monoclinic system, space group Cc or C2/c with unit‐cell dimensions a=16.087, b=8.948, c=10.159 (x10nm), β=114.52° Low‐Ba3P4O13 crystallizes in the triclinic system, space group P1 or P1 with unit‐cell dimensions a=5.757, b=7.243, c=8.104 (x10 nm) α=82.75°, β=73.94°, γ=70.71°. Low‐Ba3P4O13 transforms at 870°C into high‐Ba3P4O13 which crystallizes in the orthorhombic system, space group Pbcm (No. 57) (or Pbc2, No. 29) with unit‐cell dimensions a =7.107, b=13.883, c=19.219 (x10 nm). No relations have been found between the structures of the tribarium tetravanadate and the tribarium tetraphosphate.
Mechanical Properties of Y2O3‐Stabilized Tetragonal ZrO2 Polycrystals After Ageing at High Temperature
Authors: MASAKI TAKAKI
Published: March 2005

Yttria‐partially‐stabilized zirconia (Y‐PSZ) materials containing 2.5, 3.0, and 5.0 mol% of Y2O3 prepared by hot pressing were subjected to ageing in air for >10 h at temperatures in the range of 800°C and 1200°C. The sintered materials were measured to determine the mechanical properties and microstructures and analyzed for trace elements. A sharp reduction in bending strength was observed after the ageing, the cause for which was suggested to be the formation of cavities produced by the oxidation of carbon.
Matrix Phase in Ceramics with Composition near BaO·Nd2O3·5TiO2
Authors: Jaakola T. , Uusimäki A. , Rautioaho R. , Leppävuori S.
Published: March 2005

Phase structures of two ceramics of Compositions BaNd2Ti5O14 and Ba3.75Nd9.5Ti18O54, both of which had earlier been reported to be single‐phase materials, were investigated using electron microscopy and an electron probe microanalyzer. It was observed that the amount of secondary phases was much lower in ceramics prepared with the latter composition and that the composition of the matrix phase of both samples was near 4BaO·5 Nd2O3·18TiO2. These results indicate that only the composition Ba3.75Nd9.5Ti18O54 is a single‐phase composition.
Reinvestigation of the Solidification Point of CaO by Digital Pyrometry
Authors: Yamada Toyoaki , Yoshimura Masahiro , Sōmiya Shigeyuki
Published: March 2005

The solidification point of calcia which has been distributed by the Commission on High‐Temperature and Solid‐State Chemistry of the International Union of Pure and Applied Chemistry was measured by digital pyrometry using an arc imaging furnace. The solidification point was determined to be 2899°C with ±3°C as the standard deviation for this sample. The reliability of this solidification point was determined to be within ±17°C based upon discussions of the measuring system and the material.
Electrical Conductivity of Y2O3 as a Function of Oxygen Partial Pressure in Wet and Dry Atmospheres
Authors: NORBY TRULS , KOFSTAD PER
Published: March 2005

The electrical conductivity of polycrystalline Y2O3 has been studied as a function of the partial pressure of oxygen (10–14 to 105 Pa) at 900° to 1500°C in atmospheres saturated with water vapor at 12°C or dried with P2O5. Yttria is a p‐conductor at high oxygen activities. The p‐conductivity increases with increasing PO2 and decreases with increasing PH2O. At low oxygen activities the oxide is a mixed ionic/electronic conductor. The ionic conductivity is approximately independent of PO2 and increases with increasing PH2O. In the Y2O3 samples, excesses of lower‐valent cation impurities (in the 10 to 100 mol‐ppm range) are the dominating negatively charged defects, and in the presence of water vapor they are compensated by interstitial protons. At high PH2O levels additional protons are probably compensated by interstitial oxygen ions. At high temperatures (±1100°C) and for high PO2 and low PH2O, the protons are no longer dominant, and the lower‐valent cations are mainly compensated by electron holes. The electrical conductivity exhibits hysteresis‐like effects which are interpreted in terms of segregation/desegregation of impurities at grain boundaries. The mobility of electron holes in yttria at 1500°C is estimated to be of the order of magnitude of 0.05 cm2. s–1. V–1
Synthesis, Stability, and Crystal Chemistry of Dibarium Pentatitanate
Authors: ROTH ROBERT S. , RITTER JOSEPH J. , PARKER HARRY S. , MINOR DENNIS B.
Published: March 2005

Only ZrO2 was found to stabilize the phase previously reported as “Ba2Ti5O12.” A metastable phase corresponding to this compound was found to form between 650° and 675°C from hydrolyzed ethoxide precursors. The stability was increased to ∼850°C by the addition of 1 to 2 mol% Nb2O5 to the precursor solutions. Addition of 5 mol% SnO2 failed to yield appreciable amounts of this phase in solid‐state preparations, contrary to the previous report. Addition of 8 mol% ZrO2, however, did produce the desired phase as reported, both with and without additional Nb2O5, apparently stable to >1300°C. Small single crystals, picked from a ZrO2‐stabilized specimen with 1 mol% Nb2O5, showed the compound Ba2Ti5‐xZrxO12 to be a 10‐layer structure, triclinic, pseudo‐orthorhombic with A‐centered symmetry and a =9.941(5), b= 11.482(4), c= 23.528 (10) × 10–1 nm. The corresponding reduced triclinic unit cell has a = 9.941, b= 11.482, c= 13.090 × 10–1 nm, α= 116.01°, β= 90.0°, γ= 90.0°.
Effective Sintering Aids for Silicon Carbide Ceramics: Reactivities of Silicon Carbide with Various Additives
Authors: Negita Keishi
Published: March 2005

Effective sintering aids for SiC ceramics are discussed on the basis of their reactivities with various sintering aids around sintering temperatures (2300 to 2400 K). The free energy consideration of the reactions suggests that metals and metal oxides which do not decompose SiC in the sintering process are effective as sintering aids for SiC ceramics.
Transformation‐Toughened ZrO2: Correlations between Grain Size Control and Composition in the System ZrO2‐Y2O3
Authors: LANGE F.F.
Published: March 2005

The average grain size of ZrO2(+Y, o,) materials sintered at 1400°C was observed to depend significantly on the Y2O3 content. The average grain size decreased by a factor of 4 to 5 for Y2O3 contents between 0.8 and 1.4 mol% and increased at Y2O3 contents of 6.6 mol%. Grain growth control by a second phase is the concept used to interpret these data; compositions with a small grain size lie within the two‐phase tetragonal + cubic phase field, and the size of the tetragonal grains is believed to be controlled by the cubic grains. This interpretation suggests that the Y2O3‐rich boundary of the two‐phase field lies between 0.8 and 1.4 mol% Y2O3. Transformation toughened materials fabricated in this binary system must have a composition that lies within the two‐phase field to obtain the small grain size required, in part, to retain the tetragonal toughening agent.
Interfaces in Oriented Al2O3‐ZrO2 (Y2O3) Eutectics
Authors: MAZEROLLES L. , MICHEL D. , PORTIER R.
Published: March 2005

Oriented samples of Al2O3‐ZrO2 (Y2O3) eutectics consisting of an alumina matrix with zirconia dispersoids were grown by directional solidification. Preferred growth directions and epitaxial relations were determined from X‐ray and electron diffraction analyses. Imaging of interfaces was performed by high‐resolution transmission electron microscopy on oriented platelets. Semicoherent interfaces were observed with faceting along crystallographic planes of both phases.
Structure of Incoherent ZrO2/Al2O3 Interfaces
Authors: KRAUS‐LANTERI S. P. , MITCHELL T. E. , HEUER A. H.
Published: March 2005

High‐resolution electron microscopy was used to image incoherent ZrO2/Al2O3 interfaces in ZrO2‐toughened Al2O3 containing intragranular ZrO2. These particles are generally spherical but are sometimes faceted. High‐resolution electron micrographs provide atomic‐level information on the interfacial structure. For spherical particles, both ledgelike images and misfit dislocation‐like images accommodated the lattice misfit, depending on the orientation of the interface, while faceted particles imply at least one low‐energy ZrO2/Al2O3 interface.
EXAFS Study of Yttria‐Stabilized Zirconia
Authors: CATLOW C. R. A. , CHADWICK A. V. , GREAVES G. N. , MORONEY L. M.
Published: March 2005

The local structural environments of Y3+ and Zr4+ in 18 wt% Y2O3‐stabilized zirconia were studied using extended X‐ray absorption fine structure spectroscopy over the temperature range –120° to 770°C. The measured cation‐oxygen distances reflect those of the parent oxides, with the mean Zr‐O distance 0.017 nm shorter than the mean Y‐O distance. The spread in the Zr–nearest‐neighbor and Zr–next‐nearest‐neighbor distances is considerably larger than observed for Y3+. This result is attributed to the anion vacancies being preferentially sited adjacent to the smaller Zr4+ cation which, with ensuing relaxations, permits a closer contact between Zr4+ and its oxygen neighbors. Thus, the structural environment of these Zr4+ ions resembles that of the 7‐coordinated Zr4+ in monoclinic zirconia. Increasing the temperature of the sample results in the local structural environments of the two cations becoming more alike, suggesting that increased anionic mobility leads to an increasingly random distribution of anion vacancies.
Solid‐State27Al and 29Si Magic‐Angle Spinning NMR of Aluminosilicate Gels
Authors: Komarneni Sridhar , Roy Rustum , Fyee Colin A. , Kennedy Gordon J. , Strobl Harold
Published: March 2005

The environment of the Al and Si atoms of diphasic and single‐phase aluminosilicate gels was determined by solid‐state 27Al and 29Si magic‐angle spinning nuclear magnetic resonance (MASNMR) spectroscopy, The tetrahedral coordination of Al increased with decreasing Al/Si ratio in single‐phase gels but not in diphasic gels. The results showed that ultrahomogeneous mixing on a next‐nearest‐neighbor level is achieved in single‐phase aluminosilicate gels, while in diphasic gels this has successfully been avoided.
Grain‐Boundary Effect in Ceria Doped with Trivalent Cations: II, Microstructure and Microanalysis
Authors: GERHARDT R. , NOWICK A. S. , MOCHEL M. E. , DUMLER I.
Published: March 2005

Various samples studied for their electrical behavior in the previous paper are here examined in detail by microstructural and microanalytical techniques. While several microstructural features are observed, the presence of “thick boundaries” (an amorphous silica‐rich phase that surrounds grain boundaries and forms a continuous network) appears to be the principal feature responsible for the grain‐boundary effect. Such features are absent from samples prepared with nearly silicon‐free materials, for which the grain‐boundary effect is also virtually absent.
Thermochemical Nitridation of Microporous Silica Films in Ammonia
Authors: BROW RICHARD K. , PANTANO CARLO G.
Published: March 2005

Microporous silicon dioxide thin Films were deposited on silicon substrates from a solution of tetraethoxysilane, ethanol, and water. These were converted to dense oxynitrides through a high‐temperature reaction with ammonia. The ammonia treatments yielded amorphous, compositionally homogeneous films with overall nitrogen contents ranging up to 40 mol%. For ammonia treatments below 800°C, nitrogen was incorporated into the films as an amine species, whereas higher temperature treatments produced a nitride material.
Aluminum Titanate Formation by Solid‐State Reaction of Fine Al2O3 and TiO2 Powders
Authors: FREUDENBERG BERNHARD , MOCELLIN ALAIN
Published: March 2005

The formation of Al2TiO5 has been studied in equimolar Al2O3‐TiO2 powder mixtures of ∼1μm particle sizes and moderate purity (∼99.8 wt%) at temperatures around 1300°C, where the free energy of formation is very small. Micro‐structural development and reaction kinetics indicate that different mechanisms operate depending on the advancement of the reaction. The rapid initial reaction stage is interpreted as the nucleation‐growth of Al2TiO5 cells in a virtually non‐reacting matrix. The final reaction stage corresponds to the slow diffusion‐controlled elimination of Al2O3 and TiO2 dispersoids trapped during the growth of the initial Al2TiO5 cells.
Effect of Crystallization on Thermal Shock Behavior of a Chain‐Silicate Canasite Glass‐Ceramic
Authors: Oguma Masaomi , Chyung Kenneth , Donaldson Kimberly Yates , Hasselman D. P. H.
Published: March 2005

The resistance of a canasite glass‐ceramic to the initiation of thermal stress fracture due to a water quench was found to be higher than for the original glass, due to higher values of strength and thermal conductivity which offset increases in thermal expansion and Young's modulus. Relative strength retention behavior of the glass‐ceramic was also higher than for the glass, attributed to its crack‐size‐dependent fracture toughness.
Effect of Sol‐Gel Mixing on Mullite Microstructure and Phase Equilibria in the α‐Al2O3‐SiO2 System
Authors: PASK J. A. , ZHANG X.W. , TOMSIA A. P. , YOLDAS B.E.
Published: March 2005

Starting powders containing 72 wt% Al2O3 and 28 wt% SiO2, were prepared by sol‐gel methods classified as colloidal and polymeric. Compacts fired at 1700°C showed significant differences in microstructure. The specimens formed with the colloidal powder had mullite grains of prismatic shape and a liquid phase; with polymeric powder, mullite grains were granular with no liquid phase present. It is shown that the mullite grains in the first case are higher in AI2O3 content, resulting in an excess of SiO2 which is the base for the liquid phase. In the second case, the mullite grains have the same Al2O3 content as the starting powders. The presence of a liquid phase in the first case is considered to be metastable, resulting from the nature of the starting materials and processing conditions employed.
Synthesis and Thermal Expansion of MZr4P6O24 (M=Mg, Ca, Sr, Ba)
Authors: Limaye S. Y. , Agrawal D. K. , Mckinstry H. A.
Published: March 2005

MZr4P6O24 (M=Mg, Ca, Sr, Ba), which belongs to a new, low‐thermal‐expansion family of materials known as [NZP] or [CTP], were synthesized by solid‐state reaction (oxide mixing) and sol‐gel methods, and their sinterability in two cases was investigated and compared. Thermal‐expansion measurements were made on sintered samples by dilatometry, high‐temperature X‐ray diffractometry, and the laser speckle technique. An anisotropy in axial thermal‐expansion coefficients was observed in these materials. CaZr4P6O24 and SrZ4P6O24 showed reverse anisotropy as well as opposite bulk thermal expansion; i.e., CaZr4P6O24 had negative bulk thermal expansion and SrZr4P6O24 positive bulk thermal expansion in the temperature range 25° to 500°C. The microstructure of the sintered samples was also examined by scanning electron microscopy.
Effects of Free Silicon on the α to βPhase Transformation in Silicon Nitride
Authors: Park Ji Yeon , Kim Jae Ryong , Kim Chong Hee
Published: March 2005

Free silicon in silicon nitride compacts can act as suitable liquid solvent for Si3N4 and assists in the α to β phase transformation. The rate of transformation depends on the size of the added silicon particles. When submicrometer silicon particles are added, the rate of transformation is more rapid than when large particles are added; the complete transformation can be achieved at 1700°C in 1 h.
Preparation of High‐Tc Superconducting Oxides by the Amorphous Citrate Process
Authors: Chu Chung‐tse , Dunn Bruce
Published: March 2005

The high‐Tc superconducting oxide Yba2Cu3O7–y has been prepared by the amorphous citrate process. A citrate‐nitrate solution was prepared at room temperature and dehydrated at around 80°C to yield a solid precursor material. The precursor was fired to high temperature to form the desired compound. The decomposition mechanism was studied with thermogravimetric analysis and X‐ray diffraction. Intermediate products were formed during the decomposition reactions. Nearly phase‐pure Yba2Cu3O7‐y powders were obtained by firing the precursor in air to 900°Cfor2 h. Sintered samples were typically over 90% dense and exhibited good superconducting properties.
Preparation of Cerium‐Activated Silica Glasses: Phosphorus and Aluminum Codoping Effects on Absorption and Fluorescence Properties
Authors: ISHII YOSHIRO , ARAI KAZUO , NAMIKAWA HIROSHI , TANAKA MITSUHIRO , NEGISHI AKIRA , HANDA TAKASHI
Published: March 2005

Cerium‐activated silica (SiO2) glasses were prepared by plasma torch chemical vapor deposition (CVD). In Ce‐doped SiO2 glasses, most Ce exists as Ce4+ ions; the remaining small amount of Ce3+ ions exhibits a broad fluorescence spectrum with a large Stokes shift, ∼9600 cm‐1, from the excitation spectrum peak of 324 nm. Aluminum and phosphorus codoping considerably increases the Ce3+ ratio and shifts the peaks of both spectra to shorter wavelengths. P codoping is the more effective way to achieve this result and in some cases produces an absorption spectrum similar to that of a Ce‐doped phosphate glass. These findings are consistent with the solvatiorn shell model for codoping, as previously proposed. To codope P, a soot remelting method was devised to deal with the highly volatile P2O5.
H2O‐Catalyzed Sintering of ∼2‐nm‐Cross‐ Section Particles of MgO
Authors: BERUTO DARIO , BOTTER RODOLFO , SEARCY ALAN W.
Published: March 2005

MgO produced by vacuum decomposition of Mg(OH) 2 is formed as aggregates containing both open and closed pores. The surface area and the volume of the open pores, as measured by N2 adsorption, were found to be 300 m2/g and 0.14 cm3/g, respectively. Through calorimetric and TEM studies, reported elsewhere, the initial surface area and volume of the closed pores are shown to be 550 ± 150 m2/g and 0.19 cm3/g, respectively. The samples were sintered in the presence of water at 823 K. The elimination of the closed pores and coarsening of the open pores dominate early stage sintering under the conditions studied. From the above observations, it is argued that the sintering behavior is governed primarily, not by diffusion, but by a surface step. It is postulated that the nature of the surface step is the formation of new ion layers by random fluctuations in closed pores and in smaller open pores for which edge effects are thermodynamically favorable.
Reaction Sintering of Submicrometer Silicon Powder
Authors: Gregory Otto J. , Lee Sang‐Baek , Flagan Richard C.
Published: March 2005

Submicrometer silicon powder synthesized by thermally induced, vapor‐phase reaction in an aerosol reactor was densified by reaction sintering to form Si3N4. The densification behavior of these spherical, nonagglomerated particles in the 0.1 to 0.2 μm size range is described. Competition between densification by silicon sintering and reaction product infilling was observed at typical reaction sintering temperatures. In addition, pore growth during the early stages of silicon presintering adversely affected nitrogen permeability and nitriding rates. The factors influencing the nitridation of ultrafine silicon powders are discussed.
Solid Solubility Effect on Properties of Titanium Diboride
Authors: ZDANIEWSKI WIESLAW A.
Published: March 2005

The effect of solute additions on the lattice constants of (Ti,Me)B2 alloys is reported. The data are based on the literature and on additional experimental work. Variation of lattice constants, calculated from crystallochemical principles, agrees satisfactorily with measured values for dilute solid solutions. Increased solute concentration causes positive deviation for (Ti,Cr)B2, (Ti,Zr)B2, and (Ti,Al)B2 because lattice dilation is affected by both the valence of the solute and the size of the metallic radii. It is postulated that lattice anisotropy and elastic strain energy increase in the solid solutions and that they determine the grain‐boundary cohesion in polycrystalline TiB2. Knowledge of the lattice dilation properties of TiB2 solid solutions indicates how the mechanical behavior of diboride ceramics could be improved.
Elastic Behavior of Open‐Cell Alumina
Authors: HAGIWARA HIROSHI , GREEN DAVID J.
Published: March 2005

The elastic constants of open‐cell aluminas were measured as a function of their relative density and cell size. The density exponent was found to be in excellent agreement with previous theoretical work that considered cell strut bending as a major deformation mode. The measured constants in the elastic behavior relationships were found to be less than previously suggested, and it was found that this factor is sensitive to the microstructure of the cell struts, especially porosity within these struts. The materials studied were found to contain soem closed cells, but these were not found to have a major effect on the elastic behavior. The values of Young's modulus and the shear modulus depended on the relative density in the same way, and this is consistent with previous theoretical work which showed that Poisson's ratio should be independent of density.
Hydration of Sodium β‐ and β′′‐Aluminas
Authors: DUDNEY NANCY J. , BATES J. B.
Published: March 2005

The enthalpy and entropy for the hydration of sodium β‐ and β′′‐aluminas have been determined by measuring the infrared absorbance of single‐crystal samples following equilibration at elevated temperatures in water vapor pressures ranging from 3 to 70 kPa. The equilibrium water concentrations can be varied continuously and reversibly up to saturation concentrations of about 0.9H2O‐Na1.2AI11O17.1 for the β‐phase and 0.4H2O.Na1.67Mg.67Al10.33O17 for the β′′‐phase. The hydration reactions are exothermic; ΔH=−56 ± 2 for sodium β′′‐aIumina and ΔH =−67 ± 2 kJ/mol for sodium β‐alumina. The entropies of hydration are about −143 ± 6 J/(mol‐K) for both sodium β‐ and β′′‐aIuminas.
Spinel Phase Formation During the 980°C Exothermic Reaction in the Kaolinite‐to‐Mullite Reaction Series
Authors: Sonuparlak Birol , Sarikaya Mehmet , Aksay Ilhan A.
Published: March 2005

With the use of differential thermal analysis, X‐ray diffraction, and transmission electron microscopic techniques, we showed that γ‐Al2O3 type spinel phase is solely responsible for the 980°C exotherm in the kaolinite‐to‐mullite reaction series. Transmission electron microscopic characterization indicated that the spinel formation is preceded by a phase separation in the amorphous dehydroxylated kaolinite matrix. Chemical analysis of the spinel phase by energy dispersive X‐ray spectroscopy revealed a nearly pure Al3O2 composition.
Corrosion of Phosphorus Oxynitride Glasses in Water and Humid Air
Authors: BUNKER BRUCE C. , ARNOLD GEORGE W. , RAJARAM MOHAN , DAY DELBERT E.
Published: March 2005

Phosphorus oxynitride (PON) glasses, prepared by remelting phosphate glasses in anhydrous ammonia vapor, are more resistant to dissolution in water and corrosion in humid environments than the parent phosphate glasses. The chemical durability of PON glasses is directly related to their nitrogen content. Solution analyses, pH stat titrations, and hydrogen depth profiles suggest that nitrogen improves the durability of phosphate glasses by cross‐linking the polymeric phosphate chains in the network structure.
New Modification of LaYO3
Authors: Yamaguchi Osamu , Kawabata Hidenao , Hashimoto Hiroyuki , Shimizu Kiyoshi
Published: March 2005

A new modification of LaYO3 crystallizes at 750° to 1000°C from an amorphous material prepared by the simultaneous hydrolysis of lanthanum and yttrium alkoxides. It has a cubic unit cell with a =1.0906 nm. Cubic LaYO3 transforms to the orthorhombic modification at 1210° to 1250°C.
Penetration of Polycrystalline Alumina by Glass at High Temperatures
Authors: FLAITZ PHILIP L. , PASK JOSEPH A.
Published: March 2005

An analysis of interfacial energies in a solid‐liquid system showed that complete penetration of a liquid along grain boundaries in a microstructure forming during liquid‐phase sintering is not necessarily associated with complete wetting or spreading at the solid‐liquid interface. Investigations were made on the penetration of CaO‐Al2O3‐SiO2 glasses into dense polycrystalline aluminas. Initial penetration was along three‐grain junctions or grain boundaries by a solution/reaction between the liquid and defect‐containing alumina along interfaces. Degree of penetration was variable, and it was dependent on internal strain and MgO addition. Extended heat treatments reduced liquid penetration.
Free Volume of Network‐Forming Oxide Glasses in the Systems P2O5‐(GeO2,TeO2,Sb2O3,V2O5)
Authors: Suzuki Suguru , Takahashi Minoru , Hikich Yasio
Published: March 2005

The free‐volume fraction (Vf) defined by Simha and Boyer was measured for network‐forming oxide glasses in the systems P2O5‐(GeO2, TeO2,Sb2O3.V2O5). The Vf values varied from 0.06 to 0.25. The systems P2O5‐TeO2: and P2O5‐Sb2O3 have Vf∼0.1, which is near the magnitude of the free‐volume fraction for normal metaphosphate glasses and many organic high polymers.
Oxygen Evolution During MnO‐Mn3O4 Dissolution in a Borosilicate Melt
Authors: LUCKTONG CHARTRE , HRMA PAVEL
Published: March 2005

Foam evolution during dissolution of MnO‐Mn3O4 pellets and powders in borosilicate glass was recorded photographically. The pellets were placed horizontally in transparent crucibles, covered with molten glass, and held at 1150°C. If the Mn3O4 content in pellets was more than 31 wt%, they developed foam after an initial foamless period. The length of the foamless period decreased and the duration of foaming increased as the Mn3O4 content increased. Batches prepared from MnO‐Mn3O4 powders and frit, and soaked at 1150°C, foamed without an initial foamless period. The foam developed and collapsed before the set temperature was established within the melt and rose to a higher level than foam produced by pellets. Thermogravimetry of batches heated in 1 atm (∼105 Pa) of O2 shows oxidation at 400° to 600°C followed by mass loss due to volatilization and oxygen evolution.
Coordination of Zinc(II) in ZnO–K2O–SiO2 Glasses by X‐ray Diffraction
Authors: Musinu Anna , Piccaluga Giorgio , Magini Mauro
Published: March 2005

The radial distribution functions of ZnO–K2O–SiO2 glasses with 7 and 10 wt% ZnO are compared with that of the corresponding K2O–SiO2 matrix leading to “difference distribution curves’representative of the zinc structural arrangement. Analysis of the curves indicates that Zn2+ ions are prevalent (65% to 80%) in the glasses in tetracoordinated form.
Experiments on Pore Closure During Hot Isostatic Pressing and Forging
Authors: KELLETT B.J. , LANGE FRED F.
Published: March 2005

The effect of stress on pore closure was studied by hot isostatic pressing and hot forging of sintered Al2O3, cubic ZrO2, and finer‐grained Al2O3/ZrO2 (cubic) composite materials containing pores remnant of monosized plastic spheres. For the temperature‐time conditions explored, plastic deformation was the dominant mechanism for pore shape change and closure. Namely, only pores in the highly deformable two‐phase material were observed to either change shape (under uniaxial forging) or shrink (during hot isostatic pressing). Large plastic strains (0.3 to 0.6, dependent on location) were required to produce pore closure under forging conditions. At temperatures where the two‐phase materials were sufficiently deformable to affect pore closure, pores close to the surface would puncture as the thin web of material separating the pore from the surface was deformed into the pore. These results are discussed in terms of the common practice of finishing by hot isostatic pressing of sintered materials.
Indentation Deformation and Fracture of Sapphire
Authors: CHAN HELEN M. , LAWN BRIAN R.
Published: March 2005

Relatively little is known about the fundamental deformation processes in intrinsically hard, brittle materials, and even less about how these processes lead to the initiation of cracks. In this paper, transmission electron microscopy is used to study the deformation structure within Vickers indentation zones of single‐crystal sapphire with {} surface orientation. The relative misorientation of regions within these zones, as mapped by convergent‐beam kikuchi patterns, is found to be severe, indicative of shear processes operating close to the cohesive limit. Two principal types of deformation are identified, basal twinning and pyramidal slip. Incipient microcracks are observed at both the twin interfaces and the slip planes. These incipient “flaws” act as nucleation sites for the ensuing radial and lateral cracks.
Strength Distributions of a Quench‐Strengthened Aluminosilicate Ceramic
Authors: OHIRA HIROYUKI , BRADT RICHARD C.
Published: March 2005

The quench strengthening of an aluminosilicate ceramic body was studied by measuring the strengths and determining the strength distributions, estimating the residual compressive stresses at the surface by measuring the bending moments, and directly observing the surface crack patterns of quench‐strengthened specimens. When considered in combination, these related results enable the assessment of the individual contributions of the residual compressive surface stresses and the changes in the flaw populations to the quench strengthening phenomenon. The quench strengthening phenomenon is discussed as a combination of those features of the process and a general schematic diagram of the phenomenon is presented.
Atomistic Simulation of Defect Structures and Ion Transport in α‐Fe2O3 and α‐Cr2O3
Authors: CATLOW C. RICHARD A. , CORISH JOHN , HENNESSY JOHN , MACKRODT WILLIAM C.
Published: March 2005

Computer‐modelling techniques are applied to the calculation of defect formation and migration energies in α‐Fe2O3 and α‐Cr2O3: both electronic and lattice defects are considered. The results are used to predict Arrhenius energies for cation and anion migration in different composition and temperature regimes and show reasonable agreement with experimental data where these are available.
BaO‐TiO2‐WO3 Microwave Ceramics and Crystalline BaWO4
Authors: Nishigaki Susumu , Yano Shinsuke , Kato Hiroshi , Hirai Takami , Nonomura Toshio
Published: March 2005

Microwave ceramic resonators composed of BaO‐TiO2‐WO3 were developed. The effect of WO3 addition on the system of BaO·xTiO2·(1+x)yWO3 (x=4 and 4.5, y=0 to 0.04) was studied. The ceramics of this system are composed of crystallines including Ba2Ti9O20, BaTi4O9, BaWO4, and TiO2. At y=0.02, the BaO·4TiO2·0.1WO3 ceramic was found to have excellent microwave properties such as ε=35, Q=8400 at 6 GHz, and nearly 0 ppm/°C of τf.
Homogeneity and Properties of Lead Zirconate Titanate Prepared by a Combination of Thermal Spray Decomposition Method with Solid‐Phase Reaction
Authors: Kakegawa Kazuyuki , Arai Kenji , Sasaki Yoshinori , Tomizawa Toshiaki
Published: March 2005

A solution containing titanium and zirconium ions was spray decomposed. The product thus obtained was mixed with PbO powder and fired at high temperatures to obtain Pb(Zr,Ti)O3 (PZT). A phase of PZT began to form at a very low temperature (450°C). This formation reaction was complete at about 650°C. Reactivity of the spray‐decomposed product with lead titanate powder was high. For PZT prepared by this process with a firing condition of 1100°C for 1 h, the compositional fluctuation was estimated from the width of the X‐ray diffraction peaks. Fluctuations were about 3 at.%. This value agreed with that estimated from the range of the tetragonal‐rhombohedral coexistence region near the morphotropic phase boundary. The peak of the dielectric constant near the Curie temperature was sharp and very high (ε∼12000).