Journal of the American Ceramic Society
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Dielectric Temperature Characteristics of Cerium‐Modified Barium Titanate Based Ceramics with Core—Shell Grain Structure Various particle sizes of starting barium titanate were used to investigate the effect of chemical inhomogeneity on the dielectric temperature characteristics of a dilute solid solution of cerium‐modified barium titanate. Transmission electron microscopy and energy dispersive spectroscopy confirmed three distinct areas in the modified barium titanate: a grain core, a grain shell, and gradient regions. The grain size and volume fractions of the grain core were somewhat proportional to the particle size of the starting barium titanate. The dielectric temperature characteristics will be explained in the present paper in terms of the three inhomogeneous regions. Actually, the dielectric temperature characteristics of the large grains (3μm) proved to be a function of variation in the T c values, whereas those of the small grains (,3μm) were a function of both the T c values and the internal stress.
Journal of the American Ceramic Society - Tập 80 Số 1 - Trang 106-112 - 1997
Piezoelectric and Dielectric Properties of (Ba<sub>1−<i>x</i></sub>Ca<i><sub>x</sub></i>)(Ti<sub>0.95</sub>Zr<sub>0.05</sub>)O<sub>3</sub> Lead‐Free Ceramics Lead‐free (Ba1−x Cax 0.95 Zr0.05 )O3 (x =0.02–0.20) ceramics were prepared successfully using a solid‐state reaction technique. The polymorphic phase transitions from orthorhombic to tetragonal phase around room temperature were identified in the composition range of 0.06<x <0.10. A high piezoelectric coefficient of d 33 =365 pC/N and high planar electromechanical coupling factor of k p =48.5% were obtained for the sample of x =0.08. With the doping of Ca content, the orthorhombic–tetragonal phase transition point shifted toward room temperature while the relative high Curie temperature (T c ) was still maintained about 110°C.
Journal of the American Ceramic Society - Tập 93 Số 10 - Trang 2942-2944 - 2010
Preparation and Characterization of Hydroxyapatite Coatings on Ti6Al4V Alloy by a Sol‐Gel Method Hydroxyapatite coatings on Ti6Al4V substrates were prepared by a sol–gel method, and characterized by X‐ray diffraction, scanning electron microscopy, and infrared reflection spectroscopy. The coatings obtained at 500°C in air had a hydroxyapatite phase, some of which was carbonated hydroxyapatite, and had a dense and smooth morphology. When the coatings were treated in a simulated body fluid, the coatings had an increase in large hydroxyapatite grains, and a rough and porous morphology. The adhesive strength of the coatings was more than 14 MPa.
Journal of the American Ceramic Society - Tập 82 Số 1 - Trang 27-32 - 1999
Evaluated Material Properties for a Sintered alpha‐Alumina Results of a data evaluation exercise are presented for a particular specification of sintered alpha‐alumina (mass fraction of Al2O3, ≥0.995; relative density (rho/rhotheoretical), ≥0.98; and nominal grain size, 5 μm). A comprehensive set of material property data is established based on published physical, mechanical, and thermal properties of alumina specimens that conform to the constraints of the material specification. The criteria imposed on the properties are that the values should be derived from independent experimental studies, that the values for physically related properties should be mutually self‐consistent, and that the sets of values should be compatible with established material property relations. The properties assessed in this manner include crystallography, thermal expansion, density, sound velocity, elastic modulus, shear modulus, Poisson's ratio, bulk modulus, compressive strength, flexural strength, Weibull characteristic strength, Weibull modulus, tensile strength, hardness, fracture toughness, creep rate, creep rate stress exponent, creep activation energy, friction coefficient, wear coefficient, melting point, specific heat, thermal conductivity, and thermal diffusivity.
Journal of the American Ceramic Society - Tập 80 Số 8 - Trang 1919-1928 - 1997
The Filler Effect: The Influence of Filler Content and Surface Area on Cementitious Reaction Rates Finely ground mineral powders are known to accelerate cement hydration rates. This “filler effect” has been attributed to the effects of dilution (w/c increase) when the cement content is reduced or to the provision of additional surface area by fine powders. The latter contribution (i.e., surface area increase) is speculated to provide additional sites for the nucleation of the hydration products, which accelerates reactions. Through extensive experimentation and simulation this study describes the influence of surface area and mineral type (e.g., quartz or limestone) on cement reaction rates. Simulations using a boundary nucleation and growth (BNG ) model and a multiphase reaction ensemble (MRE ) indicate that the extent of the acceleration is linked to the: (1) magnitude of surface area increase and (2a) capacity of the filler's surface to offer favorable nucleation sites for hydration products. Other simulations using a kinetic cellular automaton model (HydratiCA ) suggest that accelerations are linked to: (2b) the interfacial properties of the filler that alters (increases or decreases) its tendency to serve as a nucleant, and (3) the chemical composition of the filler and the tendency for its dissociated ions to participate in exchange reactions with the calcium silicate hydrate product. The simulations are correlated with accelerations observed using isothermal calorimetry when fillers partially replace cement. The research correlates and unifies the fundamental parameters that drive the filler effect and provides a mechanistic understanding of the influence of filler agents on cementitious reaction rates.
Journal of the American Ceramic Society - Tập 96 Số 6 - Trang 1978-1990 - 2013
Understanding the Filler Effect on the Nucleation and Growth of C‐S‐H The “filler effect”, due to the physical presence of mineral additions in cement, is mainly known to accelerate the hydration of the clinker component. Previously, this was attributed to the surface of the filler providing nucleation sites for C‐S‐H as there is a clear dependence on the surface provided by the filler particles. Our results reveal that the increase in nucleation is quite low compared to the area provided. Based on the isothermal calorimetry experiments and SEM images, we demonstrate that the most important parameter is the interparticle distance. We propose that this is mainly the result of the shearing conditions rather than extra surface available for C‐S‐H as formerly assumed. Quantitatively slag and fly ash behave very similarly to quartz. Limestone, on the other hand, seems also to stimulate C‐S‐H nucleation giving it a higher efficiency in accelerating clinker hydration.
Journal of the American Ceramic Society - Tập 97 Số 12 - Trang 3764-3773 - 2014
Mo<sub>5</sub>Si<sub>3</sub>‐Boron Composites Fabricated by Induction Plasma Deposition and Their High‐Temperature Oxidation Resistance Induction plasma spraying was used to produce freestanding parts of Mo5 Si3 ‐boron (Mo5 Si3 ‐B) composite materials. Four different Mo5 Si3 ‐B compositions were prepared and oxidized isothermally at 1210°C in air at atmospheric pressure. The high‐temperature oxidation performance of these materials was dependent strongly on the boron content in the specimens. The composite that contained 2.0 wt% boron exhibited excellent resistance to oxidation, as indicated by the almost‐zero change in specimen mass after oxidation for 24 h.
Journal of the American Ceramic Society - Tập 82 Số 8 - Trang 1965-1968 - 1999
High‐Temperature Oxidation of Molybdenum Disilicide The oxidation of MoSi2 in air at atmospheric pressure was studied by electron diffraction, X‐ray diffraction, and thermogravimetric analyses. The oxidation process occurs in two parts: (1) formation of MoO3 and SiO2 at temperatures below the boiling point of MoO3 , and (2) formation of Mo5 Si3 and SiO2 at higher temperatures. Evidence is presented which indicates that oxygen permeation through a silica layer, which may be of a mixed crystalline‐glassy nature, controls reaction rate at high temperatures and that Mo5 Si3 is present directly beneath the protective oxide. The activation energy for oxidation of MoSi2 above 1200°C was calculated as 81.3 kcal mole−1 .
Journal of the American Ceramic Society - Tập 49 Số 4 - Trang 173-177 - 1966
Equilibrium Dependence of the Conductivity of Pure and Tin‐Doped Indium Oxide on Oxygen Partial Pressure and Formation of an Intrinsic Defect Cluster The dependence of the electrical conductivity of pure (99.999%) and tin‐doped indium oxide (In2 O3 ) ceramics on oxygen partial pressure
was investigated at 800° and 850°C. The doping amount of tin was 100–1000 ppm, which is within the solubility limit at the temperatures measured. The conductivity of doped ceramics was independent of
and the carrier concentration was almost the same as the estimated value from the tin content. The conductivity of the pure In2 O3 ceramic was proportional to By considering a singly charged defect cluster of interstitial indium and interstitial oxygen , the conductivity dependence is deduced to be proportional to There are large and three adjacent vacant sites, 8a and 16c, in the In2 O3 structure to enter indium and oxygen.
Journal of the American Ceramic Society - Tập 91 Số 1 - Trang 240-245 - 2008
Ion Depletion of Glass at a Blocking Anode: I, Theory and Experimental Results for Alkali Silicate Glasses A theory is presented for the ion depletion of glass beneath a blocking anode. The theoretical model is based on the assumption that the alkali ions in an alkali silicate glass have a much greater mobility than the nonbridging oxygen ions in the alkali‐depleted region. In this case, the dc conduction properties of the glass are determined by the motion of the uncombined oxygen ions in the depleted region. Expressions are derived for the spatial variation of the uncombined oxygen ions and for the current‐voltage relations in the high‐ and low‐field limits. In the high‐field limit, the theory predicts that the current will vary exponentially with the voltage; this behavior is shown in sodium silicate glasses.
Journal of the American Ceramic Society - Tập 57 Số 7 - Trang 291-294 - 1974
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