Bonelike Coatings onto Ceramics by Reactive Magnetron Sputtering

Bonelike coating of partially carbonated, calcium hydroxyapatite onto strong ceramics and metals is one of the current objectives in biomaterials science for the development of bioactive implant materials. We recently accomplished bonelike apatite coating onto ceramic alumina by the newly developed reactive rf-magnetron sputtering method, which was undertaken in a mixed CO₂/Ar gas. The key of this method is the use of calcium phosphate glass targets with much lower Ca/P ratios than the stoichiometric value of hydroxyapatite. Surface analyses by XRD, EDX, and FT-IR identified the formation of bonelike carbonated calcium hydroxyapatite, in which CO^2-₃ ions occupied the lattice positions of PO^3-₄. The bioactivity of the coated ceramic materials was confimed by in vitro experiments on the bonelike crystal growth on their surfaces in a simulated body fluid, and the growth rate on the coated layers was experimentally proved to be much faster than that on uncarbonated hydroxyapatite     

Concentrations of Residual Carbonate Ions in the Bi-Sr-Ca-Cu-O Glasses

It was found that the IR absorption bands appearing at 600 to 1600 cm⁻¹, which had been previously assigned to the fundamental vibrations of [BiO₃] or [BiO₆] polyhedra, are due to residual carbonate ions (CO²⁻₃) dissolved in Bi-Sr-Ca-Cu-O glasses. The concentrations of the remaining CO²⁻₃ in the Bi_2.2Sr₂Ca₁Cu₂O _x glasses that melted at 1100° and 1400°C are 170 × 10⁻⁵ mol/cm³ (3.3 mol%) and 3.2 × 10⁻⁵ mol/cm³ (0.25 mol%), respectively. The apparent activation energy for the dissociation of the carbonates was approximately 220 kJ/mol. The CO²⁻₃ content in the precursor glasses did not significantly affect the superconducting properties of the resulting glass–ceramics.     

Phase Equilibria and Structural Species in NdCl3–NaCl, NdCl3–CaCl2, PrCl3–NaCl, and PrCl3–CaCl2 Systems

Equilibrium phase diagrams for the systems NdCl₃–CaCl₂ and NdCl₃–NaCl were determined by differential thermal analysis. A simple eutectic was observed at 59 ± 1 mol% CaCl₂ and 600°± 2°C in the NdCl₃–CaCl₂ system. A compound NaCl.3NdCl₃ which melts incongruently at 545°± 5°C to NdCl₃ and a liquid containing approximately 47 mol% NaCl, and a eutectic at 68 mol% NaCl and 439°± 2°C were found in the NdCl₃–NaCl system. On the basis of agreements between the activities calculated by the Clausius–Clapeyron equation and Temkin's model using the present data for the NdCl₃–CaCl₂ system and the literature data for the PrCl₃–CaCl₂ system, the melts in the former system consist of Nd³⁺, Ca²⁺, and Cl⁻ ions and in the latter system of Pr³⁺, Ca²⁺, and Cl⁻ ions. The above approach indicates the presence of Na⁺, Cl⁻, and NdCl^2-₅ ions in the NaCl-rich melts and Nd³⁺, Cl⁻, and NdCl⁻₄ in the NdCl₃-rich melts in the NdCl₃–NaCl system. Analogous ions were indicated in the melts of the PrCl₃–NaCl system.     

Dehydroxylation of Porous Glass by Means of Chlorine

Water in reconstructed 96 % SiO₂ glass is effectively removed by exposing porous glass to chlorine at high temperatures prior to final firing in vacuum. The annealing point of the final glass is markedly increased by such treatment, which results in elimination of the OH band due to replacement of OH⁻ by Cl⁻ ions.     

Preparation and Cu+-Ion-Conducting Properties of the Glasses in the System CuBr–Cu2MoO4–Cu3PO4

Cu⁺-ion-conducting glasses were prepared in the pseudoternary system CuBr–Cu₂MoO₄–Cu₃PO₄, and the ion-conducting properties of the glasses obtained were compared to those of the glasses in the system CuI—Cu₂MoO₄—Cu₃PO₄, which contain CuI instead of CuBr. The CuBr—Cu₂MoO₄—Cu₃PO₄ glasses showed high ion conductivities in the range of 10⁰ to 10⁻² S · m⁻¹ at room temperature. The change in ion-conducting properties caused by the substitution of PO^3-₄ anions for MoO²⁻₄ anions was larger than the change caused by the substitution of Br⁻ anions for I⁻ anions in the glasses containing a constant amount of the cuprous halides.     

Ionic Substitutions in Biphasic Hydroxyapatite and β-Tricalcium Phosphate Mixtures: Structural Analysis by Rietveld Refinement

The structural information on the influence of ionic additions in biphasic (hydroxyapatite (HAP) and β-tricalciumphosphate (β-TCP)) mixtures ranging from single ionic substitutions to combined ionic substitutions of most of the essential ions embedded in biological apatite was analyzed through the Rietveld refinement technique. The results have proved that the determined quantitative phase composition of HAP and β-TCP in biphasic mixtures was dependent on the initial calcium (Ca) deficiency of the precursor powders precipitated from the different molar concentrations used in the synthesis. The substitution of cations (Na⁺, Mg²⁺, and K⁺) improved the stabilization of the β-TCP structure whereas anions (F⁻ and Cl⁻) were found incorporated at the OH⁻ site of the HAP phase. Rietveld analysis of X-ray powder diffraction data from the present study proved to be a powerful technique to describe the position and occupancy of certain ions like Mg²⁺ and Cl⁻ in the biphasic mixtures. However, it has also shown limitations in tracking back other ions like Na⁺, K⁺, and F⁻, which require the use of other complementary characterization methods.     

Optical Absorption Spectra of Chlorine-Associated Defect Centers in an Irradiated ZrF4-Based Glass

The optical absorption spectra of an irradiated zirconium-barium-lanthanum aluminum- lithium fluoride glass prepared with 1 wt% BaC12 were resolved into Gaussian bands identified as the V_k, and V_H centers, Zr³⁺, and two bands associated with Cl, i.e., FCl⁻ at 4.78 eV and Cl⁻₂ at 3.90 eV. These latter bands are more thermally stable than the VH and V, trapped hole centers, persisting to 450 and 550 K, respectively.     

Vibrational Spectra of Hydrothermally Prepared Hydroxyapatites

Apatites can be used as bioceramic materials for tooth and bone implants. Infrared (4000 to 400 cm⁻¹) and laser-Raman spectra were obtained for hydrothermally prepared hydroxyapatites with the general formula X₁₀(PO₄)₆(OH)₂ where X= Ca²⁺ Sr²⁺, Ba²⁺, or Pb²⁺ Fundamental vibrational modes were identified and empirical band assignments made. Analysis of the vibrational spectra led to the reassignment of the v₂ mode to a higher wave-number, lower-intensity band (e.g. ∼470 cm⁻¹ for Ca hydroxyapatite). Effects of solid-state interaction were noted in the vibrational spectra and interpreted by factor-group analysis. An "effective" factor group C_6h, which neglects the locations of the OH⁻ ions, best describes the vibrational spectra of the hydroxyapatites.     

Effect of Anions on Hot-Pressing of MgO

Anion impurities (S²⁻, Cl⁻, F⁻ and OH⁻) are shown to be deleterious to the densification of MgO by hot-pressing. The magnitude of the effect decreases in the order in which the anions are listed and is reduced as temperature increases. The effect is suggested to result from gas pressures within the compact and die cavity, and the magnitude of interference with densification is related to both the vapor pressure of the impurity and its rejection from the lattice (insolubility).     

Alkoxide-Hydroxide Route to Syntheltize BaTiO3-Based Powders

When preparing homogeneous, fine barium titanate powders, the major difficulty is to avoid the spontaneous self-condensation between the Ti-OH groups. In the usual way of preparing fine barium titanate powders, chelating agents (citrate, oxalate) or simply unidentate ligands (alkoxy or carboxyl groups) are used to complex titanium atoms. Another way is to mix barium and titanium precursors in a strongly basic medium. The condensation between the Ti(OH)^2-₆Ba²⁺ species directly gives the perovskite compound. Using an alkoxide-hydroxide route, a homogeneous Ba-Ti solution was prepared that completely advanced by condensation between the Ti(OH)^2-₆Ba²⁺ species and led to a controlled-stoichiometry powder. Concerning pure barium titanate, dried powders exhibited the cubic perovskite structure, and a direct sintering at 1150°C, without calcination, led to highly dense BaTiO₃ bodies with fine-grained uniform microstructure (1 μm) that exhibited a high permittivity value at room temperature ( K = 5400). The alkoxide-hydroxide method was also used to prepare dense alkaline-earth perovskite ceramics with complex compositions.     

Chemical Instability of Metal-Deficient Hexagonal Ferrites with W Structure

The hexagonal ferrite W=BaFe²⁺₂Fe³⁺₁₆O₂₇, which is in equilibrium with oxygen under 0.015 atm at 1350^°C, is oxidized in the range 250^° to 1100^°C in the same atmosphere to BaFe³⁺_16+2x Fe²_2-3x> _x O₂₇ with 2–3 x <0.03. The metal-deficient W structure is chemically unstable and decomposes after longer annealing at the same temperature. This difference in oxidation and decomposition rate is attributed to a difference in the diffusion rate of barium and iron ions.     

Microwave Characteristics of A(B3+1/2B5+1/2)O3 Ceramics (A = Ba, Ca, Sr; B3+= La, Nd, Sm, Yb; B5+= Nb, Ta)

Dielectric properties of A(B³⁺_1/2B⁵⁺_1/2)O₃ (A = Ba, Ca, Sr; B³⁺= La, Nd, Sm, Yb; B⁵⁺= Nb, Ta) ceramics have been investigated at microwave frequencies. Sr(B³⁺_1/2B⁵⁺_1/2)O₃ and Ca(B³⁺_1/2B⁵⁺_1/2)O₃ ceramics have relative dielectric constants (ε _r ) above 20 and negative temperature coefficients of resonant frequency (T _f ). In the group of Ba(B³⁺_1/2B⁵⁺_1/2)O₃ ceramics, T _f changes from + 118 ppm/° to nearly zero according to the kinds of B-site ions. Among the ceramics investigated, Sr(Sm_1/2Ta_1/2)O₃ ceramics have the highest Q values at microwave frequencies. For Sr(Sm_1/2Ta_1/2)O₃ ceramics Q = 7000, ε _r = 27.7, and T _f =−62.5 ppm/° at 8.5 GHz. The microstructure of Sr(Sm_1/2Ta_1/2)O₃ ceramics is composed of a matrix of the ternary compound (Sr-Sm-Ta-O system) and secondary phase grains of the binary compound (Sm-Ta-O system).     

Oxygen Ion Activity and the Solubility of Sulfur Trioxide in Sodium Silicate Melts

The solubility of sulfur trioxide in sodium silicate melts was determined from 1150° to 1250°C by equilibrating melts in gas mixtures of known contents of sulfur dioxide and oxygen. Sulfate forms according to the reactions: O^2-+ SO₂+ 1/2O₂= O^2-+ SO₃= SO₄^2-. The data obtained at 1200°C were interpreted by the linear equation: log(SO₄^2-) = log( P so₂½ P o₂^1/2) + log Y in which Y is a function of the soda/silica ratio. A series of parallel lines was obtained. Relative free oxygen ion activities calculated for 1200°C were in good agreement with theoretical values calculated from the thermodynamic model of Toop and Samis.     

Electrical Resistivity of Magnetite and Nickel Ferrous Ferrite Above 300°K

The electrical resistivity of Fe²⁺_0.95Fe³⁺_2.05O²⁺₄, Ni²⁺_0.51Fe²⁺_0.46Fe_1.95,³⁺O²⁻₄, and Ni_0.89,²⁺Fe²⁺_0.13Fe³⁺_2.11O²⁻₄ single crystals was determined at >300°K. The dc resistivity up to 800°K shows a monotonic decrease with increased temperature, with an average activation energy of 0.065 eV independent of temperature and Fe^z+ concentration. The ac resistivity, at frequencies of 540 kHz to 34 MHz up to 450°K, shows temperature and frequency dependences of the relative dielectric constant similar to that found when true dielectric relaxation occurs, with the activation energy depending slightly on frequency and ferrous ion content.     

Formation Mechanism of Hydrous-Zirconia Particles Produced by Hydrolysis of ZrOCl2 Solutions: II

The primary and secondary particle sizes of monoclinic hydrous-ZrO₂ particles produced by the hydrolysis of various ZrOCl₂ solutions, with and without the addition of NaCl, CaCl₂, or AlCl₃, were measured using X-ray diffraction and transmission electron microscopy in order to clarify the formation mechanisms of primary and secondary particles. The primary particle size of hydrous ZrO₂, under a constant ZrOCl₂ concentration, decreased monotonously with increasing Cl⁻-ion concentration. On the contrary, the secondary particle size increased monotonously with increasing Cl⁻-ion concentration. The present experimental results revealed that the primary and secondary particle sizes of hydrous ZrO₂ are controlled primarily by the concentrations of H⁺ and Cl⁻ ions produced during hydrolysis, and are independent of the type of added metal ions. The formation mechanisms of the primary and secondary particles of hydrous ZrO₂ were determined on the basis of the present experimental results.     

Piezoelectric Properties of Pb[Zr0.45Ti0.5-xLux(Mn1/3Sb2/3)0.05]O3 Ceramics

The piezoelectric properties of Pb[Zr_0.45Ti_{0.5- x} Lu _x (Mn_1/3-Sb_2/3)_0.05]O₃ ceramics, with 0 lessthan equal to x lessthan equal to 0.03, have been investigated. The partial substitution of Ti⁴⁺ with Lu³⁺ permitted improvement of the electromechanical coupling factor ( k _p), the dielectric constant (epsilon^T₃₃), and the piezoelectric constant ( d ₃₃), while the dielectric loss (tan delta) increased and the mechanical quality factor ( Q _m) decreased with an increase of x . A pertinent piezoelectric material for actuator applications was Pb[Zr_0.45Ti_0.48Lu_0.02(Mn_1/3Sb_2/3)_0.05]O₃, and the piezoelectric properties were k _p = (58.5 ± 0.5)%, epsilon^T₃₃ = 32 ± 25, d ₃₃ = (373 ± 6) 10^-12 C/N, Q _m = 714 ± 22, and tan delta = (0.98 ± 0.03)%.     

Incorporation of Aliovalent Dopants into the Bismuth-Layered Perovskite-Like Structure of BaBi4Ti4O15

The solid solubility of the aliovalent dopants Fe³⁺ and Nb⁵⁺ in the BaBi₄Ti₄O₁₅ compound, a member of the family of Aurivillius bismuth-based layer-structure perovskites, has been studied using quantitative wavelength-dispersive spectroscopic microanalysis (SEM/EPMA) in combination with X-ray powder diffractometry (XRPD). The samples with nominal (starting) compositions corresponding to the chemical formulas BaBi₄Ti_{4–4 X} Fe_{4 X} O₁₅ and BaBi₄Ti_{4–4 X} Nb_{4 X} O₁₅ were prepared by hot forging a mixture of BaTiO₃ and Bi₄Ti₃O₁₂ with additions of Fe₂O₃ or Nb₂O₅ followed by a long annealing at 1100°C. The study showed that an excess charge introduced into the structure by the substitution of Ti⁴⁺ ions with aliovalent dopants was preferentially compensated by a change in the ratio of Ba²⁺ to Bi³⁺ ions in the host structure according to the general formulas of the solid solutions Ba_{1–4 X} Bi_{4+4 X} Ti_{4–4 X} Fe^'_{4 X} O₁₅ and Ba_{1+4 X} Bi_{4–4 X} Ti_{4–4 X} Nb^·_{4 X} O₁₅.     

Physicochemical Mechanism for the Continuous Reaction of γ-Al2O3-Modified Aluminum Powder with Water

Previous experiments showed that γ-Al₂O₃-modified Al powder could continuously react with water and generate hydrogen at room temperature under atmospheric pressure. In this work, a possible physicochemical mechanism is proposed. It reveals that a passive oxide film on Al particle surfaces is hydrated in water. OH⁻ ions are the main mobile species in the hydrated oxide film. When the hydrated front meets the metal Al surface, OH⁻ ions react with Al and release H₂. Because of the limited H-soluble capacity in small Al particles and the low permeability of the hydrated oxide film toward H⁺ species, H₂ molecules accumulate and form small H₂ gas bubbles at the Al:Al₂O₃ interface. When the reaction equilibrium pressure in H₂ bubbles exceeds a critical gas pressure that the hydrated oxide film can sustain, the film on the Al particle surfaces breaks and the reaction of Al with water continues. As the surface oxide layer on modified Al particles has a lower tensile strength, the critical gas pressure in H₂ bubbles is lower so that under an ambient condition, the reaction of modified Al particles with water is continuous. The proposed mechanism was further confirmed by a new experiment showing that the as-received Al powder could continuously react with water at temperatures above 40°C and under low vacuum, because the vacuum makes the critical gas pressure in H₂ bubbles decrease as well.     

Temperature Dependent Luminescence of Yellow-Emitting α-Sialon:Eu2+ Oxynitride Phosphors for White Light-Emitting Diodes

Yellow-emitting α-sialon:Eu²⁺ phosphors have been reported as interesting down-conversion luminescent materials in white LEDs. In this work, the thermal quenching of α-sialon:Eu²⁺ with the compositions of M^val+_{( m /val+)}Si_{12−( m + n )}Al _{m + n} O _n N_{16− n} (M=Ca, Mg, Lu) is studied by investigating the effects of chemical composition, activator concentration, and substitution cation on the temperature-dependent luminescence. The chemical composition of α-sialon:Eu²⁺ was varied in a wide range (0.5≤ m ≤2.0, 1≤ n ≤1.8). It shows that the m value significantly affects the thermal quenching of α-sialon, whereas the n value hardly does. This difference is ascribed to the obvious lattice expansion and the increase of absolute activator concentration as m increases. The thermal quenching increases with increasing the Eu²⁺ concentration, which is due to enhanced Stokes shift. The type of substitution cation also has an influence on thermal quenching. Among the substitution cations in this work, Lu-α-sialon:Eu²⁺ exhibits largest thermal quenching. Photoionization is considered as the mechanism for the thermal quenching of Lu-α-sialon: Eu²⁺.     

Internal Oxidation of Ce3+-BaTiO3 Solid Solutions

The reoxidation process in highly Ce³⁺-doped BaTiO₃ ceramics was studied using TEM. Samples of two different types of solid solutions, Ba_1−XCe³⁺ _X Ti_1−X/4( V _Ti) X/4 O₃ and Ba_1−XCe³⁺ _X Ti⁴⁺_{1− X} Ti³⁺ _X O₃, were prepared by sintering oxide mixtures in air and in a reducing atmosphere, respectively. The solid solutions were reoxidized by annealing in air at high temperatures (1000°—1100°C). As a result of internal oxidation of Ce³⁺ and Ti³⁺, fluorite CeO₂ and monoclinic Ba₆Ti₁₇O₄₀ phases were precipitated in the perovskite matrix. In Ba_1−XCe³⁺ _X Ti_1−X/4( V _Ti)X/4O3 solid solution precipitates nucleate heterogeneously at grain boundaries and at extended defects inside the grains, whereas in Ba_1−XCe³⁺_XTi⁴⁺_1−XTi³⁺_XO₃ solid solution precipitates are nucleated mainly homogeneously inside reoxidized perovskite grains. The form of the precipitates and their orientational relationship with the matrix, as well as the mechanism of internal oxidation, are discussed.