Structural Characterization and Protein Adsorption Property of Hydroxyapatite Particles Modified With Zinc Ions

Zinc-containing hydroxyapatite particles (Zn/HAp) were prepared by an ion exchange reaction process involving hydroxyapatite (HAp) particles with aqueous solutions containing various amounts of zinc nitrate. The Zn²⁺ ion was partially substituted for the Ca²⁺ ion position in the HAp lattice, and hence, the obtained samples had changed little in crystallinity, particle size, and specific surface area. Adsorption of bovine serum albumin (BSA) and β₂-microglobulin (β₂-MG) in solutions containing both BSA and β₂-MG was examined. As the Zn²⁺ ion content in the apatites increased, the adsorbed amount of BSA was almost constant, whereas that of β₂-MG increased.     

X-Ray Study of Phase Transitions in Ferroelectric PbNb2O6 and Related Materials

The phase transitions in PbNb₂O₆ and in compositions of the type Pb_1+x (B_xNb_1-x)O₆, where B = Ti⁴⁺, Zr⁴⁺, or Sn⁴⁺, have been investigated between 25° and 650°C. using X-ray and dilatometric techniques. The modified PbNb₂o₆ compositions possess orthorhombic PbNb₂O₆-type structure, with the additional Pb²⁺ ions occupying vacant lattice sites. The lattice parameters a and c expand and b contracts during heating until, at the ferroelectric Curie temperature, a and b suddenly coincide and c expands slightly. Besides this phase change at the Curie temperature, the nonstoichiometric compounds show an additional phase transition in the range 450° to 300°C. depending on composition. The intermediate phase of Pb_l+x(Ti₂Nb_1-z)₂O₆ appears to possess orthorhombic symmetry.     

An Alternative Chemical Route for the Synthesis and Thermal Stability of Chemically Enriched Hydroxyapatite

Hydroxyapatite (HAp: Ca₁₀(PO₄)₆(OH)₂) was synthesized by aqueous precipitation using CaCl₂ and Na₃PO₄ with NaOH added to ensure completion of the reaction at room temperature. The HAp powder prepared using stoichiometric amounts of NaOH was stable even at 1200°C, but the HAp prepared with sub-stoichiometric amounts of NaOH resulted in its transformation into β-tricalcium phosphate at 600°C. The reaction pH, X-ray diffraction, thermal analysis, scanning electron microscopy, Fourier transform infrared analyses and inductively coupled plasma-optical emission spectroscopy were used to characterize the phase purity, thermal stability, morphology, and chemical composition of the synthesized HAp powder.     

Effect of Preparation Temperature on the Lattice Parameter of Nickel Aluminate Spinel

Nickel aluminate spinels were prepared by solid-state reaction. Their lattice parameters ( a ₀) changed with preparation temperature, which was explained by cation distribution, vacancies formation, and cation entrance. When the preparation temperature increased from 1100° to 1200°C, a ₀ decreased with temperature as the result of the uptake of Al₂O₃. After 1200°C, a ₀ increased to temperature, which was attributed to some Ni²⁺ exchange with tetrahedral sites and some vacancies occupancy by Ni²⁺ and Al³⁺.     

Low Temperature Synthesis of Porous NZP Ceramics

Porous phase-pure NaZr₂(PO₄)₃ monoliths were synthesized at 850°C from gels that precipitated as a consequence of mixing water-soluble precursors. The sintering temperature was limited to 850°C to permit densification in a range where NZP exhibits a low coefficient of thermal expansion. Attempts to maximize mechanical properties were made by both physical and chemical means. Particulate hydroxyapatite (HAp) was physically blended with the precipitated gels to template the crystallization of NZP. Copper nitrate was dissolved into solution as a sintering aid to stimulate liquid-phase sintering during firing. NZP made without these additives attained a specific surface area of 30 m²/g. The addition of HAp reduced the internal surface area to 5 m²/g. X-ray diffraction and scanning electron microscopy did not detect the presence of HAp in the fired samples, indicating it had been consumed during firing. Copper nitrate decomposed to CuO and its presence as a sintering aid resulted in enhanced densification and greater strengths. The presence of 5% CuO (as copper nitrate) together with 5% HAp resulted in a 40% volume shrinkage during firing. The tensile strength attained for this composition was 20 MPa as compared with that of approximately 8 MPa for the compositions fired without additives.     

Mass Spectrometric Identification of Si–O–H(g) Species from the Reaction of Silica with Water Vapor at Atmospheric Pressure

A high-pressure sampling mass spectrometer was used to detect the volatile species formed from SiO₂ at temperatures between 1200° and 1400°C in a flowing water vapor/oxygen gas mixture at 1 bar total pressure. The primary vapor species identified was Si(OH)₄. The fragment ion Si(OH)₃⁺was observed in quantities 3 to 5 times larger than the parent ion Si(OH)₄⁺. The Si(OH)₃⁺ intensity was found to have a small temperature dependence and to increase with the water vapor partial pressure as expected. In addition, SiO(OH)⁺, believed to be a fragment of SiO(OH)₂, was observed. These mass spectral results were compared to the behavior of silicon halides.     

Interaction of Low-Expansion NZP Ceramics with Na2SO4 at 1000°C

The interaction between several low-expansion NZP materials and Na₂SO₄ at 1000°C in pure O₂ was studied. Ba_1.25Zr₄P_5.5Si_0.5O₂₄ experienced extensive cracking and delamination upon reaction with Na₂SO₄. On the other hand, Ca _0.5Sr_0.5 Zr₄P₆ O₂₄ remained intact in terms of visual appearance and had no significant weight loss or gain. However, the ion exchange between Na⁺ ions and Ca⁺² ions was observed to be sufficiently rapid to allow the penetration of the Na⁺ ions into the test specimens in 100 h. The segregation of Ca to the specimen surface was observed due to the ion exchange. Ca_0.6Mg_0.4Zr₄P₆O₂₄ was also tested, but its stability could not be properly assessed because the as-received specimens contained a significant amount of MgZr₄P₆O₂₄ as an impurity phase.     

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.     

Copper ⇌ Alkali Ion Exchange of Alkali Aluminosilicate Glasses in Copper-Containing Molten Salt: II, Divalent Copper Salts, CuCl2 and CuSO4

The ion-exchange mechanism between copper and alkali ions, when 20R₂O · 10Al₂O₃· 70SiO₂ (R = Li, Na, and K) glasses are immersed in divalent copper-containing molten salts in air and nitrogen at 550°C, has been investigated. In molten CuCl₂, the ion-exchange behavior in both air and nitrogen was very close to that in molten CuCl in air reported previously. This is explained by assuming that CuCl₂ decomposes into CuCl and Cl₂ at 550°C and the Cu⁺ ions thus formed mainly diffuse in glasses to replace alkali ions, where Cl₂ acts as an oxidizing agent just like oxygen. In the case of molten CuSO₄─₂SO₄, a small amount of Cu⁺ which is present in the molten state plays a primary role in the Cu ⇌ R⁺ ion exchange process, although the contribution of direct Cu²⁺⇌ 2R⁺ ion exchange cannot be ignored.     

Effect of CuO on the Sintering Temperature and Piezoelectric Properties of (Na0.5K0.5)NbO3 Lead-Free Piezoelectric Ceramics

When a small amount of CuO was added to (Na_0.5K_0.5)NbO₃ (NKN) ceramics sintered at 960°C for 2 h, a dense microstructure with increased grains was developed, probably due to liquid-phase sintering. The Curie temperature slightly increased when CuO exceeded 1.5 mol%. The Cu²⁺ ion was considered to have replaced the Nb⁵⁺ ion and acted as a hardener, which increased the E _c and Q _m values of the NKN ceramics. High piezoelectric properties of k _p=0.37, Q _m=844, and ɛ₃ ^T /ɛ₀=229 were obtained from the specimen containing 1.5 mol% of CuO sintered at 960°C for 2 h.     

Preparation by a Sol-Gel Process of Borosilicate Glasses Containing Microcrystals of Tellurium and Zinc Telluride

Borosilicate glasses, 5B₂O₃· 95SiO₂ (mol%), containing TeO₂ and ZnO nominally equivalent to 10 wt% Te and ZnTe were prepared by a solgel method from Si(OC₂H₅)₄, B(OCH₃)₃, H₆TeO₆, and Zn(NO₃)₂. A study by electron spectroscopy for chemical analysis (ESCA) showed that glasses heated at high temperature (450°C) in air contained both Te⁶⁺ and Te⁴⁺ ions on the surface layer, but that mainly Te⁴⁺ ions occurred inside the bulk glass. When solgel-derived borosilicate glasses containing the TeO₂ compound were reduced at elevated temperature in a hydrogen atmosphere, Te crystallites ranging in size from 4 to 15 nm were produced at a lower temperature, between 200° and 250°C. The absorption edge moved from the infrared to the visible wavelength region as the particle size decreased to about 4 nm. For glasses containing both TeO₂ and ZnO, ZnTe crystallites formed at high temperature—over 300°C—and existed along with the Te phase.     

Orange- and Violet-Emitting Long-Lasting Phosphors

Orange phosphorescence from Eu³⁺-activated CaO and SrO and violet phosphorescence from Pb²⁺-activated SrO were clearly observed after the materials had been excited with ultraviolet light. The orange phosphorescence resulted from ⁵ D ₀ to ⁷ F ₁ transitions of the Eu³⁺ ions and the violet from ³ P ₀ to ¹ S ₀ transitions of the Pb²⁺ ions. The phosphorescence lasted >1 h. Trapped-electron centers and hole centers introduced into the CaO and SrO hosts by the ultraviolet light appear to have been responsible for generating the long-lasting phosphorescence.     

Axial Thermal Expansion of TetragonaI ZrO, Between 1150° and 1700°C

The lattice constants for three samples of tetragonal ZrO₂ were measured in a high-temperature X-ray diffractometer in the range 1150° to 1700°C in an ambient air atmosphere. The unrefined lattice constants were the same for these materials only after each had been previously heat-treated at 1550° to 1750°C in an ambient air atmosphere. The thermal expansions of the two axes are linear and are given by: a value, A = 3.588₂+ 4.50 X 10+(T) , within 0.001₃ A; and c value, A = 5.188₂+ 7.57 × 10⁻⁵(T), within 0.002₂ A, where T is in °C for the range 1150° to 1700°C. The lattice constant values are a = 3.639₉ A and c = 5.275₈ A at 1150°C and a = 3.678₂ A and c = 5.339₇ A at 1700°C.     

Phase Diagram of the System BaO-Fe2O3

The phase diagram of the system BaO-Fe₂0₃ was determined by X-ray diffraction, melting-point measurement, and microscopic methods. Since the reduction of Fe³⁺ to Fe²⁺ was observed by chemical analysis in the samples heated at high temperature, especially in molten samples, the samples were heated at 1 atmosphere pressure of oxygen in the temperature region in which the liquid was in equilibrium; 1 atmosphere pressure of oxygen was su5cient to restrain the reduction of Fe³⁺. In the temperature region of solid-solid equilibrium, the dissociation was not observed even when the samples were heated in air. BaO - 6Fe₂O₃ formed a solid solution with BaO.Fe₂0₃. The BaO:Fe₂0₃ ratio of the solid solution was BaO.4.5Fe₂0₃ at 1350°C. and BaO. 5.0Fe₂0_a at 800°C. The precipitation micro-structures of each primary solid solution were observed.     

Strengthening of Alkali Halides by Divalent-Ion Additions

Single crystals of NaCl, NaBr, KCl, and KBr containing divalent additions of Ca²⁺, Sr²⁺, and Ba²⁺ were tested mechanically. In the solution-treated condition, the yield strength, σ _v , as determined from compression testing in a 〈100〉 direction is essentially dependent on the concentration of the dopant only and is independent of the species of either the dopant or of the host material. All crystals soften on aging, with the exception of the NaCl:Ca²⁺, NaBr:Ca²⁺, and NaBr:Sr²⁺ systems. In addition, correlation was good between σ _v , and the Knoop hardness number, H , obtained by indentation with the long axis of the indenter aligned in 〈100〉. The equation is of the form σ _v = C ( H–H ₀), where C ≅ 0.21 for all four halide families and H₀ is near the hardness value of the pure halides. Furthermore, H ₀≅5×10⁻³E₁₁₁, the Young's modulus in the 〈111〉 direction. Hence σ _v ≅0.21 H –10⁻³E₁₁₁.     

Peculiar Dielectric Behaviors of (Na1/2Bi1/2)0.87Pb0.13TiO3 Thin Films

PbTiO₃-doped sodium bismuth titanate (Na_1/2Bi_1/2)_{1− x} Pb _x TiO₃ of perovskite structure is one of the best-known piezoelectrics/ferroelectrics. However, it has not been properly investigated in any thin-film forms. In this study, the dielectric properties of (Na_1/2Bi_1/2)_0.87Pb_0.13TiO₃ thin films synthesized via a sol–gel route were investigated. They exhibit a strong frequency dispersion of the dielectric permittivity at relatively high frequencies, which is shifted to lower frequencies with increasing temperature. The electrical behavior can be fitted using Jonscher's universal law for dielectric relaxation. The peculiar dielectric behaviors observed can be ascribed to the coexistence of two different dielectric phases in the films, which is believed to be associated with the growth of the local Pb²⁺TiO₃ nanoclusters upon substitution of Pb²⁺ for Na⁺/Bi³⁺ in the (Na_1/2Bi_1/2)_{1− x} Pb _x TiO₃ films.     

Negative Thermal Expansion in (HfMg)(WO4)3

A single-phase material (HfMg)(WO₄)₃ with an orthorhombic structure, A₂ (WO₄)₃-type tungstate, has been successfully prepared for the first time by the calcination of HfO₂, MgO, and WO₃, substituting Hf⁴⁺ and Mg²⁺ for A³⁺ cations in A₂(WO₄)₃. The new material shows a negative thermal expansion coefficient of approximately −2 ppm/°C from room temperature to 800°C. The mechanism of negative thermal expansion is assumed to be the same as that of Sc₂(WO₄)₃.     

Characterization and Microwave Dielectric Properties of M2+Nb2O6 Ceramics

This paper details the investigation of the quality factor ( Q ), dielectric permittivity (ɛ_r) and temperature coefficient of resonant frequency (τ_f) of the TE_01δ mode of the columbite binary niobate ceramics, with the formula MNb₂O₆ where M=²⁺ cation, in relation to their degree of sintering, microstructure and phase composition. The ceramics were made from a mixed oxide preparative route and fired over a range of temperatures from 800° to 1400°C, and most formed the columbite structure. A comprehensive study was made of the niobates containing the transition metal cations M=Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺, and the group II metal cations M=Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺. All columbite niobates were found to have ɛ_r between 17 and 22 and negative τ_f values between –45 and –76 ppm/°C, and ZnNb₂O₆, MgNb₂O₆, CaNb₂O₆, and CoNb₂O₆ had high Q f values of 84 500, 79 600, 49 600, and 41 700 GHz, respectively. The Q f of MgNb₂O₆ was found to rise to over 95 000 GHz when heated at 1300°C for 50 h.     

Thermal Expansion of the Hexagonal (6H) Polytype of Silicon Carbide

The thermal expansion of the hexagonal (6H) polytype of α-SiC was measured from 20° to 1000°C by the X-ray diffraction technique. The principal axial coefficients of thermal expansion were determined and can be expressed for that temperature range by second-order polynomials: α¹¹= 3.27 × 10^–6+ 3.25 × 10^–9T – 1.36 × 10^–12 T ² (1/°C), and ş₃₃= 3.18 × 10^–6+ 2.48 × 10^–9 T – 8.51 × 10^–13 T ² (1/°C). The σ₁₁ is larger than α₃₃ over the entire temperature range while the thermal expansion anisotropy, the δş value, increases continuously with increasing temperature from about 0.1 × 10^–6/°C at room temperature to 0.4 × 10^–6/°C at 1000°C. The thermal expansion and thermal expansion anisotropy are compared with previously published results for the (6H) polytype and are discussed relative to the structure.     

Novel Preparation Method of Hydroxyapatite Fibers

A novel method for preparing calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂: HAp) fibers has been developed. HAp fibers can be prepared successfully by heating a compact consisting of calcium metaphosphate (ß-Ca(PO₃)₂) fibers with Ca(OH)₂ particles in air at 1000°C and subsequently treating the resultant compact with dilute aqueous HCl solution. The ß-Ca(PO₃)₂ fibers and the Ca(OH)₂ in the compact were converted into fibrous HAp and CaO phases by the heating, and the CaO phase was removed by acid-leaching. HAp fibers obtained in the present work were 40-150 µm in length and 2-10 µm in diameter. The fibers had almost the same dimensions as those of the ß-Ca(PO₃)₂ fibers.