Sintering Behavior of Cadmium-Doped Pb(Ni1/3Nb2/3)O3–PbZrO3–PbTiO3 Ceramics

Substituting Cd²⁺ ions into the A and B sites in a Pb(Ni_1/3Nb_2/3)O₃PbZrO₃PbTiO₃ (PNNPZPT) ternary perovskite material made it possible to determine the effects of the Cd²⁺ ion substitution site on sintering behavior. The substitution site of the Cd²⁺ ion was identified by using X-ray photoelectron spectroscopy spectra. Although Cd²⁺ ions were substituted into the A and B sites in PNNPZPT, the Cd²⁺ ions preferred the A site over the B site. When Cd²⁺ ions replaced Pb²⁺ ions, a weight gain was observed during sintering. On the other hand, replacing Ni2 ions with Cd²⁺ ions promoted weight loss. Those weight changes indicated that Cd²⁺ ions change the bonding strength between the B-site cations and the oxygen of the octahedron in a perovskite structure. Density was influenced by the Cd²⁺ ion substitution site, and the A-site-doped compositions had higher densities than the B-site-doped compositions.     

Improvement in Wear Resistance of High-Strength and High-Toughness Silicon Nitride Modified by Ion Implantation

Surface modification by ion implantation has been conducted to improve the tribological properties of a high-strength and high-fracture-toughness unidirectionally aligned silicon nitride (UA-SN). B⁺, N⁺, Si⁺, and Ti⁺ ions were implanted into the planes parallel and normal to the grain alignment of the UA-SN with a fluence of 2 × 10¹⁷ ions/cm² at an energy of 200 keV. The ion implanted UA-SN showed a dramatic improvement in wear resistance. For example, the specific wear rate of the Si⁺-implanted specimen in the direction parallel to the grain alignment was reduced to a value of 3 × 10⁻¹⁰ mm²/N, equal to 1/20 of the unimplanted one. Cross-sectional transmission electron microscopy indicates the high wear resistance was attributed to the amorphous surface caused by the ion implantation.     

Two-Dimensional Mapping of Er3+ Photoluminescence in CaF2 Crystal Lines Patterned by Lasers in Oxyfluoride Glass

The laser-induced crystallization method is applied to an oxyfluoride glass with the composition of 41.5SiO₂–21.3Al₂O₃–4.8CaO–12.6NaF–16.4CaF₂–2.9NiO–0.5ErF₃ (mol%), and the lines consisting of CaF₂ nanocrystals (diameter: ∼20 nm) are patterned on the glass surface. It is found from micro-photoluminescence (PL) spectra of Er³⁺ ions that Er³⁺ ions are incorporated into CaF₂ nanocrystals formed by laser (continuous-wave Yb:YVO₄ fiber laser with a wavelength of 1080 nm) irradiations. Two-dimensional mappings of the PL intensity for the ⁴S_3/2→⁴I_15/2 transition of Er³⁺ ions are measured for the surface and cross section of the patterned lines. It is found that two phases giving different PL intensities are formed in the laser-irradiated region, suggesting that the center part of the laser-irradiated region consists of Er³⁺-doped CaF₂ nanocrystals and the surrounding of the center part gives the fluoride ion rich coordination state for Er³⁺ ions. The formation mechanism of Er³⁺-doped CaF₂ nanocrystals is related to the temperature distribution of the laser-irradiated region.     

Photocatalytic Characteristics of Nanometer-Sized Titania Powders Fabricated by a Homogeneous-Precipitation Process

The photocatalytic characteristics of nanometer-sized TiO₂ powder prepared by a homogeneous-precipitation process (HPP) were compared with those of a commercial powder to determine which powder was better able to remove metal ions, such as lead and copper, from aqueous equimolar metal-ethylenediaminetetraacetic acid (EDTA) solution. In aqueous lead-EDTA solution, the TiO₂ powder fabricated by HPP had 3.5 times higher initial adsorption of lead ion and a 1.5 times faster rate for the complete elimination of lead ions than did the commercial powder. In an aqueous copper-EDTA solution, the TiO₂ powder fabricated by HPP also showed higher initial adsorption and a faster elimination rate for copper ions than did the commercial powder. Similarly, the photocatalytic properties were enhanced as the specific surface area increased, and the TiO₂ powder fabricated by HPP, which consisted of coagulated primary particles 20 nm in size, with chestnut-burr shapes, had a larger specific surface area (∼180 m²/g) than that of the commercial powder (∼55 m²/g).     

Interactions in the Silicon Carbide–Polyacrylic Acid–Yttrium Ion System

Interactions in the SiC powder–polyacrylic acid (PAA, dispersant)–Y³⁺ ion (sintering additive) system were investigated in the pH range from 2 to 6. The amount of Y³⁺ ions adsorbed on SiC particles increased with an increase of pH because of the electrostatic attraction between the negatively charged SiC surface and Y³⁺ ions. On the other hand, the amount of PAA adsorbed on SiC particles decreased with increasing pH because of the electrostatic repulsion between the negatively charged SiC surface and dissociated PAA. The addition of PAA to the SiC suspension with Y³⁺ ions increased the amount of Y³⁺ ions fixed to SiC particles through the strong interaction between Y³⁺ ions and PAA adsorbed on SiC particles. The above-described interactions in the SiC–PAA–Y³⁺ ions system were closely related to the coagulation of SiC particles and the rheology of SiC suspensions. The coagulation of SiC particles through the adsorbed Y³⁺ ions decreased the specific surface area of SiC powder after calcination in an argon atmosphere. The addition of PAA to the SiC suspensions with Y³⁺ ions kept the SiC particles separate during calcination, i.e., the PAA addition contributed to enhancement of the driving force of sintering (no decrease of specific surface area) and to control of the amount of Y³⁺ ions uniformly fixed to the SiC surface.     

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.     

Raman Spectroscopic Studies on the Formation Mechanism of Hydrous-Zirconia Fine Particles

The Raman spectra of hydrous-zirconia fine particles produced by the hydrolysis of various ZrOCl₂ solutions were investigated. The Raman spectra of hydrous zirconia synthesized at HCl concentrations below 1 mol/L were similar to those of monoclinic, crystalline ZrO₂; those of hydrous zirconia synthesized at HCl concentrations greater than 1 mol/L showed a crystal structure change. The line width of the Raman bands increased with increasing H⁺ ion concentration. Analyzing the relationship between Raman band width and particle size revealed that the primary particle size of hydrous zirconia was controlled by the H⁺ and Cl⁻ ions, because these ions interfered with the polymerization in a hydrolysis reaction. Based on the experimental results, the formation mechanism for primary particles of hydrous zirconia was determined.     

Cation-Exchange Characteristics of Sintered Hydroxyapatite in the Strongly Acidic Region

The ion-exchange behavior of hydroxyapatite (Ca₁₀(PO₄)₆-OH)₂) (HAp), fired at high temperatures, has been investigated in the strongly acidic region (pH 2 and 3). According to the present study, HAp fired above 1000°C can exchange ions from Ca²⁺ to Pb²⁺, even at pH 2, without dissolution. The molar ratios of Pb²⁺/Ca²⁺ after ion exchange are approximately unity in all cases. Ion exchange occurs in a thin layer near the surface of HAp particles fired at 1300°C. After ion exchange, Pb-Cl-apatite crystals are created in the strongly acidic region (pH 2).     

Improvement in Corrosion Resistance of Biomaterial Alumina after 60 keV Nitrogen Ion Implantation

Surface modification of polycrystalline α-alumina is carried out using ion implantation. Samples were implanted at 60 keV N⁺ ions with different ion doses ranging from 1 × 10¹⁵ to 1 × 10¹⁷ ions/cm². Corrosion resistance is studied in a Ringer solution. The increase in corrosion resistance is due to the compound formation studied using Fourier transform infrared spectroscopy and glancing-angle X-ray diffraction techniques. Nanohardness is more at a lower ion dose and decreases at a higher ion dose. Microstrutural investigation shows that the decrease in corrosion resistance and nanohardness at a higher ion dose is due to the damage accumulation at the surface.     

Fast Li+ Ion Conduction in Li2O-Al2O3-TiO2-SiO2-P2O5 Glass-Ceramics

Fast lithium ion conducting glass-ceramics have been successfully prepared from the pseudobinary system 2[Li_{1+ x} Ti₂Si _x P_{3− x} O₁₂]-AlPO₄. The major phase present in the glass-ceramics was LiTi₂P₃O₁₂ in which Ti⁴⁺ ions and P⁵⁺ ions were partially replaced by Al³⁺ ions and Si⁴⁺ ions, respectively. Increasing x resulted in a considerable enhancement in conductivity, and in a wide composition range extremely high conductivity over 10⁻³ S/cm was obtained at room temperature.     

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.     

Optical and Magnetic Properties of Some Transition Metal Ions in Barium Phosphate Glass

In barium phosphate glass containing first-row transition metal ions, the ions appear to possess normal oxidation states: Cr³⁺, Mn³⁺, Fe^2+,3+, Co²⁺, Ni²⁺, and Cu²⁺. Room temperature and 77°K spectra for Cr³⁺-, Mn³⁺-, Fe^2+,3+-, Ni²⁺-, and Cu²⁺-containing glasses can be interpreted, on the, basis of octahedrally coordinated metal ions, whereas the spectrum of the Co²⁺ glass correlates with a tetrahedrally coordinated metal ion. Magnetic moments for the glasses are similar to those for the spin-only values of the various metal ions.     

Enhanced Oxygen Diffusion at 1400°C in Deformed Single-Crystal Magnesium Oxide

The rate of oxygen difusion at 1400°C into pure, deformed, and scandium-doped MgO was measured using a secondary-ion mass spectrometer with ¹⁶O^- primary ions as sputtering agents to monitor the penetration of ¹⁸O into the sample from an ¹⁸O-enriched surface layer. In samples doped with scandium, oxygen diffusivity did not differ significantly from the value, 1.3 × 10-¹⁵ cm²/s, found for the pure sample. In deformed samples, the diffusion coefficient was 5.8 × 10^-15 cm²/s .     

Habit Changes of Sapphire Grown from PbO-PbF2, and MoO3-PbF2 Fluxes

Single crystals of Al₂O₃ (sapphire) were grown from PbO-PbF₂ and MoO₃-PbF₂ fluxes; they varied from flat plates (PbF₂-rich melts) to equidimensional crystals (PbO- or MoO₃-rich melts). The primary growth planes are basal {0001}, first-order rhombohedral {1011}, and second-order rhombohedral {0112}. The habit change is interpreted on the basis of F^- contamination and Pb²⁺ surface adsorption. Possible ion species in the melts and their relative importance on crystal growth from these systems are discussed.     

Segregation of Isovalent Impurity Cations at the Surfaces of MgO and CaO

Enthalpies of segregation for isovalent impurities in magnesium and calcium oxide as a function of surface concentration were calculated by using an atomistic computer simulation method. We have considered Be²⁺, Mg²⁺, Ca²⁺, Ba²⁺, and Ni²⁺, segregating to both (001) and (110) faces. The results obtained can be extrapolated to predict the behavior of other impurities including Mn²⁺, Fe²⁺, and Co²⁺, We find, for example, that Fe²⁺, Mn²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ will concentrate at the (001) surface of MgO, while Ni²⁺ will be depleted. The enthalpy of segregation is found to vary substantially with coverage particularly for the larger impurities. The enthalpy becomes less negative with increasing impurity concentration due to the increasing lattice strain until the surface is nearly saturated. Then additional stabilization is obtained by restructuring of the surface layer. We predict reconstructed surfaces for both the (001) and (110) faces, which contain a high concentration of a larger impurity ion. The enthalpy of segregation shows a maximum at around 50% surface coverage implying a bimodal surface distribution of segregant. The influence of segregation on surface energy suggests two unusual effects. The (001) surface energy of the impure crystal becomes negative for surface concentrations of impurity greater than 10% Ba²⁺ or 75% Sr²⁺ in MgO. This implies a thermodynamic barrier to sintering. At high coverages of Ba²⁺ in MgO the (110) surface becomes more stable than the (001) face suggesting that facetting may occur.     

Effects of Cd-Substitution Site on the Electrical Conductivities in Pb(Ni1/3Nb2/3)O3-PbZrO3-PbTiO3 Ceramics

The effects of Cd²⁺ substitution for Pb²⁺ and Ni²⁺ ions (on the A-site and B-site of the ABO₃ perovskite structure, respectively) on the electrical conductivities in Pb(Ni_1/3-Nb_2/3)O₃-PbZrO₃-PbTiO₃ (PNN-PZ-PT) ceramics have been investigated. Generally, the compounds that contain PbO show p -type conductivity, because of PbO evaporation. Thus, the conductivities are known to be proportional to the PbO evaporation. However, PNN-PZ-PT ceramics exhibit a reciprocal relationship between the conductivities and the evaporation of PbO. Generally, no vacancy change is observed with the substitution of the same-charge valence ion. However, in the PNN-PZ-PT ceramic, lead vacancies could be created or annihilated by replacing Pb²⁺ and Ni²⁺ ions with Cd²⁺ ions, because of incomplete substitution. The electrical conductivities are influenced by this incomplete substitution.     

EXAFS Study of Cation Distribution in Nickel Aluminate Ferrites

A new method for analyzing the cation distribution of spinel crystals by extended X-ray absorption fine-structure spectroscopy has been developed to overcome the disadvantage of X-ray diffraction, which cannot readily distinguish among different transition-metal ions. EXAFS analysis was conducted on Ni²⁺ and Fe³⁺ ions in nickel aluminate ferrites, and the cation distributions obtained were in good agreement with values obtained by other methods. The ratio of tetrahedral sites occupied by Ni²⁺ ions decreases with increasing iron content. Fe³⁺ ions distribute nearly equally to both tetrahedral and octahedral sites. Apparently, not only crystal-field stabilization energy but also ion size affects cation distribution.     

X-ray Photoelectron Spectroscopy Study on the Process of Apatite Formation on a Sodium Silicate Glass in Simulated Body Fluid

The process of apatite formation on the surface of Na₂O–SiO₂ glass in a body environment was investigated, mainly by X-ray photoelectron spectroscopy, as a function of soaking time in a simulated body fluid (SBF). The glass was found to release Na⁺ ions via exchange with H₃O⁺ ions in the SBF to form Si—OH groups on its surface. These Si—OH groups induced apatite formation indirectly, by forming calcium silicate and amorphous calcium phosphate. The formation of the calcium silicate and amorphous calcium phosphate is attributed to electrostatic interactions between the Si—OH groups on the glass surface and the calcium and phosphate ions in the SBF.     

Crystal Chemistry of Mixed Bismuth Oxides with Layer-Type Structure

Several compounds with m = 2, 3, 4, and 5 in the general formula (Me₂'O₂)²⁺ (Me_m–1 R_mO_3m+1)^2– were synthesized, a number of them for the first time. They possess a layer-type crystal structure. Bi³⁺ may be the only suitable ion for the Me' sites; R may be Ga^s+, Ti⁴⁺, Nb⁵⁺, or Ta⁵⁺. The restrictions on the size of Me ions increases with increasing value of m . Lattice parameter data for the compounds and indexed X-ray powder patterns for m = 5 compounds are presented.     

Formation of Sm2+ lons in Sol-Gel-Derived Glasses of the System Na2 O-Al2O3-SiO2

Samarium ions (Sm²⁺) incorporated into aluminosilicate glasses by a sol-gel process showed persistent spectral hole burning at room temperature. Gels of the system Na₂O-Al₂O₃SiO₂ synthesized by the hydrolysis of Si(OC₂H₅)₄, Al(OC₄H₉)₃, CH₃ COONa, and SmCl₃·6H₂O were heated in air at 500°C, then reacted with H₂ gas to form Sm²⁺ ions. Whereas Al³⁺ ions effectively dispersed the Sm³⁺ ions in the glass structure, Na⁺ ions were not effective. The Al₂O₃-SiO₂ glasses proved appropriate for reacting the Sm³⁺ ions with H₂ gas and exhibited the intense photoluminescence of Sm²⁺ ions. The reaction of Sm³⁺ ions with H₂ in the Al₂O₂-SiO₂ glasses was determined by first-order kinetics, and the activation energy equaled 95 kJ/mol. At 800°C, the maximum photoluminescence of the Sm²⁺ ions was achieved within 20 min.