Bismuth Phase Research Articles

Experimental characterization of CaCO 3 powder for use in compressible gaskets up to ultra-high pressure

High Pressure High Temperature (HPHT) equipment is used for commercially produce synthetic diamond and other polycrystalline products. The common denominator for almost all high-pressure systems is to use capsules where a powder material encloses the core material. In this work, the properties of CaCO 3 powder up to ultra-high pressure have been studied using an instrumented Bridgman anvil apparatus. Bismuth phase transformations were used as fix point calibrant. Three different parameters were studied, density, moisture and diametral support dependence on the load–thickness and pressure build-up. The experiments are done such as they can be used as validation and calibration of constitutive models for finite element simulations of the HPHT-process. The results show that increasing the density of the powder compact increases the load needed to reach maximum pressure. In addition, the residual stresses in the compact seem to delay the phase transition on the down-ramp. Moisture content within 0.5%–1.2% does not significantly influence the compaction properties of the discs. Diametral support increases the phase transition load.

Investigation of preparation and characteristics of Sn–Bi eutectic powders derived from a high shear mechanical approach

Fusible Sn–Bi eutectic alloy particles were synthesized from bulk Sn–Bi alloy via a high-shear mechanical approach. The morphology, composition, and structure of the as-prepared Sn–Bi alloy particles were characterized by XRD, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, differential scanning calorimetry, thermogravimetry, and Fourier-transform infrared spectroscopy. The particles were found to be spherical and consist of the tetragonal phase of tin as well as the rhombohedral phase of bismuth. In addition, there were large amounts of poly(N-vinylpyrrolidone) coated on the particles.

Temperature Effect on Phase Formation of Nanocrystalline Bismuth Titanate Synthesized via Hot Injection Method

Nanocrystalline bismuth titanate materials were synthesized via hot injection method for the first time. Bismuth nitrate and titanium butoxide were used as precursors of Bi and Ti, respectively. The synthesis method was modified to use aqueous solution as the solvent instead of non coordinating solvent which enable production of nanosized compounds at lower reaction temperature. During the synthesis process, titanium precursor was injected into mixture of bismuth nitrate and oleic acid at 130°C, leading to a rapid burst nucleation and followed by nuclei growth at room temperature. The synthesized compound was heated at various temperatures. XRD results showed formation of cubic phase bismuth titanate compound with space group of Fm3m at room temperature after the reaction. Presence of cubic phase bismuth titanate compound with space group of I23 was observed as secondary phase at 300°C. Meanwhile, a single phase cubic form, space group I23 was obtained for material synthesized at 600°C. FESEM images indicated nano particles of bismuth titanate materials were produced at lower temperatures. However, sintering effect was observed in material heated at 600°C, resulting micro-sized particles.

Effects of K nonstoichiometry in bismuth layer-structured K 0.5+ xBi 4.5Ti 4O 15 ceramics

The effects of K nonstoichiometry on phase formation, grain morphology, dielectric and piezoelectric properties of K 0.5+ x Bi 4.5Ti 4O 15 (KBT) were studied in the range of excess up to +2 mol% and deficient down to −8 mol% of K 0.5. The relative densities of the sintered KBT ceramics with various K contents prepared by a solid state reaction method were all higher than 95%. In all samples, a bismuth layer-structured phase was confirmed, although a secondary phase appeared as K deficiency became larger than −6 mol%. Piezoelectric coefficient ( d 33) increased, showing a high of 16 pC/N at x = −3 mol%, and then decreased with further K deficiency while Curie temperature ( T C) decreased showing a low of 540 °C at x = −8 mol% from 551 °C at x = 0 mol%. Mechanical quality factor ( Q m) of all samples was in the range of 900–1860.

Properties of metallic cements formed upon the interaction of mechanochemically synthesized copper alloys with liquid gallium and its eutectics: Interaction of Cu/Bi composites with liquid gallium

Atomic force microscopy and scanning electron microscopy were used to study the structure of metallic cements that are formed upon the interaction of Cu/Bi mechanocomposites with liquid gallium at room temperature. It has been established that the intermetallic compound CuGa2, which is the basic component of this metallic cement, is formed as tetragonal crystals 1–4 μm in size with a characteristic layeredspiral growth. The second phase—bismuth—is adsorbed at the growth steps in the form of disperse formations 70–250 nm in size; local bismuth accumulations of micron size are also observed. It is shown that in the metallic cement that is formed at room temperature regions of incompletely reacted Cu/Bi composite are retained.

Structural and Ferroelectric Properties of Large c/a Phase Bismuth Ferrite Thin Films Prepared by Ion Beam Sputtering

ABSTRACTBiFeO3 (BFO) thin films have been deposited on SrRuO3/SrTiO3 (001) substrate by using ion beam sputtering process. At low oxygen partial pressure of 11 m Pa, rhombohedral and large c/a mixed phase thin film have been obtained in spite of rhombohedral BFO single phase formation at high oxygen partial pressure of 73 mPa. From wide area 2θ-Ψ mappings, diffraction peaks from large c/a phase BFO thin film were obtained with the same extinction rule as those of rhombohedral BFO. Reciprocal space mappings around BFO (003) and BFO (103) spots indicate that lattice parameters of large c/a phase BFO were a = 0.381 nm and c = 0.461 nm (c/a =1.22), respectively. Moreover ferroelectric domain switching could be observed in both of rhombohedral BFO and mixed phase BFO thin films.

Crystallization of nanosized Aurivillius phase Bi 2W 2O 9 from amorphous precursor

Nanoparticles of bismuth layered Aurivillius phase, Bi 2W 2O 9, have been synthesized by annealing of precursor prepared by high energy milling in ball mill. The obtained powders have been investigated using the XRD, TEM, SEM, diffuse reflectivity, Raman and infrared spectroscopy. The results show that mechanochemical activation allows obtaining Bi 2W 2O 9 at much lower temperatures than those required in a conventional solid state reaction or synthesis through a complex organic precursor. As a result, material with smaller grain size can be obtained. Therefore this synthesis method is the best route to enhance photocatalytic activity of Bi 2W 2O 9. Our results also show that milling time has great impact on the crystallization mechanism. Bi 2W 2O 9 crystallizes easily already at 600 °C from precursor milled by 8 h. However, prolong milling time results in stabilization of an unknown phase or phases, which crystallize below 700 °C, and transform into the well-known Bi 2W 2O 9 phase after annealing at 750 °C.

Sol-gel synthesis and characterization of nanocrystalline (Bi0.5Na0.5)TiO3 powders from the poly vinyl alcohol evaporation route

Nanocrystalline pure perovskite phase bismuth sodium titanate (Bi0.5Na0.5)TiO3(BNT) powders have been prepared by a sol-gel method from the poly vinyl alcohol evaporation route, bismuth nitrate [Bi(NO3)3], tetra-butyl titanate [Ti(OC4H9)4] and sodium acetate(CH3COONa) were used as raw materials and poly vinyl alcohol(PVA) as the sol-gel forming solvent. Stoichiometric amounts of the individual raw materials were thoroughly mixed in accordance with the BNT composition to form the stock solution. The pH of the stock was adjusted to 1–3 by adding acetate. Aqueous solution of PVA[10%(w/v)] was then added to the cationic mixture with thorough stirring. The weight ratio of the cationic mixture to the PVA aqueous solution was maintained at 2:1. The resulting viscous liquid was then heated over a hot crucible up to form a fluffy dry gel. The fluffy dry gels were calcined at different temperatures and times and then cooled to room temperature naturally. The X-ray powder diffraction(XRD) patterns of the heat-treated powders were obtained using a Bruker D8 Advance X-ray diffractometer with Cu Kα radiation and nickel filter. Scanning electron microscope (SEM) studies of the NBT powders were performed using a JSM-6700F electron microscope. Phase-pure BNT powders were obtained at 550°C for 2–2.5h which is relatively lower calcination temperature than other reports. The BNT powders consists of phase-pure perovskite nanocrystals with an average size of 100–200nm.

Low‐temperature urea‐assisted hydrothermal synthesis of Bi2S3 nanostructures with different morphologies

AbstractDifferent morphologies of single‐crystalline orthorhombic phase bismuth sulfide (Bi2S3) nanostructures, including sub‐microtubes, nanoflowers and nanorods were synthesized by a urea‐assisted hydrothermal method at a low temperature below 120 °C for 12 h. The as‐synthesized powders were characterized by X‐ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM) and UV‐vis spectrophotometry. The experimental results showed that the sulfur sources had a great effect on the morphology and size of the resulting powders. The formation mechanism of the Bi2S3 nanostructures with different morphologies was discussed. All Bi2S3 nanostructures showed an appearance of blue shift relative to the bulk orthorhombic Bi2S3, which might be ascribed to the quantum size effect of the final products. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dielectric and piezoelectric properties of (Li, Ce) modified NaBi 5Ti 5O 18 composite ceramics

Nominal (Li 0.5Ce 0.5) x (Na 0.5Bi 0.5) (1– x) Na 0.5Bi 4.5Ti 5O 18 composite ceramics were fabricated using conventional solid-state reaction method. The coexistence of bismuth layer-structured phase and perovskite phase was determined in these ceramics using XRD technique. At room temperature, the x=0.11 sample showed the largest piezoelectric constant, d 33, of about 26.5 pC/N and the largest electromechanical coupling factor, k t, of about 30%. Even after annealing at 500 °C, the value of d 33 was still about 19 pC/N, in x=0.08–0.11 samples. Moreover, these composite ceramics showed low temperature coefficients of dielectric constant and high electrical resistivity in the temperature region of 450–550 °C. These results indicated that (Li, Ce) modified NaBi 5Ti 5O 18 composite ceramics were promising piezoelectric materials for high-temperature applications.

Experimental measurement of the solubility of bismuth phases in water vapor from 220°C to 300°C: Implications for ore formation

Abstract Preliminary measurements were carried out of the solubility of the O 2- buffering assemblage bismuth + bismite (Bi 2 O 3 ) in aqueous liquid–vapor and vapor-only systems at temperatures of 220, 250 and 300 °C. All experiments were carried out in Ti reaction vessels and were designed such that the Bi solids were contained in a silica tube that prevented contact with liquid water at any time during the experiment. Two blank (no Bi solids present) liquid–vapor experiments at 220 °C yielded Bi concentrations (±1 σ ) in the condensed liquid of 0.22 ± 0.02 mg/L, whereas the solubility measurements at this temperature yielded an average value of approximately 6 ± 9 mg/L, with replicate experiments ranging from 0.3 to 26 mg/L. Although the 6 mg/L value is associated with a considerable degree of uncertainty, the experiments do indicate transport of Bi through the vapor phase. Measured Bi concentrations in the condensed liquid at 250 °C were in the same range as those at 220 °C, whereas those at 300 °C were significantly lower (i.e., all below the blank value). Vapor-only experiments necessarily contained much smaller initial volumes of water, thereby making the results more susceptible to contamination. Single blank runs at 220 and 300 °C yielded Bi concentrations of 82 and 16 mg/L, respectively. Measured concentrations (±1 σ ) of Bi in the vapor-only solubility experiments at 220 °C were 235 ± 78 mg/L for an initial water volume of 0.5 mL, and at 300 °C were 56 ± 30 mg/L and 33 ± 21 for initial water volumes of 1 and 2 mL, respectively, suggesting strong preferential partitioning of Bi into the vapor. The results indicate a negative dependence of Bi solubility on temperature, but are inconclusive with respect to the dependence of Bi solubility on water density or fugacity. The experiments reported here suggest that significant Bi transport is possible in the vapor phase. Comparison of the liquid–vapor and vapor-only experiments further suggests that, at the conditions studied, the solubility of Bi in the vapor is significantly higher than that in the liquid phase (calculated distribution coefficients, i.e., C Vapor / C Liquid at 220 °C ranged from 81 to 168, where C is concentration in mg/L). The concentrations measured in the vapor-only experiments at 220 °C are approximately 11 orders of magnitude higher than those calculated from available thermodynamic data assuming no interaction between volatile Bi species and water molecules. This finding indicates that hydration of volatile Bi species probably occurs to a significant extent; similar to behavior observed previously in published vapor phase solubility studies of other metals. However, the interpretation of the results was complicated by the formation of Bi silicate phases and the lack of certainty that O 2 fugacity buffering was effective throughout the experiments.

Comments and reconciliation of the Ni–Bi‐system thermodynamic reassessments

AbstractThe binary Ni‐Bi alloys as well as multicomponent materials comprising systems like Ni‐Bi‐Sn, Ni‐Bi‐Sb etc. are recently considered as prospective for design of lead‐free solders. For that reason various authors focused their attention to the Ni‐Bi system thermodynamics. The studies identified five phases in the above system. Two of them (i.e., (Ni) and liquid), were treated as disordered substitutional solutions. The phase NiBi3 is stoichiometric and a standard two‐sublattice model was repeatedly applied to describe its Gibbs free energy, while for the nonstoichiometric NiBi phase, a three‐sublattice model was retained. The pure bismuth phase ((Bi)) is stoichiometric as well. The results are discussed and compared to literature thermochemical and topological data. In liquid state, strong repulsions between nickel and bismuth atoms are anticipated in the nickel rich‐side, but no data about a liquid phase miscibility gap is available yet. Therefore, the stability of the liquid phase has to be reassured, in spite of positive deviations from ideal behaviour. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structure and properties of ultrafast-quenched Sn-Bi foils

The effect of bismuth on the microstructure of ultrafast-quenched foils of Sn-Bi alloys has been investigated. Bismuth phase precipitation is observed in alloys containing more than 2 at % Bi. With an increase in the bismuth concentration to 8 at %, most precipitates acquire a needle-like shape. Cross-sectional inhomogeneity of the initial foils is revealed. It is found that addition of bismuth leads to an increase in the foil microhardness by a factor of 2.5.

Lead-Free Ferroelectric Material: Dysprosium Doped Bi<sub>4</sub>Ti<sub>3</sub>O<sub>12</sub>

This study investigated fundamental of phase formation, crystal structure and calcination process for bismuth dysprosium titanate (Bi4-xDyxTi3O12; BDT) powders when x = 0, 0.25, 0.5, 0.75 and 1.0. BDT powders were prepared using a simple solid-state reaction on mixtures of reagent grade Bi2O3, Dy2O3 and TiO2 powders. The mixtures were calcined at temperature in the range of 500-800°C for 4 h at a heating/cooling rate of 5°C/min. Thermal characteristics of powders were studied using thermogravimetric/differential thermal analyses which indicated that the formation of Bi4Ti3O12 and Bi3Dy1Ti3O12 powders occurred at ~500oC. Effect of Dy3+ concentration on phase and crystal structure was investigated using X-ray diffractometry. The results revealed that at small concentration of Dy dopant (x £ 0.25), optimum calcination temperature for providing bismuth titanate-based phase was 650oC. Increasing content of Dy dopant seemed to reduce calcination temperature to 600oC. This study suggested the alternative environmental friendly BDT materials which may be used as starting powders for production of high quality BDT ceramics.

Aurivillius Phase Potassium Bismuth Titanate: K0.5Bi4.5Ti4O15

An Aurivillius phase bismuth layer‐structured compound potassium bismuth titanate is synthesized using conventional solid‐state processing. It was found that the range of sintering temperature for the potassium bismuth titanate is very narrow. Phase analysis was performed by X‐ray diffraction, and microstructural morphology was assessed by scanning electron microscopy. The Curie temperature TC, piezoelectric coefficient d33, and mechanical quality factor Qm (kp mode) of the dense potassium bismuth titanate were found to be 555°C, 21.2 pC/N, and 1602, respectively. Dielectric spectroscopy showed that potassium bismuth titanate possesses stable high‐temperature dielectric properties.

Electrodeposition of high-pressure-stable bcc phase bismuth flowerlike micro/nanocomposite architectures at room temperature without surfactant

Three-dimensional (3D) bismuth flowerlike micro/nanocomposite architectures were successfully prepared on Cu substrates by electrochemical self-assembly in aqueous solution at room temperature. The morphology, crystal structure, and composition were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). Results show that the synthesized 3D architectures are built with dozens of two-dimensional (2D) single crystal nanoscaled petals, which are high-pressure-stable bcc phase Bi. The thickness of the 2D petals is about 60 nm. The effects of the concentration of Bi 3+ ions and the electric potential gradient on the evolution of the Bi flowerlike micro/nanocomposite architectures are discussed.

The photocatalytic properties of bismuth oxide films prepared through the sol–gel method

In this research, thin bismuth oxide films were prepared through the sol–gel method. In order to study the influence of bismuth oxide crystal phases on the photocatalytic properties of bismuth oxide films, these films were annealed at different temperatures and then applied to decompose a typical textile industry pollutant (Rhodamine B). Scanning electron microscopy, X-ray diffraction and profilometry were applied to characterize these films. It has been found that different annealing temperatures cause the transformation of different bismuth oxide crystal phases, which leads to the different removals of Rhodamine B photolyzed using bismuth oxide films as photocatalyst.

Thin bismuth oxide films prepared through the sol–gel method as photocatalyst

In this paper, thin bismuth oxide films were prepared by the sol–gel method. The films were annealed at different temperatures, and then applied to degrade a kind of typical textile industry pollutant (Rhodamine B), respectively, in order to study the influence of bismuth oxide crystal phases on their photocatalytic properties. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) techniques and a surface profiler were applied to characterize the thin films annealed at different temperatures. The results show that different annealed temperatures cause the transformation between monoclinic phase and tetragonal phase of bismuth oxides and bismuth oxide films annealed at 550 °C contain a higher proportion of the tetragonal phase of bismuth oxides than those annealed at other temperatures, which leads to higher electronic binding energy and photocatalytic properties for these oxides in the films.

Nonhydrostatic compression of bismuth to 222GPa: Some constraints on elasticity of the bcc-phase

Polycrystalline bismuth sample was compressed in a diamond anvil cell and X-ray diffraction patterns from the body centered cubic phase of bismuth (bcc-Bi) recorded in the pressure range 12–222 GPa. The analysis of diffraction data indicates that the factor S =( S 11 − S 12 − S 44 /2) is positive, where S ij are the single-crystal elastic compliances. The data suggest S / S 11 ≅0.5 in the entire pressure range if stress continuity across the grain boundaries is assumed, and S / S 11 ≅0.9 if a condition halfway between the stress and strain continuities is assumed. These results are compared with the first principle calculations of the elastic moduli carried out recently. The upper bound of the uniaxial stress component (the difference between the axial and radial stress components) increases linearly from very low value at 12 to ≈3 GPa at 222 GPa.

Microstructure and physical properties of bismuth–lead–tin ternary eutectic alloy

Using different experimental techniques, microstructure, electrical resistivity, attenuation coefficient, and mechanical and thermal properties of the quenched Bi–Pb–Sn ternary eutectic alloy have been investigated. From the X-ray analysis, Bi3Pb7 and Bi–Sn meta-stable phases are detected, in addition to rhombohedral bismuth and Sn body-centered tetragonal phases. This study also compared the physical properties of the Bi–Sn–Pb ternary eutectic alloys with the base binary Bi–Sn and Bi–Pb eutectic alloys.