X-ray investigation of sintered cadmium doped hydroxyapatites

Pure and cadmium (Cd) doped hydroxyapatites (HA, Ca₁₀(PO₄)₆(OH)₂) were synthesized by a precipitation method from aqueous solutions of Ca(NO₃)₂4·H₂O for the former and Cd(NO₃)₂4·H₂O for the latter, by using (NH₄)₂HPO₄ as the phosphate source, while pH was kept in the range of 11–12. The effect of incorporation of Cd²⁺ ions into the structure of HA was investigated after the air sintering at 1100 °C for 1 h. The results indicate that Cd²⁺ addition into HA yields nearly fully densified products with respect to pure stoichiometric HA. The XRD patterns showed that Cd doping increases the crystallinity of HA. The 2, 4.4, and 8.8 mol% Cd doped HAs had calcium oxide (CaO) impurity phase in their lattice. The CaO phase in the HA structure gradually disappeared with increasing Cd amount, and was replaced with cadmium oxide (CdO) in the CdHA doped with 11 mol% Cd. Cd²⁺ ion incorporation decreased the a- and c-axis lattice constants and unit cell volume of HA.     

Properties of sol–gel derived Al2O3–15 wt.% ZrO2 (3 mol% Y2O3) nanopowders using two different precursors

An alumina–15 wt.% zirconia (3 mol% yttria) nanopowder was synthesized by sol–gel method using salt and alkoxide as precursors. Al(NO₃)₃·9H₂O, ZrOCl₂·8H₂O and Y(NO₃)₃·6H₂O were used as salt precursors and Al(OC₄H₉)₃ and Zr(OC₄H₉)₄ were used as alkoxide precursors. The dried gels of two precursors were heat treated in the range of 450–1350 °C. The powders produced by alkoxide precursors calcined at 750 °C were in the range of 15–75 nm, while those prepared by salt precursors had the size in the range of 30–90 nm. The former powders had a higher surface area and smaller mean pore diameter compared with the later powder, i.e. 152 m²/g and 5.63 nm comparing with 121 m²/g and 9.79 nm, respectively. Therefore phase transformation in the former occurred in lower temperatures.     

Deposition behavior and characteristics of hydroxyapatite coatings on Al2O3, Ti,and Ti6Al4V formed by a chemical bath method

A simple chemical bath method was used to deposit hydroxyapatite (HA) coatings on Al₂O₃, Ti, and Ti6Al4V substrates at ambient pressure by heating to 65–95 °C in an aqueous solution prepared with Ca(NO₃)₂·4H₂O, KH₂PO₄, KOH, and EDTA. The deposition behavior, morphology, thickness, and phase of the coatings were investigated using scanning electron microscopy and X-ray diffractometry. The bonding strength of the coatings was measured using an epoxy resin method. The HA coatings deposited on the three kinds of substrates were fairly dense and uniform and exhibited good crystallinity without any additional heat treatment. A coating thickness of 1–1.8 μm was obtained for the samples coated once. By repeating the coating process three times, the thickness could be increased to 4.5 μm on the Al₂O₃ substrate. The bonding strength of these coatings was 18 MPa.     

Precursor effects on ZrW2O8 formation kinetics

The synthesis of ZrW₂O₈ from different kinds of mixtures containing ZrO₂–WO₃, ZrO(NO₃)₂·2H₂O–WO₃, ZrCl₂O·8H₂O–WO₃, and ZrO₂–(NH₄)₁₀W₁₂O₄₁·5H₂O was investigated, and the kinetics was analyzed using JMA equation. It was found that ZrO(NO₃)₂·2H₂O, ZrCl₂O·8H₂O H₂O and (NH₄)₁₀W₁₂O₄₁·5H₂O that were used as inorganic precursors formed ZrO₂ and WO₃ after firing above 500 °C. The content of ZrW₂O₈ obtained by firing the mixtures is influenced by the kinds of precursors as well as mixing methods. The formation rate of ZrW₂O₈ depends on homogeneity related to mixing methods as well as the particle size of starting powders. Phase-pure ZrW₂O₈ is obtained from the ZrCl₂O·8H₂O–WO₃ mixtures at 1200 °C for 4 h, which is much shorter time than in the case of conventional ZrO₂–WO₃ mixtures. In the reaction kinetics of ZrO₂–WO₃ system, the Avrami exponent (n) is ∼0.5 above 1175 °C, indicating that the reaction is controlled by the diffusion-controlled reaction.     

One step solid state synthesis of FeF3·0.33H2O/C nano-composite as cathode material for lithium-ion batteries

Nanometer-sized FeF₃·0.33H₂O/acetylene black composite has been synthesized by one step chemico-mechanical ball-milling process using Fe (NO₃)₃?9H₂O and NH₄F as precursors and investigated as cathode materials for secondary lithium batteries. The obtained FeF₃·0.33H₂O/C composite was described in terms of structure, morphology, and electro-chemical performance. The composite exhibited a noticeable capacity of 233.9 mAh g⁻¹ at a current density of 20 mA g⁻¹ within potential range 1.8–4.5 V and good rate capability. These results showed that FeF₃·0.33H₂O/C nano-composite prepared from an easily scalable chemico-mechanical ball-milling process was of great industrial interest.     

Effect of surfactant and heat treatment on morphology,surface area and crystallinity in hydroxyapatite nanocrystals

Hydroxyapatite (HA) powders were synthesized by the wet precipitation method, with and without surfactant, under identical processing parameters. These powders were then heat treated at 900 °C for 3 h in air. The detailed characterization of the powders was done by using SEM, dynamic light scattering, nitrogen adsorption, XRD, Raman spectroscopy, and FTIR techniques. The HA phase, identified by well defined PO₄^3? and OH^? ion peaks in Raman and FTIR spectra, was observed in all the powder samples. The addition of surfactant changed the morphology of the particles from spherical to needle/rod-like structure and increased the surface area up to three times (from 33 to 96 m²/g). Also, suppression in the evolution of β-TCP phase was observed along with decrease in the crystal size and crystallinity of the powder due to the addition of surfactant. Synthesized nano-HA crystals were found to have diameters and lengths in the range 10–25 nm and 75–150 nm, respectively. The heat treatment changed the architecture of the particles, increased the crystallinity and reduced the surface area to ≈7 m²/g. However, the relative increase in crystallinity was much higher for the powder synthesized with surfactant. The ratio of the average crystallite size to the crystallinity degree was about 0.53±0.07 for all the powders. The particle size distribution was bimodal and coarser for the powder synthesized without surfactant. The pore size analysis showed transformation of a predominantly mesoporous structure into a meso- plus macroporous one on heat treatment. The intensity of OH^? group peak in Raman spectra was found to be highly sensitive to the crystalline state of the HA powder and may be used to assess crystallinity.     

Controllable synthesis and flame retardant properties of bunch-, chrysanthemum-, and plumy-like 4ZnO·B2O3·H2O nanostructures

Three kinds of new 4ZnO·B₂O₃·H₂O nanostructures of bunch-, chrysanthemum-, and plumy-like morphologies have been synthesized under hydrothermal conditions at 140 °C in the presence of ethanol. The as-synthesized products were characterized by the chemical analysis, TG, XRD, FT-IR, SEM and TEM. All the synthesized 4ZnO·B₂O₃·H₂O nanostructures consist of nanoribbons. A series of control experiments confirmed that the morphologies of the products were influenced by the reaction time, temperature, and the presence of the surfactant of PEG-300. Furthermore, the flame retardant properties of the synthesized 4ZnO·B₂O₃·H₂O nanostructures were investigated by the thermal analysis method, demonstrating that they had the better behaviors than the non-nanostructure sample.     

Effect of the addition ZrO2–Al2O3 on nanocrystalline hydroxyapatite bending strength and fracture toughness

Nanocrystalline hydroxyapatite powder has been synthesized from a Ca(NO₃)₂·4H₂O and (NH₄)₂HPO₄ solution by the precipitation method. In the next step we prepared ZrO₂–Al₂O₃ powder. After preparation, the powder was dried at 80 °C and calcined at 1200 °C for 1 h. Various amounts (HAP–15 wt% ZA, HAP–30 wt% ZA) of powder were mixed with the hydroxyapatite by ball milling. The powder mixtures were pressed and sintered at 1000 °C, 1100 °C and 1200 °C for 1 h. In order to study the structural evolution, X-ray diffraction (XRD) was used. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to estimate the particle size of the powder and observe fracture surfaces. Results show that the bending strength of pressed nanocrystalline HAP was improved significantly by the addition 15 wt% of ZrO₂–Al₂O₃ powders at 1200 °C, but the fracture toughness was not changed, however when 30 wt% of ZA powders were added to nanocrystalline HAP, the bending strength and fracture toughness of the specimens decreased at all sintering temperature.     

Synthesis of YAG powders by the co-precipitation method

YAG (Y₃Al₅O₁₂) powders have been prepared by co-precipitation technique in which NH₄HCO₃ is used as a precipitant and Y₂O₃, A1((NO₃)₃·9H₂O—as raw materials. Two kinds of surfactant are added into the solution, i.e. Polyethylene glycol (PEG10000) as steric stabilizer and (NH₄)₂SO₄ as electrical stabilizer. The composition of YAG precursor, the phase formation process of YAG and the properties of the powders were investigated by means of differential scanning calorimetry and thermogravimetry analysis (DSC–TG), X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FT-IR) and Scanning electron microscopy (SEM). The results of XRD show that phase YAG crystallite can be obtained as precursors when heated at 900 °C for 2 h. The powders loosely dispersed with narrow size distribution and spherical shapes could be observed by SEM. It has been found that the presence of PEG and (NH₄)₂SO₄ is beneficial for the dispersion of the resulting YAG powder. In the presence of surfactants, the synthesized product consists of highly dispersed nano-sized particles.     

Synthesis of nano-crystalline NiO-YSZ by microwave-assisted combustion synthesis

Nano-crystalline NiO-YSZ composite powders have been successfully prepared by microwave-assisted combustion of a gel derived from an aqueous solution containing ZrO(NO₃)₂·6H₂O ,Y(NO₃)₃·6H₂O, Ni(NO₃)₂·6H₂O and glycine. The as-prepared powders were examined using X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques. It was found that the process took only a few seconds to obtain NiO-YSZ composite powders. The as synthesized composite powder was a homogeneous mixture of YSZ, NiO and Ni phases with crystallite size of 24.2, 33.6 and 25.3 nm respectively.     

Study of vanadium(IV) species and corresponding electrochemical performance in concentrated sulfuric acid media

The vanadium(IV) ion is found to form the [VO(SO₄)(H₂O)₄]·H₂O complex, as well as the dimer, [VO(H₂O)₃]₂(μ-SO₄)₂, in concentrated H₂SO₄ media. Their formation mechanisms were investigated by UV–Visible spectroscopy (UV–Vis), Raman spectroscopy, X-ray diffraction (XRD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). UV–Vis spectroscopy study showed that [VO(SO₄)(H₂O)₄]·H₂O concentration in H₂SO₄ solution was proportional to concentrations of VO²⁺ and SO₄²⁻. The increased deviation from the near centrosymmetry of the octahedral complexes is due to the replacement of an equatorial water oxygen in [VO(H₂O)₅]SO₄ by a sulfate oxygen in [VO(SO₄)(H₂O)₄]·H₂O. The dimer shows symmetrical structure, which correlates very well with non-activity in UV–Vis spectroscopic analysis. Structural information on both vanadium(IV) species can be confirmed by Raman and XRD measurements of crystals from the supersaturated solution of VOSO₄ in 1 M, 6 M and 12 M sulfuric acid. A solution of vanadium(IV) (0.05 M) in 12 M H₂SO₄, in which the vanadium(IV) species is [VO(H₂O)₃]₂(μ-SO₄)₂, exhibits a reversible redox behavior near 1.14 V (vs. SCE) on the carbon paper electrode.     

Highly dispersed carbon-supported Pd nanoparticles catalyst synthesized by novel precipitation–reduction method for formic acid electrooxidation

The highly dispersed and ultrafine carbon-supported Pd nanoparticles (Pd/C) catalyst is synthesized by using an improved precipitation–reduction method, which involves in Pd^II → PdO·H₂O → Pd⁰ reaction path. In the method, palladium oxide hydrate (PdO·H₂O) nanoparticles (NPs) with high dispersion is obtained easily by adjusting solution pH in the presence of 1,4-butylenediphosphonic acid (H₂O₃P-(CH₂)₄-PO₃H₂, BDPA). After NaBH₄ reduction, the resulting Pd/C catalyst possesses high dispersion and small particle size. As a result, the electrochemical measurements indicate that the resulting Pd/C catalyst exhibits significantly high electrochemical active surface area and high electrocatalytic performance for formic acid electrooxidation compared with that prepared by general NaBH₄ reduction method.     

A three-dimensional organic–inorganic 3d–4f hybrid polymer constructed with organic pyridinedicarboxylic acid and inorganic lanthanide sulfate skeletons

One 3d–4f heterometallic polymer, namely, {[Eu₂Cu(PDC)₂(SO₄)₂(H₂O)₆]·2H₂O}_n (H₂PDC = pyridine-3,5-dicarboxylic acid), has been successfully synthesized under hydrothermal conditions and structurally characterized. Single-crystal X-ray diffraction analysis reveals that the polymer features an unusual three-dimensional network structure in which infinite lanthanide-carboxylate chains are linked by [Cu(SO₄)₂]²⁻ metalloligands to form a mixed-metal coordination network. Furthermore, luminescent property of the hybrid material has also been investigated at room temperature.     

Formation of LiNi0.5Co0.5VO4 nano-crystals by solvothermal reaction

LiNi_0.5Co_0.5VO₄ nano-crystals were solvothermally prepared using a mixture of LiOH·H₂O, Ni(NO₃)₂·6H₂O, Co(NO₃)₂·6H₂O and NH₄VO₃ in isopropanol at 150–200 °C followed by 300–600 °C calcination to form powders. TGA curves of the solvothermal products show weight losses due to evaporation and decomposition processes. The purified products seem to form at 500 °C and above. The products analyzed by XRD, selected area electron diffraction (SAED), energy dispersive X-ray (EDX) and atomic absorption spectrophotometer (AAS) correspond to LiNi_0.5Co_0.5VO₄. V–O stretching vibrations of VO₄ tetrahedrons analyzed using FTIR and Raman spectrometer are in the range of 620–900 cm⁻¹. A solvothermal reaction at 150 °C for 10 h followed by calcination at 600 °C for 6 h yields crystals with lattice parameter of 0.8252 ± 0.0008 nm. Transmission electron microscope (TEM) images clearly show that the solvothermal temperatures play a more important role in the size formation than the reaction times.     

Electrodeposition of catalytically active nickel-thallium alloy powders from sulphate baths

The electrodeposition of nickel-thallium alloy powder was investigated from acidic sulphate baths containing 0.0125 NiSO₄·6H₂O, 0.005–0.020 Tl Cl, 0.05–0.23 (NH₄)₂SO₄, 0.1 H₃BO₃ and 0.07 mol l^–1 Na₂SO₄ · 10H₂O. The polarization curves, the percentage composition and the current efficiency of the electrodeposited alloy powders were determined as a function of the bath composition. In addition, some properties of the deposits were examined such as the surface morphology, the structure as revealed by X-ray diffraction analysis and the catalytic activity towards the decomposition of 0.4% H₂O₂ solution. The results indicate that the characteristics of the alloy deposition and the properties of the alloy powder are affected to different extents by the bath composition.     

Synthesis and electrochemical performance of LiNi0.5Mn1.5O4 spinel compound

Spinel compound LiNi_0.5Mn_1.5O₄ was synthesized by a chemical wet method. Mn(NO₃)₂, Ni(NO₃)₂·6H₂O, NH₄HCO₃ and LiOH·H₂O were used as the starting materials. At first, Mn(NO₃)₂ and Ni(NO₃)₂·6H₂O reacted with NH₄HCO₃ to produce a precursor, then the precursor reacted with LiOH·H₂O to synthesize product LiNi_0.5Mn_1.5O₄. The product showed a single spinel phase under appropriate calcination conditions, and exhibited a high voltage plateau at about 4.6-4.8 V in the charge/discharge process. The LiNi_0.5Mn_1.5O₄ had a discharge specific capacity of 118 mAh/g at about 4.6 V and 126 mAh/g in total in the first cycle at a discharge current density of 2 mA/cm². After 50 cycles, the total discharge capacity was above 118 mAh/g.     

Hydrolysis Control of AlN Powders for the Aqueous Processing of Spherical AlN Granules

Spherical granules of aluminum nitride (AlN) with an average particle size of about 50 μm were produced from aqueous suspensions using an AlN powder surface treated against hydrolysis with aluminum dihydrogenphosphate [Al(H₂PO₄)₃]. Two different amounts of Al(H₂PO₄)₃ were tested and the effects of surface treatment and aging time were evaluated by various techniques (XRD, TG‐DTA, zeta potential and pH measurements). The treated powder exhibited antihydrolytic property and good dispersing behavior, enabling the preparation of low‐viscosity and high‐concentration aqueous AlN slurries for freeze granulation. The spherical AlN granules were sintered in a boron nitride (BN) powder bed followed by ultrasonic washing of the AlN granulates/BN mixture to remove BN. The sintered spherical AlN granules present excellent crystallinity and high sphericity as observed from SEM micrographs.     

Simple fabrication of polyhedral grain-like microparticle Cu0.5Zn0.5HPO4·H2O and porous structure CuZnP2O7

Polyhedral grain-like microparticle Cu_0.5Zn_0.5(HPO₄)·H₂O was simply synthesized by heterogeneous reaction using a mixture of CuCO₃, ZnO, phosphoric acid and water at room temperature for 30 min. The thermogravimetric study indicates that the synthesized compound is stable below 250 °C and its final decomposed product is CuZnP₂O₇. The pure monoclinic phases of the synthesized Cu_0.5Zn_0.5(HPO₄)·H₂O and its final decomposed product CuZnP₂O₇ are verified by XRD data. The presences of the HPO₄²⁻ ion and H₂O molecule in the Cu_0.5Zn_0.5(HPO₄)·H₂O structure and the P₂O₇⁴⁻ ion in the CuZnP₂O₇ structure are confirmed by FTIR data. The thermal stability, the morphology based on polyhedral grain-like microparticles and porous structure of the studied compounds are different from previously reported phosphates, and may affect their activities for potential applications (catalysis, electronics, etc.).     

Reaction products of triammonium pyrophosphate in different Indian soils

Studies were undertaken on the isolation and identification of reaction products of triammonium pyrophosphate (TPP), the major non-orthophosphate constituent of ammonium polyphosphate newly introduced in India, in representative soils of the alfisol, oxisol, entisol, mollisol and vertisol groups of India. Saturated solution of TPP were reacted with soils for periods of 30 minutes and one day with corresponding precipitation times of 15 days, three months and one year to isolate reaction products which were identified by X-ray diffraction technique, infra-red spectroscopy and chemical analyses. Six reaction products, namely, Ca(NH₄)₂P₂O₇ · H₂O, Mg(NH₄)₂P₂O₇ · 4H₂O, Ca(NH₄)₄H₂(P₂O₇)₂, Ca₃(NH₄)₄H₆(P₂O₇)₄·3H₂O, FeNH₄P₂O₇ and NH₄Al_0·33 Fe_0·67P₂O₇ were identified in different soils; Ca(NH₄)₂P₂O₇·H₂O and Mg(NH₄)₂P₂O₇ · 4H₂O occurring in abundance in most soils. Significant hydrolytic degradation of pyrophosphate reaction products to orthophosphate was not observed.Complementary studies where TPP in solid form was applied to soil, and reaction formed at and around the site of TPP placement were identified after six weeks incubation also showed the formation of Ca(NH₄)₂P₂O₇ · H₂O and Mg(NH₄)₂P₂O₇ · 4H₂O in the soils examined.     

Sonochemical synthesis of monosized spherical BaTiO3 particles

Monosized spherical particles of BaTiO₃ have been successfully synthesized by a sonochemical method in a strong alkaline environment using BaCl₂·2H₂O as the barium source and TiCl₄ as the titanium source. The as-prepared BaTiO₃ powders were characterized by employing techniques including X-ray powder diffraction (XRD), scanning electron microscope (SEM), energy dispersive analysis of X-rays (EDAX) and laser particle size analyzer. The effects of reactant concentrations and Ba/Ti molar ratio on the precipitation of BaTiO₃ particles were briefly investigated. The particles have a monosized spherical morphology and the particle size ranges from submicron (600-800 nm) to nanometer (60-70 nm) by increasing the reactant concentration (from 0.072 mol/L to 0.72 mol/L). The studies indicated that increasing the Ba/Ti ratio can promote synthesis of BaTiO₃.