Structural and phase analysis of multi-ion doped hydroxyapatite for biomedical applications

Multi-ion doping in synthetic HA was carried out using high energy planetary ball milling followed by calcination at 1250?°C for 2?h. The influence of Sr⁺², Zn⁺², Ag⁺, and F^- ion doping on crystallinity and crystallite size was analyzed using Taguchi design of experiments (DOE) and optimal concentration of different dopants has been identified to achieve desired crystallinity and crystallite size. The doped HA samples have been characterized using X-ray diffraction and Fourier transform infrared spectroscopy to determine their phase purity, degree of crystallinity, crystallite size and functional groups. Standard Analysis of variance (ANOVA) showed relatively high contribution of Sr⁺² and Zn⁺² doping in changing the crystallinity and crystal size of HA compared to the effect of Ag⁺ and F^- doping. Our analysis demonstrated strong interaction between dopants at binary level doping, while ternary and quaternary doping of elements did not exhibit any interaction in influencing the crystallinity and crystallite size of HA. In general, multi-ion doping in HA found to decrease its crystallinity from 92% to 72% (max.), but enhance the hardness, depending on the type and concentration of doping element. Similarly, a minimum crystallite size of 31?nm was achieved with some binary compositions and other combinations resulted in crystallite sizes up to 59?nm. The compositions that ensure desired crystallinity and crystallite size can also provide high hardness. Our results can be used to tailor the composition of HA in achieving desired functional properties, dependent on crystallinity and crystallite size, such as strength, bioactivity and degradation to suit variety of implant applications.     

Effect of crystallite size,Raman surface modes and surface basicity on the gas sensing behavior of terbium-doped SnO2 nanoparticles

In the present work, we report the structural, optical and gas sensing properties of Tb³⁺-doped SnO₂ nanoparticles. XRD results confirmed tetragonal rutile structure of both undoped and Tb³⁺-doped SnO₂ nanoparticles which was further confirmed from Raman results. The increase of dopant concentration resulted in decrease in crystallite size which has been confirmed from XRD and TEM results. Raman spectra exhibited bands positioned at 562 and 487 cm⁻¹ whose contribution has been found to increase with decrease in crystallite size. The shifting and broadening of Raman active bands has been explained by well-known phonon confinement model. EDS analysis inveterate presence of terbium in the doped SnO₂ nanoparticles. It has been observed that 3% doped samples exhibited optimum sensor response towards ethanol vapor. The optimum operable temperature of doped samples has been reduced as compared to undoped samples. The enhanced sensor response of doped nanoparticles is attributed to the small crystallite size, high surface basicity and enhanced contribution of Raman surface vibration modes of nanoparticles.     

The influence of reactive milling on the structure and magnetic properties of nanocrystalline MnFe2O4

Nanocrystalline manganese ferrites (MnFe₂O₄) have been synthesized by direct milling of metallic manganese (Mn) and iron (Fe) powders in distilled water (H₂O). In order to overcome the limitation of wet milling, dry milling procedure has also been utilized to reduce crystallite size. The effects of milling time on the formation and crystallite size of wet milled MnFe₂O₄ nanoparticles have been investigated. It has been observed that single phase 18.4 nm nanocrystalline MnFe₂O₄ is obtained after 24 h milling at 400 rpm. Further milling caused deformation of the structure as well as increased crystallite size. With the aim of reducing the crystallite size of 18.4 nm, MnFe₂O₄ sample dry milling has been implemented for 2 and 4 h at 300 rpm. As a result, the crystallite size has been reduced to 12.4 and 8.7 nm, respectively. Effects of the crystalline sizes on magnetic properties were also investigated. Magnetization results clearly demonstrated that crystallite size has much more effect on the magnetic properties than average particle size.     

Crystalline character of native and chemically treated egyptian cottons. II. Computation of variance of x-ray line profile and paracrystalline lattice distortions

A variance range analysis of the x-ray line profiles for seven cottons (native, ureatreated, and mercerized) has been carried out to get two estimates of the crystallite size from (1) the slope and (2) the variance intercept. Assuming the crystallite length of cellulose to be the same in ramie and native cottons under ideal conditions of growth, the relative fluctuation of the repeat length along the b-axis has been calculated for all the samples. This degree of paracrystalline lattice distortions is negatively correlated with the fiber bundle strength at zero gauge and appears to be the same as the imperfections referred to in the weak link theories of fiber strength. While the orientation parameters are also well correlated with strength, the degree of crystallinity does not seem to have any influence. Wilson's rigorous mathematical treatment of the number-average particle size, in relation to the two estimates from the variance slope and intercept as well as the particle size distribution, has been successfully applied for the first time to cotton fibers leading to a clearer understanding of crystallite size–strength relationship.     

Preparation of nanosized TiO2 particles via ultrasonic irradiation and their photocatalytic activity on the decomposition of 4-nitrophenol

TiO₂ nanoparticles were prepared by hydrolysis of TTIP (titanium tetraisopropoxide) using an ultrasonication technique coupled with a sol-gel method. The physical properties of nanosized TiO₂ were investigated. The photocatalytic degradation of 4-nitrophenol was studied by using a batch reactor in the presence of UV light. The crystallite size of the anatase phase is increased with an increase of R_EtOH ratio (EtOH/H₂O molar ratio). The particles’ crystallite size prepared with and without ultrasonic irradiation is marginally different. Those particles prepared with ultrasonic irradiation show a higher activity on the photocatalytic decomposition of 4-nitrophenol compared to those prepared without ultrasonic irradiation. The photocatalytic activity decreases with an increase of R_EtOH ratio. In addition, the photocatalytic activity shows the highest value on the titania particle calcined at 500 ‡C. This paper was presented at the 2004 Korea/Japan/Taiwan Chemical Engineering Conference held at Busan, Korea between November 3 and 4,2004.     

Liquid induced crystallization of poly(ethylene naphthalate) oligomers

Amorphous poly(ethylene naphthalate) (PEN) oligomer has been crystallized at room temperature by treating in liquids having solubility parameter, δ, in the range of 15-29 (J cm⁻³)^1/2. It has been observed that the liquids having δ in the range of 18.5-25 are able to crystallize PEN oligomer efficiently. A direct correlation has been observed between δ and crystallite size calculated from WAXS technique.     

Preparation of Li2TiO3 ceramic with nano-sized pores by ultrasonic-assisted solution combustion

Li₂TiO₃ is a candidate material for tritium breeding in the future nuclear fusion reactor. In this study, Li₂TiO₃ powder was synthesized by ultrasonic-assisted solution combustion synthesis (USCS) in a single step. The ultrasonic transducer with the power of 1000 W was introduced in the synthesis process. The crystallite size of Li₂TiO₃ powder prepared by utilization of ultrasonic power is significantly decreased to ∼5.0 nm, while the one obtained without ultrasonic power is 20.0 nm. Li₂TiO₃ ceramic sintered from USCS powder at 800 °C exhibits the small grain size of 330 nm and the open pores size of 140 nm. The crush load of the ceramic reaches 37.2 N although the structure is porous. Compared with the ceramic prepared by solid-state reaction and conventional solution combustion synthesis, USCS sample has a higher conductivity of 2.0 × 10⁻⁶ S m⁻¹ at room temperature, indicating the lower tritium diffusion barrier in the ceramic.     

Effects of doping content and crystallite size on luminescence properties of Eu3+ doped fluorapatites obtained from natural waste

In this study, Eu³⁺ doped natural fluorapatites [Ca₁₀(PO₄)₆F₂:xEu³⁺ (x = 0.1, 0.3 and 0.5)] were produced from a natural waste by solid-state powder synthesis, conventional sintering, and spark plasma sintering techniques. The effects of doping content and crystallite size on luminescence properties of fluorapatite were investigated by XRD, SEM, and PL analysis. The obtained results showed that luminescence emission's intensity significantly increased with doping content, but no effect was observed on the density and crystallite size. For the samples produced with different methods, emission intensity was the lowest for sintered samples by SPS (1150 °C, 10 min, 50 MPa) with the smallest crystalline size. In contrast, emission intensity was found much higher for synthesized powders with the largest crystallite size. Furthermore, upon excitation under UV radiation, the Eu doped fluorapatites demonstrated the characteristic ⁵D₀–⁷F₂ and ⁵D₀–⁷F₄ emission lines of Eu³⁺ at 618 nm and 704 nm (red region) with an ultrahigh intensity that has been firstly observed in the literature. Therefore, Eu doped fluorapatites, quickly produced from a natural waste in an eco-friendly and cost-effective way, carry a potential to be used in biological applications and lightning applications.     

Thermal conductivity of semicrystalline polymers — a model

The thermal conductivity of semicrystalline polymers, regarded as two-phase materials, is discussed in terms of the Maxwell model generalized to the case where the inclusions are thermally anisotropic. The predicted effect of orientation agrees well with the large anisotropy observed in oriented polymers. The conductivity of the crystallites normal to the chain axes has also been extracted using this model. A recently proposed model for composites which incorporates interfacial boundary resistance has been applied to the low temperature data for poly(ethylene terephthalate), not only explaining the decrease of conductivity with crystallinity, but also allowing the effective crystallite shape and the boundary resistance to be determined. The latter is found to vary as T^?2.     

Electron Microscopy Study of γ-Al2O3 Supported Cobalt Fischer–Tropsch Synthesis Catalysts

Three supported catalysts containing 20 wt% cobalt and 0.5 wt% rhenium were subjected to electron microscopy studies in their calcined state. The catalysts were prepared by incipient wetness impregnation of γ-Al₂O₃ supports of different pore characteristics with aqueous solutions of cobalt nitrate hexahydrate and perrhenic acid. The influence of the support on the Co₃O₄ crystallite size and distribution was studied by X-ray diffraction and electron microscopy. There was a positive correlation between the pore diameter of the support and the post calcination Co₃O₄ crystallite size. On all three γ-Al₂O₃ supports, Co₃O₄ was present as aggregates of many crystallites (20–270 nm in size). Cobalt oxide did not crystallise as independent crystallites, but as an interconnected network, with a roughly common crystallographic orientation, within the matrix pore structure. The internal variations in crystallite size between the catalysts were maintained after reduction. Fischer–Tropsch synthesis was carried out in a fixed-bed reactor at industrial conditions (T = 483 K, P = 20 bar, H₂/CO = 2.1). Although the cobalt-time yields varied significantly (4.6–6.7 × 10^?3 mol CO/mol Co s), the site-time yields were constant (63–68 × 10^?3 s^?1) for the three samples. The C₅₊ selectivity could not be correlated to the cobalt oxide aggregate size and is more likely related to the cobalt particle size and chemical properties of the γ-Al₂O₃ support.     

Synthesis of BaTiO3 by applying the sample controlled reaction temperature (SCRT) method to the thermal decomposition of barium titanyl oxalate

BaTiO₃ samples with a tailored microstructure, specific surface areas ranging from 6.5 to 18.5 m²/g, were obtained from the thermal decomposition of barium titanyl oxalate (BTO) by using a sample controlled reaction temperature (SCRT) method. These samples are constituted by nanosized crystallites with cubic structure. The use of reducing atmosphere promotes the size diminution of the coherently diffraction domains. The crystallite size and the strain of powdered BaTiO₃ samples were measured in several crystallographic directions by using the Warren-Averbach multiple order method. The results have shown that crystallite size is isotropic, whereas the strain has a marked anisotropic character.     

Relations between the structure and the mechanical properties of fluidized-bed pyrolytic carbons

The mechanical properties of fluidized-bed pyrolytic carbons derived from a number of hydrocarbon gases have been related to the density, apparent crystallite size, and degree of preferred orientation. For isotropic carbons with constant crystallite size, the Young's modulus and the fracture stress increase with increasing density. Over a considerable range of density, the Young's modulus follows the relation E = E₀ exp (−BP) where E₀ and B are constants and P is the fractional porosity. Over a similar range of density the increase in fracture stress is apparently related to the changing volume fraction of the pores and not to changes in the critical flaw size or the work of fracture. For isotropic carbons with constant density, the Young's modulus and fracture stress increase with decreasing crystallite size possibly due to cross-linking either between crystallites or between layer planes. For carbons with constant density and crystallite size, the Young's modulus increases and the fracture stress decreases with increasing anisotropy. The variation of the Young's modulus shows fair agreement with the variation expected from constant-stress crystallite averaging while the variation of the fracture stress might be explained by a change in the mode of fracture propagation.     

Low Temperature Electrode Materials Synthesized by Citrate Precursor Method for Solid Oxide Fuel Cells

Homogeneous nanocrystalline NiO–Ce_0.9Ln_0.1O_2–δ (Ln = La, Sm, Gd, and Pr) composite anode and nanocrystalline Ce_0.9Gd_0.1O_2–δ electrolyte material have been successfully synthesized by citrate precursor method. LSCF has been synthesized by conventional solid state method and used as cathode material in our studies. The synthesized powders have been characterized by powder X‐ray diffraction, microscopy, and surface area studies. The average crystallite size of the anode materials has been found to be in the range of 5–15 nm by HRTEM. Highly dense electrolyte and porous electrode materials have been observed by FESEM and confirmed by BET surface area studies. Three cells have been fabricated successfully. Based on the performance of the three cells containing three different anode materials we have achieved better electrochemical characteristics in Ni–GDC with maximum power density of 302 mW cm^–2 and open circuit voltage of 1.012 V at 500 °C. The difference in the performance of the cells containing Ni–GDC as compared to Ni–LDC and Ni–SDC anode is due to changes in the microstructure and crystallite size of anode which affects the electrochemical performance of the cells. The performances of all the cells containing nanocomposite powders are suitable anode materials for low temperature SOFCs.     

Hydrodeoxygenation of p-cresol on unsupported Ni–P catalysts prepared by thermal decomposition method

Unsupported Ni–P catalysts were prepared from the mixed precursor of NiCl₂ and NaH₂PO₂ by thermal decomposition method, and their catalytic activities were measured using the hydrodeoxygenation (HDO) of p-cresol as probe. The effects of the H₂PO₂⁻/Ni^2 + molar ratio in the precursor and the thermal decomposition temperature on the catalyst purity, crystallite size and HDO activity were studied. The HDO of p-cresol on these Ni–P catalysts proceeded with two parallel pathways yielding methylbenzene and methylcyclohexane as final products. The higher HDO catalytic activity of the catalyst was attributed to its bigger crystallite size and purer phase of Ni₂P.     

Controllable crystallite and particle sizes of WO3 particles prepared by a spray‐pyrolysis method and their photocatalytic activity

Information about correlation of material properties parameters (i.e., crystallite and particle sizes) and photocatalytic activity of tungsten trioxide (WO₃) particles are still lacking. For this reason, the purpose of this study was to synthesize WO₃ particles with controllable crystallite (from 18 to 50 nm) and particle sizes (from 58 to 677 nm) using a spray‐pyrolysis method and to investigate correlation of crystallite/particle size and photocatalytic activity. To gain control of crystallite/particle size, synthesis temperature (120–1300^°C) and initial precursor concentration (2.5–15 mmol/L) were investigated, which were then compared with the proposal of the particle formation mechanism. The results showed that both crystallite and particle sizes played an important role in photocatalytic activity. In this research, the optimum condition to produce the highest photocatalytic performance of WO₃ particles was at the temperature of 1200^°C (crystallite size: 25 nm), and initial concentration of 10 mmol/L (particle size: 105 nm). © 2013 American Institute of Chemical Engineers AIChE J, 60: 41–49, 2014     

Effect of mineral acids on the production of alumina nanopowder from raw bauxite

In this study a novel synthetic method for the large-scale production of spherical, high surface area and ultra-fine alumina (Al₂O₃) powder has been described. Synthetic Bayer liquor was extracted by alkali fusion of raw bauxite with sodium hydoxide. Alumina nanopowders were synthesised through a ball mill-aided precipitation method using the synthetic Bayer liquor and mineral acid precipitants. The powders produced were characterised by X-ray diffraction (XRD), particle size distribution (PSD), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller surface area and pore size analysis, energy-dispersive spectroscopy (EDS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In this article, the effects of precipitants such as H₂SO₄, HCl and HNO₃ on crystallite and particle size, surface area, pore volume, and pore size and shape are reported. The experimental results prove that precipitation leads to an aggregated particle that is disaggregated by the ball-milling method. The ball milling process strongly influences the formation of uniform-sized spherical particles with a high surface area. It was revealed that nitric acid is an effective precipitant for controlling particle size and textural properties of Al₂O₃ powder. A nanopowder of γ-Al₂O₃ with an average crystallite size of 3 nm and an average particle size of 58 nm with a specific surface area (SSA) of 190 m² g^− 1 is produced. This article elucidates a new method with a simple reaction scheme for the mass production of Al₂O₃ nanoparticles from raw bauxite for various commercial applications.     

Irradiation behavior of nuclear graphites at elevated temperatures

A number of anisotropic and near-isotropic graphites were irradiated at 300° to 1500°C to fluences of up to 1.5 × 10²²n/cm² (E > 0.18 MeV). The maximum volume contraction of the graphites ranged from 4 to 9 per cent at 4 to 6 × 10²¹ n/cm² at 1175° to 1280°C, and the maximum expansions ranged from 11 to 50 per cent at 1.5 × 10²² n/cm². Pores, located between crystallite clusters, were identified and are shown to be those eliminated by c-axis expansion during densification while intercrystallite pores formed. The rate of elimination of the pores located between crystallite clusters increases while the rate of formation of intercrystallite pores decreases with increasing temperature. During expansion new pores form between filler particles increasing the bulk volume expansion. The dimensional and microstructural changes are correlated with the distribution of apparent crystallite sizes in the graphites; a predominance of highly graphitic structure in each material causes maximum contraction strain and higher expansion rates after turnaround. The thermal expansivity of materials, composed predominantly of anisotropic and highly graphitic structure, increases by a factor of 2, whereas the thermal expansivity of materials predominant in isotropic structure decreases by a factor of 2. Thermal expansivity changes coincide with volume expansions. A graphite with evenly balanced volumes of isotropic and anisotropic structures shows no change in thermal expansivity with fluence. The thermal expansivity changes follow the same correlation with apparent crystallite size and distribution of crystallite sizes as does the maximum volume contraction and expansion rates of the graphites. Near-isotropic graphites that contain a narrow range of crystallite sizes are more stable under fast neutron irradiation at high temperatures than are anisotropic materials which have a wide range of crystallite sizes. The addition of semigraphitic isotropic carbon structure to an anisotropic material improves its stability and reduces the magnitude of the increase in thermal expansivity.     

The influence of concentration on the formation of BaTiO3 by direct reaction of TiCl4 with Ba(OH)2 in aqueous solution

The formation of fine BaTiO₃ particles by reaction between liquid TiCl₄ and Ba(OH)₂ in aqueous solution at 85 °C and pH⩾13 has been studied for 0.062⩽[Ba²⁺]⩽0.51 mol l⁻¹. The concentration of Ba²⁺ ions has a strong influence on reaction kinetics, particle size and crystallite size. When [Ba²⁺]>≈0.12 mol l⁻¹, the precipitate consists of nanosized (≈30 nm) to submicron (100–300 nm) particles of crystalline BaTiO₃. At lower concentrations, the final product is a mixture of crystalline BaTiO₃ and a Ti-rich amorphous phase even for very long reaction times. A two-steps precipitation mechanism is proposed. Initially, a Ti-rich amorphous precipitate is rapidly produced. Reaction between the amorphous phase and the Ba²⁺ ions left in solution then leads to crystallisation of BaTiO₃. In addition to nucleation and growth of nanocrystals, the final size and morphology of BaTiO₃ particles obtained at low concentration can be determined by aggregation of nanocrystals and heterogeneous nucleation on existing crystal surfaces.     

Nanocrystalline gamma-alumina: A highly active catalyst for dimethyl ether synthesis

In this article, mesoporous nanocrystalline γ-Al₂O₃ with high surface area is synthesized by a simple sol-gel method with cationic surfactant as template. This sample is used for vapor-phase dehydration of methanol to Dimethyl ether. The synthesized catalyst showed a high surface area of 375 m² g^− 1 and a crystallite size of about 3.9 nm. NH₃-TPD analysis revealed that the sample with smaller crystallite size possesses higher concentration of medium acidic sites and consequently the catalytic activity.     

Preparation and characterization of nanocrystalline and mesoporous strontium titanate thin films at room temperature

The low temperature perovskite-type strontium titanate (SrTiO₃) thin films and powders with nanocrystalline and mesoporous structure were prepared by a straightforward particulate sol–gel route. The prepared sol had a narrow particle size distribution with hydrodynamic diameter of about 17 nm. X-ray diffraction (XRD) revealed that the synthesized powders had a perovskite-SrTiO₃ structure with preferable orientation growth along the (1 0 0) direction. TEM images showed that the average crystallite size of the powders annealed in the range 300–800°C was around 8 nm. FE-SEM analysis and AFM images revealed that the deposited thin films had mesoporous and nanocrystalline structure with the average grain size of 25 nm at 600°C. Based on Brunauer–Emmett–Taylor (BET) analysis, the synthesized powders showed mesoporous structure with BET surface area in the range 92–75 m²/g at 400–600°C. One of the smallest crystallite sizes and one of the highest surface areas reported in the literature were obtained, which can be used in many applications, such as photocatalysts.