• Volume 36, Issue 5

October 2013,   pages  765-943

• Morphological evolution in single-crystalline Bi2Te3 nanoparticles, nanosheets and nanotubes with different synthesis temperatures

A general surfactant-assisted wet chemical route has been developed for the synthesis of a variety of bismuth telluride (Bi2Te3) single-crystalline nanostructures with varied morphologies at different temperatures in which hydrazine hydrate plays as an important solvent. Bi2Te3 sheet grown nanoparticles, nanosheets and nanotubes have been synthesized by a simplest wet chemical route at 50, 70 and 100 °C within 4 h. Bi2Te3 sheet grown nanoparticles are obtained in agglomerate state and they are found with many wrinkles. Various types of Bi2Te3 nanotubes are also found which are tapered with one end open and the other closed. X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) pattern and energy dispersive X-ray (EDX) spectroscopy were employed to characterize the powder product. It is found that all nanoparticles, nanosheets and nanotubes are well-crystallized nanocrystals and morphologies of the powder products are greatly affected by different synthesis temperatures. The formation mechanisms of bismuth telluride nanostructures are also discussed.

• Synthesis of PbTe nanocubes, worm-like structures and nanoparticles by simple thermal evaporation method

Nanocrystalline PbTe thin films are prepared by thermal evaporation on glass substrates. The investigations of X-ray diffractograms have shown that the structure of film is found to possess stable face centred cubic (fcc) phase in which the grains predominantly grow in the direction of (200) plane. The grain size of the films is within the range of 27–43 nm. Morphologies like assembly of nanoparticles, worm-like structures and nanocubes were prepared by tuning the film thickness. Electrical resistivity is measured using four-probe technique and its thickness dependence has been analysed on the basis of ‘effective mean free path model’. A change in conductivity from 𝑛-type to 𝑝-type is observed due to the increase of migration of tellurium vacancies in the films with temperature. Bandgap energy of the PbTe nanocrystalline thin films suffered a large blue shift of about 1.299 eV due to quantum confinement of charge carriers. The nanocrystalline PbTe thin films of different morphologies such as nanoparticles, wormlike and nanocubes have the optical bandgap energies of 1.61, 1.23 and 1.01 eV, respectively. Photoconductivity measurement shows that the prepared nanocrystalline PbTe thin films of different morphology exhibits good response. This structure induced change in optical properties may have potential applications in optoelectronics devices.

• Study on photocatalysis of TiO2 nanotubes prepared by methanol-thermal synthesis at low temperature

TiO2 nanotubes were synthesized by the solvothermal process at low temperature in a highly alkaline water–methanol mixed solution. Their characteristics were identified by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), specific surface area (BET), Fourier transform infrared spectroscopy (FTIR) and UV–Vis absorption spectroscopy. The as-prepared samples were tested by the photodegradation reaction of methylene blue (MB) dye under visible-light irradiation. The ratios of methanol and water, as well as calcination temperature, affected the morphology, nanostructure and photocatalytic performance. The methanol solvent plays an important role in improving crystallization of the anatase phase, which affects the photocatalytic reaction. Titanate nanotubes were synthesized in methanol–water volume ratios of 10:90, 20:80 and 30:70 which still had high absorbability. Titania nanotubes formed at a calcination temperature of 300 °C using methanol–water volume ratio of 30:70 showed highest photocatalytic performance, much higher than that using water solvent and TiO2–P25 powder.

• Synthesis and properties of new polyimide/clay nanocomposite films

A series of polymer–clay nanocomposite (PCN) materials consisting of polyimide and typical clay were prepared by solution dispersion. Quaternary alkylammonium modified montmorillonite, Cloisite 20A, was used as organoclay. Poly(amic acid) solution was prepared fromthe reaction of benzophenone-4,4′,3,3′-tetracarboxylic dianhydride and 2-(5-(3,5-diaminophenyl)-1,3,4-oxadiazole-2-yl) pyridine in dimethylacetamide. Thermal imidization was performed on poly(amic acid)/organoclay dispersion in a regular temperature-programmed circulation oven. The study of interlayer 𝑑-spacing with X-ray diffraction pattern indicates that an exfoliated structure may be present in the nanocomposite 1%. Intercalated structures were obtained at higher organoclay loadings. Nanocomposites were studied using thermogravimertic analysis and differential scanning calorimetry. Nanocomposites exhibit higher glass transition temperature and improved thermal properties compared to neat polyimide due to the interaction between polymer matrix and organoclay particles. The results are also compared with data of a similar work. Morphology study with scanning electron microscopy showed that the surface roughness in nanocomposite 1%increased with respect to pristine polyimide. Solvent uptake measurements were also carried out for the prepared materials. Maximum solvent adsorption was observed for dimethyl sulfoxide (DMSO). It was found that the solvent uptake capacity decreased with increasing clay content.

• Influence of surfactant concentration on nanohydroxyapatite growth

Nanohydroxyapatite particles with different morphologies were synthesized through a microwave coupled hydrothermal method using CTAB as a template. A successful synthesis of nanosized HAP spheres, rods and fibres is achieved through this method by controlling the concentration of the surfactant. The concentration of the surfactant was tuned in such a way that the desired HAP nanostructures were obtained. The resultant powders were sintered at 900 °C in order to obtain phase pure HAP particles. The results obtained by Fourier transform infrared spectroscopy (FT–IR), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques have substantiated the formation of nanosized HAP spheres and fibres.

• Thickness effect on properties of titanium film deposited by d.c. magnetron sputtering and electron beam evaporation techniques

This paper reports effect of thickness on the properties of titanium (Ti) film deposited on Si/SiO2 (100) substrate using two different methods: d.c. magnetron sputtering and electron beam (e-beam) evaporation technique. The structural and morphological characterization of Ti film were performed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). XRD pattern revealed that the films deposited using d.c. magnetron sputtering have HCP symmetry with preferred orientation along (002) plane, while those deposited with e-beam evaporation possessed fcc symmetry with preferred orientation along (200) plane. The presence of metallic Ti was also confirmed by XPS analysis. FESEM images depicted that the finite sized grains were uniformly distributed on the surface and AFM micrographs revealed roughness of the film. The electrical resistivity measured using four-point probe showed that the film deposited using d.c. magnetron sputtering has lower resistivity of ∼13 𝜇 𝛺 cm than the film deposited using e-beam evaporation technique, i.e. ∼60 𝜇 𝛺 cm. The hardness of Ti films deposited using d.c. magnetron sputtering has lower value (∼7.9 GPa) than the film deposited using e-beam technique (∼9.4 GPa).

• Swift heavy ion irradiation induced modification of structure and surface morphology of BiFeO3 thin film

BiFeO3 (BFO) thin films of thickness about 800 nm deposited on Si (100) substrates by sol–gel spin coating method were irradiated by 200 MeV Ag ions. Modification of structure and surface morphology of the films under irradiation was studied using glancing incidence X-ray diffraction (GIXRD) and atomic force microscope (AFM). Fluence dependence of GIXRD peak intensity indicated formation of 10 nm diameter cylindrical amorphous columns in crystalline BFO due to 200 MeV Ag ion irradiation. AFM analysis indicated that the pristine film consists of agglomerated grains with diffuse grain boundary. Irradiation led to reduced agglomeration of the grains with the formation of sharper grain boundaries. The rms roughness (𝜎rms) estimated from AFM analysis increased from 6.2 in pristine film to 12.7 nm when the film irradiated at a fluence of 1 × 1011 ions cm-2. Further irradiation led to decrease of 𝜎rms which finally saturated at a value of 7–8 nm at high ion fluences. The power spectral density analysis indicated that the evolution of surface morphology of the pristine film is governed by the combined effect of evaporation condensation and volume diffusion processes. Swift heavy ion irradiation seems to increase the dominance of volume diffusion in controlling surface morphology of the film at high ion fluences.

• Study of high mobility carriers in Ni-doped CdO films

Cadmium oxide (CdO) doped with different amounts of nickel ion thin films have been prepared on silicon and glass substrates by vacuum evaporation technique. The effects of nickel doping on the structural, electrical, optical and optoelectronic properties of the host CdO films were systematically studied. The sample elemental composition was determined by the X-ray fluorescence spectroscopy method. The X-ray diffraction method was used to study the crystalline structure of the samples. It shows that some of Ni3+ ions occupy mainly locations when in interstitial positions and Cd2+-ion vacancies of CdO lattice. The bandgap of Ni-doped CdO suffers narrowing till 10–12% compared to undoped CdO. Such bandgap narrowing was studied within the framework of the available models. The electrical behaviours show that all the prepared Ni-doped CdO films are degenerate semiconductors. However, the nickel doping influences all the optoelectrical properties of CdO. Their d.c. conductivity, carrier concentration and mobility increased compared to undoped CdO film. The largest mobility of 112.6 cm2/V.s was measured for 1–2% Ni-doped CdO film. From optoelectronics point of view, Ni-doped CdO can be used in infrared-transparent-conducting-oxide (NIR–TCO) applications.

• Use of co-spray pyrolysis for synthesizing nitrogen-doped TiO2 films

Nitrogen-doped nanocrystalline TiO2 is well known as the most promising photocatalyst. Despite many years after discovery, seeking of efficient method to prepare TiO2 doped with nitrogen still attracts a lot of attention. In this paper, we present the result of using co-spray pyrolysis to synthesize nitrogen-doped TiO2 films from TiCl4 and NH4NO3. The grown films were subjected to XRD, SEM, photocatalysis, absorption spectra and visible-light photovoltaic investigations. All the deposited films were of nanosized polycrystal, high crystallinity, pure anatase and porosity. Specific characteristics involved nitrogen doping such as enhanced photocatalytic activity, bandgap narrowing, visible light responsibility and typical correlation of the photoactivity with nitrogen concentration were all exhibited. Obtained results proved that high photoactive nitrogen-doped TiO2 films can be synthesized by co-spray pyrolysis.

• Effect of chain conformation on micro-mechanical behaviour of MEH–PPV thin film

The morphology, photoluminescent properties and micro-mechanical character of poly[2-methoxy-5-(2'-ethylhexyloxy)-𝑝-phenylene vinylene] (MEH–PPV) thin films prepared from toluene (T film) and chloroform (C film) were studied by transmission electron microscopy (TEM), absorption, photoluminescence spectrophotometry and nanoindentation test. The morphological feature of worm-like entities which appeared in T film was ∼10–20 nm in length and 3–5 nm in width. The C film displayed the continuous cotton fibre-shaped morphology. In contrast with C film, the band-edge absorption and maximum emission for T film shifted to the longer wavelength. An analysis fromTEM photograph, absorption and photoluminescence spectra indicated that different chain conformation presented in these two kinds of films. The nanoindentation test showed that the elastic modulus and indentation hardness of T film under the same experimental parameter (load: 50–200 𝜇N, loading rate: 20 𝜇N/s and holding time: 20 s) decreased by 33.3 ± 0.3 and 8.9 ± 0.5%, respectively comparing with C film. In addition, critical bending radius of these two films based on the flexible base was also evaluated from the obtained experimental results.

• Microstructure and properties of Ti–Nb–V–Mo-alloyed high chromium cast iron

The correlations of microstructure, hardness and fracture toughness of high chromium cast iron with the addition of alloys (titanium, vanadium, niobium and molybdenum) were investigated. The results indicated that the as-cast microstructure changed from hypereutectic, eutectic to hypoeutectic with the increase of alloy contents. Mo dissolved in austenite and increased the hardness by solid solution strengthening. TiC and NbC mainly existed in austenite and impeded the austenite dendrite development. V existed in multicomponent systems in forms of V alloy compounds (VCrFe8 and VCr2C2).With the increase of alloy additions, carbides size changed gradually from refinement to coarseness, hardness and impact toughness were increased and then decreased. Compared with the fracture toughness (6 J/cm2) and hardness (50.8HRC) without any alloy addition, the toughness and hardness at 0.60 V–0.60Ti–0.60Nb–0.35Mo (wt%) additions were improved and achieved to 11 J/cm2 and 58.9HRC, respectively. The synergistic roles of Ti, Nb, V and Mo influenced the solidification behaviour of alloy. The refinement of microstructure and improvement of carbides morphologies, size and distribution improved the impact toughness.

• Optimum synthesis conditions of nanometric Fe50Ni50 alloy formed by chemical reduction in aqueous solution

In the present article, various nanometric Fe50Ni50 alloys were synthesized by chemical reduction of the corresponding metal ions, with hydrazine in an aqueous solution. Process variables of reaction temperature, pH of the hydrazine solution and concentration of metal ions were varied in order to determine the optimum synthesis conditions regarding quality, productivity and cost. It is found that pH of hydrazine solution, at low concentration of metal ions, is the most crucial variable affecting the reaction rate, average crystallite and particle sizes of the synthesized nanometric Fe50Ni50 alloy, followed by the total concentration of metal ions. Thus, increase of pH of hydrazine solution acts as an efficient stabilizer in reducing the particle size. On the contrary, at high concentration of metal ions, the structural characteristics of the nanometric Fe50Ni50 alloy are almost insensitive to reaction temperature and pH of hydrazine solution, but the reduction rate is remarkably sensitive to reaction temperature. Based on these results, it is decided that a reaction temperature of 80 °C, pH of the hydrazine solution of 12.5 and concentration of metal ions of 0.6 M represent the optimum synthesis conditions. The role of pH of hydrazine solution in reducing the alloy’s average particle size as well as efficient stabilizer confirms tremendous effect of synthesis conditions on the alloy structure and therefore, the importance of this study for industrial production of nanometric Fe50Ni50 alloy.

• Reduction in thermal conductivity of Bi–Te alloys through grain refinement method

Ternary alloys of thermoelectric materials Bi–Sb–Te and Bi–Se–Te of molecular formula, Bi0.5Sb1.5Te3 (𝑝 type) and Bi0.36Se0.064Te0.576 (𝑛 type), were prepared by mechanical alloying method. The preparation of materials by mechanical alloying method has effectively reduced the thermal conductivity by generating a large number of induced grain boundaries with required degree of disorder. The process of frequent milling was adapted for grain refinement. Substantial reduction in thermal conductivity was achieved due to nano-structuring of these alloys. Thermal conductivity values were found to be very low at room temperature, 0.5W/mK and 0.8W/mK, respectively for p and n type materials.

• Structural and mechanical behaviour of 5% Al2O3-reinforced Fe metal matrix composites (MMCs) produced by powder metallurgy (P/M) route

The aim of this paper is to investigate the effect of sintering temperature and time on the properties of Fe–Al2O3 composite (5 wt% Al2O3; 95 wt% Fe) prepared by powder metallurgy process. X-ray diffraction, microstructure, density, hardness and compressive strength of prepared samples have been investigated. XRD studies show the presence of Fe and Al2O3 along with iron aluminate phase. Iron aluminate is formed as a result of reactive sintering between iron and alumina particles. Microstructural examination of the specimen showed a dense structure with nanosize dispersion of the reinforcement of ceramic phase. Density as well as hardness of specimens depend on the formation of iron aluminate phase, which in turn depends on sintering temperature and time.

• Preparation of novel CdS-graphene/TiO2 composites with high photocatalytic activity for methylene blue dye under visible light

In this study, CdS combined graphene/TiO2 (CdS-graphene/TiO2) composites were prepared by a sol–gel method to improve on the photocatalytic performance of TiO2. These composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and transmission electron microscopy (TEM). The photocatalytic activities were examined by the degradation of methylene blue (MB) under visible light irradiation. The photodegradation rate of MB under visible light irradiation reached 90.1% during 150 min. The kinetics of MB degradation were plotted alongside the values calculated from the Langmuir–Hinshelwood equation. 0.1 CGT sample showed the best photocatalytic activity, which was attributed to a cooperative reaction between the increase of photo-absorption effect by graphene and photocatalytic effect by CdS.

• Effect of CuO addition on structure and electrical properties of low temperature sintered quaternary piezoelectric ceramics

The ceramics were prepared successfully by CuO additions to Pb[(Mn1/3Sb2/3)0.06(Ni1/2W1/2)0.02-(Zr0.49Ti0.51)0.92]O3. Effect of the addition on sintering temperature, structure and electrical properties of ceramics was investigated. The piezoelectric ceramics was prepared by solid-state reaction. Sintering experiments were accomplished at temperature between 950 and 1100 °C added 0.3–1.0 wt% CuO. The sintering temperature was reduced from 1250 °C (without CuO additions) to 970 °C when CuO-doped. The ceramics sintered at 970 °C for 2 h with 0.7 wt% CuO exhibited 𝜀r = 1845, tan 𝛿 = 0.15%, 𝑑33 = 395 pC/N, 𝑘p = 0.58 and 𝑄m = 1830, which were the highest values. With increasing CuO doping, 𝑇c becomes lower. Jahn–Teller effect was used to explain the contraction of 𝑐-axis and simultaneous extension of 𝑎-axis in the lattice.

• Structural, dielectric and electrical properties of Li2Pb2La2W2Ti4Nb4O30 ceramic

Li2Pb2La2W2Ti4Nb4O30 complex ferroelectric oxide was prepared by using a high-temperature solidstate reaction method (calcination temperature, ∼1100 °C and sintering temperature, ∼1150 °C). Room temperature preliminary structural analysis shows formation of a single-phase compound. The nature of microstructure (i.e. grain distribution, presence of voids, grain size, etc) recorded using scanning electron microscope (SEM) clearly suggests the formation of high quality and density of pellet samples. Studies of temperature dependence of dielectric constant, tangent loss and polarization show the existence of ferroelectric phase transition in the material at high temperature (307 °C). Detailed studies of temperature dependence of electrical parameters (i.e. impedance (400−475 °C),modulus, conductivity, etc) of the material clearly suggest a strong correlation between itsmicrostructure (i.e. bulk, grain boundary, etc) and electrical properties. The nature of temperature variation of d.c. conductivity showed an Arrhenius behaviour of the material. A signature of ionic conductivity in the material was observed in its a.c. conductivity spectrum. The nature of frequency dependence of a.c. conductivity of the material can be explained by Jonscher’s universal power law. Electrical transport properties of the material show existence of non-exponential type of conductivity relaxation.

• Relaxor behaviour and dielectric properties of BiFeO3 doped Ba(Zr0.1Ti0.9)O3 ceramics

Ba1−𝑥Bi𝑥(Ti0.9Zr0.1)1−𝑥Fe𝑥O3 (𝑥 = 0–0.075) ceramics are prepared using a conventional solid state reaction method. X-ray diffraction shows the presence of a single phase. Addition of Bi3+ and Fe3+ strongly influences the crystal structure and dielectric properties of the ceramics. The evolution from a normal ferroelectric to a relaxor ferroelectric is emphasized. Ba0.99Bi0.01(Ti0.9Zr0.1)0.99Fe0.01O3 ceramic shows a relaxor behaviour at room temperature with 𝛥 𝑇m =12 K. 𝑃–𝐸 hysteresis loop of the composition, 𝑥 = 0.007, shows a remanent polarization (𝑃r) of 0.5 𝜇C/cm2 with a coercive field (𝐸C) of 2 kV/cm. Raman spectra of all compounds are performed and correlated well with the X-ray diffraction and dielectric measurement results.

• Effect of stabilizer on optical and structural properties of MgO thin films prepared by sol–gel method

The effects of monoethanolamine (MEA) and acetylacetone (ACAC) addition as stabilizer on the crystallization behaviour, morphology and optical properties of magnesium oxide were investigated using thermogravimetry (TG/DTG), X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Visible, photoluminescence (PL) and Fourier transform infrared (FTIR) spectroscopy. Stabilizer addition reduces transparency of the films. MgO films prepared at 500 °C showed weak orientation of (200). However, the films prepared by addition of stabilizer are amorphous. MgO powders were prepared for exhibiting the structural properties. The patterns of MgO powders showed a preferred orientation of (200). The addition of stabilizer causes a reduction in grain size. SEM micrographs show that a homogenous and crack-free film can be prepared at 500 °C and addition of stabilizer causes an increase in packing density.

• Sintering behaviour and mechanical properties of Cr3C2–NiCr cermets

Cr3C2–NiCr cermets are used as metal cutting tools due to their relatively high hardness and low sintering temperatures. In this study, a powder mixture consisting of 75 wt% Cr3C2–25 wt% NiCr was sintered at four different temperatures and characterized for itsmicrostructure and mechanical properties. The highest relative density obtained was 97% when sintered at 1350 °C. As the relative density increased, elastic modulus, transverse rupture strength, fracture toughness and hardness of the samples reached to a maximum of 314 GPa, 810 MPa, 10.4 MPa.m1/2 and 11.3 GPa, respectively. However, sintering at 1400 °C caused further grain growth and pore coalescence which resulted in decreasing density and degradation of all mechanical properties. Fracture surface investigation showed that the main failure mechanism was the intergranular fracture of ceramic phase accompanied by the ductile fracture of the metal phase which deformed plastically during crack propagation and enhanced the fracture toughness.

• Thermally stimulated luminescence and photoluminescence investigations of Eu3+ and Eu2+ doped SrBPO5

Thermally stimulated luminescence (TSL) investigations of SrBPO5:Eu3+ and SrBPO5:Eu2+ phosphors were carried out in the temperature range of 300–650 K. In order to characterize the phosphors, X-ray diffraction and photoluminescence (PL) techniques were used. The emission spectrum of air heated SrBPO5:Eu3+ phosphor exhibited emission bands at 590, 614, 651 and 702 nm under 248 nm excitation, assigned to transitions of Eu3+ ion. In phosphor prepared in reducing (Ar + 8% H2) atmosphere, a broad emission band due to Eu2+ ranging from 350 to 400 nm was observed with 340 nm excitation. EPR studies have confirmed the presence of Eu2+ ions in the samples prepared in reducing atmosphere. TSL glow curve of SrBPO5:Eu3+ had shown intense peaks around 397, 510, 547 K and a weak peak around 440 K whereas in case of SrBPO5:Eu2+ system, glow peaks at 414, 478 and weak peak at 516 nm were observed. The shift in TSL glow pattern can be attributed to stabilization of different oxidation states of the dopant ion in the host lattice. Apart from this, TSL trap parameters such as trap depth and frequency factor were determined. Spectral characteristics of TSL emission have shown that Eu3+/Eu2+ ion acts as the luminescent centre in the respective phosphors.

• Structural properties of Cd–Co ferrites

Ferrite samples with composition, Cd𝑥Co1−𝑥Fe2O4 (𝑥 = 0.80, 0.85, 0.90, 0.95 and 1.0), were prepared by standard ceramic method and characterized by XRD, IR and SEM techniques. X-ray analysis confirms the formation of single phase cubic spinel structure. Lattice constant and grain size of the samples increase with increase in cadmium content. Bond length (A–O) and ionic radii (𝑟A) on 𝐴-sites increase, whereas bond length (B–O) and ionic radii (𝑟B) on 𝐵-site decrease. The crystallite sites of the samples lie in the range of 29.1–42.8 nm. IR study shows two absorption bands around 400 cm-1 and 600 cm-1 corresponding to tetrahedral and octahedral sites, respectively.

• Electronic spectra of anions intercalated in layered double hydroxides

Transition metal complexes intercalated in layered double hydroxides have a different electronic structure as compared to their free state owing to their confinement within the interlayer gallery. UV–Vis absorptions of the intercalated complex anions show a significant shift as compared to their free state. The ligand to metal charge transfer transitions of the ferricyanide anion show a red shift on intercalation. The ferrocyanide ion shows a significant blue shift of 𝑑–𝑑 bands due to the increased separation between 𝑡2g and 𝑒g levels on intercalation. MnO$^{-}_{4}$ ion shows a blue shift in its ligand to metal charge transfer transition since the non-bonding 𝑡1 level of oxygen from which the transition arises is stabilized.

• Effect of anodization on corrosion behaviour and biocompatibility of Cp-titanium in simulated body fluid

The objective of this investigation is to study the effectiveness of anodized surface of commercial purity titanium (Cp-Ti) on its corrosion behaviour in simulated body fluid (SBF) and proliferation of osteoblast cells on it, to assess its potentiality as a process of surface modification in enhancing corrosion resistance and osseointegration of dental implants. Highly ordered nano-porous oxide layer, with nano-sized pores, is developed on the surface of Cp-Ti through electrochemical anodization in the electrolyte of aqueous solution of 0.5% HF at 15 V for 30 min at 24 °C. The nano-porous feature of the anodized surface is characterized by field-emission scanning electron microscope (FESEM). Pores of some anodized samples are sealed by exposing the anodized surface in boiling water. Corrosion behaviour of the anodized specimen is studied in Ringer’s solution at 30 ± 2 °C, using electrochemical impedance and cyclic polarization technique. Biocompatibility of the anodized surface is accessed using MG63 osteoblast cells. Both corrosion as well as pitting resistance of Cp-Ti in simulated body fluid are found to be highest in the anodized and sealed condition and followed in decreasing order by those of anodized and unanodized ones. Significantly higher MG63 osteoblast cell proliferations are found on the anodized surface than that on the unanodized one. Anodized Cp-Ti develops nano-size surface pores, like that of natural bone. It enhances corrosion and pitting resistance and also the process of osteoblast cell proliferation on Cp-Ti.

• Crystalline perfection and optical properties of rapid grown KH2PO4 crystal with chromate additive

Potassium dihydrogen phosphate (KDP) crystals were grown in the presence of a series of chromate (CrO$^{2-}_{4}$) additive concentrations via rapid growth method. CrO$^{2-}_{4}$ made KDP crystals were coloured by yellowgreen, suggesting CrO$^{2-}_{4}$ had entered into the crystal lattice. The elemental analysis indicated that Cr element in KDP crystal was at ppm level. High resolution X-ray diffraction data revealed that the crystalline perfection of these as-grown KDP crystals was destroyed after CrO$^{2-}_{4}$ entered into crystal lattice, embedded in the full width at half maximum was broadened and satellite peaks appeared. Additionally, the extinction ratio was decreased with rise of CrO$^{2-}_{4}$ concentration. CrO$^{2-}_{4}$ introduced two absorption peaks centred at 360 and 280 nm and enhanced the intrinsic absorption near 220 nm, which were at the same band positions compared with the CrO$^{2-}_{4}$ or HCrO$^{-}_{4}$ transmittance spectra. Additionally, CrO$^{2-}_{4}$ could increase the size of light scattering, which was attributed to the point defects and microscopic defects by the replacement by CrO$^{2-}_{4}$ at PO$^{3-}_{4}$ position.

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