Issues

Journal & Issues

AHEAD OF PRINT

Volume 40 (2022): Issue 2 (August 2022)

Volume 40 (2022): Issue 1 (March 2022)

Volume 39 (2021): Issue 4 (December 2021)

Volume 39 (2021): Issue 3 (September 2021)

Volume 39 (2021): Issue 2 (June 2021)

Volume 39 (2021): Issue 1 (March 2021)

Volume 38 (2020): Issue 4 (December 2020)

Volume 38 (2020): Issue 3 (September 2020)

Volume 38 (2020): Issue 2 (June 2020)

Volume 38 (2020): Issue 1 (March 2020)

Volume 37 (2019): Issue 4 (December 2019)

Volume 37 (2019): Issue 3 (September 2019)

Volume 37 (2019): Issue 2 (June 2019)

Volume 37 (2019): Issue 1 (March 2019)

Volume 36 (2018): Issue 4 (December 2018)

Volume 36 (2018): Issue 3 (September 2018)

Volume 36 (2018): Issue 2 (June 2018)

Volume 36 (2018): Issue 1 (March 2018)

Volume 35 (2017): Issue 4 (December 2017)

Volume 35 (2017): Issue 3 (October 2017)

Volume 35 (2017): Issue 2 (July 2017)

Volume 35 (2017): Issue 1 (March 2017)

Volume 34 (2016): Issue 4 (December 2016)

Volume 34 (2016): Issue 3 (September 2016)

Volume 34 (2016): Issue 2 (June 2016)

Volume 34 (2016): Issue 1 (March 2016)

Volume 33 (2015): Issue 4 (December 2015)

Volume 33 (2015): Issue 3 (September 2015)

Volume 33 (2015): Issue 2 (June 2015)

Volume 33 (2015): Issue 1 (March 2015)

Volume 32 (2014): Issue 4 (December 2014)

Volume 32 (2014): Issue 3 (September 2014)

Volume 32 (2014): Issue 2 (June 2014)

Volume 32 (2014): Issue 1 (January 2014)

Volume 31 (2013): Issue 4 (October 2013)

Volume 31 (2013): Issue 3 (August 2013)

Volume 31 (2013): Issue 2 (April 2013)

Volume 31 (2013): Issue 1 (January 2013)

Volume 30 (2012): Issue 4 (December 2012)

Volume 30 (2012): Issue 3 (September 2012)

Volume 30 (2012): Issue 2 (June 2012)

Volume 30 (2012): Issue 1 (March 2012)

Volume 29 (2011): Issue 4 (December 2011)

Volume 29 (2011): Issue 3 (September 2011)

Volume 29 (2011): Issue 2 (June 2011)

Volume 29 (2011): Issue 1 (March 2011)

Journal Details
Format
Journal
eISSN
2083-134X
First Published
16 Apr 2011
Publication timeframe
4 times per year
Languages
English

Search

Volume 32 (2014): Issue 3 (September 2014)

Journal Details
Format
Journal
eISSN
2083-134X
First Published
16 Apr 2011
Publication timeframe
4 times per year
Languages
English

Search

30 Articles
Open Access

Capacitive behavior of highly-oxidized graphite

Published Online: 17 Oct 2014
Page range: 307 - 314

Abstract

Abstract

Capacitive behavior of a highly-oxidized graphite is presented in this paper. The graphite oxide was synthesized using an oxidizing mixture of potassium chlorate and concentrated fuming nitric acid. As-oxidized graphite was quantitatively and qualitatively analyzed with respect to the oxygen content and the species of oxygen-containing groups. Electrochemical measurements were performed in a two-electrode symmetric cell using KOH electrolyte.

It was shown that prolonged oxidation causes an increase in the oxygen content while the interlayer distance remains constant. Specific capacitance increased with oxygen content in the electrode as a result of pseudo-capacitive effects, from 0.47 to 0.54 F/g for a scan rate of 20 mV/s and 0.67 to 1.15 F/g for a scan rate of 5 mV/s. Better cyclability was observed for the electrode with a higher oxygen amount.

Keywords

  • graphite oxide
  • oxidation
  • supercapacitors
Open Access

Synthesis, characterization, DC-electrical conductivity and γ-ray effect on Ag1+, Y3+ double doped nano lithium manganates (LiMn2−2x AgxYxO4) for rechargeable batteries

Published Online: 17 Oct 2014
Page range: 315 - 323

Abstract

Abstract

Pristine lithium manganate (LiMn2O4) and Ag1+, Y3+ double doped nano lithium manganate [LiMn2−2x AgxYxO4, (x = 0.025, 0.05)] spinels were synthesized via a coprecipitation method for rechargeable batteries applications. The synthesized LiMn1.9Ag0.05Y0.05O4 was exposed to different doses of γ-irradiation (10 and 30 kGy). The resulting spinel products were characterized by using thermogravimetric and differential thermal analysis (TG/DTA), X-ray diffraction (XRD), infrared (IR) spectroscopy, scanning electron microscopy (SEM), energy dispersive analysis of X-rays (EDAX), electronic (UV-Vis) and electron spin resonance (ESR) spectra. LiMn2O4 exhibited a discharge capacity of 124 mAhg−1 while LiMn1.9Ag0.05Y0.05O4 had discharge capacities of 129 and 137 mAhg−1 for non irradiated and γ-irradiated (30 kGy) samples, respectively. The effects of the dopant cations and γ-irradiation on the discharge capacity and DC-electrical conductivity of some synthesized spinels were studied.

Keywords

  • nano lithium manganates
  • Ag1+, Y3+ double doped
  • γ-ray effect
Open Access

Ab-initio studies of thermal and superconducting properties of HfX2 alloys (X = Tc, Re, and Os)

Published Online: 17 Oct 2014
Page range: 324 - 330

Abstract

Abstract

A systematic study of thermal properties such as the Debye temperature, specific heat coefficient, Grüneisen constant, electron-phonon coupling constant and transition temperature have been carried out using the results of electronic band structure and related characteristics, for hafnium superconducting alloys, namely, HfTc2, HfRe2 and HfOs2. Computation of the electronic band structure and associated properties has been carried out using the tight-binding-linear-muffin-tin-orbital (TBLMTO) method within atomic sphere approximation (ASA). The calculated values have been compared with the available results of literature data.

Keywords

  • Debye temperature
  • specific heat coefficient
  • Grüneisen constant
  • electron-phonon coupling constant
  • transition temperature
Open Access

Correlation between structural and electrical properties in highly porous (Y,Sr)(Ti,Nb)O3−δ SOFC anodes

Published Online: 17 Oct 2014
Page range: 331 - 340

Abstract

Abstract

In order to find a relationship between structural and electrical properties, niobium and yttrium doped SrTiO3 ceramics were prepared via solid-state reaction. The samples were sintered in hydrogen and air conditions. The samples were also fabricated with a pore-former to obtain highly porous specimens. The electrical properties of Nb-doped SrTiO3 samples and yttrium and niobium co-doped SrTiO3 were compared. The comparable electrical properties were observed and discussed according to previous literature reports. It was noticed that the synthesis in a reducing hydrogen atmosphere can increase the solubility of dopants. Moreover, the samples sintered in air presented lower conductivity level and worse structural properties than the samples sintered in hydrogen. The explanation of obtained results was also suggested and discussed.

Keywords

  • perovskite
  • doped strontium titanate
  • porous ceramic
  • SOFC anodes
Open Access

Investigation on compressive behavior of Cu-35Ni-15Al alloy at high temperatures

Published Online: 17 Oct 2014
Page range: 341 - 349

Abstract

Abstract

Microstructures and mechanical properties of Cu-35Ni-15Al alloy in cast and porous states were studied by scanning electron microscopy and compression tests. The influence of porosity, deformation temperature and loading rate on mechanical properties of the two kinds of alloys was investigated. The results show that the as cast alloy and porous alloys have almost the same phase constitution: Cu rich phase, Ni rich phase and K intermetallics. The yield strength of porous alloys increases continuously with decreasing porosity, the relationship between porosity and yield stress follows Gibson-Ashby equation. With decreasing deformation temperature, the yield strength of as cast alloy and porous alloy increase. With the increase of loading rate, the yield strength of these alloys shows an increasing trend. After compression, the microstructure of as cast alloy is more uniform, and porous alloys are more prone to have localized deformations.

Keywords

  • Cu-35Ni-15Al alloy
  • compression
  • deformation temperature
  • loading rate
Open Access

Structural elastic and thermal properties of SrxCd1−x O mixed compounds — a theoretical approach

Published Online: 17 Oct 2014
Page range: 350 - 357

Abstract

Abstract

In the present paper, the structural and mechanical properties of alkaline earth oxides mixed compound SrxCd1−x O (0 ≤ x ≤ 1) under high pressure have been reported. An extended interaction potential (EIP) model, including the zero point vibrational energy effect, has been developed for this study. Phase transition pressures are associated with a sudden collapse in volume. Phase transition pressure and associated volume collapses [ΔV (Pt)/V(0)] calculated from this approach are in good agreement with the experimental values for the parent compounds (x = 0 and x = 1). The results for the mixed crystal counterparts are also in fair agreement with experimental data generated from the application of Vegard’s law to the data for the parent compounds.

Keywords

  • oxide
  • alloy
  • volume collapse
  • phase transition
  • high pressure
Open Access

Fabrication of highly-transparent Er:CaF2 ceramics by hot-pressing technique

Published Online: 17 Oct 2014
Page range: 358 - 363

Abstract

Abstract

Highly-transparent trivalent erbium ion doped calcium fluoride (5 mol % Er:CaF2) ceramics were fabricated by a hotpressing (HP) method using high-purity Er:CaF2 nanoparticles, which were synthesized by co-precipitation method. The mean grain size of the nanoparticles was about 24.7 nm. The nanoparticles were sintered at 600 °C, 700 °C, 800 °C and 900 °C, respectively, for 30 min under a uniaxial pressure of 30 MPa and vacuum of 10−3 Pa with 1 mol % lithium fluoride (LiF) as sintering additive. The 5 mol % Er:CaF2 ceramics sintered at 800 °C exhibits high density and pore-free microstructure with an average grain size of about 8 μm. The optical transmittance of the transparent ceramics is close to 85 % at visible and nearinfrared wavelengths. The strong and broad absorptions peaks corresponding to characteristic absorption of trivalent erbium ions make the ceramics a potential candidate for infrared and upconversion laser operating.

Keywords

  • calcium fluoride
  • transparent ceramics
  • nanoparticles
  • transmittance
Open Access

In vitro evaluation of bioactivity of SiO2-CaO-P2O5-Na2O-CaF2-ZnO glass-ceramics

Published Online: 17 Oct 2014
Page range: 364 - 374

Abstract

Abstract

Zinc is an essential trace element that stimulates bone formation but it is also known as an inhibitor of apatite crystal growth. In this work addition of ZnO to SiO2-CaO-P2O5-Na2O-CaF2 glass-ceramic system was made by conventional melt-quenching technique. DSC curves showed that the addition of ZnO moved the endothermic and exothermic peaks to lower temperatures. X-ray diffraction analysis did not reveal any additional phase caused by ZnO addition and showed the presence of wollastonite and hydroxyapatite crystalline phases only in all the glass-ceramic samples. As bio-implant apatite forming ability is an essential condition, the surface reactivity of the prepared glass-ceramic specimens was studied in vitro in Kokubo’s simulated body fluid (SBF) [1] with ion concentration nearly equal to human blood plasma for 30 days at 37 °C under static condition. Atomic absorption spectroscopy (AAS) was used to study the changes in element concentrations in soaking solutions and XRD, FT-IR and SEM were used to elucidate surface properties of prepared glass-ceramics, which confirmed the formation of HCAp on the surface of all glass-ceramics. It was found that the addition of ZnO had a positive effect on bioactivity of glass-ceramics and made it a potential candidate for restoration of damaged bones.

Keywords

  • bioactive glass ceramics
  • in vitro bioactivity
  • apatite layer
  • zinc oxide
Open Access

Effect of substrate temperature and precursor ratio on properties of thin ZnS films sprayed by improved method

Published Online: 17 Oct 2014
Page range: 375 - 384

Abstract

Abstract

Zinc sulphide (ZnS) thin films were prepared by improved spray pyrolysis (ISP) method. The ISP parameters, such as carrier gas flow rate, solution flow rate and substrate temperature, were controlled with an accuracy of ±0.25 lpm, ±1 ml/h and ±1 °C, respectively. The solution was sprayed in a pulsed mode. The substrate temperature was optimized by analyzing substrate temperature dependent properties of thin films. The thin film deposited at a temperature of 450 °C was dense and fairly smooth with satisfactory crystallinity and very small impurity content. The effect of precursor ratio in the solution on structural, compositional and optical properties of thin ZnS films, deposited at a temperature of 450 °C, was studied. A gradual increase in band gap energy from 3.524 eV to 3.634 eV, refractive index from 2.5 to 2.9 and dielectric constant from 6.6 to 8.7 were observed with the variation of solution precursor (Zn:S) ratio from (1:2) to (1:6). The structural and compositional studies support this kind of enhancement in optical properties. The results show that the thin ZnS film prepared by ISP at the substrate temperature of 450 °C from a solution with specific precursor ratio can be used for optoelectronic and photovoltaic applications.

Keywords

  • improved spray pyrolysis
  • pulsed mode of spray
  • crystalline ZnS
  • precursor ratio
  • (S/Zn) atomic ratio
  • optical properties
Open Access

Hydrogen desorption kinetics of MgH2 synthesized from modified waste magnesium

Published Online: 17 Oct 2014
Page range: 385 - 390

Abstract

Abstract

In the present study, hydrogen desorption properties of magnesium hydride (MgH2) synthesized from modified waste magnesium chips (WMC) were investigated. MgH2 was synthesized by hydrogenation of modified waste magnesium at 320 °C for 90 min under a pressure of 6 × 106 Pa. The modified waste magnesium was prepared by mixing waste magnesium with tetrahydrofuran (THF) and NaCl additions, applying mechanical milling. Next, it was investigated by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) techniques in order to characterize its structural properties. Hydrogen desorption properties were determined by differential scanning calorimetry (DSC) under nitrogen atmosphere at different heating rates (5, 10, and 15 °C/min). Doyle and Kissenger non-isothermal kinetic models were applied to calculate energy (Ea) values, which were found equal to 254.68 kJ/mol and 255.88 kJ/mol, respectively.

Keywords

  • hydrogen desorption
  • magnesium hydride
  • kinetics
  • waste magnesium chips
Open Access

Studies of CdI2-Bi3 microstructures with optical methods, atomic force microscopy and positron annihilation spectroscopy

Published Online: 17 Oct 2014
Page range: 391 - 395

Abstract

Abstract

Results of the comprehensive morphological study of CdI2-BiI3 layered crystals are presented. Direct AFM observations of micro- and nanostructures formed in the volume of the crystals confirm the predictions made on the basis of positron annihilation spectroscopy studies. The model explaining the possible pores formation mechanism is proposed and validated by the results of luminescence measurements at 8 K.

Keywords

  • layered crystals
  • microstructures
  • atomic force microscopy
  • positron annihilation
Open Access

Electronic structure and possible martensitic transformation in Ni2FeIn alloy

Published Online: 17 Oct 2014
Page range: 396 - 401

Abstract

Abstract

The electronic structure and magnetic properties of Heusler alloys (Ni2FeIn) have been studied by first principle calculations. The possible tetragonal martensitic transformation has been predicted and the structure optimization was made on cubic austenitic Ni2FeIn in Cu2MnAl type. The equilibrium lattice constant of austenitic Ni2FeIn is 6.03 Å. In tetragonal phase, the global energy minimum occurs at c/a = 1.29. The corresponding equilibrium lattice constants for martensite Ni2FeIn are a = b = 5.5393 Å and c = 7.1457 Å, respectively. In the austenitic phase, E F is located at the peak in the minority DOS for c/a = 0.96 to 1.20, but in the martensitic phase, E F moves to the bottom of the valley in the minority DOS, reducing the value of N(E F) effectively. Both austenitic and martensitic phases are ferromagnetic and the Ni and Fe partial moments contribute mainly to the total moments. Therefore, the martensitic transformation behavior in Ni2FeIn is predicted.

Keywords

  • electrical structure
  • martensitic transformations
  • first principle calculations
Open Access

Synthesis and characterization of a new type of electro-optic polymer without carbon main chains

Published Online: 17 Oct 2014
Page range: 402 - 407

Abstract

Abstract

A new type of electro-optic (EO) polymer is prepared in this work. The main chain of the EO polymer is made of polyphosphazenes, and the side chain consists of carbazole based nitro azobenzene. The principle and method of preparation are given and the characteristics of this material are studied in details. The polymer with an EO coefficient of 35 pm/V has fine stability and can be easily processed. It also shows photoconductivity due to the carbazole group. This polymer thin film is obtained through performance improvement. Terahertz (THz) wave can be detected using the device, which is made of the new polymer. Owing to its fascinating properties, this new type of EO polymer has the potential to be widely applied in photorefractive materials as well as for emission and detection of THz radiation.

Keywords

  • EO polymer
  • polyphosphazenes
  • carbazole based nitro azobenzene
  • THz radiation
Open Access

Green synthesis of silver nanoparticles using tannins

Published Online: 17 Oct 2014
Page range: 408 - 413

Abstract

Abstract

Colloidal silver nanoparticles were prepared by rapid green synthesis using different tannin sources as reducing agent viz. chestnut (CN), mangrove (MG) and quebracho (QB). The aqueous silver ions when exposed to CN, MG and QB tannins were reduced which resulted in formation of silver nanoparticles. The resultant silver nanoparticles were characterized using UV-Visible, X-ray diffraction (XRD), scanning electron microscopy (SEM/EDX), and transmission electron microscopy (TEM) techniques. Furthermore, the possible mechanism of nanoparticles synthesis was also derived using FT-IR analysis. Spectroscopy analysis revealed that the synthesized nanoparticles were within 30 to 75 nm in size, while XRD results showed that nanoparticles formed were crystalline with face centered cubic geometry.

Keywords

  • tannins
  • silver nanoparticles
  • green synthesis
  • XRD
  • SEM
  • TEM
Open Access

Study of structures and properties of ZnO-Sb2O3-P2O5-Na2O glasses

Published Online: 17 Oct 2014
Page range: 414 - 418

Abstract

Abstract

The influence of ZnO substitution by 0–12 wt.% Na2O on the properties of ZnO-Sb2O3-P2O5-Na2O glasses has been investigated. The structure and properties of the glasses with the composition of (13.86-x)ZnO-57.93Sb2O3-28.21P2O5−x Na2O (x = 0–12 wt.%) were characterized by infrared spectra (IR), X-ray diffraction and differential thermal analysis (DTA). The results of IR indicated an increase in the intensity of symmetric vibrations of P-O-P bond, which was confirmed by the improvement of water durability with the increasing amount of Na2O in the range of 0–10 wt.%. Substitution of 10 wt.% Na2O led to the weight loss of the glass to 5.93 mg/cm−2 after immersion in deionized water at 50 °C for 24 h. The results of XRD showed that the ability of crystallization decreased, indicating the good thermal stability of the glass. The glass containing 8 wt.% Na2O had the best properties in every respect and might be an alternative to lead based glasses for the applications, providing further composition improvement.

Keywords

  • spectroscopy
  • X-ray method
  • chemical properties
  • antimony phosphate
Open Access

Preparation of polyaniline nanostructures doped with different dicarboxylic acids through template-free method

Published Online: 17 Oct 2014
Page range: 419 - 422

Abstract

Abstract

In this article nanoscaled polyanilines (PANI) were prepared based on template-free method in the presence of dicarboxylic acid dopants (e.g. D-tartaric acid, succinic acid, maleic acid and fumaric acid). The trans-cis isomerization of butenedioic acid played an important role in the formation of nanostructures from the plane-like to nanofibers, and the PANI doped with maleic acid (MA) had larger diameter, higher crystallinity and conductivity than PANI doped with fumaric acid (FA).

Keywords

  • polyaniline
  • nanostructures
  • dicarboxylic acid
  • trans-cis isomerization
Open Access

Magnetic characterization of nanocrystalline iron samples with different size distributions

Published Online: 17 Oct 2014
Page range: 423 - 429

Abstract

Abstract

Nanocrystalline iron was obtained by fusing magnetite and promoters. The oxidized form was reduced with hydrogen and passivated (sample P0). The average nanocrystallite size in sample P0 was d(P0) =16 nm and the width of size distribution was σ(P0) = 18 nm. Samples of nanocrystalline iron with narrower diameter ranges and larger and smaller average crystallite sizes were also synthesized. They were: sample P1 (d(P1) = 28 nm, σ(P1) = 5 nm), sample P2 (d(P2) = 22 nm, σ(P1) = 5 nm), sample P3 (d(P3) = 12 nm, σ(P1) = 9 nm). These four samples were studied at room temperature by dc magnetization measurements and ferromagnetic resonance at microwave frequency. Correlations between samples sizes distributions (average size and width of the sizes) and magnetic parameters (effective magnetization, anisotropy field, anisotropy constant, FMR linewidth) were investigated. It was found that the anisotropy field and effective magnetization determined from FMR spectra scale linearly with nanoparticle sizes, while the effective magnetic anisotropy constant determined from the hysteresis loops decreases with nanoparticle size increase.

Keywords

  • nanocrystalline iron
  • ferromagnetic resonance
  • magnetic property
Open Access

Investigation on structure of BaTi1−x NbxO3 compound prepared by rotary-hydrothermal synthesis methods

Published Online: 17 Oct 2014
Page range: 430 - 435

Abstract

Abstract

BaTi1−x NbxO3 compounds (with x = 0.0, 0.01, 0.03, 0.06, and 0.09) were synthesized by rotary-hydrothermal (RH) method. The process was conducted at 180 °C for 5 hours in a Teflon vessel that was rotated at a speed of 160 rpm during the hydrothermal reaction. The effects of donor concentration on the structure and properties of BaTi1−x NbxO3 compounds were investigated. The experiments for the BaTiO3±Nb2O3 system produced by a solid state reaction at high temperature at different concentrations of niobium, with the use of RH processing have not been reported in previous works. For the phase evolution studies, X-ray diffraction patterns (XRD) were analyzed and Raman spectroscopy measurements were performed. The transmission electron microscope (TEM) and the field emission scanning electron microscope (FE-SEM) images were taken for the detailed analysis of the grain size, surface and morphology of the compound.

Keywords

  • Nb-doping
  • chemical synthesis
  • microwave-hydrothermal synthesis
  • microstructure
  • perovskites
Open Access

Hydroxyapatite growth on cotton fibers modified chemically

Published Online: 17 Oct 2014
Page range: 436 - 441

Abstract

Abstract

We have prepared carboxymethyl cellulose fibers (CMC) by chemically modifying cotton cellulose with monochloroacetic acid and calcium chloride solution. This modification favored the growth of hydroxyapatite (HAP) on the surface of the CMC fibers in contact with simulated body fluid solutions (SBF). After soaking in SBF for periods of 7, 14 and 21 days, formation of HAP was observed. Analysis by scanning electron microscopy and X-ray diffraction showed that crystallinity, crystallite size, and growth of HAP increased with the soaking time. The amount of HAP deposited on CMC fibers increased greatly after 21 days of immersion in the SBF, while the substrate surface was totally covered with hemispherical aggregates with the size of the order of 2 microns. Elemental analysis showed the presence of calcium and phosphate, with calcium/phosphate atomic ratio of 1.54. Fourier transform infrared spectroscopy bands confirmed the presence of HAP. The results suggest that cotton modified by calcium treatment has a nucleating ability and can accelerate the nucleation of HAP crystals.

Keywords

  • hydroxyapatite
  • biomimetics
  • simulated body fluid
Open Access

Structure and tensile properties of polypropylene/carbon nanotubes composites prepared by melt extrusion

Published Online: 17 Oct 2014
Page range: 442 - 447

Abstract

Abstract

Polypropylene/carbon nanotubes (PP/CNTs) nancomposites were prepared with a single screw extruder by adding maleic anhydride-grafted poplypropylene (PP-g-MAH) as compatibilizer to polypropylene (PP) with different amounts of carbon nanotubes (CNTs) in the range of 0.1–0.7 wt.%. Structure and morphology of the prepared samples were examined by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), polarizing light microscopy (PLM) and X-ray diffraction (XRD). The results showed that PP spherulites decreased in size when CNTs were introduced into the polymer. Mechanical properties of the samples were also studied. Tensile tests showed that with increasing amount of CNTs the strain at break decreased whereas the Young’s modulus was improved of 16.41 % to 36.05 % and tensile strength of 36.67 % to 64.70 % compared to pristine PP. The SEM microphotographs showed that majority of the CNTs were dispersed individually and oriented along the shear flow direction.

Keywords

  • carbon nanotubes
  • orientation
  • nanocomposites
  • polypropylene
  • tensile properties
Open Access

Role of substrate temperature on the growth mechanism and physical properties of spray deposited lead oxide thin films

Published Online: 17 Oct 2014
Page range: 448 - 456

Abstract

Abstract

Thin films of lead oxide were synthesized by cost effective spray pyrolysis technique at different substrate temperatures on glass substrates. Effect of substrate temperature on the growth mechanism and physical properties of the films was investigated. All the films were polycrystalline in nature with tetragonal structure corresponding to α-PbO. The films coated at 225 °C and 275 °C were (1 0 1) oriented, while the films deposited at 325 °C and 375 °C were (0 0 2) oriented. Above 375 °C, the pure tetragonal nature deteriorated and the peaks corresponding to orthorhombic phase were observed. The band gap value was found to be in the range of 2.3 to 2.62 eV. All the films had a resistivity of the order of 103 ohm-cm. A minimum resistivity of 0.0191 × 103 ohm-cm was obtained for the film coated at 325 °C. The activation energy increased with increase in substrate temperature.

Keywords

  • thin films
  • X-ray diffraction
  • crystal structure
  • energy band gap
  • electrical properties
Open Access

Investigation of structural, optical and electrical properties of (Ti,Nb)Ox thin films deposited by high energy reactive magnetron sputtering

Published Online: 17 Oct 2014
Page range: 457 - 464

Abstract

Abstract

In this work the results of investigations of the titanium-niobium oxides thin films have been reported. The thin films were manufactured with the aid of a modified reactive magnetron sputtering process. The aim of the research was the analysis of structural, optical and electrical properties of the deposited thin films. Additionally, the influence of post-process annealing on the properties of studied coatings has been presented. The as-deposited coatings were amorphous, while annealing at 873 K caused a structural change to the mixture of TiO2 anatase-rutile phases. The prepared thin films exhibited good transparency with transmission level of ca. 50 % and low resistivity varying from 2 Ωcm to 5×10−2 Ωcm, depending on the time and temperature of annealing. What is worth to emphasize, the sign of Seebeck coefficient changed after the annealing process from the electron to hole type electrical conduction.

Keywords

  • (Ti,Nb)Ox thin films
  • transparent oxide semiconductor
  • p-type electrical conduction
  • niobium doped titanium dioxide
  • transparent electronics
Open Access

Specific heat jump of two-band superconductor KFe2As2 using Ginzburg-Landau theory

Published Online: 17 Oct 2014
Page range: 465 - 469

Abstract

Abstract

In this study specific heat jump using two-gap Ginzburg-Landau (GL) theory has been calculated. In contrast to the previous approaches, we have taken into account intergradient order parameters interaction in the GL free energy functional. The thermodynamic magnetic field revealed nonlinear temperature dependence due to interband interaction between order parameters and their gradients. The calculations showed that the specific heat jump in two-order parameter superconductors was smaller than that of single-order parameter superconductors. It has been shown that such a model is in good agreement with experimental data for KFe2As2 superconductors.

Keywords

  • Fe based superconductors
  • Ginzburg-Landau theory
  • specific heat jump
  • two-band superconductivity
Open Access

Preparation and electromagnetic properties of zinc ferrite/expanded graphite composites

Published Online: 17 Oct 2014
Page range: 470 - 474

Abstract

Abstract

An effective process for the synthesis of nano spinel zinc ferrite/expanded graphite composites was developed in order to get an electromagnetic interference shielding material. Firstly, expandable graphite was prepared using sulfuric and nitric acid solutions. Then, the precursor of the composites was produced by chemical co-precipitation method, followed by heating treatment. The obtained composites were characterized by X-ray diffraction and scanning electron microscopy. The dielectric and magnetic properties were determined using vector network analyzer and vibrating sample magnetometry. The results showed that ferrite nanoparticles with the sizes of about 50–150 nm were uniformly dispersed on the surface and interspace of EG. The magnetic properties of the composites changed by adjusting the ferrite/EG ratio and the composites had high dielectric constant in the range of 2–18 GHz. These properties of the prepared composites suggest that they can be used as a promising electromagnetic interference shielding material.

Keywords

  • ferrite
  • graphite
  • composites
  • nanocomposites
  • magnetic properties
Open Access

CVD diamond layers for electrochemistry

Published Online: 17 Oct 2014
Page range: 475 - 480

Abstract

Abstract

Diamond electrodes of different morphologies and qualities were manufactured by hot filament chemical deposition (HF CVD) techniques by changing the parameters of diamond growth process. The estimation of diamond quality and identification of different carbon phases was performed by Raman spectroscopy measurements. The effect of diamond quality and amorphous carbon phase content on the electrochemical response of an obtained diamond electrode in 0.5 M H2SO4 as supporting electrolyte was investigated by cyclic voltammetry with [Fe(CN)6]4−/3− as a redox probe. The kinetic parameters such as catalytic reaction rate constant k0 and electron transfer coefficient α were determined. The obtained results show that the analytical performance of undoped diamond electrodes can be implemented just by the change of diamond layers quality.

Keywords

  • cyclic voltammetry
  • Raman spectroscopy
  • undoped diamond layer
  • amorphous carbon phase
Open Access

Synthesis and Mossbauer studies of mesoporous γ-Fe2O3

Published Online: 17 Oct 2014
Page range: 481 - 486

Abstract

Abstract

A method of synthesis of mesoporous γ-Fe2O3 by thermal decomposition of iron citrate has been proposed. Investigations of the crystalline and magnetic structure of obtained materials were done. Nanodispersed maghemite (γ-Fe2O3) with the sizes of coherent scattering regions of about 4–7 nm consisted of one phase only after gel sintering at 200, 250 and 300 °C. The particles of synthesized materials were both in magnetically ordered, and superparamagnetic states, and they formed a grid-like mesoporous structure. The influence of magnetic dipole interparticle interaction on the parameters of Mossbauer spectra was observed. A phenomenological model of the differences between nanodispersed γ-Fe2O3 magnetic microstructures obtained after annealing at different temperatures was presented.

Keywords

  • γ-Fe2O3
  • mesoporous structure
  • Mossbauer spectroscopy
  • superparamagnetic properties
Open Access

Properties of graphite-stainless steel composite in bipolar plates in simulated anode and cathode environments of PEM fuel cells

Published Online: 17 Oct 2014
Page range: 487 - 497

Abstract

Abstract

The use of a graphite-stainless steel composite as bipolar plates (BP) in polymer electrolyte membrane fuel cells (PEMFCs) has been evaluated. The study covers measurements of mechanical properties, microstructural examination, analysis of surface profile, wettability, porosity and corrosion resistance of the composite. The corrosion properties of the composite were examined in 0.1 mol·dm−3 H2SO4 + 2 ppm F− saturated with H2 or with O2 and in solutions with different pH: in Na2SO4+ 2 ppm F− (pH = 1.00, 3.00, 5.00) at 80 °C. The performed tests indicate that the graphite modified with stainless steel can be a good choice to be used as a bipolar plate in PEM fuel cells.

Keywords

  • powder metallurgy
  • sintering
  • graphite
  • bipolar plates
  • fuel cells
  • PEMFC
Open Access

Fabrication and characterization of compositionally graded Bi1−x GdxFeO3 thin films

Published Online: 17 Oct 2014
Page range: 498 - 502

Abstract

Abstract

An undoped BiFeO3 thin film, Gd doped Bi0.95Gd0.05FeO3 thin film with a constant composition, Gd up-graded doped Bi1−x GdxFeO3 and Gd down-graded doped Bi1−x GdxFeO3 thin films were successfully grown on Pt (111)/Ti/SiO2/Si (100) substrates using a sol-gel and spin coating technique. The crystal structure, ferroelectric and dielectric characteristics as well as the leakage currents of these samples were thoroughly investigated. The XRD (X-Ray Diffraction) patterns indicate that all these thin films consist of solely perovskite phase with polycrystalline structure. No other secondary phases have been detected. Clear polarization-electric field (P-E) hysteresis loops of all these thin films demonstrate that the incorporation of Gd3+ into the Bi site of BFO thin film have enhanced the ferroelectric performance of pure BiFeO3 thin film, and the Gd down-graded doped Bi1−x GdxFeO3 thin film has the best ferroelectric properties. Compared to other thin films, the optimal ferroelectric behavior of the Gd down-graded doped Bi1−x GdxFeO3 thin film results from its large dielectric constant, low dissipation factor and low leakage current.

Keywords

  • Gd substituted BiFeO3 thin films
  • crystal structure
  • ferroelectric properties
  • sol-gel technique
Open Access

Low-temperature synthesis of zeolite from perlite waste — Part I: review of methods and phase compositions of resulting products

Published Online: 17 Oct 2014
Page range: 503 - 513

Abstract

Abstract

In this paper a review of the recent studies on the synthesis of zeolites from expanded perlite under hydrothermal conditions is presented. Attention is paid to possible outcomes of synthesis from low cost glass material, such as perlite. The study also investigates the phase composition of zeolitic materials obtained by modification of by-product derived from an expanded perlite production process. The synthesis was made using the hydrothermal method with sodium hydroxide under autogenous pressure at a temperature below 100 °C for 1 to 72 h. It was possible to obtain a zeolitic material at a temperature as low as 60 °C using 4.0 M NaOH. The X-ray diffraction pattern showed the biggest peak intensity of zeolite X with 4.0 M NaOH at the temperature of 70 °C. During synthesis at higher temperature zeolite Na-P1 (with 3.0 M NaOH at 90 °C) and hydroxysodalite (with 5.0 M NaOH at 90 °C) were obtained.

Keywords

  • synthesis of zeolites
  • zeolite X
  • expanded perlite waste
  • FT-IR spectra
Open Access

Synthesis of porous ZnO nanostructures using bamboo fibers as templates

Published Online: 17 Oct 2014
Page range: 514 - 520

Abstract

Abstract

In this study, we fabricated ZnO nanostructures using bamboo fibers as templates. The starting material used was zinc acetate, and the nanostructures were synthesized by soaking and calcining the bamboo fibers. The fabricated nanostructures were characterized using X-ray powder diffraction (XRD) analysis, scanning electron microscopy (SEM), and ultraviolet-visible spectrophotometry. The results showed that the size of the ZnO nanoparticles was approximately 20–100 nm. When the ZnO nanoparticles were used as the catalyst in the photodegradation of methyl orange, the dye degraded by 95.98 % in 80 min. The response and recovery times of a gas sensor based on the ZnO nanoparticles were 25 and 24 s, respectively, during the detection of C2H5OH in a concentration of 10 ppm at 270 °C.

Keywords

  • ZnO
  • bamboo fiber template
  • photocatalysis
  • gas sensitivity
30 Articles
Open Access

Capacitive behavior of highly-oxidized graphite

Published Online: 17 Oct 2014
Page range: 307 - 314

Abstract

Abstract

Capacitive behavior of a highly-oxidized graphite is presented in this paper. The graphite oxide was synthesized using an oxidizing mixture of potassium chlorate and concentrated fuming nitric acid. As-oxidized graphite was quantitatively and qualitatively analyzed with respect to the oxygen content and the species of oxygen-containing groups. Electrochemical measurements were performed in a two-electrode symmetric cell using KOH electrolyte.

It was shown that prolonged oxidation causes an increase in the oxygen content while the interlayer distance remains constant. Specific capacitance increased with oxygen content in the electrode as a result of pseudo-capacitive effects, from 0.47 to 0.54 F/g for a scan rate of 20 mV/s and 0.67 to 1.15 F/g for a scan rate of 5 mV/s. Better cyclability was observed for the electrode with a higher oxygen amount.

Keywords

  • graphite oxide
  • oxidation
  • supercapacitors
Open Access

Synthesis, characterization, DC-electrical conductivity and γ-ray effect on Ag1+, Y3+ double doped nano lithium manganates (LiMn2−2x AgxYxO4) for rechargeable batteries

Published Online: 17 Oct 2014
Page range: 315 - 323

Abstract

Abstract

Pristine lithium manganate (LiMn2O4) and Ag1+, Y3+ double doped nano lithium manganate [LiMn2−2x AgxYxO4, (x = 0.025, 0.05)] spinels were synthesized via a coprecipitation method for rechargeable batteries applications. The synthesized LiMn1.9Ag0.05Y0.05O4 was exposed to different doses of γ-irradiation (10 and 30 kGy). The resulting spinel products were characterized by using thermogravimetric and differential thermal analysis (TG/DTA), X-ray diffraction (XRD), infrared (IR) spectroscopy, scanning electron microscopy (SEM), energy dispersive analysis of X-rays (EDAX), electronic (UV-Vis) and electron spin resonance (ESR) spectra. LiMn2O4 exhibited a discharge capacity of 124 mAhg−1 while LiMn1.9Ag0.05Y0.05O4 had discharge capacities of 129 and 137 mAhg−1 for non irradiated and γ-irradiated (30 kGy) samples, respectively. The effects of the dopant cations and γ-irradiation on the discharge capacity and DC-electrical conductivity of some synthesized spinels were studied.

Keywords

  • nano lithium manganates
  • Ag1+, Y3+ double doped
  • γ-ray effect
Open Access

Ab-initio studies of thermal and superconducting properties of HfX2 alloys (X = Tc, Re, and Os)

Published Online: 17 Oct 2014
Page range: 324 - 330

Abstract

Abstract

A systematic study of thermal properties such as the Debye temperature, specific heat coefficient, Grüneisen constant, electron-phonon coupling constant and transition temperature have been carried out using the results of electronic band structure and related characteristics, for hafnium superconducting alloys, namely, HfTc2, HfRe2 and HfOs2. Computation of the electronic band structure and associated properties has been carried out using the tight-binding-linear-muffin-tin-orbital (TBLMTO) method within atomic sphere approximation (ASA). The calculated values have been compared with the available results of literature data.

Keywords

  • Debye temperature
  • specific heat coefficient
  • Grüneisen constant
  • electron-phonon coupling constant
  • transition temperature
Open Access

Correlation between structural and electrical properties in highly porous (Y,Sr)(Ti,Nb)O3−δ SOFC anodes

Published Online: 17 Oct 2014
Page range: 331 - 340

Abstract

Abstract

In order to find a relationship between structural and electrical properties, niobium and yttrium doped SrTiO3 ceramics were prepared via solid-state reaction. The samples were sintered in hydrogen and air conditions. The samples were also fabricated with a pore-former to obtain highly porous specimens. The electrical properties of Nb-doped SrTiO3 samples and yttrium and niobium co-doped SrTiO3 were compared. The comparable electrical properties were observed and discussed according to previous literature reports. It was noticed that the synthesis in a reducing hydrogen atmosphere can increase the solubility of dopants. Moreover, the samples sintered in air presented lower conductivity level and worse structural properties than the samples sintered in hydrogen. The explanation of obtained results was also suggested and discussed.

Keywords

  • perovskite
  • doped strontium titanate
  • porous ceramic
  • SOFC anodes
Open Access

Investigation on compressive behavior of Cu-35Ni-15Al alloy at high temperatures

Published Online: 17 Oct 2014
Page range: 341 - 349

Abstract

Abstract

Microstructures and mechanical properties of Cu-35Ni-15Al alloy in cast and porous states were studied by scanning electron microscopy and compression tests. The influence of porosity, deformation temperature and loading rate on mechanical properties of the two kinds of alloys was investigated. The results show that the as cast alloy and porous alloys have almost the same phase constitution: Cu rich phase, Ni rich phase and K intermetallics. The yield strength of porous alloys increases continuously with decreasing porosity, the relationship between porosity and yield stress follows Gibson-Ashby equation. With decreasing deformation temperature, the yield strength of as cast alloy and porous alloy increase. With the increase of loading rate, the yield strength of these alloys shows an increasing trend. After compression, the microstructure of as cast alloy is more uniform, and porous alloys are more prone to have localized deformations.

Keywords

  • Cu-35Ni-15Al alloy
  • compression
  • deformation temperature
  • loading rate
Open Access

Structural elastic and thermal properties of SrxCd1−x O mixed compounds — a theoretical approach

Published Online: 17 Oct 2014
Page range: 350 - 357

Abstract

Abstract

In the present paper, the structural and mechanical properties of alkaline earth oxides mixed compound SrxCd1−x O (0 ≤ x ≤ 1) under high pressure have been reported. An extended interaction potential (EIP) model, including the zero point vibrational energy effect, has been developed for this study. Phase transition pressures are associated with a sudden collapse in volume. Phase transition pressure and associated volume collapses [ΔV (Pt)/V(0)] calculated from this approach are in good agreement with the experimental values for the parent compounds (x = 0 and x = 1). The results for the mixed crystal counterparts are also in fair agreement with experimental data generated from the application of Vegard’s law to the data for the parent compounds.

Keywords

  • oxide
  • alloy
  • volume collapse
  • phase transition
  • high pressure
Open Access

Fabrication of highly-transparent Er:CaF2 ceramics by hot-pressing technique

Published Online: 17 Oct 2014
Page range: 358 - 363

Abstract

Abstract

Highly-transparent trivalent erbium ion doped calcium fluoride (5 mol % Er:CaF2) ceramics were fabricated by a hotpressing (HP) method using high-purity Er:CaF2 nanoparticles, which were synthesized by co-precipitation method. The mean grain size of the nanoparticles was about 24.7 nm. The nanoparticles were sintered at 600 °C, 700 °C, 800 °C and 900 °C, respectively, for 30 min under a uniaxial pressure of 30 MPa and vacuum of 10−3 Pa with 1 mol % lithium fluoride (LiF) as sintering additive. The 5 mol % Er:CaF2 ceramics sintered at 800 °C exhibits high density and pore-free microstructure with an average grain size of about 8 μm. The optical transmittance of the transparent ceramics is close to 85 % at visible and nearinfrared wavelengths. The strong and broad absorptions peaks corresponding to characteristic absorption of trivalent erbium ions make the ceramics a potential candidate for infrared and upconversion laser operating.

Keywords

  • calcium fluoride
  • transparent ceramics
  • nanoparticles
  • transmittance
Open Access

In vitro evaluation of bioactivity of SiO2-CaO-P2O5-Na2O-CaF2-ZnO glass-ceramics

Published Online: 17 Oct 2014
Page range: 364 - 374

Abstract

Abstract

Zinc is an essential trace element that stimulates bone formation but it is also known as an inhibitor of apatite crystal growth. In this work addition of ZnO to SiO2-CaO-P2O5-Na2O-CaF2 glass-ceramic system was made by conventional melt-quenching technique. DSC curves showed that the addition of ZnO moved the endothermic and exothermic peaks to lower temperatures. X-ray diffraction analysis did not reveal any additional phase caused by ZnO addition and showed the presence of wollastonite and hydroxyapatite crystalline phases only in all the glass-ceramic samples. As bio-implant apatite forming ability is an essential condition, the surface reactivity of the prepared glass-ceramic specimens was studied in vitro in Kokubo’s simulated body fluid (SBF) [1] with ion concentration nearly equal to human blood plasma for 30 days at 37 °C under static condition. Atomic absorption spectroscopy (AAS) was used to study the changes in element concentrations in soaking solutions and XRD, FT-IR and SEM were used to elucidate surface properties of prepared glass-ceramics, which confirmed the formation of HCAp on the surface of all glass-ceramics. It was found that the addition of ZnO had a positive effect on bioactivity of glass-ceramics and made it a potential candidate for restoration of damaged bones.

Keywords

  • bioactive glass ceramics
  • in vitro bioactivity
  • apatite layer
  • zinc oxide
Open Access

Effect of substrate temperature and precursor ratio on properties of thin ZnS films sprayed by improved method

Published Online: 17 Oct 2014
Page range: 375 - 384

Abstract

Abstract

Zinc sulphide (ZnS) thin films were prepared by improved spray pyrolysis (ISP) method. The ISP parameters, such as carrier gas flow rate, solution flow rate and substrate temperature, were controlled with an accuracy of ±0.25 lpm, ±1 ml/h and ±1 °C, respectively. The solution was sprayed in a pulsed mode. The substrate temperature was optimized by analyzing substrate temperature dependent properties of thin films. The thin film deposited at a temperature of 450 °C was dense and fairly smooth with satisfactory crystallinity and very small impurity content. The effect of precursor ratio in the solution on structural, compositional and optical properties of thin ZnS films, deposited at a temperature of 450 °C, was studied. A gradual increase in band gap energy from 3.524 eV to 3.634 eV, refractive index from 2.5 to 2.9 and dielectric constant from 6.6 to 8.7 were observed with the variation of solution precursor (Zn:S) ratio from (1:2) to (1:6). The structural and compositional studies support this kind of enhancement in optical properties. The results show that the thin ZnS film prepared by ISP at the substrate temperature of 450 °C from a solution with specific precursor ratio can be used for optoelectronic and photovoltaic applications.

Keywords

  • improved spray pyrolysis
  • pulsed mode of spray
  • crystalline ZnS
  • precursor ratio
  • (S/Zn) atomic ratio
  • optical properties
Open Access

Hydrogen desorption kinetics of MgH2 synthesized from modified waste magnesium

Published Online: 17 Oct 2014
Page range: 385 - 390

Abstract

Abstract

In the present study, hydrogen desorption properties of magnesium hydride (MgH2) synthesized from modified waste magnesium chips (WMC) were investigated. MgH2 was synthesized by hydrogenation of modified waste magnesium at 320 °C for 90 min under a pressure of 6 × 106 Pa. The modified waste magnesium was prepared by mixing waste magnesium with tetrahydrofuran (THF) and NaCl additions, applying mechanical milling. Next, it was investigated by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) techniques in order to characterize its structural properties. Hydrogen desorption properties were determined by differential scanning calorimetry (DSC) under nitrogen atmosphere at different heating rates (5, 10, and 15 °C/min). Doyle and Kissenger non-isothermal kinetic models were applied to calculate energy (Ea) values, which were found equal to 254.68 kJ/mol and 255.88 kJ/mol, respectively.

Keywords

  • hydrogen desorption
  • magnesium hydride
  • kinetics
  • waste magnesium chips
Open Access

Studies of CdI2-Bi3 microstructures with optical methods, atomic force microscopy and positron annihilation spectroscopy

Published Online: 17 Oct 2014
Page range: 391 - 395

Abstract

Abstract

Results of the comprehensive morphological study of CdI2-BiI3 layered crystals are presented. Direct AFM observations of micro- and nanostructures formed in the volume of the crystals confirm the predictions made on the basis of positron annihilation spectroscopy studies. The model explaining the possible pores formation mechanism is proposed and validated by the results of luminescence measurements at 8 K.

Keywords

  • layered crystals
  • microstructures
  • atomic force microscopy
  • positron annihilation
Open Access

Electronic structure and possible martensitic transformation in Ni2FeIn alloy

Published Online: 17 Oct 2014
Page range: 396 - 401

Abstract

Abstract

The electronic structure and magnetic properties of Heusler alloys (Ni2FeIn) have been studied by first principle calculations. The possible tetragonal martensitic transformation has been predicted and the structure optimization was made on cubic austenitic Ni2FeIn in Cu2MnAl type. The equilibrium lattice constant of austenitic Ni2FeIn is 6.03 Å. In tetragonal phase, the global energy minimum occurs at c/a = 1.29. The corresponding equilibrium lattice constants for martensite Ni2FeIn are a = b = 5.5393 Å and c = 7.1457 Å, respectively. In the austenitic phase, E F is located at the peak in the minority DOS for c/a = 0.96 to 1.20, but in the martensitic phase, E F moves to the bottom of the valley in the minority DOS, reducing the value of N(E F) effectively. Both austenitic and martensitic phases are ferromagnetic and the Ni and Fe partial moments contribute mainly to the total moments. Therefore, the martensitic transformation behavior in Ni2FeIn is predicted.

Keywords

  • electrical structure
  • martensitic transformations
  • first principle calculations
Open Access

Synthesis and characterization of a new type of electro-optic polymer without carbon main chains

Published Online: 17 Oct 2014
Page range: 402 - 407

Abstract

Abstract

A new type of electro-optic (EO) polymer is prepared in this work. The main chain of the EO polymer is made of polyphosphazenes, and the side chain consists of carbazole based nitro azobenzene. The principle and method of preparation are given and the characteristics of this material are studied in details. The polymer with an EO coefficient of 35 pm/V has fine stability and can be easily processed. It also shows photoconductivity due to the carbazole group. This polymer thin film is obtained through performance improvement. Terahertz (THz) wave can be detected using the device, which is made of the new polymer. Owing to its fascinating properties, this new type of EO polymer has the potential to be widely applied in photorefractive materials as well as for emission and detection of THz radiation.

Keywords

  • EO polymer
  • polyphosphazenes
  • carbazole based nitro azobenzene
  • THz radiation
Open Access

Green synthesis of silver nanoparticles using tannins

Published Online: 17 Oct 2014
Page range: 408 - 413

Abstract

Abstract

Colloidal silver nanoparticles were prepared by rapid green synthesis using different tannin sources as reducing agent viz. chestnut (CN), mangrove (MG) and quebracho (QB). The aqueous silver ions when exposed to CN, MG and QB tannins were reduced which resulted in formation of silver nanoparticles. The resultant silver nanoparticles were characterized using UV-Visible, X-ray diffraction (XRD), scanning electron microscopy (SEM/EDX), and transmission electron microscopy (TEM) techniques. Furthermore, the possible mechanism of nanoparticles synthesis was also derived using FT-IR analysis. Spectroscopy analysis revealed that the synthesized nanoparticles were within 30 to 75 nm in size, while XRD results showed that nanoparticles formed were crystalline with face centered cubic geometry.

Keywords

  • tannins
  • silver nanoparticles
  • green synthesis
  • XRD
  • SEM
  • TEM
Open Access

Study of structures and properties of ZnO-Sb2O3-P2O5-Na2O glasses

Published Online: 17 Oct 2014
Page range: 414 - 418

Abstract

Abstract

The influence of ZnO substitution by 0–12 wt.% Na2O on the properties of ZnO-Sb2O3-P2O5-Na2O glasses has been investigated. The structure and properties of the glasses with the composition of (13.86-x)ZnO-57.93Sb2O3-28.21P2O5−x Na2O (x = 0–12 wt.%) were characterized by infrared spectra (IR), X-ray diffraction and differential thermal analysis (DTA). The results of IR indicated an increase in the intensity of symmetric vibrations of P-O-P bond, which was confirmed by the improvement of water durability with the increasing amount of Na2O in the range of 0–10 wt.%. Substitution of 10 wt.% Na2O led to the weight loss of the glass to 5.93 mg/cm−2 after immersion in deionized water at 50 °C for 24 h. The results of XRD showed that the ability of crystallization decreased, indicating the good thermal stability of the glass. The glass containing 8 wt.% Na2O had the best properties in every respect and might be an alternative to lead based glasses for the applications, providing further composition improvement.

Keywords

  • spectroscopy
  • X-ray method
  • chemical properties
  • antimony phosphate
Open Access

Preparation of polyaniline nanostructures doped with different dicarboxylic acids through template-free method

Published Online: 17 Oct 2014
Page range: 419 - 422

Abstract

Abstract

In this article nanoscaled polyanilines (PANI) were prepared based on template-free method in the presence of dicarboxylic acid dopants (e.g. D-tartaric acid, succinic acid, maleic acid and fumaric acid). The trans-cis isomerization of butenedioic acid played an important role in the formation of nanostructures from the plane-like to nanofibers, and the PANI doped with maleic acid (MA) had larger diameter, higher crystallinity and conductivity than PANI doped with fumaric acid (FA).

Keywords

  • polyaniline
  • nanostructures
  • dicarboxylic acid
  • trans-cis isomerization
Open Access

Magnetic characterization of nanocrystalline iron samples with different size distributions

Published Online: 17 Oct 2014
Page range: 423 - 429

Abstract

Abstract

Nanocrystalline iron was obtained by fusing magnetite and promoters. The oxidized form was reduced with hydrogen and passivated (sample P0). The average nanocrystallite size in sample P0 was d(P0) =16 nm and the width of size distribution was σ(P0) = 18 nm. Samples of nanocrystalline iron with narrower diameter ranges and larger and smaller average crystallite sizes were also synthesized. They were: sample P1 (d(P1) = 28 nm, σ(P1) = 5 nm), sample P2 (d(P2) = 22 nm, σ(P1) = 5 nm), sample P3 (d(P3) = 12 nm, σ(P1) = 9 nm). These four samples were studied at room temperature by dc magnetization measurements and ferromagnetic resonance at microwave frequency. Correlations between samples sizes distributions (average size and width of the sizes) and magnetic parameters (effective magnetization, anisotropy field, anisotropy constant, FMR linewidth) were investigated. It was found that the anisotropy field and effective magnetization determined from FMR spectra scale linearly with nanoparticle sizes, while the effective magnetic anisotropy constant determined from the hysteresis loops decreases with nanoparticle size increase.

Keywords

  • nanocrystalline iron
  • ferromagnetic resonance
  • magnetic property
Open Access

Investigation on structure of BaTi1−x NbxO3 compound prepared by rotary-hydrothermal synthesis methods

Published Online: 17 Oct 2014
Page range: 430 - 435

Abstract

Abstract

BaTi1−x NbxO3 compounds (with x = 0.0, 0.01, 0.03, 0.06, and 0.09) were synthesized by rotary-hydrothermal (RH) method. The process was conducted at 180 °C for 5 hours in a Teflon vessel that was rotated at a speed of 160 rpm during the hydrothermal reaction. The effects of donor concentration on the structure and properties of BaTi1−x NbxO3 compounds were investigated. The experiments for the BaTiO3±Nb2O3 system produced by a solid state reaction at high temperature at different concentrations of niobium, with the use of RH processing have not been reported in previous works. For the phase evolution studies, X-ray diffraction patterns (XRD) were analyzed and Raman spectroscopy measurements were performed. The transmission electron microscope (TEM) and the field emission scanning electron microscope (FE-SEM) images were taken for the detailed analysis of the grain size, surface and morphology of the compound.

Keywords

  • Nb-doping
  • chemical synthesis
  • microwave-hydrothermal synthesis
  • microstructure
  • perovskites
Open Access

Hydroxyapatite growth on cotton fibers modified chemically

Published Online: 17 Oct 2014
Page range: 436 - 441

Abstract

Abstract

We have prepared carboxymethyl cellulose fibers (CMC) by chemically modifying cotton cellulose with monochloroacetic acid and calcium chloride solution. This modification favored the growth of hydroxyapatite (HAP) on the surface of the CMC fibers in contact with simulated body fluid solutions (SBF). After soaking in SBF for periods of 7, 14 and 21 days, formation of HAP was observed. Analysis by scanning electron microscopy and X-ray diffraction showed that crystallinity, crystallite size, and growth of HAP increased with the soaking time. The amount of HAP deposited on CMC fibers increased greatly after 21 days of immersion in the SBF, while the substrate surface was totally covered with hemispherical aggregates with the size of the order of 2 microns. Elemental analysis showed the presence of calcium and phosphate, with calcium/phosphate atomic ratio of 1.54. Fourier transform infrared spectroscopy bands confirmed the presence of HAP. The results suggest that cotton modified by calcium treatment has a nucleating ability and can accelerate the nucleation of HAP crystals.

Keywords

  • hydroxyapatite
  • biomimetics
  • simulated body fluid
Open Access

Structure and tensile properties of polypropylene/carbon nanotubes composites prepared by melt extrusion

Published Online: 17 Oct 2014
Page range: 442 - 447

Abstract

Abstract

Polypropylene/carbon nanotubes (PP/CNTs) nancomposites were prepared with a single screw extruder by adding maleic anhydride-grafted poplypropylene (PP-g-MAH) as compatibilizer to polypropylene (PP) with different amounts of carbon nanotubes (CNTs) in the range of 0.1–0.7 wt.%. Structure and morphology of the prepared samples were examined by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), polarizing light microscopy (PLM) and X-ray diffraction (XRD). The results showed that PP spherulites decreased in size when CNTs were introduced into the polymer. Mechanical properties of the samples were also studied. Tensile tests showed that with increasing amount of CNTs the strain at break decreased whereas the Young’s modulus was improved of 16.41 % to 36.05 % and tensile strength of 36.67 % to 64.70 % compared to pristine PP. The SEM microphotographs showed that majority of the CNTs were dispersed individually and oriented along the shear flow direction.

Keywords

  • carbon nanotubes
  • orientation
  • nanocomposites
  • polypropylene
  • tensile properties
Open Access

Role of substrate temperature on the growth mechanism and physical properties of spray deposited lead oxide thin films

Published Online: 17 Oct 2014
Page range: 448 - 456

Abstract

Abstract

Thin films of lead oxide were synthesized by cost effective spray pyrolysis technique at different substrate temperatures on glass substrates. Effect of substrate temperature on the growth mechanism and physical properties of the films was investigated. All the films were polycrystalline in nature with tetragonal structure corresponding to α-PbO. The films coated at 225 °C and 275 °C were (1 0 1) oriented, while the films deposited at 325 °C and 375 °C were (0 0 2) oriented. Above 375 °C, the pure tetragonal nature deteriorated and the peaks corresponding to orthorhombic phase were observed. The band gap value was found to be in the range of 2.3 to 2.62 eV. All the films had a resistivity of the order of 103 ohm-cm. A minimum resistivity of 0.0191 × 103 ohm-cm was obtained for the film coated at 325 °C. The activation energy increased with increase in substrate temperature.

Keywords

  • thin films
  • X-ray diffraction
  • crystal structure
  • energy band gap
  • electrical properties
Open Access

Investigation of structural, optical and electrical properties of (Ti,Nb)Ox thin films deposited by high energy reactive magnetron sputtering

Published Online: 17 Oct 2014
Page range: 457 - 464

Abstract

Abstract

In this work the results of investigations of the titanium-niobium oxides thin films have been reported. The thin films were manufactured with the aid of a modified reactive magnetron sputtering process. The aim of the research was the analysis of structural, optical and electrical properties of the deposited thin films. Additionally, the influence of post-process annealing on the properties of studied coatings has been presented. The as-deposited coatings were amorphous, while annealing at 873 K caused a structural change to the mixture of TiO2 anatase-rutile phases. The prepared thin films exhibited good transparency with transmission level of ca. 50 % and low resistivity varying from 2 Ωcm to 5×10−2 Ωcm, depending on the time and temperature of annealing. What is worth to emphasize, the sign of Seebeck coefficient changed after the annealing process from the electron to hole type electrical conduction.

Keywords

  • (Ti,Nb)Ox thin films
  • transparent oxide semiconductor
  • p-type electrical conduction
  • niobium doped titanium dioxide
  • transparent electronics
Open Access

Specific heat jump of two-band superconductor KFe2As2 using Ginzburg-Landau theory

Published Online: 17 Oct 2014
Page range: 465 - 469

Abstract

Abstract

In this study specific heat jump using two-gap Ginzburg-Landau (GL) theory has been calculated. In contrast to the previous approaches, we have taken into account intergradient order parameters interaction in the GL free energy functional. The thermodynamic magnetic field revealed nonlinear temperature dependence due to interband interaction between order parameters and their gradients. The calculations showed that the specific heat jump in two-order parameter superconductors was smaller than that of single-order parameter superconductors. It has been shown that such a model is in good agreement with experimental data for KFe2As2 superconductors.

Keywords

  • Fe based superconductors
  • Ginzburg-Landau theory
  • specific heat jump
  • two-band superconductivity
Open Access

Preparation and electromagnetic properties of zinc ferrite/expanded graphite composites

Published Online: 17 Oct 2014
Page range: 470 - 474

Abstract

Abstract

An effective process for the synthesis of nano spinel zinc ferrite/expanded graphite composites was developed in order to get an electromagnetic interference shielding material. Firstly, expandable graphite was prepared using sulfuric and nitric acid solutions. Then, the precursor of the composites was produced by chemical co-precipitation method, followed by heating treatment. The obtained composites were characterized by X-ray diffraction and scanning electron microscopy. The dielectric and magnetic properties were determined using vector network analyzer and vibrating sample magnetometry. The results showed that ferrite nanoparticles with the sizes of about 50–150 nm were uniformly dispersed on the surface and interspace of EG. The magnetic properties of the composites changed by adjusting the ferrite/EG ratio and the composites had high dielectric constant in the range of 2–18 GHz. These properties of the prepared composites suggest that they can be used as a promising electromagnetic interference shielding material.

Keywords

  • ferrite
  • graphite
  • composites
  • nanocomposites
  • magnetic properties
Open Access

CVD diamond layers for electrochemistry

Published Online: 17 Oct 2014
Page range: 475 - 480

Abstract

Abstract

Diamond electrodes of different morphologies and qualities were manufactured by hot filament chemical deposition (HF CVD) techniques by changing the parameters of diamond growth process. The estimation of diamond quality and identification of different carbon phases was performed by Raman spectroscopy measurements. The effect of diamond quality and amorphous carbon phase content on the electrochemical response of an obtained diamond electrode in 0.5 M H2SO4 as supporting electrolyte was investigated by cyclic voltammetry with [Fe(CN)6]4−/3− as a redox probe. The kinetic parameters such as catalytic reaction rate constant k0 and electron transfer coefficient α were determined. The obtained results show that the analytical performance of undoped diamond electrodes can be implemented just by the change of diamond layers quality.

Keywords

  • cyclic voltammetry
  • Raman spectroscopy
  • undoped diamond layer
  • amorphous carbon phase
Open Access

Synthesis and Mossbauer studies of mesoporous γ-Fe2O3

Published Online: 17 Oct 2014
Page range: 481 - 486

Abstract

Abstract

A method of synthesis of mesoporous γ-Fe2O3 by thermal decomposition of iron citrate has been proposed. Investigations of the crystalline and magnetic structure of obtained materials were done. Nanodispersed maghemite (γ-Fe2O3) with the sizes of coherent scattering regions of about 4–7 nm consisted of one phase only after gel sintering at 200, 250 and 300 °C. The particles of synthesized materials were both in magnetically ordered, and superparamagnetic states, and they formed a grid-like mesoporous structure. The influence of magnetic dipole interparticle interaction on the parameters of Mossbauer spectra was observed. A phenomenological model of the differences between nanodispersed γ-Fe2O3 magnetic microstructures obtained after annealing at different temperatures was presented.

Keywords

  • γ-Fe2O3
  • mesoporous structure
  • Mossbauer spectroscopy
  • superparamagnetic properties
Open Access

Properties of graphite-stainless steel composite in bipolar plates in simulated anode and cathode environments of PEM fuel cells

Published Online: 17 Oct 2014
Page range: 487 - 497

Abstract

Abstract

The use of a graphite-stainless steel composite as bipolar plates (BP) in polymer electrolyte membrane fuel cells (PEMFCs) has been evaluated. The study covers measurements of mechanical properties, microstructural examination, analysis of surface profile, wettability, porosity and corrosion resistance of the composite. The corrosion properties of the composite were examined in 0.1 mol·dm−3 H2SO4 + 2 ppm F− saturated with H2 or with O2 and in solutions with different pH: in Na2SO4+ 2 ppm F− (pH = 1.00, 3.00, 5.00) at 80 °C. The performed tests indicate that the graphite modified with stainless steel can be a good choice to be used as a bipolar plate in PEM fuel cells.

Keywords

  • powder metallurgy
  • sintering
  • graphite
  • bipolar plates
  • fuel cells
  • PEMFC
Open Access

Fabrication and characterization of compositionally graded Bi1−x GdxFeO3 thin films

Published Online: 17 Oct 2014
Page range: 498 - 502

Abstract

Abstract

An undoped BiFeO3 thin film, Gd doped Bi0.95Gd0.05FeO3 thin film with a constant composition, Gd up-graded doped Bi1−x GdxFeO3 and Gd down-graded doped Bi1−x GdxFeO3 thin films were successfully grown on Pt (111)/Ti/SiO2/Si (100) substrates using a sol-gel and spin coating technique. The crystal structure, ferroelectric and dielectric characteristics as well as the leakage currents of these samples were thoroughly investigated. The XRD (X-Ray Diffraction) patterns indicate that all these thin films consist of solely perovskite phase with polycrystalline structure. No other secondary phases have been detected. Clear polarization-electric field (P-E) hysteresis loops of all these thin films demonstrate that the incorporation of Gd3+ into the Bi site of BFO thin film have enhanced the ferroelectric performance of pure BiFeO3 thin film, and the Gd down-graded doped Bi1−x GdxFeO3 thin film has the best ferroelectric properties. Compared to other thin films, the optimal ferroelectric behavior of the Gd down-graded doped Bi1−x GdxFeO3 thin film results from its large dielectric constant, low dissipation factor and low leakage current.

Keywords

  • Gd substituted BiFeO3 thin films
  • crystal structure
  • ferroelectric properties
  • sol-gel technique
Open Access

Low-temperature synthesis of zeolite from perlite waste — Part I: review of methods and phase compositions of resulting products

Published Online: 17 Oct 2014
Page range: 503 - 513

Abstract

Abstract

In this paper a review of the recent studies on the synthesis of zeolites from expanded perlite under hydrothermal conditions is presented. Attention is paid to possible outcomes of synthesis from low cost glass material, such as perlite. The study also investigates the phase composition of zeolitic materials obtained by modification of by-product derived from an expanded perlite production process. The synthesis was made using the hydrothermal method with sodium hydroxide under autogenous pressure at a temperature below 100 °C for 1 to 72 h. It was possible to obtain a zeolitic material at a temperature as low as 60 °C using 4.0 M NaOH. The X-ray diffraction pattern showed the biggest peak intensity of zeolite X with 4.0 M NaOH at the temperature of 70 °C. During synthesis at higher temperature zeolite Na-P1 (with 3.0 M NaOH at 90 °C) and hydroxysodalite (with 5.0 M NaOH at 90 °C) were obtained.

Keywords

  • synthesis of zeolites
  • zeolite X
  • expanded perlite waste
  • FT-IR spectra
Open Access

Synthesis of porous ZnO nanostructures using bamboo fibers as templates

Published Online: 17 Oct 2014
Page range: 514 - 520

Abstract

Abstract

In this study, we fabricated ZnO nanostructures using bamboo fibers as templates. The starting material used was zinc acetate, and the nanostructures were synthesized by soaking and calcining the bamboo fibers. The fabricated nanostructures were characterized using X-ray powder diffraction (XRD) analysis, scanning electron microscopy (SEM), and ultraviolet-visible spectrophotometry. The results showed that the size of the ZnO nanoparticles was approximately 20–100 nm. When the ZnO nanoparticles were used as the catalyst in the photodegradation of methyl orange, the dye degraded by 95.98 % in 80 min. The response and recovery times of a gas sensor based on the ZnO nanoparticles were 25 and 24 s, respectively, during the detection of C2H5OH in a concentration of 10 ppm at 270 °C.

Keywords

  • ZnO
  • bamboo fiber template
  • photocatalysis
  • gas sensitivity

Plan your remote conference with Sciendo