• Issue front cover thumbnail

      Volume 35, Issue 2

      April 2012,   pages  129-290

    • Development and characterization of new phosphorus based flame retardant tetraglycidyl epoxy nanocomposites for aerospace application

      K Shree Meenakshi E Pradeep Jaya Sudhan S Ananda Kumar

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      A study was made in the present investigation on the development and characterization of triphenyl phosphine oxide based phosphorus tetraglycidyl epoxy nanocomposites denoted as ‘C’ and to find out its suitability for use in high performance applications. The synthesized resin was characterized by Fourier transform infrared spectra (FT–IR) and 1H, 13C nuclear magnetic resonance (NMR) spectra. Nanoclay and POSS-amine nanoreinforcements denoted as N1 and N2 were incorporated into the synthesized epoxy resin. Curing was done with diaminodiphenylmethane (DDM) and bis(3-aminophenyl) phenylphosphine oxide (BAPPO) curing agents denoted as 𝑋 and 𝑌, respectively. Mechanical, thermal, flame retardant, water absorption behaviour and electrical properties of the epoxy nanocomposites were studied and the results are discussed.

    • Investigation of superhydrophilic mechanism of titania nano layer thin film—Silica and indium oxide dopant effect

      Akbar Eshaghi Ameneh Eshaghi

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      In this paper, TiO2–SiO2–In2O3 nano layer thin films were deposited on glass substrate using sol–gel dip coating method. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and water contact angle measurements were used to evaluate chemical structure, surface composition, hydroxyl group contents and superhydrophilicity of titania films. FTIR result indicated that Si–O–Si, Si–O–Ti and Ti–O–Ti bands formed in TiO2–SiO2–In2O3 sample. According to XPS, the hydroxyl content for TiO2, TiO2–SiO2 and TiO2–SiO2–In2O3 films was calculated as 11.6, 17.1 and 20.7%, respectively. The water contact angle measurements indicated that silica and indium oxide dopant improved the superhydrophilicity of titania nano film surface especially in a dark place. The enhanced superhydrophilicity can be related to the generation of surface acidity on the titania nano film surfaces. In the present state, superhydrophilicity is induced by the simultaneous presence of both Lewis and Bronsted sites.

    • Effects of particle size and surrounding media on optical radiation efficiencies of spherical plasmonic metal nanoparticles

      Vinayak A Dhumale Preeti V Shah Rishi B Sharma Katsuaki Tanabe

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      The optical radiation efficiency (𝜂), the ratio of scattering cross-section to extinction cross-section, of spherical metal nanoparticles (M= Al, Ag, Au and Cu) surrounded by glass and water was calculated using classical electrostatics. The effect of varying particle diameter (∼100 nm) on 𝜂 was also studied for free space wavelengths in the range of 400–1200 nm. The variations in the value of 𝜂 with the diameter (𝑑) of the metal nanoparticles were calculated on the basis of quasi-static approximation. The 𝜂 increases with the size of metal nanoparticles. Corresponding to a metal nanoparticle, 𝜂 was found to exhibit a sharp dip (𝜂dip) at a characteristic wavelength (𝜆𝜇)M in a particular medium (𝜇 = air, glass and water). (𝜆𝜇)M was independent of particle size. The (𝜆medium)M was found to be slightly blue shifted for all metal nanoparticles surrounded by glass or water with respect to those in the air.

    • Surface texture modification of spin-coated SiO2 xerogel thin films by TMCS silylation

      Yogesh S Mhaisagar Bhavana N Joshi A M Mahajan

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      The SiO2 xerogel thin films were deposited successfully by sol–gel technique via the acid-catalyzed hydrolysis and condensation of tetraethylorthosilicate (TEOS) with ethanol as a solvent. Further, the deposited thin films were treated wet chemically by trimethylchlorosilane (TMCS) and hexane solution with 10% and 15% volume ratio to remove the hydroxyl groups from the surface of deposited SiO2 thin films. These as deposited and surfacemodified films were characterized by ellipsometer, Fourier transform infrared (FTIR) spectrometer and contact angle meter. The presence of 2900 and 850 cm-1 peaks of CH3 vibrations in FTIR spectra of surface-modified films confirms the hydrphobisation of SiO2 surface. The maximum contact angle of 108.7° was observed for the surface-modified film at 10% TMCS.

    • Synthesis of BiFeO3 by carbonate precipitation

      V Kothai Rajeev Ranjan

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      Magnetoelectric multiferroic BiFeO3 (BFO) was synthesized by a simple carbonate precipitation technique of metal nitrate solutions. X-ray powder diffraction and thermo-gravimetric analysis (TGA) revealed that the precipitate consists of an intimate mixture of crystalline bismuth carbonate and an amorphous hydroxide of iron. The precipitate yielded BiFeO3 at an optimal calcination temperature of ∼560°C. Energy dispersive X-ray (EDX) analysis showed 1:1 ratio between Bi and Fe in the oxide. X-ray photoelectron spectroscopy (XPS) studies confirmed that Fe to be in +3 oxidation states both in the precipitated powder and BiFeO3. The synthesized BFO exhibits a very weak ferromagnetic correlation at room temperature and the degree of which increases slightly on cooling down to 10 K suggesting alteration in the long range spatial modulation of the spins arrangement as compared to the bulk BiFeO3.

    • Purification of cadmium by selective volatilization in vacuum in presence of oxide phase on its melt

      N R Munirathnam K Srinivasa Rao T L Prakash

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      Purification of cadmium in the presence of a thin (∼0.001 mm) oxide layer on the surface of the molten metal was carried out using a simple system designed and fabricated locally. The analytical results revealed that the distillation through oxide layer gave better separation for Co, Ni, Cu, Zn, Ag, Sn, Hg and Tl, when compared to the distillation without oxide layer. This was attributed due to the impurity metal oxide phases formation on the surface of the molten metal. The influence of oxygen flow time on the distillation rate of cadmium was established. There was no excess oxygen (O) retained in the distillate after two consecutive vacuum distillations through oxide route. The experiments were conducted at the level of nearly 1.5 kg a batch to study the impurities behaviour due to upscaling. The detailed chemical analysis of 58 impurity elements in Cd in presence and absence of oxide layer was carried out by glow discharge mass spectrometry (GDMS).

    • Structural, optical, photoluminescence, dielectric and electrical studies of vacuum-evaporated CdTe thin films

      Ziaul Raza Khan M Zulfequar Mohd Shahid Khan

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      Highly-oriented CdTe thin films were fabricated on quartz and glass substrates by thermal evaporation technique in the vacuum of about 2 × 10-5 torr. The CdTe thin films were characterized by X-ray diffraction (XRD), UV–VIS–NIR, photoluminescence spectroscopy and scanning electron microscopy (SEM). X-ray diffraction results showed that the films were polycrystalline with cubic structure and had preferred growth of grains along the (111) crystallographic direction. Scanning electron micrographs showed that the growth of crystallites of comparable size on both the substrates. At the room temperature, photoluminescence spectra of the films on both the substrates showed sharp peaks with a maximum at 805 nm. This band showed significant narrowing suggesting that it originates from the transitions involving grain boundary defects. The refractive index of CdTe thin films was calculated using interference pattern of transmission spectra. The optical band gap of thin films was found to allow direct transition with energy gap of 1.47–1.50 eV. a.c. conductivity of CdTe thin films was found to increase with the increase in frequency whereas dielectric constant was observed to decrease with the increase in frequency.

    • Phase relation of LaFe11.6Si1.4 compounds annealed at different high-temperature and the magnetic property of LaFe11.6−𝑥Co𝑥Si1.4 compounds

      Xiang Chen Yungui Chen Yongbai Tang

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      LaFe11.6Si1.4 compounds are annealed at different high temperatures from 1323 to 1623 K. The powder X-ray diffraction patterns show that large amount of NaZn13-type phase begins to be observed in LaFe11.6Si1.4 compound after being annealed at 1423 K for 5 h. In the temperature range from 1423 to 1523 K, the 𝛼-Fe and LaFeSi phases rapidly decrease to form 1:13 phase. LaFeSi phase is rarely observed in the XRD pattern in the LaFe11.6Si1.4 compound annealed at 1523 K (5 h).With annealing temperature increasing to 1573 K and 1673 K, La5Si3 phase is detected, and there is a certain amount of LaFeSi phase when the annealing temperature is 1673 K. The amount of impurity phases in the LaFe11.6Si1.4 compound annealed by the two-stage annealing consisting of high temperature (>1523 K) and 1523 K is larger than that of the single stage annealing at 1523 K under the same time. According to the results of different high-temperature annealing, LaFe11.6−𝑥Co𝑥Si1.4 (0.1 ≤ 𝑥 ≤ 0.8) compounds are annealed at 1523 K (5 h). The main phase is NaZn13-type phase, and the impurity phase is a small amount of 𝛼-Fe in LaFe11.6−𝑥Co𝑥Si1.4 compounds. With increase in Co content from 𝑥 = 0.1 to 0.8, the Curie temperature 𝑇C, goes up from 207 to 285 K. The introduction of Co element weakens the itinerant electron metamagnetic transition, and also results in the change of magnetic transition type from first to second order at about 𝑥 = 0.5. The magnetic entropy change decreases from 19.94 to 4.57 J /kg K with increasing Co concentration at a low magnetic field of 0–2 T. But the magnetic hysteresis loss around 𝑇C reduces remarkably from 26.2 J /kg for 𝑥 = 0.1 to 0 J /kg for 𝑥 = 0.8.

    • Influence of pH and bath composition on properties of Ni–Fe alloy films synthesized by electrodeposition

      Xinghua Su Chengwen Qiang

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      Fe–Ni films were electrodeposited on ITO glass substrates from the electrolytes with different molar ratio of Ni2+/Fe2+ and different pH values (2.1, 2.9, 3.7 and 4.3) at 25°C. The properties of Fe–Ni alloy films depend on both Ni2+ and Fe2+ concentrations in electrolyte and pH values. The content of Ni increases from 38% to 84% as the mole ratio of NiSO4/FeSO4 increasing from 0.50/0.50 to 0.90/0.10 in electrolyte and slightly decreases from 65% to 42% as the pH values increase from 2.1 to 4.3. The X-ray diffraction analysis reveals that the structures of the films strongly depend on the Ni content in the binary films. The magnetic performance of the films shows that the saturation magnetization (𝑀s) decreases from 1775.01 emu/cm3 to 1501.46 emu/cm3 with the pH value increasing from 2.1 to 4.3 and the saturation magnetization (𝑀s) and coercivity (𝐻c) move up from 1150.44 emu/cm3 and 58.86 Oe to 2498.88 emu/cm3 and 93.12 Oe with the increase of Ni2+ concentration in the electrolyte, respectively.

    • Development of P/M Fe–P soft magnetic materials

      S K Chaurasia Ujjwal Prakash P S Misra K Chandra

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      Phosphorous is treated as an impurity in conventional steels owing to segregation of phosphorous and formation of brittle phosphides along the grain boundaries. It is responsible for cold and hot shortness in wrought steels. In conventional powder metallurgy, involving compaction and sintering, high phosphorous content (up to 0.7%) in Fe-based alloys exhibit attractive set ofmechanical andmagnetic properties. These powder-processed alloys suffer from increasing volumetric shrinkage during sintering as phosphorous is increased beyond 0.6%. Thus both cast as well as conventional powder metallurgy routes have their own limitations in dealing with iron–phosphorous alloys. Hot-powder forging was used in the present investigation for the development of high-density soft magnetic materials containing 0.3–0.8% phosphorous to overcome these difficulties. It was observed that phosphorous addition improves the final density of the resulting product. It was further observed that hot-forged iron–phosphorous alloys have excellent hot/cold workability and could be easily shaped to thin strips (0.5–1.0 mm thick) and wires (0.5–1.0 mm diameter). The powder hot-forged alloys were characterized in terms of microstructure, porosity content/densification, hardness, softmagnetic properties and electrical resistivity.Magnetic properties such as coercivity 0.35–1.24 Oe, saturation magnetization 14145–17490 G and retentivity 6402–10836 G were observed. The obtained results were discussed based on the microstructures evolved.

    • Diffuse phase transition, piezoelectric and optical study of Bi0.5Na0.5TiO3 ceramic

      B Parija T Badapanda V Senthil S K Rout S Panigrahi

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      Bismuth sodium titanate, Bi0.5Na0.5TiO3 (BNT) is considered to be an excellent candidate for a key material of lead-free dielectric ceramics. In this study, we propose the dielectric and optical study of single phase BNT powder prepared by solid-state reaction route. The phase formation and structural study were done by X-ray diffraction (XRD) which shows well developed crystallite with a pure perovskite phase. The ceramic was sintered at different temperatures from 1050°C to 1175°C to study the effect of sintering temperature on the morphology and density. It was found that the sample sintered at 1150°C shows the highest density. The microstructure of the ceramic was investigated by scanning electron microscopic (SEM) technique. The temperature-dependent dielectric study of the sample sintered at 1150°C was done in the frequency range of 50 kHz–1 MHz which shows a diffuse phase transition. The piezoelectric constant (𝑑33) was found to be 41 pCN-1. The P–E hysteresis loop confirms the ferroelectric behaviour in the ceramic. The UV–Vis spectrum indicated that the Bi0.5Na0.5TiO3 ceramic has an optical band gap of 2.94 eV.

    • Mechanism for formation of NaBH4 proposed as low-pressure process for storing hydrogen in borosilicate glass–sodium solid system: a hydrogen storage material

      Aysel Kantürk Figen Sabriye Pişkin

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      The mechanism for the formation of sodium borohydride (NaBH4) was investigated for its ability to store hydrogen in the borosilicate glass–sodium (BSG–Na) solid system under low hydrogen pressure. BSG, which was prepared by melting borax with silica, was used as the starting material in the BSG–Na system that would be prepared to store hydrogen. It was observed that the mechanism for storing hydrogen in the BSG–Na solid system consisted of six steps and when the BSG–Na system was heated under a pressure of 4 atm, which was created through the use of hydrogen atmosphere, the storage of hydrogen occurred at nearly 480°C for approximate duration of 200 min, with the excellent yield (97%). In addition, the hydrogen storage capacity of the NaBH4 sample was measured using the Au–PS structure, which was designed as a mini-hydrogen cell. It was determined that the minimum amount of NaBH4 to generate the maximum volume of hydrogen gas was 12 mg/ml at 270 mV.

    • Removal of two ionic dyes from water by MgO-loaded porous carbons prepared through one-step process from poly(ethylene terephthalate)/magnesium carbonate mixtures

      A Czyżewski J Karolczyk A Usarek J Przepiórski

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      Mixtures of poly(ethylene terephthalate) and magnesium carbonate at different weight ratios were heated up to 850°C in argon atmosphere. During heating, components of the initial mixtures underwent thermal decomposition yielding porous carbon materials loaded with different amounts of magnesium oxide. Structural characteristics of the prepared materials were determined from adsorption/desorption isotherms of nitrogen, measured at 77 K. For reference, portions of the products obtained were acid-washed to obtain MgO-free carbons. Pore structures of the prepared materials were strongly dependent on the quantitative compositions of starting mixtures. As a rule, specific surface areas determined for acid-washed materials were much higher than those for MgO-loaded carbons. The adsorption abilities of obtained materials towards cationic (Basic Red 18) and anionic (Reactive Red 198) dyes as model contaminants were examined. Surprisingly, in spite of relatively low specific surface areas, substantially high adsorption of the dyes on MgO-loaded carbons was observed. An influence of specific surface area and the role of magnesium oxide presence on the adsorption capacity of the acquired sorbents were studied.

    • Investigation of nonionic diazo dye-doped polymer dispersed liquid crystal film

      Farzana Ahmad Muhammad Jamil Young Jae Jeon Lee Jin Woo Jae Eun Jung Jae Eun Jang

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      Sudan black B (SBB) was used to investigate as the nonionic diazo dye-doped in polymer dispersed liquid crystal (PDLC) display, by polymerization-induced phase separation (PIPS) method. The maximum absorbance, contrast ratio, dichroic ratio and the order parameter of nonionic diazo dye in nemetic host (TL203) were investigated using UV–Vis polarized spectroscopy. The orientation of the dye molecules was controlled by electric field, which enabled the contrast ratio of the dye to be obtained by electrically switching. The change occurring on droplet morphologies and electro-optical properties of PDLC film with the change in contents of Sudan black dye and liquid crystals (LC) contents was investigated. We found an increase in LC droplet sizes with the increase of diazo dye and LC contents. Moreover the addition of small amount of nonionic diazo dye reduced the threshold voltage (Vth), increased off-state transmittance, enhanced the contrast ratio and decreased the response time of dye-doped PDLC. Additionally the change in transition temperature of LC and changes in LC droplet morphologies with the addition of dye were also observed. Such changes were observed with the images taken by polarized optical microscope (POM). The detail discussions on such behaviours were also made.

    • Study on crystallization behaviour of co-polyamide 66 containing triaryl phosphine oxide

      Yang Xiao Feng Li Qiao Ling Chen Zhi Ping Yang Yong Feng Zhang Lei

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      In this paper, the isothermal crystallization and non-isothermal crystallization behaviour of flame retardant co-polyamide 66 (FR-PA66) containing triaryl phosphine oxide (TPO) were researched by employing differential scanning calorimetry (DSC), polarized optical microscopy (POM), respectively. The effects of TPO groups on nucleation mechanism, nucleation pattern and crystallization rate of FR-PA66 were discussed in detail. Experimental results show that TPO unit does not nucleate first during crystallization process of FR-PA66. The nucleationmechanism and nucleation pattern of FR-PA66 do not virtually change with incorporation of TPO groups when compared with polyamide 66 (PA66). The mainly crystallization process of FR-PA66 is still free nucleation and growing during the prime crystallization stage, and is unimensional nucleation and growing during the second crystallization stage. But at the second crystallization stage, we think there is a para-crystal forming with the maincrystal unimensional nucleation and growing. In addition, incorporation of TPO groups result in the decrement of both nucleation rate and crystallization rate of FR-PA66, and the increment of crystallization activation energy. Hence the TPO groups were unfavourable for FR-PA66 crystallization. In addition, incorporation of TPO groups also result in the decrement of crystallization region of FR-PA66, and increment of spherulite defect.

    • Influence of polyols on properties of bio-based polyurethanes

      S Gopalakrishnan T Linda Fernando

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      Polyurethane elastomers from cardanol-based polyol, polypropylene glycol (PPG-1200 and PPG-2000) and isophorone diisocyanate were prepared in the form of thin sheets. The sorption,mechanical and thermal properties were studied. The solubility parameter and molecular weight between crosslinks of polyurethane samples were calculated from swelling experiments. The swelling study of polyurethanes revealed that the sorption is found to decrease with an increase in chain length of PPG. The stress–strain data showed that the elastomers obtained using PPG-1200 gave the best mechanical properties. The thermal degradation of all the three elastomers starts almost at 270°C, regardless of the PPG chain length. The value of activation energy of degradation calculated using the Broido method was in the range of 40–70 kJ/mol.

    • High resolution X-ray diffraction studies on unirradiated and irradiated strontium hexaferrite crystals

      Balwinder Kaur Monita Bhat F Licci Ravi Kumar K K Bamzai P N Kotru

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      High-resolution X-ray diffraction technique, employing a three-crystal monochromator–collimator combination is used to study the irradiation induced defects in flux grown Sr-hexaferrite crystals irradiated with 50 MeV Li3+ ion beams at room temperature with a fluence value of 1 × 1014 ions/cm2. The diffraction curves of the irradiated crystals suggest the possibility of creation of low angle grain boundaries and other point/clusters of defects causing amorphization in the irradiated crystals. The perfection of the irradiated and unirradiated (0001) cleaved surfaces of the crystals is studied using the bulk method of X-ray topography. The topographs supplement the findings suggestive of modifications in the crystalline quality of SrFe12O19 on irradiation with SHI of Li3+. Etching of the (0001) cleaved surfaces in H3PO4 at 120°C suggests that the dissolution characteristics of the surfaces get affected on irradiation with SHI of Li3+, besides supporting the findings of HRXRD and X-ray topography regarding modifications in the perfection of SrFe12O19 on irradiation.

    • Crystal growth and magnetic property of YFeO3 crystal

      Anhua Wu Hui Shen Jun Xu Zhanliang Wang Linwen Jiang Liqing Luo Shujuan Yuan Shixun Cao Huaijin Zhang

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      YFeO3 and other rare earth substituted crystals with distorted orthorhombic pervoskite-like structure (space group, 𝑃𝑏𝑛𝑚) have attracted much attention due to their remarkable magnetic properties of primary significance for technological applications. In the present work, the floating zone growth of YFeO3 crystals has been systematically investigated and high quality YFeO3 crystal was obtained by optimized process. The magnetic properties of YFeO3 crystal were investigated, and it indicated the high magneto-optical property in YFeO3 crystals with specific orientation due to its anisotropy. YFeO3 crystals display superior performance in the application magneto-optical current sensors and fast latching optical switches.

    • Structural and spectral properties of 4-phenoxyphthalonitrile dye sensitizer for solar cell applications

      P M Anbarasan K Vasudevan P Senthil Kumar A Prakasam M Geetha K Lalithambigai

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      The geometries, electronic structures, polarizabilities and hyperpolarizabilities of organic dye sensitizer 4-phenoxyphthalonitrile was studied based on ab initio HF and density functional theory (DFT) using the hybrid functional B3LYP. Ultraviolet–visible (UV–Vis) spectrum was investigated by time dependent DFT (TDDFT). Features of the electronic absorption spectrum in the visible and near-UV regions were assigned based on TD-DFT calculations. The absorption bands were assigned to 𝜋 → 𝜋* transitions. Calculated results suggest that the three excited states with the lowest excited energies in 4-phenoxyphthalonitrile was due to photo-induced electron transfer processes. The interfacial electron transfer between semiconductor TiO2 electrode and dye sensitizer 4-phenoxyphthalonitrile was due to an electron injection process from excited dye to the semiconductor’s conduction band. The role of phenoxy group in 4-phenoxyphthalonitrile in geometries, electronic structures and spectral properties were analysed.

    • Study of MEH–PPV/PCBM active layer morphology and its application for hybrid solar cell performance

      Quynh Nhu Nguyen Truong Nguyen Tam Nguyen Truong Chinho Park Jae Hak Jung

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      Surface morphologies of MEH–PPV:PCBM active layers were optimized by investigating ITO substrate treated with oxygen and nitrogen plasma. This treatment effectively improved smoothness, transmittance, and contact angle of ITO’s, resulting in good anode contacts for hybrid device structures. The consistently improved performance of hybrid solar cells was also achieved. The surface properties of treated and untreated ITO substrates were compared by contact angle, four point probe, scanning electron microscopy, and atomic force microscopy.

    • Electrochemical impedance study on the corrosion of Al-Pure in hydrochloric acid solution using Schiff bases

      A S Patel V A Panchal N K Shah

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      The inhibition effect of newly synthesized Schiff bases 𝑁-benzylidene benzylamine (A) and benzenemethanamine-𝛼-methyl-𝑁-(phenylmethylene) (B) on the corrosion behaviour of Al-Pure in 1.0 M HCl was studied using galvanostatic polarization and electrochemical impedance spectroscopy (EIS) and adsorption studies. The effects of inhibitor concentration, temperature and surface coverage are investigated. The effect of inhibitor concentration and other parameters are evaluated for different inhibitor concentrations and the probable mechanism was also proposed. The results show that (A) and (B) possess excellent inhibiting effect for the corrosion of Al-Pure and the inhibitors act as mixed type inhibitors. The inhibitors do not affect the mechanism of the electrode processes and inhibit corrosion by blocking the reaction sites. The high inhibition efficiency of (A) and (B) were due to the adsorption of inhibitor molecules on the metal surface. The decrease of surface area available for electrode reactions to take place is due to the formation of a protective film. Activation energy and free energy of adsorption have been calculated.

© 2017 Indian Academy of Sciences, Bengaluru.