Synthesis and characterization of bismuth alkaline titanate powders

In this work, samples of bismuth alkaline titanate, (K_0.5Na_0.5)_(2?x/2)Bi_(x/6)TiO₃, (x = 0.05–0.75) have been prepared by conventional ceramic technique and molten salts. Metal oxides or carbonates powders were used as starting raw materials. The crystalline phase of the synthesized powders was identified by the X-ray diffraction (XRD) and particle morphology was characterized by scanning electron microscopy (SEM). Solid state reaction method was unsuccessful to obtain pellets. From XRD results, a rhombohedral structure was detected and the parameter lattice were estimated to be a = 5.5478 Å and α = 59.48°. These parameters were used to refine the structure by Rietveld analysis. SEM results showed several morphologies. Apparently, bismuth is promoting the grain growth whose sizes vary from 30 nm to 180 nm It is expected that these materials can be utilized in practical applications as substitutes for lead zirconatetitanate (PZT)-based ceramics.     

Preparation of Fe2B boride coating on low-carbon steel surfaces and its evaluation of hardness and corrosion resistance

Fe₂B coating was prepared on low-carbon steel by surface alloying. A series of experiments were carried out to examine some surface properties of boride coating. The surface heat treatment of coated low-carbon steel was performed at 700 °C, 800 °C and 900 °C for 2 h, 4 h, 6 h and 8 h under hydrogen atmosphere. The boride coating was revealed by XRD analysis and the microstructure of the boride coating was analyzed by scanning electron microscopy (SEM). Depending on the temperature and time of the process, the hardness of the borided low-carbon steel ranged from 99 to 1100 HV. The hardness showed a maximum (about 1100 HV) at 900 °C for 8 h. The corrosion resistance of the borided samples was evaluated by the Tafel polarization and electrochemical impedance spectroscopy (EIS). Shift in the corrosion potential (E_corr) towards the noble direction was observed, together with decrease in the corrosion current density (I_corr), increase in the charge transfer resistance (R_ct) and decrease in the capacitance (C_c), which indicated an improvement in corrosion resistance with increasing temperature and time of the treatment.     

An analysis of the machinability of ASTM grades 2 and 3 austempered ductile iron

The main goal of this work is to perform an analysis of the machinability of two ASTM grades of ADI, namely 2 and 3. The samples used in this work were cast and austempered according to ASTM standards for the production of grade 2 (G2) and grade 3 (G3) ADI. Characterization was accomplished through tensile and hardness tests, metallography and X-ray diffraction. Machinability was evaluated by analyzing tool life, cutting forces, surface finish and chip characteristics in turning operations. A quick-stop test was also performed in order to verify some mechanical processes during the chip formation and to analyze the shear plane angle. Tool life when machining G2 was 33% lower than G3 (18 min against 26 min), although the latter is a harder material. Abrasion and adhesion were the wear mechanisms observed through SEM images, whereas in other cast irons mainly abrasion is observed. Cutting forces measurements showed that the value of K_c1,1 decreased 19%, from 1448 to 1175 N/mm², for G2 as the depth of cut increased from 2 to 5 mm at a cutting speed of 80 m/min and 18%, from 1501 to 1236 N/mm², for G3. Surface roughness measurements proved that a smoother surface is obtained for both alloys at f = 0.10 mm/rev when using an insert with nose radius 1.6 mm instead of smaller radii. Both alloys presented similar surface quality. All chips observed were segmented.     

Supercapacitive behavior of electrosynthesized marygold-like structured nickel doped iron hydroxide thin film

Herein, we report the electrosynthesized marygold-like structured nickel doped (5 at.%) iron hydroxide thin film from the aqueous solution of 0.1 M iron sulphate using galavanostatic mode of electrodeposition method for supercapacitor application. The compositional analysis of film was studied by AAS. Amorphous structure of nickel doped iron hydroxide film revealed from XRD analysis. The formation of elemental bands of iron hydroxide was confirmed from FTIR study. The SEM images and surface wettability showed marygold-like structure with contact angle 79° with surface of film. The supercapacitive properties of film using cyclic voltammetry and galvanostatic charge–discharge showed the highest specific capacitance 287 F g^?1 in 1 M Na₂SO₃ electrolyte at the scan rate of 10 mV s^?1. The supercapacitive parameters such as, specific energy (S.E.), specific power (S.P.) and coulomb efficiency (η%) are 8.32 Wh kg^?1, 2.5 kW kg^?1 and 92%, respectively.     

Study on removal mechanism and removal characters for SiC and fused silica by fixed abrasive diamond pellets

Fixed abrasive is known as a high-efficient and stable technique for fabricating various materials. This work studies the removal mechanism and removal characters of fixed abrasive diamond pellets (FADPs) for lapping SiC and fused silica. The critical sizes of diamond particles changing brittle fracture to ductile removal (with better surface roughness and less damages) are figured out for SiC (9.56 μm) and fused silica (0.53 μm). Multi-distribution models are presented and a mathematical removal model is built based on Preston law. Then, removal characters of FADPs are investigated, including removal profile, removal rate, linear removal, removal stability, surface roughness, subsurface damage etc. Results show that (i) the removal shape is predictable and the removal rate is highly correlative with diamond size, velocity and pressure; (ii) the cumulative removal is temporally linear and removal stability is within ±10%; (iii) SiC can be ductilely lapped by 1.5, 3, 5 μm pellets, with best roughness Ra=4.8 nm and a specular surface for optical metrology; (iv) removal of fused silica is mostly brittle fracture and it can change as semi-ductile by 1.5 μm pellets, with a non-specular or semi-specular surface which is hard for optical metrology; (v) subsurface damage is highly dependent on diamond size, but free to pressure and velocity. Finally, two engineering applications validated its feasibility in uniform or deterministic lapping/polishing of optical mirrors.     

The influence of Lavandula angustifolia L. oil on corrosion of Al-3Mg alloy

Natural oil extracted from Lavandula angustifolia L. was investigated as corrosion inhibitor of Al-3 Mg alloy in 3% NaCl solution using weight loss, polarization measurements and SEM. The oil dissolved in ethanol and used as 30% (v/v) solution, was found to retard the corrosion rate of Al-3 Mg alloy even at high temperatures. The inhibiting effect of lavender oil components on Al-3 Mg surface was attributed to the Langmuir’s adsorption isotherm. It was found that the L. angustifolia L. oil provides a good protection to Al-3 Mg alloy against pitting corrosion in sodium chloride solution.     

Effect of vacuum annealing on characteristics of the HCl-doped polyaniline pellets

Powders of HCl-doped polyanilines were prepared by using a solution polymerization process and then were pressed to the polyaniline pellets. The pellets were annealed in vacuum at 140, 200 and 260 °C for times up to 120 min, respectively. Electrical property and micromorphology of the pellets were studied by using a four-point probe technique and a scanning electron microscopy. The conductivity of the pellets decreases sharply when the annealing time reaches 30 min and then decreases gradually with further increasing annealing time. When the pellets are annealed under the conditions of 200 °C/120 min, 260 °C/90 min and 260 °C/120 min, the resistance of the pellets could not be measured by the four-point probe technique and the pellets show an insulating characteristic. The breakdown voltage increases with increasing annealing temperature and time. The maximum breakdown voltage is about 875 V/cm. The degradation of the conductivity is mainly attributed to the loss of chlorine in the polyaniline pellets. The micromorphology of the pellets becomes heterogeneous with thermal aging.     

SEM/STM studies on the surface structure of a novel carbon fiber from lyocell

The surface structure and strengths of two types of cellulose-based carbon fibers, rayon-based carbon fiber (RCF) and lyocell-based carbon fiber (LCF), were investigated through scanning electronic microscopy (SEM) and scanning tunneling microscopy (STM). SEM delineated much smoother surface for LCF, while rougher surface with obvious cracks and grooves for RCF. It is believed that the difference of surface structure between these two carbon fibers results in a decrease in tensile strength for RCF. It can be found from the image of STM (500 nm × 500 nm) that the surfaces of LCF are characterized by bulk structure. Furthermore, it is proven that the bulk structure is composed of the smaller slug-like microstructures, each of which has a width of about 25 nm and length of 150 nm aligned with an angle at 45° to fiber axis when the observation scales down to 50 nm × 50 nm. The distance between two adjacent carbon atoms of LCF estimated by section analysis of STM reveals that no hexagonal carbon ring is formed on the surface of LCF examined.     

Solvent-drop assisted mechanochemical synthesis of the black and green polymorphs of the tetrathiafulvalene–chloranil charge transfer salt

This work describes the synthesis of the green and black polymorphic forms of the tetrathiafulvalene–chloranil (TTF–CA) charge transfer salt as pure phases, by solvent-assisted mechanochemistry. Both materials were characterized using laboratory and high-resolution X-ray powder diffraction (XRPD), elemental analysis and scanning electron microscopy (SEM). The high-resolution XRPD pattern of the TTF–CA black polymorph was indexed with a triclinic lattice a = 10.756(5) Å, b = 11.057(4) Å, c = 6.614(2) Å, α = 101.36(2)°, β = 93.69(3)°, γ = 89.37(3)°, V = 769.6(5) Å³. The chemical stability of these phases upon heating was investigated using thermogravimetric analysis (TGA), elemental analysis and X-ray powder diffraction (XRPD), indicating that both polymorphs undergo chemical decomposition, and ruling out the transition to an air-stable high temperature polymorph.     

Mechanical properties of polyaniline

In spite of extensive electrical characterization of polyaniline, the information on its mechanical properties is missing in the literature. Complex Young's modulus of polyaniline compressed into pellets was measured at room temperature and an influence of preparation conditions of the polyaniline pellets on mechanical properties was studied. Young's modulus of PANI hydrochloride pellets was 0.9 ± 0.2 GPa and that of polyaniline base 1.3 ± 0.2 GPa. These values are comparable with common polymers, such as bulk polystyrene, 1.8 ± 0.1 GPa, or compressed polystyrene powder, 0.80 ± 0.02 GPa. Modulus of polyaniline is independent of the compression pressure above 300 MPa, the time of compression had no effect.     

Electrical and magnetic properties of the composite pellets containing DBSA-doped polyaniline and Fe nanoparticles

DBSA-doped polyaniline powder (DBSA-PANI) was mixed with Fe nanoparticles to obtain the DBSA-PANI-Fe composite. Powder of the composite was compacted to the pellets to study the electrical property and magnetization characteristic by measuring the conductivity in 100–300 K and the magnetization curve at room temperature. The conductivity of the composite pellet is linearly decreased from 0.25 ± 0.02 to 0.07 ± 0.01 S/cm with increasing the Fe nanoparticle content from 0 to 70 wt.%. For the pellets containing the Fe nanoparticles less than 70 wt.%, the variation of conductivity with temperature reveals that the charge transport mechanism can be considered to be one-dimensional variable-range-hopping (1D-VRH). For the pellet with 70 wt.%-Fe nanoparticles, however, the charge transport mechanism cannot be well understood in terms of the VRH model. All the DBSA-PANI-Fe composite pellets show a magnetic hysteresis loop and a hard magnetization characteristic. The saturation magnetization monotonously increases from 32 to 78 emu/g with increasing the Fe nanoparticle content from 30 to 70 wt.%. The saturation field and the coercivity are estimated to be about 5500 and 385 Oe, respectively, independent of the Fe nanoparticle content.     

Electrosynthesis of polyaniline films on titanium by pulse potentiostatic method

Polyaniline (PANI) was synthesized on titanium electrode from aqueous solution containing 0.3 mol L⁻¹ aniline and 1 mol L⁻¹ HNO₃ by pulse potentiostatic method. The chronoamperogram during polymerization process of aniline was recorded. The effects of the synthesis parameters, such as anodic pulse duration (t_a), cathodic pulse duration (t_c), lower limit potential (E_c) and upper limit potential (E_a), on the morphology and electroactivity of the PANI films were investigated by scanning electron microscopy (SEM) and cyclic voltammetry (CV). SEM results present that flake, mica-like, quasi-fibrous and nano-fibrous PANI film could be synthesized with various polymerization parameters. Under the following conditions, t_a = 0.8 s, t_c = 0.1 s, E_c = 0 V and E_a = 1.0 V, high quality nano-fibrous PANI film with the best electroactivity was obtained. The CV results show that the PANI films with different morphologies, which were prepared under the same anodic polymerization charge, have obvious different characteristics. This means that the PANI films with different morphologies have different electrochemical activity.     

Synthesis and characterization of aniline copolymers containing carboxylic groups and their application as sensitizer and hole conductor in solar cells

Copolymers of m-aminobenzoic acid and o-anisidine doped with p-toluenesulphonic acid in different proportions were successfully synthesized by oxidative polymerization. The copolymers were characterized by FT-IR, UV–vis, ¹H NMR and EPR spectroscopies, cyclic voltammetry, conductivity and SEM. The copolymer with equivalent amounts of the monomers o-anisidine and m-aminobenzoic acid presented the highest conductivity, The EPR analyses and SEM images show that this copolymer provides more homogeneous films with particle size distribution of approximately 1–2 μm. The copolymer with a high fraction of o-anisidine gives rises to films with larger particle sizes and a more defined electrochemical process. The m-aminobenzoic acid monomer was intentionally chosen in order to promote a better electronic coupling between the conducting copolymer and the TiO₂ surface. The copolymers were tested as both sensitizers and hole conducting materials in dye-sensitized solar cells. The device assembled using the copolymer with the highest proportion of m-aminobenzoic acid units as sensitizer produced the highest photocurrent (I_sc = 0.254 mA cm^?2) and photovoltage (V_oc = 0.252 V) at 100 mW cm^?2. The energy diagram shows that although the electronic injection from the conducting polymer excited state is an allowed process the regeneration of the positive charges created after the electron transfer process is forbidden, thus explaining the low efficiency of solar energy conversion. When this copolymer was applied as a hole conducting material, an improvement in the V_oc to 0.4 V, was observed, indicating that this material is more suitable for charge transport when applied in this type of solar cells.     

Synthesis and hydrogen reduction of nano-sized copper tungstate powders produced by a hydrothermal method

The pure nano-sized copper tungstate (CuWO₄) powders were prepared by hydrothermal method and consequent annealing at 500 °C for 120 min. The thermogravimetric analysis was used to study dehydration processes, and the scanning electron microscopy (SEM) indicated that CuWO₄ particles were mostly spherical in the size range from 60 to 90 nm. Hydrogen reduction at 800 °C for 60 min converted the CuWO₄ to W–Cu composite powders. The hydrogen reduction results showed that nano-sized CuWO₄ particles calcining at 500 °C for 120 min indicated finer microstructure than the other calcination temperatures of 0 °C, 400 °C, 620 °C, 650 °C and 700 °C. W–Cu particles were observed finest and homogeneous in the size range from 90 to 150 nm by SEM images. Homogeneous distribution of W and Cu particles was clearly demonstrated by elemental mapping. Encapsulation of Cu phase by the W phase was observed by EDS and TEM. From FFT and HRTEM images, the orientation relationship of (01-1)_Cu ∥(01-1)_W and a semicoherent interface between W and Cu phases could be observed. A good correlation between the HRTEM image and the calculated lattice misfit (δ) was obtained.     

Electrochemical impedance spectroscopy and electrochemical noise measurements as tools to evaluate corrosion inhibition of azole compounds on stainless steel in acidic media

The corrosion inhibition function of two azole derivatives namely benzotriazole (BTR) and benzothiazole (BNS) on stainless steel in 1 M HCl was investigated using electrochemical techniques and SEM surface analysis as well. In consistency with the data obtained from EIS and polarization curves, electrochemical current noise transient analysis, noise resistance and characteristic charge from shot noise theory indicated effectiveness of the inhibitors. The corrosion damage mitigation was also confirmed through SEM in the presence of BNS. To remove the DC trend from noise data, the appropriate p value was proposed based on the correlation with polarization and EIS data.     

Studies on magnetic,dielectric and magnetoelectric behavior of (x) NiFe1.9Mn0.1O4 and (1 − x) BaZr0.08Ti0.92O3 magnetoelectric composites

In the present research work, the magnetoelectric (ME) composites of ferrite and ferroelectric phases with (x) NiFe_1.9Mn_0.1O₄ and (1 ? x) BaZr_0.08Ti_0.92O₃ (where x = 0.10, 0.20 and 0.30) respectively were synthesized by the conventional ceramic method. The X-ray diffraction pattern of the composite reveals a spinel phase formation for the ferrite and perovskite phase formation for the ferroelectric phase without any other phase. The SEM micrographs of composites were taken to determine the average grain size and also to study the surface morphology. The effect of constituent phase variation on the B–H hysteresis behavior and the dielectric properties was examined. The dielectric constant shows usual dielectric dispersion behavior with increasing frequency which is due to the Maxwell–Wagner type surface interfacial polarization. From the ac conductivity study, it is confirmed that the conduction in the present composites is of small polaron type. The static magnetoelectric (ME) voltage coefficient developed on the surface of magnetoelectric material was measured as a function of applied dc magnetic field. The maximum ME conversion factor of 1.18 mV/cm Oe was observed for x = 0.10 composite. Such composites may be useful to fabricate the magnetic field sensors and applicable in many linear ME devices.     

Electrical,structural and magnetic properties of polyaniline/pTSA-TiO2 nanocomposites

Polyaniline (PANI)/para-toluene sulfonic acid (pTSA) and PANI/pTSA-TiO₂ composites were prepared using chemical method and characterized by infrared spectroscopy (IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM). The electrical conductivity and magnetic properties were also measured. In corroboration with XRD, the micrographs of SEM indicated the homogeneous dispersion of TiO₂ nanoparticles in bulk PANI/pTSA matrix. Conductivity of the PANI/pTSA-TiO₂ was higher than the PANI/pTSA, and the maximum conductivity obtained was 9.48 (S/cm) at 5 wt% of TiO₂. Using SQUID magnetometer, it was found that PANI/pTSA was either paramagnetic or weakly ferromagnetic from 300 K down to 5 K with H_C ≈ 30 Oe and M_r ≈ 0.015 emu/g. On the other hand, PANI/pTSA-TiO₂ was diamagnetic from 300 K down to about 50 K and below which it was weakly ferromagnetic. Furthermore, a nearly temperature-independent magnetization was observed in both the cases down to 50 K and below which the magnetization increased rapidly (a Curie like susceptibility was observed). The Pauli susceptibility (χ_pauli) was calculated to be about 4.8 × 10^?5 and 1.6 × 10^?5 emu g^?1 Oe^?1 K for PANI/pTSA and PANI/pTSA-TiO₂, respectively. The details of these investigations are presented and discussed in this paper.     

Chemical,physical and morphological characterization of ZnNi films electrodeposited on 1010 steel substrate from acid baths containing polyalcohol

ZnNi alloy electrodeposition on a 1010 steel electrode in boric-acid baths containing sorbitol, mannitol or glycerol was investigated by cyclic voltammetry. Electrodeposits obtained galvanostatically were characterized by SEM, EDS and XRD. It was found that in baths containing sorbitol or mannitol, the deposition current density (j_d) was reduced, but in none of the baths was the initial deposition potential affected. SEM images of deposits revealed that the boric-sorbitol and boric-mannitol complexes refine the grain, even at high j_d. XRD patterns of the ZnNi deposits produced at j_d = 50 mA cm^? 2, in ZnNi1 bath and in ZnNi1 bath contained sorbitol or mannitol, indicated that the films were formed mainly of Zn and γ¹ phases. To ZnNi2 baths contained glycerol the films were formed of γ and γ¹ phases. The Ni content in the deposits produced in the bath without polyalcohol or containing glycerol increased from ~ 5 to 19 wt.% with increasing j_d. With sorbitol or mannitol, there was a smaller rise from ~ 7 to 10 wt.% Ni. Thus, ZnNi deposits providing sacrificial protection can be obtained in baths with or without polyalcohol. The linear polarization method showed that ZnNi alloy deposited from baths contained polyalcohol have greate R_p.     

Densification and oxidation behavior of a novel TiB2–MoSi2–CrB2 composite

Titanium diboride (TiB₂) composite with MoSi₂ and CrB₂ has been prepared and tested to possess excellent oxidation resistance. Dense composite pellets were fabricated by hot pressing of powder mixtures. Microstructural characterization was carried out by XRD and SEM. Hardness and fracture toughness values were measured. Extensive oxidation studies of the composites were also carried out. Density of ≥ 96% ρ_th was obtained by hot pressing at 1800 °C under a pressure of 35 MPa for 1 h. Hardness and fracture toughness were in the range of 18–24 GPa and 3.5–4 MPa·m^1/2 respectively. Crack branching, deflection and bridging mechanisms were observed in the crack propagation paths. Isothermal and continuous oxidation studies of these composites up to 1000 °C showed improved oxidation resistance with the formation of protective glassy layer. TiO₂, Cr₂O₃ and SiO₂ phases were identified on the oxidized surface. Diffusion controlled mechanism of oxidation was observed in the composites.     

Titanium-supported Ce-, Zr-containing oxide coatings modified by platinum or nickel and copper oxides and their catalytic activity in CO oxidation

A combination of plasma electrolytic oxidation (PEO) and impregnation techniques followed by annealing in air has been used to obtain composites Pt/nZrO₂ + pTiO₂/Ti, Pt/nZrO₂ + pTiO₂ + zCeO_x/Ti, NiO + CuO/nZrO₂ + pTiO₂/Ti, NiO + CuO/nZrO₂ + pTiO₂ + zCeO_x/Ti with different zirconium and titanium contents and ZrO₂/TiO₂ phase ratio. The composites have been investigated by means of XRD, XPS and SEM/XSA methods. According to the XPS data, the platinum content on the coating surface is ~ 0.4 at.%, whereas the XSA measurements have shown that the nickel and copper contents in coatings attain 16 and 8 at.%, respectively, depending on the initial oxide coatings composition. Nickel and copper oxides form either extended islets or solid layers (“crusts”) on the coating surface. Both the composites promoted with platinum and those with the “crust” built from nickel and copper oxides are active in CO oxidation at the temperatures above 200 °C and 300 °C, respectively.