Polypyrrole grafting onto the surface of pyrrole-modified silica nanoparticles prepared by one-step synthesis

The grafting of polypyrrole onto the surface of modified silica nanoparticles has been investigated. These silica nanoparticles were modified with pyrrole moieties prepared by the well-known Stober method in one-step starting from TEOS and a pyrrole-bearing trialkoxysilane compound. The effects of various reaction conditions, including reaction time, solvent, and molar ratio of water to alkoxy groups, have been investigated in order to obtain pyrrole-modified silica nanoparticles with the optimal core–shell structure and the smallest possible particle size. The grafting was carried out in aqueous FeCl₃ solution containing the modified silica nanoparticles, with pyrrole monomers already adsorbed on the surface of the particles by soaking. Several analytical tools have been employed to characterize the particles and to assess the degree of grafting, namely TEM, SEM, TGA, FTIR, and XPS. The final polypyrrole-grafted silica nanoparticles obtained had a mean diameter of about 220 nm and 50 wt.% of grafted polypyrrole with respect to the total weight of polypyrrole formed around the surface of the cores.     

Preparation and characterization of sol–gel derived (1 0 0)-textured Pb(Zr,Ti)O3 thin films: PbO seeding role in the formation of preferential orientation

Lead zirconate titanate (PZT) thin films with a composition near the morphotropic phase boundary region were deposited onto Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates using a sol–gel method. A seeding layer was introduced between the most underlying surface of the PZT film and the platinum electrode surface to control the texture of the PZT thin film. The lead oxide seeding layer resulted in the formation of a single-phase perovskite and absolutely (1 0 0)-textured PZT film. SEM, XRD, XPS, and AES were used to characterize the evolution of the lead oxide layer and the PZT thin films. The growth kinetic mechanism of the (1 0 0)-textured PZT thin films was proposed phenomenologically. The ferroelectric and piezoelectric properties of the PZT films were also evaluated and discussed in association with different preferential orientations.     

2-Mercaptobenzoxazole as a copper corrosion inhibitor in chloride solution: Electrochemistry, 3D-profilometry,and XPS surface analysis

2-Mercaptobenzoxazole (MBOH) was studied as a corrosion inhibitor for Cu in 3 wt.% NaCl solution using EIS, a potentiodynamic curve, 3D-profilometry, and XPS measurements. It was shown that Cu corrosion in solution containing MBOH follows kinetic-controlled and diffusion-controlled processes and that MBOH is a mixed-type inhibitor. The diffusion coefficient of the Cu ions travelling through the solid surface layers was estimated to be on the order of 10⁻¹⁵–10⁻¹⁴ cm² s⁻¹. It was also demonstrated that the Cu(I)–MBOH complex is formed on the Cu surface and that the thickness of this surface layer is 1.4 ± 0.4 nm.     

Structural and optical properties of epitaxial ZnO thin films on 4H–SiC (0 0 0 1) substrates prepared by pulsed laser deposition

Epitaxially grown ZnO thin films on 4H–SiC (0 0 0 1) substrates were prepared by using a pulsed laser deposition (PLD) technique at various substrate temperatures from room temperature to 600 °C. The crystallinity, in-plane relationship, surface morphology and optical properties of the ZnO films were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL) measurements, respectively. XRD analysis showed that highly c-axis oriented ZnO films were grown epitaxially on 4H–SiC (0 0 0 1) with no lattice rotation at all substrate temperatures, unlike on other hexagonal-structured substrates, due to the very small lattice mismatch between ZnO and 4H–SiC of ～5.49%. Further characterization showed that the substrate temperature has a great influence on the properties of the ZnO films on 4H–SiC substrates. The crystalline quality of the films was improved, and surfaces became denser and smoother as the substrate temperature increased. The temperature-dependent PL measurements revealed the strong near-band-edge (NBE) ultraviolet (UV) emission and the weak deep-level (DL) blue-green band emission at a substrate temperature of 400 °C.     

(Ti,Cr,Nb)CN coatings deposited on nitrided high-speed steel by cathodic arc method

The combined processes of plasma nitriding and cathodic arc deposition of (Ti,Cr,Nb)CN coatings were applied to HSS substrates. The nitrided layers, obtained in a mixture of H₂ (70%) and N₂ (30%) at two different temperatures (480 °C and 510 °C), were examined for the microhardness depth profiles. Characterization of the duplex coatings was performed by investigating elemental and phase composition, texture, hardness, friction and wear. XRD and XPS analyses revealed the formation of a mixture of a carbonitride fcc solid solution, in a dominant proportion, and metallic chromium. The film hardness was measured to be ~ 34 GPa. The duplex (Ti,Cr,Nb)CN coatings exhibited superior tribological behavior as compared to both nitrided layers and non-duplex coatings.     

Ex situ XANES,XPS and Raman studies of poly(3,4-ethylenedioxythiophene) modified by iron hexacyanoferrate

X-ray (XPS and XANES) and Raman spectra of poly(3,4-ethylenedioxythiophene) (pEDOT) modified by iron hexacyanoferrate (Fehcf) network are presented. XANES studies allowed to postulate an octahedral surrounding of iron atoms in the material and identified nitrogen and carbon atoms as nearest neighbourhoods. XPS measurements reveal iron–nitrogen and iron–carbon bonds, supporting the XANES results. Chemical interaction between sulphur from pEDOT and iron was also evidenced by XPS. Although both methods give proof of Prussian Blue structure inside the polymer, Raman studies did not show any signal typical for CN at about 2160 cm^?1 (ν). However, the presence of Fehcf was confirmed by the stretching vibrations of Fe–N bond at 146 cm^?1 and Fe–CN vibrations at 270 cm^?1. AFM imaging was performed to illustrate the roughness and morphology of the pEDOT/Fehcf surface.     

Surface modeling and chemical solution deposition of SrO(SrTiO3)n Ruddlesden–Popper phases

Strontium titanate (STO) is a preferred substrate material for functional oxide growth, whose surface properties can be adjusted through the presence of Ruddlesden–Popper (RP) phases. Here, density functional theory (DFT) is used to model the (1 0 0) and (0 0 1) surfaces of SrO(SrTiO₃)_n RP phases. Relaxed surface structures, electronic properties and stability relations have been determined. In contrast to pure STO, the near-surface SrO–OSr stacking fault can be employed to control surface roughness by adjusting SrO and TiO₂ surface rumpling, to stabilize SrO termination in an SrO-rich surrounding or to increase the band gap in the case of TiO₂ termination. RP thin films have been epitaxially grown on (0 0 1) STO substrates by chemical solution deposition. In agreement with DFT results, the fraction of particular RP phases n = 1–3 changes with varying heating rate and molar ratio Sr:Ti. This is discussed in terms of bulk formation energy.     

Fabrication of modified-poly(divinylbenzene)/Au core–shell structure

A novel PDVB/Au core–shell structure was prepared by the chemical reduction of a gold–phenanthroline complex on the surface of a poly(divinylbenzene) (PDVB) cores (2–4 μm). The PDVB cores were synthesized by precipitation polymerization, and the surface was modified by introducing thiol and sulfonic acid groups. The modified surface structure was examined by FT-IR, XPS and EDS and the degree of sulfonation was measured according to its ion exchange capacity (IEC, 5.72 meq/g). The modified PDVB cores were immersed in a solution of a gold–phenanthroline complex and subsequently reduced to form gold nanoseeds. These were further grown in a solution of HAuCl₄ and NH₂OH to form gold nanoshells. The effects of the functional groups on the PDVB cores on fabrication of the core–shell structure were carefully examined. SEM and XPS were used to characterize the gold nanoshells. The presence of the functional groups could be of great assistance for the gold shell formation.     

Heat treatment of molybdenum under vacuum conditions

Oxide coverage of molybdenum plays an important role in several applications, for example in lighting industry. Surface conditioning procedures were simulated in an XPS instrument by in situ heat treatments while monitoring the surface composition and changes in the chemical states of molybdenum. Heat treatments have been made at different temperatures between 435 and 690 °C under vacuum conditions. It has been observed that during heating the molybdenum test samples the native MoO₃ layer on the surface dissociates, and a layer of suboxides forms on the surface. This layer hinders the further reduction of the surface, thus reaction speed decreases after the initial phase. It has been established that in the second phase of the heat treatment the activation energy of the process is 1.1 ± 0.2 eV. Reduction of MoO₃ to elemental molybdenum runs through two intermediate states: Mo⁶⁺ → Mo⁵⁺ → Mo⁴⁺ → Mo⁰.     

Chill zone copper with the strength of stainless steel and tailorable color

We report here on 90 at.% copper 2–4 mm thick castings with fracture strengths up to 1.9 MPa due to the formation of a thick, scratch-resistant nanocrystalline chill-zone next to the copper mold contact surfaces. It is found that the unusually hard nanocrystalline surface layers of thicknesses in the range of 200–300 μm form when the melt can be undercooled: when the alloy composition is such that the contact surface of the copper mold with the liquid alloy does not serve as a preferred site for crystal nucleation, supercooling of the melt in the chill-zone is possible. These castings are the hardest coppers ever reported to date in macroscopic specimens. They have mechanical strength superior to those of many stainless steels as well as to Cu–Be alloys and of the order of those of Cu-based bulk metallic glasses (BMGs) of similar dimensions. In addition, and unlike in copper-based BMGs, the color and luster can be tailored by elemental additions to vary from copper-like to gold-like.     

Study on the formation of cubic texture in Ni–7 at.% W alloy substrates by powder metallurgy routes

One of the main challenges for coated conductor applications is to produce sharp cubic textured alloy substrates with high strength and low magnetism. In this work, the cubic textured Ni–7 at.% W substrates were prepared from different powder metallurgy ingots by rolling-assisted biaxially textured substrate processing. The fabrication processes of cubic texture in the Ni–7 at.% W tapes by two powder metallurgy routes are described in detail. Through the optimized process, full width at half maximum values of 6.7° and 5.0° were obtained, as estimated by X-ray (1 1 1) phi scan and (2 0 0) rocking curve in the textured Ni–7 at.% W tape, respectively. By electron backscattering diffraction (EBSD) analysis, the percentage of the cubic textured component in the Ni–7 at.% W tape surface was found to reach 97.0% within a tolerance angle smaller than 10°. Moreover, the formation mechanism of the cubic texture in the Ni–7 at.% W tape were also investigated by EBSD. Particular attention was focused on the difference in the texture components along the thickness of the partially recrystallized samples.     

Conductive surface via graft polymerization of aniline on a modified glass surface

A functionalization with an aniline monolayer of a modified glass surface, followed by the surface grafting of polyaniline (PANI) was used to prepare a conductive surface. A bromopropylsilane monolayer was first generated by reacting a hydroxylated surface with 3-bromopropyltrichlorosilane under an inert atmosphere. This layer was functionalized by its reaction with aniline, which substituted the bromide atoms of the silane chain. Further, the tethered aniline molecules were used as active sites for the graft polymerization of PANI on the surface. The composition and microstructure of the PANI-grafted glass surfaces were examined by X-ray photoelectron spectroscopy (XPS), and ultra-violet (UV) spectroscopy, as well as by contact angle measurements. The surface conductivity of the modified glass surface-grafted with PANI was of the order of 10 S/cm, hence, larger than the usual value (∼1 S/cm) of the bulk PANI.     

Microstructural characterization and hardness evaluation of HVOF sprayed Ni–5Al coatings on Ni- and Fe-based superalloys

HVOF sprayed Ni–5Al coatings on Ni- and Fe-based superalloy substrates were characterized to assess the microstructural features and strength in the as deposition condition for their applications in high-temperature corrosive environment of gas turbine. X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDAX), and X-ray mapping analysis are used to characterize the Ni–5Al coatings. The dense coatings with less porosity and inclusions were produced using HVOF process. The deposited Ni–5Al coatings exhibited splat like layered morphologies due to deposition and resolidification of successive molten and semi molten powder particles. The hardness of coatings on three different superalloy substrates was measured and it was in the range of 210–272 Hv. The average bond strength and surface roughness of the as-sprayed coatings were 42.62 MPa and 9.22–9.45 μm, respectively. Diffusion of alloying elements from the substrate into the coating has occurred in all the three superalloy substrates as observed from the X-ray mapping analysis.     

Conductive polymer-coated textiles: The role of fabric treatment by pyrrole-functionalized triethoxysilane

Polypropylene (PP) and viscose (VS) textiles were modified by the in situ synthesis of a conducting polypyrrole (PPy) overlayer. To improve adhesion of the conducting layer to the textile surface, a pyrrole-functionalized silane (SP) was synthesized and bonded onto the surface before polypyrrole formation. Moreover, to introduce hydroxyl groups into the surface, PP was pretreated by grafting vinyltrimethoxysilane by means of a radiofrequency plasma discharge. The study is focused on the influence of SP on the washing fastness of a PPy layer and, consequently, on the overall conductivity of the textiles after washing. In the case of viscose, PPy was found to penetrate the substrate. A compromise was found between the influence of SP and penetration phenomenon (best conductivity after washing: wVS–0.2SP/25Py = 3 × 10⁻⁵ S/square). In the case of polypropylene the effect of pretreatment with SP is much better than for viscose, and a higher concentration of SP leads to improved fastness of the conductive layer (wmPP–0.2SP/25Py = 3 × 10⁻⁵ S/square; wmPP–1SP/25Py = 8 × 10⁻⁵ S/square), which indicates that the coating promoted by means of SP is more favoured than for viscose.     

Design and synthesis of a novel class of inhibitors for mild steel corrosion in acidic and carbon dioxide-saturated saline media

p-(9-(2-Methylisoxazolidin-5-yl)nonyloxy)benzaldehyde I, prepared using a cycloaddition protocol, was elaborated into its cinnamaldehyde derivative II which upon quarternization with propargyl chloride afforded III bearing an interesting blend of structural traits suitable for imparting inhibition of mild steel corrosion. Novel compounds I–III showed efficient inhibition against mild steel corrosion in CO₂–0.5 M NaCl (40 °C, 1 atm; 120 °C, 10 bar), 1, 4, 7.7 M HCl, and 0.5 M H₂SO₄ at 60 °C as determined by gravimetry and electrochemical methods. The presence of carbonaceous surface and nitrogen, as revealed by XPS study, indicated the formation of a film covering the metal surface, which imparted corrosion inhibition.     

Influence of coatings on microstructure and mechanical properties of preceramic paper-derived porous alumina substrates

Preceramic papers loaded with inorganic fillers may be used as preforms in a novel manufacturing technique to fabricate lightweight ceramic structures. In order to reduce the porosity caused by burning out cellulosic fibers and organics, porous preceramic paper-derived alumina substrates were post-treated via two different coating routes using silica suspension or methylphenylvinylhydrogen polysiloxane. Sintering of the alumina-filled preceramic papers in air at 1600 °C for 2 h resulted in a non-uniform distributed open porosity ranging from 23 to 26%. After coating and infiltration, all samples were additionally heat treated up to at 1500 °C for 2 h. Thermal analysis (DTA/TG) was applied to determine the pyrolysis temperature of polysiloxane. Microstructure and phase analysis were performed respectively by SEM and XRD. After sintering, water absorption, apparent density and open porosity of test pieces were determined, and mechanical properties of the substrates were evaluated before and after coating. For the samples coated with silica suspension, the mechanical strength remained in the same range of those for uncoated samples, while for the polysiloxane coated samples the mechanical strength steadily increases after repeated impregnation steps, reaching ～350 MPa.     

Thin nanocrystalline TiO2–SnO2 sprayed films: Influence of the dopant concentration,substrate and thermal treatment on the phase composition and crystallites sizes

Thin nanocrystalline TiO₂–SnO₂ films (0–50 mol% SnO₂) are coated on quartz and stainless steel substrates by spray pyrolysis method. The synthesized films are investigated by XRD, Raman spectroscopy and XPS.The diffraction peaks of anatase phase fade while the peaks of rutile phase appear in the X-ray profiles with increasing of the treatment temperature and the content of SnO₂ in the sprayed films. It is found that SiO₂ coming from the quartz substrate stabilizes the anatase phase up to 700 °C. A more pronounced crystallization of rutile is registered with the films deposited on stainless steel substrate, which probably is caused by combined effect of SnO₂ doping and penetration of iron and chromium from the substrate inside the films.Dopant concentration (SnO₂) influences the size of the crystallites of the titania films deposited on quartz substrates The size of crystallites in the titania films decreases from 45 to 25 nm with increasing of SnO₂ amount.The SnO₂ amount does not affects substantially the size of crystallites (about 23 nm) for the films deposited on stainless steel.     

Characterization and properties of an advanced composite substrate for YBCO-coated conductors

Thin, biaxially textured Ni5W/Ni12W/Ni5W composite substrates for coated conductor applications have been fabricated. The particularity of this three-layer composite configuration resides in the elemental diffusion between the outer layer and the core layer. Due to the migration of elemental W, the diffusion layer in the as-annealed substrate becomes broader than that of the as-rolled substrate. The obtained tape has a sharp cubic texture on the Ni5W outer layers, and the volume fraction of cubic grains exceeds 98.8% (<10°) at the outer surfaces. In situ electron backscatter diffraction strain–stress analysis shows that the high-quality cubic texture was stable until elongations as high as 2%. The yield strength of the composite substrate approaches 240 MPa and its saturation magnetization at 77 K has been strongly reduced with respect to pure Ni and Ni5W substrates. The present results demonstrate that this advanced three-layer substrate is suitable for the epitaxial growth of the LZO buffer layers.     

Influence of nanocrystalline Ni–Ti reaction agent on self-propagating high-temperature synthesized porous NiTi

Nanocrystalline Ni–Ti was used in self-propagating high-temperature synthesis (SHS) to fabricate porous NiTi. The SHS of porous NiTi using elemental powders was also prepared for comparison. Results showed that the main phase was NiTi with unreacted Ni when using elemental powders, which is detrimental to medical use. A large amount of Ti₂Ni secondary phase was also detected. By employing mechanically alloyed nanocrystalline Ni–Ti as a reaction agent, the secondary intermetallic phase (i.e. Ti₂Ni) was significantly reduced and the unreacted Ni was eliminated. The addition of 25 wt% nanocrystalline Ni–Ti reaction agent produced porous NiTi with an average porosity of 52–55 vol% and a general pore size of 100–600 μm under preheating temperatures of 200 and 300 °C. This general pore size in the range of 100–600 μm is beneficial to biomedical application for osseointegration. By further increase of the reaction agent to 50 wt% in the reactant, a porous NiTi part was produced at ambient temperature (i.e. no preheating was necessary) and a dense part was formed at preheated temperature of 200 °C due to the large amount of energies in the nanocrystalline reaction agent. This revealed that the use of nanocrystalline reaction agent effectively lowered the activation barriers for combustion synthesis reaction.     

2-Mercaptobenzimidazole as a copper corrosion inhibitor: Part II. Surface analysis using X-ray photoelectron spectroscopy

In Part I of this study, the high corrosion inhibition effectiveness of 2-mercaptobenzimidazole (MBIH) in 3 wt.% NaCl solution was unambiguously proven. In Part II, using angle-resolved X-ray photoelectron spectroscopy (XPS), the surface chemical structure and composition of adsorbed MBIH on Cu from the same solution was investigated. It was found that MBIH molecules are directed toward the Cu surface through their N and S atoms. The MBIH layer thickness is 1.9 ± 0.5 nm, as determined from a detailed analysis of the background in the XPS spectra. Tentative MBIH orientations on Cu were suggested based on the XPS measurements.