Influence of Fe concentration on the properties of the electrodeposited Zn–Fe coatings

Electrodeposition of Zn–Fe alloys on a copper substrate from a sulfate bath with different Fe²⁺ concentration (0.05, 0.10 and 0.20 mol L^?1) at room temperature was investigated using cyclic voltammetry. The influence of the Fe²⁺ content in the plating bath on the surface morphology, structural and magnetic properties of the coatings were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Vibrating Sample Magnetometer (VSM). The results show that the morphology of Zn–Fe films changes with different Fe²⁺ concentration. The EDS analysis demonstrated that the Fe content of the coatings increased with increasing the Fe concentration in the bath. XRD measurements shows the presence of ?Zn (hcp), δ1ZnFe (hcp) and the ΓZnFe (bcc) phases with a (101) preferential orientation in all the electrodeposited films. The magnetic analysis of Zn–Fe films indicated that the saturation magnetization was largely enhanced in comparison to pure Zn, especially with 0.2 at. % Fe, while the coercivity decreased.     

Influence of the substrate type on the microstructural,optical and electrical properties of sol–gel ITO films

Indium tin oxide (ITO) is recognized as the best transparent and conductive material [transparent conducting oxide (TCO)] until now and its properties are dependent on the preparation method. In the present work ITO films with In:Sn atomic ratio 9:1 were prepared by a sol–gel route on different substrates (microscope glass slides, microscope glass covered with one layer of SiO₂ and Si wafers) for TCO applications. The multilayer ITO films were obtained by successive deposition by the dip-coating method and the films were characterized from the structural, morphological, optical, and electrical points of view using X-ray diffraction, scanning electron microscopy, atomic force microscopy, spectroscopic ellipsometry and by Hall effect measurements, respectively. The results showed that the thickness, optical constants and carrier numbers depend strongly on the type of substrate, number of deposited layers and sol concentration. The optical properties of ITO films are closely related to their electrical properties. The enhancement of the conductivity was possible with the increase of crystallite size (which occurred after thermal treatment) and with the reduction of surface roughness.     

Influence of erbium on the structural,optical and magnetic properties of sol–gel Ce: YIG films

Journal of Sol-Gel Science and Technology - Sol–gel Y2.8-xCe0.2Er x Fe5O12 (x?=?0.0, 0.2, 0. 4, 0.6, 0.8 and 1.0) nanofilms were successfully prepared for their potential use in...     

Modification of hemp shiv properties using water-repellent sol–gel coatings

For the first time, the hydrophilicity of hemp shiv was modified without the compromise of its hygroscopic properties. This research focused on the use of sol–gel method in preparation of coatings on the natural plant material, hemp shiv, that has growing potential in the construction industry as a thermal insulator. The sol–gel coatings were produced by cohydrolysis and polycondensation of tetraethyl orthosilicate (TEOS) using an acidic catalyst. Methyltriethoxysilane (MTES) was added as the hydrophobic precursor to provide water resistance to the bio-based material. Scanning electron microscopy (SEM) and focused ion beam (FIB) have been used to determine the morphological changes on the surface as well as within the hemp shiv. It was found that the sol–gel coatings caused a reduction in water uptake but did not strongly influence the moisture sorption behaviour of hemp shiv. Fourier transformed infrared (FTIR) spectroscopy shows that the coating layer on hemp shiv acts a shield, thereby lowering peak intensity in the wavelength range 1200–1800?cm^?1. The sol–gel coating affected pore size distribution and cumulative pore volume of the shiv resulting in tailored porosity. The overall porosity of shiv decreased with a refinement in diameter of the larger pores. Thermal analysis was performed using TGA and stability of coated and uncoated hemp shiv have been evaluated. Hemp shiv modified with sol–gel coating can potentially develop sustainable heat insulating composites with better hygrothermal properties.

Open image in new window

     

Effect of sol–gel hydrophobicity on the distribution and structure of different proteins in organically modified sol–gel thin films

Although the use of silica sol–gels for protein entrapment has been studied extensively our understanding of the interactions between the immobilization matrix and the entrapped biomolecules is still relatively poor. Non-invasive in situ spectroscopic characterization is a promising approach to gain a better understanding of the fundamentals governing sol–gel immobilization of biomolecules. This work describes the application of Fourier transform infrared (FTIR) microscopy to determine the influence of modifying the sol–gel hydrophobicity, by varying the content of the organically modified precursor propyltrimethoxysilane (PTMS), on the distribution and structure of three model proteins (lysozyme [EC 3.2.1.17], lipase [EC 3.1.1.3] and bovine serum albumin (BSA)) in silica sol–gel thin films. FTIR analysis of the overall immobilized protein positional distribution showed a Gaussian type distribution. FTIR microscopic mapping however, revealed that the spatial distribution of proteins was heterogeneous in the sol–gel thin films. When this positional information provided by FTIR microscopy was taken into account, areas of high protein concentration (clusters) were found and were not found to be homogeneously distributed. The shape of these clusters was found to depend on the type of protein entrapped, and in some cases on the composition of the sol–gel. Positional analysis of the distribution of the organically modified precursor PTMS in relation to the protein distribution was also conducted. The localized concentration of PTMS was found to positively correlate with the protein concentration in the case of lipase and negatively correlate in the case of lysozyme and BSA. These results indicate that lysozyme and BSA concentration was higher in areas of low hydrophobicity, while lipase concentration was higher in areas of high hydrophobicity within the sol–gel. Additionally, as determined by peak shape analysis of the amide I peak a higher PTMS content appeared to conserve protein structure in high concentration clusters for lipase. In contrast, lysozyme and BSA, appeared to retain their structure in high concentration clusters better at lower PTMS contents. A hypothesis speculating on the nature of the hydrophobic/hydrophilic interactions between the proteins and the sol–gel domains as the reason for these differences is presented.     

Effect of microstructure and surface roughness on the wettability of superhydrophobic sol–gel nanocomposite coatings

Sol–gel nanocomposite coatings were fabricated by spraying precursor mixtures containing hydrophobically modified silica (HMS) nanoparticles dispersed in sol–gel matrices prepared with acid-catalyzed tetraethoxysilane (TEOS), and methyltriethoxysilane (MTEOS). The hydrophobicity of the coatings increased with increase in the concentration of HMS nanoparticles. Superhydrophobic coatings with water contact angle (WCA) of 166° and roll-off angle <2° were obtained by optimizing the sol–gel processing parameters and the concentration of silica nanoparticles in the coating. FESEM studies have shown that surface has a micro-nano binary structure composed of microscale bumps and craters with protrusions of nanospheres. The properties of composite coatings fabricated by spin coating and spray coating methods were compared. It was found that the microstructure and the wettability were also dependent on the method of application of the coating.     

Influence of oxygen atmosphere on the photoluminescence properties of sol–gel derived ZrO2 thin films

Homogeneous and transparent ZrO₂ thin films were prepared by sol?Cgel dip coating method. The prepared ZrO₂ thin films were annealed in air and O₂ atmosphere at 500, 700 and 900?°C for 1, 5 and 10?h. X-Ray diffraction (XRD) pattern showed the formation of tetragonal phase with a change of stress in the films. Scanning electron microscope (SEM) revealed the nucleation and particle growth on the films. An average transmittance of >80?% (in UV?CVis region) was observed for all samples. The refractive index and direct energy band gap were found to vary as functions of annealing atmosphere, temperature and time. Photoluminescence (PL) revealed an intense emission peak at 379?nm weak emission peaks at 294, 586 and 754?nm. An enhancement of PL intensity was observed in films annealed in O₂ atmosphere. This is due to reconstruction of zirconium nanocrystals interfaces, which help passivate the non-radiative defects. At 900?°C, oxygen atoms react with Zr easily at the interface and destroy the interface states acting as emission centres and quench the PL intensity of the film. The enhancement of the luminescence properties of ZrO₂ by the passivation of non radiative defects presents in the films make it suitable for gas sensors development, tuneable lasers and compact disc (CD) read-heads.     

Effect of glycerol on the optical and physical properties of sol–gel glass matrices

Glass samples are prepared with different amount of glycerol as drying control chemical additive (DCCA) via acid catalysed sol–gel method. These samples are given solvent treatment namely rinse and dip with methanol while drying of the sample. In rinse treatment solid sample is rinsed with small amount of methanol while in dip treatment sample is dipped for 5 h in methanol. Comparative studies of these treated samples containing varied DCCA concentration are carried out by measuring optical transmission, mechanical strength and bulk density. Various instrumental techniques used for analysis are FTIR, DTA-TGA, XRD, SEM and TEM. The untreated samples take long time to dry up and to come out of the cuvette and show very less transmission in UV region which is much enhanced by solvent treatment. On the basis of this study, the solvent treated glass samples with DCCA amount 8 ml in the composition used are found to have the maximum UV transmission, good mechanical strength and may be useful as silica gel host matrices for solid state dye lasers and other applications. The UV transmission reported in the present studies is 90% in 337 nm region, which is the wavelength of N₂ laser pumping.     

The influence of the inhibitor particle sizes to the corrosion properties of hybrid sol–gel coatings

The influence of the inhibitor particle size (nano and micro cerium dioxide) embedded in several hybrid sol–gel coating systems for the corrosion protection of aluminium AA2024 alloy was studied, as well as the influence of other parameters like the inhibitor loading level and the method of reticulation. The properties of the obtained coatings were evaluated by means of transmission electron microscopy, accelerated salt spray test and electrochemical impedance spectroscopy. All the varied parameters proved to have an important influence on the corrosion mechanism, and an improvement induced by the use of nanometric inhibitors in comparison with the micrometric ones was demonstrated. In the case of the strong reticulated matrix, an inhomogeneous dispersion of the inhibiting species (micro inhibitor) favours the tension formation, making the coating more vulnerable to the corrosion attack. For the same doping level it was observed that the reticulation with 1-methylimidazole (MI) leads to a slightly better corrosion protection. Concomitantly, it was shown that high loadings with inhibitors have an adverse effect on the corrosion protection.     

Effects of Cu addition on the structure and magnetic properties of L10-FePt nanoparticles prepared by sol–gel method

(FePt)₁₀₀Cu₀, (FePt)₉₅Cu₅ and (FePt)₉₀Cu₁₀ nanoparticles (NPs) were successfully synthesized by the sol–gel method. The relationship between Cu doping and structure and magnetic properties of L1₀-FePt NPs was studied. The results indicated that all three samples originated a L1₀-FePt structure and Cu doping did not destroy the ordered structure of L1₀-FePt. By increasing the Cu content, c/a ratio of the FePtCu NPs linearly decreased. Pawley refinement showed symmetry of (FePt)₉₅Cu₅ NPs was still tetragonal. When the Cu concentration increased from 0 to 10 %, coercivity increased from 7,050 to 11,250 Oe. This result confirms that the prepared alloys can be promising candidates for magnetic storage applications.     

Preparation of sol–gel based nano-structured hybrid coatings: effects of combined precursor’s mixtures on coatings morphological and mechanical properties

Nanostructured hybrid clearcoats were produced using sol–gel based organic/inorganic precursors. To this end, clearcoats containing mixtures of a network former (tetraethyl ortosilicate; TEOS) and a network modifier (methacryloxy propyltrimethoxysilane; MEMO) and their hydrolyzed forms were prepared. Scanning electron microscope and atomic force microscope were utilized in order to investigate the morphology of different sol–gel prepared films. The mechanical properties of the bulk and surface of the clearcoats were studied by dynamic mechanical thermal analysis and nanoindentation techniques. The scratch resistance of the hybrid clearcoats was also studied by a laboratory carwash simulator. Decrease in glass transition temperature (Tg), cross-linking density, hardness and elastic modulus were seen for the clearcoat composed of hydrolyzed network modifier combined with hydrolyzed and non-hydrolyzed network former. However, a reverse effect was seen when the hydrolyzed TEOS and non-hydrolyzed MEMO was used. No improvement was observed using hydrolyzed MEMO in the clearcoat composition. Generally, results revealed improved mechanical properties of the clearcoat when the hydrolyzed network former was used together with non-hydrolyzed MEMO. Greater phase separation and silica cluster formation were seen for the clearcoats loaded with hydrolyzed MEMO compared with hydrolyzed TEOS.