Development of new processes to protect zinc against corrosion, suitable for on-site use

Protection against corrosion of metals is well known as an important issue in numerous fields. In all cases, the improvement of durability of these metals has to be connected to the development of environmentally friendly processes. Sol–gel protective coatings have shown excellent chemical stability and enhanced corrosion resistance for zinc substrates. Further, the sol–gel method, used as technique of surface protection, showed the potential for the replacement of toxic pre-treatments. This paper highlights the recent developments and applications of silane based sol–gel coatings on zinc substrates. Then, the challenges for industrial transfer of the developed process are also discussed because this process presents a disadvantage for on-site use, which is the too time-consuming thermal treatment. So, the goal of this study was to determine the convenient experimental conditions to reduce the duration of heat treatment of the hybrid sol–gel layer, compatible with the severe industrial requirements, without reducing the protection against corrosion. To reach this objective, a correlation between the results of chemical analyses and the protection against corrosion efficiency was established

SERS Detection of Graphene Oxide in Acid Catalyzed Sol-Gels

Silica sol-gel and aerogel substrates were synthesized using a modified acid catalyzed hydrolysis of tetramethyl orthosilicate method that incorporated graphene oxide and silver nanoparticles into the matrix. The effectiveness of loading of graphene oxide was monitored by UV-vis and surface enhanced Raman spectroscopy (SERS). Characterization data suggests that graphene oxide is detectable through SERS while integrated into a sol-gel and that size of silver nanoparticles has an impact on the SERS spectrum of graphene oxide

The preparation and characterization of alumina membranes with ultrafine pores 2. The formation of supported membranes

Supported γ-A12O3 membranes are prepared by a dipping procedure. According to this method, a capillary pressure drop is created by bringing a microporous ceramic support into contact with a boehmite (γ-A1OOH) sol. This pressure drop forces the dispersion medium of the sol to flow into the dry part of the support. The sol particles are concentrated at the entrance of the pores and a gel is formed. This gel can be dried and calcined to form a crack-free alumina membrane with pores measuring only a few nanometers, if the membrane thickness after calcination is about 5 μm or less. The gel formation process can be quantitatively well described with the slibcasting model. The observations that the membrane thickness increases linearly with the square root of the dipping time and that the casting rate increases if the sol concentration increases, the pore size of the support decreases or the gelling concentration decreases, are all in accordance with this slibcasting model

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

Properties of protective oxide scales containing cerium on Incoloy 800H in oxidizing and sulfidizing environments. I. Constant-extension-rate study of mechanical properties

The mechanical properties of ceramic coatings containing cerium oxide, prepared by the sol-gel method and used to protect Incoloy 800H against aggressive environments, are reported. Deformation and cracking behavior in oxidizing and sulfidizing environments has been investigated by constant-extension-rate tests. Extension rates were between 9.3×10−6 and 3.7×10−7 sec−1 at 823 <T<973 K. Under these conditions, cerium oxide sol-gel-coated specimens do not show any failure at extensions of 1.0% or more, but in hydrogen, sulfide failure is found at lower extensions than in air

Novel sol–gel preparation of (PO)–(CaO)–(NaO)–(TiO) bioresorbable glasses (X = 0.05, 0.1, and 0.15)

Quaternary phosphate-based glasses in the PO–CaO–NaO–TiO system with a fixed PO and CaO content of 40 and 25 mol% respectively have been successfully synthesised via sol–gel method and bulk, transparent samples were obtained. The structure, elemental proportion, and thermal properties of stabilised sol–gel glasses have been characterised using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), P nuclear magnetic resonance (P NMR), titanium K-edge X-ray absorption near-edge structure (XANES), fourier transform infrared (FTIR) spectroscopy, and differential thermal analysis (DTA). The XRD results confirmed the amorphous nature for all stabilized sol–gel derived glasses. The EDX result shows the relatively low loss of phosphorus during the sol–gel process and Ti K-edge XANES confirmed titanium in the glass structure is in mainly six-fold coordination environment. The P NMR and FTIR results revealed that the glass structure consist of mainly Q and Q phosphate units and the Ti cation was acting as a cross-linking between phosphate units. In addition DTA results confirmed a decrease in the glass transition and crystallisation temperature with increasing NaO content. Ion release studies also demonstrated a decrease in degradation rates with increasing TiO content therefore supporting the use of these glasses for biomedical applications that require a degree of control over glass degradation. These sol–gel glasses also offer the potential to incorporate proactive molecules for drug delivery application due to the low synthesis temperature employed

Mechanical compatibility of sol–gel annealing with titanium for orthopaedic prostheses

Sol–gel processing is an attractive method for large-scale surface coating due to its facile and inexpensive preparation, even with the inclusion of precision nanotopographies. These are desirable traits for metal orthopaedic prostheses where ceramic coatings are known to be osteoinductive and the effects may be amplified through nanotexturing. However there are a few concerns associated with the application of sol–gel technology to orthopaedics. Primarily, the annealing stage required to transform the sol–gel into a ceramic may compromise the physical integrity of the underlying metal. Secondly, loose particles on medical implants can be carcinogenic and cause inflammation so the coating needs to be strongly bonded to the implant. These concerns are addressed in this paper. Titanium, the dominant material for orthopaedics at present, is examined before and after sol–gel processing for changes in hardness and flexural modulus. Wear resistance, bending and pull tests are also performed to evaluate the ceramic coating. The findings suggest that sol–gel coatings will be compatible with titanium implants for an optimum temperature of 500 °C

A sol-gel method for growing superconducting MgB2 films

In this paper we report a new sol-gel method for the fabrication of MgB2 films. Polycrystalline MgB2 films were prepared by spin-coating a precursor solution of Mg(BH_4)_2 diethyl ether on (001)Al2O3 substrates followed with annealing in Mg vapor. In comparison with the MgB2 films grown by other techniques, our films show medium qualities including a superconducting transition temperature of Tc ~ 37 K, a critical current density of Jc(5 K, 0 T) ~ 5 {\times} 10^6 A cm^{-2}, and a critical field of H_{c2}(0) ~ 19 T. Such a sol-gel technique shows potential in the commercial fabrication of practically used MgB2 films as well as MgB2 wires and tapes.Comment: 8 pages, 5 figure