Bioactive Sol-Gel Coatings for Orthopaedic Prosthesis

Sol-gel materials have been proposed in last years for clinical applications. In this work, bioactive sol-gel coatings were prepared from suspensions of up to 25% wt. of bioactive glass (CaO·SiO₂·P₂O₅) particles in a hybrid sol obtained from TEOS and MTES. Thick dip-coatings showed in vitro bioactivity after a few days, but glass-particles dissolution promotes a slight reduction in the corrosion resistance. In order to overpass this problem, a two-stage sol-gel coating system that includes a first SiO₂ hybrid film, acting as barrier against corrosion, and an external bioactive layer from glass particle suspension is proposed. The obtained samples revealed significant improvement in their electrochemical behaviour, and showed in vitro bioactivity.     

Effect of Sintering Temperature on the Corrosion and Wear Behavior of Protective SiO2-Based Sol-Gel Coatings

Sol-gel hybrid organic-inorganic and inorganic SiO₂-based protective coatings with and without added 3 m glass particles were developed and tested for their corrosion and wear behavior of an stainless steel substrate (AISI316L). The corrosion resistance greatly increases by incorporating glass particles in the sols. The incorporation of particles in the coatings allows the synthesis of thicker crack-free coatings. On the other hand, the corrosion resistance increases for coatings with a higher organic content obtained at lower sintering temperature. These coatings are also highly stable in saline aqueous solutions. However, the wear resistance is badly affected by the hybrid character of the SiO₂ matrix. The optimum coating process in terms of corrosion and wear resistance, appears to be a hybrid system with a dense SiO₂ network achieved at intermediate sintering temperatures.     

Zn-Al-[V10O28]6-双层氢氧化物掺杂对LY12铝合金表面溶胶-凝胶涂层性能的影响

采用共沉淀法制备Zn-Al-[V₁₀O₂₈]^6-双层氢氧化物(以下简称LDH-V), 研究不同添加浓度(0.0、0.25×10^-3、0.75×10^-3、1.5×10^-3、3.0×10^-3 mol·L^-1)的LDH-V对LY12 铝合金溶胶-凝胶涂层形貌、耐蚀性的影响. 采用扫描电子显微镜(SEM)和傅里叶变换红外(FTIR)光谱研究LDH-V对涂层形貌和结构的影响. 运用中性盐雾实验对涂层进行耐蚀性评估. 利用电化学方法对涂层在0.05 mol·L^-1的NaCl 溶液中的腐蚀行为进行研究. 探讨加入LDH-V后溶胶-凝胶涂层的耐蚀机理. 结果表明, 一定量LDH-V的加入不仅可以提高溶胶-凝胶涂层的耐蚀性能, 还可对涂层被破坏区域进行自修复, 起到延缓铝合金基体腐蚀的作用. 然而, 当LDH-V的添加溶度超过一定值时, 会破坏涂层的完整性并降低涂层的腐蚀防护性能. 实验结果表明LDH-V最佳的添加浓度为1.5×10^-3mol·L^-1.     

Infiltration of SiO<Subscript>2</Subscript>/SiOC Nanocomposites by a Multiple Sol Infiltration-Pyrolysis Process

SiO₂ containing hybrid inorganic-organic nanocomposites prepared by the sol-gel method from silica nanoparticles, tetraethylorthosilicate and silanol terminated polydimethylsiloxane were used as precursors for obtaining porous SiO₂/SiOC nanocomposites by pyrolysis in nitrogen atmosphere. A tetraethylorthosilicate sol and a triethoxysilane/methyldiethoxysilane sol, prepared by the sol-gel method and investigated by FT-IR, were used for a multiple sol infiltration-pyrolysis process in vacuum as precursors for a secondary SiO₂ and SiOC glassy phase respectively. As the density and porosity of these materials depends on the starting precursor composition, the sol infiltration-pyrolysis process was carried out in order to decrease the porosity and increase the density of such materials. This process was monitored using the sample weight gain and by a non-destructive method for measuring of the E modulus on each cycle. The initial and final material was also characterized by means of Hg porosimetry and the three-point bend test, at room temperature, of the nanocomposites was also examined.     

Electrochemical behaviour of SiO2 sol-gel coatings on stainless steel

SiO₂ coatings onto stainless steel substrates have been prepared by sol-gel in order to study the performance and mechanism of attack in different corrosive solutions. The electrochemical behaviour of the samples has been evaluated by Electrochemical Impedance Spectroscopy using NaCl and HCl as electrolytes. Comparative tests have been performed on samples with one and two silica layers as well as on uncoated ones. SiO₂ coatings produce no important protection of stainless steels subjected to electrochemical corrosion. This behaviour may be explained by micropores and microcracks produced during the coating sintering.     

Surface topography control of NiS/Ni<Subscript>3</Subscript>S<Subscript>4</Subscript> nanosheets for the promotion of electrochemical performance

One of the promising candidates to replace the chromate conversion coatings for corrosion protection of aluminium alloy AA7075 are the hybrid sol–gel coatings. In the present work hybrid silica sol–gel coatings doped with cerium nitrate were prepared and characterized. Tetraethoxysilane (TEOS) and 3-glycidoxypropyl-trimethoxysilane (GPTMS) were used as precursors. Silica SiO₂ (Ludox) particles were added to achieve a barrier properties of coating, while Ce(NO₃)₃·6H₂O was added in order to obtain an active corrosion protection. Optimization of sol synthesis was based on the results of ATR-FTIR spectroscopy and UV–vis–NIR spectroscopy. Opening of epoxy rings and completion of hydrolysis and the condensation reactions during the synthesis process were confirmed. Coatings were characterized through thickness, water contact angle, roughness, adhesion, electrochemical properties (potentiodynamic and electrochemical impedance spectroscopy) and the response to prolonged immersion time in 0.1?M NaCl. The high degree of cross-linking of Si–O–Si network structure and high density was achieved during the synthesis of the sol. Moreover, the results showed that the curing process and the incorporation of cerium nitrate into the hybrid sol–gel coating affected to the corrosion properties of the coating. The observed enhancement in corrosion protection properties is attributed to the combination of the barrier properties of the silica matrix with the active protection of the cerium nitrate.

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Development of a New Alkali Resistant Coating

The effect of different new sol-gel BaO—TiO₂—SiO₂ and CaO—BaO—TiO₂—SiO₂ coatings on long-term durability of glass fiber reinforced cement (GRC) was examined. Flexural strength of GRC was measured after curing for 7 to 150 days. Significant improvement was observed for coated GRC in this study and discussed in terms of the hydrate formation at interface. Concerned with the alkali resistance, CaO—BaO—TiO₂—SiO₂ coating was more effective than BaO—TiO₂—SiO₂ coating. In special, the 10CaO—10BaO—60TiO₂—20SiO₂ coating, prepared by sol-gel method, was recommended for the highest flexural strength of GRC and least corrosion at surface of E-glass fiber.     

Sol-Gel Processing of Zirconia Coating for HR Mirrors with High Laser Damage Threshold

High laser-damage resistant coatings are very important in high power laser systems. In this study ZrO₂ thin films are prepared by sol-gel spin-coating technology from suitable zirconia aqueous colloidal suspensions containing nano-crystalline ZrO₂ at room temperature synthesized by a hydrothermal process from an inorganic precursor (ZrOCl₂·8H₂O). By adding a soluble organic binder PVP to the suspension prior to application, it is possible to substantially increase the coating refractive index and the abrasion-resistance as well as the laser damage threshold. The features of the coatings and the colloidal suspensions are investigated. Multilayer highly reflective dielectric coatings are also elaborated by applying quarterwave-thick alternating coatings of the binder-aided zirconia and silica, which is prepared with the sol-gel process from TEOS. To achieve 99% reflectivity, 19–21 layers are required. Single shot laser damage tests are carried out using a high power laser at 1064 nm wavelength with a pulse duration of 2.5 ns. The laser damage thresholds of 18 and 15 J/cm² are achieved for single ZrO₂-PVP coating and ZrO₂-PVP/SiO₂ multilayers respectively.     

Anti-Reflective Coatings for CRTs by Sol-Gel Process

Two types of anti-reflective coatings composed of nano-particles were developed for cathode ray tubes (CRTs). The anti-reflective and anti-static coating is composed of two layers. An outer SiO₂ layer is formed over a porous inner layer composed of titanium oxynitride (TiO _x N_y), antimony-doped tin oxide (ATO) and SiO₂. To control the reflection of the film, a porous structure is formed using a mixed sol composed of TiO _x N _y -ATO particles and hydrolyzed-polymerized tetraethoxy-silane (TEOS). The resulting double layered coating is shown to consist in a nanocomposite pseudo three-layer structure. The antireflective electromagnetic-wave-shielding coating is also composed of two layers. An outer SiO₂ layer is formed over an electric-conductive inner layer composed of silver colloids, TiO _x N _y nano particles. Silver colloids are used to obtain a film having low surface resistivity and TiO _x N _y nano-particles contained in the inner layer enhance the durability of the film. To reduce the plasma-resonance absorption caused by silver colloids, silver ions are added to the outer layer solution. The silver ions diffuse into the inner layer from the outer layer when the film is cured, touch to the surface of silver colloids, suppress the silver colloid growth and reduce the specific absorption of the film. These coatings are successfully applied to the panel glass for CRTs on an industrial scale.     

疏水性对溶胶-凝胶SiO2薄膜抗真空污染及抗激光损伤能力的影响

以正硅酸乙酯作为前驱体, 利用碱催化方式制备了SiO₂溶胶, 通过在溶胶中添加含疏水基团(-CH₃)的六甲基二硅氮烷(HMDS)对溶胶进行改性, 使用添加不同物质的量比HMDS改性后的溶胶用提拉法在K9基片上镀膜, 获得了具有疏水性能的SiO₂薄膜。采用自制接触角测量仪、紫外-可见-近红外分光光度计研究了薄膜的水接触角和透过率。测试了薄膜的激光损伤阈值, 并观察了激光辐照后薄膜的损伤形貌。通过真空污染实验对薄膜的抗污染能力及抗激光损伤能力进行了研究。实验结果表明:经疏水改性的溶胶所镀制的薄膜激光损伤阈值由未改性样品的24.3 J·cm^-2增加到37 J·cm^-2(1 064 nm, 10 ns), 且抗真空污染能力大大加强:在真空环境下保存168 h后, 未改性样品的峰值透过率下降了2%, 而疏水改性后的样品峰值透过率仅下降了0.25%, 并保持了较高的激光损伤阈值(30.8 J·cm^-2)。     

A study on superhydrophobic coating in anti-icing of glass/porcelain insulator

This paper focuses on the preparation of a superhydrophobic coating on glass/porcelain insulators which possess anti-icing property below freezing temperature. Inspired by lotus-effect, the fabrication of a superhydrophobic coating has two steps: the first step is to construct a hierarchical SiO₂ coating on the substrate surface, and the second step is the chemical modification of the SiO₂ coating with 1H,1H,2H,2H-Perfluorodecyltriethoxysilane (PDTS). The precursor for the hierarchical SiO₂ coating is a suspension of SiO₂ sol particles and dispersible SiO₂ powder particles. According to the TEM testing, SiO₂ sol particles prepared by sol–gel method has an average particle size about 2–5 nm, while the size of the dispersible SiO₂ particles is ca. 20 nm. The precursor was sprayed on glass/porcelain insulators, and then dried at ambient condition, finally heat-treated at 773 K for 2 h. The morphology of the superhydrophobic coating was characterized by TEM and AFM, and experimental results indicated that the coating featured [hierarchical structure consisting of both large bumps with micron-sized height (0.8 μm) and tiny papillae with the size about 30 nm] micron-sized roughness (0.8 μm) combined with nano-sized roughness (about 2 nm). Moreover, the scratch test showed that the coating tightly adhered to the surface of the glass/porcelain insulators. The superhydrophobic property of the coating was examined by a contact angle measurement, and the results demonstrated that the static water contact angle is high up to 163.6°, and the sliding angle is 1.4°. The superhydrophobic property of the coating was also confirmed by the outdoor tests in winter, and it was found that the superhydrophobic coating had the function in anti-icing, based on which the anti-icing mechanism underlying was discussed in terms of the interaction between impacting droplets and superhydrophobic surface.     

Planar step-index waveguides obtained via sol–gel synthesis from organometallic precursors

Inorganic and hybrid sols obtained from Si, Ti, Zr and Ce organometallic precursors were used to prepare single and multilayer coatings with different thicknesses. Planar step-index waveguides with different refractive indices were thus prepared by dip-coating the above sols onto commercial soda-lime glass substrates, followed by appropriate thermal annealing. The resultant coatings were characterized by transmission electron microscopy and energy dispersive X-ray spectrometry to elucidate the interface and bonding between the sol–gel derived coatings and the glass substrates. Diffusion of alkali and alkaline earth elements from the glass into the coating layer was confirmed and proposed to play a role in the coating-substrate bonding, inducing excellent optical quality planar interfaces. Optical waveguide characterization performed on a 4.15 μm thick hybrid SiO₂:CeO₂ (95:5) step-index waveguide yielded losses of 1.50 dB/cm.     

Morphological,mechanical, and in vitro cytocompatibility analysis of poly(vinyl alcohol)–silica glass hybrid scaffolds reinforced with cellulose nanocrystals

Cellulose nanocrystal-reinforced poly(vinyl alcohol)/silica glass hybrid scaffolds were fabricated using the freeze-drying method. In this study, we develop molecular-level-based hybrid scaffolds with possible bioactivity behavior by adding silica sol–gel. The results showed a highly porous structure and a significant improvement in mechanical performance (stiffness) of hybrid scaffolds with an increased content of cellulose nanocrystals followed by the addition of silica-based bioactive glass. In vitro cell study with MC3T3-E1 cells on hybrid scaffolds for 1 and 3 days revealed good cell adhesion and growth. Thus, the obtained hybrid scaffold may be a competitive candidate for bone tissue engineering applications.     

Atomic force microscopy of coated glasses

Atomic force microscopy has been used to investigate the topology of alkoxide gel dip coatings on different substrates. Results of SiO₂ – TiO₂ – ZrO₂ (STZ) coatings are presented on float glass, on polished fused silica, on commercially coated insulating flat glass, and on PtRh.· Consolidated STZ coatings display the so-called glass pattern with ripples equal or less than 2 nm high. The same pattern is seen on partially dense STZ coatings, as soon as the surface is stiff enough for scanning, and also on the bottom of a 50 nm deep sputtering crater in the consolidated coating.· The vitreous STZ coating on the fire side of the float glass is as flat as the float glass itself. It has the same tendency to contamination. 100 nm wide and 50 nm deep polishing grooves on fused silica have been filled up with the 80 nm thick coating, only dips of a few nm remain. The trenches between the SnO₂ crystallites on the insulating flat glass were filled up and the roughness of the substrate was partially reduced. PtRh sheet remained rough even after the coating.· On the partially densified STZ coating, sputtering generates a grained surface.     

SANS Study of Zirconia-Silica and Titania-Silica Hybrid Materials

New silica-based hybrid materials have been produced by the sol-gel process. Samples with compositions xMO₂·(100 – x)SiO₂ (with M = Zr, Ti and x 10 mol%) were prepared with polydimethylsiloxane, silanol terminated, with different molecular weights. In the present work the microstructure of samples prepared with a volume ratio organic/inorganic of 2/3 was investigated by Small Angle Neutron Scattering. The results show that a rather homogeneous hybrid material can be obtained. It is observed that the polymer is well distributed in the inorganic matrix and that the addition of MO₂ perturbs its local conformation when it has low molecular weight. The inorganic oxide network in the hybrid was found to develop as in pure inorganic dried gels.     

Inhibition effect of cerium in hybrid sol–gel films on aluminium alloy AA2024

Aluminium alloys such as AA2024 are susceptible to severe corrosion attack in aggressive solutions (e.g. chlorides). Conversion coatings, like chromate, or rare earth conversion coatings are usually applied in order to improve corrosion behaviour of aluminium alloys. Methacrylate‐based hybrid films deposited with sol–gel technique might be an alternative to conversion coatings. Barrier properties, paint adhesion and possibly self‐healing ability are important aspects for replacement of chromate‐based pre‐treatments. This work evaluates the behaviour of cerium as corrosion inhibitor in methacrylate silane‐based hybrid films containing SiO₂ nano‐particles on AA2024. Hybrid films were deposited on aluminium alloy AA2024 by means of dip‐coating technique. Two different types of coating were applied: a non‐inhibited film consisting of two layers (non‐inhibited system) and a similar film doped with cerium nitrate in an intermediate layer (inhibited system). The film thickness was 5 µm for the non‐inhibited system and 8 µm for the inhibited system. Film morphology and composition were investigated by means of GDOES (glow discharge optical emission spectroscopy). Moreover, GDOES qualitative composition profiles were recorded in order to investigate Ce content in the hybrid films as a function of immersion time in 0.05 M NaCl solution. The electrochemical behaviour of the hybrid films was studied in the same electrolyte by means of EIS technique (electrochemical impedance spectroscopy). Electrochemical measurements provide evidence that the inhibited system containing cerium displays recovery of electrochemical properties. This behaviour is not observed for the non‐inhibited coating. GDOES measurements provide evidence that the behaviour of inhibited system can be related to migration of Ce species to the substrate/coating interface. Copyright © 2010 John Wiley & Sons, Ltd.     

Study of Antibacterial Composite Cu/SiO2 Thin Coatings

In the present work, composite copper containing silicate thin coatings (Cu/SiO₂) were prepared on glass substrates by the sol-gel route. The preparation process included hydrolysis and subsequent polycondensation of corresponding alkoxide under refluxing and addition of soluble salt of antibacterial metal to the resulting sol. The coatings deposited by dipping process, were thermally treated in oxidative and reductive conditions up to 500°C for metal nanoparticles formation. The coating structure and the nanoparticles formation were studied by the X-ray Diffraction (XRD), UV-VIS and Heavy Ion Rutherford Backscattering (HIRBS) Spectroscopies. The antibacterial activity against Escherichia Coli was examined by the so-called antibacterial-drop test. The possible correlation between the layer interdiffusion after the thermal treatment and the antibacterial activity was considered and analyzed. The coatings exhibited a high antibacterial activity, which was enhanced with the increase of the metal concentration and was decreased with the increase of temperature of thermal treatment and metal nanoparticles formation.     

Effect of formulation of silica‐based solution on corrosion resistance of silicate coating on hot‐dip galvanized steel

Several silica‐based solutions with 50 g/l of SiO₂ were prepared from sodium silicate solutions and silica sol; the silicate conversion coatings were obtained by immersing hot‐dip galvanized steel sheets in these solutions. These solutions were characterized using high‐resolution transmission electron microscopy and ²⁹Si nuclear magnetic resonance; the morphology of the coatings was observed by SEM and atomic force microscopy while the corrosion resistance was evaluated by electrochemical measurements as well as neutral salt spray tests. The results show that the coatings obtained from the single silica sol solution had poor adhesion and the coating obtained from the sodium silicate solution with low SiO₂/Na₂O molar ratio was uneven. By adding the silica sol to the silicate solution with low molar ratio, uniform coatings with better protection property were obtained. According to the results of ²⁹Si nuclear magnetic resonance spectra, the effects of the distribution of silicate anions with various polymerization degrees in the silica‐based solutions on the microstructure and corrosion resistance of the silicate coatings are discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

Photochromic Coatings Containing Ag(Cl1−xBrx) Microcrystals

Photochromic ormosil coatings containing Ag(Cl_1–x Br _x ) microcrystals were formed on a glass substrate via the sol-gel process. Methyltrimethoxysilane and 3-glycidoxypropyltrimethoxysilane were used as starting materials of the ormosil matrices. 3-chloropropyltrimethoxysilane and bromophenyltrimethoxysilane were added as halogen sources and silver colloidal dispersion was introduced into the precursor sol. The coated glass became transparent and photosensitive after Ag(Cl_1–x Br _x ) microcrystals were precipitated in the coatings above 300°C. Insertion of a SiO₂ buffer layer between the substrate and photochromic layer was effective in preventing Ag⁺ migration into the substrate. Photochromic performances were improved by the substitution of Cl with Br and the incorporation of a minute amount of Cu.     

Synthesis of Ag-Colloids in Sol-Gel Derived SiO2-Coatings on Glass

Ag colloid-containing coatings on soda lime glass and fused silica are prepared via the sol-gel process. To incorporate Ag⁺-ions in the coatings homogeneously, they are stabilized by a functionalised silane (aminosilane) and then mixed with the basic sol prepared from 3-glycidoxypropyl trimethoxysilane (GPTS) and tetraethoxysilane (TEOS). Crack-free and transparent coatings with a thickness of 0.5 to 1.2 m, are obtained by heat treatment between 120°C and 600°C. The Ag-colloid formation was monitored by UV-VIS spectroscopy as a function of temperature. The investigations reveal that the substrate has a deciding influence on the Ag-colloid formation caused by alkali diffusion from the substrate into the coating. High resolution transmission electron microscopy (HRTEM) investigations prove that poly-crystalline Ag_xO_y-nanoparticles are formed during thermal densification in the coatings and that this change is accompanied by a vanishing of the yellow colour of the coatings. A post-heat treatment in a reducing atmosphere (90% N₂, 10% H₂) turns back the yellow colour and single-crystalline Ag-colloids can be detected by HRTEM. A suitable choice of the temperature and time conditions allows the control of the colloid size during heat treatment in a reducing atmosphere. For comparison, ion-exchange experiments have been carried out which showed that a spontaneous Ag-colloid formation was achieved in the soda lime substrate at 400°C. Since Ag containing SiO₂-coatings remained colourless after thermal treatment between 400°C and 600°C in air, on soda lime substrates, a remarkable diffusion of Ag⁺ into the substrate was excluded.