Hydrophobic siloxane paper coatings: the effect of increasing methyl substitution

Paper is an organic material widely used in cultural heritage and mainly composed of cellulose mixed with lignin, hemicellulose and small amounts of additives. This paper deals with siloxane coatings on pure cellulose paper, applied by sol–gel dipping in sols prepared with different siloxane precursors (tetraethoxysilane, methyl triethoxysilane, dimethyl diethoxysilane, trimethyl monoethoxysilane). The coated samples were characterized using various techniques (Fourier Transform Infrared Spectroscopy FT-IR, Nuclear Magnetic Resonance NMR and Scanning Electron Microscopy and Energy Dispersive Spectroscopy SEM–EDS), measuring their mechanical properties, flame resistance and contact angles, and a colorimetric test. The coated samples’ behavior was more hydrophobic the higher the methyl number of siloxane precursor, regardless of the coating’s thickness. Increasing the thickness improved the mechanical and thermal properties. The thickest coatings were obtained using a double coating process and a basic catalyst for the hydrolysis step, but this latter condition facilitated the formation of surface agglomerates, which make the paper too stiff and yellow.     

Corrosion resistance and cytotoxicity of a MgF2 coating on biomedical Mg–1Ca alloy via vacuum evaporation deposition method

To reduce the biocorrosion rate and enhance the biocompatibility by surface modification, MgF₂ coatings were prepared on Mg–1Ca alloy using vacuum evaporation deposition method. The average thickness of the coating was about 0.95 µm. The results of immersion test and electrochemical test indicated that the corrosion rate of Mg–1Ca alloy was effectively decreased after coating with MgF₂. The MgF₂ coating induced calcium phosphate deposition on Mg–1Ca alloy. After 72 h culture, MG63 cells and MC3T3‐E1 cells were well spread on the surface of the MgF₂‐coated Mg–1Ca alloy, while few cells were observed on uncoated Mg–1Ca alloy samples. In summary, MgF₂ coating showed beneficial effects on the corrosion resistance and thus improved cell response of the Mg–1Ca alloy effectively and should be a good surface modification method for other biomedical magnesium alloys. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of TiO2–Ti and TiO2–TiN composite coatings on corrosion behavior of NiTi alloy

Two kinds of biocompatible coatings were produced in order to improve the corrosion resistance of nickel titanium (NiTi) alloy. A titanium oxide–titanium (TiO₂–Ti) composite was coated on NiTi alloy using electrophoretic method. After the coating process, the samples were heat‐treated at 1000 °C in two tube furnaces, the first one in argon atmosphere and the second one in nitrogen atmosphere at 1000 °C. The morphology and phase analysis of coatings were investigated using scanning electron microscopy and X‐ray diffraction analysis, respectively. The electrochemical behavior of the NiTi and coated samples was examined using polarization and electrochemical impedance spectroscopy tests. Electrochemical tests in simulated body fluid demonstrated a considerable increase in corrosion resistance of composite‐coated NiTi specimens compared to the non‐coated one. The heat‐treated composite coating sample in nitrogen atmosphere had a higher level of corrosion resistance compared to the heat‐treated sample in argon atmosphere, which is mainly due to having nitride phases. Copyright © 2014 John Wiley & Sons, Ltd.     

Mechanism and kinetics of the formation of zinc pack coatings

A zinc deposition method that could be used instead hot-dip galvanizing is pack cementation, where the substrate is heated immersed in a powder mixture containing Zn and a halide activator (NH₄Cl). In the present work the mechanism of this process is examined, along with the effect of temperature and heating time on the coating thickness and structure. For this purpose the coating was deposited and characterized with SEM, while the deposition mechanism was investigated with DSC. From the above examination it was deduced that the deposition of Zn takes place with a multiple-step mechanism, which involves several reactions in the gaseous phase including the formation of volatile zinc halides and finally the diffusion of zinc in the crystal lattice of the ferrous substrate. This procedure is accomplished at about 300°C and leads to the growth of a coating composed by two layers referring to Γ and δ phase of the Fe-Zn system. The coating deposition rate seems to be controlled by the zinc diffusion as its determination at 300 and 350°C showed, where it was deduced that the coating thickness is a linear function of the square root of heating time. However the coating structure is not affected by the heating time and temperature.     

Effects of organic-inorganic hybrid coatings on durability of cross-linked polyethylene

Cross-linked polyethylene (XLPE) films have been coated with nanostructured hybrid organic-inorganic coatings in order to improve their durability. For this purpose, bi- and mono-layer coatings containing different amount of silica and different organic polymers have been prepared through sol-gel reactions and applied to XLPE commercial films. The thermo-oxidative stability, electrical strength and conductivity of XLPE coated films have been investigated after ageing in air at temperatures above the on-service conditions, i.e. at 105 and 120 °C for 1900 and 600 h, respectively. The performed investigations (FT-IR, DSC, TGA and electrical properties) showed that all the coatings tested were able to strongly protect XLPE against oxidation, and that the coating with a PVOH/SiO₂ layer gave the best protection. The increase of thermal resistance induced by the coatings reflects on the electrical strength after ageing, which is higher for coated samples than for uncoated ones. Moreover, while ageing has only a slight effect on electrical conductivity in different coated samples, a strong increase of conductivity was observed after ageing for highly oxidated uncoated samples.     

水热温度对SiC-C/C复合材料表面水热电泳沉积MoSi2抗氧化涂层的影响

采用水热电泳沉积法和固相渗透法在C/C复合材料表面制备了MoSi2/SiC复合抗氧化涂层。分别采用X射线衍射、扫描电子显微镜和等温静态氧化实验对复合涂层的晶相组成、显微结构和抗氧化性能进行了表征。主要研究了水热电泳沉积温度对MoSi2外涂层显微结构及高温抗氧化性能的影响,重点分析了涂层试样在1500℃和1630℃下的静态氧化行为及失效机理。结果表明:外涂层主要由MoSi2和少量MoO3晶相组成。外涂层的致密程度、厚度及抗氧化性能随着水热温度的升高而提高。MoSi2/SiC复合涂层具有较好的抗氧化和抗热震能力,在1 500℃下有效保护基体320 h同时经历17次1 500℃与室温之间的热循环后,氧化失重率仅为1.07%;在1630℃下氧化88 h后失重率为2.17%。复合涂层在1 630℃下的氧化失效主要是由于经过长时间氧化后SiO2玻璃膜层不能及时有效填补涂层中的缺陷,涂层试样在热循环过程中产生了贯穿性的孔洞导致的。     

纳米级包覆层厚度对染料敏化太阳电池中电子注入效率和电子寿命的影响

选取氧化钐作为包覆材料, 采用浸渍法对已烧结好的纳米TiO₂多孔薄膜电极进行修饰, 并将其应用于染料敏化太阳电池中, 研究了纳米级氧化钐包覆层厚度及均匀性对染料敏化太阳电池中电子注入效率和电子复合过程的影响和作用机制. 结果表明, 包覆层厚度对电子注入效率和电子复合具有明显影响, 且电子注入效率和电子寿命随包覆层厚度的增加而呈现相反的变化趋势, 包覆层厚度在0.4 nm以内, 电池性能最好.     

Corrosion protection of AA6061-T4 alloy by sol–gel derived micro and nano-scale hydroxyapatite (HA) coating

Micron and nano-scale hydroxyapatite (HA) were coated successfully on AA6061-T4 substrates by sol–gel method. Besides, the effects of coating thickness on adhesion strength and corrosion behaviour of the coatings were studied. Corrosion resistance was measured by potentiodynamic polarization test using a potentiostat under in vitro conditions. The coatings before and after corrosion tests were characterized by adhesion tests, a scanning electron microscopy attached with EDS and X-ray diffraction analysis. The results revealed that all the coatings exhibit a passive behaviour in Ringer’s solution. Specimens coated with nano-scale HA had the higher corrosion resistance than micro-scale coatings. The highest corrosion resistance appeared to be for the ~30 μm nano-scale HA coated substrates. However, for micro-scale HA coatings, the highest adhesion resistance was obtained at ~30 μm film thickness.     

Protective coatings for stainless steel for SOFC applications

In this paper, a coating procedure based on spin coating of metal oxide polymer precursors on stainless steel, which decreases the oxide scale growth rate, is evaluated. The yttrium and cobalt solutions were used as polymer precursors, while a ferritic stainless steel Crofer 22 APU was used for the deposition of protective coatings. The thickness of deposited protective film was about ~500 nm. The effectiveness of protective layer was evaluated by cyclic thermogravimetry, oxide scale electrical conductivity, and X-ray diffractometry. The results show that steel coated with yttrium polymer precursor has better properties than uncoated or cobalt-coated sample.     

The effect of cerium pre-treatment on the corrosion resistance of steel sheets

The steel samples have been coated with cerium layer by cathodic electrolytic deposition from the Ce(NO₃)₃·6H₂O solution in aqueous ethyleneglycol in the presence of hydrogen peroxide. The influence of the coating parameters (cathodic current density, pH, cerium concentration, hydrogen peroxide concentration, temperature, and treatment duration) on the surface properties; the optimum conditions of the formation of corrosion preventing coating have been elucidated. Hydrogen peroxide concentration and pH are the major factors influencing the deposition process. The corrosion resistance has been further enhanced after treatment with Na₃PO₄·12H₂O solution. The cerium-coated samples have been subsequently coated by cathodic electrostatic deposition from the colloidal solution of the paint. The coated materials have been subjected to mechanical testing (hardness, impact, cross cut, bending, and cupping tests), and their structure has been visualized by electron microscopy. The cerium coating has been found to improve the steel corrosion resistance by 15%.     

Study on the coating of nano-scale SiO<Subscript>2</Subscript> film on the surface of nanocrystalline Mg-Al layered double hydroxides

Since the layered double hydroxides (abbreviatedas LDHs) were firstly reported to be used as precur-sors of new catalytic materials by S. Miyata[1] in 1971,their preparations, ion-exchanges with the balancinginterlayer anions, structure characteristics an…     

Effects of hydrophobic polyhedral oligomeric silsesquioxane coating on water vapour barrier and water resistance properties of paperboard

The substitution of fossil based packaging materials with materials from renewable sources is a topic of current interest. Polyhedral oligomeric silsesquioxanes with fatty acid moieties can have a renewable content of more than 90 % and are therefore called bio-POSS. In this study the bio-POSS octa-(ethyl erucamide) silsesquioxane was coated on a paperboard substrate as a liquid coating. The water resistance and the water vapour barrier properties of the paperboard were improved. Samples on which the bio-POSS coating layer was dried at 80 °C had a slightly higher water resistance and water vapour barrier than samples dried at room temperature. UV treatment of the coating layer had little effect. Solid state ¹H-NMR of UV treated coatings showed no reaction of double bonds of bio-POSS in the coating layer. Multiple coating considerably enhanced the water resistance and water vapour barrier properties of the paperboard, due to an increase in the coating thickness and a reduction in number of pores on top coated surfaces.     

Controlled, rapid deposition of structured coatings from micro- and nanoparticle suspensions

The objective of the study was to develop the operational basis for rapid and controlled deposition of crystal coatings from particles of a wide size range. We deposited such structured coatings by dragging with constant velocity a small volume of liquid confined in a meniscus between two plates. Two types of structured coatings were characterized: latex colloidal crystals and thin layers from metallic nanoparticles. The crystal deposition was sped up by use of preconcentrated suspensions. Crystal coatings larger than a few square centimeters were deposited in minutes from aqueous suspension volumes of approximately 10 microL. The governing mechanism of crystal deposition is convective assembly at high volume fractions. The two major process parameters that allow control over the coating thickness and structure were the deposition speed and particle volume fraction. The evaporation rate was not found to affect the process to a large extent. A volumetric flux balance was used to relate the deposition parameters to coating structure and properties. Operational "phase" diagrams were constructed, relating the crystal layer thickness and packing symmetry to the process parameters. These diagrams could be instrumental in transforming the convective colloidal deposition into a robust scaleable technology.     

Zinc coatings for oxidation protection of ferrous substrates

A common phenomenon in the process industries is the oxidation of the exterior surface of steel pipes used in superheated steam or hot oils networks. For their protection different coatings could be used. In the present work the performance of zinc coatings deposited with hot-dip galvanizing, pack cementation and thermal spraying was considered, in order to protect industrial equipment up to 400°C. For that purpose coated carbon steel coupons were exposed at 400°C and their behavior was examined with light microscopy, scanning electron microscopy and X-ray diffraction. Thermogravimetric analysis was also used in order to observe in situ the oxidation phenomena. From this investigation it was deduced that in every coating a scale is formed that is mainly composed of ZnO, while Fe oxides were also detected in galvanized and pack coatings. The growth of this scale took place at the metal/scale interface. Moreover, as far as it regards the kinetics of the oxidation, it was concluded that the increase of the mass of the specimens is a function of the square root of the exposure time, which means that the scale formed is rather protective for the underlying zinc. From the above observation it seems that the behavior of zinc coatings would be excellent at 400°C. However, the presence of the Fe/Zn phases inside the galvanized and pack coatings led to the formation of cracks, which could expose the substrate and thus destabilize the coating. This phenomenon does not take place in the thermal sprayed coatings, where the Fe/Zn phases are absent.     

Encasement of metallic cardiovascular stents with endothelial cell‐selective copolyetheresterurethane microfibers

Cardiovascular metallic stents established in clinical application are typically coated by a thin polymeric layer on the stent struts to improve hemocompatibility, whereby often a drug is added to the coating to inhibit neointimal hyperplasia. Besides such thin film coatings recently nano/microfiber coated stents are investigated, whereby the fibrous coating was applied circumferential on stents. Here, we explored whether a thin fibrous encasement of metallic stents with preferentially longitudinal aligned fibers and different local fiber densities can be achieved by electrospinning. An elastic degradable copolyetheresterurethane, which is reported to selectively enhance the adhesion of endothelial cells, while simultaneously rejecting smooth muscle cells, was utilized for stent coating. The fibrous stent encasements were microscopically assessed regarding their single fiber diameters, fiber covered area and fiber alignment at three characteristic stent regions before and after stent expansion. Stent coatings with thicknesses in the range from 30 to 50 µm were achieved via electrospinning with 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFP)‐based polymer solution, while a mixture of HFP and formic acid as solvent resulted in encasements with a thickness below 5 µm comprising submicron sized single fibers. All polymeric encasements were mechanically stable during expansion, whereby the fibers deposited on the struts remained their position. The observed changes in fiber density and diameter indicated diverse local deformation mechanisms of the microfibers at the different regions between the struts. Based on these results it can be anticipated that the presented fibrous encasement of stents might be a promising alternative to stents with polymeric strut coatings releasing anti‐proliferative drugs. Copyright © 2015 John Wiley & Sons, Ltd.     

液相沉积法制备TiO2颗粒表面包覆SiO2纳米膜

研究了用液相沉积法在TiO2颗粒表面包覆SiO2纳米膜的过程.通过透射电镜(TEM)和酸溶实验分析,证实本实验在TiO2颗粒表面包覆了一层连续、致密的SiO2纳米膜.ζ-电位分析表明,颗粒表面只需少量包覆就可以显著改变颗粒表面的电动力学行为.采用 X射线荧光光谱分析仪（XRF）测定SiO2包覆量随包覆过程的变化.通过X射线光电子能谱（XPS）分析,获得Ti 2p、Si 2p及 O 1s电子结合能及其相对强度随包覆过程的变化规律,揭示硅酸分子在TiO2颗粒表面的包覆过程.分析表明,初期形成的活性硅酸分子与TiO2颗粒表面的羟基反应形成Ti－O－Si键,后期形成的硅酸分子与已键合在表面的硅酸发生缩合反应,形成连续致密的硅膜,膜层在陈化过程中继续缓慢生长.     

Improved wetting of bare and pre-coated steels by aqueous alumina sols for optimum coating success

Alumina coatings are a promising candidate for the protection of metals prone to high temperature corrosion. If applied via sol–gel process, especially by using so called aqueous modified Yoldas-sols, the deposition is hardened by differences in surface free energy of substrate and sol. In this paper the apparent surface properties of samples to be coated and sols were examined by contact angle measurements, IR-spectroscopy and tensiometry. The results imply, after consideration of possible uncertainties, the use of surface tension reducing 2-butanol already present during hydrolysis of the sols to obtain an easy and successful coating process.     

Hybrid silica coatings on polycarbonate: enhanced properties

Hybrid silica coatings based on 3- glycidoxypropyltriethoxysilane (GPTES), tetraethylorthosilicate (TEOS) and colloidal silica were deposited on polycarbonate (PC) by the sol–gel method, in order to obtain a material with enhanced properties with respect to raw PC (mainly scratch resistance, hydrophobicity and density), and consequently reach increased durability. The necessity of performing a N₂-plasma treatment on PC (before coating deposition) was highlighted in order to obtain a good adherence between the coating and the substrate: XPS measurements showed that after treatment, nitrogenous radicals had formed on the PC surface and were able to link covalently with the sol during its deposition. Adherence was also higher when young sols (<8-day-old) were used. Different alkoxysilanes/colloidal silica ratios were tested to optimize the coating resistance: crack resistance of the coatings was found to be greater when the ratio was high. Scratch resistance of raw PC was enhanced as soon as PC was coated, irrespective of the alkoxysilanes/colloidal silica ratio or the sol ageing time. The density of the coatings was assessed by environmental ellipsometric porosimetry and found to be very high. Water contact angle measurements showed that the hydrophobicity of the coatings was inferior to raw PC. The addition in the sol of a small wt% of octyltriethoxysilane (OTES), 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FTES) and silicone surface additive (BYK-306) allowed a significant increase in hydrophobicity of the samples.     

Protective yttria coatings of melting crucible for metallic fuel slugs

As one of the candidate coating materials for a melting crucible, yttrium oxides were deposited on graphite and niobium substrates using slurry and plasma spraying methods. Thermal cycling tests and interaction studies between U–Zr/U–Zr–RE fuel melt and the Y₂O₃ coatings were carried out to evaluate the performance as reusable coatings for a melting crucible. A multi‐layer coating method was also applied to overcome the issue of a thermal expansion mismatch between the coating and substrate. The results showed that the plasma‐sprayed coatings showed a good consolidation after deposition compared to slurry coating. The plasma‐sprayed Y₂O₃ coating on the niobium substrate showed better thermal cycling resistance than those coated on a graphite substrate. The proposed TaC/Y₂O₃ double‐layer coating which was plasma‐sprayed on the niobium substrate showed improved characteristics with no reaction layer formation and no separation from the substrate after the interaction with the U–Zr–RE melt. Copyright © 2014 John Wiley & Sons, Ltd.     

Combinatorial materials research applied to the development of new surface coatings I: a multiwell plate screening method for the high-throughput assessment of bacterial biofilm retention on surfaces

Combinatorial, high-throughput capabilities have been established to aid in the rapid development of new and effective antifouling marine coatings for naval applications. A biological screening process involving marine bacteria was developed that allows for rapid and effective quantification of bacterial biofilm growth and retention on large numbers of coating surfaces in parallel. The screening process involves (1) multiwell plate modifications for coating deposition, (2) deposition of combinatorial coating libraries via an automated liquid dispensing robot, (3) coating thickness measurements of cured coatings, (4) preconditioning of coatings via immersion in deionized water, (5) bacterial incubation, (6) plate processing, and (7) data analysis for identification of promising candidates. The details of the method developed are described in this document.