Supertough UV-curable silane/silica gas barrier coatings on polymers

Ultra-thin (10-500 nm) photo-polymerized γ-methacryloxypropyltriethoxysilane (MPMS) and vinyltrimethoxysilane (VTS) layers applied to SiO₂ coatings on polyethylene terephthalate films improved the oxygen barrier performance of the oxide coated films by more than two-fold, and the coating strain to failure from 1.5% to beyond 5%, depending on the processing conditions. The oxygen transmission rate of composite films was measured under tensile strain. The chemical conversion of both MPMS and VTS with two different photoinitiators was studied by means of photo-calorimetry experiments, with attention paid to the influence of temperature, UV-light intensity and photoinitiator concentration. The conversion data were analyzed using an n^th-order kinetic model, including an Arrhenius dependence of the temperature and a power-law dependence of the light intensity on the reaction rate. The improvement in mechanical integrity of the silane/silica barrier coating, with a toughness as high as 80 J/m² was found to be controlled by the conversion state of the silane.     

Novel hybrid organo-silicate corrosion resistant coatings based on hyperbranched polymers

Corrosion protective sol-gel coatings were developed on AA2024-T3 through an aqueous sol-gel process (Modified Self-Assembled Nanophase Particle method) which includes in-situ formation of a dense silica network from hydrolyzed 3-glycidoxy-propyltri-methoxysilane and tetraethoxysilane by proper cross-linking. In the present study, hyperbranched poly(ethylene imine) of two different molecular weights was investigated as a cross-linking agent since this polymer is able to solubilize non-water-soluble organic molecules. In this respect, two organic corrosion inhibitors (2-mercaptobenzothiazole and 2-mercaptobenzimidazole) were combined with poly(ethylene imine) to induce self healing properties. The as developed coatings were also compared with Si/Zr containing coatings developed by a solvent based sol-gel technique. The potentiodynamic scan and the electrochemical impedance spectroscopy methods were employed to evaluate the corrosion protection performance, whereas the chemical structure, morphology and integrity of the coatings were evaluated by Fourier transformed infrared spectroscopy and scanning electron microscopy studies. Formulations that contain poly(ethylene imine) demonstrate better corrosion barrier properties compared to formulations cross-linked with the simple molecule of diethylenetriamine in all cases and especially when combined with the organic inhibitors.     

Study on gas permeation behaviour through atmospheric plasma-sprayed yttria stabilized zirconia coating

Gas permeation behaviour through atmospheric plasma-sprayed 8 mol% yttria stabilized zirconia (YSZ) electrolyte coating was studied experimentally. YSZ coatings were fabricated using different powder feedstock. The temperature and velocity of in-flight particles during spraying were measured with a diagnostic system. The results showed that particle temperature and velocity were significantly influenced by the size of powders. The gas permeability of these coatings was estimated by a specific instrument with pure O₂, N₂ and H₂. It was found that the gas permeability was reduced by decreasing the size of powder. Gas permeation behaviour through plasma-sprayed YSZ coating was studied. Transition flow was compatible to gas permeation behaviour for all three plasma-sprayed YSZ coatings. The relationship between gas permeation behaviour and coating microstructure is discussed in this article.     

Co-electrodeposition and characterization of Cu-Si3N4 composite coatings

Smooth copper coatings containing well-distributed silicon nitride particles were obtained by co-electrodeposition in acidic sulfate bath. The cathodic current density did not show significant influence on incorporated particle volume fraction, whereas the increase of particle concentration in the bath led to its decrease. The increase of stirring rate increased the amount of embedded particles. The microhardness of the composite layers was higher than that of pure copper deposits obtained under the same conditions due to dispersion-strengthening and copper matrix grain refinement and increased with the increase of incorporated particle volume fraction. The microhardness of composites also increased with the increase of current density due to copper matrix grain refining. The composite coatings presented higher strength but lower ductility than pure copper layers. Pure copper and composite coatings showed the same corrosion resistance in 0.5 wt.% H₂SO₄ solution at room temperature.     

Syntheses and mechanical properties of Mo-Si-N coatings by a hybrid coating system

In this work, comparative studies on microstructure and mechanical properties between Mo₂N and Mo-Si-N coatings were conducted. Ternary Mo-Si-N coatings were deposited on steel substrates (AISI D2) and Si wafers by a hybrid method, where arc ion plating (AIP) technique was combined with a magnetron sputtering technique. Instrumental analyses of X-ray diffractometer (XRD), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS) revealed that the Mo-Si-N coatings must be a composite consisting of fine Mo₂N crystallites and amorphous Si₃N₄. The hardness value of Mo-Si-N coatings significantly increased from 22 GPa of Mo₂N coatings to about 37 GPa with Si content of 10 at.% due to the refinement of Mo₂N crystallites and the composite microstructure characteristics. The average friction coefficient of the Mo-Si-N coatings gradually decreased from 0.65 to 0.4 with increasing Si content up to 15 at.%. The effects of Si content on microstructure and mechanical properties of Mo-N coatings were systematically investigated.     

Role of deposition parameters on microstructure and mechanical properties of chromium oxide coatings

Chromium oxide coatings were deposited by reactive magnetron sputtering on high speed steel (HSS) substrate under various oxygen flow rates and radio frequency (RF) powers. The effect of deposition conditions on the microstructure, hardness and critical load of chromium oxide coating failure was studied. The results indicated that a crystalline chromium oxide coating formed at a high oxygen flow rate and a low RF power exhibited a higher hardness and a lower critical load as compared to a chromium oxide coating with an amorphous microstructure.     

Analytical characterisation and corrosion behaviour of bis-aminosilane coatings modified with carbon nanotubes activated with rare-earth salts applied on AZ31 Magnesium alloy

The present work investigates the corrosion behaviour of AZ31 Magnesium alloy (Mg AZ31) substrates pre-treated with a water soluble bis-aminosilane modified with multiwall carbon nanotubes (CNTs). Prior addition to the silane solution, the CNTs were submitted to a treatment in an aqueous solution containing cerium nitrate or lanthanum nitrate. The chemical composition of the treated CNTs and of the modified silane coatings was assessed by X-ray Photoelectron spectroscopy (XPS). The thickness and the morphology of the silane coatings were investigated by scanning electron microscopy (FEG/SEM).The pre-treatment of the Mg AZ31 was performed by dipping the metallic coupons in the silane solution modified with the CNTs. The electrochemical behaviour of the silane coated coupons was studied during immersion in 0.05 M NaCl solutions, using the scanning vibrating electrode technique.The electrochemical investigation showed that the activation of the CNTs with the rare-earth salt delays the corrosion activity of the Mg AZ31 substrates. The analytical and microscopic study suggested that the CNTs are homogeneously dispersed in the silane coating and that the CNTs act as support for inhibitor storage.     

Syntheses and mechanical properties of Cr-Mo-N coatings by a hybrid coating system

Effects of Mo content up to 30.4 at.% on the microstructure and mechanical properties of CrN coatings are reported in this study. Ternary Cr-Mo-N coatings were deposited onto steel substrates (AISI D2) using a hybrid coating method of arc ion plating (AIP) using Cr target and DC magnetron sputtering technique using Mo target in N₂/Ar gaseous mixture. The synthesized Cr-Mo-N coatings formed a substitutional solid solution of (Cr,Mo)N where larger Mo atoms replaced Cr in CrN crystal. The Cr-Mo-N coatings showed increased hardness value of approximately 34 GPa at 21 at.% Mo, compared with 18 GPa for pure CrN. The friction coefficient decreased from 0.49 for pure CrN coating to 0.37 for Cr-Mo-N with 30.4 at.% Mo. This result is believed to be due to tribo-layer formation of MoO₃ which is known to function as a solid lubricant.     

Low temperature growth of thin film coatings for the surface modification of dental prostheses

In this work we present some results about the low temperature, plasma-assisted growth of silicon-oxygen amorphous thin film alloys (a-SiO_x) on different types of dental materials used for the fabrication of dental prostheses. The a-SiO_x films were grown at substrate temperatures lower than 70 °C by a PECVD deposition system using silane (SiH₄) and nitrous oxide (N₂O) as precursor gases. The chemical bonding structure of the films was investigated by Fourier transform infra-red spectroscopy (FTIR), while the morphological characteristics of the dental materials were analyzed before and after the coating deposition by means of high-resolution mechanical profilometry. The surface energy of dental materials was estimated before and after the coating process by contact angle measurements, revealing that the coating produced a considerable change of surface energy in all the tested samples, evidenced by a contact angle reduction from more than 90° to less than 10°. Some tests were also performed to estimate the effect of the coating on the bacterial adhesion properties, revealing that the a-SiO_x coatings show some effectiveness in reducing the bacterial adhesion on the dental materials surface.     

Silicon oxynitride gas barrier coatings on poly(ether sulfone) by plasma-enhanced chemical vapor deposition

Thin silicon oxynitride (SiO_xN_y) has been deposited for a gas barrier layer on the surface of poly(ether sulfone) film using plasma-enhanced chemical vapor deposition (PECVD) of a mixture of hexamethyldisiloxane (HMDSO) and ammonia. The chemical structure of the deposited layer varied from organic to inorganic structures depending on RF plasma input power applied to the reaction system. A silicon-based undercoat layer, which has an organic/inorganic hybrid structure, was used as an interfacial buffer layer between the organic PES and inorganic SiO_xN_y layer. With the help of the undercoat layer, the dense inorganic SiO_xN_y layer gave a superior oxygen barrier property of 0.2 cm³/m² day at a critical coating thickness of ca. 20 nm. In a highly stressed SiO_xN_y film, the effect of the undercoat layer was remarkable in preventing crack formation during bending tests.     

Slurry based multilayer environmental barrier coatings for silicon carbide and silicon nitride ceramics — I. Processing

Multilayer mullite/gadolinium silicate (Gd₂SiO₅) environmental barrier coatings (EBCs) were deposited on α-SiC (Hexaloy) and Si₃N₄ (SN282) substrates through cost-effective slurry based dip-coat processing. Coatings applied by two approaches, alcohol and sol-based slurries, were examined and optimized in terms of their recipes and air sintering temperatures. A significant increase in densification rates was found for the sol-based EBCs applied on both SiC and SN282 substrates due to the fine mullite particles formed during reaction sintering of well-mixed silica and alumina sols. Mechanical alloying of the starting powder mixtures instead of their simple rotary-blending was found to be beneficial in terms of enhanced coat sintering kinetics. Dense thick coatings that were well-bonded to the substrate were obtained.     

Evaluation of the mechanical behaviour of nanometre-thick coatings deposited using an atmospheric pressure plasma system

This study evaluated the use of pin-on-disc wear testing as a technique to examine the mechanical behaviour of nanometre thick plasma deposited coatings. The coatings were deposited onto polyethylene terephthalate and silicon wafer substrates by directly injecting an aerosol of siloxane liquid precursors into a helium/oxygen atmospheric pressure plasma. The siloxane precursors examined were hexamethyldisiloxane, polydimethylsiloxane and tetramethyldisiloxane. The mechanical performance of 21 (± 3) nm thick coatings was compared using a pin-on-disc wear test technique and fragmentation tests. An increase in the level of precursor plasma exposure was found to be associated with an increase in coating surface energy and a reduction in coating roughness and resulted in enhanced wear resistance. Fragmentation tests revealed a transition from ductile failure to brittle failure as the level of plasma exposure increased. This correlated with the reduction in coating wear rates. Wear track depth and proximity to the coating/substrate interface were both found to influence the rate or wear. A simple correlation between wear rate and applied force is presented as a method for comparing coating performance using pin-on-disc wear testing.     

Characterization of the mechanical properties and failure modes of hard coatings deposited by RF magnetron sputtering

Chromium oxide coatings with thicknesses of several micrometers were deposited by RF magnetron sputtering at various oxygen flow rates and sputter powers on carbon steel and high speed steel (HSS) substrates, respectively. The compositions and structures of the coatings were characterized by EDS, XRD, and XPS. The mechanical properties of the coatings, in terms of hardness and reduced elastic modulus, were determined by nanoindentation technique. UMT was used to carry out scratch test to study the coating failure mode. Correlations between the mechanical properties of the coating and substrates and the coating failure mode are discussed, which reveal that the coating with a low thickness and high hardness underwent plastic deformation during the scratch process, while the thicker coating with a lower hardness failed in chipping or spallation. The substrate plays a more important role than the coating itself in determining the coating failure mode.     

Effect of antimony doped tin oxide on behaviors of waterborne polyurethane acrylate nanocomposite coatings

A multi-functional waterborne polyurethane acrylate (WPUA) nanocomposite coating was prepared through introducing the acrylate groups into the end of the polyurethane main chains and then modified by antimony doped tin oxide (ATO) nanoparticles by ultrasonic dispersion. Structural and morphological features of coatings were assessed using Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and a 3D measuring laser microscope. Performance of the coatings was evaluated using water resistance studies, thermogravimetric analysis (TGA), dynamic mechanical thermal analysis (DMTA) and mechanical tests such as tensile strength, elongation at break. The data showed that the WPUA/ATO coatings possessed good mechanical properties and thermal stability. The UV-visible-near infrared (UV-VIS-NIR) spectra results suggested that the WPUA/ATO coatings could absorb near infrared radiation so that it would prevent heat transmission and heat diffusion effectively.     

混合电容器多孔氧化钌阴极涂层的制备与表征

采用电沉积方法制备了混合电容器钽基多孔氧化钌阴极涂层材料,探讨了电沉积过程中电沉积液的pH值随电沉积时间的变化关系,研究了电沉积时间对氧化钌沉积质量的影响.用X射线衍射和扫描电镜分别表征了热处理前后的涂层结构及涂层的多孔形貌,用循环伏安法测量了涂层的电容,并研究了热处理温度对电容量大小及其稳定性的影响.结果表明:电沉积的氧化钌为非晶态,涂层为纳米多孔结构;热处理有利于涂层孔隙结构及大小的均匀性,不同温度的热处理使涂层具有不同的电容,经热处理后涂层的电容稳定;经100℃热处理1 h后的多孔氧化钌涂层具有最大的比电容.     

Thermal plasma chemical vapor deposition of wear-resistant, hard Si-C-N coatings

Wear-resistant, hard Si-C-N coatings were synthesized in a triple torch plasma reactor using a thermal plasma chemical vapor deposition process. In this reactor, three dc plasma torches were angled so that their jets converge to form a highly chemically reactive region at the substrate. Vaporized hexamethyldisilazane (HMDSN) was injected through a central injection probe, while nitrogen or hydrogen gases were added through the torches to the argon plasma.Various dissociation, recombination and intermediate reactions were considered to determine what major species exist in the gas phase during the deposition of Si-C-N films. Reactant flow rates were varied to evaluate the thermodynamic equilibrium compositions across a linear temperature profile above the substrate and to identify the species that lead to the production of wear-resistant, hard Si-C-N films.A series of experiments were conducted at low HMDSN flows (∼ 1 sccm) and varying hydrogen and nitrogen flows. Films were characterized by micro X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. Indentation tests were conducted on the polished film cross-sections, while wear tests were carried out on the film surfaces. At substrate temperatures below 1000 °C, amorphous Si-C-N films were deposited, while higher temperatures produced crystalline composite films of α- and β-Si₃N₄ and α- and β-SiC. Films produced with hydrogen at low HMDSN flows displayed non-columnar morphology and therefore had higher wear-resistance, indicating the benefit of low reactant-to-plasma gas flow concentrations on film growth. At low HMDSN flows, low nitrogen-to-hydrogen ratios had also shown an increase in film linear density. Small variations in mechanical properties and wear were observed between films grown under low N:H flow ratio conditions (smooth film surfaces). Wear-resistance of films with columnar structures from high N:H conditions was significantly lower, while the hardness was unobtainable. This result indicates the importance of film morphology on mechanical performance.     

Scratch testing of hybrid coatings on float glass

Results of scratch testing on hybrid organic–inorganic coatings on float glass are reported. The effects of the preparation conditions on the apparent scratch resistance are tested using a sphere. As parameters to quantify the scratch resistance the load and the area of delamination as well as the length and number of surface cracks are considered. It is concluded that the main reason for delamination is the deflection of cracks at the interface. A model is proposed to estimate the distance between cracks.     

Proposal of self-healing coatings for nuclear fusion applications

Avoiding cracks in ceramic coatings is one of the most important problems to be solved for the thermally sprayed tritium permeation barriers in fusion reactor. In this paper, a self-healing composite coating composed of TiC + mixture (TiC/Al₂O₃) + Al₂O₃ was developed to address this problem. The coating was deposited on certain martensitic steel by plasma spraying. The morphology and phase of the coating were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD) while the porosity was analyzed by using Image Pro software. The thermal shock resistance test and residual stress measurement of the coating were also performed. In the experiment, NiAl + TiC + mixture (TiC/Al₂O₃) + Al₂O₃ and mixture (TiC/Al₂O₃) + Al₂O₃ films were also fabricated and studied respectively. The results showed that the TiC + mixture (TiC/Al₂O₃) + Al₂O₃ coating exhibited the best mechanical integrity and self-healing ability among the three samples with the porosity decreased by 90% after heat-treatment under normal atmosphere. The oxidation/expansion of TiC in the coating played an important role in the sealing of pores. This self-healing coating made by thermal spraying is proposed as a good candidate for tritium permeation barrier in fusion reactors.     

A microstructure and mechanical property investigation on thermally sprayed nanostructured ceramic coatings before and after a sintering treatment

Coatings have been deposited by air plasma spraying of alumina powders in the form of conventional particles (C), nanostructured agglomerates (N) and sintered–nanostructured agglomerates (S). Sintering alleviated the stresses introduced in the nanopowder by the manufacturing process (high energy ball milling). The coating porosity is a direct consequence of the powder melting degree, which is related to the feedstock porosity. The mechanical performance of the coatings is also closely associated with the powder melting degree. The N coatings present the highest surface roughness due to the lowest melting degree. The slightly higher hardness values of the N and S coatings, as compared to the C coatings, are attributed to the higher percentages of α-Al₂O₃ and the presence of nanostructure. The S coatings exhibit superior adhesion strength, relative fracture toughness and wear resistance, due to sintering consequences (intraparticle cohesion, strain relief, tough splat boundaries), random dispersion of coherent nanozones and stress dissipation at nanograin boundaries.     

Effects of Si Addition and Long-Term Thermal Exposure on the Tensile Properties of a Ni–Mo–Cr Superalloy

The effect of long-term thermal exposure on the grain boundary carbides and the tensile behavior of two kinds of Ni–Mo–Cr superalloys with different silicon contents(0 and 0.46 wt%) was investigated. Experimental results showed granular M2C carbides formed at the grain boundaries after exposure for 100 h for the non-silicon alloy. Furthermore, these fine granular M2C carbides will transform into plate-like M6C carbides as exposure time increases. For the Si-containing alloys,only the granular M6C carbides formed at the grain boundaries during the whole exposure time. The coarsening of the grain boundary carbides occurred in both alloys with increasing exposure time. In addition, the coarsening kinetics of the grain boundary carbides for the non-silicon alloy is faster than that of the standard alloy. The tensile properties of both alloys are improved after exposure for 100 h due to the formation of nano-sized grain boundary carbides. The grain boundary carbides are coarsened more seriously for non-silicon alloys than that of Si-containing alloys, resulting in a more significant decrease in the tensile strength and elongation for the former case. Silicon additions can effectively inhibit the severe coarsening of the grain boundary carbides and thus avoid the obvious deterioration of the tensile properties after a long-term thermal exposure.