Effect of changes of the coating thickness on the in-line monitoring of the conversion of photopolymerized acrylate coatings by near-infrared reflection spectroscopy

Near-infrared (NIR) reflection spectroscopy was used for in-line monitoring of the conversion and the thickness of thin UV-cured acrylate coatings applied to polymer foils. Quantitative analysis of the spectroscopic data was performed either with the aid of PLS-based chemometric models or by band integration according to the Beer-Lambert law. Unintended changes of the thickness of the coating, e.g. caused by variation of the web speed, were found to preclude the correct analysis of the conversion by chemometric methods. In order to correct the conversion data for such changes, NIR spectra were recorded before and after UV irradiation. The conversion was determined from the ratio of the band integrals of the overtone of the acrylic double bond at 1620 nm. It was shown that quantitative conversion data with high precision were achieved in this way. The method was used for in-line monitoring of the conversion in clear and pigmented coatings, which were applied to OPP foil by roll coating at line speeds up to 120 m min⁻¹.     

Evaluation of the corrosion barrier properties of nano‐reinforced vinyl chloride/vinyl acetate coatings

A poly(vinyl chloride/vinyl acetate) copolymer (VYHH) with and without multiwalled carbon nanotubes (MWCNTs) as reinforcements were used as a coating for steel substrates to evaluate their barrier properties against corrosion. Electrical impedance and thermal properties of the coatings were evaluated. The coatings were formulated with 0.1% MWCNT, by weight. Neat and nano‐filled VYHH was used to coat polished, degreased steel substrates via a dipping method. The substrates were either dipped once, for a target coating thickness of 30–40 μm, or twice for a target coating thickness of 60–75 μm. The coated and uncoated control samples were submerged in a tank with a 5% NaCl solution for a 45‐day period. Electrochemical impedance spectroscopy (EIS) revealed that coating thickness plays a role in corrosion resistance. EIS also showed that nano‐reinforced VYHH had the highest charge transfer resistance within its coating thickness. Fourier transform infrared spectroscopy (FTIR) indicated that hydrolysis occurred in the single coatings for both the neat and nanoreinforced coatings. Differential scanning calorimetry (DSC) and thermo gravimetric analysis (TGA) both showed that the addition of MWCNTs improved the thermal stability of the VYHH. DSC thermograms revealed that the thermal properties of the nano VYHH were largely unchanged after 45 days of submersion as compared with the unaged nano VYHH. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

High‐performance infrared emissivity of micro‐arc oxidation coatings formed on titanium alloy for aerospace applications

Aerospace vehicles are subjected to high temperatures because of surrounding aerodynamic drag and the formation of large temperature gradients across the external structural parts of their airframe. To protect the vehicles, high‐infrared emissivity coatings that can radiate a large amount of heat into outer space are in demand. In this work, we describe the development and characterization of high emissivity ceramic coatings formed on a TC4 alloy surface by micro‐arc oxidation. We evaluate, in particular, the influence of NiSO₄ concentration on current‐time response, the thickness, surface roughness, morphologies, bonding strength, and emissivity of these coatings. The results indicate that by increasing the NiSO₄ concentration in electrolytes, the thickness and surface roughness of the coatings increase. The bonding strength becomes smaller with increasing concentration of NiSO₄, but is still maintains a value higher 30 MPa. The coatings possess good thermal shock resistance after being subjected to severe thermal shocks for 50 cycles, and no peeling of the coating is observed. A higher concentration of NiSO₄ in electrolytes also leads to an increasing percentage of the nickel components in the coating to form a NiO phase, which enhances the emissivity of the coatings in the wavelength range of 3‐8 μm.     

Measurement of adhesion for thermally sprayed materials

Thermally sprayed coatings have a distinctive microstructure which can be described as 'a three-dimensional layered structure of discs which are interlaced to form a material of composite nature'. The coatings are normally greater than 25 μm in thickness and can thus be described as bulk coatings. The minimum microstructural detail would be a single splat (often described as a lamella), which is about 5 μm in thickness and up to 80 μm in diameter. This paper focuses on methods used to define and measure the adhesion of coatings or deposits formed by thermal spray technology. The properties distinguished include those of strength and toughness. Measurements such as the tensile adhesion (according to ASTM C633) and double cantilever beam (DCB) tests will be addressed to illustrate the relevance (if any) of such methods to present industrial practice. Acoustic emission studies have also assessed a function termed as the 'crack density function', i.e. a product of the number of cracks and crack size. Other measuring methods applied to this technology include micro-hardness and scratch testing. The former technique has demonstrated that the material properties of coatings are anisotropic, and the latter method is being considered within the biomedical industry to assess the adhesion of hydroxyapatite to orthopedic prostheses. These techniques, among others, may be used for both fundamental understanding of coating performance (i.e. life prediction and cracking mechanisms) and as tests for quality control.     

Ablation behavior of HfC coating with different thickness for carbon/carbon composites at ultra-high temperature

The thickness of the different HfC coatings from 20 μm to 50 μm were prepared on the surface of carbon/carbon (C/C) composites by low pressure chemical vapor deposition (LPCVD). The microstructure and thermal stress of the coatings after ablation were investigated, as well as the effect of thickness and thermal stress on the ablation resistance of the HfC coating was analyzed. After being ablated at a heat flux of 2.4 MW/m² for 60 s, the thermal stress gradually increased at first and then rapidly increased with the increasing thickness of coating. The results indicated that the moderate coating thickness can effectively release the thermal stress generated during the ablation process. The 40 μm-thick HfC coating showed the best ablation resistance with the mass ablation rate and line ablation rate were only 0.13 mg/s and 0.09 μm/s, respectively.     

甲醛在水泥基涂层中的吸附扩散研究

以白水泥为胶凝材料,添加重钙、滑石粉等填料、助剂,制备了不同厚度的水泥基涂层,使用双仓法研究了甲醛在涂层中的吸附、扩散行为.同时,利用X射线衍射仪(XRD)、扫描电镜(SEM)、压汞仪(MIP)、氮气吸附仪表征了涂层材料的物相、结构等性质,并对吸附、扩散机理进行了探讨.结果表明,甲醛在水泥基涂层中具有扩散能力,扩散量随厚度呈现线性减小趋势,扩散的临界厚度为3 mm.涂层对甲醛具有吸附能力,吸附量随时间、厚度呈现一阶指数增长变化规律.表征测试显示涂层微观呈多孔性,总孔隙率为36.5％,孔径范围为3.6 nm～212.7μm,具有大孔、中孔结构.涂层的多孔结构是其具有吸附、扩散能力的结构基础,而矿物表面吸附与过渡扩散共同作用是影响吸附、扩散的主要机制.     

Microstructure and wear properties of plasma‐sprayed aluminum–silicon–polyester coatings

Powder coatings, which are made by plasma‐spraying processes, are being used in industrial applications because of their wear resistance, chemical resistance, and high impact strength even at low service temperatures. These factors increase the importance of plastic and plastic‐based coatings in industrial applications. In this study, an aluminum–silicon–polyester‐based composite coating was applied by plasma‐spraying processes with and without an intermediate bond coat (Ni–Al). The effects of the coating thickness, intermediate bond coat, and processes parameters on the microstructure and wear properties of the coating were studied experimentally. The wear properties of the coatings were determined according to ball‐on‐disk procedure. The microstructures of the coating were examined by optical microscopy and scanning electron microscopy. The results indicated that the plasma‐spraying current and thickness had a strong influence on the wear resistance and microstructural properties of the aluminum–silicon–polyester coating. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3609–3614, 2006     

Atomic layer deposition onto carbon fiber fabrics

Carbon fiber fabrics, consisting of interwoven bundles of 3000 single fibers, were coated with Al₂O₃ using the atomic layer deposition (ALD) process, exposing the fabrics to alternating pulses of trimethyl aluminium and water vapors. The thickness and uniformity of the coatings were investigated using scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The obtained coatings were conformal, 84 ALD cycles gave rise to approximately 20‐nm‐thick coatings and 168 ALD cycles to approximately 40‐nm‐thick coatings. It was found, that a uniform coating can be obtained at a purge time of 40 seconds. Reducing purge times below 20 seconds gives rise to increased particle growth and thus the coating becomes inhomogeneous. Initially, the samples that were coated had a size of 2×10 cm (thickness 0.3 mm). The size of the fabric was subsequently increased up to 8×20 cm and a uniform coating of the same quality was obtained. By oxidizing the coated fabrics, fabrics composed of interwoven alumina microtubes were obtained. Infiltration of the microtubes with solutions of two distinguishable fluorescent dyes showed that interchange of the dyes between warp and weft microtubes occurs, but is absent at approximately 20% of the crossovers. Taking all our findings into account, we conclude that the majority of the fibers were separated from each other by the coating prior to the oxidation. This work demonstrates that ALD is a suitable method to produce thin, conformal coatings on the surface of carbon fiber fabrics.     

Hybrid coatings as transducers in optical biosensors

Sensitive coatings are described for a novel enzyme-based optical sensor for in-situ continuous monitoring of reactants, such as glucose, in biotechnological production processes. Glucose oxidase, incorporated into suitable coating materials that are applied on lenses or optical fibers, is used to catalyze oxidization of glucose to gluconic acid in the presence of oxygen. The presence and consumption of oxygen is determined by measuring the fluorescence signal of incorporated metal organic ruthenium complexes, which is quenched by oxygen. Inorganic–organic hybrid polymers, synthesized via sol-gel processing, were used as coating material. Due to the hybrid character of the coating, good adhesion is achieved on both glass and polymer surfaces. Good compatibility is also given with enzymes and ruthenium complexes. The sensitive optical coating was built up as double-layer and single-layer structures. The double layer comprised a primary coating containing the oxygen-sensitive ruthenium complex, and a secondary coating containing the enzyme. The single layer comprised a single coating containing both the ruthenium complex and the enzyme.     

Laser and furnace pyrolyzed organosilazane-based glass/ZrO2 composite coating system—A comparison

The laser pyrolysis of a ceramic coating system composed of an organosilazane (Durazane 1800) with monoclinic ZrO₂ and glass particles as fillers was investigated. The samples were produced by spray coating on pre-treated stainless steel substrates and subsequently pyrolyzed by Nd:YV0₄ laser radiation (λ =1064 nm). The interaction of laser radiation with the polysilazane-based glass/ZrO₂ coating system led to formation of semi-crystalline dense coatings with a thickness up to 20 μm in a short time.Laser pyrolyzed ceramic coatings were characterized and compared with furnace pyrolyzed coatings. The microstructure of the coatings was investigated by scanning electron microscopy (SEM). Additionally the corrosion resistance and mechanical properties, such as hardness, adhesive strength and the tribological behaviour have been investigated. Ceramic coatings generated by laser pyrolysis showing promising mechanical properties, a super-hydrophobic surface as well as a high corrosion resistance.     

激光强化电刷镀n-Al2O3/Ni复合镀层残余应力研究

利用Nd3+:YAG激光器对电刷镀过程进行强化,在45钢上制备了n-Al2O3/Ni复合镀层。采用X射线衍射法测定了镀层的轴向残余应力及其随镀层厚度变化情况。结果表明,镀层厚度从10μm增加到200μm,激光强化电刷复合镀层的轴向残余应力由压应力逐渐转变为拉应力。当激光功率为600W时,厚度为200μm的镀层的残余应力为103MPa,比普通电刷镀层降低约255MPa。分析了激光对n-Al2O3/Ni电刷复合镀层轴向残余应力的影响机理。     

Dielectric properties and ferroelectric behavior of poly(vinylidene fluoride‐trifluoroethylene) 50/50 copolymer ultrathin films

Ultrathin films of poly(vinylidene fluoride‐trifluoroethylene) copolymer [P(VDF‐TrFE), with a content (mol %) ratio of 50/50 VDF/TrFE] were fabricated on silicon wafers covered with platinum by a spin‐coating technique, ranging in thickness from 20 nm to 1 μm. The effect of thickness on dielectric properties and polarization behavior was investigated. A critical thickness was found to be about 0.1 μm. An abrupt drop of dielectric constant was observed, although there is no significant change in dielectric loss at this thickness. Square and symmetric hysteresis loops were obtained in films thicker than 0.1 μm. However, for films thinner than 0.1 μm, fewer square hysteresis loops were observed. SEM and X‐ray results demonstrate that the effect of thickness on dielectric and ferroelectric properties could be explained by the changes of crystal structure in these films. In addition, the effects of irradiation on dielectric property and polarization response for ultrathin P(VDF‐TrFE) films were also presented. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2259–2266, 2001     

城轨车辆用聚氨酯半光漆光泽稳定性研究

以丙烯酸树脂为基料,制得了适合城轨车辆使用的聚氨酯半光漆.研究了不同丙烯酸树脂、不同CAB助剂、不同涂膜干燥方式及不同涂膜厚度对半光漆光泽稳定性的影响.通过SEM和IR等检测手段对涂料性能进行了表征.结果表明,当选用某高羟值树脂和低羟值树脂搭配使用时,半光漆具有较好的光泽稳定性,当助剂CAB381和CAB551搭配使用时,此时消光粉有最佳的定向效果,当采用常温晾1h、60℃烘干1h的干燥工艺及涂膜厚度控制在40～60μm时,此时涂料光泽波动最小.     

The dependence of pendulum hardness on the thickness of acrylic coating

Pendulum hardness, which is widely used in the characterization of organic coatings, depends greatly on the thickness of the coating. However, it is still unclear whether a qualitative or quantitative relationship exists between pendulum hardness and coating thickness. In the present article, the pendulum hardness values of acrylic coatings with different thicknesses are measured using a König pendulum hardness tester to clarify the dependence of pendulum hardness on thickness of coating. The results show that the pendulum hardness of acrylic coatings decreases gradually with the increasing thickness of coating within a thickness range, and the sensitivity of pendulum hardness to thickness of coating depends greatly on the glass transition temperature of the coatings. An equation suitable for describing the relationship between logarithmic decrement of the amplitude of pendulum's oscillation and thickness of coating is presented, which can separate the contributions of substrate and coating on the logarithmic decrement. This study demonstrates that the measured value of pendulum hardness is not the bulk hardness value for the coating but the representative value of the system consisting of substrate and coating. An excellent correlation between pendulum hardness and thickness of acrylic coatings is obtained, which is fairly supported by the experimental data.     

Core‐shell structured ferrite‐silsesquioxane‐epoxy nanocomposites: Composite homogeneity and mechanical and magnetic properties

Epoxy‐based composites of ferrite nanoparticles (50 nm) with 3‐glycidoxypropyl‐ (GPTMS), aminopropyl‐ (APTMS), or methyl‐silsesquioxane (MTMS) coatings are reported. The GPTMS coatings (30‐nm thick) allowed uniform particle dispersion in the epoxy and prevented sedimentation of the nanoparticles, whereas the APTMS‐coated particles formed agglomerates, leading to particle sedimentation. The particles with the thinnest coating (MTMS – 3 nm) agglomerated in the composites without sedimentation. The composites based on GPTMS‐coated particles showed higher fracture toughness than the composites based on MTMS‐coated particles. The uniformity and thickness of the coatings were related to alcohol composition of the coating media. Coating removal by a novel ultrasonic etching allowed precise determination of the effective ferrite content in the coated nanoparticles. A markedly lower coercivity for nanoparticles without coatings as compared with the nanoparticles with thicker coatings was observed. The saturation magnetization and the coercivity of the composites were independent of coating and casting procedures. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Advanced antistatic/anticorrosion coatings prepared from polystyrene composites incorporating dodecylbenzenesulfonic acid‐doped SiO2@polyaniline core–shell microspheres

We present the preparation of advanced antistatic and anticorrosion coatings of polystyrene (PS) incorporating a suitable amount of dodecylbenzenesulfonic acid (DBSA)‐doped SiO₂@polyaniline (SP) core–shell microspheres. First, aniline‐anchored SiO₂ (AS) microspheres that were about 850 nm in diameter were synthesized using the conventional base‐catalyzed sol–gel process with tetraethyl orthosilicate in the presence of N‐[3‐(trimethoxysilyl)propyl]aniline. SP core–shell microspheres were then synthesized by chemical oxidative polymerization of aniline monomers with ammonium persulfate as an oxidizing agent in the presence of the AS microspheres. The polyaniline shell thickness of the as‐prepared core–shell microspheres was estimated to be about 120 nm. The AS and SP microspheres were further characterized using Fourier transform infrared spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy. The as‐synthesized DBSA‐doped SP core–shell microspheres were then blended into PS using N‐methyl‐2‐pyrrolidone as solvent and then cast onto a cold–rolled steel (CRS) electrode to obtain antistatic and anticorrosion coatings with a thickness of about 10 µm. The corrosion protection efficiency of the as‐prepared coating materials on the CRS electrode was investigated using a series of systematic electrochemical measurements under saline conditions. The enhanced corrosion protection ability of the PS/SP composite coatings may be attributed to the formation of a dense passive metal oxide layer induced by the redox catalytic effect of the polyaniline shell of the as‐synthesized core–shell microspheres, as evidenced by electron spectroscopy for chemical analysis and SEM observations. Moreover, the PS composite coating containing 10 wt% of the SP core–shell microspheres showed an electrical resistance of about 3.65 × 10⁹Ω cm^?2, which meets the requirements for antistatic applications. Copyright © 2012 Society of Chemical Industry     

Microstructural characterization of plasma-sprayed nanostructured zirconia powders and coatings

The objective of this paper was to study the melting state of nanoscale zirconia powders in plasma jet, examine the crystalline phase and microstructural characterization of the plasma sprayed nanostructured zirconia powders and coatings. The cross-section morphology of water-quenched powders revealed that most of the starting powders were molten in the plasma jet. Phase analysis using XRD spectra proved that the monoclinic phase zirconia of the starting powders transferred into tetragonal phase zirconia after the plasma spraying. SEM analysis indicated that the as-sprayed coatings exhibited lamellar structure, about 0.5–5 μm in thickness of a single lamella, which was found to be a characteristic feature of the plasma-sprayed nanostructured zirconia coating. Inside of the lamellae, columnar grains were observed. The mean grain size of the as-sprayed zirconia coating is about 80 nm.     

Electrophoretic deposition of electroless nickel coated YSZ core-shell nanoparticles on a nickel based superalloy

In this work, yttria-stabilized zirconia (YSZ) nanoparticles were covered by a thin Ni layer with approximately 10 nm thickness by electroless deposition method to reduce sintering temperature of the ceramic coating which was applied on a Ni based superalloy via electrophoretic deposition (EPD). Suspensions containing the processed Ni-YSZ core-shell nanoparticles in acetone and isopropyl alcohol solvents were stabilized by addition of 0.4 wt% iodine and 1.5 wt% polyethylenimine, respectively, to find more effective stabilization method for EPD. It was seen that the presence of the Ni layer on YSZ nanoparticles improved performance and sticking factor of EPD and uniform coatings were obtained in both suspensions. The Ni-YSZ green coating which was produced by EPD at voltage of 35 V and deposition time of 30 min in acetone with thickness of 41 μm was sintered in 1100 °C and finally a uniform NiO-YSZ coating was formed on the metallic surface.     

Novel capacitance sensor design for measuring coating debonding: the effects of thermal-hygroscopic cycling

The effects of combined thermal and hygroscopic cycling on the adhesion performance of an epoxy coating were measured using a novel electrode sensor. The sensor is uniquely designed, consisting of a series of independent interdigitated electrode traces which are arranged parallel to the sensor edges. Coupled with single-frequency capacitance measurements, the sensor detects changes in capacitance in the adhered coating–sensor interfacial region as a function of the distance from the edge of the sensor, x. Recently, this sensor was utilized by O'Brien and co-workers to measure interfacial diffusion and the concentration profile of fluid in an adhesive joint (Int. J. Adhesion Adhesives 23, 335–338 (2003)). In the present work, large capacitance changes due to debonding and displacement of the coating by fluids at the sensor surface were used to monitor coating delamination. The apparent debond growth rate and number of cycles until failure were determined as a function of coating thickness, fluid environment and sensor surface chemistry. The results show that the coating becomes more durable as the thickness is reduced; and also that thermal and hygroscopic cycling of coatings produces different results than conventional continuous adhesion tests. This study suggests that this novel sensor or a similar design is applicable for the study of adhesion loss and interfacial diffusion processes, and could be extended to other coatings or adhesives in a variety of environments. General trends about coating durability are also discussed.     

Electrical conductivity and electromagnetic interference shielding of polyaniline/polyacrylate composite coatings

Lightweight and flexible composite coatings of p‐toluene sulfonic acid doped polyaniline (PANI–TSA) with various mass fractions and polyacrylate were prepared for electromagnetic interference (EMI) shielding. Both the volume and surface conductivities of the composite coatings increased with increasing PANI–TSA; furthermore, the volume conductivity showed a typical percolation behavior with a percolation threshold at about 0.21. The EMI shielding effectiveness (SE) of the PANI–TSA/polyacrylate coatings over the range of 14 kHz to 15 GHz increased with increasing PANI–TSA as the direct‐current conductivity did. EMI SE of the coatings at the low frequencies (14 kHz to 1 GHz) was around 30–80 dB, higher than that at the high frequencies (1–15 GHz); this indicated possible commercial application of the coatings for far‐field EMI shielding. The highest EMI SE value was 79 dB at 200 MHz with a coating thickness of 70 ± 5 μm. The moderate SE, light weight, and easy preparation of the coating are advantages for future applications for EMI shielding. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2149–2156, 2005