Investigation of a new reactant for fluorinated polymer surface treatments with atmospheric pressure glow plasma to improve the adhesive strength

Poly(tetrafluoroethylene-co-perfluoro [alkyl vinyl ether]) (PFA) and polytetrafluoroethylene (PTFE) films were treated by three kinds of atmospheric pressure glow plasmas: an untreated sample was treated by He plasma or trimethoxyborane (TMB)/H₂/He plasma, and a TMB-absorbed sample was treated by H₂/He plasma. TMB was a new reactant for the treatment, to increase the films’ adhesive strength with an epoxy glue. These films were also treated by a wet method using a sodium solution (Tetra-Etch compound) and such films were used as the control samples. The peel strength values of the controls of PFA and PTFE were 3.5 and 9.5 N cm⁻¹, respectively. The adhesive strengths of all plasma-treated PFAs were stronger than those of untreated one. Especially, the peel strength of the TMB/H₂/He plasma-treated PFA showed the maximum value of 4.5 N cm⁻¹, which was bigger than that of the control one. The adhesive strength of the TMB/H₂/He plasma-treated PTFE films also showed the maximum peel strength, 7.9 N cm⁻¹, but this value did not exceed that of the control PTFE. Such results suggested that the TMB/H₂/He plasma had the advantage of providing better adhesive improvement of those polymers, especially PFA than the wet method could provide. The results of XPS and SEM indicated that TMB actively removed fluorine atoms from the polymer surface. Therefore, boron compounds are effective for the improvement of the adhesive strength between the fluorinated polymer and the epoxy glue.     

Oxygen vacancy levels on gadolinia-doped ceria interlayer deposited by atmospheric pressure plasma jet for solid oxide fuel cells

The oxygen vacancy levels as a factor on different gadolinia-doped ceria interlayer (GDCi) films deposited on yttria stabilized zirconia (YSZ) electrolyte substrates by an atmospheric pressure plasma jet (APPJ) via precursor solution of nitrate salts are investigated. Focusing on the effect of carrier gases, scanning electron microscopy (SEM), Raman, and X-ray diffraction (XRD) are implemented for the materials characterization of the as-deposited GDCi films and sintered-GDCi films at various temperatures. The higher level of oxygen vacancies in GDCi films adhered on 8YSZ electrolyte are evidently analyzed using Ar as the carrier gas during the deposition, of which the interdiffusion resulted in the formation of (GDC + YSZ) solid solution for sintering over 1300?°C degraded the total conductivity. The deposition of GDCi films on 8YSZ by APPJ method using O₂ carrier gas significantly improved the total conductivities of the whole electrolyte layers. Moreover, this study provides the useful insight into the oxygen vacancy levels on GDC films as interlayer (GDCi) to improve the values of open circuit voltage in LSM/GDCi/YSZ/Pt full-cell, as well as offering the efficiency of APPJ as one step deposition process.     

Hydrophobic coating of silicate phosphor powder using atmospheric pressure dielectric barrier discharge plasma

A stable superhydrophobic coating was successfully deposited on commercial silicate‐based orange phosphor by using atmospheric pressure dielectric barrier discharge plasma with hexamethyldisiloxane (HMDSO) and HMDSO/toluene mixture as precursors. Owning to the good optical properties, the deposited film acts not only as a hydrophobic protective layer but also as an antireflection optical thin film capable of improving the phosphor photoluminescence efficiency. The plasma‐polymerized film based on Si?O?Si backbone containing methyl and phenyl nonpolar functional groups exhibited high‐water‐repellent characteristics. It was found that the water contact angle gradually increased with increasing the aging time and remained unchanged at about 140° after 1‐month aging. Besides, the thermal stability of the coated phosphor under high‐temperature condition was substantially enhanced by the aging. The findings of this work can contribute to improving the durability and reliability of the phosphor, eventually the long‐term stability of phosphor‐based light emitting diodes in practical applications. © 2014 American Institute of Chemical Engineers AIChE J, 60: 829–838, 2014     

常压等离子体射流对聚乙烯醇薄膜性能的影响

用常压等离子体射流处理不同含水率聚乙烯醇（PVA）薄膜,通过扫描电镜（SEM）观察薄膜表面形态,并用红外光谱测试仪（FTIR）、X光电子能谱（XPS）、X射线衍射仪（XRD）分析了等离子体处理前后含水率为1.85%MC及41.33%MC两种 PVA化学结构及结晶结构的变化。试验结果表明:水分可加速氦气/氧气等离子体对PVA刻蚀及氧化,其中刻蚀速率达0.68μm/min,氧含量从30.8%提高到34.8％;同时,经过处理的薄膜结晶度增加了48％。     

常压辉光放电等离子体研究进展及聚合物表面改性

综述了常压辉光放电等离子体(APGDP)的产生机理及研究进展。介绍了难以产生稳定的APGDP 是由于辉光放电容易向细丝放电和弧光放电过渡,其解决措施是选择合适的介质板材料、电极间距、电源电压及频率、气体成分等。指出APGDP对化纤聚合物表面改性的效果与聚合物的分子结构、等离子体气体、介质板材料等因素有关,且改性效果具有时效性,要根据聚合物的分子结构选择合适的等离子体。     

Preparation and characterization of a composite ceramic coating containing absorber LaFe12O19 by plasma spraying

A ceramic coating with both heat-resistant and electromagnetic (EM) wave absorption performances is prepared by the atmospheric plasma spraying (APS) method. The spraying powder is a composite material mainly containing LaFeO₃ and La(Mg/Fe)Al₁₁O₁₉ without EM absorption ability. During APS procedure, a new phase of LaFe₁₂O₁₉ is fabricated by the chemical reaction between Fe₂O₃ and LaFeO₃ at extremely high temperatures. The ceramic coating exhibits larger saturation magnetization (M_s) and higher EM absorption performance than that of the unsprayed sample. The coating Ms is 31 emu/g, and the optimal reflection loss is −39.30 dB at 3.5–5.2 GHz with 4.5 mm thickness. The ceramic coating with both heat-resistant and EM absorption properties is a potential application prospect material in the military industry.     

Atmospheric pressure plasma enhanced synthesis of flame retardant cellulosic materials

Flame retardant cellulosic materials have been produced using a silicon dioxide (SiO₂) network coating. SiO₂ network armor was prepared through hydrolysis and condensation of the precursor tetraethyl orthosilicate (TEOS), prior coating the substrates, and was cross linked on the surface of the substrates using atmospheric pressure plasma (APP) technique. Because of protection effects of the SiO₂ network armor, the cellulosic based fibers exhibit enhanced thermal properties (characterized by TGA and DSC) and improved flame retardant (proven by ASTM D1230‐99). Furthermore, the surface analysis (XPS and SEM) confirmed the presence of the SiO₂ network attached to the substrates even after intense ultrasound washes. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Atmospheric pressure plasma surface modification of titanium for high temperature adhesive bonding

In this investigation surface treatment of titanium is carried out by plasma ion implantation under atmospheric pressure plasma in order to increase the adhesive bond strength. Prior to the plasma treatment, titanium surfaces were mechanically treated by sand blasting. It is observed that the contact angle of de-ionized water decreases with the grit blast treatment time. Optical microscopy and scanning electron microscopic (SEM) analysis of untreated and atmospheric plasma treated titanium are carried out to examine the surface characteristics. A substantial improvement in the surface energy of titanium is observed after the atmospheric pressure plasma treatment. The surface energy increases with increasing exposure time of atmospheric pressure plasma. The optimized time of plasma treatment suggested in this investigation results in maximum adhesive bond strength of the titanium. Unmodified and surface modified titanium sheets by atmospheric pressure plasma were adhesively bonded by high temperature resistant polyimide adhesive. The glass transition temperature of this adhesive is 310 °C and these adhesively bonded joints were cured at high temperature. A substantial improvement in adhesive bond strength was observed after atmospheric pressure plasma treatment.     

Surface modification of ultra high modulus polyethylene fibers by an atmospheric pressure plasma jet

To improve their adhesion properties, ultra high modulus polyethylene (UHMPE) fibers were treated by an atmospheric pressure helium plasma jet (APPJ), which was operated at radio frequency (13.56 MHz). The surface properties of the fibers were investigated by X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and contact angle measurement. The surface dyeability improvement after plasma treatments was investigated using laser scanning confocal microscopy (LSCM). The adhesion strengths of the fibers with epoxy were evaluated by microbond tests. In addition, the influence of operational parameters of the plasma treatment including power input and treatment temperature was studied. XPS analysis showed a significant increase in the surface oxygen content. LSCM results showed that the plasma treatments greatly increased fluorescence dye concentrations on the surface and higher diffusion rate to the fiber center. The tensile strength of UHMPE fiber either remained unchanged or decreased by 10–13.6% after plasma treatment. The contact angle exhibited a characteristic increase in wettability, due to the polar groups introduced by plasma treatment. The microbond test showed that the interfacial shear strengths (IFSS) increase significantly (57–139%) after plasma treatment for all groups and the optimum activation is obtained at 100°C and 5 W power input. SEM analysis showed roughened surfaces after the plasma treatments. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Microstructure and phase evolution of atmospheric plasma sprayed Mn-Co-Fe oxide protection layers for solid oxide fuel cells

Dense protective layers are needed to reduce chromium-related degradation in SOFC stacks. In particular, atmospheric plasma sprayed (APS) Mn_1.0Co_1.9Fe_0.1O₄ (MCF) coatings demonstrated low degradation rates in stack tests. We show that short-term annealing in air induces crack healing within these coatings. Parallel to this effect, a phase transformation is observed originating from oxidation that proceeds by solid state-diffusion. The present contribution reveals the basic mechanisms of the microstructural and phase changes of coatings in long-term annealing tests of up to 10,000 h at 700 °C. The layer develops differently at the air-facing surface and in the bulk. Due to cation deficiency, oxidation is dominated by cation outward diffusion, leading to a Co-enriched surface layer. The bulk displays a fine distribution of the initial (rock salt) and the final (spinel) phases. Understanding the mechanisms leading to these irreversible changes enables predictions to be made concerning durable protectivecoatings in SOFCs.     

The effect of argon shielding gas at plasma spray process on the structure and properties of MoSi2 coating

In this work, MoSi₂ powder was agglomerated for using it in atmospheric plasma spray (APS) process. MoSi₂ coatings were manufactured by APS and argon-shrouded plasma spray (ASPS) processes. Phase composition and structural properties of coatings were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Also, the mechanical properties of coatings (such as microhardness and adhesion strength) were evaluated. Using the ASPS method, the coatings were found to have a low porosity and highly homogeneous structure. In addition, the argon protection gas was used to prevent the oxidation of the powder. Finally, the ASPS method revealed better microhardness and bending strength results for the corresponding tests.     

Thermodynamics of metal reactants for ammonia synthesis from steam,nitrogen and biomass at atmospheric pressure

Catalytic ammonia synthesis at approximately 30 MPa and 800 K consumes about 5% of the global annual natural gas production causing significant CO₂ emissions. A conceptual solar thermochemical reaction cycle to produce NH₃ at near atmospheric pressure without natural gas is explored here and compared to solar thermochemical steam/air reforming to provide H₂ used in the Haber‐Bosch process for NH₃ synthesis. Mapping of Gibbs free energy planes quantifies the tradeoff between the yield of N₂ reduction via metal nitridation, and NH₃ liberation via steam hydrolysis vs. the temperatures required for reactant recovery from undesirably stable metal oxides. Equilibrium composition simulations suggest that reactants combining an ionic nitride‐forming element (e.g., Mg or Ce) with a transition metal (e.g., MgCr₂O₄, MgFe₂O₄, or MgMoO₄) may enable the concept near 0.1 MPa (at maximum 64 mol % yield of Mg₃N₂ through nitridation of MgFe₂O₄ at 1,300 K, and 72 mol % of the nitrogen in Mg₃N₂ as NH₃ during hydrolysis at 500 K). © 2011 American Institute of Chemical Engineers AIChE J, 58: 3203–3213, 2012     

Electrochemical quartz crystal impedance study on immobilization of glucose oxidase in a polymer grown from dopamine oxidation at an Au electrode for glucose sensing

Glucose oxidase (GOD) was codeposited into a polymer grown from oxidation of dopamine (DA) at an Au electrode in a neutral phosphate aqueous solution for the first time. The electrochemical quartz crystal impedance analysis (EQCIA) method was used to monitor the GOD-immobilization process. Effects of concentrations of phosphate buffer, DA and GOD were investigated, and the optimal concentrations were found to be 20.0 mM phosphate buffer (pH 7.0), 30.0 mM DA and 5.00 mg ml⁻¹ GOD. A glucose biosensor was thus constructed, and effects of various experimental parameters on the sensor performance, including applied potential, solution pH and electroactive interferents, were examined. At an optimal potential of 0.6 V versus the KCl-saturated calomel electrode (SCE), the current response of the biosensor in the selected phosphate buffer (pH 7.0) was linear with the concentration of glucose from 0.05 to 9 mM, with a lower detection limit of 3 μM (S/N = 3), short response time (within 15 s) and good anti-interferent ability. The Michaelis constant () was estimated to be 9.6 mM. The biosensor exhibited good storage stability, i.e. 96% of its initial response was retained after 7-day storage in the selected phosphate buffer at 4 °C, and even after another 3 weeks the biosensor retained 86% of its initial response. In addition, the enzymatic specific activity and enzymatic relative activity of the GOD immobilized in the polymer from dopamine oxidation (PFDO) were estimated from the EQCIA method to be 1.43 kU g⁻¹ and 3.7%, respectively, which were larger than the relevant values obtained experimentally using poly(o-aminophenol) and poly(N-methylpyrrole) matrices, suggesting that the PFDO is a better matrix to immobilize GOD.