Improvement of thermo-oxidative stability of electrically insulating polymeric materials by organic-inorganic hybrid coating

The thermo-oxidative stability of poly(ethylene terephthalate) (PET) and low-density polyethylene (LDPE) films, coated with organic-inorganic hybrid coatings of various compositions, has been investigated after accelerated ageing tests, in order to ascertain a possible beneficial effect of these coatings on the electrical performances of these insulating materials. The results have shown that the coating affects degradation mechanisms for both LDPE and PET.Thermo-oxidation is slow in LDPE, leading to significantly better insulating characteristics after ageing: a strong reduction of the embrittlement time was also observed.The strong increase of crystallinity upon ageing, observed for both coated and uncoated PET samples, probably dominates the effect of ageing on the electrical properties. As a consequence, only slight beneficial effects on PET electrical performances have been observed (both on conductivity and electrical strength). On the other hand, the coating has a strong effect on molecular weight changes leading to a significant increase of molecular weight for coated PET, while uncoated PET undergoes a significant decrease. This suggests that coated PET should present significantly better properties upon very long times of ageing.     

High-Temperature Oxidation Resistance of PDC Coatings in Synthetic Air and Water Vapor Atmospheres

This work is aimed at the development and investigation of the oxidation behavior of ferritic stainless-steel grade AISI 441 and polymer-derived ceramic (PDC) protective coatings. Double-layer coatings of a PDC bond coat below a PDC top coat with glass and ceramic passive fillers’ oxidative resistance were studied at temperatures up to 1000 °C in a flow-through atmosphere of synthetic air and in air saturated with water vapor. Investigation of the oxide products formed at the surface of the samples in synthetic air and water vapor atmospheres, at different temperatures (900, 950, 1000 °C) and exposure times (24, 96 h) was carried out on both uncoated steel and steel coated with selected coatings by scanning electron microscopy (SEM) and X-Ray diffraction (XRD). The Fe, Cr₂O₃, TiO₂, and spinel (Mn,Cr)₃O₄ phases were identified by XRD on oxidized steel substrates in both atmospheres. In the cases of the coated samples, m- ZrO₂, c- ZrO₂, YAG, and crystalline phases (Ba(AlSiO₄)₂–hexacelsian, celsian) were identified. Scratch tests performed on both coating compositions revealed strong adhesion after pyrolysis as well as after oxidation tests in both atmospheres. After testing in the water vapor atmosphere, Cr ions diffused through the bond coat, but no delamination of the coatings was observed.     

Water sorption isotherms on aminopropyltriethoxysilane coated surface acoustic wave sensors

Water sorption isotherms were obtained on surface acoustic wave sensors (SAWS) coated with aminopropyltriethyoxysilane (APTES), and on uncoated SAWS of which the substrate material was polished ST-quartz. The isotherms were obtained at 25 degrees , 30 degrees and 40 degrees over the range 1-80% relative humidity (RH). The isotherms exhibit BDDT type III characteristics typical of weak gas-solid interaction. The isotherms showed good fit to quadratic equations relating frequency change on exposure to humid air with relative humidity. There was no significant hysteresis in the isotherms when the SAWS was taken through a cycle of relative humidity at any of the three temperatures employed. These results are similar to those obtained in earlier work on FPOL and polyvinylpyrollidone coated SAWS. They demonstrate that a correction algorithm based on a quadratic equation should be possible to overcome water vapour response of coated SAWS.     

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.     

Gas chromatographic retention in uncoated fused silica capillaries

Understanding of retention in uncoated fused‐silica capillaries is of interest due to increased attention on precolumn backflushing in capillary GC. Uncoated capillaries offer several advantages as precolumns compared to coated precolumns. In order to examine the possibility of predicting elution temperatures of alkanes from uncoated capillaries a priori, several sizes of deactivated but uncoated fused‐silica capillaries were evaluated under various operating conditions. Retention was found to depend on dimensionless ramp rate (°C/t_M), sample loading (capacity), flow mode, and column dimensions (probably related to surface area).     

The Effect of a Magnetic Field on a RAPET (Reaction under Autogenic Pressure at Elevated Temperature) of MoO(OMe)(4): Fabrication of MoO(2) Nanoparticles Coated with Carbon or Separated MoO(2) and Carbon Particles

In this article, we present results of the RAPET dissociation of MoO(OMe)4 at 700 degrees C in a closed Swagelok cell. The reaction produces molybdenum dioxide nanoparticles (20 nm) coated with carbon (20 nm). We have also carried out the same reaction under an applied magnetic field of 10 T. This reaction yielded different products. It produces a mixture of comparatively larger (50 nm) molybdenum dioxide nanoparticles and separated uncoated carbon particles (20-30 nm).     

Novel UV-protective formulations for cotton, PET fabrics and their blend utilizing irradiation technique

A novel coating formulation to impart ultraviolet (UV) protection property to cotton, Polyethylene trephethalate (PET) and cotton/PET fabrics was prepared and gamma rays as an ionizing radiation was utilized for surface curing. Natural occurring aluminum potassium sulfate (Alum) was used individually and in binary coat with Zinc Oxide (ZnO), to induce the UV-blocking properties. It was found that using Alum (0.3 g/ml) caused a prompt increase in ultraviolet protection factor (UPF) over the uncoated fabrics. Moreover, the incorporated ZnO in the binary coat increased the UPF for two to threefold than the stand-alone Alum coating, specially in case of PET coated fabric. Water absorbance and moisture regain of ZnO and Alum/ZnO coated fabrics showed a decrease over the blank samples, due to the usage of oligomer/monomer combination. On contrary, Alum showed a hydrophilic effect with the increase in its content in the formulation. Surface Electron Microscope showed the homogenous coating of fibers. X-ray diffraction (XRD), energy dispersive X-ray (EDX) and water vapor permeability were also tested for coated samples.     

Synthesis of high performance,conductive PEDOT‐coated polyester yarns by OCVD technique

Production of high performance conductive textile yarn fibers for different electronic applications has become a prominent area of many research groups throughout the world. We have used oxidative chemical vapor deposition (OCVD) technique to coat flexible and high strength polyester yarns with conjugated polymer, poly(3,4‐ethylenedioxythiophene) (PEDOT) in presence of ferric (III) chloride (FeCl₃) oxidant. OCVD is an efficient solvent free technique used to get uniform, thin, and highly conductive polymer layers on different substrates. In this paper, PEDOT‐coated polyester (PET) yarns were prepared under specific reaction conditions, and the electrical, mechanical and thermal properties were compared to previously studied PEDOT‐coated viscose yarns. Scanning electron microscopy (SEM) and FT‐IR analysis revealed that polymerization of PEDOT on the surface of the polyester yarns has been taken place successfully and structural analysis showed that PEDOT has strong interactions with viscose yarns as compared to PET yarns. The voltage–current (V–I) characteristics showed that PET yarns are more conductive than PEDOT‐coated viscose yarns. The variation in the conductivity of PEDOT‐coated yarns and the heat generation properties during the flow of current through coated yarns for longer period of time, was studied by time–current (t–I) characteristics. Thermogravimeteric analysis (TGA) was employed to investigate the thermal properties and the amount of PEDOT in PEDOT‐coated PET yarns compared to PEDOT‐coated viscose. The effect of PEDOT coating and ferric (III) chloride concentration on the mechanical properties of coated yarns was evaluated by tensile testing. The obtained PEDOT‐coated conductive polyester yarns could be used in smart clothing for medical and military applications. Copyright © 2011 John Wiley & Sons, Ltd.     

Atomic layer deposition (ALD) as a coating tool for reinforcing fibers

Layers of alumina were deposited on to bundled carbon fibers in an atomic layer deposition (ALD) process via sequential exposure to vapors of aluminium chloride and water, respectively. Scanning electron microscopic (SEM) images of the coated fibers revealed that each individual fiber within a bundle was coated evenly and separately, fibers are not bridged by the coating. SEM and transmission electron microscopic (TEM) images indicate that the coating was uniform and conformal with good adhesion to the fiber surface. Average deposition rate, measured from SEM images, was 0.06 nm per cycle at 500 °C. SEM also revealed that at deposition temperatures of 500 °C few of the fibers were damaged. At temperatures of 300 °C, no damaged fibers were observed, the average deposition rate decreased down to 0.033 nm per cycle. Oxidation resistance of the alumina-coated fibers was characterized by thermogravimetric analysis (TGA). The alumina coating improved oxidation resistance of the carbon fiber significantly. Oxidation onset temperature was 600 °C for fibers coated with a 45 nm thick alumina. Uncoated fibers, on the other hand, started to oxidize at temperatures as low as 250 °C.     

Pyrolytic carbon coating method for contoured graphite tubes and their use in furnace atomic absorption spectrometric determination of boron and uranium

Tubes are machined from rods of suitable graphite according to a modified design so that there is a recess of 20-μl capacity in the inner surface at the tube centre; this improves reproducibility and sensitivity. Pyrolytic carbon coating is accomplished independently of the atomic absorption instrument by using a simple apparatus (dimensions are given). Tube lifetimes are considerably longer than those of both coated and uncoated commercial tubes. The coated tubes described have lifetimes long anough at high atomizing temperatures to determine uranium and boron on a routine basis. The boron memory is eliminated and that of uranium successfully controlled. The addition of organic solvents to the analyte solution to enhance sensitivity for uranium is reported.     

Effect of Radiofrequency Plasma Assisted Grafting of Polypropylene on the Properties of Muga Silk Yarn

Radiofrequency (RF) Ar/propylene glow discharge is utilized for grafting polypropylene onto muga silk yarn at working pressure of 1.2?×?10^?1 mbar and in the of RF power range of 20?C80?W. The plasma discharge is diagnosed using self-compensated emissive probe to study the variation of ion energy impinging on the substrates with RF power. From chemical compositional analysis, a possible grafting mechanism between propylene and muga yarn is proposed by considering the charge-transfer initiation through the formation of electron-donor?Cacceptor (EDA) complex. X-ray photoelectron spectroscopy reveals that at RF power values of 60?C80?W, the ion sputtering effect becomes dominant over plasma grafting thereby leading to severe destruction in chemical structure of the polypropylene grafted (PP-grafted) muga yarns. The experimental results show that PP-grafted muga yarns exhibit improved mechanical strength and hydrophobic behavior as compared to the virgin yarn. The properties of the PP-grafted muga yarns are observed to be dependent on atomic concentration, surface morphology as well as the results obtained from plasma discharge characteristics.     

Flammability properties of PI fabric coated with montmorillonite

In this study, polyimide (PI) fabric was coated with montmorillonite (MMT) which performed as a kind of flame retardant. Thermogravimetric analysis showed that PI coated with MMT left as much as 69 % char after heating to 700 °C, about 15 % more than uncoated PI fabric. Cone calorimeter testing (heat flux: 60 kW m^?2) showed that coated fabric reduced the total heat release and showed resistance to degradation from direct flame. Post-burn residues of samples were examined with SEM and revealed that the weave structure and fiber shape in all coated fabrics were preserved. In addition, heat-insulting test showed that the temperature difference of coated PI could reach 400 °C after 10 min at 800 °C. These results demonstrate that MMT coating is relatively effective for improving flame-retardant behavior to PI fabric.     

Interaction of surfactant with antistatic polymer thin layers

Thin layers made from three kinds of hydrophilic polymer were coated onto poly(ethylene terephthalate)(PET) fibers to study the interaction of an anionic surfactant, sodiumn-dodecyl benzenesulfonate, with the polymer layers. The coated layers include a) poly(vinyl alcohol) (PVA) crosslinked with glutaraldehyde [nonionic], b) crosslinked, sulfated PVA [anionic], and c) polyethyleneimine crosslinked with poly(ethyleneglycol diglycidylether) [cationic]. All of these coatings were found to reduce the electrostatic charging of the PET cloths, indicating that they were effectively coated with the hydrophilic polymers. The PET cloth coated with the thin layers was immersed in the aqueous solution of surfactant at 40°C for different durations and the electrostatic voltage as well as the weight change were determined after drying. When the cloth coated with the nonionic or the anionic layer was brought into contact with the surfactant, neither the electrostatic voltage nor the weight of PET changed. On the contrary, immersion in the surfactant solution brought about an increase in both the electrostatic voltage and the weight for the PET coated with the cationic layer. This suggested that the surfactant molecules were bound to the cationic layer, in contrast to the nonionic and the anionic layer. It was concluded that the binding was due to ion complexing between the cationic groups in the polymeric layer and the sulfate groups in the surfactant molecules.     

Coating of powder-blasted channels for high-performance microchip electrophoresis

Channels in microfluidic glass chips manufactured with the alternative powder blasting technology were permanently coated with poly(vinyl alcohol) (PVA) in order to improve the performance in microchip electrophoresis. The performance of coated and uncoated powder-blasted (pb) devices as well as coated and uncoated wet chemical etched (wc) chips was compared in electrophoretic separations of fluorescently labeled test compounds. The limited electrophoretic resolution obtained in pb-chips could significantly be improved by coating the channels with PVA. The resolution of test compounds in such coated pb-devices was even higher than in uncoated wc-chips. PVA-coated pb-chips could also successfully be applied in chiral separations. While in an uncoated pb-chip using a cyclodextrins buffer only one broad signal was obtained, two well-resolved signals were obtained in a coated device.     

TiO2包覆对LiCo1/3Ni1/3Mn1/3O2材料的表面改性

为了提高材料LiCo1/3Ni1/3Mn1/3O2的循环性能, 采用浸渍-水解法对其进行TiO2包覆. 用X射线衍射(XRD)、电化学交流阻抗谱(EIS)、电感耦合等离子体发射光谱(ICP-OES)和恒流充放电测试研究包覆材料的结构和电化学性能. TiO2仅在材料表面形成包覆层, 并未改变材料的结构. TiO2包覆能提高材料LiCo1/3Ni1/3Mn1/3O2的倍率性能和循环性能, TiO2包覆后的材料在5.0C(1.0C=160 mA·g-1)下的放电容量达到0.2C下的66.0%, 而包覆前的材料在5.0C下的放电容量仅为其0.2C下的31.5%. 包覆后的材料在2.0C下循环12周后的容量没有衰减, 而未包覆的材料容量保持率仅为94.4%. EIS测试表明包覆材料性能的提高是由于循环过程中材料的界面稳定性得到了提高. 循环后材料的XRD和ICP-OES测试表明, 包覆层能提高材料LiCo1/3Ni1/3Mn1/3O2的结构稳定性.     

Surface-treatment of Alkaline Earth Sulfides Based Phosphor

A series of alkaline earth sulfides based phosphors Ca0.8Sr0.2S : Eu^2 , Tm^3 were covered with a layerof protective coating with alkaline earth fluorides by heating the mixture of phosphor and NH4HF2 at elevatedtemperatures. The coatings were characterized by means of XRD and SEM. The optical properties of thecoated phosphors and the influences of the coating on their properties have been discussed extensively. Thestabilities of the coated and uncoated phosphors have been compared.     

TiO2包覆对LiCO1/3Ni1/3Mn1/3O2材料的表面改性

为了提高材料LiCo1/3Ni1/3MnO2的循环件能,采用浸渍-水解法对其进行TiO2包覆.用X射线衍射(XRD)、电化学交流阻抗谱(EIS)、电感耦合等离子体发射光谱(ICP-OES)和恒流允放电测试研究包覆材料的结构和电化学性能.TiO2仅在材料表面形成包覆层,并未改变材料的结构.TiO2包覆能提高材料LiCo1/3Ni1/3Mn1/3O2的倍率性能和循环性能,TiO2包覆后的材料在5.0C(1.0C=160 mA·g-1)下的放电容量达到0.2C下的66.0%,而包覆前的材料在5.0C下的放电容量仅为其0.2C下的31.5%.包覆后的材料在2.0C下循环12周后的容最没有衰减,而未包覆的材料容量保持率仅为94.4%.EIS测试表明包覆材料性能的提高是由于循环过程中材料的界面稳定性得到了提高.循环后材料的XRD和ICP-OES测试表明,包覆层能提高材料LiCo1/3Ni1/3Mn1/3O2的结构稳定性.     

Kinetics of indium atomization from different atomizer surfaces in electrothermal atomic absorption spectrometry (ETAAS)

The kinetic parameters of indium atomization in electrothermal atomic absorption spectrometry (ETAAS) have been determined by a newly proposed method. Effect of the atomizer surface and the palladium modifier on the kinetics of indium atomization has been investigated. The mechanisms of indium atomization seem to be identical for the pyrolytically coated graphite and the uncoated graphite tubes, i.e. the rate-limiting step for the atomization changes from a first order kinetics at lower temperatures into a nearly 1/3 order kinetics at higher temperatures, which may suggest that the analyte moves from a dispersed state to agglomates with increasing temperature. However, for the zirconium coated graphite tube, the atomization of indium is controlled by a single mechanism with the kinetic order of near 2/3 and the activation energy of 186 ± 13 kJ/mol. Relatively weak indium—zirconium carbide interactions and the release of indium from the sphere of molten indium metal on the zirconium coated surface are suggested. In the presence of palladium, a simple mechanism, i.e. the release of indium from the solid solution of the In and the Pd on the pyrolytically coated graphite surface, is proposed to account for the observed first order kinetics and the activation energy of 421 ± 27 kJ/mol.     

Tribo-corrosion behavior of Zn-Ni-Cu and Zn-Ni-Cu-TiB2 coated mild steel

In this investigation , Zn-Ni-Cu and Zn-Ni-Cu-TiB₂ were coated on a mild steel specimen using a high velocity oxy fuel thermal spray (HVOF) process. The surface morphology and coated powder distribution of coated specimens were characterized using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray-Elemental mapping. The pin-on-disc (ASTM G99-17) method was used to examine the wear resistance of the coated and uncoated mild steel specimens. Both coated Zn-Ni-Cu and Zn-Ni-Cu-TiB2 on mild steel saw reduced wear volume loss than uncoated mild steel. The coated samples of Zn-Ni-Cu and Zn-Ni-Cu-TiB2 on Mild Steel were put through a scratch test to determine the adhesion strength of the coating with the substrate. The adhesion strength of coated Zn-Ni-Cu and Zn-Ni-Cu TiB2 mild steel was higher than that of untreated mild steel, indicating a solid link between the coating and substrate and minimal delamination. Using the Vickers hardness test to measure the hardness caused by the coating, it was shown that coated samples of Zn-Ni-Cu and Zn-Ni-Cu-TiB2 coated mild steel had significantly higher hardness than uncoated mild steel. Using ASTM G1-03 and ASTM G-31 standards, a 0.2 M HCl immersion cycle test was conducted for 28 days to test the corrosion resistance of coatings in an acidic media (672Hrs). When compared to Zn-Ni-Cu and Zn-Ni-Cu-TiB2 coated mild steel, the weight loss for the uncoated mild steel was significantly larger. Additionally, XRD examination showed that coated samples had less rust on their surface than uncoated samples. Both Zn-Ni-Cu and Zn-Ni-Cu-TiB2 on Mild Steel were anti-corrosive, as evidenced by increased corrosion potential and reduced corrosion current density when compared to uncoated mild steel, according to electrochemical impedance spectroscopy (EIS)/Tafel study in 0.2 MHCl. The outcomes of each test were very encouraging and demonstrated the durability of these coatings against wear and corrosion.     

Elementary processes in the radiation-induced degradation of poly(ethylene terephthalate)—A note

Elementary processes of γ-irradiated poly(ethylene terephthalate) (PET) have been investigated by electron spin resonance (esr) and optical absorption measurements. On irradiating PET films with γ-rays at ?196°C and in the dark, they develop a reddish purple color and show esr spectra which are assigned to ionic species of PET. The optical absorption spectra of γ-irradiated PET films at ?196°C and those of a model compound (diethylterephthalate(DET))-2-methyltetrahydrofuran system also confirm these assignments. A possible mechanism for the elementary processes of γ-ray-induced degradation of PET is proposed.