A study of film thickness dependence of the graphitizability of PMDA–ODA polyimide-derived carbon film

PMDA–ODA (pyromellitic dianhydride–4,4′-oxydianiline) polyimide (PI) films with thickness of 2–26 μm were synthesized and heat-treated at 2200–2500°C. The effect of film thickness on both the graphitizability of the PI-derived carbon film and the crystalline organization of the initial PI film was investigated by X-ray diffraction. The degree of graphitization of the resultant carbon film was observed to increase with decreasing initial PI film thickness, corresponding to the film thickness dependence of the crystalline ordering in the initial PI films. Structural factors related to PI film thickness are discussed for understanding the graphitizability of the resultant carbon.     

Effects of film and substrate dimensions on warpage of film insert molded parts

Three‐dimensional flow and structural analyses were carried out for film insert injection molding to investigate warpage of film insert molded (FIM) parts with respect to variation of film and substrate thickness. Asymmetry of temperature distribution in the thickness direction was increased with increasing film thickness but decreased with increasing substrate thickness. Asymmetry of the in‐mold residual stress distribution in the FIM specimen was generated by the nonuniform temperature distribution, and it was increased with increasing film thickness but reduced with increasing substrate thickness. Warpage of the ejected FIM specimen was determined by relaxation of the asymmetric in‐mold residual stress distribution, and it was increased with increasing film thickness but reduced with increasing substrate thickness. Warpage of FIM specimens annealed at 80°C for 30 min showed complex behavior, and the behavior was understood by using factors such as degree of warpage of the ejected part, thermal shrinkage of the inserted film, and retardation of heat transfer. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Transparency of recycled polypropylene film

Turbidity of quenched polypropylene films was measured as a function of the film thickness and number of times film was recycled. Turbidity τ is defined by τ = (1/d) ln (I_o/I_t), where I_o and I_t are the intensity of the incident and transmitted lights, respectively, and d is the thickness of the sample. We assume here that most of the attenuation of light is due to scattering from superstructure in the film, such as spherulites, since no characteristic absorption bands are present in the wavelength region studied in this work. Turbidity varied sigmoidally with film thickness. It remained constant when the film thickness was lower than ca. 400 μm and then increased with film thickness and reached a plateau around 800 μm. When the film preparation was repeated, turbidity increased exponentially with the number of recycles. The spherulite size, however, was an invariant against the number of recycles and was dependent upon film thickness. The variation of turbidity with film thickness and the number of recycles is discussed.     

Distribution characteristics of falling film thickness around a horizontal tube

An experimental investigation of a liquid film falling around a horizontal tube was performed using a displacement micrometer to determine the distribution characteristics of the film thickness. Measurements were carried out for circumferential angles ranging from 15° to 165°, outside diameters varying from 20 to 32 mm, intertube spacings ranging from 10 to 40 mm, and film Reynolds numbers varying from 150 to 800. It is found that the distribution characteristics of the film thickness are mainly affected by circumferential angle, intertube spacing and film Reynolds number. However, the outside diameter has little influence on the film thickness. The experimental results also validate the Nusselt's theory giving a relatively reasonable prediction of the film thickness around the upper perimeter of the tube but a poor prediction around the lower perimeter. The minimal values of the film thickness locate at different circumferential angles in the range of 90°–115° rather than at the single point of β = 90° predicted by Nusselt. Moreover, the liquid film gets thinner around the scaled tube, and the thickness distributions for pure water agree well with those for seawater. Based on the experimental data, a new correlation has been suggested to predict the film thickness.     

管内垂直下降液膜速度与厚度分布特性

对洗涤冷却管内垂直降膜的流动特性进行研究,采用超声波多普勒测速仪对管内不同周向以及轴向位置的液膜厚度和速度进行了无接触式的测量,液膜Reynolds数范围为1.0×10⁴~3.1×10⁴。结果表明:在0°周向位置上液膜厚度与速度均达到最大值,导致该位置局部液膜厚度过大而不能保持稳定,部分液体脱离液膜表面,此外还造成了8°和16°位置的液膜厚度激增。在轴向上,当Reynolds数小于2.0×10⁴时,液膜速度在重力作用下随流动距离增加而增加,反之,液膜速度因为流动阻力会随距离增加而减小。随着Reynolds数的增大,液膜平均厚度和速度呈增大趋势。此外,Reynolds数的增大还会使得液膜更加不稳定。     

洗涤冷却管内垂直降膜流动特性

采用双平行电导探针对多喷嘴煤气化过程中洗涤冷却管内垂直降膜的液膜厚度分布进行了实验研究,研究发现,经洗涤冷却水分布环分配后在洗涤冷却管内形成的液膜在进口段200～400 mm处呈明显的不均匀分布,液膜厚度差值高达3 mm。流动方向上的液膜波动变化与平均液膜厚度变化相似,但具有滞后性。研究还表明,在2.4～14 m³·h^-1的进水流量范围内,整体液膜厚度随着流量的增大而增大,由此对洗涤冷却管内液膜充分发展区的平均液膜厚度建立了经验关联式。实验还发现,洗涤冷却水分布环的槽缝宽度对液膜分布影响显著,在本文研究条件下,最佳槽缝宽度为3 mm,槽缝宽度继续增大,液膜的均匀性下降。另外,随着气相表观速度的增大,整体液膜厚度减小,但一定程度上改善了液膜分布的均匀性。     

EIS study of potentiostatically formed passive film on 304 stainless steel

Passive film was potentiostatically grown on Type 304 stainless steel at potentials between −0.4 and 0.3 V vs. Hg/HgSO₄ in 50 mV intervals. Electrochemical impedance spectroscopy was used to study properties of the grown passive films. Relevant circuit analogs were selected to fit the electrochemical impedance data obtained at each potential. The resultant parameters were used to calculate film thickness through both film capacitance and resistance. The calculated thicknesses were compared with ellipsometry thickness measurement results. An overestimation occurred when the film resistance was used to calculate the film thickness. On the other hand, when the CPE parameter Q was used, the film thickness was underestimated. Available approaches were employed to calculate the effective capacitance of the film. A comparison between the film thickness calculated from the effective capacitance and ellipsometry measurements suggested a surface distribution of time constants on the surface.     

水平单管外液膜厚度的CFD模拟

利用CFD中的VOF模型研究了在不同进料高度、质量流量、管道转速和气流条件下单管外液体流动状况,获得了管外液膜厚度分布图,讨论了各种因素对液膜厚度的影响情况。结果表明,进料高度对液膜厚度基本无影响;在一定流量范围内,膜厚度随着流量的增加而增加;管道转速和气流对液膜厚度的影响具有一定的局限性;平均液膜厚度变化率随着各种因素变化率变化较缓慢。将模拟分析得出的结论与文献结果或经验公式进行比较,发现吻合性较好。     

The effect of film thickness on contact electrification

Contact electrification experiments have been performed for the purpose of studying the effect of varying film thickness on charge transfer during metal-insulator contact. Thin films of plasma polymerized methane are deposited on silicon substrates using a magnetically enhanced glow discharge system. Film uniformity across the wafer is verified by ellipsometric techniques. Variations in film thickness from approximately 100 to 600 Å result in a variable amount of charge transfer when the films come in contact with a metal probe. Charging of the polymer film increases with increasing film thickness up to a limiting thickness of approximately 375–400 Å. Similar results are obtained when various substrate treatments are performed previous to film deposition and charge measurements are obtained as a function of film thickness. Contact electrification measurements show the metal-insulator contact is influenced by the insulator/substrate interface up to the same limiting film thickness (375–400 Å). The instrumentation used in this series of experiments is based on measurement of the currents associated with the contact and subsequent separation of the surface state systems of a metal and an insulating polymer. This technique relies on measurement of currents in the picoampere range and appears to be a novel method to experimentally determine charge penetration depth. © 1996 John Wiley & Sons, Inc.     

Initial thickness measurements and insights into crystal growth of methane hydrate film

The initial thickness of methane hydrate film was directly measured by suspending a single methane bubble in water at 274.0, 276.0, and 278.0 K. The results show that the initial hydrate film thickness decreases from tens of micrometers to about 10 µm with the subcooling increased from 0.5 K to about 3 K. When subcooling is higher than 1.0 K, all initial film thickness data measured under different temperatures vary inversely with the subcooling. Notable three‐dimensional growths of hydrate crystals of different sizes and shapes at film front and emergence of new crystal were clearly observed at lower subcooling that resulting in the rougher surface of hydrate film and uncertainty of initial thickness measurement under lower subcooling. The hydrate film growth was dominated by film growth in thickness, not by lateral growth at low subcooling. The growth in thickness of hydrate shell covering one whole bubble surface was also investigated. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2145–2154, 2013     

Development of formation and growth models of CO2 hydrate film

This study aims to develop models to estimate the CO₂ hydrate film formation and growth for different temperature and flow velocity conditions. First, the CO₂ hydrate film thickness at the initial stage of its formation is experimentally measured under different temperature and flow velocity conditions using laser interferometry. Based on the results, the CO₂ hydrate film thickness was found to decrease with increasing temperature and flow velocity. Next, the CO₂ hydrate film formation model and growth model are developed, and the models are verified using the present experimental data. Finally, the long term growth of CO₂ hydrate film thickness is estimated by the proposed growth model of CO₂ hydrate film thickness. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4078–4089, 2016     

Spin coating of thin and ultrathin polymer films

The spin coating of thin (> 200 nm thick) and ultrathin (< 200 nm thick) polymer films is examined in several solvents of varying volatility over a broad range of polymer solution concentrations and spin speeds. Experimentally measured film thicknesses are compared with a simple model proposed by Bornside, Macosko, and Scriven, which predicts film thickness based on the initial properties of the polymer solution, solvent, and spin speed. This model is found to predict film thickness values within 10% over the entire range of conditions explored, which gave film thicknesses from 10 nm to 33 μ:m. The model underpredicts film thickness for cases in which a very volatile solvent is used or the initial concentration of polymer is high, while overpredicting film thickness for cases in which a low volatility solvent is used or the initial polymer concentration is very low. These deviations are a consequence of how the model decouples fluid flow and solvent evaporation.     

厚度对掺铝氧化锌透明导电薄膜性质的影响

采用紫外光助溶胶一凝胶法在玻璃基底上制备了掺铝氧化锌薄膜。研究了厚度对薄膜性质的影响,结果表明：所有薄膜均由具有c轴优先生长取向的六角纤锌矿结构的ZnO晶体构成,晶体的粒径随厚度的增加而先增大,达到最大值后,不再随厚度的增加而改变;薄膜的方阻随厚度的增加先减小,在达刮最小值2．1×10^2Ω／口后,随厚度的增加又略有增大;而所有薄膜均是透明的,在可见光区的透光率〉80％。     

接触式机械密封端面磨合过程平均膜厚预测

为研究和掌握接触式机械密封端面磨合过程平均膜厚的变化规律,采用分形参数表征磨合过程中密封端面形貌的变化,基于机械密封端面接触分形模型,通过求解端面上微空穴的体积,建立接触式机械密封端面平均膜厚预测模型。对两套B104a-70型机械密封进行磨合试验,试验密封流体为20℃清水,压力为0.5 MPa,转速为2900 r·min^-1,弹簧比压分别为0.15 MPa和0.3 MPa。研究结果表明,随着磨合过程的进行,软质环端面迅速趋于光滑,端面平均膜厚迅速减小;当进入正常磨损阶段后,两套机械密封试件的平均膜厚均稳定在0.295 μm左右。这也表明,密封端面的形貌对平均膜厚的影响较大,而弹簧比压对平均膜厚的影响较小。掌握磨合过程中端面形貌及平均膜厚的变化规律,对接触式机械密封实际运行时端面间工作特性的预测和密封端面设计具有重要意义。     

Estimation of film thickness nonuniformity effects on coating optical properties

Film nonuniformities cause many problems for the coating scientist. One area of coating film performance that they impact directly is optical properties. Measurements and predictions of film optical performance are all made assuming uniform film thickness. Incomplete leveling and other film application problems often yield nonuniform films with significant film thickness fluctuations. These film thickness imperfections can be modeled by a sine wave thickness fluctuation, and this fluctuation can be used to estimate the effects of nonuniformity in thickness on optical properties. This has been done using both approximate equations for scattering, transmission, and reflectance in films (zero absorption) and for the Kubelka-Munk equations including absorption. the effects of average film thickness and amplitude of fluctuation on measured S, R, and T values are predicted numerically for several cases of [K, S] pairs consistent with wavelength independent situations (white or similar films) over black substrates, and then the calculations are used to consider colored films [considering δE(L*a*b*)] over black substrates. Film thickness fluctuations are shown to have considerable impact on film optical properties, especially in thin highly scattering films. Examples of the types of predictions that can be made are given; how the results depend on the coating optical parameters is also shown.     

Nonisothermal two‐dimensional film casting of a viscous polymer

A model is presented for simulating two‐dimensional, nonisothermal film casting of a viscous polymer. The model accommodates the effects of inertia and gravity, and allows the thickness of the film to vary across the width, but it excludes film sag and die swell. Based on the simulation results, three factors are shown to contribute to reducing neck‐in and promoting a uniform thickness: the self‐weight of the material, for low viscosity polymers; nonuniform thickness and/or velocity profiles at the die; and cooling of the film, especially when localized cooling jets are employed.     

幅宽14m PO涂布膜机组的关键技术

介绍了聚烯烃(PO)涂布膜的性能以及在线涂覆法生产PO膜的工艺流程及工艺难点,研究了PO膜对螺杆、机头、自动膜厚控制系统、牵引张力控制以及收卷的特殊要求。结果表明:采用Φ150低剪切分离型螺杆可以很好地加工长支链茂金属树脂;采用新型中心进料机头和自动横向厚度控制系统可以提高PO膜的厚度均匀性,满足涂覆的要求;采用S型牵引装置可以解决宽幅牵引夹紧时两头紧、中间松的"哈壳"现象;采用摆动折叠方法可以解决宽幅膜较难卷绕的有关问题。试验表明,幅宽10 m以上的PO膜并非不可生产,配置合理、技术先进的PO涂布膜机组可以生产幅宽14 m的PO膜。     

Effects of film thickness and inhibitor concentration on the sorption and thermal polymerization of acrylic acid in low-density polyethylene

We investigated the effects of hydroquinone monomethyl ether concentration and film thickness upon the thermal polymerization of acrylic acid on low-density polyethylene. The thermal polymerization of acrylic acid on low-density polyethylene depended on the concentration of hydroquinone monomethyl ether inhibitor. It was a free-radical reaction with initiation on the film surface and then proceeding to the bulk matrix. The process was not controlled by monomer diffusion for the range of film thickness of 90–200 μm. It became a diffusion-controlled process at higher film thicknesses ( > 200 μm). A film layer of up to 100 μm was proposed as the limiting thickness for a diffusion-free process. © 1993 John Wiley & Sons, Inc.     

Ozone-oxygen gas enhanced passivation of pure iron

Pure iron samples were passivated in borate buffer solution and were exposed to ozone-oxygen gas to study the possibility of improving the surface nanostructure such as atomically flat terrace structure. The treated samples were analyzed with spectroscopic ellipsometry and scanning tunneling microscopy, and the test of corrosion resistance was also carried out. The thickness of the oxide film increased by passivation at 800 mV (Ag/AgCl) and increased by ozone-oxygen gas exposure, but the oxidation film thickness decreased in air due to the reconstruction after rapid growth of oxides by passivation. The reconstruction of the oxide film was estimated by the change of the film thickness and compositions which were analyzed by spectroscopic ellipsometry using several layer models of Fe(OH)₃, γ-Fe₂O₃ and Fe₃O₄ and so on. The widest terrace width of the oxidation film was obtained on large particles based on the reconstruction after the combination treatment of passivation at 800 mV as well as subsequent ozone-oxygen gas treatment. The terrace width of the oxide film after passivation and ozone-oxygen gas treatment was three times larger than that of air-formed oxide film. The terrace width with atomic scale flatness was correlated with the corrosion resistance except for the increase in oxide film thickness.     

An ellipsometric study of anodic passivation of nickel in borate buffer solution

Ellipsometric and electrochemical measurements of the anodic passivation and secondary passivation films on nickel in borate buffer solution at pH 8·42 were made. The reference bare surface, obtained by cathodic reduction of electropolished nickel, gives the optical constants N₃ = 1·65?3·81 i for nickel. In the passivity region, where a little dissolution of nickel occurs, the surface film has the optical constants N₂ = 2·7?0·25 i and the film thickness as estimated by ellipsometry increases linearly with rise of the potential, from 4 to 13 Å, which is in fairly good agreement with the coulometrically estimated film thickness. In the oxygen evolution region, secondary passivation occurs with an abrupt increase in both optical constants and thickness of the surface film.The anodic passivation of nickel is compared with that of iron in terms of thickness of the surface film as a function of potential.