Numerical Investigation of Substrate Melting and Deformation During Thermal Spray Coating by SPH Method

The fluid–solid coupling model is developed to simulate substrate melting and deformation during molten droplet impact. In this model, the liquid and solid parts of splat and substrate are governed by the SPH formulations of the Navier–Stokes equations and the conservation equations of continuum mechanics, respectively. This is the first time that the fluid–solid coupling by the SPH method is applied to simulation of the interaction between droplet and substrate during thermal spray coating. The simulation results on formation of the crater are presented to study the Ni droplet impacting onto the Sn substrate, and Mo droplet impacting onto the Steel, Al, and Brass substrates, respectively. It is found that the initial temperatures and thermal properties of droplet and substrate have great effects on the substrate melting and the morphologies of the splat and the substrate.     

The Solution Precursor Plasma Spray Coatings: Influence of Solvent Type

The influence of solvent type on splat formation and coating microstructure using the Solution Precursor Plasma Spray process was studied. Droplet with a high surface tension and high boiling point solvent experiences incomplete solvent evaporation process in the plasma jet leading to a porous coating. Droplet created from a low surface tension and low boiling point solvent undergoes rapid solvent evaporation, solute precipitation, pyrolysis, melting process in the plasma jet and forms splat upon impacting on the substrate; the build-up of splats results in a dense coating.     

Toward the Achievement of Substrate Melting and Controlled Solidification in Thermal Spraying

The substrate is usually kept at a distant location in traditional thermal spraying, and substrate melting, which can improve splat adhesion usually does not happen. By moving the substrate close to the plasma flame and attaching a temperature control device to the backside of the substrate, as well as by additional heating from the molten droplets, substrate melting may occur and directional splat solidification becomes possible. In this proposed design, the substrate temperature is controlled by spray distance, flame temperature and initial substrate temperature. The variations of particle in-flight characteristics and contact interface temperature on spray distance are investigated. Optimal operating conditions are determined.     

Parameters controlling the generation and properties of plasma sprayed zirconia coatings

D.C. plasma jets temperature and velocity distributions as well as the arc root fluctuations at the anode were studied for Ar-H₂ (25 vol%) plasma forming gases. The parameters were the arc current up to 700 A, the total gas flow rate up to 100 slm, and the nozzle diameter which was varied from 6 to 10 mm. The trajectories of partially stabilized zirconia particles into the jet were studied by a 2D laser imaging technique and two fast (100 ns) two color pyrometers. The results have revealed the difficulty to inject small particles into the plasma flow since most were found to by-pass the jet rather than penetrate it. The results also show the broad trajectory distribution within the jet and the influence of the arc root fluctuations on the mean particle trajectory distribution within the jet. Beside the measurements of the particle surface temperature and velocity distributions in flight, the particle flattening and the cooling of the resulting splats were studied statistically for single particles all over the spray cone. Such studies have emphasized the drastic influence of the substrates or previously deposited layers temperature on the contact between them and the splats. At 200–300°C this contact is excellent (cooling rates of the order of 100 K/μs for 1 μm thick splats) and it results in a columnar growth within the splats and the layered splats of a bead (up to 500 layered splats). This growth can be observed through passes provided the bead surface temperature has not cooled too much (a few tens of K) before the next bead covers it. A/C values up to 60 MPa were achieved with PSZ coatings. The effect of impact velocity of the particles, of substrate preheating temperature, of relative movments torch to substrate, of substrate oxidation on A/C values and splat formation were also studied.     

水/甲苯界面制备均匀可循环SERS基底

采用在沸水浴中还原硅酸钠的方法制备壳层约4nm的Au@SiO2核壳纳米粒子,利用水/ 甲苯两相界面诱捕出其单粒子层膜并将这层膜转移到Si片上.作为对比,采用化学方法自组装Au@SiO2膜至ITO玻璃表面. 以1,4-对苯二硫作为探针分子考察了它们的SERS活性以及可循环使用性能. 研究结果表明,Au@SiO2核壳粒子可避免待测分子与基底直接接触,NaBH4溶液可作为基底循环的洗涤剂,经化学组装的基底的可循环性能较差,每次洗涤SERS效应均有一定程度降低,而两相界面形成的单粒子致密膜的SERS效应稳定性较好,其循环性能较高,即使洗涤10次后,SERS效应仍未明显降低,此膜可作为循环使用的SERS基底.     

On the spreading and solidification of molten particles in a plasma spray process effect of thermal contact resistance

The spreading and simultaneous solidification of a liquid droplet upon its impingement onto a substrate permitting thermal contact resistance has been numerically simulated; the effect of contact resistance and the importance of solidification on droplet spreading are investigated. The numerical solution for the complete Navier-Stokes equations is based on the modified SOLA-VOF method using rectangular mesh in axisymmetric geometry. The solidification of the deforming droplet is considered by a one-dimensional heat conduction model. The predictions are in good agreement with the available experimental data and the model may be well suited for investigating droplet impact and simultaneous solidification permitting contact resistance at the substrate. We found that the final splat diameter could be extremely sensitive to the magnitude of the thermal contact resistance. The results also show that for the condition of higher Reynolds and/or higher Stefan numbers the effect of solidification on the final splat diameter is more important.     

Impact dynamics of colloidal quantum dot solids

We use aerosol techniques to investigate the cohesive and granular properties of solids composed of colloidal semiconductor nanocrystals (quantum dot solids). We form spherical agglomerates of nanocrystals with a nebulizer and direct them toward a carbon substrate at low (~0.01 m/s) or high (~100 m/s) velocities. We then study the morphology of the deposit (i.e., the "splat") after impact. By varying the size of the agglomerate and the spacing between the nanocrystals within it, we observe influences on the mechanical properties of the quantum dot solid. We observe a liquid-to-solid transition as the nanocrystals become more densely packed. Agglomerates with weakly interacting nanocrystals exhibit liquidlike splashing and coalescence of overlapping splats. More dense agglomerates exhibit arching and thickening effects, which is behavior typical of granular materials.     

Experimental and Theoretical Study of the Impact of Alumina Droplets on Cold and Hot Substrates

A complex experimental set-up was built to study the impact of liquid alumina droplets on different substrates (stainless steel 304L, sintered alumina, carbon–carbon) kept at temperatures up to 2100 K. The impact behavior: rebound, deposition, splashing, spattering was systematically studied as well as the resulting splat shapes. The set-up consists in a controlled atmosphere chamber where molten alumina particles with diameters between 10 and 90 m, are produced by a d.c. plasma torch, substrates being heated by a second d.c. plasma torch. In such conditions, it was possible to achieve particle temperatures between 2300 and 4200 K with velocities in the range 50 to 300 m/s. The particle behavior at impact was characterized by the Sommerfeld parameter K (K=We^1/2 Re^1/4 We and Re being respectively the Weber and Reynolds numbers of impacting particles). It was possible to vary K between 3 and 1300. Low K values were obtained by tilting the substrate up to 60°. The parameters of a single particle at impact were measured: its velocity v_p and diameter d_p by Phase Doppler Anemometry (v_p=5%, d_p=10%) and its temperature T_p by fast (100 ns) two color pyrometry (T_p=15%). The particle impact was visualized by a fast camera coupled to a microscope (exposure delay time 50 ns . . .100 ms) with complex synchronization and light intensity problems. To solve the latter, the impacting particle had to be illuminated with a 2 W c.w. Ar⁺ laser at 488 nm. Unfortunately, the controlled atmosphere chamber did not allow to change the substrate after each particle impact. Starting from a smooth surface for the first impact, due to the successively deposited splats, rapidly droplets impacted on a rough surface (Ra5 m). For splats collected on a hot alumina substrate (2100 K), where flattening is completed before solidification starts (case similar to that of ethanol droplets on cold copper) deposition occurs for K between 4 and 90 while splashing occurs for K as low as 30. These results are slightly different from those related to the ethanol droplet for which deposition occurs for 357.7. This could be due to the precision of measured values and the rough surface. For splats collected in spraying conditions splashing is always the rule K values up to 1400) especially on rough surfaces. However the particle impact velocity and temperature, the substrate temperature and tilting plays an important role on the resulting splat diameters, distortion and elongation rates. The question which is still pending is which quantity of splashed material is incorporated within the constructing coating and how does it affect its thermophysical properties.     

Substrate effect on the melting temperature of gold nanoparticles

Previous experimental, molecular dynamics, and thermodynamic researches on the melting temperature of Au nanoparticles on tungsten substrate provide entirely different results. To account for the substrate effect upon the melting point of nanoparticles, three different substrates were tested by using a thermodynamic model: tungsten, amorphous carbon, and graphite. The results reveal that the melting point suppression of a substrate-supported Au nanoparticle is principally ruled by the free surface-to-volume ratio of the particle or the contact angle between the particle and the substrate. When the contact angle θ is less than 90°, a stronger size-dependent melting point depression compared with those for free nanoparticles is predicted; when the contact angle θ is greater than 90°, the melting temperature of the supported Au nanoparticles are somewhat higher than those for free nanoparticles.     

水/正己烷界面上超声波介导组装金纳米粒子薄膜用作SERS基底

本文以高能量的超声波作用于溶胶/疏水溶剂两相体系, 使溶胶相中的纳米颗粒先被加速吸附到乳液油滴的小表面. 随着乳液油滴向上转移, 在界面处破乳, 纳米颗粒就被释放到水/油界面上来, 形成自组装纳米薄膜. 尽管这种组装机制尚不完全清楚(如超声波是否确实如预期那样可以提高纳米粒子的动能), 但这种方法不需要预先对纳米粒子表面疏水修饰, 也不需向体系中添加表面活性有机小分子或电解质等诱导剂, 可快速有效制备表面“洁净”的纳米粒子薄膜, 并可用作高活性SERS基底.     

聚合物基板表面状态对异相接枝的影响研究

研究了对于羟丙基纤维素（HPC）基板进行表面修饰时,基板表面状态的调控 对基板表面化学接枝的影响。用双官能团化合物2,4-甲苯二异氰酸酯（TDI）作为 接枝桥梁,其对位的异氰酸酯基先和基板上的羟基反应,保留的邻位异氰酸酯基进 一步再与丙烯酸的羟基反应,让接枝在基板上的活性丙烯酸分子继续和丙烯酸溶液 聚合,通过这种途径在基板表面修饰聚丙烯酸。基板制备时,由于不同介质对HPC 基板表面的不同诱导作用,导致表面组成各异,大大影响了接枝反应的效果。红外 光谱和二次离子飞行时间质谱均证明了可以用2,4-甲苯-二异氰酸酯（TDI）分子 做接枝桥梁在基板表面异相接枝上羟基并进一步接枝聚丙烯酸,从而达到修饰基板 的目的。     

基板界面对PS/PMMA共混物薄膜相逆转组成比的影响

近年来高分子共混体系中的界面、表面效应逐渐引起了越来越多研究者的兴趣 .人们发现 ,当共混物薄膜厚度减至一定程度时 ,聚合物共混物薄膜中的相形态、相容性及相分离动力学与本体中有较大的不同[1～ 3] .基板界面作用对共混薄膜体系的热力学、动力学行为产生很大的影响 .我们以往的研究 [4 ,5]也发现 ,PP/EVAc(70 /30 )共混体系退火过程中 ,基板界面 (如玻璃 )作用可大大加速分散相(EVAc)粒子的粗化凝聚过程 .本研究用聚甲基丙烯酸甲酯和聚苯乙烯共混物的四氢呋喃溶液在不同基板介质 (如玻璃基板 ,PP基板 )上成膜 ,用相差显微镜观测了…     

Substrate role in coating of microfibrillated cellulose suspensions

Interest in nanocellulose-based coatings for packaging applications has been growing due to their excellent oil and gas barrier properties combined with their sustainable, recyclable, biodegradable, and non-toxic nature. Coating of nanocellulose materials such as microfibrillated cellulose (MFC) on paper/paperboard is challenging compared to traditional paper coating materials due to excessively high viscosity and yield stress of MFC suspensions at rather low solids content, typically below 5%. Possessing large amounts of water and a distinct rheological behavior such suspensions set tough demands on the substrate to be coated. It is important to understand and quantify substrate requirements in order to coat these suspensions successfully and achieve a satisfactory coating quality. A custom-built slot geometry is used herein to enable coating of highly viscous MFC suspensions on different paper-based substrates in a roll-to-roll process. The impact of substrate properties, such as surface chemistry and surface energy, surface roughness and surface porosity, and water absorption capacity on MFC coatability and coating quality is reported. Coating adhesion to the substrate was quantified with surface strength testing of MFC coated substrates. Various techniques, such as Scanning Electron Microscopy, IGT print penetration tests, and air permeability tests were employed for measuring coating coverage and surface porosity. MFC coating was found to adhere best to a highly hydrophilic surface, whereas the most uniform and defect-free film at low coat weights was formed on a smooth surface. It was also found that the MFC coat weight needed for full coverage, and therefore potentially good barrier, needs to exceed the surface roughness volume of the substrate. Water absorption capacity of the substrate also determines the final MFC coating quality obtained. The results clearly highlight the role of paper-based substrate for successful and effective coating of the micro and nanocellulose suspension.     

Reverse micellar aggregates: effect on ketone reduction. 1. Substrate role

The reduction of three aromatic ketones, acetophenone (AF), 4-methoxyacetophenone (MAF), and 3-chloroacetophenone (CAF), by NaBH(4) was followed by UV-vis spectroscopy in reverse micellar systems of water/AOT/isooctane at 25.0 degrees C (AOT is sodium 1,4-bis-2-ethylhexylsulfosuccinate). The first-order rate constants, k(obs), increase with the concentration of surfactant due to the substrate incorporation at the reverse micelle interface, where the reaction occurs. For all the ketones the reactivity is lower at the micellar interface than in water, probably reflecting the low affinity of the anionic interface for BH(4)(-). Kinetic profiles upon water addition show maxima in k(obs) at W(0) approximately 5 probably reflecting a strong interaction between water and the ionic headgroup of AOT; at W(0) < 5 by increasing W(0) BH(4)(-) is repelled from the anionic interface once the water pool forms. The order of reactivity was CAF > AF > MAF. Application of a kinetic model based on the pseudophase formalism, which considers distribution of the ketones between the continuous medium and the interface, and assumes that reaction take place only at the interface, gives values of the rate constants at the interface of the reverse micellar system. At W(0) = 5, we conclude that NaBH(4) is wholly at the interface, and at W(0) = 10 and 15, where there are free water molecules, the partitioning between the interface and the water pool has to be considered. The results were used to estimate the ketone and borohydride distribution constants between the different pseudophases as well as the second-order reaction rate constant at the micellar interface.     

A Novel Method for Synthesis of ZSM‐5 Coatings on Monolithic Cordierite Substrate

ZSM‐5 coatings, have been synthesized onto a monolithic cordierite substrate by an environmental friendly and high coating selectivity method—Vapor Phase Transport (VPT). With this method, an aluminosilicate gel coated onto the monolithic cordierite substrate has been transformed into a ZSM‐5 layer under vapors of n‐butylamine and water, n‐Butylamine played a key role in the forming of ZSM‐5 layer on the cordierite substrate. The ZSM‐5/cordierite monolith composites prepared by this method were ion‐exchanged with Cu²⁺ and tested for the selective catalytic reduction of NO by propane. The deNO_x activities of Cu/ZSM‐5 monolith catalysts were not only dependent on the ion‐exchange methods, but also on the ZSM‐5 loading of the monolith catalysts. The best result was obtained over the Cu (B3)/ZSM‐5 monolith catalyst, which had a ZSM‐5 loading of about 13% and was prepared by a pressure exchange procedure. At a temperature of 723 K and a space velocity of 10,000 h^?1 (based on the monolith volume), 85% of NO conversion and 93% of C₃H₃ conversion were achieved over the Cu(B3)/ZSM‐5 monolith catalyst.     

聚乙酰亚胺涂敷单晶硅表面上全氟亏酸单层膜

Ultra-thin film of perfluorodecanoic acid expected to be excellent lubricant for micro-machines was prepared successfully on single crystal silicon substrate.The film was characterized by means of X-ray photoelectron spectroscopy (XPS) and contact-angle meter.The chemical reaction involved in the preparation of the ultra-thin film was discussed as well.After being immersed in a dilute aqueous solution of polyethyleneimine (PEI) for 15 minutes and rinsed with distilled water,the silicon substrate was coated with a thin film of PEI,which was then put into a dilute solution (1× 10－ 3 mol· L－ 1) of perfluorodecanoic acid in hexadecane.Subsequently the steady perfluorodecanoic acid ultra-thin film was developed on PEI coating in the presence of a covalent amide bond between carboxylic group and the primary or secondary amine groups of PEI.This process was accompanied by the contact angle changes of water droplet on the Si surface (see Table 1).Moreover,the reaction between perfluorodecanoic acid and PEI was significantly influenced by N,N′ -dicyclohexylcarbodiimide (DCCD).The contact angle on the ultra-thin film of perfluorodecanoic acid is only 66.3° in the absence of DCCD in the reacting solution; it rises to 89.4° in the presence of DCCD.This indicates that the reaction between perfluorodecanoic acid and PEI was accelerated by DCCD,and the quality of perfluorodecanoic acid ultra-thin film thus improved.XPS analysis of the ultra-thin film indicates that the derivatization of PEI with perfluorodecanoic acid was accompanied by several changes.First,a large and highly symmetrical F 1s peak appeared at 688.3 eV (C－ F*).Secondly,a new peak of N 1s appeared at 400.7 eV (chemical shift 1.4 eV),which was attributed to the N atom attached to the carbonyl group (O=C－ N*).Thirdly,three new peaks of C 1s appeared at 286.1 eV (chemical shift 1.5 eV),288.1 eV (chemical shift 3.5 eV),and 291.0 eV (chemical shift 5.4 eV),respectively.These C 1s peaks were attributed to the C atom attached to the O=C－ N group (O=C－ N－ C*),the carboxyl C atom (O=C*－ N),and the C atom in － CF3 group (C*－ F),respectively.Therefore it can be concluded that perfluorodecanoic acid has been chemically adsorbed onto the surface of PEI and perfluorodecanoic acid ultra-thin film prepared successfully.     

Inclined Substrate Deposition of Nanostructured TiO2 Thin Films for DSSC Application

Nanostructured TiO₂ films were deposited onto Indium Tin Oxide (ITO) and glass substrates by dc reactive magnetron sputtering at different substrate inclination angles. The structural and optical properties of the deposited films were studied by X-ray diffraction, scanning electron microscopy and UV–Vis spectrophotometer, respectively. Dye-sensitized solar cells (DSSC) were assembled using these TiO₂ films as photoelectrodes and the effect of the substrate inclination angle in the preparing process of TiO₂ films on the DSSC conversion efficiency was studied.     

The Effect of Substrate on the Annealing of Poly(butylene succinate) Single Crystals

The morphological evolution of poly(butylene succinate) (PBS) solution‐grown single crystals during annealing was studied using hot‐stage atomic force microscopy. Their morphology changed with increasing temperature and annealing time. The annealing behavior and melting temperature were found to be affected by the substrate. Morphological changes occurred at a much lower temperature on an amorphous carbon film than that on a mica surface. Moreover, the pattern of morphological evolution of the single crystals on a carbon film was different from that on a mica surface. Since the PBS melt had a larger contact angle on the mica surface, these differences in the melting behavior were ascribed to the different interfacial interactions between the chain‐folded surface of the single crystal and the substrate.

     

Structural Evolution of an Organic Semiconducting Molecule onto a Soft Substrate

The structural organization and evolution of the organic semiconducting molecule 2,7‐dioctyloxy[1]benzothieno[3,2‐b]‐benzothiophene on a soft matrix is studied. Thin films of a blend formed from polystyrene and the molecule were prepared by spin‐coating onto silicon substrates, which were subsequently studied by using a combination of microscopy and scattering techniques. The organic semiconducting molecule segregated to the surface and developed a phase with a different structure to the bulk, as in the case of a substrate induced phase observed previously. Under a solvent vapor annealing procedure, the growth of micrometer‐sized tetragonal crystals onto the polymer surface was observed, which was not evidenced for the silicon substrates.