Surface Of Alumina Substrate Research Articles

The fusion process of successive droplets impinging onto a substrate surface

Successive deposition of uniform metal droplet is a new kind of 3D printing and rapid prototyping technology. This paper presents a systematic numerical investigation of the transient transport phenomenon during the fusion of successive droplets impinging onto a substrate surface. The physical mechanisms of the fusion process, including the bulk liquid, capillarity effects at the liquid–solid interface, heat transfer, and solidification, are identified and quantified numerically. The 3D models based on a volume of fluid method were developed to investigate the successive deposition of molten metal droplets on a horizontally aluminum substrate surface. The numerical models are validated with experiments. The comparison between numerical simulations and experimental findings shows a good agreement. The effects of relative distances between two successive molten droplets on the end-shapes of impact regime are examined. This investigation is essential to implement effective process control in metal micro-droplet deposition manufacture.

Low friction Ti-B coatings deposited by dual beam IBAD method for wear resistant applications

Thin Ti-B coatings of 500 nm in thickness were deposited by dual beam ion beam assisted deposition method (DB IBAD) on the surfaces of sintered α-Al2O3 (with 1% vol. MgO) cutting inserts. Deposition of Ti-B coating was conducted in vacuum. Two beams of Ar+ ions were applied of the same energy of ~10 keV. First ion beam was directed to TiB2 target at angle 67 and used for sputtering, the second one was directed perpendicularly to the surface of alumina substrate. XPS was applied to investigate chemical bonds in Ti-B coatings. Detailed spectra of B1s and Ti 2p indicated the presence of TiB2, TiO2 and B2O3. Mechanical properties of coated and uncoated alumina composites were examined by nanoindentation test using diamond indenter of Berkovich-type geometry, loaded in range 0.5 mN to 50 mN. The frictionwear performance of coated alumina were examined in ball-on-disc test using an alumina and a 100Cr6 steel balls as counterparts, loaded at 1 N. Cutting test was carried out in longitudinal turning of 100Cr6 steel shaft without use of any liquid coolant. Coated alumina inserts were harder and more resistant to wear than uncoated ones. The highest hardness of 45 GPa, was calculated by Oliver & Pharr method for coated sample tested under the load of 1 mN. It was almost 3 times the value calculated for uncoated substrate (16.5 GPa). The wear mechanism of Ti-B coated alumina was of abrasive type with alumina ball and of mixed abrasive and adhesive type in the case of friction contact with the steel ball. SEM observation of the surface of Ti-B coated alumina tools after turning revealed the presence of a liquid phase at the worn edge.

Study of Cerium-modified Triazinedithiol Electrodeposited Nanofilm on Corrosion Protection for Aluminum Alloy

The cerium-modified polymeric nanofilm of 6-(N,N-dibutyl)amino-1,3,5-triazine-2,4-dithiol monosodium (DBN) was fabricated by two-step potential electrodeposition onto aluminum alloy for corrosion protection. The structure, surface wettability and corrosion protection of the polymeric nanofilm were investigated by means of fourier transform infrared spectroscopy (FT-IR), water contact angle (WCA), open-circuit potential (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), respectively. FT-IR result revealed that DBN monomer had successfully been polymerized on aluminum alloy surface by electrochemical deposition in the absence and presence of cerium and the addition of cerium had no influence on FT-IR of the polymeric nanofilm. The result of surface wettability showed that WCA of aluminum alloy cerium-modified polymeric nanofilm was slightly higher compared with that without cerium. Electrochemical measurements demonstrated that the cerium-modified polymeric nanofilm on aluminum alloy surface exhibited remarkable corrosion protection property, which could be ascribed to the precipitation of cerium oxides or hydroxides on aluminum surface or the coordination between cerium and heterocyclic π-electron in polymeric nanofilm to prevent corrosive particles to the surface of aluminum substrate.

Mechanism of Migration of Sintered Nanosilver at High Temperatures in Dry Air for Electronic Packaging

Low-temperature joining of semiconductor chips by sintering of silver paste is emerging as an alternative lead-free solution for die-attaching power electronic device, particularly for high-temperature applications. However, migration of sintered nanosilver should be fully understood for reliability evaluation. In this paper, we reported our findings and possible mechanism on high-temperature migration of sintered nanosilver on alumina substrate. Oxygen plays an important role in the migration of sintered nanosilver at high temperatures. The migrating silver bridges were presented as discrete silver particles on the surface of alumina substrate. The discrete silver particles preferentially emerged at the boundaries of the alumina particles at the initial stage. The mechanism would be useful to alleviate the migration of sintered nanosilver at high temperatures.

Preparation of Micro/Nano-Structure Superhydrophobic Film on Aluminum Plates Using Galvanic Corrosion Method

A simple and novel approach has been developed to obtain a microporous film with compound nanoparticles on the surface of aluminum alloy substrate using the galvanic corrosion method. The wettability of the surface changes from hydrophilicity to superhydrophobicity after chemical modification with stearic acid (SA). The water contact angle (WCA) and sliding angle (WSA) of superhydrophobic aluminum alloy surface (SAAS) are 154 degrees and 9 degrees, respectively. The roughness of the aluminum substrate increases after the oxidation reaction. The porous aluminum matrix surface is covered with irregularly shaped holes with a mean radius of about 15 microm, similar to the surface papillae of natural Lotus leaf, with villus-like nanoparticles array on pore surfaces. The superhydrophobic property is attributed to this special surface morphology and low surface energy SA. X-ray powder diffraction (XRD) pattern and Energy Dispersive X-Ray Spectroscopy (EDS) spectrum indicate that Al2O3, Al(OH)3 and AIO(OH) has been formed on the surface of aluminum substrate after the oxidation reaction. The Raman spectra indicate that C-H bond from SA and the Al-O are formed on the SAAS. The as-formed SAAS has good stability.

Mechanical metallization of alumina substrate through shot impact treatment

Abstract The present study examines the potentialities of a novel surface treatment process for the metallization of ceramics. The process combines the principles of ball milling and shot peening using the energy of ultrasonic vibrations. Experiments were performed by using alumina and powdered nickel as a ceramic substrate and metallizing agent, respectively. The main emphasis was placed on characterizing the deposited films and elucidating their formation mechanisms. The results showed that 3-min impact treatment at ambient temperature and pressure leads to the formation of 2–4 μm thin, dense, and highly adherent films of nanostructured Ni on the surface of alumina substrate. SEM and TEM observations revealed a very tight contact between the deposited films and substrate suggesting the shot-impact induced plastic flow in the Ni film. It is assumed that the van der Waals interaction is the main origin of the high adhesion strength observed.

Effect of Substrate Wettability and Surface Structure on Nucleation of Crystal

The heterogeneous nucleation behaviors of NH4Cl crystal on rough aluminum substrate surface immerged in NH4Cl-H2O solution were experimentally analyzed, and the influence mechanism of the micro/nano-scale surface structures on heterogeneous nucleation was investigated. It has been shown that wettability and nucleation are affected by substrate surface condition. The intrinsic wetting properties between nucleus and substrate surface, and the surface structure of certain geometrical scales, both impose effects on the heterogeneous nucleation properties. For a nucleus-wetting substrate surface, heterogeneous nucleation is promoted by a higher complexity of the surface morphology; but for a nucleus-nonwetting substrate surface, heterogeneous nucleation is inhibited by a higher complexity of the surface morphology.

Effect of ion cleaning pretreatment on interface microstructure, adhesive strength and tribological properties of GLC coatings on Al substrates

In this work, a series of ion cleaning procedures (bias and time) were performed on aluminum substrate surface prior to the deposition of graphite-like carbon (GLC) coatings. Special attention has been paid on the interface microstructure, coating/substrate bonding strength and tribological properties. It was found that ion cleaning critically influenced the adhesion and the wear resistance of GLC coatings. The optimization of ion cleaning pretreatment revealed that 400 V/30 min is the best ion cleaning conditions. HRTEM observations on the interfacial region showed that the oxide layer has been removed completely, a strong bonding diffusion interface formed. However, for the low energy ion cleaning (300 V/10 min), TEM observations on the interfacial region between the coating and the Al substrate showed that the oxide contamination still existed. The optimization of GLC layer thickness revealed that the GLC coating with 1 μm GLC layer exhibited the highest critical load and the lowest friction coefficient of 14.7 N and 0.065, respectively.

Microstructures and photocatalytic properties of porous ZnO films synthesized by chemical bath deposition method

Different porous ZnO film structures on the surface of alumina substrates were prepared through a simple chemical bath deposition method in the methanolic zinc acetate solution. The surface morphology and phase structure of porous ZnO film were determined by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Both initial zinc acetate concentration and sintering temperature have great impact on the final film structures. With the increase of initial zinc acetate concentration, the porous structures can be finely tuned from circular nest like assemblies composed film into successive nest like film, and finally to globular aggregates composed film. By increasing the sintering temperature, the porous structure of successive nest like film can be further controlled. Furthermore, the crystallinity of photocatalysts also can be greatly improved. The photodegradation results of Methyl Orange revealed that porous ZnO film with successive nest like structure sintered at 500°C exhibited the highest photocatalytic activity under UV illumination.

Orthogonal Fluxgate Sensor Fabricated With a Co-Based Amorphous Wire Embedded Onto Surface of Alumina Substrate

The orthogonal fluxgate sensor with a novel structure is presented in this paper for the first time. To overcome a weakness (tiny and flexible) of an amorphous wire in mass production, the sensor proposed in this study is composed of a pickup coil and a CoFeSiB amorphous wire which was embedded onto the surface of alumina substrate. We demonstrate that the fundamental mode operation can be achieved, and the sensitivity is enhanced by adding a suitable bias to excitation current. We present there is a close correspondence between the impedance resonance frequency and the optimal frequency of the sensor output. This can be explained with the equivalent circuit of the pickup coil and the maximum power transfer theorem. The experimental result says the operation frequency has to be decided by measuring the impedance of the pickup coil. The maximum sensitivity of the fabricated sensor at the optimal operation frequency is 0.8 V/Oe with the excitation current of 25 mA and DC bias of 15 mA.

Super Smooth Modification of Al2O3 Ceramic Substrate by High Temperature Glaze of CaO–Al2O3–SiO2 System

The rough surface of ceramic substrate is an obstacle for the scale down of line-width for thin film passive integrated devices (PID). In this paper, a modification method for Al2O3 ceramic substrate with super smooth in surface was proposed. Coating a layer of CaO–Al2O3–SiO2 (CAS) glass was performed to flat the rough surface of alumina substrate by sol–gel method. It was found that addition of 0.06% V2O5 can inhibit the recrystallization of the glaze. The root-mean-square (RMS) roughness of the glazed substrates reached a surprising flatness as small as 0.5 nm, and its melting temperature is higher than 1300 °C. This substrate with super flatness and high temperature endurance may be promising for high performance thin film devices.

Effect of Surfactants on the Morphologies of ZnO Nanostructures Synthesized by Hydrothermal Method and its Gas Sensitivity to Formaldehyde

Based on the principle of the higher surface-to-volume ratios, the higher formaldehyde gas sensitivity, different morphologies’s ZnO nanostructures have been synthesized by hydrother- mal method using different surfactants including polyvinyl alcohol (PVA), cetyltrimethyl ammon- ium bromide (CTAB), sodium tripolyp hosphate (STPP) and citric acid(CA). The crystal structur- es and morphologies were characterized by XRD and FESEM. The results show that different morphologies’s ZnO nanostructures were induced on the surface of alumina substrate, and the surfactants had an important effect on the morphologies of ZnO nanostructures and then affected the formaldehyde gas sensitivity. The ZnO nanorods with diameters of 100-500 nm and lengths of 200-900nm were obtained using PVA surfactant. The ZnO nanosheets with thickness of about 10nm were obtained using CTAB surfactant. The ZnO nanodisks with two layers and thickness of 5-10nm were obtained using STPP surfactant. The ZnO microspheres composed of thin flakes with thickness of about 10 nm were obtained using CA surfactant. The growth mechanisms of different morphologies’s ZnO nanostructures using different surfactants were given in detail. In addition, the formaldehyde gas sensitivities of different morphologies’s ZnO nanostructures were measured and showed the higher formaldehyde gas sensitivity compared with nano-ZnO without surfactant.

Method of Applying DLC Coating on Aluminum Alloys

A method was developed for applying a diamond-like carbon (DLC) coating on aluminum alloys to obtain sufficient adhesion strength and wear resistance. The key points of this technology consist of two main processes. First, the surface of the aluminum substrate is modified by forming a top layer of dispersed fine tungsten particles on a mechanically hardened layer obtained in a fine tungsten particle shot-peening process. Second, the sharp top edges formed by the shot-peening process are polished lightly to remove them. A DLC film is then coated on the aluminum substrate by plasma chemical vapor deposition (PE-CVD). The adhesion strength and wear resistance of the DLC film were evaluated in sliding tests under a continuously increasing load. The critical load, which was defined as the load where the friction coefficient increased markedly, was compared for three types of DLC-coated samples. One sample had the DLC film coated directly on the smooth surface of aluminum substrate after polishing; another had the DLC film coated on the rough surface following tungsten shot-peening; the third had the DLC film coated on the substrate surface with plateau roughness obtained by polishing the top edges lightly after the shot-peening process. The critical load of the DLC coating on the substrate with light polishing after the tungsten shot-peening process was 40-70% higher than that of the coating on the polished substrate, while that of the coating on the substrate subjected only to tungsten shot-peening was markedly lower.

Influence of Ion Bombardment Process on Adhesion between CrN Coatings and Aluminum Alloy

Scratch tests were carried out to examine the influence of gas pressure during ion bombarding on adhesion between CrN coatings and aluminum alloy using nitrogen and argon gas. The critical load clearly increased with increasing the nitrogen gas pressure. However, argon gas pressure hardly affected the critical load. The result of SIMS showed that ion bombardment in nitrogen gas generated high Cr content layer at the aluminum substrate surface and the Cr content increased with increasing the pressure. The ion bombardment in argon gas generated low Cr content surface layer and the pressure hardly affected the critical load. Thus, the high Cr content layer by ion bombardment in the high nitrogen pressure improved adhesion between CrN coatings and aluminum alloy

8% Efficient thin‐film polycrystalline‐silicon solar cells based on aluminum‐ induced crystallization and thermal CVD

AbstractA considerable cost reduction could be achieved in photovoltaics if efficient solar cells could be made from polycrystalline‐silicon (pc‐Si) thin films on inexpensive substrates. We recently showed promising solar cell results using pc‐Si layers obtained by aluminum‐induced crystallization (AIC) of amorphous silicon in combination with thermal chemical vapor deposition (CVD). To obtain highly efficient pc‐Si solar cells, however, the material quality has to be optimized and cell processes different from those applied for standard bulk‐Si solar cells have to be developed. In this work, we present the different process steps that we recently developed to enhance the efficiency of pc‐Si solar cells on alumina substrates made by AIC in combination with thermal CVD. Our present pc‐Si solar cell process yields cells in substrate configuration with efficiencies so far of up to 8·0%. Spin‐on oxides are used to smoothen the alumina substrate surface to enhance the electronic quality of the absorber layers. The cells have heterojunction emitters consisting of thin a‐Si layers that yield much higher Voc values than classical diffused emitters. Base and emitter contacts are on top of the cell in interdigitated finger patterns, leading to fill factors above 70%. The front surface of the cells is plasma textured to increase the current density. Our present pc‐Si solar cell efficiency of 8% together with the fast progression that we have made over the last few years indicate the large potential of pc‐Si solar cells based on the AIC seed layer approach. Copyright © 2007 John Wiley & Sons, Ltd.

Bonding strength investigation of plasma-sprayed HA coatings on alumina substrate with porcelain intermediate layer

Hydroxyapatite (HA) has recently been used as a bone substitute in orthopedic and dental surgery applications, owing to its excellent biocompatibility. However, the poor mechanical properties of HA limit the material's application in the loading condition. In this study, HA was coated onto the surface of alumina substrate, with a view to overcome the poor mechanical properties of HA and the biocompatibility of alumina. Improvement of the bonding strength of HA coatings to alumina substrate was attempted by adding a bond coat of porcelain via plasma-spraying and by post-heat-treatment. HA–50 wt% porcelain and pure porcelain were used to manufacture two kinds of bond coat before HA coating, and then all the specimens were heat-treated at 750, 800, 850, and 900 °C for 0.5 h. The results shows that the bond strength between HA coating and Al 2O 3 substrate could be improved by employing the porcelain as the bond coat after the heat-treatment. The strengthening mechanisms of the two systems are discussed.

2410 CrN薄膜/アルミニウム基板界面の性状に及ぼすイオンボンバード処理の影響(S09-2 新表面改質技術と界面,環境,S09 表面改質)

Scratch tests were carried out to examine the influence of gas pressure during ion bombarding on adhesive strength between CrN coatings and aluminum alloy using nitrogen and argon gas. The critical load clearly increased with increasing the nitrogen gas pressure. However, the influence of argon gas pressure on the critical load was small. As the results of AES analysis, ion bombardment in nitrogen gas generated Cr layer for low pressure and CrN layer for high pressure at the aluminum substrate surface and the thickness of the Cr and CrN layer increased with increasing the pressure. In contrast with this, ion bombardment in argon gas generated thinner Cr surface layer than that in nitrogen gas at the same pressure. The adhesive strength improved for thick CrN layer which was generated by ion bombardment in the high nitrogen pressure.

Electrochemical behavior of a novel palladium pentacyanonitrosylferrate modified aluminum electrode

Novel inorganic film modified electrodes have been prepared by chemical deposition of a thin palladium pentacyanonitrosylferrate (PdPCNF) film on the surface of aluminum substrate. The modification process including the electroless deposition of metallic palladium on the aluminum electrode surface from PdCl 2+25% ammonia solution and chemical derivatization of deposited palladium to the PdPCNF film in 0.1 M Na 2[Fe(CN) 5NO]+0.5 M KNO 3+HNO 3 solution (pH 1.5–2.5), are described. The aluminum-based modified electrodes exhibit, one pair of well-defined voltammetric peaks which correspond to the Fe(III)/Fe(II) transition in complex structure. The effect of pH, ammonium, alkali metal and alkaline earth metal cations of supporting electrolyte on the electrochemical characteristics of the modified electrode was studied in detail. Diffusion coefficients of hydrated ammonium and alkali metal cations in the film (D), transfer coefficient ( α) and transfer rate constant for electron ( k s), were determined. The high stability of this modified electrode makes it attractive in practical application.

Electrocatalytic Characteristics of Thiosulfate Oxidationat Nickel Plated Aluminum Electrode Modified with Nickel Pentacyanonitrosylferrate Films

Nickel pentacyanonitrosylferrate (NiPCNF) films have been deposited on the surface of aluminum substrate by a simple electroless dipping method. The cyclic voltammogram of the resulting surface modified Al electrode prepared under optimum conditions, shows a well-behaved redox couple due to the [NiIIFeIII/II(CN)5NO]0/–1 system. The NiPCNF films formed on the Al electrode show electrocatalytic activity towards the oxidation of thiosulfate in sodium nitrate solution. A linear calibration plot is obtained over the thiosulfate concentration range 5–110 mM and 0.001–100 mM, using linear sweep voltammetry and hydrodynamic voltammetry (at a fixed potential and stirred solutions), respectively. The kinetics of the catalytic reaction were investigated using cyclic voltammetry, rotating disk electrode (RDE) voltammetry and chronoamperometry. The results were explained using the theory of electrocatalytic reactions at chemically modified electrodes. The average value of the rate constant for the catalytic reaction evaluated by the three different approaches, is 9×10−3 cm s−1. Further examinations of the modified electrodes show that the modifying layers (NiPCNF) on the aluminum substrate show reproducible behavior and a high level of stability.

A nucleation mechanism for diamond film deposited on alumina substrates by microwave plasma CVD

Diamond films were deposited on alumina substrates by a microwave plasma chemical vapor deposition (MPCVD) method. It is shown that by using appropriate pre-treatments, such as polishing the substrate surface carefully and by in situ pre-deposition of a carbon layer on the alumina substrate surface, one can significantly enhance the nucleation of diamond. The mechanism of the process has been considered using a droplet model with a quasi-equilibrium approximation.