Surface Of Alumina Substrate Research Articles

Laser etching ultra-black coating with novel anti-icing performance

Ultra-black coating has more than 99 % absorbance and is widely applied in aerospace, optical instruments, and solar industries. However, preparing the presently available ultra-black coatings requires high temperatures, significantly limiting their application. Based on a resin-matrix composite coating filled with carbon nanotubes (CNTs), this study provides a new method for preparing resin-matrix ultra-black coatings using laser etching technology at room temperature. The obtained results indicated that the laser etching process could effectively remove the pure resin film coated on the coating surface and change the light contact interface from air/resin to air/CNTs. The highest average absorption achieved by the coating was 99.49 %. The morphological characteristics prove that the laser etching changed the coating surface from a smooth resin to a porous microstructure. The porous microstructure played a significant role in light absorption and remarkably improved surface roughness and hydrophobicity. In addition, the excellent light absorption performance significantly improved the photothermal conversion, which translated to enhanced anti-icing and anti-frosting performance over an aluminum substrate. Under 1 sun illumination at −10 °C, the frozen time of water drop on the coating surface was 692 s, 11.2 times longer than that on an aluminum substrate surface. No frosting was observed on the coating surface after 600 s of testing. Furthermore, the coating also showed remarkable anti-icing and anti-frosting performance at −20 °C. Hence, the reported ultra-black layer demonstrated room-temperature synthesis and extremely high light absorbance, making it a promising candidate for various cold-weather applications.

Surface coating on aluminum substrate with polymeric guanidine derivative to protect jet fuel tanks from microbial contamination

Antimicrobial coatings can act as an effective barrier to microbial growth and colonization in jet fuel tanks, which can effectively avoid the safety problems and economic losses. In this study, we initially synthesized an antimicrobial and water-insoluble complex, poly (hexamethylene guanidine) hydrochloride-sodium stearate (PHMG-SS), and its minimum inhibitory concentrations (MICs) were measured as 0.25 g/L, 0.25 g/L, 0.25 g/Land 0.5 g/L against Escherichia coli , Staphylococcus aureus , Bacillus subtilis and Yarrowia lipolytica , respectively; then, PHMG-SS was facilely coated onto the surface of aluminum substrate by the aid of a green linker, polyvinyl butyral (PVB). The PHMG-SS-coated aluminum exhibited a powerful microbicidal activity against the above four microorganisms , and provided a greater than 99.999% (5 log) reduction in viable counts of experimental microorganisms within 30 min through contact. In addition, the antimicrobial performance could still be observed after 7 d of ultraviolet radiation or soaking in jet fuel. Furthermore, the antimicrobial mechanism was investigated and concluded as damaging the microbicidal morphologies and suppressing the activity of respiratory chain dehydrogenase . Finally, PHMG-SS-coated aluminum was evaluated as interior surface of jet fuel tanks to protect jet fuel, and the experimental results showed that PHMG-SS-coated aluminum achieved a greater than 99.9999% (6 log) reduction in viable counts of a mixed suspension of Escherichia coli , Staphylococcus aureus , Bacillus subtilis and Yarrowia lipolytica within 30 min. The outputs from this work represent a highly versatile approach to build an antimicrobial barrier to protect jet fuel from microbial contamination, and such approach is also worthy of wide application to treat other surfaces. • The antimicrobial coating and the coating technology were environmental-friendly and could be applied on a large scale. • The developed antimicrobial coating exhibited desirable biocidal efficacy without detectable PHMG leaching. • The antimicrobial aluminum sheet could quickly kill the mixed microorganisms and exhibited desirable UV resistance. • The antimicrobial aluminum sheet showed the potential to protect jet fuel tanks from microbial contamination.

Production of TiC – Co and TiC – NiCr Composite Powders and Study of Their Interaction with a Target under Cold Spray Conditions

In the first part of the paper, the effect of mechanical treatment of particles of reacting Ti + C + Me (Me = NiCr or Co) mixtures on the process of self-propagating high-temperature synthesis (SHS) is investigated. It is shown that as a result of SH-synthesis in the free burning mode, a metal-ceramic sinter of high porosity is formed, which is easily destroyed by mechanical action. An increase in the volume fraction of the metal binder (NiCr or Co) leads to a redistribution of the sizes of carbides towards smaller values.In the second part of the paper, the results of cold spraying nickel-chromium alloy particles and cermet particles of the TiC – NiCr composition on an aluminum substrate are presented. Produced NiCr coatings have a high porosity (up to 10 %) and a layered structure with clearly defined contours of individual deformed particles (splats). Due to the high hardness and low plasticity of metal – ceramic particles of the TiC – NiCr composition, during their interaction with the surface of aluminum substrate, continuous coating cannot be produced, only individual adhered particles are observed. With prolonged exposure to the flow of such particles, erosion of the substrate takes place.

High-Bandwidth Low-Inductance Current Shunt for Wide-Bandgap Devices Dynamic Characterization

High bandwidth sensors are required to measure the wide-bandgap devices' transient behavior because of their fast switching speed. In addition to high bandwidth, the current sensor must introduce little extra parasitic inductance to the switching power loop. The analysis of conventional shunt resistors shows the key to high bandwidth is the coaxial structure and its parasitic inductance is proportional to its transient heat energy rating. By combining the structure of coaxial shunt resistor and alumina substrate surface mount thin film resistors, a novel surface mount coaxial shunt resistor is introduced. Experimental measurement verifies its capability of achieving very high bandwidth while introducing very low parasitic inductance. The design can achieve up to 2.23-GHz measurement bandwidth while keeping its parasitic inductance as low as 0.12 nH. Application in gallium nitride heterojunction-field-effect-transistors double pulse test shows it can faithfully capture the transient current waveform while introducing little interference to the switching behavior.

Durability and mechanical behavior of CFRP/Al structural joints in accelerated cyclic corrosion environments

This study aims to evaluate detailed corrosion characteristics and mechanical performance of CFRP/Al bonded and hybrid bonded-riveted joints subjected to cyclic salt mist-dry-wet environments. Results indicated that joint strength of both bonded and hybrid joints progressively declined with increased ageing cycles with up to 40.4% and 31.9% degradation, respectively. Compared with purely bonded joints, hybrid joints presented superior mechanical properties and less degradation rate. Light fiber tearing failure and cohesive failure predominated for less aged joints, while more apparent interface failure and accumulated corrosion products were observed at higher ageing cycles. The main corrosion mechanism was the pitting corrosion on the aluminum substrate surface, which further led to the formation of accumulated corrosion products and disbonding of the aluminum/adhesive interface. Rivet body of hybrid joints remained pristine and rivet heads experienced severe galvanic corrosion, while these corrosion features generated limited impact on joint performance.

Influence of the Mg and Bi content on brazeability of MONOBRAZE material under flux-free brazing conditions

In the conventional brazing, the clad materials with the filler layer and the flux coating have been used to get good brazeability. However, an innovative Al-Si based single-layer brazing material (MONOBRAZE® material) has been developed recently which does not need filler layer by supplying molten filler from the inside of the material during brazing. In addition, a new flux-free brazing technique has also been developed. In the flux-free brazing, Mg and Bi are added to break the oxide film and to improve the wettability of molten filler, respectively. However, it is not clarified how these element works on the brazeability of MONOBRAZE® material in flux-free brazing. Therefore, in this study the effect of Mg and Bi content on the brazeability of MONOBRAZE® material was investigated. From the result, it is found that MONOBRAZE® material is applicable for flux-free brazing by adding Mg. Mg is considered to break the oxide film into fine particles and Bi is considered to assist the destruction of oxide film. From this cause, a new aluminum substrate surface was exposed which allow molten filler to move on the surface and contribute to the formation of the fillet.

Surface Characteristics of Plasma Treated and Titanium Nitride (TiN) Deposited Aluminum Alloy

Abstract This investigation highlights the rationale of the magnetron sputtering technique to deposit titanium nitride (TiN) coatings on aluminum alloy 2024 (AA 2024). TiN deposition on aluminum was systematically optimized, with nitrogen flow rate (mL/min) as the varying parameter. The developed TiN coatings were compared with the atmospheric pressure plasma treated and raw (uncoated) AA 2024 aluminum substrate surface. The crystalline phase formations of TiN on the alloy surface were studied using X-ray diffractometer technique. The scanning electron microscopy imaging technique was used to study the morphology of the formed ceramic layer. Fine and pore-free grains of TiN on the alloy surface were obtained at 1.5 mL/min nitrogen flow rate (TiN layer thickness ∼ 630 nm). X-ray photoelectron spectroscopy analysis was conducted on the surface in order to characterize elemental composition of the surface. Surface characteristic and wettability studies on the developed coatings were conducted using atomic force microscopy (AFM) and by measurement of contact angle, respectively. The roughness parameter (Ra) (obtained from AFM) increased by ∼72 % with TiN deposition on the AA 2024, while the contact angle value decreased by ∼18 %. The adhesion of the coating to the metal substrate (using scratch test) and the Vickers hardness measurements were also performed. Corrosion resistance imparted by the coatings was also confirmed from the electrochemical measurements. A significant positive shift in the corrosion potential (Ecorr) value from −0.96 V to −0.75 V was observed from the analysis.

In situ growth of Co3O4@NiMoO4 composite arrays on alumina substrate with improved triethylamine sensing performance

Array-based sensors are considered as potential candidates for gas detection due to their low cost and great miniaturization potential. However, the fabrication process of array-based sensors is complex and time-consuming since it usually contains the formation and growth processes of seed layers on the surface of alumina substrates. In addition, the gas-sensing materials for the fabrication of array-based sensors are mainly confined to n-type semiconductors such as ZnO, TiO2 and WO3. In this work, a kind of p-type heterostructures arrays composed of NiMoO4 nanosheets and Co3O4 nanowire (Co3O4@NiMoO4) was fabricated in-situ on flat alumina substrates via a simple hydrothermal method without seed layers. SEM and TEM characterizations revealed that the Co3O4 nanowire arrays were fully covered with NiMoO4 nanosheets. The gas-sensing measurements revealed that the Co3O4@NiMoO4 composite arrays showed the highest response (Rg/Ra = 17.12) towards 100 ppm trimethylamine at its optimal operating temperature of 250 °C. This response value was 3.91 times higher than that of Co3O4 arrays (Rg/Ra = 4.39) and 9.25 times higher than that of NiMoO4 nanosheets (Rg/Ra = 1.85) at their optimal operating temperatures of 250 and 350 °C, respectively. Meanwhile, the enhanced sensing mechanism of the Co3O4@NiMoO4 composite arrays was also discussed. It could be explained by the special heterojunction structure of the Co3O4@NiMoO4 composite arrays, which offered a high surface area and an additional modulation in resistance. Our studies shed a new light to design p-type heterostructure arrays in-situ for fabricating sensing device by a facile method. Moreover, the as-designed Co3O4@NiMoO4 composite arrays are potential candidates in the fabricating of high performance trimethylamine sensors.

Thin Film Deposition and Carbon Nanotube Synthesis

Carbon nanotubes (CNTs) are a viable product for many different markets. One specific area of promise is the use of CNTs in supercapacitors. The CNT synthesis is a two-step process with the first being the formation of a thin film layer. The thin film substrate is created by means of the Thermal Evaporation Physical Vapor Deposition (TPVD) process. After the thin film substrate is deposited, the CNTs are grown in a Chemical Vapor Deposition (CVD) growth chamber. Analysis of the thin film substrate and CNTs is performed primarily using Scanning Electron Microscopy (SEM). The results show the inclusion of ultrapure water in the CVD process contributed to the success of CNT growth. Multiple prong CNT grow is seen for CVDs trails of silver thin film layer deposited on silicon substrates. The silver nanoparticle had a large diameter with an acute contact angle. The single prong growth indicates the iron nanoparticles formed an obtuse contact angle due to the amorphic surface of alumina substrate. The focus of this project is to explore and investigate different materials and conditions for optimal CNT synthesis in the hopes of creating a uniform forest of vertically aligned carbon nanotubes.

Nickel Electrochemical Deposition onto the Surface of Anodized Aluminum

The use of ordered anodic aluminum oxide for nickel electrochemical deposition is studied. The conditions for aluminum anodization in a bath based on oxalic acid, thinning of the barrier oxide layer, and nickel electrochemical deposition from a sulfamate bath are described. The deposited nickel has a lattice constant of 3.51 A and a texture in which the (100) grain planes are parallel to the surface. The surface morphologies of the anodic oxide layer and the upper and lower parts of the deposited nickel layers are examined using electron microscopy. The mean size of the oxide pores is 50 nm, the mean interpore diameter is 102 nm, and the oxide porosity is 21.5%. The surface topography of the bottom of the deposited nickel layer features a nanoscopic pattern formed by rods, which is identical in pore size and morphology to the oxide surface. The rod length is defined by the thickness of the anodic oxide layer formed on the aluminum-substrate surface. This feature is due to the homogeneous filling of oxide pores during nickel electrodeposition. We find that thinning of the anodic oxide layer to below 10 nm may impair adhesion of the oxide layer to the aluminum substrate and thus lead to nickel deposition on both sides of the oxide layer. The formation of dendrites is noted, and the possible causes of this as well as conditions favoring their growth are discussed.

Failure analysis of adhesively bonded GFRP/ aluminum matrix single composite lap joint with cold worked penetrative reinforcements

A new cold worked, penetrative mechanical reinforcement method was evaluated for its potential to enhance joining between 2024-T3 aluminum matrix and glass fiber reinforced polymer (GFRP) for aerospace and automotive applications. In this study, the aluminum substrate surface was modified using a new cold working process which formed hooks directly from the substrate material. This surface was then treated with grit blast and Sol-Gel surface treatment before it was co-cured to both side of a GFRP, forming a single lap joint for testing. This type of joints was compared to a baseline bonded joint without mechanical reinforcement using the same surface treatment. The joint strength and fatigue performance of these sets of samples were experimentally evaluated under quasi-static and fatigue loading conditions. The bonded joints with penetrative mechanical reinforcements withstood greater peak load and higher strain prior to failure, as compared to non-reinforced bonded joints. Fatigue testing on the other hand showed better performance of non-reinforced joints over the reinforced ones. The failure surfaces of both quasi-static samples and fatigue samples were evaluated using a scanning electron microscope to determine failure mode(s). It was determined that the stress concentration at the base of reinforcements could be the main underlying cause for earlier onset of fatigue failure of reinforced samples.

Experimental Investigation of the Overlap Process in Metal Droplet Successive Deposition and Solidification

This paper presents a systematic numerical and experimental investigation of the transient transport phenomenon during the overlap of successive aluminum droplets impinging onto a substrate surface. The 3D models based on a volume of fluid (VOF) method were developed to investigate the successive deposition of molten metal droplets on a horizontally fixed aluminum substrate surface. The numerical models are validated with experiments. The comparisons between numerical simulations and experimental findings show a good agreement. The effects of various parameters such as impact velocities, substrate temperatures and droplet diameters on the maximum spread factor during impacting and spreading with solidification of a molten droplet onto an aluminum substrate surface under different parameters were studied. Based on the above research, the relationships between external morphology and internal microstructure were proposed, which was further certified by investigating the overlap of successive droplets.

Enhancing mode I inter-laminar fracture toughness of aluminum/fiberglass fiber-metal laminates by combining surface pre-treatments

This paper investigates the influence of multiple surface treatment, including chemical etching and plasma treatments, on the mode I inter-laminar fracture toughness (G1C) of aluminum/fiberglass fiber-metal laminates. Laser technology was employed to further enhance aluminum substrate surface morphology to promote micro-mechanical interlocks (MMI) with non-crimp [0°/−45°/90°/+45°] fiberglass/epoxy resin. A vacuum assisted resin transfer molding technique was used to produce the hybrid laminates. Five surface pre-treatments were compared; N2 plasma, O2 plasma, alkaline etch, laser, and laser+N2 plasma. Alkaline etched specimens absorbed the highest energy (237.8%) whereas laser+N2 plasma treated specimens exhibited the highest G1C (73.2%). In addition, when MMI is promoted, the mechanical locks acted as localized obstacles resisting the propagating crack and caused transition of failure mode from adhesive to adhesive-cohesive mixed mode.

An efficient piezoelectric energy harvester with frequency self-tuning

A beam energy harvester made of an aluminum substrate surface bonded with piezoelectric patches and a stack actuator is developed to achieve an efficient energy harvesting technology with a new developed frequency self-tuning process. To accomplish the self-tuning process, an adjustable axial force applied to the energy harvester is generated by the piezoelectric stack actuator. The stack actuator is controlled by a charged voltage on a small tuning capacitor, which is connected to and charged by the harvester. The function of the stack actuator is to automatically tune the natural frequency of the harvester to match the major exciting frequency of the ambient vibration through the tuning capacitor. To describe the energy harvesting and the self-tuning process, an iteration numerical method is developed to solve the dynamic response of the harvester and the generated electric charge. Effects of the piezoelectric patch sizes on the energy harvester's power generation are conducted and discussed. Research findings show that the self-tuning process significantly increases the power output from the harvester by more than 26 times compared to the one without the developed tuning process. Furthermore, the finite element method (FEM) is employed to verify the effectiveness of the proposed self-tuning method.

Numerical and experimental investigation of molten metal droplet deposition applied to rapid prototyping

Rapid prototyping based on molten metal droplets deposition is an additive process in which parts are produced from molten materials in a single operation without the use of any mold or other tooling. Near-net shaped parts are fabricated by sequentially depositing molten droplets layer by layer. This paper presents a systematic numerical and experimental investigation of the transient transport phenomenon during the droplets impinging onto a substrate surface. The 3D models based on a volume of fluid (VOF) method were developed to investigate the deposition of molten metal droplets on a horizontally aluminum substrate surface. Based on the above research, a semiquantitative relationship between external morphology and internal microstructure was proposed, which was further certified by investigating the piled vertical columns and the three-dimensional parts. The works should be helpful for the process optimization and non-destructive detection of drop-based rapid prototyping techniques.

Effect of Aluminum Substrate Surface Modification on Wettability and Freezing Delay of Water Droplet at Subzero Temperatures.

In this study, we have investigated the freezing delay of a water droplet on precooled substrates of an aluminum alloy that is commonly used for heat-exchanger fins. The surfaces of the substrates were modified to obtain surfaces with different hydrophilicity/hydrophobicity and different surface chemistry but without significantly modifying the surface topography. The freezing delays and water contact angles were measured as a function of the substrate temperature and the results were compared to the predictions of the heterogeneous ice nucleation theory. Although the trends for each sample followed the trend in this theory, the differences in the extents of freezing delays were in apparent disagreement with the predictions. Concretely, a slightly hydrophilic substrate modified by (3-aminopropyl) triethoxysilane (APTES) showed longer freezing delays than both more hydrophilic and more hydrophobic substrates. We suggest that this is because this particular surface chemistry prevents ice formation at the interface of the substrate, prior to the deposition of the water droplet. On the basis of our results, we suggest that not only wettability and topography but also the concrete surface chemistry plays a significant role in the kinetics of the ice formation process when a water droplet is placed on a precooled substrate.

Non-heat assistance chemical vapor deposition of amorphous silicon carbide using monomethylsilane gas under argon plasma

Abstract Without any heating assistance, argon plasma and monomethylsilane gas were used for forming silicon carbide film on various substrates, such as aluminum, stainless steel and polyimide. After cleaning the substrate surface by an argon plasma treatment at less than 10 Pa and 0.36 W/cm2, the monomethylsilane gas at the concentration of 5% was introduced into the argon plasma at 10–15 Pa within 20 min. Based on this process, a dense amorphous silicon carbide film thicker than 200 nm could be produced. The obtained film could perfectly protect the aluminum substrate surface from corrosion by a hydrogen chloride aqueous solution. The same process could form a silicon carbide film on the surfaces of a stainless steel plate and polyimide film.

Substrate temperature dependence of splat morphology for plasma-sprayed cast iron on aluminum surface

Abstract In the plasma-sprayed coatings, the morphology of the splats plays an important role in optimizing the microstructure and performance of the coating. Especially, the splashing of impinging droplets during deposition weakens the splat–substrate/intersplat bonding and increases the porosity of the coating. Consequently, the integration of the coating is deteriorated. In the present study, cast iron particles were plasma-sprayed on the surface of polished aluminum substrate to form a single splat. During spraying, the surface of aluminum substrate was preheated in a temperature range from 25 °C to 320 °C. The impact of the substrate preheating temperature on the morphology of the splats was studied using a field emission scanning electron microscope. Results showed that the substrate temperature had significant effects on the morphology of splats. At room temperature, the splats mainly exhibited a splash type with network or radial lines on the splat periphery. While, the splashed splats deposited onto a high temperature substrate showed a star shape on the splat periphery. When the substrate was preheated to 130 °C, the mean percentage of the splashed splats decreased to a minimum value of 18.4% and the disk-like splats prevailed. With the increase of the substrate temperature from 130 °C to 290 °C, the mean percentage of the splashed splats increased monotonically to 78.3%. When the substrate temperature reached to 320 °C, the mean percentage of the splashed splats slightly reduced to 76.6%.

Role of aluminum doping on phase transformations in nanoporous titania anodic oxides

The role of aluminium doping on anatase to rutile phase transformation of nanoporous titanium oxide films were investigated. For this purpose pure and aluminum doped metal films were deposited on alumina substrates by cathodic arc physical deposition. The nanoporous anodic oxides were prepared by porous anodizing of pure and aluminum doped titanium metallic films in an ethylene glycol + NH4F based electrolyte. Nanoporous amorphous structures with 60–80 nm diameter and 2–4 μm length were formed on the surfaces of alumina substrates. The amorphous undoped and Al-doped TiO2 anodic oxides were heat-treated at different temperatures in the range of 280–720 °C for the investigation of their crystallization behavior. The combined effects of nanoporous structure and Al doping on crystallization behavior of titania were investigated using X-ray diffraction (XRD) and micro Raman analysis. The results indicated that both Al ions incorporated into the TiO2 structure and the nanoporous structure retarded the rutile formation. It was also revealed that presence or absence of metallic film underneath the nanopores has a major contribution to anatase-rutile transformation.

Facile fabrication of superhydrophobic surface with needle-like microflower structure on aluminum substrate

A superhydrophobic surface on aluminum substrate was fabricated by creating a needle-like microflower structure based on a simple hydrothermal synthesis process, and subsequently reducing the surface free energy via the self-assembly of lauric acid. The surface morphology, chemical compositions, and hydrophobicity of the as-prepared films on aluminum substrates were measured using a scanning electron microscope, X-ray powder diffraction, Fourier transform infrared spectroscopy, and water contact angle (WCA) measurements. The optimal hydrothermal synthesis conditions, such as reaction temperature, reaction time, and the concentration of zinc ion, were investigated. In addition, the formation mechanism of the microstructure on aluminum surface was also examined. The results showed the surface of aluminum substrate was endowed with a needle-like microflower structure when hydrothermal synthesis was conducted at 90°C for 2 h with 6 mM of zinc ion concentration. In addition, the as-prepared superhydrophobic aluminum surface has a WCA as high as 154.2° and a sliding angle close to 0°.