Increase In Deposition Efficiency Research Articles

Micro-cold Spray Deposition of YSZ Films from Ultrafine Powders Using a Pressure Relief Channel Nozzle

The use of ultrafine powders in the micro-cold spray (MCS) process, also referred to as the aerosol deposition method, typically results in porous and/or poorly adhering films because the particles do not impact at a high enough velocity for sufficient plastic deformation and interparticle bonding to occur. Under typical operating conditions, particles < 100 nm accelerate to high velocities but then are slowed by the stagnant gas in the bow shock that forms just upstream of the substrate. Using larger particles reduces particle slowing, but large particles can cause erosion of the film at high impact velocity, decreasing deposition efficiency. In this study, a pressure relief channel nozzle using helium as a carrier gas is proposed such that high-velocity deposition of yttria-stabilized zirconia particles as small as 10 nm in diameter is possible. This is well below the size range of powders previously used for MCS. The proposed nozzle design increases impact velocities for 10, 20, and 50 nm particles by ~ 880, 560, and 160 m/s, respectively, when compared to a conventional nozzle. Experimental deposition of ultrafine 8YSZ powder shows that the pressure relief channel nozzle results in lower porosity and more uniform deposits, with a ∼ 186% increase in deposition efficiency.

On the Importance of Secondary Component Properties for Cold Spray Metallization of Carbon Fiber Reinforced Polymers.

In previous studies at McGill University, tin was successfully cold sprayed onto carbon fiber reinforced polymers (CFRPs). A “crack-filling” mechanism was described as the deposition mechanism that allowed deposition of tin onto the CFRP. Improving the coating conductivity for lightning strike protection (LSP) purposes was explored by adding other metal powders (aluminum, copper, zinc) to tin and cold spraying on the CFRP. At the same time, it was noticed that the addition of this secondary component (SC) provided an increase in deposition efficiency (DE); tamping was initially hypothesized to explain this improvement, thus prompting a study solely on the effect of SC hardness. However, it is recognized that other powder characteristics may also be influencing the DE. Thus, in this study, SCs with a wider variety of particle sizes, morphologies, densities and hardness values were mixed with tin and sprayed on CFRPs. The effect of SC properties on tin deposition is discussed and, while SC particle size, morphology and density individually do not notably influence the DE, the impact energy of the SC does. This opens a discussion on optimal parameters for deposition of metals on CFRP, based on results and observations from the literature.

Epoxy Resin-Encapsulated Polymer Microparticles for Room-Temperature Cold Sprayable Coatings.

We designed and synthesized epoxy-encapsulated microparticles with core-shell structures via suspension polymerization to enable high-efficiency, room-temperature cold spray processing. The soft core of the microparticles was comprised of a thermoset resin, diglycidyl ether of bisphenol A (DGEBA), which was optionally blended with the thermoplastic, poly(butyl acrylate); the protective shell was formed using polyurea. The composition, morphology, and thermal behavior of the microparticles were investigated. An inverse relationship between deposition efficiency and particle size was demonstrated by varying the surfactant concentration that was used during particle synthesis. We also determined that the microparticles that had pure resin as the core had the lowest viscosity, exhibited a decrease in the critical impact velocity required for adhesion, had the best flowability, and yielded a dramatic increase in deposition efficiency (56%). We have demonstrated that our in-house synthesized particles can form homogeneous, smooth, and fully coalesced coatings using room-temperature cold spray.

Influence of Secondary Component Hardness When Cold Spraying Mixed Metal Powders on Carbon Fiber Reinforced Polymers

In previous studies at McGill University, tin has successfully been cold sprayed onto carbon fiber reinforced polymers (CFRPs) and, with the idea of improving the coating conductivity, other metal powders (aluminum, copper and zinc) were added to tin and also sprayed. Results indicated that addition of any of the aforementioned secondary components (SCs) provided a noticeable increase in deposition efficiency (DE); it was hypothesized that a tamping mechanism might explain the improvement. In this study, aluminum and several aluminum alloys (5083, 6061, 7075) were mixed with tin powders to understand how the hardness of secondary components with similar densities may affect the deposition of tin on CFRPs. The top-surface and cross section of the coatings were examined, and DE and coating thicknesses were measured. Profilometric data were acquired on some coating top surfaces, as well as directly on some substrates after coatings peeled off. Mixing tin with other metallic powders is discussed and a refined “crack filling” mechanism related to SC hardness is explored as an improvement mechanism in the cold spraying of mixed powders on CFRPs.

Influence of Magnetic Field on the Electrodeposition and Capacitive Performances of MnO2

This study focuses on the influence of an applied external magnetic field on the electrodeposition process and capacitive performances of MnO2, as pseudo-capacitive active material for supercapacitors electrodes. MnO2 was electrochemically deposited on Si/Au substrates in the presence and in the absence of a 0.5 T magnet, and its capacitive performance was tested via electrochemical characterization. The samples obtained in the presence of the magnetic field show a positive influence on the deposition process: the increase in deposition efficiency leads to more compact and uniform MnO2 coatings, with a decrease in capacitance values for the samples produced with the magnetic field.

Improving deposition efficiency and inter-particle bonding of cold sprayed Cu through removing the surficial oxide scale of the feedstock powder

In cold spray, surficial oxide scale of the feedstock powder not only reduces the deposition efficiency of spraying powder, but also deteriorates the properties of the deposit due to its influence on inter-particle bonding. To simultaneously improve the deposition efficiency of spraying powder and the properties of the deposit, in this study, taking Cu as a typical material, acid pickling was used to remove the oxide scale on the surface of the as-received powder. During acid pickling, Cu powder particles were immersed into the acid alcohol solution and then dried in a low-pressure tank. Using the as-received powder and acid-pickled powder as the spraying powder, Cu deposits were prepared under the same spraying conditions. The deposition behavior of spraying powders, the microstructure and properties, including mechanical properties, conductivities and anti-corrosion behavior of the Cu deposits were systematically studied. Results show that acid pickling can effectively remove the oxide scale on the surface of the as-received powder and reduce the powder oxygen content from 0.12 wt% to 0.044 wt%, leading to an increase in deposition efficiency of the spraying powder from 74% to 84%. Although both the Cu deposits reveal dense microstructure and thereby show good anti-corrosion, the tensile properties and conductivities of Cu deposits, which are sensitive to the inter-particle bonding, decrease with increase of the oxygen content in spray powder. Cu deposit prepared by acid-pickled powder shows the superior tensile properties and conductivities, and the tests yielded the tensile strength of 245 MPa, Young modulus of 85 GPa, electrical and thermal conductivities of 90%IACS and 298 W·m−1·K−1. Therefore, it is an effective approach to improve the deposition efficiency of spraying powder and prepare high-property cold-sprayed metallic deposit simultaneously by using acid pickling to remove the surficial oxide scale of particle.

Inter-particle bonding in cold spray deposition of a gas-atomised and a solution heat-treated Al 6061 powder

The heat treatment of a number of gas-atomised aluminium alloys prior to cold spraying recently showed that the resultant microstructural modification was accompanied by an improvement in deposition; however, the relationship between the microstructural homogenisation occurring after recrystallisation and the increase in deposition efficiency and particle–particle bonding had not been investigated. In this study, Al 6061 gas-atomised feedstock powder, before and after solution heat treatment, was cold sprayed and these materials were characterised using electron backscatter diffraction and transmission electron microscopy. The solution heat-treated Al 6061 powder showed large stress-free grains as opposed to the as-atomised feedstock powder which exhibited smaller grains with the presence of dislocations. The coating produced from as-received powder exhibited a homogeneous distribution of misorientation and lattice defects throughout the particles, whereas the coating produced from solution heat-treated powder showed a strain concentration in the interfacial zones. This was attributed to the partial dissolution and the clustering of solute atoms, allowing the aluminium matrix to deform around the newly formed precipitates.

Cold Spray Aluminum–Alumina Cermet Coatings: Effect of Alumina Morphology

The feedstock powder morphology has an important effect on the deposition behavior of cold spray coatings, and this effect is even more significant while spraying cermet coating by the mixture powders. The effect of alumina powder morphology on the deposition efficiency and coatings mechanical properties is investigated in the cold spray deposition of aluminum–alumina cermets. The deposition of aluminum mixed with spherical and angular alumina is studied and compared for six different feedstock powder compositions for each particle morphology. The addition of angular alumina particles in the feedstock powder induces an increase in deposition efficiency followed by a decrease as the alumina content increases beyond a specific value. This effect is not observed when spherical alumina is used. The creation of asperities during deposition was explored for the two alumina powder morphologies, and it was determined that spherical alumina does not produce intricate asperities at the coating surface, explaining the difference in deposition efficiencies. Coatings produced with spherical alumina were harder and showed a greater increase in adhesion strength than coatings produced with angular alumina for similar coating alumina content. These differences are attributed to a larger amount of plastic deformation of the matrix material in coatings sprayed with spherical alumina.

Cold Spray Aluminum–Alumina Cermet Coatings: Effect of Alumina Content

Deposition behavior and deposition efficiency were investigated for several aluminum–alumina mixture compositions sprayed by cold spray. An increase in deposition efficiency was observed. Three theories postulated in the literature, explaining this increase in deposition efficiency, were investigated and assessed. Through finite element analysis, the interaction between a ceramic particle peening an impacting aluminum particle was found to be a possible mechanism to increase the deposition efficiency of the aluminum particle, but a probability analysis demonstrated that this peening event is too unlikely to contribute to the increment in deposition efficiency observed. The presence of asperities at the substrate and deposited layers was confirmed by a single-layer deposition efficiency measurement and proved to be a major mechanism in the increment of deposition efficiency of the studied mixtures. Finally, oxide removal produced by the impact of ceramic particles on substrate and deposited layers was evaluated as the complement of the other effects and found to also play a major role in increasing the deposition efficiency. It was found that the coatings retained approximately half of the feedstock powder alumina content. Hardness tests have shown a steady increase with the coating alumina content. Dry wear tests have revealed no improvement in wear resistance in samples with an alumina content lower than 22 wt.% compared to pure aluminum coatings. Adhesion strength showed a steady improvement with increasing alumina content in the feedstock powder from 18.5 MPa for pure aluminum coatings to values above 70 MPa for the ones sprayed with the highest feedstock powder alumina content.

コールドスプレー法を用いた高力黄銅膜形成の試み

Cu-Zn-based brasses possess excellent strength and corrosion resistance. However, producing bulk brass parts/bodies via conventional powder metallurgy has been difficult due to the high vapor pressure of Zn. This problem is circumvented in Cold Spray, in which solid powder particles, accelerated in a supersonic gas stream, are deposited on a substrate to form dense coatings without long exposure of powder particles to high temperature. In this study, a water-atomized Cu-Zn-Mn-Al-Fe brass powder about 30 μm in average diameter was cold sprayed with and without powder pre-annealing on an aluminum substrate in a nitrogen gas stream heated to 873 K. The as-atomized brass powder consisted predominantly of β solid solution, while the powder pre-annealed at 1023 K had both α and β solutions. Coatings with more than 3 mm in thickness and of nearly full density were produced with or without powder pre-annealing. An increase in deposition efficiency was noted with the coatings sprayed with the pre-annealed powder. Cold Spray provides a viable means for the fabrication of high-strength brass coatings.

Electrostatic effects on inertial particle transport in bifurcated tubes

Most aerosols found naturally in the ambient environment or those dispersed from artificial devices such as dry powder inhalers, are electrically charged. It is known that a strong electrostatic charge on aerosols can result in transport behavior dramatically different from that of uncharged aerosols, even in the absence of an external electric field. In the present work, we study pneumatic transport of corona-charged particles in bifurcated tubes. This is accomplished by tracking the motion of discrete particles numerically under the influence of drag, gravitational, and electrostatic forces. The model aerosol is fly ash powder, whose size and charge distributions have been determined experimentally. The electrical mobility of the charged particle cloud is modeled through coulombic interactions between discrete point charges. For the case of polydispersed particles electrically charged across a distribution, the deposition efficiency was found to be greater than what is indicated by the mean charge and size. In particular, use of negatively charged fly ash powder of mean size of 2 μm and mean charge of −1.5 C/kg led to significant increase in deposition efficiency (∼29%) compared with uncharged fly ash powder of the same size distribution (∼8%). Analysis of particle residence times suggests significant interaction between electrical and drag forces. These findings could have implications for pneumatic powder conveying or pulmonary drug delivery applications. © 2009 American Institute of Chemical Engineers AIChE J, 2009

DEPOSITION STUDIES OF AN ELECTROSTATIC SPINNING DISC SPRAYER

ABSTRACT ABSTRACT Laboratory experiments were conducted to determine spray distribution patterns and deposition characteristics of an induction-type electrostatic spinning disc sprayer at various operating conditions. Spray distribution patterns were obtained using a spray pattemator table. Fluorometric analysis quantified tracer deposits on different elevations within aluminum targets modeled as soybean plants. Variables investigated were electrode voltage, disc rotational speed, liquid flow rate, application height, and disc tilt angle. The results showed that electrostatic charging resulted in 1.6- to 2.0-fold increase in deposition efficiency. Deposition efficiency improved as disc speed increased and deteriorated as flow rate increased. Between 2.2- to 6.5-fold relative increases in deposition was found at the intermediate and lower target levels, and between 1.1- to 1.7-fold on the top levels of the target. Leaf underside deposition occurred only at the upper levels of the target and accounted only between 4 to 10% of the total deposition. The spray distribution pattern uniformity improved while tilting the disc axis at 30° backward and utilizing two liquid feed tubes positioned 180° apart.