Powder Substrate Research Articles

Preparation and characterization of a new low infrared-emissivity coating based on modified aluminum

A low infrared-emissivity coating was prepared using modified Al powder and polyurethane as metallic pigment and adhesive. Al powder was coated with polyethylene wax by the flux-capping method to reduce the emissivity and gloss of the coating. The surface morphology and chemical composition of pure and modified Al powders were characterized by scanning electron microscopy and X-ray diffraction. The infrared emissivity of the product was measured by an infrared emissometer. The influences of the modified Al powder content, substrate material, coating thickness, and aging time on infrared emissivity were systematically investigated. The results indicate that modified Al powder decreases not only the gloss of the coating, but also its emissivity within the wavelength range of 8–14μm. The polyethylene wax/Al composites have a homogenous sheet structure at 30wt.% Al content, and a lower infrared emissivity. The optimum content of modified Al powder is around 18wt.%. The coating exhibits a lower emissivity value and excellent optical properties. The infrared emissivity of the composite coating significantly increases with increased thickness, and approaches a constant value when the thickness is more than 80μm. Accelerated aging test results show that with increased aging time, the coating with modified Al powder has a better aging resistance and lower infrared emissivity than that with pure Al powder.

Microstructure and mechanical properties of steel/TiC nano-composite surface layer produced by friction stir processing

A steel/TiC nano-composite surface layer with ultra fine grains of less than 600nm was fabricated on mild steel substrate by introduction of nano-sized TiC powder into the stir zone employing four passes of friction stir processing. TiC clusters were formed after the first pass. Sequential break-up of clusters and refinement of matrix grains were caused by subsequent FSP passes. A near uniform dispersion of nano-sized TiC particles was achieved after the fourth pass. The fabricated nano-composite layer exhibited a maximum micro hardness value of ~450HV; this is much greater than 185 and 130HV of the friction stir processed layer without introduction of TiC powder and as-received substrates, respectively. Moreover, a significant improvement in wear resistance of the nano-composite layer was observed as compared with that of the as-received substrate. The enhanced properties are attributed to the uniform dispersion of hard nano-sized TiC reinforcements in a matrix of ultra fine dynamically recrystallized grains.

Deformation behavior of the oxide film on the surface of cold sprayed powder particle

In cold spraying, oxide-free interface is an important factor for metal-to-metal contact between powder particles and substrate, which determines the bonding strength and final coating quality. In this study, a systematic finite element analysis (FEA) is performed to examine the deformation behavior of the oxide film on an Al 6061-T6 particle surface after deposition. The simulation results show that the oxide film can be disrupted during the high velocity impact. Part of the cracked oxides remains at the interface and mainly accumulates at the central region after particle deposition. Substrate hardness, particle velocity and spray angle are found to influence the deformation behavior and final state of the oxide film. Besides, interparticle interaction is also investigated in the present work to clarify the deformation behavior of the oxide film inside the coating.

Effects of MMP Inhibitors Incorporated within Dental Adhesives

Matrix metalloproteinase (MMP) inhibition has been shown to reduce adhesive bond degradation when applied as a pre-conditioner, adding to clinical steps in the placement of adhesives, but their incorporation within dental adhesives has not been fully explored. This study examined the effect of including 2 MMP inhibitors (BB94 and GM6001) within the primers of 3 commercially available adhesives. Fluorometric assay and zymography showed that adhesives with MMP inhibitors had high affinity toward both synthetic fluorogenic FRET peptides (95%) and dentin powder substrates, respectively. The immediate microtensile bond strength was enhanced for 2 types of adhesives following the addition of both inhibitors. However, no changes were detected between the control and the inhibitor groups following 3-month storage. The modified two-step etch-and-rinse and single-step systems showed less Rhodamine B penetration to the “hybrid layer” and to the “adhesive”, respectively. The incorporation of BB94 and GM6001 within the primers resulted in the inhibition of dentin MMPs with improved initial bond strength and enhanced sealing ability.

Preparation of Ni60-Cr3C2 coating by plasma spraying, plasma re-melting and plasma spray welding on W6Mo5Cr4V2

In order to prepare heat-resistant inner layer of hot-forging die, plasma spraying, plasma remelting and plasma spray welding were adopted. Cr3C2 coatings of Ni-Based were prepared respectively with 10%, 20% and 30% Cr3C2 powder and W6Mo5Cr4V2 substrate. The coating microstructure analysis, the micro-hardness test, and the measurement of thermal parameters of coating were conducted. The experimental results show that the coating has the better thermo-physical property by using plasma spray welding method with the powder ratio of 90% Ni60 and 10% Cr3C2, and by this way the micro-hardness of coating can achieve 1100 HV.

Effect of Powder Substrate on Foam Drainage and Collapse: Implications to Foam Granulation

Foam granulation is a relatively newer wet granulation process whereby foamed binder solutions are added to powders in a mixer. It is essential to understand the effect of powder substrate on foam drainage and half-life, which are relevant to nucleation and agglomeration during foam granulation. Hydroxypropyl methylcellulose (HPMC) and hydroxypropyl cellulose (HPC) foams were characterized. Anhydrous lactose and stearic acid were selected as model soluble and insoluble substrates, respectively. The effect of these substrates on foam stability was measured by foam drainage and collapse time and microscopic observations. Both HPMC and HPC foams were similar in foam quality and foam density. Lactose destabilized both HPMC and HPC foams and foam drainage and collapse times were reduced two to four times in the presence of lactose. On the contrary, stearic acid did not significantly change foam drainage and collapse times. Microscopically, lactose exhibited rapid wetting within 15 s upon contacting the HPMC and HPC foam beds, whereas stearic acid remained unwetted even after 8 min and collapse of the foam beds. Substrate solubility can influence foam-substrate interaction. On the basis of this, we suggest potential mechanisms of nucleation and agglomeration of soluble and insoluble substrates during foam granulation.

Evolution of Microstructure of Cold‐Spray Aluminum Coatings on Al2O3 Substrates

AbstractElectron backscatter diffraction is used to study the microstructural evolution of cold‐spray aluminum coatings on Al2O3 substrates. The influence of powder purity and substrate heating on the kernel average misorientation and the distribution of low‐angle grain boundaries in as‐sprayed and annealed coatings are discussed in terms of dynamic recovery and dynamic recrystallization.

Superparamagnetic Carbon Electrodes: A Versatile Approach for Performing Magnetic Coupled Electrochemical Analysis of Mercury Ions

AbstractMercury ions can be captured with superparamagnetic carbon powder substrates and transported to the electrode surface using an external miniature magnet. The magnetic carbon substrate is electronically conducting, and more than promoting efficient preconcentration of the element at the electrode, it increases the electrochemical surface area by forming an extended 3D structure in the presence of a magnetic field. The external magnet allows to perform direct electrochemical analysis, leading to a strong enhancement of the analytical signals for the reduction of the Hg(II) ions.

Influence of Powder Type and Substrate Hardness on the Deposition Behavior of WC-17Co Particle in Cold Spraying

In this study, the influence of particle type and substrate hardness on the deposition behavior of single WC-17Co particle during the cold spraying process was investigated. The morphology of the deposited particles was examined by scanning electron microscopy (SEM) from the particle surface and cross-sections. It was found that with increasing substrate hardness, the deposition behavior of WC-17Co particles transformed from completely embedding into soft substrate to partially flattening and even rebounding from the hard substrate. In the comparison between different powder types, spherical nanostructured WC-17Co particles experienced the more intensive deformation due to the smaller WC size.

Growth of SiC and SiO<sub>2</sub> Nanostructures Prepared from Rice Husk Ash Using Carbon-Metal Assisted

This work suggested the growth of SiC and SiO2nanostructures from heating of rice husk ash and carbon-metal assisted. The rice husk was boiled in 1 M hydrochloric acid solution with temperature of around 90 °C for 1 hour, and then washed in distilled water and dried under the sun. The dried acid-treated rice husk was burned in the furnace with normal air for 1 hour, then high purity SiO2was produced. The high silica ash mixed with Cu or SnO2powder and coconut shell charcoal were grounded for mixtures powder. The mixtures powder and Si substrates were placed on the alumina boat and put in the middle of furnace. The furnace was heated at high temperature under atmosphere of argon gas. The heated products and Si substrates were studied by X-rays diffraction and scanning electron microscope. The SiC and SiO2nanostructures were observed.

Evaluation of Several Carbon-Supported Nanostructured Ni-Doped Manganese Oxide Materials for the Electrochemical Reduction of Oxygen

Physical and electrochemical properties of nanostructured Ni-doped manganese oxides catalysts supported on different carbon powder substrates were investigated so as to characterize any carbon substrate effect toward the oxygen reduction reaction (ORR) kinetics in alkaline medium. These materials were characterized using physicochemical analyses. Small insertion of Ni atoms in the lattice was observed, which consists of a true doping of the manganese oxide phase. The corresponding phase is present in the form of needles or agglomerates, with crystallite sizes in the order of (from x-ray diffraction analyses). Layered manganite (MnOOH) phase has been detected for the Monarch1000-supported material, while different species of phases are present at the E350G and MM225 carbons. Electrochemical studies in thin porous coating active layers in the rotating ring-disk electrode setup revealed that the catalysts present better ORR kinetics and electrochemical stability upon Ni doping. The ORR follows the so-called peroxide mechanism on catalysts, with the occurrence of minority disproportionation reaction. The disproportionation reaction progressively increases with the Ni content in materials. The catalysts supported on the MM225 and E350G carbons promote faster disproportionation reaction, thus leading to an overall four-electron ORR pathway.

Proposal of Residual Stress Evaluation Method for Ceramic Thermal Barrier Coatings in Consideration of Plasma-Spray Condition

Thermal barrier coatings (TBCs) are applied to high-temperature components of land-based gas turbine (GT). In TBC deposited by plasma-spray process, spallation damage has been often observed in the component, because of subjecting to cyclic thermal stress due to start-steady-stop operation of GT. Thus, it is necessary to grasp the stress generated in the coating during service, in order to predict precisely life of TBC spallation. The coating stress is composed of residual stress formed by plasma-spray process and thermo-mechanical stress generated during the operation. The residual stress is especially known to take different value with dependence on plasma-spray condition (powder velocity and substrate temperature). This paper presents influence of the spray condition on the residual stress of TBC. Then, the residual stress evaluation method, which had been already proposed, is improved based on particle deposition modeling plasma-spray process. As obtained results, it was found that the residual stress measured by strain gage method increased compressively with a higher particle velocity. Influence of substrate temperature on the residual stress was very few. It was considered with the particle deposition model that the residual stress increased compressively with elastic modulus of TBC due to stronger splat-to-splat cohesion by high-speed impact of particles. The residual stress evaluation method was improved in consideration of the elastic modulus changing by particle velocity. The result estimated method agreed with one measured by the strain gage method.

Optimization of processing parameters for laser powder deposition using finite element method

In order to investigate the effects of powder materials and processing parameters on thermal and stress field during laser powder deposition (LPD), a finite element model was developed with the help of ANSYS software. The finite element model was verified by the comparison between the experimental results and computed results. Then LPD processes with different powder materials and processing parameters were simulated by using the FE model. The results show that less difference of thermal conductivity and thermal expansion coefficient between powder material and substrate material produces lower residual stress; higher laser power, laser scanning speed and smaller laser beam diameter can lead higher peak temperature and higher residual stress. The research opens up a way to rational selection of the powder materials and processing parameters for ensured quality.

Liquisolid Systems: A Review

Liquisolid technique is a new and promising method that can change the dissolution rate of water insoluble drugs. According to the new formulation method of liquisolid compacts, liquid medications such as solutions or suspensions of water insoluble drugs in suitable non-volatile liquid vehicles can be converted into acceptably flowing and compressible powders by blending with selected powder excipients. It has been speculated that such systems exhibit enhanced release profiles. In this case, even though the drug is in a solid dosage form, it is held within the powder substrate in solution or, in a solubilized, almost molecularly dispersed state, which contributes to the enhanced drug dissolution properties.

Preparation and characterization of amorphous SiO2 nanowires

Abstract Amorphous SiO 2 nanowires were prepared by heating Si powder and Au-coated Si(1 1 1) substrates for different times. The SiO 2 nanowires were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results show that large amounts of amorphous SiO 2 nanowires with a diameter of about 40 nm were formed on the entire surface of the substrates. Au particles were observed at the tip of the SiO 2 nanowires, which is consistent with the well-known vapor–liquid–solid (VLS) process. It is found that the annealing time affects the morphology of the products. Finally, the growth mechanism of the SiO 2 nanowires was discussed.

A CFD model of the laser, coaxial powder stream and substrate interaction in laser cladding

In laser cladding, the interaction of the substrate material, the laser beam and the powder stream play important roles in determining how the material is deposited. Previous models of the coaxial powder stream have concentrated either on mass flow dynamics or stream heating, neglecting the effect of the substrate. In this work, a comprehensive numerical model that considers the important parameters of the powder stream, the laser beam and the substrate material, is developed. It is clear from the work that the full three-way interaction of these elements, as in real processing situations, is necessary to accurately and reliably predict particle heating and effective fusion into the melt pool.

Bonding mechanisms of thermally softened metallic powder particles and substrates impacted at high velocity

Thermally softened titanium powder particles were impacted at about 760 m/s onto three substrate materials, i.e., titanium, aluminum, and zirconia, at the same time. In spite of the very different physicochemical properties of these substrate materials, most of particles were bonded to the substrate. However, their microstructures suggested different dynamic deformation behaviors and interface features. On titanium or zirconia substrate, particles showed shear instability and direct metallurgical bonding or metal-ceramic bonding that resulted from the removal of oxide covered on them, while on aluminum, although the particle was not heavily deformed and its oxide remained it was also bonded to the substrate due to the instability of substrate and the removal of aluminum oxide. The results have demonstrated the complex and material dependent nature of bonding formation in kinetic spraying using thermally softened metallic powder particles.

Anomalous Coating of Iron Microparticles by Ni–Co Layers in the 3D Stirred Heterogeneous System: Impedance Study

A high level controlled electrochemical metal plating of the homogeneous, uniform, and adhesive Ni–Co nano-/microlayer on an Fe microparticle powder substrate in the stirred heterogeneous system (SHS) is reported. The influence of the volume fraction of suspended powder particles on the partial current efficiency of the electrolytic coating process is evaluated using electrochemical impedance spectroscopy. The role of both the solid Fe powder microparticles and the electrochemical deposition of binary coating on the particle surface of the charge-transfer mechanism through SHS is discussed. The equivalent circuit on the porous electrode model is proposed and, adopting this approach, some calculations and simulations of the experimental data are done. The optimal volume fraction of solid particles in the charge transfer of our SHS is suggested. The formation of permanent aggregates of powder microparticles during the electrolysis is proved. Scanning electron microscopy, optical microscopy, atomic absorption spectroscopy, and energy dispersive X-ray spectroscopy are used to characterize the coating on the microparticle surface.

Liquid-phase sintering of nanodiamond composite coatings on aluminum A319 using a focused laser beam

Laser-induced phase transition and sintering of nanodiamond (ND) powders (4–8 nm) were used to produce 50–75 µm thick, strongly adherent composite coatings of nanodiamond, amorphous carbon and aluminum on cast alloy A319. First, ND powders, produced by detonation synthesis, were electrostatically sprayed on the surfaces of aluminum substrates. Second, a continuous wave CO 2 laser was used to heat the ND powder and aluminum substrate in a controlled fashion to cause liquid-phase nano-sintering that led to a dispersion and phase transformation of ND particles in a molten pool of aluminum. Raman spectroscopy, scanning electron microscopy, optical profilometry, and microhardness, nanoindentation and friction/wear tests were used to evaluate the coating characteristics. Tribology tests showed that the coefficient of friction was under 0.2 in the beginning and then increased to an average value of 0.39. By comparison, the uncoated substrate exhibited a much higher friction (up to 1.03) despite having the finer surface (1.8 µm Ra). Wear loss is also reduced by over 500% in the laser-sintered coupon compared to the uncoated aluminum. The potential application of the work is hard and wear-resistant coatings for lightweight engine components and biomedical implants to improve the tribological characteristics.

Growth and characterization of electroless deposited Cu films on carbon nanofibers

Carbon nanofibers with two different microstructures, herringbone and platelet have been used as substrates to study the influence of electroless deposition parameters on the growth of Cu deposits. Flat glassy carbon and graphite powder substrates were also included in the study for comparison. Samples were analyzed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, FT-IR, and energy dispersive X-ray spectroscopy in terms of microstructure and chemical composition. The specific surface area was determined by sorption techniques. High quality copper films can be grown on carbon nanofibers at room temperature if carbon nanofibers' pretreatment is properly adjusted. The optimized process is easily up scaled to larger batches of carbon nanofibers.