Effect of Peak Current and Pulse On Time on the Coating Layer Thickness using Electrical Discharge Coating

The present study focused on the surface modification of aluminum 6061 by using electrical discharge coating (EDC) with powder suspension. The effects of peak current (Ip) and pulse on time (Ton) on the coating layer thickness were investigated. This study used Tungsten powder as an additive and mixed it with the kerosene oil and surfactant Span 83. The results indicated that peak current and pulse on-time significantly affected the coating layer thickness. The thinnest coating layer was observed at 3A, 150 µs, while the thickest coating layer with an average value of 17.239 µm was obtained at parameter 4A and 250 µs. In conclusion, the high value of peak current and longer pulse duration on time increased the thickness of the coating layer.

Spray coating of cellulose aerogel particles in a miniaturized spouted bed

Aim of this work is to apply protective and homogeneous shellac coating layers on the surface of hydrophilic open-pore cellulose aerogel particles with low densities ≤ 0.1 g/cm3 and high specific surface areas in the range of ~ 400–450 m2/g while keeping the aerogels’ microstructure intact during processing. For this purpose, an innovative miniaturized spouted bed setup was used. Successful process settings for application of enclosed films on aerogel surfaces without intrusion of coating material into the pores were determined. Precise control of coating layer thickness in the range of 10–50 µm was achieved due to variation of coating solution amount without agglomeration and clogging events occurring during processing. Comparison of bulk densities and specific surface areas before and after coating proved the intactness of the porous structure. Coating of particles loaded with vanillin led to controlled release, enhancing release half-life times from 20 to 1600 min. Overall, a successful strategy for coating of organic low-density aerogels was developed.

Investigation of the SHS Process Initiation in Base Mixture during HFC-Heating and the Combustion Rate Dependence on Various Factors

The paper describes the researches of the SHS process initiation in samples of powder mixtures of reagents intended for steel parts hardening with an excess of Al or B2O3 by a heat source. Mixtures of reagents with different weight ratios of components were used as samples. Thereat, the initiation of SHS process in thin layers was conducted with a coating layer thickness of no more than 6 mm for all tested compositions. The dependences of the combustion rate on various factors including particle size of powder materials and charge composition have been obtained. The main factors influencing the dependences of initiation (ignition) and combustion rate are established, and the degree of influence of these factors on the dependences is estimated. The obtained results made it possible to correct the composition of the base mixture reasonably in order to achieve the required combustion rate.

A comparison on microstructure and mechanical properties of electric discharge metal matrix nickel and silica composite coating on duplex stainless steel

Electric Discharge Alloying/Coating a thermal process of elemental deposition together with pyrolysis carbon enhance various properties. Nickel and silica both provide excellent property, but the solidification rate differs the material microstructural properties (amorphous) that improves its properties under diverse working conditions. In present study analysis of properties such as surface roughness, Microstructure, layer thickness, elemental composition, porosity, decarburizing depth is detailed through metallurgical characterizations and mechanical testing are compared to nickel and silica. Nickel holds a hardness value of 1272 HV and across 968 HV with minimal in carter, pokes, splatters having uniform boundaries that improves friction co-efficient, limiting wear resistant, phase transformation, oxidation, and graphite flakes confirm self-lubrication properties at room temperature under higher loading condition. Silica having 1284 HV on the surface and across it reaches to 980 HV due to dispersed elements and its phase transformation of silica to silica carbide directs secondary arching improves bonding by restrictive carbon deposition promotes passage to speak. This limits the porosity, coating layer thickness and increases metal matrix composition in decarburizing layer holds stability towards coating. Nickel affords surface properties limiting matrix composite, oxidation, and grain growth where else silica provides exceptional in metallurgical mixed composition improves the mechanical behaviour of coating.

Microstructures and Oxidation Behaviors of Silicide Coated Nb Alloys by Halide Activated Pack Cementation Process

In this study, we tried to improve the oxidation resistance of Nb-12Si (wt%) alloys at 1200 °C or higher through pack cementation coatings. Nb-12Si (wt%) alloys were prepared by arc-melting under Ar atmosphere. When the alloys were coated using pack powder mixtures composed of Si, Al2O3 and NaF, two silicide layers composed of NbSi2 and Nb5Si3 phases were successfully produced on the substrate. The Si-pack coatings were performed with various heat treatment temperatures and time conditions. The microstructures and thickness changes of the coating layers were analyzed to determine the growth behaviors of the coating layer. The growth constant of 8.4 10–9 cm2/sec was obtained with a diffusion growth mode. In addition, in order to examine the resistance of the Si-pack coated alloys, isothermal static oxidation tests were performed at 1200 °C and higher temperatures. As a result, the oxidation resistance of the alloys was determined by protecting the surface of the alloys with silicide oxide layers formed by the silicide coatings. The uncoated specimens exhibited an abnormal weight increase due to the formation of Nb oxide. The coated specimen showed excellent oxidation resistance at 1200 °C for up to 12 hrs, while the previous reports on the same alloy verified oxidation resistance only up to 1100 °C. It appears that the excellent oxidation resistance is closely related to the NbSi2 coating layer thickness. The oxidation behaviors of the coating layers after the oxidation tests were discussed in terms of microstructural and phase analyses.

Vapor Sensing with Polymer Coated Straight Optical Fiber Microtapers Based on Index Sensitive Interference Spectroscopy of Surface Stress Birefringence

Optical microfiber tapers provide an advantageous platform for sensing in aqueous and gas environments. We study experimentally the photonic transmission in optical fiber tapers coated with polymethyl methacrylate (PMMA), a polymeric material widely used in optical applications. We demonstrate a durable and simple humidity sensing approach incorporating tapered microfibers attached to silicon (Si) substrate coated with active polymer layer. A model is described for the load stress effect on the birefringence giving rise to interferences in the transmission spectra, strongly dependent on the coating layer thickness, and disappearing following its slow uniform removal. The sensing approach is based on characterization of the interference patterns observed in the transmission spectra of the taper in the NIR range. The device demonstrated persistent detection capability in humid environment and a linear response followed by saturation to calibration analytes. In each analyte of interest, we define principal components and observe unique calibration plot regimes in the principal component space, demonstrating vapor sensing using polymer coated microtapers.

Measurement of mechanical properties of multilayer waterborne coatings on wood by nanoindentation

Waterborne coatings are widely used for environmental protection. However, they lead to many defects and lower the mechanical properties when applied to wood surfaces. To address this challenge, the effects of multilayer waterborne polycrylic coatings on the mechanical properties of southern pine cell walls were investigated by nanoindentation. The experimental results indicated that the coating layers significantly reduced the elastic modulus (Er) and hardness (H) values than the wood cell walls. TheErandHvalues measured along the coating layer thickness direction increased significantly as the distance of the indents to the wood surface decreased. Intact cell walls adjacent to or away from the coating layers had higherErandHvalues than partial ones. This study will also be useful in helping to understand the bonding mechanism at the interface between coatings and wood cell walls.