Measurement of Surface Topography, Packing Density, and Surface Charge Distribution of an Electrostatically Deposited Powder Layer by Image Analysis of Fluorescent Latex Spheres

A novel method of nonintrusive measurement of surface profile, packing density, and surface charge distributions of a powder layer deposited on a substrate is reported. The method employs the deposition of electrostatically charged monodispersed fluorescent latex spheres (FLS), approximately 2 µm in diameter, on the surface of: (1) the substrate before deposition, (2) the powder layer after deposition, and (3) the film formed by curing the powder layer. The surface topography in all cases was mapped using an epi-fluorescent microscope with a vertical resolution of ±2 µm in the z axis and ±10 µm in the x and y axes. An area of 1 cm ×1 cm is scanned in 1 mm segments, providing approximately 100 data points per cm 2 for the surface topography. For each measurement of surface topography, the substrate was positioned on the microscope stage in a manner such that the reference points (x, y, and z) remained the same for all measurements of the substrate. The surface profiles, with respect to the same reference points, were plotted using Origin 6.0 software for 3D presentation of the topography. The method was also applied to map the surface charge density distribution of electrostatically charged surfaces. The FLS imaging method provides a new tool for examination of surface profiles, packing density, and charge distribution of powder layers on a microscopic scale not provided by optical or atomic force/electrostatic force microscopy (AFM/EFM). While AFM and EFM are very effective in providing similar information with nanometer resolution, they cannot be directly applied on a larger macroscopic scale to study powder layers and for a larger surface area (up to 1 cm 2 or greater) involving deposited particles in the range of 1-50 µm in diameter. For AFM, the range in the z-axis is limited to ±3 µm and the x-y scan area is limited to 100 µm ×100 µm. The FLS method has a much wider range but it is operated manually; an automated scanning process is required for rapid measurement. A comparison of the FLS and EFM techniques as they apply to analyzing charge distribution on coal surfaces is presented.     

Surface microstructure of powder layers influenced by the forces ofdeposition and adhesion in electrostatic coating process

In the electrostatic powder coating process, several factors affect the deposition of charged polymer paint particles and the adhesion of the deposited particles on the grounded substrate being coated. In this paper, the roles and relative magnitudes of these forces are discussed. A model on the deposition of a charged particle approaching the surface of the substrate is presented. The electrostatic fields that are considered here to be responsible for particle deposition are the following: (1) corona field between gun tip and grounded plane; (2) image field between a particle and its image charge; (3) field due to the space charge of charged particles; and (4) net repulsive field between a charged particle and the powder layer. Once the particle deposits on the surface and the high voltage is turned off, the particle experiences the following forces: (1) the force due to the image charge of the underlying powder layer; (2) the force due to the image charge of the particle; and (3) the repulsive force between the charged particle and the charged powder layer. The model shows criteria on whether the particles will deposit on the substrate and, if deposited, whether they will remain on the surface of the powder layer once the corona field is turned off. These relative forces influence the microstructure of the powder layer and may affect the ultimate appearance or the texture of paint film after curing     

Triboelectric charging of polymer powders in fluidization andtransport processes

In this paper, we investigated the role of tribocharging in fluidization, flowability, and q/m distribution as functions of particle size distribution (PSD), fluidization time, and transport tubes of different materials. A charge separator was used to determine mass fractions of powder that had positive, zero, and negative charges. For the two acrylic powders tested, one (Sample A) had volume median diameter d₅₀ 18.73 μm while the other (Sample B) had d₅₀ 24.17-μm diameter. During fluidization for 1 h at a relative humidity of 57%, powder B acquired positive charge with charge-to-mass ratio Q/M=0.3 μC/g, and 25% of the powder mass had negative charge with Q/M=-0.36 μC/g. About 35% of the powder mass had particles with nearly zero net charge. Tribocharging during fluidization and transport processes was attributed to particle-particle and particle-wall collisions. Of the total charged particles, about 60% were positively charged while 40% were negatively charged. Each particle may have had patches of charges on its surface, some positive and some negative. The sum total of all patches of charges may yield positive, negative, or essentially neutral polarities on a given particle. For a relatively narrow size distribution of powder, the PSD is often assumed to be conserved during fluidization. A shift in PSD toward larger diameter particles was anticipated because of the possible elutriation of the fine fraction of the powder, but the actual shift was only about 1 μm after 1 h of fluidization. Under identical operational conditions using a fluidized bed, powder pump, transport hose, and corona gun, powder B had nearly twice the mass flow rate of Powder A. Such differences in flowability of powders influence charging and deposition efficiencies in powder coating applications     

Correction to: A novel 0.9KNbO3–0.1BaNi0.5Nb0.5O3(KBNNO): Ag2O/Bi2O3 heterojunction photocatalyst: synthesis,characterization and excellent photocatalytic performance

Journal of Materials Science: Materials in Electronics - A correction to this paper has been published: https://doi.org/10.1007/s10854-021-06220-x     

Integrated Ejector-Based Flare Gas Recovery and On-Site Desalination of Produced Water in Shale Gas Production

Flaring is a major concern in the oil and gas industry as it wastes valuable raw materials/energy and emits a substantial amount of air pollutants. The produced water treatment during oil and gas production is very troublesome due to its large processing volume, high salinity, and expensive disposal cost. Thus, the on-site integration of the flaring gas recovery (FGR) and desalination processes for handling the produced water could not only monetize flare emission sources but could also generate freshwater for versatile usages. Here, a novel process was developed integrating the ejector-based FGR (EFGR) process with the thermal vapor compression (TVC)-based desalination process. The newly developed EFGR-TVC process is shown to be technically viable and cost-effective under normal operating conditions.     

Laser Direct Metal Deposition Technology and Microstructure and Composition Segregation of Inconel 718 Superalloy

  Multilayer of laser direct metal deposition (DMD) was prepared by depositing a gas atomized pre alloyed powder with a composition close to Inconel 718 alloy on Inconel 718 high temperature alloy substrate. The effects of the DMD parameters on the build up rate and the structure of the deposited layer were studied. The laser DMD sample was further processed by a solution treatment. The microstructure and property of the laser DMD zone before and after heat treatment were investigated as well. The results show that the laser parameters of actual laser power of 650 W, scanning speed of 58 mm/s, beam diameter of 1 mm, powder feed rate of 645 g/min, with a corresponding specific energy of 90-130 J/mm2, can be recommended as optimum parameters for high build up rate of Inconel 718 alloy. Under the condition of optimized parameters, a directional solidification microstructure was obtained and the average distance between the columnar crystals was 5-10 μm. The microcomposition segregation was found between the columnar crystal trunk and columnar crystal. The elements of Nb, Mo, Ti concentrated in the columnar crystal trunk. After the heat treatment, the segregation was greatly minimized, and the segregation ratios were close to 1. The hardness of the laser deposited layer did not show obvious difference along the height of the layer either for the as deposited layer or for the heat treated layer. However, the microhardness of the laser DMD zone after heat treatment was obviously higher than that after the as deposited treatment. During the heat treatment process, some Nb and Mo rich phases precipitated and strengthened DMD layer.     

Synthesis and solution properties of a new sulfobetaine/sulfur dioxide copolymer and its use in aqueous two-phase polymer systems

The zwitterionic monomer, 3-(N,N-diallylammonio)propanesulfonate, was copolymerized with sulfur dioxide in dimethyl sulfoxide using azo-bis-isobutyronitrile (AIBN) to afford the polysulfobetaine (PSB) copolymer in excellent yields. The PSB was converted into the corresponding anionic polyelectrolyte (APE) by treatment with 1 equiv. of sodium hydroxide. The solution properties of PSB and APE were investigated by potentiometric and viscometric techniques. The critical (minimum) salt concentrations (CSC) required to promote water solubility for the PSB at 23 °C have been measured. Basicity constant of the amine functionality in APE is found to be ‘apparent’ and as such follow the modified Henderson-Hasselbalch equation. The composition and phase diagram of the aqueous two-phase polymer systems of PSB (treated with 0.60 equiv. sodium hydroxide) and poly(ethyelene glycol) (PEG) in 0.1N KCl has been studied for the first time for this class of PSB copolymer.     

Lipid composition and amino acid transport in a nystatin-resistant mutant ofAspergillus niger

A nystatin-resistant mutant ofAspergillus niger has been isolated and used as a model system to study the effect of altered sterol levels on lipid composition, transport behavior and physical properties of membrane lipids. There is a decrease in the sterol to phospholipid ratio in the mutant compared to the wild type. Although there is no qualitative change in phospholipid composition, the mutant contains a higher amount of phosphatidylcholine and a lower amount of phosphatidylethanolamine compared to the wild type. The most significant change is the elevated level of linoleic acid in the mutant, concomitant with a decreased level of oleic acid. These adaptive changes to nystatin resistance are manifested in the altered thermotropic behavior of membrane lipids as studied by the steady-state fluorescence polarization technique. These changes are also associated with altered membrane permeability as evidenced by the change in V_max values for uptake of some amino acids in the mutant compared to the wild type.