Solid transfer technology from mixtures is gaining ever-increasing attention from materials scientists and production engineers due to their high potential in near net-shaped production of cost-effective engineering components. Dip coating, a wet deposition method, is an effective and straightforward way of thin-film/layers formation. The dipping mixtures are often embedded with inorganic fillers, nanoparticles, or clusters (d<30 nm) that produce a thin film ranging from nm to couple microns. An increase in the volume of solid transfer by the dipping process can open-up a novel 3D near-net-shape production. However, adding larger inorganic particle size (>1µm) or adding a higher solid fraction will increase the solid transfer but may result in a multi-phase heterogeneous mixture. In this work, the physical mechanism of an increased volume of solid transfer with a larger spherical particle size (>5 µm) is investigated. Polymer-based glue and evaporating solvent are mixed to construct the liquid carrier system (LCS). Moderate volume fraction of inorganic particles (20% < ?p < 50%) are added into the LCS solution as solid loading. Three levels of binder volume fraction are considered to investigate the effect of the solid transfer. Cylindrical AISI 304 steel wire with dia 0.81 mm is dipped and the coating thickness, weight, and the surface packing coverage by the particles are measured in our lab. The results presented the influence of volume fraction of inorganic particle and glue composition on the solid transfer from the heterogeneous mixture.

Micro-scale inorganic particles (d > 1 µm) have reduced surface area and higher density, making them negatively buoyant in most dip-coating mixtures. Their controlled delivery in hard-to-reach places through entrainment is possible but challenging due to the density mismatch between them and the liquid matrix called liquid carrier system (LCS). In this work, the particle transfer mechanism from the complex density mismatching mixture was investigated. The LCS solution was prepared and optimized using a polymer binder and an evaporating solvent. The inorganic particles were dispersed in the LCS by stirring at the just suspending speed to maintain the pseudo suspension characteristics for the heterogeneous mixture. The effect of solid loading and the binder volume fraction on solid transfer has been reported at room temperature. Two coating regimes are observed (i) heterogeneous coating where particle clusters are formed at a low capillary number and (ii) effective viscous regime, where full coverage can be observed on the substrate. ‘Zero’ particle entrainment was not observed even at a low capillary number of the mixture, which can be attributed to the presence of the binder and hydrodynamic flow of the particles due to the stirring of the mixture. The critical film thickness for particle entrainment is $${h}^{*}=0.16a$$ h ∗ = 0.16 a for 6.5% binder and $${h}^{*}=0.26a$$ h ∗ = 0.26 a for 10.5% binder, which are smaller than previously reported in literature. Furthermore, the transferred particle matrices closely follow the analytical expression (modified LLD) of density matching suspension which demonstrate that the density mismatch effect can be neutralized with the stirring energy. The findings of this research will help to understand this high-volume solid transfer technique and develop novel manufacturing processes.

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Solid transfer technology from mixtures is gaining ever-increasing attention from both materials scientists and production engineers due to their high potential in near net shape production of cost-effective engineering components. Dip coating, a wet deposition method is an effective and straightforward way of thin-film/layers formation. It is extensively used as a coating method due to its simplicity, low cost, and reasonable control over the thickness. The dipping mixture can be homogeneous, composite, hybrid, or heterogeneous. The mixtures are often embedded with inorganic fillers, nanoparticles, or clusters (d < 30 nm) that produce a thin film ranging from nm to couple microns. An increase in the volume of solid transfer by the dipping process can open-up a novel technique for the 3D near-net-shape production process via sintering, robocasting or additive manufacturing, and material joining. Adding larger inorganic particle size (> 1μm) and/or by adding higher solid fraction will increase the solid transfer but may result in a multi-phase heterogeneous mixture or slurry. In this work, the physical mechanism of an increased volume of solid transfer with a larger particle size (> 5 μm) is investigated. The metallic particles are spherical in shape with an average diameter of 5.69 μm is considered as the coating material. Polymer-based glue and evaporating solvent are mixed to construct the liquid carrier system (LCS) for large inorganic hard particles. Moderate volume fraction (VF) of inorganic particles (20% < ϕp < 50%) are added into the LCS solution as solid loading. Cylindrical AISI 304 steel wire with dia 0.81 mm is used as the substrate for dipping and coating. The coating thickness (CT) and the surface packing coverage by the particles are measured in our lab. The results presented the influence of volume fraction of inorganic particle and glue composition on the solid transfer from the heterogeneous mixture.