Investigation of the Powder Aerosol Deposition Method Using Shadowgraph Imaging

Abstract

The powder aerosol deposition method (PAD) is a vacuum-based spray coating technology. It allows for production of highly dense coatings at room temperature, especially of brittle-breaking materials. This yields new options for coating substrate materials that even melt at low temperatures. The film formation mechanism is called room temperature impact consolidation (RTIC). The occurrence of this mechanism is strongly linked to the gas jet used in the process. The velocity and direction of the particles in the gas jet forming between the nozzle orifice and the substrate are the main factors influencing the quality of the coating. This dependency aimed to be elaborated with a measurement setup and coating experiments and is shown in this work. We investigated the gas jet formation using a shadow optical imaging system. Regions of different gas density are visualized by this technique. Several parameter sets, in particular gas flow rates and chamber pressures, were investigated. In addition, coatings were produced on glass substrates with the same parameters. As a coating material, the superconducting ceramic-like magnesium diboride (MgB2) was chosen. A correlation between shadow images and thickness profiles of the coatings shows how the gas jet formation affects the uniformity of thickness. Shadow optical images provide valuable information on the flight direction of the particles and allow validation of simulation results.

Powder Aerosol Deposition and Polymers: Is There Hope for a Common Future?

“…Several characteristics of the experimental setup and the powder used influence the PAD process and the properties of the layers obtained. Many authors studied the effects of varying the powder characteristics (i.e., crystallite size, particle size, and morphology), the powder pretreatment (i.e., sieving, drying, preheating, and milling), [48,[57][58][59][60][61][62][63][64][65][66][67] the process parameters (i.e., mode of aerosol generation, [58,68] carrier gas type and carrier gas flow rate, [11,19,[35][36][37][69][70][71] nozzle type and the evolution of the gas flow field, [19,35,37,44] deposition angle [72] ), as well as characteristics of the substrate (i.e., roughness, hardness, and substrate temperature). [31,44,73,74]…”

“…[1] Since then, AD technology spread throughout the world, [2] with research being conducted primarily in South Korea, [3][4][5] Japan, [6][7][8] the United States of America, [9,10] and Germany. [11][12][13] Today, PAD research is still confined to a small number of research groups working on mechanistic studies, [14][15][16] in some cases combined with simulation methods, [13] on process parameter studies, [17][18][19][20] on process setup modifications, [21,22] or on the development of new types of materials with unique architectures that are not easily accessible by other processes. Examples for the latter are solar cells with a dry-processed perovskite absorber layer, [23] flexible thermoelectric generators, [24] or multilayered materials such as metal-ceramics composites.…”

Compressibility and Rarefaction Effects on Particle Dynamics and Heat Transfer in Aerosol Deposition Process

“…Therefore, a two-dimensional axisymmetric nozzle with 4 mm 2 exit surface area is used. It should be noted that the surface area of the nozzles in different experimental and numerical studies are in the range of 2 to 5 mm 2 [13,18,28,40]. The slit nozzles with rectangular cross-sections, in which axis-switching phenomena for the gas phase can happen, were modeled using 3D geometries and meshes in the previous paper [30].…”

“…It is worth mentioning that, in order to control the particle velocity in a broad range, helium gas is usually used, while air or nitrogen gas can be used to reduce the cost [17]. Glosse et al [18] investigated the effect of gas flow rates and chamber pressures on the jet formation using a shadow optical imaging system and were able to estimate the gas flow structure and the particle trajectories. Particle size also significantly affects the particle trajectory and velocity.…”

Is simply covering the patient's mouth with a surgical mask during transnasal endoscopy sufficient as an anti-COVID-19 measure?

“…This method is extremely useful for the visualization and evaluation of high-speed phenomena, mainly in the engineering field. 8,9 The following experiments were conducted with the intra-gastric pressure of an excised swine stomach maintained at 8 mmHg using a carbon dioxide insufflation system (GW-200; Fujifilm, Tokyo, Japan). A thin endoscope (EG-6400N; Fujifilm) was advanced into the stomach, and gas leakage from the biopsy valve during insertion and withdrawal of the biopsy forceps was visualized (Fig.…”