Abstract
The reflective properties of micro glass spheres (MGS) such as Solid Micro Glass Spheres (SMGS, “glass beads”) and Micro Hollow Glass Spheres (MHGS, “glass bubbles”) are utilized in various applications, for example, as retro-reflector for traffic road stripe paints or facade paints. The reflection behavior of the spheres can be further adapted by coating the surfaces of the spheres, e.g., by titanium dioxide or a metallic coating. Such coated spheres can be employed as, e.g., mid infrared (MIR)-reflective additives in wall paints to increase the thermal comfort in rooms. As a result, the demand of heating energy can be reduced. In this paper, the increase of the MIR-reflectance by applying an aluminum coating on MGS is discussed. Aluminum coatings are normally produced via the well-known Physical Vapor Deposition (PVD) or Chemical Vapor Deposition (CVD). In our work, the Liquid Phase Deposition (LPD) method, as a new, non-vacuum method for aluminum coating on spherical spheres, is investigated as an alternative, scalable, and simple coating process. The LPD-coating is characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and reflection measurements. The results are compared to a reference PVD-coating. It is shown that both sphere types, SMGS and MHGS, can be homogeneously coated with metallic aluminum using the LPD method but the surface morphology plays an important role concerning the reflection properties. With the SMGS, a smooth surface morphology and a reflectance increase to a value of 30% can be obtained. Due to a structured surface morphology, a reflection of only 5% could be achieved with the MHGS. However, post-treatments showed that a further increase is possible.
Highlights
IntroductionMicro glass spheres (MGS), such as micro solid glass spheres and micro hollow glass spheres, are utilized in various technical fields due to their excellent physical and chemical properties
Micro glass spheres (MGS), such as micro solid glass spheres and micro hollow glass spheres, are utilized in various technical fields due to their excellent physical and chemical properties.Solid Micro Glass Spheres (SMGS) exhibit high strength, as well as smooth surfaces, and are excellently suited as grinding and dispersing balls [1]
An error of less than 0.01% was preparation and measurements of the powder samples
Summary
Micro glass spheres (MGS), such as micro solid glass spheres and micro hollow glass spheres, are utilized in various technical fields due to their excellent physical and chemical properties. Solid Micro Glass Spheres (SMGS) exhibit high strength, as well as smooth surfaces, and are excellently suited as grinding and dispersing balls [1]. They are utilized as fillers in thermoplastics and thermosets to enhance the physical properties of the matrix, like increasing the Young Modulus and hardness [2,3,4]. Micro Hollow Glass Spheres (MHGS) are characterized by a low density, as well as by low thermal conductivity. E.g., in polymers or building materials, a decrease in weight and minimization of thermal conductivity is possible and could lead to energy savings, especially in the automotive and building industry [5,6,7,8,9,10,11].
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