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A. Eder, G. Schmid, H. Mahr, C. Eisenmenger-Sittner:
"Construction and characterisation of a device to coat large quantities of granular materials by magnetron aputtering";
Vortrag: Int. Conf. for Metallurgical Coatings and Thin Films, San Diego, CA, USA; 20.04.2015 - 24.04.2015.

Granular Materials have many applications in the field of material science and catalysis, especially if coated with functional surface layers. With Physical Vapor Deposition (PVD) processes in general and DC magnetron sputtering in special, as used within this work, various layers ranging from metals via oxides and nitrides to complex composite materials such as nanocomposites and multilayered heterostructures can be deposited. Due to the line-of-sight nature of magnetron sputtering each particle surface has to be exposed equally to the vapour beam to achieve homogeneous layers. Therefore continuous intermixing is necessary with special attention to not damage fragile granulate and avoid agglomeration.
A device has been designed to coat up to one liter of granular material with particle diameters ranging from 20 µm to 500 µm. Basically this device is an upscaled version of special coating geometries developed and tested in former projects at the Vienna University of Technology [1,2] and has similarities to a concrete mixer regarding rotation of the mixing bowl and gear mechanism.
The most efficient way to suppress agglomeration during sputter process is to execute strokes against the bowl containing the granular materials. The optimisation of the deposition rate and coating uniformity is made possible by using two sputtering sources which can be tilted in different angles to obtain a vapour beam ideally directed exactly towards the exposed surface of the particle ensemble. In addition the sputter rate varies with the distance between sources and substrate, which leads to higher deposition rates at higher amounts of granulate.
Within this work hollow glass micro spheres are the most used substrate. To characterize the deposition device and the behaviour of the micro spheres under vacuum conditions, the films deposited are mostly Copper and Aluminium due to the high sputter yield. The filmthickness and filmthickness distribution of mono metallic layers can be determined by using a light microscope and a software developed at the Vienna University of Technology [3]. The uniformity of the films was also verified with the scanning electron microscope (SEM).

The financial support of the Austrian Science Fund (FWF) under Grant Nr. TRP-281-N20 is gratefully acknowledged.

References
[1] G. H. S. Schmid, C. Eisenmenger-Sittner, J. Hell, M. Horkel, M. Keding, H. Mahr, Surface & Coatings Technology 205(7) (2010) 1929.
[2] G. H. S. Schmid, C. Eisenmenger-Sittner, Surface & Coatings Technology 236 (2013) 353.
[3] M. Horkel, H. Mahr, J. Hell, C. Eisenmenger- Sittner, E. Neubauer, Vacuum 84(1) (2009) 57.