Flame coating

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The flame coating , often Flammenpyrolytische coating ( English combustion chemical vapor deposition , CCVD) a process for the deposition of functional thin films at atmospheric pressure. The method belongs to the group of chemical vapor deposition (engl. Chemical vapor deposition , CVD).

history

In the 1980s, the first attempts to improve the adhesive strength of were metal - plastic - Connected at Dental - ceramics by flame-pyrolytically deposited silicon dioxide (SiO 2 performed). The silicoater process derived from this represents a starting point in the development of the CCVD processes. In the period that followed, this process was continuously developed and new areas of application for SiO 2 applied by flame pyrolysis were found. At this time, the term "Pyrosil", which is often used today, was coined for these layers. In addition to improving the adhesive strength, this includes broadband reflection reduction of flat glass surfaces or the effect as a barrier layer against various ions.

Procedural principle

During flame coating, a starting compound ( precursor ) suitable for producing the desired layer is added to a fuel gas . This takes place in gas control systems, which guarantee precise dosing and optimal mixing. Organometallic compounds (e.g. silanes , siloxanes and various metal alcoholates such as titanium tetraisopropoxide ) are particularly suitable as precursors ; salts such as metal acetates and metal nitrates or nanoparticles are also used more rarely . The flame is moved at a short distance over the substrate to be coated . Due to the high combustion energy, the precursors form very reactive species that bond firmly to the substrate surface. Since the substrates only come into contact with the flame for a short time, the thermal load is low; this is an advantage over CVD processes such as LPCVD and PECVD (plasma-assisted chemical vapor deposition), in which the substrates usually have to be at high temperatures.

Advantages and disadvantages

Compared to other coating processes, flame coating is particularly cost-effective, among other things because no systems are required to generate and maintain a vacuum . There are very different designs, ranging from burners the size of a ballpoint pen to large production systems with a flame width of more than one meter, making this process very flexible. The disadvantage, however, is that fewer layer materials can be deposited than with some low-pressure processes. The layers are also primarily limited to oxides; Exceptions are some precious metals such as silver , gold and platinum , which can be deposited in metallic form. Only layers can be created for which suitable precursors are available; however, this is the case for most metals.

Applications

Common applications of layers created by flame coating
Layer material Applications
SiO 2
  • Silicon oxide layers are the most commonly produced layers. Freshly created layers are very reactive and are therefore well suited as adhesion-promoting layers for paints and bonds. The additional use of silane-based adhesion promoters such as Glymo can also improve adhesion.
  • Change in optical properties (e.g. increase in transmission )
  • Barrier protection, e.g. B. against gases like O 2 and mobile ions like Na +
WHERE x , MoO x
  • chromogenic materials in "intelligent glazing"
ZnO
ZrO 2
  • Protective layer against mechanical influences (e.g. scratch protection)
SnO 2
TiO 2
  • photocatalytic layers
Ag
  • high electrical conductivity
  • Thermal insulation glazing
  • antibacterial coatings
Al 2 O 3
  • Protection against glass corrosion

literature

  • T. Struppert: The C-CVD process: Fast and inexpensive to thin functional layers - status and outlook . In: Electroplating . No. 8 , 2009, p. 1864-1869 .
  • Thomas Richter, Hans-Jürgen Tiller: Flame pyrolytic silicate coating at normal pressure as an alternative to vacuum processes . In: Vacuum in research and practice . tape 16 , no. 2 , April 2004, p. 85-87 , doi : 10.1002 / vipr.200400218 ( PDF ).

Individual evidence

  1. ↑ R. Janda, J.-F. Roulet, M. Wulf, H.-J. Tiller: A new adhesive technology for all-ceramics . In: Dental Materials . tape 19 , no. 6 , September 2003, p. 567-573 , doi : 10.1016 / s0109-5641 (02) 00106-9 ( PDF ).
  2. ↑ A. Heft, T. Hädrich, T. Struppert, A. Pfuch, M. Homuth, B. Grünler: Deposition of thin functional layers at atmospheric pressure . In: Yearbook Surface Technology . tape 64 . Leuze Verlag, 2008, ISBN 978-3-87480-245-1 , p. 137-149 .
  3. ↑ Aluminum oxide from the flame makes glass surfaces corrosion-resistant Report in the innovation report