Combustion chemical vapor deposition (CCVD) is a

chemical process In a scientific sense, a chemical process is a method or means of somehow changing one or more chemicals or chemical compounds. Such a chemical process can occur by itself or be caused by an outside force, and involves a chemical reaction of som ...

by which thin-film coatings are deposited onto substrates in the open atmosphere.

History

In the 1980s initial attempts were performed to improve the adhesion of metal-plastic composites in dental ceramics using flame-pyrolytically deposited silicon dioxide (SiO₂). The silicoater process derived from these studies provided a starting point in the development of CCVD processes. This process was constantly developed and new applications for flame-pyrolytically deposited SiO₂ layers where found. At this time, the name "Pyrosil" was coined for these layers. Newer and ongoing studies deal with deposition of other materials (''vide infra'').

Principles and procedure

In the CCVD process, a precursor compound, usually a metal-organic compound or a metal salt, is added to the burning gas. The flame is moved closely above the surface to be coated. The high energy within the flame converts the precursors into highly reactive intermediates, which readily react with the substrate, forming a firmly adhering deposit. The

microstructure Microstructure is the very small scale structure of a material, defined as the structure of a prepared surface of material as revealed by an optical microscope above 25× magnification. The microstructure of a material (such as metals, polymer ...

and thickness of the deposited layer can be controlled by varying process parameters such as speed of substrate or flame, number of passes, substrate temperature and distance between flame and substrate. CCVD can produce coatings with orientation from preferred to

epitaxial Epitaxy (prefix ''epi-'' means "on top of”) is a type of crystal growth or material deposition in which new crystalline layers are formed with one or more well-defined orientations with respect to the crystalline seed layer. The deposited cry ...

, and can produce conformal layers less than 10 nm thick. Thus, CCVD technique is a true vapor deposition process for making thin film coatings. The CCVD coating process has the ability to deposit

thin film A thin film is a layer of materials ranging from fractions of a nanometer ( monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many ...

s in the open atmosphere using inexpensive precursor chemicals in solution leading to continuous, production-line manufacturing. It does not require post-deposition treatment e.g., annealing. The throughput potential is high. Coatings can be deposited at substantial temperatures, for example, alpha-alumina was deposited on Ni-20Cr at temperatures between 1050 and 1125 C. A 1999 review article summarizes the various oxide coatings that had been deposited to date, which included Al₂O₃, Cr₂O₃, SiO₂, CeO₂, some spinel oxides (MgAl₂O₄, NiAl₂O₄), and yttria stabilized zirconia (YSZ).

Remote combustion chemical vapor deposition (r-CCVD)

The so-called remote combustion chemical vapour deposition is a new variant of the classical CCVD process. It likewise uses flames to deposit thin films, however, this method is based on other chemical reaction mechanisms and offers further abilities for deposition of layer systems which are not practicable by means of CCVD, e.g. titanium dioxide.

Applications

Pros and cons

* Cost-effective, partly because no devices for generation and maintenance of a

vacuum A vacuum (: vacuums or vacua) is space devoid of matter. The word is derived from the Latin adjective (neuter ) meaning "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressur ...

are needed * Flexible in use due to various implementations * Fewer layer materials compared to some low-pressure methods, limited primarily to oxides. The exceptions are some precious metals such as silver, gold and platinum * Limited to layer materials, for which suitable precursors are available, however, this is the case for most metals

References