Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2000-07-28
2002-07-09
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S704000, C428S701000, C428S702000, C428S472000, C428S469000, C428S220000, C428S336000, C427S327000, C427S375000
Reexamination Certificate
active
06416870
ABSTRACT:
TECHNICAL FIELD
This invention relates to corrosion-resistant coating compositions and a process for applying multilayer coatings. More particularly, this invention relates to thin, multiple layer coatings composed of layers of at least two differing compositions. Preferably, the multiple layers of the coating are applied by a combustion chemical vapor deposition process. The coatings can be applied to the surfaces of various articles in order to provide beneficial surface properties to the articles.
BACKGROUND OF THE INVENTION
The use of coatings to provide corrosion protection to an underlying article or substrate is common. Protective coatings can include organic coatings such as paints and epoxies; nonmetallic coatings such as cements, enamels and oxides; and metallic coatings such as chrome and gold plating. Application of these coatings can be accomplished by such differing processes as painting and spraying to plating and vapor deposition. The process of applying the coating is often dependent on or limited by the properties of the material being deposited and of the properties of the substrate.
Research on improving protective coatings has been extensive for many different materials and applications. The object of protective coatings is to provide corrosion resistance to the underlying substrate and enhance the corrosion resistance of the substrate to the various environments the substrate may encounter. Many coatings are limited to particular environments because of their inability to withstand certain temperature and/or corrosive conditions. The use of organic binders in many coatings limits the use of those coatings at elevated temperatures. A coating not requiring organic binders may withstand elevated temperatures.
Additionally, many articles requiring corrosion protection have specific weight limitations. Therefore, thinner and accordingly lighter coatings are desired. Thinner coatings are also desirable because they require less material, do not significantly change the substrate size, and offer the potential to reduce material costs. Protective coatings, regardless of their composition and the manner in which they are applied, must be adherent to the substrate they are to protect. In order to protect the underlying substrate, the protective coatings must act as a protective barrier against the corrosive agent or as a sacrificial layer. Sacrificial protective layers have the disadvantage that a sacrificial protective layer only provides temporary protection and must be replaced once it has been expended.
Inorganic coatings have also been used for corrosion protection. However, inorganic coatings are typically made of materials that have low coefficients of the thermal expansion relative to the higher coefficient of thermal expansion metal substrates they are intended to protect. While inorganic coatings may perform adequately at a particular temperature, the inorganic coatings on the metal substrates are not able to withstand large temperature changes. When the metal substrate and the coating are subject to large temperature increases and decreases, the underlying metal substrate expands and contracts, respectively, to a greater degree than the inorganic coating. The coefficient of expansion mismatch causes the brittle inorganic coating to crack and break away from the surface of the metal, a phenomenon known as spalling. Thus, the metal is no longer protected by the coating and may become exposed to the corrosive agents.
Metals have been used as protective coatings. However, most metals are subject to corrosion, especially at elevated temperatures and in aqueous, salt and acidic environments. Additionally, metal coatings are expensive, heavy and can be removed by abrasion.
Accordingly, there is a need for an improved corrosion-resistant coating which is more durable and effective under a broader range of conditions, particularly at elevated temperatures and in acidic and saline environments.
SUMMARY OF THE INVENTION
The present invention fulfills the above described needs by providing a multilayer coating for an article or substrate and a method of protecting article substrates. The coating and coated article comprise a coating system which comprises a first distinct layer of a first composition over a metal substrate and a second distinct layer of a second composition over the first distinct layer, wherein the composition of the second distinct layer is different than the composition of the first distinct layer. The coating system may comprise additional layers.
A corresponding method of protecting a substrate or article is also disclosed. The method comprises the steps of depositing a first distinct layer of a first composition over the substrate and depositing a second distinct layer of a second composition over the first distinct layer wherein the composition of the second distinct layer is different than the composition of the first distinct layer. Preferably, the multiple layers of the coating are deposited by a combustion chemical vapor deposition process. In a first preferred embodiment, the coating comprises alternating, discrete layers of silica and chromia. In a second preferred embodiment, the coating comprises alternating, discrete layers of silica and zinc phosphate, wherein the silica layer may be a doped or undoped layer of silica. In a third preferred embodiment, the coating comprises alternating, discrete layers of silica and zinc phosphate, wherein the silica layer may be a doped or undoped layer of ceria.
Accordingly, an object of the present invention is to provide an improved corrosion-resistant coating.
Another object of this invention is to provide an improved method of protecting a corrosion susceptible substrate or article.
Still another object is to provide a coating system that is economical and easy to apply.
Other objects, features and advantages of the present invention will become apparent from the following detailed description, drawings, examples and claims.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Metals, in particular non-noble metals, are susceptible to corrosion. Corrosion-resistant coatings have been applied to the surface of metals to protect the metal from the corrosive agent(s). The coatings must be able to withstand the corrosive agents and any environmental conditions which the coating and underlying metal are likely encounter. Two types of corrosion-resistant coatings currently used include organic coatings, such as plastic coatings and paints, and inorganic coatings. The organic coatings, while typically easy to apply, do not always provide sufficient protection in all environmental conditions. Organic coatings and coatings containing organic components degrade or melt at high temperatures and therefore are not able to withstand elevated temperatures. The multilayer coatings in accordance with the present invention do not require organic components which degrade or melt at high temperatures. Additionally, the multilayer coatings in accordance with the present invention do not require the use of any intermediate compounds such as binders, etc. to add additional weight and cost or limit the use of the coatings at high temperatures. The multilayer coatings in accordance with the invention are better able to withstand elevated temperatures and liquid corrosive environments than conventional coatings.
Although, inorganic coatings are better able to withstand elevated temperatures they are more difficult to apply than organic coatings. Additionally, inorganic coatings, such as aluminum oxide, silicon dioxide, chromium oxide, etc., typically have low coefficients of thermal expansion relative to the metals, steel, aluminum, copper, brass, etc., upon which they are coated to protect. When the metal substrates and the overlying inorganic coatings are subject to large temperature changes, the metal substrate expands to a greater degree than the overlying inorganic coating. The coefficient of expansion mismatch causes the brittle inorganic coatings to crack and break away from the surfaces of the metal substrate, a p
Hendrick Michelle R.
Hunt Andrew Tye
Hwang Tzyy Jiuan
Shao Hong
Thomas Joseph R.
Boss Wendy
Jones Deborah
MicroCoating Technologies, Inc.
Muratori Alfred H.
Nacker Wayne E.
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