Electrolysis: processes – compositions used therein – and methods – Electrolytic material treatment – Metal or metal alloy
Reexamination Certificate
2002-11-12
2004-11-02
Bell, Bruce F. (Department: 1746)
Electrolysis: processes, compositions used therein, and methods
Electrolytic material treatment
Metal or metal alloy
C205S724000, C205S730000, C205S731000, C205S734000, C205S735000, C205S736000, C205S740000, C204S196020, C204S196040, C204S196060, C204S196070, C204S196110, C204S196120, C204S196160, C204S196260, C204S196370
Reexamination Certificate
active
06811681
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control apparatus, system, and method for controlling a semiconductor-based corrosion and fouling prevention system.
2. Discussion of the Background Art
The annual cost of metallic corrosion in the United States economy is approximately $300 billion, according to a report released by Battelle and the Specialty Steel Industry of North America entitled “Economic Effects of Metallic Corrosion in the United States,” dated 1995, the entire contents of which is hereby incorporated by reference. The report estimates that about one-third of the cost of corrosion ($100 billion) is avoidable and could be saved by broader application of corrosion-resistant materials and application of best anti-corrosive practice from design through maintenance. The estimates result from a partial update by Battelle scientists of the findings of a study conducted by Battelle and the National Institute of Standards and Technology titled “Economic Effects of Metallic Corrosion in the United States,” the entire contents of which are hereby incorporated by reference. The original work in 1978 included an estimate that, in 1975 metallic corrosion cost the U.S. $82 billion (4.9 percent of the Gross National Product), and approximately $33 billion was avoidable because best practices were not used at the time.
Regarding aviation, corrosion and the magnitude of its associated cost and effect on safety is a leading concern of global aircraft manufacturers, airline companies, and passengers. In North America alone, aircraft industry corrosion costs exceed $13 billion a year. The impact is equally as great for government aircraft with, for example, the U.S. Air Force spending in excess of $800 million annually for aircraft corrosion control and repair. Corrosion, not design life, is the primary factor in the grounding and retirement of aircraft. The FAA has ranked preventing aircraft structural failure as a top priority for improving aircraft and passenger safety. Aircraft corrosion is linked to a significant number of mishaps, accidents, and plane crashes. The tragedy of the loss of human life aside, the FAA has calculated the monetary cost per passenger fatality at $2.7 million. Left undetected and/or untreated, corrosion undermines the integrity of an aircraft, increasing maintenance costs, and the risk to passenger safety.
Regarding marine vessels, interior and exterior hull corrosion and exterior hull surface fouling are major factors affecting ship operating costs and vessel life. Fuel expenses represent 35% to 50% of overall operating costs. Corrosion, fouling, and the associated exterior hull roughness and skin friction contribute up to an additional 50% to these costs due to the increased power requirement necessary to attain and maintain vessel cruising speeds. Corrosion damage to interior hull surfaces, its cumulative effects on structural integrity, and the cost of correction, not vessel age, are the major deciding factors in vessel retirement and can significantly shorten the useful life of a ship.
Regarding water towers, there are an estimated 150,000 to 200,000 municipal water towers in the United States. An average water tower has a surface area, inside and outside, and of 23,000 square feet and holds 310,000 gallons. These towers are particularly corrosion prone due to excessive condensation resulting from the storage of cool water. To maintain structurally sound water towers, municipalities refurbish tanks approximately every six years in coastal areas and every seven to nine years inland, with an average cost per water tower in excess of $100,000.
Regarding bridges, the National Bridge Inventory lists 575,413 highway bridges in the United States, with 199,277 of them described as structurally deficient or obsolete as of 1992. The Intermodal Surface Transportation Efficiency Act of 1991 authorized $16.1 billion over a period of 6 years for the Highway Bridge Replacement and Rehabilitation Program. The Transportation Equity Act for the 21
st
Century, signed in 1998, continues the program with the authorization of $20.3 billion over the next 6 years for bridge rehabilitation and replacement. The Federal Highway Administration and the Transportation Research Board estimate that 100 million square feet of bridge surface is coated annually. The square footage painted per year has been restricted due to the costs and time required for the removal and containment of lead based paints. As a result, many states have delayed bridge maintenance painting and only an estimated 1,500 steel bridges are painted annually. With current coatings lasting only 10 to 12 years, the backlog of bridge recoating continues to grow.
Regarding automotive concerns, corrosion issues affecting vehicle safety are a major problem for automobile manufacturers and consumers alike. According to the National Highway Transportation Safety Administration, between 1975 and 2001, over 25,000,000 vehicles have been officially recalled in the United States for corrosion related safety problems. In 1998 alone, Ford Motor Company recalled over 2,000,000 vehicles for safety related corrosion problems at a cost estimated to be in excess of $200 million.
A variety of methods for controlling corrosion have evolved over the past several centuries, with particular emphasis on methods to extend the life of metallic structures in corrosive environments. These methods typically include protective coatings, which are used principally to upgrade the corrosion resistance of ferrous metals, such as steel, and some nonferrous metals, such as aluminum, and to avoid the necessity for using more costly alloys. Thus, they both improve performance and reduce costs. However, such protective coatings typically have several pitfalls, including poor applicability to non-metallic structures that suffer from corrosion or fouling.
Protective coatings fall into two main categories. The largest of these categories is the topical coating such as a paint that acts as a physical barrier against the environment. The second category consists of sacrificial coatings, such as zinc or cadmium that are designed to preferentially corrode in order to save the base metal from attack.
Cathodic protection and coatings are both engineering disciplines with a primary purpose of mitigating and preventing corrosion. Each process is different: cathodic protection prevents corrosion by introducing an electrical current from external sources to counteract the normal electrical chemical corrosion reactions whereas coatings form a barrier to prevent the flow of corrosion current or electrons between the naturally occurring anodes and cathodes or within galvanic couples. Each of these processes provided limited success. Coatings by far represent the most wide-spread method of general corrosion prevention (see Leon et al U.S. Pat. No. 3,562,124 and Hayashi et al U.S. Pat. No. 4,219,358). Cathodic protection, however, has been used to protect hundreds of thousands of miles of pipe and acres of steel surfaces subject to buried or immersion conditions.
Cathodic protection is used to reduce the corrosion of the metal surface by providing it with enough cathodic current to make its anodic dissolution rate become negligible (for examples, see Pryor, U.S. Pat. No. 3,574,801; Wasson U.S. Pat. No. 3,864,234; Maes U.S. Pat. No. 4,381,981; Wilson et al U.S. Pat. No. 4,836,768; Webster U.S. Pat. No. 4,863,578; and Stewart et al U.S. Pat. No. 4,957,612). Cathodic protection operates by extinguishing the potential difference between the local anodic and cathodic surfaces through the application of sufficient current to polarize the cathodes to the potential of the anodes. In other words, the effect of applying cathodic currents is to reduce the area that continues to act as an anode, rather than reduce the rate of corrosion of such remaining anodes. Complete protection is achieved when all of the anodes have been extinguished. From an electrochemical standpoint, this indicates that sufficient electrons have been suppli
Dowling David B.
Khorrami Farshad
Applied Semiconductor International Ltd.
Bell Bruce F.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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