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Despite the many decades of experience and the expensive equipment employed by the traditional anodizing plants, the acid bath based DC anodizing process has severe limitations. ' By the very nature of the low voltage DC power employed, the anodic coating is quite porous. Much as the traditional process, the Microplasmic process is an electrochemical process, but there ends the similarity. Because of the high voltage, a microplasma surrounds the electrodes and the oxygen ions produced in the plasma diffuse through the anodic film into the aluminum substrate to react and form more anodic film. ' The high voltage and high current allow the production of anodic films of the same thickness as that of the traditional process in a fraction of the time. ' Because the voltages are higher than the breakdown voltage of the film formed, open channels are not necessary for sustaining the process and hence dense thick layers of nonporous film can be readily formed. ' Because the process employs AC power, the productivity is increased. Indeed, successful coatings can be obtained even if the temperature excursions are as much as 10-20 oC, further simplifying the process. ' The electrolytic composition itself is quite variable for different types of coatings. ' Because of the high density of the coating, practically there is no change Article: 1.0 Introduction The practice of anodizing, or controlled oxidation, of aluminum and aluminum alloys is more than seven decades old. The primary intent of anodizing aluminum and aluminum alter parts is to protect the highly reactive surface headed for corrosion in liquid environments, such as humid air and sea water. seeing the anodic veiling can be produced in a variety of colors, painted anodized parts are used in tectonic applications. Furthermore, for the anodization process produces a hard ceramic coating, many times harder than that of the substrate from which it is formed, anodic coatings are also used to protect aluminum parts from abrasion, especially sand abrasion. 2.0 Traditional Anodizing Traditional anodizing is an electrochemical oxidation process. The part to be anodized is connected to the positive terminal of a Direct Current (DC) power source and a nonreactive metal, such as stainless steel, is connected to the negative terminal. The aluminum part, or the anode, and the stainless steel generator are immersed in an electrolytic bath and a DC voltage is used sidewise them. The potential difference is of the order of 20 -100 V and the current densities are 1-10 A/dm2. The electrolytic comprise fluid solutions of chromic acid, orthophosphoric acid, sulfuric acid, oxalic acid, or combinations thereof. as things go the electrolytic sweat room have manifest resistivity and insofar as the anodization process itself is exothermic the temperature of the electrolytic bath increases greatly during anodizing. Since the anodizing process is quite sensitive to temperature, the bath temperature is controlled rather only just by heat exchanger or refrigeration equipment. Today's white-haired anodizing technologies include several proprietary hard anodizing processes that employ a wide range of electrolyte compositions, operating conditions and a limited aluminum alter compositions. The type and thickness of gilding obtained greatly depends on the composition of the electrolytic bath, operating conditions and combo compositions. The military specification MIL-A-8625F, for example, lists at least six types and two classes of electrolytically formed anodic coatings on aluminum and aluminum alloys for non Byzantine applications. Despite the many decades of experience and the expensive equipment employed by the traditional anodizing plants, the acid bath based DC anodizing process has severe limitations. · By the very nature of the low voltage DC power employed, the anodic overlaying is quite porous. Often the volume percent of pores is as much as 50%. · considering of the low current densities employed, it takes many hours to produce a lap of a few tens of micrometers thick. · The electrolytic hangout comprise extremely low pH corrosive electrolytes and thus the process does not meet many of today's environmental regulations. The expensive equipment, such as the electric power supplies and heat exchanger, makes the process pica intensive. · The traditional process, for reasons not quite apparent, cannot be used for anodizing aluminum alloys containing high concentrations of Cu and Si. · Thus, many empty space and automotive parts cannot be satisfactorily anodized, if at all. · The present process, while serviceable for a limited range of the wrought aluminum alloys, cannot be used for anodizing other reactive metals, such as Ti, Zr, Mg, etc., and intermetallic compounds and metal matrix composites. Thus, most of the promising aluminum based polished alloys and composites cannot be protected by the traditional anodizing process. · greater all, the hardness of even the so named hard anodic coatings is far underneath the hardness of dawning alumina, the principal component of the anodic coating. Accordingly, the full strength potential of the anodic layer cannot be realized by the traditional process. · Indeed, the other potentially capital properties of aluminum oxide, such as the high thermal and electrical resistivities and the high dielectric smash-up strength are not even addressed. This state of junction is primarily due to the porosity of the overspreading produced by the traditional acid based electrolytic processes at low power levels, and to perfectly sure extent the poor bonding betwixt and between the aluminum fusion substrate and the anodic layer. 3.0 The Microplasmic Process In recent years, the Microplasmic Corporation, a start up R&D pool of Peabody, MA, U.S.A. has developed a unique anodizing technology, styled the Microplasmic Process for all types of aluminum alloys. It is an electrochemical micro arc oxidation process for which a US patent is pending. A controlled high voltage AC power is practical to the aluminum part submerged in an electrolytic bath of proprietary composition. Due to the high voltage and high current, intense plasma is created by micro arcing at the specimen surface and this plasma in turn oxidizes the surface of the aluminum specimen. Thus the process is named Microplasmic Process. The oxide film is produced by subsurface oxidation and considerably thicker coatings can be produced. Much as the traditional process, the Microplasmic process is an electrochemical process, but there ends the similarity. The Microplasmic process is radically different from the traditional anodizing processes in many respects. The distinguishing features of the process may be summarized as follows. · The process employs alkaline electrolytes whose composition is extremely critical to the upholstering rate and the properties of the anodic film that is formed. The pH of the electrolyte is in the range 8 -12 and is thus environmentally sound. · The process employs capricious Currents at high voltage and high current. being of the high voltage, a microplasma surrounds the electrodes and the oxygen ions produced in the plasma diffuse through the anodic film into the aluminum substrate to react and form more anodic film. · The high voltage and high current tender the production of anodic films of the same thickness as that of the traditional process in a fraction of the time. · for the voltages are higher than the draining voltage of the film formed, open channels are not necessary for sustaining the process and hence dense thick layers of nonporous film can be readily formed. · the process employs AC power, the productivity is increased. · The power from an electrical utility supply can be used with proper controls to the electrochemical tank thus making the process less ultimate intensive. There is no need for power rectification and waveform smoothing. · The temperature of the electrolytic bath need not be precisely maintained. Indeed, successful coatings can be obtained even if the temperature excursions are as much as 10-20 oC, further simplifying the process. · The electrolytic composition itself is quite variable for different types of coatings. · seeing of the high density of the coating, practically there is no innovation in the dimension of the anodized part, and a completely finished part can be floored without major post processing finishing operations. The Microplasmic Process, however, produces an outer soft cloaking of all round 15% that may be satiny off; the remaining inner layer, is an extremely hard ceramic layer. · therewith all, unlike with the traditional anodization process, aluminum jumble parts of any composition can be successfully anodized by the Microplasmic Process. Even more importantly, a variety of ceramic 'alloy' coatings, such as Al2O3.SiO2, Al2O3.MgO, Al2O3..CaO etc. can only be produced by the Microplasmic Process. · The Microplasmic Process is also suited for a hard wafer inside surface of a part i.e. cylindrical, conical or spherical hollow parts. Many blanketing processes in the market, like CVD, PVD, IVD, PEPVD, Sputtering, Thermal Spraying etc. are unable to coat inside surface of a long part. 4.0 Applications Because the microplasmic process produces a thick, well set ceramic colourant on a variety of reactive light metal alloys, it can be used for a brusque range of applications. The primary fidelity could be the replacement of heavier metallic alloys or the more expensive composite materials required by the low-pressure area and automotive industries by light metals (e.g., Al, Ti, Mg, and their alloys) sheathed by the Microplasmic Process. Other applications can be divided into the following categories: Chemical, Mechanical, Thermal, Electrical and Electronics, and combinations of these. · Chemical: The ceramic blanketing can resist both watery and moderately high temperature and is resistant to strong acids and bases. Thus it can be used in chemical, and food processing industries. · Mechanical: The hardness of the film is over 1300 kg/mm2 and thus the film can be used to resist sliding, burnish and erosive wear. In over and above the friction common is low and thus can be used in marginally lubricated systems. · Thermal: The thermal conductivity of the anodic film is much less than of metals. Thus anodized parts can be used to maintain uniform distribution of temperature and resist thermal shock. · Electrical and Electronic: The dielectric injury strength of the Microplasmic film is uniform to that of creation Al2O3 and hence can be used as an insulating film on electrical and electronic components. Additionally, the Microplasmic Process is also well suited for hard plait interior surfaces (such as those of hollow cylindrical and conical parts), recesses, choked off holes, threaded sections, and so on. Many cloaking processes in the market, such as trimer Vapor Deposition (CVD), Physical Vapor Deposition (PVD), Plasma Enhanced Physical Vapor Deposition (PEPVD), Sputtering, Thermal Spraying, etc. are unable to coat the inside surface of a long part. Thus, where mock these expensive blotting out processes can be readily replaced by the Microplasmic Process. Microplasmic Corporation Contact Information: Microplasmic Corporation 17 Esquire Drive Peabody, MA, USA Tel (978) 531-9145 Fax (978) 531-3671 Email: info@microplasmic.com Company Website http://www.microplasmic.com/ Public Relations Website http://www.microarcanodizing.com/
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