Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B08—CLEANING
  • B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
  • B08B7/00—Cleaning by methods not provided for in a single other subclass or a single group in this subclass
  • B08B7/0021—Cleaning by methods not provided for in a single other subclass or a single group in this subclass by liquid gases or supercritical fluids

Definitions

• This invention relates in general to a method of removing contaminants from articles and, in particular, to a simple, rapid and effective method of removing from the surface and interstices of a solid article a variety of contaminants with which the article may possibly have come in contact during its manufacture. More specifically, the present invention relates to a method of removing organic contaminants from such articles using gases in the super-critical state.
• Components and materials used in the manufacture of instruments for aerospace applications must be free from contaminants.
• the contamination of the component may consist of saponifiable- materials such as oils as well as non-saponifiable materials such as resins.
• Components formed from metal or synthetic plastic materials may contain gaseous or vaporizable contaminant residues from the manufacture and processing of the metal such as uncured prepolymers, release agents and unreacted monomers used in the processing of these materials.
• thermal vacuum cleaning To effect the required level of cleaning of the materials used in the manufacture of components which meet government standards for cleanliness, the art has developed cleaning processes for these materials utilizing high vacuum, e.g., lO""**-* torr (millimeters of mercury or mmHg) and elevated temperatures up to 250°C to remove absorbed and adsorbed organic contaminants from the materials.
• This cleaning technique referred to in the art as "thermal vacuum cleaning" is not completely satisfactory in that the cleaning process must be carried out in an expensive and complex high vacuum system which normally requires about fifteen hours to obtain the desired contaminant free surface.
• the rapid removal of organic-based contaminants from articles, both porous and non-porous, without damage or contamination to the article is effected by contacting the article bearing the contaminant in a pressure vessel with a gas under super-critical conditions of temperature and pressure, whereby the contaminant on the surface and/or in the interstices of the article is absorbed by the gas and, thereafter, purging the gas from the pressure vessel to obtain the article having the contaminant removed therefrom.
• surfaces is meant not only exterior surfaces but also interior surfaces which communicate therewith.
• the critical temperature As the gas is subjected to increasingly higher pressure, e.g., on the order of several thousand pounds per square inch (psi) (one psi equals 51.71493 mm of mercury), the density of the gas approaches that of a liquid and the gas acts as a solvent for a variety of different types of organic and organo-metallic materials, including aliphatic and aromatic hydrocarbon organo- metallics such as metal alkyIs and alcoholates, silicones and boroalkyls and organic esters or inorganic acids such as sulfuric and phosphoric acid.
• the critical temperatures and pressures for a variety of gases at which they exist in the super-critical condition may be found in U.S. Patent No. 4,124,528, the teachings of which are hereby incorporated by reference.
• the article of manufacture to be cleaned is placed in a suitable vessel such as a pressure chamber or autoclave and the gas which is to effect the cleaning of the article surface is admitted to the vessel in a super ⁇ critical condition.
• Cleaning of the article is accomplished in the pressurized vessel under conditions which maintain the super-critical condition of the gas used for cleaning.
• the cleaning is conducted at a temperature range of about 35°C to about 100°C at about 1200 psi (62,058 mmHg) to about 10,000 psi (517,149 mmHg) pressure and preferably about 40°C to about 50°C and about 3,000 psi (155,145 mmHg) to about 8,000 psi (413,719 mmHg) pressure.
• Inert gases having a critical temperature below about 200°C are considered most advantageous in the practice of the present invention.
• CC1 2 F 2 , 2 0, noble gases such as argon, NH3 and N .
• Gases such as CO2 are preferred in the practice of the present invention as the super-critical temperature of such gases is near ambient temperature; the gases are inexpensive, non-toxic, and relatively inert to most solid substrates.
• C0 is especially preferred as this gas in the super-critical state has a very low viscosity, namely 0.05 centipoise, which is one-twentieth that of water. As a result, the gas in the super-critical state can penetrate very readily into the contaminant to effect its rapid removal from the article being cleaned.
• the article to be cleaned be preheated prior to its place ⁇ ment in the pressure vessel to a temperature above ambient, e.g., about 30°C to about 100°C, and preferably about 40° to 50°C.
• the absorptive capacity of the gases in the super ⁇ critical condition with respect to most contaminants, and particularly contaminants of basically organic origin, is raised with increased pressure.
• a pressure which is substantially higher than the critical pressure of the gas and a temperature only slightly above the critical temperature is selected for maintaining the gas in the super-critical condition.
• the temperature and pressure conditions under which the gas is caused to contact the article to be cleaned be sufficiently above the critical temperature and pressure in order to have a single physical phase, i.e., the gaseous phase, of the gas present in the pressurized vessel during the cleaning operation.
• the gas when such gas is used as the cleaning medium, the gas is maintained at a temperature of about 35°C to about 100°C and a pressure of 2,000 psi (103,430 mmHg) to 10,000 psi (517,149 mmHg) in the pressure vessel.
• the article when placed in the pressure vessel for cleaning, is contacted with the gas under super-critical conditions for a period of time ranging from about 0.25 hour to about four hours and preferably about 0.5 hour to about one hour to effect complete removal of contaminants.
• the pressure in the vessel is released and the gas containing the absorbed contaminants are vented or purged from the vessel into the atmosphere.
• the cleaned article is then removed from the vessel.
• the gas in the super ⁇ critical condition is vented or purged from the pressurized vessel into a suitable collection vessel where the pressure is reduced or the temperature lowered at constant pressure, which conditions render the gas a non-solvent for the contaminant which then precipitates from the gas.
• the gas, freed of contaminants, can then be recompressed and recycled for use in the cleaning of contaminated articles.
• Example I A high pressure autoclave (10,000 psi or 517,149 mmHg maximum working pressure) of 300 milliliter (ml) capacity was equipped with a gas inlet, a gas outlet, pressure gauge, a thermocouple well, and heating means. Connected to the gas inlet was a CO2 supply bottle which delivered the C0 at 800 psi (41,372 mmHg) gauge. A gas booster pump operating on the 100 psi (5171 mmHg) shop air and having the capability to raise the bottle pressure to a maximum to 10,000 psi
• Example I The procedure of Example I was repeated to clean a polyimide polymer containing contamination in the form of volatile solvents by exposure to CO2 for one hour under super-critical conditions of 8,000 psi (413,719 mmHg) pressure and a temperature of 45 ⁇ C.
• OMPI under conditions of 125°C temperature and a vacuum of 10 ⁇ 5 torr (mmHg) or thermogravimetry mass spectrometry (TGA-MS) under conditions of one atmosphere and temperatures of 210°C or 820 ⁇ C.
• TGA-MS thermogravimetry mass spectrometry
• Example III The procedure of Example I was repeated with the exception that thin-sectioned parts of less than 0.25 inch thickness of a diverse selection of organic and inorganic materials were cleaned by exposure to C0 2 under super-critical conditions with only minor changes in the mechanical and physical properties of the materials being observed thereafter.
• the laser casting alloy was subjected to a vacuum- pressure cycle in silicone oil (Dow-Corning DC-200) to saturate the metal with the silicone oil.
• the oil- saturated metal part was then cleaned according to Military Interim Specification (MIS) 23542D, a cleaning specification for these parts.
• MIS-23542D the material to be cleaned is subjected to an exhaustive extraction in a Soxhlet apparatus using toluene as the solvent followed by evaporation of the solvent and an infrared (IR) spectra examination of the residue.
• the IR examination must indicate the absence of silicone or other residues to establish removal of all traces of silicone oil contaminant. To achieve this result required four days of treatment with the Soxhlet extraction apparatus, whereas by using the procedure of Example I, removal of all traces of silicon oil contaminants from a similar laser casting alloy similarly saturated with silicone oil was achieved in two hours.

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• Cleaning In General (AREA)
• Detergent Compositions (AREA)

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Cited By (21)

Citations (2)

• 1983
  • 1983-10-31 EP EP83903757A patent/EP0127643A1/en not_active Withdrawn
  • 1983-10-31 WO PCT/US1983/001713 patent/WO1984002291A1/en not_active Application Discontinuation
  • 1983-12-02 IT IT49424/83A patent/IT1175802B/it active
  • 1983-12-05 ES ES527786A patent/ES527786A1/es not_active Expired
  • 1983-12-05 KR KR1019830005750A patent/KR840007367A/ko not_active Application Discontinuation

Patent Citations (2)

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