Engineers Clean JWST Secondary Reflector with Carbon Dioxide Snow

Carbon dioxide cleaning (CO₂ cleaning) comprises a family of methods for

parts cleaning Parts cleaning is essential to many industrial processes, as a prelude to surface finishing or to protect sensitive components. Electroplating is particularly a sensitive to part cleanliness, since molecular layers of oil can prevent the adhesion ...

and sterilization, using

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...

in its various phases. Due to being non-destructive, non-abrasive, and residue-free, it is often preferred for use on delicate surfaces. CO₂ cleaning has found application in the

aerospace Aerospace is a term used to collectively refer to the atmosphere and outer space. Aerospace activity is very diverse, with a multitude of commercial, industrial and military applications. Aerospace engineering consists of aeronautics and astr ...

, automotive,

electronics The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...

medical Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care practic ...

, and other industries. Carbon dioxide snow cleaning has been used to remove particles and organic residues from metals,

polymer A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...

ceramic A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain ...

glass Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling ( quenching ...

es, and other materials, and from surfaces including

hard drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magne ...

s and optical surfaces.

Applications

cleaning has found application in many industries and technical areas, including aerospace, automotive, electronics, medical, manufacturing, basic and applied research, and

optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultrav ...

. The different carbon dioxide cleaning methods can remove gross contamination, paint, overlayers, grease,

fingerprint A fingerprint is an impression left by the friction ridges of a human finger. The recovery of partial fingerprints from a crime scene is an important method of forensic science. Moisture and grease on a finger result in fingerprints on surfac ...

s, particles down to nanometers in size,

hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...

and organic

residue Residue may refer to: Chemistry and biology * An amino acid, within a peptide chain * Crop residue, materials left after agricultural processes * Pesticide residue, refers to the pesticides that may remain on or in food after they are applied ...

s, and

radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consi ...

residues. Materials cleaned include metals, polymers, ceramics, and glasses. The key limitation is that the contamination must be on the surface, not buried within the material. Porous materials are not good candidates for pellets or snow, but can be cleaned using liquid or supercritical CO₂.

Methods

Carbon dioxide cleaning refers to several different methods for parts cleaning, making use of all phases of : basic methods include solid

dry ice Dry ice is the solid form of carbon dioxide. It is commonly used for temporary refrigeration as CO2 does not have a liquid state at normal atmospheric pressure and sublimates directly from the solid state to the gas state. It is used primarily ...

pellets, liquid , snow (a hybrid method), and supercritical . The different forms of cleaning can clean many types of objects, from large generators to small and delicate parts, including hard drives and optics.

Pellets

In pellet cleaning ("

dry-ice blasting Dry-ice blasting is a form of carbon dioxide cleaning, where dry ice, the solid form of carbon dioxide, is accelerated in a pressurized air stream and directed at a surface in order to clean it. The method is similar to other forms of media bla ...

"), relatively large pellets of solid CO₂ are fired at the surface to be cleaned. These pellets impinge on the surface, mechanically dislodging contaminant particles. Pellet cleaning is only appropriate for surfaces sturdy enough to withstand significant impacts.

Snow cleaning

In CO₂ snow cleaning, compressed liquid or gaseous

is expelled from a nozzle, condensing into a mixture of solid particles and gas, which impact the surface to be cleaned. Jet velocities are frequently supersonic. Snow cleaning works by a combination of momentum transfer (mechanically dislodging contaminant particles) and

solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

action. The CO₂ sublimates on contact, increasing in volume up to 800 times, thereby generating pressure to sweep particles away. The CO₂ also dissolves hydrocarbon contaminants, and its low temperature embrittles residues such as fingerprints, making them easier to blow away. Snow cleaning has found application in the aeronautical, automotive,

optical Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultravio ...

semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...

, and

space Space is the boundless three-dimensional extent in which objects and events have relative position and direction. In classical physics, physical space is often conceived in three linear dimensions, although modern physicists usually cons ...

industries. It can provide a gentle cleaning, appropriate for delicate surfaces. The effectiveness of carbon dioxide snow cleaning has been demonstrated via light microscopy, particle counting, scanning electron microscopy, microprobing,

X-ray photoelectron spectroscopy X-ray photoelectron spectroscopy (XPS) is a surface-sensitive quantitative spectroscopic technique based on the photoelectric effect that can identify the elements that exist within a material (elemental composition) or are covering its surface, ...

atomic-force microscopy Atomic force microscopy (AFM) or scanning force microscopy (SFM) is a very-high-resolution type of scanning probe microscopy (SPM), with demonstrated resolution on the order of fractions of a nanometer, more than 1000 times better than the opti ...

, and mass spectroscopy. Equipment costs for a carbon dioxide snow cleaning system can range from US$1500 for a basic system to $50,000 for a high-end automated unit. Material costs are comparatively low, although ultra-pure CO₂ must often be used to avoid the introduction of new contaminants.

Supercritical fluid

At temperatures and pressures above its critical point, CO₂ can be maintained as a supercritical fluid, exhibiting extremely low

viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...

and high

solvency Solvency, in finance or business, is the degree to which the current assets of an individual or entity exceed the current liabilities of that individual or entity. Solvency can also be described as the ability of a corporation to meet its long-t ...

. To apply this method, parts to be cleaned are enclosed in a pressure vessel that is then filled with supercritical CO₂. This method is appropriate for small and delicate parts such as microelectronics, and is not ideal for particulate removal. Aside from cleaning, applications of supercritical carbon dioxide include targeted chemical supercritical fluid extraction and materials processing.

Liquid CO₂ washing

Liquid CO₂ washing, like supercritical fluid CO₂ washing, relies on the high solvent power of CO₂, but at lower temperatures and pressures, the latter making it simpler to implement. Because liquid CO₂ does not have the solvent power of the supercritical fluid, agitation and surfactants may be added to improve the effectiveness of the method. Liquid CO₂ has been used in

dry cleaning Dry cleaning is any cleaning process for clothing and textiles using a solvent other than water. Dry cleaning still involves liquid, but clothes are instead soaked in a water-free liquid solvent. Tetrachloroethylene (perchloroethylene), known i ...

and machined parts

degreasing Degreasing, often called defatting or fat trimming, is the removal of fatty acids from an object. In culinary science, degreasing is done with the intention of reducing the fat content of a meal. Degreasing food Degreasing is often used by diete ...

History

Carbon dioxide cleaning was contemplated in the 1930s, and the "pellet" approach was developed in the 1970s by E.E. Rice, C.H. Franklin, and C.C. Wong. The introduction of CO₂ snow cleaning, with its ability to remove sub-micron-scale particles, is credited to Stuart Hoenig of the

University of Arizona The University of Arizona (Arizona, U of A, UArizona, or UA) is a public land-grant research university in Tucson, Arizona. Founded in 1885 by the 13th Arizona Territorial Legislature, it was the first university in the Arizona Territory. T ...

, who first published on the topic in 1985–1986. Hoenig traveled the US to demonstrate the technology, eventually attracting the interest of

The BOC Group BOC Ltd is a British based multinational, industrial gas company, more commonly known as BOC, now a part of Linde plc. In September 2004, BOC had over 30,000 employees on six continents, with sales of over £10.6 billion. BOC was a constituent ...

, which developed Venturi nozzles for the process, and

Hughes Aircraft The Hughes Aircraft Company was a major American aerospace and defense contractor founded on February 14, 1934 by Howard Hughes in Glendale, California, as a division of Hughes Tool Company. The company was known for producing, among other pro ...

, which developed straight nozzles. CO₂ snow cleaning was further developed by the Fraunhofer Institute for Manufacturing Engineering and Automation IPA, for the purpose of removing paint from aircraft

fuselage The fuselage (; from the French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds crew, passengers, or cargo. In single-engine aircraft, it will usually contain an engine as well, although in some amphibious aircraf ...

s. Nozzle design is the most significant factor in carbon dioxide snow cleaning performance, affecting the size and velocity of the dry ice particles. Variations in nozzle design have been developed by W.H. Whitlock, L.L. Layden, Applied Surface Technologies, and Sierra Systems Group.

Issues

Safety

CO₂ cleaning may present certain safety risks. If the process is used to remove hazardous materials, precautions must be taken to avoid exposure to these materials in the vent stream. Because the CO₂ stream is cryogenic, it may cause injury with direct skin contact. In addition, care must be taken to prevent the concentration of carbon dioxide in the work area from exceeding safe levels.

Contamination

Some commercial grades of carbon dioxide may contain traces of heavy

s, which can be left behind on the surface being cleaned. Abrasive particles originating in the cleaning equipment itself may need to be filtered out as well. The low temperature of the carbon dioxide stream can also induce moisture condensation on the part, which may be mitigated with hot plates,

heat gun A heat gun is a device used to emit a stream of hot air, usually at temperatures between 100 °C and 550 °C (200-1000 °F), with some hotter models running around 760 °C (1400 °F), which can be held by hand. Heat ...

heat lamp Infrared lamps are electrical devices which emit infrared radiation. Infrared lamps are commonly used in radiant heating for industrial processes and building heating. Infrared LEDs are used for communication over optical fibers and in remote ...

s, or dry boxes.

Static charge

Ionization Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecul ...

caused by the flowing gas can result in potentially damaging

static charge Static electricity is an imbalance of electric charges within or on the surface of a material or between materials. The charge remains until it is able to move away by means of an electric current or electrical discharge. Static electricity is na ...

buildup on non-

conductive In physics and electrical engineering, a conductor is an object or type of material that allows the flow of charge (electric current) in one or more directions. Materials made of metal are common electrical conductors. Electric current is gene ...

parts. This can be mitigated by grounding or positive ionization sources.

References

{{reflist, 30em, refs= {{cite patent , inventor-last = Swain , inventor-first = Eugene A. , inventor2-last = Carter , inventor2-first = Stephen R. , inventor3-last = Hoenig , inventor3-first = Stuart A. , publication-date = Jun 30, 1992 , title = Carbon dioxide snow agglomeration and acceleration , country-code = US , patent-number = 5125979 A {{cite journal, last1=Sherman, first1=Robert, last2=Adams, first2=Paul, title=Carbon Dioxide Snow Cleaning – The Next Generation of Clean, journal=Precision Cleaning, date=1995, pages=271–300, url=http://infohouse.p2ric.org/ref/02/01017.pdf, access-date=24 September 2015 {{cite web, title=Applications, website=Carbon Dioxide Snow Cleaning, url=http://www.co2clean.com/applications, publisher=Applied Surface Technologies, access-date=23 September 2015 {{cite web, title=FAQs, website=Carbon Dioxide Snow Cleaning, url=http://www.co2clean.com/faqs, publisher=Applied Surface Technologies, access-date=23 September 2015 {{cite web, title=AFM, website=Carbon Dioxide Snow Cleaning, url=http://www.co2clean.com/afm, publisher=Applied Surface Technologies, access-date=24 May 2016 {{cite journal , last1 = Chernoff , last2 = Sherman , year = 2010 , title = Resurrecting dirty atomic force microscopy calibration standards , journal = Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena , volume = 28 , issue = 3, page = 643 , doi = 10.1116/1.3388847 , bibcode = 2010JVSTB..28..643C {{cite web, title=What is Dry Ice Blasting (Cleaning)?, url=http://www.coldjet.com/en/information/what-is-dry-ice-blasting.php, publisher=Cold Jet, access-date=23 September 2015 {{cite web, title=About Us, website=Carbon Dioxide Snow Cleaning, url=http://www.co2clean.com/, publisher=Applied Surface Technologies, access-date=4 August 2015 {{cite web, title=Cleaning Methods, url=http://www.co2clean.com/cleaners, website=Carbon Dioxide Snow Cleaning, publisher=Applied Surface Technologies, access-date=13 August 2015 {{cite web, title=Safety Issues, website=Carbon Dioxide Snow Cleaning, url=http://www.co2clean.com/safety, publisher=Applied Surface Technologies, access-date=23 September 2015 {{cite web, title=How does CO2 Blasting Work?, url=http://www.coldjet.com/en/information/how-does-it-work.php, publisher=Cold Jet, access-date=23 September 2015 {{cite web, title=Industries and applications, url=http://www.coldjet.com/en/industries/index.php, publisher=Cold Jet, access-date=23 September 2015 {{cite news, title=Space probes: sterile launch into outer space, url=http://phys.org/news/2015-08-space-probes-sterile-outer.html, access-date=4 August 2015, work=Phys Org, agency=Fraunhofer-Gesellschaft, date=August 3, 2015 {{cite journal, last1=Weibel, first1=Gina, last2=Ober, first2=Christopher, title=An overview of supercritical CO ₂ applications in microelectronics processing, journal=Microelectronic Engineering, volume=65, issue=1–2, date=2003, pages=145–152, url=https://www.researchgate.net/publication/222729244, doi=10.1016/S0167-9317(02)00747-5 Cleaning tools Industrial processes Broad-concept articles Cleaning methods

cleaning Cleaning is the process of removing unwanted substances, such as dirt, infectious agents, and other impurities, from an object or environment. Cleaning is often performed for aesthetic, hygienic, functional, environmental, or safety purposes ...