CO2 Changes Surfaces in Different Ways
The most practical and unique aspect of CO2 processing technology is its ability to transform the chemical and physical nature of a manufactured surface, selectively or non-selectively, and in many different ways. Example surface transformations include dirty-to-clean, hot-to-cool, low surface free energy-to-high surface free energy, high outgassing-to-low outgassing, and non-polar-to-polar.
Surface Contamination Constrains Manufacturing
Manufacturing systems comprise numerous processes and apparatuses needed to fabricate a product. In addition, manufacturing systems require inputs such as space, energy, materials, labor, and time. Processes include wire bonding, hard metal turning, precision assembly, adhesive bonding, welding, and inspection, among many other examples.
Problem-Opportunity-Solution
The CO2 processing system comprises three components, as follows:
CO2 as a Solvent, Coolant, and Lubricant
It has been known for more than 80 years that CO2 behaves in a manner similar to an organic “solvent” when compressed to liquid-like densities and as an organic “solute” when compressed into and mixed with another organic solid or liquid. Examples include CO2 plasticization of polymers such as low density polyethylene (LDPE) and solid CO2 mixed into and complexed with cold hydrocarbon solvents. CO2 modifies the physical and chemical properties of solids and liquids having similar cohesion energies, for example expanding organic solvents to reduce viscosity and increasing permeability of gases into polymers.
Cleaning, Cooling, and Lubrication
Carbon dioxide (CO2) is a colorless, odorless, and naturally occurring chemical compound made up of one carbon atom covalently double bonded (resonantly) to two oxygen atoms. Carbon dioxide exists in Earth's atmosphere as a trace gas at a concentration of about 400 ppm. Natural sources include volcanoes, hot springs, and geysers. It is present in deposits of petroleum (liquid), natural gas, and calcium carbonate (limestone). It is released from limestone by heat and pressure (sublimation) and by dissolution in water and acids. Because carbon dioxide is soluble in water, it occurs naturally in groundwater, rivers and lakes, in ice caps and glaciers, and also in seawater. Major industrial sources of CO2 include fermentation, fertilizer production, energy production, and petroleum oil processing plants. CO2 is continuously generated from and/or transformed into various carbon-based compounds - liquid, gas, and solid - through numerous natural and industrial processes such as photosynthesis, fermentation, combustion, and chemical synthesis. CO2-laden emissions from natural and industrial sources are captured, purified, liquefied, stored, and distributed for reuse in many industrial processes.
CO2 Processing Units (CPU®)
CO2 technology innovation continues today with an emphasis on new market and application development, and more particularly the development and implementation of a new business model innovation uniquely adapted to this disruptive technology. For example, CO2 surface treatment technology performs three basic functions (or processes) – precision cleaning, cooling, and modification. CO2 technology performs these functions in unique ways which are lean, green, 100% dry, inherently compatible with materials and tools, and enhance performance of manufacturing processes requiring one or a combination of these functions [36].
Purification, Delivery, and Recycling
During the initial CO2 technology development period, adjunct innovations were co-developed to support the CO2 immersion and spray cleaning platforms. Shown in Figure 1-20, technologies include single- and multi-stage CO2 distillation systems, cold-trap refluxing stills, in-situ condenser-purifiers, and high pressure-capacity CO2 delivery systems.
SnoBot and CleanFlex
Small affordable (so-called) desktop robots were being introduced in the early 1990’s. While watching the movie Jurassic Park in a theater in 1993, I saw a small robot – called the Mitsubishi RV-M1 – being used to pick up, rotate, and place eggs in a dinosaur nursery incubator. Fascinated by the small robot operation, I quickly realized that this type of system would be the perfect automation solution for the new CO2 spray cleaning technology that I was just beginning to develop at the time. Shown in Figure 1-16, the first prototype SnoBot™ robotic CO2 spray cleaning system was developed by late 1995 using the RV-M1 robot. The SnoBot system featured an end-of-arm CO2 composite spray applicator equipped with a red light laser pointer to assist with teaching point-to-point CO2 spray cleaning paths using the built-in teach pendant and BASIC (Basic All-Purpose Symbolic Instruction Code) programming platform.
Pencil Snow Blaster
Concurrent with centrifugal liquid CO2 immersion cleaning process commercialization, development of a new CO2 spray cleaning technology also began in the early 1990’s. CO2 spray cleaning is a selective line-of-sight surface cleaning process. The first precision CO2 spray cleaning system, called the SNOGUN™, was developed by Dr. Stuart Hoenig, Arizona State University in the mid-1980’s [27]. The SNOGUN innovation was refined by Hughes Aircraft (and many others) in the 1990’s. My interest in the SNOGUN was that a CO2 spray cleaning process complements a CO2 immersion cleaning process. Analogous to conventional solvent vapor degreasers, a CO2 spray (wand) provides a final clean or rinse step to remove thin films and micro-particulate contamination following general cleaning using centrifugal liquid CO2 immersion processes.
SuperFuge™
Design and development of a new high performance dense fluid immersion cleaning system began in late 1989. Previous studies at Hughes comparing the cleaning rates and efficacy between scCO2 and liquid CO2 showed that – although not as effective as scCO2 for certain polar or more complex (waxy) contaminants – liquid CO2 demonstrated higher contaminant carrying capacity and faster cleaning rates, particularly for non-polar oily hydrocarbon and silicone contaminants. Lack of solubility for a particular contamination was easily remedied with the addition of a suitable liquid CO2 fluid modifier (2% to 5% by vol.) comprising various mixtures of non-ionic surfactants (i.e., Dow Triton® X-15) dissolved in a carrier solvent such as a paraffin, ester, or alcohol.
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