There is burgeoning interest in the development of particle beam processing techniques for commercial applications, according to Fred Dylla of CEBAF, who opened a Friday morning session on the topic at the 1996 Joint APS/AAPT Meeting. There is increasing consumer and regulatory pressure to develop "greener" products using "dry chemistry" with reduced environmental impact, as well as production processes that yield only product and no waste. These objectives can be achieved with the use of photons or elementary particles in such commercial processes as surface modification, polymerization of materials, micromachining, and deposition and etching of materials, to name a few.
However, apart from a handful of high value-added applications, the commercial impact of these emerging technologies is limited because the unit cost is too high, and production capacity too low, to compete with existing chemistry-based methods. "Accelerated particle beams offer many diverse opportunities to process materials if economic targets can be met," said Dylla.
Electron Beam Processing. "The commercialization of electron processing applications is driven by demonstrated technical advantages over current practice," said Joseph McKeown of AECL Accelerators. "Mature and reliable accelerator technology has permitted more consistent product quality and the development of new processes. However, the barriers to commercial adoption are often not amenable to solution within the laboratory alone." Plant engineering, production, project management, financing, regulatory control, product throughput, and plant operational efficiency all contribute to the business risk.
McKeown reported on his company's efforts to develop and market three IMPELA electron accelerators (10 MeV, 50kW) to commercial environments. The accelerators cost about $8 million each, and are designed to displace expensive chemicals used in the pulp and paper industry, to sterilize sewage sludge, detoxify chemically contaminated soils, to irradiate foodstuffs such as cellulose, and build radiation service centers for a diversity of other applications. Trials on 200 tons produced by paper mills in 1995 resulted in savings of $55 million and a 33% reduction in pollution. But competition from traditional chemical methods is stiff, and the investment capital required is considerable. McKeown estimated that about $1.5 million in revenue is needed annually to support outlays of this scale.
Electron Beam Curing. Victoria Weinberg of Northrup Grumman described progress in electron beam curing of metals used in construction of military and commercial aircraft, automobiles, and recreational equipment, such as tennis rackets and golf clubs. Despite the high capital and operation costs of conventional thermal curing methods, manufacturers in the past were willing to pay those higher prices to achieve optimal performance. Now, however, economic pressures are causing them to explore more cost-effective alternatives while maintaining high performance, the most promising of which is electron beam curing.
Electron beam curing uses high-energy radiation to effect physical and chemical changes in materials, and the process is 10 to 1000 times faster than conventional thermal curing, which usually takes 12-14 hours. Thermal curing requires cumbersome tooling and equipment. The autoclaves used in the process run about $3 million apiece, whereas an electron beam accelerator like the IMPELA can achieve the same production yields as four or five autoclaves, provided the volumes are high enough. Electron beam curing also has lower energy costs, reduced environmental costs due to lower toxic emissions and the use of solvent-free resins, and lower residual distress to parts. In addition, it allows manufacturers to vary the dosage to do selective curing.
UV FEL Processing. According to Michael Kelley, a senior research associate with DuPont Central Science & Engineering, the ability of ultraviolet light to transform materials was recognized at the turn on this century, and ever since, its use for processing has been re-investigated each time a new UV light source technology has become available. Particularly promising are results in the surface modification of metals and polymers, and in micromachining, using short, intense, single-wavelength pulses from excimer lasers. However, the cost of excimer laser light and their maximum unit size have limited their commercialization to high-value applications, mostly in medicine and electronics manufacturing. Also, the bulbs are too small for mass production quantities.
Kelley estimates that the horizon for commercialization is an energy cost below 0.5 cents per kilojoule of light, with a unit capacity above 10 kW. The only technology capable of reaching this goal is the free electron laser (FEL) based on a superconducting radiofrequency accelerator. The FEL's picosecond pulse length and high peak power offer further advantages for micromachining, and progress is being made toward a 1 kW technology demonstration, the minimum required for micromaching applications; surface processing requires about 10 kW.
Crystallography. According to C. Abad-Zapatero of Abbot Laboratories in Illinois, the unraveling of the three-dimensional structure of nucleic acids and proteins by physics-based experimental techniques - including x-ray diffraction from single crystals - has had a tremendous impact on our understanding of many biomedical processes. This structural knowledge is finding applications of macromolecular crystallography in biotechnology. For example, the knowledge of the three-dimensional structure of the target enzymes, complexed with their inhibitors, is helping to accelerate the design of future drugs.
Novel enzymes with new characteristics and improved catalytic properties are being produced by random and site-directed mutagenesis, and understanding these structural alterations in the mutant enzymes is facilitating the design of novel proteins with still unknown properties. In addition, the advent of the third generation synchrotron radiation sources such as the Advanced Proton Source (APS) has opened yet another avenue for the interaction between the physical and biomedical sciences. Abad-Zapatero believes that the wide availability of high brilliance, easily tunable x-ray sources will have a tremendous impact on the biotechnology of the future.
Other particle beam processing techniques described in the session included x-ray lithography, ion beam surface treatment, magnetically nozzled plasma accelerators for materials surface treatments, and high-power proton beam applications for such objectives as acclerator production of tritium.
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