Two years ago, the British Aerospace Sowerby Research Centre (BAe; Filton, England) purchased a few molecular modeling modules from Molecular Simulation Inc. (MSI; Cambridge, England; (+) 44-122-341-3300) to analyze XPS and IR spectra. The purchase was a big step for BAe, since the company had not yet used molecular modeling technology in its labs. After a yearlong testing program, BAe researchers approved the systems and may now replace some of their traditional instruments with the technology. BAe is using the software to analyze XPS spectra of rare earths to see if they are an environmentally safe alternative to the toxic chromates currently used as anticorrosive aircraft coatings.
Selecting The Software
Testing Molecular Modeling Tools
Researching Aircraft Coatings
Analyzing Cerium And Rare Earths
About British Aerospace
Selecting The Software (Back to Top)
Computer aided design (CAD) is an integral part of BAe's design philosophy. All of the company's engineers use software to work out the stress and yield on bodywork. Sophisticated computational fluid dynamics algorithms compute the aerodynamic flow around moving aircraft. These tools have been used throughout BAe with great success.
However, it is only recently that molecular modeling has played a serious role in research at BAe. Many of the company's scientists had come across molecular modeling techniques in the 1970s when the technology was not well developed, results were unreliable, and graphical user interfaces were non-existent. This had left them reluctant to turn to what was then an underdeveloped technology.
Aware of the major improvements to the technology, Terry Knibb, director of the Sowerby Research Centre, advocated the use of molecular modeling for research projects at Sowerby. In response, several scientists, including Chris Somerton and Steve Harris, took another look at molecular modeling. When they started to investigate the software available, they found that it bore very little similarity to the tools that they had used in the 1970s.
Testing Molecular Modeling Tools (Back to Top)
Two years ago, BAe purchased some modules from MSI's Cerius2 modeling environment to aid the analysis of XPS and IR spectra. Treating the software like any other piece of lab equipment, they embarked on an extensive testing program.
Safety is of prime importance to the aerospace industry. Every component in an aircraft can be traced back to the engineer who chose it or designed it. In fact, engineers have to sign their names to components stating that they can be held responsible if the component is faulty or unreliable. In this environment, the reliability of results is of paramount importance.
BAe tested its first piece of MSI software for a year after they purchased it until they were convinced that the results were reliable. However, the results weren't the only aspect of the software that scored highly in their tests. The ease of use of the Cerius2 windows-type interface also impacted the researchers' attitudes toward the software.
Despite this success, BAe researchers couldn't justify buying a complete suite of software all at onceafter all, they already had traditional lab equipment that they could use. Instead, they followed a pattern of buying a few modules, letting them prove their value, then buying more. This has been successful both for ensuring their reliability and for arranging budgets to accommodate the purchases.
"Validation of the software has been relatively easy, and getting the funding has been straightforward too," Harris says. "Even the former molecular modeling skeptics are very impressed by the results. It has been suggested that in the future molecular modeling may be the only piece of lab equipment that we use!"
Researching Anticorrosive Coatings (Back to Top)
The BAe materials science group is particularly focused on analyzing XPS spectra to determine the composition and chemical nature of thin-film surfaces such as anti-corrosive aircraft coatings. BAe researchers are investigating rare earths as an environmentally safe alternative to the toxic chromates currently used for the coatings. Molecular modeling should help decipher their complex structures.
Aircraft are generally constructed out of an aluminum copper alloy. The copper both strengthens the lightweight aluminum and acts as a cathode that increases the corrosion rate of the alloy. Some manufacturers anodize their aircraft to prevent corrosion, while others use chromate conversion coatings. Chromate coatings have a lower electrical contact resistance than anodized coatings, and are widely used as a primer for paint to form a protective surface. Chromates are particularly suitable as conversion coatings due to their excellent surface properties:
- They can be applied in thin layers.
- They adhere to aluminum alloys.
- They provide a high degree of protection against marine and humid environments.
- If a surface is scratched, the chromate coating leaks from the surrounding surface to cover the exposed metal.
The toxic effects of chromates have been known for some time, but it is only recently that they have been confirmed as carcinogens that are dangerous when they contact the skin or when they are inhaled as dust. This makes chromates hazardous to work with, particularly when sanding down old aircraft with chromate coatings, and when spraying on new coatings. BAe representatives predict that there will be environmental legislation over the next four of five years with measures to drastically decrease the use of chromates. Zinc would perform well as an anti-corrosive, but it has a harmful effect on aircraft engines and therefore cannot be used.
Due to concern over the lack of a safe coating process, Harris, Somerton, and other members of the materials sciences group at the Sowerby Research Centre are conducting research to find an effective alternative to chromates.
Analyzing Cerium And Rare Earths (Back to Top)
A strong candidate for the next generation of anticorrosive coatings comes from a group of materials known as rare earths. Rare earths are the series of elements of atomic number 57 to 71. BAe researchers have been studying the rare earth cerium to assess its anticorrosive potential.
Cerium was independently discovered in Sweden and Germany in 1803 by Jöns Jacob Berzelius, Wilhelm Hisinger, and Martin Klaproth. It is the most abundant of the rare earth metalsthere is more cerium in the earth's crust than there is aluminum. It is found in minerals including allanite, monazite, cerite, and bastanite.
This image shows a crystal of cerium. Like all rare earths, cerium produces a complex XPS spectra. It is found in large deposits in India, Brazil, and the United States.
Rare earths such as cerium produce complex XPS spectra. The layers of cerium required for anticorrosive coatings are about one micron thick. The films are complex both structurally and chemically and contain both Ce(III) and Ce(IV) oxidation states.
Harris, Somerton, and their team are working to understand the nature of these cerium depositions. They are using XPS to discern the oxidation states in a non-destructive manner. However, the spectra of Ce(III) and Ce(IV) are complex and hard to interpret.
To calculate and test spectra over the last two years, Harris and Somerton have used MSI's software extensively because they say it is accurate, reliable, and user friendly. They are hoping that molecular modeling techniques hold the answer to the problem of interpreting the Ce spectra.
Dmol3 is a density functional theory (DFT) program from MSI that handles either molecular clusters or periodic systems. Harris and Somerton will soon start work with Dmol3's density of states algorithm to decipher the composition of the deposited cerium. This work will determine how easy it will be to work with cerium as an environmentally friendly anti-corrosive aircraft coating.
About British Aerospace (Back to Top)
British Aerospace is a major aerospace and engineering group employing approximately 43,000 people, with annual sales exceeding £8 billion, of which 89% are overseas. The company is one of the world's leading defense and aerospace companies and Europe's main systems integrator. The company is a pioneer and leader of major international collaborative programs involving 27 nations.
BAe has a strong commitment to partnerships and is an active participant in strengthening the European aerospace industry. The company offers total defense packages encompassing most aspects of land, sea, and air defense. It creates military aircraft including the Tornado (Europe's biggest military collaborative program), the Eurofighter, the Harrier, and the Hawk. It has developed a range of regional jet aircraft for the commercial aircraft market. BAe is also a partner in Airbus Industriea major European consortium.
The BAe Sowerby Research Centre is the company's main research and technology facility. Founded in 1982, it helps acquire new technologies and provides a central resource of expertise. Sowerby's activities include all stages of the R&D process. The research groups are split into areas of expertise. Among the areas they investigate are coatings technologies, ceramic and metal thin films, information processing and aerodynamics simulations, acoustic emissions, MEMS sensors for accelerometers and pressure sensors, and structural fatigue detectors.
For more information about this application, call Steve Harris or Chris Somerton at the British Aerospace Sowerby Research Centre at (+) 44-117-936-3400. For information about this software, call MSI's Katriona Knapman at (+) 44-122-341-3300.