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New Materials

No attrition

Film prevents wear and tear of industrial parts and could send lubricating oils into retirement

Wear protection in industrial parts

Eduardo cesarWear protection in industrial partsEduardo cesar

A very fine film of a nanostructured material based on amorphous carbon, also known as diamond-like carbon, showed good performance when reducing the attrition and wear-and-tear of industrial parts, such as ceramic rings.  The simple application of this film which is a few microns thick – equivalent to one millimeter divided by one thousand – was developed at the Coordenação dos Programas de Pós-graduação de Engenharia/Coppe department of post-graduate courses of the Federal University of /UFRJ. After functioning for 419 hours, no wear-and-tear was observed. The experiment was conducted while the ring was rubbing against another ring on a test bench; both rings were submitted to movements of 1 thousand to 2 thousand rotations per minute (rpm), equivalent to a journey of 4,300 kilometers if the rings had been traveling on a highway. “We measured the attrition coefficient and obtained a value  less than 0,001, which is considered extremely low, and wear-and-tear was virtually nil, similar to what happens with systems using lubricating oil”, says professor Sérgio de Souza Camargo Júnior, from the Metallurgical and Materials Engineering Program at the UFRJ.

This experiment and other similar ones conducted in several laboratories around the world with amorphous carbon (that does not have a crystalline chemical structure),  also referred to as Diamond-like Carbon (DLC), makes it possible to envision, for the near future, the existence of industrial machines and equipment and even engines of vehicles that run without lubricating oil, provided that the internal parts are coated with films that prevent the wear-and-tear of ceramic, metal, or even rubber parts.  DLC is already used in industry to provide products ranging from medical and dental instruments to ophthalmology lenses and computer hard drives with more resistance.

Reducing the attrition of machine and engine parts reduces energy loss and improves the efficiency of the entire system. This is one of the main objectives of tribology, the science that studies the phenomena of attrition, wear-and-tear and lubrication in various kinds of materials. Another important factor that might also lead industry to adopt the nanostructured film is the significant lessening of noise resulting from the reduction of the attrition.  “Another problem is the discarding of oil, after it is used, which is an environmental issue”, says Camargo.

The experiment was conducted by using two silicon nitride (Si3N4) rings, produced by researchers from Portugal’s University of Aveiro, under the coordination of Rui Silva and the collaboration of researchers from the Higher Institute of Engineering of Coimbra and the University of Minho. The film was developed and applied at the UFRJ and the coated parts were sent to Portugal to undergo tribology tests. These films were produced under special conditions that cannot be described in detail. “This is our cake recipe which we cannot disclose”, says Camargo, who has not decided yet if he will file for a patent for this film.

Proof of the scales
The rings used in the experiment have a diameter of approximately 4 centimeters, and each ring is 7 millimeters thick.  They are identical to the rings used in fluid sealing systems such as water pumps and cooling systems and for several other applications. Camargo says that other researchers had obtained similar results under very special conditions, such as, for example, in an inert atmosphere or even in a vacuum. “In our case, we had no wear-and-tear under real operating conditions”. To evaluate the wear-and-tear of the parts after the test, the researchers weighed the two rings on scales with accuracy in micrograms (10-6), before and after the experiment. As the parts had exactly the same mass before and after, the conclusion was that there had been no wear-and-tear.

A number of possible commercial applications have been developed and initially cover water pumps or industrial equipment such as compressors. “This material is very versatile and can be used in several kinds of applications”, says Camargo. “We are in contact with a company, exploring the possibility of technology transfer. This company manufactures and uses sealing rings.  The contact arose from a lecture I presented on the topic at the Nanotec [the International Congress of Nanotechnology held in São Paulo in November 2008] where a company representative was in the audience”.

As negotiations with the company – whose name cannot be disclosed – move forward to possible product feasibility tests, the researchers from the UFRJ are working on the development of similar coatings for metallic materials. If they obtain positive results, then new frontiers will open up for materials engineering.

Scientific article
Vila, M. et al. Ultra-high performance of DLC-coated Si3N4 rings for mechanical seals. Wear. v. 265, p. 940-944, Jan. 2008.