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The journey of the friction industry: – Part 2: The influence of dust emissions

Our little journey takes us now to Chile, more specifically to one of the biggest marine ports in South America, in Valparaiso. We invite you to evoke the smell of tar and salt, the sound of the sea shore combined with the continuous traffic of heavy vehicles. We will use this atmosphere to explain one of the mechanisms of how elements from dust emissions like antimony can get through our body.

A group of analytic chemists from the Catholic University of Valparaíso (UCV) collected blood samples of volunteer workers from the harbour and compared the %Sb with blood samples of two control groups: UCV students (located at a commercial area at 300 m of the port) and volunteers from Quebrada Alvarado, a 100 % rural village at 100 km of Valparaíso [1].

Results clearly suggest a direct relationship between the systematic exposure to heavy vehicles traffic with the antimony content in blood. If particulate matter in the airborne is small enough it can go through the lungs and attach to the erythrocyte membrane by chemical interaction.

Several studies reveal that occupations closely related to antimony have been more prone to cardiac diseases, skin irritations and digestive disorders. Moreover, Sb-subproducts has been reported to be partially soluble in physiological fluids and carcinogenic in laboratory animals, though for human beings is still under suspicion [2] [3] [4].

Antimony trisulfide is still a widely used additive in brake PADS, as it improves fade resistance and wear resistance. We can ascribe these properties to the complex tribochemical reactions and interactions occurred in the PAD, which contribute to the formation of a stable transfer layer, and its low hardness (2 on Mohs scale). 

However, even reducing emissions (less wear), these become more harmful as they contain Sb-subproducts. Consequently, the intention to replace it is growing in the industry and raw material manufacturers have the duty to provide efficient alternatives.

While the industry is in the research of a substitute, at rimsa we have been able to design an environmentally friendly additive which replace  Sb2Swith minimum reformulation by providing thermal conductivity to the PAD and reducing wear. Suitable for all applications, and without busting the bank.

See here more information about our LM09

There is however another indirect mechanism through which brake dust emissions are getting to us. It is quite common that rain drags pollution (including brake dust) to the sewerage and then to the sea, where it is absorbed by our future seafood. 

The Al2O is a standard abrasive used in brake pads to increase the coefficient of friction and keep clean the rotor surface. It derives however in aluminium contamination when in service, aluminum oxide is released to the environment. Roots from plants can absorb the ionic species of metals such as aluminium in acid soils, which has a clear environmental impact, including the growth of these plants due to the bioaccumulation capacity of this element. Furthermore, there are also articles suggesting a possible connection between the increase of the concentration of  Al3+ ions in the environment due to human activity and some neurotoxic diseases in human beings [5].

Ironically, the increase in the use of the “green” metal by automotive industry looking to reduce vehicle weight, can bring massive disruption to supply chain  [6] [7] [8]. China is the largest producer of aluminum and Alumina, and uses mainly coal for power. The worrying increase of smog and airborne particulate matter has forced China to boot on his “blue skies” politics, which will cut the production up to 30 %, due to its enormous environmental impact.

Zirconium compounds are getting more and more applications as abrasives in friction industry and, despite their usual higher cost, do not present the previously commented hazards. They can come from natural, like the zirconium silicate, or synthetic origin, like the zirconium oxide. Moreover, Zircon Industry Association (ZIA) reveals the lower environmental impact of zircon products in comparison with Al2O3 regarding [9]: 

Being a natural product, it is essential to control the origin of zirconium silicate to guarantee stable properties and results. Our ecoZir comes from partnership with reliable and established sources in the industry, allowing us to ensure very consistent particle size distribution and chemical composition. 

Furthermore, we are able to offer also aeronautical quality zirconium oxide as we are official distributors of referential manufacturer TAM Ceramics for friction applications. ZIROX monoclinic zirconia powders have been produced consistently for over 50 years by electrically fusion of zirconium silicate and subsequent dry-milling operation. ULTRA-FINE grades (d50 below 0,9 microns) can be obtained by exclusive wet-milling process.  

→See here more information about our zirconium silicate (ecoZir) and zirconium oxide (Zirox) 

PART: 1 | 3

Sources consulted
[1] Quiroz, W., De Gregori, I., Basilio, P., Bravo, M., Pinto, M. and Lobos, M.G. J. Environ. Monit. (2009), 11, 1051-1055.
[2] O. von Uexküll et al. Journal of Cleaner Production (2005), 13, 19–31.
[3] Iijima, A., Sato, K., Yano, K., Kato, M., Kozawa, K., Furuta, N. Environmental Science & Technology (2008), 42, 2937-2942.
[4] A.M. Martínez, J. Echeberria, Wear (2016), 27-42
[5] Torrellas Hidalgo, R., “La exposición al aluminio y su relación con el ambiente y la salud” Tecnogestión. (2012), 9, 3-11.
[6] Andy Home (Reuters, 2017) “Why China’s aluminum industry is praying for blue skies”
[7] James Borton (RealClear World, 2018) “Blue Skies and a Booming Economy: China Can Have Both”
[8] Angel Hsu (TED Conference, 2018) “How China is (and isn’t) fighting pollution and climate change”
[9] Zirconium Industry Association (ZIA, 2018) “ Demonstrating the low environmental impact of zircon in ceramic tile production”