Abstract
KEYWORDS – metals, ICP-AES, microwave, PM, chemometrics.
ABSTRACT
The friction materials used for the production of brake pads are not constituted by a single element or compound, but by various types of substances (abrasives, friction modifiers, fillers, reinforcements and binder materials). More than 2000 raw materials are on the market today. The compositional characterization of brake pads is a goal not so simple to achieve. In this work Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) has been chosen to analyze the brake pad materials.
Research and /or Engineering Questions/Objective:
The aim of this study is to optimize the procedure of ICP-AES analysis used for the compositional characterization of brake pads.
Methodology:
ICP-AES analysis provides the use of liquid samples, and the biggest obstacle is to extract the analytes of interest by this type of materials. For this purpose, procedures of microwave acid digestion are applied, which must be optimized for both the individual raw materials and the final mixes. The application of chemometric techniques (such as Principal Component Analysis and Cluster Analysis) is fundamental to evaluate the correlations between the wide range of elements (ingredients) that come into play.
Results:
In this study, in particular, the dependence of the results of the acid digestion by parameters such as temperatures, times and acid mixtures for the mineralization is evaluated. Thanks to the exploitation of the statistical approach, a correlation between the digestion results (partial or total) and the real composition of the samples (raw materials or pad mixes) can be achieved.
Limitations of this study:
The ICP-AES is a powerful technique for the inorganic analysis: the limitation is related to the preparative steps (acid digestion) because different families of materials need very specific mineralization set-up (temperature, acid mix, time). A generic single procedure to digest the wide spectra of ingredients (and of brake pads matrices) is difficult to obtain.
2 Conclusion:
In the last decades several laws have been enacted in order to decrease the contribution of the emissions from the exhaust fumes of motor vehicles to the content of heavy metals in the PM. However, non-exhaust emissions, originated from brake wear, road wear, tyre wear and road dust resuspension, are unaffected by such measures in Europe and may become the dominant PM source in the near future. In this contest, the optimization of an analytical technique able to characterize critical components of brake pads could be very important in order to respect the future environmental standards.