Insights on non-exhaust emissions: An approach for the chemical characterization of debris generated during braking.

Up to 50 % of total PM2.5 emissions are due to particles derived from the automotive sector, and both exhaust and non-exhaust emissions contribute to the pollution of urban areas. Fuel incomplete combustion, or lubricant degradation due to high temperatures during the combustion process, are responsible for exhaust emissions. The non-exhaust ones concern brakes, tires and road surface-wear emissions and road resuspension contribution. The present study aims to provide a methodological approach for a detailed chemical characterization of wear friction products by means of a large array of techniques including spectroscopic tools, thermogravimetric analysis (TGA), chromatography, morphological and elemental analysis. The dust sample derived from the wear of a brake pad material was collected after a Noise & Vibration Harshness (NVH) test under loads similar to a Worldwide Light vehicle Test Procedure (WLTP) braking cycle. The TGA shows that only a small fraction is burned during the test in an oxidizing environment, testifying that the sample consists mostly of metals (more than 90 %). Fe exhibits the highest concentrations (50-80 %, even in the form of oxides). Also other kinds of metals, such as Zn, Al, Mg, Si, S, Sn, Mn, occur in small quantities (about 1-2% each). This finding is confirmed by X-ray diffraction (XRD) analysis. The organic fraction of the debris, investigated by means of Raman spectroscopy, has an evident aromatic character, probably due to oxidative phenomena occurring during the braking cycle test. Noteworthy, the extraction of the dust sample with organic solvents, revealed for the first time the presence of ultrafine particles (UFPs), even in the range of few nanometers (nanoparticles), and polycyclic aromatic hydrocarbons (PAHs), recognized as highly toxic compounds. The simultaneous presence of toxic organic carbon and metals makes of concern the non-exhaust emissions and mandatory a deep insight on their structure and detailed composition.

Alumina-zirconia composites functionalized with laminin-1 and laminin-5 for dentistry: effect of protein adsorption on cellular response.

The present paper describes a study on laminin interaction with the surface of two alumina-zirconia composites with different percentages of ZrO2, both with submicrometric grain size. As major molecules within the basement membrane (BM), laminins are important protein fragments for epithelial cell adhesion and migration. On the other hand, alumina-zirconia composites are very attractive materials for dental applications due to their esthetic and mechanical properties. X-Ray photoelectron spectroscopy and atomic force microscopy were used to study the adsorption of two types of laminin, laminin-1 (Ln-1) and laminin-5 (Ln-5), onto the ceramics surfaces. The in vitro cell response was determined by intracellular phosphorylation of major kinases. Ceramics samples functionalized with laminins showed better cellular activation than untreated specimens; furthermore, cellular activation was found to be greater for the composite with higher percentage in zirconia when functionalized with Ln-5, whereas the adsorption of Ln-1 resulted in a greater activation for the alumina-rich oxide.

Characterization of Co-Cr-Mo alloys after a thermal treatment for high wear resistance.

The cobalt-chromium-molybdenum alloys are characterized by a high resistance to wear and corrosion, as well as good mechanical properties, allowing their use in the substitution of hip and knee joints. Five alloys were used as substrates for a coating deposition by a thermal treatment in molten salts, as reported elsewhere, in order to form a tantalum-rich coating on the sample surface, able to improve the biocompatibility and wear resistance of the materials. However, the temperature (970°C), reached during this process, is considered critical for the phase transformation of the Co-based alloys. The aim of this work is the evaluation of the temperature effects on the structure, microstructure, mechanical and tribological properties of the considered substrates, after the removal of the coating by polishing. The substrates are characterized through X-ray diffraction (XRD), scanning electron microscopy with energy dispersion spectrometry (SEM-EDS) and profilometry. The mechanical behavior is evaluated by the macro- and micro-hardness and bending tests, whereas the tribological properties are analyzed through a ball on disc test. A comparison between the as-received alloys and thermal treated substrates is reported. The biocompatibility feature is not reported in this work. The substrate crystalline structure changed during the heat treatment, inducing the formation of the hexagonal cobalt phase and the decrement of the cubic one. This crystallographic modification does not seem to influence the tribological behavior of the substrates. On the contrary, it affects the strength and ductility of the substrates.

Surface modification of Ti-6Al-4V alloy for biomineralization and specific biological response: Part I, inorganic modification.

Titanium and its alloys represent the gold standard for orthopaedic and dental prosthetic devices, because of their good mechanical properties and biocompatibility. Recent research has been focused on surface treatments designed to promote their rapid osteointegration also in case of poor bone quality. A new surface treatment has been investigated in this research work, in order to improve tissue integration of titanium based implants. The surface treatment is able to induce a bioactive behaviour, without the introduction of a coating, and preserving mechanical properties of Ti6Al4V substrates (fatigue resistance). The application of the proposed technique results in a complex surface topography, characterized by the combination of a micro-roughness and a nanotexture, which can be coupled with the conventional macro-roughness induced by blasting. Modified metallic surfaces are rich in hydroxyls groups: this feature is extremely important for inorganic bioactivity (in vitro and in vivo apatite precipitation) and also for further functionalization procedures (grafting of biomolecules). Modified Ti6Al4V induced hydroxyapatite precipitation after 15 days soaking in simulated body fluid (SBF). The process was optimised in order to not induce cracks or damages on the surface. The surface oxide layer presents high scratch resistance.

Tantalum-based thin film coatings for wear resistant arthroprostheses.

Cobalt-chromium-molybdenum alloys with high carbon content (HC-CoCrMo) are widely used as materials for arthroprosthesis, in particular in metal-on-metal (MoM) hip joints. In spite of their good wear and corrosion resistance, production of metallic wear particles and metal ion release will occur on a large time-scale. An enhancement of the metal ion level in the patient's blood and urine is often reported in clinical data. Hypersensitivity, inflammatory response and cell necrosis can occur as consequence. So implants on young patients and women on childbearing age are not so widespread. The aim of this research is the realization of a thin film coating in order to improve the biocompatibility of Co-based alloys and to reduce debris production, ion release and citotoxicity. The innovative process consists of a thermal treatment in molten salts, in order to obtain a tantalum enriched thin film coating. Tantalum is chosen because it is considered a biocompatible metal with high corrosion resistance and low ion release. Three HC-CoCrMo alloys, produced by different manufacturing processes, are tested as substrates. The coating is a thin film of TaC or it can be composed by a multilayer of two tantalum carbides and metallic tantalum, depending on the temperature of the treatment and on the carbon content of the substrate. The thin films as well the substrates are characterized from the structural, chemical and morphological point of view. Moreover mechanical behaviour of treated and untreated materials is analyzed by means of nanohardness, scratch and ball-on-disc wear tests. The coating increases the mechanical and tribological properties of HC-CoCrMo.