Modeling, design and experimental characterization of Micro-Electro-Mechanical-Systems for gas chromatographic applications

Design parameters, process flows, electro-thermal-fluidic simulations and experimental characterizations of Micro-Electro-Mechanical-Systems (MEMS) suited for gas-chromatographic (GC) applications are presented and thoroughly described in this thesis, whose topic belongs to the research activities the Institute for Microelectronics and Microsystems (IMM)-Bologna is involved since several years, i.e. the development of micro-systems for chemical analysis, based on silicon micro-machining techniques and able to perform analysis of complex gaseous mixtures, especially in the field of environmental monitoring. In this regard, attention has been focused on the development of micro-fabricated devices to be employed in a portable mini-GC system for the analysis of aromatic Volatile Organic Compounds (VOC) like Benzene, Toluene, Ethyl-benzene and Xylene (BTEX), i.e. chemical compounds which can significantly affect environment and human health because of their demonstrated carcinogenicity (benzene) or toxicity (toluene, xylene) even at parts per billion (ppb) concentrations. The most significant results achieved through the laboratory functional characterization of the mini-GC system have been reported, together with in-field analysis results carried out in a station of the Bologna air monitoring network and compared with those provided by a commercial GC system. The development of more advanced prototypes of micro-fabricated devices specifically suited for FAST-GC have been also presented (silicon capillary columns, Ultra-Low-Power (ULP) Metal OXide (MOX) sensor, Thermal Conductivity Detector (TCD)), together with the technological processes for their fabrication. The experimentally demonstrated very high sensitivity of ULP-MOX sensors to VOCs, coupled with the extremely low power consumption, makes the developed ULP-MOX sensor the most performing metal oxide sensor reported up to now in literature, while preliminary test results proved that the developed silicon capillary columns are capable of performances comparable to those of the best fused silica capillary columns. Finally, the development and the validation of a coupled electro-thermal Finite Element Model suited for both steady-state and transient analysis of the micro-devices has been described, and subsequently implemented with a fluidic part to investigate devices behaviour in presence of a gas flowing with certain volumetric flow rates.

Development and chemo-mechanical characterization of eco-compatible extenders containing REOB and recycled tyres’ rubber for the production of greener bituminous binders

The concepts of circular economy and sustainability are the basis of the present experimental research that seeks to reduce the environmental impact of traditional road construction materials. This study mainly focuses on the development and the chemo-mechanical characterization of bitumen extenders containing rubber (R) from end-of-life tyres (ELTs) and re-refined engine oil bottoms (REOBs) for the production of innovative and eco-friendly extended bitumens (i.e. bituminous binders containing 25%wt. of recycled products) and asphalt mixtures. In order to create more sustainable asphalt mixes, also recycled aggregates are used for partial replacement of virgin natural aggregates in the aggregate skeleton. The experimental program encompassed five successive steps: (i) the evaluation of physicochemical properties of R and REOB, (ii) the definition of the optimal extenders by the development of a new protocol and their characterizations, (iii) the realization and investigation of the chemo-rheological responses of the extended bitumens at different boundary conditions, (iv) the assessment of the effectiveness of analytical method to predict the rheological parameters of extended bitumens and, finally, (v) the analysis of the mechanical performances of the corresponding asphalt mixtures. A standard 50/70 penetration grade bitumen was chosen as a reference material and the main constituent of the innovative bituminous products. The results of this study underlined the importance of material characterization. The incorporation of R-REOB extenders strongly affects the chemo-rheological responses of the resulting extended bitumens and asphalt mixtures overall the boundary conditions. While the presence of R and the consequent formation of a polymer network improves the elasticity of the final products, especially at high test temperatures; the addition of REOB, softens the bituminous binders and asphalt mixes increasing their response at low test temperatures. Nonetheless, the use of recycled products increased the susceptibility of bituminous material under damaging conditions, which would need further investigations.