Marcelo Machado Viana

Nanocrystalline Titanium Oxide thin Films Prepared by Sol-Gel Process

Crystalline films of pure titanium oxide have been prepared on soda lime slide glasses by sol-gel process and dip-coating. The definition of various parameters such as chemical concentration, viscosity, catalyst type and withdrawal speed led to the preparation of transparent, crystalline and adherent coatings with hydrophobic characteristics. Their crystalline structure was evaluated as anatase phase by low angle X-ray diffraction. Thicknesses were measured by perfilometry, and the refractive indices were determined from transmittance spectrum taking into consideration the layers deposited onto the two sides of the substrate. Porosity was also estimated by UV-visible spectroscopy by using the Lorentz - Lorenz equation. The average grain size was evaluated by atomic force microscopy. The thicker and denser films presented hydrophobicity, which decreased when the film porosity increased.

Fundamental Studies of Adhesion of Dust to PV Module Surfaces: Chemical and Physical Relationships at the Microscale

Photovoltaic (PV) module soiling is a growing area of concern for performance and reliability. This paper provides evaluations of the fundamental interactions of dust/soiling particles with several PV module surfaces. The purpose is to investigate the basic mechanisms involving the chemistry, morphology, and resulting particle adhesion to the first photon-incident surface. The evaluation and mapping of the chemistry and composition of single dust particles collected from operating PV module surfaces are presented. The first correlated direct measurements of the adhesive force of individual grains from field-operating collectors on identical PV module glass are reported, including correlations with specific compositions. Special microscale atomic force microscopy techniques are adapted to determine the force between the particle and the module glass surface. Results are presented for samples under dry and moisture-exposed conditions, confirming the effects of cementation for surfaces having soluble mineral and/or organic concentrations. Additionally, the effects of hydrocarbon fuels on the enhanced bonding of soiling particles to surfaces are determined for samples from urban and highly trafficked regions. Comparisons between glass and dust-mitigating superhydrophobic and superhydrophilic coatings are presented. Potential limitations of this proximal probe technique are discussed in terms of results and initial proof-of-concept experiments.

Facile Graphene Oxide Preparation by Microwave-Assisted Acid Method

Few-layered graphene oxide (GO) was prepared using a fast and energy-saving method by microwave-assisted acid technique. The oxygenated groups existing on the GO surface were determined using UV-Vis, X-ray photoelectron and Fourier-transform infrared spectroscopies. An oxygenated group percentage of 30% in mass for the GO was observed by thermogravimetric analysis. The reduced few-layered graphene oxide (rGO) film annealed at 110 °C deposited onto a silicon/silica wafer showed expanded graphite-like structure with 0.70 nm between the rGO sheets, as determined by X-ray diffraction. This rGO film exhibited a relatively high electrical conductivity value of 7.36 × 102 S m-1 confirming the good restoration of the π-conjugated system. The prepared GO sample exhibited good stability in water from pH 4 to 12, as determined by its zeta potential, and contained 5 to 9 layers, as determined by atomic force microscopy (AFM) and transmission electron microscopy (TEM).

Fundamental studies of the adhesion of dust to PV module chemical and physical relationships at the microscale

PV module soiling is a growing area of concern for performance and reliability. This paper provides evaluations of the fundamental interactions of dust/soiling particles with a several PV module surfaces. The purpose is to investigate the basic mechanisms involving the chemistry, morphology and resulting particle adhesion to that first photon-incident surface The first-time evaluation and mapping of the chemistry of single dust particles from operating PV module surfaces is presented. The first direct measurements of the adhesive force of individual grains are reported, including correlations to the specific surface chemistry. Special nanoscale techniques using atomic force microscopy (AFM) are adapted to determine the force between the particle and the surface. Results are presented for samples under dry and moisture-exposed conditions confirming the effects of cementation for surfaces having organic/soluble mineral concentrations. Additionally, the effects of hydrocarbon fuels on the enhanced bonding and adhesive force of soiling particles to surfaces are determined for samples from urban and highly-trafficked regions. Comparisons between glass and superhydrophobic and superhydrophilic coatings are presented, showing the effectiveness of the lower-surface energy conditions on the particle adhesion. The potential, limitations of this novel proximal probe technique are discussed in terms of the results and initial, proof-of-concept experiments.

Soiling particle interactions on PV modules: Surface and inter-particle adhesion and chemistry effects

The understanding of the fundamental physics and chemistry of dust and the interaction of these soiling fragments with the PV module surface and each other is potentially important to developing viable mitigation approaches. This paper builds on our previous reports and observations investigating individual soiling particle adhesion on PV module glass using microscale proximal probe techniques. Specifically, in this presentation we report on the refinement of those adhesive force measurements by gaining and including information on the contact area of those particles with the surface, the specific chemistry of interactive surfaces, and the quantification of the force values using materials standard. We also investigate the adhesive forces holding the soiling particles together and the effects of the critical parameters of surface compositional properties, moisture (humidity), and hydrocarbons. This allows for the comparisons of the inter-particle adhesion to the adhesive force holding the particle to the glass module surface. These evaluations are performed on soiling particles collected from operating modules in differing climate zones in Brazil and Middle-East Gulf regions.

Preparation of thin films using freeze drier alumina

Synthesis of polymorphous of nanoparticulate alumina has been the subject of many works. The stabilization of these nanoparticles in aqueous suspensions is necessary in many technologic application and industrial products. Recently, a number of routes have been developed using various dispersants to prepare these nanoparticles dispersed in aqueous solution. In this work, nanoparticulate alumina prepared by precipitation and freezing drying was investigated as potential material for aqueous dispersion. These nanoparticles were dispersed in methylethylglycol (MEG), polyvinylalcohol (PVA) and polymethacrylate (PMA). The alumina nanoparticles and the dispersions were characterized physical-chemically and tested in the preparation of thin films.

Automotive Catalysts: Performance, Characterization and Development

Nowadays, automotive catalysts have been used to reduce atmospheric emissions, due to significant parcels of the global emissions of pollutants agents provoked by vehicles. Automotive exhaust catalysts were introduced in the 70’s decade, because some countries established restricting laws related to emissions of carbon monoxide (CO), nitrogen oxides (NOx) and hydrocarbons (HC) by the engines. These products generated by the combustion process are extremely harmful to health and the environment (Massad et al, 1985). For example, CO combined with hemoglobin in the bloodstream promotes the reduction of oxygen-active sites that provokes asphyxia. Nitrogen dioxide (NO2) contributes to photochemical smog and acid rain, and is irritating to the eyes, skin and respiratory system. Nitrogen monoxide (NO) is toxic by inhalation and irritating to the eyes and skin. Polycyclic aromatic hydrocarbons (PAHS) have been identified as carcinogenic compounds. Other combustion products are: ash, formed mainly by particulate residues of components of the lubricating oil, and soot, combustible matter in the exhaust gas (smoke). Automotive catalytic converters have been developed precisely to make these products less toxic (Morterra et al, 1995; Ismagilov et al, 1998). The development of catalysts only was possible with the improvement in automotive engines as the replacement of carburetion system for electronic injection and introduction of the catalyst in the exhaust systems (Kaspar et al, 2003). The catalysts of three ways (TWC –Three-Way Catalyst) are advanced systems of emission treatment of gasoline vehicles that reduce significantly the emissions of carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx) in atmosphere (Collins & Twigg 2007). Nevertheless, there is a steady increase in world production of vehicles powered by gasoline and by other types of fuel such as alcohol, gas and mix of fuel, leading to constant research in order to improve the catalysts already known and to develop new models (Mizukami et al, 1991; Silva et al, 2009 & Sideris, 1997). Automotive catalysts are generally available in the form of monolith ceramic as cordierite and zeolites or metal substrate. The catalyst substrates more used are composed of magnesium cordierite (2MgO.2A12O3.5SiO2) with a honeycomb structure, which provides a high geometric surface area, coated with γ-alumina (catalyst wash-coat). This wash-coat is designed to increase the specific surface area and is the support for precious metals, mainly platinum (Pt), palladium (Pd) and rhodium (Rh), which promotes the catalytic reduction and oxidation of