http://hdl.handle.net/11422/92 2026-07-25T23:27:40Z 2026-07-25T23:27:40Z http://hdl.handle.net/11422/29768 2026-07-24T03:00:11Z 2020-03-01T00:00:00Z

Title: Produção e caracterização de arcabouços híbridos de policaprolactona (PCL) e hidrogel produzidos por bioimpressora 3D Author(s)/Inventor(s): Andrade, Carolina Barbosa de Advisor: Thiré, Rossana Mara da Silva Moreira Abstract: The main goal of this work was to produce hybrid scaffolds, composed of polycaprolactone and chitosan/gelatin hydrogel using a bioprinter, aiming its application for bone regeneration and the development of the bioprinting technique. A cheaper alternative was also sought in relation to the use of modified gelatins for bone regeneration. Initially, the adjustment of the printing parameters was made, and the ability of the bioprinter to produce parts compatible with its virtual model was evaluated. The influences of speed and extrusion factor for printing hydrogels were analyzed and the best parameters for scaffolds’ printing were defined. A PCL frame was produced, with filaments of 0.3 mm in diameter and 8.3 mm in length and width, was printed at 77ºC, with an infill of 20%, at a speed of 30 mm.s-1, with an extrusion factor of 1.2 and nozzle diameter of 0.3. The hydrogel piece filled the pores and was printed at a speed of 5 mm.s-1, extrusion factor 1, temperature of 23 ºC, infill of 20% and the nozzle diameter of 0.4 mm. Under these conditions, the frameworks produced have demonstrated good printability, there was a chemical interaction between chitosan and gelatin to form the hydrogel, partial degradation of the framework after 4 weeks was detected, there is hemostatic potential in the material, it releases ions to the environment and captures fluids, and it is no toxic to the cells studied. Thus, the proposed framework may be a cheaper alternative to the use of modified gelatine as a biotint Publisher: Universidade Federal do Rio de Janeiro Type: Dissertação

2020-03-01T00:00:00Z http://hdl.handle.net/11422/28417 2026-05-16T03:08:58Z 2022-05-01T00:00:00Z

Title: CO2 corrosion of high strength steel wires in the annulus of flexible pipes Author(s)/Inventor(s): Campos, Tatiane Seixas Advisor: Gomes, José Antônio da Cunha Ponciano Abstract: Corrosion of carbon steel may occur at near neutral pH in deoxygenated solutions with high bicarbonate concentration when the corrosion reaction produces elemental hydrogen. Such conditions are encountered in the annulus of flexible pipes when it contains water with dissolved CO2, which produces high concentration of ferrous ion (Fe2+) and bicarbonate (HCO3-). The objective of the present study was to investigate if high levels of Fe2+ and HCO3- can persist for the time required to induce SCC in armor wire steels. It implies that the nucleation and growth of siderite (FeCO3) is so slow that the solution remains supersaturated for several days. The role of surface finishing and cathodic areas composed of cementite were also evaluated, as well as the salinity, temperature, and pCO2. The results show that, at temperatures lower than 40 °C and CO2 partial pressure of 5 to 10 kPa, the saturation ratio (SR) of siderite can persist at values much higher than 1 and maintain a near neutral pH for several hundred hours. The uniform corrosion rate of armor wire steel is low if pH soon achieves near neutral range. The siderite forms a layer on the steel surface and the cathodic reaction becomes limited by diffusion through it. The corrosion rate increases with increasing salt content and exposed cementite, being even more pronounced at 25 °C. In such cases, siderite could not completely inhibit localized corrosion, which may be a great site for SCC cracks to start. That is related with a join action of the higher solubility of siderite and the effect of ion chloride. At 25°C and brine, the pCO2 is the main parameter to concern in active surfaces of armor steels. Publisher: Universidade Federal do Rio de Janeiro Type: Dissertação

2022-05-01T00:00:00Z http://hdl.handle.net/11422/28416 2026-05-16T03:08:58Z 2022-01-01T00:00:00Z

Title: Caracterização de frações segregadas de catalisadores de equilíbrio de FCC por microscopia eletrônica de varredura e transmissão Author(s)/Inventor(s): Carvalho, Paulo Sergio da Silva Advisor: Jardim, Paula Mendes Abstract: In the present study, two FCC equilibrium catalysts (e-cat) were fractionated by density, each generating 4 fractions that represent increasing levels of particles density and contamination. The eight samples were characterized by X-Ray Fluorescence Spectroscopy (XRF), Nitrogen Physisorption, X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) combined with Energy Dispersive X-Ray Spectroscopy (XEDS) and Transmission Electron Microscopy (TEM) combined with XEDS and Electron Diffraction. An image analysis methodology was developed and allowed the realization of a quantitative visual characterization of the elements of interest based on the SEM/XEDS mappings. The XRF, XRD and textural analyses indicated that the density separation was successful and that the contaminating metals are more concentrated in the denser fractions, which also presented greater deterioration of zeolites crystal structure. The SEM/XEDS analyses revealed the existence of particles populations with different compositions regarding the Si/Al ratio, making it possible to relate the type of catalyst with its level of contamination by Ni. A strong interaction between Ni and Al was observed by STEM/EDS and electron diffraction analyses, possibly due formation of a nickel aluminate. Publisher: Universidade Federal do Rio de Janeiro Type: Dissertação

2022-01-01T00:00:00Z http://hdl.handle.net/11422/28411 2026-05-16T03:08:58Z 2022-06-01T00:00:00Z

Title: Investigação de gradiente de propriedades ao longo da espessura em amostras de PVDF exposto a fluido nitrogenado Author(s)/Inventor(s): Souza, Josefa Nágila Cabral de Advisor: Costa, Marysilvia Ferreira da Abstract: In this work, PVDF samples were aged in nitrogen fluid at 93°C and 120°C, for up to 100 days, to investigate the effect of aging on the mechanical, thermal and microstructure properties of the polymer along its thickness. The samples were divided into three groups and were subjected to different aging conditions: samples completely exposed to the fluid, samples partially exposed to the fluid, control group, which consisted of samples exposed to air at high temperature, for evaluation only of the thermal effect over the polymer. After aging, the samples were sectioned into three regions of their thickness, each of which was characterized by TGA, DSC and instrumented microindentation analysis. With the results obtained, it was verified that only the temperature did not impose great changes in the thermal and mechanical behavior of the PVDF, the contact with the fluid induced a high mass gain and promoted changes both in the mechanical properties, EIT and HIT, as in the crystallinity, microstructure and melting temperature, originally presented by the polymer. The second heating in the DSC showed that these changes were permanent. A property gradient was also identified along the thickness of the samples partially in contact with the fluid, evidencing how the presence of the fluid is a key factor for the reordering of the crystalline structure and for the changes in the material properties, which occur gradually and heterogeneously in the different regions of the thickness of the samples, as the diffusion of the fluid from the surface to the interior of the polymer progresses. Publisher: Universidade Federal do Rio de Janeiro Type: Dissertação

2022-06-01T00:00:00Z