Using alternative routes to obtain functional graphene derivatives is imperative, as traditional methods such as Brodie, Staudenmaier, and Hummers employ highly potent oxidizing agents. In this study, a nanocomposite comprising graphene oxide (GO), metallic copper (Cu0), and copper (I) oxide (Cu2O) was developed through electrochemical synthesis. Initially, GO was prepared via electrochemical exfoliation of graphite (Gr) in a 0.5 M sulfuric acid (H2SO4) electrolyte solution, with the voltage ranging from +3 V to +7 V over 20 minutes. Subsequently, the GO/Cu-Cu2O nanocomposite was synthesized in three different ratios via electrosynthesis, maintaining a constant current of 50 mA for one hour using the galvanostatic method. During electrosynthesis, cupric ions (Cu2+) were reduced to copper and copper (I) oxide (Cu-Cu2O) nanoparticles (NPs), stabilized in an aqueous dispersion of GO. The NPs, GO, and nanocomposites (NCs) underwent characterization using various techniques, including UV-vis spectroscopy, FTIR, Raman spectroscopy, TGA, XRD, and SEM. The results confirmed a 72% yield of GO with a good oxidation level, although TGA revealed impurities in the final material. The successful synthesis of NCs was achieved, and XRD analysis indicated that a low GO content hinders the oxidation of Cu0.

In the pursuit of clean and sustainable energy, In the quest for clean and sustainable energy,
thermoelectric materials have been extensively studied and improved, with calcium manganite,
CaMnO3 (CMO), being one of the most relevant materials. In this context, a study was
conducted on the production of CaMnO3 ceramics in different atmospheres to optimize their
thermoelectric properties. CMO powders were synthesized using solid-state reaction (SSR) and
the modified Pechini chemical method (QUI). Reducing and oxidizing atmospheres (air, O2, or
10% H2/N2) were used during the sample preparation stages, calcination, and sintering. The
influence of the synthesis route was investigated by modifying the calcination and sintering
times (3, 6, 12, and 24 hours), evaluating their effects on the formed phases as well as the
properties of the produced ceramics. Differential thermal analysis conducted in different
atmospheres identified 800 ºC as the crystallization temperature of the CMO phase, but it
resulted in excessive undesirable secondary phases. Therefore, batches of powders were
calcined at 1000 ºC for 3 or 24 hours in different atmospheres. Scanning electron microscopy
(SEM/EDS) observations were carried out to evaluate the morphology, chemical microanalysis,
and particle size distribution of the particles obtained in SSR and QUI syntheses. X-ray
diffraction (XRD) analysis, coupled with Rietveld refinement, was used to quantify the formed
phases. Measurements of the Seebeck coefficient and thermal and electrical conductivities as a
function of temperature were performed to characterize the thermoelectric properties and
calculate the Figure of Merit (zT) values for each studied condition. Little variation was
observed between the phases and their respective amounts under O2 and air atmospheres;
however, using the H2/N2 atmosphere during sintering resulted in the complete reduction of
CMO, thus not forming the desired phase. Calcination at 1000 ºC (in air or O2) favored the
formation of the CMO phase, especially for SSR powders, which presented mass fractions of
the desired phase between 78% and 100%, while for QUI powders, the CMO phase fraction
ranged between 60% and 70%. The powders calcined at 1000 ºC were relevant in forming the
microstructure of the sintered ceramics, as the quantities of the CMO phase in the powders
influenced the densification and grain growth processes, whereas using powders calcined at
800 ºC resulted in ceramics with the lowest relative densities (64.1%). Ceramics sintered in
H2/N2 were found to be highly electrically resistive, whereas ceramics sintered in oxygen
exhibited the highest electrical conductivity values (4117 S/m) and the highest zT values (0.08)
among the produced samples. CMO ceramics obtained by the QUI route presented very low
electrical conductivity compared to those produced by SSR, and therefore, achieved the lowest
zT values, even though they exhibited the desirable low thermal conductivity values
(1.42 W/mK) compared to those obtained for SSR CMO ceramics (4.02 W/mK).

The main materials used in this work were neutral sludge produced by the company Nexa in one of its plants in Cajamaquilla, Peru and commercial gypsum. The technical and economic feasibility of reusing neutral sludge in the form of a blend (mixture of neutral sludge and commercial plaster) as a coating for civil construction was evaluated. According to Nexa (2022), neutral sludge refers to a type of waste generated in wastewater treatment processes, being a product originating from the biological and physical-chemical purification process, where most contaminants are eliminated. present in wastewater. The studies carried out with this material consisted of evaluating the physical-chemical and mechanical properties of mixtures of sludge and commercial gypsum, with percentages by weight of sludge in relation to pure commercial gypsum (control material) that varied between 10%, 20%, 30%, 40% and 50%. The samples were characterized in powder form through thermal, mineralogical and granulometric analyses. In the fresh state, the samples underwent setting time analysis. In the hardened state, the compressive and tensile strengths were evaluated. To carry out the economic viability analysis, consultancy was hired from the company FEA Junior from USP - SP, which through specialists carried out the gypsum market study, considering the Peruvian market. The results suggest that all traits were within the American Standard C28/C28M for compressive strength, and within NBR 13528-2 and the European Standard EN 13279-1 for tensile adhesion strength. Although the 30% mix without additive met these standards, there were difficulties during testing due to the reduced setting time. When applying the blend to the wall, according to the considerations of the applicator hired to do the service, the 20% percentage without additive was easy to apply, but it dried quickly, this quick drying according to a professional is an advantage in relation to plaster commercial. With a percentage of 50% with Blok Gesso additive, the applicator reported the occurrence of accelerated drying, but stated that this characteristic made the finish easier compared to commercial plaster. Given the results, it was possible to conclude that it is technically viable to use a blend of neutral sludge and commercial plaster as wall coverings in civil construction, with a percentage of 20% without additive and percentages of 30% to 50% with an additive being able to be used. However, for use on large scales, especially for mixes with higher percentages of neutral sludge (40% and 50%), it may be necessary to adjust the amount of additive to obtain better setting times. According to the economic viability analysis carried out by FEA Junior at USP - SP, it was observed that civil construction is a promising market to direct the production of the blend, using as a parameter mainly the correlation between the two markets and the indication that the demand for plaster in civil construction overlaps with the sum of other markets that use plaster for other purposes, however, according to studies, the application of the blend as an alternative product to plaster should not be limited to wall coverings, it should be considered also the hypotheses of application in the production of Drywall and in the cement industry, thus adding value to the product produced.

Mining is an activity with great economic impact; however, the generation of waste such as IOT has caused concern in the scientific community and governments, which has driven the search for ways to use these materials on a large scale. This work verified the effects of adding iron ore tailing (IOT) impregnated with Carbon Nanotubes (CNT), i.e., nanostructured IOT in the manufacture of mortars (cementitious composite), observing the increase in mechanical resistance and electrical conductivity. With this in mind, the effects of applying multi-walled carbon nanotubes (MWCNT) in mortars with different concentrations of CNTs, synthesized in situ on IOT, using an innovative method of dispersion of the nanomaterial, without the use of functionalization elements, additives and/or surfactants, and specialized labor, were investigated. Mechanical tensile tests in flexion and compression, water absorption tests by immersion, moisture loss tests by heat treatment, and electrical tests and characterizations (morphological, chemical, and microstructural) were performed, proving the efficiency of dispersion by the proposed method. The samples studied were prepared with MWCNT concentrations of 0.12%, 0.20%, and 0.80% of CNTs by the weight of cement in the mix, obtaining, in mechanical tests, an increase of 16%, 27% and 30% in flexural traction, respectively. With the electrical tests, an increase of 2266,35% in the electrical conductivity of the 0.80% CNT sample was observed. In the immersion absorption test, a decrease in water absorption was observed with an increase in the concentration of CNTs in the samples due to the hydrophobic nature of the CNTs. From the evaluation of moisture loss due to heat treatment, a behavior was observed in agreement with the literature regarding the loss of physical water (below 300°C), increasing the evaporation rate with the increase in the concentration of CNT in the samples. Together with X-ray diffraction (XRD), scanning electron microscopy (SEM), and infrared spectroscopy (FTIR) tests, the results obtained show the homogeneous dispersion of nanomaterials in the mortar. Thus, this work proposed a new method for incorporating CNTs into mortars in an effective, economically viable, and simple way using IOT in a quarter of the aggregates in the mortar mix.

Two Ti-Si-B alloys (namely: Ti-2Si-1B, Ti-6Si-3B) were produced by HIGH ENERGY MILLING (MAE). The MAE was carried out with a rotation of 200rpm, in a proportion of 1:20 mass/ball, observing times of 4h and 8h, for homogenization. The best sintering temperature was evaluated, namely: 1250°C, for a treatment time of 4h. In this way, the material was characterized in terms of phase variations and porosity to establish the best parameters for both alloys. Granulometry, SEM, DTA/TG, XRD, MO, density analyses, in addition to microhardness, wettability and cell growth tests were also carried out to better characterize the material obtained.

The development of high-entropy alloys has become in recent years as an alternative for producing alloys with enhanced properties. High-entropy alloys are multicomponent alloys composed of five or more main elements in equiatomic or near-equiatomic ratios. The high configurational entropy in a multicomponent alloy, compared to conventional alloys, results in the stabilization of alloying elements in stable solid solutions. Among the groups of multicomponent alloys, refractory high-entropy alloys stands out; they are composed of refractory elements and are considered a significant innovation in the development of materials for high-temperature applications. Thus, these materials must ensure thermal stability, wear resistance, and oxidation resistance at high temperatures and in oxidizing environments. Traditionally, these alloys are produced through melting, one of the most known manufacturing techniques. However, this method increases the probablility of heterogeneous structures with elemental segregation and other crystal defects, such as dislocations and grain boundaries. To solve this troublesome, powder metallurgy will be adopted as an alternative production method. This manufacturing method promotes solubility in the solid state and the formation of homogeneous alloys, providing the final product with properties equivalent to those obtained by melting. Additionally, the process offers significant energy savings, making it a viable alternative to traditional manufacturing methods. Taking into consideration, this work aims to produce and microstructurally characterize five combinations of the refractory multicomponent alloy based on AlCrNiNbMoW, manufactured by powder metallurgy. The atomic proportions of Al and Cr will be varied in 25% increments, from the equiatomic ratio to the total substitution of aluminum by chromium, to evaluate the influence of these variations on phase formation and oxidation resistance. The results revealed that all produced alloys exhibited a similar microstructural composition, characterized by the formation of a solid solution with a BCC crystalline structure and Laves phase. Oxidation tests resulted in the formation of oxides of aluminum, niobium, chromium, and tungsten. The alloy with the lowest mass gain was Al_4.2Cr_29.2, at 0.037 g/cm². The reduction in aluminum content in the produced alloys proved beneficial, as it proportionally decreased the mass gain. The studies carried out in this thesis enable the exploration of the potential of the four high-entropy effects in the design of new refractory multicomponent alloys produced via powder metallurgy, resulting in the formation of solid solutions with a BCC crystalline structure and Laves phase observed through microstructural characterization and X-ray diffraction. This thesis explores the potential of the four high-entropy effects in the development and understanding of new refractory multicomponent alloys produced by powder metallurgy. The studies demonstrate that these alloys form simple solid solutions with a BCC crystalline structure and Laves phase, confirmed by microstructural characterization and X-ray diffraction.

In this study, syntheses of cerium oxide (CeO2) nanoparticles with different concentrations of manganese were carried out using the microwave-assisted hydrothermal synthesis technique. In order to obtain different compositions, the nanoparticles were modified following the stoichiometric formulas: Ce1-(3/4x)MnxO2, where x varied in the values of 0.0, 4.0, 8.0, 12.0 in mol. The system was then subjected to a thermal treatment at 100 °C for 8 minutes in a conventional microwave oven, with a constant heating rate of 10 °C/min. The resulting powders were subjected to various characterization techniques to evaluate their properties. These techniques included X-ray diffraction (XRD), Raman scattering spectroscopy, ultraviolet-visible (UV-Vis) absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), field emission scanning electron microscopy (FESEM), positron annihilation lifetime spectroscopy (PALS), thermogravimetry (TG), differential thermal analysis (DTA), and electrical characterization. Both pure CeO2 system and manganese-doped system demonstrated high stability, showing similar diffraction patterns. From the analyses performed, it was possible to establish the response times of the sensors when exposed to CO, where a significant improvement was observed for the system doped with different concentrations of Mn compared to the pure system. The modification with higher Mn content (12%) did not show significant changes in terms of sensor response compared to the lower Mn content (4%), indicating that the lower doping of 4% Mn becomes promising for the application of sensors for carbon monoxide detection.

Corrosion is a natural process that has a significant economic impact. It degrades metal sand reduces the use fullife of metal structures. Currently, the most widely used form of prevention is to apply organic coatings, which form a physical barrier that prevents the metal from contacting the aggressive environment. The primer, in the automotive industry, is the layer that supports and protects the paint system against corrosion. The protection provide disgenerally at tributed to the presence of anti-corrosion pigments. Nevertheless, the effectiveness of the coating decreases when it is damaged. This study involved the encapsulation of chia oil (MC) and chia oil containing 1% v/v cobaltoctoate II 6% (MCOc) with polyureaformaldehyde (PUF) applying the in situ oil-in-wateremulsionpolymerisation technique. The encapsulation of the oils was confirmed through Fourier transform infraredspectroscopy (FTIR). The microcapsules MC and MCOc were determined to have a spherical shape and varied particle size distribution, with an average size of 47 (±13) µm and 76 (±14) µm, respectively, when examined by optical microscopy. The oil content of both samples was greater than 90%, as estimated through the Sohxlet Oil Extraction method. Scanning electron microscopy (SEM) images illustrated the existence of unencapsulated core material. The microcapsules were added to an automotive primer, and their self-repair effectiveness was evaluated. To conduct the corrosion studies, 10% by mass of the microcapsules were dispersed in a commercial automotive primer and subsequently applied to ordinary steel. The protective effect was studied using the electroanalytical techniques of Linear SweepVoltammetry (LSV) and Electrochemical Impedance Spectroscopy (EIE). The responses of uncoated steel, pure primer (P) and microcapsules (P+MC and P+MCOc) were compared. Abbreviations were explained upon first use. The language used was clear, precise and objective, adhering to conventional academic structures and maintaining formal register throughout. The text was also free from grammatical and punctuational errors. During the investigation, defects were intentionally formed at different times (0h, 1h, 2h, 4h, and 24h). According to LSV data, coating application enhanced the corrosion potential (Ecorr) of the steel. Additionally, samples assessed 24 hours following the creation of the defect exhibited improve defficiency for all three types of coating studied. EIE experiments demonstrated that incorporating microcapsules enhanced the resistive response ofthe primer, resulting in largersemi-circleradii in the Nyquist diagram. The P+MCOc coating demonstrated the best protective response among the methods analyzed.

In this thesis we study how the electrical transport properties in Zn1-xCdxO/CdO, heterostructures grown by spray pyrolysis, modified by doping and growing on substrates of glass and silicon. In the glass substrate, the x-doping values in the heterostructures were 0.50; 0.60; 0.75 and 0.95 and in silicon 0.60 and 0.95. CdO and Zn0,40Cd0,60O films were also grown on glass and silicon to analyze the contribution of these layers to heterostructures. From the diffractograms obtained from all the samples, it was verified that all are polycrystalline with phase-centered cubic structure (CFC) and that in the heterostructures grown on glass, the crystallite size is larger with the increase of doping. From the scanning electron microscopy (SEM) images of the surface of the samples, it was found that those grown on a glass substrate are less rough and those grown on silicon have domes on the surface. From the measurements of Hall effects it was observed that the samples are n-type independent of the substrate, having a high concentration of carriers being higher in the samples grown in glass, while the mobility was higher in the samples grown in silicon varying in up to four orders of magnitude. guarantee compared to those grown in glass. The high mobility in the samples grown on silicon was attributed to the domes. Electrical characterization and magnetotransport measurements were performed at temperatures ranging from 1.9 to 300 K and magnetic fields up to 9 T. All samples grown on glass showed metal-insulator transition (TMI) with different transition temperatures. The TMI observed in samples grown on glass is due to the degree of disorder being known as an Anderson-type transition. The heterostructure grown on silicon Zn0.40Cd0.60O/CdO also presented the TMI, but of the Mott type, which was verified by measuring resistance as a function of temperature (RT) applying a magnetic field. The Zn0.05Cd0.95O/CdO heterostructure and the CdO film grown on silicon showed insulating behavior in the RT curves throughout the analyzed temperature range. In the magnetoresistance (MR) curves, all samples grown on glass and the CdO film grown on silicon showed negative magnetoresistance (MRN) due to the weak localization effect. The MR curves of these samples were fitted using the Kawabata 3D model and from the fit it was obtained the phase coherence length and that the mechanism of electrical transport at low temperatures is the electron-electron interaction. As for the MR curves of the heterostructure Zn0.40Cd0.60O/CdO grown on silicon, it can be seen that the MR curves are totally influenced by the substrate since this sample exhibited positive magnetoresistance (MRP) while in the glass it was MRN. Although this sample exhibited high mobility, no wobbling pattern in the MR curves was detected due to high roughness. The Zn0.40Cd0.60O film measurements showed that the MRP exhibited by the Zn0.40Cd0.60O/CdO heterostructure grown on silicon comes from the upper layer. From all the results obtained, it was possible to verify that the heterostructures presented better electrical properties than the CdO films and that the heterostructure with silicon substrate is much more sensitive to the application of magnetic field than the one grown on glass.

Functional three-dimensional structures, or scaffolds, are of great interest in the area of tissue engineering associated with regenerative medicine, as they allow the mimicry of biological structures. The electrospinning technique, considered a simplified and low-cost process, presents versatility in producing structures with high porosity and surface area, which allows interaction between cell materials at the molecular level. Scaffolds synthesized from piezoelectric materials, when subjected to electrical and/or mechanical forces, can stimulate cell growth and differentiation in specific tissues such as bones. Recent studies have indicated that the copolymer polyvinyl fluoride trifluoroethylene (PVDF-TrFE) associated with ceramic Barium Titanate (BaTiO3) has biological properties that are inspired by electronic characteristics owing to their high piezoelectric, pyroelectric, and ferroelectric responses. Thus, this work studies functional scaffolds with suitable characteristics for use in the area of tissue regeneration, from the development of an equipment that associates the direct-write near-field electrospinning (NFES) technique with the three-dimensional printing technique. The prototype allows the development of three-dimensional structures from fibers with suitable properties that mimic an electrophysiological environment, providing the formation/regeneration of biological tissue. The structural, physicochemical, and electrical characterizations of the material were carried out at the Universidade Federal de Itajubá (UNIFEI) - Itajubá, including scanning electron microscopy (SEM), surface wettability, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), solution viscosity, X-ray diffraction (XRD), impedance, and surface potential of the scaffolds. Biological characterization of the material was performed using in vitro studies to evaluate the proliferation, collagen, and cell behavior of the scaffold. For this, we used osteoblast-like MG-63 cells seeded on NFES and CES scaffolds. This work was conducted jointly with the AGH University of Science and Technology, Poland. Together with Biological Tests, the piezoresponse of the fibers was analyzed. The microstructure results showed the fibers diameter of 341 nm and 2,69 µm for CES and NFES scaffolds, respectively. The wettability assay demonstrated that the surface was hydrophobic, with contact angle of 115,6° for the CES scaffold and 100,6° for the NFES scaffold. Regarding physicochemical tests, the thermal stability of both materials was up to 440 °C, and the crystallinity of the CES scaffold corresponds to 79,63 % with a β phase content of 78,23. In contrast, the crystallinity of the NFES scaffold corresponds to 65,10% and presents 78,03% of β phase content. The XRD and FTIR analyses indicated that the absorption peaks and diffraction peaks of the membrane and scaffold characterized both materials as piezoelectric owing to the strong presence of the β phase, independent of the technique used to obtain the scaffolds. PFM analysis of both scaffolds showed fibers with piezoresponse properties superior to the bone tissue (NFES piezoresponse potential = 4.873 ± 0.637 mV; CES piezoresponse potential = 2.728 ± 0.411 mV; bone piezoresponse potential = ≈ 300 µV). These findings imply that the both scaffolds could mimic an electrophysiological environment that allows cell growth and proliferation. Biological findings showed good compatibility with cells and both scaffolds, and we noted that the proliferation and cell alignment follow the fiber pattern for NFES scaffolds.