Estudo de titanatos nanoestruturados obtidos por tratamento hidrotérmico de óxido de titânio em meio alcalino

TiTanate NanoTubes (TTNT) were synthesized by hydrothermal alkali treatment of TiO2 anatase followed by repeated washings with distinct degrees of proton exchange. TTNT samples with different sodium contents were characterized, as synthesized and after heattreatment (200-800ºC), by X-ray diffraction, scanning and transmission electron microscopy, electron diffraction, thermal analysis, nitrogen adsorption and spectroscopic techniques like FTIR and UV-Vis diffuse reflectance. It was demonstrated that TTNTs consist of trititanate structure with general formula NaxH2−xTi3O7·nH2O, retaining interlayer water in its multiwalled structure. The removal of sodium reduces the amount of water and contracts the interlayer space leading, combined with other factors, to increased specific surface area and mesopore volume. TTNTs are mesoporous materials with two main contributions: pores smaller than 10 nm due to the inner volume of nanotubes and larger pores within 5-60 nm attributed to the interparticles space. Chemical composition and crystal structure of TTNTs do not depend on the average crystal size of the precursor TiO2-anatase, but this parameter affects significantly the morphology and textural properties of the nanostructured product. Such dependence has been rationalized using a dissolution-recrystallization mechanism, which takes into account the dissolution rate of the starting anatase and its influence on the relative rates of growth and curving of intermediate nanosheets. The thermal stability of TTNT is defined by the sodium content and in a lower extent by the crystallinity of the starting anatase. It has been demonstrated that after losing interlayer water within the range 100-200ºC, TTNT transforms, at least partially, into an intermediate hexatitanate NaxH2−xTi6O13 still retaining the nanotubular morphology. Further thermal transformation of the nanostructured tri- and hexatitanates occurs at higher or lower temperature and follows different routes depending on the sodium content in the structure. At high sodium load (water washed samples) they sinter and grow towards bigger crystals of Na2Ti3O7 and Na2Ti6O13 in the form of rods and ribbons. In contrast, protonated TTNTs evolve to nanotubes of TiO2(B), which easily convert to anatase nanorods above 400ºC. Besides hydroxyls and Lewis acidity typical of titanium oxides, TTNTs show a small contribution of protonic acidity capable of coordinating with pyridine at 150ºC, which is lost after calcination and conversion into anatase. The isoeletric point of TTNTs was measured within the range 2.5-4.0, indicating behavior of a weak acid. Despite displaying semiconductor characteristics exhibiting typical absorption in the UV-Vis spectrum with estimated bandgap energy slightly higher than that of its TiO2 precursor, TTNTs showed very low performance in the photocatalytic degradation of cationic and anionic dyes. It was concluded that the basic reason resides in its layered titanate structure, which in comparison with the TiO2 form would be more prone to the so undesired electron-hole pair recombination, thus inhibiting the photooxidation reactions. After calcination of the protonated TTNT into anatase nanorods, the photocatalytic activity improved but not to the same level as that exhibited by its precursor anatase

Síntese e Caracterização de Titanatos de Cobalto e Níquel, dopados com Praseodímio, obtidos a partir da decomposição de Nitrilotriacetatos

In recent years, studies about the physicochemical properties of mixed oxides, call attention of the scientific community, properties like as piezoelectricity, photoluminescence, or applications as catalysts, arise in these compounds, when their chemical compositions are modified, in this context some routes are employed in the synthesis of these materials, among which can be cited these methods: ceramic, combustion, co-precipitation, Pechini or polymeric precursor method, hydrothermal, sol-gel; these routes are divided into traditional routes or chemical routes. In this work were synthesized oxides with variable composition, from the thermal decomposition of titanium, cobalt, nickel and praseodymium nitrilotriacetates. The nitrilotriacetates were characterized by IR Spectroscopy (FTIR), Thermogravimetric (TG/ DTG) and Differential Scanning Calorimetry (DSC), while oxides have been characterized by X-ray diffraction (XRD), Spectrofluorimetry and IR Spectroscopy (FTIR). From FTIR data, it was demonstrated that the displacement of the band corresponding to the carboxylate group (νCOOH) at 1712 cm-1, present in nitrilotriacetic acid (H3NTA), for 1680-1545 cm-1, these stretches are characteristics of coordinated nitrilotriacetates, By thermal analysis (TG/DTG /DSC), it was suggested, that in an oxidizing atmosphere (air) oxides are obtained at lower temperatures than in an inert atmosphere N2(g). By results from X-ray Diffraction (XRD), it was determinated that the oxides are crystalline and the predominant phases obtained are summarized titanate phases rutile and ilmenite. By fluorimetry was observed that the intensity of emission bands are directly proportional to the concentration of ions Ni2+, Co2+ and Pr3+, and IR spectroscopy (FTIR) from oxides, demonstrated the disappearance of characteristic bands by nitrilotriacetates, determining the complete decomposition of the nitrilotriacetates in oxides

Avaliação da estabilidade térmica e oxidativa do biodiesel de algodão e do efeito da adição de antioxidantes (α-tocoferol e BHT)

This work aims to study the effects of adding antioxidants, such as, α- tocopherol and BHT on the thermal and oxidative stability of biodiesel from cottonseed (B100). The Biodiesel was obtained through the methylical and ethylical routes. The main physical and chemical properties of cotton seed oil and the B100 were determined and characterized by FTIR and GC. The study of the efficiency of antioxidants, mentioned above, in concentrations of 200, 500, 1000, 1500, 2000ppm, to thermal and oxidative stability, was achieved by Thermogravimetry (TG), Differential Thermal Analysis (DTA), Differential Scanning Calorimetry (DSC), Differential Scanning Calorimetry - Hi-Pressure (P-DSC) and Rancimat. The Biodiesel obtained are within the specifications laid down by Resolution of ANP No7/2008. The results of TG curves show that the addition of both antioxidants, even in the lowest concentration, increases the thermal stability of Biodieseis. Through the DTA and DSC it was possible to study the physical and chemical transitions occurred in the process of volatilization and decomposition of the material under study. The initial time (OT) and temperature (Tp) of oxidation were determined through the P-DSC curve and they showed that the α-tocopherol has a pro-oxidant behavior for some high concentrations. The BHT showed better results than the α-tocopherol, with regard to the resistance to oxidation

Síntese e caracterização de redes metalorgânicas baseadas em zinco e ácidos benzenodicarboxílicos

Metal Organic Frameworks (MOFs) are supramolecular structures consisted of ions or metal clusters coordinated to organic ligands which are repeated in two or three dimensions. These structures have atracted much attention due to their properties such as low density, high specific surface area and large volume of pores. In this work, MOFs consisted of zinc clusters connected by ditopic ligands, terephthalic acid (1,4- H2BDC) or isophthalic acid (1,3-H2BDC) were synthesized. To obtain the proposed materials, different routes and synthetic parameters were tested, such as the molar ratio of the precursors, the addition of template molecules, the type of solvente, the addition of organic base or the type of a counter-ion of Zn salt. It was found that the variation of these parameters led to the formation of different metalorganic structures. The solids obtained were characterized by XRD, SEM and IR. For the samples identified as MOF- 5, it was verified that the structure was composed of both interpenetrated and non interpenetrated structures. These samples showed a low stability, becoming totally transformed into another structure within less than 72 hours. The addition of the nickel and/or cobalt was found to be a promissing method for increasing the stability of MOF- 5, which in this case, still remained unconverted to another structure even after 15 days of exposure to air. The samples prepared from 1,3-H2BDC were probably new, still unknown Metal Organic Frameworks

Um estudo algorítmico de problemas logísticos na indústria de petróleo e gás natural

This work consists on the study of two important problems arising from the operations of petroleum and natural gas industries. The first problem the pipe dimensioning problem on constrained gas distribution networks consists in finding the least cost combination of diameters from a discrete set of commercially available ones for the pipes of a given gas network, such that it respects minimum pressure requirements at each demand node and upstream pipe conditions. On its turn, the second problem the piston pump unit routing problem comes from the need of defining the piston pump unit routes for visiting a number of non-emergent wells in on-shore fields, i.e., wells which don t have enough pressure to make the oil emerge to surface. The periodic version of this problem takes into account the wells re-filling equation to provide a more accurate planning in the long term. Besides the mathematical formulation of both problems, an exact algorithm and a taboo search were developed for the solution of the first problem and a theoretical limit and a ProtoGene transgenetic algorithm were developed for the solution of the second problem. The main concepts of the metaheuristics are presented along with the details of their application to the cited problems. The obtained results for both applications are promising when compared to theoretical limits and alternate solutions, either relative to the quality of the solutions or to associated running time

O Circuito inferior da economia urbana em Mossoró: a dinâmica do comércio ambulante

This study was based on the analysis and understanding of the dynamics of the lower circuit of the economy and the size of the street trading in the city of Mossoro (RN). The operationalization of the theory of the two circuits of the urban economy, based on Santos (2008a) was essential to understand the street trading as part of the entire city of Mossoro. It was given emphasis on the study of the lower circuit of the economy and its coverage in the street trading in the commercial center of the city, specifically in street trading in Coronel Gurgel. The dynamics of that street reveals the different ways that the territory is used simultaneously by different social actors as pedestrians, consumers, business owners, and especially by street vendors. These vendors occupy the spaces along the streets of the city commercial center, placing their tents or stalls, especially on sidewalks, excellent strategic locations for the marketing of their products, due to the large influx of people seeking goods and services nearby. As methodological and technical procedures for gathering primary data, we opted for the use of questionnaires and interviews, with many users of the lower circuit, both consumers and vendors. The analysis of these questionnaires, along with the theoretical background, has revealed that there are several social and political conflicts related to the use of public spaces, such as sidewalks and flowerbeds, in the city commercial center, and that these conflicts are increasingly demonstrating that vendors need a space endowed with infrastructure to conduct their activities. The lack of efficiency of the government, as well as the slowness of their actions to organize a space that is able to properly fit salespersons, constitutes one of the main problems faced by these small traders who have limited financial resources and materials to get their activities through in the globalized world. At the same time, this study revealed the importance of these agents, as the last link of the urban economy, in the distribution of various consumer goods, enabling the satisfaction of some needs of the population, especially the poorer people

Otimização da síntese do AlSBA-15 para produção de biodiesel por transesteri-ficação do óleo de coco

Stimulus encouraging the production and consumption of biodiesel favors the policy of pre-serving the environment, contributing to the reduction of greenhouse gas reducing climate change. The current trend of research in this field focuses on improving these processes with the use of heterogeneous catalysts, seeing has significant advantages such as: low contamination of products, ease of separation of the catalyst from the reaction medium, possibili-ty of reuse of the catalyst, decreased corrosion problems. The objective of this research was to optimize the synthesis of AlSBA-15 for the production of biodiesel through transesterification process via ethyl route. For the optimization of hydrothermal synthesis of type AlSBA-15 catalyst has assembled a 23 factorial experimental matrix with eleven trials. The stoichiometric amounts of starting materials were varied according to different ratios Si / Al which is a factor in the experimental design, in addition to the time and temperature of aging of the synthesis gel. The material showed the best results of characterization (SBET = 591.7 (m2 / g), Vp = 0.83 (cm3 / g), Dp = 5.59 (nm), w = 6.48 (nm) was synthesized at 100 ° C for 24 hours, with a ratio Si / Al = 10.This material was applied as a heterogeneous catalyst in the reaction of ethyl transesterification as raw coconut oil in natura. Coconut oil presented suitable for obtaining biodiesel via ethyl route.The visual aspects and physical-chemical characteristics of the reaction products show that AlSBA-15 catalyst favored the reaction. According to physical-chemical analysis the order of oxidative stability of the product of the transesterification reaction was: catalytic reaction at 1500 ° C> non-catalytic reaction at 100 ° C> 100 ° C catalytic> catalytic reaction at 200 ° C Reaction. The results of oxidative stability and kinematic viscosity shows that the biodiesel produced in the catalytic sandblasting held at 150 ° C which was maintained within the ABNT NBR 7148, ABNT NBR 10441 and EN 14112.

Processing of highly porous titanium parts by metal injection moulding in combination with innovative plasma treatment

A combinação da Moldagem por Injeção de pós Metálicos (Metal Injection Moulding MIM) e o Método do Retentor Espacial (Space Holder Method - SHM) é uma técnica promissora para fabricação de peças porosas de titânio com porosidade bem definida como implantes biomédicos, uma vez que permite um alto grau de automatização e redução dos custos de produção em larga escala quando comparado a técnica tradicional (SHM e usinagem a verde). Contudo a aplicação desta técnica é limitada pelo fato que há o fechamento parcial da porosidade na superfície das amostras, levando ao deterioramento da fixação do implante ao osso. E além disso, até o presente momento não foi possível atingir condições de processamento estáveis quando a quantidade de retentor espacial excede 50 vol. %. Entretanto, a literatura descreve que a melhor faixa de porosidade para implantes de titânio para coluna vertebral está entre 60 - 65 vol. %. Portanto, no presente estudo, duas abordagens foram conduzidas visando a produção de amostras altamente porosas através da combinação de MIM e SHM com o valor constante de retentor espacial de 70 vol. % e uma porosidade aberta na superfície. Na primeira abordagem, a quantidade ótima de retentor espacial foi investigada, para tal foram melhorados a homogeneização do feedstock e os parâmetros de processo com o propósito de permitir a injeção do feedstock. Na segunda abordagem, tratamento por plasma foi aplicado nas amostras antes da etapa final de sinterização. Ambas rotas resultaram na melhoria da estabilidade dimensional das amostras durante a extração térmica do ligante e sinterização, permitindo a sinterização de amostras de titânio altamente porosas sem deformação da estrutura.

Síntese de carreadores de oxigênio à base de Ni e Co para estudo do processo de Chemical Looping usando CH4 como combustível

Increasing energy demand is being met largely by fossil fuel reserves, which emit CO2, SOx gases and various other pollutants. So does the search for fuels that emit fewer pollutants and have the same energy efficiency. In this context, hydrogen (H2) has been increasingly recognized as a potential carrier of energy for the near future. This is because the H2 can be obtained by different routes and has a wide application area , in addition to having clean burning, generating only H2O as a product of combustion , and higher energy density per unit mass . The Chemical Looping Reforming process (CLR) has been extensively investigated in recent years, it is possible to regenerate the catalyst by applying cycles of reduction and oxidation. This work has as main objective to develop catalysts based on nickel and cobalt to study the reactivity of reform with chemical recycling process. The catalysts were prepared by three different methods: combustion assisted by microwave, wet impregnation and co-precipitation. All catalysts synthesized have the same amount by weight of the active phases (60% w / w). The other 40 % m/m consists in La2O3 (8% w / w), Al2O3 (30% w / w) and MgO (2%). Oxygen carriers have been named as follows: N or C, nickel or cobalt, followed by the number 3 or 6, meaning 30 to 60% of active phase in the oxide form and C, CI or CP, which means self-combustion assisted by microwave, self-combustion assisted by microwave followed by wet impregnation and co-precipitation. The oxygen carriers were then characterized by the techniques of X-ray diffraction (XRD), surface area (BET), temperature programmed reduction (TPR) and scanning electron microscopy (SEM). The characterization results showed that the different synthesis methods have led to obtaining different morphologies and structures. Redox tests using CH4 as reducing agent and sintetic air as oxidant agent was done with N6C and C6C, N6CI and C6CI and N6CP and C6CP oxygen carriers. The tests revealed different behaviors, depending on active phase and on synthesis procedure. N6C oxygen carrier produced high levels of H2. The C6CI oxygen carrier produced CO2 and H2O without carbon deposits.

Tomada de decisão individual e aprendizado em Dinoponera quadríceps (Ponerinae, Hymenoptera) forrageando em ambientes dinâmicos

When searching for food, animals often make decisions of where to go, how long to stay in a foraging area and whether or not to return to the last visited spot. These decisions can be enhanced by cognitive traits and adjusted based on previous experience. In social insects such as ants, foraging efficiency have an impact on both individual and colony level. The present study investigated, in the laboratory, the effect of distance from food, capture success and food size, and reward rate on decisions of where to forage in Dinoponera quadriceps, a ponerine ant that forage solitarily and individually make their foraging decisions. We also investigated the influence of learning on the performance of workers over successive trips searching for food by measuring the patch residence time in each foraging trip. Four scenarios were created differing in food reward rates, food size offered and distances colony-food site. Our work has shown that as a rule-of-thumb, workers of D. quadriceps return to the place where a prey item was found on the previous trip, regardless of distance, food size and reward rate. When ants did not capture preys, they were more likely to change path to search for food. However, in one of the scenarios, this decision to switch paths when unsuccessful was less evident, possibly due to the greater variation of possible outcomes ants could experience in this scenario and cognitive constraints of D. quadriceps to predict variations of food distribution. Our results also indicated a learning process of routes of exploration as well as the food site conditions for exploration. After repeated trips, foragers reduced the patch residence time in areas that they did not capture food and quickly changed of foraging area, increasing their foraging efficiency.

Classificação de técnicas e auxílio à navegação de busca com base em sua carga cognitiva, precisão e eficiência

Navigation, in both virtual and real environments, is the process of a deliberated movement to a specific place that is usually away from the origin point, and that cannot be perceived from it. Navigation aid techniques (TANs) have as their main objective help finding a path through a virtual environment to a desired location and, are widely used because they ease the navigation on these unknown environments. Tools like maps, GPS (Global Positioning System) or even oral instructions are real world examples of TAN usage. Most of the works which propose new TANs for virtual environments aim to analyze their impact in efficiency gain on navigation tasks from a known place to an unknown place. However, such papers tend to ignore the effect caused by a TAN usage over the route knowledge acquisition process, which is important on virtual to real training transfer, for example. Based on a user study, it was possible to confirm that TANs with different strategies affects the performance of search tasks differently and that the efficiency of the help provided by a TAN is not inversely related to the cognitive load of the technique’s aids. A technique classification formula was created. This formula utilizes three factors instead of only efficiency. The experiment’s data were applied to the formula and we obtained a better refinement of help level provided by TANs.

Determinação da condutividade do solo para agricultura: uma metodologia utilizando propagação de ondas AM

Agriculture is an essential activity to the human development, the tendency is that their need to increase according to the increase in world population. It is very important to take the maximum performance that is possible of each land without degrading it, a frequently monitoring is essential for the best performance. The purpose of this work is, nondestructively, to monitor the surface electrical conductivity of the soil in a demarcated area, as on a plantation, using low frequency radio waves. The conductivity is directly linked to the amount of water in the area and nutrients, therefore a periodic or even permanent monitoring increases significantly the efficient of the use of the soil. They will be used long-wave radio transmission or medium whose main characteristic to spread over the surface of the earth. It is possible to choose an AM radio with location, frequency and power of the transmission known or generate the signal. The studied method computes the conductivity of the ground in a straight line between two measured points, so it can be used in smaller or larger size fields. Measurements were carried out using an electromagnetic field strength analyzer. The data obtained in the measurements are processed by a numerical calculation program, in our case Matlab. It is concluded that the recommendations of the ITU (International Telecommunication Union) on the conductivity of soil in Brazil is far from reality, on some routes the recommendations indicate the use of the electrical conductivity of the soil 1 mS/m, while the measurements was found 19 mS/m. With the method described a precision farmer, once initial research for about a year, can monitor the humidity and salinity of the land, with the ability to predict the area and the most suitable time for irrigation and fertilization, making management more efficient and less expensive, while optimizing water use, natural resource increasingly precious.

Planejamento de trajetórias e navegação de robôs móveis

Oil exploration at great depths requires the use of mobile robots to perform various operations such as maintenance, assembly etc. In this context, the trajectory planning and navigation study of these robots is relevant, as the great challenge is to navigate in an environment that is not fully known. The main objective is to develop a navigation algorithm to plan the path of a mobile robot that is in a given position (

Planejamento de trajetórias e navegação de robôs móveis

Oil exploration at great depths requires the use of mobile robots to perform various operations such as maintenance, assembly etc. In this context, the trajectory planning and navigation study of these robots is relevant, as the great challenge is to navigate in an environment that is not fully known. The main objective is to develop a navigation algorithm to plan the path of a mobile robot that is in a given position (

Efeitos da privação do sono em tarefas cognitivas

Learning and memory are important mechanism for species, since its allows to recognize conspecifics, routes and food place. Sleep is one of behaviors known by facilitate learning, it is a widespread phenomenon, present in most of vertebrates lives and highly investigated in many aspects. It is known that sleep deprivation modifies physiologic behavioral processes in animals, however, sleep function in organism is still debatable. Hypothesis range from energy conservation to memory consolidation, with different roles in animal’s evolution. The zebrafish (Danio rerio) emerg e in the last years as vertebrate model in genetics and developmental biology and quickly become popular in behavioral studies, as learning and memory. Despite the fact that zebrafish is a diurnal animal and have well characterized sleep behavior, zebrafish fish still has advantages due to its small size and low cost of maintenance, whichestablishes this species as interesting model for research on sleep. In this study we aimed to analyze the effects of partial and total sleep deprivation on learning acquisition, as well the concomitant administration of alcohol and melatonin. For this, the research was divided in three phases, each one with a different kind of conditioning: (1) object Recognition, (2) avoidance conditioning and (3) appetitive conditioning. The results showed the fish partially sleep deprived and totally sleep deprived + et hanol could perform the tasks just like the control group, however, fish totally sleep deprived and totally sleep deprived + melatonin showed impairments in attention and memory during the tests. Our results suggest that only one night of sleep deprivation is enough to harm the zebrafish performance in cognitive tasks. In addition, ethanol exposure on the night previously the test seems to suppress the negative effects of sleep deprivation, while the melatonin treatment seems not to be enough to promote sleep state, at least on the protocol applied here.