A successful transition from fossil fuels to renewable energies such as wind and solar will require the implementation of high-energy-density storage technologies. Promising energy storage technologies include lithium-ion batteries, metal-air batteries, and hydrogen production via photoelectrochemical water splitting. While these technologies differ substantially in their mode of operation, they often involve transition-metal oxides as a component. Thus, fundamental materials research on metal oxides will continue to provide much needed advances in these technologies. In this thesis, the electrochemical and electrocatalytic properties of Fe- and Mn-substituted layered LiNiO₂ materials were investigated. These materials were prepared by heating mixed nitrate precursors in O₂ atmosphere at 700-850 °C for 12 h with intermediate grindings. The products were chemically delithiated with NO₂BF₄, and the delithiated samples were annealed at moderate temperatures in order to transform them to a spinel-like phase. Samples were characterized by inductively coupled plasma analysis and Rietveld refinement of the X-ray diffraction patterns, which were found to be in reasonably close agreement regarding lithium stoichiometry. Spinel-like materials were found to possess an imperfect spinel structure when heated at lower temperatures and a significant amount of NiO impurity was formed when heated to higher temperatures. This structural disorder was manifested during electrochemical cycling -- only Mn-rich compositions showed reversible capacities at a voltage of around 4.5 V. The layered materials exhibited significant capacity loss upon cycling, and this effect was magnified with increasing Fe content. These materials were further investigated as catalysts for the oxygen evolution reaction (OER). All samples containing Mn exhibited low OER activity. In addition, delithiation degraded catalyst performance and moderate temperature annealing resulted in further degradation. Because delithiation significantly increased surface area, activities were compared to the relative to BET surface area. Li₀.₉₂Ni₀.₉Fe₀.₁O₂ exhibited significantly higher catalytic activity than Li₀.₈₉Ni₀.₇Fe₀.₃O₂. This prompted testing of Li[subscript x]Ni₁₋[subscript y]Fe[subscript y]O₂ (y = 0, 0.05, 0.1, 0.2, and 0.3) samples. It was found that a Fe content of approximately 10% resulted in the highest OER activity, with decreased activities for both larger and smaller Fe contents. These results were found to be consistent with studies of Fe substituted nickel oxides and oxyhydroxides, suggesting a similar activation mechanism. / text

In this thesis an architecture, similar to subsumption architectures, is presented which uses low level behaviour modules, based on combinations of machine learning techniques, to create teams of autonomous agents cooperating via shared plans for interaction. The purpose of this is to perform effective single plan execution within multiple scenarios, using a modern team based first person shooter video game as the domain and visualiser. The main focus is showing that through basic machine learning mechanisms, applied in a multi-agent setting on sparse data, plans can be executed on game levels of varying size and shape without sacrificing team goals. It is also shown how different team members can perform locally sub-optimal operations which contribute to a globally better strategy by adding exploration data to the machine learning mechanisms. This contributes to the reinforcement learning problem of exploration versus exploitation, from a multi-agent perspective.

The investigation into the syntheses and the intercalations of LDHs is the focus of the work described in this thesis. An introduction to Layered Double Hydroxide (LDH) materials with an emphasis on the possible host lattices and to their applications is given in <strong>Chapter 1</strong>. The application of LDHs in cement including; history of cement, cement production process, and cement hydration is detailed. The synthesis of the Ga-doped Ca₂Al(OH)₆Cl•nH₂O LDHs (Ca₂Ga_xAl_(1–x)-Cl; where 0 < x < 1) via the co-precipitation method is reported in <strong>Chapter 2</strong>. The effect of doping Ga³⁺ on a parameter of Ca₂Ga_xAl_(1–x)-Cl was determined by using Vegard’s law and the correlation between a parameter and x value was derived. The intercalation of organic anions including; sodium styrene sulfonate, sodium butene dicarboxylate, sodium fumarate and ammonium poly(styrene sulfonate), in Ca₂Ga-Cl structure is described. The intercalation of lignosulfonate, naphthalene sulfonate and polycarboxylate into Ca₂Al(OH)₆NO₃·6H₂O (Ca₂Al-NO₃) is detailed in <strong>Chapter 3</strong>. The release behaviour for the LDHs and the kinetic modelling of the release are reported. The effects of these LDHs on cement hydration studied by using the in situ X-ray diffraction and the ultrasound shear-wave reflection are discussed. In <strong>Chapter 4</strong>, the synthesis of Ca₂Al(OH)₆NO₃·nH₂O via a non-ionic surfactant reverse microemulsion is reported. The effects of the amount and the solubility [Hydrophile-Lipophile Balance (HLB)] of non-ionic surfactant on the morphology and the size distribution of the LDHs are discussed. Two new nitrite intercalated Ca₂Al-LDHs [Ca₂Al(OH)₆NO₂·nH₂O] synthesised via both the co-precipitation and the reverse micro-emulsion method are detailed in <strong>Chapter 5</strong>. The hydration of Portland cement samples with additive nitrate- and nitrite-intercalated Ca₂Al-LDH made using co-precipitation is discussed. The synthesis of dispersed, uniform nanoplatelet [Ca₂Al(OH)₆DDS]•H₂O LDHs is reported in <strong>Chapter 6</strong>. The effects of the amount of the surfactant on the morphology and size distribution of the LDHs are described. The experimental procedures and characterising techniques employed in this study are listed in <strong>Chapter 7</strong>. Additional data are provided in the <strong>Appendices</strong>.

A series of oxide materials were modified with different nanoparticles (NPs). Novel cobalt@H4Nb6O17 nanopeapod structures were fabricated and magnetic NPs modified oxide nanosheets and nanoscrolls were prepared. Both aqueous method and two-phase method were applied to prepare gold NPs onto oxide nanosheets, nanoscrolls and other nanocrystals. The combination of H4Nb6O17 nanoscrolls and cobalt NPs generate a novel method to fabricate nanopeapod structures. Cobalt NPs were synthesized in the presence of exfoliated H4Nb6O17 nanosheets and the resulting magnetic chain structures, formed due to the dipole-dipole interaction, were captured within scrolled lamella. The yield of peapod structures can be improved by using proper reagents and reaction temperatures. As similar method with iron oxide NPs also produced peapod-like structures in a low yield. Exfoliated Dion-Jacobson phase layered perovskite HLaNb2O7 (HLN), its organic derivate propoxyl-HLaNb2O7 (pHLN), Ruddlesden-Popper phase perovskite H2SrTa2O7 (HSTO) and Aurivillius phase perovskite H2W2O7 (HWO) were synthesized and functionalized with gold NPs by in-situ methods. Gold NPs were prepared by both an aqueous method and two-phase method. The size of NPs can be adjusted by different reaction times. Overall, the latter method shows a narrower size distribution and better dispersion. In addition, most gold NPs prepared by the two-phase method were attached on the surface of nanosheets and almost no free gold NPs were observed in solution. This approach should be applicable to most layered perovskites. The aqueous and two-phase methods were also applied on the preparation of gold NPs onto H4Nb6O17 nanosheets and nanoscrolls. H4Nb6O17 nanosheets were prepared by two approaches and showed similar gold NPs attachment. LiNbO3 nanocrystals can be also modified with gold NPs by the two-phase method though free gold NPs were observed. Further studies involved the functionalization of layered perovskites and related compounds with magnetic NPs. Iron oxide and cobalt NPs were synthesized in the presence of layered perovskite and modified perovskite nanosheets were obtained.

Metastable layered perovskites containing interlayer transition metals can readily be obtained by simple ion exchange reactions on receptive hosts, such as those of the Dion-Jacobson and Ruddlesden-Popper structure types. In this work, we focused on adding to the library of layered perovskites by not only creating new compounds, but by also showing their ability to be further manipulated, and by studying the stability of the series through thermal behavior studies. The reactions with transition metal halides are particularly interesting since they often lead to novel architectures and magnetic behavior. On subsequent heat treatment, these exchange products typically decompose to thermodynamically more stable phases. The newly synthesized spin glass-like material, FeLa2Ti3O10, obtained by ion exchange of Li2La2Ti3O10 with FeCl2 at 350 °C, behaves differently. When heated to 700 °C, the compound undergoes a significant cell contraction (Δc ≈ -2.7 Å) with an increase in the oxidation state of iron present in the interlayer that not been observed before in such compounds. Efforts were also made to synthesize new series of compounds, here MSrTa2O7 (M= Co and Zn), with vacancies in the interlayer that could lead to future topochemical manipulations. The ability to vary the composition of different phases to form solid-solutions through atomic substitution at the A or B sites with ions of similar or different charge can lead to new structures as well an enhancement of the properties of the original compound or new ones. The synthesis and characterization of the new mixed A-cation containing layered perovskite RbLaNaNb3O10, where La3+ and Na+ share the same site in the perovskite slab and RbLaCaNb2MnO10 that exhibits an ordering of the B site with Mn in the center of the perovskite slab will be presented. Further topochemical manipulation of these phases via ion exchange reactions at low temperatures (< 500 °C), lead to the new series A’LaNaNb3O10 and A’LaCaNb2MnO10 where A’= H, Li, Na, K and CuCl.

Hidróxidos Duplos Lamelares (HDL) são materiais lamelares constituídos de camadas positivamente carregadas de um hidróxido misto de dois metais (um di e um trivalente), com ânions hidratados no domínio interlamelar. Apesar de serem potenciais adsorventes, o estudo da adsorção de colato de sódio sobre estes sólidos foi pouco explorado até hoje. Este estudo é importante, pois abre caminho para uma potencial aplicação farmacêutica de HDL na remoção de colato produzido em excesso pelo corpo humano, e diminuindo o risco de doenças conseqüentes desse excesso. Este trabalho teve por objetivo estudar a adsorção e a sorção de colato de sódio a partir de soluções aquosas, em hidróxido duplo lamelar de magnésio e alumínio intercalado com carbonato, Mg-Al-CO3-HDL, verificando o efeito de variáveis como temperatura, pH e força iônica do meio. O adsorvente foi preparado pelo método de coprecipitação a pH variável e caracterizado quanto à composição, organização estrutural, textura e morfologia, sendo utilizado na forma original ou após calcinação. A adsorção de colato de sódio no HDL não calcinado indicou que não ocorre a substituição do ânion interlamelar (CO32-), mas sim a adsorção por interação do ânion orgânico com as cargas residuais na superfície do HDL. O processo mostrou uma grande dependência das variáveis estudadas. A análise multivariacional confirmou e quantificou a importância de cada variável. Em todos os casos, o aumento da temperatura resultou em uma diminuição na quantidade máxima adsorvida. O aumento da força iônica do meio, por meio da adição de um sal neutro, resulta em uma melhoria na capacidade de remoção de ânions. Na faixa avaliada, quanto maior o valor do pH das soluções de colato, menor a quantidade máxima adsorvida. Os resultados obtidos para a sorção no HDL calcinado mostraram que inicialmente o HDL é reconstituído com a intercalação de ânions OH-. Em casos onde a concentração do composto orgânico era alta, o colato foi intercalado formando uma nova fase. Neste caso, a sorção de colato apresentou curvas com perfil semelhante às da adsorção: as isotermas atingem um patamar onde a sorção torna-se constante e o aumento da temperatura diminui a quantidade sorvida. Pelos resultados obtidos, foi proposto um modelo de intercalação de colato em bicamada. Os resultados indicam também que a remoção do colato pelo HDL calcinado se mostra mais eficiente do que aquela obtida com o HDL não calcinado. / Layered Double Hydroxides (LDH), are lamellar materials constituted of positively charged layers of two mixed cations hydroxide (a bi and a trivalent one), with hydrated anions in the interlayer domain. In spite of being potential adsorbents, the study of the sodium cholate adsorption on these solids has not been well explored yet. This study is important, because it opens the perspective for the application of LDH in the pharmaceutical field in the removal of cholate produced in excess by the human organism and decreasing the risk of consequent diseases from this excess. The aim of this work was to study the adsorption and the sorption of sodium cholate from aqueous solutions, in Mg-Al-CO3-LDH, verifying the effect of the variables: temperature, pH and ionic strength of the media. The adsorbent was prepared by the coprecipitation at variable pH method and characterized with respect to their composition, structural organization, texture and morphology, being utilized in the pristine form or after calcination. The adsorption of sodium cholate in pristine LDH indicated that the exchange of the interlayer anion (CO32-) doesn\'t occur, but the adsorption process occurs by the interaction of the anion with the residual charges on the LDH surface. The process showed great dependence on the parameters studied. The multivariational analysis confirmed and quantified the influence of each variable. In all the experiments, increasing the temperature resulted in a decrease in the maximum adsorbed quantity. Increasing the ionic strength of the media, by the addition of a neutral salt, results in a better anions removal capacity. In the evaluated interval, the bigger the initial pH value of the cholate solutions, the lower the maximum adsorbed quantity. The results obtained for the sorption in calcined LDH showed that initially the LDH are reconstituted with the OH- anions intercalated. In the experiments at high concentration, the cholate is intercalated forming a new phase. The profile of cholate sorption are similar to that of the adsorption: the isotherms reach a plateau where the sorption becomes constant and the raise in the temperature decreases the sorbed quantity. By the obtained results, it was proposed a cholate intercalation model forming a bilayered structure. The results indicate that the cholate removal by the calcined LDH is more efficient than that presented by the uncalcined one.

O presente trabalho teve como objetivo principal estudar os processos de intercalação e esfoliação do niobato lamelar H2K2Nb6O17 em soluções aquosas de n-hexilamina, n-propilamina e hidróxido de tetrabutilamônio (TBAOH). Procurou-se avaliar a influência do agente esfoliante no processo de separação das lamelas do niobato. Para tanto, uma quantidade fixa de H2K2Nb6O17 foi suspensa em solução do agente esfoliante, nas razões molares amina/H+-niobato iguais a 0,25, 0,50, 0,75 e 1,0, e mantida sob agitação à temperatura ambiente por 2 semanas. O sólido depositado foi separado do sobrenadante opaco (isto é, do sólido esfoliado). Para a caracterização do sólido depositado, determinou-se a composição química e registrou-se o difratograma de raios-X, a curva termogravimétrica e os espectros vibracionais no IV e Raman. A dispersão de partículas esfoliadas foi caracterizada por espectroscopia eletrônica enquanto o sólido esfoliado, por DRX, medidas de área superficial, MEV e HRTEM. Nos sólidos depositados, as alquilaminas se encontram intercaladas em um arranjo de monocamada e praticamente orientadas perpendicularmente em relação às lamelas do niobato. As suspensões contendo as razões molares amina/H+-niobato = 0,5 para a n-hexilamina e 1,0 para a n-propilamina produziram a maior quantidade de sólido esfoliado (ca. 35%). As micrografias revelam que o sólido esfoliado é formado por partículas flexíveis em um arranjo desorganizado, muito diferente da morfologia do K4Nb6O17. Os difratogramas mostram perfil de material com organização somente no eixo de empilhamento das lamelas e, ainda, que nessas partículas as aminas mantêm o arranjo de monocamadas. As partículas esfoliadas contêm 50% e 70% de n-hexilamina e n-propilamina, respectivamente, neutralizando os íons H+ do niobato. Esses dados mostram que a insaturação das lamelas em relação às aminas favorecem a estabilização dos sistemas esfoliados, uma vez que diminuem as interações de van der Waals entre as cadeias carbônicas e promovem a hidratação da superfície das lamelas. Os sólidos depositados em suspensão de TBAOH não possuem espécie orgânica intercalada e as suspensões contendo as razões TBA+/H+-niobato ? 0,5 produziram maior quantidade de sólido disperso (ca. 65%). O sólido esfoliado isolado da suspensão com razão 0,75 contém 10% de TBA+ neutralizando os íons H+ do niobato. À medida que o pH das suspensões é diminuído, o TBA+ é substituído por H3O+ e as partículas planas começam a encaracolar. Observou-se a formação de nanotubos nas razões molares TBA+/H+-niobato = 0,5 e 1,0, que tiveram o pH alterado para 1 e 7 respectivamente. A amostra isolada em pH 1 apresenta área específica de 139 m²g?¹ enquanto o K4Nb6O17 possui apenas 2 m²g?¹ . Os sistemas contendo tanto partículas tabulares quanto tubulares possuem potencial aplicação na área de (foto)catálise e de sensores. / The main aim of this work was to study the intercalation and exfoliation processes of the layered niobate H2K2Nb6O17 in aqueous solutions of n-hexylamine, n-propylamine and tetra-n-butylammonium hydroxide (TBAOH). It was evaluated the influence of the exfoliation agent in the process of separation of the niobate layers. A fixed amount of H2K2Nb6O17 was suspended in solution of the exfoliation agent, in the molar ratios amine/H+-niobate 0.25, 0.50, 0.75 and 1.0, and maintained under stirring at room temperature for 2 weeks. The deposited solid was separated from the opaque suspension (i.e., the exfoliated solid). For the characterization of the deposited solid, it was determined the chemical composition and the X-ray diffractogram, the termogravimetric curve and the infrared and Raman vibrational spectra were recorded. The dispersion of exfoliated particles was characterized by electronic spectroscopy while the exfoliated solid, for XRD, surface area measurement, SEM and HRTEM. Considering the deposited solids, the alkylamines are intercalated in a monolayer arrangement and practically oriented perpendicularly in relation to the niobate layers. The suspensions containing the molar ratios amine/H+-niobate 0.5 for the n-hexylamine and 1.0 for the n-propylamine produced the highest amount of exfoliated solid (ca. 35%). SEM images reveal that exfoliated solid is formed by flexible particles in a disorganized arrangement, very different from the K4Nb6O17 morphology. The diffractograms profile show a solid with organization only in the axis of piling up of the layers and also that in these particles the amines maintain the monolayer arrangement. The exfoliated particles contain 50% and 70% of n-hexylamine and n-propylamine, respectively, neutralizing the H+ ions of the niobate. These data show that the layers insaturation in relation to the amines seems to favor the stabilization of the exfoliated systems, once it reduces the van der Waals interactions among the carbon chains and facilitate the hydration of the layer surfaces. The deposited solids in suspension of TBAOH do not possess organic species intercalated and the suspensions containing the ratio TBA+/H+-niobate ? 0.5 produce the highest amount of dispersed solid (ca. 65%). The exfoliated solid isolated from suspensions with ratio 0.75 contains 10% of TBA+ neutralizing the H+ ions of the niobate. As the pH of the suspensions is decreased, TBA+ ion is replaced by H3O+ and the tabular particles begin to scroll. The nanotubes formation was observed to molar ratios TBA+/H+-niobate = 0.5 and 1.0, which pH values were changed to 1 and 7 respectively. The sample isolated at pH 1 presents specific area of 139 m²g?¹ while K4Nb6O17 possesses only 2 m²g?¹ . The systems containing plate and tubular particles possesses potential application in (photo)catalysis and sensors areas.

The Low-Density Parity-Check (LDPC) codes, which were invented by Gallager back in 1960s, have attracted considerable attentions recently. Compared with other error correction codes, LDPC codes are well suited for wireless, optical, and magnetic recording systems due to their near- Shannon-limit error-correcting capacity, high intrinsic parallelism and high-throughput potentials. With these remarkable characteristics, LDPC codes have been adopted in several recent communication standards such as 802.11n (Wi-Fi), 802.16e (WiMax), 802.15.3c (WPAN), DVB-S2 and CMMB. This dissertation is devoted to exploring efficient VLSI architectures for high-performance LDPC decoders and LDPC-like detectors in sparse inter-symbol interference (ISI) channels. The performance of an LDPC decoder is mainly evaluated by area efficiency, error-correcting capability, throughput and rate flexibility. With this work we investigate tradeoffs between the four performance aspects and develop several decoder architectures to improve one or several performance aspects while maintaining acceptable values for other aspects. Firstly, we present a high-throughput decoder design for the Quasi-Cyclic (QC) LDPC codes. Two new techniques are proposed for the first time, including parallel layered decoding architecture (PLDA) and critical path splitting. Parallel layered decoding architecture enables parallel processing for all layers by establishing dedicated message passing paths among them. The decoder avoids crossbar-based large interconnect network. Critical path splitting technique is based on articulate adjustment of the starting point of each layer to maximize the time intervals between adjacent layers, such that the critical path delay can be split into pipeline stages. Furthermore, min-sum and loosely coupled algorithms are employed for area efficiency. As a case study, a rate-1/2 2304-bit irregular LDPC decoder is implemented using ASIC design in 90 nm CMOS process. The decoder can achieve an input throughput of 1.1 Gbps, that is, 3 or 4 times improvement over state-of-art LDPC decoders, while maintaining a comparable chip size of 2.9 mm^2. Secondly, we present a high-throughput decoder architecture for rate-compatible (RC) LDPC codes which supports arbitrary code rates between the rate of mother code and 1. While the original PLDA is lack of rate flexibility, the problem is solved gracefully by incorporating the puncturing scheme. Simulation results show that our selected puncturing scheme only introduces the BER performance degradation of less than 0.2dB, compared with the dedicated codes for different rates specified in the IEEE 802.16e (WiMax) standard. Subsequently, PLDA is employed for high throughput decoder design. As a case study, a RC- LDPC decoder based on the rate-1/2 WiMax LDPC code is implemented in CMOS 90 nm process. The decoder can achieve an input throughput of 975 Mbps and supports any rate between 1/2 and 1. Thirdly, we develop a low-complexity VLSI architecture and implementation for LDPC decoder used in China Multimedia Mobile Broadcasting (CMMB) systems. An area-efficient layered decoding architecture based on min-sum algorithm is incorporated in the design. A novel split-memory architecture is developed to efficiently handle the weight-2 submatrices that are rarely seen in conventional LDPC decoders. In addition, the check-node processing unit is highly optimized to minimize complexity and computing latency while facilitating a reconfigurable decoding core. Finally, we propose an LDPC-decoder-like channel detector for sparse ISI channels using belief propagation (BP). The BP-based detection computationally depends on the number of nonzero interferers only and are thus more suited for sparse ISI channels which are characterized by long delay but a small fraction of nonzero interferers. Layered decoding algorithm, which is popular in LDPC decoding, is also adopted in this paper. Simulation results show that the layered decoding doubles the convergence speed of the iterative belief propagation process. Exploring the special structure of the connections between the check nodes and the variable nodes on the factor graph, we propose an effective detector architecture for generic sparse ISI channels to facilitate the practical application of the proposed detection algorithm. The proposed architecture is also reconfigurable in order to switch flexible connections on the factor graph in the time-varying ISI channels.

O presente trabalho teve como objetivo principal estudar os processos de intercalação e esfoliação do niobato lamelar H2K2Nb6O17 em soluções aquosas de n-hexilamina, n-propilamina e hidróxido de tetrabutilamônio (TBAOH). Procurou-se avaliar a influência do agente esfoliante no processo de separação das lamelas do niobato. Para tanto, uma quantidade fixa de H2K2Nb6O17 foi suspensa em solução do agente esfoliante, nas razões molares amina/H+-niobato iguais a 0,25, 0,50, 0,75 e 1,0, e mantida sob agitação à temperatura ambiente por 2 semanas. O sólido depositado foi separado do sobrenadante opaco (isto é, do sólido esfoliado). Para a caracterização do sólido depositado, determinou-se a composição química e registrou-se o difratograma de raios-X, a curva termogravimétrica e os espectros vibracionais no IV e Raman. A dispersão de partículas esfoliadas foi caracterizada por espectroscopia eletrônica enquanto o sólido esfoliado, por DRX, medidas de área superficial, MEV e HRTEM. Nos sólidos depositados, as alquilaminas se encontram intercaladas em um arranjo de monocamada e praticamente orientadas perpendicularmente em relação às lamelas do niobato. As suspensões contendo as razões molares amina/H+-niobato = 0,5 para a n-hexilamina e 1,0 para a n-propilamina produziram a maior quantidade de sólido esfoliado (ca. 35%). As micrografias revelam que o sólido esfoliado é formado por partículas flexíveis em um arranjo desorganizado, muito diferente da morfologia do K4Nb6O17. Os difratogramas mostram perfil de material com organização somente no eixo de empilhamento das lamelas e, ainda, que nessas partículas as aminas mantêm o arranjo de monocamadas. As partículas esfoliadas contêm 50% e 70% de n-hexilamina e n-propilamina, respectivamente, neutralizando os íons H+ do niobato. Esses dados mostram que a insaturação das lamelas em relação às aminas favorecem a estabilização dos sistemas esfoliados, uma vez que diminuem as interações de van der Waals entre as cadeias carbônicas e promovem a hidratação da superfície das lamelas. Os sólidos depositados em suspensão de TBAOH não possuem espécie orgânica intercalada e as suspensões contendo as razões TBA+/H+-niobato ? 0,5 produziram maior quantidade de sólido disperso (ca. 65%). O sólido esfoliado isolado da suspensão com razão 0,75 contém 10% de TBA+ neutralizando os íons H+ do niobato. À medida que o pH das suspensões é diminuído, o TBA+ é substituído por H3O+ e as partículas planas começam a encaracolar. Observou-se a formação de nanotubos nas razões molares TBA+/H+-niobato = 0,5 e 1,0, que tiveram o pH alterado para 1 e 7 respectivamente. A amostra isolada em pH 1 apresenta área específica de 139 m²g?¹ enquanto o K4Nb6O17 possui apenas 2 m²g?¹ . Os sistemas contendo tanto partículas tabulares quanto tubulares possuem potencial aplicação na área de (foto)catálise e de sensores. / The main aim of this work was to study the intercalation and exfoliation processes of the layered niobate H2K2Nb6O17 in aqueous solutions of n-hexylamine, n-propylamine and tetra-n-butylammonium hydroxide (TBAOH). It was evaluated the influence of the exfoliation agent in the process of separation of the niobate layers. A fixed amount of H2K2Nb6O17 was suspended in solution of the exfoliation agent, in the molar ratios amine/H+-niobate 0.25, 0.50, 0.75 and 1.0, and maintained under stirring at room temperature for 2 weeks. The deposited solid was separated from the opaque suspension (i.e., the exfoliated solid). For the characterization of the deposited solid, it was determined the chemical composition and the X-ray diffractogram, the termogravimetric curve and the infrared and Raman vibrational spectra were recorded. The dispersion of exfoliated particles was characterized by electronic spectroscopy while the exfoliated solid, for XRD, surface area measurement, SEM and HRTEM. Considering the deposited solids, the alkylamines are intercalated in a monolayer arrangement and practically oriented perpendicularly in relation to the niobate layers. The suspensions containing the molar ratios amine/H+-niobate 0.5 for the n-hexylamine and 1.0 for the n-propylamine produced the highest amount of exfoliated solid (ca. 35%). SEM images reveal that exfoliated solid is formed by flexible particles in a disorganized arrangement, very different from the K4Nb6O17 morphology. The diffractograms profile show a solid with organization only in the axis of piling up of the layers and also that in these particles the amines maintain the monolayer arrangement. The exfoliated particles contain 50% and 70% of n-hexylamine and n-propylamine, respectively, neutralizing the H+ ions of the niobate. These data show that the layers insaturation in relation to the amines seems to favor the stabilization of the exfoliated systems, once it reduces the van der Waals interactions among the carbon chains and facilitate the hydration of the layer surfaces. The deposited solids in suspension of TBAOH do not possess organic species intercalated and the suspensions containing the ratio TBA+/H+-niobate ? 0.5 produce the highest amount of dispersed solid (ca. 65%). The exfoliated solid isolated from suspensions with ratio 0.75 contains 10% of TBA+ neutralizing the H+ ions of the niobate. As the pH of the suspensions is decreased, TBA+ ion is replaced by H3O+ and the tabular particles begin to scroll. The nanotubes formation was observed to molar ratios TBA+/H+-niobate = 0.5 and 1.0, which pH values were changed to 1 and 7 respectively. The sample isolated at pH 1 presents specific area of 139 m²g?¹ while K4Nb6O17 possesses only 2 m²g?¹ . The systems containing plate and tubular particles possesses potential application in (photo)catalysis and sensors areas.

Earthquakes have been historically perceived as one of the most damaging natural hazards. Seismic soil liquefaction is often one of the major sources of damage and disruptions, and has been observed to severely affect key lifelines. Settlement and tilting of shallow foundations resting on saturated sandy/silty soils has been repeatedly observed throughout the world as a consequence of liquefaction or softening of the foundation soil. Such settlements and tilts can render structures unusable, and homes uninhabitable, causing significant economic losses. Despite the undoubted relevance of this phenomenon, field data on the liquefaction induced settlement of shallow foundations are scarce. New data from 24 buildings that suffered settlement and tilting as a consequences of soil liquefaction during the February 27th 2010 Maule earthquake in Chile, are presented in this work to supplement the existing field cases database. Due to the complexity of this phenomenon, field data are not suffcient to fully understand the mechanisms controlling the settlement of structures resting on liquefied or softened ground.In this framework, centrifuge modelling provides a valuable tool for research by reproducing field conditions in a controlled environment. A series of 10 dynamic centrifuge tests were performed as part of this work. Thanks to the University of Dundee newly installed centrifuge-mounted servohydraulic earthquake simulator, scaled version of field earthquake motions were reproduced in the models tested, enhancing the reliability of experimental results. Particular attention was given to the effect of key parameters on the observed foundation settlement. These parameters are the bearing pressure of the foundation, the thickness of the liquefied soil layer and the soil's relative density. The effect of the soil layering pattern was also investigated, with particular attention to the effect of a low permeability soil crust overlying the liquefied soil. Results suggest that the excess pore pressure generation in the foundation soil is significantly influenced by the stress distribution due to the presence of the foundation itself. In particular, lower excess pore pressure where measured in soil subjected to high static shear stresses (i.e. below the edge of a footing). The soil stratification pattern, and the relative thicknesses of the liquefied and un-liquefied portions of the soil profile, were also found to play a crucial role in determining the seismic demand at foundation level and the type of failure mechanism leading to foundation settlement. Observed differences between centrifuge (i.e. field) and element testing soil response are also discussed. Experimental results are compared to field observations, with the aim of improving the current understanding of the behaviour of structures built on shallow foundations in the eventuality of seismic induced liquefaction of their foundation soil.