Made available in DSpace on 2017-07-21T20:42:35Z (GMT). No. of bitstreams: 1 JulianeCiorcero.pdf: 6092625 bytes, checksum: d6ae5b000ef3bf54c409ce74be787173 (MD5) Previous issue date: 2011-12-19 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / This work studied systematically the substitution of Nb2O5 by Sb2O3 in composition of a ternary varistor system and study of calcination of binary and multi-component systems and their relationship microstructure-electric property. In part I of the work, study of substitution of Nb2O5 by Sb2O3, the compositions were prepared by conventional ceramic processing and dried by "spray-dryer" Pellets were produced at 25 MPa and sintering was produced at 1350ºC/ 2h.Increasing the concentration of Sb2O3, the nonlinear behavior of ceramics was reduced, accompanied by the reduction of the breakdown electric field and increased leakage current. With increasing concentration of 0.05% Sb2O3 to 0.5% (mol%), the samples were more porous, suggesting that higher concentrations of Sb2O3 decreases the rate of sintering. This decrease was linked to the increased concentration of tin vacancies that leads to nondensifying processes. In part II, was studied the influence of calcination (700oC, 1000oC and 1200oC) of binary and multi-component systems. The compositions were prepared by the conventional method, with the addition of the calcination process. The samples were comformed at 75 MPa and sintered at 1300oC for systems calcined at 1200oC and 1300oC, and at 1350oC for systems calcined at 700oC and 1000oC. Some studied systems have showed cassiterite phase associated to the SnO phase. With the addition of dopants, there was an increase in density of the systems, and the increase in temperature of sintering also led to a slight increase in density. The addition of chromium to systems calcined at 700oC and 1000oC led to a decrease in the breakdown electric field, with the exception of the systems 99.5% +0.5% Sb2O3 + 0.5% Co3O4 e 99.5% +0.5% Sb2O3 + 0.5% Co3O4 (excess) + 0.05% Cr2O3 (excess), where there was a decrease of breakdown electric field with the addition of chromium, and this can be explained because of their densities. All samples calcined at 1200oC regardless of the composition, showed very similar microstructure, high porosity and small grain size. The sample that presented the best varistor behavior with the lower leakage current was the FCC25% (75% of varistor formulation, 99,4%SnO2. 0,5%Co3O4. 0,05%Nb2O5. 0,05%Cr2O3 and 25% of conductive formulation, 99,0%SnO2. 0,5%Co3O4. 0,5%Sb2O3). / Neste trabalho estudou-se sistematicamente a substituição do Nb2O5 por Sb2O3 na composição de um sistema varistor ternário e estudo da calcinação de sistemas binários e multicomponentes e sua relação microestruturapropriedade elétricas. Na Parte I do trabalho, estudo da substituição do Nb2O5 por Sb2O3, as composições foram preparadas via processamento cerâmico convencional e secadas via “spray-dryer”. A conformação foi realizada a 25 MPa e a sinterização foi realizada a 1350C por 2 horas. Com o aumento da concentração de Sb2O3 o comportamento não linear da cerâmica foi reduzido, acompanhado da redução do campo elétrico de ruptura e aumento da corrente de fuga. Com o aumenta da concentração de Sb2O3 de 0,05% para 0,5% em mol, as amostras apresentaram-se mais porosas, sugerindo que concentrações mais elevadas de Sb2O3 diminuem a taxa de sinterização. Esta diminuição foi associada ao aumento da concentração de vacâncias de estanho que conduz a processos não densificantes. Na parte II, estudou-se a influência da calcinação (700oC, 1000oC e 1200oC) de sistemas binários e multicomponentes. As composições foram preparadas pelo método convencional, com a adição do processo de calcinação. As amostras foram conformadas a 75 MPa e sinterizados a 1300oC para os sistemas calcinados a 1200OC e 1300OC e 1350OC por 2 horas para os sistemas calcinados a 700OC e 1000OC. Alguns sistemas estudados apresentaram a fase cassiterita associada a fase SnO. Com a adição de dopantes ocorreu um aumento na densidade dos sistemas e o aumento da temperatura de sinterização também levou a um leve aumento na densidade. A adição de cromo aos sistemas calcinados a 700OC e 1000OC levou a uma diminuição do campo elétrico de ruptura, com exceção dos sistemas, 9,5%+0,5%Sb2O3 + 0,5% Co3O4 e 99,5%+0,5%Sb2O3 + 0,5% Co3O4 (excesso) + 0,05% Cr2O3 (excesso), onde ocorreu a diminuição do campo elétrico de ruptura com a adição de cromo, podendo isto ser explicado através de suas densidades. Todas as amostras calcinadas a 1200oC, independentemente da composição, apresentaram microestrutura muito semelhantes, apresentaram alta porosidade e pequeno tamanho de grão. A amostra que apresentou o melhor comportamento varistor, com menor corrente de fuga foi a FCC25% (75% da formulação varistora, 99,4%SnO2.0,5%Co3O4. 0,05%Nb2O5.0,05%Cr2O3 e 25% da formulação condutora, 99,0%SnO2. 0,5%Co3O4. 0,5%Sb2O3).

<p>Electrochemical deposition finds applications in the electronics- and protective coating industries. The technique is a versatile tool for the synthesis of alloys and thin films. Knowledge of the fundamental aspects of the electrode processes enables the design of nanostructured materials. In this thesis, electrodeposition processes in solutions containing metal ion complexes were studied and new methods for the preparation of metal/metal-oxide coatings were developed and evaluated. </p><p>Metal/metal oxide coatings were electrodeposited from aqueous solutions containing metal complexes of hydroxycarboxylic acids under reducing conditions. The mass changes of the working electrode were monitored <i>in-situ</i> with the electrochemical quartz crystal microbalance (EQCM) technique and ellipsometry was used to detect the formation of Cu₂O. The coatings were further characterized with XRD, XPS, SEM, TEM, and Raman spectroscopy. Electrochemical methods, including reduction of Sb/Sb₂O₃ in an organic electrolyte, were also used to study the properties of the deposited materials. </p><p>Nanostructured coatings of Cu/Cu₂O were obtained during spontaneous potential or current oscillations in alkaline Cu(II)-citrate solutions. The oscillations were due to local pH variations induced by a subsequent chemical step and comproportionation between Cu and Cu²⁺. Well-defined layers of Cu and Cu₂O could be prepared by a galvanostatic pulsing technique, allowing independently controlled thickness of several hundred nanometers. Coatings, containing Sb and co-deposited, nanograins of Sb₂O_3, with a thickness of up to 200 nm were prepared from poorly buffered Sb(III)-tartrate solutions. Galvanostatic cycling showed that the latter material could be reversibly charged and discharged in a Li-ion battery for more than 50 cycles with a capacity of 660 mAh/g. </p><p>The results show that precipitations of metal oxides can occur due to local pH increases during electrochemical deposition from metal complexes with ligands containing hydroxyl groups. The ability to deposit metal oxides using cathodic deposition relies on a sufficiently slow reduction of the oxide. </p>

Electrochemical deposition finds applications in the electronics- and protective coating industries. The technique is a versatile tool for the synthesis of alloys and thin films. Knowledge of the fundamental aspects of the electrode processes enables the design of nanostructured materials. In this thesis, electrodeposition processes in solutions containing metal ion complexes were studied and new methods for the preparation of metal/metal-oxide coatings were developed and evaluated. Metal/metal oxide coatings were electrodeposited from aqueous solutions containing metal complexes of hydroxycarboxylic acids under reducing conditions. The mass changes of the working electrode were monitored in-situ with the electrochemical quartz crystal microbalance (EQCM) technique and ellipsometry was used to detect the formation of Cu2O. The coatings were further characterized with XRD, XPS, SEM, TEM, and Raman spectroscopy. Electrochemical methods, including reduction of Sb/Sb2O3 in an organic electrolyte, were also used to study the properties of the deposited materials. Nanostructured coatings of Cu/Cu2O were obtained during spontaneous potential or current oscillations in alkaline Cu(II)-citrate solutions. The oscillations were due to local pH variations induced by a subsequent chemical step and comproportionation between Cu and Cu2+. Well-defined layers of Cu and Cu2O could be prepared by a galvanostatic pulsing technique, allowing independently controlled thickness of several hundred nanometers. Coatings, containing Sb and co-deposited, nanograins of Sb2O3, with a thickness of up to 200 nm were prepared from poorly buffered Sb(III)-tartrate solutions. Galvanostatic cycling showed that the latter material could be reversibly charged and discharged in a Li-ion battery for more than 50 cycles with a capacity of 660 mAh/g. The results show that precipitations of metal oxides can occur due to local pH increases during electrochemical deposition from metal complexes with ligands containing hydroxyl groups. The ability to deposit metal oxides using cathodic deposition relies on a sufficiently slow reduction of the oxide.

In this thesis, the author proposed and developed nanostructured materials based Surface Acoustic Wave (SAW) and conductometric transducers for gas sensing applications. The device fabrication, nanostructured materials synthesis and characterization, as well as their gas sensing performance have been undertaken. The investigated structures are based on two structures: lithium niobate (LiNbO3) and lithium tantalate (LiTaO3). These two substrates were chosen for their high electromechanical coupling coefficient. The conductometric structure is based on langasite (LGS) substrate. LGS was selected because it does not exhibit any phase transition up to its melting point (1470°C). Four types of nanostructured materials were investigated as gas sensing layers, they are: polyaniline, polyvinylpyrrolidone (PVP), graphene and antimony oxide (Sb2O3). The developed nanostructured materials based sensors have high surface to volume ratio, resulting in high sensitivity towards di¤erent gas species. Several synthesis methods were conducted to deposit nanostructured materials on the whole area of SAW based and conductometric transducers. Electropolymerization method was used to synthesize and deposit polyaniline nanofibers on 36° YX LiTaO3 and 64° YX LiNbO3 SAW substrates. By varying several parameters during electropolymerization, the effect on gas sensing properties were investigated. The author also extended her research to successfully develop polyaniline/inorganic nanocomposites based SAW structures for room temperature gas sensing applications. Via electrospinning method, PVP fibres and its composites were successfully deposited on 36° YX LiTaO3 SAW transducers. Again in this method, the author varied several parameters of electrospinning such as distance and concentration, and investigated the effect on gas sensing performance. Graphene-like nano-sheets were synthesized on 36° YX LiTaO3 SAW devices. This material was synthesized by spin-coating graphite oxide (GO) on the substrate and then exposin g the GO to hydrazine to reduce it to graphene. X-ray photoelectron spectroscopy (XPS) and Raman characterizations showed that the reduced GO was not an ideal graphene. This information was required to understand the properties of the deposited graphene and link its properties to the gas sensing properties. Thermal evaporation method was used to grow Sb2O3 nanostructures on LGS conductometric transducers. Using this method, different nanoscale structures such as nanorods and lobe-like shapes were found on the gold interdigitated transducers (IDTs) and LGS substrate. The gas sensing performance of the deposited nanostructured Sb2O3 based LGS conductometric sensors was investigated at elevated temperatures. The gas sensing performance of the investigated nanostructured materials/SAW and conductometric structures provide a way for further investigation to future commerciallization of these types of sensors.

Silver and palladium can be found in the so called palladium-ceramics which comes from catalyst production. These valuable metals needs to be recovered from these wastes in order to further increase both the environmental and economic sustainability of our society. This material has also been suspected of causing some problems at Boliden’s smelter Rönnskär during the silver smelting. Unfortunately due to the nature of massive economics at work in precious metal production there has not been much published work around this subject. Therefore this works seeks to increase the understanding of how this waste affects the A-slag in the precious metal production at Rönnskär.   This work takes a look at how certain fluxes and temperatures affects the slag and metal phases, as well as how increasing the addition of the palladium-ceramic affects the melt. It does so by making screening tests with a basic setup of slag from the process, silver granules and additions of coke and sodium carbonate at different temperatures.   The results show that using a reducing environment by adding coke does increase the recovery of the precious metals. Increasing the temperature of the melt also shows an improvement in the recovery of the precious metals.  Furthermore the basis to an alternative way of using this material, consisting of smelting it together with silver and fluxing materials has been suggested in this work in order to eliminate the possible problems it causes in the current process. / Silver och palladium kan finnas i materialet som kallas katalysatormassa som kommer från framställningen av katalysatorer. Dessa värdefulla metaller måste återvinnas från detta avfall för att öka hållbarheten i vårt samhälle både miljömässigt och ekonomiskt. Materialet har också varit en möjlig orsak till problem vid silversmältningen på Bolidens smältverk, Rönnskär. Tyvärr på grund av den enorma ekonomin kring ädelmetaller och deras produktion har det inte publicerats många artiklar om detta ämne. Därför försöker detta arbete att öka förståelsen av hur detta avfall påverkar A-slaggen hos ädelmetallframställningen på Rönnskär.   Detta arbete undersöker på hur olika flussmedel och temperaturer påverkar slaggen och metallfasen, samt hur en ökad mängd katalysatormassa påverkar smältan. Det görs genom att göra flera testsmältor med en bas med slagg från processen, silvergranuler samt tillsatser av koks eller natriumkarbonat vid olika temperaturer.   Resultaten visar att användandet av en reducerande miljö genom tillsättningen av koks ökar återvinningen av ädelmetallerna. En ökad temperatur på smältan har också visat på en ökad återvinning. Utöver detta så har grunden till ett alternativt sätt att använda sig av materialet tagits fram. Detta alternativ består av att smälta materialet tillsammans med silver och flussmedel och har tagits fram för att undvika möjliga problem i befintlig process.

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