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This thesis describes novel microel ectromechanical system (MEMS) based electrochemical gas sensors and methods of fabrication. This thesis presents the research in two parts. In the first part, a method to handle a thin silicon wafer using an electrochemically active adhesive is described. Handling of a thin silicon wafer is an important issue in 3D-IC manufacturing where through silicon vias (TSVs) is an enabling technology. Thin silicon wafers are flexible and fragile, therefore difficult to handle. In addressing the need for a reliable solution, a method based on an electrochemically active adhesive was developed. In this method, an electrochemically active adhesive was diluted and spin coated on a 100 mm diameter silicon wafer (carrier wafer) on which another silicon wafer (device wafer) was bonded. Device wafer was subjected to post processing fabrication technique such as wafer thinning. Successful debonding of the device wafer was achieved by applying a voltage between the two wafers. In another part of the research, a fabrication process for developing a functional nanoporous material using atomic layer deposition is presented. In order to realize a nanoporous electrode, a nanoporous anodized aluminum oxide (AAO) substrate was used, which was functionalized with very thin layers (~ 10 nm) of platinum (Pt) and aluminum oxide (Al2O3) using atomic layer deposition. Nanoporous material when used as an electrode delivers high sensitivity due to the inherent high surface area and is potentially applicable in fuel cells and in electrochemical sensing. The second part of the thesis addresses the need for a high performance gas sensor that is applicable for asthma monitoring. Asthma is a disease related to the inflammation in the airways of the lungs and is characterized by the presence of nitric oxide gas in the exhaled breath. The gas concentration of above approximately 50 parts-per-billion indicates a likely presence of asthma. A MEMS based electrochemical gas sensor was successfully designed and developed to meet the stringent requirements needed for asthma detection. Furthermore, to enable a hand held asthma measuring instrument, a miniaturized sensor with integrated electrodes and liquid electrolyte was developed. The electrodes were assembled at a wafer-level to demonstrate the feasibility towards a high volume fabrication of the gas sensors. In addition, the designed amperometric gas sensor was successfully tested for hydrogen sulphide concentration, which is a bio marker for bad breath. / <p>QC 20150907</p>

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This thesis is missing page 89, no other copy of the thesis has this page. -Digitization Centre / The vanadium mediated electrolysis of hydrogen sulphide has been demonstrated in a bench top pilot plant. The first step in the process is the absorption of hydrogen sulphide from a sour gas stream into an carbonate buffered liquor, pH 9. In the presence of citrate ion, the vanadium (V) in the liquor is reduced to vanadium (IV) by (hydro) sulphide ion, which is oxidized to yellow elemental sulphur. The vanadium (IV) rich solution is then pumped to an electrolysis cell where the vanadium (IV) is reoxidized to vanadium (V) and protons are reduced to elemental hydrogen. The reoxidized liquor is then returned to the absorber. The oxidation of vanadium (IV) to vanadium (V) in the liquor was found to be electrochemically irreversible. The current efficiency for vanadium (IV) oxidation exceeded 90 percent. The voltametric half-wave potential at platinum, was 0.34 v (vs Ag/AgCl, sat. KC1). With the slippage of sulphide or polysulphide ion into the electrolysis cells, the electrodes became passivated with electrodeposited sulphur. This resulted in an increased anode potential demand which may promote the electrosynthesis of oxygen and sulphate ion. The oxidation of vanadium (IV) at the anode releases 4 protons and acidifies the solution adjacent the electrode surface. This may induce carbon dioxide evolution and inhibit the discharge of vanadium (IV). The inhibition appears as a suppressed current and an anodic shift in the voltametric half-wave potential. This inhibition can be minimized at high pH levels in the liquor, buffer capacity., and citrate concentration. The irreversibility of the vanadium (IV/V) couple allows electrolysis cells to be constructed without a cell membrane. This is a significant advantage which will offset the cost of large electrolysis cells. Large cells will enable high energy efficiencies to hydrogen production to be realized. Energy efficiencies greater than 0.28 m3 /kwhr may be indicated. This study features a critical review of sulphide electro-oxidation, a factorial designed voltametric experiment, and a newly identified catalytic response in the polarographic analysis of sulphide ion. / Thesis / Master of Science (MS)

O H2S é um gás que causa preocupação devido aos efeitos que pode provocar a saúde, a corrosão sobre alguns materiais e a redução do poder calorífero no aproveitamento de biogás, mesmo quando presente em baixas concentrações. O uso de biogás como fonte energética tem crescido nos últimos anos, impulsionando a remoção do sulfeto de hidrogênio, uma vez que a presença de tal gás reduz a capacidade calorífica do biogás e causa danos às instalações. Diante disso, várias técnicas são utilizadas na remoção de H2S, sendo uma delas, a adsorção. Os processos de separação por adsorção são muito utilizados para a remoção de poluentes gasosos de misturas gasosas. Neste trabalho foram realizados experimentos da adsorção do H2S sobre lodo seco, em coluna de leito fixo, para obtenção da capacidade de adsorção dinâmica do lodo e como esta seria afetada pelas variáveis de processo: concentração de alimentação e vazão de alimentação. Para tanto, foi concebida e instalada uma unidade de bancada de adsorção em leito fixo, com facilidades experimentais necessárias para testes dinâmicos, com o emprego da técnica de interpretação de curvas de efluência, um método útil para a avaliação do desempenho de um adsorvente em colunas de leito fixo. Testes preliminares mostraram que a unidade de bancada apresentou versatilidade, podendo ser operada com vazões de até 5 L/ min e concentração de H2S na mistura gasosa de até 500 ppm. Os resultados obtidos mostraram que a capacidade de adsorção do lodo seco foi muito baixa, com valores variando de 3,30 x 10-5 a 2,54 x 10-3 mg de H2S/g de lodo seco e existência de caminhos preferenciais no leito. / It is widely known that H2S is a gas which causes preoccupation due to the potential risks to health, corrosion in materials and reduction of the calorific value, even when present in low concentrations. The application of biogas as an energetic source has increased in last years, promoting the hydrogen sulphide removal, so that H2S presence can reduce the biogas energetic capacity and cause damage in the installations. Therefore, many techniques are used to H2S removal, one them is adsorption. The adsorption separation processes are widely used in the removal of pollutants gaseous from gas mixtures. In this work, experiments were performed on the adsorption of H2S the dry sludge in a fixed bed column, aiming to obtain the dynamic adsorption capacity and how this would be affected by the process variables: feed concentration and feed flow rate . For that, we designed and installed a bench unit to fixed bed adsorption with necessary experimental facilities for dynamic tests with the use of the technique of interpretation breakthrough curves, an useful method for evaluating the performance of an adsorbent columns fixed bed . Preliminary tests showed that the bench unit has presented versatility and efficiency and it can be operated at flow rates up to 5 L/min and H2S concentration in the gas mixture up to 500 ppm. The results showed that the adsorption capacity of the dried sludge was very low , with values varied from 3.30 × 10-5 to 2.54 × 10-3 mg H2S/g of dry sludge and the existence of preferential paths in the bed .

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Research goal and objective. To investigate the possibilities of the use of mineral raw materials of local origin for the purification of biogas produced from sewage sludge, by-products and waste and to assess the environmental benefits of the use of biogas in the transport sector. The properties of by-products and waste generated in Lithuania as well as the possibilities of their use in the production of biogas from sewage sludge have been assessed. The potential and properties of local mineral raw materials suitable for the purification of biogas have been assessed. The process of the removal of hydrogen sulphide and carbon dioxide from biogas using natural sorbents has been investigated. It was found that large dolomite resources available in Lithuania allow using this natural raw material for biogas purification because sorbent solutions and suspensions of dolomite powder effectively remove hydrogen sulphide and absorb carbon dioxide from biogas sufficiently quickly. A principal biogas purification technology was developed on the basis of the performed assessment of the process kinetic calculations. Engine perfomance tests were carried out using a mixture of biogas and mineral diesel fuel and exhaust gas emissions were assessed. / Darbo tikslas – ištirti gamtinių sorbentų (vietinės kilmės mineralinių žaliavų) panaudojimo biodujų, pagamintų iš nuotekų dumblo, šalutinių produktų ir atliekų, valymui galimybes bei įvertinti biodujų panaudojimo transporto sektoriuje aplinkosauginę naudą. Įvertintos Lietuvoje susidarančių šalutinių produktų ir atliekų savybės bei panaudojimo biodujų gamyboje iš nuotekų dumblo galimybės. Įvertintos vietinės kilmės mineralinių žaliavų, tinkančių biodujų valymui, potencialas ir savybės. Ištirtas biodujų valymo nuo sieros vandenilio ir anglies dioksido procesas, naudojant gamtinius sorbentus. Nustatyta, kad Lietuvoje eantys dideli dolomito ištekliai leidžia panaudoti šią natūralią žaliavą biodujų valymui, nes absorbciniai tirpalai iš dolomito miltelių efektyviai pašalina sieros vandenilį ir pakankamai gerai sugeria anglies dioksidą. Remiantis atliktu proceso kinetinių skaičiavimų įvertinimu buvo parengta principinė biodujų valymo technologija. Atlikti stendiniai variklio bandymai naudojant biodujų ir mineralinio dyzelino mišinį bei įvertintos deginių emisijos.

Research goal and objective. To investigate the possibilities of the use of mineral raw materials of local origin for the purification of biogas produced from sewage sludge, by-products and waste and to assess the environmental benefits of the use of biogas in the transport sector. The properties of by-products and waste generated in Lithuania as well as the possibilities of their use in the production of biogas from sewage sludge have been assessed. The potential and properties of local mineral raw materials suitable for the purification of biogas have been assessed. The process of the removal of hydrogen sulphide and carbon dioxide from biogas using natural sorbents has been investigated. It was found that large dolomite resources available in Lithuania allow using this natural raw material for biogas purification because sorbent solutions and suspensions of dolomite powder effectively remove hydrogen sulphide and absorb carbon dioxide from biogas sufficiently quickly. A principal biogas purification technology was developed on the basis of the performed assessment of the process kinetic calculations. Engine perfomance tests were carried out using a mixture of biogas and mineral diesel fuel and exhaust gas emissions were assessed. / Darbo tikslas – ištirti gamtinių sorbentų (vietinės kilmės mineralinių žaliavų) panaudojimo biodujų, pagamintų iš nuotekų dumblo, šalutinių produktų ir atliekų, valymui galimybes bei įvertinti biodujų panaudojimo transporto sektoriuje aplinkosauginę naudą. Įvertintos Lietuvoje susidarančių šalutinių produktų ir atliekų savybės bei panaudojimo biodujų gamyboje iš nuotekų dumblo galimybės. Įvertintos vietinės kilmės mineralinių žaliavų, tinkančių biodujų valymui, potencialas ir savybės. Ištirtas biodujų valymo nuo sieros vandenilio ir anglies dioksido procesas, naudojant gamtinius sorbentus. Nustatyta, kad Lietuvoje eantys dideli dolomito ištekliai leidžia panaudoti šią natūralią žaliavą biodujų valymui, nes absorbciniai tirpalai iš dolomito miltelių efektyviai pašalina sieros vandenilį ir pakankamai gerai sugeria anglies dioksidą. Remiantis atliktu proceso kinetinių skaičiavimų įvertinimu buvo parengta principinė biodujų valymo technologija. Atlikti stendiniai variklio bandymai naudojant biodujų ir mineralinio dyzelino mišinį bei įvertintos deginių emisijos.