Electroluminescence of silicon- and some metal oxides

In the present work electroluminescence in Si-SiO2 structures has been investigated. Electroluminescence has been recorded in the range of 250-900 nm in a system of electrolyte-insulator-semiconductor at the room temperature. The heating process of electrons in SiO2 was studied and possibility of separation it into two phases has been shown. The nature of luminescence centers and the model of its formation were proposed. This paper also includes consideration of oxide layer formation. Charge transfer mechanisms have been attended as well. The nature of electroluminescence is understood in detail. As a matter of fact, electron traps in silicon are the centers of luminescence. Electroluminescence occurs when electrons move from one trap to another. Thus the radiation of light quantum occurs. These traps appear as a result of the oxide growth. At the same time the bonds deformation of silicon atoms with SiOH groups is not excludes. As a result, dangling bonds are appeared, which are the trapping centers or the centers of luminescence.

Recovery and refining of manganese as by-product from hydrometallurgical processes

The consumption of manganese is increasing, but huge amounts of manganese still end up in waste in hydrometallurgical processes. The recovery of manganese from multi-metal solutions at low concentrations may not be economical. In addition, poor iron control typically prevents the production of high purity manganese. Separation of iron from manganese can be done with chemical precipitation or solvent extraction methods. Combined carbonate precipitation with air oxidation is a feasible method to separate iron and manganese due to the fast kinetics, good controllability and economical reagents. In addition the leaching of manganese carbonate is easier and less acid consuming than that of hydroxide or sulfide precipitates. Selective iron removal with great efficiency from MnSO4 solution is achieved by combined oxygen or air oxidation and CaCO3 precipitation at pH > 5.8 and at a redox potential of > 200 mV. In order to avoid gypsum formation, soda ash should be used instead of limestone. In such case, however, extra attention needs to be paid on the reagents mole ratios in order to avoid manganese coprecipitation. After iron removal, pure MnSO4 solution was obtained by solvent extraction using organophosphorus reagents, di-(2-ethylhexyl)phosphoric acid (D2EHPA) and bis(2,4,4- trimethylpentyl)phosphinic acid (CYANEX 272). The Mn/Ca and Mn/Mg selectivities can be increased by decreasing the temperature from the commonly used temperatures (40 –60oC) to 5oC. The extraction order of D2EHPA (Ca before Mn) at low temperature remains unchanged but the lowering of temperature causes an increase in viscosity and slower phase separation. Of these regents, CYANEX 272 is selective for Mn over Ca and, therefore, it would be the better choice if there is Ca present in solution. A three-stage Mn extraction followed by a two-stage scrubbing and two-stage sulfuric acid stripping is an effective method of producing a very pure MnSO4 intermediate solution for further processing. From the intermediate MnSO4 some special Mn- products for ion exchange applications were synthesized and studied. Three types of octahedrally coordinated manganese oxide materials as an alternative final product for manganese were chosen for synthesis: layer structured Nabirnessite, tunnel structured Mg-todorokite and K-kryptomelane. As an alternative source of pure MnSO4 intermediate, kryptomelane was synthesized by using a synthetic hydrometallurgical tailings. The results show that the studied OMS materials adsorb selectively Cu, Ni, Cd and K in the presence of Ca and Mg. It was also found that the exchange rates were reasonably high due to the small particle dimensions. Materials are stable in the studied conditions and their maximum Cu uptake capacity was 1.3 mmol/g. Competitive uptake of metals and acid was studied using equilibrium, batch kinetic and fixed-bed measurements. The experimental data was correlated with a dynamic model, which also accounts for the dissolution of the framework manganese. Manganese oxide micro-crystals were also bound onto silica to prepare a composite material having a particle size large enough to be used in column separation experiments. The MnOx/SiO2 ratio was found to affect significantly the properties of the composite. The higher the ratio, the lower is the specific surface area, the pore volume and the pore size. On the other hand, higher amount of silica binder gives composites better mechanical properties. Birnesite and todorokite can be aggregated successfully with colloidal silica at pH 4 and with MnO2/SiO2 weight ratio of 0.7. The best gelation and drying temperature was 110oC and sufficiently strong composites were obtained by additional heat-treatment at 250oC for 2 h. The results show that silica–supported MnO2 materials can be utilized to separate copper from nickel and cadmium. The behavior of the composites can be explained reasonably well with the presented model and the parameters estimated from the data of the unsupported oxides. The metal uptake capacities of the prepared materials were quite small. For example, the final copper loading was 0.14 mmol/gMnO2. According to the results the special MnO2 materials are potential for a specific environmental application to uptake harmful metal ions.

Features of a Ziegler-Natta catalyst prepared with the Sirius emulsion-based catalyst production technology

Traditionellt har man ansett att Ziegler-Natta katalysatorer för framställning av polypropen bör ha stor inre yta och hög porositet för att ge hög aktivitet och bra polymerpartikelmorfologi. Den av Borealis utvecklade Sirius emulsionsbaserade katalysatortillverkningsteknologin ger katalysatorer utan mätbar inre yta och porositet. Katalysatorn ger, trots sin kompakthet, polymerpartiklar med utmärkt morfologi och har hög aktivitet. Sirius katalysatorns prestanda, beträffande polymerisationskinetik och polymerstruktur, undersöktes i detta doktorsarbete. En jämn och kontrollerad tidig fragmentering av katalysatorn är av största vikt för att uppnå bra partikelmorfologi i en kommersiell process. Det visades att fragmenteringen av Sirius katalysatorn under de första sekunderna och minuterna av reaktionen framskred på ett homogent sätt. Oligomerhalten i den slutliga produkten är viktig i många applikationer, tex. i applikationer där polymeren kommer i kontakt med mat. Polymerer producerade med Sirius katalysatorn hade en låg oligomerhalt på grund av den smala molekylviktsfördelningen. Analys av kedjeändorna avslöjade att Sirius katalysatorn hade en hög frekvens av kedjeöverföring till monomer, vilket förklarade Sirius katalysatorns något begränsade förmåga att producera polymerer med hög molekylvikt. Sampolymerer av propen och eten producerade med Sirius uppvisade jämnare eten fördelning mellan långa och korta kedjor samt en mera randomiserad fördelning av eten längs med kedjorna än med den konventionella referenskatalysatorn. Tillsammans med den smala molekylviktsfördelningen indikerade resultaten att fördelningen av typer av aktiva centrum i Sirius katalysatorn är smal. Då man producerar polypropen med hög slagseghet skall polymerpartiklarna ha hög porositet för att kunna ackumulera eten/propen gummit. SiO2 nanopartiklar tillsatta under framställningen av Sirius katalysatorn ökade polymerpartikelns porositet, vilket möjliggjorde en dramatisk ökning av gummihalten.

Physico-chemical characterization of nanoparticle coated paper

Förståelse av olika ytors vätningsegenskaper är viktig i många pappers-relaterade industriella processer eftersom vätningen påverkar materialbeteendet, t.ex. vid bestrykning, tryckning och laminering. Förmågan att kontrollera vätningen är av intresse, därför att den ger nya möjligheter till modifikation av ytor. Vätningen styrs av ytans struktur och kemi. Kunskap om dessa egenskaper krävs både i fundamentala studier och för industriella applikationer. Nanopartiklar används ofta för att skapa funktionella ytor med mångsidiga egenskaper. Detta arbete strävar till att förstå de fysikalisk-kemiska egenskaperna hos papper och kartong som är bestrukna med nanopartiklar, för att sedan kunna förklara de observerade förändringarna i ytornas vätningsförmåga. Funktionella ytor med justerbar vätningsförmåga tillverkades genom att deponera nanopartiklar i en rulle-till-rulle vätskeflammasprutningprocess (LFS). TiO2 -nanopartikelbeläggningen skapar en superhydrofob yta som har över 160° kontaktvinkelmed vatten, medan SiO2-nanopartikelbeläggningar skapar mycket hydrofila ytor med kontaktvinklar så låga som 21° med vatten. Superhydrofobiciteten eller hydrofiliteten är ett resultat av den kombinerade effekten hos ytstrukturen och ytkemin, såsom nanopartiklarnas oxidationsnivå eller karbonatiseringsnivå. Kartongytor som är bestrukna med TiO2-nanopartiklar kan vara såväl superhydrofoba som hydrofila. Hydrofilitet kan induceras genom UVA-strålning, medan behandling i hög temperatur i ugn resulterar i en superhydrofob yta. Ett mål med arbetet var att förstå mekanismerna hos de kemiska för ändringar som sker under UVA-bestrålning och värmebehandling av ytor, bestrukna med TiO2-nanopartiklar. Ytornas abrasions- och kompressionsmotstånd samt relaterade förändringar i funktionella egenskaper undersöktes. Resultaten skapar en bättre förståelse för potentiell användning av LFS-nanopartikelbeläggningar i pappersrelaterade applikationer. En förståelse för stabiliteten hos nanopartikelbeläggningarna när de exponeras för externa krafter är viktig för att försäkra deras funktionalitet i industriella applikationer och för att garantera beläggningarnas miljö-, hälso- och säkerhetsaspekter. ------------------------------------------ Pinnan kastumisominaisuuksien hallinta on tärkeää monissa paperiteollisuuden prosesseissa, sillä pinnan kastuminen vaikuttaa esimerkiksi päällystämiseen, painamiseen ja laminointiin. Pinnan kastuvuuden säätäminen avaa mielenkiintoisia uusia mahdollisuuksia pintojen ominaisuuksien hallintaan. Pinnan kastuvuus määräytyy pinnan rakenteesta ja kemiasta, ja näiden ominaisuuksien ymmärtäminen on tärkeää sekä perustutkimuksessa että teollisissa sovelluksissa. Nanopartikkeleita käytetään usein toiminnallisten ja hallitusti kastuvien pintojen aikaansaamiseksi. Tässä työssä on tarkasteltu nanopartikkelipinnoitetun paperin ja kartongin fysikaalis-kemiallisia pintaominaisuuksia, jotka selittävät havaittuja muutoksia pinnan kastuvuudessa. Toiminnalliset pinnat säädettävillä kastuvuusominaisuuksilla valmistettiin nesteliekkiruiskutus (LFS) nanopartikkelipinnoituksella rullalta rullalle-menetelmällä. TiO2-nanopartikkelipäällystys saa aikaan superhydrofobisen pinnan, jonka veden kontaktikulma on suurempi kuin 160°. Toisaalta SiO2-nanopartikkelipäällystys muuttaa pinnan hyvin hydrofiiliseksi, veden kontaktikulman ollessa vain 21°. Pinnan superhydrofobisuus tai hydrofiilisyys riippuu nanopartikkelipinnan rakenteesta ja pintakemiasta kuten pinnan hapettumisasteesta ja hiilipitoisuudesta. TiO2-nanopartikkelipinnoitetun kartonkipinnan kastumista voidaan säätää superhydrofobisen ja hydrofiilisen välillä. Pinnan hydrofiilisyys saadaan aikaan UVA-valolla, kun taas superhydrofobinen pinta voidaan palauttaa korkeassa lämpötilassa uunissa. Tämän työn tavoitteena oli selvittää, millaisia muutoksia TiO2-nanopartikkelipäällystetyn pinnan kemiassa tapahtuu UVA-valon ja lämpökäsittelyn vaikutuksesta. Työssä tarkasteltiin myös pinnan mekaanisen hankauksen ja kokoonpuristuksen vaikutusta toiminnallisiin ominaisuuksiin. Työssä saavutetut tulokset auttavat ymmärtämään LFS-nanopartikkelipäällystettyjen pintojen soveltuvuutta paperiin liittyvissä sovelluksissa. Nanopartikkelipäällystettyjen pintojen stabiilius ulkoisten voimien alaisena on tärkeää toiminnallisten päällystysten ympäristö-, terveys- ja turvallisuusnäkökulmia tarkasteltaessa.

Spectroscopic Studies of III-V Semiconductor Materials for Improved Devices

Defects in semiconductor crystals and at their interfaces usually impair the properties and the performance of devices. These defects include, for example, vacancies (i.e., missing crystal atoms), interstitials (i.e., extra atoms between the host crystal sites), and impurities such as oxygen atoms. The defects can decrease (i) the rate of the radiative electron transition from the conduction band to the valence band, (ii) the amount of charge carriers, and (iii) the mobility of the electrons in the conduction band. It is a common situation that the presence of crystal defects can be readily concluded as a decrease in the luminescence intensity or in the current flow for example. However, the identification of the harmful defects is not straightforward at all because it is challenging to characterize local defects with atomic resolution and identification. Such atomic-scale knowledge is however essential to find methods for reducing the amount of defects in energy-efficient semiconductor devices. The defects formed in thin interface layers of semiconductors are particularly difficult to characterize due to their buried and amorphous structures. Characterization methods which are sensitive to defects often require well-defined samples with long range order. Photoelectron spectroscopy (PES) combined with photoluminescence (PL) or electrical measurements is a potential approach to elucidate the structure and defects of the interface. It is essential to combine the PES with complementary measurements of similar samples to relate the PES changes to changes in the interface defect density. Understanding of the nature of defects related to III-V materials is relevant to developing for example field-effect transistors which include a III-V channel, but research is still far from complete. In this thesis, PES measurements are utilized in studies of various III-V compound semiconductor materials. PES is combined with photoluminescence measurements to study the SiO2/GaAs, SiNx/GaAs and BaO/GaAs interfaces. Also the formation of novel materials InN and photoluminescent GaAs nanoparticles are studied. Finally, the formation of Ga interstitial defects in GaAsN is elucidated by combining calculational results with PES measurements.

Transformation of carbon dioxide to diethyl carbonate over ceria and ceria-supported catalysts

Carbon dioxide is regarded, nowadays, as a primary anthropogenic greenhouse gas leading to global warming. Hence, chemical fixation of CO2 has attracted much attention as a possible way to manufacture useful chemicals. One of the most interesting approaches of CO2 transformations is the synthesis of organic carbonates. Since conventional production technologies of these compounds involve poisonous phosgene and carbon monoxide, there is a need to develop novel synthetic methods that would better match the principles of "Green Chemistry" towards protection of the environment and human health. Over the years, synthesis of dimethyl carbonate was under intensive investigation in the academia and industry. Therefore, this study was entirely directed towards equally important homologue of carbonic esters family namely diethyl carbonate (DEC). Novel synthesis method of DEC starting from ethanol and CO2 over heterogeneous catalysts based on ceria (CeO2) was studied in the batch reactor. However, the plausible drawback of the reaction is thermodynamic limitations. The calculated values revealed that the reaction is exothermic (ΔrHØ298K = ─ 16.6 J/ ) and does not occur spontaneously at rooms temperature (ΔrGØ 298K = 35.85 kJ/mol). Moreover, co-produced water easily shifts the reaction equilibrium towards reactants excluding achievement of high yields of the carbonate. Therefore, in-situ dehydration has been applied using butylene oxide as a chemical water trap. A 9-fold enhancement in the amount of DEC was observed upon introduction of butylene oxide to the reaction media in comparison to the synthetic method without any water removal. This result confirms that reaction equilibrium was shifted in favour of the desired product and thermodynamic boundaries of the reaction were suppressed by using butylene oxide as a water scavenger. In order to obtain insight into the reaction network, the kinetic experiments were performed over commercial cerium oxide. On the basis of the selectivity/conversion profile it could be concluded that the one-pot synthesis of diethyl carbonate from ethanol, CO2 and butylene oxide occurs via a consecutive route involving cyclic carbonate as an intermediate. Since commercial cerium oxide suffers from the deactivation problems already after first reaction cycle, in-house CeO2 was prepared applying room temperature precipitation technique. Variation of the synthesis parameters such as synthesis time, calcination temperature and pH of the reaction solution turned to have considerable influence on the physico-chemical and catalytic properties of CeO2. The increase of the synthesis time resulted in high specific surface area of cerium oxide and catalyst prepared within 50 h exhibited the highest amount of basic sites on its surface. Furthermore, synthesis under pH 11 yielded cerium oxide with the highest specific surface area, 139 m2/g, among all prepared catalysts. Moreover, CeO2─pH11 catalyst demonstrated the best catalytic activity and 2 mmol of DEC was produced at 180 oC and 9 MPa of the final reaction pressure. In addition, ceria-supported onto high specific surface area silicas MCM-41, SBA-15 and silica gel were synthesized and tested for the first time as catalysts in the synthesis of DEC. Deposition of cerium oxide on MCM-41 and SiO2 supports resulted in a substantial increase of the alkalinity of the carrier materials. Hexagonal SBA-15 modified with 20 wt % of ceria exhibited the second highest basicity in the series of supported catalysts. Evaluation of the catalytic activity of ceria-supported catalysts showed that reaction carried out over 20 wt % CeO2-SBA-15 generated the highest amount of DEC.

Hydrogen Sensor Application of Anodic Titanium Oxide Nanostructures

Hydrogen (H2) fuel cells have been considered a promising renewable energy source. The recent growth of H2 economy has required highly sensitive, micro-sized and cost-effective H2 sensor for monitoring concentrations and alerting to leakages due to the flammability and explosiveness of H2 Titanium dioxide (TiO2) made by electrochemical anodic oxidation has shown great potential as a H2 sensing material. The aim of this thesis is to develop highly sensitive H2 sensor using anodized TiO2. The sensor enables mass production and integration with microelectronics by preparing the oxide layer on suitable substrate. Morphology, elemental composition, crystal phase, electrical properties and H2 sensing properties of TiO2 nanostructures prepared on Ti foil, Si and SiO2/Si substrates were characterized. Initially, vertically oriented TiO2 nanotubes as the sensing material were obtained by anodizing Ti foil. The morphological properties of tubes could be tailored by varying the applied voltages of the anodization. The transparent oxide layer creates an interference color phenomena with white light illumination on the oxide surface. This coloration effect can be used to predict the morphological properties of the TiO2 nanostructures. The crystal phase transition from amorphous to anatase or rutile, or the mixture of anatase and rutile was observed with varying heat treatment temperatures. However, the H2 sensing properties of TiO2 nanotubes at room temperature were insufficient. H2 sensors using TiO2 nanostructures formed on Si and SiO2/Si substrates were demonstrated. In both cases, a Ti layer deposited on the substrates by a DC magnetron sputtering method was successfully anodized. A mesoporous TiO2 layer obtained on Si by anodization in an aqueous electrolyte at 5°C showed diode behavior, which was influenced by the work function difference of Pt metal electrodes and the oxide layer. The sensor enabled the detection of H2 (20-1000 ppm) at low operating temperatures (50–140°C) in ambient air. A Pd decorated tubular TiO2 layer was prepared on metal electrodes patterned SiO2/Si wafer by anodization in an organic electrolyte at 5°C. The sensor showed significantly enhanced H2 sensing properties, and detected hydrogen in the range of a few ppm with fast response/recovery time. The metal electrodes placed under the oxide layer also enhanced the mechanical tolerance of the sensor. The concept of TiO2 nanostructures on alternative substrates could be a prospect for microelectronic applications and mass production of gas sensors. The gas sensor properties can be further improved by modifying material morphologies and decorating it with catalytic materials.

Metal oxides prepared through the nanocasting approach-mechanistic study, surface interactions and applications in separation

Mesoporous metal oxides are nowadays widely used in various technological applications, for instance in catalysis, biomolecular separations and drug delivery. A popular technique used to synthesize mesoporous metal oxides is the nanocasting process. Mesoporous metal oxide replicas are obtained from the impregnation of a porous template with a metal oxide precursor followed by thermal treatment and removal of the template by etching in NaOH or HF solutions. In a similar manner to the traditional casting wherein the product inherits the features of the mold, the metal oxide replicas are supposed to have an inverse structure of the starting porous template. This is however not the case, as broken or deformed particles and other structural defects have all been experienced during nanocasting experiments. Although the nanocasting technique is widely used, not all the processing steps are well understood. Questions over the fidelity of replication and morphology control are yet to be adequately answered. This work therefore attempts to answer some of these questions by elucidating the nanocasting process, pin pointing the crucial steps involved and how to harness this knowledge in making wholesome replicas which are a true replication of the starting templates. The rich surface chemistry of mesoporous metal oxides is an important reason why they are widely used in applications such as catalysis, biomolecular separation, etc. At times the surface is modified or functionalized with organic species for stability or for a particular application. In this work, nanocast metal oxides (TiO2, ZrO2 and SnO2) and SiO2 were modified with amino-containing molecules using four different approaches, namely (a) covalent bonding of 3-aminopropyltriethoxysilane (APTES), (b) adsorption of 2-aminoethyl dihydrogen phosphate (AEDP), (c) surface polymerization of aziridine and (d) adsorption of poly(ethylenimine) (PEI) through electrostatic interactions. Afterwards, the hydrolytic stability of each functionalization was investigated at pH 2 and 10 by zeta potential measurements. The modifications were successful except for the AEDP approach which was unable to produce efficient amino-modification on any of the metal oxides used. The APTES, aziridine and PEI amino-modifications were fairly stable at pH 10 for all the metal oxides tested while only AZ and PEI modified-SnO2 were stable at pH 2 after 40 h. Furthermore, the functionalized metal oxides (SiO2, Mn2O3, ZrO2 and SnO2) were packed into columns for capillary liquid chromatography (CLC) and capillary electrochromatography (CEC). Among the functionalized metal oxides, aziridinefunctionalized SiO2, (SiO2-AZ) showed good chemical stability, and was the most useful packing material in both CLC and CEC. Lastly, nanocast metal oxides were synthesized for phosphopeptide enrichment which is a technique used to enrich phosphorylated proteins in biological samples prior to mass spectrometry analysis. By using the nanocasting technique to prepare the metal oxides, the surface area was controlled within a range of 42-75 m2/g thereby enabling an objective comparison of the metal oxides. The binding characteristics of these metal oxides were compared by using samples with different levels of complexity such as synthetic peptides and cell lysates. The results show that nanocast TiO2, ZrO2, Fe2O3 and In2O3 have comparable binding characteristics. Furthermore, In2O3 which is a novel material in phosphopeptide enrichment applications performed comparably with standard TiO2 which is the benchmark for such phosphopeptide enrichment procedures. The performance of the metal oxides was explained by ranking the metal oxides according to their isoelectric points and acidity. Overall, the clarification of the nanocasting process provided in this work will aid the synthesis of metal oxides with true fidelity of replication. Also, the different applications of the metal oxides based on their surface interactions and binding characteristics show the versatility of metal oxide materials. Some of these results can form the basis from which further applications and protocols can be developed.

Green diesel synthesis by hydrodeoxygenation of lipids extracted from Chlorella algae in supercritical hexane

Lipids were extracted from Chlorella algae with supercritical hexane. The high lipids yield of approximately 10% was obtained at optimum conditions of 300 rpm stirring speed and 2 h duration compared to the total contents of lipids being 12%. Furthermore, an easiness of hexane recovery may be considered as economically and ecologically attractive. For the first time, in the current work catalytic hydrodeoxygenation (HDO) of Chlorella algal lipids was studied over 5 wt% Ni/H-Y-80 and 5 wt% Ni/SiO2 at 300 C and under 30 bar total pressure in H2. A comparative HDO of stearic acid was carried out under similar conditions. The conversion of lipids was about 35% over 5 wt% Ni/H-Y-80 after 6h, whereas, 5 wt% Ni/SiO2 was totally deactivated after 60 min. The selectivity to hydrocarbons (C15-C18) is 6%. As a comparison, complete conversion of stearic acid over 5 wt% Ni/H-Y-80 was achieved in 6 h. The transformation of lipids proceeded mostly via hydrogenation and hydrolysis with formation of free fatty acid (FFA). The lower activity might be attributed to deactivation of catalysts caused by chlorophylls and carotenoids. Even though the conversion is low, future studies in HDO of lipids extracted from other algae species having higher lipid content could be proposed. Coke resistant catalyst might be considered to improve catalytic activity.