Buvo tiriama Co(II) ir Ni(II) įvairių kompleksų elektroredukcija chloridiniuose, sulfatiniuose, citratiniuose, pirofosfatiniuose bei pirofosfatiniouose-amoniakiniuose tirpaluose, Ni ir Co lydinių su W ir Mo elektronusodinimas, gautų dangų sudėtis ir paviršiaus morfologija, struktūra bei korozinės savybės. W ir Mo lydiniai buvo nusodinami iš citratinių - boratinių ir pirofosfatinių – amoniakinių elektrolitų, o koroziniai tyrimai atlikti sulfatiniuose tirpaluose. Tiriant Co(II) ir Ni(II) elektroredukciją nustatyta, kad voltamperinių kreivių forma primena būdingas mišriai kinetikai voltamperines kreives, jose yra ryškus persilenkimas. Tačiau tyrimai EIS metodu parodė, kad šio persilenkimo negalima sieti su difuziniais apribojimais. Padaryta prielaida apie elektrochemiškai aktyvaus Co arba Ni komplekso lėtą adsorbciją ant elektrodo. Nustatyta, kad Ni elektonusodinimo greitis iš pirofosfatinių tirpalų be amonio jonų yra labai mažas. Pridėjus (NH4)2SO4 ir taip formuojant amoniakinius nikelio kompleksus tirpale, labai pagreitėja Ni elektronusodinimas. Šis efektas labai gerai koreliuoja su didėjančia apskaičiuotų įvairių Ni (II) kompleksų su amonio jonais frakcija. Tačiau amonio jonų buvimas praktiškai neturi įtakos Co elektronusodinimo greičiui. Iš gautų duomenų daroma išvada, kad elektrochemiškai aktyvus Ni ir Co kompleksai yra skirtingi, t.y. CoOH+ ir Ni(NH3)162+ yra krūvį pernešančios dalelės pirofosfatiniuose – amoniakiniuose tirpaluose. Tiriant Co-Mo ir Co-Mo-P lydinius... [toliau žr. visą tekstą] / Electroreduction of various Ni(II) and Co(II) complexes in chloride, sulfate, citrate, pyrophosphate and pyrophosphate –ammonia solutions, electrodeposition of Ni and Co and their alloys with W and Mo and composition of obtained coatings and surface morphology, structure and corrosion properties have been studied. W and Mo alloys were electrodeposited from citrate – borate and pyrophosphate –ammonia solutions, and the corrosion behavior of obtained alloys was investigated in sulfate solutions. The shapes of voltammetric curves obtained for Co(II) and Ni(II) electroreduction are similar to the typical shapes of curves for processes occurring under mixed kinetics, and clear plateau presences in voltammogram. However, based on the data obtained by the electrochemical impedance spectroscopy was confirmed that the obtained plateau does not attribute to the diffusion limitations. A slow adsorption stage of electrochemicaly active complex of Co and Ni on the electrode was assumed. It was determined that Ni electrodeposition rate from pyrophosphate baths without ammonia is relatively small. Adding of (NH4)2SO4 and further forming of Ni(II) complexes with ammonia in the solution accelerates sufficiently the rate of Ni electrodeposition. The effect well correlates with increasing the calculated molar fraction of various ammonia complexes with Ni(II). Based on the received data we conclude that electrochemicaly active Ni and Co complexes are different, i.e. CoOH+ and Ni(NH3)162+... [to full text]

Electroreduction of various Ni(II) and Co(II) complexes in chloride, sulfate, citrate, pyrophosphate and pyrophosphate –ammonia solutions, electrodeposition of Ni and Co and their alloys with W and Mo and composition of obtained coatings and surface morphology, structure and corrosion properties have been studied. W and Mo alloys were electrodeposited from citrate – borate and pyrophosphate –ammonia solutions, and the corrosion behavior of obtained alloys was investigated in sulfate solutions. The shapes of voltammetric curves obtained for Co(II) and Ni(II) electroreduction are similar to the typical shapes of curves for processes occurring under mixed kinetics, and clear plateau presences in voltammogram. However, based on the data obtained by the electrochemical impedance spectroscopy was confirmed that the obtained plateau does not attribute to the diffusion limitations. A slow adsorption stage of electrochemicaly active complex of Co and Ni on the electrode was assumed. It was determined that Ni electrodeposition rate from pyrophosphate baths without ammonia is relatively small. Adding of (NH4)2SO4 and further forming of Ni(II) complexes with ammonia in the solution accelerates sufficiently the rate of Ni electrodeposition. The effect well correlates with increasing the calculated molar fraction of various ammonia complexes with Ni(II). Based on the received data we conclude that electrochemicaly active Ni and Co complexes are different, i.e. CoOH+ and Ni(NH3)162+... [to full text] / Buvo tiriama Co(II) ir Ni(II) įvairių kompleksų elektroredukcija chloridiniuose, sulfatiniuose, citratiniuose, pirofosfatiniuose bei pirofosfatiniouose-amoniakiniuose tirpaluose, Ni ir Co lydinių su W ir Mo elektronusodinimas, gautų dangų sudėtis ir paviršiaus morfologija, struktūra bei korozinės savybės. W ir Mo lydiniai buvo nusodinami iš citratinių - boratinių ir pirofosfatinių – amoniakinių elektrolitų, o koroziniai tyrimai atlikti sulfatiniuose tirpaluose. Tiriant Co(II) ir Ni(II) elektroredukciją nustatyta, kad voltamperinių kreivių forma primena būdingas mišriai kinetikai voltamperines kreives, jose yra ryškus persilenkimas. Tačiau tyrimai EIS metodu parodė, kad šio persilenkimo negalima sieti su difuziniais apribojimais. Padaryta prielaida apie elektrochemiškai aktyvaus Co arba Ni komplekso lėtą adsorbciją ant elektrodo. Nustatyta, kad Ni elektonusodinimo greitis iš pirofosfatinių tirpalų be amonio jonų yra labai mažas. Pridėjus (NH4)2SO4 ir taip formuojant amoniakinius nikelio kompleksus tirpale, labai pagreitėja Ni elektronusodinimas. Šis efektas labai gerai koreliuoja su didėjančia apskaičiuotų įvairių Ni (II) kompleksų su amonio jonais frakcija. Tačiau amonio jonų buvimas praktiškai neturi įtakos Co elektronusodinimo greičiui. Iš gautų duomenų daroma išvada, kad elektrochemiškai aktyvus Ni ir Co kompleksai yra skirtingi, t.y. CoOH+ ir Ni(NH3)162+ yra krūvį pernešančios dalelės pirofosfatiniuose – amoniakiniuose tirpaluose. Tiriant Co-Mo ir Co-Mo-P lydinius... [toliau žr. visą tekstą]

The thin film technology is of great importance in modern society and is a key technology in wide spread applications from electronics and solar cells to hard protective coatings on cutting tools and diffusion barriers in food packaging. This thesis deals with various aspects of thin film processing and the aim of the work is twofold; firstly, to obtain a fundamental understanding of the sputter deposition and the reactive sputter deposition processes, and secondly, to evaluate sputter deposition of specific material systems with low friction properties and to improve their performance.From studies of the reactive sputtering process, two new methods of eliminating the problematic and undesirable hysteresis effect were found. In the first method it was demonstrated that an increased process pressure caused a reduction and, in some cases, even elimination of the hysteresis. In the second method it was shown that sufficiently high oxide content in the target will eliminate the hysteresis. Further studies of non-reactive magnetron sputtering of multi-element targets at different pressures resulted in huge pressure dependent compositional gradients over the chamber due to different gas phase scattering of the elements. This has been qualitatively known for a long time but the results presented here now enable a quantitative estimation of such effects. For example, by taking gas phase scattering into consideration during sputtering from a WS2 target it was possible to deposit WSx films with a sulphur content going from sub-stoichiometric to over-stoichiometric composition depending on the substrate position relative the target. By alloying tungsten disulphide (WS2) with carbon and titanium (W-S-C-Ti) its hardness was significantly increased due to the formation of a new titanium carbide phase (TiCxSy). The best sample increased its hardness to 18 GPa (compared to 4 GPa for the corresponding W-S-C coating) while still maintaining a low friction (µ=0.02) due to the formation of easily sheared WS2 planes in the wear track.

This thesis concerns experimental studies of nanocrystalline tungsten trioxide thin films. Functional properties of WO3 have interesting applications in research areas connected to energy efficiency and green nanotechnology. The studies in this thesis are focused on characterization of fundamental electronic and optical properties in the semiconducting transition metal oxide WO3. The thesis includes also applied studies of photocatalytic and photoelectrochemical properties of the material.     All nanocrystalline WO3 thin films were prepared using DC magnetron sputtering. It was found that structures like hexagonal and triclinic phase with different properties can be produced with sputtering technique. Thin film deposition has been performed using different process parameters with emphasis on sputter pressure and films that mainly consist of monoclinic γ-phase, with small contributions of ε-phase. Changes in the pressure are shown to affect the number of oxygen vacancies in the WO3 thin film, with close to stoichiometric WO3 formed at high pressures (30 mTorr), and slightly sub-stochiometric WO3-x, x = 0.005 at lower pressures (10 mTorr). Both stoichiometric and sub-stoichiometric thin films have been characterized by several structural, optical and electronic techniques.    The electronic structure and especially band gap states have been explored and optical properties of WO3 and WO3-x have been studied in detail. The band gap has been determined to be in the range 2.7-2.9 eV. Absorption due to polaron absorption (W5+  -W6+), oxygen vacancy sites (Vo -W6+), and due to differently charged oxygen vacancy states in the band gap have been determined by spectrophotometry and photoluminescence spectroscopy, in good agreement with resonant inelastic x-ray spectroscopy and theoretical calculations. The density of electronic states in the band gap was determined from cyclic voltammetry measurements, which correlate with O vacancy concentration as compared with near infrared absorption.      By combining different experimental methods a thorough characterization of the band gap states have been possible and this opens up the opportunity to tailor the WO3 functionalities. WO3 has been shown to be visible active photocatalyst, and a promising electrode material as inferred from photo-oxidation and water splitting measurements, respectively. Links between device performance in photoelectrochemical experiments, charge transport and the electronic structure have been elucidated.

Nanoparticles of MoS2 and WS2 were synthesized by decomposing the appropriate metal hexacarbonyl in the presence of sulfur dissolved in decalin at 140°C. A significant fraction of the nanoparticles was ≤ 15 nm in diameter as verified by Transmission Electron Microscopy. The process was repeated in the presence of silica and then titania to produce supported metal sulfides. The unsupported nanoparticles were found to exhibit a size-dependent shift in their threshold UV-visible absorption due to quantum confinement. Photocatalytic properties of each sulfide from synthesis in decalin were explored by using each as a catalyst in the photodegradation of methylene blue by visible light. These sulfides were also used to catalyze the photodegradation of acetone. Unsupported MoS2 and WS2 nanoparticles catalyzed the photodegradation of acetone under visible light of ≥ 400 nm wavelength. This is the first study reporting the photocatalytic properties of the unsupported WS2 nanoparticles. Photodegradation of methylene blue under ≥ 435 nm irradiation was detected using unsupported WS2 but not unsupported MoS2, likely because activity was masked by the likely photobleaching of the dye. When deposited on silica or titania, the nanosized MoS2 and WS2 could be uniformly distributed in aqueous solutions to maximize the photocatalytic efficiency. Correcting the absorbance measurements for light scattering by solids proved to be beneficial for extracting kinetic information. Both silica deposited sulfides were found to significantly increase the rate of methylene blue photodegradation, and deposited WS2 increased this rate significantly more than deposited MoS2. Similarly, both titania deposited sulfides significantly increased the rate of methylene blue photodegradation, and the deposited WS2 increased this rate significantly more than the deposited MoS2 / Synthesis of the sulfide photocatalysts -- Characterization of synthesized nanoparticles -- Photocatalytic degradation tests : setup and protocols -- Photocatalytic degradation tests : results. / Department of Chemistry

Pasaulyje neslopsta susidomėjimas fotokataliziniais procesais, kuriuos siekiama pritaikyti vandens skaidymo į vandenilį ir deguonį, organinių ar neorganinių junginių nukenksminimo technologijose. Fotoelektrocheminis vandens skaidymas į elementus vertinamas kaip vienas perspektyviausių būdų, galinčių ateityje užtikrinti efektyvų atsinaujinančių energijos šaltinių panaudojimą. Kuriant fotokatalizines sistemas, nanostruktūrinis titano dioksidas (TiO2) išlieka viena tinkamiausių ir labiausiai tyrinėtų medžiagų. Tačiau titano dioksidas neaktyvus regimosios spinduliuotės srityje, todėl alternatyva TiO2 fotokatalizatoriui gali būti kitas n-tipo puslaidininkis – volframo trioksidas (WO3). Volframo trioksidui yra būdingos fotochrominės savybės, jis absorbuoja dalį regimosios spinduliuotės. Daugelio tyrėjų nuomone, norint padidinti jo fotokatalizinį aktyvumą, tikslinga kurti mišrius oksidinius katalizatorius arba modifikuoti paviršių kitomis medžiagomis. Atsižvelgiant į literatūroje pateiktus duomenis, šiame darbe buvo siekiama pagaminti aktyvius kompozitinius fotokatalizatorius, kurių pagrindinė sudedamoji dalis yra volframo trioksidas. Darbas skirtas naujų medžiagų, kurios galėtų būti naudojamos fotokataliziniuose ir fotoelektrocheminiuose procesuose, paieškai ir charakterizavimui. Šio darbo tikslas – susintetinti TiO2, Se ir Co–P priedais modifikuotus volframo trioksido katalizatorius, ištirti jų struktūrą, fotokatalizines bei fotoelektrochemines savybes. / Scientific community exhibits a great interest in photocatalytic processes such as water photosplitting or photooxidation of organic substances. The photoelectrochemical splitting of water into hydrogen and oxygen is considered as the very promising pathway in the development of a long-term, sustainable energy economy. Titania (TiO2) still remains to be the most suitable for practical applications. However, using it as a photocatalyst still has some major issues: due to the fast recombination of photogenerated charge carriers, the overall quantum efficiency is relatively low, and titania is mostly sensitive to UV irradiation. Tungsten trioxide (WO3) is another semiconductor which can be employed in photocatalysis. Besides its photochromic properties, it has a smaller band gap than titania and may be activated under visible light illumination. In order to improve the photocatalytic efficiency it may be reasonable enough to combine both titania and tungsten trioxide into one photocatalyst or to modify their surface with various compounds. This work is relevant in the search of new materials suitable for photocatalytic and photoelectrocatalytic processes. The main object of this work was to synthesize active tungsten oxide-based composite catalysts and evaluate their structure and properties. Aim of the work was to synthesize WO3 catalysts modified with TiO2, Se and Co-P additives, to investigate their structure, photocatalytic and photoelectrochemical properties.

This research is concerned with identifying and characterizing four solid-state precipitation reactions in the W-Ni-Fe system that can be induced by appropriate heat treatments. Previous work in this area is reviewed, and a general overview of the research on this system that may, directly or indirectly, further the understanding of microstructure/mechanical property relationships in the W-Ni-Fe heavy alloy is presented. The many metallographic and analytical techniques that have been employed in the course of this investigation are also briefly reviewed. The specific precipitation reactions studied in the 90W-5Ni-5Fe heavy alloy are listed and briefly described. Interfacial precipitation - interfacial precipitates at the W-andgamma; and andgamma;-andgamma; boundaries were found to be andeta;-carbides. This morphology is expected to severely embrittle the alloy. Matrix-phase precipitation - discontinuous precipitation of W was observed in the matrix region. W-W grain boundary precipitation - W-W grain boundary allotriomorphs (andgamma;-phase) were identified and characterized. W-phase precipitation hardening - fine scale precipitation in the W-phase was found to strengthen the alloy. Deformation prior to aging significantly increased the rate of precipitate nucleation. TEM contrast analysis showed the precipitates to be plate-like with a {100} habit plane, and the strain in the W lattice normal to the precipitates was found to be tensile in nature. Matrix-composition alloys were manufactured to simulate the andgamma;-phase in the 90W-5Ni-5Fe alloy. Metallographic observations of these alloys furthered the understanding of reactions 1) and 2) above. These results are discussed in terms of (a) current theories of solid-state precipitation and (b) the influence of the various morphologies on mechanical properties.

Experiments are described in which the momentum flux of gas atoms, remitted normal to the surface of a hot clean tungsten ribbon immersed in a low pressure of helium or argon, is measured with a torsion balance and the thermal accommodation coefficient deduced. Data are presented in which the tungsten temperature range was 700 to 1900 K for helium and 1100 to 1700 K for argon. If it is assumed that the normal remitted momentum flux is that expected on assumption of the cosine emission relation, accommodation coefficients much larger (and for argon physically impossible) than those found previously by other workers are implied. A model is proposed which assumes that atoms impinging on and remitted from the hot tungsten ribbon conserve momentum in directions parallel to the surface. This results in a remitted flux, in the direction of the normal, greater than the cosine relation would predict. The resulting accommodation coefficients are then of the same order as those found using the total heat loss method. The method here reported is believed to be novel. Its accuracy increases with the temperature of the hot solid. It permits the measurement of translational thermal accommodation without relying on the temperature coefficient of resistance of the solid and hence is applicable to alloys and to non-metals. For metals., which have a normal temperature coefficient of resistance, the method allows translational accommodation to be measured and internal energy accommodation to be deduced.

In this study, the effect of a donor ligand on the stabilization of a carbonyl pyrazine tungsten complex was studied. The pentacarbonylpyrazinetungsten(0) complex could be formed from the photolysis of hexacarbonyltungsten(0) in the presence of pyrazine and could be isolated as crystalline solid. However, the complex was found to be unstable in solution, being converted to a bimetallic complex, (CO)5W(pyz)W(CO)5 and free pyrazine molecule. Two complexes exist in solution at equilibrium. The equilibrium constant could be determined by 1H-NMR spectroscopy and found to be 0.0396 at 25&deg / C. To test whether the introduction of a second pyrazine ligand might provide stability for the carbonyl-pyrazine-tungsten complex, W(CO)4(pyz)2 was attempted to be synthesized. The cis-W(CO)4(pyz)2 complex could be generated from the thermal substitution reaction of cis-W(CO)4(piperidine)2 with excess pyrazine in dichloromethane. However, this complex could not be isolated because of the lack of stability. The complex could only be identified by IR spectroscopy in solution. To stabilize the pentacarbonylpyrazinetungsten(0) complex, trimethylphosphite was introduced to the complex as a donor ligand. For this purpose, cis-W(CO)4[P(OCH3)3](thf), photogenerated from W(CO)5[P(OCH3)3] in tetrahydrofuran (thf), was reacted with pyrazine. The replacement of tetrahydrofuran with pyrazine (pyz) yielded cis-W(CO)4[P(OCH3)3](pyz). The complex could be isolated from the reaction solution and characterized by means of IR, 1H-, 13C-, 31P-NMR, and Mass spectroscopies. The introduction of P(OCH3)3 has proved that a donor ligand will strengthen the metal-pyrazine bond and thus stabilizes the complex. As a result of this stabilization, the complex could be isolated as the first example of tungsten pyrazine complexes that contain a donor ligand.

Pentacarbonylacryloylferrocenetungsten(0) complex was synthesized photochemically from hexacarbonyltungsten(0) and acryloyferrocene (acfc). UV irradiation of W(CO)6 in the presence of acryloylferrocene at 10 oC for 4 hours in n-hexane solution generates the W(CO)5(&amp / #61544 / 2-acfc) complex as the sole monosubstitution product of the photolysis, as monitored by FT-IR spectroscopy. The product complex could be isolated from the reaction solution and characterized by IR, Raman, 1H-NMR, 13C-NMR spectroscopies, mass spectrometry and elemental analysis. The complex was found to be unstable in solution and to decompose to the parent W(CO)6 complex and free acryloylferrocene molecule. The instability of the complex makes its isolation as analytically pure substance difficult. In order to stabilize the tungsten-olefin bond, trimethylphosphite was introduced as a donor ligand into the molecule. Thus, a complex containing a donor ligand in addition to the olefinic ligand was prepared starting with W(CO)6, trimethylphosphite, and acryloylferrocene. UV irradiation of W(CO)5[P(OMe)3] with acryloylferrocene in n-hexane solution at room temperature generates W(CO)4[P(OMe)3](&amp / #61544 / 2-acfc), which was isolated from the reaction solution and characterized by IR, 1H-NMR, 13C-NMR spectroscopies and mass spectrometry. The complex was found to have a cis arrangement of four CO groups in the pseudo-octahedral geometry. However, the cis-W(CO)4[P(OMe)3](&amp / #61544 / 2-acfc) complex was found to be less stable than W(CO)5(&amp / #61544 / 2-acfc).