AB SOMAS Ventiler manufactures valves for different applications. A valve of type DN VSSL 400, PN 100, used in high-temperature and high-pressure applications was investigated in this thesis. This type of valve is coated with high cobalt alloys to achieve the tribological properties needed for this severe condition. However there is a request from AB Somas Ventiler to find another solution. This request is based on the fact that demands on higher temperatures, from customers, yields higher requirements on the material. It is also a price issue since cobalt is quite expensive. Materials investigated were high-nitrogen steel, Vanax 75, nickel-based superalloy Inconel 718 and hardened steels, EN 1.4903 and EN 1.4923 presently used as base material in the valve. Calculation of contact pressure that arises when the valve is closed was first approached by using finite element method (FEM). Several models were constructed to show the behavior of the valve during closing in terms of deformation. Hot wear tests, in which a specimen was pressed against a rotating cylinder, were performed to be able to compare the materials to the solution of today and among each other. Data extracted from the tests were compiled in the form of coefficients of friction. Profilometer examinations were used to reveal the volumes of worn and adhered material and together with scanning electron microscopy (SEM) the wear situation for each material couple could be assessed. Wear mechanisms detected in SEM were adhesive and abrasive and the results clearly showed that the steels were not a good solution because of severe adhesive wear due to the similarity of mating materials creating a more efficient bonding between the asperities. Vanax 75 showed much better performance but there was still an obvious difference between the steels and the superalloy in terms of both coefficient of friction and amount of wear. On this basis, Inconel 718 was selected as the most suitable material to replace the high cobalt alloys used in the valves today. / AB Somas ventiler är ett företag som tillverkar ventiler för ett brett spann av applikationer. I det här examensarbetet har undersökningar genomförts på en ventil av modell DN VSSL 400, PN 100, som normalt används i applikationer för höga tryck och höga temperaturer. Ventilen beläggs i dagsläget med höghaltiga koboltlegeringar för att uppnå de tribologiska egenskaper som krävs i de påfrestande arbetsförhållanden som råder. AB Somas Ventiler har dock framfört en förfrågan om att hitta en alternativ lösning, en förfrågan som grundar sig i att kundernas ständiga önskemål på att ventilerna ska klara högre arbetstemperaturer också medför högre krav på ventilmaterialen. Det är även en prisfråga, då kobolt är en dyr legering att använda sig av. De material som inkluderades i undersökningen var det kvävelegerade stålet Vanax 75, nickelbaserade superlegeringen Inconel 718 samt de två stålen EN 1.4903 och EN 1.4923 i härdat tillstånd. De två sistnämnda används idag som basmaterial i ventilen. Genom att använda den finita element metoden (FEM) kunde en första beräkning göras av det kontakttryck som uppstår då ventilen stängs. Flera modeller konstruerades för att simulera ventilens deformation vid stängning. Där efter utfördes nötningstester i hög temperatur på de alternativa materialen, genom att låta en provbit pressas mot en roterande cylinder, för att sedan kunna göra en jämförelse mellan materialen och även med den nuvarande lösningen. Från nötningstesterna erhölls data som kunde användas för att ta fram friktionskoefficienter för de olika materialparen. Med hjälp av undersökningar med profilometer och svepelektronmikroskop (SEM) kunde värden på nötta och vidhäfta volymer erhållas tillsammans med information om nötningssituationer för ytorna mellan de olika materialparen. De nötningsmekanismer som påvisades med hjälp av SEM-undersökningen var adhesiv och abrasiv nötning, och resultaten visade tydligt att nötningen av stålen var omfattande, på grund av att lika material i kontakt med varandra skapar starkare band mellan ytorna, och att de därför inte var en intressant lösning. Det kvävelegerade Vanax 75 uppförde sig visserligen bättre men en tydlig skillnad mot superlegeringarna kunde dock fortfarande konstateras, sett till både friktionskoefficient och mängden slitage. Baserat på dessa resultat valdes Inconel 718 som det bäst lämpade materialet att ersätta de höghaltiga koboltlegeringarna som idag används i ventilen.

<p>Tantalum diffusion barrier coatings were investigated as a way to improve the conversion efficiency of CIGS (copper indium gallium diselenide) solar cells.  Tantalum coatings were deposited upon silicon and stainless steel foil substrates using direct current magnetron sputtering (DcMS) and high power impulse magnetron sputtering (HiPIMS).  The coatings were characterized using scanning electron microscopy (SEM).  Cross-sectional scanning electron micrographs revealed that the HiPIMS coatings appeared denser than the DcMS coatings.</p>

<p>Summary</p><p>I have a great interest in bouzoukis and since I, during my education in guitar making, mainly have focused on building bouzoukis and other traditional folk instruments, I have chosen the bouzouki as the object of my degree project.</p><p>In connection to the making of these instruments, I started to consider the construction of the bouzouki and why the bouzouki has such a characteristic sound.</p><p>One of my theories is based on the fact that most bouzoukis are made with floating bridges instead of glued pinbridges. Do these types of bridges differ from each other tonally and if so, how much and in what way?</p><p>To receive answers to my questions, I have built two identical bouzoukis with different types of bridges, one with a glued pinbridge and one with a floating bridge. I have been very precise in the making of these instruments, giving them the exact same dimensions and using material from the same piece of wood. This to make sure that the instruments should be as exactly alike as possible.</p><p>After finishing the making of the bouzoukis, I arranged for a sound test where I let musicians play and listen to the instruments. After doing this I let the same musicians fill in a form with questions regarding each instruments tonal characteristics and it’s fields of application.</p><p>By compiling the answers from the sound test, I have come to a conclusion regarding what tonally separates a bouzouki with a glued pinbridge from a bouzouki with a floating bridge.</p><p>In addition to this I have found out what other instrument makers considers to be the difference between these two types of bridges.</p><p>Beside the project described above I also present a brief history of the bouzouki.</p> / <p>Sammanfattning</p><p>Jag har valt att göra ett examensarbete som grundar sig på mitt stora intresse för bouzoukis. Jag har under min utbildning i gitarrbyggeri främst riktat in mig på att bygga bouzoukis samt liknande folkinstrument. I samband med dessa byggen så har jag fundera mycket över instrumentets konstruktion och vad det är som gör att bouzoukin har ett så karakteristiskt ljud.</p><p>En av mina funderingar består i varför de flesta bouzoukis är utrustade med ett tryckande stall istället för ett limmat stall. Skiljer sig dessa stalltyper från varandra tonalt och i sådant fall hur mycket och på vilket sätt?</p><p>För att få svar på mina frågor har jag byggt två stycken bouzoukis som är identiskt lika bortsett från stalltypen. Den ena har ett limmat stall och den andra ett tryckande stall.</p><p>Jag har varit mycket noggrann med att tillverka bouzoukierna med exakt samma dimensioner och med material som kommer från samma trästock. Detta för att försäkra mig om att instrumenten ska bli så lika som det bara går.</p><p>Därefter har jag anordnat ett ”lyssningstest” där jag har låtit musiker spela och lyssna på instrumenten. Musikerna har sedan fått fylla i ett formulär innehållande frågor om instrumentens tonala egenskaper samt om deras användningsområden.</p><p>Genom att sammanställa svaren från lyssningstestet har jag kommit fram till en slutsats om vad det är som tonalt skiljer ett limmat från ett tryckande stall hos en bouzouki.</p><p>Jag har även att tagit reda på vad andra instrumentbyggare anser att det är för skillnader mellan de olika stalltyperna, samt hur bouzoukins historia i stora drag ser ut.</p>

<p>The main objectives of the thesis work were: (1), to study the oxidation of methanol and formic acid on platinum electrodes by employing conventional and advanced electrochemical methods, and (2), to develop membrane electrode assemblies based on polybenzimidazole membranes that can be used in fuel cells up to 200 °C.</p><p>D.c. voltammetry and a.c. voltammetry studies of methanol and formic acid on polycrystalline platinum in sulphuric acid electrolyte were performed to determine the mechanism and kinetics of the oxidation reactions.</p><p>A combined potential step and fast cyclic voltammetry experiment was employed to investigate the time dependence primarily of methanol oxidation on platinum. Charge measurements clearly demonstrated the existence of a parallel path at low potentials and short times without formation of adsorbed CO. Furthermore, experimental results showed that only the serial path, via adsorbed CO, exists during continuous cycling, with the first step being diffusion controlled dissociative adsorption of methanol directly from the bulk electrolyte. The saturation charge of adsorbed CO derived from methanol was found to be significantly lower than CO derived from formic acid or dissolved CO. This was attributed to the site requirements of the dehydrogenation steps, and possibly different compositions of linear, bridged or multiply bonded CO. The coverage of adsorbed CO from formic acid decreased significantly at potentials just outside of the hydrogen region (0.35 V vs. RHE), while it did not start to decrease significantly until about 0.6 V vs. RHE for methanol. Adsorbed CO from dissolved CO rapidly oxidized at potentials above about 0.75 V due to formation of platinum oxide.</p><p>Data from a.c. voltammograms from 0.5 Hz up to 30 kHz were assembled into electrochemical impedance spectra (EIS) and analyzed using equivalent circuits. The main advantages of collecting EIS spectra from a.c. voltammetry experiments are the ability to directly correlate the impedance spectra with features in the corresponding d.c. voltammograms, and the ability to investigate conditions with partially covered surfaces that are inaccessible in steady-state measurements.</p><p>A variety of spectral types were observed, and for methanol these showed only a single adsorption relaxation aside from the double-layer/charge-transfer relaxation, though some structure in the phase of the latter relaxation hints at another process. The charge-transfer resistance showed Tafel behaviour for potentials in the rising part of the oxidation peak consistent with a one-electron process in the rate-determining step. The rate limiting step was proposed to be the electrochemical reaction between adsorbed CO and OH at the edge of islands of OH, with competition between OH and CO adsorption for the released reaction sites. Only a single adsorption relaxation in methanol oxidation was observed, implying that only one single coverage is required to describe the state of the surface and the kinetics. It was assumed that this single coverage is that of OH, and all the surface not covered with OH is covered with CO so that the coverage of CO is not an independent variable. Inductive behaviour and negative relaxation times in the methanol oxidation were attributed to nucleation and growth behaviour. Linear voltammetry reversal and sweep-hold experiments also indicated nucleation-growth-collision behaviour in distinct potential regions, both in the forward and reverse potential scan for methanol oxidation on platinum.</p><p>In both methanol oxidation and formic acid oxidation, a negative differential resistance (NDR) was observed in the potential regions that possess a negative d.c. polarization slope, and was attributed to the formation of surface oxide which inhibited the oxidation of methanol or formic acid.</p><p>EIS spectra for formic acid clearly showed the presence of an additional low frequency relaxation at potentials where we expect adsorbed dissociated water or platinum oxide to be present, implying that more than one single coverage is required to describe the state of the surface and the kinetics. Two potential regions with hidden negative differential resistance (HNDR) behaviour were identified in the positive-going sweep, one prior to platinum oxide formation, assumed to involve adsorbed dissociated water, and one just negative of the main oxidation peak, assumed to involve platinum oxide. Oscillatory behaviour was found in the formic acid oxidation on platinum by adding a large external resistance to the working electrode circuit, which means that there is no longer true potentiostatic control at the interface. By revealing the system time constants, impedance measurements can be used to assist in explaining the origin of the oscillations. In the case of formic acid, these measurements showed that the oscillations do not arise from the chemical mechanism alone, but that the potential plays an essential role.</p><p>Preparation and optimization of gas-diffusion electrodes for high temperature polymer electrolyte fuel cells based on phosphoric acid doped polybenzimidazole (PBI) membranes was performed. This fuel cell allows for operating temperatures up to 200 °C with increased tolerance towards catalytic poisons, typical carbon monoxide. In this work we employed pure hydrogen and oxygen as the fuel cell feeds, and determined the optimum morphology of the support layer, and subsequently optimized the catalytic layer with respect to platinum content in the Pt/C catalyst and PBI loading. A smooth and compact support layer with small crevices and large islands was found to be beneficial with our spraying technique in respect to adhesion to the carbon backing and to the catalyst layer. We found that a high platinum content catalyst gave a significantly thinner catalyst layer (decreased porosity) on both anode and cathode with superior performance. The PBI loading was found to be crucial for the performance of the electrodes, and a relatively high loading gave the best performing electrodes.</p>

<p>The main part of this work has been a literature survey, reviewing scientifical reports forinformation on how steel cleanness is evaluated today, and also how the steel cleanness is related tothe fatigue performance of clean steels.</p>

<p>The general trend in the car body manufacturing industry is towards low-series production and reduction of press lubricants and car weight. The limited use of press lubricants, in combination with the introduction of high and ultra-high strength sheet materials, continuously increases the demands of the forming tools. To provide the means of forming new generations of sheet material, development of new tool materials with improved galling resistance is required, which may include tailored microstructures, introducing of specific(MC, M(C,N))carbides and nitrides, coatings and improved surface finish. In the present work, the wear mechanisms in real forming operations have been studied and emulated on a laboratory scale by developing a test equipment. The wear mechanisms identified in the real forming process, were distinguished into a sequence of events consisting of initial local adhesive wear of the sheets resulting in transfer of sheet material to the tool surfaces. Successive forming operations led to growth of the transfer layer and initiation of scratching of the sheets. Finally, scratching changed into severe adhesive wear, associated with gross macroscopic damage. The wear process was repeated in the laboratory test-equipment in sliding between several tool materials, ranging from cast iron to conventional ingot cast tool steels to advanced powder metallurgy tool steel, against dual-phase carbon steel sheets. By use of the test-equipment, selected tool materials were ranked regarding wear resistance in sliding against ferritic-martensitic steel sheets at different contact pressures.</p><p>Wear in sheet metal forming is mainly determined by adhesion; initially between the tool and sheet surface interaction and subsequently, after initiation of material transfer, between a sheet to sheet contact. Atomic force microscopy force curves showed that adhesion is sensitive to both chemical composition and temperature. By alloying of iron with 18wt.% Cr and 8wt.% Ni, alloying in itself, or changes in crystal structure, led to an increase of 3 times in adhesion at room temperature. Hence, alloying may be assumed a promising way for control of adhesive properties. Additionally, frictional heating should be controlled to avoid high adhesion as, generally, adhesion was found to increase with increasing temperature for all investigated materials.</p>

<p>Syftet med examensarbetet var att undersöka manganhaltens inverkan på skärbarheten och de mekaniska egenskaperna i varmarbetsstål Dievar samt kontrollera och undersöka hypotesen<em> </em>att material med låga Ac1 temperaturer maskinbearbetas svårare än material med högre temperaturer. </p><p>Skärbarhet hos Dievar med olika Mn-halt från 0,084 till 1,59 vikts% studerades i härdat tillstånd med ett pinnfräsningstest. Skärbarheten karakteriserades genom mätning av verktygslivslängd och skärkrafter. Verktygslivslängd bestämdes av fasförslitningsutvecklingen på verktyget. Förslitningsmekanismer studerades på verktygets spån- och släppningssidor med hjälp av svepelektronmikroskop (SEM). Dragprov vid rums- och förhöjd temperatur genomfördes för att studera mangans inverkan på hållfasthetsegenskaper hos Dievar. Mikrostrukturen av stålen i härdat och anlöpt tillstånd undersöktes i SEM. Ac1 temperatur i stålen uppmättes med dilatometer.</p><p>Mangan visade sig ha en positiv inverkan på skärbarheten i Dievar. Verktygets livslängd var två gånger längre vid pinnfräsning av Dievar 1,59 vikts% Mn i jämförelse med Dievar 0,084 och 0,27 vikts% Mn. Mer påkletningsbenägna stål med lägre Mn-halt orsakade mer adhesiv nötning och urflisning av fräsens skäregg. Detta ledde till att förslitningen utvecklades hastigare under bearbetningen av Dievar med lägre Mn-halt.</p><p>De uppmätta skärkrafterna under bearbetning förklarade inte skillnaden i skärbarheten mellan Dievar med olika Mn-halt; skärkrafter var lika i alla material.</p><p>Dievar med högre Mn-halt innehöll mindre primära molybdenrika karbider än Dievar med lägre Mn-halt. Detta berodde på att manganet minskade Ac1 temperaturen i Dievar.</p><p>Mn-halten i Dievar påverkade inte hållfasthetsegenskaperna vid rumstemperatur men visade en tendens att minska stålets hållfasthet vid hög temperatur.</p><p>De genomförda undersökningarna bekräftade inte hypotesen att material med lägre Ac1 temperaturer har sämre maskinbearbetbarhet än material med högre temperaturer. Dievar 1,59 vikts% Mn hade betydligt lägre Ac1 temperatur än andra Dievar-material samt modifierat Orvar men visade sig vara lättare att bearbeta.</p> / <p>The aim of the study was to investigate influence of manganese content on the machinability and mechanical properties of a hot-work tool steel Dievar and verify a hypothesis that materials with low Ac1 temperatures are more difficult to machine than steels with higher Ac1 temperatures.</p><p>Machinability of Dievar with varying manganese content from 0,084 to 1,59 wt% was investigated in the hardened condition in the milling operation. The machinability of the steels was characterized by measuring tool life and cutting forces during machining. The tool life was estimated by measuring flank wear on the tools. Wear mechanisms were investigated on the clearance and rake faces of the tools by SEM. Tensile tests at room and elevated temperatures were carried out to examine the manganese influence on the mechanical properties of Dievar. Microstructure of the steels in hardened and tempered condition was investigated by SEM. Dilatometer tests were done to determine the Ac1 temperature for the steels.</p><p>Manganese content showed to have a positive effect on the machinability of Dievar. Two times longer tool life was reached when end milling Dievar 1,59 wt% Mn comparing to end milling Dievar 0,084 and 0,27 wt% Mn. More adhesive wear and chipping were observed on the tools after end milling the lower manganese containing steels. This resulted in more progressive wear and shorter tool life during machining of these steels.</p><p>The measured cutting forces could not be related to the difference in machinability of the steels with different manganese content. The generated cutting forces were similar for all the tested steels.</p><p>Dievar with higher manganese content contained less primary molybdenum-rich carbides in the microstructure. It was related to the lower Ac1 temperature of Dievar 1,59 wt% Mn comparing to the lower manganese containing steels.</p><p>The manganese content showed no influence on the tensile properties of Dievar at room temperature and a tendency to a slight decrease in yield and ultimate strength at the elevated temperature.</p><p>The machinability tests carried out in the present study did not confirm the hypothesis that materials with low Ac1 temperatures have poor machinability.  Dievar 1,59 wt% Mn had much lower Ac1 temperatures than the other Dievar steels and the modified Orvar steel but showed to have an improved machinability compared to the others.</p>

<p>This thesis consists of two parts, one dominating part concerning spectrally selective solar absorbers and one dealing with thermal solar systems. The appended papers I to VIII concern the solar absorber part, papers dealing with the systems part have not been included in the thesis.</p><p>A new spectrally selective absorber derived from a novel solution-chemistry method has been developed and optimized. The main objective was to investigate the potential of the spectrally selective surface. Some of the questions at issue were; would it be possible to create a suitable absorber composite using this method, how high selectivity could be obtained, could the performance be enhanced by using anti-reflection coatings, which was the optimal layer composition, would the thin films be durable and what was the structure and morphology like on a nano scale? The absorber consists of absorbing thin films of nickel nano-particles embedded in a dielectric matrix of alumina and an overlying anti-reflection film consisting of one of the following materials silica, hybrid-silica, alumina or silica-titania. Solution and sol-gel chemistry were used in the process. The thin films were spin-coated onto an aluminum substrate followed by a heat-treatment that generated the multi layer selective solar absorber. </p><p>The optical constants for the thin film materials in question were determined. An optimal three layer structure was modeled using the experimentally determined optical constants. The theoretical three layer stack was experimentally confirmed and achieved a solar absorptance of 0.97 and a thermal emittance of 0.05 which definitely are commercially competitive values. The configuration of the three layer stack is: an 80%nickel-20%alumina film at the base, a 40%nickel-60%alumina film in the middle and a silica or hybrid-silica film at the top. The three layer absorber was subjected to high temperature and condensation accelerated ageing tests designed by IEA Task 27. The condensation test did not degrade the absorber whatsoever but the high temperature test did reveal some oxidation of the nickel particles. The oxidation occurs initially and then stops. A formed nickel-oxide layer hinders further oxidation. The level of oxidation is small and the absorber is qualified according to the IEA Task 27 test procedure.</p>

<p>Today, the dominating way of patterning nanosystems is by irradiation-based lithography (e-beam, DUV, EUV, and ions). Compared to the other irradiations, ion tracks created by swift heavy ions in matter give the highest contrast, and its inelastic scattering facilitate minute widening and high aspect ratios (up to several thousands). Combining this with high resolution masks it may have potential as lithography technology for nanotechnology. Even if this ‘ion track lithography’ would not give a higher resolution than the others, it still can pattern otherwise irradiation insensitive materials, and enabling direct lithographic patterning of relevant material properties without further processing. In this thesis ion tracks in thin films of polyimide, amorphous SiO₂ and crystalline TiO₂ were made. Nanopores were used as templates for electrodeposition of nanowires.</p><p>In lithography patterns are defined by masks. To write a nanopattern onto masks e-beam lithography is used. It is time-consuming since the pattern is written serially, point by point. An alternative approach is to use self-assembled patterns. In these first demonstrations of ion track lithography for micro and nanopatterning, self-assembly masks of silica microspheres and porous alumina membranes (PAM) have been used. </p><p>For pattern transfer, different heavy ions were used with energies of several MeV at different fluences. The patterns were transferred to SiO₂ and TiO₂. From an ordered PAM with pores of 70 nm in diameter and 100 nm inter-pore distances, the transferred, ordered patterns had 355 nm deep pores of 77 nm diameter for SiO₂and 70 nm in diameter and 1,100 nm deep for TiO₂. The TiO₂ substrate was also irradiated through ordered silica microspheres, yielding different patterns depending on the configuration of the silica ball layers. </p><p>Finally, swift heavy ion irradiation with high fluence (above 10¹⁵/cm²) was assisting carbon nanopillars deposition in a PAM used as template. </p>

<p>The present thesis thoroughly treats a special friction reduction phenomenon that may appear in boundary lubricated tribological contacts, of the type encountered in numerous mechanical components made of steel. The phenomenon involves the formation of a special type of tribofilm that offers very low coefficients of friction. Typically the friction level becomes halved when the film is formed, compared to when it is not formed. Since boundary lubricated mechanical components are so common in all sorts of machinery, the technical and economical potential of this phenomenon is gigantic.</p><p>The tribofilm is produced on the steel surface, resulting in friction coefficient reduction from typically 0.08–0.1 to 0.04–0.06. The tribofilm is formed from the metal in the carbon coating and sulfur in the oil additive. The main film studied was WS₂, which is a well-known low-friction material. It includes easy shearing atomic planes, in the same fashion as the solid lubricants MoS₂ and graphite. Virtually no carbon is present in the tribofilm, despite carbon being the main constituent of both the coating and the additive. No films form on the Me-DLC coated part.</p><p>It was also found that WSi₂-particles could result in the formation of WS₂-containing tribofilms. It was concluded that they, just as the W-DLC film, were sufficiently weak to mill down to very small particles, and chemically reactive in the prevailing tribological conditions. However, WC particles were too stable, both mechanically and chemically, to result in any film formation.</p><p>The chemical driving forces for formation of the tribofilms were analyzed using EkviCalc, a commercial software for thermodynamical calculations based on minimization of Gibbs free energy for a system as a function of temperature and pressure. The simulations indeed confirmed that both WS₂ and MoS₂ should be expected to be stable compounds, coexisting with FeS, in the studied environment. As a spin-off result, the thermodynamical calculations indicated that coatings of the Cr-C type should impose very little tribochemical wear of the uncoated steel surface, and even reduce the forma-tion of FeS (the “traditional” tribofilm) on the steel surface in S-containing environments. </p><p>As a final spin-off, the thermodynamical calculations indicate that the Ti-C coating should be very resistant to tribochemical wear in the S-containing environment. </p>