The vision of this thesis is to study how it is possible to obtain optimised workpieces during metal cutting processes in industry. Specifically, the work is aimed to increase the understanding between the steel characteristics and their link to the chip breaking and tool wear during metal cutting. The emphasis is on the influence of the cleanliness and the characteristics of non-metallic inclusions in the workpiece on the machinability of carburising steel grades. The machinability of a case hardening steel is improved by a M-treatment (additions of Ca). Also, the improved machinability of the M-steels offers an attractive potential to save money which makes it possible to reduce the tooling costs with up to 50%. The improved machinability of Ca-treated steels is correlated to the formation of lubricating slag layers consisting of Ca-enriched sulfide inclusions and oxy-sulfide inclusions, which are formed on the rake face during the machining operation. It is proposed that the formations of slag layers from the workpiece constituents are essential to minimise the chemical degradation of the tool edge due to a contact with the chip. During this process, sulfur minimises the material transfer from the chip flow, whilst Ca-treated impurities have a stabilising effect on the protective deposits made of slag layers. Since there is a remaining industrial need to increase the production rate, whilst maintaining a high quality of the finished parts, the future production will continue to require extreme demands on the quality of workpieces. If the emphasis is focused on the workpiece, it should be possible to obtain a robust manufacturing process. Therefore, the challenge for future steel metallurgists is to develop high performance grades with optimised combined properties. / Syftet med denna avhandling är att studera hur det är möjligt att framställa optimala ämnen för skärande bearbetning i industriell skala. Målsättningen med arbetet är att öka förståelsen för ståls egenskaper och dess inverkan på spånbrytning och slitage av verktyg vid skärande bearbetning. Avhandlingen fokuserar på kopplingen mellan arbetsstyckets renhet och inneslutningskarakteristik och dess inverkan på skärbarhet hos sätthärdningsstål. Skärbarheten hos vanligt sätthärdningsstål kan förbättras markant genom en Ca-behandling, dvs. en så kallad M-behandling. Den förbättrade skärbarheten hos M-stål möjliggör stora kostnadsbesparingar, som uppskattas kunna reducera verktygskostnader med upp till 50%. Den förbättrade skärbarheten hos M-stål beror på bildningen utav tribologiska skikt som är anrikade med (Mn,Ca)S- och (CaO)x-Al2O3-S-slagg. Dessa tribologiska skikt bildas på skärverktygets spånsida under ingrepp vid skärande bearbetning och består utav vissa atomer som överförts från det bearbetade ämnet till skäret. Bildandet av ett skyddande skikt anses nödvändigt för att undvika att verktygets skäregg utsätts för ett kemiskt angrepp i kontaktytan med spånflödet. Svavel anses minimera att rent arbetsmaterial överförs till skärverktyget medans kalcium-berikade inneslutningar hjälper till att bilda ett stabilt och skyddande tribologiskt skikt. Det eviga behovet att öka produktionstakten, utan att för dess skull riskera slutproduktens kvalité ställer stora krav på framtidens material. Med utgångspunkt från arbetsstycken så ska det vara möjligt att uppnå en robust industriell produktion. Utmaningen är därför att utveckla högpresterande stål med en förhöjd kombinerad funktionsegenskap.

Metallic glass is a class of materials which have a disordered structure of atoms, due to this, glasses lack grains and grain boundaries, which are present in their crystalline counterparts. Metallic glasses have many interesting properties worth investigating, such as high corrosion resistance or high mechanical strength. However, metallic glasses are metastable and will therefore crystallise if heated above the crystallisation temperature. MoSiZr alloys have been studied and to gain knowledge of how the composition affects the crystallisation temperature, which enables further improvement of thermal stability. Crystallisation temperatures of the MoSiZr alloys were investigated by heat treatments in vacuum and ex-situ X-ray diffraction and X-ray reflectivity analysis. The highest thermal stability of the alloys was exhibited by M48Si48Zr4, Mo43Si50Zr7, Mo50Si40Zr10 and Mo45Si43Zr12, they remained amorphous after heat treatment at 1073 K. The resulting crystalline phases are Mo3Si, Mo5Si3 and ZrO2. Oxidation of Zr in the alloys is present only when the Zr content is at least 10 at%, crystallisation is otherwise mainly driven by formation of Mo3Si. Further improvement of the thermal stability is possible by introducing new alloying elements at the cost of those that promote crystallisation. Keeping the content of Zr below 10 at% is of great importance to prevent oxidation.

Dissertation (PhD)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: This study investigates the electrochemical oxidation of phenol. Phenol is a major toxin and water pollutant. In addition, during water treatment it reacts with chlorine to produce carcinogenic chlorophenols. lts treatment down to trace levels is therefore of increasing concern. For this purpose, dynamically stable anodes for the breakdown of phenols to carbon dioxide or other less harmful substances were developed and characterized. The anodes were prepared from mixed oxides of tin (Sn) and the precious metals ruthenium (Ru), tantalum (Ta) and iridium (Ir), which in tum were prepared using sol-gel techniques. This involved dip-coating the aqueous salts of the respective metals onto titanium substrates and heating to temperatures of several hundreds of degree Celsius. The properties of these mixed oxide thin films were investigated and characterized using thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), atomic force microscopy (AFM), elemental dispersive energy X-ray analysis (EDX), X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), particle induced X-ray emission (PIXE) and electrochemical measurements. A variety of different electrode materials including Til Sn02-Ru02-Ir02, Ti/Ta20s-Ir02 and Ti/RhOx-Ir02 were developed and tested for their potential as oxidation catalysts for organic pollutants in wastewaters. Depending on the anode type, phenol was found to be electrochemically degraded, to different extents, on these surfaces during electrolysis. It was however found that the oxidation rate not only depended on the chemical composition but also on the oxide morphology revealed, resulting from the preparation procedure. The Ti/SnOz-Ru02-Ir02 film was found to be the most efficient surface for the electrolytic breakdown of phenol. This film oxidized phenol at a potential of 200 mV vs Ag/AgC!. The activity of the catalytic systems was evaluated both on the basis of phenol removal efficiency as well as the kinetics of these reactions. Phenol removal efficiency was more than 90% for all the film surfaces prepared and the rate of the reaction followed first order kinetics. A pathway for the electrochemical degradation of phenol was derived using techniques such as HPLC to identify the breakdown products. These pathway products included the formation of benzoquinone and the further oxidation of benzoquinone to the carboxylic acids malic, malonic and oxalic. / AFRIKAANSE OPSOMMING: Die onderwerp van hierdie studie is die elektrochemiese oksidasie van fenol deur nuwe gemengde-oksied elektrodes. Fenol is 'n belangrike gifstof en besoedelingsmiddel in water. Daarbenewens kan fenolook met chloor reageer tydens waterbehandeling om sodoende karsinogeniese chlorofenole te vorm. Dit is dus belangrik dat metodes ondersoek word wat die konsentrasie van fenol in water verminder. Hierdie studie behels die bereiding en karakterisering van nuwe dinamiese stabiele anodes (DSA) vir die afbreek van fenol tot koolstofdioksied en ander minder gevaarlike verbindings. Hierdie nuwe anodes is berei vanaf die gemengde-okside van die edelmetale tin (Sn), ruthenium (Ru), tantalum (Ta) en iridium (Ir), met behulp van sol-gel tegnieke. Die finale stap in die bereiding behels kalsinering van die oksides by temperature van "n paar honderd grade Celsius. Hierdie nuwe elektrodes is later gebruik om die oksidasie van fenol te evalueer. Die gemengde-oksied dunlae/anodes IS d.m.v. die volgende analitiesetegnieke gekarakteriseer: termiese-gravimetriese analise (TGA), skandeerelektronmikroskopie (SEM), atoomkragmikroskopie (AFM), elementverstrooiingsenergie- X-straalanalise (EDX), X-straaldiffraksie (XRD), Rutherford terug-verstrooiingspektroskopie (RBS), partikel-geinduseerde X-straal emissie (PIXE), en elektrochemiese metings. 'n Verskeidenheid elektrodes van verskillende materiale is berei en hul potensiaal as oksidasie-kataliste vir organiese besoedelingsmiddels in afloopwater bepaal. Hierdie elektrodes het die volgende ingesluit: Ti/Sn02-Ru02-Ir02, Ti/Ta20s-Ir02 en Ti/RhOx-Ir02. Gedurende elektrolise is fenol elektrochemies afgebreek tot verskillende vlakke, afhangende van die tipe elektrode. Die oksidasietempo het egter nie alleen van die chemiese samestelling van die elektrode afgehang nie, maar ook van die morfologie van die okside, wat op hulle beurt van die voorbereidingsprosedure afgehang het. Daar is bevind dat die Ti/Sn02-Ru02-Ir02 elektrode die mees effektiewe oppervlakke vir die afbreek van fenol is. Hier het die oksidasie van fenol by 'n potensiaal van 200 mV plaasgevind. Die aktiwiteite van die katalitiese sisteme IS bepaal op grond van hulle fenolverwyderingsdoeltreffendheid. Die kinetika van die reaksies is ook bepaal. Al die elektrodes het >90% fenolverwyderingsdoeltreffendheid getoon en die reaksietempos was van die eerste-orde. Deur van analitiese tegnieke soos hoëdrukvloeistofchromatografie (HPLC) gebruik te maak is die afbreekprodukte van fenol geïdentifiseer en 'n skema vir die elektrochemiese afbreek van fenol uitgewerk. Daar is bevind dat bensokinoon gevorm het, wat later oksidasie ondergaan het om karboksielsure te vorm.

Thesis (PhD)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: Please see fulltext for abstract / AFRIKAANSE OPSOMMING: Sien asb volteks vir opsomming

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

No description available.

Various metal phthalocyanines have been used as dyes, catalysts, indicators, electrophotographic receptors and more recently as active elements in chemical sensors and photoconductive materials for solar energy conversion applications. Of the MPc's, VOPc, GaPc-Cl and TiOPc have shown promise for solar energy conversion devices. GaPc-Cl has also shown promise as a chemical sensor. Up to this point in time, the focus of Pc research in this group has been in the direction of characterizing the photoelectrochemical properties of these materials. Recently, solid state studies of TiOPc have been done to determine the electronic properties of a tetravalent metal Pc, such as conductivity and photoconductivity. Such solid state measurements are facilitated by the use of interdigitated microelectrode arrays which are coated with thin films of various Pc's.

<p>The direct methanol fuel cell or DMFC is emerging as a promising alternative energy source for many applications. Developed and developing countries, through research, are fast seeking a cheap and stable supply of energy for an ever-increasing number of energy-consuming portable devices. The research focus is to have DMFCs meeet this need at an affordable cost is problematic. There are means and ways of making this a reality as the DMFC is found to be complementary to secondary batteries when used as a trickle charger, full charger, or in some other hybrid fuel cell combination. The core functioning component is a catalyst containing MEA, where when pure platinum is used, carbon monoxide is the thermodynamic sink and poisons by preventing further reactions at catalytic sites decreasing the life span of the catalyst if the CO is not removed. Research has shown that the bi-functional mechanism of a platinum-ruthenium catalyst is best because methanol dehydrogenates best on platinumand water dehydrogenation is best facilitated on ruthenium. It is also evident that the addition of other metals to that of PtRu/C can make the catalyst more effective and effective and increase the life span even further. In addition to this, my research has attempted to reduce catalyst cost for DMFCs by developing a low-cost manufacturing technique for catalysts, identify potential non-noblel, less expensive metallic systems to form binary, ternary and quarternary catalysts.</p>

The Semiconductor Industry Association (SIA) has identified the integration of copper (Cu) with low-dielectric-constant (low-k) materials as a critical goal for future interconnect architectures. A fundamental understanding of the chemical interaction of Cu with various substrates, including diffusion barriers and adhesion promoters, is essential to achieve this goal. The objective of this research is to develop novel organic polymers as Cu/low-k interfacial layers and to investigate popular barrier candidates, such as clean and modified tantalum (Ta) substrates. Carbon-silicon (C-Si) polymeric films have been formed by electron beam bombardment or ultraviolet (UV) radiation of molecularly adsorbed vinyl silane precursors on metal substrates under ultra-high vacuum (UHV) conditions. Temperature programmed desorption (TPD) studies show that polymerization is via the vinyl groups, while Auger electron spectroscopy (AES) results show that the polymerized films have compositions similar to the precursors. Films derived from vinyltrimethyl silane (VTMS) are adherent and stable on Ta substrates until 1100 K. Diffusion of deposited Cu overlayers is not observed below 800 K, with dewetting occurred only above 400 K. Hexafluorobenzene moieties can also be incorporated into the growing film with good thermal stability. Studies on the Ta substrates demonstrate that even sub-monolayer coverages of oxygen or carbide on polycrystalline Ta significantly degrade the strength of Cu/Ta chemical interactions, and affect the kinetics of Cu diffusion into bulk Ta. On clean Ta, monolayer coverages of Cu will de-wet only above 600 K. A partial monolayer of adsorbed oxygen (3L O2 at 300 K) results in a lowering of the de-wetting temperature to 500 K, while saturation oxygen coverage (10 L O2, 300 K) results in de-wetting at 300 K. Carbide formation also lowers the de-wetting temperature to 300 K. Diffusion of Cu into the Ta substrate at 1100 K occurs only after a 5-minute induction period. This induction period increases to 10 min for partially oxidized Ta, 15 min for carbidic Ta and 20 min for fully oxidized Ta.