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dc.contributor.advisorErasmus, J. J. C.
dc.contributor.advisorSwart, H. C.
dc.contributor.advisorTerblans, J. J.
dc.contributor.authorJonker, Arnoldus Jacobus
dc.date.accessioned2018-07-26T11:10:16Z
dc.date.available2018-07-26T11:10:16Z
dc.date.issued2005-03
dc.identifier.urihttp://hdl.handle.net/11660/8994
dc.description.abstractEnglish: The valve metal characteristic of Ti provides, together with a number of other physical properties, the appropriate anode material for the production of battery grade electrolytic MnO2 (EMD). However, electro-oxidation of Mn(II) to Mn(IV) in an acidic medium creates conditions for anodic oxidation of the surface of a Ti metal electrode. The ohmic potential drop in an interelectrode gap, ∆VΩ, is inter alia a function of the extent of anodic oxidation on an electrode’s surface. The magnitude of electrical currents in large-scale electrolysis cells compels attention to ∆VΩ since it equates to power consumption that has large economic incentives. Electrocatalytic transition metal oxide electrodes, termed dimensionally stable anodes (DSA’s), not only provide high electrical conductivity, but it also has the added advantage of lowering electrode polarization via catalytic considerations. DSA’s have numerous other applications, but it is last mentioned properties that draw attention to these electrodes as substrates for MnO2 electroformation. The basic construction of a DSA is a mixture of a transition metal oxide (more than often a Pt group metal) and a valve metal oxide that adheres to a valve metal substrate. The primary objective of preparing and evaluating DSA’s using different precursor solutions in a thermal decomposition technique is combined with an electrosynthesis method to grow RuOx.nH2O films. Interpretation of X-ray diffraction (XRD) measurements demonstrated the ability of a higher calcination temperature to form larger quantities of RuO2 on Ti. It was also conclusive that an increase in the Ru metal concentration in a precursor solution results in a measurable increase in intensity of the (1 1 0) reflection from RuO2. Electrolysis experiments in conjunction with Auger electron spectroscopy (AES) depth profiling and AES surface spectra vividly illustrated the dominance of the surface concentration of Ru over the total depth distribution of Ru in lowering electrode polarization in the current density range between 155A.m-2 and 170A.m-2. The parameter referred to as polarization slope were derived from electrolysis measurements and a value of 1.63 ± 0.03mV/A.m-2 places the DSA prepared with a 0.8wt/wt% Ru precursor solution at the top of the rankings in terms of preparation cost and electrocatalytic properties. Repetitive potential cycling between –200mV and 1000mV vs. Ag/AgCl in 5mM RuCl3.3H2O was used to electroform RuOx.nH2O films. Cyclic voltammetry yielded results that indicate that the growth of RuOx.nH2O is inextricably associated with a complex redox process, while it was furthermore observed that the peak current density of the cyclic voltammogram increases with cycle number. This suggests another complicating factor that most likely results from the electrocatalytic property of the growing oxide film. XRD conclusively showed that subsequent annealing results in a phase transformation of the hydrous Ru oxide that affects its behaviour when used as a DSA for MnO2 electroplating. AES depth profiling was used to arrive at the conclusion that an unannealed RuOx.nH2O film is most probably porous, but electrochemistry showed that it lacks stability under anodic load. With a polarization slope of 1.590 ± 0.006mV/A.m-2, an annealed Ti/RuOx.nH2O electrode (30min at 600°C) is the most advantageous in terms of MnO2 electroplating of all RuOx.nH2O films studied. Electrode polarization measurements on Ti/TiC electrodes as well as commercial Ti-Mn and Ti-Pb electrodes showed promising results, but none of these materials are in contention when compared with said DSA’s. The study was complemented with an investigation into the effect of an acidic MnSO4 solution on Ti metal. The reactivity of Ti towards atmospheric O2 gives stability to the metal in the form of a superficial oxide film. Dissolution of this passive film can occur under appropriate conditions. Single electrode potential measurements were employed to observe metal activation that is accompanied by H2 evolution at temperatures above 52°C. An activation potential of –0.67 ± 0.01V vs. Ag/AgCl has proven to remain constant at room temperature after activation was induced via temperature perturbation to 86 ± 2°C. A hypothesis is presented that describes spontaneous H2 evolution as a supporting reduction half reaction to the reduction of TiO2. Electroplating of MnO2 onto Ti substrates that were subjected to spontaneous H2 evolution shows a linear increase in electrode polarization (at 100.5A.m-2) as a function of exposure time with a slope of 0.19 ± 0.02V.hr-1 vs. Ag/AgCl. This attests existing theories that the change in free energy for the formation of TiO2 from TiH2 is more negative than for oxidation from Ti metal or that unrecombined hydrogen is present on the Ti surface at the onset of electrolysis.en_ZA
dc.description.abstractTesame met ‘n aantal ander fisiese eienskappe voorsien die “valve” metaal eienskap van Ti die geskikte anode materiaal vir die produksie van battery-graad elektrolitiese MnO2 (EMD). Tydens oksidasie van Mn(II) na Mn(IV) in ‘n suur medium word kondisies egter geskep wat anodiese oksidasie van die oppervlak van ‘n Ti metaal elektrode bevorder. Die ohmiese potensiaal verskil oor ‘n inter-elektrode gaping, ∆VΩ, is onder andere ‘n funksie van die mate van anodiese oksidasie op ‘n elektrode-oppervlak. Die grootte van elektriese stroom in kommersiële elektrolitiese selle veroorsaak dat aandag gevestig word op ∆VΩ aangesien die produk van laasgenoemde twee veranderlikes gelykstaande is aan elektriese drywing wat groot ekonomiese implikasies inhou. Elektrokatalitiese oorgangsmetaaloksied elektrodes wat bekend staan as “dimensionally stable anodes” (DSA’s) voorsien hoë elektriese geleidingsvermoë en is ook instaat om elektrode-polarisasie te verlaag deur middel van katalitiese eienskappe. DSA’s het verskeie toepassings, maar dit is die katalitiese- en geleidings-eienskappe wat dit van belang maak vir die toepassing as anode-substrate vir MnO2 elektroplatering. Die basiese konstruksie van ‘n DSA is ‘n mengsel van ‘n oorgangsmetaaloksied (gewoonlik ‘n Pt-groep metaal) en ‘n “valve” metaaloksied in die vaste toestand op ‘n “valve” metaal substraat. Die hoof doelwit van voorbereiding en evaluering van DSA’s met behulp van verskillende voorloper oplossings in ‘n termiese ontbindings tegniek is gekombineer met ‘n elektrosintetiese roete om RuOx.nH2O films te groei. Die moontlikheid om groter hoeveelhede RuO2 met die substraat oppervlak te kombineer by hoër uitgloei temperature is bevestig d.m.v. X-straal diffraksie (XRD) metings. Daar is verder bewys dat ‘n toename in Ru konsentrasie in die voorloper oplossing veroorsaak dat die (1 1 0) refleksie van RuO2 beduidend toeneem. Elektroliese eksperimente tesame met Auger elektronspektroskopie (AES) diepteprofiele en oppervlakspektra het duidelik aangetoon dat die oppervlakkonsentrasie van Ru baie belangriker is vir die verlaging van elektrode polarisasie tussen stroomdigthede van 155A.m-2 en 170A.m-2, eerder as die totale diepte verspreiding van Ru. ‘n Veranderlike wat bekend staan as “polarisasie helling” is afgelei uit elektroliese resultate en ‘n waarde van 1.63 ± 0.03mV/A.m-2 vir die DSA wat berei is met ‘n 0.8massa/massa% Ru voorloper oplossing maak hierdie elektrode aanloklik in terme van voorbereidingskoste en elektrokatalitiese vermoë. RuOx.nH2O films is gegroei deur middel van herhaaldelike potensiaal skanderings tussen –200mV en 1000mV vs. Ag/AgCl in 5mM RuCl3.3H2O. Sikliese voltammetrie het resultate gelewer wat aandui dat die groeiproses van RuOx.nH2O geassosieer word met ‘n komplekse redoksproses. Daar is ook gevind dat die piek stroomdigtheid van die sikliese voltammogram toeneem met siklus nommer. Dit dui op ‘n verdere komplekserende faktor wat heel waarskynlik die gevolg is van die elektrokatalitiese eienskap van die groeiende oksiedfilm. XRD het oortuigende bewys gelewer dat ‘n fase-transformasie van die gegroeide oksiedfilm plaasvind tydens hittebehandeling, wat verder ook die DSA se gedrag beïnvloed tydens MnO2 elektroplatering. AES diepteprofiele is aangewend om aan te toon dat ‘n onverhitte RuOx.nH2O film heel waarskynlik poreus is, maar elektrochemie het aangedui dat sodanige film onstabiel is wanneer ‘n anodiese spanning daaroor aangewend word. ‘n Uitgegloeide Ti/RuOx.nH2O elektrode (30min by 600°C) met ‘n polarisasie helling van 1.590 ± 0.006mV/A.m-2 hou die meeste potensiaal in van al die bestudeerde RuOx.nH2O films, spesifiek ten opsigte van die toepassing daarvan vir elektroplatering van MnO2. Gemete polarisasie hellings vir Ti/TiC elektrodes sowel as kommersiële Ti-Mn en Ti-Pb elektrodes het belowende resultate getoon, maar kan nie in hierdie toepassing met DSA’s kompeteer nie. Die studie is verder uitgebrei met ‘n ondersoek aangaande die effek van ‘n suur MnSO4 oplossing op Ti metaal. Die reaktiwiteit van Ti t.o.v. atmosferiese O2 maak die metaal stabiel via die vorming van ‘n oksied film op die metaal-oppervlak. Laasgenoemde film kan egter oplos onder geskikte omstandighede. Enkel-elektrode potensiaal metings is aangewend om metaal aktivering waar te neem soos vergesel word deur H2 ontwikkeling by temperature bokant 52°C. Daar is gevind dat ‘n aktiveringspotensiaal van –0.67 ± 0.01V vs. Ag/AgCl konstant bly by kamertemperatuur nadat aktivering geïnduseer is via temperatuur versteuring tot 86 ± 2°C. ‘n Teorie is voorgestel wat H2 ontwikkeling beskryf as a sekondêre reduksie halfreaksie wat kompeteer met die reduksie van TiO2. MnO2 elektroplatering op Ti elektrodes wat vooraf blootgestel is aan H2 ontwikkeling toon ‘n lineêre elektrode-polarisasie toename van 0.19 ± 0.02V.hr-1 vs. Ag/AgCl teenoor tyd by 100.5A.m-2. Hierdie waarneming ondersteun bestaande teorië dat die vrye energie verandering vir vorming van TiO2 vanaf TiH2 meer negatief is as vanaf Ti metaal of dat geadsorbeerde H-radikale Ti metaal teenwoordig is wat na H+ geoksideer word sodra ‘n anodiese potensiaal aangewend word.en_ZA
dc.description.sponsorshipDelta E.M.D. (Pty) Ltd.en_ZA
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectDimensionally stable anodesen_ZA
dc.subjectElectrolytic manganese dioxideen_ZA
dc.subjectElectrocatalystsen_ZA
dc.subjectTitaniumen_ZA
dc.subjectRutheniumen_ZA
dc.subjectElectrolysisen_ZA
dc.subjectVoltammetryen_ZA
dc.subjectAuger electron spectroscopyen_ZA
dc.subjectX-ray diffractionen_ZA
dc.subjectAnodesen_ZA
dc.subjectSurface chemistryen_ZA
dc.subjectElectroplatingen_ZA
dc.subjectMetals -- Finishingen_ZA
dc.subjectDissertation (M.Sc. (Physics))--University of the Free State, 2005en_ZA
dc.titleSurface modified tatanium anodes for electroplating of manganese dioxideen_ZA
dc.typeDissertationen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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