Faculty of Engineering, Built Environment and Information Technology
School of Engineering
Department of Materials Science and Metallurgical Engineering
Selected Highlights from Research Findings
In casting titanium-bearing stainless steel, some titanium oxide ends up in the molten oxide-based flux which is used as lubricant during continuous casting; the concern is that this titanium pick-up is detrimental. Our measurements have shown that, if anything, titanium oxide is a slag thinner, lowering the viscosity. However, where titanium pick-up is associated with a loss of silica from the mould flux (through chemical reaction), solid perovskite can precipitate, with an associated sharp (and detrimental) increase in apparent viscosity.
Electrochemical sensors at high temperature. Electrochemical sensors are used to measure oxygen activities at high temperatures; we found the unexpected result that these sensitive measurements are significantly affected by stray currents between the heating elements of the laboratory furnace — at temperatures in excess of 1500°C, the alumina working tube and the working gases are sufficiently conductive to allow current to leak to the electrodes.
Flotation. The newly-established research group in minerals processing focuses for now on flotation of sulphide minerals, and the use of trithiocarbonate collectors. Previous work by others indicated that there is a synergistic effect between this collector and the more commonly used xanthate (dithiocarbonate). We found such an effect for platinum-bearing ores; the current work aims to understand this effect!
Zinc is becoming a strong theme in the hydrometallurgical work. In the zinc extraction route, iron which is co-leached is precipitated by controlling temperature, acidity and seeding. Recent work showed that silica — which apparently also leaches in the hot sulphuric acid solutions — also precipitates at this stage. This may be beneficial (contributing to nucleation of the iron-bearing precipitates), or very detrimental if a gel should form.
Gold and platinum alloys. Gold and platinum form alloys which are homogeneous at high temperatures, but which separate out into gold-rich and platinum-rich alloys at lower temperatures. This much is well-known from the phase diagram of this system. The unexpected kinetic effect is that porosity forms in these alloys when they are then reheated into the single-phase region (through a Kirkendall effect). This is certainly interesting, and quite possibly important in the use of these alloys in electrochemical treatment of organic contaminants in waste water.
Wanneer titaanhoudende roesvrystale gegiet word, beland 'n bietjie titaanoksied in die oksiedbasis vloeimiddel (wat as smeermiddel tydens stringgieting dien); dit mag tot die nadeel van smering wees. In der waarheid toon ons metings dat titaanoksied die gietslak se viskositeit verlaag — maar dat vastestof (perovskiet) in die vloeistof kan presipiteer wanneer silika deur chemiese reaksie uit die gietslak verwyder word, tegelyk met die titaanopname. Hierdie vastestof geen 'n skerp en nadelige toename in die skynbare viskositeit.
Elektrochemiese sensors word gebruik om suurstofaktiwiteite by hoë temperature te meet; ons het die onverwagte resultaat gevind dat hierdie sensitiewe metings deur lekstrome tussen die verhittingselemente van die laboratoriumoond beïnvloed word — by temperature bokant 1500°C is die alumina-werksbuis en die werksgasse voldoende geleidend sodat stroom na die elektrodes kan lek.
Die nuutgevestigde navorsingsgroep in mineraalprosessering fokus tans op flottasie van sulfiedminerale, en die gebruik van tritiokarbonaat as versamelaar. Vorige werk deur ander het aangedui dat daar moontlik sinergie tussen hierdie versamelaar en die meer algemeen gebruikte xanthaat (ditiokarbonaat) ontstaan. Ons het hierdie effek vir platinumdraende erts getoon — die taak is nou om dit te verstaan!
Sink word 'n sterk tema in die hidrometallurgiese werk. In die ekstraksieroete van sink word yster (wat noodwendig saam met die sink loog) uitgepresipiteer deur die temperatuur, suurgehalte en toevoeging van saadkristalle te beheer. Onlangse werk het getoon dat silika — wat duidelik ook in die warm swaelsuuroplossings loog — ook in hierdie stadium presipiteer. Dit kan 'n gunstige rol speel (deur kernvorming van die ysterdraende presipitate), of baie nadelig indien 'n jel sou vorm.
Goud en platinum vorm homogene legerings by hoë temperature, wat weer by laer temperature in goud-ryk en platinum-ryk fases skei — 'n welbekende verskynsel wat in hierdie sisteem se fasediagram sigbaar is. Die onverwagte kinetiese verskynsel is dat porositeit in hierdie legering vorm wanneer hulle weer na die enkelfasegebied herverhit word (deur 'n Kirkendall-verskynsel). Beslis interessant, en heel moontlik belangrik in die gebruik van hierdie legerings vir die elektrochemiese behandeling van organiese kontaminasie in afvalwater.
Contact person: Prof PC Pistorius.
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