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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

The microstructure and deformation of two-phase titanium alloys

Shelton, C. G. January 1984 (has links)
No description available.
2

A review of legislative and safety requirements for running the titanium-production pilot plant at Anglo Research

Yumba, Nomsa 07 May 2009 (has links)
Anglo Research is due to commission a novel pilot plant for the manufacturing of titanium metal from ilmenite ore. The process requires the use of hydrofluoric acid, a very toxic chemical, in large volumes. A health and environmental study and legislative requirements of the process were thus required before commencing with the plant design. Metallurgical processes have resulted in some degree of environmental impact, from water, air and soil pollution. A prominent example is acid mine drainage, which pollutes ground water. It is therefore important to ensure that proper steps are taken in minimising or mitigating negative environmental effects when developing new process routes. Hydrofluoric acid (HF) is classified as extremely toxic. This acid is very aggressive physiologically because of the fluoride ion which penetrates the skin and robs the bone tissue of calcium. Because of the hazardous nature of HF, the following legislations were reviewed: o Hazardous Substances Act 15 of 1973 o Occupational Health & Safety Act of 1993 o National Road Traffic Act 93 of 1996: Chapter VIII o National Environmental Management Act 107 of 1998 o Environmental Conservation Act 73 of 1989 HF has been used in many other industrial applications including manufacturing of fluorocarbons and other chemicals, aluminium manufacturing, petroleum alkylation and uranium purification. Steps should be taken to minimise exposure to hydrofluoric acid in areas where there is a likelihood of worker exposure. Control measures include, but are not limited to, elimination/substitution and process modification, isolation, engineering controls, administrative controls, and use of personal protective equipment and hazard communication. HF is corrosive to most metals and materials of construction suitable for HF include fluoropolymers and other metal alloys such as nickel based alloy 400. Every design aspect of the plant must be done in a way that minimises the environmental and worker exposure to HF. Once safety of the plant design has been extensively reviewed, the pilot plant can then be built. The success of this campaign will be based not only on the achievement of process and product specification, but also on whether it was run without any incidents.
3

Measurement of magnetic susceptibility in titanium minerals processing /

Cavanough, Gary. January 2003 (has links) (PDF)
Thesis (Ph.D.) - University of Queensland, 2004. / Includes bibliography.
4

Phase transformations in titanium-rich alloys with iron and nickel

Polonis, Douglas Hugh January 1955 (has links)
Phase transformations have been studied in titanium-rich binary alloys with iron and nickel. Particular attention has been given to the formation and decomposition of metastable phases in powder specimens. All alloys were prepared by a levitation melting technique and precautions were taken throughout the experimental work to minimize contamination. In the Ti=Fe system martensitic α'is produced when powder specimens containing up to 12% iron are quenched-from 1000⁰C. The hardness of hypoeutectoid specimens increases with iron content to a maximum at 12% Fe The eutectoid temperature for the system has been reassessed at 625 ± 10⁰C. During tempering the decomposition rates of retained β phase are slow but the appearance of FeTi is accompanied by an increase in slope of the β /log time curve. The hardness of tempered alloys increases as the FeTi content increases. Contrary to the results of other Investigators Ti₂Fe has been found to exist in sensibly oxygen-free -alloys. This phase forms at 1000⁰C in crushed powder specimens but decomposes below the euteetoid temperature. In the Ti-Ni system the .constitution of quenched alloys is found to depend on both composition and cooling rate from the β range. An 'inverse stabilization' of the β phase has been observed and the 100% β phase exhibits two types of substructures which have been attributed to polygonization and stacking faults. The hardness of quenched alloys is higher for higher nickel contents and for faster cooling rates. Orientation relationships were observed between β and α¹ and a shear mechanism suggested by Burgers for Zr is proposed for this system. Decomposition studies have shown that α¹ breaks down by a growth-controlled process similar to that described by Johnson and Mehl. An activation energy of 84000 cal/mole has been determined and a model has been proposed which involves planar interfaces of Ti₂Ni advancing into α regions to produce a Widmanstatten-type microstructure. The self-diffusion of titanium is believed to be the growth -controlling factor. Hardness values decrease with longer tempering times and higher tempering temperature. Retained β decomposes on tempering by a two stage process: β →α" →α + Ti₂Ni X-ray diffraction data indicate that α" has the same crystal structure as α'. The β-α" reaction appears to be a diffusion process although reaction curves are similar to those observed for isothermal martensite formation in steels. During the first stage of the reaction (β-α") the hardnesses and x-ray diffraction line breadths initially show a sharp increase, probably due to coherence between β and α¹¹ The reaction α" →α + Ti₂Ni proceeds In a similar way to the decomposition of α ; but with a shorter induction period for Ti2Ni formation. Further, the. activation energy for the α" →α + Ti₂Ni growth process (71000 cal/mole) is lower than that for α' decomposition. These observations suggest that Ni-rich regions exist in the α" phase and accelerate the nucleation and growth processes. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate
5

Effect of substrate bias and temperature on the structure of ion-plated titanium

Yoon, Hyungjin 05 1900 (has links)
No description available.
6

The thermal regime during electron beam hearth remelting

Tripp, David William January 1987 (has links)
Electron beam hearth remelting is extensively used in refining of superalloys, titanium alloys and the recycling of these materials. The removal of impurities and exhogenous particles during the hearth melting operation depends primarily on the time at temperature relationship developed within a pool of molten metal. In the past hearth melters have acted largely on empirical evidence to specify such parameters as melt rates, power levels and skull sizes. This work describes a mathematical model which could be used to predict certain parameters (such as pool volume or alloy element evaporation rates) when given skull geometry, power input and melt rate. A three dimensional steady state heat transfer model of both the skull and water cooled copper mould during electron beam hearth remelting has been developed. The model has been used to investigate the effects of surface temperature, liquid motion, power input, skull geometry, presence of the hearth mould and melt rate on parameters such as pool volume during skull melting. In general the choice of any combination of operating parameters depends on a balance between the refining capacity of the process (i.e. liquid volume) and the loss of alloy elements by evaporation. In the case of melting pure materials (e.g. CP titanium) the balance is between refining capacity and efficient energy use. It was found that forced convection is significantly more effective in increasing the volume of the liquid pool than any other single parameter. Increasing the power input to the skull, increasing the skull width and removing the water cooled copper mould from around the skull also increase the pool volume. The evaporation rates of alloy elements within the skull were most effected by changes in the power distribution and the degree of liquid motion. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate
7

Relationship between flow stress recovery and dislocation structure in polycrystalline alpha-titanium

Pawar, P. Gnanandranath January 1969 (has links)
Cell structure was observed in polycrystalline alpha-titanium deformed up to 10% true strain at room temperature. These cells appeared to be slightly elongated rather than equiaxed. The cell boundaries were identified to be the {101̄0} type planes. Flow stress recovery of alpha titanium at 500 and 550ºC proceeded in two stages: (1) an initial rapid recovery during the first 6 hours and (2) a leveling off after 6 hours. Dislocation structure was studied by using transmission electron microscopy. During the first stage of recovery, significant rearrangement of dislocations took place. At this stage fairly regular dislocation loops appeared to surround the subgrains. The segments of the dislocation loop were found to lie along <101̄0> type directions on the (0001) plane, and [0001] type directions on the {112̄0} planes. In the second stage, continued rearrangement of dislocations formed low angle boundaries. The segments of dislocations lying along the <101̄0> type direction reacted to form networks on the basal plane, and those lying on the {112̄0} planes continued to remain aligned along [0001] direction. It was postulated that some of the subgrains formed as a result of rearrangement and interaction of dislocations developed twist networks on the (0001) planes and tilt boundaries on the {112̄0} type planes. An inverse relationship between the strength contributed by subgrain structure and the subboundary spacing predicted an increase in the subgrain size at the higher recovery temperature. The measured and the predicted value were in reasonably good agreement. / Master of Science
8

South African titanium : techno-economic evaluation of the alternatives to the Kroll process

Van Tonder, Willem 03 1900 (has links)
Thesis (MScEng (Industrial Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: the potential to serve as a strategic economic driver for the country if a local processing and production industry could be successfully established. According to the US Geological Survey, conducted in January 2009, South Africa has approximately 14% of the world’s reserves in ilmenite and rutile, the two most important titanium-containing minerals, but no metal producing abilities. The only role players, Exxaro and Richards Bay Minerals, have smelting operations and produce an enriched titania slag, but all the slag is exported. The processing steps between titanium-containing minerals and the metal represent a significant portion of the total production costs and this study is chiefly concerned with recommending a more cost-effective alternative for these steps. The existing industrial process is archaic, cost and energy intensive, batch operated with unfavourable economics. A large number of internationally research initiatives are actively trying to address the problem of high production costs by searching for and developing alternative, more costeffective, processes. It was the purpose of this study to provide the decision making authorities with a ranking and evaluation of these alternatives to produce titanium metal. A 2-Phase Filtering System, based on both qualitative and quantitative techniques, was designed to assess, evaluate and formulate a final ranking. This evaluation was followed by a detailed sensitivity analysis of both local and global parameters. A total of 26 process alternatives were selected to be evaluated in this techno-economic evaluation. The complete ranking is given in Table 8.8, and the four leading process alternatives, based on this evaluation and the findings of the sensitivity analysis, are as follows: 1. CardQIT: The Canadian affiliate of Rio Tinto, QIT, developed a high-temperature titanium extraction process based on an electrolysis reaction, where molten titania slag is the cathode. 2. ArmITP: The Armstrong process is a continuous process that produces titanium in a very similar fashion as with the Hunter process, by the reduction of TiCl4 with sodium. TiCl4 vapour is injected into a stream of molten sodium to form titanium powder as the reaction product. 3. Kroll: This process was developed in the 1950s and the reduction step remains very much similar to the original process used by the USBM (United States Bureau of Mines). Two criteria played a big part in the unexpected high ranking of the Kroll process, and that were academic coverage, with almost 60 years of research, and the commercial readiness of an industrial process. 4. FFC: Solid pre-forms are pressed and sintered from pigment grade TiO2, to be directly electrochemically reduced to metallic titanium in a molten electrolyte of CaCl2. For future work, it is recommended that an additional filtering stage, a detailed profitability analysis, be added to the decision model. The top 4 alternatives, as mentioned above, should be used to estimate the cost-reduction potential as well as the capital investment and production costs based on process, industrial and economic engineering fundamentals. / AFRIKAANSE OPSOMMING: Titaan is deur die Suid Afrikaanse regering geidentifiseer as 'n mineraalhulpbron met die potensiaal om te dien as 'n strategiese ekonomiese drywer, indien 'n plaaslike verwerkingen verwaardingsbedryf suksesvol op die been gebring kan word. Volgens die US Geological Survey, wat in Januarie 2009 gedoen is, het Suid Afrika ongeveer 14% van die wêreld se reserwes in ilmeniet en rutiel, die twee belangrikste titaanhoudende minerale. Suid Afrika het egter geen metaal-vervaardigingsaanlegte nie. Die enigste twee rolspelers, Exxaro en Richards Bay Minerals, het smelteraanlegte en vervaardig 'n verrykte titaandioksiedkonsentraat, wat alles uitgevoer word. Die waardetoevoegingsaktiwiteite tussen die titaanhoudende minerale en die metaal verteenwoordig ‘n groot gedeelte van die produksiekoste van titaanmetaal en hierdie studie is hoofsaaklik daarmee gemoeid om ‘n meer koste-effektiewe aanbeveling te maak, m.b.t. dié stappe. Die bestaande bedryfsproses is argaïes, koste- en energieintensief, en is ontwerp as ‘n lot proses met ongunstige ekonomiese eienskappe. 'n Groot aantal internasionale navorsingsinstansies is aktief besig om oplossings te soek vir die probleem van hoë verwerking- en vervaardigingkostes, deur alternatiewe opsies te ondersoek en te ontwikkel. Die doel van hierdie studie was om vir die besluitnemingsgesag 'n rangorde en vergelyking van die alternatiewe opsies om titaniummetaal te vervaardig, te gee. 'n Tweeledige Filter Stelsel, gebaseer op beide kwalitatiewe- en kwantitatiewe tegnieke, is ontwerp om die rangorde te vorm, te bereken en te formuleer. 'n Sensitiwiteitsanalise is gedoen om die besluitnemingsparameters se invloed op die finale rangorde en uitslag te toets. 'n Totaal van 26 prosesse is geidentifiseer en gekies om aan hierdie tegno-ekonomiese evaluasie, te onderwerp. Die volledige rangorde word in Table 8.8 getoon, en die vier leidende prosesalternatiewe, gebaseer op die uitkomste van dié evaluering en die bevindinge van die sensitiwiteitsanaliese, is as volg: 1. CardQIT: Die Kanadese filiaal van Rio Tinto, QIT, het ‘n hoë-temperatuur titaan ontginningsproses ontwikkel, gebaseer op ‘n elektrolitiese reaksie, waarin gesmelte titaandioksiedkonsentraat die katode vorm. 2. ArmITP: Die Armstrong proses is ‘n kontinue opsie wat titaan produseer op ‘n baie soortgelyke wyse as die Hunter proses, deur die reduksie van TiCl4 met natrium, Na. TiCl4 damp word in ‘n gesmelte stroom natrium ingespuit om titaanmetaalpoeier te vorm as die reaksie produk. 3. Kroll: Die proses is ontwikkel in die 1950s en die reduksie stap wat vandag gebruik word is steeds soortgelyk soos die oorspronklike proses, aan gebruik deur die USBM. Veral twee besluitnemingskriteria het ‘n belangrike rol gespeel om tot die onverwagte hoë plasing van die Kroll proses te lei. Eerstens, akademiese dekking en die feit dat omtrent 60 jaar se navorsing in hierdie opsie ingepomp is en tweedens, die kommersiële gereedheid van hierdie prosesalternatief as ‘n volskaalse bedryfsproses. 4. FFC: Gegoe vorms van pigmentgehalte TiO2, word gepers en gesinter om die katodes te vorm wat dan direk elektrochemies gereduseer word tot titaanmetaal in ‘n gesmelte bad van CaCl2, as die elektroliet. Vir toekomstige werk word aanbeveel dat ‘n addisionele filtervlak, ‘n winsgewendheidsanalise, by die besluitnemingsmodel gevoeg word. Die vier prosesalternatiewe, soos hierbo genoem, kan gebruik word en vir elk moet die kostebesparingspotensiaal, die kapitaal insetkoste en die produksiekostes bereken word. Hierdie berekeninge kan gebaseer word op proses-, bedryfs- en ekonomiese ingenieurswese beginsels.

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