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Thesis (B.Sc.(Hons))--University of Adelaide, Department of Economic Geology,1976.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 49-54). Also available via the Internet.

Thesis (Ph. D.)--University of Adelaide, 1982. / Errata sheet inserted. Includes bibliographical references (leaves 215-226).

Melt inclusions record valuable information about pre-eruptive melt volatile concentrations. However, a vapor bubble commonly forms in inclusions after trapping, and this decreases the dissolved CO2 concentration in the trapped melt. To quantify CO2 loss to bubbles, Raman spectroscopic analysis was used to determine the densities of CO2 vapor in the bubbles. The samples analyzed in this study are from two Cascade cinder cones near Mt. Lassen and two Mexican cinder cones (Jorullo, Paricutin). Using analyses of dissolved CO2 and H2O in the glass in the inclusions, the measured CO2 vapor densities were used to reconstruct the original dissolved CO2 contents of the melt inclusions at the time of trapping. The Raman-restored CO2 values are similar to restored CO2 values calculated using a model of cooling and olivine crystallization in the trapped melts. This thesis includes unpublished co-authored material.

The Abrahamskraal kimberlite pipe (group I) occurs approximately 5 km to the south-west of the geophysically defined margin of the Kaapvaal craton in the central Cape Province, and contains a variety of crustal and mantle xenoliths. This study focusses on xenoliths of deep-seated origin (mantle and lower-crustal), and in particular on garnet-orthopyroxene bearing assemblages which are amenable to thermobarometric techniques. Four major types of deep-seated xenolith have been identified, i.e. peridotites, dunites , eclogites, and garnet pyroxenites. The petrographic features and mineral compositions of these xenoliths are described . Pressures and temperatures of equilibration have been calculated primarily using the garnet-orthopyroxene thermometer of Harley (1984), and the Al-in-enstatite barometer of Nickel and Green (1985). The peridotites are coarse-textured (Harte, 1977), magnesium -rich rocks, and are typical examples of the common type I peridotites which generally dominate mantle xenolith suites in kimberlites. Garnet peridotite xenoliths define a geotherm which lies along a typical theoretical conductive geothermal gradient for shield areas (Pollack and Chapman, 1977), and which extends to a maximum pressure of 41 kb (~130 km). Comparison of the Abrahamskraal geotherm with that constructed for the northern Lesotho xenolith suite (calculated using the same thermobarometer couple), suggests that the lithosphere at the Namaqua /Kaapvaal boundary is not significantly thinner or hotter than that underlying the craton. Modelling of the craton boundary under the constraints provided by the Abrahamskraal geotherm, and by the distribution of diamond-bearing kimberlites in southern Africa, indicates that the Abrahamskraal kimberlite has sampled relatively thick, cool , Namaqua lithosphere. It is suggested that, in terms of diamond distribution, the age and magmatic history of the Namaqua lithosphere is of greater significance than its thickness. Two varieties of dunite occur at Abrahamskraal. Coarse-textured dunites with Mg-rich olivine compositions similar to those of the peridotitic olivines, probably originated by similar (but perhaps more extreme) processes to those which formed the peridotites. A finer-grained and relatively Fe-rich variety of dunite may represent ultramafic cumulates formed by fractionation of basic or ultrabasic magmas within the mantle. Two varieties of eclogite have been distinguished. Coarse-grained eclogites which yield relatively high temperature estimates, are believed to have originated from depths similar to those determined for the garnet peridotites, i.e. from the lower lithosphere. A distinctly finer grained variety of eclogite, yields significantly lower temperatures which may be based on frozen-in equilibria. A maximum depth of approximately 87 km (~ 27 kb) has been estimated for these xenoliths, but they may have originated from significantly shallower (possibly lower-crustal) levels. The garnet pyroxenite xenoliths are generally orthopyroxene-rich rocks which contain varying amounts of garnet (8 to 33 %) and clinopyroxene (0 to 64 %). Textural features indicate that the garnet and possibly some of the clinopyroxene has exsolved from an originally A l -rich orthopyroxene. The rocks are significantly more Fe-rich than the peridotite xenoliths, and their constituent minerals show a wide range of Mg/Mg+Fe ratios. The pressure-temperature array defined by the garnet pyroxenites is approximately isothermal, and spans a depth range from approximately 30 to 95 km. It deviates strongly (to higher temperatures) from the ambient geothermal gradient at the time of kimberlite emplacement, as inferred from the garnet peridotite xenoliths. The pressures and temperatures calculated for the garnet pyroxenites are based on mineral equilibria which are believed to have been frozen-in during cooling from an intial high­temperature (probably molten) state. Qualitative modelling of possible cooling paths in pressure-temperature-composition space, indicates that the apparent depth range displayed by the garnet pyroxenites, approximates the true depth range over which these rocks were emplaced. However, the apparent pressures calculated from core compositions are significantly lower than the true pressures at which the original rocks formed . The garnet pyroxenite xenoliths appear to represent a major, possibly Namaqua ­ age (~1000-1400 Ma), magmatic event involving the emplacement of large amounts of mafic magma over a significant depth range in the shallow upper mantle

The effect of increasing hot deformation on inclusion parameters such as area fraction (AF), the average inclusion length (Co), the inter-inclusion distance (D), the aspect ratio (FF) and the density of distributions (N);bas been quantitatively analysed by use of Quantimet 720, an image analysing computer and direct microstructural measurements. Two types of X-70 pipeline steel, one a semi-killed conventional (CON) steel, the other a fully killed and calcium treated for inclusion shape control (CAT) steel were examined in this research. Four stages of hot reduction of the CON steel viz. S2 (38% reduced), S3 (70% reduced), S4 (88% reduced) and S6 (97% reduced) and two stages of the CAT steel viz. CI (63% reduced) and C2 (95% reduced) were used in the investigation. The effect of inclusion parameters on the yield strength, total ductility and elastic and elastic-plastic fracture toughness of these materials were investigated to establish the role of inclusions in the ductile, ductile-brittle transition and brittle fracture processes. The elastic and elastic-plastic fracture toughness of the specimens were measured by KJC testing as per ASTM standard E-399-78a method and unloading compliance J-integral technique as per ASTM standard respectively. It was observed that the semi-killed CON steel containing elongated inclusions shows anisotropy in elastic-plastic fracture toughness; whereas the CAT steels with globular inclusions exhibited isotropic elastic-plastic fracture toughness. The inclusion parameters shape, size and distribution do not affect the yield strength of the X-70 steel. The inclusion parameters markedly affect the elastic-plastic fracture toughness properties of the X-70 CON steel, particularly in the ductile and transition temperature region where failure occurs by the mechanism of microvoid coalescence. The effect of inclusions on the elastic fracture toughness in the brittle temperature region, where fracture occurs by cleavage mechanism, is insignificant. The most significent inclusion parameters which affect the elastic-plastic fracture toughness in the ductile fracture regime are the area fraction AF and the inter-inclusion spacing (D). The elastic-plastic fracture toughness of the CON and CAT X-70 pipeline steel at RT has been correlated (i) with AF by the following relation: [figure 1]. (ii) with D by the following relation: [figure 2]. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

This study involves the experimental and modelling work of high temperature reactions pertaining to steelmaking. / Certain non-metallic inclusions are known to cause deleterious effects in steel products and affect the production efficiency of steelmaking if not controlled. Most of these are oxide inclusions formed during deoxidation in refining processes, especially in the ladle metallurgy furnace (LMF), an understanding of which is essential for process control. The composition of these inclusions changes subsequently while interacting with other phases like slag, alloy additions, and refractories. The efficient removal and composition control of inclusions are important variables to consider for any steelmaker. Moreover, desulphurisation of steel is another aspect that needs attention since excess sulphur can precipitate sulfide inclusions while cooling. Hence, tracking the composition evolution of different phases in a ladle furnace is beneficial for the steelmaking industry. Previous researchers in the authors’ laboratory developed a model that could be used to predict the kinetics of steel-slag-inclusion reactions in aluminium (Al) killed steel. The current work focusses on developing a kinetic model that can be used to describe the inclusion evolution during ladle treatment of silicon-manganese (Si-Mn) killed steel. For this, first, the formation of complex oxides in Si-Mn-killed steel was analyzed using a mathematical model of nucleation and growth of particles in melts. The results revealed that spontaneous nucleation of complex oxides occur during alloy additions, resulting in different compositions of oxide nuclei, based on the local supersaturation conditions. Sensitivity analysis with different parameters was carried out to understand the influence of physicochemical variables on the model. Following this, two kinetic models were built: 1) average inclusion composition tracking method; and 2) multi oxide inclusion (MOI) composition tracking method. The latter approach included the thermodynamics and kinetics of each inclusion formation and could further incorporate the total inclusion number density variation in steel. The MOI model can be used to predict the changes in not only the average inclusion composition but also the type of inclusions precipitating in steel. Following this, laboratory deoxidation experiments were carried out using FeSi and FeMn to understand the inclusion behaviour post alloy additions. The MOI model showed good potential in simulating these laboratory deoxidation experiments and was then coupled with a previously developed steel-slag model to simulate actual ladle refining reactions. The calculated results were compared with different industrial data and showed good agreement with what is observed in reality, showing the success of this new approach. Similar to previous investigations, the rate-determining step could be attributed to the availability of solutes in steel (from slag or alloys) along with their transport to the steel-inclusion interface. The overall model was also able to simulate the desulphurization behaviour in steel. The effects of different processing conditions such as [Al], [O] content, reoxidation, and stirring conditions, were also examined and discussed through a parametric analysis. / Dissertation / Candidate in Philosophy

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