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The paper describes and discusses the results ofthermodynamic studies carried out in the authors' laboratory on slags containing Ti02• The activities of FeO and MnO, measured by gas-slag equilibration techniques in the overall system FeO-MnO-CaO-Si02-Ti02, are represented as isoactivity curves on various ternary and pseudo-ternary diagrams. Good agreement is obtained with those calculated using a model which assumes that 0 2 -ions are the only anions present.Measurements of viscosity and electrical conductivity in melts containing Ti02 under both oxidising and reducing conditions are reviewed. The structural behaviour of Ti02 deduced from these studies is clearly different from that of Si02 and is consistent with the indications from the phase diagrams and solution thermodynamics.The reduction behaviour ofTi02 is also very different from that ofSi02. The reasons for these differences and the possible industrial significance of these results are briefly discussed.Titaniferous iron ores are found throughout the world, often in very large deposits. A survey of the main deposits has been made fairly recently by Nafziger [1 J, and in view of the dwindling reserves of titania-free iron ores, it is becoming increasingly clear that these titaniferous deposits will have to be seriously considered as a source of iron as well as titania or titanium in the reasonably near future. In view of this, a programme of investigating slag systems involving titania was commenced in our laboratory some years ago. This programme involved phase diagram studies, which are not included in this paper, and the determination of activities of FeO and MnO and of sulphide capacities in such melts. This paper summarises the main findings of this work, and combines it with data on physical properties and reduction behaviour determined elsewhere to formulate our present understanding of the behaviour of titania in metallurgical slags. THERMODYNAMIC BEHAVIOUR OF TITANIA IN SLAGSThe experimental method employed in the determination of the activities of FeO and MnO and the sulphide capacities was gas-slag equilibrium, in each case involving a gas of known oxygen potential. For measurements of the activity of FeO, melts were held in iron crucibles and equilibrated with H 2 -C0 2 -A mixtures flowing at 400 cm 3 min -1, while for determination of MnO activities, melts were held in platinum crucibles in which manganese dissolved until equilibrium was achieved with CO-C02 mixtures flowing at 400 cm 3 min -1. In the case of sulphide capacity measurements the sulphur potentials as well as the oxygen potentials of the gas were controlled by using H2-C02-S02-A mixtures flowing at 800 cm 3 min -1. Prior experiments were performed in each case to determine the time required for equilibration and the flowrate necessary to obviate thermal diffusion. The experimental temperatures were 1475°C for QFeO measurements and 1500°C for QMnO and Cs determinations.After each equilibration, the slags were analysed so that the thermodynamic quantity measured could be ascribed ...

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Typical plasma etching techniques used in integrated circuit fabrication can generate steep topographies that cannot be covered adequately by subsequent deposition steps. An SF6/O2 plasma etching process for polysilicon using controlled photoresist erosion produces tapered edge profiles compatible with step coverage requirements. The degree of taper is a function of the photoresist profile, the photoresist to polysilicon etch rate ratio, and the extent of overetch. The photoresist and the polysilicon appear to etch predominantly anisotropically with the isotropic component of the polysilicon etch rate increasing during the overetch period.