In this paper, the fundamental aspects of oxide melts pertaining to the removal of impurities from hot metal and liquid steel are discussed with particular emphasis on the concepts of slag basicity and slag capacity. The capacities of various species in molten slags are evaluated using the traditional method of empirical ratios to describe slag basicity as well as the relatively new concept of optical basicity. Examples are provided to illustrate how these concepts can be used to control the behaviour of alkalies in the blast furnace as well as phosphorus, sulphur, water vapour and nitrogen during steelmaking. It is shown that optical basicity avoids the confusion that can arise from the use of empirical basicity ratios, particularly with regard to the effect of magnesia, and in addition, facilitates the design-of slags with appropriate characteristics and properties for the treatment of hot metal and liquid steel.

During continuous casting of steel, the properties of mold fluxes strongly affect the casting performance, steel quality and environment of casting operation. The high temperature microscopy technique was used to investigate the melting behaviour of mold fluxes, and drip test method was used to determine their melting rate. The results showed that free carbon is a dominant factor in governing the melting behaviour of fluxes, and the melting rate is increased with increasing carbon reactivity and decreasing carbon content.

Over the past twenty years an ultrasonic sensor has been developed that is able to provide continuous, online monitoring of non-metallic and intermetallic inclusions in liquid aluminum. The sensor assembly consists of a pair of air-cooled guide rods (one transmitter and one receiver) and a reflector plate that are submerged into the liquid aluminum. The ultrasound is reflected from both the inclusions in the liquid metal and reflector and the system receives and processes both of these signals. The system produces three pieces of information: (1) largest particle size, (2) particle count and (3) cleanliness value. Particle size is determined by measuring the amplitude of the reflections from the inclusions. The system can count and measure the sizes of particles as small as 20 mu n to as large as 160 mu m and detect and count signals from particles larger than 160 mu m. The system measures particle size 100 times per second and records how frequently particles are detected. The cleanliness value is a number between 0 and 10 that represents the clarity of the liquid metal that is derived from the attenuation of the signal from the reflector. The cleanliness value is an indicator of the overall concentration of inclusions in the metal, including those too small to produce discrete reflections (i.e., < 20 mu m). As a quality control unit, the system is thus capable of monitoring the acceptability of metal for a wide range of applications from very high quality metal required for continuous casting to lesser quality metal for foundry and die casting operations. The technique is virtually non-obtrusive and is capable of monitoring significantly large proportions of the total metal volume on a continuous basis. In the case of flowing metal in a launder it is possible to achieve analysis of at least 25% of the metal.

Metal processing systems can often be described in terms of a series of metallurgical reactors linked together by a number of transfer operations. There is good evidence from plant observations that quality achieved within one reactor can be lost during transfer to the next. These aspects will be discussed with reference to measurements of reoxidation and the influence of the surface-active elements oxygen and sulphur on the absorption of nitrogen and hydrogen by molten steel. An important consideration with respect to metallurgical processing is the availability of appropriate sensors that will detect signals pertaining to product quality. Two examples are presented of recent developments in this area, an FeO determinator for the characterization of slag behaviour and an ultrasonic sensor for the on-line monitoring of molten metal cleanliness.

The experiments were carried out at 1175-1450degreesC to study the phosphorus distribution ratio between molten CaO-based slags and carbon saturated hot metal. The phosphate capacity of the slags and the activity coefficient Of PO2.5 were calculated from the phosphorus distribution ratio. The effect of addition of CaF2 and/or CaCl2 on the thermodynamic properties of slags was discussed. The correlation of optical basicity with phosphate capacity of slags was studied, and the dephosphorization ability of CaO-based fluxes with various additives was compared with the results from different studies.

Trials were conducted on Co-Steel Lasco's electric arc furnace (EAF) to evaluate the effect of oxyfuel burner ratio changes on furnace energy efficiency and productivity. Carefully controlled trials with the collection of numerous process and sample data over 331 heats provided statistically significant results. The oxygen available for post-combustion in the furnace was increased by 19%. As the burners were operating at their maximum oxygen constraint, this was achieved by decreasing the natural gas consumption by 43%. Results of this study indicate that decreases in terms of specific electrical energy consumption (4.0%), power on time (5.0%), and tap to tap time (4.5%) were realised. Slag chemistry, electrode consumption, and yield were not affected. Measurement data support the finding that more heat was transferred into the steel with the post-combustion burners: a flat bath was achieved earlier; high bath temperatures were reached more quickly; power on time was reduced, leading to reduced electrical energy consumption. Analysis suggests that furnace thermal energy losses were reduced by less air inleakage, less incomplete methane combustion, and earlier achievement of foamy slag conditions.

A thermogravimetric method has been used to determine the carbon dioxide content of CaO-CaF 2 -NaF slags equilibrated with controlled partial pressures of CO 2 at 1,423 to 1,623°K. The carbonate capacities of the slags were calculated, and it was found that they increased with increasing CaO content and decreased with increasing temperature. Replacing CaF 2 with NaF in CaO saturated slags increased CaO solubility and significantly increased the carbonate capacity. With the aid of correlations from the literature, the phosphate and sulphide capacities of CaO-CaF 2 -NaF slags were calculated from the carbonate capacities. The results obtained are consistent with those derived from previous experimental studies of molten slags containing halide constituents.

In this paper, the thermodynamic aspects of alkali behavior in the blast furnace operation are considered with particular emphasis on alkali control through the modification and optimization of slag chemistry. Three factors that affect alkali dissolution in slags are reviewed: temperature, magnesia content and slag basicity. Two concepts, the basicity ratio and optical basicity, are used to characterize slag performance, and the results obtained by these two methods are compared. Potassium oxide capacity of blast furnace slag was calculated using data from published papers and a linear relationship established with optical basicity. From correlations of alkali and sulfide capacities with optical basicity, a new relationship is proposed by means of which it is possible to design blast furnace slags that will possess a high alkali capacity and a reasonable desulfurization ability.

In the quest to generate information pertaining to the characterization, properties and performance of molten slags, measurements and models are two interdependent requirements. Without measurements, our models are incomplete and unsatisfactory. Without models, we fail to realize, or perhaps even comprehend, the potential significance of our measurements. In this context, the concept of optical basicity will be revisited and examples presented of how optical basicity can be used to design slags with appropriate characteristics for specific applications in iron and steelmaking.

Despite the importance and usefulness of basicity in metallurgical slags, the optimum quantitative expression of it has remained elusive, partly due to the fact that the precise concept of basicity has not been properly clarified. The two basic approaches to the concept of basicity are the Lux-Flood, which perceives basicity in terms of the activity of the free oxide ion, a(O2-), and the Lewis, which perceives basicity in terms of the ability to donate negative charge. The former has been almost universally adopted in the area of metallurgical slags, while the latter has been increasingly accepted in the field of glass chemistry. In this paper, some difficulties of the Lux-Flood approach are pointed out, including the need for indirect measures of a which have proliferated in recent years. Accordingly, it is suggested;that the Lewis approach has a good deal to commend it, and that the quantification of it in terms of optical basicity is the best measure of basicity available, which should therefore be more widely applied in metallurgical slags than it currently is. The fact that there are intrinsic problems in evaluating the optical basicities for the transition metal oxides is acknowledged, and a new scale is recommended. The patterns of iso-optical basicity lines in ternary systems are shown to agree well with the pattern of iso-activity and iso-capacity lines under appropriate conditions.

This paper presents an overview of the researches carried out in our laboratory on the application of plasma in recovery of alloy elements from waste slags and the treatment of lean ores, which are examples of advanced materials processing.After briefly reviewing the early work on the reduction of nickel, chromium, manganese, vanadium and titanium oxides, and a short investigation of the reduction of titanium oxide from the slag resulting from the blast furnace smelting of a titanomagnetite ore, the paper concentrates on the more recent studies on the reduction of an Australian scheelite. In some of these experiments, aluminium was used in addition to carbon as a reductant, in virtually all cases complete reduction was achieved within a relatively few minutes even with carbon alone during plasma processing. It therefore appears that this technique provides a possible processing route to facilitate the recovery of valuable alloying elements from non-traditional sources, or to permit process step elimination.

The use of solid state carbothermic reduction as a precursor to the smelting of transition metal ores was examined. The advantages of the introduction of a prereduction stage include enabling the more efficient use of fines and the achievement of higher energy efficiencies. A solid state reduction using carbon as the reductant offers a simpler alternative for their treatment. Subsequent treatment of the reduced material could include intensive bath smelting to produce ferroalloys or, in some case, solid state separation of the transition metal carbide where this has commercial significance.

An ultrasonic sensor for cleanliness measurement in liquid metals has been developed, and is in the process of commercialization for aluminum melts. In this paper, attention is focussed on practical aspects associated with its industrial validation. The relative roles of counting and attenuation in assessing melt cleanliness in the dynamic situation of casting are explained, and the ability to conduct sampling simultaneously in several locations is also mentioned. Particular attention has been paid to the signal processing and the conversion of the information contained in the CRT trace to a user-friendly format for quick and easy apprehension of the metal quality as a function of time.

During recent years, in parallel with developments in high-speed casting, there have been increasing demands for improved steel quality. These demands are bring met by advances in our knowledge of the chemical, physical and thermal interactions between steel, gas, slag and refractory phases which take place within individual reactors as well as during transfer operations. Transfer operations must be precisely controlled, otherwise they become destroyers of quality, and quality achieved within one reactor can be lost during transfer to the next. (C) 2000 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.

In the present work, the solubility of water vapour in tundish slag has been studied in the temperature range from 1 400 degrees C to 1 600 degrees C by a thermogravimetric technique. The water vapour capacity of the slags was calculated and compared with the data from earlier studies. The results confirm that the solubility of water vapour in slags increases with increasing water vapour pressure. The relation between the two parameters obeys Sievert's law. For slags with optical basicities from 0.5 to 0.8, a regression equation was obtained to express the relation between the water vapour capacity and optical basicity of slags. A tundish slag system with the desired properties can be designed according to the correlations between the optical basicity and various capacities of slags.

After briefly reviewing the early work in liquid iron and steel, the paper concentrates on the more recent work in aluminum and some of its industrially important alloys. Considerable progress has been made in measuring and monitoring the cleanliness of melts, but in the laboratory and in plant trials involving pressure die casting and the direct casting of billets, The principles developed are directly applicable to liquid steel.

Aluminum alloys can contain heterogeneous impurities that will affect the strength of the final product and result in failure during manufacture or in service. The detection and counting of these particles by a continuous samp ling procedure is described in this paper.Pulsed ultrasound conveyed down metal guide-rods from energized pieza-electric crystals, is passed into the liquid metal, and reflections from any impurities can be recorded by special counting devices. Small particles of the order of 10-15 mu m can be resolved and their behavior (such as in settling) recorded.Sequential tests using particles of identified size and distribution, such as SiC and TiAl3, demonstrated the system's reproducibility. Such changes in composition, resulting from imposed turbulent transfer with the associated pickup of very small oxide particles, could also be shown. The effect of sludge formation, such as that found in diecasting applications due to intermetallic phase precipitation, could also be measured. This could be of value in process control of diecasting systems. The developed system is adaptable to on-fine quality measurement, and for the recording of molten aluminum cleanliness in crucibles, ladies, furnace wells, launders and other transfer systems.

Aluminum alloys can contain heterogeneous impurities which will affect the strength of the final product and result in either failure during manufacture or in service.Pulsed ultrasound, conveyed down metal guide-rods from energized piezo-electric crystals, is passed into the liquid metal and reflections from any impurities can be recorded by special counting devices. Small particles of the order of 10 to 15 mu m can be resolved and their behaviour such as in settling recorded.Sequential tests using particles of identified size and distribution such as SiC and TiAl3 demonstrated the systems reproducibility. Such changes in composition resulting from imposed turbulent transfer with the associated pick up of very small oxide particles could also be shown. The effect of "sludge" formation such as that found in die-casting applications due to intermetallic phase precipitation could also be measured. This could be of value in process control of die casting systems. The developed system is adaptable to on line quality measurement and the recording of molten aluminium cleanliness in crucible, ladies, furnace wells, launders and other transfer systems.