The freeze lining of an industrial copper flash smelting furnace slag, its growth kinetics and microstructure have been studied using a water cooled probe technique in a rotating crucible furnace at 1350uC. The first layers of iron silicate slag solidify on the water cooled metal surface as amorphous or glassy material with a minor fraction of crystalline spinel phase precipitated. At a distance of 4-5 mm from the cold face about 50% of the structure is composed of crystalline olivine (fayalite) and spinel phases embedded in a glassy matrix. Major thickness of the freeze lining is formed within first 15 min of slag contact with a cooled metal surface. The solidified microstructures obtained were compared with equilibrium phase assemblages calculated. The equilibrium solidification in the near solidus reactions includes the formation of pyroxene and rhodonite type phases, but they were not identified in the lining microstructures.
Copper smelting in one processing step directly from concentrates to blister copper has been realized on an industrial scale in a few smelters, using concentrates with a high Cu/Fe-ratio. The fluxing of any direct-to-blister slag is demanding task as it must be fluid and maintain suitable properties in the oxidising conditions of copper making, and the reducing conditions of slag cleaning. The smelting slags in the direct-to-blister furnaces contain much more chemically dissolved copper than typical matte making slags. In this investigation, an industrial direct-to-blister slag was used in a freeze lining growth kinetics study. The freeze lining was formed on a water cooled metal finger at typical smelting temperatures using different dipping times from 5 to 120 min. The growth kinetics of the lining was very fast in the initial stage of the slag contact with the cooled metal surface. The quenched samples showed characteristic solidification zones from the cold end towards the hot side of the freeze lining and the molten slag shown already in other freeze linings and different slag types. The slag chemistry modifies the solidification pattern very much and thus the crystalline phases in the lining included also phases created by the high copper oxide concentration as well as the specific gangue assay of the smelters feed mixture. The thermal stability of the freeze lining in high-in-copper DB slags is discussed as well as the mechanism of delafossite precipitation.
The experimental study was focused into effects of a ceramic refractory lining, covering a metallic cooling element, as well as to properties and microstructures of the freeze lining formed in such cases in copper smelting and converting slags. The modified heat transfer pattern, due to the ceramic refractory lining and its air gap(s), increases effectively the average freeze lining temperature, heating its cold face from 30 to 50°C of the direct contact close to 800–900°C, even with refractory thicknesses of a few millimetres. This general feature has direct consequences to the microstructure and thickness of the freeze lining and probably also to its growth rate. The observations about effects of high copper iron silicate slag on the chemical corrosion of direct bonded magnesia–chromia refractories suggest that copper oxides are not the most aggressive components of direct to blister smelting slags. Impregnation of the fluid direct to blister slag into the open porosity of the brick, even on the cooled furnace wall, extends quickly in the initial contact several hundred micrometres into the refractory.
The initial growth rate offreeze linings on water-cooled elements submerged in molten iron silicate slag is fast. The freeze lining microstructure forming on water cooled steel surface in a high-silica, slag cleaning furnace slag o f a direct-to-blister copper smelter is mostly glassy or amorphous. It contains 5-30 pm magnetite crystals, very small and larger copper droplets as well as small magnetite and silicate nuclei embedded in the glassy silica-rich matrix. Chemically the form ed freeze linings are more silica-rich than the slag from which they were generated. Magnetite (spinel) is the primary phase o f the solidifying SCF slag but it does not form a continuous network through the freeze lining. Its strength is given by the intergranular silica-rich phase which initially is glassy or microcrystalline. Due to only partial slag reduction in the SCF process, large magnetite crystals are present in the freeze lining and seem to interact physically with copper droplets.
The high temperature corrosion behaviour of some nickel aluminides alloyed with zirconium or hafnium is presented. The corrosion tests were carried out in the temperature range 920 to 1010 "C, both in air and in atmospheres containing sulphur dioxide, using a thermobalance.The results obtained in air show that all the nickel aluminides display sufficient corrosion resistance up to 920 "C. Nickel aluminide alloyed with hafnium is more resistant than the aluminide alloyed with zirconium. The oxide layer on the specimens tested in air is always very thin, exhibits low porosity and consists mainly of A1203. Without controlled preoxidation these materials are rather susceptible to corrosion in atmospheres containing sulphur dioxide. The preoxidation in gas mixture containing water vapor and hydrogen markedly improves the corrosion resistance of these alloys. The corrosion implies the selective oxidation of nickcl aluminides. The protective layer consists mainly of aluminum oxide and protects the base material also in atmospheres containing sulphur dioxide.Das Verhalten von einigen mit Zirkonium oder Hafnium legierten Nickelaluminiden unter den Bedingungen der Hochtemperaturkorrosion wird anhand der Ergebiiisse behandelt, die bei Temperaturen zwischen 920 und 1010°C in Luft und in Schwefeldioxid enthaltenden Atmosphiiren mit Hilfe einer Thermowaage erhalten wurden. Die in Luft erhaltenen Ergebnisse zeigen, da8 alle Nickelaluminide bis 920 "C gut korrosionsbestandig sind. Dabei ist mit Hafnium lcgiertes Nickelaluminid bestandiger als das mit Zirkonium legierte. Die in Luft entstandenc Oxidschicht ist immer sehr diinn und sehr wenig poros und besteht vonviegend aus Aluminiumoxid. In Schwefeldioxid enthaltenden Atmospharen werden diese Legierungcn. wenn sie nicht voroxidiert wurden, stark angegriffen. Die Voroxidation in Wasserdampf und Wasserstoff enthaltenden Gasgemischen verbessert die Korrosionsbestandigkeit der Legierungen betrachtlich. Dabei wird das Nickelaluminid selektiv oxidiert, und es entsteht eine hauptsachlich aus Aluminiumoxid bestehende schutzende Schicht. welche den Grundwerkstoff auch in Schwefeldioxid enthaltenden Atmospharen schutzt.
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