Crucible Reaction Research Articles

Metallurgical Synthesis Methods for Mg-Al-Ca Scientific Model Materials

Further improving the mechanical and corrosion properties of Mg-based alloys requires the investigation of underlying causalities between synthesis, processing, and microstructure, ideally down to the near atomic scale. However, such investigations with high resolution characterisation techniques require model materials of exceptionally controlled chemical composition and microstructure. In this context, the Mg-Al-Ca system, being attractive for offering significant improvement of the inherent brittleness of Mg alloys, is exceptionally challenging from a metallurgical perspective due to the inclusion of components with high reactivity and vapor pressures. Here, we demonstrate the applicability of various synthesis methods from arc-melting over solution growth to diffusion couples, extending to parameters for thermomechanical processing. Suitable pathways to overcome the specific challenges of the Mg-Al-Ca system are demonstrated, as well as the persistent limitations of the current state-of-the-art metallurgical laboratory technology. Solid solution sheet or wrought materials are ideally produced by induction melting in steel crucibles and casting under elevated pressure, with intermittent annealing steps between hot rolling passes to ensure homogenous chemical composition without excessive grain growth. Composite microstructures strongly depend on the solidification rate, and special care needs to be taken with regards to crucible reactions with increasing Al concentrations. Binary intermetallic compounds can be successfully produced in bulk by a variety of techniques, but the interplay between reactivity and evaporation of the melt when both Ca and Al are present required more complex approaches such as the Bridgman method for the synthesis of ternary compounds.

Towards High-Quality Investment Casting of Ti-6Al-4V with Novel Calcium Zirconate Crucibles and Optimized Process Control

The investment casting of titanium and its alloys relies on a high resistance of the crucibles and shell molds in terms of temperature and reactivity. The availability of ceramic crucibles that offer sufficient resistance to the titanium melt enables vacuum induction melting (VIM). CaZrO3 prepared from a mixture of CaO and ZrO2 as a raw material for refractory ceramics shows a high corrosion resistance against metallic melts even under very high temperatures up to 1800 °C. Crucibles and shell molds of CaZrO3 were successfully produced and used in subsequent casting trials. This study is focused on the refractory crucibles suitable for casting Ti-6Al-4V (Ti-64) using a tilt casting machine. In order to evaluate the crucible reaction and, therefore, the quality of the castings, chemical analyses, investigations of the microstructures and hardness measurements were carried out. Careful control of the melting duration is mandatory to avoid crucible reactions that otherwise result in contamination of the cast with oxygen and zirconium. This was achieved by modified coil geometries. Under optimized casting conditions, the oxygen and zirconium impurity limits of ASTM B367-09 for titanium castings were met. Based on the correlations found, optimized casting parameters with regard to material quantity, coil geometry and heating power could be determined in order to provide guidance for a high-quality casting process with VIM.

Effect of steel-refractory reactions on inclusion modification in lanthanum-, cerium-, and yttrium-added steels

The reactions of rare earth elements (REEs) with refractory materials significantly affect their effective concentrations and inclusion modifications in molten steel. This study investigated the influence of steel-refractory reactions on the modification of inclusions in lanthanum-, cerium-, and yttrium-added steels utilizing three types of commonly used crucibles as smelting vessels. Steel-refractory reactions were found to strongly affect inclusions with different outcomes for smelting in MgO, Al2O3, and MgO·Al2O3 crucibles. The RE-crucible reactions affected the evolution and size of inclusions in molten steel by influencing the content of [Mg] and [Al]. The RE-MgO crucible reactions increased [Mg] content, leading to more MgO inclusions and a smaller average size. The RE-Al2O3 crucible reactions increased [Al] content, resulting in more REAlO3 inclusions and a bigger average size. The reactions of La, Ce, and Y with MgO·Al2O3 crucibles had varying effects on the evolution of inclusions. La and Ce selectively eroded the crucible, mostly reacting with the Al2O3 component and generating REAlO3 inclusions. In contrast, the slow reaction rate of Y with the crucible and the formation of the dense Y2O3 layer at the steel/crucible interface made it react almost simultaneously with both MgO and Al2O3 components, and the modification of inclusions was dominated by [Mg] rather than [Al]. The above conclusions provided more information on how the reactions between rare earth elements and refractory materials affected inclusions in rare earth steels during smelting. They also enriched the theory of inclusion control in steel and offered new controlling strategies.

Resistance of Refractories of the Al2O3–Cr2O3 System Under Liquid-Phase Reduction Conditions of Iron-Containing Technogenic Waste

Results are provided for a laboratory study of the applicability of refractories in the Al2O3–Cr2O3 system in bubble-agitated double-chamber laboratory furnaces during processing of a broad spectrum of iron-containing materials, including technogenic waste. Laboratory tests are conducted for refractory life in a medium of molten iron. Conditions are modeled for exploitation of a refractory in melting and reducing zones of a bubble-agitated type furnace. Optical microscopy is used to study zones and the overall depth of crucible reaction with melt at the melt – refractory crucible interface.

Thermodynamics and mechanism of reduction of silicon with carbon in a crucible reaction

A thermodynamic analysis of a crucible reaction, which takes place in crucible induction furnaces, has been represented. A new diagram of a crucible reaction, with due account for partial pressures and activities of the participating components, has been suggested. For the first time ever, the electrochemical mechanism of a crucible reaction has been studied; the research has confirmed the correctness of the suggested diagram.

Features of Cast Iron Smelting in Induction Crucible Furnaces

Abstract The article describes the trend towards increased use of induction crucible furnaces for cast iron smelting. The use of gas cupola’s duplex process – induction crucible furnace – has been proved the effective direction of scientific and technical advance in the foundry industry. Gas cupolas and induction furnaces are used for cast iron smelting at the Penza Compressor Plant where in the 1960s the author developed and introduced gas cupolas for the first time in the world. In the article, the author represents the findings of the investigation on thermodynamics of crucible reduction of silicon, which is pivotal when choosing the technological mode for cast iron smelting in induction furnaces. The author proposes a new reaction crucible diagram with due account of both partial pressure and activity of the components involved into the process. For the first time ever, the electrochemical mechanism of a crucible reaction has been studied and the correctness of the proposed diagram has been confirmed.

Influence of reaction between silica crucible and graphite susceptor on impurities of multicrystalline silicon in a unidirectional solidification furnace

The influence of silica crucible reaction with graphite susceptor on carbon and oxygen impurities in multicrystalline silicon was studied by global numerical simulations. Results showed that the crucible reaction has a marked effect on carbon and oxygen impurities in the crystal. When the activity of carbon on the surface of the graphite susceptor increases, both oxygen and carbon impurities in the melt increase rapidly. Therefore, the production of high-purity multicrystalline silicon requires setting a free space between the silica crucible and the graphite susceptor or depositing a layer of SiC film on the surface of susceptor to prevent reaction between them.

PbO Reduction and Crucible Reactions of 70 wt% PbO · 30 wt% B2O3 Glass

AbstractSeventy wt% PbO · 30 wt% B2O3 glass was melted in Pt and graphite crucibles; PbO reduction and subsequent crucible reactions were empirically investigated as a function of temperature and oxygen partial pressure. This research was conducted at NASA to determine optimum processing conditions for subcentimeter glass hollow spheres to be used as inertial confinement fusion targets for a particle beam fusion accelerator at Sandia National Laboratories. The research enables selection of appropriate crucible materials and oxygen partial pressure-temperature combinations necessary to avoid phase separation from PbO reduction and/or crucible reactions. Phase separation from PbO reduction was not detected in glass samples melted in Pt crucibles under oxidizing atmospheres. Under reducing atmospheres from mechanical and diffusion pump vacuum, oxygen gas emissions were detected along with Pb-Pt compounds forming on Pt crucibles. With graphite crucibles, glasses contained lead-rich phases and CO2 gas bubbles. Experimental results were compared with the theoretical Pb-PbO stability boundary predicted on the basis of the standard free energy change of PbO reduction.

1207. Thermochemistry of liquid metal-gas crucible reactions in vacuum: S A Jansson, J Vac Sci Technol, 7 (6), Nov/Dec 1970, S5– S13

1207. Thermochemistry of liquid metal-gas crucible reactions in vacuum: S A Jansson, J Vac Sci Technol, 7 (6), Nov/Dec 1970, S5– S13

Thermochemistry of Liquid Metal–Gas Crucible Reactions in Vacuum

Thermochemical analyses are performed for the Ti–O–C, Fe–O–C, Al–O–C, Si–O–C, Mg–O–C, Be–O–C, Y–O–C, Cr–O–C, and U–O–C systems at 1800 K. The role of hydrogen, water vapor, and nitrogen in connection with these systems is exemplified. Log pMexOy vs log pO2 and log pC vs log pO2 diagrams are prepared to illustrate in a simple manner the relations between condensed phases and the equilibrium pressures of gaseous species over the different condensed phases. The diagrams are used to evaluate the correctness or applicability of available thermochemical data, and to predict or interpret reactions in or between the different systems, with particular reference to vacuum metallurgical processes.

電熱用ニクロムの低圧溶解について

The influence of different sort of raw material chromium on properties of Nichrome for electric heating materials has been clarified, this paper being the first report. The alloys containing the different sort of chromium were melted in magnesia crucible by high frequency induction heating under air of 100 mmHg, deoxidized with Ni-C or Ni-Mg, and then cast in a copper mold. The chemical compositions and the plastic workability of these ingots were examined. The results obtained were as follows.(1) The Ni-C alloy was found to be mixed easily into the melt due to its high density, and a vigorous boiling phenomenon was observed to occur immediately after its addition causing the reduction of the oxygen content of the melt to a marked degree. (2) All ingots prepared by such process were capable of being forged, rolled and drawn, and also they did not show any noticeable difference among them. There was no trouble for both hot and cold working of ingots obtained from the home-made electrolytic chromium. However, air-melted Nichrome showed somewhat deterioration in the plastic workability, the effect of raw materials of chromium being found a little. (3) For the addition of 0.1% carbon by the Ni-C alloy, a boiling occurred for 14∼27 minutes, and 0.021∼0.007%C was found to remain in those ingots. The degree of the deoxidation of the molten metal was estimated to be about 0.1% as oxygen. Besides the deoxidation of molten Nichrome, some crucible reaction appeared to proceed.

誘導式真空溶解での炭素による脱酸平衡についての一考察

As pointed out in previous report, (Tetsu-to-Hagane, Vol 47 (1961) pp.715-720), the degassing effect in vacuum induction melting by carbon should be considered with the study of the phenomenon of the kinetics.Standing on this point, series of melts of iron-base alloys containning chromium have been made in magnesia crucibles in vacuum by carbon degassing practice, and some fundamentals such as the carbon-oxygen relationship, influence of the hydrostatic pressure on degassing effect, the process of CO bubble formation, crucible reaction and effect of Si during the procedure were investigated.The results were as follows:(1) The oxygen in the melt was rapidly reduced down with vigorous boiling. After the boiling was completed, the oxygen reached nearly the constant value. In the author's experiments, the critical value of Pco at this stage obtained by substitution of the experimental activities of carbon and oxygen was some 10mmHg regardless of the alloy composition melted.(2) The oxygen level attainable by carbon degassing process was not influenced by changing the hydrostatic pressure in the vacuum tank in range of 1μHg-10mmHg.(3) Comparing the change in the carbon and oxygen contents during the melt, the carbon lost was far in excess of that necessary to account for the observed oxygen drop.(4) The abovementioned results could be explained as follow:The rapid removal rate of oxygen, at the early stage of the melting, was mainly dependent on the high value of the Pco. As the internal pressure of CO bubbles was gradually reduced and attained to the summed value of the factors, the hydrostatic pressure and surface tension of the molten metal, that limits growth of the bubbles, the bath became quiescent. It was presumed that an equilibrium state might be set up at the stage when the rate of removal of oxygen from the melt was equal to the rate of solution from the refractory.(5) In vacuum melting of austenitic stainless steel, the residual oxygen after the carbondegassing process was determined by the dynamic equilibrium relationship. In this case, the presence of silicon was apt to lower the residual oxygen in comparing with silicon free melts. Such an effect seemed to be attributed to the vaporization of silicon as Si suboxide gas in vacuum.