Chemical assessment of the electric arc furnace slag as construction material: Expansive compounds

To carry out a correct management of electric arc furnace slags (EAS) requires a detailed knowledge of their properties. From a chemical point of view, the EAS are surrounded by some chemical problems related to its volume instability when they are used as construction materials, due to the presence of potentially expansive compounds such as free lime and mainly free MgO. The current work focuses on the chemical assessment of the black slags coming from an electric arc furnace in order to know the possible chemical disadvantages as construction materials. A complete study of chemical and mineralogical compositions, pozzolanic activity and the quantification of main expansive compounds in EAS were realised. The results show that the nature of these slags has a very high crystallinity; total absence of pozzolanic activity and the presence of expansive compounds in slags (Cl⁻, SO₃, free CaO and free MgO) were very low, if not null concentrations.     

Making electrofused magnesia-alumina spinel for producing high-grade refractories

Conclusions The basic technical parameters for melting and producing magnesia-alumina spinel in an electric arc furnace OKB-514 were evaluated and specified. A study was made of the properties of certain compositions of spinel, the melting of an experimental batch of spinel, and using this as a basis, high-qualityroof products were made.Translated from Ogneupory, No. 4, pp. 41–45, April, 1972.     

PbO-Fe2O3-P2O5系统半导体玻璃的电导性能研究

研究了(0.4-x)PbO—xFe2O3—0.6P2O5半导体玻璃的电导性能。首先熔制了SF系列玻璃,测定了玻璃的氧化还原指数和电导率,并计算了铁离子浓度和铁离子的平均距离。讨论了玻璃组成、熔制条件以及氧化还原指数对电导的影响,揭示了它们的电导性质不仅与组成有关,而且与铁离子的氧化-还原状态有关。随着熔制温度的升高,氧化还原指数提高,从而使电导增加。研究表明,该半导体玻璃的电导机制符合Mott的小极化子跳跃理论。     

熔炼AZS材料的电弧炉炉底料的研究

目前国内熔炼AZS材料的生产,都是用三相电弧炉,从投料、电弧加热熔炼、澄清到浇铸周期地进行,对3t级电炉,通常是3h左右一个周期,每次浇铸时倾出大部分熔体,而留下一部分于炉底,转入下一个周期;而国外同样规模电炉,每次仅浇出炉内的三分之一到四分之一熔体,一个周期也仅2h左右,同时,他们还采用荧光仪快速分析进行炉前熔料的化学组成校正调节。我国目前还没有条件这样生产。国内炉体外壳同样采用水冷却     

Production of high-alumina cement clinker by fusion in an electric furnace

Conclusions The possibility of obtaining clinker from high-alumina cement by melting a mixture of lime and technical alumina in an electric-arc furnace at the Klyuchevsk Ferroalloy Plant has been shown.The high-alumina cement obtained from fused clinker is significantly better in its physicochemical properties than the cement produced on the basis of the lime-alumina slags from the ferroalloy industry.Translated from Ogneupory, No. 5, pp. 25–27, May, 1984.     

Removal of Boron from Molten Silicon using Na2O-CaO-SiO2 Slags

The global shortage of solar grade silicon for production of solar cells has motivated a lot of research on the refining of metallurgical grade silicon. However, approaches to upgrade metallurgical grade silicon have been mainly handicapped by difficulties in reducing boron and phosphorus levels. In the present study, the possibility of refining metallurgical grade silicon to remove impurity boron using Na₂O-CaO-SiO₂ slags was investigated. Before slag melting, a process of mixing pulverized slags and silicon under an action of mechanical force was used to provide a higher probability of contact and reaction of slags and silicon. The melting time was reduced with an increase in contact area A _S , resulting in improved efficiency of boron removal. The parameters, including the slag basicity, and the weight ratio of silicon to slag were discussed. The process of slag treatment was performed twice and directional solidification was conducted to promote the separation of slags from silicon. A maximum value of L _B (5.81) was obtained when the basicity was 1.21, and the weight ratio of silicon to slag was 5.     

Characteristics of a nuclides distribution during a melt decontamination of radioactive aluminum wastes

The characteristics of an aluminum melting and the distribution of surrogate nuclide have been investigated in a muffle furnace and a lab-scale arc furnace as part of the fundamental research for a melting of the metallic wastes generated by dismantling research reactors. The melting of aluminum was carried out with the use of surrogate nuclides such as cobalt, cesium, and strontium, and fluxes such as NaCl-KCl-Na₃AlF₆ (flux A), NaCl-NaF-KF (flux B), CaF₂ (flux C), and LiF-KCl-BaCl₂ (flux D). The effects of the melting temperature and the type of flux on the melting of the aluminum and the surrogate nuclide distribution in the ingot, slag, and dust phase were investigated in a muffle furnace. The addition of the flux increased the fluidity of the aluminum melt, which has a slight difference according to the type of fluxes, and the amounts of the slag generated during the melting with the flux types B and C were larger than those with flux types A and D. The results of the XRD analysis showed that the surrogate nuclides move into the slag, which can be easily separated from the melt, and then they combine with the aluminum oxide to form a more stable compound. The remaining cobalt in the ingot phase was less than 20% and the others were transferred into the slag and dust. A removal efficiency of more than 99.5% for cesium and strontium from the ingot phase could be achieved. Similar results for the slag formation and the distribution of the surrogate nuclides were obtained in a DC graphite arc melting system. Therefore, it is expected that a greater part of the aluminum wastes generated from the retired research reactors can be recycled or their volume reduced to be disposed of by melting.     

电弧炉熔融医疗垃圾焚烧灰的实验研究

利用处理量为2 kg的直流电弧炉对医疗垃圾焚烧的底灰、底灰与布袋飞灰的混合灰分别进行熔融实验研究,并比较了熔融前后灰和熔渣的化学成分、物相、微观形貌、浸出毒性及重金属残留率. 结果表明,底灰主要由复杂的硅酸盐晶体组成,布袋飞灰含有大量的硬石膏(CaSO4)、氯化钠(NaCl)晶体,熔融后两种熔渣均为无定形非晶态的玻璃熔岩. 底灰、混合灰熔融后减容率分别达到78%和80.5%;熔融前布袋飞灰浸出液中Pb, Cd, Zn浓度远超过危险废物填埋限值,熔融后的熔渣中重金属固化在Si-O网格中,渗沥液中浓度极低,完全符合环保要求. 熔融后2种熔渣中Pb, Cd, Zn的残留率较低,而且混合灰熔渣中重金属残留率均低于底灰熔渣.     

The fate of iron during the alkali‐activation of synthetic (CaO‐)FeOx‐SiO2 slags: An Fe K‐edge XANES study

Slags from the nonferrous metals industry have great potential to be used as feedstocks for the production of alkali‐activated materials. Until now, however, only very limited information has been available about the structural characteristics of these materials. In the work presented herein, synthetic slags in the CaO–FeO_x–SiO₂ system, representing typical compositions of Fe‐rich slags, and inorganic polymers (IPs) produced from the synthetic slags by activation with alkali silicate solutions have been studied by means of X‐ray absorption near‐edge structure (XANES) spectroscopy at the Fe K‐edge. The iron in the slags was largely Fe²⁺, with an average coordination number of approximately 5 for the iron in the amorphous fraction. The increase in average oxidation number after alkali‐activation was conceptualized as the consequence of slag dissolution and IP precipitation, and employed to calculate the degrees of reaction of the slags. The degree of reaction of the slags increased with increasing amorphous fraction. The iron in the IPs had an average coordination number of approximately 5; thus, IPs produced from the Fe‐rich slags studied here are not Fe‐analogs of aluminosilicate geopolymers, but differ significantly in terms of structure from the latter.     

Carbon atmosphere effect on Ti3SiC2 based composites made from TiC/Si powders

The effect of carbon activity and CO pressure in the furnace atmosphere is investigated with respect to the phase reactions during heat treatment of TiC/Si powders. Special attention is given to the production and decomposition of Ti₃SiC₂. Samples were heated in graphite and alumina furnaces, connected to a dilatometer which enabled in situ analysis of the phase reactions. The phase compositions of the heat treated samples were determined by X-ray diffraction. The reducing atmosphere of the graphite furnace enhanced the reactivity of the starting powder and enabled phase reactions to take place at a lower temperature than in the alumina furnace. TiSi₂ and SiC phases formed at temperatures below the melting point of Si and were continuously consumed at higher temperatures. Ti₃SiC₂ formed at the melting point of Si regardless of furnace atmosphere. No decomposition of the Ti₃SiC₂ was observed in either furnace.     

The growth and composition of layers of slags of the system CaO-Al2O3

Conclusions The conditions for the formation of a slag layer in an unlined and uncooled steel pipe were determined by methods of mathematical experiment design and on hot models.Within the investigated limits of variation of the factors the growth of the layer is governed by the degree of excess heating of the slag and its stay time in the pipe. The results of calculations of the thickness of the layer from the mathematical model constructed for this purpose agree very closely with the results of the industrial-scale experiment.An analysis of the mineral composition and melting point of four slags of the system CaO-Al₂O₃ showed that among the compositions investigated the slag lining approaching the composition of CaO-Al₂O₃ possesses the best combination of properties.Translated from Ogneupory, No. 7, pp. 58–64, July, 1976.     

Thermal calculation of the water-cooled elements of the lining of an electric arc steel melting furnace

Conclusions A model and a computer program using it have been developed making it possible to evaluate the influence of the electrical conditions after melt-down in an electric arc steel melting furnace on the thermal operation of tubular water cooled elements of the lining.The calculation is made for steady and nonsteady thermal conditions and makes it possible to determine the following parameters of thermal operation of the element: the temperature distribution across the layer of lining slag and tube wall; the temperature losses with the water and the water temperature at the exit of the element; the equilibrium lining slag thickness for a specified arc radiant power and heat exchange conditions in the furnace space.The heat losses with the water of a tubular wall panel of a DSP-100I6 furnace (tube diam. 76 mm and wall thickness 12 mm, lining slag thickness 20 mm, water consumption 5 m³/h per m² of panel) after meltdown of the heat were calculated.The equilibrium thickness of the lining slag decreases with a reduction in its melting point and in increase in arc radiant power P_a.rad.Translated from Ogneupory, No. 6, pp. 40–43, June, 1988.     

Thermodynamics and crystallization kinetics of REEs in CaO–SiO2–Ce2O3 system

Rare earth elements (REEs) have become increasingly important as ceramic materials. The RE-bearing slags contain massive REEs resources, whereas the lack of thermodynamic and kinetic data of REEs has brought great difficulties to efficient recovery of REEs from RE-bearing slags and the application in ceramics. According to the compositions of the RE-bearing slags in industrial production, the isothermal phase equilibria of CaO–SiO₂–Ce₂O₃ system at 1500°C and 1300°C were constructed by means of liquid-quenching method combined with a series of analyses, which provides the thermodynamic data for the equilibria of REEs. On this basis, the crystallization behaviors of the RE phase (Ce_9.33−xCa_x(SiO₄)₆O_2−0.5x) was investigated, and the temperature range in which the RE phase crystallized singly in RE-bearing slags with a selected compositions was acquired. CCT and TTT diagrams for CaO–SiO₂–Ce₂O₃ system were established to characterize the crystallization kinetics of the RE phase, and the favorable conditions for its crystallization and growth in RE-bearing slags were determined. In this study, the complete thermodynamic and kinetic basic data of REEs in CaO–SiO₂–Ce₂O₃ system are provided for RE-bearing slags.     

Use of metallurgical slags in the technology of dolomite refractories

The elemental and mineral compositions of slags of blast-furnace, open-hearth, and electrosmelting production at some enterprises are analyzed. Laboratory development of a technology of stabilized dolomite refractories using 40 – 45% metallurgical slags is carried out. A high-quality product is attained by using open-hearth slags and slags from electrosmelting of alloyed steels. The quality parameters of the stabilized dolomite articles make them an alternative to chromite-periclase articles.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 12, pp. 16 – 20, December, 1996.     

THE EFFECTS OF ADDITIONS OF ZINC OXIDE AND CADMIUM OXIDE ON SIMPLE GLASSES1

The glass consisted of the composition SiO₂ 58%, PbO 22%, and Na₂O 20%. Zinc oxide was introduced in increments of 5% up to a maximum of 20% as a substitute for equivalent parts of Na₂O. Similar substitutions were made with cadmium oxide. The following physical properties were studied: thermal expansions, solubilities in hydrochloric acid, indices of refraction, and annealing conduct. Analyses of the glasses were made. The suitability of these glasses as vitreous enamels is discussed. A vacuum electric furnace for melting and fining glass under reduced pressures is described.     

Service of Bakor-33 and Corhart-Zac in a glass furnace

Conclusions Bakor-33 in the main is as good in its physicochemical and service properties as the Corhart-ZAC refractory. The use in the walls of a tank furnace of Bakor-33 and dense silica allowed us to raise the melting temperature from 1480 to 1505–1510°C, to improve the quality of the glass, to prolong the campaign from 22 to 27 months and to melt an extra 46,000 tons of glass or more.When high-temperature melting (above 1500°C) is used it is best to employ Soviet fusion-cast Bakor-33 for the upper course of the tank walls in the melting part if window and technical glass are being produced. It is undesirable to use Bakor-33 blocks in the pouring section inside the furnace.In view of the serious wear of firebrick with high-temperature melting it is recommended that the low-lying courses of the walls of the melting part be made of fused corundum refractory Bakor-20.The first five pairs of ports in the glass furnace should be made of Bakor-33 blocks and the other of silica.To obtain high-grade glass from high-temperature melting it is desirable to make the upper courses of the walls of the cooler and working parts in fused corundum or Bakor-20, and in the extreme case, of high-Al₂O₃ blocks.     

日产34 t保温瓶胆玻璃全电熔窑的调试运行

通过对一座日产34 t保温瓶胆玻璃全电熔窑的介绍和前期调试中遇到的问题,表明玻璃电熔窑整体熔化效果良好,利用多边形全电熔窑熔化保温瓶胆玻璃是可行的,为保温瓶玻璃的全电熔窑技术应用提供借鉴。     

Liquid-phase flash sintering 8YSZ with alkali halide sintering aids

The properties of ZrO₂: 8 mol% Y₂O₃ (8YSZ) ceramics with LiF and KCl sintering aids for liquid phase formation during electric field-assisted sintering were studied. Sintering experiments were carried out at 650 °C under 200 V cm⁻¹ AC electric field by varying current density, current application time, as well as LiF and KCl contents. Pellets sintered with KCl addition had cavities, cracks and fractures. Pellets sintered with 15 wt.% LiF, on the other hand, were homogeneous after thermal removal of LiF upon Joule heating. Low electric current densities coupled with longer application times produced homogeneous specimens. Three different stages were identified during sintering experiments: (i) LiF melting with the electric field applied at furnace temperatures lower than its melting point, (ii) shrinkage due to liquid phase formation and LiF removal, (iii) final densification due to grain growth and pore elimination. The electrical behavior and an estimate of the porosity were carried out by electrochemical impedance spectroscopy measurements.     

Processing and properties of Bi0.98R0.02FeO3 (R = La,Sm, Y) ceramics flash sintered at ~650°C in <5 s

We show that flash sintering produces single-phase, nanograin-sized polycrystals of isovalent-substituted multiferroic ceramics of complex compositions. Single-phase polycrystals of Bi_0.98R_0.02FeO₃ (R = La, Sm, Y) were produced at a furnace temperature of ~650°C in a few seconds by the application of an electric field of 50 V cm⁻¹, with the current limit set to 40 mA mm⁻². The dielectric and insulating properties compared favorably with expected values. Impedance spectroscopy suggests electrically homogenous microstructure, except for the sample Bi_0.98La_0.02FeO₃ that shows a small grain boundary contribution to the impedance. These results reinforce the enabling nature of flash sintering for ceramics which pose difficulties in conventional sintering because they contain low melting constituents or develop secondary phases during the sintering protocol.     

Improving the durability of the lining of a DSP-135 furnace at the Severskii pipe plant by forming high-magnesia slags in the furnace

Results are presented from a study of the effectiveness of using of high-magnesia slags to increase the campaign of electric-arc steelmaking furnaces. It is found that the use of such slags prolongs the life of the furnace lining and reduces the unit consumption of electric power, lime, fettling and carbon-bearing materials, and gunite.