Hot corrosion mechanism of tundish plaster with steel slags in continuous casting

This study concerns the chemical reactions involved and the phases formed during penetration of slags of variable composition into porous plaster structure of tundish. Tundish plaster is mainly composed of MgO with minor amounts of SiO₂ and impurities, with a grain size of less than 1 mm, inorganic or organic fibers in order to decrease density and provide porosity for insulation, plasticizers and stiffening agents and some other additions. Tundish slag analysis for different grades of steel (7176D and 1191D, according to DIN standard) at different sequences, indicated a very variable composition of CaO (11–42%), SiO₂ (28–46%), Al₂O₃ (6–12%), MgO (11–20%), MnO (0–13%) and some minor variations of Fe, FeO and TiO₂. Experimental work indicated that slag when penetrated into pores of plaster, develop the phases of Monticellite (CaO · MgO · SiO₂) and Merwinite (CaO_1.5 · MgO_0.5 · SiO₂) around MgO particles and decrease the liquidus temperature from 2,800 °C to about 1,500 °C and provide dissolution of MgO grains in steel making process. Calculation based on two kinetic equations developed for diffusion controlled dissolution, indicated that the dissolution of MgO in tundish plaster is not a diffusion controlled process and is affected by turbulent flow parameters. Phase diagram of CaO–SiO₂–MgO indicates that decreasing SiO₂ to below 20% and increasing CaO content to as high as possible, increases the liquidus temperature to above 2,000 °C. Sources of SiO₂ in the process are the rice husk addition, which is used as an insulating material on top of the melt, and the slag flux addition. These sources should be reduced to as low a level as possible. This fact does not affect the fluidity of slag which is required for inclusion removal. Fluidity of slag comes from low melting point eutectics in CaO–Fe₂O₃ and CaO–FeO (about 1,200 °C) due to iron oxide on top of the steel melt.     

Effect of chemical composition of slag on chloride penetration resistance of concrete

Three ground granulated slags (FeMn arc-furnace (GGAS), Corex (GGCS) and blastfurnace (GGBS) slags) of varying chemical composition, and from different sources were used to make concretes using two w/b ratios (0.40 and 0.60) and three slag replacement levels (20%, 35% and 50%). The effect of chemical composition and replacement level of slags on the chloride penetration resistance of the concretes was assessed using the chloride conductivity test. The results showed that the chloride penetration resistance of concrete increases with decreasing w/b ratio and increasing slag replacement level. In the GGAS concretes, despite having relatively low SiO₂ and high MgO content, its significantly high Mn₂O₃ and low Al₂O₃ content was found to have a negative effect on the chloride penetration resistance of the concrete. The significantly high chloride penetration resistance of GGCS concretes was partly attributed to both its high CaO content and particle fineness. Only GGCS concretes showed a trend of increasing chloride penetration resistance with increased particle fineness; GGBS and GGAS concretes did not show any trend between particle fineness and chloride penetration resistance. The slag activity index was found to be a better indicator of chloride penetration resistance in concrete than the slag hydraulic index.     

Investigation of high ferriferous sulphide lead concentrates processing technology

This article is dedicated to the investigations of the individual complex processing of the high ferriferrous sulphide lead concentrates by the way of lead blast furnace reducing melting. The data of the trials series of high ferriferrous lead sinters' reduction melting with the operating blast furnace have been presented. The results of investigations indicate that low lead losses with the slag (1.4÷1.8 wt.‐%) can be achieved by maintaining a slag composition of 38.4÷41.1 wt.‐% FeO and 0.70÷0.74 CaO/SiO₂ ratio, with a lead sinter throughput – 55÷60 tonnes/m² · day. The slag liquidus temperature is estimated to be ?1170°C.     

Synthesis of CaOSiO2 compounds and their testing as heterogeneous catalysts for transesterification of sunflower oil

The powder mixtures of calcium oxide (CaO) and silica gel (SiO₂) in molar ratios of 1:1, 1.5:1, 2:1 and 3:1 were mechanochemically treated with the addition of water, and were subsequently calcined with a goal of synthesizing CaSiO_3, Ca₃Si₂O₇, Ca₂SiO₄ compounds and CaO/Ca₂SiO₄ two-phase mixture. The prepared materials were characterized by XRD, FTIR, SEM/EDS, particle size laser diffraction (PSLD), UV–vis diffuse reflectance spectroscopy (DRS), N₂ adsorption/desorption isotherms, Hammett indicator for basic strength and volumetric analysis for free CaO content. The catalytic activity of calcium silicates with different Ca/Si ratios was tested in the transesterification of triacylglycerols (sunflower oil) with methanol. Samples obtained with initial composition 2CaO·SiO₂ and 3CaO·SiO₂ calcined at 700?°C, and 3CaO·SiO₂ calcined at 900?°C had high catalytic activity, resulting with triacylglycerols conversion and fatty acids methyl ester formation (FAME or biodiesel) above 96%. The activity of these samples can be attributed to the existence of free CaO defined by CaO/Ca₂SiO₄ complex mixture. The effect of different amount of catalyst used for transesterification (0.2–2?wt%) was analyzed using the most active catalyst i.e. 3CaO·SiO₂ calcined at 700?°C as well as possibility of its reuse for biodiesel synthesis. It was also found that CaSiO₃, Ca₃Si₂O₇ and Ca₂SiO₄, phases did not possess catalytic activity.     

The kinetics and mechanism of crystallization in enstatite-type glass-ceramic materials

The general crystallization behaviour of a model glass-forming melt having a composition (wt%) 7.5 SiO₂ · 1.0 Al₂O₃ · 1.0 MgO · 1.5 CaO + 10 TiO₂ is investigated. The composition and the morphology of the crystalline phases formed in the system and the structure of the resulting glass-ceramic material are examined by X-ray diffraction, electron microscopy and DTA. Detailed kinetic measurements indicate that the process of nucleation of the initially formed anosovite-type phase may be described from the viewpoint of the non-steady state theory of nucleation. It is also demonstrated that the crystal growth of the spherulites in this phase is diffusion-limited. The role played by TiO₂ in the system under investigation and in similar glass-forming melts is also discussed.     

Thermal behaviour of bioactive alkaline-earth silicophosphate glasses

The thermal behaviour (sinterability and first crystallization) of a series of alkaline-earth silicophosphate glasses has been studied by differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The samples were prepared from a base bioactive glass of the system CaO–P₂O₅–SiO₂–CaF₂, by (a) slightly changing the F/O ratio; (b) replacing part of the CaO by SrO or MgO; and (c) increasing the total alkaline earth concentration by MgO additions. The results show that the addition of MgO is the most effective way of improving sinterability. In these samples, a decrease of the glass transition temperature, together with an increase in the temperature of the first crystallization, is observed. The difference between both temperatures is proposed to be an adequate indicator of the sinterability. The initial stages of the first crystallization (which produces an oxo-fluorapatite), and its composition dependence, are discussed in terms of the results of sinterability, and the classical theory of nucleation.     

Optical and structural investigations on iron-containing phosphate glasses

The article reports the preparation and complex characterization of iron-containing phosphate glasses considered to be ecological materials, as they contain non-toxic compounds related to environment. The oxide system Li₂O?CMgO?C(CaO)?CAl₂O₃?CP₂O₅?C(FeO/Fe₂O₃) was investigated in respect to its structural changes caused by MgO replacement with CaO and by the iron addition. UV?Cvis?CNIR (ultraviolet?Cvisible?Cnear infrared) spectroscopy as well as thermo-gravimetric (TG) measurements, differential thermo-analysis (DTA), X-ray diffraction (XRD) analysis, electronic paramagnetic resonance (EPR), and Mossbauer (nuclear gamma resonance) spectroscopy have been used to investigate redox states and coordination symmetry of iron, together with vitreous network changes during the heat treatment up to 1000 °C. UV?Cvis?CNIR transmission spectroscopy revealed no structural modifications when MgO was substituted by CaO, but noteworthy absorption bands attributed to Fe²⁺/Fe³⁺ species. TG analysis made in the 20?C1000 °C range shows low weight loss accompanied by several thermal effects, as evidenced by DTA. XRD patterns for the glass samples heat treated at about 700 °C revealed the presence of different phosphate crystalline phases containing Mg, Al, and Fe ions. EPR spectroscopy revealed the presence of paramagnetic Fe³⁺ ions and the change of the first coordination symmetry, when the samples are heated below the vitreous transition temperature. Mossbauer spectroscopy has evidenced two paramagnetic species, Fe²⁺ and Fe³⁺, both in octahedral coordination symmetry and a clustering process supported by only Fe³⁺ ions.     

Mechanical properties and microstructure of steel/iron slag blended mortar

This study aims to examine the mechanical properties and microstructures of steel/iron slag blended mortar (SISBM), which contains two by-products of the steel and iron industries: steel slag (basic oxygen furnace slag, BOFS) and iron slag (blast furnace slag, BFS). Test results indicate that steel slag will have effective hydration reactions with iron slag and contribute strength. The optimal mixing ratio of steel to iron slags was 3:7 (by weight), and the compressive strength was about 83.59% compared with that of ordinary Portland cement mortar (OPM). The strength development was similar to that of OPM and the strength increased as the curing period increased. The X-ray diffraction analysis results implied that the main products of hydration could be C–S–H, C–A–S–H, CaO–MgO–Al₂O₃–SiO₂, Fe_0.974O, and C₄AF. The scanning electron microscope images indicated that the distribution of Ca(OH)₂ and CaCO₃ increased as the inclusion of steel slag increased, perhaps resulting from insufficient reactions between BFS and Ca(OH)₂ and f-CaO due to excessive BOFS. In addition, the results indicated that the density of OPM was superior to that of SISBM. This may be the reason for lower strength of SISBM compared to OPM.     

Origin and sedimentation of Cu-droplets sticking to spinel solids in pyrometallurgical slags

Cu-droplet losses in slags are an important problem in Cu-industry, limiting the metal recovery. An important cause responsible for the entrainment of copper droplet losses in slags is their sticking behaviour to spinel solids. In the present study, the interaction between spinel solids and Cu-droplets is investigated in an industrially relevant slag system (PbO–CaO–SiO₂–Cu₂O–Al₂O₃–FeO–ZnO) using two complementary experimental set-ups. Firstly the influence of the sedimentation time is studied and secondly the presence of entrained (sticking) droplets is studied as a function of height in the slag layer. Based on the experimental results, a mechanism that explains the sticking Cu-droplets is proposed. Finally, a model describing the sedimentation of sticking and non-sticking droplets is formulated based on the experimental data.     

Microstructure and dielectric properties of glass/Al2O3 composites with various low softening point borosilicate glasses

The effects of various low softening point borosilicate glasses on both the sintering behavior and dielectric properties of glass/Al₂O₃ composites were investigated by FTIR, DSC, XRD, SEM and EDS. Results show that the addition of alkali oxides and PbO can decrease the glass softening temperature. While, the addition of Al₂O₃ and more SiO₂ content in the glass can increase the continuity of glass network and further increase the glass softening temperature of samples. Glass with lower softening temperature has more time to flow to finish the densification of samples, and that can contribute to get better sintered composites. By contrast, CaO–PbO–B₂O₃–SiO₂–Na₂O–K₂O glass/Al₂O₃ composites sintered at 875?°C for 15?min exhibit better properties of a bulk density of 3.06?g/cm³, a porosity of 0.17?%, a λ value of 2.47?W/m?K, a ε _r value of 8.05 and a tan δ value of 8.8?×?10^?4 at 10?MHz.     

Interactions of vanadium-rich slags with crucible materials during viscosity measurements

Slag chemistry is important for the assessment of flow behaviour of slags produced during gasification of coal and coal–petroleum coke blends. Slags containing vanadium species react readily with the crucible and spindle materials used for viscosity measurements. Interaction of vanadium-rich slags with various materials has been investigated in order to obtain a better understanding of the impact of containment materials on the resulting slag chemistry and viscosity. The bulk and phase compositions of two petroleum coke slags in Al₂O₃, Mo, Pt and Ni crucibles produced under different laboratory conditions were analysed, and kinetics of slag composition changes at 1400 °C were determined. Mechanisms of the slag interactions with crucibles are described. They involve exchanging of crucible and slag constituents, formation of interfaces with distinct compositions, and continuously changing phase equilibria in the system. For slag processed in Ni and Pt crucibles, reduction of Fe and Ni from oxide to metallic form occurs and is followed by dissolution into the crucible materials. Viscosity of slags with Mo, Ni and Al₂O₃ crucibles are determined in the temperature range 1200–1500 °C. Resulting changes in the bulk composition of the processed slag has an impact on the slag viscosity. At given temperatures, viscosities of the slags produced in different crucibles are different. The impact of crucible materials and their applicability in viscosity measurements of high vanadium-containing slags are also discussed in order to define the optimal conditions.     

Effects of MgO/CaO on the structural, thermal and dielectric properties of aluminoborosilicate glasses

Glasses with compositions xMgO-(20?x)CaO-10Al₂O₃-20B₂O₃-50SiO₂ (x = 0, 5, 10, 15 and 20 mol%) were prepared by conventional melting method. X-ray photoelectron spectroscopy (XPS) results indicated that the proportion of non-bridging oxygen increased with increasing MgO content. Nuclear magnetic resonance spectra showed that the fraction of the four-coordinated boron ions N_4(B) and aluminum ions N_4(Al) decreased with increasing MgO/CaO. Thus, higher field strength cations were expected to weaken the glass network. However, the increase in the glass transition temperature (T_g) indicated that the magnesium ions strengthened the glass network. The decrease in dielectric constant ε_r and loss tanδ could be attributed to the increase in the rigidity of the glass network as the MgO content increased.     

Effect of replacement of MgO by CaO on sintering,crystallization and properties of MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> system glass-ceramics

The effects of replacement of MgO by CaO on the sintering and crystallization behavior of MgO–Al₂O₃–SiO₂ system glass-ceramics were investigated. The results show that with increasing CaO content, the glass transition temperature firstly increased and then decreased, the melting temperature was lowered and the crystallization temperature of the glass-ceramics shifted clearly towards higher temperatures. With the replacement of MgO by less than 3 wt.% CaO, the predominant crystalline phase in the glass-ceramics fired at 900 °C was found to be α-cordierite and the secondary crystalline phase to be μ-cordierite. When the replacement was increased to 10 wt.%, the predominant crystalline phase was found to be anorthite and the secondary phase to be α-cordierite. Both thermal expansion coefficient (TCE) and dielectric constant of samples increases with the replacement of MgO by CaO. The dielectric loss of sample with 5 wt.% CaO fired at 900 °C has the lowest value of 0.08%. Only the sample containing 5 wt.% and10 wt.% CaO (abbreviated as sample C5 and C10) can be fully sintered before 900 °C. Therefore, a dense and low dielectric loss glass-ceramic with predominant crystal phase of α-cordierite and some amount of anorthite was achieved by using fine glass powders (D₅₀ = 3 μm) fired at 875–900 °C. The as-sintered density approaches 98% theoretical density. The flexural strength of sample C5 firstly increases and then decreases with sintering temperature, which closely corresponds to its relative density. The TCE of sample C5 increases with increasing temperature. The dielectric property of sample C5 sintered at different temperatures depends on not only its relative density but also its crystalline phases. The dense and crystallized glass-ceramic C5 exhibits a low sintering temperature (≤900 °C), a fairly low dielectric constant (5.2–5.3), a low dielectric loss (≤10⁻³) at 1 MHz, a low TCE (4.0–4.25 × 10⁻⁶ K⁻¹), very close to that of Si (∼3.5 × 10⁻⁶ K⁻¹), and a higher flexural strength (≥134 MPa), suggesting that it would be a promising material in the electronic packaging field.     

Single hot thermocouple technique for the characterization of the crystallization behavior of transparent or translucent liquids

Both time–temperature-transformation (TTT) and continuous-cooling-transformation (CCT) diagrams have been established to characterize the crystallization behavior of slags in a selected temperature range. Therefore, the single hot thermocouple technique based on already existing equipment was constructed showing also some different approaches. Furthermore, the procedure was enhanced using a stretching device enabling the formation of very thin slag layers. This device permits the investigation of not only transparent but also translucent liquids with low amounts of coloring oxides, e.g. Fe₂O₃. For the initiation of this method, a transparent synthetic NCAS-slag showing a high crystallization tendency was used to proper adjust the control parameters. Afterward, two industrial mould slags for the continuous casting of steel were investigated and TTT- as well as CCT-diagrams created. The TTT-diagrams for both mould slags show only one nose but the shapes of crystals formed differ dependent on temperature. This is contributed to the ratio of the growth to nucleation rate which is raised at higher temperatures where dendritic crystals are formed. For the case of continuous-cooling experiments observing only the formation of dendritic crystals precipitating at temperatures close to the liquidus temperatures the same explanation is assumed. Contrary, this ratio is decreased for rather low temperatures where only fine separate crystals precipitate.     

Effect of a small amount of liquid-forming additives on the microstructure of Al2O3 ceramics

Sintering behaviour and microstructure of Al₂O₃ ceramics without additives and with 0.02–0.25 mol% CaO + SiO₂ (CaO/SiO₂ = 1) were investigated. When Al₂O₃ bodies were sintered at 1400 °C, the sinterability and the grain size decreased as the content of CaO + Si₂ increased. When Al₂O₃ ceramics with 0.05 – 0.25 mol% CaO + SiO₂ were sintered at higher sintering temperature, both CaO and SiO₂ reacted with Al₂O₃ to produce the liquid phase along grain boundaries, and exaggerated platelet Al₂O₃ grains, with an aspect ratio of about 4.5, were formed. Because the size of platelet grains decreased as the content of CaO + SiO₂ increased, the distribution of either SiO₂ particles or this intergranular phase of CaO – Al₂O₃ – SiO₂ might control the microstructure.     

Zirconia nucleating agent on microstructural and electrical properties of a CaMgSi2O6 diopside glass–ceramic for microwave dielectrics

Addition of different amount of zirconia (ZrO₂) nucleating agent into MgO–CaO–SiO₂ system to enhance the quality factor (Q × f) of CaMgSi₂O₆ diopside glass–ceramic for low sintering temperature process (from 850 to 950 °C) was carried out in this work. The microstructures, microwave dielectric properties and nucleating/growth mechanism of m-ZrO₂ added CaMgSi₂O₆ system were analyzed using transmission electron microscopy (TEM) and electrical property measurements. Experimental results demonstrate that a solid solution of an amorphous phase MgO–CaO–SiO₂ and ZrO₂ forms after melted at 1500 °C. The t-ZrO₂ appears in the amorphous matrix first and then crystalline CaMgSi₂O₆ particle grows up at around the boundary of t-ZrO₂ after thermal treatment at 850 °C due to heterogeneous nucleating. Formation of t-ZrO₂ is attributed to diffusion of Ca²⁺ to stabilize the m-ZrO₂. The quality factor of CaMgSi₂O₆ was significantly enhanced by adding 3 wt.% m-ZrO₂, indicating that the ZrO₂ nucleating agent could enhance crystallization and therefore increase the quality factor.     

A study on the interfacial tension between solid iron and CaO–SiO<Subscript>2</Subscript>–MO system

Interfacial tension is an important property that plays an essential role in understanding wetting behavior between refractories–molten slag–steel in the steelmaking process. Most work on interfacial tensions of molten slag system have been done to clarify the effect of surface active elements in molten metal and slag composition, but there has been little work done with respect to the slags ionic structure. In this study, the interfacial tension between molten slag and solid Fe was investigated to understand the effect of the ionic structure of molten slag on interfacial tension by using solid Fe instead of molten steel. Interfacial tension measurements in CaO–SiO₂–FeO and CaO–SiO₂–MnO slags were carried out at 1,773 K on interstitial free (IF)-steel substrates using the sessile drop method. The composition of the slag was varied with amphoteric oxides of either FeO or MnO at unit basicity (C/S = 1.0). Results indicated a decrease in the interfacial tension with increased amphoteric oxide additions. The ionic species of molten slags were analyzed by FT-IR and the various types of oxygen ions (O²⁻, O⁻, O⁰⁾ in the slag was determined by X-ray photoelectron spectroscopy. The silicate bonding degree and the slags ionic behavior were semi-quantitatively analyzed with respect to the slag’s ionic structure model. By dissociating the slags networking structure with increased free oxygen ions, the interfacial tension decreased. Considering the ionic theory of molten slags, results indicate that the interfacial properties are directly affected by the ionic structure of the slag. This work hopes to clarify the relationship between the interfacial tension and the distribution of various oxygen ions.     

The crystallization of diabase glass

The crystallization behaviour of diabase glass at elevated temperatures was studied in samples prepared by melting the diabase rock. DTA and X-ray analyses revealed the crystallization of diopside (CaO · MgO · 2SiO₂) at 865 C and anorthite (CaO · Al₂O₃ · 2SiO₂) at 1060 C. Further, the kinetics of crystallization of diopside were studied. The phenomenological Johnson-Mehl-Avrami equation was used and the exponentn=3/2 determined from the dependency of the volume fraction of the crystal phase (diopside) on time. The activation energy of crystallization of diabase glass 248 kJ mol^–1 was estimated on the basis of DTA measurements carried out at different heating rates and found to be in good agreement with literature data for similar glass.     

Properties of sealants based on alkaline-earth silicate glasses

In the present work, sealant compounds based on MO-BaO-SiO₂ (where MO is MgO, CaO, and SrO) were synthesized. These materials are used for manufacture of electrochemical devices with solid electrolytes. The sealant properties such as the temperature coefficient of linear expansion, softening temperature, and temperature of electrolyte wetting were studied, and X-ray diffraction analysis of the samples was carried out. Original Russian Text ? V.P. Ishchuk, M.V. Glumov, A.K. Demin, 2009, published in Neorganicheskie Materialy, 2009, Vol. 45, No. 4, pp. 492–495.     

Influence of alumina content on the nucleation crystallization and microstructure of barium fluorphlogopite glass-ceramics based on 8SiO2·YAl2O34MgO2MgF2BaO Part I Nucleation and crystallization behaviour

The effect of varying the aluminium oxide content on the nucleation and crystallization behaviour of barium containing glasses based on 8SiO₂·YAl₂O₃4MgO2MgF₂BaO was investigated in order to develop novel, high strength, machinable glass-ceramics. Nine glasses were synthesized and characterized by Differential Scanning Calorimetry (DSC) Combined Differential Thermal Analysis Thermal Gravimetric Analysis (DTA/TGA), X-ray diffraction (XRD) and dilatometry. The glass transition temperature (T _g) and first peak crystallization temperature (Tp1) reduced with reducing alumina content. Glasses with Y > 1.5 exhibited a second peak crystallization temperature (Tp2). Tp1 was shown to correspond to the crystallization of barium fluorphlogopite (BaSi₆Al₂Mg₆F₂O₁₉) and Tp2 to the crystallization of cordierite (Mg₂Al₂Si₅O₁₈). The thermal expansion coefficient (TEC) was insensitive to alumina content. All the glasses exhibited an optimum nucleation temperature just above T _g, which was thought to be a result of amorphous phase separation (APS). DTA/TGA showed the glasses to undergo weight loss corresponding to silicon tetrafluoride volatilization from the surface, which resulted in a fluorphlogopite deficient surface layer.