Increasing MgO Content Research Articles

Kinetics and Mechanisms of Dolime Dissolution in Steelmaking Slag

The kinetics of dolime dissolution containing 20 and 50 pct of magnesium oxide in steelmaking slags has been studied in a high-temperature experiment. The dissolution tests were carried out under static conditions at temperatures of between 1573 K and 1873 K (1300 °C to 1600 °C). Cylindrical samples of dolime were introduced into pre-melted slag at predetermined time intervals. The changes in mass and geometrical parameters of the samples, as well as CaO and MgO concentrations in the melt, were determined to calculate mass transfer and diffusion coefficients. The results revealed that the rate-limiting step in the process of dolime dissolution is diffusion. The increase in MgO content in the initial sample caused a drop in dolime dissolution rate and diffusion coefficients. The prediction of MgO solubility in steel slag, as well as the effect of slag basicity, was carried out using the thermodynamic software FactSage 7.1. In addition, the activation energy of diffusion has been calculated using the dependence of the logarithm of diffusion coefficients on the inverse temperature.

Effects of flux components on the properties and pore structure of ceramic foams produced from coal bottom ash

Abstract Ceramic foams with low bulk density and uniform tiny pores were successfully prepared from coal bottom ash (CBA) by introducing only a small amount of sodium carbonate and magnesium oxide as fluxing agents. The effects were investigated of the Na2O and MgO contents on the bulk density, the crystalline phases, the pore structure and the compressive strength of the ceramic foams. The results indicated that, at firing temperature, an increase in Na2O content significantly improved the pore formation ability of CBA powder compacts. The samples that contained 8 wt% Na2O exhibited a low bulk density and large-sized pores but the Na2O caused a dramatic change in bulk density with firing temperature. Nevertheless, if MgO was introduced, the increasing MgO content resulted in a further decrease in bulk density as well as a decrease and homogenization of the pore size. The improved pore structure of samples that contained more than 4 wt% of MgO contributed to a relative increase in their compressive strength. It was concluded that MgO can be used as a foam stabilizer for ceramic foams produced from CBA powder. 4–6 wt% of MgO combined with 6 wt% of Na2O in the composition of CBA powder was determined to be the best proportions for preparing ceramic foams with an optimal pore structure and good mechanical properties.

Effect of soluble Cr2O3 on the silicate network, crystallization kinetics, mineral phase, microstructure of CaO-MgO-SiO2-(Na2O) glass ceramics with different CaO/MgO ratio

Cr2O3 is often used as a glass additive to prepare glass ceramics. Chromium element exists mainly in two parts in the glass ceramics: chromium-containing spinel and soluble chromium in glass matrix. Herein, effect of soluble chromium on the CaO-MgO-SiO2-(Na2O) glass system is researched. Glass and glass ceramics were characterized by Raman spectrum, X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry. It is found that the addition of Cr2O3 increased the Q2si structure unit in glass networks, especially in glass systems with high MgO content. The crystallization temperatures of the systems were increased with the addition of Cr2O3. Soluble chromium reduced the crystallization activation energy of the glass system slightly, but did not alter its crystallization behavior (surface crystallization). With the increase of MgO content, the mineral phases of the glass ceramics gradually changed from wollastonite to diopside. Cr2O3 reduced the lattice parameters of the mineral phases. The addition of Cr2O3 has a significant effect on grain refinement and structural compactness of the glass ceramics system with high MgO content.

Experimental Investigation of Relationship between Enthalpy Change and Viscosity in Blast Furnace Type Slags

The effects of MgO, AlO and basicity on the heat capacity and enthalpy change of CaO-SiO-MgO-AlO slags at 1 673 K and 1 773 K as well as the thermal stability were investigated. The enthalpy change at 1 773 K increased with the addition of AlO and MgO, but decreased with increasing basicity. Thus, the higher basicity helped to reduce the heat consumption and fuel ratio of blast furnace. With increasing MgO content, the fluctuations of the temperature and viscosity caused by the reduction of the slag heat quantity decreased. Furthermore, the slag will have a better fluidity and thermal stability when MgO content is greater than 8 mass%. The increase of AlO content deteriorated the fluidity and thermal stability of the slag to some extent. When the reduction of the slag heat quantity was fixed, as the basicity increased, the slag temperature increased obviously and the viscosity significantly decreased. Also, the fluctuations of slag temperature and viscosity became less pronounced with increasing basicity. The increase of the basicity was favorable to improve the fluidity and thermal stability of the slag. For the slag system of this experiment, the suitable basicity was 1.10-1.15.

Effect of MgO addition on the metallurgical properties of the vanadium-titanium pellet with simulating blast furnace conditions

ABSTRACTMgO addition plays a vital role in improving the quality of pellets. In this study, the effects of MgO addition on the compressive strength, reducibility, reduction swelling characteristics and softening-melting performance of V-Ti pellets were explored systematically with simulating BF conditions. From the results, it can be observed that the compressive strength decreased with increasing MgO due to the formation of magnesioferrite, the restriction of recrystallization-agglomeration of haematite and the decreasing of molten slag. The reducibility of V-Ti pellets improved substantially due to the increase of the porosity. The decreasing of RSI is mainly caused by the decreasing of lattice volume swelling during the transition from MgO·Fe2O3 to (Mg,Fe)O. In addition, the softening-melting behavior and permeability of V-Ti pellets packed bed was found to be improved with increasing MgO content. In sum, the V-Ti pellets with a MgO content higher than 2.4% exhibits optimum metallurgical properties.

Influence of low magnesia content on the CaO-Al2O3-SiO2 glass-ceramics: Its crystallization behaviour, microstructure and physical properties

This study illuminates the role of low amounts of magnesia (≤ 3 wt%) on the crystallization behaviour of CaO-Al2O3-SiO2 glass-ceramics. Differential thermal analysis demonstrates that the peak temperature and activation energy for crystallization decrease with the addition of MgO. The crystallization pattern changes from one-dimensional crystallization to two-dimensional growth, as indicated by higher values of the Avrami parameter (n) with increasing MgO contents. Analyses of the Rietveld refinement of XRD data, FTIR, Raman spectra and scanning electron microscopy reveal that MgO causes a simple change in CaO-Al2O3-SiO2 glass-ceramics, which form an Mg-containing solid solution (Ca1-xMgxSiO3; 0 ≤ x ≤ 1) by replacement of some of the CaO with small amounts of MgO. When the MgO content increases to 1.8 wt%, diopside is primarily formed at the interfaces of sintered glass frits, acting as nucleation sites for the inward growth of wollastonite. The density of glass-ceramics increases with magnesia addition. Their hardness is strongly influenced by the phase species present, and can be enhanced by the crystallization of diopside.

Preparation and characterization of biodegradable Mg-Zn-Ca/MgO nanocomposites for biomedical applications

In order to improve the corrosion resistance and mechanical properties of magnesium alloys for biomedical implant applications, novel biodegradable Mg-3Zn-0.2Ca (wt%) matrix composites, reinforced by adding various contents of MgO nanoparticles (0.1, 0.2, 0.3, 0.5 wt%), were devised and prepared using high shear melt conditioning. An optimum solution treatment (450 °C, 48 h) and subsequent hot extrusion was carried out to produce the Mg-3Zn-0.2Ca/MgO composites. It was found that the as-extruded composite exhibited a fine grain structure with relatively uniformly distributed MgO particles. The orientation relationships (ORs) of (1 1 1)MgO ~ 2.62° from (0 0 0 2)α-Mg and [0 −1 1]MgO // [2 −1 −1 0]α-Mg, were observed between the MgO particles and the α-Mg matrix via high resolution transmission electron microscopy (HRTEM) investigation and fast Fourier transform (FFT) pattern analysis, verifying the excellent interfacial bonding between the phases. Additionally, a substantial reduction in the secondary phase content was found in the solution treated sample. In vitro immersion, electrochemical, and mechanical tensile tests were used to characterize the corrosion behavior and mechanical properties. The ultimate tensile strength (UTS) increased to 329.03 ± 2.01 MPa and the yield tensile strength (YTS) increased by 22.81% with 0.5 wt% MgO loading, while the ductility did not substantially deteriorate. The polarization resistance (Rp) of the composite was shown to increase from 0.95 kΩ cm2 to 2.02 kΩ cm2 with the addition of 0.2 wt% MgO. With increasing MgO content, agglomeration of the MgO particles was detected in the analyzed composite, resulting in decreased ductility and the occurrence of pitting corrosion.

Formation of Non-metallic Inclusions of Si-killed Stainless Steel during GOR Refining Process

AbstractThe formation mechanism of inclusions in Si-killed 304 stainless steel was studied by industrial experiments during GOR refining process and thermodynamic calculations. A lager number of CaO-SiO2-MgO-Al2O3-MnO-CrOx liquid spherical inclusions with different size (from 1 μm to 22 μm) had been found after deoxidization of FeSi alloy in 10 minutes. The calculation result of FactSage 6.3 software assisted in confirming that the inclusions in size of less than 5 μm that had less than 30 % CaO mainly came from the deoxidation of FeSi alloy with Ca and Al. The inclusions in size of more than 5 μm that had more than 30 % CaO mainly came from the modification of involved slag droplets through the oxidation of Si and Al and the collision with deoxidation-type inclusions, and the degree of change was bigger for smaller inclusions. The MgO in slag and refractory was reduced by Si and Al in steel, which leaded to the unceasingly increase of Mg content in steel. Subsequently, SiO2, MnO and CrOx in inclusion were reduced by Mg, which resulted in the increase of MgO content in inclusion and the degree of increase of MgO content was greater for the larger size of inclusions.

Melting Behavior of Titanium-Bearing Electric Furnace Slag for Effective Smelting of Vanadium Titanomagnetite

The melting behavior of titanium-bearing electric furnace slag is a key factor for effective smelting of vanadium titanomagnetite in electric furnaces. The melting behavior of synthetically produced CaO-SiO2-MgO-Al2O3-TiO2 slags with different TiO2 contents (48 wt.% to 54 wt.%), CaO/SiO2 mass ratios (0.8 to 1.4), and MgO contents (8 wt.% to 14 wt.%) was experimentally investigated in this study. The results demonstrate that the softening and melting temperatures decreased as the CaO/SiO2 ratio was increased but increased with increasing contents of TiO2 and MgO. The predicted slag phase composition showed that increasing the CaO/SiO2 mass ratio promoted CaTiO3 formation, whereas the proportion of MgTi2O5 phase increased with increasing MgO content. Appropriate slag compositions with binary basicity of 0.8 to 1.0, 10 wt.% to 12 wt.% MgO, and more than 48 wt.% TiO2 are suggested to obtain titanium-bearing electric furnace slag with low melting temperature and appropriate phase composition for titanium extraction.

Laser joining of Al2O3 liners with Al2O3–MgO–SiO2 glass-ceramic fillers

The influence of fillers composition on microstructure, the physical and chemical properties of joints is studied. Thermal mismatch between fillers and Al2O3 liners during laser joining process could be effectively reduced with the increase of MgO content. The mutual diffusion and the substitution reaction lead to the formation of the eutectic spinel phase (Mg, Fe)Al2O4. The interfacial atomic diffusion is enhanced by the addition of MgO. The joints corresponding to fillers composed of 70 wt.% Al2O3-15 wt.% MgO-15 wt.% SiO2 have the optimal mechanical performance. The average flexural strength of joints reaches 168 Mpa which is 80% of the Al2O3 liner (200Mpa). The weight loss of the joint interlayer in 10 wt.% HCl (pH = 0.45) for 24 h is 0.62 mg/cm2 which is 0.16 mg/cm2 lower than that of the liner. The softening temperature of joint interlayer exceeds 1500 °C. The reliability of Al2O3-lined joints could be maintained during the sequential process of arc welding for outer steel pipe layers. The corrosion of pipe layers could be effectively avoided.

Behavior of Titanium During the Smelting of Vanadium Titanomagnetite Metallized Pellets in an Electric Furnace

The suppression of titanium oxide reduction enables both successful separation of iron from slag and smooth production operations for the smelting of vanadium titanomagnetite. This study investigates the distribution behavior of titanium between the hot metal and enriched titanium slag during the electric furnace smelting of vanadium titanomagnetite metallized pellets. Activity calculations indicate that the TiO2 activity decreases with increasing amounts of CaO and MgO, whereas the TiO2 activity increases with smelting temperature. Additionally, high temperature experiments demonstrate that the titanium distribution ratio between the molten iron and titanium slag decreases with increasing CaO content in the slag. With the presence of high CaO content, increasing MgO content does not have a significant influence on the titanium distribution ratio. The titanium distribution ratio decreases with an increase in slag optical basicity but increases with an increment of the smelting temperature.

The Preparation and Properties of Alumina Ceramics through a Two-Step Pressureless Sintering Process

In this paper, a high-dense alumina ceramics were prepared through the two-step pressureless sintering process with high-purity alumina powder as raw materials and high-purity MgO as sintering aids. The effects of the sintering temperature in the first-step (T1) and the soaking time (t) in the second sintering step (T2) on the density, microstructure and mechanical properties of the alumina ceramics were studied. The results indicated that the relative density increased with the increase of T1 temperature whereas it increased and then decreased with the increase of MgO content. Higher T1 temperature and extended soaking time caused larger grain size, which accompanied with the Ostwald ripening of the grain and led to non-uniformity of grain size distribution. The addition of MgO was beneficial to the decrease in grain size due to pinning effect of the second phase. For samples with shorter soaking time, sintering with higher T1 temperature led to better mechanical properties because of its high density. However, for the long soaking time, all samples after sintering at different T1 temperature were fully-densified, so the grain size become to the dominant factor of strength, thus samples with lower T1 temperature exhibited better mechanical properties due to the refinement grain. Excessive addition of MgO resulted in defects, by which the strength increased firstly and then decreased slightly with the increased MgO content. For the samples with 2.5wt.% MgO, the optimum condition for the two-step pressureless sintering was T1=1450°C and T2=1400°C for 20h, and the obtained sample achieved the relative density of 96% and the strength of 507±32MPa.

Effect of MgO on the Crystallization Behavior and Properties of Glass-Ceramics

ABSTRACTAs an important advanced decoration material, glass-ceramics has attracted much attention. By means of XRD, SEM and mechanical properties tests, this research studied the sintering and crystallization behavior during the preparation of CaO-MgO-Al2O3-SiO2 glass-ceramics. Results showed that with increase in MgO content, crystallization temperature increased, linear sintering shrinkage (%) decreased and porosity number increased, leading to a lower apparent density. However, with increase in temperature and time, linear shrinkage (%) increased. In addition, the increase of MgO made the vibration frequency of infrared spectrum move to the low-frequency, showing transformation from wollastonite to pyroxene phase. With increase in MgO content, particle size decreased, crystallization rate increased, microhardness of glass-ceramic material increased and flexural strength increased initially, then decreased. The flexural strength of glass-ceramics with 10% MgO can be 103 MPa.

Property Investigations of Low‐Grade Vanadium‐Titanium Magnetite Pellets with Different MgO Contents

Properties of low‐grade vanadium‐titanium magnetite pellets (LGVTMP) with different MgO contents are investigated. Since MgO can ameliorate the properties of acid pellets, pure MgO reagent is added to LGVTMP as a MgO additive in this paper. The experimental results show that the compressive strength (CS) of different MgO‐bearing LGVTMP has a decreasing trend with the increase of MgO content, but all of the pellets are above 2000 N/pellet and meet the requirement of the blast furnace production when the roasting temperature is 1250 °C. And the mechanism of MgO on reduction swelling (RS) is different from hematite and magnetite. At 900 °C, the RS of LGVTMP mainly occurs in the reduction process of Fe2O3 → Fe3O4 → FeO and Fe2TiO5 → Fe2TiO4 under the atmosphere of 70% N2 and 30% CO. Moreover, reduction swelling index (RSI) of LGVTMP increases first and then decreases with the increase of MgO content, and 1.25% MgO pellets have worse RSI of 17.9%. In addition, adding MgO can improve the reducibility of LGVTMP due to the decrease of Fe2TiO5 content.

Study on desulfurization capacity of high alumina blast furnace slag at 1773 K using slag-metal equilibrium technique

In the current paper, we have determined the desulfurization ability of a CaO–MgO–SiO2–Al2O3 slag system using slag-metal equilibrium technique. The chemical composition of slag samples consists of Al2O3 in the range of 25–30 wt%, CaO/SiO2 ratio (0.8–1.6) and MgO (8–16 wt%). All the experiments are conducted at a temperature of 1773 K. The sulphur content in the slag as well as in metal after desulfurization reaction is analyzed using XRF (X-ray Fluorescence Spectroscopy) for calculating sulphur partition ratio (LS) of the slags. The influence of Al2O3, CaO/SiO2 ratio and MgO content on LS have been studied. It is observed that LS increase with an increase in CaO/SiO2 ratio and MgO content, but it reduces as the Al2O3 content increase in slag. Also, the amount of bridge oxygen ([BO]) represented by (O0) decreases with increase in basicity and MgO content. However, O0 increases with increase in Al2O3. It is witnessed that the experimental values closely fit with the values obtained from corrected optical basicity model.

Melting phlogopite-rich MARID: Lamproites and the role of alkalis in olivine-liquid Ni-partitioning

In this study, we show how veined lithospheric mantle is involved in the genesis of ultrapotassic magmatism in cratonic settings. We conducted high pressure experiments to simulate vein+wall rock melting within the Earth's lithospheric mantle by reacting assemblages of harzburgite and phlogopite-rich hydrous mantle xenoliths. These comprised a mica-, amphibole-, rutile-, ilmenite-, diopside (MARID) assemblage at 3–5GPa and 1325–1450°C. Melting of the MARID assemblages results in infiltration of melt through the harzburgite, leading to its chemical alteration. At 3 and 4GPa, melts are high in K2O (>9wt%) with K2O/Na2O>>2 comparable to anorogenic lamproites. Higher pressures and temperatures (5GPa/1450°C) lead to increasing MgO contents of the melt and to some extent lower K2O contents (5–7wt%) at equally high K2O/Na2O ratios. Our experiments provide insights into the role of alkalis in nickel-partitioning (DNi) between olivine and ultrapotassic melt. We observe that the high contents of Na, K, and Al are indicative of high DNi values, implying that the melt polymerization is the dominant factor influencing the olivine/melt nickel partitioning. The change of DNi as a function of melt composition results in a pressure independent, empirical geothermometer:T°C=−88.14·lnliq(Na2O+K2O·liq1+SiO2TiO2·liqAl2O3liqMgO+FeO·DNi+1906.2Element oxides represent the composition of the glass (in wt%), and DNi is the liquid/olivine Ni-partitioning coefficient. We propose that this geothermometer is applicable to all natural silicate melts that crystallized olivine in a temperature interval between 1000 and 1600°C. Application to glass-olivine pairs from calc-alkaline settings (Mexico), MORB (East Pacific Rise), and OIB (Hawaii) yielded reasonable values of 996–1199°C, 1265°C, and 1330°C, respectively.

Effects of Dolomite on Mineral Compositions and Metallurgical Properties of Chromium-Bearing Vanadium–Titanium Magnetite Sinter

Chengde chromium-bearing vanadium–titanium magnetite (CCVTM) has been used as an important mineral resource in sinter making. The MgO content of this sinter can be enhanced by adding dolomite, which improved operation of the blast furnace. The effects of MgO in the form of dolomite on metallurgical properties, microstructure and mineral compositions of CCVTM sinter were studied by a sinter pot test, X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), and mineral phase microanalysis. The results were as follows: The flame front speed and sinter coefficient decreased with an increase in MgO content from 2.66 to 3.86% by adding dolomite. With an increase in MgO content from 2.66 to 3.86%, the flame front speed, sintering utilization factor, and the value of RI decreased, while RDI and the softening–melting properties improved. In addition, the value of sinter strength (TI) reached a maximum value at MgO = 3.56%. In addition, an increase in the abundance of magnetite, magnesium ferrite, and silicate phase, as well as a decrease in hematite, was found with an increase in MgO content. We concluded that the most appropriate MgO content in the sinter is 3.56%.

Solidification Behavior of CaO–SiO2–Al2O3 Mold Fluxes Containing MgO and Low TiO2 Content Using Single Hot Thermocouple Technique (SHTT): Continuous‐Cooling‐Transformation (CCT) and Viscosity Analysis

The effect of MgO and low TiO2 content on the solidification of CaO–SiO2–Al2O3 based mold fluxes is investigated. The crystallization and viscosity behaviors are analyzed using single hot thermocouple technique (SHTT) and rotating viscometer, respectively. Continuous‐cooling‐transformation (CCT) results point to an increase of critical cooling rate (CCR) with increasing MgO content. Conversely, the presence of TiO2 seems to mitigate the effect of MgO on the crystallization due to the strong glass former characteristic of titanium dioxide. Viscosity measurements show an increase with increasing MgO content in slags containing TiO2. Break temperatures (Tbr) are compared to the onset crystallization temperatures from CCT experiments. Scanning electron microscopy (SEM) and X‐ray diffraction (XRD) analysis results indicate the presence of melilite (Al2Ca2Mg0.5O7Si1.5) for all samples of mold flux containing both MgO and TiO2.

Basaltic glass fibers with advanced mechanical properties

In the present research the dependence of compositional variations on the basaltic glass fibers mechanical properties was explored. Addition of 15 mol % MgO or 5 mol % ZnO led to enhanced for tensile strength up to 43% and 47% and for modulus up to 13% and 25% respectively. The structure of basaltic glass fibers with varying MgO and ZnO contents was investigated by solid-state 29Si and 27Al nuclear magnetic resonance with magic angle spinning (MAS-NMR) and infrared (IR) spectroscopy. It was indicated that the increase of MgO and ZnO contents slightly decreased the degree of network polymerization. 27Al MAS NMR exhibit a peak consistent with tetrahedral aluminum units AlO4. The noticeable fraction peaks of narrow octahedral aluminum units AlO6 are observed. Presence of aluminum cations in coordination 4 and 6 was confirmed by IR spectroscopy. In order to study their crystallization ability the glasses were heated at various temperatures for various time periods with following self-cooling. The crystalline phases were identified by X-ray diffraction analysis. Obtained results have shown the possibility to increase mechanical properties of continuous fibers and composites on their base by 50–60%.

Structural, electrical and enhanced low field magneto-transport properties of La0.7Sr0.3MnO3 and (1−x) La0.7Ca0.2Sr0.1MnO3 (LCSMO) + (x) MgO composites

We report the effect of MgO phase on structural, electric and thermo electric properties of La0.8Sr0.2MnO3 (LSMO) and manganite matrix-based composite series (1−x) La0.7Ca 0.2Sr0.1MnO3 + (x) MgO with x = 0.0, 0.05, 0.10, 0.15 (abbreviated as LCSMO - MgO) synthesized by solid-state reaction method. X-ray diffraction (XRD) data infers that manganite LSMO compound possesses a rhombohedrally-distorted structure (space group R3c), LCSMO has an orthorhombic structure (Pnma space group) while to that MgO compound crystallizes in cubic structure (space group Fd3m). XRD shows coexistence of MgO and La0.7Ca0.2Sr0.1MnO3 phases in doped composites through their characteristic peaks. The temperature dependence of resistivity shows that the transport behavior of the composites is governed by the grain boundaries. These composites shows metal–insulator transitions at T = TMI which decreases with increasing MgO concentration. The magnetoresistance (MR) in this system increases with increasing MgO content, showing a maximum value (91% at 50 K and at lower fields) for (0.85) LCSMO - (0.15) MgO sample, which is larger than the largest MR value of pure La0.7Ca0.2 Sr0.1MnO3 (44% at 50 K). From thermoelectric power measurements, it is observed that electron-magnon scattering process is dominant mechanism in the low temperature region.