MgO Al2O3 SiO2 Research Articles

Prediction on the spatial distribution of the composition of inclusions in a heavy rail steel continuous casting bloom

Industrial trials were performed to investigate the evolution of inclusions in the molten steel of the continuous casing tundish and the bloom of a heavy rail steel, and the spatial distribution of inclusion composition along the bloom thickness was studied. An integrated model was established to predict the spatial distribution of the inclusion composition on the entire cross-section of a heavy rail steel continuous casting, which coupled the heat transfer and solidification of steel during continuous casting, the thermodynamic transformation of inclusions with temperature and the kinetic diffusion of dissolved elements in the steel. Both industrial trials and model predictions achieved similar conclusions.Inclusions within the 30mm subsurface layer had a similar composition and size to those of the molten steel and were more than other locations of the bloom and at 1/4 thickness of the bloom inclusions were larger and contained the biggest concentration of CaS. Along the thickness of the bloom, an opposite fluctuation of CaO to that of CaS in inclusions existed so that the main reaction between the inclusion and the steel matrix was (CaO)+[S]=(CaS)+[O]. When the cooling rate was larger than 150K/s, the newly precipitated CaO–Al2O3–MgO–SiO2–(<5 pct CaS) inclusions averaged <1.5μm in diameter. If the cooling rate was smaller than 150K/s, inclusions were transformed to larger CaO–Al2O3–MgO–SiO2–(>10 pct CaS) ones. In order to achieve an optimized composition of inclusions, the total oxygen and aluminum in the steel should be <10ppm and <40ppm.

Effects of CaF2 on the sintering and crystallisation of CaO–MgO–Al2O3–SiO2 glass-ceramics

The effects of CaF2 (1–5 wt.%) on the glass structure, crystallisation behaviour, sinterability, microstructure, and properties of a CaO–MgO–Al2O3–SiO2 glass-ceramic system were investigated. The results show that the glass transition temperature, crystallisation peak temperature and the activation energy for crystallisation decreased with the addition of CaF2. The crystallisation of diopside was initiated at the particle boundaries and followed with progressive advancing towards the centre. The enhanced crystallisation for CaF2-containing samples was observed and is likely due to the depolymerisation of the glass structure. However, the enrichment of Ca–2F complexes resulted in fluorite phase precipitation at the crystallisation front of the diopside phase when the CaF2 addition exceeded 3 wt.%. The hindered viscous flow sintering from a lower crystallisation temperature led to a decline in the sintering shrinkage, the extent of which was proportional to the amount of added CaF2. Plastic deformation was observed along with the newly-formed amorphous phase as the sintering temperature approached the glass melting point, which benefits densification. The performance analysis reveals that the fabricated glass-ceramics with the proper addition of CaF2 exhibited significant improvements in its density and bending strength. Whereas, the Vickers hardness, water absorption and chemical resistance all decreased.

Zircon U–Pb geochronology and clockwise P–T evolution of garnet-bearing migmatites from the Qinling complex in the Weiziping area of the Qinling Orogen, Central China: Implications for thermal relaxation after crustal thickening

Zircon U–Pb dating and phase equilibrium modeling in the Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O2 system were carried out to garnet-bearing migmatites from the Qinling Complex in the Weiziping area of the Qinling Orogen, Central China, to constrain their metamorphic P–T path and elucidate the tectonic setting and geodynamic mechanism of Early to Middle Devonian high-temperature (HT) metamorphism in the North Qinling Belt. The mesosomes of the migmatites are composed of garnet-bearing biotite–hornblende–plagioclase and biotite–plagioclase gneisses, and the leucosomes can be divided into two types: wide leucosomes that were deformed, and narrow penetrative leucosomes. Laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) zircon U–Pb analyses yielded weighted mean 206Pb/238U ages of 398.8 ± 4.7, 394.6 ± 2.6, 399.5 ± 7.3, 372.5 ± 4.2, 370.8 ± 4.3, and 368.5 ± 4.2 Ma for metamorphic zircons within the sampled mesosomes, and a weighted mean age of 408.7 ± 5.7 Ma for igneous zircons within a deformed leucosome. Based on the published data and the results in this study, the timing of granulite-facies metamorphism is constrained to be ca. 409–395 Ma. The mesosome sample (garnet-bearing biotite–hornblende–plagioclase gneiss) has a peak mineral assemblage of garnet, biotite, plagioclase, hornblende, quartz, ilmenite, and melt, which equilibrated at P–T condition of 8.5–9.7 kbar at 745–820 °C as constrained by isopleths of XAn and XPy in a P–T pseudosection, suggesting that these gneisses underwent medium-pressure granulite-facies metamorphism. Conventional garnet–biotite–plagioclase–quartz (GBPQ) geothermobarometry yielded P–T conditions of 703 °C at 10 kbar and 685–748 °C at 7.1–8.9 kbar, which correspond to prograde and retrograde metamorphic stages, respectively. On the basis of these P–T results, the studied samples document a clockwise P–T path characterized by temperature increase and pressure decrease during the prograde stage, and temperature decrease and pressure decrease during the retrograde stage. Ti-in-zircon thermometry yielded a temperature range of 781–793 °C for metamorphic zircons from the mesosomes, further demonstrating that they underwent granulite-facies metamorphism at ca. 409–395 Ma. The prograde metamorphic stage characterized by temperature increase and pressure decrease suggests that thermal relaxation after crustal thickening has induced the partial melting and migmatization. Thus, the crustal thickening that may be caused by continental collision between the North China Block and the South China Block should occur no later than ca. 409 Ma.

Crystallization, sinterability, and dielectric properties of MgO–Al2O3–SiO2 glass-ceramics doped with TiO2

The effects of TiO2 on crystallization, microstructure, thermal, and dielectric properties of MgO–Al2O3–SiO2 (MAS) glass-ceramics were investigated. The results showed that with the TiO2 content increasing, the glass transition temperature (Tg) increased gradually, while the onset of crystallization temperature (Tx) and crystallization peak temperature (Tp) increased firstly and then decreased. The main crystalline phase for all the samples was μ-cordierite. β-Quartz and α-cordierite precipitated as the minor crystalline phases with TiO2 content ≥ 2 mol%. A small amount of TiO2 could promote the sintering process and improve the dielectric properties of MAS glass-ceramics. However, an excess of TiO2 addition could worsen the sintering and dielectric properties. The addition of TiO2 was beneficial to decrease the coefficient of thermal expansion (CTE). The MAS glass-ceramics doped with 2 mol% TiO2 heated at 925 °C showed excellent properties: high density (2.64 g/cm3), low CTE value (3.34 × 10–6/°C), low dielectric constant (5.44), and dielectric loss (2.17 × 10–3) at 1 MHz, which was a promising material for LTCC applications.

Anatexis and metamorphic history of Permian pelitic granulites from the southern Chinese Altai: Constraints from petrology, melt inclusions and phase equilibria modelling

Pelitic granulites from the southern Chinese Altai record a prominent Permian high–temperature reworking event. The lack of solid constraints on anatexis and metamorphic P–T path of these rocks has hindered our understanding of the thermo–tectonic history of Chinese Altai orogen. Here, we present a detailed field and petrological study of the pelitic granulites cropping out at Wuqiagou area, Fuyun county. They occur as lenses or interlayers hosted within biotite–plagioclase gneisses, with a rutile–bearing assemblage composed of garnet ± orthopyroxene + cordierite + biotite ± K–feldspar + plagioclase + quartz ± spinel ± sillimanite + ilmenite. These pelitic granulites preserve diagnostic features of anatexis, such as small patches of leucosomes at macroscopic scale, melt inclusions in garnet porphyroblasts and highly cuspate quartz at microscopic scale. Melt inclusions (up to ~40 μm) are now crystallized into a cryptocrystalline aggregate of feldspars, quartz and biotite (i.e. they are nanogranitoids). Phase equilibria modelling in the NCKFMASHTO (Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3) 10–compositional model system suggests a possible clockwise P–T path involving a post–peak isobaric cooling (IBC) process from 800 to 850 °C to near solidus conditions (700–720 °C) at 5.0–6.0 kbar. SIMS zircon UPb geochronology indicates that the granulite–facies metamorphism took place at 284.1 ± 2.6 Ma, which is coeval with spatially associated mantle–derived mafic intrusions. Therefore, we propose that the Permian granulite–facies metamorphic event occurred in a post–orogenic extensional tectonic setting, which was associated with the input of external heat, related to underplating and intruding of mantle–derived magmas possibly as a result of the Tarim mantle plume activity.

Density of MgO–Al2O3–SiO2, MgO–CaO–SiO2 and MgO–CaO–Al2O3–SiO2 glasses and the structural role of MgO

Density and molar volume of MgO–Al2O3–SiO2, MgO–CaO–SiO2 and MgO–CaO–Al2O3–SiO2 glasses have been correlated with the structure by following the change in type and concentration of structural units with composition. It is assumed that for (MgO+CaO)≥Al2O3 all Al atoms form AlO4 tetrahedra. The type of modified units of SiO2 (Q3 and Q2) are determined by the ratio [(MgO+CaO)−Al2O3]/SiO2. In the case of (MgO+CaO)&lt;Al2O3, there is a fraction of Al2O3 that forms units based on the AlO3/2 formula. The entire SiO2 content would be in the form of Q4 units. Any of the structural units has its own constant volume that is independent of the type of glass. The agreement between calculated and experimental density and molar volume strongly suggests that MgO has only a modifier role in the studied glasses. Formation of assumed MgO4, MgO5 and MgO6 polyhedra can be due to change in coordination of oxygen, rather being looked as structural units.

Relationship between thermophysical properties and structure of CMAS glass melts based on chromium slag

In an attempt to determine the relationship among the network structure, viscosity, electrical conductivity, surface tension, and density of chromium-containing glass melts, the variation in glass melt thermophysical properties of the CaO–MgO–Al2O3–SiO2 quaternary system were investigated by comprehensive physical property analysis and Raman spectroscopy. The results demonstrated that the network structural units Qn (n = 0, 1, 2, 3) coexisted in the glass melts and their mutual transformation caused changes in the depolymerization degree, leading to a range of viscous activation energies, conductive activation energies, surface tension, and melt densities. Additionally, the logarithm of viscosity varied linearly with the logarithm of electrical conductivity (slope: 0.67–1.54). Meanwhile, the surface tension and melt density decreased with temperature. Consideration of these interrelations is indispensable during the development of chromium-containing slag glass ceramics, particularly for pilot and industrial applications.

Sintering and dielectric behavior for doped cordierite by xCuO within MgO (1-x)–Al2O3–SiO2 ceramics

Crystalline structure, morphology, quantitative chemical constitution and dielectric properties of pure cordierite ceramic (CC) bodies and these doped with xCuO in formula MgO(1-x)Al2O3SiO2 (x = 0, 0.02, 0.04 and 0.06 wt%), prepared by a conventional solid state ceramic process, were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray fluorescence (XRF) and broadband dielectric spectrometer (BDS), respectively. Experimental results showed that doping with CuO results in lowering sintering temperature, lowering porosity, increasing bulk density and formation of copper magnesium silicate (CuMgSi2O) phase. CuMgSi2O which was formed with the highest content of CuO (0.06 wt %) increases the glassy phase, i.e. crystalline phase decreases of CC. Accordingly, the dielectric properties of CC found to be affected by CuO content. For instance, the permittivity and loss tangent slightly increased upon doping with 0.02 wt % CuO and then considerably decreased for sample doped with 0.06 wt % CuO due to formation of CuMgSi2O phase. Particularly, the loss tangent attained much lower values (0.003 at 25 °C) upon doping with 0.06 wt% CuO. Interestingly, such materials of very low loss can be used as candidates for wireless communication systems as well as in several electronic devices.

Modification of glass network and crystallization of CaO–Al2O3–MgO–SiO2 based glass ceramics with addition of iron oxide

Modification of glass network and crystallization process of a CaO–Al2O3–MgO–SiO2 (CAMS) based glass ceramic to form diopside through addition of iron oxide were investigated using differential thermal analysis (DTA), Raman spectrum, X-ray diffraction, SEM and EBSD techniques. The experimental results showed that addition of Fe2O3 led to remarkable reductions in both the glass transition temperature (Tg) and crystallization temperature (Tp) of the CAMS glass ceramic. At addition level below 5 wt%, the Tg and Tp temperatures were 651°C and 903°C, respectively, and the crystallization only occurred on the surface of the glass ceramic samples. Increasing the addition level to 10 wt% and 15 wt%, not only led to reduction in the Tg and Tp temperatures to 643-641°C and 892-876°C, respectively, but also promoted the formation of crystalline diopside throughout the CAMS samples. Based on the results of Raman spectrums, it was confirmed that Fe2O3 addition reduced the strength of glass connection as a result of chemical reactions between the isolated Si–O tetrahedron and Fe3+ ion, forming Fe3+O4–SiO4, which can be regarded as Q2 unit. And this is the first experimental evidence that proving the approach of Fe3+ mending glass network. Microstructural examination also identified the formation of large numbers of spherical Fe-enriched regions within the CAMS glass matrix as a result of the amorphous phase separation due to the Fe2O3 addition. The interfaces between the Fe-enriched regions and the glass matrix acted as preferred nucleation sites for the diopside, facilitating the crystallization. Crystallographic analysis using EBSD technique determined the <001> as the most favorite growth direction for the diopside crystals in the CAMS based glass ceramic.

Determination of Al2O3 Activity by Reference Slag Method in CaO–SiO2–Al2O3–MgO Melts for Blast Furnace Slag with High Al2O3 at 1873 K

With the increase in using high Al2O3 iron ore, the content of Al2O3 in blast furnace slag has increased sharply in recent years. Thus, the activity of high Al2O3 slag in the blast furnace slag system needs further study. Herein, the activity of Al2O3 () in CaO–SiO2–Al2O3–MgO slag equilibrated with molten Cu at 1873 K is determined by applying the reference slag method. Isoactivity contours for Al2O3 in the (CaO + MgO)–SiO2–Al2O3 pseudoternary system are achieved for blast furnace slag, and the effects of R (mass% CaO/mass% SiO2) and MgO/Al2O3 on the activity of Al2O3 are discussed. When Al2O3 = 20 wt% and MgO/Al2O3 = 0.4, with R increasing from 1.10 to 1.30, the activity of Al2O3 decreases from 0.0423 to 0.0244. When Al2O3 = 20 wt% and R = 1.25, with MgO/Al2O3 increasing from 0.35 to 0.55, the activity of Al2O3 decreases from 0.0470 to 0.0366. The reference slag method, herein, is feasible based on the experimental results and the reference slag method is simple, reasonable, and of high accuracy.

Application of phase equilibrium studies of CaO–SiO2–Al2O3–MgO system for oxide inclusions in Si-deoxidized steels

In the steelmaking process, the compositions of the oxide inclusions could be modified by refining slags to a large extent. The chemistries of the oxide inclusions and refining slags can be described by the system CaO–SiO2–Al2O3–MgO. Phase equilibria and liquidus temperatures in this system have been experimentally investigated in the composition and temperature ranges related to the oxide inclusions and refining slags by means of high-temperature equilibration, quenching and electron probe X-ray microanalysis. Isotherms in the interval of 20 °C between 1260 and 1560 °C were determined in the primary phase fields of wollastonite, anorthite, spinel, and melilite. Effects of the mass ratio of (Al2O3+SiO2)/((Al2O3+SiO2)+(CaO + SiO2)) and MgO content on the liquidus temperatures have been discussed to assist inclusion control. To obtain the lowest liquidus temperature of Al2O3–SiO2–CaO–MgO system inclusions, refining time ought to be properly controlled.

Glass forming ability, structure and properties of Cr2O3–Fe2O3 co-doped MgO–Al2O3–SiO2–B2O3 glasses and glass-ceramics

Cr2O3–Fe2O3 co-doped MgO–Al2O3–SiO2–B2O3 (CFMASB) glasses and glass-ceramics were prepared successfully by conventional melt-quenching method and nucleation-crystallization method respectively. The glass forming ability, structure and properties of Cr2O3–Fe2O3 replacing Al2O3 on the MgO–Al2O3–SiO2–B2O3 glasses and glass-ceramics were investigated by differential scanning calorimeter (DSC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (SEM) figures and other characterizations. The results show that with the increase of Cr2O3 content and decrease of Fe2O3 content, the glass forming ability reduces and phase change occurs from α-cordierite to sapphirine in glass-ceramics. Whether glasses or glass-ceramics, the emission spectra from 450 nm to 850 nm have two broad bands, showing that this material is a potential tunable radiation source at room temperature. As for the mechanical properties of the glass-ceramics, the glass-ceramic doped with 0.1 mol% Cr2O3 and 0.9 mol% Fe2O3 has excellent comprehensive properties.

Retrieval of P–T–t–d paths in a syn-metamorphic shear zone: Implications for P-T calculations and the Permian–Triassic orogeny on the Korean Peninsula

Crustal-scale shear zones developed on the boundaries of the Precambrian Gyeonggi Massif (GM) can play key role on understanding collisional orogeny during the Late Paleozoic to Early Mesozoic in the Korean Peninsula. Garnet schist formed on the boundary between the GM and Okcheon Metamorphic Belt (OMB) experienced contractional (Dn) and extensional (Dn+1) shearing combined with a clockwise pressure–temperature–deformation (P–T–d) path. Two distinct mineral assemblages were found in the schists, (1) garnet (pre- and/or syn-Dn) + staurolite (syn-Dn and/or inter Dn and Dn+1, and syn-Dn+1) + andalusite (syn-Dn+1)-bearing and (2) garnet (pre- and/or syn-Dn) + epidote-bearing assemblages, depending on bulk-rock compositions. Various compositions (An10–40 in the former assemblage and An45–70 in the latter one) and texture of plagioclase resulted from bulk-rock compositions, heterogeneous strain and dissolution and precipitation during the multiple shearing. The P–T conditions estimated for the early contractional shearing (top-to-the-north reverse shear) are 560 °C–600 °C and 5.5–7.0 kbar based on the intersections between compositional isopleths for pre- and/or syn-Dn garnet and plagioclase (An30–40 & An45–55) calculated in the MnO–Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O and MnO–Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3 systems. Subsequent extensional shearing (top-to-the-south normal shear) was characterized by recrystallization of fine-grained syn-Dn+1 staurolite with growth of syn-Dn+1 andalusite porphyroblasts during cooling and decompression to 560 °C and 3.5 kbar. The contractional and extensional shearing probably occurred at the Permian and the Late Triassic to Early Jurassic, respectively, based on the previous geochronological data. Consequently, inferred P–T–t–d paths on the GM–OMB boundary probably suggest not only crustal thickening followed by thinning, but also multiple amalgamations of several terranes.

Dehydration of Glaucophane in the System Na2O–MgO–Al2O3–SiO2–H2O and the Effects of NaCl-, CO2- and Silicate-bearing Aqueous Fluids

Abstract Arc magmas are thought to be generated by partial melting of the mantle wedge above the subduction slab, which is triggered by the fluids from the dehydration of subducting oceanic crust. Among the dehydration reactions, those occurring at the depths of the blueschist-to-eclogite transition are considered to be very important. The sodium amphibole glaucophane (□Na2Mg3Al2Si8O22(OH)2, where □ represents a vacancy) is characteristic of blueschists, so that determining the higher-temperature stability of end-member glaucophane helps constrain the maximum temperature of the transition between blueschists and eclogites. A reversed determination of the dehydration reaction 2 glaucophane = 4 jadeite + 3 enstatite + 2 quartz + 2 H2O was done in the system Na2O–MgO–Al2O3–SiO2–H2O over the pressure-temperature (P–T) range of 2·5–3·3 GPa and 760–900 °C for durations of 24–96 hours, using synthetic phases as starting materials. The reaction was bracketed at 830–850 °C at 2·5 GPa and at 810–830 °C at 2·9 GPa in the presence of water. In addition to pure water, 5 molality H2O–NaCl (mole fraction XNaCl = 0·08) and 5 molality H2O–CO2 (XCO2 = 0·08) fluids were used to check the effects of NaCl and CO2, respectively, on the dehydration reaction. The H2O–NaCl fluid shifts the reaction boundary at 2·5 GPa from 840 °C to a lower T (800 °C), while the CO2–H2O fluid shifts the boundary to a higher T (860 °C). At these high P–T conditions, the fluid, even without any added NaCl or CO2, is a silicate-bearing aqueous fluid. The different effects of NaCl and CO2 are attributed to differences in their capabilities to inhibit the solubility of silicates, such as quartz in water, and in changing the activity of water at such P–T conditions. The difference can shift the depth of dehydration by 6 km for an average low dT/dP geothermal gradient of 325 °C/GPa. The shift in the boundary could be considerably larger for shallower dT/dP slab-top geothermal gradients. The experimental results show a good fit with those from thermodynamic modelling and aqueous geochemical calculation.

Experimental investigation on high temperature wettability and structural behaviour of SAW fluxes using MgO–TiO2–SiO2 and Al2O3–MgO–SiO2 flux system

To establish the relationship between wettability and structure with the change in SAW flux composition, the contact angle measurement study was performed at 1700 K. For MgO–TiO2–SiO2 and Al2O3–MgO–SiO2 flux system the wetting behaviour was studied by evaluating the contact angle as well as surface tension properties. Sessile drop method was used to determine the wetting properties of SAW fluxes. Twenty-one SAW fluxes were designed & developed by applying mixture design approach of design of experiments. Chemical, phase and structural properties of SAW fluxes were measured using modern techniques such as X-ray fluorescence (XRF), X-ray diffraction (XRD) & Fourier Transform Infra-red spectroscopy (FTIR). As per the calculated contact angle value, different surface tension values for MgO–TiO2–SiO2 and Al2O3–MgO–SiO2 flux system was calculated using Young's & Boni's equations. Using Dupre's equation the adhesion energy for twenty-one basic fluxes was also calculated. Measured contact angle value increased with increase in the TiO2/MgO & TiO2/Al2O3 flux ratio. Lower contact angle gives higher wettability between the flux and the heating substrate. With increase of TiO2/SiO2 ratio up to 1.5 to 2.0 the calculated surface tension value is decreasing while after that it is increased with increase in TiO2/SiO2 ratio.

Preparation of Al2O3 nanowires on 7YSZ thermal barrier coatings against CMAS corrosion

Abstract The commonly-employed material for thermal barrier coatings (TBCs) is 7 wt.%Y2O3–ZrO2 (7YSZ), generally deposited by electron beam-physical vapor deposition (EB-PVD). Due to the increasing demand for higher operating temperature in aero-derivative gas turbines, a lot of effort has been made to prevent the premature failure of columnar 7YSZ TBCs, which is induced by the microstructure degradation, sintering and spallation after the deposition of infiltrated siliceous mineral (consisting of calcium–magnesium–aluminum–silicate (CaO–MgO–Al2O3–SiO2, i.e., CMAS)). A new method called Al-modification for columnar 7YSZ TBCs against CMAS corrosion was present. The Al film was magnetron-sputtered on the surface of the columnar 7YSZ TBCs, followed by performing vacuum heat treatment of the Al-deposited TBCs. During the heat treatment, the molten Al reacted with ZrO2 to form α-Al2O3 overlay that effectively hindered CMAS infiltration. Moreover, the Al film could evaporate and re-nucleate, leading to the generation of Al2O3 nanowires, which further restrained the moving of molten CMAS.

Titanium Distribution Ratio Model of Ladle Furnace Slags for Tire Cord Steel Production Based on the Ion–Molecule Coexistence Theory at 1853 K

High-strength tire cord steel is mainly used in radial ply tires, but the presence of brittle Ti inclusions can cause failure of the wires and jeopardize their performance in production. In order to control the titanium content during steel production, a thermodynamic model for predicting the titanium distribution ratio between CaO–SiO2–Al2O3–MgO–FeO–MnO–TiO2 slags during the ladle furnace (LF) refining process at 1853 K has been established based on the ion–molecule coexistence theory (IMCT), combined with industrial measurements, and the effect of basicity on the titanium distribution ratio was discussed. The results showed that the titanium distribution ratio predicted by the developed IMCT exhibited a dependable agreement with the measurements, and the optical basicity is suggested to reflect the correlation between basicity and the titanium distribution ratio. Furthermore, quantitative titanium distribution ratios of TiO2, CaO·TiO2, MgO·TiO2, FeO·TiO2, and MnO·TiO2 were acquired by the IMCT model, respectively. Calculation results revealed that the structural unit CaO plays a pivotal role in the slags in the de-titanium process.

Mechanical behavior of the joints between carbon/carbon composites and Li2O–Al2O3–SiO2 glass ceramics with YAS interlayer at high temperature

YAS (Y2O3–Al2O3–SiO2) glass ceramics were selected to join carbon/carbon (C/C) composites and Li2O–Al2O3–SiO2 (LAS) glass ceramics through vacuum hot-pressing sintering, due to the corresponding excellent compositional and structural stability at high temperature. Microstructures, mechanical properties and fracture features of the C/C-LAS joints were investigated. The joints with YAS interlayer exhibited more favorable results than the joints with MAS (MgO–Al2O3–SiO2) interlayer subsequently to shear testing at 300 and 600 °C. Strength retention of 70% for YAS joints was achieved at 600 °C, while for MAS joints the strength retention was only 28%. The joining properties amount decrease of YAS joints was due to degradation of the intrinsic properties of YAS and LAS glass ceramics. Regarding MAS joints, the poor structural stability of MAS interlayer at high temperature was the reason for the corresponding decrease. As a result, the mechanical behavior of joints at elevated temperatures was not only related to wettability and interfacial bonding, but it was also related to the intrinsic properties as well as to high-temperature stability of the interlayer and the joined substrates.

Influence of Cr2O3 on the viscosity and crystallization behavior of glass ceramics based on blast furnace slag

CaO–MgO–Al2O3–SiO2 glass-ceramics with various Cr2O3 contents are successfully prepared from blast furnace slag as the main raw material using a conventional melting method. The influence of Cr2O3 addition on the viscosity, crystallization kinetics, structure, and properties of the obtained materials are systematically determined by viscometry, differential scanning calorimetry, Fourier-transform infrared spectroscopy, X-ray powder diffraction, thermal-field-emission environmental scanning electron microscopy, and corrosion-resistance property tests. The results showed that the obtained glass-ceramics is composed of dendritic diopside (main crystalline phase) and bulk spinel (second crystalline phase). With increasing amount of Cr2O3, the viscosity of the slag glass melt increases. In addition, the samples exhibit crystallization activation energies in the range 378–454 kJ/mol, with slight fluctuations. Moreover, the crystallization index increases from 0.84 to 2.80. The obtained glass-ceramics exhibit a maximum density, bending strength, and acid and alkali resistances of 2.97 g/cm3, 196.69 MPa, 97.61%, and 98.04% respectively, demonstrating their wide application potential for various industrial applications.

Erosion resistance of CMAS infiltrated sacrificial suspension sprayed alumina top layer on EB-PVD 7YSZ coatings

The development of CMAS (CaO–MgO–Al2O3–SiO2) -resistant thermal barrier coatings is an urgent issue, as the operating temperatures of aero-engines exceed the melting point of the CMAS. Application of alumina as top layer on 7YSZ coatings has shown promising CMAS resistance behavior. It reacts with the CMAS and crystallizes into new stable phases, which seals the CMAS penetration paths in the top layer to save the underlying 7YSZ layer from infiltration.This paper deals with the study of the erosion behavior of porous thermally sprayed Al2O3 sacrificial layer on top of EB-PVD 7YSZ coatings before and after the CMAS infiltration and investigates the combined erosion/corrosion regime. The TBC system has been infiltrated with three different CMAS compositions having a different Ca/Si ratio which resulted in different reaction scenarios and products. The change in the erosion behavior of the coating system as a function of CMAS infiltration depth was investigated and an erosion model has been proposed. The key factors that dictate the erosion resistance of such alumina layers were found to be the thickness and morphology of the reaction layer, the porosity of the non-reacted alumina layer underneath the reaction layer as well as the coating adhesion mechanism between alumina and 7YSZ.