System CaO MgO Al2O3 SiO2 Research Articles

Phase equilibria in the low-TiO2 part of the CaO–MgO–SiO2–Al2O3–TiO2 system at a fixed MgO/CaO mass ratio of 0.2 and Al2O3/SiO2 mass ratio of 0.4

Adding titanium oxide has become a common practice in modern blast furnace operating procedures. The blast furnace slag is based on the CaO–MgO–Al2O3–SiO2–TiO2 low titanium slag system rather than CaO–MgO–Al2O3–SiO2 system. Phase equilibria in the CaO–SiO2–Al2O3–MgO–TiO2 system in the low-TiO2 part have been experimentally determined by means of high temperature equilibration and quenching technique followed by electron probe X-ray microanalysis. Introducing a small quantity of titanium-bearing materials can lower the liquidus temperature. The TiO2 content in the slag should be controlled below 4.6 wt%, otherwise it will enter the perovskite phase region where the liquidus temperatures increases rapidly. The compositions of the solid solutions corresponding to the liquidus have been precisely measured and should be utilized for developing the thermodynamic database.

Preparation of innovative glass-ceramic materials based on mica schist within the CaO–MgO–Al2O3–SiO2 system

The preparation of affordable glass-ceramic materials by induced crystallization of glass-based mica schists and other natural raw materials (dolomite & limestone), as well as magnesite as a mine waste, was investigated for the first time. Five glass batches were designed based on the eutectic composition of the diopside-anorthite ratio with increasing the enstatite content from 0–40 wt.% within the quaternary CaO–MgO–Al2O3–SiO2 system. After melting at 1400 to 1500 °C, casting into discs & rod shapes, and annealing process, the prepared glasses were subjected to careful heat treatment schedules. Several techniques were used to characterize the applied raw materials, glass, and glass-ceramic materials such as X-ray Fluorescence (XRF), Differential Thermal Analysis (DTA), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Polarizing-light Microscopy. The produced glass-ceramic from the glass batch with 30 wt% enstatite that was nucleated at 750 °C /2h followed by crystallization at 950 °C /h, displayed the well-developed product on the level of volume crystallization and pore formation.

Xenoliths of High-Alumina Pyroxenites in the Basalts of the Sigurd Volcano, Spitsbergen Island (Svalbard Archipelago), as Indicators of the Paleozoic Geodynamics of the Regional Lithosphere

Abstract—Xenoliths of high-alumina pyroxenites in the Quaternary basalts of the Sigurd Volcano of West Spitsbergen are spinel and spinel–garnet clinopyroxenites, spinel–garnet websterites, and websterites. The granoblastic texture with relics of subhedral magmatic texture, the change of mineral assemblages, and the signs of partial melting in the xenoliths reflect their multistage formation. The goal of our study was to determine the sequence and thermodynamic conditions of the change of mineral assemblages and to establish their age by Re–Os, U–Pb, Sm–Nd, and Rb–Sr isotope dating. It has been established that the primary assemblage in the pyroxenites, which included high-alumina Opx, Cpx, and Spl, was transformed in several stages: (1) Spl→Grt replacement with the formation of garnet-containing websterites and clinopyroxenites, (2) development of kelyphitic Opx–Spl rims over Grt grains, (3) formation of Amph, (4) exsolution with the formation of Cpx and Opx, and (5) partial melting. Comparison of the obtained results with published data shows that the primary assemblage is similar in Al2O3/MgO ratio to Opx + Cpx ± Spl cumulates resulted from the crystallization of basaltic melts at 1.2 GPa and the degree of crystallization of ~15%, i.e., in the lower crust (at 2.0 GPa, Grt and Cpx crystallize from the solution). The equilibrium parameters of the Grt–Opx assemblage in the pyroxenites are 1060–1310 ºC and 2.2–3.3 GPa; in the P–T diagram, their points are localized below the Spl→Grt phase transition curve, in the system CaO–MgO–Al2O3–SiO2, thus corresponding to the model continental geotherm with a surface heat flow density of 60 mV/m2 and somewhat higher. This indicates the Spl→Grt replacement and the formation of garnet-containing pyroxenites in the shallow-depth upper mantle. The formation of kelyphitic Opx–Spl rims over the Grt grains indicates a subsequent temperature and pressure decrease to values above the Grt→Spl phase transition curve. This is confirmed by the presence of exsolution structures in pyroxene, which formed when the temperature decreased by 100–150 ºC. The Re and Os isotope composition in the bulk samples of Spl–Grt websterites that did not undergo partial melting corresponds to an age of 457.0 ± 3.5 Ma, which reflects the time of transformation of the primary Cpx–Opx–Spl assemblage into a garnet-including one. A similar value (488.6 ± 5.9 Ma) was obtained by U–Pb dating of zircon from Spl–Grt websterite, also without signs of melting. Zircon crystals from Spl–Grt clinopyroxenite with clear signs of partial melting have typomorphic features of autochthonous magmatic zircons. They form a single age cluster of 310.7 ± 3.3 Ma, which marks the age of melt crystallization in the pyroxenites. Thus, Spl pyroxenites are, most likely, Opx + Cpx ± Spl cumulates, products of crystallization of basaltic melts in the lower crust. The subsequent Spl→Grt replacement and the formation of garnet-containing websterites and clinopyroxenites in the shallow-depth upper mantle can be regarded as an indicator of the delamination of the continental crust into the mantle, and the Re–Os isochron date of 457.0 ± 3.5 Ma is the most likely upper age bound of the crust delamination into the mantle. The subsequent uplifting of the Spitsbergen lithosphere, which was expressed as the formation of kelyphitic Opx–Spl rims over garnet, exsolution in pyroxene, and partial melting, was not far in time from the delamination stage and lasted ≤ 300 Ma.

Thermodynamic analysis of the reactions of diopside phase formation during synthesis of ceramic pigments from granulated blast-furnace slag

The purpose of this study is to perform the thermodynamic analysis of the reactions of diopside phase (CaOMgO2SiO2) formation during the synthesis of ceramic pigments based on the granulated blast-furnace slag. Thermodynamic analysis is of great practical importance in studying solid-phase interactions, which are involved in the pigment technology. At the same time, the scope of energy-intensive experimental studies of ceramic pigments is significantly reduced. When performing thermodynamic calculations, we assessed the fundamental possibility and direction of occurrence of chemical reactions by determining the changes in the Gibbs energy. In order to verify the calculation data, the change in the mineralogy of the diopside compositions was evaluated with the use of X-ray phase analysis at different firing temperatures. It was found that the diopside phase in the CaO–MgO–Al2O3–SiO2 system is formed in several stages. The merwinite (3CaOMgO2SiO2) mineral is formed first. Further, merwinite, along with blast-furnace slag minerals, is involved in the diopside formation. The formation of diopside is completed at the temperature of 12000С. The findings of the study will provide a reasonable approach to the choice of compositions of ceramic pigments using complex raw materials, including the wastes of various industries.

Variation in viscosity of aluminosilicate melts with MgO/CaO molar ratio: Influence of five-fold coordinated aluminum

Viscosity of aluminosilicate melts is important for estimating transport phenomena in industrial processes. Viscosity variations with increasing MgO/CaO molar ratio have been reported for CaO–MgO–SiO2 (CMS) and CaO–MgO–Al2O3–SiO2 (CMAS) systems; however, the viscosity variation was not clearly correlated with the change in the melt structure. The present study investigated the influence of the MgO/CaO molar ratio on the viscosity of CMAS melts at temperatures higher than the liquidus using the rotating crucible method. The viscosity decreased with increasing substitution of CaO by MgO in the chosen CMAS system, whereas the opposite behavior has been reported for the CMS system. Aluminum-27 magic-angle spinning nuclear magnetic resonance spectra of the CMAS glasses show that the fraction of aluminum atoms in five-fold coordination ([5]Al) increased with increasing substitution of CaO by MgO. Our findings indicate that the formation of [5]Al reduces the viscosity of aluminosilicate melts.

Glass‐ceramics in the CaO–MgO–Al2O3–SiO2 system as potential dental restorative materials

AbstractThis paper reports on development of novel alumina‐containing glass‐ceramics (GCs) with a high content of Al2O3 (12.5 wt.%) in the CaO–MgO–Al2O3–SiO2 system aimed for dental restorations. The thermal properties of the parent glasses, the microstructure and the mechanical properties of the produced sintered and crystallized GCs along with bio‐inertia performance were experimentally studied. Dense, white, and bio‐inert GCs, comprised of melilite, either as a single‐phase or with diopside, were produced. The values of flexural strength ranged between 120 and 171 MPa, the modulus of elasticity varied between 28 and 42 GPa, while the values of the hardness and the fracture toughness (measured by the indentation–Niihara equation) ranged from 6.3 to 7.0 GPa, and from 2.6 to 2.8 MPa m0.5, respectively. The mechanical properties of the produced GCs, after being meticulously compared with the mechanical properties of GCs of various compositions reported in literature, including commercial ones, are a good match to the properties of dental hard tissues, and satisfy the requirements of the ISO 6872 “Dentistry‐Ceramic Materials”.

A Reappraisal of Peridotite Solidus Phase Equilibria from 6 to 14 GPa in the System CaO–MgO–Al2O3–SiO2

AbstractExperimentally determined isobaric invariant melting phase relations from 6 to 14 GPa in the system CaO–MgO–Al2O3–SiO2 (CMAS), involving the crystalline phases forsterite + orthopyroxene + clinopyroxene + garnet and liquid, are reported. Experiments were conducted using a multianvil device with stepped lanthanum chromite heaters in the pressure cells. At a fixed pressure, the five-phase assemblage identified above can exist only at a single temperature. As such, these isobaric invariant points correspond to the solidus of model garnet peridotite in this part of the composition space in the studied system, as is the case at lower pressures in some previous studies. The solidus of model peridotite is univariant in pressure–temperature space, has a positive Clapeyron slope, and the isobaric invariant solidus temperatures, at 6, 8, 10, 12, and 14 GPa, are 1965 °C, 2090 °C, 2200 °C, 2280 °C, and 2320 °C, respectively. Over the investigated pressure range, orthopyroxene is in reaction relation with the liquid, with the fusion reaction taking the form forsterite + clinopyroxene + garnet = orthopyroxene + liquid. The compositions of liquids reported here do not seem to depend on orthopyroxene being present in the experiments. Compositionally, liquids here are fairly magnesian and siliceous, and have lower alumina and lime concentrations than at lower pressures with the identical crystalline phase assemblage in the system CMAS. In contrast to some previous studies, in this study, there is no evidence of maximum and minimum normative forsterite concentration of the isobaric invariant liquid at around 8 and 12 GPa, respectively, nor of a substantial curvature in the track of liquid compositions, when such liquids coexist with the above-mentioned four-phase crystalline phase assemblage. Instead, here, with increasing pressure from 6 to 14 GPa, liquids at the isobaric invariant points (defining the univariant solidus) become progressively (quasi-linearly) enstatite-normative. This experimental observation on liquid compositions from the present study might be important for future work aimed at investigating the chemistry of liquids derived from partial fusion of anhydrous peridotite at pressures, and corresponding depths in Earth, greater than investigated here.

The viscosity and conductivity of the molten glass and crystallization behavior of the glass ceramics derived from stainless steel slag

The glass and glass ceramics in the CaO–MgO–Al2O3–SiO2 system were successfully synthesized from the stainless steel (SS) slag. The effect of slag content on the viscosity and conductivity of the glass melt, as well as the crystallization behavior and microstructure of the glass ceramics were investigated. The results proved that the viscosity of the molten glass decreases with increasing temperature and SS slag content; however, an inverse relation is observed in case of conductivity. Furthermore, the logarithm of viscosity varies linearly with that of conductivity. Thus, the viscosity and conductivity values can be calculated with respect to each other under melting conditions. The crystallization activation energies range from 335 to 473 kJ/mol, which are significantly higher than the viscous energies and conductance activation energies. Additionally, the obtained glass ceramics comprise augite, gehlenite, and wollastonite. Furthermore, augite grain coarsening and the number of crystals increase with increasing SS slag content.

Trace element partitioning between MgAl2O4-spinel and carbonatitic silicate melt from 3 to 6 GPa, with emphasis on the role of cation order-disorder

To better understand the partitioning of trace elements between spinels and silicate melts at high P, a series of experiments have been conducted in the system CaO–MgO–Al2O3–SiO2–K2O–CO2 at the P-T conditions of 3–6 GPa and 1500–1650 °C. These experiments successfully produced large MgAl2O4-spinel crystals coexisting with large carbonatitic silicate melt pools (plus large crystals of olivine and garnet in some cases). The experimental products were analyzed by using an electron microprobe in the wavelength-dispersive mode and an Agilent 7500 Ce laser ablation inductively-coupled plasma mass spectrometry, which led to high-P partition coefficients for 34 elements. The results suggest that pressure may have nominal significant impacts on the partition coefficients of some trace elements such as Nb, Ta, Ti, and nearly all rare earth elements (REEs), with the partition coefficients varying in several orders of magnitudes, but may play negligible roles in the partitioning of U, Mn, Fe, Sr, Ba, Na, K, Rb, and etc. Further analyses have revealed that much of the nominal P effects can be assigned to the Mg–Al cation order-disorder reaction. Cation exchange reactions are common in many geologically important minerals such as olivine, garnet, pyroxene, and plagioclase, and their effects on trace element partitioning should be extensively investigated in the near future before better understanding of the trace element partitioning systematics can be achieved. As one example, our experimental results have clearly demonstrated that due to much larger degrees of the Mg–Al cation order-disorder triggered by high P, spinel can strongly fractionate the REEs (with some heavy REEs compatible in the spinels and thus depleted in the relevant magmas), a phenomenon conventionally attributed to the presence of garnet. Some other important conclusions from our experiments include that Cr (or Ni) in the spinel structure at Cr-poor (or Ni-poor) conditions may be not as compatible as conventionally thought for Cr-rich (or Ni-rich) conditions, and Fe isotopes may be fractionated by spinels at high P.

High-Alumina Pyroxenite Xenoliths from Quaternary Basalt of Spitsbergen Island: Evidence for Continental Crust Delamination

The origin of spinel–garnet pyroxenite from xenoliths in Quaternary basaltoids of Spitsbergen Island (Svalbard Archipelago) is discussed. The rocks have a high concentration of Al2O3 and MgO and low Cr. The primary magmatic association Spl–Opx–Cpx and the high Al content in pyroxenes provide evidence for the formation of these rocks as cumulates of hydrous basaltic melts in the lower crust at a pressure of ~1.2 GPa. Transformation of the texture from the magmatic hypidiomorphic to the metamorphic granoblastic and growth of garnet at the expense of spinel and high-alumina pyroxenes indicate transport of rocks to a depth below the spinel/garnet phase transition boundary in the Cr2O3-free CaO–MgO–Al2O3–SiO2 system. The parameters of the Grt–Opx equilibrium range within 1060–1120°C and 2.2–2.6 GPa. Thus, magmatic pyroxenite was transported to a great depth into the mantle, which provides evidence for delamination in the region of the lower continental crust containing ultramafic cumulates.

The influence of melt composition on the partitioning of trace elements between anorthite and silicate melt

The effect of melt composition on the partitioning of trace elements between anorthite and silicate melts has been studied experimentally in five compositions in the system CaO–Al2O3–SiO2 (CAS) at ~ 1400 °C and four compositions in the system CaO–MgO–Al2O3–SiO2 (CMAS) at 1332 °C. Melt composition has a significant impact on the substitution of trace elements into anorthite, particularly if the trace-element substitution is aliovalent and requires a charge balance for substitution. Melt composition strongly influences the partitioning of the trivalent rare earth element (REE) cations into the large-cation site (M) of anorthite. Due to charge balance requirements, the activity of alumina in the melt is the most important compositional variable for the REE partitioning in anorthite. Scandium, another trivalent cation, is much more compatible than is predicted for trivalent cations partitioning on the M-site. Therefore, scandium is likely partitioning onto the tetrahedral site in place of aluminium, which requires no charge balance and therefore is not affected strongly by melt composition. Similarly, the partitioning of the small divalent cations (Be and Mg) show a stronger relationship with changing melt composition than the large divalent cations (Ca, Sr, and Ba) and therefore are likely to partition on the tetrahedral site (T) of plagioclase rather than the large-cation site (M). Detailed thermodynamic modelling of the effects of melt composition is required for an adequate parameterization of trace-element mineral/melt partition coefficients, in addition to models of the effects of mineral composition.

Retention of phosphates from aqueous solutions with in sol–gel-derived amorphous CaO–MgO–Al2O3–SiO2 system as a model of blast furnace slag

The article proposes new possibilities for the estimation of the maximum phosphate retention capacities (PRC) in blast furnace slags using their modeling. The amorphous blast furnace slag model (BFS–SG) and slag samples along the joining of the CaO:SiO2 = 1 and (CaO + MgO):SiO2 = 1 of the CaO–MgO–Al2O3–SiO2 phase diagram were prepared by the sol–gel method. The surface analysis of BFS–SG was performed and the results were compared with real BFS. Batch adsorption experiments were performed to evaluate the phosphate removal of slags. SEM analysis and Raman spectroscopy were used to identify phosphate adsorbed forms. Phosphate retention is realized by the surface reactions of hydration products resulting in a nanostructured Ca-hydroxyapatite. The acid–base properties of the model samples in the selected cross-sections were characterized by the values of the optical basicity. An excellent linear relation between the phosphorus retention capacity (PRC) and the optical basicity of the model samples was found, which allows an estimation of slag retention capacities and the forms of adsorbed phosphorus.

Production of Uvarovite Ceramic Pigments Using Granulated Blast-Furnace Slag

The conditions for obtaining and the rules for changing the color indices of ceramic pigments in the system CaO–MgO–Al2O3–SiO2–Cr2O3 are established. The main phase of such pigments is chromium garnet, formed with the direct participation of blast-furnace slag minerals. It is shown that as the acidity of pigment batches is increased by equimolecular substitution of free silicon dioxide in their composition based on phosphorus oxide (V) the purity and intensity of the green color of uvarovite pigments intensifies and the firing temperature of the pigments increases to 1100 – 1150°C.

Viscosity and liquidus temperature of quaternary glasses close to an eutectic composition in the CaO–MgO–Al2O3–SiO2 system

The thermal properties of the quaternary glass-forming CaO–MgO–Al2O3–SiO2 system were evaluated. Different glass compositions with an expected liquidus temperature—the lowest temperature at which both the crystal phase and the melt are thermodynamically stable—below 1300 °C were melted from pure raw materials. Each oxide concentration did not deviate by more than ±3 mol% from that of the centre glass composition of 61.2 SiO2, 26.3 CaO, 8.6 Al2O3 and 3.8 MgO. Viscosity data and the liquidus temperatures were determined, as well as the exact compositions of the respective glasses by X-ray fluorescence. It was of special interest for this study, whether small compositional changes have a stronger influence on TLiq or T3. The T3-values, which are the temperatures attributed to a viscosity of 103 dPa s—showed a much larger variation and are in the range from 1263 to 1363 °C. An exchange of the network formers Al2O3 or SiO2 by network modifiers CaO and MgO resulted in a decrease in viscosity. The effect of MgO was also shown by a comparison with glasses of similar compositions but without any MgO. The exchange between Al2O3 and SiO2 did not show a significant difference in viscosity whereas the substitution of CaO by MgO increased the viscosity. The liquidus temperature varied between 1137 and 1192 °C—less than expected for a composition close to an eutectic system.

X-ray absorption study of 3d transition-metals and Mg in glasses and analogue crystalline materials in AFe3 + Si2O6 and A2X2 + Si5O12, where A = K, Rb, or Cs and X = Mg, Mn, Fe, Co, Ni, Cu, or Zn

Crystalline and glassy phases in the ‘leucite’ systems (K,Rb,Cs)Fe3+Si2O6 and (K,Rb,Cs)2(Mg,Mn,Fe,Co,Ni,Cu,Zn)2+–Si5O12 have been studied using K-edge X-ray Absorption Spectroscopy (XAS) for 3d transition elements and Mg. Crystalline samples of known structure are used as model compounds for deducing the local structures of the equivalent glasses. ‘Ideal’ tetrahedral framework X2+–O distances are: Mn2+–O 2.02, Fe2+–O 1.98; Co2+–O 1.96, Ni2+–O 1.95, Cu2+–O 1.92, Zn2+–O 1.93 and Mg2+–O 1.93Å. The quenched glasses have Extended X-ray Absorption Fine Structure (EXAFS) first-shell distances and coordination numbers consistent with Mg and 3d elements occurring in tetrahedral coordination in most cases. The X-ray Absorption Near Edge Structure (XANES) spectra of the glasses are basically the same as those for the crystalline samples showing that they have similar medium range order, consistent with most of the Mg and 3d elements acting as network formers along with the associated alkalis as X2Y2+O2 complexes. Anhydrous glasses in the system CaO–MgO–Al2O3–SiO2 together with a basalt glass from Hawaii show examples of Mg in octahedral- (2.07Å, basalt), tetrahedral- (~1.87Å, siliceous glass) and 5-coordinated (2.01–2.04Å) sites. Although most Earth scientists assume that Mg and Fe2+ act as network modifiers in natural magmas, ultra-potassic, peralkaline compositions ((Na+K)/(Al+Fe3+)>1) could have had some Fe2+ and Mg complexes with alkalis in the melt network as K2(Mg,Fe2+)O2 and the implications of this to melt density and viscosity are considered.

Phase formation, microstructure and luminescence properties of calcium–magnesium–aluminosilicate based glass-ceramics with Eu3+ doping

The glass-ceramics from CaO–MgO–Al2O3–SiO2 system with the Eu3+ doping were prepared by a melt-quenching technique following by a controlled crystallization step employing the heat treatment process. The selected treatment temperatures were guided by the DTA measurement. The obtained glass-ceramic samples were characterized by the XRD, SEM and fluorescence spectroscopy. The results of XRD revealed that Mg2(Si2O6) and Diopside (CaMg(SiO3)2) presented as two major embedded crystalline phases. This observation was consistent with the result of SEM which showed the presence of well-shaped crystallites with size in nano-scale. With the increasing of the heat treatment temperature, the approximated crystallite volume fraction increased gradually and induced the change of phase type. Fluorescence technique was applied to characterize the role of Eu3+ ions after entering into the glass-ceramics. By recording the excitation and emission spectra at room temperature, the main emission peak of the samples located at a wavelength of 613nm after subjecting to 394nm excitations. This indicated that the obtained glass-ceramics can be applied as a red phosphor.

Carbon dioxide in silicate melts at upper mantle conditions: Insights from atomistic simulations

The detail of the incorporation of carbon dioxide in silicate melts at upper mantle conditions is still badly known. To give some theoretical guidance, we have performed first-principle molecular dynamics simulations (FPMD) to quantify the speciation and the incorporation of carbon dioxide in two CO2-rich silicate melts (~20wt.% CO2 at 2073K and 12GPa), a basaltic and a kimberlitic composition chosen in the CaO–MgO–Al2O3–SiO2 system. In the basaltic composition, carbon dioxide is incorporated under the form of a minority population of CO2 molecules and a prevailing population of carbonate ions (CO32−). In contrast, the amount of CO2 molecules is found to be very small in the kimberlitic melt. Moreover, a new (transient) species has been identified, the pyrocarbonate ion C2O52− issued from the reaction between CO2 and CO32−. With regard to the structure of the CO2-bearing melts, it is shown that the carbonate ions modify the silicate network by transforming some of the oxygen atoms into bridging carbonates, non-bridging carbonates, and free carbonates, with a distribution depending on the melt composition. In the basaltic melt a majority of carbonate ions are non-bridging or free, whereas in the kimberlitic melt, most of the carbonate ions are under the form of free carbonates linked to alkaline earth cations. Surprisingly, the addition of CO2 only has a weak influence on the diffusion coefficients of the elements of the melt. The consequence is that the strong enhancement of the electrical conductivity reported recently for carbonated basalts (Sifré et al., 2014, Nature 509, 81), can be reproduced by simulation only if one assumes that the ionic charges assigned to the elements of the melt depend, in a non-trivial way, on the CO2 content. Finally, a comparison of the FPMD calculations with classical molecular dynamics simulations using an empirical force field of the literature (Guillot and Sator, 2011, GCA 75, 1829) shows that the latter one needs some improvement.

CaO–MgO–Al2O3–SiO2 glass-ceramics from lithium porcelain clay tailings for new building materials

Lithium porcelain clay tailings (containing 1.2wt.% Li2O) blended with other chemical raw materials were used to develop a new glass-ceramic of CaO–MgO–Al2O3–SiO2 system for rolling process. The effects of TiO2 and ZnO oxides on melting and crystallization behaviors of glasses were investigated by DTA, XRD, EPMA and viscosity test. The results showed that melting temperature, forming temperature and glass transition temperature (Tg) of glasses were decreased with the increase of ZnO addition. Nevertheless, the crystallization temperature was shifted from 864 to 901°C when the addition of TiO2 decreased from 2wt.% to 0.5wt.%. Diopside as a major crystalline phase and spinel as a minor phase are precipitated in M3 specimen with 2.5wt.% ZnO and 0.5wt.% TiO2. The columnar and granular crystalline phases were distributed in M3 specimen nucleated at 750°C for 2h and followed by crystallization at 1110°C for 2h, which resulted in proper appearance suitable for decorative materials.

Low-Temperature-Tunnel of High-Alumina Ceramics with Good Wear Resistance

As for the liquid-phase sintered (LPS) Al2O3 based on the CaO-MgO-Al2O3-SiO2 (CMAS) system, we found a strange phenomenon. It is commonly acknowledged that, the sintering temperature should be high corresponding with the increase of the content of Al2O3 in a special system. However, when the content of Al2O3 is limited within 95-98wt%, the conclusion is opposite. It means that there is a low-temperature sintering-tunnel. What’s more, as wear resistant materials, the wear rate of alumina ceramics reduces with the increasing of the content of Al2O3 among 95-98wt%. In this paper, taking industrial alumina as raw material, we obtain low-wear-rate high-alumina ceramics by conventional sintering in CMAS system. We explain and analyze the condition from the perspective of crystalline phase and microstructure by XRD and FESEM. The results show that the 98 porcelain is of better wear resistance and indicate excellent prospect in the fabrication of lower wear rate of high-alumina ceramics.

Development of a Thermodynamic Database for Mold Flux and Application to the Continuous Casting Process

A thermodynamic database for the oxyfluoride system CaO–MgO–Al2O3–SiO2–Na2O–K2O–Li2O–MnO–FeO–F has been developed based on the critical evaluation and optimization of all available experimental thermodynamic and phase diagram data. The developed database can be used for phase diagram and equilibrium solidification calculations for multicomponent systems. Such accurate database with high predictability capability assists in understanding the crystallization behavior of mold fluxes. In addition, a kinetic model was developed to simulate the interactions between the mold flux and molten steel using effective equilibrium reaction volumes combined with the thermodynamic database. The kinetic model successfully reproduced the significant Al2O3 accumulation observed when casting high Al steel with CaO–SiO2 based mold flux. Equilibrium solidification calculation performed on the Al2O3-rich mold slag revealed detrimental changes in the solidification temperature, the primary phase and the evolution of the liquid fraction with temperature.