High Melting Point Phase Research Articles

A comparative study on the slag resistance of MgO–C, low‐carbon MgO–C, and MgO–SiC–C refractories

AbstractThe corrosion of slag on refractories usually starts from the matrix, so improving the slag resistance of the matrix is of great significance for the slag resistance of the refractories. To clarify the influence of matrix on the slag resistance of magnesia–carbon refractories, the slag corrosion experiments were conducted at 1873 K on MgO–C refractories, low‐carbon MgO–C refractories, and MgO–SiC–C refractories. The results showed that the slag resistance of MgO–C refractories was higher than that of low‐carbon MgO–C refractories, and the slag resistance of MgO–SiC–C refractories was superior to that of low‐carbon MgO–C refractories. The interaction between MgO–SiC–C refractories and slag generated high melting point phases such as forsterite and spinel, reducing the routes for the slag to infiltrate the inside of the refractories. MgO–SiC–C refractories reacted with slag to increase the viscosity of the slag, the viscosity being 86.3% and 51.9% higher than in the case of low‐carbon MgO–C and MgO–C refractories, respectively. Compared with MgO–SiC–C refractories, MgO–C refractories did not exhibit overwhelming advantages in slag resistance. Due to the low‐carbon content and good slag resistance, MgO–SiC–C refractories were promising low‐carbon magnesia‐based refractories for high‐temperature industries.

Effect of nano-oxides on corrosion resistance of Al2O3–ZrO2–C material

The Al2O3–ZrO2–C material was prepared using tabular alumina aggregates and fines, zirconia-corundum, zirconia-mullite, flake graphite, B4C powder, Si powder and different nano-oxides (nano-ZrO2, nano-TiO2, and nano-Al2O3) as raw materials, the effects of different nano-oxides on the corrosion resistance and microstructure evolution of Al2O3–ZrO2–C material were investigated. The results showed that the high reactivity nano-ZrO2, nano-TiO2, and nano-Al2O3 particles reacted with CaO to generate high melting point phases of CaZrO3, CaTiO3, CaO·6Al2O3 (CA6) at high temperature, which forms a protective layer at the interface between corroded media and samples, inhibiting CaO penetration into the material. Additionally, nano-oxides can fill the pores and increase the density of material, thereby contributing to improving the penetration resistance and corrosion resistance of material.

Slag resistance mechanism of MgO–Mg2SiO4–SiC–C refractories containing porous multiphase aggregates

The slag resistance of MgO–SiC–C (MSC) refractories should be improved because of the mismatch in the thermal expansion coefficient between the aggregates and matrix, as well as the defects caused by the affinity between periclase and slag. In this study, MgO–Mg2SiO4–SiC–C (MMSC) refractories were prepared using porous multiphase MgO–Mg2SiO4 (M-M2S) aggregates to replace dense fused magnesia aggregates. Compared to MSC, the slag penetration index of MMSC decreased by 43.5%. The structure of the porous aggregates increased the surface roughness, and the multiphase composition of the aggregates decreased the mismatch of the thermal expansion coefficient with the matrix, thus reducing debonding between the aggregates and matrix. The aggregates and matrix in the MMSC formed an interlocking structure, which bound them more tightly to improve the slag resistance. The slag viscosity at different depths from the initial slag/refractory interface was calculated using the Ribond model. The M-M2S aggregates increased SixOyz− in the slag, which increased the slag polymerization and slag viscosity. The aggregates and matrix in the MMSC reacted with the slag to form high melting point phases, which reduced the channel of the slag. In addition, the penetration depth and velocity derived from the Washburn Equation were modified for the CaO–SiO2–Al2O3–MgO–FeO slag and magnesia based refractory to accurately evaluate slag penetration.

Effect of in situ formation of Ti(C,N) on the properties of Al2O3–ZrO2–C slide plate material

AbstractAl2O3–ZrO2–C slide plate was ordinarily used in sliding nozzle system because of its excellent mechanical properties and slag corrosion resistance. This study improved the slag corrosion resistance of the slide plate by the carbothermic reduction of TiO2 and aluminothermic reduction of TiO2 under high temperature in coke bed to generate Ti(C,N) phase in situ. The result revealed that TiC of the high melting point phase could enter into anorthite (CaAl2Si2O8) of the low melting point phase, forming eutectic phase CaAl2Si2O8–TiC, and improve the viscosity of the slag. Furthermore, TiC and CaAl2Si2O8 captured FeO and MnO from the slag, resulting in the increase of the slag viscosity, inhibiting the penetration corrosion of the slag, and improving the slag corrosion resistance of the materials. In general, compared with the material without TiO2 powder, the slag corrosion resistance of the material introduced 2 wt.% TiO2 powder was increased by 24%. Meanwhile, the cold crushing strength of fired specimen at room temperature was increased by 35.6%.

High-entropy perovskite RETa3O9 ceramics for high-temperature environmental/thermal barrier coatings

Four high-entropy perovskite (HEP) RETa3O9 samples were fabricated via a spark plasma sintering (SPS) method, and the corresponding thermophysical properties and underlying mechanisms were investigated for environmental/thermal barrier coating (E/TBC) applications. The prepared samples maintained low thermal conductivity (1.50 W·m−1·K−1), high hardness (10 GPa), and an appropriate Young’s modulus (180 GPa), while the fracture toughness increased to 2.5 MPa·m1/2. Nanoindentation results showed the HEP ceramics had excellent mechanical properties and good component homogeneity. We analysed the influence of different parameters (the disorder parameters of the electronegativity, ionic radius, and atomic mass, as well as the tolerance factor) of A-site atoms on the thermal conductivity. Enhanced thermal expansion coefficients, combined with a high melting point and extraordinary phase stability, expanded the applications of the HEP RETa3O9. The results of this study had motivated a follow-up study on tantalate high-entropy ceramics with desirable properties.

Study on the protective effect of the dense slag layer on converter lining

AbstractIn this paper, the protective effect of the dense slag layer on the furnace lining is investigated through comparative sampling of residual bricks. The physical and chemical properties of the residual brick samples were tested, and the result showed that sample NO.1 had 7.9% higher bulk density, 37.6% lower apparent porosity, 41% higher flexural strength, and 14.3% higher compressive strength than sample NO.2. The residual carbon of sample NO.1 was normal, while the residual carbon oxidation loss rate of sample NO.2 was 36%. X‐ray diffractomer (XRD), optical microscope (OM), and EDS: scanning electron microscope‐Energy Dispersive Spectrometer (SEM+EDS) were adopted to study the physical phase composition, microscopic morphology, and mineral phase composition and distribution of the dense slag layer. The slag layer was found to be highly alkaline and oxidizing, with 58–73% RO phase, 17–26% phosphorus‐rich phase, and 6–16% base phase in the mineral phases. The FactSage 8.1 thermodynamic software was used to simulate and calculate the melting temperature of each mineral phase. The presence of the high melting point phase and RO phase in the dense slag layer is an important reason for its ability against high temperature and high oxidation. The formation of the dense slag layer was related to the saturated solubility of MgO. The results indicated that the extremely unstable saturated solubility of magnesia had a greater effect on the dissolution rate of magnesia particles. External temperature and oxidation changes are important factors affecting the saturated solubility of MgO in the slag layer, and reducing the internal‐external heat and mass transfer rate could effectively improve the service life of the furnace lining.

Joining of SiC ceramics using the Ni-Mo filler alloy for heat exchanger applications

In order to meet the sealing demands of SiC heat exchanger, the Ni-Mo filler alloy was designed, prepared and employed to braze SiC ceramics. Wetting behavior of the Ni-Mo filler alloy on SiC ceramics and interfacial microstructure of the brazed joints were systematically characterized using optical observation furnace and XRD, SEM, EDS, TEM, respectively. Flexural strengths of the brazed joints at room temperature and high temperature were measured with four-point flexural strength method. HCl immersion test was performed to evaluate the corrosion resistance of the joints. The Ni-Mo filler alloy exhibited excellent wettability on SiC ceramics. During the process of brazing, SiC reacted with element Ni of the Ni-Mo filler alloy, resulting in the formation of Ni2Si + graphite reaction layer adjacent to the SiC substrate. Ni3Mo3C and Ni2Si compounds were precipitated at the center of brazing seam. When the brazing temperature increased from 1250 ℃ to 1400 ℃, the thickness of Ni2Si + graphite layer increased gradually. The maximum room-temperature flexural strength of 174 ± 33 MPa was obtained when brazed at 1300 ℃ for 40 min. The joints also exhibited stable high-temperature strength and acid corrosion resistance. When the test temperature was 700 ℃, 800 ℃, 900 ℃, the joints gave the strength retention rate of 92.5 %, 79.8 %, 67.2 %, respectively. It was believed that the formation of high melting point phases played an important role. Residual strength of the joints after HCl corrosion exceeded 130 MPa, revealing a good potential for applications in corrosion environment.

Latent Heat Thermophotovoltaic Batteries

Latent heat thermophotovoltaic (LHTPV) batteries are a kind of power-to-heat-to-power storage (PHPS) system that combines very high melting point phase change material (PCM) with thermophotovoltaic (TPV) energy conversion. Electricity is employed to produce the solid-liquid phase transition in the PCM. Consequently, electrical energy is stored in the form of latent heat at very high temperatures (> 1000oC). When needed, stored energy is released as thermal radiation, and converted back to electricity on demand using TPV. Additionally, heat can be also delivered from the cooling of the TPV cells, or directly from the PCM to provide the heating demands. In this study we discuss on the techno-economics of LHTPV systems, focusing on parameters like the round-trip efficiency, the energy-to-power ratio (storage duration), the cost per energy and power capacities, and the levelized cost of storage, all of them depending on the specific selection of PCM and TPV generator. In a purely electrical system, the relatively low TPV conversion efficiency (< 50%) and the low cost of the PCMs (< 4 €/kWh) result in optimal system designs with small power-to-energy ratios, fitting long duration storage application. LHTPV systems delivering also heat can be used for short duration storage applications in fully electrified energy systems where there is heat demand. In all the cases, large-scale LHTPV systems are preferable to minimize the impact of thermal insulation in the total cost of the system. The use of lower melting point PCMs, like FeSiB, enable a significant reduction of the cost per energy capacity, favoring their use in smaller scale applications. On the contrary, higher melting point PCMs, like Si, enable a significant reduction of the cost per power, favoring their use in shorter duration applications. Preliminary experimental results using copper PCM and GaSb TPV cells are provided to illustrate the real operation of a LHTPV system.

Microstructural evolution of Al-Cu-Li alloys with different Li contents by coupling of near-rapid solidification and two-stage homogenization treatment

Microstructural improvement of Al-Cu-Li alloys with high Li content plays a critical role for the acquisition of excellent mechanical properties and ultra-low density. In this regard, the Al-Cu-Li alloy castings with high Li content from 1.5wt.% to 4.5wt.% were prepared by near-rapid solidification, followed by two-stage homogenization treatment (490 °C/16 h and 530 °C/16 h). The microstructural evolution and solidification behavior of the as-cast and homogenized alloys with different Li contents were systematically studied by combining experiments with calculations by Pandat software. The results indicate that with the increase of Li content, the grain sizes decrease, the solution ability of Cu in the matrix α-Al phase increases, while the content of secondary dendrites increases and the precipitated phases change from low melting point phases to high melting point phases under the near-rapid solidification. Additionally, by the coupling of near-rapid solidification and two-stage homogenization, the metastable precipitated phases (Al7Cu4Li and AlCu3) can be dissolved effectively in the alloys with Li content of 1.5wt.%–2.5wt.%; moreover, the stable precipitated phases (Al6CuLi3 and Al2CuLi) uniformly distribute at the grain boundaries in the alloys with Li content of 3.5wt.%–4.5wt.%. As a result, the refined and homogenized microstructure can be obtained.

The Online Research of B2O3 on Crystal Behavior of High Ti-Bearing Blast Furnace Slag

The existence and phase structures of high Ti-bearing blast furnace slag at a high temperature are the key issue to flow performance and reaction temperature. It is essential to evaluate the physical-chemical properties, such as viscosity and melting point In this work, a new method of online research of B2O3 on crystal behavior of high Ti-bearing blast furnace slag is proposed. By ultrahigh-temperature confocal laser scanning microscope and area scanning analysis, it can be concluded that the effect of B2O3 additives on the viscosity has a more obvious effect among the low-temperature region of the slag. Compared to the samples without B2O3 additives, the liquid phase of Ti-bearing slag with B2O3 additives appears earlier at the same experimental temperature, and the solid particles floating on the surface of liquid slag become less. Moreover, the B2O3 additives can promote the migration of titanium elements from the high melting point phase to the low melting point phase, and the transferring quantity increases with the addition of the amount of B2O3 additives. These results demonstrate that B2O3 additives can restrain the appearance of the perovskite phase, decrease the apparent viscosity, and promote the metallurgical properties of Ti-bearing blast furnace slag.

From ferronickel slag to value-added refractory materials: A microwave sintering strategy

The present study proposes a novel strategy for preparation of refractory materials from potentially hazardous ferronickel slag by microwave sintering of the slag with addition of sintered magnesia in which a series of chemical reactions were involved. This strategy was developed based on examination of the phase transformations and microstructural changes of the slag during microwave sintering through X-ray diffraction (XRD) analysis and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analysis, which determined the properties of refractory materials derived from the slag. It was shown that under microwave irradiation there existed rapid transformation of the olivine phase in the slag to high-melting point phases, including forsterite and spinels (e.g., magnesium iron chromate spinel, magnesium chromate spinel, and magnesium iron aluminate spinel). As a result, a high-quality refractory material with refractoriness of 1730 °C, bulk density of 2.80 g/cm3, apparent porosity of 1.6%, and compressive strength of 206.62 MPa was obtained by microwave sintering of the slag at 1350 °C for only 20 min with addition of 25 wt % sintered magnesia. Because the microwave sintering strategy not only elevated the refractoriness by 70 °C, but also reduced the heating duration required by the conventional approach by 6 times, it demonstrated apparent technological superiority and wide application prospect in preparing superior-quality refractory materials from ferronickel slag and relevant industrial waste, which contributed to conservation of resources and energy as well as environmental protection.

Anisotropy of mechanical and thermal properties of perovskite LaYbO3: first-principles calculations

ABSTRACTLaYbO3 ceramic material with a perovskite structure has the advantages of a high melting point, sintering resistance and high-temperature phase stability. It is a promising candidate for a structurally and functionally integrated material. However, the anisotropy of physical properties of LaYbO3 has rarely been studied. Herein, the anisotropy of the mechanical and thermal properties of LaYbO3 was studied by first-principles calculations. The elastic coefficients, Young’s modulus, Poisson’s ratio and minimum thermal conductivity of LaYbO3 were found to exhibit anisotropic characteristics. In particular, the sound velocity of the longitudinal wave was nearly twice that of the transverse wave. Especially, the minimum thermal conductivity of LaYbO3 at high temperature was found to be as low as 0.88 W/m K, indicating that the compound has potential for use in thermal insulation applications.

Corrosion behavior of alumina-carbon composite brick in typical blast furnace slag and iron

The corrosion behavior of alumina-carbon composite brick (ACCB) in CaO-8%MgO-14%Al2O3-SiO2 blast furnace slag and iron was investigated at different slag basicity and time via rotating immersion method. The results show that the erosion caused by slag is lightest and increases with the increase of basicity, while the slag and iron region is the most eroded area. The erosion caused by iron decreases with increasing basicity, and the whole erosion extent increases with time elapsing. The penetration of slag into ACCB is mainly appears on the boundary of corundum and mullite, while some unwashed-away high melting point phase like MgAl2O4 can mitigate the corrosion. The dissolution of carbon from ACCB into iron is one of the erosion reasons of ACCB, and the reaction between carbon and silica in ACCB can also be promoted by the appearance of iron. A synthetic action caused by slag and iron in this region leads to the worst erosion. And the reduction of SiO2 on the slag-iron interface relates the basicity of slag to the iron erosion degree.

Facile Route for Preparing Refractory Materials from Ferronickel Slag with Addition of Magnesia

The feasibility of a facile technological route to preparation of refractory materials from a ferronickel slag with the addition of sintered magnesia was verified in this study based on the thermodynamics analysis and the experimental exploration of the effect of the sintered magnesia addition on the phase transformation of ferronickel slag during the sintering process. For the first time, the results of thermodynamics calculation, X-ray diffraction (XRD), and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analyses revealed that the original phase of the slag can be transformed to high melting point phases by addition of MgO during the sintering process at high temperatures (e.g., 1350 °C). Specifically, the olivine in ferronickel slag decomposed initially, generating a low-iron olivine phase and an enstatite phase. With increasing addition of sintered magnesia, the enstatite phase changed to forsterite, and the iron, aluminum, and chromium components in the ferronickel slag c...

A promising new class of plasticine: Metallic plasticine

Soft, malleable, and non-dry on exposure in air are the typical features for plain plasticine, which lead plasticine to be widely used in many industrial fields and our daily life. As a kind of clay, poorly electric conductivity and thermal conductivity of plain plasticine seriously limit its applications. Therefore, synthesizing a kind of plasticine having metallic bond is of importance for extending its applications in some special cases, such as thermal-cooling medium, anti-static electricity, electromagnetic shielding, etc. Here, we report a novel GaInSnCdZn2 alloy, which exhibits similar behavior as compared to those of plasticine at near room temperature (30–40°C), and a good electrical conductivity due to its nature of metal. This new GaInSnCdZn2 alloy can be called as metallic plasticine that contains the near-eutectic structure with low melting point and the other relatively high melting point phases. In this metallic plasticine, the near-eutectic structure with low melting point plays the same role as the oily ingredient in plain plasticine, dominating the plastic deformation, while the other relatively high melting point phases act as the stuffing like the CaCO3 in plain plasticine. The creation of metallic plasticine offers a general strategy for designing/preparing a new class of plasticine which possesses both the nature of metal and plasticine.

Study on a Lime-Fluorite Slag Melting Agent for Ladle Slag Buildup

The Al2O3-MgO-Cr2O3 brick, which is used for wear lining in the ladle slag line, was selected, and the static crucible method was applied to perform a slag sticking test with the refining slag and then investigate the effect of the lime-fluorite slag melting agent with different recipes. The slag corrosion and penetration rate of samples were measured, and the microscopic structure was analyzed through a scanning electron microscope (SEM), the possible slag melting effect and the proportion of active lime and fluorite were discussed. The results show that, with an increase of CaF2 in the slag melting agent, the corrosion and penetration rate rise as well, and a corrosion ring in the sample was observed while the content of CaF2 reached the certain value. The high melting point phases including MA, CA2, CA6, C3T2 and the low melting point phases including C2AS, CAS2, CA were distributed discontinuously. Suitable slag melting agents could reduce the viscosity of the slag, form the discontinuous high melting phases and corrosion ring, so as to achieve the purpose of slag melting for ladle lining.

Research on Elements Distribution in Hot Dip Aluminum Silicon Coating of Hot Stamping Steel

Al-Si coating in different hot dip process conditions were made by a hot-dip galvanizing simulator, and distribution regularities of chemical elements in coating were studied by means of GDS, SEM, EDS and XRD. The results show that the hot dip temperature has no obvious impact on elements distribution in coating, but has some impact on Si content in surface coating. The hot dip time has no obvious impact on surface coating element content, but has distinct impact on deep coating element content. With the hot dip time increasing, Al content decreases, Fe content increases, and Si content decreases. Al-Si coating is composed of 3 layers, surface layer contains fine and close Al2O3 film, which has good anti-oxidation property on high temperature and hot stamping property, middle layer contains high melting point phase ,such as rich Fe phase , FeAl3 ,which has excellent anti-oxidation property on high temperature. The elements in diffusion layer can even be transited to basic steel, so coating has good adhesion property.

Effect of LPC on the Corrosion Behavior of AZ81 Magnesium Alloy

The corrosion behavior of AZ81 magnesium alloy with the LPC addition has been investigated in this paper. The results show that with the addition of 1-5% LPC, the microstructure of AZ81 magnesium alloy is remarkably refined, and the spotted, high-melting point phase Al-RE intermetallic compounds is found in the alloy. The corrosion behavior of AZ81 alloy decreases firstly and then increases sharply with the increase of LPC addition. When the content of LPC is 2.5%, AZ81 magnesium alloy shows the lowest corrosion rate. The corrosion rates in 3.5%NaCl solution are always higher than those in 0.5%NaCl solution. The corrosion products from the surface are mainly composed of Mg (OH) 2 compositions.

Application of Alumina-Magnesia Precast Blocks for LF Refining Ladle

The alumina-magnesia precast blocks developed in authors company have been successfully used in 90-ton LF refining with an average service life 80-85 heats to meet the smelting demand of low carbon steel and ultra low carbon steel. The observation of the residual blocks revealed that the section of the used blocks was divided into four layers from inside to the surface, i.e., slag layer, reaction layer, penetration layer and the original block. It has been found that there was a certain degree of structure spalling of the used blocks. The main factor of blocks damage may be due to the penetration and erosion of molten slag. The results of SEM microstructure analysis indicated that the calcium oxide (CaO) of high basicity slag easily penetrated into the blocks and formed CA6 phase, and then transformed into CA2 or C12A7 phases gradually with the decreasing content of alumina (Al2O3). It has been found that an annular distribution structure, and the silicon dioxide (SiO2) was easily lost together with slag and formed SiO2-rich part in the penetration layer due to the formation of low viscosity and low melting point phase of C2AS. A large number of-5um spinel particles (MgAl2O4) were synthesized at 1600~ 1700, which could absorb FeO, MnO and other impurities in slag to form composite spinel phase. It is believed that the high melting point phases intertwined to form a dense area which was beneficial to improve the bricks' slag resistances to penetration and corrosion

06/01663 Screening of high melting point phase change materials (PCM) in solar thermal concentrating technology based on CLFR: Hoshi, A. et al. Solar Energy, 2005, 79, (3), 332–339

06/01663 Screening of high melting point phase change materials (PCM) in solar thermal concentrating technology based on CLFR: Hoshi, A. et al. Solar Energy, 2005, 79, (3), 332–339