Microstructure of geopolymer accounting for associated mechanical characteristics under various stress states

Geopolymer was prepared with various SiO₂/Na₂O mole ratios and mechanical tests and microstructural analyses are performed to investigate how the constituents affect its mechanical behavior in distinct stress states. Laboratory results reveal that the SiO₂/Na₂O ratio affects the polymerization by influencing the formation of silicon Q⁴(mAl) structures. The proportion of Q⁴(4Al) correlates positively with the mechanical characteristics of geopolymer, and the proportion of Q⁴(2Al) correlates negatively with the mechanical characteristics of geopolymer. The proportions of Q⁴(mAl) affect the stress–strain curve and the failure modes of geopolymer under various confining pressures. Three types of stress–strain curves with different peak strengths and plastic deformations are obtained. Incomplete polymerization generates a geopolymer with an imperfect microstructure, which determines the plastic deformation while unloading. Polymerization of a geopolymer affects its apparent cohesion and friction angle. However, the friction-induced strength declines drastically when the failure mode changes from the split mode to the shear mode.     

Synthesis and adsorption performance of fly ash/steel slag-based geopolymer for removal of Cu (II) and methylene blue

In order to realize the value-added resource utilization of solid waste, geopolymer particle adsorbents were prepared at low temperatures using silica-aluminum-rich fly ash and steel slag powders as raw materials. In order to investigate the mechanism of their adsorption of dyes and heavy metal ions from wastewater, the effects of steel slag/fly ash ratio, adsorbent dosage, initial concentration of methylene blue (MB) and Cu²⁺ solution, adsorption time and temperature on the adsorption performance of the fly ash/steel slag-based geopolymer adsorbents were investigated, systematically. Results presented that the adsorption capacities of MB and Cu²⁺ were 33.30 and 24.15 mg/g, and the removal efficiencies were 99.90% and 96.59% with the dosages of 3 and 4 g/L geopolymer adsorbents (steel slag/fly ash ratio of 20 wt.%), respectively. The adsorption processes of MB and Cu²⁺ on the adsorbents were in accordance with the proposed pseudo-second-order and Langmuir isotherm models, which mainly included physical and chemical adsorption mechanisms. The adsorption was a spontaneous endothermic process. The fly ash/steel slag-based geopolymer had good removal ability for dyes and heavy metal ions, and it could maintain good adsorption performance after three cycles of regeneration. It had potential application in wastewater treatment.     

煤气化粗渣-矿渣基地质聚合物的制备与性能

在煤气化粗渣基地质聚合物中复掺矿渣可改善其早期力学性能。本文以煤气化粗渣和矿渣为原料制备地质聚合物,系统研究了不同矿渣掺量对煤气化粗渣基地质聚合物早期力学性能及微观结构的影响。利用X射线衍射、压汞测试、扫描电镜、傅里叶红外光谱等方法对煤气化粗渣-矿渣基地质聚合物的微观结构进行分析表征。结果表明,当矿渣掺量增加时,地质聚合物抗压强度呈逐渐增大趋势。矿渣掺量为40%(质量分数)时,样品28 d抗压强度高达53.1 MPa。由微观分析可知,掺入矿渣后地质聚合物表面生成了大量水化硅铝酸钙/钠(C(N)-A-S-H)凝胶,使地质聚合物微观结构更为致密,力学性能得到改善。     

Preparation and corrosion resistance of cordierite–spodumene composite ceramics using zircon as a modifying agent

To prolong the service life of cordierite–spodumene composite ceramics applied to the solar heat transmission pipeline, the zircon modifier was introduced to improve the corrosion resistance of the ceramics. The effects of zircon on the density, bending strength, crystalline phase, microstructure and chemical stability were studied. The results showed that the sintering temperature range of the composite ceramics was broadened to 40–60?°C with the introduction of 5–15?wt% zircon. Moreover, the mechanical strength and corrosion resistance of the ceramic materials were improved with the zircon introduction. In particular, sample C3 containing 15?wt% of zircon and sintered at 1360?°C exhibited the best performance, which had the 0.03% Wa, 0.07% Pa, 2.34?g?cm^?3 Db and 100.17?MPa bending strength. After acid and alkali corrosion, the water absorption was still less than 0.5% and the strength loss rate decreased to less than 5.3%. The XRD and SEM analyses demonstrated that the ZrSiO₄ grains dispersed at the grain boundaries could enhance the mechanical properties. Furthermore, the existence of the Zr⁴⁺ ions not only reduced the cationic solubility of the glassy phases but also led to a reaction with OH^? to form Zr(OH)₄ on the surfaces. This improved the corrosion resistance of the composite ceramics and endowed it with a high residual strength after the acid and alkali corrosion.     

Influence of modified multi-walled carbon nanotubes on the mechanical behavior and toughening mechanism of an environmentally friendly granulated blast furnace slag-based geopolymer matrix

This study aimed to investigate the mechanical behavior of an environmentally friendly granulated blast furnace slag-based geopolymer matrix reinforced with modified multi-walled carbon nanotubes (MWCNTs). The modified MWCNTs were obtained using a modification method combining nitric acid and sulfuric acid and were then dispersed using sodium dodecylsulfate (SDS) as a dispersant. Two types and three concentrations of MWCNTs were mixed directly into the aqueous solution, sonicated, and then mechanically mixed with waste granulated blast furnace slag to form the geopolymer matrix. Raman and Fourier transform infrared (FT-IR) spectroscopy were used to evaluate the ordered structure and crystallization degree of the modified MWCNTs. Then, the dispersity of the modified MWCNTs was characterized using transmission electron microscopy (TEM). The compressive and bending strengths were measured to evaluate the mechanical behavior of specimens. Moreover, the polycondensation products, polycondensation degree, pore structure, and microscopic morphology of the geopolymer matrix were analyzed using X-ray diffraction (XRD), FT-IR spectroscopy, nuclear magnetic resonance (NMR), mercury intrusion porosimetry (MIP), and field emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FESEM-EDS). The experimental results showed that the incorporation of 0.1% functionalized MWCNTs had an optimal influence on the fluidity and mechanical behavior. The slump diameters of geopolymers with 0.1% functionalized MWCNTs with and without SDS were increased by 16.3% and 23.5%, respectively, compared with the reference geopolymer matrix. For geopolymer matrix samples at a curing age of 28 d, the compressive strength of geopolymers with 0.1% functionalized MWCNTs with and without SDS were increased by 16.3% and 17.6%, respectively. For the bending strength, the corresponding increases were 17.6% and 18.7%, respectively. It was found that functionalized MWCNTs could increase the degree of polycondensation, leading to a more traditional amorphous N-A-S-H phase, a finer C–S–H phase, more Q⁴ (2Al) and Q⁴ (3Al), and lower porosity. In addition, the propagation of micro-cracks in the geopolymers was inhibited by the incorporation of functionalized MWCNTs.     

Effect of sodium polyacrylate on mechanical properties and microstructure of metakaolin-based geopolymer with different SiO2/Al2O3 ratio

The mechanical properties and microstructure of geopolymer are affected by the molar ratio of SiO₂/Al₂O₃. Meanwhile, organic polymer has the effect of improving the toughness of geopolymer, which depends on the SiO₂/Al₂O₃ ratio of geopolymer inevitably. Therefore, it is important to investigate the effect of the organic polymer on the mechanical properties and microstructure of geopolymer with varying SiO₂/Al₂O₃ ratio for using organic polymer to modify geopolymer. In this work, the SiO₂/Al₂O₃ ratios of metakaolin-based geopolymers are adjusted to 2.0, 2.5, 3.0, 3.5 and 4.0 by adding silica fume and β-Al₂O₃, with Na₂O/SiO₂, H₂O/SiO₂ being maintained at 0.2, 4.0, respectively. The geopolymers with each SiO₂/Al₂O₃ ratios are modified by addition of 0, 0.4, 0.8, 1.2 and 1.6?wt% of sodium polyacrylate (PAAS).The mechanical properties of these samples are measured and the rate of change is used to characterize the effect of PAAS on the metakalin-based geopolymers. The mechanism is also shown by 29Si NMR, XPS and FTIR. The results show that the effects of polymer on the mechanical properties of metakaolin-based geopolymer are affected by SiO₂/Al₂O₃ ratio and the effect becomes less obvious with SiO₂/Al₂O₃ ratio increasing from 2.0 to 4.0. Incorporation of PAAS can reduce the degree of polymerization of [SiO]₄ or [AlO]₄ in geopolymer and form the Si?O?C bond, which are two main reasons for polymer improving the toughness of geopolymer. But these effects decrease when the SiO₂/Al₂O₃ ratio of geopolymer increases from 2.0 to 4.0, which is corresponding to the effect on the mechanical properties. The toughening effect of organic polymer on geopolymer depends on the SiO₂/Al₂O₃ ratio of geopolymer, and only the geopolymer with lower SiO₂/Al₂O₃ ratio (no more than 2.5 in this work) can be significantly toughening modified by organic polymer. Therefore, it is necessary to consider the SiO₂/Al₂O₃ ratio of the geopolymer when geopolymer modified by organic polymer is designed.     

Synergistic effect of glass fibre and Al powder on the mechanical properties of glass-ceramics

To explore the synergistic effect of glass fibre and Al powder on the mechanical properties of glass-ceramics, blast furnace slag was chosen as the main material, and glass fibre and Al powder as reinforcement materials. The phase compositions, microstructures, compressive properties, and apparent density of the glass-ceramics with varying quantities of glass fibre and Al powder were investigated. The experimental results indicated that Al powder could exist as a simple substance in glass-ceramics and form a dense net coating on the surface of blast furnace slag to improve the plasticity of the glass-ceramic. The glass fibre had better reinforcement effect than Al powder because of its extremely high mechanical strength. The plasticity of glass-ceramics, however, severely decreased; the glass-ceramics exhibited brittle failure during compression. A slight increase in the content of CaSi₂ and SiO₂ in the glass-ceramics was closely related to the addition of glass fibre. Considering safety and economy, glass-ceramics with 6% Al and 14% glass fibre (S4) have the best mechanical properties. The compressive strength, strain at maximum force, and apparent density were 40?MPa, 19% and 1.974?g/cm³, respectively.     

XRD Analysis of the Role of Cesium in Sodium‐Based Geopolymer

The purpose of this work was to study the role of cesium in sodium‐based geopolymer and its thermal stability for nuclear waste management. A series of mixed sodium and cesium geopolymer samples (Na_1?x Cs _x )₂O·Al₂O₃·SiO₂·12H₂O (referred to as (Na_{1? x} Cs _x )‐GP, where x = 0, 0.08, 0.15, 0.42, 1) have been prepared. All geopolymer samples were heated at 1100°C for 24 h. Pollucite (CsAlSi₂O₆) and feldspathoid (CsAlSiO₄) were crystallized from Cs‐GP. Nepheline (NaAlSiO₄) and a small amount of crystallized silica were obtained from Na‐GP. The other geopolymers (Na_{1? x} Cs _x )‐GP (x = 0.08, 0.15, 0.42) led to pollucite and nepheline main phases. Amorphous silica phase was observed in all the geopolymer samples with various amounts. Phase quantification and scanning electron microscope revealed that higher Cs concentrations in Na‐GP tend to decrease the amorphous phase while improving pollucite and nepheline phase quantification. The amorphous geopolymers have also been studied by pair distribution function analysis. Tetrahedral chains formed by T–O bonding (with T = Si, Al) were shown to be more tighten around Cs⁺ than around Na⁺. It led to shorter Cs–T bond than Na–T bond matching the higher solvation property of Na⁺. Furthermore, thermal study analysis pointed out the fact that geopolymer samples (Na_{1? x} Cs _x )‐GP, can be considered as solid solutions.     

Phase equilibria of CaO–SiO2–CaF2–P2O5–Ce2O3 system and formation mechanism of britholite

Recently, the sustainable utilization of REE-bearing slag for the recovery and application of rare-earth elements (REEs) has attracted considerable attention. However, a limited amount of thermodynamic data and crystal information for REE systems has been reported, which greatly limits the utilization of REE-bearing slag. In this study, the isothermal phase diagram of the CaO–SiO₂–CaF₂(30 wt%)-P₂O₅(10 wt%)-Ce₂O₃ system was constructed to provide phase equilibria data for the REEs in REE-bearing slag. The formation mechanism of britholite (Ca_5-xCe_x[(Si,P)O₄]₃F) in the quinary system was found: it evolved from Ca₅(PO₄)₃F, when a Ce³⁺ replaced a Ca²⁺, there would be a SiO₄^4? instead of a PO₄^3?. The phase equilibria and formation mechanism of REEs in the CaO–SiO₂–CaF₂–P₂O₅–Ce₂O₃ system are supplied to provide the data required for sustainable utilization of REE-bearing slag.     

Modification of interface chemistry and slag structure by transition element Cr

A comparative study on CaO–MgO–Al₂O₃–SiO₂ slag and CaO–MgO–Al₂O₃–SiO₂–Cr₂O₃ slag was conducted to investigate the distribution of the elements at the gas-slag interface. The effect of redox states of chromium on the distribution of sulfur and oxygen at the interface was revealed by gas-slag equilibrium method using X-ray photoelectron spectroscopy at 1873K. From the analysis of the S2p core-level spectra, the negative divalent sulfur(S^2?) was detected at the interface in the Cr-bearing slag, which directly proved that sulfur exists in the form of S^2? in the slag for the first time. However, the S^2? peak is very weak at the interface of Cr-free slag. The reason for the difference between the two slags may be due to chromium changing the interface structure. According to the O1s and Cr2p core-level spectra, non-bridged oxygen(O^?) increased, while bridged oxygen(O⁰) decreased with the etching depth deepened. The increase of NBO/BO and Cr²⁺/Cr³⁺ elucidates that Cr³⁺ can modify the structure of the slag as basicity substance, but its effect is weaker than that of Cr²⁺. Meanwhile, due to the affinity of sulfur and chromium, the addition of chromium may also lead to the enhancement of the S^2? peak at the gas-slag interface. Gradient change of elements at the interface proved the existence of the boundary layer.     

Interfacial reaction between magnesia refractory and “FeO”-rich slag: Formation of magnesiowüstite layer

This study investigated the reaction between CaO-SiO₂-Al₂O₃-xFeO-MgO-MnO (CaO/SiO₂?=?1.2, x?=?20–50?wt%) slag and magnesia refractory. Using SEM-EDS analysis, we confirmed the formation of a (Mg,Fe)O_{ss(solid_solution)}, called magesiowüstite (MW), intermediate layer at the slag-refractory interface. MgO dissolved from refractory and reacted with the bulk slag to form MW layer at the interface. Simultaneously, slag penetrated through micro-pores and reacted with the refractory to form MW layer. In other words, the MW layer built up in both directions from initial refractory-slag interface. The thickness of the MW layer increased as the FeO content in the slag increased, and using EDS line scanning, a Mg and Fe concentration gradient was confirmed within the MW layer. The slag, which penetrated into the refractory, had a chemical composition of the CaO-SiO₂-Al₂O₃-MgO system without FeO, indicating that FeO was consumed by forming a MW layer at the refractory hot face. The slag-refractory interfacial reaction was simulated using thermochemical software, FactSage?7.0. The results predicted a MW monoxide composed of MgO and FeO. A spinel phase was formed when FeO was greater than 40?wt%. These thermochemical computations were comparable to our experimental findings.     

Performance evaluation of basalt fiber-reinforced geopolymer composites with various contents of nano CaCO3

High carbon footprint of cement production is the major drawback of plain cement concrete resulting in environmental pollution. Geopolymer composites paste can be effectively used as an alternative to Portland cement in the construction industry for a sustainable environment. The demand for high-performance composites and sustainable construction is increasing day by day. Therefore, the present experimental program has endeavored to investigate the mechanical performance of basalt fiber-reinforced fly ash-based geopolymer pastes with various contents of nano CaCO₃. The content of basalt fibers was fixed at 2% by weight for all specimens while the studied contents of nano CaCO₃ were 0%, 1%, 2%, and 3%, respectively. The compressive strength, compressive stress-strain response, flexural strength, bending stress-strain response, elastic modulus, toughness modulus, toughness indices, fracture toughness, impact strength, hardness, and microstructural analysis of all four geopolymer composite pastes with varying contents of nano CaCO₃ using scanning electron microscopy (SEM) were evaluated. The results revealed that the use of 3% nano CaCO₃ in basalt fiber-reinforced geopolymer paste presented the highest values of compressive strength and hardness while the use of 2% nano CaCO₃ showed the highest values of flexural strength, impact strength, and fracture toughness of composite paste. The SEM results indicated that the addition of nano CaCO₃ improved the microstructure and provided a denser geopolymer paste by refining the interfacial zones and accelerating the geopolymerization reaction.     

Integrated experimental phase equilibria study and thermodynamic modelling of the binary ZnO–Al2O3, ZnO–SiO2, Al2O3–SiO2 and ternary ZnO–Al2O3–SiO2 systems

Phase equilibria of the ZnO–SiO₂, Al₂O₃–SiO₂ and ZnO–Al₂O₃–SiO₂ systems at liquidus were characterized at 1340–1740 °C in air. The ZnO–Al₂O₃ subsolidus phase equilibria were derived from the experiments with the SiO₂- and CaO + SiO₂-containing slags. High-temperature equilibration on silica or platinum substrates, followed by quenching and direct measurement of Zn, Al, Si and Ca concentrations in the phases with the electron probe X-ray microanalysis (EPMA) was used to accurately characterize the system. Special attention was given to zincite phase that was shown to consist of two separate ranges of compositions: round-shaped low-Al zincite (<2 mol.% AlO_1.5) and platy high-Al zincite (4–11 mol.% AlO_1.5). A technique was developed for more accurate measurement of the ZnO solubility in the low-ZnO phases (corundum, mullite, tridymite and cristobalite) surrounded by the ZnO-containing slag, using l-line for Zn instead of K-line, avoiding the interference of secondary X-ray fluorescence. Solubility of ZnO was found to be below 0.03 mol.% in corundum and cristobalite, and below 0.3 mol.% in mullite. Present experimental data were used to obtain a self-consistent set of parameters of the thermodynamic models for all phases in this system using FactSage computer package. The modified quasichemical model with two sublattices (Zn²⁺, Al³⁺, Si⁴⁺) (O^2?) was used for the liquid slag phase; the compound energy formalism was used for the spinel (Zn²⁺,Al³⁺)[Zn²⁺,Al³⁺,Va]₂O^2-₄ and mullite Al³⁺₂(Al³⁺,Si⁴⁺) (O^2?,Va)₅ phases; the Bragg-Williams formalism was used for the zincite (ZnO, Al₂O₃); other solid phases (tridymite and cristobalite SiO₂, corundum Al₂O₃, and willemite Zn₂SiO₄) were described as stoichiometric. Present study is a part of the research program on the characterization of the multicomponent Pb–Zn–Cu–Fe–Ca–Si–O–S–Al–Mg–Cr–As–Sn–Sb–Bi–Ag–Au–Ni system.     

Bone ash reinforced geopolymer composites

Potassium-based, geopolymer composites were made with BASF^® metakaolin and Mymensingh clay-derived metakaolin from Bangladesh. Since the natural Mymensingh clay contained 40 wt.% quartz, this same amount of quartz particulates was added to the BASF^® metakaolin to make a synthetic analog of the natural calcined clay. By analogy with bone china, bone ash or calcined hydroxyapatite (5CaO•3P₂O₅ or “HA”) particles, having a Ca: P ratio of 3.3:1, were added to make the three types of geopolymer-based composites described above. For less refractory particulate additions, dicalcium phosphate (DCP) (2CaO•P₂O₅ or “DCP”) particles, having a Ca: P ratio of 2:1, were also added to another set of geopolymers. The ambient temperature compressive and flexural strengths were measured for all of the geopolymer composites. The HA or DCP reinforced geopolymer composites were fabricated and heat-treated to 1150°C/1 h, after which they were converted to their mineralogical analogs. Their mechanical properties of compressive and 3-point flexural strengths were again measured. Flexural strengths of 22.42 ± 11.0 MPa and 31.97 ± 8.3 MPa were measured in 1 × 1 × 10 cm³ heat-treated geopolymer bars reinforced with 10 wt.% of DCP and in geopolymer reinforced with 10 wt.% DCP +40 wt.% quartz additions, respectively. Significant improvements to ambient temperature properties were observed due to the self-healing effect of the flowing amorphous DCP, whose presence was verified by SEM. The geopolymer samples exhibited reduced water absorption (WA) (on a percentage dry weight basis) of within 0.03-0.5% after being heated at 1100℃/1 h and 1125℃/1 h, as compared with those at room temperature, which varied between 2.56% and 7.89%.     

Crystal structure,microstructure, thermal expansion and electrical conductivity of CeO2–ZrO2 solid solution

CeO₂–ZrO₂ solid solution was synthesised by mechanical activation solid-state chemical reaction method and characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal dilatometer, Hebb–Wagner method and DC van der Pauw method. The effects of CeO₂ content on the crystal structure, microstructure, thermal expansion coefficient (TEC), electronic conductivity and total conductivity were investigated. XRD analysis showed that (25 and 75?mol-%) CeO₂–ZrO₂ solid solutions corresponded to tetragonal and cubic phase, and 50?mol-% CeO₂–ZrO₂ belonged to the mixture of tetragonal and cubic phases. SEM analysis showed that doping CeO₂ was helpful to the sinterability of CeO₂–ZrO₂ samples. The TECs increased from 13.27?×?10^?6 to 14.72?×?10^?6?K^?1 with increasing CeO₂ content. The electronic and total conductivities of 75?mol-% CeO₂–ZrO₂ were largest, reaching 1.02?×?10^?4?S?cm^?1 and 1.02?×?10^?2?S?cm^?1 at 850°C, respectively.     

Mechanical properties and prediction of fracture parameters of geopolymer/alkali-activated mortar modified with PVA fiber and nano-SiO2

Properties of fly ash (FA) and metakaolin (MK) based geopolymer/alkali-activated mortar modified with polyvinyl alcohol (PVA) fiber and nano-SiO₂, including workability, compressive strength, flexural performance, elastic modulus and fracture property were tested in this study. PVA fiber content varies from 0 to 1.2%. Nano-SiO₂ content is 0 and 1%. Adaptive neuro-fuzzy interfacial systems (ANFIS) method was used to establish the artificial intelligence (AI) model to predict the fracture parameters of geopolymer/alkali-activated mortars. The inputs of ANFIS models include PVA fiber content, nano-SiO₂ content, compressive strength, flexural strength, elastic modulus, critical crack mouth opening displacement, crack load and peak load. The outputs of ANFIS model include critical effective crack length, initiation fracture toughness, unstable fracture toughness, and fracture energy. Experiment results showed that PVA fiber addition enhanced the mechanical properties especially the compressive strength and fracture performance, but decreased the workability. 0.8%–1.0% was considered as the optimal content of PVA fiber. Addition of 1% nano-SiO₂ shows a slight improvement on both workability and mechanical properties of the mortar no matter how much fiber is added. Based on the ANFIS algorithm and 42 sets of experimental data, the trained models were proved to have high accuracy with root mean square error (RMSE) under 0.15, mean absolute error (MAE) under 0.01, and coefficient of determination (R²) over 0.85. The ANFIS model established in this study combined the fracture properties with the basic mechanical properties of geopolymer/alkali-activated composites, which can provide a new method to assess the fracture performance of geopolymer/alkali-activated mortars modified with PVA fiber and nano-SiO₂ in the future.     

Anionic effect of chloride,fluoride, and sulfide ions on the viscosity of slag melt

The effect of the addition of CaX (X=Cl₂, F₂ and S) on the viscous behavior and structure of CaO–SiO₂–Al₂O₃–MgO–CaX slag was investigated by measuring its viscosity. The viscosity of the slag without CaX gradually decreased with an increase in the C/S ratio because of the depolymerization of the silicate groups in the slag. While the viscosity of the CaX‐bearing slag decreased with an increase in the CaX content, depolymerization was not observed in this case. Three distinct compositional regions for the activation energy of the viscous flow were observed because of the effect of the equilibrium of the polymeric silicate groups. The relaxation effect of the CaX groups on the activation energy was also observed. Raman spectroscopic analysis indicated that the relaxation in the viscosity and activation energy by CaX addition stemmed from the breaking of the NBO‐M²⁺‐NBO linkage to form NBO‐M²⁺‐F^?, NBO‐M²⁺‐Cl^?, or M²⁺‐S^2?. All these results are discussed in detail with the help of a viscous flow model based on the ionic interactions.     

Slag erosion-resistant coating for periclase-magnesia-aluminum spinel brick

The magnesia-carbon bricks are used at the ladle slag line adds carbon to molten steel and thus has an adverse effect on the smelting process. Steel production enterprises hope to remove carbon from the ladle slag line. This study presents a Silica sol (SS)–magnesium aluminate spinel(MA) coating that can be applied to the surfaces of periclase–MA spinel brick (spinel brick) to improve their slag erosion resistance, facilitating the elimination of carbon from the ladle slag line. The slag corrosion resistance mechanism of a spinel brick covered with the SS–MA coating was analyzed through scanning electron microscopy and simulation using FactSage software. The results show that increasing the SS content (C_SS) led to the formation of fine cracks during the coating-drying process and was detrimental to the slag erosion resistance of the coating. The optimum C_SS was 20%. In the high-temperature slag erosion experiment, the MA in the coating was capable of forming solid solutions with Fe and Mn in the slag, and the nano-SiO₂ in the coating interacted with the slag, increasing the viscosity of the slag and reducing its penetration. In addition, the presence of the coating extended the penetration path of the slag and reduced the contact area between the slag and the spinel brick and their chances to undergo chemical reactions, thereby protecting the spinel brick from slag erosion. The coated spinel bricks outperformed the magnesia-carbon brick in terms of slag erosion resistance, providing a basis for selecting carbon-free refractory materials for the ladle slag line.     

Preparation and ladle slag resistance mechanism of MgAlON bonded Al2O3 -MgAlON-Zr2Al3C4-(Al2CO)1-x(AlN)x refractories

MgAlON bonded Al₂O₃-MgAlON-Zr₂Al₃C₄-(Al₂CO)_1-x(AlN)_x refractories were prepared at high temperatures from 1300?℃ to 1600?℃ in N₂-flowing based on the design of Al-AlN core-shell. The refractory prepared at 1500?℃ was chosen to conduct the ladle slag resistance test at 1600?℃ in air. All the refractories are composed of MgAlON, Zr₂Al₃C₄, (Al₂CO)_1-x(AlN)_x and Al₂O₃. The ladle slag resistance test for the chosen refractory presents a good result and there exist two different reaction layers —— the reacted slag layer and the spinel solid solution layer. The reacted slag layer consists of spinel solid solution, Ca-ZrO₂ and gehlenite/gehlenite solution, where the formation of those phases has changed the chemical composition and phase composition of the original ladle slag. The compact spinel solid solution layer forms by the decomposition of MgAlON into rich-Al₂O₃ spinel and the incorporation of Mn²⁺ and Fe^2+/3+ into rich-Al₂O₃ spinel, which plays an important role in slag penetration resistance.     

Preparation of in situ grown silicon carbide whiskers onto graphite for application in Al2O3-C refractories

C-SiC composite powders were prepared by salt-assisted synthesis from Si powders, graphite, and a molten salt medium (NaCl and NaF) with the molar ratio of Si/C =?1/2 at 1300?°C for 3?h. After the C-SiC composite powders part and complete replacement of the graphite, the mechanical properties, oxidation resistance and slag-corrosion resistance of the Al₂O₃-C materials were studied by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), as well as with dedicated equipment. The results indicated that SiC whiskers, with lengths of 10–50?nm, formed on the surface of the flake graphite, and the activation energy of oxidation of the C-SiC composite powder increased by 45.72?kJ?mol^?1 as compared to that of flake graphite. Furthermore, the decarburization area and slag erosion area of the Al₂O₃-C material decreased after 3?wt% of C-SiC composite powder was substituted for the flake graphite. Meanwhile, the cold modulus of rupture was maintained when 3?wt% of C-SiC composite powder was added. This improved both the oxidation and slag resistance of the Al₂O₃-C materials.