Compared with conventional heat treatment, microwave heating demonstrates advantages for refractory castables, offering faster heating rates, lower drying explosion risk, and much higher energy efficiency. However, how the microwave heating affects their microstructure and properties remains insufficiently understood. This study systematically evaluates three heating methods: conventional electric furnace, pure microwave heating, and microwave-electric furnace hybrid, focusing on their impacts on properties of calcium aluminate cement (CAC)-bonded alumina-spinel castables. Results demonstrate that the microwave-electric furnace hybrid process effectively regulates morphology and distribution of plate-like calcium hexaluminate (CA(6)), while significantly refining pore structure and enhancing the mechanical properties. Among the designed processes, the microwave drying at 700 degrees C similar to 900 degrees C followed by electric furnace heating at 1600 degrees C presents optimal performance, attributed to the refined growth of CA(6) and the preserved micro-scale pore structure that delivers balanced strength-toughness performance through structural energy consumption. Therefore, it is feasible to apply microwave drying in ladle lining monolithic.

Alumina–spinel castables are critical refractory linings in ladle furnaces, significantly impacting refining efficiency and steel cleanliness. During secondary refining, slag composition fluctuates considerably due to varying steel grades, ranging from CaO‐rich basic slags to SiO 2 ‐rich acidic slags. Extensive research exists on basic slag corrosion with established mitigation strategies. In contrast, acidic (low‐basicity) slag corrosion remains a significant challenge, leading to drastically reduced service life and compromised steel purity. This study systematically investigates the corrosion behavior of alumina–spinel castables against slags of varying basicity, complemented by thermodynamic simulations using FactSage to elucidate the underlying mechanisms. To address the critical issue of acidic slag attack, La 2 O 3 was employed to enhance the refractory. Based on comprehensive slag corrosion test, detailed microstructural analysis, and structural characterization, a novel slag corrosion resistance mechanism of La 2 O 3 ‐doped castables was revealed. La 2 O 3 primarily incorporates into the calcium hexaluminate (CA 6 ) phase within the matrix. Upon contact with SiO 2 ‐rich acidic slag, La 2 O 3 promotes the preferential formation of a high‐melting‐point, high‐viscosity lanthanum‐calcium–silicate (La‐Ca‐Si‐O) phase. This newly formed silicate network with high structural stability and more bridging oxygen bonds reduces the rapid dissolution of alumina and CA 6 in the matrix, thereby enhancing the acidic slag corrosion resistance. Consequently, a dense, protective interfacial barrier analogous to the CA 2 /CA 6 layer formed under basic slag conditions is established.

This study aims to enhance the thermal stress resistance of alumina-spinel castables by incorporating different mass fractions (0.5-2.0 wt%) of randomly oriented steel fiber. The mechanical properties of the steel fiber-reinforced castables were investigated, and the thermal shock resistance was evaluated using the water quenching method at 1100 degrees C. Additionally, high-temperature wedge splitting test was employed to evaluate the steel fiber enhanced fracture behavior at 1200 degrees C and 1400 degrees C. The results demonstrate that the incorporation of steel fiber improves the overall mechanical properties of the castables, and 1 wt% steel fiber enhanced castables exhibit approximately double the residual mechanical properties after one thermal shock at 1100 degrees C, and the corresponding number of thermal shock cycles to reach critical thermal shock damage has doubled. At elevated temperatures (<1400 degrees C), 1 wt% steel fiber shows significant improvement in toughness through fiber bridging, crack deflection and branching mechanisms.

Despite the successful preparation of high-performance calcium aluminate cement-bonded castables, occasional explosions have been reported. The occurrence of castable explosions is commonly attributed to water vapor overflow retarding and vapor pressure generated by rapid temperature rise. To enhance the explosion resistance of castables, methods such as incorporating various fibers (e.g., polypropylene [PP], polyethylene [ED], aramidic [Par], and steel fibers) have been proposed. However, limited studies have investigated the impact of fiber content on pore structure and fracture behavior of castables. This study aims to assess the influence of different PP fiber contents on comprehensive properties of castables. The explosion resistance was evaluated in conjunction with air permeability and pore structures, and fracture behavior was tested through wedge splitting tests at both room temperature and elevated temperatures. Results indicated that the addition of PP fibers significantly improves air permeability thus enhancing anti-explosive capabilities. Simultaneously, the combustion of fibers resulted in the formation of residual pores, which contributed to an enhanced resistance against stress-induced damage.

Lamellar hydrates such as mono-carbonate (C4AcH11) and Mg-Al hydrotalcite (M-A-H) were formed by incorporating nano-CaCO3 and nano-hydromagnesite into calcium aluminate cement (CAC), and their impacts on the early setting behavior, microstructure, thermo-mechanical properties and slag penetration resistance of alumina- magnesia castables were investigated. The results indicated that the introduction of nano-CaCO3 and nanohydromagnesite into CAC could induce the formation of lamellar hydrates after curing at temperatures ranging from 40 degrees C to 80 degrees C, facilitating the hydration of cement, which enhanced the early strength of castables. The further sintering effect of CaCO3 and the specific C2AH8-like plate structure of C4AcH11 optimized medium- temperature strength. After undergoing high-temperature treatment, the interlocking structure of needle-like CA6 and in-situ formed MA at temperatures in the range of 1400-1600 degrees C strengthened the ceramic bonding, resulting in high resistance to dynamic thermo-mechanical damage and slag penetration. In conclusion, the evolution of phases with temperature and refined pore structures related to the nano-additives optimized the overall properties of alumina-magnesia refractory concrete.

Hydratable alumina-bonded castable is a promising non-cement bonded refractory for ladle lining. An in situ formation of layered double hydroxides (Mg-Al hydrotalcite, M-A-H) using reactive MgO powders is proposed as a means of enhancing the castables during curing, drying, and after the high-temperature treatment. The formation of hydrotalcite, spinel transformation, pore structure, mechanical properties, fracture behavior, and slag corrosion resistance have been systematically investigated. The results indicate that the hydrotalcite formation is governed by the hydration reactivity of MgO, which promotes the formation of Mg(OH)2 as an intermediate hydrate, and the ultimate growth of hydrotalcite. The residual MgO and newly formed hydrotalcite are eventually transformed into micron size and submicron size spinel, respectively. This structural evolution contributes to an optimized pore structure and microstructure, enhancing the castables. The ultimate pore structure and enhanced interfaces between aggregate and matrix facilitate the improvement of toughness and slag corrosion/penetration resistance.

In this study, nano CaCO3 was added to CAC to prepare mono-carbonate hydrate (C4AcH11). The mechanical properties, pore structure, and fracture behavior at high temperatures of mono-carbonate bonded alumina-spinel castables were assessed. The results showed that the plate-like mono-carbonate promotes early setting behaviors and higher demolding strength. The sintering effects of nano CaCO3 compensate for the strength decay at intermediate temperatures. Moreover, well-distributed CaO sources are essential to forming smaller and elongated CA(6) interlocking laminar structures and contribute to the refinement of pore structures (<10 m) after firing at 1600 degrees C. The fracture behavior of CAC-bonded alumina-spinel castables evaluated at 1400 degrees C shows that the deformation of fine grains/matrices and pores leads to typical nonbrittle fracture.

Lamellar hydrates of CAC were designed with the introduction of Mg -Al hydrotalcite (M -A -H), and the effects on the early setting behavior, demolding strength, pore structures, mechanical properties, and fracture behavior of alumina-spinel castables were investigated. The results showed that Mg -Al hydrotalcite stimulated rapidly the hydration of CAC and the formation of lamellar C2AH8 and C4AcH11 when curing at 25 and 40 degrees C. In comparison, CAH10 and C2AH8 were detected without M -A -H and were transformed completely into C3AH6 at 40 degrees C. The formation of lamellar C2AH8 and C4AcH11 would contribute to a more complicated pore structure, especially in the range of 1-10 mu m. Meanwhile, the incorporation of MgO from M -A -H also regulates the distribution of CA6 and spinel (pre -formed and in -situ). Consequently, the optimized microstructure and complicated pore structure can induce the deflection and bridging of cracks, thus facilitating the consumption of fracture energy when testing at 1400 degrees C.

水氯镁石是一种非常具有应用前景的镁盐资源,其储量丰富,成本低廉.以青海盐湖水氯镁石和水玻璃合成不同MgO/SiO2摩尔比(0.5:1,1:1,1.5:1)的水合硅酸镁(M-S-H)凝胶,采用XRD、SEM、红外和核磁共振等测试手段研究M-S-H的合成机理和结构特征,进而将合成的M-S-H与硅微粉复合制备镁质浇注料,探究M-S-H结构对浇注料结合特性的影响规律.结果表明:不同MgO/SiO2摩尔比的M-S-H呈层状堆叠结构,MgO/SiO2摩尔比为1:1时M-S-H的层间自由水少,结晶度最高;M-S-H替代部分硅微粉制备镁质浇注料能显著提高1550℃热处理后浇注料的力学性能,其中MgO/SiO2摩尔比为1:1的M-S-H复合硅微粉制备的镁质浇注料综合性能最佳,与添加6％(质量分数)硅微粉制备的镁质浇注料相比,其常温抗折强度和高温抗折强度分别提高75％和8％.

水合硅酸镁是炼钢连铸过程中间包用镁质浇注料的重要结合相,其含量多少决定着浇注料的强度大小.本工作以Na2SiO3·9H2O和MgCl2·6H2O为原料,采用水热法合成水合硅酸镁(MgO-SiO2-H2O,M-S-H),研究了焙烧温度和焙烧次数对水合硅酸镁的"结构记忆"特性;随后将预合成M-S-H复合硅微粉制备镁质浇注料,研究其对镁质浇注料性能的影响.结果表明:当焙烧温度低于400℃时,水合硅酸镁具有"结构记忆"特性,焙烧次数增加有利于M-S-H凝胶中层间羟基的插入,促进其层状结构晶粒的长大和结构稳定性的提高;在镁质浇注料制备过程中引入一定量的预合成水合硅酸镁和少量的硅微粉,使浇注料具有很好的施工性能和足够的早期结合强度;同时减少了高温热处理后浇注料缺陷形成,提高了材料力学性能,为开发低硅微粉镁质浇注料提供支撑.

In the present study, the characteristic hydrates (CAH10, C2AH8, and C3AH6) were evaluated at individual curing temperatures (10 degrees C, 25 degrees C, and 40 degrees C), and the influences of these characteristic hydrates on the pore structure and fracture behaviors of alumina-spinel castables were systematically investigated. The results revealed that the specimens cured at 10 and 25 degrees C showed refined and complicated pore structures (higher fractal dimension) after treatment at 1600 degrees C owing to a higher dispersion of CaO and closely interlocked CA6 structures. In comparison, the enhanced hydration degree at 40 degrees C (mostly C3AH6) had no positive effect on the formation of nano-pores. Consequently, the generation of plate-like C2AH8 at 25 degrees C contributed to higher bonding strength after demolding and firing. The optimized microstructures facilitated cracks propagation within the matrixes and along aggregate-matrix interfaces, improving the toughness of castables and obtaining optimal comprehensive properties.

The present work investigated the pore structure evolution and fracture behavior of calcium aluminate cement (CAC)-bonded alumina-spinel castables treated at 110 and 1600 degrees C after curing at 25 degrees C for 1 day and 3 days. The pore structure and fracture behavior were characterized by mercury intrusion combined with micro-CT scanning and a wedge splitting test coupled with acoustic emission, respectively. The results showed that the hydration degree was enhanced by extending the curing time, and more hydrates were conducive to the generation of complex pore structures after drying. In comparison, the heat treatment at 1600 degrees C resulted in a substantial reduction in nano-sized pores, the 3 d sample obtained developed and complex micro-sized pores than 1 d sample. Therefore, specimens cured for 3 d had better hot modulus of rupture (HMOR) and thermal shock resistance compared to those cured for 1 d, which could be attributed to the induced tortuous microcrack propagation within the matrix and along the aggregate-matrix interfaces.

铝酸钙水泥的水化行为与物相组成、粉体粒径、水化温度、外加剂等因素密切相关.已有研究发现沸石结构矿物对铝酸钙水泥的水化行为影响显著,而作用机制有待进一步研究.本文采用XRD、SEM、FTIR、综合热分析以及电导率测试方法,系统研究了不同养护温度(20℃、25℃、30℃和40℃)下合成沸石对铝酸钙水泥水化行为的影响及作用机理.结果表明,合成沸石对铝酸钙水泥水化行为的影响与不同养护温度下离子浓度有关.在20℃养护时,铝酸钙水泥的溶解程度较低且沸石具有超高的比表面积及离子吸附能力,离子浓度难以达到饱和,延长了诱导期,从而延缓了铝酸钙水泥的水化;在25～40℃养护时,沸石的微孔结构和超高比表面积为水化产物提供更多成核位点,进而促进了铝酸钙水泥的水化.此外,合成沸石的引入有效消除了铝酸钙水泥在25℃养护时的异常凝结行为.

An in-depth investigation of pore structure evolution and corresponding fracture behavior of calcium aluminate cement (CAC) bonded alumina-spinel castables treated at 110-1600 degrees C has been carried out by taking the respective advantages of mercury intrusion and micro-CT scanning, wedge splitting test and acoustic emission, respectively. The results showed that the complexity of nano-sized and submicron-sized pores increased from 110 to 800 degrees C, and then decreased gradually from 800 to 1600 degrees C due to the dehydration of hydrates and formation of C(12)A(7), CA, CA(2), and CA(6) phases. In comparison, the complexity of the pores above 1 mu m increased with the ascent of treating temperatures. Consequently, the heat treatment resulted in deterioration of "toughness" owing to the vanish of majority of nano-sized and submicron-sized pores and the subsequent formation of strong ceramic bonding. The fractal dimension of pore structure presented positive correlation with "toughness" of castables, where higher fractal dimension standed for higher frature energy consumption within matrix caused by tortuous crack propagation paths.

h-BN can be applied in Al2O3–C refractories to substitute graphite due to their similar crystal structure and better resistance to molten steel and oxidation. The effects of h-BN particle size on the mechanical properties and fracture behavior of Al2O3–C refractories were investigated through wedge splitting test and microstructural analyses. The obtained results demonstrated that the addition of larger-sized h-BN was conducive to the growth of in situ formed SiC whiskers, which contributed to the highest flexural strength (42.63 ± 3.10 MPa) of specimen D10. In comparison, the smaller-sized h-BN can induce more crack propagation paths along the interface and within matrix, leading to more tortuous crack propagation paths, and thus the thermal shock-related parameters such as specific fracture energy, characteristic length, and thermal shock resistance were improved. Consequently, the residual strength ratio of Al2O3–C refractories was increased from 35.5% to 42.5% with decreasing the h-BN particle size from 10 to 0.1 μm.