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Refractory materials are an important pillar for the stable development of the high-temperature industry. A large amount of waste refractories needs to be further disposed of every year, so it is of great significance to carry out research on the recycling of used refractories. In this work, lightweight composite aggregate was prepared by using discarded Al[sub.2]O[sub.3]-ZrO[sub.2]-C refractories as the main raw material, and the performance of the prepared lightweight aggregate was improved by adjusting the calcination temperature and introducing light calcined magnesia additives. The results showed that the cold compressive strength and thermal shock resistance of the lightweight aggregates were significantly improved with increasing calcination temperature. Moreover, the introduction of light calcined magnesia can effectively improve the apparent porosity, cold compressive strength, and thermal shock resistance of the prepared lightweight aggregates at the calcination temperature of 1400 °C. Consequently, this work provides a useful reference for the resource utilization of used refractories, while the prepared lightweight aggregates are expected to be applied in the field of high-temperature insulation.

MnO[sub.2] and CeO[sub.2] were doped to improve the corrosion resistance of CSZ (calcia-stabilized zirconia), and we studied the phase formation, mechanical properties, and corrosion resistance by molten mold flux. The volume fraction of the monoclinic phase gradually decreased as the amount of MnO[sub.2] doping increased. The splitting phenomenon of the t(101) peak was observed in 2Mn_CSZ, and in 4Mn_CSZ, it was completely split, forming a cubic phase. The relative density increased and the monoclinic phase decreased as the doping amount increased, leading to an increase in Vickers hardness and flexural strength. However, in 3Mn_CSZ and 4Mn_CSZ, where cubic phase formation occurred, the tetragonal phase decreased, leading to a reduction in these properties. MnO[sub.2]-doped CSZ exhibited a larger fraction of the monoclinic phase compared to the original CSZ after the corrosion test, indicating worsened corrosion resistance. These results are attributed to the predominant presence of Mn[sup.3+] and Mn[sup.2+] forms, rather than the Mn[sup.4+] form, which has a smaller basicity difference with SiO[sub.2], and due to the low melting point. The monoclinic phase fraction decreased as the doping amount of CeO[sub.2] increased in CeO[sub.2]-doped CSZ, but the rate of decrease was lower compared to MnO[sub.2]-doped CSZ. The monoclinic phase decreased as the doping amount increased, but the Vickers hardness and flexural strength showed a decreasing trend due to the low relative density. The destabilization behavior of Ca in SEM-EDS images before and after corrosion was difficult to identify due to the presence of Ca in the slag, and the destabilization behavior of Ce due to slag after corrosion was not observed. In the XRD data of the specimen surface after the corrosion test, the fraction of the monoclinic phase increased compared to before the test but showed a lower monoclinic phase fraction compared to CSZ. It is believed that CeO[sub.2] has superior corrosion resistance compared to CaO because Ce predominantly exists in the form of Ce[sup.4+], which has a smaller difference in basicity within the zirconia lattice.

Coatings based on refractory metals and compounds have been used in various industries since the last century due to their high thermal and heat resistance, as well as their excellent mechanical and tribological properties. Advances have made it possible to apply high-tech methods for their production, which has improved their availability and expanded their range of applications. A promising area of use of coatings based on refractory systems is the anticorrosion protection of structural materials. The high wear resistance and anticorrosion ability of these materials will allow for the protection of critical units of equipment of various industries from the complex destructive effects of factors of chemical and mechanical nature. For the effective choice of coating composition, it is necessary to know the basic characteristics of refractory material layers and the method of their production. The purpose of this article is to summarize modern scientific data on methods of obtaining refractory coatings, as well as on their composition, structure, and protective properties. The information presented in this review will bridge the gap between research and industrial development and expand the niche area of utilization.

Nowadays, digitalization and automation in both industrial and research activities are driving forces of innovations. In recent years, machine learning (ML) techniques have been widely applied in these areas. A paramount direction in the application of ML models is the prediction of the material service time in heating devices. The results of ML algorithms are easy to interpret and can significantly shorten the time required for research and decision-making, substituting the trial-and-error approach and allowing for more sustainable processes. This work presents the state of the art in the application of machine learning for the investigation of MgO-C refractories, which are materials mainly consumed by the steel industry. Firstly, ML algorithms are presented, with an emphasis on the most commonly used ones in refractories engineering. Then, we reveal the application of ML in laboratory and industrial-scale investigations of MgO-C refractories. The first group reveals the implementation of ML techniques in the prediction of the most critical properties of MgO-C, including oxidation resistance, optimization of the C content, corrosion resistance, and thermomechanical properties. For the second group, ML was shown to be mostly utilized for the prediction of the service time of refractories. The work is summarized by indicating the opportunities and limitations of ML in the refractories engineering field. Above all, reliable models require an appropriate amount of high-quality data, which is the greatest current challenge and a call to the industry for data sharing, which will be reimbursed over the longer lifetimes of devices.

This study presents the development of a novel alumina-based ceramic composite designed for refractory applications in auxiliary components of sintering furnaces. The innovative concept relies on a three-phase microstructural architecture: a fine-grained alumina matrix improves cohesion, coarse particles act as crack propagation barriers, and spherical granules are intentionally introduced to increase porosity while preserving mechanical strength. This design reduces thermal capacity, enhancing the material’s energy efficiency under high-frequency thermal cycling and offering potential for operating cost reduction. A further novelty is the water-free forming process, which eliminates issues related to drying and deformation. The material was characterized using scanning electron microscopy (SEM), mechanical strength testing, and refractoriness under load (RUL) analysis to establish the structure–property relationships of the developed composite. The results demonstrate that the developed spherical alumina-based composite possesses excellent thermal and mechanical properties, making it a promising candidate for high-temperature industrial applications, particularly as auxiliary refractory plates.

The nonhydraulic minerals (Fe[sub.3]O[sub.4], RO phase, Fe) in slag are important indicators for evaluating the pozzolanic activity and detecting the quality of the slag activation processing technology. Fe[sub.3]O[sub.4] is an important characteristic mineral among the nonhydraulic minerals. In order to accurately assess the pozzolanic activity of steel slag powder and to monitor the quality of the activation process of steel slag powder for separate nonhydraulic minerals, it is imperative to precisely determine the nonhydraulic mineral content within the steel slag. Further refinement and enhancement are required for both the HNO[sub.3] dissolution method used in determining Fe[sub.3]O[sub.4] content in steel slag, as well as for the EDTA-DEA-TEA (ethylenediamine tetraacetate sodium-diethylamine-triethanolamine) dissolution method employed in determining total nonhydraulic minerals, due to potential deviations caused by challenging impurity separations. The results show that the content of Fe[sub.3]O[sub.4] is determined by 10%HNO[sub.3]-20%NaOH-chemical analysis method, which solves the problem that the impurities of refractory materials (quartz, corundum, mullite) and amorphous phase affects the content determination in HNO[sub.3] dissolution method. The total amount of nonhydraulic minerals (Fe[sub.3]O[sub.4], RO phase, Fe) was determined by the EDTA-NaOH-TEA dissolution method, which solved the problem that the incomplete dissolution of C[sub.2]F in the EDTA-DEA-TEA dissolution method affected the content determination. The maximum error between the content determination value and the theoretical calculation value of the two methods is less than 0.50%. The improved Fe[sub.3]O[sub.4] and total nonhydraulic mineral quantification methods are feasible and reliable.

In recent years, research in the field of the sustainable production of refractory ceramics has become topical. Significant attention has been paid to the use of secondary raw materials for obtaining high-quality materials. The purpose of the current study was to develop new high-temperature porous materials based on the magnesium sulfate-refractory clay–chamotte–aluminum system using environmentally friendly raw components. To synthesize porous refractories, rice husk and the by-products of its thermal processing were used as substitutes for ingredients usually introduced into the composition of high-temperature materials. Ground rice husk was used as both a burnout additive and a silica source. It was added to the mixture instead of chamotte. An organic condensate from rice husk pyrolysis was used as a binder. A sodium silicate solution, after activating pyrolyzed rice husk with alkali, was also tested as a binder. These liquid ingredients served as replacements for lignosulfonate and liquid glass. The new raw material components and the porous refractories obtained with their use were studied using methods of chemical analysis, XRD, GC-MS, TA, SEM, and EDS. Standard methods for studying the properties of refractories were used to evaluate the physicomechanical and thermal characteristics of the experimental materials. The sample with the maximum content of rice husk (14.4 wt.%) and organic condensate from its pyrolysis (10.5 wt.%) demonstrated promising properties as a light porous refractory: an apparent porosity of 44%, a volumetric weight of 1.1 g·cm−3, compressive strength of 2.1 MPa, tensile strength in bending of 4.5 MPa, bond strength of 0.01 MPa, thermal shock resistance of 155 thermal cycles, and thermal conductivity of 0.05 W (m·K)−1. It can be used as a prospective thermal insulating material.

Forsterite (Mg[sub.2]SiO[sub.4]) materials have been used in the industrial applications of refractory materials, bone grafting materials, and microwave dielectric materials. In order to avoid the formation of the secondary phase of MgO or MgSiO[sub.3], spray pyrolysis with the precursors of magnesium nitrate hydrate and tetraethyl orthosilicate has been applied to synthesized Mg[sub.2]SiO[sub.4] powders. In this study, three typical morphologies of smooth solid sphere, rough hollow sphere, and concaved hollow sphere were observed using scanning electron microscopy and transmission electron microscopy. The experimental results suggested that morphology and particle size distribution are strongly influenced by the calcination temperature. Finally, the corresponding powder formation mechanisms were proposed and discussed.

The refractory lining of high-temperature aggregates determines the duration of their operation before major repairs. The ability to retain technological material within the aggregate’s working area is the main factor for its continued operation. The analysis shows that the main reason for the destruction of the lining of ferroalloy production casting ladles is the occurrence of thermal stresses in the processes of heating and cooling the lining. When the stresses exceed the ultimate strength of the refractory material used, the material is destroyed. The greater the magnitude and duration of the excess thermal stresses, the faster the lining destruction occurs. Streamlining thermal regimes is the most low-cost and sufficiently effective way to increase the durability of linings. The development of lining heating and cooling regimes can be carried out on the basis of determining the thermal stress state by calculating the maximum permissible heating rates. The developed regimes allow for working at speeds at which the resulting stresses do not exceed the ultimate strength of the refractory materials. The aim of this study is to develop efficient cooling regimes for the lining of a ferroalloy production casting ladle from the standpoint of the resulting thermal stresses. A method for determining the thermal stresses in the lining has been developed and implemented using Microsoft Excel. This facilitates the use of the developed methodology in production without the need for special skills on the part of operating personnel. Using the developed methodology, the cooling schedules for the lining of ferroalloy production ladles were improved. To reduce temperature unevenness across the lining cross-section, a decision was made to initially heat the outer surface of the lining and cool the inner surface of the lining. Heating the outer surface can be achieved by using the heat of combustion of the ferroalloy gas or the heat of the exhaust gases from the stand for drying and heating casting ladles. Cooling the inner surface of the lining can be achieved by natural convection. The result of the development and implementation of an efficient cooling regime is a reduction in thermal stresses to the required level throughout almost the entire cooling process.

Physicomechanical properties and structure of mullite-corundum unmolded refractories are investigated and tests of a pilot batch of refractory products for various purposes are conducted. The effect of the adding nanosize SiO.sub.2 (1 wt.%) on strength, structural (density, porosity) and operational properties of unmolded refractories is studied. Results show that this additive contributes to formation of a structure with high apparent density and compressive strength (2.93 and 2.98 g/cm.sup.3, 87.3 and 162.1 MPa, respectively for two types of refractories), reduces open porosity from 20 to 14%, and also increases the life of refractory products (according to operating duration) by 25 - 35% compared with basic refractory life. The use of SiO.sub.2 nanoparticle additives reduces refractory product and raw material consumption for their manufacture, and also increases production profitability.