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MgO-SiC-C refractories demonstrate distinguished thermal shock resistance and slag resistance, making them a promising alternative to magnesia-chrome refractories in matte smelting furnaces. Herein, we propose a novel approach to enhance both oxidation resistance and slag penetration resistance of such refractories by incorporating Si 3 N 4 -Fe powder. The results demonstrated that adding Si 3 N 4 -Fe powder effectively enhanced their overall performance. The oxidation resistance of the specimen with 6 wt% Si 3 N 4 -Fe was greatly improved because Si 3 N 4 in Si 3 N 4 -Fe could promote in-situ reactions to form more forsterite, and the FeO formed by iron oxidation could react with SiC to form Fe-Si alloys; the formed forsterite and Fe-Si alloys worked together to prevent oxygen intrusion. Meanwhile, Si 3 N 4 in Si 3 N 4 -Fe promoted the formation of forsterite layer in the corrosion area of refractories, and the reaction of Si 3 N 4 and Fe in Si 3 N 4 -Fe formed Fe-Si alloys to prevent slag penetration, which greatly improved the resistance to matte slag penetration of the refractories. [ABSTRACT FROM AUTHOR]

High-purity magnesia refractories were fabricated by brine magnesium hydroxide from the salt-lake brine (Qinghai Salt Lake) and Y 2 O 3 as an additive at 1780 °C. It avoided the substantial CO 2 emissions and ultra high temperature sintering process (＞1900 °C) when compared with the conventional magnesite-calcination technical approach. The results confirmed that Y 2 O 3 was dispersed on the MgO grains boundaries in the fabricated MgO aggregates, resulting in a decrease in apparent porosity and enhancing the grains' boundaries. With 3 wt% addition of Y 2 O 3 , the apparent porosity and bulk density of the sample reached to 15.9 % and 3.10 g/cm3 from 37.9 % to 2.30 g/cm3 of blank control group, respectively. Compared to the blank control without Y 2 O 3 -adding, the sample with 5 wt% Y 2 O 3 exhibited a 54.17 % increase in the resistance to molten slag. SEM results indicated that the incorporation of Y 2 O 3 in samples increased the porosity of small pores and enhanced grains boundaries, thereby suppressing slag's penetration. Furthermore, the Y 2 O 3 -adding was employed to disperse the MgO grains boundaries and existed as separate phases for grains boundaries enhancement. The slag attack of the fabricated MgO–Y 2 O 3 refractory raw materials were controlled by an inter-crystalline corrosion process. [ABSTRACT FROM AUTHOR]

This study deals with the design and development of a new generation of MgO–C refractory material implementing spent MgO–C recyclate as a partial replacement of fresh raw materials, and a non-hazardous environment-friendly lactose- and tannin-based binder system. Throughout the experimental campaign the used MgO–C recyclate, which was received in three size fractions, was analysed, and building on the obtained results, multiple batches of various compositions of next-generation MgO–C bulks were prepared. These bulks varied in the ratio between the individual size fractions of the MgO–C recyclate, the ratio between the individual binder components and the amount of water used during the preparation of the raw material batches. The bulk samples were prepared in the form of cylinders through uniaxial pressing, cured and coked, and studied in terms of their cold crushing strength, microstructural parameters, thermal behaviour, residual carbon content, and microstructure. The proposed next generation of MgO–C composites represents a potential eco-friendly alternative to MgO–C refractories prepared from traditional raw materials while utilizing waste material which would otherwise end up landfilled. [ABSTRACT FROM AUTHOR]

Carbon fibers (C f) were incorporated into Al 2 O 3 –C refractories to enhance their toughness in this work. The results indicated the 0.3 wt% C f -adding improved the high-temperature bending strength to 1.93 MPa from 1.07 MPa, and led to a 55 % enhancement in thermal shock resistance. The above enhancement could attributed to the in-situ formed SiC coating which was observed on the carbon fiber's surface and strengthened the interface bonding between the carbon fiber and refractory matrix. A solid-liquid diffusion reaction was employed to describe the formation process of in-situ SiC layer on the carbon fibers. Furthermore, the wedge-splitting test with digital images was carried out to investigate the crack-growth trajectory during the splitting process. It was confirmed that C f -adding could enhance the strength and reduce brittleness with the crack-bridging, pullout, and interlock behaviors of carbon fibers in the refractory matrix. [ABSTRACT FROM AUTHOR]

On the rising demand for eco‐friendly refractories, reducing the use of likely toxic magnesia‐chromium aggregates remains a challenge. Previous studies by some of the authors have proposed Cr‐free alternative compositions, although the morphology of the spinel precipitates has varied across the different suggested systems. The mechanisms involved in the formation of these distinct morphologies were unclear and, therefore, are the focus of this work. In all compositions, SEM/electron backscatter diffraction revealed cube–cube orientation relationships between matrix and precipitates, indicating that their formation is influenced by the lattice parameter misfit (δ), which was measured using synchrotron X‐ray diffraction. It could be concluded that coarser and spherical precipitates form to minimize their surface‐to‐volume ratio in compositions with high absolute δ‐values. Conversely, low‐misfit systems enable the spinel to form a 3D‐network. The potential use of this knowledge to tailor the microstructure of novel compositions was demonstrated by a small Nb2O5 addition into one of the proposed compositions. [ABSTRACT FROM AUTHOR]

In this study, a novel MgO–C refractory, fabricated through high–temperature nitriding, was developed by incorporating Si–Al 4 SiC 4 to in–situ form plate–like Mg–sialon ceramic bonding phase in situ. The influences of Al 4 SiC 4 content and nitriding temperature on the phase transformation, microstructure, and mechanical properties of MgO–C refractories were examined. The synergistic effect of Si co–existed with Al 4 SiC 4 promoted the in–situ formation of plate–like Mg–sialon, thereby accelerating the densification of MgO–C refractories. The primary crystal growth surface for Mg–sialon was identified as the (100) facet. The plate–like Mg–sialon was integrally bonded within the matrix, enhancing the interfacial bonding with MgO particles, rather than merely adhering to the surface. The incorporation of 2 wt% Al 4 SiC 4 significantly optimized the microstructure of MgO–C refractories, culminating in superior mechanical properties when nitrided at 1400 °C. Furthermore, the formation mechanism and morphological evolution of the plate–like Mg–sialon in MgO–C refractories were explored. • Novel in–situ Mg–sialon enhanced low–carbon MgO–C refractories have been developed. • The coexistence of Si with Al 4 SiC 4 synergistically facilitated the in-situ formation of plate-like Mg-sialon. • The addition of 3 wt% Si and 2 wt% Al 4 SiC 4 demonstrated optimal properties for the novel refractories. • The thermodynamics of the nitridation process was simulated and calculated. • Mg–sialon formation occurs predominantly through a solution–precipitation mechanism. [ABSTRACT FROM AUTHOR]

In order to overcome the serious corrosion problem of furnace hearth refractory materials for smelting reduction ironmaking, the Cr 2 O 3 –Al 2 O 3 –MgO–ZrO 2 refractories were synthesized, and the phase component, microstructure, mechanical characteristics, and slag erosion behavior of composite refractories were investigated and evaluated. The results indicate that the composite refractories mainly consist of Mg(Al, Cr) 2 O 4 spinel phase, (Al, Cr) 2 O 3 solid solution and ZrO 2. The content of Mg (Al, Cr) 2 O 4 spinel significantly increases with the increasing MgO content, while the content of (Al, Cr) 2 O 3 obviously decreases. Furthermore, the comprehensive mechanical properties of the MgO modified composite refractories can be obviously enhanced by increasing the MgO content, and sample S4 presents the best mechanical characteristics when the MgO addition is 10 wt%. The corresponding hardness, compressive strength and bending strength are 14.22 GPa, 267.14 MPa and 80.0 MPa, respectively. This is mainly because the formation of Mg(Al, Cr) 2 O 4 significantly improves the densification of composite refractories, and a large number of high-strength Mg (Al, Cr) 2 O 4 spinel "bridge" formed between the large-sized (Al, Cr) 2 O 3 grains. The erosion test results indicate that increasing the MgO content can significantly improve the slag infiltration resistance of composite refractories, because the formation of Mg (Al, Cr) 2 O 4 spinel layer significantly improves the densification of MgO reinforced composite refractories. Although the slag corrosion resistance of Mg(Al, Cr) 2 O 4 is lower than that of (Al, Cr) 2 O 3 , the Cr 2 O 3 –Al 2 O 3 –MgO–ZrO 2 refractories still presents good erosion resistance, permeability resistance, and excellent mechanical characteristics. [ABSTRACT FROM AUTHOR]

This study explored the feasibility of utilizing varying proportions of metakaolin – MK (4, 6, or 8 wt%) and two types of alkaline liquid reagents – LR (incorporating nanosilica and NaOH or KOH) to induce in situ geopolymer formation in high-alumina refractory castables. The impact of geopolymeric binders on processing behavior, as well as on the physico-mechanical and structural properties of the designed refractories, was investigated within a temperature range of 40–1250 °C. Optimal physico-mechanical performance and thermal shock resistance were achieved with compositions 8 MK-Na (prepared with 8 wt% MK and NaOH-based LR) and 6 MK-K (containing 6 wt% MK and KOH-based LR). The liquid generation during viscous sintering enhanced castable densification at 1100–1250 °C and promoted the formation of nepheline, kalsilite or leucite phases. This resulted in microstructures featuring a suitable interfacial bond strength between the glassy phase and alumina grains, leading to an interlocking structure and improved castable properties. These achievements underscore the potential of geopolymer-bonded high-alumina castables for applications involving intermediate temperatures (800–1200 °C), such as those found in the petrochemical and non-ferrous metal industries. [ABSTRACT FROM AUTHOR]

A Ti1.5Nb1Ta0.5Zr1Mo0.5 (TNTZM) refractory high entropy alloy (HEA) with a cellular structure was successfully fabricated by laser powder bed fusion (L-PBF). Compression testing and cyclic deformation testing results revealed that, in the cellular structure, the cell walls could store dislocations. Furthermore, the local chemical order (LCO) plays a crucial role in controlling dislocations within the cell wall region. The LCO not only facilitates dislocation slip but also generates additional lattice distortion upon stress-induced LCO destruction to enable dislocation pinning. This work offers novel insights into the microstructure of additively manufactured refractory HEAs and uncovers a distinct dislocation regulation mechanism. [ABSTRACT FROM AUTHOR]

In this work, microporous MgO–Al2O3 refractory aggregates were prepared with Mg(OH)2 and Al(OH)3 via the in situ decomposition synthesis method. The effect of Al(OH)3 addition on the microstructure and properties of microporous MgO–Al2O3 refractory aggregates was investigated with scanning electron microscope and mercury intrusion porosimetry. The results indicated that the improved green density of the samples and the reaction sintering accelerated the mass transport rate with adding Al(OH)3 from 0 to 4.0 wt%. Besides, a small amount of Al3+ diffused into porous MgO particles, accelerating the merging and growth of nanopores in the porous MgO particles. The intra‐particle pore size and the densification degree of microparticles were increased, and thus the strength of the samples was improved. Due to the formation of Kirkendall voids by interdiffusion of Mg2+ and Al3+, the inter‐particle pore size increased. Adding Al(OH)3 from 4.0 to 17.6 wt%, the Kirkendall voids weakened the mass transport rate and improved the inter‐particle pore size. The merging and growth of nanopores in the MgO particles were limited, resulting in the reduced intra‐particle pore size and increased intra‐particle pore number. The densification degree of microparticles was reduced, and thus the strength of the samples decreased. At the Al(OH)3 addition of 4.0 wt%, microporous MgO–Al2O3 refractory aggregates had the best comprehensive properties, a bulk density of 2.48 g/cm3, an apparent porosity of 29.4%, a median pore size of 1.6 μm with 42.2 vol% nanopores and the thermal conductivity of 4.0 W/(m K). [ABSTRACT FROM AUTHOR]

Herein, MgO–C refractories were prepared using fused magnesite, aluminum powder, and silicon powder as antioxidants and different kinds of graphite as carbon sources at 1200°C–1600°C. The microstructure and mechanical strength of MgO–C refractories were studied. The results showed that using cobalt‐loaded expanded graphite as partial carbon source, carbon nanotubes (CNTs) were formed in situ in MgO–C refractories at 1200°C, and the CNTs gradually reacted with Si to form SiC fibers over 1400°C. Consequently, the mechanical strength of MgO–C refractories was significantly improved. [ABSTRACT FROM AUTHOR]

X‐ray computed tomography (XRT) is a three‐dimensional (3D), non‐destructive, and reproducible investigation method capable of visualizing and examining internal and external structures of components independent of the material and geometry. In this work, XRT with its unique abilities complements conventionally utilized examination methods for the investigation of microstructure weakening induced by hydrogen corrosion and furthermore provides a new approach to corrosion research. The motivation for this is the current inevitable transformation to hydrogen‐based steel production. Refractories of the system Al2O3‐SiO2 are significant as lining materials. Two exemplary material types A and B, which differ mainly in their Al2O3:SiO2 ratio, are examined here using XRT. Identical samples of the two materials are measured, analyzed, and then compared before and after the hydrogen attack. In this context, hydrogen corrosion‐induced porosity and its spatial distribution and morphology are investigated. The results show that sample B has a higher resistance to hydrogen‐induced attack than sample A. Furthermore, the 3D representation revealed a differential porosity increase within the microstructure. [ABSTRACT FROM AUTHOR]

In this work, microporous MgO–Al2O3 refractory aggregates were prepared with Mg(OH)2 and Al(OH)3 via the in situ decomposition synthesis method. The effect of Al(OH)3 addition on the microstructure and properties of microporous MgO–Al2O3 refractory aggregates was investigated with scanning electron microscope and mercury intrusion porosimetry. The results indicated that the improved green density of the samples and the reaction sintering accelerated the mass transport rate with adding Al(OH)3 from 0 to 4.0 wt%. Besides, a small amount of Al3+ diffused into porous MgO particles, accelerating the merging and growth of nanopores in the porous MgO particles. The intra‐particle pore size and the densification degree of microparticles were increased, and thus the strength of the samples was improved. Due to the formation of Kirkendall voids by interdiffusion of Mg2+ and Al3+, the inter‐particle pore size increased. Adding Al(OH)3 from 4.0 to 17.6 wt%, the Kirkendall voids weakened the mass transport rate and improved the inter‐particle pore size. The merging and growth of nanopores in the MgO particles were limited, resulting in the reduced intra‐particle pore size and increased intra‐particle pore number. The densification degree of microparticles was reduced, and thus the strength of the samples decreased. At the Al(OH)3 addition of 4.0 wt%, microporous MgO–Al2O3 refractory aggregates had the best comprehensive properties, a bulk density of 2.48 g/cm3, an apparent porosity of 29.4%, a median pore size of 1.6 μm with 42.2 vol% nanopores and the thermal conductivity of 4.0 W/(m K). [ABSTRACT FROM AUTHOR]

A periclase–galaxite refractory is prepared using high-purity sintered magnesia and galaxite particles as raw materials, with pulp waste liquid serving as a binder. The effects of particle size and quantity of added galaxite on the properties of the magnesia refractories are determined. As the quantity of fine galaxite powder increased, the cold modulus of rupture (CMOR) of the sample gradually decreased, and the hot modulus of rupture (HMOR) of the sample gradually increased. With a fine powder content of 4 wt%, the CMOR is 22.8 MP. Similarly, with a fine powder content of 12 wt%, the HMOR is 29.6 MP. The addition of galaxite improves the thermal shock resistance of magnesia refractories, with galaxite particles having a stronger effect than the fine powder. A sample with a particle content of 8 wt% exhibited the highest residual strength retention rate, which is 32.4 % higher than that of the pure magnesia refractory sample. At high temperatures, a Mg–Mn–Al composite spinel was formed in the material owing to the interdiffusion of Mn2+ and Mg2+, which promoted bonding and improved the strength of the material. The mismatch in the thermal expansion of the manganite spinel and periclase resulted in microcracks inside the material, thereby improving its thermal shock resistance. [ABSTRACT FROM AUTHOR]

Spinel has been widely used in refractories because of its excellent properties, but conventional spinel has the problem of poor activity and high cost. In this study, a highly reactive alumina-rich spinel micro-powder was synthesized at a low temperature by solid-phase reaction using commercial alumina and commercial light-burned magnesia. The MA90 spinel micro-powder was added to MgO-C refractories for the slag line of steelmaking ladles to investigate its effect on the microstructure, physical properties, and corrosion resistance of MgO-C refractories. The results showed that the addition of MA90 spinel micro-powder improved the performance of MgO-C refractories significantly, and its optimal addition was 3 wt%. The addition of MA90 spinel micro-powder optimized the microstructure of the matrix and enhance the mechanical strength and corrosion resistance of the MgO-C refractories. The formation and growth of SiC whiskers in MgO-C refractories facilitated by the addition of MA90 spinel micro-powder. [ABSTRACT FROM AUTHOR]

Refractory multi-principal element alloys (RMPEAs), HfNbTaTiZr, (HfNbTaTiZr)9Cr, and (HfNbTaTiZr)9Al, were manufactured using vacuum arc melting followed by laser remelting to mimic additive manufacturing. The microhardness of the as-cast HfNbTaTiZr, (HfNbTaTiZr)9Cr, and (HfNbTaTiZr)9Al samples after arc melting was measured as 6.20, 7.63, and 6.89 Gpa, respectively. After laser remelting and re-solidification, the hardness increased by ~ 30% for each composition; the hardest was (HfNbTaTiZr)9Cr measured at 9.60 GPa, while the softest was HfNbTaTiZr with a hardness of 8.42 GPa, which was still harder compared to all the other samples. The addition of Al and Cr led to enhanced oxidation resistance for the respective RMPEA systems. The Al-containing composition showed the best oxidation resistance for the samples; however, after laser remelting, the Cr-containing RMPEA had the best overall oxidation resistance, and the increase in weight after oxidation dropped by 42% when compared to that for the as-cast alloy. Laser remelting the RMPEAs led to an improvement in mechanical properties; it also resulted in enhanced oxidation resistance for (HfNbTaTiZr)9Cr. However, laser remelting barely changed the oxidation resistance for (HfNbTaTiZr)9Al, and it decreased the oxidation resistance for HfNbTaTiZr. These phenomena are related to microstructure changes induced by the laser remelting/additive manufacturing compared to conventional casting-based manufacturing. [ABSTRACT FROM AUTHOR]

Microporous MgO–Mg(Al, Fe) 2 O 4 refractory aggregates were prepared by the in-situ decomposition synthesis method using the magnesite, Al(OH) 3 and Fe 2 O 3 as raw materials. The effect of raw material composition (theoretical Mg(Al, Fe) 2 O 4 contents were 0–55 wt %) on their microstructure and strengths was investigated. When the theoretical Mg(Al, Fe) 2 O 4 contents were relatively low (0–5.5 wt %), the number of neck connections between the particles in the microporous MgO–Mg(Al, Fe) 2 O 4 refractory aggregates was small. As the theoretical Mg(Al, Fe) 2 O 4 contents increased to be 11–22 wt %, the number of neck connections increased and the compressive strengths were enhanced. When the theoretical Mg(Al, Fe) 2 O 4 contents increased to be excessive (33–55 wt %), the inter-particle pore size further increased due to the increase of volume expansion caused by the formation of more spinel, resulting in a decrease of compressive strength. Overall, when the theoretical Mg(Al, Fe) 2 O 4 contents were 11–22 wt %, the microporous MgO–Mg(Al, Fe) 2 O 4 refractory aggregates showed the excellent performances with the median pore sizes of 17.37–25.46 μm, the apparent porosities of 23.4–28.1%, the bulk densities of 2.57–2.79 g/cm3 as well as the compressive strengths of 41.2–75.8 MPa. [ABSTRACT FROM AUTHOR]

In this study, refractory bricks were produced with semi dry pressing method using grinded olivine sand and clay. The produced bricks were sintered at different temperatures and the optimum sintering temperature was determined as 1350 0C. The water absorption values of the bricks were also tested. Microstructure examinations were carried out on the materials which exhibited the best mechanical and physical properties. Such a basic study has been carried out in order to guide the modifications that to be made in brick composition for applying in various areas as a material which can be used at high temperatures produced using raw materials that belong to Aegean Region. Material, which has lower density value than forsterite bricks and provides their mechanical strength, has been produced. Forsterite bricks are the closest commercial product to obtained olivine brick. A material showing similar properties to forsterite brick with bulk density between 2.55-2.70 g/cm³, apparent porosity between 18-24% and mechanical strength of 50 MPa was obtained [ABSTRACT FROM AUTHOR]

Microporous aggregates are the key to the lightweight design and preparation of refractories for the working linings of the high temperature furnaces. In this work, the lightweight MgO-MgAl 2 O 4 refractory aggregates with core-shell structures were prepared by in-situ decomposition synthesis technology using Mg(OH) 2 and nano-size Al 2 O 3 as raw materials. The influence of the nano-size Al 2 O 3 content on the microstructures and properties was thoroughly studied. The results demonstrated that the microporous MgO core structures were formed after the decomposition of Mg(OH) 2 , and the MgAl 2 O 4 bonds between the microporous MgO core structures were formed through the reaction between the nano-size Al 2 O 3 and MgO. When the nano-size Al 2 O 3 contents were less than 9 wt%, the MgAl 2 O 4 bonds were discontinuous. With the increase of the nano-size Al 2 O 3 contents to 9–15 wt%, more continuous MgAl 2 O 4 bonds (i.e. MgAl 2 O 4 shell structures) were formed at the surface of the microporous MgO core structures. Overall, the optimized specimens were lightweight MgO-MgAl 2 O 4 refractory aggregates with the addition of 9 wt% nano-size Al 2 O 3 , which exhibited the microporous MgO@MgAl 2 O 4 core-shell structures, a median pore size of 268 nm, a high compressive strength of 105 MPa, and a low thermal conductivity of 4.1 W/(m·K) at 800 ℃. [ABSTRACT FROM AUTHOR]

The use of a lightweight corundum–spinel refractory in working lining could reduce the thermal conductivity of industrial furnaces. In this study, bubble alumina was introduced to realize a lightweight Al2O3-MgAl2O4 refractory assisted by the reactive sintering of Al2O3 and MgO. The effects of alumina bubble content and sintering temperature on the phase compositions, microstructure and properties of the lightweight refractory were investigated. The results indicated that the overall performance of the lightweight Al2O3-MgAl2O4 refractory was mainly dominated by the content of alumina bubbles. The bulk density, compressive strength and thermal conductivity all decreased when the alumina bubble content increased from 10 to 30 wt%. Meanwhile, the sintering temperature also significantly affected the properties of the obtained refractory. It is worth noting that specimens fired at 1650 °C achieved a high refractoriness under load (RUL) of more than 1700 °C when alumina bubble content was less than 30 wt%, which was comparable to that of the dense Al2O3-MgAl2O4 refractory. The thermal conductivity of the obtained samples was remarkably decreased to no more than 2.13 W/(m·K). In order to overcome the trade-off between the light weight of the refractory and overall performance, it is feasible to adjust the content of alumina bubbles and raise the sintering temperature appropriately. [ABSTRACT FROM AUTHOR]

Refractory high-entropy films (RHEFs) are a new type of high-temperature material with great prospects for applications due to their superior properties. They have the potential to replace nickel-based superalloys in order to develop a new generation of materials that can be used under extreme conditions. (TiTaZrHf)100−xYx RHEFs are prepared using the magnetron sputtering technique. The yttrium (Y) content varies from 0 to 56 at.%. XRD analysis indicates the formation of an amorphous phase in Y-free films, while new phases are formed after the addition of Y. The results are confirmed by TEM analysis, revealing the formation of nano-grains with two phases L12 and Y-P6/mmm structure. With an increasing Y content, the grain size of the nano-grains increases, which has a significant effect on the mechanical properties of the films. Hardness decreases from 9.7 GPa to 5 GPa when the Y amount increases. A similar trend is observed for the Young's modulus, ranging from 111.6 to 82 GPa. A smooth and featureless morphology is observed on the low Y content films, while those with a larger Y content appear columnar near the substrate. Furthermore, the phase evolution is evaluated by calculating the thermodynamic criteria ΔHmix, ΔSmix, Ω, and δ. The calculation results predict the formation of new phases and are then in good agreement with the experimental characterization. [ABSTRACT FROM AUTHOR]

Functional refractory remains critical due to its intrinsic properties such as: saving space, lightweight and excellent thermal stability to achieve the trade-off between insulating and overall performances. The present study deals with the production of low carbon footprint and lightweight refractory matrices, with controllable pores structures, thermally stable and having low thermal conductivities. The lightweight refractory products were obtained through the direct foaming of geopolymer pastes and sintered from 900 to 1200 °C. The mechanism of pores formation, pores structures and the effect of both sintering temperature and foaming agent ratio on the thermal insulation, physical and microstructural characteristics were evaluated. The results showed that the produced matrices could be described as low thermal conductors, with thermal conductivity values between 0.49 and 0.18 W/mK. The 3D internal pore structures under laser microscopy observations confirms the mechanism of pore enlargement when high concentration of the foaming agent was added. Furthermore, the decomposition of kyanite particles within the matrices, at high temperature, favoured the extend reduction in porosity and the limitation of the liquid phase, by ensuring the formation of macro-porosities sized between 360 μm and 2 mm. The formation of the refractory crystalline phases namely: cordierite, mullite, enstatite, leucite, as well as, kalsilite, acting as filler, ensure thermal stability of the matrices. The produced materials provide an energy-saving, lightweight ceramic foams with high-strength and low thermal conductivities, potential candidates for refractory applications. [ABSTRACT FROM AUTHOR]

Effects of sintering atmosphere on the microstructure and strength of magnesite were investigated using magnesite powder as raw material through X‐ray diffraction, scanning electron microscopy, mercury porosimetry measurement, and so on. The results showed that the sintering atmosphere strongly affected the sintering behavior of magnesite. The specimens sintered in the reducing atmosphere had more and finer micro‐sized pores inside the MgO particles compared with that in the oxidizing atmosphere at the same sintering temperature. Besides, MgO refractory raw material containing porous MgO microparticles with core–shell structure was obtained through the carbothermal reduction of MgO microparticles and subsequent oxidation of Mg vapor at the surface of MgO particles at 1500°C in the reducing atmosphere. At the reducing atmosphere and 1500°C, the microporous MgO refractory raw material with the core–shell structure of external dense and internal porous had an apparent porosity of 22.1% and a compressive strength of 51.6 MPa. [ABSTRACT FROM AUTHOR]

The 90W-7Ni-3Fe refractory alloy was first sintered using hot oscillating pressure (HOP) and hot pressure, which were then heat treated in this work. The microstructure and hardness of the obtained samples were characterized to assess the effect of heat treatment on the diffusion behavior of HOP samples. The results found that HOP could significantly improve densification and inhibit the grain growth of the alloy to get a Vickers hardness of 450.08 HV0.5. The heat treatment could further promote the inter-diffusion between the W phase and Ni(Fe) binding phase, and the appearance of a large number of Ni(Fe) bonding phases reduced the weaker W-W interfaces in the HOP sample to improve its Vickers hardness of 467.84 HV0.5. HOP and post-heat treatment is an effective and promising technique for sintering high-performance refractory alloys. [ABSTRACT FROM AUTHOR]

The lightweight of ladle lining refractories is of great significance to energy saving and consumption reduction. In this work, the lightweight alumina aggregates were selected to partially replace traditional tabular alumina aggregates to prepare lightweight Al 2 O 3 -MgO-C refractories used for steel ladle linings. And, the influence of lightweight alumina aggregates on the comprehensive properties of Al 2 O 3 -MgO-C refractories was investigated in detail. The results illustrated that the introduction of lightweight alumina aggregates can improve the strength of Al 2 O 3 -MgO-C refractories, due to the optimized interface bonding between aggregates and matrix. In addition, the thermal shock resistance of Al 2 O 3 -MgO-C refractories was also enhanced after adding lightweight alumina aggregates, which should be attributed to that the addition of lightweight alumina aggregates reduced the thermal expansion coefficient of such refractories, and micron-sized pores of lightweight alumina aggregates absorbed partial thermal stresses during thermal shock test. Furthermore, the addition of lightweight alumina aggregates improved the slag corrosion resistance of Al 2 O 3 -MgO-C refractories remarkably, which can be ascribed to the formation of continuous CA 6 protective layer and densified matrix. [ABSTRACT FROM AUTHOR]

Microporous MgO-Mg(Al, Fe) 2 O 4 refractory aggregates were prepared using magnesite, Al(OH) 3 and Fe 2 O 3 applying an in-situ decomposition synthesis method. At 1400–1600 °C, there was a Mg(Al, Fe) 2 O 4 with Fe3+, which had two structures. One was a ring structure formed from Al(OH) 3 pseudomorph particle as a template and a low content of Fe3+. The other was the dot and strip structures precipitated in magnesite pseudomorph particles with a high content of Fe3+. Besides, at 1550–1600 °C, microporous MgO-Mg(Al, Fe) 2 O 4 refractory aggregates had an excellent compressive strength (75.8–81.5 MPa) and apparent porosity (26.8%−28.2%). [ABSTRACT FROM AUTHOR]

The beneficial effects of adding nanostructured expandable graphite (EG) hybridized yttrium aluminium garnet (EG\YAG) powder as a composite reinforcement in improving the oxidation resistance, hot-strength, and microstructure development in Al 2 O 3 –MgO–C refractories were studied. The refractory components reinforced with EG\YAG exhibited more than 60% of oxidation resistance enhancement and as high as 200% increase in hot-strength performance over the standard refractories, formulated without EG\YAG. Correlating the damage parameter (D E) calculations based on ultrasonic measurements with residual strength data (R c , R b) showed that there was a progressive increase in R c and R b values with consistent reduction in the oxidative damage of EG\YAG reinforced refractories. Analysis indicated that these beneficial features were majorly ascribed to the in-situ development of bimodal microstructure with EG\YAG sintered framework throughout the refractory interior in these new class of reinforced systems. Additionally, the mechanism of toughening and implications of these results to materials design are discussed. [Display omitted] • Refractories were formulated with EG\YAG based composite reinforcement. • Oxidation resistance and hot-strength properties were significantly improved. • The effect of oxidative damage on strengthening performance was minimized. • Higher energy-to-failure characteristics were attained. • Benefits were credited to the bimodal microstructure development with EG\YAG. [ABSTRACT FROM AUTHOR]

Monticellite (CMS) refers to a silicate phase that exhibits the worst refractoriness, whereas it exists widely in magnesia refractories, such that the high temperature performance of magnesia refractories is seriously reduced. Given the above-described problem, CaLa 4 (SiO 4) 3 O was fabricated in this study, and the effect of La 2 O 3 addition on modification and microstructure evolution of low-melting phase monticellite (CMS) was investigated. As indicated by the results, La 2 O 3 reacted with SiO 2 and CaO to directly synthesize CaLa 4 (SiO 4) 3 O while modifying and transforming the existing CMS into the high-melting-point phase CaLa 4 (SiO 4) 3 O for its higher activity, such that the content of CMS in the system was significantly reduced. Besides, CaLa 4 (SiO 4) 3 O grains exhibited a hollow tubular to club-shaped morphology by controlling the addition of La 2 O 3. On that basis, contributing to the microstructure of form CaLa 4 (SiO 4) 3 O grains interlocking and enveloping the low-melting phases inside after heating at 1400 °C. It is noteworthy that the CaLa 4 (SiO 4) 3 O test cone had no softening and bending during the refractoriness test (the highest test temperature was 1800 °C), thus confirming CaLa 4 (SiO 4) 3 O as a high-melting-point phase. [ABSTRACT FROM AUTHOR]

In this work, microporous MgO refractory aggregates with nano-sized pores were prepared by in situ decomposition method using Mg(OH)2 as raw material. The effects of firing temperatures (1600–1700°C) and compacting pressures (100–200 MPa) on the microstructures and properties of microporous MgO refractory aggregates were thoroughly studied. The results showed that the microporous MgO refractory aggregates contained two types of pore structures, which were intra-particle pores with pore sizes of 180.0–230.0 nm formed by in situ decomposition of Mg(OH)2 and inter-particle pores with pore sizes of 1.5–3.0 μm derived from particle packing between Mg(OH)2 pseudomorph particles, respectively. Besides, the firing temperatures had a great influence on the intra-particle pore size and microcrystallite size. And the compacting pressures not only influenced the intra-particle pore size via packing behaviors but also affected the inner firing behaviors of the pseudomorph particles due to the increase in H2O vapor pressure. Overall, at a compacting pressure of 150 MPa and firing temperature of 1650°C, the sample had the best comprehensive performance with a bulk density of 1.92 g/cm3, a compressive strength of 11.9 MPa, an apparent porosity of 45.0%, a relative aggregate tube strength of 25.2% and a median pore size of 262.3 nm. [ABSTRACT FROM AUTHOR]

Conventional refractory materials used for calcining ternary lithium‐ion battery cathode materials, such as mullite, cordierite, and magnesia‐alumina spinel, are vulnerable to attack by Li(NixCoyMn1−x−y)O2 (LNCM) materials and therefore have a short service life. In order to improve the corrosion resistance of refractory materials to LNCM materials, mullite‐Al2TiO5 materials with different contents were synthesized in this paper by using calcined mullite powder, TiO2 powder, and La2O3 powder as raw materials, which were calcined at 1500–1600°C temperature, respectively. In this study, the potential of the materials for the preparation of LNCM materials was investigated in terms of its physical properties, resistance to the corrosion of LNCM materials, and resistance to thermal shock. The results showed that mullite‐Al2TiO5 composites can be successfully synthesized at 1500–1600°C, and the physical properties of the materials met the production requirements. The prepared mullite‐Al2TiO5 composites also exhibited better physical properties, good corrosion resistance, and proper thermal shock resistance compared with mullite refractories. [ABSTRACT FROM AUTHOR]

Results of a comprehensive study of the material microstructure of refractory samples after service in a blast furnace with a useful volume of 2200 m3 for 14 years are presented. Structural and genetic analysis establishes a typical sequence of degeneration and wear processes of the ceramic furnace skull, including six stages: formation of micro-and macro-cracks; condensation of zinc vapor; zinc oxidation with formation of fire-resistant ZnO zincite and deposition of carbon black; chemical interaction of zincite with mullite and corundum to form ganite ZnAl2O4 and willemite 2ZnO·SiO2; partial oxidation of silicon carbide with the release of silica glass SiO2, eutectic melt of complex composition, and willemite. Due to intense accumulation of capillary pores, infiltration of molten slag into the volume of refractories does not occur. Wear of refractories within the furnace is a complex, mainly thermochemical mechanism, and a slow rate due to formation of a garnish containing refractory compounds. [ABSTRACT FROM AUTHOR]

Microstructure, texture, and mechanical and fracture characterization of three insulating commercial refractories were carried out in order to establish a correlation between these properties. The materials were characterized using X-ray powder diffraction (XRD) with Rietveld and Le Bail approximation to perform phase quantification, mercury intrusion porosimetry, and scanning electron microscopy. The mechanical behavior of insulating commercial refractories was studied with a multi-technique approach that involved a three-point bending test, uniaxial compression test, and singleedge notched beam (SENB) test. Stable fracture tests were successfully performed. The obtained results showed that the main differences between the materials studied were pore size distribution and mineralogical composition. Materials with the major amount of mullite had the highest values of the mechanical parameters in the different performed tests. [ABSTRACT FROM AUTHOR]

The effect of heat treatments of synthesized corrosion-resistant refractory nickel alloy VZhL718 on its structural and phase condition, short-term mechanical characteristics and heat resistance at 650°C is determined. The microstructure of the synthesized material is studied after each treatment stage and after testing for long-term strength. The causes of the differences in the obtained mechanical characteristics are determined as a function of the phase condition of the synthesized material. [ABSTRACT FROM AUTHOR]

Titanium alloys based on orthorhombic titanium aluminide Ti2AlNb are promising refractory materials for aircraft engine parts in the operating temperature range from 600–700 °C. Parts made of Ti2AlNb-based alloys by traditional technologies, such as casting and metal forming, have not yet found wide application due to the sensitivity of processability and mechanical properties in chemical composition and microstructure compared with commercial solid-solution-based titanium alloys. In the last three decades, metal additive manufacturing (MAM) has attracted the attention of scientists and engineers for the production of intermetallic alloys based on Ti2AlNb. This review summarizes the recent achievements in the production of O-phase-based Ti alloys using MAM, including the analysis of the feedstock materials, technological processes, machines, microstructure, phase composition and mechanical properties. Powder bed fusion (PBF) and direct energy deposition (DED) are the most widely employed MAM processes to produce O-phase alloys. MAM provides fully dense, fine-grained material with a superior combination of mechanical properties at room temperature. Further research on MAM for the production of critical parts made of Ti2AlNb-based alloys can be focused on a detailed study of the influence of post-processing and chemical composition on the formation of the structure and mechanical properties, including cyclic loading, fracture toughness, and creep resistance. [ABSTRACT FROM AUTHOR]

Al2O3–C refractories are potential candidates for use in gasifiers, and they are Cr2O3‐free. However, the oxidation of the carbon species and ceramic phases within the high‐temperature water vapor environment may deteriorate the integrity of the working lining. Ti3AlC2 has been verified as an effective antioxidant for Al2O3–C refractories in air. In this study, the structural transformation of Ti3AlC2 during heat treatment and the water vapor resistance of Ti3AlC2‐containing Al2O3–C refractories are investigated. The results show that the oxidation of Ti3AlC2 and Si in the matrix contributes to the in situ formation of a multilayer core–shell structure of TiC–AlTi2O5–Al6Si2O13. These structural evolutions improve densification and stimulate pore size refinement, which enhances the mechanical properties and thermal stress resistance of the specimens. In particular, the refined pore size contributes to the significantly improved water vapor resistance at high temperatures. [ABSTRACT FROM AUTHOR]

A range of steel making vessels and continuous casting components use graphite containing MgO-C refractories that work from ambient to 1600 °C or higher. In the current study, a detailed review on the key importance behind the rightful selection of raw material quality in the development of MgO-C refractories with improved high-temperature microstructure stability is provided. Special cases of carbon\ceramic reinforcements (SiC, nanocarbon, EG, CNT's, Zircon, Titania) are also included in this review study with the combination of regular raw materials used in refractory formulation such as magnesia, graphite, resin binder, antioxidant additives, and alloys thereof. Additionally, the material design concept based on strength factor (f s) has been applied to implicate the raw material quality analysis in the development of carbon containing refractory recipe exhibiting satisfactory hot-strength performance with the recyclable MgO-C grog over the commercially available carbon\ceramic reinforcements is discussed. [Display omitted] • Processing and performance of MgO-C refractory products are reviewed. • Raw material quality analysis is provided. • Methodology of improving high-temperature microstructure stability is discussed. • Material design parameter, strength factor (f s) is applied for recipe development. • MgO-C grog is identified as the efficient reinforcement for hot-strength benefits. [ABSTRACT FROM AUTHOR]

With the increasing demand for high-specific-strength materials for high-temperature applications, particularly in the aerospace field, novel (TiVCrZr)100−xWx (x = 5, 10, 15 and 20) refractory high-entropy alloys (RHEAs) were developed. The phase formation, microstructure, and mechanical properties were studied. The (TiVCrZr)100−xWx RHEAs exhibit a relatively high specific strength and low density compared with the W-containing RHEAs and most of the W-free RHEAs. In (TiVCrZr)100−xWx RHEAs, Laves, BCC and Ti-rich phases are formed, where the Laves phase is the major phase, and the volume fraction of the BCC phase increases with increasing W content. (TiVCrZr)100−xWx RHEAs exhibit dendrite structures, where W is enriched in the dendrite region, and increasing W-rich precipitations corresponding to the BCC phase are observed. The improvement of the strength and hardness of RHEAs is mainly attributed to the evolution of the microstructure and corresponding strengthening effect of W. The empirical parameters and calculated phase diagram were investigated, which further explain and verify the formation and variation of phases. The present findings give more insights into the formation of multi phases in (TiVCrZr)100−xWx RHEAs, and explore their application potential in the aerospace industry and nuclear reactors due to their high specific strength and low-activation constituent elements. [ABSTRACT FROM AUTHOR]

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In order to obtain corundum refractories with good thermal shock resistance and long service life, the samples were prepared using white corundum (5-3,3-1, ≤1, and ≤0.044 mm) as the main raw material, and chromium (≤0.074 mm) as the additive. Effects of the chromium addition (0,1%,3%, and 5%, by mass) on the physical properties, the thermal shock resistance and the slag corrosion resistance were studied. The results show that: (1) with the chromium addition increasing, the bulk density, the compressive strength and the thermal shock resistance of the samples increase and reach the maximum with 3% chromium addition; (2) the oxidation of chromium at high temperatures produces Cr2O3, causing volume expansion, filling partial pores among corundum particles in the sample, and increasing the bulk density; the generated Cr2O3 reacts with Al2O3 to form alumina chromia solid solution, improving the bonding strength between the matrix and the corundum particles; (3) the addition of chromium can also effectively inhibit the immersion of slag into the refractories and reduce the corrosion depth; when the addition increases from 0 to 3%, the corrosion depth decreases from 6.4 mm to 4.1 mm. [ABSTRACT FROM AUTHOR]

A novel strategy was exploited for the fabrication of AlN–AlON refractories via nitrogen gas pressure sintering of Al4O4C. The phase transformation and microstructure evolution during the reaction at 1600–1800°C were thoroughly investigated. The results indicated that the high N2 pressure was essential for the effective nitridation. The in situ generated AlN–AlON refractories had a homogeneous local chemical composition, and the (101) plane of AlN and the (222) lattice plane of Al5O6N were bonded at their grain boundary with no amorphous phase. The as‐fabricated AlN–AlON refractories treated at 1700°C by a 20 atm nitrogen pressure exhibited an optimum bending strength of 111.10 MPa, combining an apparent porosity of 20% with a low bulk density of 1.97 g/cm3. The diffusion of the generated oxygen led to an increase in the apparent porosity and decrease in the bulk density at 1800°C. Furthermore, the fabrication mechanism of AlN–AlON refractories under the nitrogen gas‐pressure was discussed. [ABSTRACT FROM AUTHOR]

Although refractory high entropy films exhibit excellent strength and hardness, their high brittleness often leads to cracking upon frictional contact, resulting in wear resistance that falls short of expectations. This limitation severely restricts their application in industries such as aerospace. In order to address this issue, the development of high entropy composite films has emerged as a viable approach to mitigate friction and enhance reliability. In this paper, a series of (NbMoWTa) 1−x Ag x films were prepared by introducing nano phase Ag into the NbMoWTa system by magnetron sputtering co-deposition. Despite the soft second phase potentially deteriorating the mechanical performance of the composite films, our study demonstrates that the unique chemical nanolayering in the NbMoWTa/Ag can lead to a significant reduction in friction while maintain a high hardness. Compared with the monolithic NbMoWTa film, the (NbMoWTa) 75 Ag 25 film exhibited a 54.3 % reduction in friction coefficient and an 81.6 % decrease in wear rate, demonstrating superior tribological behavior compared to most Ag-containing composite films. The present work provides an effective strategy and facile route, through self-assembling of layered phase, for developing high performance refractory high entropy alloy films. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pure B particles in the RHEA powder allowed the in-situ precipitation of borides. • Borides limited the grain growth and led to a more homogeneous strain distribution. • Cracking susceptibility of the RHEA was reduced, improving LPBF processability. The equiatomic MoNbTaTiZr biocompatible and refractory high-entropy alloy (RHEA) was additively manufactured by laser powder bed fusion (LPBF). The possibility to reduce the cracking susceptibility of the RHEA during LPBF was investigated. By the addition of pure B to the RHEA powder feedstock, the in-situ precipitation of boride particles was promoted. These precipitates limited the grain growth, thus avoiding the formation of cracks. [ABSTRACT FROM AUTHOR]

This study investigated the effect of Si content on the corrosion behavior of AlZrNbTiSi x (x=0, 0.3, 0.6, 1.0 at%) lightweight refractory high-entropy alloys in a 1 M HNO 3 solution. The results showed a transformation in the microstructures of AlZrNbTiSi x from a single BCC phase (x=0) to a BCC matrix phase with Zr 5 Al 3 hexagonal precipitated phases (x=0.3, 0.6, 1.0). AlZrNbTiSi 0.6 exhibited the best corrosion resistance, attributed to the addition of Si promoting the growth of continuous and dense oxides. Microgalvanic corrosion affected the formation of the oxide film, triggering an excessive amount of Si worsening the stability of the passive film. • The moderate addition of Si improves the corrosion resistance of AlZrNbTi lightweight refractory high-entropy alloys. • The corrosion resistance mechanism of AlZrNbTiSi x lightweight refractory high-entropy alloys in a 1 M HNO 3 are clarified. • The precipitation of Zr 5 Al 3 phases and Si oxides play a key role on the formation of a continuous protective passive film. [ABSTRACT FROM AUTHOR]

Refractory alloys often possess superior thermomechanical properties compared to conventional materials, such as steels, Ni-based superalloys, and Ti alloys, especially in high-temperature environments. While these materials promise to revolutionize numerous industries, significant hurdles remain for insertion into applications due to an incomplete understanding of structure-property relationships and conventional processing challenges. We explore laser-based additive manufacturing (AM) to construct refractory alloys consisting of combinations of Mo, Nb, Ta, and Ti with systematically increasing compositional complexity. Microstructure, composition, and hardness of the AM-processed alloys were characterized. Results are discussed in the context of pairing additive manufacturing with refractory metals to enable next-generation alloys. [ABSTRACT FROM AUTHOR]

Five microporous mullite‐corundum refractory aggregates were prepared from Al(OH)3 and kaolinite gangue through in situ decomposition synthesis technique. The effects of the sintering temperature (1400–1600°C) and the particle sizes of raw materials (20.6–94.5 μm) on the microstructures and strengths of the aggregates were investigated through X‐ray diffractometer, scanning electron microscopy, and energy‐dispersive spectrometer etc., to find out the technological conditions to be controlled in industrial production. The higher sintering temperature promoted the reaction between Al(OH)3 and kaolinite gangue, leading to the development of primary‐mullite as well as the generation of secondary‐mullite, which promoted the formation of the neck and improved the strength. Meanwhile, the dense mullite layers were formed continuously on the surface of Al(OH)3 pseudomorphs, making the micropores inside the pseudomorphs become closed pores, which increased the closed porosity of the aggregates. The reduction of the particle sizes of raw materials changed the particle packing behavior, accelerated the rearrangement of the Al(OH)3 pseudomorph particles during the process of reactive sintering, and then reduced the closed porosity. To realize the industrial production of microporous mullite‐corundum refractory aggregate with high strength (103 MPa) and high closed porosity (16.1%), the sintering temperature should be at about 1600°C, and the median diameter of raw materials should be at 94.5 μm. [ABSTRACT FROM AUTHOR]

To develop strong refractory high-entropy alloys for use at elevated temperatures as well as to overcome grain-boundary brittleness, an equimolar HfMoNbTaTiZr alloy was prepared, and a minor amount of boron (0.1 at.%) was added into the alloy. The microstructures of the alloys were characterized, and their macro-to-microscale mechanical properties were measured. The microstructural observations indicated that the matrices of both the alloys were composed of a body-centered cubic solid-solution structure, and the added boron induced the precipitation of hexagonal close-packed borides (most likely the (Hf, Zr)B2) at the grain boundaries. The modulus and hardness of differently oriented grains were about equivalent, suggesting a diminished anisotropy, and many small slips occurred on multiple {110} planes. While the hardness of the matrix was not increased, the intergranular precipitation of the borides markedly raised the hardness of the grain boundaries. Owing to the enhanced grain boundary cohesion, the work hardenability and ductility were effectively improved with the addition of boron. [ABSTRACT FROM AUTHOR]

In the present work, a refractory high-entropy alloy of the composition MoNbTaW has been synthesized by vacuum arc melting starting with elemental powders. The alloy formed as a solid solution with the body-centered cubic crystal structure. Thermomechanical processing was performed, and the sizeable compressive strain induced during this step aided in removing the dendritic microstructure in the as-cast sample. Further homogenization at 1400 °C for 20 h showed partial recrystallization (as studied by Electron Backscatter Diffraction). The sample subjected to thermomechanical processing followed by homogenization exhibited higher hardness than similar refractory high-entropy alloys in the literature. Detailed estimations on probable strengthening mechanisms in this system under various processing conditions suggest that solid solution strengthening is the dominant mechanism. The obtained Tabor factor for each processing condition of this alloy is in the range of 2.6–2.9, and these numbers are in close agreement with those observed for various metallic materials, including high-entropy alloys. [ABSTRACT FROM AUTHOR]

Results are presented for a comprehensive study of the chemical and material composition, as well as the macrostructure, of refractory samples after over 14 years service in a blast furnace hearth with a useful volume of 2200 m3. Sample carbon content is determined using a comprehensive method. Zinc-containing phase formation is established in both the ceramic nozzle area oxide refractories and within the carbon lining of the furnace tuyere zone and hearth. Furnace refractory wear is complex, predominantly by a thermochemical mechanism, and a slow rate due to garnish formation containing refractory compounds. [ABSTRACT FROM AUTHOR]