High-Temperature Materials Open Access

Thermogravimetric Study of the Oxidation Behavior of the Cantor’s Alloy at 1000 °C and Beyond

A polycrystalline Cantor alloy, equimolar in Co, Cr, Fe, Mn and Ni, was cast. It was subjected to oxidation in a thermo-balance in a flow of synthetic dry air, at 1000, 1050, 1100 and 1150 °C. The mass gain was globally parabolic but rather irregular. The parabolic constants, ranging from 55 to 700 × 10⁻¹²·g²·cm⁻⁴·s⁻¹, are much higher than for a chromia-forming alloy. They obey an Arrhenius law with an activation energy equal to 270 kJ/mol. The external oxide scales formed are composed of an outer part made of manganese oxide and an inner part made of (Cr, Mn) oxide containing a thin internal layer of chromia. The Mn and Cr-depleted depths and the Mn and Cr masses lost by the alloy increase with the oxidation temperature. Cr-rich acicular particles precipitated in subsurface at 1100 °C and internal oxidation along the grain boundaries are present in the whole thickness of the sample oxidized at 1150 °C. Oxide spallation occurred during the cooling, at temperatures in the 200–350 °C range, only for the alloys oxidized at 1050 and 1100 °C. Not too thick scale (1000 °C) or deep internal oxidation (1150 °C) may be favorable for scale adherence.

Recent Advancements in Alumina-Based High-Temperature Insulating Materials: Properties, Applications, and Future Perspectives

As a high-temperature thermal insulation material with excellent mechanical properties, alumina (Al₂O₃)-based materials hold significant potential for applications in aerospace, advanced manufacturing, automobiles, industrial furnaces, and other fields. However, the inherent brittleness of alumina poses a limitation to its wider application. Therefore, there is a pressing need to develop alumina-based materials that offer high toughness while retaining superior mechanical properties. This paper begins by exploring the structure of alumina, highlighting its thermal conductivity, insulation, and mechanical properties in high-temperature environments. It then reviews the classification and synthesis methods of alumina-based materials, along with the latest advances in design strategies. Notably, the rational design of alumina composition, structure, and morphology is emphasized as crucial for optimizing material performance, thereby supporting the industrial development and application of these materials in high-tech sectors. Finally, the paper discusses the challenges and evolution of alumina-based materials in real-world industrial applications and suggests potential directions for future development.

A Review on the Application of Nanomaterials to Boost the Service Performances of Carbon-Containing Refractories

To meet the high-quality requirements for clean steel production and fully exploit the performance advantages of carbon-containing refractories, nanomaterial has been introduced into the matrix to develop advanced carbon-containing refractories. Nanomaterials, as critical additives, play a crucial role in developing novel refractories. The service performances of carbon-containing refractories are affected not only by their physical and chemical properties but also by their microstructure. This review provides a comprehensive overview of the latest research on oxide-carbon composite refractories containing nanomaterials, categorized by their composition: nanocarbons, nano oxides, and nano non-oxides. Incorporating nanomaterials can enhance the service performances of the refractories, optimizing phase composition and microstructure. Furthermore, future research directions in nanomaterial technology for carbon-containing refractories are discussed.

High-Temperature Materials: A New Open-access Journal to Share Your Research on Materials Relating High-temperature Processing or Applications

Porous 430L Stainless Steel as a Support Layer for Planar Solid Oxide Cells: Effect of Porosity on Mechanical Properties

Porous 430L stainless steel components fabricated via tape casting underwent mechanical testing for potential in-vehicle application as mechanical supports of solid oxide cells. Tests included three-point bending up to 5% strain to assess flexural strength, yield strength, Young’s modulus, indentation hardness, and microstructural characterization. This study aimed to establish the relationship between pore former size and volume fraction and the resulting yield strength. It also compared sintered material without pore former, focusing on the influence of a wide range of porosity of up to 46.5%. The materials exhibited an inverse relationship for Young’s modulus, hardness and yield strength as a function of porosity. The lowest flexural yield strength obtained was approximately 120 MPa at the highest porosity of 46.5%, meeting the requirement of 59 MPa for the bipolar plates of existing proton-exchange membrane fuel cells.

Strongly Correlated Electrons and High Temperature Superconductivity

It is very important to clarify the mechanism of high-temperature superconductivity in strongly correlated electron systems. The mechanism of superconductivity in high temperature cuprate superconductors has been studied extensively since their discovery. We investigate the properties of correlated electron systems and mechanism of superconductivity by using the optimization quantum variational Monte Carlo method. The many-body wave function is constructed by multiplying by correlation operators of exponential type. We show that d-wave superconducting phase exists in the strongly correlated region where the on-site repulsive interaction is as large as the bandwidth or more than the bandwidth. The d-wave pairing correlation function is shown as a function of lattice sites, showing that the long-range order indeed exists.

Cement-Free Binders in Alumina-Magnesia Refractory Castables—A Review

To solve the problem of the accelerated deterioration of calcium aluminate (CAC)-bonded alumina-magnesia refractory castables during the secondary refining process, the development of cement-free binders has emerged as one significant research field of castables. The hydration behavior, curing mechanism, and properties of the most recent research on cement-free binders are compared in this paper. The problems and the modification of each binder of recent research are summarized. High-temperature performance of the castables bonded by traditional hydraulic cement-free binders (ρ-Al₂O₃ and activated MgO) is outstanding, explosive spalling resistance of the castables bonded by sol binders (silica sol, alumina sol) is good, and the properties of the castables bonded by novel organic hydratable binder (hydratable magnesium citrate) combine the advantages of these two binders above, but the mid-temperature mechanical strength is low. Furthermore, alumina-magnesia castables bonded by organic-composited inorganic cement-free binders are expected to be a future domain.

Effect of Magnesium Aluminum Silicate Addition on the Ablation Resistance of BN Matrix Ceramics

Ablation resistance is a critical factor in evaluating the performance of BN-based ceramic composites under extreme service conditions. This study investigates the ablation behavior and underlying mechanisms of BN-MAS wave-transparent ceramic composites with varying magnesium aluminum silicate (MAS) content through oxyacetylene torch tests. The results reveal that increasing the MAS content reduces the mass ablation rate from 0.0298 g/s to 0.0176 g/s and the linear ablation rate from 0.149 mm/s to 0.112 mm/s. The incorporation of MAS into h-BN ceramics significantly lowers the surface ablation temperature, primarily due to the evaporation of B₂O₃ (g) and MAS ceramics. Cross-sectional analysis of the ablated composites indicates the presence of micro- and macro-spallation in the ablation center. The primary ablation products are magnesium-aluminum borosilicate glass and mullite. Key ablation mechanisms include the oxidation of h-BN under flame exposure, the erosion of viscous oxidation products, and the physical degradation of the matrix caused by the high-velocity gas flow.

Erosion Resistance of BaZrO₃-Y₂O₃ Two-Phase Crucibles against Highly Active Ti₂Ni Alloys

In this paper, (100-m) BaZrO₃-mY₂O₃ (m = 0, 20, 25, 33, 50, 100) crucibles were prepared, respectively. Then, the effect of crucible composition on the interaction between crucibles and highly active titanium alloys (Ti₂Ni) was investigated. The degree of the erosion resistance of crucibles was compared before and after melting as well as the contaminated extent of the alloys. The results show that the two-phase crucibles consisting of BaZr_1−xY_xO_3−δ and Y₂O₃(ZrO₂), could be prepared after adding Y₂O₃ into the BaZrO₃ crucible. As the amount of Y₂O₃ addition in the crucible was increased, the erosion resistance of the crucible to the alloy melt was gradually improved. The two-phase crucible with 50 wt.% Y₂O₃ addition exhibited the best erosion resistance with a 7 μm thick erosion layer, which was at the same level compared to the pure Y₂O₃ crucible (6.5 μm). However, the inclusion contaminants caused by this two-phase crucible were smaller than those of the pure Y₂O₃ crucible. This study provided a theoretical basis for further research on the preparation of highly stable crucibles for melting highly active titanium alloys.

Hardness-Porosity-Grain Size Interrelationship in Conventionally Sintered 3 mol% Yttria Stabilized Zirconia

Considerable research has been done in the past on expensive, <50 nm particle size 3 mol% yttria-stabilized zirconia (3YSZ) using advanced sintering techniques. However, insights are still needed to reveal which factors among grain size and porosity, when both are changing simultaneously, more strongly control the hardness of conventionally sintered, relatively coarse, 250 nm 3YSZ powder, which can be used to make large industrial engineering ceramic parts at a lower cost. This investigation showed that elevating the sintering temperature from 1500 °C to 1650 °C increased the Rockwell hardness from 49.4 HRA to 86.0 HRA, which was concomitant with an increase in grain size and bulk density. A pseudo-inverse Hall-Petch relationship between hardness and grain size was observed given by H (in HRA) = 153.1 − 69.2/$$\small\sqrt{(\mathrm{grain}\,\mathrm{size})}$$ with a somewhat low R² of 0.95, which was mainly due to the porosity being an additional important variable. Compared to grain size, the impact of open pore fraction (P) on hardness was stronger, inferred from a higher R² of 0.99 while fitting the data into the well-known exponential decay equation, H = 92.9 exp(−11.1P). Finally, it was observed that the 3YSZ conventionally sintered at 1650 °C for 2 h had 0.8% open porosity, 6.08 g/cm³ bulk density, 960 nm grain size and consisted of only tetragonal ZrO₂.

Thermogravimetric Study of the Oxidation Behavior of the Cantor’s Alloy at 1000 °C and Beyond

A polycrystalline Cantor alloy, equimolar in Co, Cr, Fe, Mn and Ni, was cast. It was subjected to oxidation in a thermo-balance in a flow of synthetic dry air, at 1000, 1050, 1100 and 1150 °C. The mass gain was globally parabolic but rather irregular. The parabolic constants, ranging from 55 to 700 × 10⁻¹²·g²·cm⁻⁴·s⁻¹, are much higher than for a chromia-forming alloy. They obey an Arrhenius law with an activation energy equal to 270 kJ/mol. The external oxide scales formed are composed of an outer part made of manganese oxide and an inner part made of (Cr, Mn) oxide containing a thin internal layer of chromia. The Mn and Cr-depleted depths and the Mn and Cr masses lost by the alloy increase with the oxidation temperature. Cr-rich acicular particles precipitated in subsurface at 1100 °C and internal oxidation along the grain boundaries are present in the whole thickness of the sample oxidized at 1150 °C. Oxide spallation occurred during the cooling, at temperatures in the 200–350 °C range, only for the alloys oxidized at 1050 and 1100 °C. Not too thick scale (1000 °C) or deep internal oxidation (1150 °C) may be favorable for scale adherence.utf-8

Characterization, Exploitation and Application of Tibetan Microcrystalline Magnesite

This paper provides a comprehensive account of the properties, development and extensive utilisation of Tibetan microcrystalline magnesite in industry. Tibetan microcrystalline magnesite has become a significant raw material for refractories, high-temperature insulating materials and magnesium chemical materials due to its high purity, low impurity content (mainly Si and Fe elements) and micrometre-sized crystallisation size (2~4 μm). The article presents a detailed analysis of the microstructure of Tibetan microcrystalline magnesite, its thermal decomposition behaviour and the key technologies employed in preparing high-purity magnesium oxide and sintered magnesia through light burning and electrofusion processes. Furthermore, this paper examines the potential applications of Tibetan microcrystalline magnesite in producing high-performance magnesium materials, including activated magnesium oxide, nano-magnesium oxide, and magnesium hydroxide, which are extensively utilized in environmental protection and high-temperature technology. It is demonstrated that the performance of Tibetan microcrystalline magnesite products can be markedly enhanced by optimising the process parameters and modification techniques, thereby further expanding their application prospects in industrial fields. This review offers a theoretical foundation and technical support for effectively utilising Tibetan microcrystalline magnesite, which possesses significant industrial application value and potential.utf-8

Recent Advancements in Alumina-Based High-Temperature Insulating Materials: Properties, Applications, and Future Perspectives

As a high-temperature thermal insulation material with excellent mechanical properties, alumina (Al₂O₃)-based materials hold significant potential for applications in aerospace, advanced manufacturing, automobiles, industrial furnaces, and other fields. However, the inherent brittleness of alumina poses a limitation to its wider application. Therefore, there is a pressing need to develop alumina-based materials that offer high toughness while retaining superior mechanical properties. This paper begins by exploring the structure of alumina, highlighting its thermal conductivity, insulation, and mechanical properties in high-temperature environments. It then reviews the classification and synthesis methods of alumina-based materials, along with the latest advances in design strategies. Notably, the rational design of alumina composition, structure, and morphology is emphasized as crucial for optimizing material performance, thereby supporting the industrial development and application of these materials in high-tech sectors. Finally, the paper discusses the challenges and evolution of alumina-based materials in real-world industrial applications and suggests potential directions for future development.utf-8

Erosion Resistance of BaZrO₃-Y₂O₃ Two-Phase Crucibles against Highly Active Ti₂Ni Alloys

In this paper, (100-m) BaZrO₃-mY₂O₃ (m = 0, 20, 25, 33, 50, 100) crucibles were prepared, respectively. Then, the effect of crucible composition on the interaction between crucibles and highly active titanium alloys (Ti₂Ni) was investigated. The degree of the erosion resistance of crucibles was compared before and after melting as well as the contaminated extent of the alloys. The results show that the two-phase crucibles consisting of BaZr_1−xY_xO_3−δ and Y₂O₃(ZrO₂), could be prepared after adding Y₂O₃ into the BaZrO₃ crucible. As the amount of Y₂O₃ addition in the crucible was increased, the erosion resistance of the crucible to the alloy melt was gradually improved. The two-phase crucible with 50 wt.% Y₂O₃ addition exhibited the best erosion resistance with a 7 μm thick erosion layer, which was at the same level compared to the pure Y₂O₃ crucible (6.5 μm). However, the inclusion contaminants caused by this two-phase crucible were smaller than those of the pure Y₂O₃ crucible. This study provided a theoretical basis for further research on the preparation of highly stable crucibles for melting highly active titanium alloys.utf-8

Strongly Correlated Electrons and High Temperature Superconductivity

It is very important to clarify the mechanism of high-temperature superconductivity in strongly correlated electron systems. The mechanism of superconductivity in high temperature cuprate superconductors has been studied extensively since their discovery. We investigate the properties of correlated electron systems and mechanism of superconductivity by using the optimization quantum variational Monte Carlo method. The many-body wave function is constructed by multiplying by correlation operators of exponential type. We show that d-wave superconducting phase exists in the strongly correlated region where the on-site repulsive interaction is as large as the bandwidth or more than the bandwidth. The d-wave pairing correlation function is shown as a function of lattice sites, showing that the long-range order indeed exists.utf-8

A Review on the Application of Nanomaterials to Boost the Service Performances of Carbon-Containing Refractories

To meet the high-quality requirements for clean steel production and fully exploit the performance advantages of carbon-containing refractories, nanomaterial has been introduced into the matrix to develop advanced carbon-containing refractories. Nanomaterials, as critical additives, play a crucial role in developing novel refractories. The service performances of carbon-containing refractories are affected not only by their physical and chemical properties but also by their microstructure. This review provides a comprehensive overview of the latest research on oxide-carbon composite refractories containing nanomaterials, categorized by their composition: nanocarbons, nano oxides, and nano non-oxides. Incorporating nanomaterials can enhance the service performances of the refractories, optimizing phase composition and microstructure. Furthermore, future research directions in nanomaterial technology for carbon-containing refractories are discussed.utf-8

Preparation of High-Temperature Resistant Hydrophilic Membrane for Oil-Water Separation

Through the molecular structure design, first starting from the molecular structure of the monomer, the monomer of the synthetic structure continues to polymerize with propanesulfonolactone, and finally reacts with quaternary ammonium salts to obtain polyimide containing biswitterionic groups. In this study, a hydrophilic polyimide membrane with a quaternary ammonium salt structure was synthesized. Then, the sulfonate hydrophilic structure was introduced into the polyimide film by electrospinning and the stencil method. Hydrophilic groups were introduced by introducing propane sulfonate, and the PI membrane was prepared by electrospinning and the template method. The results show that introduced sulfonic acid groups reduce the contact angle of polyimide membrane from 85° to 30°. The water permeability, porosity and mechanical strength of the membrane were tested and analyzed, and the membrane showed excellent oil-water separation performance.utf-8

Reactions and Phase Transformations at Sintering of Cubic Boron Nitride Based Materials

Superhard cubic boron nitride (cBN) cutting materials with different contents of cBN were investigated. The compositions of cBN-based materials included ceramic and metallic binders. The sintering of materials was performed by high-temperature hot pressing (HPHT) six-anvil apparatus at pressure 4.5 GPa and temperatures 1400–1450 °C. The process of compaction and processing of superhard cBN materials is followed by numerous chemical reactions. The chemical reactions are very important in compaction and sintering. The volume transformations during chemical reactions affect the shrinkage of the materials and may also impact the residual porosity of the finished products. The adhesion between the grains also depends on these chemical reactions. The research analyzed the volume transformations of various reactions during HPHT sintering of cBN materials, which may play a significant role in forming their structure and properties.utf-8

Effects of Changing the Specific Surface Area in the Ceramic Matrix of CAC-Containing Refractory Castables on the Initial Stiffening and Setting Behaviour

Besides the coarse and medium grain size distribution, the matrix components play a central role in the performance of refractory castables. Practical experience shows that the particle size distribution (PSD) and the specific surface area of the ceramic matrix significantly influence processing, setting, and sintering behaviour. However, there is a lack of systematic studies on how PSD or specific surface area changes affect castable properties. This study aims to address this gap by varying ceramic matrices to create refractory model castables with different matrix surface areas. Three dispersing agents with different mechanisms (electrosteric and steric) were used at graded concentrations. Results show that castables with higher specific surface areas (using (very) finely ground and highly sintered alumina raw materials with high specific surface areas) and different dispersing agents and their concentrations show substantial differences in the initial stiffening and setting behaviour. Higher specific surface areas of the matrix result in an earlier first stiffening, while adding more dispersing agents leads to delayed stiffening. The refractory model castables’ first stiffening and hydration range (with a simultaneous temperature maximum) vary considerably depending on the dispersing agent used and its concentration, caused by completely different mechanisms.utf-8

High-Temperature Dielectric Energy Storage Materials Fabricated by Crosslinking Titanium Dioxide and Polyarylene Ether Nitrile

Dielectric materials have broad application prospects in the field of high-temperature electronic power systems. Up to now, high-temperature dielectric materials are mainly prepared by using high glass transition temperature (T_g) polymers. However, the incompatibility between polymers and fillers, which are incorporated for high energy density, leads to soaring dielectric losses at high temperatures, resulting in a nosedive of discharged energy density (U_d) and efficiency (η). In this paper, we report the fabrication of high-temperature dielectric materials via the self-crosslinking of phthalonitriles from phthalonitriles modified titanium dioxide (TiO₂-2CN) and phthalonitriles terminated polyarylene ether nitrile (PEN-2CN). TiO₂-2CN is firstly synthesized and characterized, then incorporated into PEN-2CN to prepare TiO₂/PEN nanocomposites, which transform into TiO₂-PEN hybrids afterwards. The fabricated TiO₂-PEN hybrids are confirmed by the change of SEM sectional morphology, as well as the increase of their T_g and thermal decomposition temperature (T_d). With the addition of TiO₂-2CN, both the T_g, T_d, and U_d of TiO₂/PEN nanocomposites are improved. In addition, due to the formation of covalent bonds within TiO₂-PEN, the hybrids exhibit excellent high-temperature dielectric energy storage performance. Specifically, at 150 °C, the U_d of 10 wt% TiO₂-PEN is 0.60 J/cm⁻³, which is over 95% of that at RT. Moreover, η is greater than 90% and remains unchanged after 10,000 charge and discharge cycles. This method used for preparing TiO₂-PEN hybrids through a self-crosslinking reaction of phthalonitriles provides a new approach for preparing high-temperature dielectric materials.utf-8