Refractory Research Articles

Physical and Geochemical Characterisation of Pongo Pitti and Bossambo Farm Clays (Littoral Region, Cameroon) for use in Ceramics

The main objective of this work is to discern the physico-chemical and mechanical behavior of the Pongo Pitti and Bossambo Farm clay formations, located on either side of the Sanaga river in the littoral region of Cameroon. To achieve this, two field campaigns and laboratory works were carried out. Four clay materials were collected and brought back to the laboratory. The laboratory investigations involved physico-mechanical and geochemical analyses, followed by ceramic testing. The materials studied have a clayey texture, with clay percentages ranging from 26.89% to 80.3%, silt from 13.2% to 57.6% and sand from 1.58% to 47.26%. The plasticity index ranges from 11.9% to 24.2%. From a geochemical standpoint, the materials studied show a predominance of silica (49.6% to 63.5%), alumina (20.5% to 27.1%) and iron (2.39% to 8.6%), with the SiO2/Al2O3 ratio varying from 1.96 to 3.1. The Al2O3/Fe2O3 ratio is 8.4 for Pongo Pitti clays and 2.9 for Bossambo Farm clays. The geochemical weathering indices (ICV, CIA, PIA, CIW, CIW) show a high degree of weathering, with values in excess of 90%. Alkali and alkaline-earth proportions are lower, and the K2O/Na2O ratio varies between 8.45 and 14.24, showing an enrichment of potassium in relation to sodium. Lantane is the most abundant rare-earth element (323.84 ppm). The REE study shows a predominance of light REEs over heavy REEs (LREE/HREE~4.51) and a negative Europium anomaly. Infrared spectroscopy showed poor kaolinite crystallinity. Mechanically, the specimens studied, fired at temperatures ranging from 950℃ to 1050℃ showed good cohesion and metallic soundness. Linear shrinkage was 4.8%. Mass loss increases with temperature. Its value is 12.5% for Pongo Pitti materials and 8.5% for Bossambo Farm materials. Water absorption decreases with temperature and is 20.27% for Pongo Pitti samples and 15.79% for Bossambo Farm samples. Bulk density increases with temperature (2.11 at 950℃ to 2.51 at 1050℃). Flexural strength increases with temperature and is 6.66 MPa for materials from Pongo Pitti and 8.89 MPa for those from Bossambo Farm. These materials can be used to make fired bricks and roof tiles, and Pongo Pitti materials can be used to make refractory ceramics

Simulation study of multi-layer titanium nitride nanodisk broadband solar absorber and thermal emitter

Solar energy has always been a kind of energy with large reserves and wide application. It is well utilized through solar absorbers. In our study, the finite difference time domain method (FDTD) is used to simulate the absorber composed of refractory metal materials, and its absorption performance and thermal emission performance are obtained. The ultra-wide band of 200 nm–3000 nm reaches 95.93% absorption efficiency, of which the bandwidth absorption efficiency of 2533 nm (200 nm–2733 nm) is greater than 90%. The absorption efficiency in the whole spectrum range (200 nm–2733 nm) is 97.17% on average. The multilayer nanodisk structure of the absorber allows it to undergo strong surface plasmon resonance and near-field coupling when irradiated by incident light. The thermal emission performance of the absorber enables it to also be applied to the thermal emitter. The thermal emission efficiency of 95.37% can be achieved at a high temperature of up to 1500 K. Moreover, the changes of polarization and incident angle do not cause significant changes in absorption. Under the gradual change of polarization angle (0°–90°), the absorption spectrum maintains a high degree of consistency. As the incident angle increases from 0° to 60°, there is still 85% absorption efficiency. The high absorption efficiency and excellent thermal radiation intensity of ultra-wideband enable it to be deeply used in energy absorption and conversion applications.

Investigation of End-of-Life Chrome-Magnesia Refractories Using X-Ray Computed Tomography

The lifespan of refractory linings is a major industrial concern for safety, on-line availability, and financial reasons. In copper smelting, batchwise operating matte converters are the furnaces that pose the greatest challenge when it comes to refractory wear and lining life. In this work, the structure and morphology of used magnesia–chrome bricks were studied using X-ray computed tomography and mineralogical techniques. The bricks were taken from various locations of an end-of-life brick lining of an industrial Peirce–Smith converter, after a normal campaign at Boliden Harjavalta smelter (Finland). The results show that it is possible to visualize in 3D, e.g., porosity, metal-containing phases, and refractory magnesia in the used bricks. Different digital images, such as cross-sections and average volume fractions, were used as a non-destructive method to characterize the bricks’ internal structure. The metal/matte infiltration in the open porosity was found to differ based on the location in the converter, with some bricks having no metal/matte infiltration and the tuyere line showing metal/matte infiltration at a depth of about 100 mm from the hot face.

Crystal structure evolution and solid solution mechanism of Al2O3-Cr2O3 system under different reaction conditions

The (Al1-xCrx)2O3 solid solution (ACS) is expected to be an low pollution chromium source for high-performance alumina-chromium oxide refractory materials. In this work, the effects of Cr2O3 content and reaction conditions on the solid solution behavior in the Al2O3-Cr2O3 system were explored and the mechanism was revealed. The relationship between the lattice parameters of the formed ACS phase and the content of Cr2O3 was closer to a linear one as the temperature rose, serving as an indicator for a higher degree of reaction. The solid solution reaction between Al2O3 and Cr2O3 was governed by the diffusion processes of Al3+ and Cr3+ at 1300–1500 °C and 1200 °C, respectively, and thus the increase of Cr2O3 content slowed the solid solution reaction at a low temperature whereas promoted it at elevated temperatures. The diffusion process of solid solution reaction within the Al2O3-Cr2O3 system was consistent with the Cater model; The diffusion activation energy (Ea) decreased as the content of Cr2O3 increased at 1300–1500 °C. When the content of Cr2O3 increased from 25 to 60 mol%, the diffusion activation energy decreased from 92.48 to 86.49 kJ/mol−1, which was attributed to the augmentation in the diffusion rate of Cr3+ caused by the increase of Cr2O3 content and its vapor-phase transport mechanism at high temperatures.

From waste to an added-value commodity: challenges in valorization opportunity of tin-residual sand for silica-based industry

Abstract Extensive tin mining activities produce sand piles with high silica, leaving vast environmental and economic responsibilities. The circular economy implementation can address these problems by valorizing quartz sand as industrial sand. Therefore, the study assesses the quartz sand left over from tin mining and processing activities on Bangka Island to become a valuable product within the CPQvA Framework consisting of classification (C), potential utilization (P), quantity and viability (Qv), and application (A). The criteria comprise 12 weighted questions to define the criticality indices categorized as easy, moderate, and difficult. With complex purification technology, quartz sand can be used as silica sand for ceramics, foundry mould, refractory bricks, glass, and solar cells. The quantity is large and feasible for a factory scale with expensive investment and operational costs. The product performance shows good quality from a technical aspect. Due to impurities content and its complex purification technology, the valorization of quartz sand produces a difficult criticality index for the solar cells, a moderate criticality index for the glass and ceramics industry, and an easy criticality index for the glaze, refractory brick, and foundry mold industries. Therefore, proven and efficient purification technology is crucial for further research.

Novel method of fabricating lightweight thermally insulation fibrous composites for energy saving

AbstractFiberboard (FB) is extensively utilized in heat‐insulating refractory materials owing to its lightweight nature and excellent resistance to high temperatures. Nevertheless, the inadequate mechanical properties and limited dimensional stability of FB hinder its further application. The vacuum filtration was utilized in this study to manufacture inorganically modified insulation FB, incorporating plus fiber/1260 fiber and silica sol as the primary constituents and sepiolite powder (HS) as the modifier. The experimental results show that the fabricated samples exhibited extremely high porosity (75.3%–90.2%) and low thermal conductivity (.063–.15 W m−1 K−1, 200–800°C). The fibers were arranged in a three‐dimensional structure, overlapping with each other, and the silica sol adhered to the fibers, forming a spatial mesh structure through cross‐linking. Importantly, the incorporation of HS was effective in controlling the agglomeration of the silica sol, leading to a more uniform distribution within the fibers. Additionally, the study found that the mechanical properties (high hardness (64–72 HA)) and high‐temperature durability of the FBs were enhanced due to the flocculant modification. This study highlights promising prospects for industrial applications and offers a cost‐effective admixture for modifying and preparing high‐performance FBs, which is expected to see broad adoption in thermal insulation and energy conservation applications.

Metallography of tailings from the Mansfeld copper mining area

Abstract The copper slate deposit of the Mansfeld copper mining area was mined in the 19th and 20th century. Mineral collectors can still find traces of copper smelting activities on the slag heaps of the various copper smelters. A piece from the Krug smelter slag heap mainly consists of Cu and Fe sulfides. The piece in question might be the intermediate product copper matte. The pieces from Hettstedt and the August Bebel smelter contain clearly visible metallic copper. The Hettstedt specimen might be a piece of furnace lining with adhering slag. Cr and Mg could be found, suggesting that chromium magnesia was used as refractory material. The piece from the August Bebel smelter contains up to 18 wt. % Cu. It does, however, not contain any sulfur. It is most likely Fe2SiO4 slag (fayalite) with a high proportion of FeO. The presence of Sn and Zn suggests that this slag was formed during the processing of bronze or brass.

Degradation of mechanical properties of MgO-spinel bricks after pre-treatment in hydrogen-containing atmospheres at different temperatures

The current climate policy raises targets to reduce CO2 emissions, i.a. by using “green” hydrogen as a power source. However, the resulting water vapor-containing atmosphere raises uncertainties regarding its impact on the properties of refractory materials during their production and application. Therefore, this study investigates the effect of pre-treatment of unsintered MgO-spinel bricks with flue gas from firing with hydrogen, natural gas and a mixture of both at different temperatures followed by sintering in an industrial furnace as well as during differential scanning calorimetry (DSC). While the splitting tensile strength of the bricks was unaffected for a pre-treatment at 200°C, the samples pre-treated with hydrogen at 600°C revealed a decreased strength of about 14.5% compared to those pre-treated with natural gas at 600°C. DSC results indicated that, besides brucite formation, the formation of additional phases (probably magnesium-silicates) also play a non-negligible role for this strength degradation.

Resource utilization of emulsion evaporation modified aluminum industrial refractory waste in the preparation of composite modified asphalt

AbstractAluminum industrial refractory waste pose a huge risk to the environment, and hence a safe resource utilization is mandatory to build a green industrial construction industry. Herein, a thermoplastic polyester elastomers‐spent refractory material (TPEE‐SRM) modifier having a two‐layer structure of “protective layer‐functional layer” was developed. Scanning electron microscopy and surface area analysis revealed that Eps used in the protective layer formed a dense film layer (50% decrease in specific surface) with a 97.7% sequestration of fluoride. As the reaction occurred in an organic solution, fluoride posed no risk to the environment. TPEE functional layer itself melted and dissolved with asphalt under high‐temperature conditions, and hence it established a strong interfacial interaction with asphalt. This led to an increase of 99.73% in the complex modulus (G*) and 41.75% in the rutting‐resistance performance (Jnr) of the TPEE‐SRM composite modified asphalt than that of the pristine styrene‐butadiene‐styrene (SBS) modified asphalt. The performance of the TPEE‐SRM/SBS composite modified asphalt after 10 years of use was also evaluated by conducting high pressure aging simulation tests. The linear amplitude scanning test results showed a 27.1‐fold increase in Nf 5.0%. Owing to the efficient and green modification method, the newly designed TPEE‐SRM modifier poses great application prospects and feasibility for designing advanced functional modified asphalt for construction and highway industries alongside a suitable disposal aspect for SRM.

Selective Lithium Recovery from Spent Lithium Manganate Batteries Using Oxidative Stabilization Technique.

Using oxidizing compounds to handle the recycling of discarded lithium batteries has advanced significantly in recent years. One of the most prominent methods is the sintered electrode powder treatment using pre-used additives, with an aqueous solution of the oxidizing agent fueling highly selective lithium extraction and transition metals retention in the refractory material. Herein, phosphoric acid (H3PO4) was used as the exchanger and hydrogen ions provider, the oxidant (K2S2O8) activity was driven by heating, the raw material structure was deformed and adjusted by the oxidizing drive, and lithium was exhausted, while manganese was converted into manganese(III) phosphate hydrate and manganese dioxide insoluble material. The optimized conditions resulted in a lithium leaching rate of 94.16 % and a separation factor of 95.74 %, while the corresponding manganese leaching rate was limited to less than 5 %. The X-ray diffraction, X-ray spectroscopy, scanning electron microscopy, and inductively coupled plasma mass spectrometry measurements were used to investigate the influence of oxidation driving force and lithium leaching. Finally, the lithium leach solution was continuously stirred with sodium carbonate in boiling water to obtain the precipitate, which was separated and washed several times to obtain high-purity lithium carbonate.

Preparation and Properties of Lightweight Aggregates from Discarded Al2O3-ZrO2-C Refractories.

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 Al2O3-ZrO2-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.

Fabrication of Y2O3-doped MgO refractory raw materials based on magnesium hydroxide from salt-lake brine

High-purity magnesia refractories were fabricated by brine magnesium hydroxide from the salt-lake brine (Qinghai Salt Lake) and Y2O3 as an additive at 1780 °C. It avoided the substantial CO2 emissions and ultra high temperature sintering process (＞1900 °C) when compared with the conventional magnesite-calcination technical approach. The results confirmed that Y2O3 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 Y2O3, 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 Y2O3-adding, the sample with 5 wt% Y2O3 exhibited a 54.17 % increase in the resistance to molten slag. SEM results indicated that the incorporation of Y2O3 in samples increased the porosity of small pores and enhanced grains boundaries, thereby suppressing slag's penetration. Furthermore, the Y2O3-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–Y2O3 refractory raw materials were controlled by an inter-crystalline corrosion process.

Property dependence on particle size and sintering temperature of waste porcelain high‐temperature resistant material

AbstractThe rapid development of the power industry has resulted in a significant amount of electric porcelain solid waste. To address the challenges of small‐scale utilization and low added value associated with the current utilization of porcelain solid waste, a new high‐temperature resistant material was successfully developed using waste electric porcelain with varying particle sizes as the primary raw material. The dependence of composition, structure, and mechanical properties on fine particle size and sintering temperature was explored. The research has determined that the most effective particle size for the synthesis of refractory materials using waste electric porcelain is 120 mesh, and the optimal temperature is 1600°C. When the temperature exceeds 1500°C, the expansion generated by the decomposition of sillimanite will counteract the shrinkage of the liquid phase reaction, thereby maintaining the morphology of the sample. This process forms a unique interwoven mullite morphology through the decomposition of sillimanite, thereby enhancing the strength of the material. As a result, the optimal bending strength of 74 MPa and the optimal compression strength of 207 MPa were obtained. The realization of high‐temperature resistant materials based on discarded electric porcelain has shown foreseeable potential in large‐scale high‐value utilization.

Efficacy of atomic layer deposition of Al2O3 on composite LiNi0.8Mn0.1Co0.1O2 electrode for Li-ion batteries

LiNi0.8Mn0.1Co0.1O2 (NMC811) is a popular cathode material for Li-ion batteries, yet degradation and side reactions at the cathode-electrolyte interface pose significant challenges to their long-term cycling stability. Coating LiNixMnyCo1−x−yO2 (NMC) with refractory materials has been widely used to improve the stability of the cathode-electrolyte interface, but mixed results have been reported for Al2O3 coatings of the Ni-rich NMC811 materials. To elucidate the role and effect of the Al2O3 coating, we have coated commercial-grade NMC811 electrodes with Al2O3 by the atomic layer deposition (ALD) technique. Through a systematic investigation of the long-term cycling stability at different upper cutoff voltages, the stability against ambient storage, the rate capability, and the charger transfer kinetics, our results show no significant differences between the Al2O3-coated and the bare (uncoated) electrodes. This highlights the contentious role of Al2O3 coating on Ni-rich NMC cathodes and calls into question the benefits of coating on commercial-grade electrodes.

Fabrication, structure, and physical properties of three-B-site perovskite Ba(Zr1–2xTixCex)O3

In this study, three-B-site perovskite Ba(Zr1–2xTixCex)O3 (x=0–0.2) materials with the co-substitution of Ti4+ and Ce4+ at the Zr-site of barium zirconate (BaZrO3) were successfully prepared. The analyses of XRD & Rietveld method, SEM, and TEM indicated that the substituted ions Ti4+ and Ce4+ entered the BaZrO3 lattice to form a single-phase solid solution, showing a conventional primitive cubic perovskite structure (Pm-3 m space group), and its lattice parameters gradually increased from 0.4192 nm to 0.4206 nm with x value. The sample with x=0.1 exhibited relatively optimal structural uniformity and densification, as well as comprehensive physical properties. The sample Ba(Zr0.8Ti0.1Ce0.1)O3 showed a minimum mean grain size of 1.50 μm. And due to the combined effect of solid solution formation and grain refinement, it displayed an apparent porosity of 1.42 % with a cold modulus of rupture (CMOR) of 123.8 MPa, and a thermal conductivity at ambient temperature of 2.197 W/mK. Furthermore, this three-B-site perovskite Ba(Zr1–2xTixCex)O3 exhibits excellent high-temperature stability. This study demonstrates the promising application of the dense, high-strength, and low-thermal conductivity Ba(Zr0.8Ti0.1Ce0.1)O3 perovskite material in the field of advanced refractory ceramics.

Evaluating refractory material performance in pyrometallurgical recycling of lithium-ion batteries under a reducing atmosphere

Pyrometallurgical recycling of lithium-ion batteries (LIB) has emerged as the go-to approach in industrial recycling solutions, yet it encounters significant challenges, such as lithium (Li) slagging. This study explores a reactor for pyrometallurgical recycling, that offers the potential to overcome this bottleneck by simultaneously recovering lithium and phosphorous (P) via the gas stream, more noble elements including cobalt (Co), nickel (Ni) and copper (Cu) as an alloy and less noble elements like aluminum (Al), calcium (Ca) and silicium (Si) as a slag. However, to enhance the efficiency and performance of this reactor, a critical focus is placed on evaluating refractory materials with reduced corrosion and diffusion characteristics. Already explored refractory materials, including aluminum oxide (Al2O3) or magnesium oxide (MgO), have exhibited severe issues, such as accelerated corrosion and diffusion rates, leading to diminished performance and compromised efficiency. To evaluate a more suitable refractory material for pyrometallurgical recycling of LIB, tests using silicon carbide (SiC), chromium(III)-oxide (Cr2O3) and zirconium dioxide (ZrO2) were performed up to 1600 °C. The test results indicate that the investigated refractory materials offer distinct advantages and disadvantages. While SiC shows minimal to no wear by corrosion, Cr2O3 exhibits higher resistance to Li diffusion. Contrary, ZrO2 experienced severe corrosion and crack formation, showing unsuitability for LIB recycling. Based on these findings, a continuously operated reactor could use different refractory materials in specific zones. While the degasification zone could benefit from Cr2O3's minimal diffusion properties, areas with intense contact between the crucible and melt could utilize SiC's corrosion resistance. However, partial oxidation at the outer surface of the SiC crucible led to the formation of SiO2, another critical point to consider for scale-up plans, as it might influence the mechanical integrity long-term.

Application and corrosion characteristics of chrome-free SiC-MgAl2O4 refractory linings serviced in an entrained flow gasifier

This study investigated the degradation mechanisms of SiC-MgAl2O4 refractory materials in a bench-scale entrained flow gasifier. Layered degradation and protective SiO2 formation on SiC aggregates were observed by macroscopic, microscopic, phase analysis, and thermodynamic calculations. A comparative investigation of erosion rates revealed that SiC-MgAl2O4 materials located away from the burner had an unusually low erosion rate of 0.0017 mm/h, which was significantly lower than that reported in their counterparts situated near the burner (0.0167 mm/h). This performance surpassed even that of high-chrome refractory materials positioned at a similar distance from the burner. The findings underscore the remarkable durability of SiC-MgAl2O4, demonstrating its significant potential as a sustainable and chrome-free alternative for application in harsh gasification conditions. The environment-specific degradation patterns, characterized by the formation of mullite and cordierite, revealed the complex interaction between refractory materials and gasification environments. This understanding offers valuable insights that can inform the development and implementation of chrome-free refractory materials under industrial gasification conditions.

Enhancing mechanical properties of lanthanide zirconates through the cold sintering assisted sintering process

This study evaluates the impact of incorporating varying contents (10–40 wt%) and molar concentrations (0.001–1 M) of citric acid solutions, as transient liquid phases in the Cold Sintering Assisted Sintering (CSAS) process of dysprosium zirconate (Dy2Zr2O7). CSAS processed samples achieved relative densities up to 98% of the theoretical maximum and significantly increased Vickers microhardness by over 2.5 times, compared to the traditional ‘press and fired’ sintering method. The Dy2Zr2O7 crystal structure remained consistent with the fluorite-type, with no secondary phases detected. Our findings underscore the benefits of using CSAS to enhance the mechanical strength of Dy2Zr2O7, while reducing the lengthy processing times at very high temperatures typically required for sintering refractory materials such as lanthanide zirconates.

Analysis of carbon shell of billets with high casting speed

Abstract The increasing casting speed of billets is beneficial for improving single-machine production efficiency, reducing refractory material consumption, and achieving energy conservation and consumption reduction. However, as the casting speed increases, the probability of steel leakage also increases. An analysis of the thickness of the billet shell under high casting speed allows us to analyze the reasons for steel leakage and propose targeted solutions. This article analyzes the steel leakage billet shell of grade 40 steel and concludes that the thickness of the billet shell is between 8-20 mm at the upper of the mold, and only 5-10 mm at the lower of the mold. At the beginning of its formation, the shell of the cast billet is not uniform, with a maximum difference of up to 8 mm. As the casting progresses, the shell of the billet actually becomes thinner. At a distance of 100-200 mm from the mold, the maximum air gap between the billet shell and the copper tube reaches about 5.5 mm. The air gap reduces the uniformity of heat transfer, resulting in an uneven billet shell. After the liquid steel is injected into the shell, it will cause remelting of the solidification shell, resulting in thinning of the casting shell and causing steel leakage at the outlet of the mold.

Unidirectional self-actuation transport behavior of metallic aluminum nanodroplets on SiO2/Fe surfaces

To address the issue of adhesion between liquid aluminum and the inner wall of the vacuum ladle during aluminum electrolysis production, molecular dynamics simulations are used to study the self-actuation behavior of aluminum droplets on the refractory materials SiO2 or Fe. Aluminum droplets are separated from the SiO2 surface by their self-actuation behavior in order to solve the issue of aluminum liquid adhesion to the inner wall. Furthermore, the impact of temperature, size, and wedge angle on the self-actuation behavior of droplets is investigated. The results show that droplet self-actuation is not possible when the droplet temperature is below 900 K. However, when the droplet temperature exceeds 900 K, the speed of droplet motion increases with the temperature rise. Within the radius range of 25 Å–32.5 Å, smaller droplet sizes are more advantageous for the self-actuation behavior of the droplets. The displacement of a droplet on a wedge-shaped wetting gradient substrate is significantly greater than on a rectangular wetting gradient. Additionally, the initial velocity of the droplet's motion increases with the wedge angle. However, a larger wedge angle leads to a decrease in the final displacement of the droplet. The results of the study will offer a new method to address the issue of adhesion between liquid aluminum and the inner wall of the vacuum ladle.