Meridian Technology Center

This study investigates the corrosion and penetration mechanisms of glass-rich mullite castables (GRMC) exposed to Na2CO3, Na2SO4 and their mixtures at 1100 degrees C, respectively. The objective is to comprehensively elucidate the mechanisms of sulfur-induced corrosion and penetration in Na2CO3-containing environment, as well as the migration and interfacial accumulations of K+ at the interface between the corrosion and penetration layers. TGDSC and XRD analysis revealed that, in the presence of Na2CO3-containing slag, Na2CO3 initially reacts with the glass phase in GRMC through a solid-state reaction occurring between 300 and 729 degrees C. This sodium-containing glass phase effectively prevented the penetration of liquid Na2SO4 during the static crucible tests. Simultaneously, sodium originating from the slag replaces potassium in the glass phase of the GRM materials. This ion exchange process leads to the formation of a high viscosity K-rich glass layer at the interface between the corrosion and penetration layer, which effectively restricts further sodium penetration. Furthermore, the newly formed high-viscosity glass phase promotes the formation of a dense protective layer. The GRM aggregates, characterized by lower porosity and smaller micropores, significantly reduce the sodium penetration at the initial stage. These factors collectively enhance the corrosion resistance of GRMC against Na2CO3-containing slag, providing valuable insights for designing alkali-resistant refractories with a self-defense mechanism.

Refractory ceramics, used in high-temperature industries, have heterogeneous microstructures with multiphase compositions and diverse bonding systems that enable resistance to corrosion, thermal gradients, and shock. Their ability to withstand repeated thermal shocks depends on managing stresses from mismatched Coefficients of Thermal Expansion (CTE), which can initiate microcracks when exceeding tensile strength. Controlled microcracking can, however, enhance fracture energy and toughness, making fracture energy a key indicator of thermal shock resistance. Modelling such complex behaviour remains challenging, driving interest in simulating cracking phenomena like microcracking, branching, and fragmentation. An improved Distinct Lattice Spring Model (iDLSM) incorporating anisotropic thermal expansion, thermomechanical coupling, and crack closure mechanisms effectively reproduces experimental trends in thermal expansion and Young's modulus, demonstrating strong predictive capability. The enhanced model is further applied to explore micromechanics, including microcrack orientation, initiation, propagation, internal stresses, and macroscopic stress-strain behaviour to evaluate refractory ceramics' resistance to thermal shock.

Aluminum titanate is widely used in various industries due to its superior intrinsic properties for thermal shock applications. At the microstructural scale, this material is characterized by its original grain crystallinity, leading to anisotropic thermal expansion behavior at the crystallographic grain level. Consequently, aluminum titanate undergoes spontaneous microcracking at high temperatures during operational conditions due to mismatches in the Coefficient of Thermal Expansion (CTE) between grains. These microcracks within the refractory microstructure result in quasi-brittle, non-linear mechanical behavior under tensile loading. Experimental findings suggest that the non-linear macroscopic response signifies material toughening, enhancing fracture toughness and, consequently, improving its thermal shock resistance. To better understand these phenomena, this study presents a simplified polycrystalline microstructure model using the Discrete Element Method (DEM), with aluminum titanate as the reference material. The research focuses on predicting the role of grain-level thermal anisotropy in microcrack nucleation and propagation, critical for thermal shock sustainability. A novel DEM approach, based on the bonded particle element method, is proposed. This approach quantitatively accounts for anisotropic CTE, thermomechanical coupling, crack nucleation, propagation and closure under Periodic Boundary Conditions (PBC), enabling multiscale analysis. The results obtained align quantitatively with experimental macroscopic observations, including the evolution of CTE and Young’s modulus with temperature.

The main alumina aggregates used in refractory applications are Tabular Alumina (TA) and White Fused Alumina (WFA). The different processing routes applied in producing TA and WFA greatly impact the final microstructure of these aggregates. The effects of the distinct microstructural properties in the aggregates in terms of grain sizes and porosity on the thermomechanical behaviour of refractory castables are not well understood. Young's modulus evolution with temperature was measured on alumina-based refractory castables containing either tabular or white fused alumina aggregates. Acoustic emissions were also measured to monitor microcracks developed in the refractory castables during cooling after being subjected to high temperatures. Fine TA and WFA aggregates were discovered to induce little to no microcracks in the refractory castables. Meanwhile, coarse WFA aggregates induced significant microcracks compared to TA aggregates in the alumina-based refractory castables. This paper has demonstrated successfully the influence of the varying grain sizes within alumina aggregates in promoting non-linear behaviour in refractory castables that potentially can be promising in thermal shock applications.

Garnet-type Li7La3Zr2O12 (LLZO) is a promising solid electrolyte for all-solid-state batteries due to its high ionic conductivity and excellent thermal stability. However, production of high performance LLZO remains constrained by the reliance on high-purity reagents and complex synthesis routes. This study presents a cost-effective strategy to prepare high-performance Ta- and Nb-doped LLZO using commercially sourced raw materials via conventional solid-state reaction. Two lithium precursors, Li2CO3 and LiOH & sdot;H2O, were systematically compared to evaluate their impacts on formation and performances of LLZO. LiOH-derived powders showed higher phase purity and finer morphology, while Li2CO3-derived powders offered better processability. While the LLZNO-LOH sample achieved 94.4% relative density and 0.78 x 10-3 S/cm conductivity, LLZTO-LCO also reached 0.75 x 10-3 S/cm with a relative density of 94.1%. All sintered samples exhibited phase-pure cubic garnet structures. These findings demonstrate the industrial feasibility of LLZO production, paving the way for its practical deployment in next-generation solid-state batteries.